An experimental and theoretical investigation of the heat transfer during impact.

Abstract

This study considers the problem of conduction heat transfer between two bodies in contact over a bounded region for very short periods of time. First the analytical-numerical determination of the interfacial heat flux between these contacting bodies is addressed. For particles impacting a surface of a different temperature an experimental method for the measurement of the conductive heat transfer between the particles and the surface is developed. Factors such as the plastic deformation induced in the collector due to the relatively high velocities of impact, and the flexibility of the collector support, can influence the conductive heat transfer. The effects of oblique impact and particle spin are also examined. Through rigorous treatment of the transient conduction equation, numerical and analytical estimation of the contact resistance and of the conductive heat flux between two bodies in contact for very short periods of time is obtained. An experimental apparatus is designed and fabricated for the measurement of the heat transferred by conduction during the impact of spherical metallic particles with small metallic collectors embedded in low thermal conductivity substrates. The experimental results are presented for various collector materials. Then a theoretical model is developed for heat transfer during a fully plastic impact. Another model for the heat transfer is developed using the work-hardening of the collector. The effect of the hardness of the collector on the heat exchange is studied both experimentally and analytically. The effect of the flexibility of the collector support on the heat transfer is examined by using an existing model of an elastic half-space. The experimental results show that the measured heat transfer during impact is larger than that obtained from the prediction of the elastic impact model. This is mainly the result of the plastic deformation of the collector during impact. Within the uncertainty of the determination of the constants in the constitutive equations, the predictions based on the fully-plastic impact model are in good agreement with the experimental results. The results of the flexible support model show that the flexibility can increase or decrease the heat transfer during multiple impacts. However, for the conditions in the experiments the model predicts no significant effect.