Internal forced convection to low Prandtl number gas mixtures

At a Prandtl number of about 0.2, the predictions of accepted correlations for heat transfer in fully established tube flow differ by a factor more than two. Since gas turbine systems proposed for propulsion use working fluids with the Prandtl number in this range it was necessary to resolve the discrepancy. By mixing helium with xenon or hydrogen with xenon, the range 0.16 or approx. = Pr or approx. = 0.7 can be obtained. Measurements with these mixtures in a vertical tube showed that the Colburn analogy and Dittus-Boelter substantially overpredict the Nusselt number for constant property conditions; best agreement was provided by relations suggested by Petukhov and by Kays. For moderated variation of gas properties (1 T (sub w)/T (sub b) or approx. = 2.2) the correlation for average friction factor by Taylor was verified; the exponent on the Prandtl number in his equation for heat transfer was modified to 0.65 in order to accommodate these new data.