Pengembangan model mesin pengering metode vakum untuk pengeringan kayu kumea batu

Abstract

Currently, exporters of wood crafts have suffered many losses due to the rejection of their products by the importers. The reason is that many of their crafting goods are cracked after arriving in the countries of destination. The problem is caused by the difference in equilibrium moisture content. The extreme changes of humidity and temperature in the destination countries, which are mostly of temperate regions with equilibrium moisture content of around 10 percent, cause the occurrence of adaptation in moisture content. Consequently, shrinkage or expansion of wood might occur resulting in cracks. Problem in wood drying in Indonesia is particularly experienced by small scale or home industries where small and appropriate dryers are not available. So far, they usually use conventional dryers with bigger or over capacity (>25 m3) and longer drying time. More efficient and appropriate dryer is needed to overcome the problem. A new method by means of vacuum drying might be suitable for that purpose. However, characteristics of such vacuum drying have not been known specifically. Also, this kind of dryer has not been available in the domestic market. Therefore, an experiment was conducted by developing a vacuum dryer model designated for drying of kumea wood. The objectives of this research were: (a) to design and construct a model of vacuum dryer for wood, (b) to know the performance of the vacuum dryer, (c) to study the drying mechanism of kumea wood, and (d) to design small scale vacuum dryer for home industry. The vacuum dryer model was successfully made with a capacity of 0.017 m3 using convective heating. The performance of this machine was shown by its ability to dry materials at a pressure of below 1 Atm with controllable temperature. The change in wood moisture content in this vacuum drying was indicated by its decrease of around 67% at pressure condition of 64 cmHg and temperature of 45oC. Variables used in the process of vacuum drying affecting the wood moisture content were temperature, drying time and vacuum pressure. With combination of treatments of pressure and temperature of 34 cmHg, 49 cmHg, 64 cmHg and 45oC, 55oC, 75 oC, respectively, the drying rate constant (k) was around 0.015/minute or equivalent to a moisture content decrease of 0.9/h. At constant temperature, the lower the pressure of the drying chamber the higher the drying rate was; and at constant pressure, the lower the temperature of the drying chamber the lower the drying rate was. At observed and predicted temperatures that were not far different, a mathematical model was developed showing the relationship of the pressure and temperature of the drying chamber towards the value of the drying rate constant (k), i.e., 𝐤 𝐏,𝐓 =𝟎.𝟐𝟏𝟑𝐓𝟎.𝟒𝟓𝟏 𝟏𝐏 𝟎.𝟏𝟒𝟓.This mathematical model could be applied to study the heat and mass transfers in the thin layer wood vacuum drying with convective heating. This research finally resulted in small scale vacuum dryer using hot vapor flown into a heat exchanger mounted inside the drying chamber with a volume capacity of 10.5 m3.