Heat Transfer of Gas Laminar Forced Convection with Consideration of Variable Physical Properties

Abstract

The new similaritye analysis method is applied to develop a novel similarity analysis model of laminar forced convection with consideration of variable physical properties. It is a better alternative to the traditional Falkner-Skan type transformation for this issue. Meanwhile, an advanced approach on treatment of gas variable physical properties, the temperature parameter method, is first applied for convenient and reliable treatment of variable thermophysical properties in extensive study on gas laminar forced convection. Theoretical equations on skin-friction coefficient and heat transfer with consideration of variable physical properties are obtained, where only the dimensionless wall velocity and temperature gradients are no-given variables, respectively, both of which depend on Prandtl number, boundary temperature ratio, and gas temperature parameters. The numerical solutions on the dimensionless wall velocity and temperature gradients are found out rigorously on laminar forced convection on horizontal flat plate. A system of the wall dimensionless temperature gradient is formulated by a curve-fitting method, and then a difficult point was resolved for simple and reliable prediction of heat transfer with consideration of variable physical properties. It is found that not only Prandtl number but also gas temperature parameters together with the boundary temperature ratio have significant influences on velocity and temperature fields as well as heat transfer of gas laminar forced convection. Furthermore, the following regulations for the effect of the variable physical properties on heat transfer coefficient are clarified: (i) Effect of the gas variable physical properties on the heat transfer coefficient are dominated by the gas temperature parameters and boundary temperature ration; (ii) The effect of variable thermal conductivity on heat transfer coefficient is larger than that of the variable absolute viscosity, although the effect of the viscosity can never be ignored; and (iii) Increasing the boundary temperature ratio causes increase of the effect of the variable physical properties on heat transfer.