System and method for ohmic heating of a fluid

Abstract

Disclosed is a system for ohmic heating of a fluid which includes at least one chamber for receiving the fluid and at least two units each including at least one electrode. Each of the at least one electrode is associated to at least one device for galvanic separation. The electrodes of each of the two units are disposed in the chamber at a distance apart from one another and the device for galvanic separation is disposed outside of the chamber. The system also includes at least one frequency inverter that is electrically connected to the at least two electrode-units for operating the at least two electrode-units.

Claims

1. A system for ohmic heating of a fluid comprising (a) at least one chamber for receiving the fluid; (b) at least two units each comprising at least one electrode, wherein each of the at least one electrodes is associated with at least one means for galvanic separation, wherein the electrodes of each of the two units are disposed in the chamber at a distance apart from one another and the means for galvanic separation are disposed outside of the chamber; (c) at least one frequency inverter that is electrically connected to the at least two electrode-units for operating the at least two electrode-units, and configured to transform the frequency of the applied voltage to a frequency of over 200 kHz; and (d) a cooling unit placed in front of the heating chamber such that the fluid to be heated passes the cooling unit and is thereby pre-heated before entering the heating chamber, wherein the system is configured to adjust the pulse frequency continuously to control the heating performance.

2. The system according to claim 1, wherein the at least one means for galvanic separation is at least one capacitor or at least one isolation transformer.

3. The system according to claim 2, wherein the at least one capacitor is a safety capacitor also designated as X- or Y class capacitor.

4. The system according to claim 1, wherein additional elements are provided in one or each of the electrode-galvanic separation means-units.

5. The system according to claim 4, wherein one or more additional capacitors are provided as additional elements, preferably in series or parallel connection to form a resonate network, or one or more coils in series or parallel connection to form a resonate network are provided as additional elements, or sensors for optimizing the switching behaviour, for measuring the received power or the temperature of the fluid are provided as additional elements.

6. The system according to claim 1, wherein multiple electrode pairs are provided.

7. The system according to claim 1, wherein the at least one frequency inverter comprises at least one bridge circuit.

8. The system according to claim 1, wherein the at least one frequency converter comprises at least one bridge circuit comprising at least one switching arrangement of at least two switches and at least one center tap, wherein the at least one center tap is coupled to at least one electrode-galvanic separation means-unit.

9. The system according to claim 8, wherein the at least one switching arrangement comprises at least four switches, in particular in case of a full bridge.

10. The system according to claim 8, wherein each electronic switch of the switching arrangement is coupled to at least one control unit.

11. The system according to claim 10, wherein the at least one control unit is a micro-controller.

12. The system according to claim 1, further comprising at least one voltage supply for the at least one frequency inverter, wherein in particular the at least one voltage supply comprises a rectifier, in particular a diode rectifier.

13. The system according to claim 1, wherein the at least one chamber is a container, a vessel or a tube having in each case at least one inlet and at least one outlet for the fluid.

14. A cooling unit for the electronic components of a system according to claim 1, wherein the fluid to be heated is used as cooling fluid.

15. A method for ohmic heating a fluid in a system according to claim 1, comprising the steps of: providing a voltage to the at least one frequency inverter by at least one voltage supplier; and controlling the at least one frequency inverter such that the polarity of the voltage alternates over the at least two electrode-galvanic separation means-units.

16. The method according to claim 15, wherein a rectified voltage U.sub.net between 110 and 240 V and a frequency f.sub.net between 50 and 60 Hz is applied to the at least one frequency inverter.

17. The method according to claim 15, wherein the polarity of the voltage is controlled by the at least one control unit.

18. The method according to claim 15, wherein the polarity of the voltage is controlled such that a pulse frequency of up to 3 MHz is obtained.

19. The method according to claim 15, wherein the pulse frequency is adjusted continuously to control the heating performance.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The proposed solution is now explained in more detail by means of the following examples and with reference to the following figures:

(2) FIG. 1 shows a schematic view of the basic functioning of a resistance heater (ohmic heater);

(3) FIG. 2A shows a general schematic view of the basic functioning of a system according to the proposed solution;

(4) FIG. 2B shows a schematic view of a first embodiment of a system according to the proposed solution;

(5) FIG. 2C shows a schematic view of a second embodiment of a system according to the proposed solution;

(6) FIG. 2D shows a schematic view of a third embodiment of a system according to the proposed solution;

(7) FIG. 2E shows a schematic view of a fourth embodiment of a system according to the proposed solution;

(8) FIG. 2F shows a schematic view of a fifth embodiment of a system according to the proposed solution;

(9) FIG. 2G shows a schematic view of a sixth embodiment of a system according to the proposed solution;

(10) FIG. 2H shows a schematic view of a seventh embodiment of a system according to the proposed solution;

(11) FIG. 2I shows a schematic view of an eighth embodiment of a system according to the proposed solution;

(12) FIG. 2J schematic view of a ninth embodiment of a system according to the proposed solution;

(13) FIG. 2K shows a schematic view of an embodiment of a system according to the proposed solution with a cooling unit;

(14) FIG. 3A shows a schematic view of full bridge comprising the system of FIG. 2B;

(15) FIG. 3B shows a schematic view of full bridge comprising the system of FIG. 2C;

(16) FIG. 4 shows a schematic view of a half bridges comprising the system of FIG. 2B;

(17) FIG. 5 shows a schematic view of a voltage supply;

(18) FIG. 6 shows a schematic view of a control unit;

(19) FIG. 7 shows an example of a pulse frequency generated and applied by the system according to the proposed solution;

(20) FIG. 8 shows a use of the system according to the proposed solution in a milk heating set up;

(21) FIG. 9 shows a use of the system according to the proposed solution in a booster application;

(22) FIG. 10 shows a use of the system according to the proposed solution in a continuous flow heater set up.

DESCRIPTION OF THE INVENTION

(23) It is to be understood that in all applications as illustrated by the embodiments a universal voltage source can be used.

(24) FIG. 1 illustrates the basic principle of a resistance heater (ohmic heater). The fluid to be heated is guided in a continuous flow through the heating chamber 1. Two electrically conducting plates (electrodes 4a, 4b provided in the chamber 1) are contacted with the fluid; a voltage is supplied subsequently to the electrodes 4a, 4b. This causes a current flow through the fluid (such as water) to be heated. The fluid represents an electrical resistance causing a power loss or power dissipation. This power loss is converted in the fluid into heat. Thus, the fluid serves as heating element and the heat is generated directly in the fluid.

(25) FIG. 2A illustrates the basic principle of the present system. The mains voltage is chopped into multiple high frequency portions by a frequency inverter 10 in order to increase the voltage frequency. The electrodes 4a, 4b are decoupled or delinked by galvanic isolation means 5. The fluid flows through the chamber 1 and is subsequently heated when applying the mains voltage. In addition, multiple of such systems with different electrode distances can be cascaded or arranged one after the other in order to cover a larger conductivity range of the fluid passing the heating chamber.

(26) In the embodiment of FIG. 2B the galvanic isolation means 5 are provided as capacitors 5a, 5b. Electrodes 4a, 4b and capacitors 5a, 5b form an electrode-capacitor unit 6a, 6b, respectively.

(27) The galvanic isolation means 5 may also be provided as an isolation transformer 5c (see FIG. 2C).

(28) The capacitors have the advantage over a transformer in that they are smaller, have less weight, cheaper and generate less power loss. The disadvantage is however that capacitors have a larger leakage current (i.e. current that flows in case of a ground fault) compared to transformers.

(29) According to the embodiment as illustrated in FIG. 2D additional elements 11 are arranged in the electrode-capacitor path. The additional element 11 may be a coil for compensating the capacitive reactance and for increasing the converted power in the liquid. This minimizes the reactive power.

(30) According to the embodiment as illustrated in FIG. 2E the additional elements 11 may also be arranged in parallel as well as in series.

(31) The embodiment of FIG. 2F shows a system wherein capacitors are connected to coils for resonate coupling, while the embodiment of FIG. 2G shows a system wherein a transformer is connected to an inductor-capacitor network for resonant coupling. In this way it is possible to optimize the transfer behaviour

(32) The embodiment of FIG. 2H shows an equivalent circuit diagram representing the behaviour of a real transformer utilizing two inductive coils with the inductance L1 and L2 and an ideal transformer T. The inductances of the coils are determined by construction and geometry of the real transformer. The clamps K1 are connected to an inverter and the clamps K2 are connected to electrodes of the heating chamber.

(33) According to the embodiment of FIG. 2I it is possible to operate multiple heating chambers in parallel.

(34) In the embodiment of FIG. 2J multiple electrode pairs are added to the system by means of switches, for example electro-mechanical relays, in order to extend the conductivity range, in which the system operates reliable, even further.

(35) FIG. 2K shows an example of the system with a cooling unit. Here, the waste heat of the electrical components is used for pre-heating the fluid to be heated. The components are connected thermally to a cooling body 12 which is subsequently cooled by the incoming fluid. The pre-heated fluid flows then into the heating chamber 1 in which the fluid is heated to the desired final temperature

(36) In FIGS. 3A and 3B a full bridge arrangement as frequency inverter is illustrated. Here capacitors 5a, 5b as galvanic separation means (FIG. 3A) or isolation transformer 5c as galvanic separation means (FIG. 3B) are coupled to respective electrodes 4a, 4b forming an electrode-capacitor unit 6a, 6b or transformer-electrode-pair unit.

(37) Each of the electrode capacitor units 6a, 6b (or transformer-electrode-pair unit) is in turn linked and controlled by a switching arrangement comprising four switches 2 with one center tap 7 between two switches. The switches 2 are controlled by the control unit 3 (see FIG. 6) that is linked to every switch separately by S1, S2, S3, S4.

(38) The mains voltage to the circuit is provided by a voltage supply 8 (see FIG. 5). The mains voltage is rectified by using a rectifier 9 in form of a diode rectifier.

(39) In FIG. 4 a half bridge arrangement as frequency inverter is illustrated. Such a half bridge arrangement comprises in contrast to the full bridge arrangement only two switches. The center tap 7 is laid either onto the lower potential or the higher potential for alternating the voltage and frequency chopping.

Example 1

(40) The frequency inverter according to the proposed solution is made of a bridge circuit with four electronic switches (S1, S2, S3, S4) such as FET, e.g. IGBT and others (see FIG. 3). The bridge circuit may be realized as a full bridge or half bridge.

(41) There are center taps between two switches, namely one center tap between switches S1 and S2 and a second center tap between switches S3 and S4.

(42) A mains voltage of 110 to 240 V with a mains frequency of 50 to 60 Hz is applied to the circuit. The mains voltage is rectified by using a rectifier in the form of a diode rectifier.

(43) The electronic switches are controlled by a microcontroller in the way that the polarity of the voltage alternates over the center taps. This creates a voltage with the same magnitude as the mains voltage but with an increased frequency.

(44) The frequency can be changed by controlling the microcontroller. A frequency f.sub.p of more than 200 kHz, preferably 300 kHz (FIGS. 6, 7) is applied for ohmic heating for repolarization in order to prevent electrolysis. The applied frequency depends however on the liquid and the performance of the heater and has to be determined for each new set up.

(45) The electrodes and the capacitors (or transformer) are linked to the center taps off the bridge circuit. The electrodes can consist of any suitable material, for example aluminum.

Example 2

Applications of an Ohmic Heating Device in Coffee Machines

(46) In state of the art coffee machines a variety of heating mechanisms are used to heat the required liquids or to produce steam. These mechanisms range from gas boilers, electric boilers, steam injection or mixing of the liquid at two different temperatures.

(47) With the new continuous-flow heating device based on the Ohmic heating technology according to the proposed solution an alternative is now available to heat the various liquids such as water, milk, milk foam or syrup. In order to produce the four variations of the added milk; cold/hot milk and cold/hot milk foam with a single system, one can use the Ohmic heating device after a milk processing unit capable of foaming the milk in a cold state or just delivering cold milk as depicted in FIG. 8.

(48) The Ohmic heating device must not necessarily be placed in the coffee machine and could be placed somewhere after the milk processing unit. Therefore, with this setup all four milk products can be generated by turning the two modules in different combinations on or off. This gives the advantage that the required milk products can be delivered in a simple and streamlined setup without the need of bypassing the heating device or using a steam injection mechanism as needed by state of the art solutions.

(49) To provide water at the various temperatures that the coffee machine requires to deliver the different types of products such as coffee, tea water, steam or powder products; either a boiler, flow heater, a mixture of hot and cold water or a combination of the mentioned preparation methods is used as of today.

(50) With the Ohmic heating device according to the proposed solution water preparation can be simplified by using it as a booster stage after a conventional boiler or as a standalone continuous-flow heater as shown in FIG. 9 and FIG. 10.

(51) The advantages of using the Ohmic heating device over current solutions to heat water is the ability to set a precise outlet temperature, instant variation of the outlet temperature, no standby power consumption and less maintenance due to drastically reduced scaling of the heating device.

(52) The aforementioned setup with the Ohmic heating device can also be used to generate steam by superheating the water which turns into steam when released to atmospheric pressure.