Investigations of thermal boundary conditions at contact interfaces
- Untersuchungen von thermischen Randbedingungen an Kontaktstellen
Frekers, Yona Henrik; Kneer, Reinhold (Thesis advisor); Herzog, Roland (Thesis advisor)
Dissertation / PhD Thesis
Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2019
The development of methods for the description of thermal behavior is a significant challenge for numerous technical applications. Particularly relevant is the accurate prediction of thermal boundary conditions, which influence the thermal system and thereby act as the cause of temperatures and heat flows. However, the precise determination of thermal boundary conditions is a demanding procedure as no direct measurement is possible. Instead, such boundary conditions are determined by measuring the temperature field resulting from them. This constitutes an inverse problem, which reacts sensitively to measurement errors and, thus, requires elaborate measurement and evaluation procedures. The present thesis describes a measurement method, which obtains temperatures by means of infrared thermography and allows the determination of thermal boundary conditions by comparing measurements with predictions from a numerical model of the observed thermal system. The methodology is described for contact interfaces between machine components. Thermal boundary conditions at contact spots are a result of microscopic surface roughness, which leads to a reduction of the actual surface area in contact, thereby causing thermal resistance. In addition, a numerical tool is presented, which allows prediction of contact heat transfer coefficients without the need of an experiment. The mechanical deformation of surfaces under contact pressure is simulated, using half-space description of topographically measured surface profiles. Both methods are investigated for various contact pressures, sample materials and for different interstitial fluids within the contact zone. A comprehensive description of possible sources for errors and an evaluation of the quality of results is given for both methodologies. Furthermore, the experimental methodology is evaluated through an exemplary technical application, for which heat flow into a cutting tool is determined during milling.