Transient Forced Convection Heat Transfer due to Exponentially Increasing Heat Input for Helium Gas Flowing on a Narrow Plate

Abstract

Forced convection transient heat transfer for helium gas at various periods of exponentially increasing heat input (Q₀exp(t/τ)) to a horizontal plate (ribbon) was experimentally and theoretically studied. In the experimental studies, the authors measured heat flux, surface temperature, and transient heat transfer coefficients for forced convection flow of helium gas over the horizontal plate under wide experimental conditions. The platinum plate with a length of 50 mm was used as a test heater. The gas flow velocities ranged from 4 to 10 m/s, the gas temperatures ranged from 313 to 353 K, and the periods of heat generation rate, τ, ranged from 46 ms to 17 s. The pressures were from 400 to 800 kPa. It was clarified that the heat transfer coefficient approaches the quasi-steady-state one for the period longer than about 1 s, and it becomes higher for the period shorter than around 1 s. Empirical correlations for quasi-steady state heat transfer and transient one were obtained based on the experimental data under various pressures. In the theoretical study, transient heat transfer was numerically solved based on a turbulent flow model. The values of numerical solutions for surface temperature and heat flux were compared and discussed with authors' experimental values. It was obtained that the surface temperature difference and heat flux increase exponentially as the heat generation rate increases with the exponential function. It is understood that the gradient of the temperature distribution near the heater surface is higher at a higher surface temperature difference. The values of numerical solutions for heat flux agree well with the experimental data, though surface temperatures show some differences.