Liquid heater and method for heating liquid

Abstract

A liquid heater (1) comprising a container (2) for containing a liquid to be heated, a base (3), a heating device (13), and a stirring device (12), The stirring device (12) constitutes a part of a heating device (13) up to a predetermined heating level (H), exhibits a heating temperature (TH) up to the heating level (H), and includes a rotor (11) and a drive mechanism (15); The first member (16) is magnetically coupled to the second member (17); The rotor (11) is configured to rotate the liquid in the container (2) and cause it to rise along the side (9), A liquid heater (1) and a method for heating a foamable liquid in the liquid heater (1), characterized in that the rotation speed of the rotor (11) is within a range of rotation speeds that causes a defined minimum amount of liquid in the container (2) to rise to a height at least equal to the heating height (H) and within which the surface of the heated liquid does not have a continuous foam surface.

Description

[Technical Field]

[0001] The present invention relates to a liquid heater according to the preamble of claim 1 and to a method for heating a foamable liquid in a liquid heater according to claim 15. [Background technology]

[0002] Liquid heaters that agitate the liquid being heated, for example milk, while heating it, are known in the prior art.

[0003] US 9,107,533 B2 discloses an automatic milk frother comprising a container for holding milk, a base into which the container is inserted for heating and frothing the milk, a rotor of an agitator for frothing the milk contained in the container, the rotor being held in the container, and a heating device for heating the milk held in the container. The rotor is driven by a magnetic coupling via a motor arranged in the base. The container is free of electrical components and a continuous drive shaft for the agitator. Summary of the Invention [Problem to be solved by the invention]

[0004] A drawback of the milk frother according to US 9,107,533 B2 is that the heating of the milk contained in the container is limited to the case where the milk is heated at the same time as foaming.

[0005] However, when heating liquids for subsequent consumption by infants, the formation of bubbles or air bubbles in the liquid should be avoided. Avoiding the incorporation of air helps alleviate common breastfeeding problems such as colic and bloating. Furthermore, liquids, especially milk, should be heated gently to avoid so-called hot spots, i.e., areas of high temperature that damage nutrients, enzymes, and antibodies in the heated liquid, especially in breast milk. Scientific studies have shown that breast milk should not be heated to a maximum temperature of 40°C. See, for example, Bransburg-Zabary S, Virozub A, Mimouni FB, Human Milk Warming Temperatures Using a Simulation of Currently Available Storage and Warming Methods. PLoS ONE 10(6), published on June 10, 2015.

[0006] The object of the present invention is to create a liquid heater and method for heating foamable liquids as initially described, which avoids or at least reduces the drawbacks of the prior art. The liquid heater and method aim to provide the most uniform heating of the liquid contained therein, without forming superheated areas within the liquid volume and without causing the liquid to foam. Furthermore, the liquid should be heated as efficiently as possible. The liquid heater should also be inexpensive to manufacture and easy to clean.

[0007] This object is solved by a liquid heater according to claim 1 and a method according to claim 15. Advantageous and further embodiments are set forth in the dependent claims. [Means for solving the problem]

[0008] The liquid heater according to the present invention is characterized in that, in an operating state, the rotor rotates the liquid contained in the container to raise the liquid level along the side, and the rotation speed of the rotor is in a range of rotation speeds such that a specified minimum amount of the liquid in the container exposed to the rotating rotor reaches a height at least equal to the heating height and the heated liquid does not contain a surface of continuous bubbles.

[0009] The method according to the present invention is characterized in that, in operation, the rotor rotates the liquid contained in the container and causes it to rise to the side, the rotational speed of the rotor during this rotation being in a range of rotational speeds that causes a predetermined minimum amount of liquid in the container to rise to a height at least equal to its heating height, and after rotation of the rotor, the heated liquid obtained in the container is still characterized in that it does not have a continuous foam surface on its surface.

[0010] Liquid heaters are used to heat liquids, particularly milk, such as breast milk, powdered milk, or milk produced from animal milk. The liquid heater comprises a container for receiving the liquid to be heated, a base on which the container can be placed and removed, a heating device designed to heat the liquid in the container, and a stirring device designed to stir the liquid in the container. The container has a bottom and a side extending therefrom and can be designed, for example, as a can that can be filled and emptied. For this purpose, it can be equipped with a reclosable and reclosable lid and a handle for the user to grip. For example, the side can be cylindrical. Preferably, the container is designed to hold a maximum intended fill volume of 300 ml, preferably 200 ml, and particularly preferably 120 ml, of the liquid to be heated, although the actual volume of liquid that can be accommodated may be even higher. In operation, the container, particularly for heating the liquid, is positioned on a base equipped with the electrical components necessary to operate the liquid heater. For this purpose, the base can be equipped with a power cable for connection to a socket. The liquid heater can be removed from the base by the user to remove the heated liquid and clean the container.

[0011] The heating device is used to heat the liquid in the container and can include a control device that allows the user to set the desired target temperature of the liquid to be heated. The sides of the container are part of the heating device, starting from the bottom and including a predetermined heating level for heating the liquid, i.e., the heating level at which the liquid heater is activated. In this way, the liquid in the container is heated gradually through the sides. The side surfaces generally include a larger surface area than the bottom of the container, allowing the liquid to be heated particularly efficiently. Furthermore, due to the relatively large surface area of ​​the sides, particularly high heating temperatures can be avoided. For example, the heating temperature can be up to 30 degrees, preferably 20 degrees, higher than the target temperature of the liquid to be heated.

[0012] The stirring device includes a rotor. The rotor is housed in a container and includes a first element for generating a magnetic field or a magnetic field, and a drive mechanism for the rotor. The drive mechanism is housed in a base and includes a second element for generating a magnetic field or a magnetic field. The first and second elements can be permanent magnets or coils to which a current can be applied to generate a magnetic field, but the first and second magnetic elements can be ferromagnetic. The rotor is housed in the container and is set to rotate by a drive mechanism provided on the base during operation of the liquid heater, i.e., during heating of the liquid in the container. For this purpose, the first element is magnetically coupled to the second element. The rotor is also magnetically coupled to the drive mechanism via the first and second elements, and the drive mechanism is designed to rotate the rotor at at least one speed. The drive mechanism includes a motor, particularly an electric motor, for this purpose. Rotation of the rotor during heating of the liquid in the container distributes heat introduced via the heating device as evenly as possible within the liquid volume without creating overheated areas, or so-called hot spots, within the liquid volume. Avoiding such overheated areas or hot spots will have a beneficial effect on the composition of the liquid and also prevent discomfort or injury when drinking the liquid if not thoroughly stirred beforehand.

[0013] To efficiently heat the liquid in the container while simultaneously minimizing the formation of bubbles in the container, the rotor's rotation speed is set to a range that raises a specified minimum amount of liquid in the container to at least the heating level during its rotation, and within which the heated liquid does not form a continuous surface of bubbles on its surface even after the rotor's rotation has ended. Therefore, the drive mechanism is designed to rotate the rotor at a rotation speed that raises the liquid rotated by the rotor to at least the heating level, but avoids the formation of a continuous surface of bubbles on the liquid itself, for example, in (breast) milk, at the end of the rotor's rotation or after the rotor's rotation. In this way, even if the specified minimum amount of liquid in the container is efficiently heated, the entire side surface is in contact with the liquid, and the entire portion constitutes the heating temperature. For this purpose, the rotor's rotation speed is set to be at least equal to or greater than the lower limit of the rotation speed range. Furthermore, by not exceeding the upper limit of the rotor speed range, a continuous foam surface is avoided, even for foamy liquids such as milk, so that the heated liquid can be consumed immediately after removal from the container without swallowing air as bubbles formed on the liquid surface. Avoiding foam formation is particularly advantageous when small children are drinking heated liquids. However, individual bubbles or foam-covered areas may appear on the surface of the heated liquid after the rotor is turned.

[0014] Any speed within the range of rotational speeds is suitable for raising the liquid in the container to at least a high heated level and avoiding a continuous foam surface after rotation of the rotor. The rotational speed or range of rotational speeds depends on numerous design-related parameters of the liquid heater. The drive mechanism can also be designed to adjust the rotational speed and / or range of rotational speeds to match the rotational speed or range of rotational speeds to the properties of the liquid contained in the container. For example, a pre-programmed table or setting aid can be provided within the liquid heater that indicates to the user advantageous rotational speeds or advantageous rotational speed ranges for different liquids. Within the rotational speed range, the rotor rotational speed can be constant.

[0015] When reference is made in the description to a position or direction such as above, above, below, or under, these should be understood with respect to the position of use of the liquid heater and the state in which the liquid is heated within the container.

[0016] According to a preferred embodiment of the present invention, the density of the liquid is 1.018 to 1.048 g / cm 3 In this case, the Newton number corresponding to the agitator is between 0.1 and 0.3, preferably between 0.1 and 0.2. A liquid in this density range essentially corresponds to the density of milk. If the surface tension and / or viscosity of the liquid essentially corresponds to that of milk, the Newton number corresponding to the agitator is also preferably between 0.1 and 0.3, preferably between 0.1 and 0.2. In this case, the surface tension is in the range of 30 to 43.5 mN / m and the viscosity is in the range of 1.06386 to 3.27726 mm. 2 / s. The values ​​given for density, surface tension and viscosity depend on the temperature and the type of liquid, in particular milk. It is clear that differently designed rotors may require different rotational speeds to allow a specified minimum amount of liquid in the vessel to rise at least to the heated height. However, since the Newton number is characteristic of the power introduced into the liquid through the rotor, different rotors may also contain different Newton numbers. The rotor design is therefore fully specified by the Newton number. The rotor housed in the vessel can therefore have various shapes. In particular, the Newton number indicates what proportion of the rotor's power P is actually available as hydraulic power. The following applies: Ne = P / (ρ * n 3 * d 5 ) where: Ne...Newton number P ... rotor power, W ρ ... density of liquid, kg / m 3 n ... rotational speed, s -1 d ... rotor diameter, m

[0017] The rotor power P is calculated from the rotor section modulus: P = M *2* π * n where: P ... rotor power, W M ... rotor torque, Nm n ... rotational speed, s -1

[0018] It is particularly preferred if the rotor rotation speed is within the range of 370 to 450 rpm, with a rotor power within the range of 0.05 to 0.1 W, a ratio of the heating height to the rotor height within the range of 3 to 5, and a ratio of the envelope circle diameter of the vessel provided at the heating height to the envelope circle diameter of the rotor within the range of 1.20 to 1.4. The rotor height is defined in the axial direction of the rotor, and the envelope circle diameter of the vessel or rotor is defined as the smallest circular diameter that completely accommodates the inside of the vessel or rotor side when viewed in the axial direction of the working liquid heater.

[0019] To enable the container to be formed without electrical components of the heating device, it is possible to provide that the heating device is an induction heating device. Thus, the container, which is part of the heating device up to the heating level, and in particular the side surfaces, can be heated by induction from an energy source provided to the side surfaces from the outside. For this purpose, the side surfaces, at least in the region up to the heating level, are made of a material that can be heated by induction.

[0020] For heating a liquid in a container, a base having a bottom and a protruding side wall is particularly preferred. The side wall is positioned adjacent to the side wall of a container positioned on the base, preferably at a heating height, and is equipped with a magnetic field generating mechanism of an induction heating device. Particularly preferably, the side wall of the base is at least partially curved around the side wall of the container. In particular, the side wall can be formed completely around the lateral surface, for example, in a circular or cylindrical shape. Thus, the container can be inserted into the base to heat the liquid. By arranging the magnetic field generating mechanism of the induction heating device on the side wall of the base over as large an area as possible, the side wall of the container and the liquid in the container can be heated particularly efficiently. For example, the magnetic field generating mechanism can cover more than half of the surface area, particularly more than three-quarters of the surface area of ​​the side wall. In particular, the magnetic field generating mechanism can be at least one coil that generates an alternating magnetic field when an alternating current flows through it.

[0021] If the bottom of the base also includes a magnetic field generating mechanism of the induction heating device, the bottom of the container can also be heated, and the liquid in the container can be heated more efficiently. In this case, the bottom of the container is also made of a conductive material that can be heated by induction.

[0022] The containers are preferably electrically insulated from the base to make them as easy to clean as possible and to eliminate electrical contacts that could detract from their appearance. Thus, the containers have no electrical connection to the base and can be submerged in water for cleaning without fear of damaging the contacts. Furthermore, because they have no electrical components, the bottom and sides of the containers can be thin-walled.

[0023] For a durable construction of the container, for efficient heating of the liquid and the most efficient possible prevention of foaming of the liquid in the container, it may be provided that the sides of the container are made of metal, in particular stainless steel, and are preferably cylindrical, at least up to the heating level. Furthermore, the side surfaces may include metal-free portions, such as transparent observation windows, preferably at least in the region of the heating level, to enable observation of the stirring process or the level of the introduced liquid. Stainless steel also offers the advantage of corrosion resistance.

[0024] If the bottom surface of at least a portion of the container bottom is flat, the container can be easily designed, inexpensively manufactured, and reliably placed on a support surface. The bottom side of the container bottom is understood to be the side of the container bottom facing away from the interior of the container.

[0025] If the top side of the container bottom is flat and the rotor preferably does not have a circular or ring-shaped receptacle for the rotor shaft, the top side of the container bottom facing the interior of the container can be particularly easily and reliably cleaned. For this purpose, the top side of the container bottom does not have any cylindrical or peg-shaped protrusions as the rotor's axis of rotation. Furthermore, the rotor can be easily inserted into the container before the liquid heater is activated without having to be positioned exactly on or above the axis of rotation. This is particularly advantageous when the container has a small diameter compared to its height, making it difficult for a user to insert their hand deep enough into the container to accurately position the rotor on the axis of rotation. Furthermore, the rotor preferably does not have a circular or ring-shaped receptacle or recess for the axis of rotation, especially a cylindrical receptacle or recess. This also means that the rotor can be easily and carefully cleaned, since it does not include a receptacle or recess for the axis of rotation, where residues of the heated liquid can accumulate.

[0026] To allow the container to be designed independently of the drive mechanism, it is advantageous if the second member of the drive mechanism is located below the bottom of the container positioned on the base. In contrast, the rotor is located on or above the bottom of the container positioned on the base. Because the second member of the drive mechanism and the first member of the rotor are magnetically coupled and power is transmitted from the drive mechanism to the rotor via the bottom of the container, it is advantageous for the container bottom to be constructed with thin walls for efficient power transmission. For example, the thickness of the container bottom is at most 3 mm, preferably at most 2 mm.

[0027] It is particularly advantageous if the rotor is magnetically centered by the second member of the drive mechanism while coupled to the drive mechanism. In this way, the mechanical rotation axis for the rotor can be distributed. Centering of the rotor, i.e., the rotor's position convenient or required for stirring the liquid in the container, is achieved by the magnetic attraction between the first and second members. It is particularly preferred that the distance between the second member of the drive mechanism and the first member of the rotor be as large as possible, e.g., at least half, and preferably at least two-thirds, of the envelope diameter of the rotor to ensure the highest possible torque transmission from the drive mechanism to the rotor via the magnetic coupling. Furthermore, as a result of this large distance, the rotor can be reliably centered even if the user inserts the rotor into the container outside the center of the container bottom, for example, by touching the side.

[0028] To achieve a reliable magnetic coupling between the rotor and the drive mechanism, the extension of at least one of the first and second members in a plane parallel to the bottom of the container positioned on the base is preferably greater than the extension of at least one of the first and second members in a plane perpendicular to the bottom of the container positioned on the base. Preferably, at least one of the first and second bodies extends in a plane parallel to the bottom of the container positioned on the base by at least 10%, more preferably at least 20%, and particularly preferably at least 30% of the envelope diameter of the rotor.

[0029] For easy handling of the liquid heater, it may be provided that the rotor can be removed from the container without tools and is freely movable, in particular radially. This allows the rotor to be removed from the container by rotating the container removed from the base into a position where the container bottom faces upward, for example, in order to clean the rotor and container. Removal of the rotor is further facilitated by the fact that, according to this embodiment, the rotor of the container removed from the base is freely movable in the radial direction, i.e., there is no mechanical guide.

[0030] According to a further embodiment, the rotor may have at least two, preferably three, arms extending radially of the rotor, on which the first member is disposed. The arms protruding from the center or center of gravity of the rotor serve to agitate the liquid. Furthermore, the placement of the first member on the arms, particularly on the radially outer half or the radially outer third of the arms, allows for efficient transmission of torque from the drive mechanism to the rotor. For example, the arms of the rotor inserted into the container run at least partially in a plane parallel to the bottom of the container. It is also preferred that the longitudinal length of the arms in the radial direction of the rotor is greater than the vertical length of the arms in the axial direction of the rotor.

[0031] To efficiently agitate the liquid and transmit torque from the drive mechanism to the rotor with as few losses as possible, the rotor preferably has three curved arms in the rotor plane, preferably in the direction of rotation, and preferably has an axially protruding upright surface on the side facing the container bottom as a bearing surface. The rotor plane runs perpendicular to the imaginary rotation axis of the rotor, i.e., perpendicular to the axial direction of the rotor. The curvature of the arms in the direction of rotation promotes agitation of the liquid. The axially protruding protrusions of the rotor, functioning as bearing surfaces, advantageously reduce the frictional resistance of the rotor held in the container on the container bottom. For example, the axially protruding rotor height can be a bulge or pin toward the side of the container bottom.

[0032] The invention is explained in more detail below by means of preferred embodiments, but is not limited thereto. The drawings show: [Brief explanation of the drawings]

[0033] [Figure 1] FIG. 1 is a perspective view of a liquid heater according to the present invention, with a lid.

[0034] [Figure 2] FIG. 2 is a perspective view of the liquid heater of FIG. 1 without the lid.

[0035] [Figure 3] FIG. 3 is a top view of the liquid heater of FIG. 2, showing a portion of the interior.

[0036] [Figure 4] FIG. 4 is a cross-sectional view of the liquid heater of FIG.

[0037] [Figure 5] 5 is another cross-sectional view of the liquid heater of FIG. 1, corresponding to a portion rotated 90° compared to FIG. 4.

[0038] [Figure 6] 6(a) to 6(d) are views of the rotor of the liquid heater of FIG. 1 viewed from various directions.

[0039] [Figure 7] FIG. 7 is a graph of rotor power versus time.

[0040] [Figure 8] FIG. 8 is a plot of Newton number against time. DETAILED DESCRIPTION OF THE INVENTION

[0041] FIG. 1 shows a liquid heater 1 according to the present invention, comprising a container 2 (not shown in FIG. 1 ) for receiving a liquid to be heated (not shown), a base 3 on which the container 2 is placed or provided depending on the position of use, a lid 4 that can be otherwise removed or opened to cover or close the container 2, and a handle 5 (not shown) for facilitating a user's grip of the liquid heater 1. Also shown is an operating element 6 in the form of a power button 6a. The base 3 comprises a bottom surface 7 and a side surface 8 that protrudes upward therefrom toward the lid 4, the side surface 8 surrounding most of the container 2. The bottom surface 7 of the base 3 may include a cavity for housing components of the liquid heater 1 housed therein, as shown, for example, in FIG. 4 . In the example shown in FIG. 1 , the container 2 is completely surrounded by the base 3 and the lid 4. In another embodiment (not shown), the container 2 may be only partially surrounded or covered by the base 3 and the lid 4.

[0042] Figure 2 shows the liquid heater 1 of Figure 1 without the lid 4, thereby revealing the container 2, and in particular the side 9 of the container 2. In the example shown, the container 2 also includes a handle 5 and a lip 10, and is at least partially cylindrical. Preferably, the side 9 of the container 2 is at least partially cylindrical.

[0043] Figure 3 shows the liquid heater 1 of Figure 2 as seen from above, housed within a container 2. Clearly recognizable is the container 2 resting on or inserted into a base 3, and a rotor 11 of a stirring device 12 housed within the container 2 for stirring the liquid within the container 2. The rotor 11 can be made, for example, from plastic, in particular polypropylene.

[0044] FIG. 4 shows a vertical cross-sectional view of the liquid heater of FIG. 1. Clearly visible are the vessel 2, base 3, heating device 13 for heating the liquid in vessel 2, and stirring device 12. Vessel 2 has a bottom 14 and a side 9 extending from bottom 14. Side 9 is part of heating device 13 up to a predetermined heating level H of side 9. Heating level H extending from vessel bottom 14 and side 9 includes a heating temperature TH up to heating level H for heating the liquid. Stirring device 12 includes a rotor 11 housed within vessel 2 and a drive mechanism 15 for rotor 11 housed within base 3. Rotor 11 includes a first member 16 that generates a magnetic field, i.e., is magnetic, and drive mechanism 15 includes a second member 17 that generates a magnetic field, i.e., is magnetic. The drive mechanism 15 is designed to rotate the rotor 11 at at least one rotational speed. To this end, the first member 16 is magnetically coupled to the second member 17. The drive mechanism 15 includes a drive device 18, in particular a motor 18a, particularly preferably an electric motor 18b, that can be operated at a predetermined rotational speed. The rotational speed of the rotor 11 is determined within a range of rotational speeds that allows the rotor 11 to raise a predetermined minimum volume M of liquid in the container 2 at least to the heating level H during its rotation, and the heated liquid does not form a continuous foam surface on its surface O after rotation of the rotor 11. In FIG. 4, the minimum volume M of liquid in the container 2 is symbolically represented by the liquid surface O. In the illustrated embodiment, the heating device 13 is an induction heating device 13a. Also in FIG. 4, it can be seen that the side surface 8 of the base 3, rising from the bottom 7 of the base 3, is arranged next to the side surface 9 of the container 2 positioned on the base 3, preferably to the heating level H, and is equipped with a magnetic field generating mechanism 13b of the induction heating device 13a. The side surface 8 of the base 3 can be understood as a side wall having a significantly varied wall thickness to accommodate the magnetic field generating mechanism 13b of the induction heating device 13a. The magnetic field generating mechanism 13b of the induction heating device 13a can be, for example, at least one coil 13c connected to an alternating current source (not shown) that generates an alternating magnetic field during operation of the liquid heater 1. This alternating magnetic field heats the side surface 9 of the container 2, and thus the liquid therein. For this purpose, the side surface 9 of the container 2, at least up to the heating height H, is preferably made of metal, in particular stainless steel.Additionally, the bottom 7 of the base 3 may be provided with a magnetic field generating mechanism 13b of the induction heating device 13a to generate a further magnetic field. This is symbolically shown in Figure 4 by the extension of the magnetic field generating mechanism 13b below the rotor 11. Of course, the magnetic field generating mechanism 13b, which generates the further magnetic field, may also extend below the vessel bottom 14.

[0045] 4 also shows that the vessel 2 is electrically insulated from the base 3, i.e., there is no electrical connection between the vessel 2 and the base 3. In particular, the vessel 2 does not have any components that conduct electricity during operation of the liquid heater 1.

[0046] 4, it can be seen that at least one bottom surface 19 of the vessel bottom 14 is flat. Similarly, the upper surface 20 of the vessel bottom 14 may be flat. A flat bottom side 19 and / or upper surface 20 may allow for slight waviness, particularly due to the manufacturing process, but does not have a height or depression whose dimension in the axial direction A of the liquid heater 1 is greater than the thickness of the vessel bottom 14.

[0047] In the example shown in Fig. 4, the second member 17 of the drive mechanism 15 is disposed below the bottom 14 of the container 2, which is positioned on the base 3. Therefore, the container bottom 14 does not need any recess or depression to receive the second member 17. The rotor 11 is disposed within the container 2 and is magnetically centered by the first member 16 of the rotor 11 and the second member 17 of the drive mechanism 15 while being magnetically coupled to the drive mechanism 15. In particular, according to the example shown in Fig. 4, the rotor 11 can be removed from the container 2 without tools and is freely movable in the radial direction R.

[0048] Figure 5 shows another cross-sectional view of the liquid heater from Figure 1, produced by a cross-sectional plane rotated by 90° compared to Figure 4. Figure 5 also shows the outer diameter KB of the vessel 2, which is measured on the inside of the side surface 9.

[0049] Figures 6a to 6d show an exemplary rotor 11, which in the illustrated example includes at least two arms 21 extending in the radial direction R of the rotor 11 and on which the first member 16 is disposed. Figure 6(a) shows the bottom surface of the rotor 11, which faces the vessel bottom surface 14 when the liquid heater 1 is in an operating state. Figure 6(b) shows a side view of the rotor 11, Figure 6(c) shows a top view of the rotor 11 facing away from the vessel bottom surface 14 when the liquid heater 1 is in an operating state, and Figure 6(d) shows a cross-sectional view of the rotor 11 taken along line CC. The rotor 11 has a height HR and a diameter (envelope circle diameter KR).

[0050] In the example shown in the figures, it can also be seen in Figures 6a to 6c that the rotor 11 does not have a circular or ring-shaped receptacle or any other recess for the rotating shaft. Furthermore, it can be seen that the rotor 11 consists of three arms 21 curved in the rotor plane E and, in the example shown in the direction of rotation DR, a protrusion 22 protruding in the axial direction A as a bearing surface on the side facing the container bottom 14, in particular at the center of the rotor 11.

[0051] FIG. 7 shows a plot of rotor power P (Watts) as a function of time t (seconds) for three different rotor-rotational speed combinations. Combination 1: Rotor height HR = 16.5 mm, rotor diameter KR = 70 mm, rotation speed = 380 rpm Combination 2: Rotor height HR = 16.5 mm, rotor diameter KR = 65 mm, rotation speed = 390 rpm Combination 3: Rotor height HR = 10.73 mm, rotor diameter KR = 70 mm, rotation speed = 420 rpm

[0052] FIG. 8 shows a diagram of Newton number Ne as a function of time t (seconds) for the three rotor-rotational speed combinations from FIG.

[0053] Tests were carried out with the aforementioned liquid heater 1 to determine the range of rotor dimensions and associated rotational speeds at which, during rotation, the rotor 11 raises a specified minimum amount of liquid in the container 2 to at least the heating height H, such that after rotation of the rotor 11, the heated liquid does not develop a continuous surface of bubbles on its surface.

[0054] The test results are shown in Tables 1 and 2 below. [Table 1]

[0055] [Table 2]

[0056] The test results show that rotors 11 with numbers 1, 2, and 7 are particularly suitable for achieving the set objectives. Rotors 11 with numbers 8 to 11 are also at least conditionally suitable. In particular, with these rotors 11, at the specified minimum rotation speed, if 60 ml or 100 ml is taken up as the defined minimum amount of liquid in container 2, side 9 can wet the liquid up to the heating height H. In addition, up to the specified maximum rotation speed, the heated liquid does not develop a continuous foam surface on its surface at the end of the stirring process. Milk at 7°C was used as the heated liquid.

[0057] The liquid heater 1 can be designed and operated with the following characteristics, for example:

[0058] Container inner diameter: 84.7 mm Heating height: approx. 50mm Rotor height: 10.725 mm Heating height to rotor height ratio: 4.662 Rotor diameter: 65mm Ratio of vessel inner diameter to rotor diameter: 1.303 Maximum rotation speed without foaming (60ml milk): Approx. 450 rpm (depending on rotor shape) Minimum rotor power: P = 0.05 W Newton number: Ne = 0.1

[0059] If the height HR or diameter KR of the rotor 11 is small, a higher rotation speed will be required to allow the rotation of the rotor 11 to raise the liquid to the heating height H on the side 9, which may, however, generate bubbles on the surface of the liquid.

Claims

1. A liquid heater (1) comprising a container (2) for containing a liquid to be heated, a base (3) on which the container (2) is positioned, a heating device (13) for heating the liquid in the container (2), and a stirring device (12) for stirring the liquid in the container (2), The container (2) includes a bottom (14) and a side (9) extending from the bottom (14); The side (9) constitutes a part of the heating device (13) from the bottom (14) to a predetermined heating level (H) of the side (9), and indicates a heating temperature (TH) for heating the liquid to the heating level (H); The stirring device (12) includes a rotor (11) accommodated in the container (2) and including a first member (16) capable of generating a magnetic field or being magnetized, and a drive mechanism (15) for the rotor (11); the drive mechanism (15) is housed within the base (3) and includes a magnetic field generating or magnetizable second member (17), the drive mechanism (15) is designed to rotate the rotor (11) at at least one speed at which the first member (16) is magnetically coupled to the second member (17); The rotor (11) is configured such that, in an operating state, the liquid contained in the container (2) rotates and rises along the side surface (9); The rotation speed of the rotor (11) is within a range of rotation speeds that allows the defined minimum amount of liquid in the container (2) to rise to a height at least equal to the heating height (H) and within which the surface of the heated liquid does not have a continuous foam surface. The liquid heater (1) according to the present invention is characterized in that

2. 1.018~1.048g / cm ３ for a liquid density in the range of 0.1 to 0.3, the Newton number corresponding to the stirring device (12) is 0.1 to 0.2, preferably 0.1 to 0.2, A liquid heater (1) according to claim 1.

3. The output of the rotor (11) is set in a range of 0.05 to 0.1 W, the ratio of the heating height (H) to the height of the rotor (H) is set in a range of 3 to 5, the ratio of the envelope circle diameter (KB) of the container (2) to the envelope circle diameter (KB) provided at the heating height (H) is set in a range of 1.20 to 1.4, and the rotation speed of the rotor (11) is set in a range of 370 to 450 rpm. A liquid heater (1) according to claim 1 or claim 2.

4. The heating device (13) is an induction heating device (13a), A liquid heater (1) according to any one of claims 1 to 3.

5. the base (3) has a bottom (7) and a side surface (8) protruding therefrom, and is disposed adjacent to a side surface (9) of the container (2), and a magnetic field generating mechanism of the induction heating device (13a) is provided on the base (3), preferably up to a heating height (H), and preferably the bottom of the base (7) also includes the magnetic field generating mechanism of the induction heating device (13a). A liquid heater (1) according to claim 4.

6. The container (2) is electrically insulated from the base (3). The liquid heater according to any one of claims 1 to 5.

7. the side (9) of the container (2) is made of metal, in particular stainless steel, at least up to the heating height (H), and is preferably cylindrical; A liquid heater (1) according to any one of claims 1 to 6.

8. At least the bottom side (19) of the bottom (14) is flat, A liquid heater (1) according to any one of claims 1 to 7.

9. the upper surface (20) of the vessel bottom (14) is flat, and the rotor (11) is preferably characterized by the absence of a circular or ring-shaped socket for the rotating shaft; A liquid heater (1) according to any one of claims 1 to 8.

10. the second member (17) of the drive mechanism (15) is arranged below the bottom (14) of the container (2) located on the base, A liquid heater (1) according to any one of claims 1 to 9.

11. the rotor (11) is magnetically centered while being coupled to the drive mechanism (15) by a second member (17), A liquid heater (1) according to any one of claims 1 to 10.

12. the rotor (11) can be removed from the container (2) without tools and is freely movable, in particular in the radial direction (R), A liquid heater (1) according to any one of claims 1 to 11.

13. The rotor (11) comprises at least two, preferably three, arms (21) extending in a radial direction (R) of the rotor (11), and the first member (16) is arranged on the arms (21). A liquid heater (1) according to any one of claims 1 to 12.

14. The rotor (11) has three arms (21) curved in the rotor plane (E), preferably in the direction of rotation (DR), and has a protrusion (22) as a bearing surface protruding in the axial direction (A) on the side of the container bottom (14). A liquid heater (1) according to any one of claims 1 to 13.

15. A method for heating a foamable liquid in a liquid heater (1), comprising: a container (2) containing a liquid to be heated without a continuous foam surface; the container (2) being positioned on a base (3); the liquid in the container (2) being heated by a heating device (13); and the liquid in the container (2) being stirred by a stirring device (12); The container (2) includes a bottom (14) and a side (9) extending from the bottom (14); The side (9) forms part of the heating device (13) from the bottom (14) to a predetermined heating height (H) of the side (9), and indicates a heating temperature (TH) for heating the liquid to the heating height (H); The stirring device (12) includes a rotor (11) housed in the container (2), the rotor (11) having a first member (16) capable of generating a magnetic field or being magnetized; The drive mechanism (15) comprises a magnetic field generating or magnetizable second member (17) housed within the base (3); The drive mechanism (15) rotates the rotor (11) at at least one rotational speed, and in the rotation, the first member (16) is magnetically coupled to the second member (17); The rotor (11) rotates the liquid contained in the container (2) in an operating state, causing it to rise along the side (9), and during rotation, raises a defined minimum amount of liquid in the container (2) to a height at least equal to the heating height (H), and in this range of rotation speeds, the heated liquid obtained in the container (2) after rotation of the rotor (11) still does not have a continuous foam surface on its surface. A method for heating a liquid, comprising:

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