Numerical and Experimental Steady-State Investigation of Supercritical CO2 Gas Cooler Plate Heat Exchanger

Abstract

Natural environmentally friendly refrigerants have been considered as alternatives to HFC refrigerants with high Global Warming Potential. In transcritical R744 vapor compression cycles, the heat rejection process occurs above the critical point where the temperature and the pressure are independent of each other. In this work, the gas cooling in a commercial 20 plate heat exchanger (PHE) used as gas cooler is modeled numerically and compared to experimental results. The numerical model is a simplified 2D model, i.e. corrugated plates with zero chevron angle. Four different real gas models are tested in terms of agreement and convergence, and numerical results from four cases with CO2 pressure ranging from 80 to 95 bar are compared with experimental results. Each case is numerically modeled with surface area that is set to match total surface area of the 20 PHE, and with one and half times the surface area of the 20 PHE. The increase in the surface area is shown to compensate for the chevron angle effect. For the experimental investigation, a CO2 heat pump test rig is used that supports cooling and heating applications. The numerical results show that the PHE outlet temperatures are in good agreement with the experimental results. The simplified 2D numerical models could reduce the computational costs associated with 3D PHE numerical simulations.