A theoretical model of CO2 gas cooler with PAG lubricant was developed. The heat transfer coefficient was predicted based on artificial neural network

and then the model was validated with experimental results. Further calculation shows that the thermal effectiveness increases with the length of the gas cooler tube

but the increase rate decreases gradually. Therefore

the length of the gas cooler tube should be properly designed considering the economical running in the practical applications. For the gas cooler with a smaller diameter (Dh ≤ 2 mm)

a small amount of lubricant significantly deteriorates the thermal effectiveness while for that with a larger diameter (Dh ≥ 4 mm)

the influence is not so apparent. Consequently

the oil concentration should be decreased as far as possible to keep high heat transfer performance of the small diameter gas cooler. The gas cooler performances better at higher CO2 side pressure. However

the increase rate of the thermal effectiveness decrease gradually as the pressure increases. At pressure approaching to the critical pressure

the degradation of the thermal effectiveness is more significant. Additionally

the deterioration is more apparent as the diameter decreases.