Performance evaluation of a multi-evaporator NH₃-CO₂ cascade refrigeration system with IHX for seafood processing industry

Seafood processing typically has cooling demands at four different temperatures within the range -40 °C to 0 °C. An NH₃-CO₂ cascade refrigeration system equipped with an internal heat exchanger (IHX) is proposed for the same. The proposed system has two evaporators operating above the cascade condenser with NH₃ as working fluid while two other evaporators are operating below the cascade condenser and have CO₂ as working fluid. IHX in the sub-critical CO₂ refrigeration system produces required sub-cooling at the exit of the condenser, increasing the refrigeration effect, and thus the overall performance improves. The cascade temperature is optimized and the performance of the system is found to be superior to the conventional NH₃ system for various operating conditions. The effects of refrigeration loads, evaporation temperatures, and ambient temperature on the performance of the proposed cascade system are also analyzed.