HEAT-TRANSFER DURING IMPACT

The amount of heat transferred by conduction during the impact of a spherical particle with a surface depends on the thermophysical and mechanical properties of the two colliding media. Other factors, such as the surface properties (e.g. roughness, contamination, stress state, radius of curvature) and the velocity and direction of the impact, also influence the heat transfer. The available theoretical treatment of the heat transfer is based on the Hertzian theory of elastic contact, where the two colliding media are treated as two elastic half-spaces. In this study experiments are performed to measure the amount of heat transfer during impact of metallic spherical particles with small metallic collectors embedded in low thermal conductivity substrates. Convective heat transfer has been eliminated by performing the experiment in a vacuum chamber. However, radiative heat transfer is present and an effort has been made to minimize it by using highly reflective surfaces. The experimental results show that the measured heat transferred per impact is higher than that predicted by the Hertzian theory of elastic impact. The plastic deformation induced in the collector due to the relatively high velocity of impact causes an increase in the contact area and the impact duration. We analyze the heat transfer during plastic impact and discuss the role of other non-ideal conditions such as the flexibility of the support and the obliqueness of the impact.