MODELING OF CONDUCTIVE HEAT TRANSFER IN LOW-DENSITY PVC FOAMS UNDER MECHANICAL LOAD

Abstract

Due to their excellent thermal insulation properties, low-density polyvinyl chloride (PVC) foams find applications in a wide variety of technological fields. They are notably used as thermal insulation in fuel tanks of Ariane rockets at very low temperatures. For this application, a relatively high mechanical strength is also required since the foams undergo significant mechanical loads during the flight. As a consequence, the mechanical strain undergone by the foams may affect their thermal behavior and vice versa, leading to a coupling between the mechanical and thermal properties. That is the reason why, in order to improve the modeling of the mechanical and thermal behaviors and to better understand their mutual influences, an original thermal model has been developed that is based on a shell mesh of the porous structures of PVC foams obtained by X-ray tomography. This permits the quick computation of the temperature field prevailing in the solid and fluid phases constituting the material and of the equivalent thermal transfer properties. The temperature field and thermal properties could then be used as entrance data of a mechanical finite-element computation. The effective thermal conductivities computed for non-deformed structures were compared with various correlations in the literature. Thereafter, the numerical model was applied to deformed structures obtained from mechanical finite-element computations modeling various mechanical loads. The analysis of the results highlights the major modifications of the thermal properties brought by different types of mechanical loads.