Patent Publication Number: US-2016231063-A1

Title: Thermosyphon Configuration for Cascade Refrigeration Systems

Description:
RELATED APPLICATIONS 
     The present application is a non-provisional application claim priority to U.S. Provisional Application Ser. No. 62/114,603, filed on Feb. 11, 2105. U.S. Provisional Application Ser. No. 62/114,603 is incorporated by reference herein in full. 
    
    
     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 θ 1  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 θ 1  with respect to the tank inlet  430  or the centerline of the cascade outlet  440 . The angle θ 1  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 θ 2  with respect to the centerline of the cascade outlet  490 . The angle θ 2  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 θ 1  similar to that described above. Specifically, the angles θ 1  and θ 2  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 θ 1  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 θ 1  varied from about ten degrees) (10° to about thirty degrees (30°) and θ 2  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 θ 1  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 θ 1  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 θ 1  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.