Theoretical and Experimental Studies on Transient Heat Transfer for Forced Convection Flow of Helium Gas over a Horizontal Cylinder

Abstract

Forced convection transient heat transfer for helium gas at various periods of exponential increase of heat input (Q0exp(t/τ)) to a horizontal cylinder (heater) was theoretically and experimentally studied. In the theoretical study, transient heat transfer was numerically solved based on a turbulent flow model. It was clarified that the surface superheat and heat flux increase exponentially as the heat generation rate increases with the exponential function. The values of numerical solution for surface temperature and heat flux agree well with the experimental data for the cylinder diameter of 1mm. In the experimental studies, the authors measured heat flux, surface temperature, and transient heat transfer coefficients for forced convection flow of helium gas over horizontal cylinders under wide experimental conditions. The platinum cylinders with diameters of 1.0mm, 0.7mm, and 2.0mm were used as test heaters. The gas flow velocities ranged from 2 to 10m/s, and the periods ranged from 50ms to 15s. It was clarified that the heat transfer coefficient approaches the quasi-steady-state one for the period τ longer than about 1s, and it becomes higher for the period shorter than around 1s. The heat transfer shifts to the quasi-steady-state heat transfer for longer periods and shifts to the transient heat transfer for shorter periods. The transient heat transfer coefficients show significant dependence on cylinder diameters, there are higher for smaller cylinder diameters. The empirical correlations for quasi-steady-state heat transfer and transient heat transfer were obtained based on the experimental data.