An experimental method for estimating the thermal diffusivity of building elements, depending on the resolution of temperature measurement

  • Mariusz Owczarek Military University of Technology, Warsaw, Poland
Keywords: thermal diffusivity, physical properties

Abstract

Thermal diffusivity, also known as temperature equalization coefficient, is the basic parameter in the Fourier equation for non-stationary heat exchange. Its values are known for homogeneous materials with a specific composition. Building elements made of reinforced concrete, for example, have a heterogeneous structure. For such cases, table values from the literature may differ significantly from the specific object for in real constructions. More accurate thermal diffusivity values can be obtained from measurements for a given element. Since these are usually large sized elements, the measurement method should take into account the material in the entire volume of the element. Proposals for such a method based solely on temperature measurement at several depths in the sample were presented. It consists in solving the inverse problem assuming a polynomial solution of the Fourier equation. An attempt was made to validate the method through a numerical experiment. Temperature variability was simulated with one-dimensional flow in the wall with assumed thermal diffusivity. Then the value of this diffusivity was determined from the calculated temperatures. On the inside of the partition, a constant temperature was maintained and on the outside it changed periodically. The dependence of the error in the obtained diffusivity value on the precision of temperature results was analyzed. Depending on the precision of the calculations, a minimum relative error of 2 to 6 percent was obtained. With the help of the data presented in the article, conclusions can be drawn as to the conditions that must be met to determine the value of diffusivity in real measurements with the required accuracy. The obtained results indicate that this method is worth further research.

Published
2019-03-15
Section
Research articles