Finite-volume modelling of heat and mass transfer during convective drying of porous bodies – Non-conjugate and conjugate formulations involving the aerodynamic effects

In this study, a numerical procedure is outlined and representative results for heat and mass transfer during convective drying of porous bodies are presented. The Luikov model was implemented and applied both on individual samples of construction materials and agricultural products, as well as on a drying-chamber scale, with parallel flow of a hot air stream over rectangular slabs which represent the product to be dried. In the latter case the configuration is an experimental dryer in which the heat source is a solar air collector with evacuated tubes. A general approach was developed that allows a selection between modelling of phenomena either in the drying solid only, or considering an extended simulation domain encompassing, apart from the solid body, the flow of air as well. In the second case, the solution of the flow field is pursued along with a conjugate heat/mass transfer problem coupling the solid and fluid phenomena and in both cases phase change (evaporation) was taken into account. For the numerical simulation, the finite-volume method was used. The validation of the model was based on experimental and numerical results from the literature and results from simulations that were conducted in the pursuit of the energetic optimization of an experimental solar dryer of NCSR “Demokritos” are presented. In the latter case, the effect of the particular flow field features developing for a single and a double-plate configuration on the heat/mass transport and drying rates is demonstrated. Such a methodology could be used to analyze the transport phenomena in any type of convective dryer, including those utilizing solar energy as the heat source.