This paper proposes a method for determining an effective value of the thermal conductivity for moist, highly porous rigid polymer foams. The model of moist foam based on an ordered structure with interpenetrating components was developed in accordance with the moisture distribution in the pore space. With small moisture content, isolated water inclusions are formed, and the pore space is considered as a binary system (vapor-gas mixture and water) with isolated inclusions. With an increase in moisture content, isolated water inclusions merge, forming a continuous layer, and pore space is considered as a binary system of interpenetrating components. The thermal conductivity of the vapor-gas mixture is represented as the sum of the thermal conductivity of the dry gas and the thermal conductivity of the vapor caused by the diffusion transfer of vapor in the pore space, taking into account the coefficient of vapor diffusion resistance. Using the proposed scheme of calculation, a computational experiment was performed to establish the influence of the vapor diffusion, moisture content, and average temperature of the foam on its thermal conductivity.
In the paper the authors present the effectiveness of the generalized thermal conductivity method for polymer foams, including modelling their geometrical structure. Calculations of the effective thermal conductivity coefficient λ are based on the generally accepted assumption of the additivity of different thermal exchange mechanisms in porous media and this coefficient is presented as a sum the coefficients of conductive λq, radiative λp, and convective λk thermal conductivity. However, in literature not enough attention is given to relations determined by means of the theory of generalized conductivity, including modelling the geometrical structure. This paper presents an analysis of these relations and verifies their ability to predict experimental data in comparison with the best formulae included in the paper [2].
The non-stationary moisture level of a cellular concrete wall board in a heated utility building located in the northern part of the town of Brest (Belarus), depending on the climatic influence, was assessed in this work. The results were obtained both in a calculation experiment and a physical test. It was observed that the main reason for the high moisture levels in cellular concrete is wind-driven rain intensifying the process of free capillary moisture transfer. A comparative analysis of the results of the physical test and the calculation experiment showed that the THSS software elaborated by the authors was able to predict the actual moisture levels of the shielding structure under study accurately enough when precise data concerning the thermal and physical characteristics of the materials as well as the occurring climatic influences were submitted.
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