Numerical estimation of air gaps' influence on the insulating performance of multilayer thermal insulation

An attempt was made to study the benefits of multilayer thermal insulation in building applications placed in combination with two air gaps. A numerical approach was developed to determine the influence of the air gap thickness on the overall thermal resistance of a composite wall. A validated combined radiation/conduction heat transfer numerical model was used to predict the temperature distribution and heat transfer in typical multilayer insulation complexes consisting of insulating materials separated by multiple reflecting foils. The radiation scheme was based on the two-flux approximation, in order to model both optically thick and optically thin fibrous materials. The heat transfer equation was solved explicitly for a composite wall. A basic methodology for designing simulation scenarios was used to reduce the number of simulated cases. Strict entry requirements were provided to reduce extraneous variations due to the complexity of physical phenomena that should be investigated in such a case study. Nine different configurations were selected, where the theoretical thermal resistances were calculated and compared, leading to an empirical polynomial equation to calculate the overall thermal resistance of such a composite wall complex departing from the two air gap thickness values.