Similarity laws for experimental assessment of the thermal efficiency of a wall with optimized shape submitted to two-dimensional heat transfer

Abstract

To assess the energy efficiency of wall prototypes with advanced designs, real scale experimental demonstrators are difficult and expensive projects. To address this issue, this study develops a reduced scale experimental demonstrator based on similarity laws established for a problem of transient two-dimensional heat transfer with boundary conditions varying in time and space. Based on the dimensionless formulation of the problem, scaling factors are defined to link the real model and the reduced scale demonstrator. Here, a geometry and a kinetic similarity change are applied to build a reduced experimental demonstrator using 3D printing technology. To simulate external winter climate conditions, a heat flux is imposed using a heater pad at the top of the wall. It replicates the incoming radiation flux that partially heats the sunlit part of the wall. Two wall prototypes are investigated: one with a classical planar external boundary and one with a curved external boundary. The latter results from shape optimization to enhance the energy efficiency. Measurements of temperature are used to verify the reliability of the similarity laws. A satisfactory agreement is observed between the model predictions and the experimental results. Finally, the energy efficiency of the curved and plane wall prototypes is assessed based on the experimental data.