Influence of thermal boundary layer on thermophysical properties of construction materials

¹ National Research University Moscow State University of Civil Engineering (“NRU MGSU”), 26, Yaroslavskoe Shosse, Moscow, 129337, Russian Federation
² Belgorod State Technological University (BSTU named after V.G. Shukhov), 46, Kostyukova St., Belgorod, 308012, Russian Federation

^* Corresponding author: anik.tv@yandex.ru

Abstract

The paper considers the influence of thermal boundary layer on the thermal conductivity coefficient of building materials. The influence of thermal boundary layer on the thermal characteristics is shown on the example of cellular materials such as foam concrete, gas silicate and vacuum-powder thermal insulation materials.New ideas about regularities and mechanism of action of such factors as pore size, thickness and composition of interstitial partitions on thermal conductivity of porous materials are proposed. The thermal characteristics of porous systems were analyzed using the theory of similarity (calculation of Grasgoff, Rayleigh, and Prandtl criteria). Calculation of these criteria showed that in cellular materials with pore diameter up to 4 mm the convective component does not influence the heat transfer coefficient. The thermal boundary layer, a low-moving thin layer of gas adsorbed on the inner surface of the pore, has a great influence on the heat transfer processes in the pore. The paper considers the structure of the thermal boundary layer from the approach of the electrical surface properties of the pore and the gas in it. It is shown that the structure of the thermal boundary layer depends on the surface charges of the solid phase and gas. In the environment of air or oxygen denser and more homogeneous in structure thermal boundary layer will have materials, which pore walls will have an effective positive charge, and the thermal boundary layer of materials with a large negative surface charge will be loose, inhomogeneous. In hydrogen medium, on the contrary, materials with an effective negative charge will have a denser and more homogeneous thermal boundary layer structure.