Medicine and biomedical research activities require cold storage to store biomedical specimens such as, for example, stem cell, sperm, blood and other organs. During storage, to prevent the specimen from damage required a special cold storage reaches -80°C [1]. Using single cycle refrigeration machine can only reach -40°C, and performance deteriorates below -35°C drop in pressure associated with evaporation. Thus, to reach lower temperatures, use cascade refrigeration machine [2]. During this low-temperature circuit cascade refrigeration systems still use refrigerants that contain ozone-depleting or global warming (CFCs and HCFCs). To overcome this, a mixture of carbon dioxide and ethane azeotropic a promising alternative refrigerants. Simulation studies and experiments indicate a mixture of carbon dioxide and ethane were able to achieve the minimum temperature to -80°C [4-7]. With the mass ratio 70% R170 and 30% R744 circuit at low temperature refrigeration systems and uses a capillary tube expansion device 0.054 inch diameter with a length of 6 meters and 3 meters then use an electric heater as the cooling load. Cooling load is given by the variation of 90 W, 120 W and 150 W at a cabin in the low temperature circuit. From the experiment will be known characteristics of cascade refrigeration system with refrigerant mixture and will get the parameter data to make cascade refrigeration machine.
Thermodynamic Analysis of Cascade Refrigeration System using CO2 – NH3 Refrigerant for Fish Cold Storage Application