FEATURES OF HEAT AND MASS TRANSFER AT DRYING OF TIMBER BY STEPLESS MODES
According to the founders, convective drying necessarily occurs in the presence of heat and mass transfer. At the same time, wood drying is characterized by almost the highest energy consumption among other wood processing. The heat and mass transfer process has its own characteristics during drying modes of various types and they are significant very often. The system of three-stage drying lumber modes which developed in the late 60-th, has many disadvantages with sufficient ease of implementation. Multi-stage or stepless modes allow, on the one hand, to improve the drying quality, and on the other to reduce the process duration and also electricity and heat cost for it. Studies of drying processes by conducting an active experiment on industrial equipment require significant material and energy costs. On the other hand, computer simulation of the wood drying process as a heat and mass transfer process of capillary-porous body in the air allows to obtain results with sufficient accuracy describing the real processes occurring with wood during the moisture removal from it. The conducted studies are based on computer modeling, clearly demonstrated that the stepless modes advantages are based on the heat and mass transfer process features occurring during the lumber drying. The analysis of the processes of timber drying by traditional modes shows a significant irregularity of the heating and drying processes in time and sawn wood thickness. It becomes evident upon closer analysis of the mass transfer criterions change regularity in particular criterion Bio. The main feature of the stepless modes is the possibility of almost complete control of the moisture removal process, which allows provides high quality drying with minimal energy consumption. It is especially true of the distribution of the final moisture uniformity in the cross section of the dried board, and also a significantly greater value of the safety criterion of a drying mode compared with the drying three-stage modes were recommended by The Technical Guidance Materials on the Technology of the Chamber drying of a Sawn Wood. The implemented approach is characterized by efficiency and universality in respect of not only the types of modes, but also the drying wood methods.