Kettle for quiet heating of liquids

Abstract

In the technical field of beverage preparation machines, protection against unwanted noise is playing an increasingly important role. High-performance, electrically operated kettles are relatively loud and can drown out quiet music and conversations. Their operation is also often problematic during quiet hours or near sleeping children. The cause of this unwanted noise can be explained by the cavitation of steam bubbles, which is caused by localized boiling. The present invention of a low-noise kettle solves the problem by building up a sufficiently high overpressure in a heatable container (2) before heating a liquid (1) in order to prevent local boiling as a major cause of noise generation. Liquids can thus be heated and brought to a boil silently, significantly faster, and with higher efficiency.

Description

[0001] The invention relates to the field of beverage preparation machines with protection against unwanted noise and, in particular, to a kettle for quietly heating liquids. State of the artProblem:

[0002] Common household kettles, usually electric, are relatively loud, drowning out quiet music and conversations. Their operation is also often problematic during quiet hours or near sleeping children.

[0003] The cause of the unwanted noise can be explained by cavitation. Due to the relatively high heat output density (also heat flux density) in modern kettles, with the goal of providing hot or boiling water as quickly as possible, the heat transfer surfaces in contact with the water to be heated are particularly hot. This leads to local overheating and local boiling of the water. The areas of the water closest to the heat transfer surface are already boiling, while the rest of the water is still cold or barely warm. Compared to a normal saucepan, the effect is usually more pronounced in electric kettles due to the particularly high heat output density. The vapor bubbles formed during local boiling rise due to their lower density, cool down again in the colder water layers, reduce their vapor pressure (also known as saturation vapor pressure), and implode (cavitation).The pressure waves generated are clearly audible as sound waves and are responsible for the often unpleasant and loud “hissing” or “noise” shortly after the cooking process has begun.

[0004] At the end of the boiling process, the water is almost completely heated. Rising bubbles now reach the surface and burst; a slightly quieter and more pleasant "bubbling" or "fizzing" can be heard; the water is "boiling."

[0005] In addition to today's standard household kettles, there are already numerous options on the market, featuring technologies such as "Quiet Boil" (Russell Hobbs) or "Whisper Boil" (Dualit), as well as numerous patents promising improvements. Various technologies are being used to reduce the noise level when heating water.

[0006] Well-known principles for noise reduction are: - better insulating, sound-insulating or noise-damping containers and elements (e.g. GB 2 524 872 B, DE 10 2017 001 978 A1) - a lower heating output or larger, heated heat transfer surfaces and thus a lower heating power density (e.g. DE 201 19 638 U1, WO 2009 / 046 550 A2) - improved heat conduction to heat water more evenly (e.g. DE 10 2016 222 839 A1, CN 2 09 269 373 U, DE 20 2017 003 312 U1) - Coatings, special geometries of the heat transfer surfaces or diffuser plates to keep the resulting vapor bubbles as small as possible (e.g. EP 1 566 123 B1, DE 198 25 835 C2, WO 2022 / 221 914 A1)

[0007] Even cookers advertised as quiet are often still relatively loud, or very slow, large and unwieldy, difficult to clean, or have not been able to establish themselves on the market, so that available solutions are unsatisfactory.

[0008] However, principles are known from other fields that make the original problem of local boiling manageable.

[0009] Hot water systems that use water as a heat transfer medium are known from industrial applications. During heating, the water is prevented from boiling locally by high water pressures in the pipes, since, according to the phase diagram, water begins to boil later at higher pressures. This principle is also mentioned in EP 3 273 174 B1. Although this solution is not applicable to a standard household kettle, it can be used in stationary hot water dispensers with a water connection, as described, for example, in DE 691 18 036 T2.

[0010] The invention takes this principle and adapts it for stand-alone, heatable containers without additional connections. Although there are no pressurized water pipes, the required static pressure can be generated by increasing the gas pressure above the liquid to be heated. The increased gas pressure in the container can literally suppress the problematic bubble formation. If the boiling process takes place under sufficient pressure, no vapor bubbles can form, the liquid remains liquid above the normal boiling point, and noise is effectively reduced.

[0011] DE 10 2019 124 816 A1 discloses a pressure cooker that regulates the prevailing overpressure using sensors and valves. However, it cannot build up this pressure independently of the heating process, but instead uses the steam generated during heating to generate pressure. Effective noise reduction cannot be guaranteed due to the lack of overpressure at the start of cooking.

[0012] In the area of ​​rice cookers and pressure cookers, cookers are already known that can build up excess pressure in a heatable container with the help of a compressor, thus achieving various advantages.

[0013] However, the control and regulation of these cookers is primarily designed to cook foods with a low water content even under high pressure, to prevent boiling over when cooking food and to accelerate the absorption of water when cooking rice.

[0014] Although the pressure control allows for setting any desired cooking temperature, the control and regulation of these cookers are not designed to improve noise. Noise reduction is not the goal, nor is any corresponding handling or use suggested. (For example, see JP H02 - 74 219 A, JP H05 - 38 312 A, JP 2018 - 198 924 A, WO 2020 / 000 898 A1)

[0015] The invention is based on the object of providing a kettle with which liquids can be heated quietly.

[0016] This is achieved with a kettle according to claim 1. Further developments of the invention are defined in the dependent claims.

[0017] To implement the above-described solution principle according to the invention, a heatable container that can withstand a certain internal overpressure is filled with a liquid and sealed hermetically. A compressor is used to increase the static pressure in the container, creating an overpressure.

[0018] In the process to be used, it is crucial that the overpressure is built up before the liquid is heated to ensure noise reduction throughout the entire process. It is also important to ensure that a sufficiently high overpressure is built up. Ideally, the overpressure prevailing in the vessel is greater than the boiling pressure (also known as the saturation vapor pressure or vapor pressure) according to the phase diagram, at the respective temperature of the heat transfer surface. Depending on the desired heating power density, however, this temperature can be very high and the required overpressure can therefore be in a critical range. Even in these cases, simply increasing the pressure to a lower, acceptable level will result in a noticeable noise reduction.

[0019] Due to the lower vapor formation and the lack of acoustic signals that the liquid has reached the normal boiling point, the end of boiling must be detected and initiated based on the temperature using a temperature sensor.

[0020] To ensure safe removal of the heated liquid, the container should be pressure equalized. After the excess pressure has been released, the liquid may bubble briefly until the temperature drops slightly, similar to a cooling saucepan that continues to bubble briefly after being removed from the heat source.

[0021] In tests on a prototype with a medium heat output density, very good noise-reducing results were achieved at an overpressure of 1.5 bar. The cooking process was largely silent. The average noise level was 30 dB(A). The noise level in the reference test without actively generated overpressure was approximately 25 dB(A) higher.

[0022] In addition, the prototype reached the target temperature of 100°C significantly faster, taking about 75% of the time required in the reference test.

[0023] In addition to the significant advantage of significantly reducing noise during the cooking process, greater efficiency is achieved. The time required to reach the target temperature can be shortened, or the required energy consumption can be reduced.

[0024] Conversely, it is possible to use excess pressure to increase the heating power of a cooker and thus reduce cooking times without increasing the noise level.

[0025] Another advantage can be the reduced precipitation of scale (limestone, calcium carbonate) when heating hard water. During conventional heating of water, dissolved carbon dioxide escapes, and water-insoluble calcium carbonate, previously present as calcium bicarbonate, precipitates. Since the water solubility of carbon dioxide depends not only on temperature but also on pressure, boiling under elevated pressure can have a positive effect. Especially when the overpressure is generated with carbon dioxide, its high partial pressure prevents the outgassing of carbon dioxide and thus the precipitation of scale.

[0026] Unlike a simple pressure cooker, the excess pressure at the end of the cooking process can be released within a few seconds because the container doesn't contain superheated steam that needs to cool slowly. The cooker can be quickly reopened and the heated or boiling water used.

[0027] As a further advantage, the cooker can heat water to 100°C even in high mountains to ensure safe food.

[0028] The invention is described below using embodiments with reference to the drawing.

[0029] The drawing shows: Fig. 1 a schematic side view of a kettle according to the invention.

[0030] An exemplary embodiment of the invention is shown in Fig.1 and essentially corresponds to a common household electric kettle (hereinafter also referred to as a cooker), which can also be sealed airtight like a pressure cooker and can withstand a certain amount of internal pressure.

[0031] The liquid 1 is poured into the pressure-resistant, heatable container 2. The container 2 is sealed with the sealing cap 3, making it airtight and pressure-tight.

[0032] The cooking process is initiated by the user. According to the integrated control system, the cooker, with its integrated electric compressor 4, begins to build up excess pressure in the container 2, which is maintained by the check valve 5. As soon as the pressure sensor 6 detects sufficient excess pressure, the heating element 7, which is powered by the base 8, is switched on.

[0033] As soon as the target temperature is reached and detected by the temperature sensor 9, the cooker shuts off. After manual operation of the control element 10, the excess pressure can be quickly equalized by the outlet valve 11 via the outlet (an outlet opening) 12. For safe operation, the pressure relief valve 13 is provided, which automatically vents through the outlet (an outlet opening) 14 when a critical pressure is exceeded.

[0034] Different liquids 1, such as water, can be heated quietly according to the respective phase diagram using the described invention.

[0035] A wide variety of designs and materials are possible for the heatable container 2, although a simple stainless steel cylinder with a spout appears particularly suitable to meet the requirements of pressure resistance, easy cleanability, and health safety. Additionally, the container 2 can be insulated for thermal or sound insulation.

[0036] The closure 3 can close and seal the container 2 using various positive and non-positive connections. In addition to proven options such as a bayonet lock, various solutions are available for pressure cookers on the market. Other possible options include a simple screw cap, a clamp lock, a quick-closing snap connection, or a press connection that utilizes the excess pressure in the container 2 and automatically seals and closes it with sealing lips that rest against a sealing surface.

[0037] In addition to a small, compact, electric compressor 4, which can preferably be integrated into the handle or lid 3 of the cooker, several compressors 4 or pumps can also be used to build up and release the excess pressure. The compressor 4 can be activated to build up pressure when the cooking process starts, but also, for example, by closing the lid 3 or by another interaction with the cooker.

[0038] In addition to full integration, it is possible to use a separate, permanently or flexibly connected or partially integrated compressor 4.

[0039] In the simplest case, the compressor 4 is a separate, manually operated air pump, which is connected via a check valve 5 to build up pressure. The basic design with a partially integrated air pump can, for example, be similar to the design described in DE 403 282 A, in which the air pump is integrated into the housing cover. In contrast to the infusion device described here, a heating option would, of course, have to be provided.

[0040] Furthermore, instead of a compressor 4, another gas pressure source or a combination of different gas pressure sources can be used. With the help of a gas pressure source in the form of a gas pressure reservoir (also known as a compressed air reservoir or air chamber), the required overpressure in the container 2 can be built up particularly quickly and quietly. Furthermore, the activation of the compressor 4 can be decoupled from the cooking process, allowing overpressure to be generated slowly and at any time and temporarily stored in the gas pressure reservoir. For an independently operating gas pressure reservoir, gas cartridges and gas cylinders are also conceivable, if used or connected in a suitable manner.

[0041] In addition to building up an overpressure with a compressor 4 and compressing the air or gas phase by pumping additional gas into a fixed container volume, it is also conceivable to build up an overpressure by reducing the container volume.

[0042] This can be achieved, similar to a fluid power cylinder, for example, by moving the closure 3 or by inserting a body into the container 2. By means of a clamping mechanism, which, for example, resembles a clamping cap, the container volume can be reduced after the container 2 has been closed and the contained gas can be compressed or the liquid 1 can be pressurized.

[0043] The check valve 5 can be integrated into the compressor 4 or omitted under certain circumstances, particularly when the overpressure is maintained by continuous operation of the compressor 4 or a gas pressure reservoir is used. Furthermore, different valves can be used to seal the container 2. Especially when using a gas pressure reservoir, the use of a controllable and adjustable valve as part of a pressure control circuit is preferred.

[0044] In addition to a pressure sensor 6 with the corresponding electronics, simple pressure switches with a membrane and switching contacts or manual operation with the aid of a pressure gauge with display are conceivable.

[0045] For optimal cleaning, electrical heating elements 7 located outside the container 2 and indirectly heating the liquid 1 are preferred. However, internal heating elements 7 with direct contact with the liquid 1 are also possible. Furthermore, any secondary heat sources such as gas cookers or hotplates or other integrated heating options such as gas burners can be used.

[0046] The preferred and most flexible version of a kettle with a base 8 for power supply can, of course, also be replaced by a simpler design with a direct power supply to the heating elements 7. If alternative or secondary heat sources are used, the base 8 can, of course, also be omitted.

[0047] A temperature sensor 9 with the corresponding electronics allows the detection of different temperatures, such as heating to the normal boiling point (100°C), but also for lower or higher temperatures, such as brewing temperatures for green tea (70°C). Bimetallic temperature switches cannot be triggered by the resulting steam as is often the case due to the suppressed boiling, but they can offer an alternative in suitable locations. Furthermore, capillary tube thermostats, resistance thermometers (Pt100), or, in the simplest case, thermometers with a display for manual monitoring can be used.

[0048] A manual control element 10 appears most suitable for ensuring pressure equalization after the cooking process. This could, for example, be a push button embedded in the handle, with which the user can specifically initiate pressure equalization and safely vent the escaping warm air. However, since the escaping air is not superheated steam, as in a pressure cooker, and the escaping of the relatively cool air occurs quickly, automatic pressure equalization should not pose any danger. Possible options include automatic triggering upon interaction with the cooker, such as lifting the cooker, or automatic opening of a controllable valve after the target temperature is reached.

[0049] The outlet valve 11 can be omitted when active suction is used to relieve excess pressure. It can be operated manually, electrically, or pneumatically. Depending on the type of closure 3, it is possible to open the container 2 even without prior pressure equalization.

[0050] In addition, it may be advantageous to equip the outlet valve 11 with a control and regulation against uncontrolled overpressure, by heating the liquid 1, and to limit the pressure in the container 2 to a target value.

[0051] In addition to a simple opening, the outlet 12 can be arranged and designed so that escaping air cannot be directed towards the user and flows out in a muffled manner.

[0052] The pressure relief valve 13 can be combined with the outlet valve 11 to reduce the number of components and better monitor its proper functioning through regular actuation of this safety-relevant component. Various mechanisms can be used as an alternative or redundant protection to the pressure relief valve 13. For example, the pressure sensor 6 can detect the exceedance of a critical pressure, interrupt the heating process, and warn the user.

[0053] The outlet 14 is preferably combined with the outlet 12 to reduce the number of components.

[0054] In addition, thanks to the overpressure, an outlet tap with a riser pipe can be integrated for convenient tapping of small amounts of liquid 1 from the container 2.

Claims

[1] Kettle with a pressure-tight sealable and heatable container (2) for receiving and heating a liquid (1) therein and with an overpressure build-up device connected to the container (2) which is designed to build up an overpressure in the container (2) in order to reduce local boiling as a major cause of noise when heating the liquid (1), wherein the overpressure build-up device is designed to build up the overpressure even before the liquid (1) is heated. [2] Kettle according to claim 1, characterized by that the overpressure build-up device has a gas pressure source, wherein the gas pressure source is designed as a compressor (4), gas pressure reservoir or a combination of compressor (4) and gas pressure reservoir. [3] Kettle according to claim 1, characterized bythat the overpressure build-up device is designed such that an available volume of the container (2) is reduced in order to compress gas contained therein or to exert direct pressure on the liquid (1) contained therein. [4] Kettle according to one of claims 1 to 3, characterized by that it has a check valve (5), a pressure sensor (6), a temperature sensor (9), an outlet valve (11), a pressure relief valve (13) and outlet openings (12, 14) for safe and practical operation. [5] Kettle according to claim 4, characterized by that the valves (5, 11, 13) can be combined, operated manually, electrically or pneumatically, and its outlet openings (12, 14) are separate or combined and designed so that gas can escape quietly and does not pose a danger to a user. [6] Kettle according to claim 4 or 5, characterized bythat its control and regulation is manual, semi-automatic or automatic. [7] Kettle according to one of claims 4 to 6, characterized by that the overpressure built up by the overpressure build-up device is chosen to be so large that the boiling temperature of the liquid (1), according to the respective phase diagram, is above the maximum temperature of the heated heat transfer surface in order to exclude local boiling. [8] Kettle according to one of claims 4 to 7, characterized by that in order to end the heating process in a timely manner, the reaching of a target temperature, even if this is the normal boiling temperature, is determined by means of the temperature sensor (9) due to the lack of or low development of steam or noise. [9] Kettle according to one of claims 1 to 8, characterized bythat it is equipped with a riser pipe and an outlet tap in order to conveniently tap the liquid (1) contained in the container (2) using the excess pressure.

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