Theoretical Investigation of Vapor Transport Mechanism Using Tubular Membrane Distillation Module.

Shereen M. S. Abdel-Hamid,Mohamed Helmy Abdel-Aziz,Mohamed Shafick Zoromba,Yasser Elhenawy,Hassn Safi Ahmed,Mohamed Bassyouni,Adnan Alhathal Alanezi

doi:10.3390/membranes11080560

Abstract

This paper’s primary objective is to examine the vapor delivery mechanism through a tubular membrane distillation (MD) module. Experiments were conducted utilizing a hydrophobic tubular membrane module with a pore size of 0.2 µm. To establish the mass transport mechanism of water vapor, tests were carried out first with pure water as a feed. The permeate flow was then determined using NaCl aqueous feed solutions. Distilled water flux at diverse feed temperatures, feed flow rates, and feed salt concentrations was investigated. The permeate flux improved linearly with rising temperature and flow rate of the feed, however, it declined with feed concentration. Increasing temperature from 40 to 70 °C increased the permeate flux by a factor of 2.2, while increasing the feed flow rate from 60 to 120 L/h increased the permeate flux by a factor ranging from 0.7 to 1.1 depending on feed temperature. Using the Dusty gas model (DGM) the mass transport of water vapor is estimated in the membrane pores. The results showed that the water vapor delivery is controlled by way of the Knudsen molecular diffusion transition mechanism and its version changed into one capable of predicting the permeate fluxes. The mass transfer coefficient calculated and located using the Knudsen molecular transition version agreed properly with the corresponding experimental value. The delivery resistances were affected by working parameters, along with feed temperature, flow rate, and concentration. The mass transfer resistance of the membrane became the predominant controlling step to the MD process.

Highlights

Membrane distillation (MD) is a low-temperature membrane purification technique that separates vapor from a liquid solution by flowing it through membrane pores
The total heat flux of the feed solution and infiltrate bulk fluids ( Q) is obtained by the addition of the two heat fluxes occurring in the hydrophobic membrane, which are the latent heat of vaporization ( Qv ) and the conduction ( Qc ) through the vapor contained inside the membrane holes and the membrane material
The water component vaporizes at the membrane’s exterior on the feed side, is emitted from the membrane pores, and condenses on the vapor–liquid boundary at the permeate lateral with heat flux written as: Qv = J · ∆Hv where Qv W/m is a form of energy transferred to the liquid in the vapor stream in the manner of latent heat to provide the needed heat of vaporization, and to compensate for that heat by condensation on the other lateral plane of the membrane, J kg/m s is the water flux through the membrane and ∆Hv is the latent heat of vaporization of water vapor

Summary

Introduction

Membrane distillation (MD) is a low-temperature membrane purification technique that separates vapor from a liquid solution by flowing it through membrane pores. The temperature differential between feed and permeate generates driving force across the hydrophobic membrane. The vapor–liquid equilibrium is used to guide the MD separation process [1,2,3]. Membrane distillation is useful since it is inexpensive and widely available. This characteristic conserves energy in comparison to traditional desalination

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