Non-Stationary Identification of Thermal Characteristics of Building Materials

Abstract

The pore space of building materials can act as an accumulation space, as well as a free space for liquid or gas flows. Such changes in material structure force substantial modification of its effective thermal conductivity and heat capacity. The traditional methods of stationary analysis for the thermal conductivity and calorimetric measurements for the heat capacity are often inaccurate or quite not applicable to a lot of materials of practical importance. The paper demonstrates the original non-expensive non-stationary measurement device for thermal characteristics of building materials, open to a reliable uncertainty analysis of all measurements. Its very simple structure, inspired by the “hot-wire” method, controlling the heat flux generated into a layered structure, is compensated by the non-trivial computational approach, based on the semi-analytical solution of initial and boundary value problems for corresponding differential equations of heat transfer. The numerical discretization uses the Hermite finite-element interpolation technique for the temperature field and its gradient in the Euclidean space and the Crank-Nicholson scheme in time. The required material characteristics are obtained as outputs from the least squares optimization, supported by certain iterative algorithm of the Newton type.