The influence of recent heat transfer data on gas mixtures /He-Ar, H2-CO2/ on closed cycle gas turbines

Previous studies have been made on the composition of an optimal working fluid for closed cycle gas turbines. Those studies were based on the assumption that the objective could be achieved by mixing helium with a gas of higher molecular weight. The results of those calculations, based on heat transfer data of pure gases and air, indicated the possibility of significant cost advantages of gas mixtures relative to pure helium. Recent heat transfer measurements of low Prandtl number gas mixtures indicate that existing scaling laws for normal Prandtl number (∼0.7) gases do not adequately represent the heat transfer characteristic of these gas mixtures. In this paper the influence of these gas mixture heat transfer data on closed cycle gas turbine coolers, recuperators and heat source exchangers is presented. The characteristic dimensions (flow area, surface area, and length) of these heat exchangers utilizing pure gases and gas mixtures are compared.