Investigating optimized drying methods for Eucalyptus delegatensis using a solar kiln

Abstract

Drying timber is one of the most important stages in the production of high quality timber. Using solar kilns to dry timber is a simple and affordable method because it uses solar energy; furthermore, the cyclic drying process may produce better results than conventional kiln drying due to its diurnal heating and non-heating phases. Solar kiln drying is especially beneficial in tropical countries, such as Laos, where high temperature and solar radiation levels are present. The aim of this PhD study was to simulate solar kiln conditions using intermittent drying schedules in a conventional kiln to develop a model for gaining a better understanding of solar drying characteristics and to identify suitable locations for solar kilns. The specific objectives were to: • investigate the drying process in solar kilns, including the development of a method for measuring the formation of drying checks in timber boards; • investigate the application of an intermittent drying schedule to a solar kiln, based on a conventional laboratory schedule; • create a mathematical model for the moisture content profile during drying in a conventional kiln that simulates solar kiln conditions; and • create a model for identifying suitable locations for solar kilns in Vientiane, Laos, and to recommend the most productive performance of solar kiln in a calendar year. A comparison of two measurement methods (using digital callipers and Image J software) has been conducted and analysed. The study validated the application of the intermittent drying schedule of a conventional kiln to a solar kiln. A further improvement for intermittent drying to simulate solar kiln conditions has been implemented using a conventional laboratory kiln. A final experiment continued to improve the drying schedule under simulation. New methods have been developed, such as measuring internal checks using the ImageJ software and simulating solar kiln conditions, as well as a model for selecting suitable geographic locations for solar kilns. The new technique for simulating solar kilns conditions produced temperature gradient conditions 5oC less than the simple intermittent drying process. The GIS-based Fuzzy method model helped in understanding the effects of geographical conditions on the drying process using solar kilns. Application of the model can also identify the optimal performance of the kilns during a calendar year.