Effectiveness of Timber Solar Dryers in Reducing Drying Time and Drying Defects in Comparison to Air Drying

Abstract

An air drying shed and two green-house type of solar dryers of different designs were constructed at the Forest National Corporation sawmill at Suki town, Sennar State. Timber stacks in all three dryers consisted of 120 sunt (Acacia nilotica ) boards each stacked in 15 rows with 8 boards in each row..Three sample boards were selected in each stack for periodic measurement of moisture content (M.C.) and following the progress of drying in the three dryers. The three sample boards were placed at different levels of each stack. Each sample board was taken out at two days interval, weighed and returned to the stack. The dry-blub and wet-bulb thermometer readings were recoded and relative humidity worked out for each dryer. The moisture content was also calculated at two days interval. The results obtained showed that the average temperatures in the two solar dryers were significantly higher than that of the air dryer (ambient temperature). This resulted in a lower average final M.C. and lower equilibrium M.C. in solar dryers than in the air dryer. Solar dryer with high collector (SH) was the most efficient of the three dryers, with average final M.C. of 10.7% and equilibrium M.C. of 6.7%. This was followed by the solar dryer with low collector (SL) with average final M.C. of 11.9% and equilibrium M.C. of 7.5%, and lastly the air dryer with average final M.C. of 13.8% and equilibrium M.C. of 9.2%... The drying defects observed included minor warping incidents in the form of bowing which was more pronounced in air drying than in the solar dryers.