Mechanisms of Heat Transfer Augmentation around the Stagnation Point of an Impinging Air Jet Laden with Solid Particles. (Report 2. Effects of Thermal Properties of Laden Particles and Heat Transfer Surface on Heat Transfer Augmentation due to the Unsteady Heat Conduction).

Abstract

In this paper, the authors studied heat transfer augmentation around the stagnation point of an impinging air jet laden with fine solid particles. Heat transfer around the stagnation point was measured for nine combinations of solid particles and the heat transfer surface material so as to examine the effects of the thermal properties of both laden particles and heat transfer surface on the heat transfer augmentation due to unsteady heat conduction between them. The contributions of unsteady heat conduction between the laden particles and heat transfer surfaces were separated from other heat transfer augmentation mechanisms by employing the separation technique reported in our previous paper. The results clearly showed that the contribution of unsteady heat conduction increases with increase of the product of heat capacity and thermal conductivity of the heat transfer surface material as well as of the laden particles. For a given combination of solid particles and heat transfer surface materials, the contribution of unsteady heat conduction is dominated primarily by the contacting frequency between the laden particles and heat transfer surface. This means that the heat transfer augmentation due to unsteady heat conduction becomes evident as the particle diameter decreases.