Effectiveness of air dryers and solar kilns for timber wood drying

Abstract

Air drying (AD) and solar kiln ( SK) drying of timber are known to dependent on weather conditions; though they are reported to be more affordable compared to conventional kiln. The objective of this study was to evaluate the drying capacity of timber, using air dryers and solar kilns. Khaya ivorensis boards (25 mm x 300 mm x 1200 mm) were seasoned under air- and solar kiln environments for 5 weeks, and comparably assessed along with the initial moisture content (%), drying rate (%/time), moisture content gradient (%) and drying defects. From the initial moisture content of 134.65 and 137.52%, K. ivorensis wood attained average final moisture content of 13.07 and 26.29% at drying rate (%/time) of 3.47%/5 weeks and 3.18%/5 weeks for solar kiln-and air-dried samples, respectively. Using the equilibrium moisture content (12-15% MC) as the reference point, average moisture content gradient in solar kiln-dried board (13.07% MC) was 0.7%; while that of the air dried samples (26.29% MC) was not determined. Furthermore, defects were mild, and lower proportions of boards were affected more in solar kiln-dried samples than in the air counterpart. Selected climate variables (temperature and relative humidity) of the wood drying environments were measured on a daily basis. Average temperature (OC) was higher in the solar kiln (36.27) compared to air drying (26.05) for week 1, week 2, week 3, week 4 and week 5, respectively. Relative humidity was lowest (49.33 and 81.38) and highest (56.38 and 93.52) in solar kiln and air drying, respectively. Based on the selected indices examined, it is clear from this study that the response of K. ivorensis wood to drying is superior in solar kilns to in air dryers.