Cooling system using vacuum cooling

Abstract

Cooling system using vacuum cooling and method for operating the same, said system having a refrigerant circulation, the refrigerant circulation comprising: a vacuum chamber, a vacuum pump, a first flow of a heat exchanger of the cooling system having at least two flows, and a condensate reservoir, wherein the vacuum chamber, the vacuum pump, the first flow and the condensate reservoir are connected, wherein a refrigerant contained within the refrigerant circulation is liquid at 20 C and 101325 Pa, wherein the system further comprises a separator having an inlet connected to the condensate reservoir for receiving a gaseous phase from the condensate reservoir, an outlet connected to an inlet of the vacuum pump and an exhaust for leakage air.

Claims

1. A cooling system using vacuum cooling and having a refrigerant circulation, the refrigerant circulation comprising: a vacuum chamber, a vacuum pump, a first flow of a heat exchanger of the cooling system, a condensate reservoir, and a separator, wherein the heat exchanger has at least two flows, wherein the vacuum chamber, the vacuum pump, the first flow and the condensate reservoir are connected, wherein a refrigerant contained within the refrigerant circulation is liquid at 20° C. and 101325 Pa, wherein the separator has an inlet connected to the condensate reservoir for receiving a gaseous phase from the condensate reservoir, an outlet connected to an inlet of the vacuum pump and an exhaust for leakage air, and wherein the separator comprises a capturing means for capturing refrigerant vapour from the gaseous phase received via the inlet.

2. The system according to claim 1, wherein the refrigerant has a lower boiling point than water at 1 atm.

3. The system according to claim 2, wherein the refrigerant is an acetone-based refrigerant.

4. The system according to claim 1, wherein the capturing means comprises a spray chamber for producing a mist of a capturing solvent.

5. The system according to claim 4, wherein the separator comprises a first phase separator for separating leakage air in the gaseous phase from a solution of refrigerant in the capturing solvent.

6. The system according to claim 5, wherein the separator comprises a second phase separator for separating refrigerant in the gaseous phase from the solution of refrigerant in the capturing solvent, wherein the second phase separator is connected to the vacuum pump.

7. The system according to claim 4, wherein the separator comprises a solvent circulation for the capturing solvent, wherein said solvent circulation comprises a circulation pump.

8. The system according to claim 7, wherein said solvent circulation comprises a second flow of the heat exchanger and a radiator for dissipating heat from the capturing solvent to the surrounding atmosphere.

9. A method to operate a cooling system using vacuum cooling and having a refrigerant circulation, the refrigerant circulation comprising: a vacuum chamber, a vacuum pump, a first flow of a heat exchanger of the cooling system, and a condensate reservoir, wherein the heat exchanger has at least two flows, wherein the vacuum chamber, the vacuum pump, the first flow and the condensate reservoir are connected, wherein a refrigerant contained within the refrigerant circulation is liquid at 20 C and 101325 Pa, wherein the method comprises the following steps: withdrawing a gaseous phase from the refrigerant circulation at the condensate reservoir, separating refrigerant from the gaseous phase, exhausting the remaining gaseous phase, and returning the separated refrigerant to the refrigerant circulation, and wherein the separating step comprises capturing refrigerant vapour in the gaseous phase with a mist of a capturing solvent, in which the refrigerant dissolves eagerly.

10. The method according to claim 9, wherein the capturing solvent has a higher boiling point than the refrigerant.

11. The method according to claim 9, wherein all separating steps are performed at approximately room temperature.

12. The method according to claim 9, wherein the separating step further comprises phase separating the remaining gaseous phase from a solution of refrigerant in the capturing solvent.

13. The method according to claim 12, wherein the separating step further comprises phase separating the refrigerant from a solution of refrigerant in the capturing solvent.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) Referring now to the drawing, wherein the figure is for purposes of illustrating the present disclosure and not for purposes of limiting the same,

(2) FIG. 1 schematically shows a cooling system based on vacuum cooling according to the present disclosure; and

(3) FIG. 2 shows an example of a vacuum pump performance curve.

DETAILED DESCRIPTION

(4) FIG. 1 shows a cooling system 1 using vacuum cooling and having a refrigerant circulation 2. The refrigerant circulation 2 comprises a vacuum chamber 3, a vacuum pump 4, a first flow 5 of a heat exchanger 6 and a condensate reservoir 7. The vacuum chamber 3 may be arranged around a receptacle 8, e.g. for a beverage container 9 (usually a can or bottle). Heat exchange between the vacuum chamber 3 and that the beverage container 9 can be facilitated by a small amount of water 10 surrounding the beverage container 9. The beverage container 9 may be connected to a motor (not shown) to spin it to help dispense the heat inside the container 9 faster. The vacuum pump 4 is an oil-free pump, e.g. a piston pump or a diaphragm pump. It is directly connected to the vacuum chamber 3, more specifically an upper part 11 of the vacuum chamber 3, in order to be able to evacuate the vacuum chamber 3. The heat exchanger 6 can be a plate heat exchanger. The condensate reservoir 7 is connected to an electrostatic discharge 12 to avoid any static charges building up in the presence of a flammable refrigerant and leakage air.

(5) The refrigerant 13 contained within the refrigerant circulation 2 is 99 vol % pure acetone. This refrigerant 13 has a boiling point of 56° C. at 1 atm and is therefore liquid at normal temperature and pressure. In warmer locations, i.e. at relatively higher expected surrounding temperature, a refrigerant having a slightly higher boiling point may be used; for example, ethanol with a boiling point of 78° C. at 1 atm. In the vacuum chamber 3, the liquid refrigerant 13 surrounds the receptacle 8 in order to facilitate direct heat transfer from an object or substance contained in the receptacle 8 into the liquid refrigerant 13 contained in the vacuum chamber 3.

(6) The system 1 comprises a separator 14. The separator 14 has an inlet 15 connected to the condensate reservoir 7 for receiving a gaseous phase 16 from the condensate reservoir 7, an outlet 17 connected to an inlet 18 of the vacuum pump 4 and an exhaust 19 for leakage air. Moreover, the separator 14 comprises a capturing means 20 for capturing refrigerant vapour from the gaseous phase 16 received via the inlet 15. The capturing means 20 comprises a spray chamber 21 for producing a mist of water, which is used as a capturing solvent 22 for the refrigerant 13.

(7) Downstream of the spray chamber 21, the separator 14 comprises a first phase separator 23 for separating leakage air in a gaseous phase from a solution of refrigerant in a capturing solvent. The first phase separator 23 is formed by a main water tank 24.

(8) The spray chamber 21 and the main water tank 24 are parts of a solvent circulation 25 of the separator 14 for a capturing solvent (for simplicity, but without limitation, the dashed border indicating the separator 14 does not enclose the complete solvent circulation 25). The solvent circulation 25 comprises a circulation pump 26. Moreover, the solvent circulation 25 comprises a second flow 27 of the heat exchanger 6 and a radiator 28 for dissipating heat from the capturing solvent 22 (water) to the surrounding atmosphere. The circulation pump 26 is used to convey water from the main water tank 24 through the heat exchanger 6, the radiator 28 and the spray chamber 21 back to the main water tank 24. In the present example, the circulation pump 26 is arranged downstream of the heat exchanger 6 (its second flow 27) and upstream of the radiator 28.

(9) The separator 14 comprises a second phase separator 29 for separating refrigerant in a gaseous phase from a solution of refrigerant in a capturing solvent. The phase separation is performed inside a recovery tank 30 of the second phase separator 29. The recovery tank 30 is connected to the vacuum pump 4 for controlling the pressure inside the recovery tank 30. The connection between the recovery tank 30 and the vacuum pump 4 comprises a recovery outlet valve 31. The recovery tank 30 is also connected to the main water tank 24 via a recovery inlet valve 32. Finally, the recovery tank 30 comprises a ventilation valve 33.

(10) In operation, the example shown in FIG. 1 comprises multiple circulations or cycles: first, the primary cooling cycle formed by the refrigerant circulation 2; second, a secondary cooling cycle formed by the solvent circulation 25; and third, a regenerative cycle for recovering refrigerant from a gaseous phase. The regenerative cycle overlaps with the primary cooling cycle in a first section between the vacuum pump 4 and the condensate reservoir 7 and overlaps with the secondary cooling cycle in a second section between the capturing means 20 and the second phase separator 30. In the following, the different cycles will be explained in more detail.

(11) When first starting operation of the system, the cooling and regenerative cycle starts at room temperature and pressure inside the vacuum chamber 3. The acetone refrigerant 13 is mainly in a liquid state of aggregation within the vacuum chamber 3. Once the vacuum pump 4 started, it lowers the pressure inside the vacuum chamber 3 down to approximately 9870 Pa (−27 inHg) or below. While the pressure continues to be lowered, acetone refrigerant 13 inside the vacuum chamber 3 will start to boil off and evaporate at lower and lower temperatures absorbing heat from within the body of liquid acetone refrigerant 13 itself and from the beverage container 9. At approximately 9870 Pa (−27 inHg) pressure, acetone can still boil down to zero degree Celsius.

(12) On the outlet 34 of the vacuum pump 4 the pressure will be close to 1 atm and temperature of the vapor will stay at about 56° C. Since Acetone boils at 56° C., the vapour will be at this exact temperature at the moment of evaporation and it will go through the vacuum pump piston all the way across the vacuum pump outlet almost at the same temperature. Since leaks are inevitable in any vacuum system, the vacuum pump 4 will probably suck in air from the surrounding environment, which will be transported as leakage air from the vacuum pump outlet 34. Therefore, the pressure at the outlet is equalized with the surroundings, which is around 1 atm; better vacuum pumps might guarantee less leaks, hence lower outlet pressure. The mixture of acetone refrigerant vapour and leakage air enters the heat exchanger 6, where it exchanges heat with water coming from the main water tank 24. Since the water is staying at room temperature (approximately 22° C.), the acetone refrigerant will instantly condense back to liquid state and lose all its heat to the water. Once the acetone refrigerant is condensed, it enters the condensate reservoir 7. The condensate reservoir 7 acts as a phase separator between condensed and liquid refrigerant in a lower part 35 and the remaining refrigerant vapour mixed with leakage air in an upper part 36.

(13) From the condensate reservoir 7, the liquid refrigerant is sucked through a narrow tubing 37 into the vacuum chamber 3 due to the negative pressure. The diameter of the tubing may be between 0.1 and 0.5 mm. The choice of diameter depends on the rate of condensation of the refrigerant and the volume of the reservoir at the condensate reservoir 7. Thus, it can be configured to conduct at the foreseen pressure difference at maximum the same amount of refrigerant that can be condensed in the heat exchanger 6 and the condensate reservoir 7 at the foreseen temperature difference. The tube diameter is small enough to maintain a target maximum pressure difference when the vacuum pump 4 is operating at its maximum capacity or below. In other words, the diameter should be small enough to essentially avoid a pressure drop in the condensate reservoir 7 and a significant pressure increase and the vacuum chamber 3. When the operation of the vacuum pump 4 is suspended, the vacuum chamber 3 will slowly equalise pressure with the condensate reservoir 7 and the rest of the system. However, after activation of the vacuum pump 4, the pressure gradient between condensate reservoir 7 and vacuum chamber 3 can be built up within a few seconds due to the limited flow rate through the narrow tubing 37. The choice of using a narrow tubing 37 to establish a foreseen pressure gradient helps to minimise the number of moving parts in the system and consequently to minimise the probability of system faults.

(14) During condensation of the vapour acetone refrigerant, the heat will be transferred in the heat exchanger 6 from the first flow 5 containing the refrigerant at a temperature of about 56° C. to the second flow 27 containing water at about room temperature. The circulation pump 26 circulates the water from the main water tank 24 down to the heat exchanger 6 and further down to the radiator 28, where its extra heat (i.e. for a temperature above room temperature) is dissipated to the surrounding atmosphere and get back to the main water tank 24 at room temperature of approximately 22° C.

(15) Although the condensation of the vapour acetone refrigerant could reach high levels and most of it will be recovered in the heat exchanger 6 to be reused, it may not be 100% recovery since there can always be acetone vapour saturated in the leakage air leaked into the system. Since any loss of refrigerant should be avoided, the refrigerant in the system should be recovered for re-use as completely as possible. According to the present example, this recovery is achieved by withdrawing a gaseous phase from the refrigerant circulation 2 at the condensate reservoir 7, separating refrigerant from the gaseous phase, exhausting the remaining gaseous phase, and returning the separated refrigerant to the refrigerant circulation 2.

(16) More in detail, the step of separating refrigerant from the gaseous phase comprises three stages: the first stage for capturing refrigerant vapour in the gaseous phase with a mist of a capturing solvent, the second stage for separating the remaining gaseous phase from a solution of refrigerant in the capturing solvent, and the third stage for separating the refrigerant from the solution of refrigerant in the capturing solvent. As mentioned above, the capturing solvent for the acetone refrigerant can be water. Generally, it will be a solvent, in which the refrigerant dissolves eagerly.

(17) For the first stage, the water pumped by the circulation pump 26 through the radiator 28 will arrive at a water spray nozzle 38 of the spray chamber 21. This nozzle 38 will turn the arriving water to a mist that can mix with the gaseous phase received from the condensate reservoir 7 (i.e. essentially a saturated mixture of leakage air and vapour acetone refrigerant). Since acetone is highly miscible and easily dissolves in water due to its dipole moment of 2.91D, and water is a very polar substance, the water mist will attract and absorb any remaining acetone vapour that is still mixed and carried in the leakage air. The mist (now a water/acetone solution mixed in air) is guided to the main water tank 24.

(18) In the main water tank 24, acting as the first phase separator 23, the leakage air that is still in the system will vent out down through a submerged inlet 39 into the water tank 24. This requires a pressure slightly elevated over the surroundings (e.g. above 1 atm) in the spray chamber and back through the recovery tank and the heat exchanger, in order for the leakage air to be pushed below the underwater barrier. Although after the acetone vapour condenses after the heat exchanger, there will be slight pressure drop due to a lot of gaseous mass condensed to liquid, though the continuity of pumping there will eventually build-up pressure upstream of the water tank 24 high enough to push the leakage air through the water and out of the system. The vacuum pump acts as a vacuum generator on one side and as a compressor on the other, so it will eventually push the gases out.

(19) The submerged inlet 39 will serve two purposes: first, if there is still any acetone vapour in the gaseous phase, mixing it with water will absorb any acetone left; second, the water can act as a fire extinguisher, since acetone is highly flammable, in case there is a fire outside the system the first line of contact with the outside environment is the water so it will inhibit any fire from the start. From the main water tank 24, the leakage air raising from the liquid solution at room temperature will be vented out through the exhaust outlet 19 comprising a one-way valve 40.

(20) Since there will be a small amount of acetone dissolved in the main water tank 24, it needs to be recovered. For this purpose, the recovery tank 30 will trap some of the water from the main water tank 24 and will act as a temporary vacuum chamber. By closing certain valves, the vacuum pump 4 is used to evacuate the temporary vacuum chamber, while the pressure in the main vacuum chamber 3 is not affected. As a consequence, the pressure in the temporary working chamber decreases until the acetone refrigerant acetone dissolved in the water starts to boil off and can be phase separated and extracted.

(21) The regenerative cycle follows an intermittent operation, alternating between a regeneration phase where the temporary vacuum chamber is evacuated and refrigerant returned to the refrigerant circulation 2, and a reloading phase where the pressure in the temporary vacuum chamber is equalized with the main water tank 24 and the water contained in the temporary vacuum chamber is replaced. To start the regenerative cycle with a regeneration phase, the vacuum chamber outlet valve 41 and the ventilation valve 33 are closed and the recovery outlet valve 31 is opened. Once the vacuum pump 4 starts during the regeneration phase, the pressure inside the temporary vacuum chamber will be lowered. Since the pressure in the main water tank 24 is the atmospheric pressure and the temporary vacuum chamber is at a lower pressure now, water will flow to the lower pressure, from the main water tank 24 into the temporary vacuum chamber (i.e. the recovery tank 30). The connection between the two comprises a recovery inlet valve 32 formed by a floating device. Once the water level in the main water tank 24 reaches a certain minimum level, the floating device will close the outlet of the main water tank 24 to the recovery tank 30, hence isolating the temporary vacuum chamber into an airtight chamber that can be evacuated.

(22) Once the pressure starts to decrease in the temporary vacuum chamber, the acetone refrigerant will begin to boil off out of the capturing solvent (here: water) at room temperature and evaporate, turning to a vapour, because the capturing solvent has a higher boiling point than the refrigerant. The acetone refrigerant vapour will be withdrawn from the temporary vacuum chamber and returned to the refrigerant circulation 2 at the vacuum pump 4, following the primary cooling cycle described above. Once a certain target vacuum (e.g. ˜3110 Pa) is achieved in the temporary vacuum chamber, the regeneration phase ends and the recovery tank 30 moves to the reloading phase. At this level of vacuum at room temperature (or a bit less than room temperature since boiling off acetone will cool the water) means there isn't much acetone left in the system to boil. The recovery outlet valve 31 is closed and the vacuum chamber outlet valve 41 is opened. At the same time, the ventilation valve 33 is opened to depressurize the recovery tank 30. Once the recovery tank 30 equalises the pressure difference to the main water tank 24, the floating device 32 opens and the water contained in the recovery tank 30 flows down to the main water tank 24 under the influence of gravity due to the recovery tank 30 being at a higher level than the main water tank 24.