Conduction/radiation combined heat transfer with contact resistance for application to vacuum insulation

Abstract

Combined heat transfer of conduction and radiation is investigated with thermal contact resistance boundary condition to scrutinize the effect on heat transfer and to evaluate the thermal performance of vacuum insulation panels (VIPs). Numerical analysis shows that introduction of contact resistance flattens temperature profile and reduces both the conductive and the radiative heat transfer. In VIPs, if interstitial material is purely absorbing/emitting and well contacting the radiation shield, center-of-panel thermal conductivity can be more than twice larger than that estimated by separate analysis of conduction and radiation, especially when the optical thickness of the layer is moderate and the wall emissivity is low. On the other hand, this error decreases with increased scattering albedo and reduced conduction/radiation interaction. In any case, use of low-emissivity shields greatly improves the insulation performance. Further, contact resistance between the interstitial material and the shields reduces the heat transfer substantially. Thus, insulation performance of VIP with artificial core structures can be greatly improved by employing rough or embossed, and highly reflecting shields. (C) 2018 Elsevier Ltd. All rights reserved.