Ceramic heaters and liquid heating devices

Abstract

The present invention provides a ceramic heater and a liquid heating device that suppress the reduction in the lifespan of the ceramic heater due to miniaturization. [Solution] A ceramic heater 171, 172 having a ceramic substrate 17g extending in the axial direction L and a heating element 17a, wherein the axial length Lh of the heating element and the maximum outer diameter D of the ceramic heater satisfy the relationship 8 ≤ Lh / D.

Description

Technical Field

[0001] The present invention relates to a ceramic heater suitable for heating liquids such as water, and a liquid heating device using the same.

Background Art

[0002] Hot water is required for warm water washing toilet seats, fuel cell systems, water heaters, 24-hour baths, heating of vehicle washer fluid, in-vehicle air conditioners, etc. Therefore, a liquid heating device that heats water with a built-in heater is used. In particular, when aiming for rapid heating of hot water for a warm water washing toilet seat, etc., a rod-shaped ceramic heater in which a heating portion is embedded in a ceramic sheet wound around the outer periphery of an elongated ceramic substrate is used (Patent Document 1). In the technique described in Patent Document 1, the ceramic substrate is cylindrical with a through hole, water is introduced into the ceramic heater from the outside through the through hole, and the heated hot water is discharged from the tip of the ceramic heater.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in order to miniaturize the liquid heating device, it becomes necessary to miniaturize the ceramic heater. However, when the heater is miniaturized and the heat generation area becomes small, it is necessary to raise the heater temperature to generate the same amount of heat as before, and there is a risk that the heater life will be reduced due to the occurrence of cracks, etc. Therefore, an object of the present invention is to provide a ceramic heater and a liquid heating device that suppress a reduction in the life of the ceramic heater due to miniaturization.

Means for Solving the Problems

[0005] To solve the above problems, the ceramic heater of the present invention is a ceramic heater having a ceramic substrate extending in the axial direction and a heating element, wherein the axial length Lh of the heating element and the maximum outer diameter D of the ceramic heater satisfy the relationship 8 ≤ Lh / D, and the total length LM of the ceramic heater is 60 mm or less, and the maximum outer diameter D is 1.5 to 5.0 mm.

[0006] This ceramic heater increases the ratio of the heating element length to the outer diameter of the ceramic heater, resulting in a larger heating area in the axial direction. As a result, when a liquid to be heated, such as water, flows along the axial direction of the ceramic heater, the contact distance (contact area) with the liquid increases. Consequently, the heat from the heating element can be effectively transferred to the liquid, and an excessive rise in heater temperature can be suppressed. As a result, even when ceramic heaters are miniaturized and their heating temperatures increase, it is possible to suppress the reduction in lifespan due to cracks, fractures, etc. Furthermore, this ceramic heater makes it possible to significantly miniaturize ceramic heaters.

[0007] In the ceramic heater of the present invention, the length Lh may be 2 / 3 or less of the total length LM of the ceramic heater. According to this ceramic heater, the length Lh, and consequently the Lh / D ratio, can be used as a guideline.

[0008] In the ceramic heater of the present invention, the heating element may be provided only on the tip side of a position 5 mm away from the heating element side of an electrode pad connected to the heating element and located on the outer surface of one end of the ceramic heater. According to this ceramic heater, the length Lh, and consequently the Lh / D ratio, can be used as a guideline.

[0009]

[0010]

[0011] In the ceramic heater of the present invention, the electrical resistance value of the heating element may be 12Ω or more at 180°C. This ceramic heater increases the electrical resistance of the heating element, suppressing excessive heater output, preventing the heater temperature from rising too high, and further reducing the reduction in lifespan.

[0012] In the ceramic heater of the present invention, the heating portion is formed on the outer circumference of the ceramic substrate, and a ceramic sheet may be further provided that is wrapped around the outer circumference of the ceramic substrate to cover the heating portion. This ceramic heater makes manufacturing easier.

[0013] In the ceramic heater of the present invention, the heating element may be embedded in the ceramic sheet. This ceramic heater makes manufacturing easier.

[0014] The present invention provides a liquid heating device comprising: a container having an internal space, an inlet and an outlet communicating with the internal space; and one or more ceramic heaters housed in the container such that their front ends face the internal space, wherein the liquid to be heated is introduced from the inlet and flows through the internal space to the outlet, and the liquid is heated by the ceramic heaters in this process, wherein the ceramic heaters are attached to the container by being held at their base ends, the liquid flows from the inlet through the outer surface of the ceramic heaters to the outlet, and the ceramic heaters are ceramic heaters as described in any one of claims 1 to 6. [Effects of the Invention]

[0015] According to this invention, a ceramic heater and a liquid heating device can be obtained that suppress the reduction in the lifespan of the ceramic heater due to miniaturization. [Brief explanation of the drawing]

[0016] [Figure 1] This is a perspective view showing the external appearance of a liquid heating device according to an embodiment of the present invention. [Figure 2]It is a perspective view showing the appearance of a ceramic heater according to an embodiment of the present invention. [Figure 3] It is an exploded perspective view showing the configuration of the ceramic heater. [Figure 4] It is a perspective view along the line A-A of FIG. 1. [Figure 5] It is a cross-sectional view along the line B-B of FIG. 1. [Figure 6] It is a cross-sectional view along the line C-C of FIG. 5. [Figure 7] It is a cross-sectional view along the line D-D of FIG. 5. [Figure 8] It is a cross-sectional view along the line E-E of FIG. 5. [[ID=2))

MODE FOR CARRYING OUT THE INVENTION

[0017] Hereinafter, embodiments of the present invention will be described. FIG. 1 is a perspective view of a liquid heating device 200 according to an embodiment of the present invention, FIG. 2 is a perspective view showing the appearance of a ceramic heater 171, and FIG. 3 is an exploded perspective view of the ceramic heater 171.

[0018] In this embodiment, the liquid heating device 200 is installed in a warm water washing toilet seat and is configured to heat normal temperature water by two built-in ceramic heaters 171 and 172 to supply warm water.

[0019] The liquid heating device 200 has a generally elongated cylindrical shape (a cylindrical shape with a rounded rectangular cross-section) as a whole and includes a container 100 and two ceramic heaters 171 and 172. The container 100 includes an elongated cylindrical body portion 101 having an internal space 100i for accommodating a liquid W (water), a front end cap 107 and a rear end cap 109 that respectively close the openings at both axial ends of the body portion 101, and an inlet 103 and an outlet 105 for the liquid W that are provided integrally with the body portion 101. Both axial ends of the body portion 101 project radially in a flange shape, and both ends of the body portion 101 and the front end cap 107 and the rear end cap 109 are hermetically sealed by an O-ring 190 (FIG. 5).

[0020] The ceramic heaters 171 and 172 are rod-shaped and extend in the axial direction L, and are arranged in the same direction (parallel to each other). The ceramic heaters 171 and 172 are attached to the container 100 by their base ends 17R being cantilevered to the opening of the rear end lid 109 of the container 100 by a sealing part 180. The tip ends 17T of the ceramic heaters 171 and 172 are located within the internal space 100i. It goes without saying that the holding portion by the sealing part 180 is on the base end side of the heating portion 17a of the ceramic heater, which will be described later.

[0021] Here, "ceramic heaters 171 and 172 are aligned in the same direction (parallel)" means that, taking into account installation errors, the maximum angle between the axes of all ceramic heaters 171 and 172 is 10 degrees or less (including 0 degrees). Furthermore, lead wires 15 and 16, which will be described later, are connected to the base end 17R side of the ceramic heaters 171 and 172 for supplying power from an external source.

[0022] In this example, the axial direction of the body portion 101 is parallel to the axis L, and the ceramic heaters 171 and 172 are housed in the internal space 100i of the body portion 101 such that the direction in which they are arranged is along the long axis of the cross-section of the body portion 101. However, the axial direction of the body portion 101 may form a small predetermined angle with the axis L. Although not shown in the diagram, in this example, the liquid heating device 200 is installed on the bidet toilet seat with its axis L direction being approximately horizontal and the outlet 105 side positioned slightly upward, and the ceramic heaters 171 and 172 are positioned horizontally.

[0023] The inlet 103 and outlet 105 communicate with the internal space 100i and are spaced apart in the axial direction L (which is also the axial direction of the body 101). Liquid W introduced from the outside through the inlet 103 passes through the internal space 100i along the flow direction F and is discharged from the outlet 105. Furthermore, a gap is formed between the inner wall of the container 100 and the ceramic heaters 171 and 172. The liquid W introduced into the internal space 100i through the inlet 103 is heated while in contact with the outer surfaces of the ceramic heaters 171 and 172 along the axial direction L, and then flows to the outlet 105.

[0024] Next, the configuration of a ceramic heater according to an embodiment of the present invention will be described with reference to Figures 2 and 3. Since ceramic heaters 171 and 172 have the same shape, ceramic heater 171 will be described first. As shown in Figure 2, the ceramic heater 171 has a heating element 17h that generates heat when an electric current is applied from the outside via lead wires 15 and 16. The heating element 17h has a heating section 17a at its tip, which is formed by arranging a conductor in the direction of the axis L to create a heating pattern, and a pair of lead sections 17b that are drawn out from both ends of the heating section 17a towards the rear end. The heating element 17a has a length Lh in the axial direction L.

[0025] More specifically, as shown in Figure 3, the heating element 17h has a heating portion 17a, two lead portions 17b, and an electrode pattern 17c formed at the rear ends of both lead portions 17b, and this heating element 17h is sandwiched between two ceramic green sheets 17s1 and 17s2. Alumina is used as the ceramic green sheet. Tungsten or rhenium, etc., are used for the heating portion 17a and the lead portions 17b. Two electrode pads 17p to which lead terminals 18 (see Figure 2) are brazed are formed on the surface of the ceramic green sheet 17s2, and the electrode pattern 17c is connected to the electrode pads 17p by through holes to form a laminate of ceramic green sheets.

[0026] Furthermore, by wrapping this laminate around a rod-shaped ceramic substrate 17g, mainly composed of alumina, with the ceramic green sheet 17s2 facing outwards, and firing it, a ceramic heater 171 can be manufactured in which each ceramic green sheet 17s1 and 17s2 becomes a ceramic sheet 17s and is wrapped around the outer circumference of the ceramic substrate 17g, integrating them into one unit. The 17g ceramic substrate may be cylindrical with through holes or columnar without holes. However, if it is cylindrical, it is desirable to seal the through holes with resin or the like to prevent water leakage. The lead wires 15 and 16 are crimped to the lead terminals 18 and 18 and electrically connected (see Figure 2).

[0027] Here, when winding the laminate onto the ceramic substrate 17g, the ends of the laminate along the axis L are wound with a gap between them. For this reason, a slit 17v, which is a concave groove along the axis L, is formed as a non-heating part in the winding portion on the outer surface of the ceramic heater 171. Therefore, when viewing the radial cross-section of the ceramic heater 171, the heating element 17a is embedded in the ceramic heater 171 in the form of an end ring, and a slit 17v, which is a non-heating element, is formed between the two ring ends 17e of the heating element 17a.

[0028] Alternatively, the ceramic green sheet 17s1 may be omitted, and the heating element 17h may be formed on the back side of the ceramic green sheet 17s2 by printing or other means, with the ceramic green sheet 17s2 wrapped around the heating element 17h facing the ceramic substrate 17g. In this case, the heating element 17h (heating part 17a) will be positioned between the ceramic substrate 17g and the ceramic green sheet 17s2. In contrast, in the embodiment shown in Figure 3, the heating element 17h (heating section 17a) is sandwiched between ceramic sheets (ceramic green sheets 17s1, 17s2), meaning it is "embedded".

[0029] As described above, both the case in which the heating element 17a is embedded in the ceramic sheet (ceramic green sheet 17s1, 17s2) and the case in which it is placed between the ceramic substrate 17g and the ceramic green sheet 17s2 are referred to as "the ceramic sheet having a heating element."

[0030] Next, we will describe the more detailed configuration of the ceramic heater 171. As shown in Figure 2, the length Lh in the axial direction L of the heating element 17a of the ceramic heater 171 and the maximum outer diameter D satisfy the relationship 8 ≤ Lh / D. This increases the ratio of the length of the heating element to the outer diameter of the ceramic heater 171, and the heating element area in the axial direction L becomes larger. As a result, when a liquid to be heated, such as water, flows along the axial direction L of the ceramic heater 171, the contact distance (contact area) with the liquid increases. Consequently, the heat from the heating element 17a can be effectively transferred to the liquid, and an excessive rise in heater temperature can be suppressed. As a result, even when ceramic heaters are miniaturized and their heating temperatures increase, it is possible to suppress the reduction in lifespan due to cracks, fractures, etc.

[0031] If the Lh / D value is less than 8, the ratio of the heating element length to the outer diameter of the ceramic heater 171 becomes small, making it difficult to effectively transfer the heat from the heating element 17a to the liquid, causing the heater temperature to rise excessively. Also, a small D value makes the heater more prone to breakage. A higher value for Lh / D is preferable, but since the length Lh cannot be greater than the total length LM of the ceramic heater 171, the upper limit of Lh / D can be defined, for example, within the range Lh / LM ≤ 2 / 3. Furthermore, if the length Lh is made too long, it will interfere with the electrode pad 17p on the proximal end side of the ceramic heater 171. Therefore, the upper limit of Lh / D may be defined so that the heating element 17a is provided only on the tip side of the position 17u which is 5 mm away from the electrode pad 17p on the heating element 17a side.

[0032] Furthermore, from the viewpoint of miniaturizing the ceramic heater, it is preferable that the total length LM be 60 mm or less, and the maximum outer diameter D be 1.5 to 5.0 mm. Furthermore, if the electrical resistance of the heating element 17a is 12Ω or higher at 180℃, the electrical resistance of the heating element 17a will be high, suppressing excessive heater output, preventing the heater temperature from rising too high, and further suppressing the reduction in lifespan. Furthermore, ceramic heaters 171 and 172 have a power output of 100W / cm². 2Having the above watt density is preferable because it allows for miniaturization of the ceramic heater and, consequently, the entire liquid heating device 200. Furthermore, the smaller the ceramic heater, the higher the heater temperature needs to be, making the present invention even more effective.

[0033] Next, with reference to Figures 4 to 6, a more detailed configuration of the liquid heating apparatus 200 according to an embodiment of the present invention will be described. Figure 4 is a perspective view from the direction perpendicular to the axis L and the axis of the inlet 103. As shown in Figure 4, the inlet 103 and outlet 105 are arranged in the direction of the axis L of the ceramic heaters 171 and 172. Therefore, water introduced from the inlet 103 flows toward the outlet 105 along the flow direction F, contacting the outer surfaces of the ceramic heaters 171 and 172 as it flows toward the tip 17T. This, combined with the fact that the ceramic heater 171 satisfies the relationship 8 ≤ Lh / D as described above, increases the contact distance (contact area) when water flows along the axis L of the ceramic heater 171, thereby suppressing an excessive rise in heater temperature.

[0034] Next, with reference to Figures 5 to 8, the remaining components of the liquid heating device 200 will be described. As shown in Figure 6, the slits 17v of the ceramic heaters 171 and 172 face outward in the longitudinal direction of the container 100, which is the side furthest from the inlet 103. In this configuration, the slits 17v do not face the liquid that first hits the outer surface of the ceramic heaters 171 and 172 at a high flow velocity from the inlet 103, so the liquid initially introduced into the internal space 100i is effectively heated by the heating element 17a. As a result, the entire water is heated uniformly, improving heating efficiency.

[0035] Furthermore, as shown in Figure 7, a partition wall 100s is provided in the internal space 100i between the inlet 103 and the outlet 105, separating each of the multiple ceramic heaters 171 and 172 individually. The water introduced from the inlet 103 flows through the partition wall 100s, one for each individual ceramic heater 171 and 172. As a result, water flows through the narrow gap within the partition wall 100s and is heated by the individual ceramic heaters 171 and 172, further improving heating efficiency.

[0036] As shown in Figure 8, the internal space 100i near the outlet 105 is not provided with a partition wall 100s, and is a single internal space 100i. As a result, the volume of the internal space 100i increases near the outlet 105, making it easier for boiling bubbles generated on the inlet 103 side to escape to the outside through the outlet 105. In addition, the water that has been heated within the separate partition wall 100s merges, resulting in hot water at a uniform temperature. Figure 5 is a cross-sectional view of the liquid heating device 200 taken through the center of its minor axis in the direction of axis L, while Figures 6, 7, and 8 are cross-sectional views perpendicular to axis L in Figure 5.

[0037] The present invention is not limited to the embodiments described above, and it goes without saying that it extends to various modifications and equivalents that fall within the spirit and scope of the present invention. For example, the shape of the liquid heating device or ceramic heater is not limited. The liquid heating device may have one ceramic heater or three or more. Furthermore, the ceramic substrate 17g of the ceramic heater may be cylindrical with through holes, or it may be columnar without holes. Even if the ceramic substrate 17g has through holes, if the container in which the ceramic heater is installed has an inlet and an outlet in the internal space, the liquid will flow from the inlet through the outer surface of the ceramic heater to the outlet, resulting in a liquid flow similar to that of the case without holes. In other words, when the outer surface of the ceramic heater is in contact with the liquid to heat it, the heat transfer efficiency between the heater and the liquid is lower compared to the type in which the liquid passes through the inner holes of the ceramic heater, making the present invention more effective. [Examples]

[0038] We manufactured the liquid heating device 200 shown in Figure 1. First, as the raw material for the ceramic heater, alumina powder and glass component powder, which would serve as a sintering aid, were ground and mixed with water in a mill, and a binder was added to obtain a clay-like mixture. This mixture was extruded using an extruder with a core-equipped die to form a cylindrical ceramic substrate, which was then cut to a predetermined length and calcined. The outer diameter and length of the ceramic substrate were determined considering the shrinkage rate during firing. On the other hand, a heater pattern and terminal sections connecting to the opposite side of the sheet were printed and formed on an alumina green sheet using tungsten and molybdenum paste. The size of the heater printing area was determined by taking into account the shrinkage rate during ceramic firing. The heater pattern was formed by calculating the resistance at room temperature from the resistance value at high temperatures and the resistance change due to the temperature rise (temperature coefficient of resistance × temperature difference × initial resistance value). Similarly, the sheet size was prepared and cut considering the firing shrinkage rate.

[0039] A printed ceramic green sheet, cut to a predetermined size, was wrapped around a pre-fired ceramic substrate and fired as a single unit. The resulting heater had a total length LM = 60 mm and a maximum outer diameter D = 2.8 mm. Ceramic heaters were obtained by varying the axial length Lh of the heating element to various values ​​shown in Table 1. The room temperature resistance values ​​of the ceramic heaters were set to 6 Ω and 9 Ω. The resistance value of the ceramic heater was adjusted by changing the length (number of folds) and thickness of the heating element. The exposed terminals of the fired heater body were plated with Ni, and the Ni lead parts were brazed with Ag solder. Furthermore, lead wires were crimped to the lead parts to form the ceramic heater.

[0040] Next, two ceramic heaters were attached to a resin container. Specifically, each ceramic heater was passed through two through holes in the rear end lid, and epoxy adhesive was used to secure each ceramic heater as a seal. Then, the rear end lid, the body, and the front end lid were airtightly connected via O-rings to manufacture the liquid heating device 200. Water at a flow rate of 450 cc / min and a water temperature of 5°C was introduced into the resulting liquid heating device 200, and the applied voltage per ceramic heater was controlled so that the outlet water temperature was 35°C. The results obtained are shown in Table 1. In Table 1, " / unit" indicates the characteristics per heater.

[0041] [Table 1]

[0042] As is clear from Table 1, in the examples where the relationship 8 ≤ Lh / D is satisfied, the heater temperature was less than 200°C, which is the typical thermal shock strength of alumina ceramic bodies. Furthermore, it was found that the heater did not crack even when water at the above flow rate was continuously flowed through the liquid heating device 200, and a cycle of applying the water for 15 seconds and stopping the application for 15 seconds was repeated for 10 consecutive cycles. This indicates that even with a smaller ceramic heater, the reduction in lifespan can be suppressed. Furthermore, it was found that the higher the electrical resistance of the heating element at 180°C, the lower the heater temperature when voltage is applied (during heating). From this, it can be concluded that it is preferable for the electrical resistance of the heating element at 180°C to be 12Ω or higher.

[0043] On the other hand, in the comparative example where 8 > Lh / D, the heater temperature exceeded the thermal shock intensity of 200°C. Furthermore, after performing the above cycle test for three consecutive cycles, the ceramic heater cracked, and the heater's lifespan was reduced.

[0044] Commercial products 1 and 2 are of the type that heat a ceramic substrate by passing water through through holes (internal holes), similar to Figure 1 in Patent Document 1, and are constructed by preparing a container (heat exchanger) similar to Figure 1 and installing a heater. Furthermore, although the heater temperature of commercially available products 1 and 2 was less than 200°C during heating, the length Lh of the heating element and the maximum outer diameter D of the heater were larger than those of the examples, making it difficult to miniaturize the ceramic heater. In particular, the watt density was 100 W / cm². 2 It is less than [amount missing], and the heat output is small compared to the size of the ceramic heater. The reason why commercially available products 1 and 2 are large in size is likely due in part to the fact that water is passed through the internal pores for heating. [Explanation of Symbols]

[0045] 17a Heat-generating part 17g ceramic substrate 17s Ceramic Sheet 17p electrode pads 100 containers 100i interior space 103 Inlet 105 Outlet 171, 172 Ceramic heater 200 Liquid heating equipment L axis W liquid

Claims

1. A ceramic heater having a ceramic substrate extending in the axial direction and a heating element, The axial length Lh of the heating element and the maximum outer diameter D of the ceramic heater satisfy the relationship 8 ≤ Lh / D. A ceramic heater characterized in that the total length LM of the ceramic heater is 60 mm or less, and the maximum outer diameter D is 1.5 to 5.0 mm.

2. The ceramic heater according to claim 1, characterized in that the length Lh is 2 / 3 or less of the total length LM of the ceramic heater.

3. The ceramic heater according to claim 1, characterized in that the heating element is provided only on the tip side of a position 5 mm away from the heating element side of an electrode pad connected to the heating element and positioned on the outer surface of one end of the ceramic heater.

4. The ceramic heater according to claim 1, characterized in that the electrical resistance value of the heating element is 12 Ω or more at 180°C.

5. The heating element is formed on the outer circumference of the ceramic substrate. The ceramic heater according to claim 1, further comprising a ceramic sheet that is wrapped around the outer circumference of the ceramic substrate and covers the heating element.

6. The ceramic heater according to claim 5, characterized in that the heating element is embedded in the ceramic sheet.

7. A container having an internal space, and an inlet and an outlet communicating with the internal space, One or more ceramic heaters housed in the container such that their tip faces the internal space, Equipped with, A liquid heating device in which a liquid to be heated is introduced from the inlet and flows through the internal space to the outlet, and in the process the liquid is heated by the ceramic heater, The ceramic heater is attached to the container by having its base end held by the container. The liquid flows from the inlet through the outer surface of the ceramic heater to the outlet. The liquid heating apparatus is characterized in that the ceramic heater is the ceramic heater described in any one of claims 1 to 6.

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