Yona Frekers, Institute of Heat and Mass Transfer, RWTH Aachen University, Germany.

Speech Title: Accurate Quantification of Thermal Boundary Conditions within Thermal Systems

Abstract: Determining thermal boundary conditions at interfaces between different components is a necessary prerequisite for an accurate description of the thermal behavior of the system as a whole. Thermal boundary conditions include heat sources, heat losses, and thermal resistances between interfaces, which result in time-dependent temperature distributions within the thermal system.
For machine tools as an example, non-homogeneous temperature distributions cause thermal expansions of the machine and thereby result inaccuracies in the manufacturing process. Exact quantification of thermal boundaries enables prediction and thereby correction and compensation of such inaccuracies.
An experimental method is introduced, which can be used to accurately quantify thermal boundary conditions for both, steady-state and transient thermal conditions. For this, the temperature field at a contact region is determined from images obtained through a high-speed infrared camera.
Predicting thermal boundaries poses a so-called inverse problem, by which the effect (temperature distribution) is measured in order to obtain information on the underlying cause (boundary condition). This is due to measurement errors being propagated and thus, having significant influence on the accuracy of the result. Solving such inverse problems thereby is dependent on a precise measurement technique.
The accuracy of the boundary condition determination can be further improved by comparing the temperature measurement to a numerical model of the observed thermal system, instead of obtaining it directly from a measured temperature field. Within this numerical model, the desired boundary condition is iteratively varied, in order to find optimal agreement between the numerically calculated temperatures and the measured temperatures.
As will be shown, the method has potential for improving measurement results for a multitude of thermal applications.