Investigating the Influence of Helium Based Mixtures Composition on the Temperature Recovery Factor and Prandtl Number Values

Abstract

The paper studies the influence of thermo-physical and transport properties of gaseous working fluids on the efficiency of closed Brayton cycle gas turbine power plants and gas dynamic temperature stratification device (Leontiev’s tube). It is shown that using helium binary gas mixtures with low Prandtl number Pr values as working fluids instead of pure helium in closed Brayton cycle gas turbine power plants leads to significant drop in the turbo-machinery aerodynamic loading with retention of the heat transfer coefficients in heat-exchangers and with sustainable growth in the pressure losses along the power plant loop components. For the Leontiev’s tube, using the helium binary gas mixtures with low Pr values results in significant drop of the temperature recovery factor r value on the wall in supersonic flow and in rise of the available temperature difference with appropriate increase of heat flow densities and decrease of required heat transfer areas value. The paper analyses the influence of different factors on the value r . Shows that using the gas mixtures with low Pr values as working fluids, injecting gas into supersonic flow boundary layer through permeable wall and arranging regular relief on the wall surface are the most promising solutions for decreasing the value r . Examines the methodologies and correlations known from available open sources to calculate the r values depending on Pr , Reynolds number Re x and Mach number M and presents the calculation results obtained through these correlations for Pr 0,1…1, Re x 10 5 …10 9 and M up to 4. Practically, all the methodologies and correlations examined are in good agreement with experimental data obtained for air with Pr ≈ 0,7 over the intervals of Re x and M considered. However, with further reduction of Pr value the calculation results for r diverge for different methodologies and correlations with up to 35 – 40 % difference for Pr ≈ 0,2 for those which are in good agreement with the air experimental data. Thus, there is a recommendation to conduct further experimental investigations to obtain real r values for different Pr , Re x and M on the flat impermeable wall in supersonic flow for the He - Ar , He - Kr , He - Xe , He - N 2 , He - CO 2 binary gas mixtures in order to verify the methodologies and correlations examined.