Liu, Chuntao

Lun, Liyong

Xie, Yingbai

Zhang, Xuedong

English

Purdue E-Pubs

Purdue UniversityPurdue e-PubsInternational Refrigeration and Air ConditioningConference School of Mechanical Engineering2008Use of R290/R170 in Lieu of R22/R23 in CascadeRefrigeration CycleYingbai XieNorth China Electric Power UniversityChuntao LiuNorth China Electric Power UniversityLiyong LunNorth China Electric Power UniversityXuedong ZhangNorth China Electric Power UniversityFollow this and additional works at: http://docs.lib.purdue.edu/iraccThis document has been made available through Purdue e-Pubs, a service of the Purdue University Libraries. Please contact epubs@purdue.edu foradditional information.Complete proceedings may be acquired in print and on CD-ROM directly from the Ray W. Herrick Laboratories at https://engineering.purdue.edu/Herrick/Events/orderlit.htmlXie, Yingbai; Liu, Chuntao; Lun, Liyong; and Zhang, Xuedong, "Use of R290/R170 in Lieu of R22/R23 in Cascade RefrigerationCycle" (2008). International Refrigeration and Air Conditioning Conference. Paper 939.http://docs.lib.purdue.edu/iracc/939 2369, Page 1  Use of R290/R170 in lieu of R22/R23 in Cascade Refrigeration CycleYing Bai XIE1, Chun Tao LIU2*, Li Yong LUN3, Xue Dong ZHANG4 1,2,3,4North China Electric Power University, Department of Power Engineering, Baoding, Hebei, China Contact Information (86-312-7522882, 86-312-7522440)  1xieyb@ncepubd.edu.cn  2lct701@163.com  3lunliyong@126.com  4kouyizhinan@163.com    ABSTRACT  R22/R23 have been predominantly used in cascade refrigeration cycles. Even though the ODP of R22 is not as high as CFCs, it still will be phased out following the Montreal Protocol and its amendments because of the chlorine atoms. Hydrocarbons, such as R170 and R290 are natural working fluids. Thermodynamic analysis on the cascade refrigeration cycle adopted R290/R170 under the evaporation temperature from -80  to -55  and the condensation temperature from 30  to 40  are processed. System performances, such as the maximum COP, the cascade evaporating temperature, the ratio of refrigerants flow rate between high and low temperature circuits and their variations are compared with that of the R22/R23 under the same conditions. Results show that the performances of the two cascade refrigeration cycle are approximately the same. So the R290/R170 can be used as the substituting refrigerants to R22/R23 in the cascade refrigeration cycle.  1. INTRODUCTION  Cascade system consists of two separate single-stage vapor compression refrigeration cycles. For the high-temperature circuit (HTC) and low-temperature circuit (LTC) the refrigerants of R22 and R23 are typically chosen (Keumnam, 2001). The evaporation temperature of the system can be reached -80  to -90 . As is generally known, R22 will be phased out following the Montreal Protocol and its amendments because of the chlorine atoms, and R23 is a single HFC compound, it has no chlorine content, no ozone depletion potential, but has a high Global Warming Potential (GWP) and a long lifetime. Therefore, for low-temperature refrigeration, development and study of alternative refrigerants that have not only zero ozone depletion potential (ODP) but also low GWP are a pressing need in these days. Natural refrigerants, such as HCs (hydrocarbons), ammonia (R717), carbon dioxide (CO2) and so on, are the most earth-friendly substances. Not to mention that their ODP is 0, their GWP is also vanishingly small, they are most expected to be alternative refrigerants.   The HTC can normally be charged with R717 (Lee et al., 2006), propane (R290) (Niu and Zhang, 2007a), propylene (R1270) (Bhattacharyya et al., 2005), ethanol (Bansal and Jain, 2007). R717 is a naturally available refrigerant with few application constraints such as toxicity and flammability. The disadvantage of R1270, R290 and ethanol is their high flammability. The evaporating and condensing pressures of ethanol are also much below the ambient pressure, which lead to air leakage into the system. However, the risk associated with toxic and flammable refrigerants can be International Refrigeration and Air Conditioning Conference at Purdue, July 14-17, 2008  2369, Page 2  highly minimized by confining the HTC to the plant room area. Several researchers have evaluated the thermodynamic performance of the two-stage cascade refrigeration system uses these refrigerants for the HTC.  CO2, as a natural working fluid, has many advantages when used in LTC (Niu and Zhang, 2007b, Sergio et al., 2004, Christensen and Bertilsen, 2003), but it has some disadvantage such as high pressure and high freezing point (-56.56 ), which prevents it from operating in vapor compression cycles intended for used at lower temperature. For R170 (ethane), the standard boiling point and freezing point are -88.598  and -182.8  respectively, are lower than CO2 and closed to R23, can be considered as the refrigerant for LTC (Wang et al., 2005, Ma et al., 2003).  In the present study, thermodynamic analysis and comparison between R290/R170 and R22/R23 under the same working conditions were carried out to prove the potential of R290/R170 as a promising substitute.  2. THERMOPHYSICAL AND ENVIRONMENTAL CHARACTERISTICS  Table 1 lists some physical and environmental properties of R22, R290, R23 and R170. From table 1, it can be seen that R170 and R23 have quite similar normal boiling point temperature and can get quite similar evaporating temperature. Figure 1 shows the saturation characteristics curves in the temperature range -100  to 60  of refrigerants list in table 1. The saturation characteristics curves of R170 and R290 are relatively close to R23 and R22 respectively.  Table 1: Physical and environmental characteristics of selected refrigerants  refrigerants R22 R290 R23 R170 Standard Boiling Point( ) -40.76 -42.09 -82.1 -88.8 Freezing Point( ) -160 -187.7 -155 -183 Critical Temperature( ) 96.0 96.70 25.6 32.2 Critical Pressure(MPa) 4.97 4.25 4.83 4.89 ODP 0.05 0 0 0 GWP 1780 About 20 12000 About 20 Atmospheric Lifetime, in years 12  260   -100 -75 -50 -25 0 25 50012345Preeeure(MPa)Temperature( )  R170 R23 R290 R22  Figure 1: Saturation characteristic of selected refrigerants  3. THERMODYNAMIC ANALYSIS OF A CASCADED REFRIGERATION CYCLE The cascade system, illustrated in Figure 2, which consists of two separate circuits, each using a refrigerant appropriate for its temperature range. The two circuits are thermally connected by the cascade condenser, which is the condenser of the LTC and the evaporator of the HTC. Figure 3 shows the cascade pressure-enthalpy diagram.  International Refrigeration and Air Conditioning Conference at Purdue, July 14-17, 2008  2369, Page 1     Figure 3: Cascade ressure- nthalpy iagram Figure 2: Cascade efrigeration ycle  The thermodynamic analysis of the two-stage cascade refrigeration system was performed based on the following general assumptions: (1) adiabatic compression with an isentropic efficiency of 0.8 for both high- and low- temperature compressors, (2) negligible pressure and heat losses/gains in the pipe networks or system components, (3) isenthalpic expansion of refrigerants in expansion valves, and  (4) negligible change in kinetic and potential energy.   The COP of the system is defined in Equation (1).  LHEWWQCOP      (1)  Where, the capacity of the evaporator (QE), Compressor power consumption for HTC and LTC (WH and WL) are respectively given in Equations (2), (3) and (4).  51 hhmQ LE      (2)  67 hhmW HH      (3)  12 hhmW LL      (4)  The heat transfer in the cascade heat exchanger (QCAS) is defined in Equation (5).  10642 hhmhhmQ HLCAS     (5)  So mass flow ration (mH/mL) can be gained from Equation (5), see Equation (6).  10642hhhhmmLH      (6) And the COP can also be defined by substituting Equations (2), (3), (4) and (6) in Equation (1), see Equation (7).  International Refrigeration and Air Conditioning Conference at Purdue, July 14-17, 2008  2369, Page 4  10612674210651hhhhhhhhhhhhCOP    (7)  4. RESULTS AND DISCUSSION OF THE ANALYSIS  In both circuits of the R290/R170 and R22/R23 cascade system have the same heat losses of cascade condenser is 0 kW, and isentropic efficiency of compressors in both cycles, =0.8.  4.1 Effect of Condensing Temperature Figure 4 and 5 depict the variation of COP, mass flow ratio and mass flow of HTC and LTC for change in condensing temperature (TC). Condensing temperature was varied from 30  to 40 , while the other temperatures such as temperature difference in cascade condenser, cascade evaporating temperature (TCAS,E=-30 ), evaporating temperature (TE=-75  and -60  in figure 4, TE=-80  in figure 5), subcooling and superheat were held constant. As expected, a rise in condensing temperature resulted in a decrease in COP for both of R290/R170 and R22/R23 cascade system. Although the COP of R22/R23 for the same given conditions is higher than R290/R170, lower evaporating temperature (see figure 4 TE=-75 ) has little effect on the two systems. As can be seen from figure 5, the mass ratio increased with a rise in condensing temperature, R290/R170 shows higher mass flow ratio than R22/R23, however the mass flow of R290 and R170 is approximately a half of R22 and R23 respectively.  30 32 34 36 38 401.11.21.31.41.51.6TCAS,E=-30 ; TCAS=10KR290/R170 TE=-60R290/R170 TE=-75R22/R23 TE=-75R22/R23 TE=-60COPCondensing temperature( )   Figure 4: Effect of condensing temperature on system performance  30 32 34 36 38 401.01.21.41.61.82.0TCAS,E=-30 ; TCAS=10K;TE=-80R22R290R23R170R22/R23R290/R170Condensing temperature( ) mH/mL0.00.20.40.60.81.0Mass flow(kg/s)  Figure 5: Effect of condensing temperature on mass flow of HTC and LTC and their ratio 4.2 Effect of Evaporating Temperature The variation of system performance, mass flow of HTC and LTC and their ratio for changing in evaporating temperature in LTC (TE) was show in figure 6 and 7. Evaporating temperature was varied from -55  to -80  by keeping condensing temperature (TC=30  and 40  in figure 6, TC=40  in figure 7), temperature difference in cascade condenser, cascade evaporating temperature (TCAS,E=-35 ), subcooling and superheat constant. The increase in evaporating temperature resulted in much higher performance of the both systems than condensing temperature. Although the performance of R22/R23 for the same given conditions is higher than R290/R170, lower condensing temperature has little effect on the two systems. The mass flow ratio decreased with an increase in evaporating temperature (see figure 7). The other results of mass flow and mass flow ratio are the same with condensing temperature change.   International Refrigeration and Air Conditioning Conference at Purdue, July 14-17, 2008  2369, Page 5  -80 -75 -70 -65 -60 -551.01.21.41.61.8TCAS,E=-30 ; TCAS=10KR22/R23 T C=40R290/R170 T C=40R290/R170 T C=30R22/R23 T C=30COPEvaporating temperature( )  Figure 6: Effect of evaporating temperature on system performance  -80 -75 -70 -65 -601.01.21.41.61.82.0TCAS,E=-30 ; TCAS=10K;TC=40R170R23R290R22R290/R170R22/R23Evaporating temperature( )mH/mL0.20.40.60.8mass flow(kg/s) Figure 7: Effect of evaporating temperature on mass flow of HTC and LTC and their ratio 4.3 Effect of Cascade Evaporating Temperature The variation of cascade evaporating temperature (TCAS,E) on both cascade systems (see figure 8 and 9) was studied by keeping the other operating parameters constant. These parameters include condensing temperature (TC=35 ), evaporating temperature (TE=-80  in figure 8 and TE=-60  in figure 9), temperature difference in cascade condenser ( TCAS= K). The cascade evaporating temperature was varied from -50  to -15 . Figure 8 and 9 shows that there were an optimum cascade evaporating temperatures at which the COP of the both systems were maximum. For the specified operating conditions in figure 8 and 9 the maximum COP (COPMAX) and its corresponding cascade evaporating temperature for R22/R23 and R290/R170 cascade system has listed in table 2. When the cascade evaporating temperature is higher than -31.4  and -21.7 , the COP of R290/R170 cascade system is higher than R22/R23 at the operating conditions of TE=-80  and TE=-60  respectively.  -50 -40 -30 -20 -101.001.021.041.061.08TE=-80 ;TC=35 ; TCAS=10KCOPTCAS,E( ) R22/R23 R290/R170 Figure 8: Effect of cascade evaporating temperature on system performance (TE=-80 ) -50 -40 -30 -20 -101.361.401.441.48TE=-60 ;TC=35 ; TCAS=10KCOPTCAS,E( ) R22/R23 R290/R170 Figure 9: Effect of cascade evaporating temperature on system performance (TE=-60 )  Table 2: the COPMAX and its corresponding TCAS,E for R22/R23 and R290/R170 cascade system in figure 8 and 9  Figure 8 Figure 9 Cascade system COPMAX TCAS,E( ) COP TCAS,E( ) COPMAX TCAS,E( ) COP TCAS,E( )R22/R23 .078 -37.7 .492 -28.3 R290/R170 .074 -33.5 .073 -31.4 .485 -24.4 .483 -21.7 International Refrigeration and Air Conditioning Conference at Purdue, July 14-17, 2008  2369, Page 6  The variation of the COPMAX of the systems for other conditions was also analyzed (see figure 10). The evaporating temperature was varied from -80  to -55 . It was observed that the COPMAX increases with increasing evaporating temperature and decreasing condensing temperature for the two systems. The COPMAX of R22/R23 system is higher than R290/R170 system by about only 1.19% on the condition of condensing temperature and evaporating temperature is 40  and -55  respectively, but showed negligible difference with decreasing condensing temperature and evaporating temperature.  -80 -75 -70 -65 -60 -551.01.21.41.61.8TCAS=10K R290/R170,TC=40 R290/R170,TC=35 R290/R170,TC=30 R22/R23,TC=40 R22/R23,TC=35 R22/R23,TC=30COP MAXEvaporating temperature( )  Figure 10: Effect of evaporating temperature on the maximum COP 0 5 101.051.101.151.201.251.301.3515TE=-75 ;TC=35 ;TCAS,E=-30R290/R170COPTemperature difference in cascade condenser(K)R22/R23 Figure 11: Effect of temperature difference in cascade condenser on system performance  4.4 Effect of Temperature Difference in Cascade Condenser Figure 11 shows the effect of temperature difference in cascade condenser ( TCAS) from 0  to 15  on system performance, for the operating condition of evaporating temperature (TE=-75 ), condensing temperature (TC=35 ) and cascade evaporating temperature (TCAS,E=-30 ). It was easily perceived that the COP falls with raising TCAS. The COP of R22/R23 system is higher than R290/R170 by about only 0.6% on the condition of temperature difference in cascade condenser is 0K, and the both system equals in system performance when TCAS is 11.4K.  5. CONCLUSIONS  This paper presents a thermodynamic analysis of R290/R170 and R22/R23 cascade refrigeration systems, operating at evaporating temperature from -80  to -55 , condensing temperature from 30  to 40 , cascade evaporating temperature from -50  to -10 , and temperature difference in cascade condenser from 0K to 15K, as far as the thermophysical and environmental characteristics of R290 and R170 are concerned, the following conclusions are made: R290 and R170 are the most earth-friendly substances. Their ODPs are zero and GWPs are about 20. The COP and COPMAX of R290/R170 cascade system is very close to R22/R23, especially at lower condensing and evaporating temperature conditions. Although the mass flow ratio of R290/R170 cascade refrigeration cycle is higher than R22/R23, the mass flow of R290 and R170 circuits are approximately a half of R22 and R23 respectively due to their higher refrigeration capacity, so the flammability of R290 and R170 will be reduced greatly. R290/R170 can be considered as a good substitute for R22/R23 in the cascade refrigeration cycle.  NOMENCLATURE  h specific enthalpy (kJ/kg)  Subscripts m mass flow rate (kg/s) C condenser Q rate of heat transfer (kW) CAS cascade heat exchanger T temperature ( ) E evaporator International Refrigeration and Air Conditioning Conference at Purdue, July 14-17, 2008  2369, Page 7  W power (kW) MAX  maximum  change (–) sub subcooling  efficiency (–) sup superheating  REFERENCES  Bansal, P.K., Jain, S., 2007, Cascade Systems: Past, Present, and Future, ASHRAE Trans., vol. 113, no. 1: p. 245-252. Bhattacharyya, S., Mukhopadhyay, S., Kumar, A., Khurana, R.K., Sarkar, J., 2005, Optimization of a CO2–C3H8 Cascade System for Refrigeration and Heating, Int. J. Refrig., vol. 28, no. 8: p. 1284-1292. Christensen, K.G., Bertilsen, P., 2003, Refrigeration Systems in Supermarkets with Propane and CO2-Energy Consumption and Economy, 21st IIR International Congress of Refrigeration, Washington, DC: p. 1-10. George, L.M., 2001, Use of R-22/23 in Lieu of R502/13 in a Cascade Refrigeration System, Proc. of 35th National Heat Transfer Conference, Anaheim, California: p. 243-246. Keumnam, C., Jonghoon, P., Honggi, C., 2001, Performance of the Cascade System Using Alternative Refrigerants, Proc. of 35th National Heat Transfer Conference, Anaheim, California: p. 595-600. Lee, T.S., Liu, C.H., Chen, T.W., 2006, Thermodynamic Analysis of Optimal Condensing Temperature of Cascade-Condenser in CO2/NH3 Cascade Refrigeration Systems, Int. J. Refrig., vol. 29, no. 7: p. 1100-1108. Ma, Y.T., Wei, D., Wang, J.G., 2003, Worldwide State-of-the-arts and Trends of Natural Refrigerants, J. of HV&AC., vol. 33, no. 1: p. 41-46. Niu, B.L., Zhang, Y.F., 2007, Experimental Study of the Refrigeration Cycle Performance for the R744/R290 Mixtures, Int. J. Refrig., vol. 30, no. 1: p. 37-42. Sergio, G., Silvia, M., Petter, N., 2004, Commercial Refrigeration System Using CO2 as the Refrigerant, Int. J. Refrig., vol. 27, no. 7: p. 717-723. Wang, S.L., Lun, L.Y., Xie, Y.B., Cheng, Y.L., 2005, Application of Hydrocarbons in Process of Refrigerant Substituting, Natural gas industry, vol. 25, no. 12: p. 121-124.  ACKNOWLEDGEMENT  This work was supported by the National Natural Science Foundation of China under the project 306004. International Refrigeration and Air Conditioning Conference at Purdue, July 14-17, 2008 

Use of R290/R170 in Lieu of R22/R23 in Cascade Refrigeration Cycle

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Use of R290/R170 in Lieu of R22/R23 in Cascade Refrigeration Cycle

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