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Highlights • Conduction/radiation combined heat transfer is analyzed for applications in VIP. • Influences of emissivities and contact resistance on heat transfer are studied. • Conduction/radiation interaction can increases heat transfer by more than twice. • Use of reflective shields with contact resistance are recommended in VIPs. 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. [ABSTRACT FROM AUTHOR]

Radiative heat transfer is investigated for each of isotropic and backward scattering patterns to evaluate the radiative thermal conduction of vacuum insulation panels (VIPs). As a means of analysis, a new statistical formulation is proposed and the results are compared with those of diffusion approximation, Monte Carlo method and discrete ordinate interpolation method (DOIM). The results of the statistical formulation agree well with those of Monte Carlo method and DOIM within 1% error, so that it may be regarded as an exact solution method. The results show that the insulation performance of the VIP can be enhanced by increasing the optical thickness or decreasing the wall emissivity. Also, the backward scattering is about twice effective than the isotropic scattering. [ABSTRACT FROM AUTHOR]

Vacuum insulation panels (VIPs) have about ten times greater insulation performance compared with conventional insulators, and it is highly affected by the filler material. In this paper, pillar-supported vacuum insulation panel is proposed to release the filler material from the pressing load, thereby significantly decreasing the effective thermal conductivity. It is composed of the support structure and the multi-layered filler material. The support structure consists of the cover plates and pillars, as they sustain the atmospheric pressure. Thus, mechanical stability and heat transfer are considered together in the design stage. Multi-pass support (MPS) is introduced to further decrease the conduction through the pillar effectively. Also, the multi-layered filler material is composed of the glass wool sheets and radiation shields of low emissivity. The effective thermal conductivity of the tested specimen measures 1.18 mW/m K with vacuum guarded hot plate (VGHP), which shows twice better insulation performance than existing VIPs. [ABSTRACT FROM AUTHOR]