Abstract
Three novel CO2-NH3 multi-evaporator cascade refrigeration systems (CRS) are proposed and evaluated for application in seafood processing for high ambient. The CRSs have evaporators both above and below the cascade temperature and are intended to replace a multi evaporator NH3 system. They exploit the comparatively superior thermo-physical properties of CO2 in the low temperature evaporators while NH3 in the high temperature condenser keep the overall operating pressure low. Thermodynamic models of the CRSs for a single evaporator are validated against published literature. CRS1 has an individual compressor for each evaporator while CRS2 & CRS3 incorporate pumped circulation system in CO2 and NH3 circuits respectively. The CRSs improve the overall efficiency, reduce ammonia charge and contamination hazards from NH3. Suitability of the proposed CRSs are established for a wide range of tropical ambient and also for cooling demands in other prominent seafood processing and storage applications like fish fillets and shrimp/prawn. CRS1 is found to give the highest COP advantage of about 11.5% in surimi processing where the foremost cooling load is at a high temperature evaporator. While CRS3 is found gainful for fish fillet & shrimp/prawn industry where the major cooling load is at low temperature evaporator. COP advantage of 16.5% & 20.3% respectively are observed for fish fillet & shrimp/prawn processing. Dealing with surimi in climate condition of Mumbai (India), CRS1, showed a maximum 8.3% reduction in Annual average energy consumption (AAEC), while for fish fillets and shrimp/prawn CRS3 showed maximum AAEC reduction which is 7.5% & 13.2% respectively.