RACA Journal September 2025 RACA_September2025 | Page 46

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the expansion of the liquid on the receiver from 3 800 to 1 300 kPa

Operation of an ejector The function of the expansion valve is to regulate the flow of the high-pressure liquid CO2, causing it to undergo a rapid pressure drop. This drop results in a substantial decrease in temperature, turning the liquid into a mixture of liquid and vapour.

In a booster system for example, there are four expansion valves:

• High-pressure valve: controls the pressure at the gas cooler / condenser, decreasing the pressure from the high-pressure side( 9 000 kPa) to the receiver pressure( 3 800 kPa)

• Flash-gas bypass valve: controls the pressure at the receiver, decreasing the pressure down to the 3 800 kPa for medium temperature suction pressure

• Medium temperature expansion valve: responsible for the expansion of the liquid on the receiver from 3 800 to 2 700 kPa

• Low temperature expansion valve: responsible for

In the evaporator, the low-pressure and lowtemperature CO2 liquid-vapour mixture absorbs heat from its surroundings. This absorption causes the refrigerant to evaporate, transforming it back into a low-pressure gas. The cycle is complete, and the space around the evaporator becomes cooler. In a booster system there are the medium temperature evaporators and low temperature evaporators.

Cayla, hopefully this helps with your understanding of CO2 systems, components and operation. RACA

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RACA Journal I September 2025 www. refrigerationandaircon. co. za