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), the stirring device comprising a rotor (11) and a drive mechanism (15), wherein a first body (16) is magnetically coupled with a second body (17), wherein the rotor (11) is designed such that the liquid in the container (2) is rotated and such that said fluid rises along a lateral surface (9), the rotational speed of the rotor (11) being in 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 which is at least equal to the heating height (H) and in which 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 of heating a foamable liquid in a liquid heater according to claim 15. BACKGROUND

[0002] Liquid heaters are known in the art in which the liquid to be heated (e.g. milk) is also stirred during heating.

[0003] US 9,107,533 B2 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 accommodated in the container, and a heating device for heating the milk held in the container. The rotor is driven via a motor provided in the base by magnetic coupling. The container is free of electrical elements and a continuous drive shaft of the stirring device.

[0004] One disadvantage of the milk frother described in US 9,107,533 B2 is that the milk held in the container can only be heated while the milk is frothed.

[0005] However, when heating a liquid which is subsequently to be drunk by a baby, it should be avoided that foam and air bubbles are formed in the liquid. Avoiding air retention helps to alleviate common feeding problems such as colic and gas. Furthermore, the liquid (especially milk) should be gently heated and so-called hot spots, i.e. regions where the temperature can damage nutrients, enzymes and antibodies in the liquid to be heated (especially breast milk) should be avoided. According to scientific research, the maximum temperature of breast milk during heating 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

[0006] It is an object of the present invention to design a liquid heater and a method for heating a foamable liquid, as mentioned in the opening paragraph, to avoid or at least reduce the drawbacks of the prior art. The liquid heater and the method thereof are intended to heat the liquid contained therein as evenly as possible without forming over-heated areas in the volume of the liquid nor causing any foaming of the liquid. 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 achieved by a liquid heater according to claim 1 and a 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 working condition, the rotor is designed to rotate the liquid contained in the container and to make it rise along the lateral surface, and the rotational speed of the rotor is in a rotational speed range in which a minimum defined amount of the liquid in the container exposed to the rotating rotor has a height at least equal to the heating height, and in which range the heated liquid comprises a surface without a continuous foam surface.

[0009] The method according to the invention is characterized in that, in the working condition, the rotor rotates the liquid contained in the container and makes it rise along the lateral surface, the rotational speed of the rotor being in a rotational speed range in which the rotor, during rotation, makes a minimum defined amount of the liquid in the container rise to a height at least equal to the heating height, and in which range, after rotation of the rotor, a heated liquid is obtained in the container, the heated liquid still having a surface without a continuous foam surface.

[0010] The liquid heater is used for heating a liquid, in particular for heating 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 from which it can be 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 comprises a bottom and a lateral surface extending from the bottom, for example, it can be designed as a tank which can be filled and emptied, for which purpose it can comprise a lid which can be opened and reclosed and a handle for the user to hold. The lateral surface can be cylindrical, for example. Preferably, the container is designed to contain a maximum expected filling of 300 milliliters of the liquid to be heated, preferably 200 milliliters, particularly preferably 120 milliliters, although the actual amount of liquid that can be contained can be higher. In the working condition, in particular when heating the liquid, the container is placed on the base, which contains the electrical components necessary for operating the liquid heater. To this end, the base can contain a power cord for connection to a socket or a battery. In order to remove the heated liquid and to clean the container, the user of the liquid heater can remove it from the base.

[0011] The heating device serves to heat the liquid in the container and can comprise a control device for setting a desired target temperature of the liquid to be heated by a user. The lateral surface of the container is part of the heating device from the bottom up to a predetermined heating height and comprises 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 by the lateral surface. Since the lateral surface usually has a larger surface area than the bottom of the container, the liquid can be heated particularly efficiently. Furthermore, due to the relatively large surface area of the lateral surface, it is possible to avoid particularly high heating temperatures. For example, the heating temperature is at most 30 degrees, preferably at most 20 degrees, higher than the target temperature of the liquid to be heated.

[0012] The stirring device comprises a rotor accommodated in the container and comprising a first body generating a magnetic field or being magnetizable, and a drive mechanism for the rotor accommodated in the base and comprising a second body generating a magnetic field or being magnetizable. Permanent magnets or current-applyable coils can be provided as the first body and the second body generating a magnetic field, while the first body and the second body being magnetizable can be metallic, in particular ferromagnetic. The rotor is accommodated in the container and is rotated by the drive mechanism arranged in the base during operation of the liquid heater, i.e. during heating of the liquid in the container. For this purpose, the first body is magnetically coupled to the second body. Thus, the rotor is also magnetically coupled to the drive mechanism by the first body and the second body, and the drive mechanism is designed to rotate the rotor at least at one speed. For this purpose, the drive mechanism comprises an electric machine, in particular an electric motor. The rotation of the rotor when heating the liquid in the container causes the heat introduced by the heating device to be distributed as evenly as possible in the liquid, without hotspots, i.e. so-called hotspots, being formed in the liquid volume. Avoiding such hotspots or hotspots has a good effect on the composition of the liquid and can also prevent discomfort or injury when drinking the liquid due to insufficient stirring beforehand.

[0013] In order to be able to heat the liquid in the container efficiently, while at the same time avoiding the formation of foam in the container as much as possible, the rotational speed of the rotor should be in a rotational speed range in which the rotor, during rotation, causes the minimum defined amount of liquid in the container to be lifted at least to the heating height, and in which rotational speed range the heated liquid, after rotation of the rotor, does not have a continuous foam surface on the surface. The drive mechanism is therefore designed to rotate the rotor at a rotational speed which causes the liquid, as a result of the rotor, to be lifted at least to the heating height, but which avoids a continuous foam surface of the liquid, for example of mother's 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 heated efficiently, because the liquid comes into contact with the entire portion of the lateral surface, which is at the heating temperature. To this end, the rotational speed of the rotor should at least reach the lower limit of the rotational speed range. Furthermore, because the rotational speed of the rotor does not exceed the upper limit of the rotational speed range, even for a liquid which is prone to foaming, for example milk, the formation of a continuous foam surface is avoided, so that the heated liquid can be drunk immediately after it has been removed from the container, without swallowing air in the form of foam on the surface of the liquid. Avoiding the formation of foam is particularly advantageous for young children who drink the heated liquid. However, after rotation of the rotor, individual air bubbles or foam-covered sections can occur on the surface of the heated liquid.

[0014] Any speed within the rotational speed range is suitable for causing the liquid in the container to be lifted at least to the heating height and for avoiding the formation of a continuous foam surface after rotation of the rotor. The rotational speed or the rotational speed range depends on a number of design-related parameters of the liquid heater. The drive mechanism can also be designed for adjusting the rotational speed and / or the rotational speed range, in order to adapt the rotational speed or the rotational speed range to the properties of the liquid which is received in the container. For example, a table or a setting aid can be provided in the liquid heater, which is pre-programmed for indicating to the user the suitable rotational speed or the suitable rotational speed range for different liquids. Within this rotational speed range, the rotational speed of the rotor can remain constant.

[0015] If in the description reference is made to positions or directions such as top, above, below or downwards, it is to be understood that this is relative to the position of use of the liquid heater, in which position the liquid in the heating container is heated.

[0016] According to a preferred embodiment of the application, the density of the liquid is in the range of 1.018-1.048 g / cm3 3In the case of a liquid within the specified range, the Newton number assigned to the stirring device is between 0.1 and 0.3, preferably between 0.1 and 0.2. The density of the liquid within the specified range is essentially equivalent to the density of milk. Preferably, if the surface tension and / or viscosity of the liquid is essentially 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 for density, surface tension and viscosity depend on the temperature and type of the liquid, in particular milk. It is clear that different rotors of different design can require different rotational speeds in order to lift at least the minimum defined amount of liquid in the container to the heating level. However, different rotors can also have different Newton numbers, since the Newton number characterizes the power introduced into the liquid by the rotor. The design of the rotor is therefore adequately defined by the Newton number. Accordingly, the rotor accommodated in the container can have one of a plurality of shapes. In particular, the Newton number indicates how much of the proportion of the rotor power P is actually available as hydraulic power. The applicable formula is as follows:

[0017] Ne = P / (p * n 3 *d 5 )

[0018] wherein:

[0019] Ne... Newton number

[0020] P... rotor power, W

[0021] p... liquid density, kg / m 3

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

[0023] d... rotor diameter, m

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

[0025] P = M * 2 * pi * n

[0026] wherein:

[0027] P... rotor power, W

[0028] M... rotor torque, Nm

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

[0030] It is particularly advantageous if 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 diameter of the envelope circle of the container provided at the heating height to the diameter of the envelope circle of the rotor is in the range of 1.20 to 1.4, and the rotor rotational speed is in the range of 370 to 450 rpm. The rotor height is defined in the axial direction of the rotor, and the diameter of the envelope circle of the container or rotor is defined as the smallest circle diameter that is completely contained inside the lateral surface of the container or rotor as viewed in the axial direction of the working fluid heater.

[0031] In order to be able to form a container without electrical components of the heating device, the heating device can be provided as an inductive heating device. Thus, the container, in particular the lateral surface which forms part of the heating device up to the heating height, can be heated by induction from an energy source arranged outside the lateral surface. To this end, the lateral surface is made of a material which can be heated by induction, at least in the region up to the heating height.

[0032] In order to heat the liquid in the container, it is particularly advantageous if the base comprises a bottom and a side surface protruding from the bottom, which side surface is arranged next to the lateral surface of the container on the base and preferably contains a magnetic field generating means of an inductive heating device up to the heating height. It is particularly advantageous if the side surface of the base is curved at least in a section around the lateral surface of the container. In particular, the side surface can completely surround the lateral surface, for example in the form of a ring or a cylinder. Thus, the container can be inserted into the base in order to heat the liquid. If the magnetic field generating means of the inductive heating device is arranged as large-area as possible in the side surface of the base, the lateral surface of the container and the liquid inside the container can be heated particularly efficiently. For example, the magnetic field generating means can cover more than half of the surface area, in particular more than three quarters of the surface area of the side surface. In particular, the magnetic field generating means can be at least one coil which generates an alternating magnetic field when an alternating current flows through it.

[0033] If the bottom of the base also contains a magnetic field generating means of an inductive heating device, the bottom of the container can be heated and the liquid inside the container can be heated more efficiently. In this case, the bottom of the container is also made of an electrically conductive material which can be heated by induction.

[0034] The container is preferably electrically insulated from the base in order to make the container as easy to clean as possible and to avoid electrical contact which can damage its appearance. Thus, the container does not need to be electrically connected to the base and can be cleaned by immersion in water without the risk of contact damage. Furthermore, a thin-walled design can be used since there are no electrical components in the bottom and the lateral surface of the container.

[0035] In order to make the container structure robust, to heat the liquid efficiently and to prevent the liquid in the container from foaming as effectively as possible, it can be provided that the lateral surface of the container, at least up to the heating level, is made of metal, in particular stainless steel, and is preferably cylindrical. However, the lateral surface can comprise non-metallic sections, for example a transparent viewing window, which is preferably provided at least in the region of the heating level in order to be able to observe the stirring process or the level of the liquid introduced. Stainless steel also has the advantage of being resistant to corrosion.

[0036] If at least the bottom side of the container is flat, the design of the container is more simple, less expensive to manufacture and can be reliably placed on a support surface. The bottom side of the bottom of the container is understood to mean the side of the bottom of the container which faces away from the interior of the container.

[0037] If the top side of the bottom of the container is flat and the rotor preferably does not have a circular or annular receptacle for the rotational axis, the top side of the bottom of the container, which faces the interior of the container, can be cleaned particularly easily and reliably. For this purpose, the top side of the bottom of the container does not comprise any cylindrical or pin-shaped protrusions as a rotational axis for the rotor. Furthermore, the rotor can be easily inserted into the container before the liquid heater is put into operation without having to be precisely positioned above or on the rotational axis. This is particularly advantageous when the diameter of the container is small compared to its height, since it is difficult for a user to reach deep enough into the container with his hand in order to precisely position the rotor on the rotational axis. It is advantageous if the rotor does not have a circular or annular receptacle or recess, in particular a cylindrical receptacle or recess, for the rotational axis. This means that the rotor can also be easily and carefully cleaned since it does not have a receptacle or recess for the rotational axis in which residues of the heated liquid can deposit.

[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 bottom of the container on the base. In contrast, the rotor is arranged above the bottom or on the bottom of the container 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 bottom of the container, the bottom of the container is preferably composed of a thin wall in order to achieve an efficient power transmission. For example, the thickness of the bottom of the container is at most 3 mm, preferably at most 2 mm.

[0039] It is particularly advantageous if the rotor is centered by the second body of the drive mechanism in the coupled state with the drive mechanism. In this way, a mechanical rotational axis of the rotor can be dispensed with. The centering of the rotor, i.e. the position of the rotor which 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 the diameter of the envelope circle of the rotor, preferably at least two-thirds of the diameter of the envelope circle, in order to be able to transmit as large a torque as possible from the drive mechanism to the rotor by means of the magnetic coupling. Furthermore, due to the large distance, the rotor can be reliably centered even if the user inserts the rotor into the vessel from outside the center of the vessel bottom, for example by touching the lateral surface.

[0040] In order to achieve a 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 vessel located on the base is preferably greater than the extension of said at least one of the first body and the second body in a plane perpendicular to the bottom of the vessel located on the base. Preferably, at least one of the first body and the second body extends at least 10%, more preferably at least 20%, particularly preferably at least 30% of the diameter of the envelope circle of the rotor in a plane parallel to the bottom of the vessel located on the base.

[0041] In order to facilitate handling of the liquid heater, the rotor can be removed from the vessel without tools and is freely movable, in particular in the radial direction. This means that, by removing the vessel from the base, turning the vessel to a position in which the vessel bottom is facing upwards, the rotor can be dropped out of the vessel, for example for cleaning the rotor and the vessel. According to the present embodiment, the rotor of the vessel removed from the base is freely movable in the radial direction, i.e. without mechanical guidance, which further facilitates removal of the rotor.

[0042] According to a further embodiment, it can be provided that the rotor comprises at least two, preferably three, arms extending in the radial direction of the rotor, the first body being arranged on the arms. The arms protruding from the center or the center of gravity of the rotor serve for stirring the liquid. Furthermore, the first body is arranged on the arms, in particular on the radially outer half or third of the arms, which enables an efficient transmission of torque from the drive mechanism to the rotor. For example, the arms of the rotor inserted into the vessel extend at least partially in a plane parallel to the vessel 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] To efficiently agitate liquids and minimize torque losses transmitted from the drive mechanism to the rotor, it is advantageous that the rotor includes three arms curved in the rotor plane, preferably curved in the direction of rotation, and preferably includes an axially projecting protrusion as a support surface on the side facing the bottom of the container. The rotor plane is perpendicular to the rotor's virtual axis of rotation, i.e., perpendicular to the rotor's axial direction. The curvature of the arms in the direction of rotation facilitates liquid agitation. The protrusion, serving as a support surface and projecting axially, advantageously reduces the frictional resistance of the rotor held in the container at the bottom of the container. For example, the axially projecting protrusion of the rotor can be a curvature or a pin pointing towards the bottom of the container. Attached Figure Description

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

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

[0046] Figure 2 yes Figure 1 A liquid heater without a lid;

[0047] Figure 3 yes Figure 2 Top view and partial internal view of the liquid heater;

[0048] Figure 4 yes Figure 1 A cross-sectional view of a liquid heater;

[0049] Figure 5 yes Figure 1 Another cross-sectional view of the liquid heater, corresponding to... Figure 4 Compared to a cross-section rotated 90°;

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

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

[0052] Figure 8 This is a schematic diagram of Newton's number as a function of time. Detailed Implementation

[0053] Figure 1 A liquid heater 1 according to the invention is shown, which includes a container 2 for containing a liquid to be heated (not shown). Figure 1The figure includes a base 3 (not shown) for placing the container 2 on or within it depending on the location of use, a lid 4 for covering or closing the container 2 (the lid 4 can be otherwise removed or opened), and a handle 5 for easy gripping of the liquid heater 1 by the user (not shown). Additionally, an operating element 6 in the form of a power button 6a is also shown. The base 3 includes a bottom 7 and a side surface 8 projecting upward from the bottom 7 along the direction of the lid 4, which surrounds a large portion of the container 2. The bottom 7 of the base 3 may also contain a cavity for accommodating components of the liquid heater 1, see, for example, [reference needed]. Figure 4 .exist Figure 1 In the example shown, container 2 is completely covered by base 3 and lid 4. In another embodiment (not shown), container 2 may be partially surrounded or covered by base 3 and lid 4.

[0054] Figure 2 Showing Figure 1 The liquid heater 1 in the container does not include a lid 4, thus revealing the container 2, particularly 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 is at least partially cylindrical. Preferably, at least partially, the lateral surface 9 of the container 2 is cylindrical.

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

[0056] Figure 4 It shows Figure 1Figure 1 shows a vertical section of a 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 comprises 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 level H extending from the container bottom 14, and the lateral surface 9 comprises a heating temperature TH up to the heating level H for heating the liquid. The stirring device 12 comprises 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 comprises a first body 16 generating a magnetic field or being magnetizable and the drive mechanism 15 comprises a second body 17 generating a magnetic field or being magnetizable. The drive mechanism 15 is designed to rotate the rotor 11 at least at one rotational speed, for which purpose the first body 16 is magnetically coupled to the second body 17, and the drive mechanism 15 comprises a drive 18, in particular an electric motor 18a, in particular preferably an electric motor 18b, which can be operated at a defined rotational speed. The rotational speed of the rotor 11 is in a rotational speed range in which the rotor 11 lifts a minimum defined amount M of liquid in the container 2 at least up to the heating level H during rotation and in which range a continuous foam surface does not form on the surface O of the heated liquid after rotation of the rotor 11. In Figure 4 In the shown embodiment, the heating device 13 is an induction heating device 13a. In Figure 4 It can also be seen in that the lateral surface 8 of the base 3 protruding upwards from the bottom 7 of the base 3 is arranged close to the lateral surface 9 of the container 2 located on the base 3 and preferably up to the heating level H, comprising 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 lateral wall with a 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 for example be at least one coil 13c, which is connected to an alternating current source 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 and thus the liquid in the container 2. For this purpose, the lateral surface 9 of the container 2, at least up to the heating level H, is preferably made of metal, in particular stainless steel. Furthermore, the bottom 7 of the base 3 can comprise a mechanism 13b of the induction heating device 13a for generating an additional magnetic field. Figure 4 In the shown embodiment, the magnetic field generating mechanism 13b extends below the rotor 11, which is symbolically shown. Of course, the mechanism 13b for generating an additional magnetic field can also extend below the container bottom 14.

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

[0058] In addition, from Figure 4 As can be seen in 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 may also be flat. The flat bottom side 19 and / or top side 20 allow for slight ripples, 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] exist Figure 4 In 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 to accommodate the second body 17. The rotor 11 is placed in the container 2 and is magnetically coupled to the drive mechanism 15, 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 As shown in the example, rotor 11 can be removed from container 2 without tools and can move freely in the radial direction R.

[0060] Figure 5 Showing Figure 1 Another cross-sectional view of the liquid heater in the middle, with Figure 4 In contrast, it is generated by rotating a profile by 90°. Figure 5 The envelope circle diameter KB of container 2 is also shown, which is measured inside the lateral surface 9.

[0061] Figures 6a to 6d An exemplary rotor 11 is shown, which includes at least two (three in the illustrated example) arms 21 extending in the radial direction R of the rotor 11, with a first body 16 disposed on the arms 21. Figure 6a The bottom side of the rotor 11 is shown, which faces the bottom of the container 14 when the liquid heater 1 is in operation. Figure 6b A side view of rotor 11 is shown. Figure 6c The top side of rotor 11 is shown, which faces away from the bottom 14 of the container when the liquid heater 1 is in operation. Figure 6d A cross-sectional view of rotor 11 taken along line CC is shown. Rotor 11 has a height HR and a diameter (envelope circle diameter KR).

[0062] exist Figures 6a to 6cIn the example shown, it can also be seen that the rotor 11 does not have a circular or annular housing or any other recess for the rotation axis. Furthermore, it can be seen that the rotor 11 comprises three arms 21 curved in the rotor plane E (in the example shown, curved in the direction of rotation DR) and a protrusion 22 projecting in the axial direction A, which acts as a bearing surface on the side facing the container bottom 14, in particular in the center of the rotor 11.

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

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

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

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

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

[0068] The liquid heater 1 was tested to investigate the rotor size and the associated rotation speed range by which the rotor 11, during rotation, causes the minimum defined amount of liquid in the container 2 to rise at least to the heating height H, so that after rotation of the rotor 11, 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 the rotors 11 numbered 1, 2 and 7 are particularly suitable for achieving the set objectives. The rotors 11 numbered 8 to 11 are also suitable at least under certain conditions. In particular, using these rotors 11, at the minimum speed prescribed, if the container 2 is filled with the minimum defined quantity of liquid, 60 ml or 100 ml, the lateral surface 9 can be wetted with the liquid up to the heating height H; moreover, up to the maximum speed prescribed, at the end of the stirring process, the surface of the liquid heated does not present a continuous surface of foam. 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] Container internal diameter: 84.7 mm

[0078] Heating height: about 50 mm

[0079] Rotor height: 10.725 mm

[0080] Ratio between heating height and rotor height: 4.662

[0081] Rotor diameter: 65 mm

[0082] Ratio between container internal diameter and rotor diameter: 1.303

[0083] Maximum speed without foam for the liquid (60 ml of milk): about 450 rpm (depending on the rotor shape)

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

[0085] Newton number: Ne = 0.1

[0086] A lower height HR or a smaller diameter KR of the rotor 11 would require a higher speed of rotation in order to raise the liquid to the heating height H on the lateral surface 9 under the action of the rotor 11, however, such a speed of rotation could cause the liquid surface to foam.

Claims

1. Liquid heater (1) having a container (2) for containing a liquid to be heated, a base (3) for placing the container (2) thereon, 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) comprising 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) of the lateral surface (9), the heating height (H) starting from the bottom (14) and the lateral surface (9) comprising a heating temperature (TH) up to the heating height (H) for heating the liquid, the stirring device (12) comprising a rotor (11) accommodated in the container (2) and a drive mechanism (15) for the rotor (11), the rotor (11) comprising a first body (16) generating a magnetic field or being magnetizable, the drive mechanism (15) being accommodated in the base (3) and comprising a second body (17) generating a magnetic field or being magnetizable, the drive mechanism (15) being designed to rotate the rotor (11) at least at one speed, for which the first body (16) is magnetically coupled to the second body (17), characterized in that, Said rotor (11) is designed to rotate and make ascend along said lateral surface (9) the liquid contained in said container (2) in operating conditions, the rotation speed of said rotor (11) being comprised in a rotation speed range in which the minimum defined amount of liquid exposed to the rotating rotor (11) in said container (2) comprises a height at least equal to said heating height (H) and in which the heated liquid comprises a surface without a continuous foam surface, wherein in the case in which the density of said liquid is comprised in the range 1.018-1.048 g / cm 3 between 0.1 and 0.3 is assigned to said stirring device (12).

2. The liquid heater (1) according to claim 1, characterized in that in the range 1.018-1.048 g / cm 3 The Newton number assigned to the stirring device (12) is between 0.1 and 0.2 in the case where the density of the liquid is in the range 1.018-1.048 g / cm 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 of the rotor (HR) 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), and 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 2, characterized in that, The heating device (13) is an inductive heating device (13a).

5. The liquid heater (1) according to claim 4, characterized in that The base (3) comprises a bottom (7) and a side surface (8) protruding from the bottom, which is arranged next to a lateral surface (9) of the container (2) on the base (3) and which comprises a magnetic field generating means of the inductive heating device (13a).

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

8. The liquid heater (1) according to any one of claims 1 to 2, 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 2, characterized in that, The top side (20) of the container bottom (14) is flat.

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

11. The liquid heater (1) according to any one of claims 1 to 2, characterized in that, In a coupled state 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 2, characterized in that, The rotor (11) can be removed from the container (2) without tools.

13. The liquid heater (1) according to any one of claims 1 to 2, characterized in that, The rotor (11) comprises at least two arms (21) extending in a radial direction (R) of the rotor (11), the first body (16) being arranged on the arms (21).

14. The liquid heater (1) according to any one of claims 1 to 2, characterized in that, The rotor (11) comprises three arms (21) curved in a rotor plane (E).

15. The liquid heater (1) according to claim 5, characterized in that, The side surface (8) comprises a magnetic field generating means of the inductive heating device (13a) up to the heating height (H).

16. The liquid heater (1) according to claim 5, characterized in that The bottom (7) of the base comprises a magnetic field generating means of the inductive heating device (13a).

17. The liquid heater (1) according to claim 7, characterized in that The metal is stainless steel.

18. The liquid heater (1) according to claim 7, characterized in that, The lateral surface (9) of the container (2) is cylindrical.

19. The liquid heater (1) according to claim 9, characterized in that, The rotor (11) has no circular or annular accommodation for the rotational axis.

20. The liquid heater (1) according to claim 12, characterized in that, The rotor (11) is movable in a radial direction (R).

21. The liquid heater (1) according to claim 13, characterized in that, The rotor (11) comprises three arms (21) extending in a radial direction (R) of the rotor (11).

22. The liquid heater (1) according to claim 14, characterized in that The three arms (21) are curved in a rotational direction (DR).

23. The liquid heater (1) according to claim 14, characterized in that, The rotor (11) comprises a protrusion (22) protruding in an axial direction (A) on a side facing the container bottom (14) as a bearing surface.

24. Method for heating a foamable liquid in a liquid heater (1), wherein The liquid to be heated is contained in a container (2) without a continuous foam surface on its surface, said container (2) is placed on a base (3), the liquid in said container (2) is heated with a heating device (13) and the liquid in said container (2) is stirred with a stirring device (12), said container (2) comprises a bottom (14) and a lateral surface (9) extending from said bottom, which lateral surface (9) is part of said heating device (13) up to a predetermined heating height (H) of said lateral surface (9), said heating height (H) starts from said bottom (14) and said lateral surface (9) is heated to a heating temperature (TH) up to said heating height (H) to heat said liquid, and said stirring device (12) comprises a rotor (11) contained in said container (2) and a drive mechanism (15) for said rotor (11), which rotor comprises a first body (16) generating a magnetic field or magnetizable, said drive mechanism (15) is contained in said base (3) and comprises a second body (17) generating a magnetic field or magnetizable, which drive mechanism (15) rotates said rotor (11) at least at one rotational speed, for which said first body (16) is magnetically coupled with said second body (17), characterized in that said rotor (11) in the working condition rotates the liquid contained in said container (2) and makes it rise along said lateral surface (9), the rotational speed of said rotor (11) is in a rotational speed range in which said rotor (11) during rotation makes a minimum defined amount of liquid in said container (2) rise to a height at least equal to said heating height (H), and in which rotational speed range, after the rotation of said rotor (11), a heated liquid is obtained in said container (2), said heated liquid still has no continuous foam surface on its surface, wherein when a liquid having a density in the range of 1.018-1.048 g / cm 3 when a liquid having a density in the range of 1.018-1.048 g / cm

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