Analytical and Experimental Investigations on the Transient Heat Transfer Process in Moist Wood Wool Slabs

Abstract

Heat and moisture transfer in wood wool slabs (shredded wood with Portland cement binder) has been investigated both experimentally and theoretically. The purpose of this study is the analysis of the process of moisture redistribution taking place inside wood wool slabs conditioned to moisture equilibrium (e.g., in a climatic chamber) and then mounted in a guarded hot plate or heat flux meter apparatus to measure the specimen thermal resistance. A theoretical analysis of the heat and mass transfer process for such a material was performed and then a suitable numerical model was used to predict and analyse the moisture redistribution. The porous media may be modelled as a multiphase system constituted by a solid matrix and a network of interconnected pores, partly filled with liquid water and partly with moist air. Three equations have been derived: conservation of the mass of the dry air, the conservation of the mass of water species (liquid and vapour) and the energy balance. These equations have been supplemented with the thermodynamic relations and the constitutive equations needed for the closure of the model. The experimental work was performed on a slab cut into several slices. During the experimental tests, the temperature and heat flow rate data was collected both during the steady state conditions to get the thermal resistance and during the initial transient period, when the heat flow rate is continuously varying. At the end of the test, the slices were weighed to get information on the moisture redistribution. The moisture data versus heat flow rate and temperature on the two faces of the specimen, and information about the final moisture distribution were compared with those obtained by numerical simulation. Substantial agreement between numerical result and experimental data was found.