The effect of heat conduction through fins on the performance of finned-tube CO2 supercritical gas coolers

Abstract

Air cooled CO2 finned-tube gas coolers are widely used in CO2 trans-critical refrigeration systems due to simplified structural designs. However, the longitudinal heat conduction along fins can lead to inverse heat transfer between adjacent tubes and thus capacity degradation of the heat exchanger. To cope with this adverse effect, the heat exchanger design with split fins between tube rows can be applied although further verification and analysis are expected. Subsequently, as explained in this paper, detailed CFD models have been purposely developed and simulated for the CO2 gas coolers with both continuous and split fins to quantify the effect of the heat conduction through fins. At various operating conditions of both air and refrigerant sides, totally 36 cases were simulated to study the influence of air inlet velocity, air inlet temperature, CO2 pressure and CO2 mass flow rate as well as the heat conduction along fins on the performance of the finned-tube gas coolers with and without split fins. The simulation results show that the approach temperature can be reduced by 0.6–7.5 K for the heat exchanger with split fins and a specific tube circuitry arrangement. Subsequently, the maximum and average heating capacities can be increased up to 22% and 10% respectively when the finned-tube CO2 gas cooler with split fins is applied. Furthermore, the simulation results show that the application of split fins should be designed and implemented appropriately based on different designs of tube circuitry arrangement in the heat exchanger.