Investigation on local convection heat transfer of supercritical CO2 during cooling in horizontal semicircular channels of printed circuit heat exchanger

The local heat transfer characteristics of supercritical CO2 flowing in horizontal semicircular straight channel of the printed circuit heat exchanger (PCHE) geometries during cooling under forced and mixed convection conditions have been numerically investigated in the present study. A new local heat transfer correlation accounting for the thermophysical property variations and the buoyancy effects has been developed based on analysis of the thermophysical property variations and the buoyancy effects on the local heat transfer performance. It predicts 93% of the data with errors of less than +/- 15%. The developed correlation is further adopted to a preliminary design calculation of typical PCHE channels based on a generalized mean temperature difference (GMTD) method instead of the conventional logarithmic mean temperature difference (LMTD) method. The design calculation results agree fairly well with the CFD results. Moreover, a dimensionless parameter, C-vp, is developed to evaluate the deviations induced by the constant property assumptions on which the conventional LMTD method is based. Results show that the deviation is generally between -15% and 15% when C(vp )is in the range of 0.6 to 1.6.