Experimental Study On Impinging Stream Drying Of Wood Particles

Impinging stream drying (ISD) is a new drying method that is being studied presently. It can significantly improve the heat and mass-transfer process by the deep turbulence made by the impinging of the opposite streams and the rapid and unstable movement of wet particles and finish drying process of wet materials in a very short time, so, ISD bears the characteristics of drying rapidly and in a high-intensity and maintaining the quality of materials. But so far, the flow and drying characteristics of ISD still have been studied by only a few researchers. Moreover, it is a completely new field that wood particles are dried by ISD. Therefore, experimental study on impinging stream drying of wood particles bears important academic significance and practical value.In this article, the following three researches are accomplished to discover the drying characteristics, influence on the quality of wood particles and kinetic rules of ISD:First, experimental study on the influence of air temperature, velocity, initial moisture content of wood particles and mass flow rates ratio on the process of ISD has been performed. The test results show that the performance of ISD will improve with the increase of air temperature, mass flow of air and initial moisture content of wood particles and the decrease of air humidity and mass flow rates ratio. In particular, the increase of air temperature and the decrease of mass flow rates ratio can improve the performance of ISD remarkably. The influence of air temperature and humidity isn't remarkable in comparison.Next, the performances of particle-board made of wood particles dried through the two different methods: the traditional air drying and the ISD, are measured, and the fibrous structure of wood particles is observed by digital microscope. The results indicate that the exterior shape and the interior fibrous structure of wood particles aren't broken after dried by ISD.Finally, the air velocity, the velocity of the wood particle, the relative velocity between the air and the wood particle, the wood particle's residencetime and the variations of the particle's velocity along radial and circle are measured. The ISD of wood particles is analyzed on dynamics. The results indicate: the concentration of wood particle near the outside wall of the annular pipe increase under the effect of centrifugal force. It slows the particle down, thus increases the relative velocity between the air and the wood particle, which causes the speed of heat and mass-transfer increase. The velocity of the wood particle increases rapidly at the moment of acceleration, then goes up steadily, reaches the maximum at last. The surge time of the wood particle increases and the residence of the one prolongs in the semi-circle with the increase of air velocity and the decrease of mass flow rates ratio.In a word, ISD is a good method of drying particle and bears a wonderful prospect. The article tries to provide the academic and experimental basis for establishment of technological parameters, design of the equipment and industrialization of ISD of wood particle, fibre and pulp etc forestry products.