Implementation of a methodfor the inverse calculation ofthe heat flux during the impactof a drop chain onto a heatedsurface

Abstract

Spray cooling is one of the most efficient cooling methods, can achieve a very high, nearly uniform heat flux and thus reduce thermal loads. Spray-wall interaction is encountered in existing and emerging technologies and the underlying phenomenon associated with spray cooling. Spray cooling exploits the latent heat of vaporization and surpasses other conventional cooling methods. Drop impact is a punctual aspect of a monodisperse droplet chain, which reduces a spray to one dimension. The submitted thesis deals with the development of heat flux calculation models as means of solving the inverse heat conduction problem of drop impact on a heated surface. In this work different existing models for solving the inverse heat conduction problem are introduced and one of them is applied. This existing method is compared to the newly developed calculation methods which are presented and compared. Firstly drop impact phenomena are explained for the isothermal and non-isothermal case. Then the abstraction is made to sprays. The heat conduction equation is introduced and subsequently solved for our experimental set-up. The experimental set-up consists of a drop generator, a heated probe and measuring equipment. The drop generation and measuring equipment are used to obtain temperature measurements within the probe. The probe body is polished stainless steel with holes at different horizontal and radial positions for temperature measurement. These measurement points are used to calculate the surface temperature of the heated probe. The heat flux from the heated probe is the same as the heat flux absorbed by a droplet upon impact. Therefore the heat flux during drop impact is calculated from the temperature measurements within the heated probe body. The heat flux calculation results are used to understand the change in dissipated heat at different temperatures. The calculations are validated using a simulated test case with a known surface temperature and heat flux before the newly developed calculation methods are applied to real measurement data.