低温低压下工业铁粉的干燥特性及传热传质分析

本文通过搭建低温低压热泵干燥装置,研究了工业铁粉在不同低压下的干燥效果并分析了低温低压干燥过程中的传热与传质。结果表明:降低干燥环境压力会增大湿铁粉的除湿量,当环境压力从101 kPa降至10 kPa,除湿量增加2.5倍,且在10 kPa压力下铁粉含湿量能降至1%以下。当干燥空气为50℃,风速为0.5 m/s时,随着压力从101 kPa逐渐降至10 kPa,传质系数降低28.1%,传热系数降低68.4%,因此表征传热传质相对强度的刘易斯因子LF随着环境压力的降低而降低。当环境压力为10 kPa、风温为50℃时,流速从0.2 m/s增至2.0 m/s时,传质系数增加32.9%,传热系数增加67.8%,表明低压环境抑制了风速对传质系数的强化作用,因此LF随着风速的增加而增加。在10 kPa环境压力下,LF低至0.5~0.6,表明低压环境中质量扩散与热量扩散存在明显区别。

Drying Characteristics and Analysis of Heat and Mass Transfer of Industrial Iron Powder at Low Temperature and Low Pressure

In this study,a low-temperature and low-pressure heat pump drying device was built to explore the drying effect of industrial iron powder at different low pressures and analyze the heat and mass transfer in the low-temperature and low-pressure drying processes.The results show that a decrease in the drying ambient pressure can increase the dehumidification capacity of wet iron powder.When the ambient pressure drops from 101 kPa to 10 kPa,the dehumidification capacity increases by 2.5 times,and the moisture content of iron powder can be reduced to less than 1%at a pressure of 10 kPa.For drying air at 50℃and 0.5 m/s,the mass and heat transfer coefficient decrease by 28.1%and by 68.4%,respectively,as the pressure decreases from 101 kPa to 10 kPa.Therefore,the Lewis factor,which characterizes the relative intensity of heat and mass transfer,can increase with the ambient pressure decrease.In a drying environment of 10 kPa and 50℃,the mass and heat transfer coefficient increase by 32.9%and 67.8%,respectively,when the air speed increases from 0.2 m/s to 2 m/s.This indicates that the enhanced effect of air speed on the mass transfer coefficient is inhibited by the low-pressure environment;thus,the Lewis factor increases with the increase in air speed.The Lewis factor is 0.5-0.6 in an environment of 10 kPa,indicating that there are obvious differences between the mass diffusion and heat diffusion in a low-pressure environment.