Steady state experimental investigation of thermal contact conductance between curvilinear contacts using liquid crystal thermography

Abstract

Heat transfer components comprise of several types of metallic contacts. Commencing from the conventional conforming rough surface contact combinations, the situation might culminate in terms of the complex non-conforming rough curvilinear contacts of the real heat transfer devices. Available theoretical models fail to correctly predict thermal contact conductance (TCC) over the broader range of influencing parameters, even for the simplest geometry, and thus experiments plays a pivotal role in the field. Researchers are indefatigably working for developing accurate experimental methodologies to get precise estimate of TCC, and create broader database of results for upcoming theoretical models.In this regard, this paper presents steady state thermal contact conductance analysis on two solid bodies of brass, carrying flat and curvilinear contact combinations, under variable loading conditions ranging in between 0.27 and 4.0 kN. A customized and standardized experimental set up has been used to measure steady state TCC for three different types of geometrical configurations, which are flat-flat, cylinder-flat and cylinder-cylinder contacts. At the start, TCC has been evaluated on the basis of centrally placed high response, super accurate, ungrounded thermocouples, which are mounted axially across the contacting bodies. In the later part of the paper, an optical, non-invasive and inexpensive method, based upon liquid crystal thermography (LCT) has been implemented to get the precise estimate of TCC for different configurations under consideration. The region close to the interface, which has the profound effect on the axial temperature distributions, is identified. Eventually, the separation region, where dramatic variation in the thermal conductivity occurs and classical Fourier law tends to fail has been identified. The separation region is further segregated in sub-regions on the basis of distinct temperature zones, which allows estimating the effective thermal conductivity of the materials in gap. The precise temperature jump close to the interface is extrapolated, and consequentially used to predict the steady state TCC for all three geometrical configurations. The value of TCC is evaluated again on the basis of effective thermal conductivity concept, and the results have been compared together. The present investigation establish a unique methodology for TCC estimation on the basis of steady state liquid crystal (LC) measurements, and provide valuable insight of heat transfer across the curvilinear contacts, and can be treated as the base line measurements for any of the upcoming scale resolved numerical models.