Performance comparison and economic analysis of three solar dryer designs for wood using a numerical simulation

Abstract

Three designs of a direct solar dryer for wood were evaluated with computer simulations. Calculations were performed using a heat and mass transfer model to obtain and compare the wood moisture content (MC) variation, as well as other drying parameters within the three designs. The findings showed higher drying temperatures and shorter drying times for solar dryers with large transparent cover areas (i.e., greenhouse-type dryers). Comparisons between glass covered and Plexiglas (PMMA) covered systems were also performed and the results indicated reasonably similar drying curves. The effect of using plastic cover was more prominent for dryers with low transparent areas (i.e., semi-greenhouse-type dryers), that is, 5% increase in the drying time for the greenhouse-type design and 10% increase for the semi-greenhouse-type designs. The economic analysis of the three designs revealed that double-glazing reduced the drying time, though it increased the cost of the covers by more than 130%. Inserting a Plexiglas cover over the glass cover resulted in a 25% decrease in the drying time and only a 57% increase in cost. Additionally, the combined plastic-glass configuration for the semi-greenhouse-type design resulted in a drying time comparable to this of the single glazing greenhouse-type design, though at a lower cost.