Liquid heating device and refrigerator

Abstract

To shorten a heating time in a liquid heating device that heats a liquid by Joule heat generated by applying electricity to the liquid.SOLUTION: A liquid heater that heats a liquid with an initial temperature Ti to a target temperature Tf includes a container 41, an electrode pair 43 disposed within the container, and an AC power supply 44 that applies a current to the liquid via an electrode pair immersed in the liquid, and a distance d between the electrodes of the electrode pair, and an electrode area S through which the electrode pair conducts the current to the liquid are defined on the basis of the maximum current Imax, and the maximum voltage Vmax, and the electrical resistivity in which the liquid can take at the intermediate temperature Tm ((Ti+Tf) / 2) between the initial temperature Ti and the target temperature Tf is defined on the basis of ρ(Tm).SELECTED DRAWING: Figure 4A

Description

[Technical field]

[0001] The present invention relates to a liquid heating device that heats a liquid by using electric energy as Joule heat, and a refrigerator using the same. [Background technology]

[0002] There are several ways to heat a liquid, including burning a substance and transferring the heat generated to the liquid, and passing electricity through a conductor and transferring the Joule heat generated. When the liquid is water, the former is a gas water heater that boils water by burning gas, and the latter is a familiar example of an electric kettle. These methods can be considered indirect heating methods in the sense that they involve first heating something other than a liquid and then transferring the heat to the liquid. On the other hand, there are also methods that directly convert a form of energy other than heat into heat for the liquid. For example, solar water heaters heat water using the infrared rays contained in sunlight.

[0003] In most practical devices for heating liquids, an indirect heating method is used. As for direct heating methods, the aforementioned solar water heaters are used relatively widely in ordinary homes, but direct heating methods are undoubtedly in the overwhelming minority. As another example of a direct heating method, a technology (direct resistance heating technology) has long been known in which electricity is passed directly through a liquid and the liquid is directly heated by the generated Joule heat. This method has the characteristic of being extremely efficient in energy usage, since when the liquid has a high electrical resistance compared to the electrical resistance of the wiring or electrodes, almost all of the work of the electricity is used to heat the liquid.

[0004] Indirect heating methods leave a hot heating element after the heated liquid is transferred, which can lead to long-term heat diffusion to the surroundings and the risk of accidents caused by contact with objects or people. Residual heat from a hot heating element can shorten the lifespan of the device. There is also the risk that the heating element will continue to heat if the liquid runs out due to an unexpected event. Furthermore, long-term use can cause minerals (calcium and magnesium) contained in the liquid to precipitate and adhere to the heating surface. This reduces the efficiency of heat transfer from the heating element to the liquid, resulting in a decrease in the time required for overheating and power efficiency. Direct resistance heating has the advantage of being able to avoid these disadvantages.

[0005] Patent Document 1 discloses a method for heating a liquid by a direct resistance heating technique using multiple electrode pairs. The electrical conductivity of a liquid varies depending on the electric carriers (mainly positively or negatively charged ions) contained in the liquid and the temperature of the liquid, so multiple electrode pairs with different electrode spacings are prepared, and the electrodes are switched depending on the electrical conductivity of the liquid. If the current change during switching is large, a large amount of noise is generated in the power line to which the direct resistance heater is connected, which adversely affects devices connected to the same power system. For this reason, Patent Document 1 discloses an electrode spacing and control method that allows the current change to be smooth when switching electrodes by combining electrode spacings. In addition, in order to reduce the cost of the triac used as a switch during electrode switching as much as possible, the maximum current capacity of the triac is minimized. Furthermore, since it is not possible to analytically design the electrodes to actually realize such a design, it is disclosed that the purpose is achieved using an optimization method, and that the electrode spacing design and minimization of the maximum current of the triac are necessary constraints for that purpose. In other words, Patent Document 1 presents one solution to the problems of noise generation and cost reduction during electrode switching that occur when multiple electrodes are used in direct resistance heating technology. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] U.S. Patent No. 7,817,906 [Non-patent literature]

[0007] [Non-Patent Document 1] Analytical Chemistry, Vol.56, No.7, pp.1138-1142, (1984), “Temperature dependence and measurement of resistivity of pure water”, Truman S. Light. Summary of the Invention [Problem to be solved by the invention]

[0008] When heating a liquid for use, the time required for heating is important. Generally, the time required to heat a liquid is shorter the greater the thermal energy used for heating, whether indirectly or directly. In direct resistance heating technology, the energy of electricity is transferred to the liquid in the form of Joule heat, so a large amount of electrical energy can be used to shorten the heating time. On the other hand, the electrical resistivity of the liquid depends on the liquid temperature, and decreases as the temperature rises. In other words, the resistance between the electrodes decreases as the temperature increases. For this reason, in a typical power supply that operates at a constant voltage or constant current, the Joule heat generated per unit time changes due to the lower resistance caused by the rise in liquid temperature, and unless the power supply settings are appropriately selected, the time required for heating will be longer.

[0009] An example using concrete numbers will be explained. Figure 1 shows the calculations of the voltage 13 that can be applied to water when heating it using a commercial power source with a capacity of 100V and 15A, the resulting current 14 that flows, and the resulting power 15 that is applied to the water. Here, the electrical resistivity of water is set to 50 Ωm at 25°C, and the calculations were made using the temperature dependence of the resistivity of water, which will be explained later. This value corresponds to the resistivity of ordinary tap water.

[0010] As shown in FIG. 1, the maximum voltage, maximum current, and maximum power that can be supplied from the power supply are 100V, 15A, and 1500W. The maximum power can be supplied only when the voltage and current are both maximum, and therefore, according to Ohm's law, this is only possible when the resistance of the load, i.e., the water, is 100 / 15 ≒ 6.67Ω. In region 11 where the resistance of the water is smaller than 6.67Ω, the maximum current of 15A flows at less than the maximum voltage of 100V, so the power supplied is smaller than the maximum power that can be supplied. Similarly, in region 12 where the resistance of the water is greater than 6.67Ω, the maximum current of 15A cannot flow even if the maximum voltage of 100V is applied, so the power supplied is smaller than the maximum power that can be supplied. In this way, the power supplied from the commercial power supply is maximum only at the one point where the resistance of the water is 6.67Ω, and only power smaller than the maximum power can be supplied in other regions.

[0011] In this way, when heating a liquid using direct resistance heating technology, the conditions under which the maximum power that can be supplied from the power source can be used for heating are limited. Therefore, if heating is performed without taking into consideration the temperature dependency of the electrical resistivity of the liquid to be heated, the power required for heating cannot be supplied to the liquid efficiently, and the time required for heating ends up being long.

[0012] Thus, in order to shorten the heating time with direct resistance heating technology, it is necessary to devise a way to supply as much power as possible from the power source to the liquid. However, no literature has been found that discloses such a way, and the issue of shortening the heating time remains. For example, Patent Document 1 discloses a direct resistance heating technology using multiple electrode pairs, but does not disclose a method for shortening the heating time or a heating method according to the characteristics of the liquid. [Means for solving the problem]

[0013] The liquid heating device according to one embodiment of the present invention is configured to heat the liquid at an initial temperature T i of liquid to a target temperature T fThe liquid heating device includes a container, an electrode pair disposed in the container, and an AC power source that applies a current to the liquid via the electrode pair immersed in the liquid, and the electrode distance d of the electrode pair and the electrode area S through which the electrode pair applies a current to the liquid are determined by a maximum current I of the AC power source. max , maximum voltage V max , and initial temperature T i and the target temperature T f Intermediate temperature T m ((T i +T f ) / 2) is the electrical resistivity ρ(T m ) shall be determined. Effect of the Invention

[0014] The heating time can be shortened by determining the electrode specifications to satisfy the shortest heating conditions. It has also been confirmed that the effect of errors in the electrode pair size and the electrical resistivity of the liquid on the heating time can be kept small.

[0015] Problems, configurations and effects other than those described above will become apparent from the following description of the embodiments. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a diagram showing the relationship between resistance and power supply voltage, current, and power when water is heated by direct resistance heating. [Diagram 2] FIG. 1 is a diagram showing the temperature dependence of electrical resistivity of solutions having different impurity concentrations. [Diagram 3] FIG. 1 is a graph (PT graph) showing the relationship between liquid temperature and power when water is heated by direct resistance heating. [Figure 4A] FIG. 1 is a diagram illustrating a configuration of a liquid heating device. [Figure 4B] FIG. 2 is an equivalent circuit diagram of the liquid heating device. [Diagram 5] FIG. 13 is a diagram showing the change in power and water temperature over time when the size of the electrode pair is set arbitrarily. [Figure 6] FIG. 13 is a graph showing the changes in power and water temperature over time when the size of the electrode pair is optimized. [Figure 7A] FIG. 1 is a diagram illustrating a configuration of a liquid heating device. [Figure 7B] FIG. 1 is a diagram illustrating a configuration of a liquid heating device. [Figure 7C] FIG. 1 is a diagram illustrating a configuration of a liquid heating device. [Figure 8] FIG. 13 is a graph showing the changes in power and water temperature over time when the sizes of the two electrode pairs are optimized. [Figure 9] FIG. 13 is a diagram showing the relationship between temperature and power when the sizes of N electrode pairs are optimized. [Figure 10] FIG. 13 is a diagram showing the d / S value that is the optimal heating condition within the assumed range of resistivity. [Figure 11] FIG. 13 is a diagram showing the relationship between the electrode spacing and the length of one side of a square electrode that provides optimal heating conditions. [Figure 12] FIG. 13 is a diagram showing the relationship between the electrode spacing and the length of one side of a rectangular electrode that provides optimal heating conditions. [Figure 13] FIG. 13 is a diagram showing the d / S value that is the optimal heating condition within the assumed range of resistivity. [Figure 14A] FIG. 13 is a diagram showing the relationship between the electrode spacing and the length of one side of the square electrode that provides optimal heating conditions when the liquid temperature is 45° C. or less. [Figure 14B] FIG. 13 is a diagram showing the relationship between the electrode spacing and the length of one side of the square electrode that provides optimal heating conditions when the liquid temperature is 45° C. or higher. [Figure 15A] FIG. 13 is a diagram showing the relationship between the electrode spacing and the length of one side of a rectangular electrode that provides optimal heating conditions when the liquid temperature is 45° C. or less. [Figure 15B] FIG. 13 is a diagram showing the relationship between the electrode spacing and the length of one side of a rectangular electrode that provides optimal heating conditions when the liquid temperature is 45° C. or higher. [Figure 16A] FIG. 13 is a diagram showing the relationship between temperature, time, and power when the sizes of N electrode pairs are optimized. [Figure 16B] FIG. 13 is a diagram showing the relationship between temperature, time, and energy when the sizes of N electrode pairs are optimized. [Figure 17A] FIG. 1 is a diagram showing an example of the appearance of a water server. [Figure 17B] FIG. 2 is a functional block diagram of the water server. [Figure 17C] FIG. 4 is a diagram showing an electrical configuration related to a heating unit. [Figure 17D] 4 is a timing chart of the heating operation of the water server. [Figure 17E] FIG. 4 is a diagram conceptually showing changes over time in power application to a heating unit. [Figure 17F] FIG. 4 is a diagram conceptually showing the change in water temperature in a heating section over time. [Figure 18] FIG. 1 is a diagram showing an example of the appearance of a refrigerator having a water server function. [Figure 19A] FIG. 1 is a functional block diagram of a refrigerator with a water server function. [Figure 19B] FIG. 1 is a functional block diagram of a refrigerator with a water server function. [Figure 20A] 4 is a timing chart of the heating operation of the water server unit. [Figure 20B] 4 is a timing chart of the heating operation of the water server unit. [Figure 20C] 4 is a timing chart of the heating operation of the water server unit. [Figure 20D] 4 is a timing chart of the heating operation of the water server unit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The inventors have noticed that there is practically no problem in expressing the temperature dependence of electrical resistivity of a liquid, particularly a liquid mainly composed of water, by a relatively simple approximation, that is, an exponential function of temperature.

[0018] When a substance that dissolves in water is mixed into pure water, the electrical resistivity generally decreases. As a straightforward example, consider mixing impurities into ultrapure water. The impurities dissolved in ultrapure water are ionized, and the ions become carriers of electricity, facilitating electrical conduction and decreasing the electrical resistivity. Figure 2 shows the temperature dependence ρ(T) of the electrical resistivity of a solution in which a certain amount of impurity is mixed into ultrapure water. In a solution with a small amount of impurity, ρ(T) can be approximated with high accuracy by an exponential function whose exponent is a power function of temperature expressed with a finite number of terms (Non-Patent Document 1). On the other hand, although accuracy is somewhat sacrificed, ρ(T) can also be approximated by the simpler (Equation 1).

[0019]

number

[0020] Here, ρ0 and α are constants determined according to the amount of impurities. Each line in Figure 2 shows the temperature dependence of the electrical resistivity expressed by (Equation 1) for each impurity concentration. It can be seen that the higher the impurity concentration, the lower the resistivity and the higher the accuracy of the approximation by (Equation 1). Normally, city water used as drinking water, so-called tap water, has a resistivity of about 10 to 200 Ωm, and in many cases about 50 to 100 Ωm. Furthermore, liquids that contain water as the main component are thought to have components other than water dissolved in the water as impurities, and therefore have a smaller resistivity than general tap water. For this reason, (Equation 1) can be used as a good approximation formula showing the temperature dependence of resistivity for tap water and liquids that mainly contain water, which have a relatively high impurity concentration and low electrical resistivity.

[0021] If the length of the electrodes is L, the height is H, and the electrode spacing is d, the resistance between the electrodes due to the liquid is expressed by (Equation 2).

[0022]

number

[0023] For the voltage V and current I between the electrodes, the maximum voltage and current that the power supply can supply are the maximum voltage V max , the maximum current I max respectively. The power P input to the liquid is obtained by (Equation 4) or (Equation 5) according to the magnitude relationship between the resistance R between the electrodes and the resistance R’ determined by (Equation 3). (Equation 4) is for the case where R > R’, and (Equation 5) is for the case where R < R’. Note that the electrode area S = L·H

[0024]

Equation

[0025]

Equation

[0026]

Equation

[0027] Here, as shown in Figure 2, since the resistivity decreases with increasing temperature, α < 0. In the rightmost sides of (Equation 4) and (Equation 5), in order to clarify the sign of the exponential part, α is expressed with its absolute value and then given a sign. The transformation of the equation in (Equation 4) utilizes the fact that when the resistance R between the electrodes is greater than R’, the voltage V becomes constant (see Figure 1), and a current of I = V max / R flows. Similarly, the transformation of the equation in (Equation 5) utilizes the fact that when the resistance R between the electrodes is less than R’, the current I becomes constant (see Figure 1), and the voltage V = I max ×R. Once the power supply and the liquid are determined, the maximum voltage V max , the maximum current I max , the constant α, and the constant ρ0 are determined. Therefore, it shows that the power P that can be applied to the liquid in both equations is determined by the temperature T of the liquid at that time max , the maximum current I max .

[0028] (Numeral 4) and (numeral 5) are used to schematically represent the relationship between the power P and the liquid temperature T in the graph of FIG. 3 (P-T graph). When the liquid temperature T = T’ where the resistance R = R’, the power P = the maximum power P max is obtained. In both region I where the liquid temperature T < T’ and region II where the liquid temperature T > T’, the power P monotonically decreases as it moves away from the liquid temperature T’.

[0029] As will be described below, the P-T graph has a symmetric shape with respect to the liquid temperature T = T’. Differentiating the relational expressions of the power P - liquid temperature T corresponding to regions I and II, namely (numeral 4) and (numeral 5), with respect to the liquid temperature T respectively results in (numeral 6) and (numeral 7).

[0030]

Numeral

[0031]

Numeral

[0032] (Numeral 6) and (numeral 7) indicate that the slopes of the graph at the points where the power P takes equal values in regions I and II are opposite in sign and equal in magnitude. That is, the P-T graph has a symmetric shape with respect to the liquid temperature T’.

[0033] By the way, the temperature rise of the liquid is proportional to the input energy E. Let the proportionality constant be A, and expressing the liquid temperature T and the energy E as functions of time respectively to explicitly represent the time change, we get T(t) = AE(t). Using this relationship, the time derivative of the power P can be expressed as (numeral 8).

[0034]

Numeral

[0035] Note that equation 8 is transformed using equations 6, 7, and the relationship dE / dt=P. The - sign in equation 8 corresponds to region I in the PT graph (Fig. 3), and the + sign corresponds to region II in the PT graph (Fig. 3). From equation 8, we can see that even in a power P-time t graph (Pt graph), the slope of the graph at points where the power P is equal has the same magnitude but the sign is opposite. In other words, the Pt graph shows the time when resistance R=R' (power P=maximum power P max This graph is symmetrical with respect to the time when the PT curve becomes equal to the boundary line, and has a similar shape to the PT curve shown in FIG.

[0036] In order to heat the liquid in the shortest time possible, the energy used for heating should be input to the liquid in the shortest possible time. Since energy is an amount of electricity, its size corresponds to the area of ​​the Pt graph. The area of ​​the Pt graph from the time the heating of the liquid starts to the time the heating ends (the time the liquid temperature reaches the target temperature) is the amount of electricity used for heating, so the heating conditions in the shortest time (called the shortest heating conditions) are the maximum power P max This is the condition for input.

[0037] In this way, the fact that the shortest heating conditions are determined so that the time interval between the time at the symmetric center in the Pt graph and the heating start time, and the time interval between the time at the symmetric center in the Pt graph and the heating end time are equal, means that the amount of power input is equal on both sides of the symmetric center time. Since the specific heat of a liquid that is mainly water is roughly constant from room temperature to the boiling point, if the amount of input energy is the same, the amount of temperature rise will be the same regardless of the starting temperature. Therefore, the amount of temperature change on both sides of the symmetric center time will also be the same. In other words, the shortest heating conditions are set so that the liquid temperature at the heating start time is equal to the initial temperature T i , the target temperature at the end of heating T f Then, the intermediate temperature T m =(T i +T f ) / 2, the maximum power P max This can be rephrased as the condition for investment.

[0038] This condition can be satisfied by specifying the electrode specifications. Under the shortest heating conditions, (Equation 2) to (Equation 9) hold.

[0039]

number

[0040] By modifying (Equation 9), we obtain (Equation 10). By using an electrode pair with a distance d and electrode area S = L × H that satisfy (Equation 10), the liquid can be heated in the shortest time.

[0041]

number

[0042] Next, we will consider the effect of error. In reality, the electrode area (L, H) and the distance between the electrodes d are processed with a certain degree of error. Also, deviations from the design value of resistivity ρ due to variations and fluctuations in the liquid quality also result in errors. Such deviations from the optimal value cause the heating time to be longer than the shortest time. First, in the PT graph, how much the error in the electrode area affects the maximum power P max The position of the electrode is evaluated. Suppose the electrode area changes from S to S+ΔS. In this case, the maximum power P max Assuming that the liquid temperature changes from T to T', we can write it as (Equation 11).

[0043]

number

[0044] Since the liquid temperatures T and T' can be calculated from (Equation 11), the difference ΔT = T - T' can be calculated from (Equation 12).

[0045]

number

[0046] Here, the quadratic and higher terms of ΔT are ignored. In addition, since S and d are in the denominator and numerator of the exponential function coefficient in (Equation 11), even if there is an error in the distance between the electrodes ((d → d + Δd)), the same shape (ΔT ~ 1 / α Δd / d) will result, with only a change in sign. From this result, the maximum power P max It can be seen that the deviation in liquid temperature is of the same order of magnitude as the rate of dimensional change (first order).

[0047] Similarly, we evaluate how much the error in electrode area leads to an error in power at each temperature. When the electrode area is S and satisfies the optimum conditions (power P at each temperature at this time), and when it changes to S + ΔS and deviates from the optimum conditions (power P' at each temperature at this time), the difference between the two, ΔP = P-P', is expressed by (Equation 13) in Region II and (Equation 14) in Region I.

[0048]

number

[0049]

number

[0050] Here, second-order and higher terms of ΔS are ignored, and ΔS / S<1.

[0051] From the above, it can be seen that the power error at each temperature in both regions I and II is of the first order of the ratio of the error in the size of the electrode pair. Since the deviation amount ΔT explained earlier is also of the first order of the ratio of the error in the size of the electrode pair, the deviation from the optimal condition due to the error is of the first order of the ratio of the error on both the vertical and horizontal axes of the PT graph. As mentioned above, since temperature and energy are proportional, it can be said that the energy error is also of the first order of the ratio of the error in the size of the electrode pair. On the other hand, energy is expressed as the product of power and time, and the time deviation due to the error corresponds to the time required to additionally input the energy increased by the error. Since the energy and power are each of the first order of the error in the size of the electrode pair, it can be said that the time error is of the second order or lower. For example, if the size of the electrode pair changes by about 30%, the effect on the heating time is expected to be 9% or less, but it can be calculated that the actual effect will be an extension of the time by about 5%. Similarly, a 50% deviation in the size of the electrode pair is expected to lead to an extension of the heating time by 25% or less, and calculations show that it will be extended by about 10 to 15%.

[0052] How much the error needs to be reduced is a design issue, depending on how much time extension is allowed, but for example, if the error in the size of the electrode pair can be kept below 30%, the time delay will be a maximum of 10%, so this error value generally remains within a range that will not cause any problems in practical use. Here, we have described how to think about error when there is one electrode pair, but the same basic approach can be applied when multiple electrode pairs are used. Furthermore, with regard to water quality errors, small deviations that can be treated as errors can generally be overlooked. EXAMPLES

[0053] In the first embodiment, a device for heating a liquid using one electrode pair will be described. FIG. 4A shows a schematic diagram of a liquid heating device for heating a liquid by direct resistance heating technology. An electrode pair 43 is installed in a container 41 and connected to a power source 44 via wiring 45. The container 41 contains a liquid to be heated so that the electrode pair 43 is completely immersed in the electrode pair 43. The container 41 is preferably made of polycarbonate, which has relatively high heat resistance. The electrodes are made of carbon formed by CIP (Cold Isostatic Pressing), for example. A hole is drilled in the carbon material and connected to the wiring 45 with a screw and a nut. At this time, a countersink is drilled in the hole on the side facing the electrodes to eliminate the protrusion of the screw, so that the electrode and the screw do not come into contact with each other and cause a short circuit when the electrode gap is narrow. The electrode gap d is determined by sandwiching and fixing an insulator of a predetermined thickness between the electrode pair. At this time, the insulator covers only a part of the electrode to ensure a current path between the electrode pair 43. In addition, the part sandwiching the insulator is excluded from the electrode length L and electrode height H because no current flows through it. In other words, the electrode area S refers to the area of ​​the part of the electrode that can be passed through the liquid. The electrode pair 43 is placed on the bottom of the container 41. The electrodes may be placed so that they are inserted into the liquid surface from the top side of the container, but the electrode pair 43 should be designed to be inserted near the bottom of the container. If the electrode pair 43 is located near the liquid surface, the heated liquid will remain near the liquid surface, and it will take time for the temperature of the liquid near the bottom to rise. The wiring 45 is led out of the container through a small hole opened on the side of the container and connected to the power source 44. After leading out the wiring, the small hole in the container is filled with a water-resistant bond to prevent water from leaking. The power source 44 is an AC power source that can supply a maximum voltage of 100V, a maximum current of 5A, and a capacity of 500W. Although not shown in the drawing, a thermometer is inserted from the top of the container so that the liquid temperature can be measured at a position approximately halfway down the water depth.

[0054] Figure 4B is an equivalent circuit of Figure 4A. Electricity flows through the liquid between the electrode pair 43, and the electrical resistance is represented by resistor 42. The magnitude of resistor 42 changes depending on the temperature of the liquid, so it is represented as a variable resistor.

[0055] First, as a comparative example, the size of the electrodes was appropriately set to 5 cm in length and 10 cm in height. Using an electrode pair with an electrode gap of 2 mm, water at approximately 0°C was heated to 90°C. 500 mL of cooled water was placed in a container and heated by applying a voltage of 100 V between the electrodes. The resistivity of the water used at 25°C was approximately 50 Ωm. Figure 5 shows a plot of the water temperature and the input power against time. It took approximately 4,300 seconds for the water temperature to reach 90°C.

[0056] In contrast, the optimum size of the electrode pair is determined when water is heated from 0°C to 90°C according to (Equation 10). In this case, the intermediate temperature T m = 45℃, maximum voltage V max =100V, maximum current I max = 5A, d = 2mm, so from (number 10), S = L H = 5.7cm 2 For water with a resistivity of 50 Ωm at 25°C, α = -2.83 × 10 -2 , ρ0 = 20.29. The electrode length L = 5 cm, electrode height H = 1.15 cm, and electrodes of approximately 1.1 cm were used. Figure 6 shows the change in power and water temperature over time in this case. It can be seen that it took approximately 770 seconds to reach 90°C, and the maximum power was input at about half that time, around 380 seconds. In this way, by determining the size of the electrode pair based on specifications that satisfy the minimum heating conditions of the liquid heating device, it is possible to significantly shorten the heating time compared to using an electrode pair of arbitrary size.

[0057] 4A shows an embodiment in which the liquid is heated while stored in a container, but it is also possible to heat the liquid while it is flowing. In this case, the temperature of the flowing liquid at a predetermined position can be controlled by treating the flow rate per unit time as a lump of liquid and applying the same concept. In other words, it is also possible to configure the flowing liquid so that the liquid temperature at the discharge port is heated to a predetermined target temperature. This is the same in the following examples. EXAMPLES

[0058] In the second embodiment, a method for shortening the heating time using the direct resistance heating method will be described. In order to shorten the heating time, the power input to the liquid per unit time can be increased. An example using two electrode pairs is shown in Fig. 7A and Fig. 7B. In Fig. 7A, the electrode pair 71 and the electrode pair 72 are connected in series to an AC power source, and in Fig. 7B, the electrode pair 71 and the electrode pair 72 are connected in parallel to the AC power source. The electrode pair 71 has an interelectrode distance d1, an electrode area S1, and a resistance R1 at that time. Similarly, the electrode pair 72 has an interelectrode distance d2, an electrode area S2, and a resistance R2. Here, if the resistance ratio q is defined as R1 / R2, then it can be expressed as q=d1S2 / d2S1 from (Equation 2). Therefore, once the electrode specifications are determined, the value of the resistance ratio q is determined to a certain value. At this time, the load (resistance of the liquid to be heated) seen from the power source is expressed as (Equation 15) in the case of series (Fig. 7A) and as (Equation 16) in the case of parallel (Fig. 7B).

[0059]

number

[0060]

number

[0061] In this way, in either case, it is equivalent to heating with one electrode pair with a combined resistance R determined by the constant q. Therefore, although there is more freedom in electrode design, the heating time cannot be shortened.

[0062] In contrast, in FIG. 7C, a switch 73 is provided to connect either the electrode pair 71 or the electrode pair 72 connected in parallel. In this case, the initial temperature T i Then, the switching temperature T s One electrode pair is heated until the switching temperature T s to target temperature T f Therefore, for each electrode pair, the liquid temperature T i Liquid temperature T s and the liquid temperature T s Liquid temperature T fThe conditions for heating to the temperature T in the shortest time can be set. This can be determined by the method disclosed in Example 1. s The question is where to set the switching temperature T s is the initial temperature T i and the target temperature T f The intermediate temperature (T i +T f ) / 2). This can be qualitatively explained as follows.

[0063] First, the switching temperature T s at the initial temperature T i This is almost the same as when there is one electrode pair. Conversely, the switching temperature T s The target temperature T f The same is true when the switching temperature T is set to near . However, by adding one electrode pair, the condition under which maximum power can be input also increases by one, so the amount of power that can be input within a certain time can be increased. Therefore, in both cases, the time can be shortened slightly compared to when there is one electrode pair. Next, s at the initial temperature T i to target temperature T f Consider the case where the switching temperature T s at the initial temperature T i By increasing the electrode pair slightly, the time required can be reduced compared to the case of one electrode pair, and the switching temperature T s The target temperature T f The time required for the switching temperature T s at the initial temperature T i to target temperature T f When the heating time is increased toward the target temperature T f The reduction in heating time decreases as the temperature approaches the initial temperature T i and the target temperature T f Symmetry shows that the temperature is exactly halfway between

[0064] Initial temperature T i and the target temperature T fFIG. 8 shows the time changes in temperature and power when switch 73 is switched at a temperature exactly halfway between these two. FIG. 8 compares the case where there is one electrode pair and the case where there are two electrode pairs (the configuration of FIG. 7C) when 500 ml of water with a resistivity of 50 Ωm at 25°C is heated from an initial water temperature of 20°C to a target water temperature of 100°C. An AC power supply capable of supplying a maximum voltage of 100V, a maximum current of 15A, and a capacity of 1500W is used. The switching temperature T s is 60°C, which is the intermediate temperature between 20°C and 100°C. In the case of two electrode pairs, (Equation 10) shows that when the water temperature is between 20°C and 60°C, d / (L·H) is 0.204, and when the water temperature is between 60°C and 100°C, d / (L·H) is 0.632, which are the conditions for the shortest heating time. Therefore, the electrode spacing is set to d=2mm, and the former electrodes are 9.9cm square and the latter electrodes are 5.6cm square. By switching switch 73 at a water temperature of 60°C, it takes about 150 seconds to reach 100°C, as shown in waveform 81. On the other hand, in the case of one electrode pair, (Equation 10) shows that d / (L·H) is 0.414, which is the shortest condition. Here, waveform 82 shows the water temperature rise when heating with d=2mm, L=10cm, and H=5cm. It takes about 210 seconds to reach 100°C.

[0065] A comparison of the power applied when there are two electrode pairs and when there is one is shown in waveforms 83 and 84 in Figure 8. It can be seen that when heating up to 60°C, two electrode pairs allow for greater power input, which contributes to shortening the time. In this way, it can be seen that by switching between two electrode pairs, heating can be accelerated compared to when there is one electrode pair.

[0066] It is easy to see that the time can be further reduced by increasing the number of electrode pairs to three or more. The minimum time condition in this case can also be easily generalized, and the electrode condition for the shortest heating time when N electrode pairs are used can be expressed by (Equation 17). The relationship between temperature and power in this case is shown in Figure 9.

[0067]

number

[0068] That is, the initial temperature T min of liquid to a target temperature T max If we use N electrode pairs to heat up to (T max -T min ) is divided into N equal parts, and each temperature range is T1, T2, …, T N When the temperature range T i One electrode pair is assigned to (1≦i≦N), and the conditions within that range that allow the assigned electrode pair to heat in the shortest time are selected according to the method described in the first embodiment. EXAMPLES

[0069] In the above examples, a method for determining optimal electrode specifications has been described on the premise that the liquid to be heated has a certain resistivity, although the value is arbitrary. However, the optimal electrode specifications obtained for a liquid with a specific resistivity value are not optimal for liquids with different resistivities. In Example 3, a method for determining the electrode configuration and specifications that can heat the liquid to be heated in approximately the shortest time within the expected range of electrical resistivity when there is a range of possible electrical resistivities is described.

[0070] In Example 3, the resistivity of the liquid assumed is the resistivity of tap water. The resistivity of tap water varies depending on the water quality, and for example, the value varies depending on the region in Japan. However, the resistivity at 25°C generally falls within the range of 10 to 200 Ωm, so this range is assumed.

[0071] First, consider the case of one electrode pair. The initial temperature T i =0℃, target temperature T f = 90℃, maximum voltage V max =200V, maximum current I max= 15A, the value of d / S that is the optimal heating condition for each value within the assumed resistivity range is shown in Figure 10. The values ​​of parameters ρ0 and α in (Equation 1), which express the temperature dependence of resistivity, are also shown. Figure 11 is a graph showing the relationship between the electrode spacing d and the length of one side of the electrode (√S) when the electrode shape is a square, for each resistivity value, based on the calculated d / S value. For example, when the electrode spacing d is 2 mm, the lengths of one side of the electrode are 2.9, 6.5, 9.2, 11.3, and 13 cm for resistivities of 10, 50, 100, 150, and 200 Ωm, respectively. If these lengths are approximated as 3, 6, 9, 11, and 13 cm, respectively, an electrode that can heat water with a resistivity in the shortest time can be provided by preparing an electrode composed of 13 x 13 = 169 unit electrodes of 1 cm square. That is, a 1 cm square electrode is connected to a power source via a switch, and the switch is controlled so that the electrode dimensions are optimal according to the electrical resistivity. This makes it possible to provide an electrode configuration that can heat in approximately the shortest time corresponding to the expected electrical resistivity. This configuration makes it possible to reduce the total electrode area compared to installing electrode pairs of each size. Note that instead of making both of the two electrodes that make up the electrode pair into unit electrodes, only one electrode may be a spread electrode, and the other electrode may be an electrode measuring 13 x 13 cm square in this example.

[0072] In this method, the optimum size of the electrode pair is determined by considering the resistivity of five points in the assumed range of 10 to 200 Ωm, so if the resistivity is outside of the five points, the time will not be the shortest in the strict sense. However, by selecting the closest resistivity from the five points, the delay from the shortest time can be suppressed to a level that does not cause practical problems. As described above, if the resistivity deviation is within about 30%, the time deviation can be suppressed to within about 5%. In addition, since similar calculations are possible for resistance values ​​other than the five selected points, calculations can be performed for the resistivity most suitable for the liquid to be heated, and the switch can be controlled according to the optimum size of the electrode pair. This allows heating under conditions closer to the shortest heating conditions.

[0073] Here, a range of resistivity is set as an example, and five representative values ​​from that range are selected for explanation. In addition, the distance between the electrodes is set to 2 mm, and the unit electrode is set to 1 cm square, but these values ​​are all examples, and other values ​​may be selected to configure the electrodes based on the above idea.

[0074] Next, we will describe an example in which a rectangular electrode is used as a unit electrode shape other than a square. The basic concept is the same as that already described. For the value of d / S of the shortest heating condition shown in Figure 10, we need to consider different values ​​for the length and height of the electrode. Here, we consider the length of one side of a rectangular electrode to be 3 cm as an example. Figure 12 shows a graph of the relationship between the distance between the electrodes and the length of the remaining side. If the electrode spacing is 2 mm, the optimal lengths for each resistivity are 2.84, 14.2, 28.4, 42.6, and 56.8 cm, respectively. In this case, since 2.84 cm is the greatest common denominator of the other values, a 2.48 cm x 3 cm electrode is used as the unit electrode, and 20 unit electrodes are prepared to cover the selected range of resistivity. Since the number of unit electrodes can be reduced compared to square electrodes, there is an advantage in that the number of switches and wiring length can be reduced. On the other hand, since the electrode area of ​​the unit electrode is larger, there is a risk that the deviation from the shortest heating condition for water of the resistivity between the selected five representative resistivity values ​​will be greater. In this case, instead of both of the two electrodes constituting the electrode pair being unit electrodes, only one of the electrodes may be a unit electrode, and the other electrode may be an electrode measuring, for example, 56.8 x 3 cm square.

[0075] Next, an example will be described in which the method of accelerating heating by switching the electrode pair according to the temperature range described in the second embodiment is applied to the electrode configuration of the third embodiment. As in the previous example, the initial temperature T i =0℃, target temperature T f = 90℃, maximum voltage V max =200V, maximum current I max = 15A, and the assumed range of resistivity of the liquid to be heated is 10 to 200 Ωm. Here, the target temperature T f The electrode pair is switched once before the temperature reaches 90°C. Therefore, the electrode pair switching temperature T s= 45°C. Figure 13 shows the d / S that provides the shortest heating conditions for the two temperature ranges.

[0076] First, consider the case where the unit electrode shape is square. Figure 14A shows the relationship between the electrode spacing d and the length of one side of the square electrode (√S) for each resistivity when the liquid temperature is 45°C or less, based on the d / S value in Figure 13. Figure 14B shows a similar graph for the temperature range above 45°C. If the electrode spacing d=2mm, the lengths of one side of the square electrode for resistivities of 10, 50, 100, 150, and 200 Ωm when the temperature is below 45°C are 4.01(4), 8.97(9), 12.7(13), 15.5(15), and 17.9(18) cm, and when the temperature is above 45°C, they are 2.12(2), 4.75(5), 6.71(7), 8.22(8), and 9.49(9) cm. The values ​​in parentheses are approximate values. As above, if unit electrodes of 1 cm square are used, then by preparing 18 x 18 = 324 electrodes, it is possible to provide electrodes that meet the electrode specifications required for the entire range of resistivity from 10 to 200 Ωm, with a switching temperature of 45° C. By preparing electrodes of unit size, they can be used both above and below the electrode switching temperature, and as a result, the electrode area can be reduced compared to preparing electrodes for each temperature range.

[0077] Next, an example of a rectangular electrode shape will be described. One side of the rectangle is 3 cm. Figure 15A shows a graph of the relationship between the electrode spacing d and the length of the other side of the rectangular electrode for each resistivity when the liquid temperature is 45°C or less based on the d / S value in Figure 13. Figure 15B shows a similar graph for the temperature range above 45°C. If the electrode spacing d=2 mm, the lengths of the other side of the rectangle for resistivities of 10, 50, 100, 150, and 200 Ωm are 5.37, 26.8, 53.7, 80.5, and 107 cm below 45°C, and 1.50, 7.51, 15.0, 22.5, and 30.0 cm above 45°C, respectively. Since the length of the shortest electrode is the greatest common denominator of the other electrode lengths, 20 unit electrodes each of 5.37 cm x 3 cm and 1.50 cm x 3 cm should be prepared. In this case, the number of electrode pairs can be reduced compared to square electrodes, which has the advantage of reducing the amount of wiring and mounting fixtures required. On the other hand, there is a risk that the rate of deviation from the heating conditions for the shortest time will be large for liquids that exhibit resistivity values ​​other than those shown as examples.

[0078] Although the case where the electrodes are switched during heating has been described above, the dimensions used in the description are merely examples and are not limited to these values. EXAMPLES

[0079] In the fourth embodiment, a method of switching the electrode pairs during heating in the liquid heating device described in the second and third embodiments will be described. In the following description, there will be no distinction between switching the electrode pairs themselves and switching the electrode areas of the electrode pairs. In FIG. 16A, N electrode pairs are used to heat the liquid to an initial temperature T min to target temperature T max The figure shows the power change when heating to the target temperature T in the shortest time. max The time it takes to reach t N From the given conditions, it is assumed that the N electrode pairs to be used are selected to satisfy the shortest heating conditions. Since N electrode pairs are used, the point at which the electrodes are switched is the initial temperature T min and the target temperature T maxThe temperature is the boundary temperature of the region divided into N equal parts. i This corresponds to the temperature of N-1 boundaries indicated by '(i=1 to N-1). The initial temperature T min Measure the target temperature T max is input as a set value to the heating system, and the switching temperature T i Then, the liquid temperature is measured, the necessary electrode pair is selected, and the specified power is input. Then, the liquid temperature is continuously measured, and each switching temperature T i At the point where the temperature reaches the target temperature T max When the temperature reaches the target temperature, the power supply is stopped. According to this method, the electrode switching point is determined in advance from the target temperature setting and the temperature measurement information, and the electrode pair switching point can be known based on the liquid temperature measurement value.

[0080] Alternatively, the electrode pair switching can be done based on time. The initial temperature T min and the target temperature T max Once the resistivity of the liquid to be heated is determined, the amount of power required can be calculated. min and T max Since the power input pattern is determined for the shortest heating conditions in each of the N equal divisions, the switching time can also be calculated. i -t i―1 ) is equal for each of the N equal regions. In other words, as shown in FIG. 16A, the switching time t i is the switching temperature T i The electrodes are synchronized with each other. Therefore, by switching the electrode pairs at this fixed time interval, heating can be performed in the shortest time possible. In the case of switching based on temperature measurement, it is assumed that the temperature measurement is performed properly, i.e., that there is no unevenness in the liquid temperature. If the liquid temperature is uneven, there is a possibility that the electrodes will be switched at an undesirable timing. In contrast, with the time-based switching method, the electrode pairs can be switched based on the time required to input the required power.

[0081] Next, a method of switching based on power will be described. As already mentioned, when heating in the shortest time, the initial temperature T min and the target temperature T max The intermediate temperature (T min +T max The condition was that the power input pattern should be symmetrical with respect to the initial temperature T min and the target temperature T max Even when dividing into N equal parts, the shortest heating condition is to have a power input pattern that is symmetrical with respect to the midpoint temperature of each of the N equal parts. For this reason, the input power is measured, and if the measured power value for a selected electrode pair matches the input start power, this indicates that it is time to switch the electrode pair. As shown in FIG. 16A, the initial power value P c Therefore, when power supply to a certain electrode pair is started, the power value supplied starts to increase and then decreases to the initial power value P c When the intermediate temperature T becomes equal to the electrode pair, the power supply can be switched to the next electrode pair. This method also has the advantage that it is not affected by uneven liquid temperature. On the other hand, if there is an error from the design in the electrode area or spacing, or if the resistivity of the liquid to be heated deviates from the expected value, the intermediate temperature T m This can cause a shift in symmetry around the boundary, which can result in the timing of switching being shifted from the optimal timing. To address this issue, a tolerance can be set and the switchover can be performed when the power value that would normally cause the switchover falls within the tolerance range.

[0082] Finally, we will explain the method of switching based on the amount of power. The time-based switching method described above is based on the initial temperature T min and the target temperature T maxThis was based on the assumption that the amount of electric power required for heating is equal in each of the N equal-divided regions. Therefore, it is possible to switch to heat in the shortest time by directly measuring the amount of electric power. Fig. 16B shows a graph in which the vertical axis of Fig. 16A is electric power, i.e., energy, rather than electric power. Since the amount of electric power is the integrated value of electric power, Fig. 16B is an integrated graph of Fig. 16A. Since the temperature rise in each of the N equal-divided regions is the same, the electric power input is also the same. Therefore, the target temperature T max , initial temperature T min The required amount of power can be calculated from the amount of water (or the flow rate per unit time in some cases) and the number of divisions N. All that is left to do is measure the power, calculate the amount of power from that, and switch the electrode pair when the specified amount of power is reached. In other words, on the vertical axis of Figure 16B, heating starts when the energy is 0 J, and when the required energy E1 is input, the electrode pair is switched, and when the energy reaches E2, the electrode pair is switched again. This cycle is called the energy E max Here, (E i -E i-1 ) are all equal, and if this value is ΔE, then E i = i × ΔE (i = 1 to N). Another advantage of this method is that it is not necessary to worry about non-uniformity in the liquid temperature. Another advantage is that even if there is an error in the electrode area or the distance between the electrodes, or if the resistivity of the liquid to be heated deviates from the expected value, it is not affected by these factors and can be switched at the correct switching point that takes these effects into account.

[0083] Above, we have shown several methods for switching the electrode pairs or the electrode areas of the electrode pairs, but in reality, it is desirable to check the timing using multiple methods rather than choosing one method from among these. This allows for redundancy against malfunctions. Also, by looking at the methods in a composite manner, it is possible to detect device failures based on whether the timing of each method matches or does not match. EXAMPLES

[0084] In the fifth embodiment, a water server is used as an example to show an example of a method of configuring a hot water supply system. FIG. 17A shows an example of the appearance of a water server. A display unit 1702, an input unit 1703, a hot water outlet 1704, and the like are provided on the front of a housing 1701. A cup holder for placing a cup 1705 that receives hot water from the hot water outlet 1704 is provided in an opening 1706. Water is supplied to the server from a water supply mechanism 1707, and power is supplied from a power supply mechanism 1708. The display unit 1702 may be capable of displaying messages such as a liquid crystal display, or may be capable of conveying messages by a pattern of lights turning on and off. The input unit 1703 is for specifying conditions such as the temperature and amount of hot water to be supplied, and for instructing the start of hot water supply, and may be a button type or a touch panel. A wireless input / output mechanism may be provided, and instructions may be given using a smartphone or the like. When a touch panel or a smartphone is used, the display unit 1702 and the input unit 1703 may be integrated. The water supply mechanism 1707 is connected to a water pipe or a tank. The power supply is connected to the power supply mechanism 1708 via a socket or a circuit breaker.

[0085] An example of a functional block diagram of a water server is shown in FIG. 17B. The thick solid lines indicate the water path, the thin solid lines indicate the electricity path, and the dotted lines indicate the signal line. Water is supplied to the water server from a water supply mechanism 1720. The water supply mechanism 1720 is a water pipe or a tank for storing drinking water. The control unit 1730 reads information from each part of the water server and issues instructions to each part via the signal line. The control unit 1730 is equipped with a calculation processing mechanism and a memory mechanism to perform calculations using the read information and data stored in the device and to determine the contents of the instructions. The flow detection / control unit 1721 is a pressure gauge, a flow meter, or in some cases a pressure regulator. The first valve 1722 and the second valve 1724 open and close the water channel according to the command of the control unit 1730. The heating unit 1723 heats the liquid by direct resistance heating. The control unit 1730 can adjust the amount of liquid supplied to the heating unit 1723 by the flow rate detection / control unit 1721 and the first valve 1722. If the flow rate detection / control unit 1721 is a pressure gauge or a flow meter, the time for opening the first valve 1722 is adjusted according to the value. If the pressure gauge has a pressure adjustment mechanism or the flow meter has a variable flow rate, the time for opening the first valve 1722 can be made constant by setting them to appropriate values. The heating unit 1723 heats water according to given conditions. It is also desirable for the heating unit 1723 to be equipped with a thermometer for measuring the water temperature. The read water temperature is passed to the control unit 1730 as water temperature information. After heating is completed, the second valve 1724 is opened to supply hot water. There are several methods for supplying hot water, such as pumping hot water, pushing it out by pressure, and using gravity to allow the liquid to flow out naturally.

[0086] The power supplied from the power supply 1731 to the water server is supplied to the heating unit 1723 via the power adjustment unit 1732 and the electrode selection unit 1733. max and maximum current I max is basically the maximum capacity that the power supply 1731 can supply. For example, when supplying power from a standard household outlet, the maximum voltage V max is 100V or 200V, maximum current I maxAlthough it depends on the breaker capacity of the distribution board, it is generally 15A in many cases. The control unit 1730 issues a command to the power adjustment unit 1732 to supply the necessary power, and also reads the supply power measured by the power adjustment unit 1732. The simplest configuration of the power adjustment unit 1732 is a switch that switches between supplying and cutting off the power. When power is supplied from an outlet or a breaker, the power adjustment unit 1732 supplies a constant voltage to the heating unit 1723, which is the load, and a current corresponding to the magnitude of the load flows. In addition, there are power adjustment mechanisms such as the so-called phase control method and cycle control (zero cross control) method that use power semiconductors such as thyristors as inexpensive configurations. Compared to control using a simple switch, these methods have the advantage of making it easier to adjust the power. For example, when power usage in other devices increases, it is possible to control the power usage in the water server to be suppressed and the total power usage to be kept within a certain value. This feature is necessary when the water server is used in a device combined with other devices. Although it is possible to control the power supply by intermittently switching the switch, this has disadvantages such as the effect of noise on other devices and accelerated deterioration of devices due to surges.

[0087] It is desirable that the power adjustment unit 1732 can measure the voltage V applied to the heating unit 1723 and the current I flowing therethrough. The measured value of the power input by the power adjustment unit 1732 can be calculated from these values. Also, if the voltage V and the current I can be measured, the resistivity of the liquid to be heated can be obtained. Since the area of ​​the electrodes to be used can all be known in advance, the resistivity can be calculated from the current flowing when one electrode pair is selected from them and a predetermined voltage is applied, and the water temperature measured by the heating unit 1723. If the resistivity is obtained, the specifications such as the size of the electrode pair according to the heating conditions are determined as described above, so there is an advantage that it becomes easier to handle a wide range of water qualities. On the other hand, since the range of resistivity is generally limited by region with regard to water quality, the range of resistivity that can be handled may be limited according to the region where the device is installed. Also, the water quality of city water may be measured before installation, and the range of handling may be customized for each device. In these cases, since the resistivity that needs to be handled is limited, the area of ​​the electrodes attached to the heating unit 1723 can be limited, and the total area of ​​the electrodes can be reduced.

[0088] FIG. 17C shows the electrical configuration related to the heating unit 1723. Power supplied from a power source 1731 via an outlet, a circuit breaker, etc. is fed to an electrode selection unit 1733 via a power adjustment unit 1732. The electrode selection unit 1733 switches the electrodes according to instructions from a control unit 1730 according to the heating conditions of the liquid. Here, an example is shown in which the heating unit 1723 is composed of two electrode pairs (a first electrode pair 1711 and a second electrode pair 1712). FIG. 17C shows an example in which the first electrode pair 1711 is selected. The switch constituting the electrode selection unit 1733 may be a mechanical switch or an electronic switch such as a photocoupler. Since the power source often has a large capacity, it is sufficient to select a switch that corresponds to that capacity.

[0089] FIG. 17D shows a timing chart of each signal. Assume that a request for hot water supply is made from the input unit 1703 at time t1. Based on this request, at time t2, the display unit 1702 is commanded to display a message prompting the input of the amount of hot water supply and the hot water supply temperature. After that, the hot water supply conditions inputted by the input unit 1703 are read, and the first valve 1722 is opened for the time required (between time t3 and time t4) to supply the specified amount of water to the heating unit 1723. The control unit 1730 reads the initial temperature of the water measured by the heating unit 1723, and determines the electrode switching pattern in accordance with the specified hot water supply temperature. As explained in the fourth embodiment, the timing of electrode switching can be determined based on time, power, power amount, etc. in addition to switching based on water temperature. At this stage, the pattern of electrode selection, which electrode is to be energized at what timing, is determined. In this example, there are two electrode pairs, and it is assumed that switching is performed once.

[0090] FIG. 17E shows the change over time of the applied power in this case, and FIG. 17F shows the change in temperature of the water in the heating unit 1723. When switching electrodes based on the water temperature, the measured initial temperature T min The specified hot water temperature T max The intermediate temperature T mid (T mid =(T min +T max ) / 2) is calculated by the control unit 1730, and the timing of switching the electrode selection unit 1733 is determined by comparing it with the temperature information measured by the heating unit 1723 during heating. mid When this occurs, which is time t6 on the timing chart, the electrode pair is switched.

[0091] In case of time-dependent switching, the initial temperature T min and hot water temperature T maxThe timing of electrode switching is determined by adding the energy used to heat the water from the amount of hot water supplied and the energy not used to heat the water due to heat dissipation specific to the device, and calculating the time required for the device to input that energy from the value. The heat dissipation specific to the device is, so to speak, the efficiency of the device, and is a parameter that is determined in advance because it is determined by the design and configuration of the device.

[0092] When switching the electrodes by power, the power value when power application starts, that is, the power P at time t5 in FIG. i The value of is stored, and the applied power value is changed to P i In this case, it is not necessary to determine a switching pattern in advance, and the control unit 1730 can switch the electrode pairs simply by monitoring the power value read from the power adjustment unit 1732.

[0093] When the electrode switching pattern is determined based on the amount of power, the control unit 1730 calculates the amount of power by integrating the power values ​​read from the power adjustment unit 1732, and switches the electrode pairs based on that value. As in the case of time switching, the energy required for heating is calculated, and the electrode pairs are switched when the amount of power, i.e., the energy value, reaches half the value of the required energy.

[0094] The configuration example in Fig. 17C is an example of a simple combination in which two electrode pairs are switched by one switch. As explained in Examples 2 and 3, when one electrode of an electrode pair is used in combination with multiple small electrodes, a switch can be connected to each small electrode, and the small electrode can be switched ON and OFF.

[0095] According to the method and timing for switching the electrode pairs, the control unit 1730 outputs an electrode selection signal to the electrode selection section 1733 and a power adjustment signal to the power adjustment section 1732 to start applying power to the heating section 1723. In the timing chart of FIG. 17D, power application starts at time t5. At the same time, a display signal is sent to the display section 1702 to display a message informing the user that heating is in progress. Thereafter, the electrode pair is switched at a predetermined stage. In this example, an electrode selection signal is sent to the electrode selection section 1733 at time t6 to select the second electrode pair 1712. After the supply of power is completed according to a predetermined pattern, it is stopped. At this stage (time t7), hot water at the desired temperature is prepared in the heating section 1723. At time t8, a message is displayed on the display section 1702 indicating that heating has been completed, and at the same time, the second valve 1724 is opened to supply hot water. After the hot water supply is completed, at time t 10 At this point, the control unit 1730 outputs a signal to the display unit 1702 to instruct the display unit 1702 to display a completion message, and the message is displayed for a certain period of time, after which the series of operations is completed. EXAMPLES

[0096] In the sixth embodiment, an example is shown in which a hot water supply function using direct resistance heating technology is provided by combining it with another device. Here, a refrigerator is taken as an example of another device, and a refrigerator with a water server function is described. FIG. 18 shows an example of the external appearance of the device. The refrigerator is provided with three refrigerator compartments 1802, 1803, and 1804 in a housing 1801. The refrigerator is further provided with a water server section 1805. The water server section 1805 is provided with an opening 1807 for receiving water supply, and a heating section 1808 using direct resistance heating inside. A heat insulating layer 1809 is provided to insulate the heating section 1808 and the path through which the hot water passes from the refrigerator compartment. The refrigerator is provided with a display / input section 1806 with a touch panel for display and input. In this example, it is used as the display / input section of the refrigerator.

[0097] 19A and 19B show functional block diagrams of a refrigerator with a water server function. A refrigerator with a water server function 1901 is composed of a refrigeration unit 1902 that provides the refrigerator function and a water server unit 1903 that provides the water server function. The configuration shown here is an example, and is not limited to this. The functional blocks of the refrigeration unit 1902 also have different configurations depending on the functions of the refrigerator. Furthermore, the functions of each unit are merely shown as representative ones, and are not limited to these. For example, a door monitor does not have a control unit or a signal conversion unit, but a configuration is assumed in which a control mechanism is included in the configuration of the door monitor itself. In contrast, a configuration is also possible in which the opening and closing of the door is an ON / OFF switch, and the central control unit directly reads the information. Regarding the power supply, the voltage and current capacity supplied are different between the power source of the motor power system such as the compressor and the fan and the power source of the control system composed of electronic components, but these differences are not distinguished here.

[0098] The water server function can be roughly divided into two configurations depending on how the control unit that controls the water server function is arranged. FIG. 19A shows an example of a configuration in which the control unit 1904 is arranged inside the water server unit 1903a, and is a configuration in which the water server configuration shown in FIG. 17B is added to the refrigerator as is. Exchanges between the refrigeration unit 1902 are limited to matters related to display and input, available power capacity and power supply, and interrupt signals for suppressing power usage on the water server side when a large amount of power is used for a function on the refrigeration unit side. Therefore, most of the water server operations can be controlled by the water server unit 1903a alone. This makes it relatively easy to add a water server function to an existing refrigerator. It is also relatively easy to add functions other than the refrigerator.

[0099] In contrast, Fig. 19B shows a configuration in which the functions of control unit 1904 in water server unit 1903a are integrated into a control unit (central control unit 1905) for refrigeration unit 1902, and water server unit 1903b does not have the control unit function. In this configuration, control for driving the water server is also performed by central control unit 1905. In this case, because control of water server unit 1903b and refrigeration unit 1902 is performed by a single control unit, the operations of both units can be integrated and controlled, making it easier to perform fine control. Also, because a control unit is not required for water server unit 1903b, the number of parts can be reduced.

[0100] First, the flow of hot water supply in the configuration shown in Fig. 19A will be briefly described. When a request for hot water supply is made from the display and input function of the refrigerator, the central control unit 1905 notifies the request to the control unit 1904 of the water server unit 1903a. The control unit 1904 receives the request and requests the central control unit 1905 to display a message prompting the input of information necessary for heating, such as the amount of water and the hot water temperature. The central control unit 1905 displays this message and transmits the input information together with the available power estimated in consideration of the operating status of the refrigeration unit 1902 to the control unit 1904. The control unit 1904 supplies hot water using the method explained in the fourth embodiment based on this information. Here, it has been written that after receiving a hot water request, some information is exchanged between the control unit 1904 and the central control unit 1905, and then the hot water supply conditions and available power are transmitted. However, since this is a standard procedure, the central control unit 1905 may independently display and input messages in response to the hot water request, and after collecting the necessary information, provide the information to the control unit 1904 all at once.

[0101] We assume that this refrigerator with water dispenser function is also powered from an outlet. In this case, the maximum voltage V max is 100V or 200V, maximum current I maxNormally, the current consumption is 15A. While the refrigerator is running, the current consumption is measured, and when the Water Server Unit 1903a is running, the maximum current I max The current value is calculated by subtracting the current value used immediately before from (15A). max (Here we call it I max ' to be distinguished from the above) to the control unit 1904 of the water server unit 1903a. The water server unit is max =100V (or 200V), maximum current I max =I max The power is controlled so that the power is adjusted by the power adjustment unit with the capacity of the power supply set to '. If there are no continuous events occurring that would lead to an increase in the temperature inside the refrigerator, such as the opening and closing of the door, it is also possible to control the system so that the cooling function of the refrigeration unit 1902 is temporarily stopped and the power supplied to the water server unit 1903a is increased as much as possible to shorten the heating time.

[0102] The control of hot water supply in the configuration of FIG. 19B is the same as in the configuration of FIG. 19B, except that central control unit 1905 performs all of the roles previously assumed by control unit 1904 in water server unit 1903a.

[0103] The above is an example of control when no other event occurs while the water server unit 1903 is heating water. However, in reality, when the water server unit 1903 is consuming a large amount of power during heating operation, a sudden event also occurs in the refrigeration unit 1902, and the large amount of power consumed by the event causes the maximum current I max =I max It is considered that there will be a high frequency of occurrences in which the power supply capacity cannot be supplied. When such a sudden interrupt event that consumes a lot of power occurs, the following measures will be taken.

[0104] When defrosting, which is a typical example of a high power consumption event in the refrigeration unit 1902, overlaps with hot water supply in the water server unit 1903, it is possible to determine the priority order in advance and control, for example, to interrupt defrosting and concentrate power on hot water supply. Here, as an example requiring more complex control, we will take up a case where the door is opened and closed as an interrupt process when the refrigerator is full of items and input is high.

[0105] 20A to 20D show timing charts for events including the opening and closing of the refrigerator door, the heating operation of the water server unit, and the associated cooling of the refrigerator compartment. FIG. 20A shows an example in which interrupt processing is not required, in which no interrupt event (cooling operation associated with opening and closing of the door) occurs during heating in the water server unit. When the heating event of the water server unit ends, the refrigerator compartment adjacent to the heating unit is cooled. In the figure, this operation transition 2001 is indicated by an arrow. Since direct resistance heating directly heats the liquid, there is no heat transfer from the high-temperature heating element after hot water is supplied. However, the electrodes for passing electricity through the liquid must be immersed in the liquid, and the temperature of the electrodes at the immersed portion will be about the heating temperature. For this reason, a small amount of heat will dissipate from the electrodes, so a heat insulating layer 1809 (see FIG. 18) is placed between the heating unit and the refrigerator compartment, and the refrigerator compartment is cooled.

[0106] FIG. 20B shows the heater in operation at time t 21 In this example, the refrigerator door opening event occurs at the timing indicated by t 22The heating operation ends at . In this case, first, upon receipt of the end of the heating operation of the water server unit, cooling of the refrigerator compartment next to the heating unit is performed (operation transition 2002). While the cooling operation continues, a door closing event occurs, and in response, the cooling operation of the refrigerator compartment whose door was open is started (operation transition 2003). In the figure, the timing chart is shown without distinguishing between the refrigerator compartment next to the heating unit and the refrigerator compartment where the door opening event occurred, but the two refrigerator compartments may be the same or different. As the interrupt operation from the refrigerator unit to the hot water unit is the same and there is no difference in the timing of the event operation, no distinction will be made hereafter.

[0107] FIG. 20C shows the time t 23 The door opening event occurs at time t before the heating operation ends. 24 In this case, a door closing event also occurs at time t . When the door closing event occurs, the target refrigerator compartment needs to be cooled, so the refrigerator unit 1902 tries to start cooling. However, since the water server unit 1903 is in operation, the refrigerator unit 1902 does not perform the cooling operation and waits for cooling. After that, at time t 25 In response to the end of the hot water supply event, an action transition 2004 occurs, and the target refrigerator compartment and the cooling compartment beside the heating unit are cooled. Note that cooling may be given priority, hot water supply may be put on hold, and hot water supply may be resumed after cooling is finished.

[0108] FIG. 20D shows the door opening event at time t 26 When a request for heating is made to the water server unit at time t 26 At time t , the door is in the middle of an open event, so even if a heating request is received, the heating operation does not start and the system is in a waiting state. After that, the door is closed, and cooling of the refrigerator compartment starts (operation transition 2005). After cooling is completed (operation transition 2006), at time t 27 In reality, a hot water supply request is also made using the display and input unit 1806 on the front of the refrigerator, so it is unlikely that a door opening event will occur at the same time.

[0109] The present invention has been described above based on the embodiments. max shows an example of 100V or 200V, but there is no need to be limited to these as long as it is a commercial AC power source, and any commercial power source used in any country or region can be used in the same way.

[0110] The above-mentioned embodiments have been described in detail to clearly explain the present invention, and are not necessarily limited to those including all of the configurations described. It is possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. In addition, it is possible to add, delete, or replace a part of the configuration of each embodiment with the same configuration or another configuration. [Explanation of symbols]

[0111] 11, 12...area, 13...voltage, 14...current, 15...power, 41...container, 42...resistance, 43...electrode pair, 44...power supply, 45...wiring, 71, 72...electrode pair, 73...switch, 81, 82, 83, 84...waveform, 1701...housing, 1702...display unit, 1703...input unit, 1704...hot water outlet, 1705...cup, 1706...opening, 1707...water supply mechanism, 1708...power supply mechanism, 1711...first electrode pair, 1712...second electrode pair, 1720...water supply mechanism, 1721...flow rate detection / control unit, 1722...first valve, 1723...heating unit, 1724...second valve, 1730...control unit, 1731...power supply, 1732...power adjustment section, 1733...electrode selection section, 1801...casing, 1802, 1803, 1804...refrigerator compartment, 1805...water server section, 1806...display / input section, 1807...opening, 1808...heating section, 1809...insulating layer, 1901...refrigerator with water server function, 1902...refrigeration unit, 1903...water server unit, 1904...control unit, 1905...central control unit, 2001, 2002, 2003, 2004, 2005, 2006...operation transition.

Claims

1. Initial temperature T ｉ The liquid is heated to a target temperature T ｆ A liquid heating device for heating up to A container; an electrode pair disposed within the vessel; an AC power source that applies a current to the liquid via the electrode pair immersed in the liquid; The AC power source supplies a maximum current I ｍａｘ Constant current operation or maximum voltage V ｍａｘ and constant voltage operation is performed. The electrode distance of the electrode pair is d, the electrode area through which the electrode pair passes current to the liquid is S, and the initial temperature T ｉ and the target temperature T ｆ Intermediate temperature T ｍ ((T ｉ +T ｆ ) / 2), the electrical resistivity that the liquid can have is ρ(T ｍ ), the size of the electrode pair is, when the inter-electrode distance and electrode area of ​​the electrode pair that satisfy (Equation 1) are ideal values, [0010] A liquid heating device in which the error in the inter-electrode distance and the error in the electrode area of ​​the electrode pair from the ideal values ​​are each 30% or less.

2. In claim 1, The container has N (N≧2) electrode pairs, The liquid heating device heats the liquid to a minimum temperature T ｍｉｎ From the maximum temperature T ｍａｘ Heat until The minimum temperature T ｍｉｎ From the maximum temperature T ｍａｘ is divided into N sections, and N electrode pairs are assigned to each section, The initial temperature T ｉ is the initial temperature of the section assigned to the electrode pair, and the target temperature T ｆ A liquid heating device in which, when the target temperature of the section assigned to the electrode pair is set to be equal to or less than 30%, the size of each of the N electrode pairs is such that the error in the inter-electrode distance and the error in the electrode area from the ideal values ​​of the electrode pair are each 30% or less.

3. In claim 2, The temperature difference between the initial temperature and the target temperature of the section assigned to the electrode pair is (T ｍａｘ -T ｍｉｎ ) / N liquid heating device.

4. In claim 2, A control unit that switches the N electrode pairs according to the N sections, The control unit is a liquid heating device that switches the electrode pairs based on at least one of the temperature of the liquid, the heating time of the liquid, the power input by the AC power source to the liquid, and the amount of power input by the AC power source to the liquid.

5. In claim 1, The electrode pair is capable of switching the electrode area, Regarding the electrical resistivities of the plurality of liquids, the size of the electrode pair is set such that an error in the inter-electrode distance and an error in the electrode area from the ideal value of the electrode pair are each 30% or less, A liquid heating device in which the electrode area of ​​the electrode pair is switched to an electrode area determined for a possible electrical resistivity of the liquid that is closest to the electrical resistivity of the liquid.

6. In claim 1, The electrode pair is capable of switching the electrode area, The liquid heating device heats the liquid to a minimum temperature T ｍｉｎ From the maximum temperature T ｍａｘ Heat until The minimum temperature T ｍｉｎ From the maximum temperature T ｍａｘ is divided into N sections (N≧2), and the electrode areas of the electrode pairs are switched according to the N sections, The initial temperature T ｉ The initial temperature of each of the N sections, the target temperature T ｆ a target temperature for each of the N sections, in which the size of the electrode pair is such that the error in the inter-electrode distance and the error in the electrode area from the ideal values ​​of the electrode pair are each 30% or less,

7. In claim 6, The temperature difference between the initial temperature and the target temperature in each of the N sections is (T ｍａｘ -T ｍｉｎ ) / N liquid heating device.

8. In claim 6, a control unit that switches the electrode areas of the electrode pairs according to the N sections; The control unit is a liquid heating device that switches the electrode area of ​​the electrode pair based on at least one of the temperature of the liquid, the heating time of the liquid, the power input by the AC power source to the liquid, and the amount of power input by the AC power source to the liquid.

9. a refrigeration unit having a plurality of refrigeration compartments; A water server unit for heating the liquid; Power is supplied to the refrigeration unit and the water server unit, and a maximum current I ｍａｘ Constant current operation or maximum voltage V ｍａｘ and an AC power supply that performs constant voltage operation at The water server unit includes: a heating section including one or more electrode pairs for applying electrical current to the liquid; an electrode selection unit for switching the electrode pair or an electrode area through which the electrode pair passes a current to the liquid; a power adjustment unit that supplies power of a predetermined power capacity to the heating unit from the AC power source, The water server unit refrigerates the liquid at a minimum temperature T ｍｉｎ From the maximum temperature T ｍａｘ Heat until The minimum temperature T ｍｉｎ From the maximum temperature T ｍａｘ The liquid is heated in each of the N sections by the electrode selection unit. The electrode distance of the electrode pair is d, the electrode area through which the electrode pair passes a current to the liquid is S, and the initial temperature of the section is T ｉ and the target temperature T ｆ Intermediate temperature T ｍ ((T ｉ +T ｆ ) / 2), the electrical resistivity that the liquid can have is ρ(T ｍ ), the maximum current supplied by the power adjustment unit to the heating unit is I ｍａｘ ', the size of the electrode pair is, when the inter-electrode distance and electrode area of ​​the electrode pair that satisfy (Equation 2) are ideal values, [0025] The refrigerator, wherein the error in the inter-electrode distance and the error in the electrode area of ​​the electrode pair from the ideal values ​​are each 30% or less.

10. In claim 9, The temperature difference between the initial temperature and the target temperature in each of the N sections is (T ｍａｘ -T ｍｉｎ ) / N refrigerator.

11. In claim 9, A control unit for controlling the electrode selection unit, The control unit switches the electrode pair or the electrode area based on at least one of the temperature of the liquid, the heating time of the liquid, the power input to the liquid by the AC power source, and the amount of power input to the liquid by the AC power source.

12. In claim 9, A heat insulating layer is provided between the heating unit of the water server unit and a refrigerator compartment adjacent to the heating unit, After the water server unit heats the liquid, the refrigeration unit cools the refrigeration compartment adjacent to the heating unit.

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