Thermosyphon Configuration for Cascade Refrigeration Systems

Abstract

The present application provides a thermosyphon for use with a refrigeration system. The thermosyphon may include a primary flow inlet, an angled secondary flow inlet, and a mixed flow outlet. The angled secondary flow inlet may include an angle θ1 of about forty-five degrees or less with respect to the mixed flow outlet.

Description

TECHNICAL FIELD

The present application and the resultant patent relate generally to refrigeration systems and more particularly relate to a cascade refrigeration system using a thermosyphon in communication with a cascade evaporator-condenser the low side cooling cycle components.

BACKGROUND OF THE INVENTION

Cascade refrigeration systems generally include a first side cooling cycle, or a high side cooling cycle, and a second side cooling cycle, or a low side cooling cycle. The two cooling cycles interface through a common heat exchanger, i.e., a cascade evaporator-condenser. The cascade refrigeration system may provide cooling at very low temperatures in a highly efficient manner.

Current refrigeration trends promote the use of ammonia, carbon dioxide, and other types of natural refrigerants instead of conventional hydrofluorocarbon based refrigerants. Cascade refrigeration systems may use ammonia in the high cycle and carbon dioxide in the low cycle. Moreover, there is an interest in improving the overall efficiency of such natural refrigerant based refrigeration systems at least as compared to the conventional hydrofluorocarbon based systems.

There is thus a desire for an improved refrigeration system such as a cascade refrigeration system that provides cooling with increased efficiency with natural or any type of refrigerants. Such an improved refrigeration system may accommodate the high pressures needed for low temperature cascade cooling in an efficient, reliable, and safe manner.

SUMMARY OF THE INVENTION

The present application and the resultant patent thus provide a thermosyphon for use with a refrigeration system. The thermosyphon may include a primary flow inlet, an angled secondary flow inlet, and a mixed flow outlet. The angled secondary flow inlet may include an angle θ1 of about forty-five degrees or less with respect to the mixed flow outlet. The angled flow may improve the mass flow rate or reduce the pressure of the primary inlet flow and the mixed outlet flow as compared to a perpendicular orientation.

The present application and the resultant patent further provide a method of improving a mass flow rate or reducing a pressure loss of a refrigerant to a cascade evaporator-condenser. The method may include the steps of providing a thermosyphon with an outlet in communication with the cascade evaporator-condenser, providing a primary refrigerant flow from a first source, providing a secondary refrigerant flow from a second source, mixing the primary refrigerant flow and the secondary refrigerant flow at an angle less than about ninety degrees, and providing the mixed refrigerant flow to the cascade evaporator-condenser via the thermosyphon outlet.

The present application and the resultant patent further provide a thermosyphon for use with a refrigeration system. The thermosyphon may include a tank inlet in communication with a liquid vapor separator tank, an angled compressor inlet in communication with one or more compressors, and a cascade outlet in communication with a cascade evaporator-condenser. The angled compressor inlet may include an angle of about forty-five degrees or less with respect to the cascade outlet.

These and other features and improvements of the present application and the resultant patent will become apparent to one of ordinary skill in the art upon review of the following detailed description when taken in conjunction with the several drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a known cascade refrigeration system with a high side cycle and a low side cycle.

FIG. 2 is a schematic diagram of a thermosyphon configuration as used in a known cascade refrigeration system.

FIG. 3 is an alternative embodiment of a known thermosyphon configuration.

FIG. 4 is a thermosyphon configuration as may be described herein with an improved mass flow rate or reduced pressure loss.

FIG. 5 is an alternative embodiment of a thermosyphon configuration as may be described herein.

FIG. 6 is an alternative embodiment of a thermosyphon configuration as may be described herein.

DETAILED DESCRIPTION

Referring now to the drawings, in which like numerals refer to like elements throughout the several views, FIG. 1 shows an example of a cascade refrigeration system 100. The cascade refrigeration system 100 may be used to cool any type of enclosure for use in, for example, supermarkets, cold storage, and the like. The cascade refrigeration system 100 also may be applicable to other types of heating, ventilation, and air conditioning applications and/or different types of commercial and/or industrial applications. The overall cascade refrigeration system 100 may have any suitable size or capacity. Other types of refrigeration systems, cycled, and components also may be used herein.

Generally described, the cascade refrigeration system 100 may include a first or a high side cycle 110 and a second or a low side cycle 120. The high side cycle 110 may include one or more high side compressors 130, a high side oil separator 140, a high side condenser 150, a high side receiver 160, and a high side expansion device 170. The high side cycle 110 also may include a suction/liquid heat exchanger 180 and a suction accumulator 190. The high side cycle 110 may include a flow of a refrigerant 200. The refrigerant 200 may include a flow of ammonia or other type of a refrigerant. The high side cycle 110 components may have any suitable size, shape, configuration, or capacity. The high side cycle 110 may use other and additional components and configurations herein.

The low side cycle 120 similarly may include one or more low side compressors 210, a low side oil separator 220, a low side liquid vapor separator tank 230, one or more low side expansion devices 240, and one or more low side evaporators 250. The low side cycle 120 may include a medium temperature loop 260 with a pump 270 and a number of flow valves 280 as well as a low temperature loop 290. An accumulator 300 also may be used therein. The low side cycle 120 may include a flow of a refrigerant 310. The refrigerant 310 may include a flow of carbon dioxide or other type of a refrigerant. The low side cycle 120 components may have any suitable size, shape, configuration, or capacity. The low side cycle 120 may use other and additional components and configurations herein.

The two cycles 110, 120 may interface through a cascade evaporator/condenser 320. The respective flows of the refrigerants 200, 310 may exchange heat via the cascade evaporator/condenser 320. The cascade evaporator/condenser 320 may have any suitable size shape, configuration, or capacity. Other components and other configurations may be used herein.

The refrigerant 200 may be compressed by the high side compressors 130 and condensed in the high side condenser 150. The refrigerant 200 may be stored in the high side receiver 160 and may be withdrawn as needed to satisfy the load on the cascade evaporator/condenser 320. The refrigerant 200 then may pass through the suction/liquid heat exchanger 180, the high side expansion device 170 and the cascade evaporator/condenser 320. The refrigerant 200 again passes through the suction/liquid heat exchanger 180 and returns to the high side compressors 130. The suction/liquid heat exchanger 180 may be used to sub-cool the refrigerant 200 before entry into the cascade evaporator/condenser 320. Other components and other configurations may be used herein.

The low side cycle 120 may be similar. The carbon dioxide based refrigerant 310 may be compressed by the low side compressors 210 and then pass through the cascade evaporator/condenser 320. The refrigerant 310 may be stored within the low side liquid vapor separator tank 230 and withdrawn as needed. The refrigerant 310 may pass through one or more low side expansion devices 240 and one or more low side evaporators 250. The low side cycle 120 may be separated into the low temperature loop 290 and the medium temperature loop 260. Other components and other configurations may be used herein.

The low side cycle 120 also may use a thermosyphon 330. The thermosyphon 330 provides for the circulation of a fluid, in this case the refrigerant 310, based upon thermal gradients as opposed to mechanical devices such as a pump and the like. In this example, the thermosyphon 330 may have a tank inlet 340 in communication with the low side liquid vapor separator tank 230, a compressor inlet 350 in communication with the low side compressors 210, and a cascade outlet 360 in communication with the cascade evaporator-condenser 320.

In use, the liquid/gas flow of the carbon dioxide refrigerant 310 may be diverted to the low side liquid vapor separator tank 230 where the liquid and vapor may separate therein. The vapor portion may be routed to the cascade evaporator-condenser 320 through the thermosyphon 330 and mixed with the vapor exiting the low side compressors 210 so as to condense the vapor to a liquid. Other components and other configurations may be used herein.

FIGS. 1 and 2 show an example of a conventional configuration of the thermosyphon 330. The compressor inlet 350 may be in line with the cascade outlet 360. The tank inlet 340 may merge in a perpendicular relationship at approximately a ninety degree (90°) angle so as to provide the thermosyphon 330 with a substantial tank “T” like shape 370. FIG. 3 shows a similar configuration in which the tank inlet 340 is in line with the cascade outlet 360 and the compressor inlet 350 merges perpendicularly for a compressor “T” like shape 380. In either orientation, the flows merge at about the perpendicular angle.

The flow from the low side liquid vapor separator tank 230 through the tank inlet 340 may be considered a primary flow 390. The flow from the compressors 210 to the compressor inlet 350 may be considered a secondary flow 400. Given the use of the perpendicular configuration, blocking the respective flows through the pressure drop sensitive thermosyphon 330 may be an operational and an efficiency issue. In a conventional cascade system, the primary flow 390 through the tank inlet 340 may be at about 435.07 psia (about 3000 kpa) with a temperature of about 22 degrees Fahrenheit (about −5.5 degrees Celsius) and with a mass flow rate of about 0.17 or 0.18 kg/s. The secondary flow 400 through the compressor 360 may be at about 145 degrees Fahrenheit (about 63 degrees Celsius) and with a mass flow rate of about 0.09 kg/s. After merging, a mixed outlet flow 410 at the cascade outlet 360 may be at about 434.87 psia (about 2998 kpa), about 45 degrees Fahrenheit (about 7.2 degrees Celsius), and with a mass flow rate of about 0.26 or 0.27 kg/s. Other pressures, temperatures, mass flow rates, and other parameters may be used herein.

FIG. 4 shows an example of a thermosyphon 420 as may be described herein. The thermosyphon 420 may have a tank inlet 430 that is in line with a cascade outlet 440. Instead of the compressor inlet 350 merging into the tank inlet 340 in the perpendicular orientation described above, the thermosyphon 420 may include an angled inlet compressor 450. The angled compressor inlet 450 may be positioned at an angle θ1 with respect to the tank inlet 430 or the centerline of the cascade outlet 440. The angle θ1 preferably may range from about more than about zero degrees (0°) to about forty-five degrees (45°) or so. Other angles may be used herein. Other components and other configurations may be used herein.

FIG. 5 shows a further example of a thermosyphon 460 as may be described herein. In this example, the thermosyphon 460 may include an angled tank inlet 470 and/or an angled compressor inlet 480. The inlets 470, 480 then may merge into a cascade outlet 490 for a substantial “Y” like shape. The angled tank inlet 470 may be positioned at an angle of θ2 with respect to the centerline of the cascade outlet 490. The angle θ2 preferably may range from about more than about zero degrees (0°) to about forty-five degrees (45°) or so. Other angles may be used herein. The angled compressor inlet 480 also may use the angle θ1 similar to that described above. Specifically, the angles θ1 and θ2 may be the same or different. Other components and other configurations also may be used herein.

The following chart shows the mass flow rate changes with respect to the thermosyphon 330 of FIGS. 2 and 3 and the thermosyphons 420, 460 of FIGS. 4 and 5. The comparison assumes the same pressure and temperature at the tank inlet, the same mass flow rate and temperature at the compressor inlet, and the same pressure and temperature at the cascade outlet. The mass flow rate into the tank inlet and out of the cascade outlet will vary. With respect to the angled compressor inlet 450 in the thermosyphon 420 of FIG. 4, the angle θ1 was varied from six degrees (6°) to about ninety degrees (90°). Likewise, with respect to the angled tank inlet 470 and the angled compressor inlet 480 of the thermosyphon 460, angle θ1 varied from about ten degrees) (10° to about thirty degrees (30°) and θ2 varied from about three degrees (3°) to about thirty degrees (30°). The respective changes in mass flow rate thus are shown with respect to kilograms per second.

	Angle	Compressor	Tank	Cascade	Percent
	θ1	inlet	inlet	outlet	change
FIG.	θ1-θ2	(kg/s)	(kg/s)	(kg/s)	from FIG. 2
2		0.09	0.17	0.26
3		0.09	0.18	0.27	5.46
4	6°	0.09	0.24	0.33	41.17
	11°	0.09	0.24	0.33	41.17
	15°	0.09	0.23	0.32	35.29
	30°	0.09	0.23	0.32	35.29
	45°	0.09	0.23	0.32	35.29
5	90°	0.09	0.09	0.18	−47.03
	10°-10°	0.09	0.22	0.31	29.70
	15°-15°	0.09	0.20	0.29	18.29
	30°-30°	0.09	0.21	0.30	22.79
	14°-3°	0.09	0.22	0.31	32.34

The tank inlet flow rate and the cascade outlet flow rate thus varied and improved with respect to the perpendicular configuration of FIGS. 2 and 3. The use of an angle of about six degrees (6°) to about eleven degrees (11°) improved the mass flow rate at the cascade outlet from about 0.26 kg/s to about 0.33 kg/3 or an increase of about forty-one percent (41%). Varying the angle of the secondary flow 400 with respect to the primary flow 390 thus provides an enhanced primary flow rate as compared to the perpendicular angle arrangement and/or a decreased pressure drop along the primary flow for the same inlet velocity.

FIG. 6 shows a further embodiment of a thermosyphon 500 as may be described herein. In this example, the thermosyphon 500 may include a tank inlet 510 and an inline cascade outlet 520. In this example, the thermosyphon 500 may include an angled compressor inlet 530. The angle θ1 of the angled compressor inlet 530 thus may vary. The angled compressor inlet 530 may have a variable diameter 540. Likewise, the diameter of the variable diameter 540 may vary. Varying angles and diameters also may be used for the tank inlet 510. The tank inlet 510 may have a diameter of about 1⅜ inches (about 34.9 millimeters) or so. Other components and other configurations may be used herein.

The following chart shows examples in varying the angle θ1 as well as the diameter from about 0.4 inch (about 10.2 millimeters) to about one (1) inch (about 25.4 millimeters) given the constant tank inlet 510 described above.

			Compressor	Tank	Cascade	Percent
	Angle	Diameter	inlet	inlet	Outlet	change
FIG.	θ1	(mm)	(kg/s)	(kg/s)	(kg/s)	from FIG. 2
6	30°	10.2	0.09	0.35	0.44	106.89
	30°	15.2	0.09	0.27	0.36	56.44
	30°	20.3	0.09	0.22	0.31	31.27
	30°	25.4	0.09	0.22	0.31	27.61
	11°	19.1	0.09	0.24	0.33	38.86

The use of a variable diameter 540 of about 10.2 millimeters with an angle θ1 of about thirty degrees for the angled compressor inlet 530 thus results in more than a 100% improvement over the FIG. 2 baseline. Specifically, a higher secondary flow from the compressors 210 may draw more of the refrigerant 310 from the liquid vapor separator tank 230 without obstructing the flow given a jet of a smaller diameter. Likewise, the ratio of the diameters between the angled compressor inlet 530 and the tank inlet varied from about 0.7 to about 0.3 with at least a 0.5 ratio being preferred.

The variable diameter 540 also may be dynamically set depending upon operational parameters. For example, the variable diameter 540 may vary depending upon the load on the overall system and the like. Other parameters may be considered herein. Although the thermosyphons herein have been focused on the use of the carbon dioxide refrigerant 310, the thermosyphons described herein may be used to merge any type of primary and secondary flows.

It should be apparent that the foregoing relates only to certain embodiments of the present application and the resultant patent. Numerous changes and modifications may be made herein by one of ordinary skill in the art without departing from the general spirit and scope of the invention as defined by the following claims and the equivalents thereof.

Claims

1. A thermosyphon for use with a refrigeration system, comprising: a primary flow inlet;an angled secondary flow inlet; anda mixed flow outlet;wherein the angled secondary flow inlet comprises an angle θ1 of about forty-five degrees or less with respect to the mixed flow outlet.

2. The thermosyphon of claim 1, wherein the primary flow inlet comprises a tank inlet in communication with a liquid vapor separator tank.

3. The thermosyphon of claim 1, wherein the secondary flow inlet comprises a compressor inlet in communication with one or more compressors.

4. The thermosyphon of claim 1, wherein the merged flow outlet comprises a cascade outlet in communication with a cascade evaporator-condenser.

5. The thermosyphon of claim 1, wherein the primary flow inlet comprises an angled primary flow inlet.

6. The thermosyphon of claim 5, wherein the angled primary flow inlet comprises an angle θ2 of about forty-five degrees or less with respect to the mixed flow outlet.

7. The thermosyphon of claim 5, wherein the angled primary flow inlet, the angled secondary flow inlet, and the mixed flow outlet comprise a substantial Y-like shape.

8. The thermosyphon of claim 6, wherein angle θ1 equals angle θ2.

9. The thermosyphon of claim 6, wherein angle θ1 is different from angle θ2.

10. The thermosyphon of claim 1, wherein angle θ1 is thirty degrees or less with respect to the mixed flow outlet.

11. The thermosyphon of claim 1, wherein angle θ1 is eleven degrees or less with respect to the mixed flow outlet.

12. The thermosyphon of claim 1, wherein the angled secondary flow inlet comprises a variable diameter angled secondary flow inlet.

13. The thermosyphon of claim 12, wherein the variable diameter angled secondary flow inlet comprises a diameter of 10.2 millimeters or less.

14. The thermosyphon of claim 12, wherein the variable diameter angled secondary flow inlet and the primary flow inlet comprise a diameter ratio of about 0.5 or less.

15. A method of improving a mass flow rate or reducing a pressure loss of a refrigerant to a cascade evaporator-condenser, comprising: providing a thermosyphon with an outlet in communication with the cascade evaporator-condenser;providing a primary refrigerant flow from a first source;providing a secondary refrigerant flow from a second source;mixing the primary refrigerant flow and the secondary refrigerant flow at an angle less than about ninety degrees; andproviding the mixed refrigerant flow to the cascade evaporator-condenser via the thermosyphon outlet.

16. A thermosyphon for use with a refrigeration system, comprising: a tank inlet in communication with a liquid vapor separator tank;an angled compressor inlet in communication with one or more compressors; anda cascade outlet in communication with a cascade evaporator-condenser;wherein the angled compressor inlet comprises an angle θ1 of about forty-five degrees or less with respect to the cascade outlet.

17. The thermosyphon of claim 16, wherein the tank inlet comprises an angled tank inlet.

18. The thermosyphon of claim 17, wherein the angled tank inlet comprises an angle θ2 of about forty-five degrees or less with respect to the mixed flow outlet.

19. The thermosyphon of claim 18, wherein angle θ1 equals or does not equal angle θ2.

20. The thermosyphon of claim 16, wherein the angled compressor inlet comprises a variable diameter angled compressor inlet.