纤维膜在膜蒸馏过程中的膜内毛细冷凝现象

膜蒸馏过程中的膜内冷凝现象是该技术在实际应用中不可忽视的一个重要问题。本文以疏水化改性处理的纤维膜作为研究对象,采用实验现象观察和理论分析并用的方法,研究了纤维膜在膜蒸馏过程发生膜内毛细管冷凝的影响因素包括膜蒸馏模块结构、蒸馏膜参数、热力学参数,探讨了毛细冷凝对膜蒸馏的影响。实验表明毛细冷凝可以在膜蒸馏过程中发生,但并不终止膜蒸馏过程,而是减小了传质系数。毛细冷凝容易发生在蒸馏膜厚度小、热料液温度高、冷却液温度低或气隙小的情况下。实验结果和理论分析表明,传质系数实验值的降低可作为膜孔内发生毛细冷凝的判定依据。通过简化蒸气在疏水多孔介质的传递过程,建立了膜蒸馏过程发生毛细冷凝时的传质平衡模型。

Capillary Condensation in Fibrous Membranes During Membrane Distillation

Capillary condensation in the membranes during membrane distillation(MD)is an important issue that can affect the performance of the real applications of this emerging technique.This work focuses on the capillary condensation phenomenon specially in modified fibrous membranes.A set of initiated chemical vapor deposition treated electrospun fibrous membranes were tested for MD using a lab-scale air gap MD system.The influence of MD module structure,membrane parameters,and thermodynamic parameters on capillary condensation in the membranes during MD were studied theoretically and experimentally.The experimental results and theoretical analysis show that capillary condensation inside the pores of the membranes does not stop MD process,but decreases the permeate flux by decreasing the driving force across the membrane.Capillary condensation is more likely to take place in the air gap membrane distillation system with small air gap,thick membrane,high feed temperature,or low coolant temperature.An approach to indicate capillary condensation occurred in MD systems was proposed based on the study of the mass transfer coefficient.The mass transfer equilibrium when capillary condensation occurred in membrane pores was derived.