A computational study of convective heat transfer to carbon dioxide at a pressure just above the critical value

Computational simulations are reported of experiments on convective heat transfer to carbon dioxide at a pressure of 75.8 bar, which is just above the thermodynamic critical value of 73.8 bar. These have been carried out using a variable property, elliptic computational formulation incorporating low Reynolds number turbulence models of k - epsilon and V2F types. Firstly, the simulations were compared with the heat transfer measurements and then they were used in developing an understanding of interesting phenomena observed in the experiments. It has been found that the effect of buoyancy on turbulence production and heat transfer in fluids at supercritical pressure can be very significant even under conditions of relatively 'low' buoyancy parameter based on bulk properties. The effect of buoyancy, although complex, can be explained by relating it to the large-property-variation (LPV) region, i.e., the region within the flow field near to the locations where the fluid temperature has the pseudo-critical value. Under certain conditions, a very non-uniform radial distribution of the buoyancy force may be present and cause some reduction of turbulence in the core but a big increase near the wall, resulting in much improved heat transfer. It is clear that new heat transfer correlations are needed to account for such effects on heat transfer to supercritical pressure fluids as they come to be used more and more in new energy systems applications such as, advanced water-cooled nuclear reactors, environmentally friendly air-conditioning and refrigeration systems and high pressure water oxidation plant for wasteprocessing. (C) 2007 Elsevier Ltd. All rights reserved.