Numerical Simulation of Thermal Conductivity of Foam Glass Based on the Steady-State Method

Abstract

The effects of fly ash, sodium carbonate content, foaming temperature and foaming time on foam glass aperture sizes and their distribution were analyzed by the orthogonal experimental design. Results from the steady-state method showed a normal distribution of the number of apertures with change in average aperture, which ranges from 0.1 to 2.0 mm for more than 93% of apertures. For a given porosity, the thermal conductivity decreases with the increase of the aperture size. The apertures in the sample have obvious effects in blocking the heat flow transmission: heat flow is quickly diverted to both sides when encountered with the aperture. When the thickness of the sample is constant, the thermal resistance of the foam glass sample increases with increasing porosity, leading to better thermal insulation. Furthermore, our results suggest that the more evenly distributed and orderly arranged the apertures are in the foam glass material, the larger the thermal resistance of the material and hence, the better the thermal insulation.

Coupling inverse fin method with infrared thermography to determine the effective thermal conductivity of extruded thermoplastic foams

“…The assumption of the small Biot number is also well verified Bi = 0.44×0.002 0.164 = 0.0053 < 0.1 . This result is compared with the previous one [21], obtained by a numerical finite element solution and validated with the Transient Plane Source technique (TPS) method (Hot Disk) ( Table 2). The experimental values are close to numerical solution.…”

“…It is assumed that the model can be treated as adiabatic at the end ( x = L ), that the convective heat loss from the fin tip is negligible and that the temperature at the base ( x = 0 ) is constant, T 0 . To facilitate analysis of the thermal conductivity of the foam glass, the following assumptions are made as in [21,22]: the medium is an isotropic material, its boundary is adiabatic (meaning that no heat is dissipated at the boundary), thermal conductivity is independent of temperature, the temperature is linearly distributed along the heat flow direction (in the x direction), steady-state conditions are established, no heat generation, heat transfer by both convection and radiation are negligible. Moreover, the fin is assumed to be thin, which implies that the temperature variations in the longitudinal direction are much larger than those in the transverse direction [23,24].…”

“…Comparison between experimental results from fin method, and previous[21] numerical solution based on periodic homogenization techniques (NSHT) and transient plane source technique (Hot Temperature dependent convection along x axis in the 2 mm thick bulk PE sampleComparison of the experimental and computed stationary temperature profiles in a 2 mm thick sample of PE foam (45%, porosity) (a)…”

Numerical Study Using Microstructure Based Finite Element Modeling of the Onset of Convective Heat Transfer in Closed-Cell Polymeric Foam

“…The energy transfer within the bulk cellular materials is carry out via three competing mechanisms: conduction across the material matrix and the occluded gas, natural convection of the occluded gas in the pores, and radiation within the internal solid surfaces of the matrix. The effective or overall thermal conductivity is depicted as the result of these additive terms, where the conductive heat transfer is the most dominant; therefore, the transport phenomena in such systems are mainly described by the thermo-physical properties that emerge from the conductive transport [ 4 , 5 , 6 , 11 , 12 , 13 ]. Some descriptions have considered a term for radiative heat transfer flux, and they suggest that radiation may contribute 6–26% of the effective conductivity [ 5 ].…”

“…Very detailed numerical investigations of the radiative transfer on several polymeric foams were performed in the literature to study the radiative properties of the foams as a function of cell size and wall geometry [ 14 , 15 , 16 ]. In most cases, convective heat transfer is not considered by arguing that the associated heat transfer caused by this is insignificant for cell diameters less than 4 mm [ 5 , 11 , 13 , 17 ]. The investigation into the heat transfer rate due to natural convection within the microstructures of closed-cell cellular materials has received much less attention than the conductive and radiative heat transfer in the experimental and numerical studies of thermal transport [ 2 ].…”