FAPO-5干燥剂涂层等温除湿传质特性的实验与理论研究

Experimental and Theoretical Study on the Mass Transfer Characteristics of FAPO-5 Desiccant Coating Under Isothermal Dehumidification

FAPO-5磷酸铝分子筛干燥剂在低再生温度下仍具有高效吸湿能力,但其“S”形吸附等温线存在明显温度依赖性以及陡峭的平衡吸湿量变化区间,因而吸湿能力易受热影响制约。为了揭示消除热影响条件下FAPO-5干燥剂涂层的吸附传质能力,该文开展了等温除湿传质特性实验与理论研究。结果表明,吸附温度、空气湿度和流速以及干燥剂层厚度对传质特性均具有重要影响。不同实验条件下,瞬时质量传递速率jm和总传质系数Ktot存在不同变化趋势,但吸附动力学特性均可被LDF模型良好描述。空气湿度和流速的增加可增大吸附速率系数k_(LDF),减小平均总传质系数K_(tot),而吸附温度和干燥剂层厚度的增加可减小k_(LDF),相应K_(tot)随吸附温度增加而减小,随厚度增加而增加。特别地,K_(tot)与k_(LDF)可拟合为指数方程,K_(tot)随k_(LDF)增大整体成下降趋势。

FAPO-5 desiccant has high effective adsorption capacity even at low regeneration temperature,but its S-shape adsorption isotherm show a significant temperature dependence and steep gradient range.Therefore,the moisture adsorption capacity is easily restricted by the thermal side effect.In order to reveal the mass transfer capacity of adsorption process under the condition without the thermal effect,the mass transfer characteristics of FAPO-5 desiccant coating under isothermal dehumidification were experimentally and theoretically studied in this paper.Results show that the adsorption temperature,air humidity,air velocity and desiccant layer thickness have important effects on the mass transfer characteristics.The different trends of transient mass transfer rate jm and total mass transfer coefficient K_(tot) are observed under various experiment conditions,but the adsorption kinetic of FAPO-5 desiccant coating can be well described by the LDF model.The adsorption rate coeficient k_(LDF) increases with the increase of air humidity and velocity,but decreases with the increase of adsorption temperature and desiccant layer thickness.In contrast,the average total mass transfer coefficient K_(tot) decreases with the increase of air humidity,velocity and adsorption temperature,but increases with the increase of desiccant layer thickness.In particular,the correlation of K_(tot) and k_(LDF) can be fitted into an exponential equation,and the overall trend of K_(tot) is decreased as the k_(LDF) increases.