Performance analysis of a CO₂ based milk chiller with evaporative cooling arrangement operating in hot climate

In this paper, the cooling and heating performance of a parallel compression CO₂ refrigeration system with a
cooling capacity of 240 kW is analysed for milk pasteurization application. The system chills the milk to 4 ˚C
and the recovered heat partially supports the pasteurization process or is used to heat the clean-in-place
water. The annual performance of the system is evaluated theoretically for the hot climatic condition of Pilani
(Rajasthan, India). It was found that for a system with an evaporative air-cooling arrangement, the CO₂ exit
temperature of the gas cooler during peak summer conditions of 51 °C ambient can be reduced by about
10 °C. This leads to an increase in cooling COP by an average of 48%, reduction in compressor work by 32%
as well as a 21% improvement in the overall COP. The evaporative cooling reduces the compressor discharge
temperature by 32 K and the discharge pressure by 2.2 MPa. These advantages are achieved with a water
demand of about 264 litres/hr and reduced heat recovery potential of about 39%.
Keywords: CO₂ Trans-critical System, Evaporative Cooling, Parallel Compression, Milk Chilling, Split Gas Cooler