Liquid heater

Abstract

The invention relates to 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), which is part of the heating device (13) up to a predetermined heating height (H) and has a heating temperature (TH) up to said heating height (H), comprising a rotor (11) and a drive mechanism (15), the first body (16) is magnetically coupled to the second body (17), in which the rotor (11) is designed such that the liquid in the container (2) rotates and such that said fluid rises along the lateral surface (9), the rotational speed of the rotor (11) being within a rotational speed range in which a minimum defined amount of liquid in the container (2) exposed to the rotating rotor (11) is at a height at least equal to the heating height (H), and within the rotational speed range, the heated liquid comprises a surface without continuous foam formation. The invention also relates to a method of heating a foamable liquid in a liquid heater (1).

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 Art

[0002] Liquid heaters are known in the prior art that also stir the liquid to be heated (such as milk) during heating.

[0003] US9,107,533B2 discloses an automatic milk frother having: a container for holding milk; a base for heating and frothing the milk, the container being inserted into the base; a rotor of a stirring device for frothing the milk held in the container, the rotor being received in the container; and a heating device for heating the milk held in the container. The rotor is driven by magnetic coupling via a motor provided in the base. The container has no electrical components and no continuous drive shaft for the stirring device.

[0004] One disadvantage of the milk frother according to US9,107,533B2 is that the milk held in the container can only be heated while the milk is being frothed.

[0005] However, when heating a liquid that will subsequently be consumed by an infant, the formation of foam and bubbles in the liquid should be avoided. Avoiding air entrapment helps to alleviate common feeding problems such as colic and flatulence. In addition, the liquid (especially milk) should be gently heated and so-called hotspots, i.e., areas where the temperature can damage the nutrients, enzymes, and antibodies in the liquid to be heated (especially breast milk), should be avoided. According to scientific studies, the maximum temperature during the heating of breast milk should not exceed 40 °C. See, for example, Bransburg-Zabary S, Virozub A, and 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. Summary of the Invention

[0006] The object of the present invention is to design a liquid heater and a method for heating a foamable liquid, as described at the beginning of this text, in order to avoid or at least reduce the disadvantages of the prior art. The liquid heater and its method are intended to heat the liquid contained therein as evenly as possible, without forming overheated regions in the liquid volume and without causing any foaming of the liquid. In addition, the liquid should be heated as efficiently as possible. The liquid heater should also be manufactured at low cost and be easy to clean.

[0007] This object is achieved by the liquid heater according to claim 1 and the method according to claim 15. Preferred embodiments and further embodiments are given in the dependent claims.

[0008] The liquid heater according to the invention is characterized in that, in the operating state, the rotor is designed to rotate the liquid contained in the container and cause it to rise along the lateral surface, and the rotational speed of the rotor is within a rotational speed range in which the minimum limited quantity of the liquid in the container exposed to the rotating rotor has a height of at least equal to the heating height, and in this rotational speed range, the heated liquid has a surface without a continuous foam surface.

[0009] The method according to the invention is characterized in that, in the operating state, the rotor rotates the liquid contained in the container and causes it to rise along the lateral surface, the rotational speed of the rotor being in a rotational speed range in which the rotor causes the minimum limited quantity of the liquid in the container to rise to a height of at least equal to the heating height during rotation, and in this rotational speed range, after the rotor rotates, heated liquid is obtained in the container, and the heated liquid still has no continuous foam surface on its surface.

[0010] The liquid heater is used for heating liquids, especially milk, such as expressed breast milk, milk made from milk powder or animal milk. The liquid heater comprises: a container for containing the liquid to be heated; a base on which the container can be placed and removed therefrom; 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 comprises a bottom and a lateral surface extending from the bottom, and can, for example, be designed as a tank that can be filled and emptied, for which purpose the tank can comprise an openable and re-closable lid and a handle for the user to hold. For example, the lateral surface can be cylindrical. Preferably, the container is designed to accommodate a maximum expected filling quantity of 300 ml of the liquid to be heated, preferably 200 ml, and particularly preferably 120 ml, although the actual quantity of liquid that can be accommodated may be higher. In the operating state, especially when heating the liquid, the container is placed on the base, which contains the electrical components required to operate the liquid heater. For this purpose, the base can contain a power cord for connecting to a socket or a battery. In order to remove the heated liquid and clean the container, the user of the liquid heater can remove it from the base.

[0011] The heating device is used to heat the liquid in the container and may include a control device for the user to set the desired target temperature of the liquid to be heated. The lateral surface of the container is part of the heating device, starting from the bottom up to a predetermined heating height, and includes a heating temperature up to the heating height for heating the liquid, i.e., in the operating state of the liquid heater. Thus, the liquid in the container is gently heated through the lateral surface. Since the surface area of the lateral surface is generally larger than that of the bottom of the container, the liquid can be heated particularly efficiently. In addition, due to the relatively large surface area of the lateral surface, particularly high heating temperatures can be avoided. For example, the heating temperature is at most 30 degrees higher than the target temperature of the liquid to be heated, preferably at most 20 degrees.

[0012] The stirring device includes: a rotor that is accommodated in the container and includes a first body that generates a magnetic field or is magnetizable; and a drive mechanism for the rotor that is accommodated in the base and includes a second body that generates a magnetic field or is magnetizable. A permanent magnet or a coil to which an electric current can be applied can be provided as the first and second bodies that generate a magnetic field, and the first and second magnetizable bodies can be metallic, particularly ferromagnetic. The rotor is accommodated in the container and rotates during the operation of the liquid heater (i.e., while heating the liquid in the container) by the drive mechanism provided in the base. For this purpose, the first body is magnetically coupled to the second body. Thus, the rotor is also magnetically coupled to the drive mechanism through the first and second bodies, and the drive mechanism is designed to rotate the rotor at at least one speed. For this purpose, the drive mechanism includes an electric motor, particularly an electric motor. When heating the liquid in the container, the rotation of the rotor causes the heat introduced through the heating device to be distributed as evenly as possible in the liquid without forming overheated regions, i.e., so-called hot spots, in the liquid volume. Avoiding such overheated regions or hot spots has a beneficial effect on the composition of the liquid and can also prevent discomfort or injury caused by insufficient prior stirring when drinking the liquid.

[0013] In order to efficiently heat the liquid in the container and avoid the formation of foam in the container as much as possible, the rotation speed of the rotor should be within a rotation speed range, within which the rotor will cause the minimum defined amount of liquid in the container to rise to at least the heating height during the rotation process, and within this rotation speed range, the heated liquid will not form a continuous foam surface on the surface after the rotor rotates. Therefore, the drive mechanism is designed to rotate the rotor at a certain speed, which makes the liquid rotated by the rotor rise to at least the heating height, but avoids the continuous foam surface of liquid (such as breast milk) on the surface of the liquid itself at the end of the rotation of the rotor or after the rotation of the rotor. In this way, even the minimum defined amount of liquid in the container can be efficiently heated, because the liquid will contact the entire part of the lateral surface, and the entire part is at the heating temperature. For this reason, the rotation speed of the rotor should at least reach the lower limit of the rotation speed range. In addition, since the rotation speed of the rotor does not exceed the upper limit of the rotation speed range, even for easily foaming liquids such as milk, the formation of a continuous foam surface can be avoided, so that the heated liquid can be drunk immediately after being taken out of the container without swallowing the air in the form of foam formed on the surface of the liquid. Avoiding the formation of foam is particularly beneficial for young children to drink heated liquid. However, after the rotor turns, individual bubbles or foam-covered sections may appear on the surface of the heated liquid.

[0014] Any speed within the speed range is suitable for raising the liquid in the container to at least the heating height and avoiding the formation of a continuous foam surface after the rotor rotates. The speed or speed range depends on many design-related parameters of the liquid heater. The drive mechanism can also be designed to adjust the speed and / or speed range so that the speed or speed range is adapted to the characteristics of the liquid contained in the container. For example, a table or setting aid pre-programmed in the liquid heater can be provided to indicate to the user the appropriate speed or speed range suitable for different liquids. Within this speed range, the speed of the rotor can be kept constant.

[0015] If in the description reference is made to a position or direction such as top, above, below or down, this is to be understood as being relative to a use position of the liquid heater, in which liquid in a container is heated.

[0016] According to a preferred embodiment of the present invention, when the liquid density is between 1.018 and 1.048 g / cm 3In the case within the range, the Newton number assigned to the stirring device is between 0.1 and 0.3, preferably between 0.1 and 0.2. The liquid density within the specified range is substantially equivalent to the density of milk. Preferably, if the surface tension and / or viscosity of the liquid are substantially equivalent to the surface tension and / or viscosity of milk, the Newton number assigned to the stirring device should also be between 0.1 and 0.3, preferably between 0.1 and 0.2. In this case, the surface tension can be within the range of 30 to 43.5 mN / m, and the viscosity can be within the range of 1.06386 to 3.27726 mm 2 / s. The given values of density, surface tension, and viscosity depend on the temperature and type of the liquid, especially milk. Obviously, rotors with different designs may require different rotational speeds to raise at least a minimum quantity of liquid in the container to the heating height. However, different rotors may also have different Newton numbers because the Newton number characterizes the power introduced into the liquid through the rotor. Therefore, the design of the rotor is fully defined by the Newton number. Accordingly, the rotor accommodated in the container can have one of various shapes. Specifically, the Newton number indicates what proportion of the rotor power P is actually available as hydraulic power. The applicable formula is as follows:

[0017] Ne = P / (ρ * n 3 * d 5 )

[0018] Where:

[0019] Ne... Newton number

[0020] P... Rotor power, W

[0021] ρ... Liquid density, kg / m 3

[0022] n... Rotational speed, s -1

[0023] d... Rotor diameter, m

[0024] The rotor power P is calculated based on the rotor section modulus:

[0025] P = M * 2 * π * n

[0026] Where:

[0027] P... Rotor power, W

[0028] M... Rotor torque, Nm

[0029] n... Rotational speed, s -1

[0030] Particularly advantageously, the rotor power is in the range of 0.05 to 0.1 watt, the ratio of the heating height to the rotor height is in the range of 3 to 5, the ratio of the envelope circle diameter of the container provided at the heating height to the envelope circle diameter of the rotor is in the range of 1.20 to 1.4, and the rotor speed is in the range of 370 to 450 rpm. The rotor height is defined in the axial direction of the rotor, and the envelope circle diameter of the container or the rotor is defined as the minimum circle diameter that completely encloses the inside of the lateral surface of the container or the rotor when viewed in the axial direction of the working liquid heater.

[0031] In order to be able to form a container without electrical components of the heating device, the heating device can be set as an induction heating device. Thus, the container, especially the lateral surface (which forms part of the heating device up to the heating height), can be heated by induction from an energy source provided outside the lateral surface. For this purpose, the lateral surface is made of a material that can be heated by induction, at least in the area up to the heating height.

[0032] In order to heat the liquid in the container, it is particularly advantageous if the base includes a bottom and a lateral surface protruding from the bottom, the lateral surface being arranged beside the lateral surface of the container located on the base and preferably including a magnetic field generating mechanism of the induction heating device up to the heating height. Particularly advantageously, the lateral surface of the base is curved at least in the section surrounding the lateral surface of the container. Specifically, the lateral surface can completely surround the lateral surface, for example, in a circular or cylindrical shape. Thus, the container can be inserted into the base to heat the liquid. If the magnetic field generating mechanism of the induction heating device is arranged as large as possible on the lateral surface of the base, the lateral surface of the container and the liquid in the container can be heated particularly effectively. For example, the magnetic field generating mechanism can cover more than half of the surface area, especially more than three-quarters of the surface area of the lateral surface. Specifically, the magnetic field generating mechanism can be at least one coil that generates an alternating magnetic field when an alternating current passes through it.

[0033] If the bottom of the base also includes the magnetic field generating mechanism of the induction heating device, the bottom of the container can be heated, and the liquid in the container can be heated more effectively. In this case, the bottom of the container is also made of a conductive material that can be heated by induction.

[0034] The container is preferably electrically insulated from the base so that the container can be cleaned as easily as possible and electrical contacts that may damage its appearance can be avoided. Thus, the container does not need to be electrically connected to the base and can be immersed in water for cleaning without worrying about damage to the contacts. In addition, since there are no electrical components on the bottom and lateral surface of the container, a thin-walled design can be adopted.

[0035] In order to make the container structure durable, heat the liquid efficiently and prevent foaming of the liquid in the container as effectively as possible, it can be arranged such that the lateral surface of the container, at least up to the heating height, is made of metal, in particular stainless steel, and is preferably cylindrical. However, the lateral surface can include metal-free sections, such as transparent viewing windows, preferably provided at least in the heating height region, so as to be able to observe the stirring process or the height of the introduced liquid. Stainless steel also has the advantage of being corrosion-resistant.

[0036] If at least the bottom side of the container is flat, the design of the container is simpler, the manufacturing cost is lower, and it can be reliably placed on a support surface. The bottom side of the container bottom should be understood as the side of the container bottom facing away from the interior of the container.

[0037] If the top side of the container bottom is flat and the rotor preferably has no circular or annular receptacle for the rotation axis, the top side of the container bottom facing the interior of the container can be cleaned particularly easily and reliably. For this purpose, the top side of the container bottom does not include any cylindrical or pin-shaped protrusions as the rotation axis of the rotor. In addition, the rotor can be easily inserted into the container before the liquid heater is put into operation, without the need for precise positioning above or on the rotation axis. This is particularly advantageous when the diameter of the container is small compared to its height, because when the diameter of the container is small, it is difficult for the user to reach deep enough into the container with their hand to precisely position the rotor on the rotation axis. Advantageously, the rotor has no circular or annular receptacle or groove for the rotation axis, in particular no cylindrical receptacle or groove. This means that the rotor can also be easily and carefully cleaned, because it has no receptacle or groove for the rotation axis, as residues of the heated liquid may deposit therein.

[0038] In order to be able to design the container independently of the drive mechanism, it is advantageous to arrange the second body of the drive mechanism below the container bottom located on the base. In contrast, the rotor is arranged above the bottom or on the container bottom located on the base. Since the magnetic coupling between the second body of the drive mechanism and the first body of the rotor, and thus the power transmission from the drive mechanism to the rotor, is carried out through the container bottom, the container bottom is preferably made of a thin wall to achieve efficient power transmission. For example, the thickness of the container bottom is at most 3 mm, preferably at most 2 mm.

[0039] It is particularly advantageous if the rotor is magnetically centered by the second body of the drive mechanism in a state coupled to the drive mechanism. In this way, the mechanical rotating shaft of the rotor can be omitted. The centering of the rotor, that is, the position of the rotor that is advantageous or necessary for the liquid in the stirring vessel, is achieved by the magnetic attraction between the first body and the second body. The distance between the second body of the drive mechanism and the first body of the rotor is particularly preferably as large as possible, for example at least half of the envelope circle diameter of the rotor, preferably at least two-thirds of the envelope circle diameter, so that as large a torque as possible from the drive mechanism can be transmitted to the rotor through magnetic coupling. In addition, due to the large distance, even if the user inserts the rotor into the container from outside the center of the container bottom (for example, by touching the lateral surface), the rotor can be reliably centered.

[0040] To achieve reliable magnetic coupling between the rotor and the drive mechanism, the extension of at least one of the first body and the second body in a plane parallel to the bottom of the container located on the base is preferably greater than the extension of the at least one of the first body and the second body in a plane perpendicular to the bottom of the container located on the base. Preferably, the extension of at least one of the first body and the second body in a plane parallel to the bottom of the container located on the base is at least 10% of the envelope circle diameter of the rotor, more preferably at least 20%, and particularly preferably at least 30%.

[0041] To facilitate the operation of the liquid heater, the rotor can be removed from the container without tools and is freely movable, especially in the radial direction. This means that by removing the container from the base and turning it to a position with the container bottom facing up, the rotor can fall out of the container, for example, for cleaning the rotor and the container. According to this embodiment, the rotor of the container removed from the base can move freely in the radial direction, that is, without mechanical guidance, which further facilitates the removal of the rotor.

[0042] According to a further embodiment, it can be provided that the rotor includes at least two (preferably three) arms extending in the radial direction of the rotor, and the first body is arranged on the arms. The arms protruding from the center or the center of gravity of the rotor are used for stirring the liquid. In addition, the first body is arranged on the arms, especially at the outer half or one-third of the radial direction of the arms, which can efficiently transmit the torque from the drive mechanism to the rotor. For example, the arms of the rotor inserted into the container extend at least partially in a plane parallel to the container bottom. It is also advantageous if the longitudinal extension of the arms in the radial direction of the rotor is greater than the vertical extension of the arms in the axial direction of the rotor.

[0043] In order to efficiently stir a liquid and minimize the loss of torque transmitted from a drive mechanism to a rotor, it is advantageous for the rotor to include three arms that are bent in the rotor plane, preferably bent in the direction of rotation, and preferably include protrusions projecting in the axial direction on the side facing the bottom of the container as bearing surfaces. The rotor plane is perpendicular to the virtual rotation axis of the rotor, i.e., perpendicular to the axial direction of the rotor. The bending of the arms in the direction of rotation is advantageous for stirring the liquid. The protrusions that serve as bearing surfaces and project in the axial direction of the rotor advantageously reduce the frictional resistance of the rotor held in the container on the bottom of the container. For example, the protrusions of the rotor projecting in the axial direction can be curvatures or pins pointing in the direction of the bottom of the container. Description of the Drawings

[0044] The present invention will be described in more detail below in conjunction with preferred embodiments, but the present invention is not limited to these embodiments. As shown in the drawings:

[0045] Figure 1 is a perspective view of the liquid heater of the present invention with a lid;

[0046] Figure 2 is Figure 1 the liquid heater without a lid in;

[0047] Figure 3 is Figure 2 a top view and partial internal view of the liquid heater in;

[0048] Figure 4 is Figure 1 a cross-sectional view of the liquid heater in;

[0049] Figure 5 is Figure 1 another cross-sectional view of the liquid heater in, corresponding to a cross-section rotated 90° compared to Figure 4 ;

[0050] Figures 6a to 6d is Figure 1 a view of the rotor of the liquid heater in;

[0051] Figure 7 is a schematic diagram of the rotor power as a function of time; and

[0052] Figure 8 is a schematic diagram of the Newton number as a function of time. Detailed Description of the Embodiments

[0053] Figure 1 There is shown a liquid heater 1 according to the present invention, which includes a container 2 for containing a liquid to be heated (not shown in the figure) ( Figure 1(not shown in the figure), a base 3 for placing the container 2 thereon or therein according to the usage location, a lid 4 for covering or closing the container 2 (the lid 4 can be removed or opened in other ways), and a handle 5 for facilitating the user (not shown in the figure) to hold the liquid heater 1. In addition, an operating element 6 in the form of a power button 6a is also shown in the figure. The base 3 includes a bottom 7 and a side surface 8 protruding upward from the bottom 7 in the direction of the lid 4, and the side surface 8 surrounds most of the container 2. The bottom 7 of the base 3 may also contain a cavity in which components of the liquid heater 1 are accommodated, for example, see Figure 4 . In Figure 1 the example shown, the container 2 is completely covered 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.

[0054] Figure 2 shows Figure 1 the liquid heater 1 in which the lid 4 is not included, so the container 2 can be seen, especially the lateral surface 9 of the container 2. In the example shown, the container 2 also includes a handle 5 and a lip 10, and at least a section is cylindrical. Preferably, at least a section of the lateral surface 9 of the container 2 is cylindrical.

[0055] Figure 3 shows a view of Figure 2 the liquid heater 1 in the container 2 as seen from the top. It can be clearly recognized that the container 2 is placed on or inserted into the base 3, and the rotor 11 of the stirring device 12 is accommodated in the container 2 for stirring the liquid in the container 2. The rotor 11 can be made of plastic, especially polypropylene, for example.

[0056] Figure 4 shows Figure 1Vertical cross-sectional view of the liquid heater. The container 2, the base 3, the heating device 13 for heating the liquid in the container 2, and the stirring device 12 can be clearly identified. The container 2 includes a bottom 14 and a lateral surface 9 extending from the bottom 14. The lateral surface 9 is part of the heating device 13 up to a predetermined heating level H of the lateral surface 9, the heating height H extending from the bottom 14 of the container, and the lateral surface 9 includes a heating temperature TH up to the heating height H for heating the liquid. The stirring device 12 includes a rotor 11 accommodated in the container 2 and a drive mechanism 15 for the rotor 11 accommodated in the base 3, wherein the rotor 11 includes a first body 16 that generates a magnetic field or is magnetizable, and the drive mechanism 15 includes a second body 17 that generates a magnetic field or is magnetizable. The drive mechanism 15 is designed to rotate the rotor 11 at at least one rotational speed. For this purpose, the first body 16 is magnetically coupled to the second body 17. The drive mechanism 15 includes a driver 18, in particular a motor 18a, and particularly preferably an electric motor 18b, which operates at a definable rotational speed. The rotational speed of the rotor 11 is within a certain rotational speed range, within which the rotor 11 raises at least a minimum defined quantity M of the liquid in the container 2 to at least the heating height H during rotation, and within which, after the rotor 11 rotates, a continuous foam surface does not form on the surface O of the heated liquid. In Figure 4 the minimum quantity M of the 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. In Figure 4 it can also be seen that the lateral surface 8 of the base 3 protruding upward from the bottom 7 of the base 3 is arranged in the vicinity of the lateral surface 9 of the container 2 located on the base 3, and preferably up to the heating height H, and includes a magnetic field generating mechanism 13b of the induction heating device 13a. The lateral surface 8 of the base 3 can also be understood as a side wall with a relatively large wall thickness variation in order 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, which is connected to an alternating current power supply (not shown) and generates an alternating magnetic field during operation of the liquid heater 1. This alternating magnetic field heats the lateral surface 9 of the container 2, thereby heating the liquid in the container 2. For this purpose, the lateral surface 9 of the container 2 (at least up to the heating height H) is preferably made of metal, in particular stainless steel. In addition, the bottom 7 of the base 3 can include a mechanism 13b of the induction heating device 13a for generating an additional magnetic field. Figure 4 In, it is symbolically shown that the magnetic field generating mechanism 13b extends below the rotor 11. Of course, the mechanism 13b for generating the additional magnetic field can also extend below the bottom 14 of the container.

[0057] Figure 4It is also shown that the container 2 is electrically insulated from the base 3, i.e., there is no electrical connection between the container 2 and the base 3. Specifically, the container 2 does not contain components that conduct electricity during the operation of the liquid heater 1.

[0058] Furthermore, from Figure 4 the example shown, at least one bottom side 19 of the container bottom 14 is flat. Similarly, the top side 20 of the container bottom 14 can also be flat. The flat bottom side 19 and / or top side 20 allow for slight corrugations, especially due to the manufacturing process, but there are no protrusions or depressions whose dimensions in the axial direction A of the liquid heater 1 are greater than the thickness of the container bottom 14.

[0059] In Figure 4 the example shown, the second body 17 of the drive mechanism 15 is arranged below the bottom 14 of the container 2 located on the base 3. Therefore, the container bottom 14 does not require any recesses or grooves for accommodating the second body 17. The rotor 11 is placed in the container 2 and is in a magnetically coupled state with the drive mechanism 15, and is magnetically centered by the first body 16 of the rotor 11 and the second body 17 of the drive mechanism 15. Specifically, according to Figure 4 the example shown, the rotor 11 can be removed from the container 2 without tools and is freely movable in the radial direction R.

[0060] Figure 5 Shows Figure 1 another cross-sectional view of the liquid heater in Figure 4 compared to Figure 5 and is generated by rotating the section by 90°.

[0061] Figures 6a to 6d Shows an exemplary rotor 11 that includes at least two (three in the example shown) arms 21 extending in the radial direction R of the rotor 11, and the first body 16 is provided on the arms 21. Figure 6a Shows the bottom side of the rotor 11, which faces the container bottom 14 in the operating state of the liquid heater 1. Figure 6b Shows a side view of the rotor 11, Figure 6c shows the top side of the rotor 11, which faces away from the container bottom 14 in the operating state of the liquid heater 1, Figure 6d shows a cross-sectional view of the rotor 11 taken along the line C-C. The rotor 11 has a height HR and a diameter (envelope circle diameter KR).

[0062] In Figures 6a to 6cIn the example shown, it can also be seen that the rotor 11 does not have a circular or annular receiving portion or any other groove for the rotating shaft. Furthermore, it can be seen that the rotor 11 includes three arms 21 that are bent in the rotor plane E (bent in the direction of rotation DR in the example shown), and a projection 22 that projects in the axial direction A, which serves as a bearing surface on the side facing the bottom 14 of the container, specifically located at the center of the rotor 11.

[0063] Figure 7 A graph is shown of the rotor power P (in watts) as a function of time t (in seconds) for three different rotor - speed combinations.

[0064] Combination 1: Rotor height HR = 16.5 mm, rotor diameter KR = 70 mm, rotational speed = 380 rpm

[0065] Combination 2: Rotor height HR = 16.5 mm, rotor diameter KR = 65 mm, rotational speed = 390 rpm

[0066] Combination 3: Rotor height HR = 10.73 mm, rotor diameter KR = 70 mm, rotational speed = 420 rpm

[0067] Figure 8 Shows Figure 7 a graph of the Newton number Ne as a function of time t (in seconds) for three rotor - speed combinations.

[0068] The liquid heater 1 was tested to study the rotor size and the associated rotational speed range, by which the rotor 11, during rotation, raises at least a minimum limited quantity of the liquid in the container 2 to the heating height H, so that after the rotor 11 rotates, the heated liquid does not have a continuous foam surface on its surface.

[0069] The following Tables 1 and 2 contain partial test results.

[0070]

[0071] Table 1

[0072]

[0073]

[0074] Table 2

[0075] Tests have shown that rotors 11 numbered 1, 2, and 7 are particularly suitable for achieving the established goals. Rotors 11 numbered 8 to 11 are also applicable at least under certain conditions. Specifically, when using these rotors 11, at the specified minimum rotational speed, if the container 2 is filled with a minimum specified amount of 60 ml or 100 ml of liquid, the lateral surface 9 can be wetted by the liquid up to the heating height H; in addition, until the specified maximum rotational speed, at the end of the stirring process, no continuous foam surface will appear on the heated liquid surface. The liquid to be heated is milk at 7 °C.

[0076] The liquid heater 1 can be designed and operated, for example, with the following characteristic values:

[0077] Inner diameter of the container: 84.7 mm

[0078] Heating height: approximately 50 mm

[0079] Height of the rotor: 10.725 mm

[0080] Ratio of heating height to rotor height: 4.662

[0081] Diameter of the rotor: 65 mm

[0082] Ratio of inner diameter of the container to rotor diameter: 1.303

[0083] Maximum rotational speed (60 ml of milk) without causing foam in the liquid: approximately 450 rpm (depending on the rotor shape)

[0084] Minimum power of the rotor: P = 0.05 W

[0085] Newton number: Ne = 0.1

[0086] If the height HR of the rotor 11 is lower or the diameter KR is smaller, a higher rotational speed will be required to make the liquid rise to the heating height H on the lateral surface 9 under the action of the rotation of the rotor 11. However, such a rotational speed may cause foam to appear on the liquid surface.

Claims

1. A liquid heater (1) having a container (2) for receiving a liquid to be heated, a base (3) on which the container (2) is placed, 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) including a bottom (14) and a lateral surface (9) extending from the bottom (14), the lateral surface (9) being part of the heating device (13) up to a predetermined heating height (H), the heating height (H) starting from the bottom (14), and the lateral surface (9) including a heating temperature (TH) up to the heating height (H) for heating the liquid, the stirring device (12) including a rotor (11) received in the container (2) and a drive mechanism (15) for the rotor (11), the rotor (11) including a first body (16) that generates a magnetic field or is magnetizable, the drive mechanism (15) being received in the base (3) and including a second body (17) that generates a magnetic field or is magnetizable, the drive mechanism (15) being designed to rotate the rotor (11) at at least one speed, for which purpose the first body (16) is magnetically coupled to the second body (17), characterized in that, The rotor (11) is designed to rotate the liquid contained in the container (2) in the operating state and cause it to rise along the lateral surface (9). The rotational speed of the rotor (11) is within a rotational speed range, within which the minimum limited amount of liquid in the container (2) exposed to the rotating rotor (11) includes a height of at least equal to the heating height (H), and within which the heated liquid includes a surface without a continuous foam surface.

2. The liquid heater (1) according to claim 1, characterized in that, When the density of the liquid is in the range of 1.018 - 1.048 g / cm 3 the Newton number assigned to the stirring device (12) is between 0.1 and 0.3, preferably between 0.1 and 0.

2.

3. The liquid heater (1) according to claim 1 or 2, characterized in that, The power of the rotor (11) is in the range of 0.05 to 0.1 W. The ratio of the heating height (H) to the height (HR) of the rotor is in the range of 3 to 5. The ratio of the envelope circle diameter (KB) of the container (2) to the envelope circle diameter (KR) of the rotor (11) is in the range of 1.20 to 1.

4. The envelope circle diameter (KB) of the container (2) is at the heating height (H). The rotational speed of the rotor (11) is in the range of 370 to 450 rpm.

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

5. The liquid heater (1) according to claim 4, characterized in that, The base (3) includes a bottom (7) and a lateral surface (8) protruding from the bottom. The lateral surface (8) is arranged beside the lateral surface (9) of the container (2) located on the base (3), and preferably up to the heating height (H). It includes the magnetic field generating mechanism of the induction heating device (13a). And preferably, the bottom (7) of the base includes the magnetic field generating mechanism of the induction heating device (13a).

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

7. The liquid heater (1) according to any one of claims 1 to 6, characterized in that, The lateral surface (9) of the container (2) is made of metal, especially stainless steel, at least up to the heating height (H), and the lateral surface (9) of the container (2) is preferably cylindrical.

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

9. The liquid heater (1) according to any one of claims 1 to 8, characterized in that The top side (20) of the container bottom (14) is flat, and preferably, the rotor (11) has no circular or annular receiving portion for the rotating shaft.

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

11. The liquid heater (1) according to any one of claims 1 to 10, characterized in that, In the state coupled to the drive mechanism (15), the rotor (11) is magnetically centered by the second body (17) of the drive mechanism (15).

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

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

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

15. A method for heating a foamable liquid in a liquid heater (1), wherein, The liquid to be heated is contained in a container (2) having no continuous foam surface on its surface. The container (2) is placed on a base (3). The liquid in the container (2) is heated by a heating device (13), and the liquid in the container (2) is stirred by a stirring device (12). The container (2) includes a bottom (14) and a lateral surface (9) extending from the bottom. The lateral surface (9) is part of the heating device (13) up to a predetermined heating height (H) of the lateral surface (9). The heating height (H) starts from the bottom (14), and the lateral surface (9) is heated to a heating temperature (TH) up to the heating height (H) to heat the liquid. The stirring device (12) includes a rotor (11) contained in the container (2) and a drive mechanism (15) for the rotor (11). The rotor includes a first body (16) that generates a magnetic field or is magnetizable. The drive mechanism (15) is contained in the base (3) and includes a second body (17) that generates a magnetic field or is magnetizable. The drive mechanism (15) rotates the rotor (11) at least at one rotational speed. For this purpose, the first body (16) is magnetically coupled to the second body (17). It is characterized in that, in the operating state, the rotor (11) rotates the liquid contained in the container (2) and causes it to rise along the lateral surface (9). The rotational speed of the rotor (11) is within a rotational speed range in which, during rotation, the rotor (11) causes a minimum limited amount of the liquid in the container (2) to rise to a height at least equal to the heating height (H), and within this rotational speed range, after the rotor (11) rotates, heated liquid is obtained in the container (2), and the heated liquid still has no continuous foam surface on its surface.

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