Performance evaluation of an ejector-based cooling system

Abstract

With limited land for agriculture, Singapore's food resource largely depends on imports from various countries. A key consideration that takes place is how to keep those food fresh between the time it reaches our shores and before it can be kept in the refrigerator in the supermarket or at home. Multi-evaporator refrigeration system (MERS) then comes into play, as it provides an environment for food to stay fresh even during long periods of storage or transportation in the vehicle.

The typical MERS operates at 3 different temperatures, mainly for the freezing of food (-30°C), sustaining perishable food products (-5°C) and for space cooling (+7°C). Hence 3 evaporators will be used to cater to each temperature condition, with the higher temperature evaporator having a higher working pressure and vice versa. However, this conventional MERS is not energy efficient as much energy is loss due to the pressure differences in each evaporator when mixing occurs as the streams combine before entering the single compressor. A way to enable pressure recovery is to implement the Ejector based MERS (EMERS).

This report highlights the difference in performance between the conventional MERS and the EMERS. Pressure recovery ratio will be calculated to determine the efficiency of the ejectors, with the highest value obtained to be 16%. And by the plotting of graphs, a comparison of the Coefficient of performance (COP) for each system will be made to show that the EMERS is indeed more energy saving than the conventional system by up to a 25% increase in COP.

Recommendations on further possible work are also proposed.