APPARATUS FOR HEATING AND FOAMING A LIQUID, IN PARTICULAR A BEVERAGE

Abstract

The invention relates to an apparatus for heating and foaming a liquid, in particular a beverage, comprising a steam line (6), which can be connected to a steam generator (1); a pressurized gas line (4), which can be connected to a pressurized gas source (2); and a conveying means (3), connected to the steam line (6) and the pressurized gas line (4), for generating and transferring a steam/gas mixture into the liquid, and a controllable switching valve (5), wherein hot steam is supplied to the conveying means (3) via the steam line (6) and a pressurized gas flow under a defined constant pressure is supplied via the pressurized gas line (4) and pressure pulses (p) are generated from the pressurized gas flow by means of the switching valve (5). In order to damp the generated pressure pulses, the conveying means (3) comprises an expansion chamber (15) having a nozzle (14) arranged on the downstream end of the expansion chamber (15).

Claims

1. An apparatus for heating and foaming a liquid, in particular a beverage, comprising: a steam line connected to a steam generator; a compressed gas line connected to a compressed gas source; a conveying means connected to the steam line (4) and the compressed gas line for generating and transferring a steam/gas mixture into the liquid; and a controllable switching valve, wherein hot steam is fed to the conveying means via the steam line, wherein a compressed gas flow under a predetermined constant pressure is fed to the conveying means via the compressed gas line, wherein pressure pulses (p) are generated from the compressed gas flow by means of the switching valve, and wherein the conveying means comprises an expansion chamber configured to control the introduced pressure pulses (p) and a nozzle arranged at a downstream end of the expansion chamber.

2. The apparatus according to claim 1, wherein the compressed gas source comprises a compressor, and wherein the steam generator comprises a water heater.

3. The apparatus according to claim 1 wherein the switching valve comprises at least one of a solenoid valve or a pulse-width-modulated controlled solenoid valve.

4. The apparatus according to claim 1, wherein the switching valve is located upstream of the expansion chamber.

5. The apparatus according to claim 1, wherein the switching valve is controllable with a predetermined frequency (f) and generates pressure pulses (p) from the compressed gas flow by periodically opening and closing at the predetermined frequency (f) and directs the mixture into the expansion chamber.

6. The apparatus according to claim 5, wherein the predetermined frequency (f) of the pressure pulses is in the range of between about 0.1 to about 200 Hz or between 1 about and about 50 Hz.

7. The apparatus according to claim 1, wherein the introduced pressure pulses (p), characterized by one or more of a pulse frequency (f), a pulse duration (t0), and an amplitude (p0), as generated by the switching valve, is adjustable.

8. The apparatus according to claim 1, wherein the conveying means further comprises a non-return valve between the switching valve and the expansion chamber.

9. The apparatus according to claim 1, wherein a steam valve is arranged in the steam line.

10. The apparatus according to claim 9, wherein a control device is coupled to one or more of the steam generator, the steam valve, and the switching valve.

11. The apparatus according to claim 9, wherein the conveying means comprises an annular channel arranged coaxially with the cylindrically formed expansion chamber and in fluid communication with the steam line.

12. The apparatus of claim 11, wherein the annular channel is in fluid communication at an upstream end with the steam line and at a downstream end with a mixing channel.

13. The apparatus according to claim 12, wherein the downstream end of the mixing channel is connected to a discharge line.

14. The apparatus according to claim 12, wherein the nozzle opens into the mixing channel at an upstream end of the mixing channel.

15. The apparatus according to claim 1, wherein one or more or the expansion chamber and the nozzle are made of a thermally conductive material or stainless steel.

16. The apparatus according to claim 11, wherein one or more of the expansion chamber, the nozzle, the annular channel, and the mixing channel is arranged in a reactor block made at least partly of plastic or of PEEK.

17. The apparatus according to claim 16, wherein the expansion chamber is hollow, cylindrical, and extends along an axial direction in the reactor block.

18. The apparatus according to claim 17, wherein a diameter of the hollow-cylindrical expansion chamber is larger than a cross-section of the compressed gas line.

19. The apparatus according to claim 1, wherein a How cross-sect ion of the nozzle (14) is smaller than a diameter of the expansion chamber by at least a factor of 2.

20. The apparatus according to claim 5, wherein the pressure pulses (p) generated by periodically opening and closing the switching valve expand in the expansion chamber and are thereby damped.

21. The apparatus according to claim 1, wherein at least one of the expansion chamber and the nozzle act as a damping member for the pressure pulses (p) introduced into the expansion chamber.

22. The apparatus according to claim 1, wherein the steam/gas mixture flowing out of the expansion chamber through the nozzle has a pressure characteristic p(t) over time with damped, periodically repeating pressure peaks (p0).

23. The apparatus according to claim 1, wherein the steam/gas mixture flowing out of the expansion chamber through the nozzle has a pressure characteristic p(t) over time with periodically repeating and plateau-shaped flattened pressure peaks (p0), each pressure peak (p0) having an exponentially decreasing pressure characteristic up to the pressure peak following in time.

24. The apparatus according to claim 1, wherein the steam/gas mixture flowing out of the expansion chamber through the nozzle has a pressure characteristic p(t) over time with a constant pressure offset (p1).

25. The apparatus according to claim 1, further comprising at least one of an adjustable pressure reducer or an adjustable pressure relief valve located in at least one of the compressed gas line for in the conveying means.

26. The apparatus according to claim 25, wherein the pressure reducer is arranged in the conveying means upstream of the switching valve.

27. The apparatus according to claim 1, further comprising a container for holding the liquid; and a mixing device in communication with one or more of the steam line, the compressed gas line, and the container, wherein the liquid and the pulses of the steam/compressed gas mixture generated by the conveying means are supplied to the mixing device and mixed in the mixing device to facilitate hot foaming of the liquid.

28. The apparatus according to claim 27, wherein the container is connected to the compressed gas line via a branch line.

29. The apparatus according to claim 27, wherein the liquid stored in the container is conveyed into the mixing device by overpressure provided by the compressed gas source.

30. The apparatus according to claim 27, wherein the mixing device comprises a first inlet for supplying the pulses of the steam/compressed gas mixture generated by the conveying means, a second inlet for supplying the liquid, and an outlet for discharging the heated and foamed liquid.

31. The apparatus according to claim 27, wherein the mixing device is in communication with the container via a liquid line.

32. The apparatus according to claim 30, wherein at least one of the liquid supplied to the container via the second inlet and the steam/compressed gas mixture supplied to the container via the first inlet flows upwards in the mixing device against the force of gravity.

33. The apparatus according to claim 30, wherein a nozzle is arranged in the region of the second inlet of the mixing device, with which nozzle the liquid is sprayed into the mixing device.

34. The apparatus according to claim 30, wherein the mixing device comprises a linear channel communicating with the first input.

35. The apparatus according to claim 34, wherein the mixing means comprises an annular channel communicating with the second inlet and arranged concentrically around the linear channel.

36. A method for foaming a liquid, in particular a beverage, with pulses of a steam/compressed gas mixture, wherein, in order to generate pulses of the steam/compressed gas mixture, hot steam is supplied to a conveying means via a steam line and a compressed gas flow under a predetermined constant pressure is supplied via a compressed gas line, and pressure pulses (p) are generated from the compressed gas flow by means of a switching valve, wherein the pressure pulses (p) of the compressed gas flow in the conveying means are damped by the interaction of an expansion chamber and a nozzle arranged at a downstream end of the expansion chamber.

37. The method according to claim 36, wherein the liquid is stored in a mixing vessel and the steam/compressed gas mixture is introduced into the liquid via an immersion tube.

38. The method according to claim 36, wherein the liquid is stored in a container and is led fed from the container to a mixing device in which the liquid is mixed with the steam/pressure gas mixture.

39. The method according to claim 38, wherein the liquid stored in the container is conveyed into the mixing device by overpressure provided by the compressed gas source.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] These and other features and advantages of the invention will be apparent from the examples of embodiments described in more detail below with reference to the accompanying drawings. The drawings show:

[0038] FIG. 1 is a schematic representation of a first embodiment of an apparatus according to the invention with a conveying means for generating and transferring a steam/gas mixture into a liquid to be foamed, wherein the liquid is located in an open vessel;

[0039] FIG. 2 is a detailed representation of the conveying means of the apparatus of FIG. 1 in a sectional drawing,

[0040] FIG. 3 is a Pressure-Time curve of the pressurized gas flow generated in the conveying means for producing the steam/gas mixture;

[0041] FIG. 4 is a schematic representation of a second embodiment of an apparatus according to the invention with a conveying means for generating and transferring a steam/gas mixture into a mixing device to which the liquid to be foamed is fed.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0042] The schematic embodiment of an apparatus according to the invention shown in FIG. 1 comprises a steam generator 1, a steam line 6 extending from the steam generator 1, a compressed gas source 2 with a compressor 2a, a compressed gas line 4 extending from the compressed gas source and a conveying means 3 for transferring a steam/gas mixture into a liquid 11 to be foamed. The liquid 11, which is located here in an open-topped vessel 10 (e.g. in a pitcher), can in particular be a beverage such as milk or a milk-containing beverage. At the downstream end, the conveying means contains a discharge line 22, for example in the form of an immersion tube or a flexible hose, the open end of which can be immersed in the liquid for foaming. Steam generated in the steam generator 1 is fed to the conveying means 3 via the steam line 6 and a gas compressed in the compressed gas source 2 is introduced into the conveying means 3 via the compressed gas line 4. The gas is expediently air, but it can also be other gases such as carbon dioxide (CO.sub.2) or nitrogen (N.sub.2) or gas mixtures. Preferably, the compressor 2a draws in air from the environment via a gas supply line 13.

[0043] In the conveying means 3, the gas flow of the compressed gas is mixed with the steam flow to produce a steam/gas mixture, which is introduced into the liquid F via the discharge line 22.

[0044] A temperature sensor 8 is attached to the open end of the discharge line 22 immersed in the liquid, which detects the temperature of the liquid F and transmits it to a control device 9 via a measuring line. An electrically controllable steam valve 7, which can be designed as a solenoid valve, for example, is arranged in the steam line 6 between the steam generator 1 and the conveying means 3. The steam valve 7 and the compressor 2a of the compressed gas source 2 are controlled by the electronic control device 9, to which they are connected via corresponding control lines. The control device 9 contains a man-machine interface in the form of buttons, rotary knobs and a screen, which may also be touch-sensitive, for communication with a user. The user can enter control instructions and read out displayed operating states and error messages via the interface.

[0045] The conveying means 3 contains a first part 3a and a second part 3b, which are connected to each other via a compressed gas line 4′. A pressure reducer 21 is provided in the first part 3a of the conveying means 3. The pressure reducer 21 may in particular be a pressure relief valve which can be adjusted manually or via the control device 9. A switching valve 5 is arranged in the second part 3b of the conveying means 3, which can be controlled to open and close via the control device 9. The switching valve 5 can in particular be a solenoid valve which can be actuated in a pulse-width modulated manner by the control device 9.

[0046] The conveying means 3 is shown in detail in a sectional drawing in FIG. 2. As can be seen in FIG. 2, the first part 3a of the conveying means 3 contains the adjustable pressure reducer 21. The pressure of the compressed gas flow provided by the compressed gas source 2 and supplied via the compressed gas line 4 can be set to a presettable value of, for example, 2 bar via the pressure reducer 21 and is maintained constant by the pressure reducer 21. In this way, pressure fluctuations of the compressor 2a of the compressed gas source 2 can be compensated. The pressurized gas flow brought to a constant pressure in the first part 3a of the conveying means 3 is conducted via the pressurized gas line 4′ into the second part 3b of the conveying means 3. The switching valve 5 is arranged at the upstream inlet of the second part 3b of the conveying means 3, through which the compressed gas flow is passed. The switching valve is periodically opened and closed by the control device, whereby both the frequency and the duration of opening and closing are controlled by the control device, according to the control instructions set by the user via the interface.

[0047] The conveying means comprises a hollow-cylindrical expansion chamber 15 arranged downstream of the switching valve 5 with a nozzle 14 arranged at the downstream end of the expansion chamber 15. The nozzle opens centrally into a downstream mixing channel 17. A non-return valve 20 is arranged between the switching valve 5 and the expansion chamber 15. The expansion chamber 15 has a (considerably) larger diameter than the compressed gas lines 4 and 4′ and the nozzle 14.

[0048] Furthermore, the conveying means 3 contains an annular channel 16 coaxially surrounding the expansion chamber 15, which at its upstream end 16a is in connection with the steam line 6 arranged on a flange 26. At its downstream end 16b, the annular channel 16 opens into the mixing channel 17. At the downstream end of the mixing channel 17, the discharge line 22 is arranged via a flange 27.

[0049] Preferably, the expansion chamber 15 and the nozzle 14 are made of a material with good thermal conductivity, in particular stainless steel, and are arranged in a thermally insulating reactor block 18. The reactor block 18 is made, for example, of a high-temperature-resistant plastic, such as PEEK. The annular channel 16 and the mixing chamber 17 are formed in the reactor block 18.

[0050] For the operation of the apparatus according to the invention, after the steam generator 1 has been put into operation, the steam valve 7 is set to the open position by the control apparatus 9 and the compressed gas source 2 is activated at the same time. The compressed gas flow generated by compressed gas source 2 passes through compressed gas line 4 into the first part 3a of the conveying means, where a constant pressure is set via pressure reducer 21. The compressed gas flow kept at constant pressure is passed via the compressed gas line 4′ through the switching valve 5 of the second part 3a of the conveying means 3. The switching valve 5 is periodically opened and closed by the control device 9 with an adjustable frequency, whereby pressure pulses are generated from the permanent pressurized gas flow and conducted through the non-return valve 20 (open in this direction) into the expansion chamber 15. In the expansion chamber, the introduced pressure pulses can expand and are ejected through the downstream nozzle 14 into the mixing channel 17.

[0051] The steam flow generated by the steam generator 1 simultaneously passes through the steam line 6 into the annular channel 16 in the second part 3b of the conveyor means. At the downstream end 16b of the ring channel 16, the steam flows into the mixing channel 17 and mixes there with the compressed gas flow that enters the mixing channel 17 through the nozzle 14. The steam/gas mixture thus formed in the mixing channel 17 finally flows through the discharge pipe 22 into the liquid for heating and foaming it (FIG. 1).

[0052] The measuring signal of the temperature sensor 8 serves as a criterion for the termination of the foaming process. The liquid heats up due to the supply of steam. Therefore, when a predetermined temperature threshold is reached, the frothing process is terminated. In the case of milk as liquid F, this is appropriate because no further frothing takes place above a certain temperature due to coagulation of the milk proteins. In this case, both the switching valve 5 and the steam valve 7 are closed simultaneously by the control device 9 as soon as the temperature sensor 8 detects the predetermined temperature threshold.

[0053] The expansion chamber 15 and the nozzle 14 act as a damping element (“snubber”) which exerts a damping effect on the pressure pulses generated by the switching valve 5. This results in a damped temporal pressure curve p(t) of the pressurized gas flow flowing through the nozzle 14 from the expansion chamber 15 with damped, periodically repeating pressure peaks p0.

[0054] The resulting temporal pressure curve p(t) of the pressurized gas flowing into the mixing channel 17 is shown schematically in FIG. 3 for three different frequencies f1, f2 and f3. As can be seen from FIG. 3, the temporal pressure curve p(t) has periodically repeating and plateau-shaped flattened pressure peaks (p0), whereby each pressure peak (p0) up to the temporally following pressure peak has an exponentially decreasing pressure curve due to the damping effect of the damping element (15, 14), which can be described by the relation p(t)=p0.Math.e.sup.−t/τ, whereby the time constant τ depends on the volume of the expansion chamber 15 and the flow cross-section of the nozzle 14. The (maximum) amplitude of the (plateau-shaped flattened) pressure peaks (p0) depends on the constant pressure of the pressurized gas flow, which is set in the first part 3a of the conveying means 3 and kept at a predetermined constant level.

[0055] Each pressure peak has a constant, maximum pressure level (p0) over a predetermined time span t0, whereby the time span t0 is determined by the opening times (i.e. the pulse duration of the pressure pulses) of the switching valve 5 controlled by the control apparatus 9. In order to avoid influencing the subsequent exponential drop in pressure, the time span t0 should be chosen as short as possible.

[0056] Depending on the selected frequency f and the degree of damping of the damping element formed by the expansion chamber 15 and the nozzle 14, different mean pressure values of the pressurized gas flow averaged over time result, as shown in the diagram in FIG. 3 for the different frequencies f1, f2 and f3. In the diagram of FIG. 3, the time-averaged mean pressure values are indicated as a percentage of the maximum pressure for the frequencies f1, f2 and f3 respectively, whereby the maximum pressure (=100%) corresponds to the constant pressure of the pressurized gas flow which is provided by the pressure reducer 21 and flows into the second part 3b of the conveying medium.

[0057] As can be seen in FIG. 3, the gas stream flowing out of the expansion chamber 15 through the nozzle 14 has a pressure curve p(t) over time with a constant pressure offset (p1). The temporal pressure curve p(t) of the gas flow is therefore composed of the constant pressure offset p1 and the damped pressure peaks p0(t): p(t)=p1+p0(t). The constant pressure offset p1 is selected in such a way that the pressure p(t) of the pressurized gas flow is at all times higher than the pressure of the steam flow introduced via the ring channel 16 into the mixing channel 17.

[0058] In the event of a pressure drop in the expansion chamber 15, the non-return valve 20 prevents steam from the steam line 6 or liquid F from the container 10 from entering the switching valve 5. In the simplest case, the nozzle 14 can have a fixed flow cross-section. However, it can also be provided that the flow cross-section of the nozzle 14 can be controlled, for which purpose the nozzle 14 can be designed, for example, as a controllable throttle valve.

[0059] FIG. 4 shows a second embodiment of an apparatus according to the invention for heating and/or foaming a liquid. With this apparatus, a liquid, such as milk, can be simultaneously heated and foamed in a mixing device.

[0060] The apparatus shown in FIG. 4 comprises a container 10 for holding the liquid to be heated and foamed, a steam line 6 connected to a steam generator 1, a compressed gas line 4 connected to a source of compressed gas 2, and a mixing device 30 in communication with the steam line 6, the compressed gas line 4 and the container 10. The source of compressed gas 2 may be, for example, a compressor which draws in and compresses ambient air. The steam generator 1 may contain a hot water boiler which heats water to temperatures above boiling point. A steam valve 7 is arranged in the steam line 6 for opening and closing the steam line 6.

[0061] The substantially cylindrical mixing device 30 comprises a first inlet 30a arranged at the lower end of the mixing device 30 and a second inlet 30b arranged laterally approximately in the middle of the mixing device 30. Furthermore, the mixing device 30 has an output 30c at its upper end, to which an output line 9 is connected. The embodiment of an apparatus according to the invention shown in FIG. 4 further comprises a conveying means 3 for generating a steam/pressure mixture. The conveying means 3 is designed as shown in FIG. 2 and is connected to the compressed gas line 4 and to the steam line 6. Furthermore, an outlet of the conveying means 3 is connected to the first inlet 30a of the mixing device 30 via a discharge line 22. The design and function of the conveying means 3 for generating a steam/pressure mixture corresponds to the embodiment of the invention according to FIGS. 1 to 3.

[0062] The second inlet 30b of the mixing device 30 is connected to the container 10 via a liquid line 8. Preferably, one end of the liquid line 8 opens into an opening in the bottom of the container 10, as shown in FIG. 4. A nozzle 11 is arranged at the other end of the liquid line 8, which opens into the second inlet 30b of the mixing device 30. The nozzle 11 is shown outside the mixing device 30 in FIG. 4 for the sake of clarity, but is actually located in the area of the second inlet 30b of the mixing device 30.

[0063] The mixing device 30 is preferably designed as the heater unit described in WO 2017/063936 A1. WO 2017/063 936A1 is taken into reference to in this respect. The mixing device 30 comprises in particular a linear channel extending along the cylindrical mixing device 30 and standing vertically, which extends from the first inlet 30a of the mixing device 30 to its outlet 30c, wherein the steam/compressed gas mixture flows upwards in the linear channel against the force of gravity.

[0064] A branch line 12 branches off from the compressed gas line 4, and runs from the compressed gas source 2 to an inlet of the conveying means 3, which is connected to the container 10. It is also expedient that the branch line 12 opens into the bottom of the container 10, as can be seen in FIG. 4.

[0065] A switchable shut-off valve 26 is arranged in the branch line 12, with which the branch line 12 can be opened and closed. Furthermore, a pressure release valve 23 and a pressure sensor 24 are provided in the branch line 12.

[0066] An adjustable pressure reducer 21 is arranged in the compressed gas line 4. The pressure reducer 21 can be an adjustable pressure relief valve, for example. Furthermore, a switching valve 5 is arranged in the compressed gas line 4 upstream of the conveying means 3, which is expediently designed as a solenoid valve and is separated from the conveying means 3 in the embodiment example of FIG. 4.

[0067] To detect the temperature of the liquid in the container 10, the latter is coupled to a temperature sensor 27. To detect the temperature of the heated and foamed liquid, another temperature sensor 25 is coupled to the outlet pipe 9.

[0068] For heating and simultaneous foaming of the liquid, the compressed gas source 2 generates a pressurized gas, in particular compressed air, at a constant pressure. The pressure of the pressurized gas provided by the pressurized gas source 2 is regulated to a desired value by the pressure reducer 21 and introduced into the pressurized gas line 4. The switching valve 5 arranged in the compressed gas line 4 or integrated in the conveying means 3 is preferably opened and closed periodically so that periodic pressure pulses of the compressed gas are supplied to the expansion chamber 15 of the conveying means 3. At the same time, hot steam provided by the steam generator 1 is supplied to the conveying means 3 via the steam line 6 when the steam valve 7 is open. The pressure pulses of the compressed gas and the hot steam are mixed together in the conveying means 3 to produce a steam/pressure mixture, as explained above with reference to FIG. 2. The pulsed steam/pressure gas mixture formed in this way in the mixing channel 17 of the conveying means 3 is discharged through the discharge line 22 and directed to the first inlet 30a of the mixing device 30.

[0069] At the same time, the mixing device 30 is supplied with (cold) liquid from the container 10 via the second inlet 30b and the liquid line 8 connected thereto. In order to provide a supply pressure which is sufficient to transfer the liquid from the container 10 through the liquid line 8 and through the nozzle 11 into the mixing device 30, pressurized gas is introduced into the container 10 via the branch line 12 when the shut-off valve 26 is open and the pressure release valve 23 is closed. This creates an overpressure in the container 10, which conveys the liquid via the liquid line 8 and through the nozzle 11 into the second inlet 30b of the mixing device 30.

[0070] The steam/compressed gas mixture introduced at the first inlet 30a and the liquid introduced at the second inlet 30b are mixed in the mixing device 30, whereby the liquid is heated by the hot steam of the steam/compressed gas mixture and simultaneously foamed by the (damped) pressure pulses of the compressed gas. The heated liquid foam is discharged via the outlet line 9 and can be introduced into a collecting container 28, for example a cup, which is arranged at the mouth of the outlet line 9 and is open at the top.

[0071] The controllable valves, i.e. the steam valve 7, the switching valve 5, the shut-off valve 22 and the pressure release valve 23, as well as the adjustable pressure reducer 21 and the output of the steam generator 1 are controlled by a central control device. The valves and the pressure reducer 21 are controlled as a function of the pressure in the branch line 12 detected by the pressure sensor 24. The measurement signal from the temperature sensor 27 is used to monitor the temperature of the heated and foamed liquid. If the temperature detected by the temperature sensor 27 deviates from a set target temperature, the temperature of the heated and foamed liquid can be readjusted by either adjusting the pressure in the branch line 21 detected by the pressure sensor 24 (via the pressure reducer 21) and thus the amount of cold liquid supplied per unit of time and/or by adjusting the steam pressure provided by the steam generator 1 and thus the heating power used to heat the liquid by the control device.