Experimental Studies of the Effective Thermal Conductivity of Polyurethane Foams with Different Morphologies

Abstract

Polyurethane foam (PUF) is actively used for thermal insulation. The main characteristic of thermal insulation is effective thermal conductivity. We studied the effective thermal conductivity of six samples of PUF with different types and sizes of cells. In the course of the research, heat was supplied to the foam using an induction heater in three different positions: above, below, or from the side of the foam. The studies were carried out in the temperature range from 30 to 100 °C. The research results showed that for all positions of the heater, the parameter that makes the greatest contribution to the change in thermal conductivity is the cell size. Two open-cell foam samples of different sizes (d = 3.1 mm and d = 0.725 mm) have thermal conductivity values of 0.0452 and 0.0287 W/m⸱K, respectively, at 50 °C. In the case of similar cell sizes for any position of the heater, the determining factor is the type of cells. Mixed-cell foam (d = 3.28 mm) at 50 °C has a thermal conductivity value of 0.0377 W/m⸱K, and open-cell foam (d = 3.1 mm) at the same temperature has a thermal conductivity value of 0.0452 W/m⸱K. The same foam sample shows different values of effective thermal conductivity when changing the position of the heater. When the heater is located from below the foam, for example, mixed-cell foam (d = 3.4 mm) has higher values of thermal conductivity (0.0446 W/m⸱K), than if the heater is located from above (0.0390 W/m⸱K). There are different values of the effective thermal conductivity in the upper and lower parts of the samples when the heater is located from the side of the foam. At 80 °C the difference is 40% for the open-cell foam (d = 3.1 mm).

Effect of the shape and the distribution of cells on the effective thermal conductivity of polyurethane foam

“…The REV must represent the right fraction of closed and open cells. 27 The PU foam is isotropic, while our REV is not. Actually, the isotropic REVs are tested; the geometry constructions of these REVs for the periodic case are obtained by cubes of unit cells pavements.…”

“…For the REV of PU mixed cell foam, the solid part is continuous and the gas part is continuous in three cells of the REV and discontinuous in the rest of the cells. The REV must represent the right fraction of closed and open cells 27 …”

“…The heat transfer in any cellular material is the result of three different mechanisms 26 : the conduction in the matrix, the convection in the gas, and the radiation in both of them. The contribution of convection is studied experimentally for different categories of PU foams 27 . It is meaningful in open cell PU foams in comparison to other types of foams.…”

“…The thermal characterization tests of PU foam give the apparent conductivity is given by Equation (1) as defined by Soloveva et al 27 …”

“…The contribution of convection is studied experimentally for different categories of PU foams. 27 It is meaningful in open cell PU foams in comparison to other types of foams. This contribution increases with cell size and temperature.…”