木片散堆碎料水分迁移系数的研究

本文首次提出利用梯度转换法,实验测定动态传质控制方程中的质扩散系数及传质边界条件中的质交换系数,求算了表面以下蒸发界面深度及其对蒸发速率与相对蒸发深度的关系。实验表明,多孔物料表面下的相对蒸发深度在1%以下时,对质迁移率的影响极为显著。质交换系数也是蒸发界面深度的函数。质扩散系数是含水率的函数。本文采用变系数分段线性化的方法,利用质扩散方程的解析解验算了所求出的质扩散系数、质交换系数及蒸发界面深度的可靠性。理论验算表明,无量纲质迁移势的理论值与实验值之间的相对误差不大于6%,从而说明,利用梯度转换法测定木片料床的质迁移系数的方法是可行的。

A study on the coefficients of water movement in piled wood chips

The method of gradient transformation was initialized in the paper. The diffusion coefficient in the governing differential equation of mass transfer and the surface emission coefficient on the boundary condition were experimentally determined. The effect of undersurface evaporation was quantitatively analyzed. The relationship between relative evaporation rate and the relative depth of evaporation surface was given. The experiment showed that the relative depth of evaporation below 1% influenced the relative evaporation rate significantly. The surface emission coefficient was also a function of the relative depth of evaporation.* The diffusion coefficient was a function of moisture content. By taking into account of the dependent of the above mentioned coefficients on the relative depth of evaporation and moisture content, the reliability of the given coefficients was tested by using the analytical solution of the governing differential equation of mass trapsfer. This showed a deviation in less than 6 between the measured values and the calculated values, which posed the results of the study as a valid exploring.