Thermodynamics: The Theory of a Solar Timber Dryer
Thermodynamics: The Theory of a Solar Timber Dryer
The theory of a timber solar kiln
The main parts of a solar dryer for timber are the transparent roof (the solar collector) heat storage inside the kiln, ventilation and insulation. Most assume the shape of a solar greenhouse. The transparent roof (collector) is positioned in such a way that maximum incident sun rays can be harnessed. Most of the dryers have roofs positioned facing the south side. The optimum roof angle (mostly 45 degrees) is highly dependent on slope and season. (Brian Band, 2014). The amount of incident solar collected depends on the positioning and angle of the roof, the type of transparent material used (glazing), and the season of operation. The glazing must be capable of transmitting solar energy without reflecting any, and must possess very little vulnerability to degradation by UV rays (Virginia univ. cooperative extension, 2008).
Insulated walls ensure little heat loss and help maintain local temperatures inside solar kilns constant for uniform and all day long drying. Generally, the heat gain through the transparent roof is not large enough to start off evaporation process in timber and hence storage of as much heat as possible and reducing possible losses through both the roof band the floor is necessary. Mostly plastic sheets on the inside of the wall, or coating the wall with a vapor resistant material helps achieve this. Aluminum coats are recommended. (Wengert et al, 2014)Thermodynamics: The Theory of a Solar Timber Dryer .
Ventilation in solar kilns is enhanced by manipulating the relative humidity in the dryer. Lower humidity would result in faster drying as opposed to high humidity within kilns. Humidity within kilns is controlled by venting. Some of the warm moist air is exhausted and fresh cold and dry air brought in to do the balance. The fresh cooler air is thus heated, and its RH lowered. This cyclic activity results in drying. It must be noted that excessive venting is wasteful and is therefore not recommended as it leads to slow drying while inadequate venting also result to very high RH and similarly reduces the speed of drying.
The incident solar coming through the transparent roof hits and warms the air inside the kiln, which in turn reaches the optimum temperatures required to start off the evaporation of moisture from timber. Factors that affect the time taken by timber to dry inside solar kilns include; species of the wood, season and materials used. (Wengert,et al 2014)
ORDER A PLAGIARISM-FREE PAPER NOW
Cost effectiveness of a solar kiln for timber.
The cost effectiveness of a solar kiln assessed from a greenhouse type solar kiln working on a conventional technique. A study on both the operational and capital costs revealed to be much lower than those of the steam kilns. In comparison to air drying, the solar kilns were cheaper. Furthermore, the kiln cost less than half the price of a steam kiln. In terms of the pay back period, solar kilns took close to one year to accrue the investment while steam kiln took between 31-45 years to pay back the invested amounts. Sattar et al, 1994 therefore deduced that solar kilns were more cost effective than steam kilns in Bangladesh. Thermodynamics: The Theory of a Solar Timber Dryer .
In an attempt to assess the financial viability of solar heated drying kilns for timber, R.A Plumptre, 1979 discusses the various types of solar heated kilns, their advantages and their disadvantages and compared to other common methods such as air drying and steam heated kilns Their ability to achieve the desired moisture content, while retaining quality of wood. A number of kilns are discussed under this literature, and simple costings are included for each method. Its deduced that solar heated kilns are far much affordable both in effectiveness and the overall cost. Thermodynamics: The Theory of a Solar Timber Dryer .
