Vacuum Membrane Distillation Module Research Articles

Analysis of Effect on Freshwater Production of Vacuum Membrane Distillation Module according to Housing Leak

In this study, the performance experiment was conducted to compare the permeate flux of hollow fiber Vacuum Membrane Distillation module according to leak problem between module housing and membrane bundle. For the permeate flux performance experiment of the two Vacuum Membrane Distillation modules, the Lab-scale experimental equipment was built in the capacity of . The performance test of the two Vacuum Membrane Distillation modules were analyzed according to the feed water conditions. As a result, it was analyzed that the leak VMD module decreased about 14% of permeate flux than normal VMD module.

A numerical approach to module design for crossflow vacuum membrane distillation systems

Abstract A numerical model for heat and mass transfer in vacuum membrane distillation (VMD) under laminar flow was developed using Computational Fluid Dynamics (CFD). Three-dimensional (3D) simulations of temperature and concentration polarization in single and multiple fibre VMD modules were used to estimate permeate flux (kg m−2 h−1) over a range of temperatures (30–70 °C), vacuum pressures (10–100 mmHg), crossflow velocities (0.0072–0.72 m/s), and feed concentrations (0–0.4 kg/L NaCl). Simulated flux differed by less than 7% from experimental data for a module with comparable dimensions. Simulations indicate that a 56% increase in fibre packing density resulted in a 24% flux decline at high operating temperature (70 °C), and more than 50% flux decline at low crossflow velocity (0.0072 m/s). The effect of vacuum pressure on flux was found to be independent to the module packing density, while the effect of salt concentration was found to be 28% lower than estimates based on Raoult's law, due to lower spatial variations in membrane surface temperatures at higher salt concentrations. The approach developed in this paper may be used to evaluate performance of alternative configurations for VMD models to aid module design, scale-up and process optimization.

Freshwater production characteristics of vacuum membrane distillation module for seawater desalination using a solar thermal system by seawater feed conditions

AbstractIn this study, the thermal performance experiment was conducted by seawater feed conditions of the VMD module prior to building the VMD module to be used in pilot plants in the capacity of 10 m3/d for seawater desalination using the solar thermal system. For the thermal performance experiment of the VMD module, the lab-scale desalination equipment was designed and made in the capacity of 1 m3/d and it was used to analyze changes in freshwater production by feedwater salinity, flow rate, and temperature conditions of the VMD module. By the result, it was analyzed that the VMD module used in this study required an average of 580 kWh/d heat capacity to produce 1 m3/d of freshwater.

Freshwater Production Characteristics according to the Feed Sea Water Conditions of Vacuum Membrane Distillation Module for Solar Desalination

In this study we built a lab scale VMD (Vacuum Membrane Distillation)system with a capacity of 1 m³ per day. The basic design data of the solar desalination plant, (freshwater production system) using a VMD module exhibited reduced energy requirements compared to other membrane distillation methods, as well as a relatively high production rate, and analyzed the performance characteristics of the VMD module under various sea water temperature, flow rates and salinities.BR The VMD module used in this study has an energy requirement of about 24.2 kWh per hour to produce 1 m³ of fresh water over a period of 24 h, The total heat input required for this production is about 580 kWh. The equation of permeate flux according to the quantity of heat input is y = 0.2621x + 1.2384, so that the permeate flux is increased as the quantity of heat input is increased. When salinity or flow rate of the feed water increases, the RR (Recovery Ratio) value is reduced. If the temperature of feed water increases, the RR value is increased.BR

Performance Investigation of O-Ring Vacuum Membrane Distillation Module for Water Desalination

A new O-ring flat sheet membrane module design was used to investigate the performance of Vacuum Membrane Distillation (VMD) for water desalination using two commercial polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) flat sheet hydrophobic membranes. The design of the membrane module proved its applicability for achieving a high heat transfer coefficient of the order of 103 (W/m2 K) and a high Reynolds number (Re). VMD experiments were conducted to measure the heat and mass transfer coefficients within the membrane module. The effects of the process parameters, such as the feed temperature, feed flow rate, vacuum degree, and feed concentration, on the permeate flux have been investigated. The feed temperature, feed flow rate, and vacuum degree play an important role in enhancing the performance of the VMD process; therefore, optimizing all of these parameters is the best way to achieve a high permeate flux. The PTFE membrane showed better performance than the PVDF membrane in VMD desalination. The obtained water flux is relatively high compared to that reported in the literature, reaching 43.8 and 52.6 (kg/m2 h) for PVDF and PTFE, respectively. The salt rejection of NaCl was higher than 99% for both membranes.

Dynamic performance of vacuum membrane distillation system

The aim of this work was the development of a numerical methodology to simulate and study the dynamic behavior of vacuum membrane distillation (VMD) system. A time-dependent one-dimensional finite difference numerical model is developed to study the flow as well as thermal regimes and the dynamic operational performance of VMD under stepped flow disturbance function in the hot channel. The study simulates the process parameters including mass flow rates, temperatures, vapor pressures, and concentration distributions for the hot feed channels along the flat-plate membrane length with transmembrane flux. The developed dynamic tool predicts the hydrodynamic behaviors and thermal characteristics of the very thin channels of VMD module. A rectangular pulse disturbance function is applied to rise up the inlet hot mass flow rate from steady state (SS) value of 1 to 1.34 kg/s for 60 s. The model ran for 3 min, which included the 60 s of applied dynamic disturbance; it started at the 10th s and finished at the 70th s. The results show that the probability of the pressure rise and the salt precipitation (scaling problem) will appear on the second half of the membrane length more than on the first half. The hydrodynamic influence of the flow conditions on the permeate flux appears to be more significant at the feed side of the VMD module fillet.

A new vacuum membrane distillation system using an aspirator: concept modeling and optimization

The aim of this study is to validate and optimize a new concept of implementing an aspirator as the vacuum generator for a vacuum membrane distillation (VMD) setup. Numerical models are developed for the aspirator, and its interconnectivity with the VMD chamber is demonstrated. A correlation to estimate the minimum aspirator pump size for a given permeate mass flow is deduced from these models. The dependence of the system’s specific power consumption (per unit permeate flow) on the feed flow rate, number of membrane sheets in the VMD module, and vacuum pressure is investigated. The gained output ratio (GOR) of the proposed system is comparable (GOR ≈ 0.8) to conventional single-stage VMD with a vacuum pump, if brine heat is recovered using a regenerator to preheat the incoming feed. The theoretical power requirement for a vacuum pump is lower than that used by the aspirator system, if all vapor is condensed and only non-condensable gasses are removed by the vacuum pump. At lower vapor pressures, when complete condensation is difficult, the vacuum pump power consumption is comparable to that of the aspirator system if about 60% of the vapor produced reaches the vacuum pump.

Experimental evaluation for the freshwater production characteristics according to the salinity conditions of vacuum membrane distillation module

This study builds a lab-scale vacuum membrane distillation (VMD) system with 1 m3/d to analyze the performance characteristics of VMD module, which has a relatively high freshwater production rate and low heating energy consumption during the membrane distillation process and experimentally evaluates freshwater production characteristics of VMD module according to temperature (55, 65, and 75°C), flow rate of (2, 4, 6, and 8 m3/h), and salinity (25,000, 35,000, and 45,000 ppm) conditions of feed water to the system.

Simulation of Vacuum Membrane Distillation Process for Desalination with Aspen Plus

This paper presents a simulation study of vacuum membrane distillation (VMD) for desalination. A simulation model was built on the Aspen Plus platform as a user defined unit operation for the VMD module. A simplified mathematical model was verified, and the analysis of process performance based on simulation was also carried out. Temperature and concentration polarization effects are significant in the conditions of higher feed temperature and/or vacuum pressure. The sign of (PI,f – PI,p), difference of the vapor pressures between the membranes at the interfaces, is an indicator of the vacuum pressure threshold. Increasing the vacuum pressure at lower feed temperature is an effective way to increase the permeate flux and reduce the energy consumption simultaneously.

VMD 모듈의 열성능 특성 연구

VMD 모듈의 열성능 특성 연구

Evaluation of hollow fiber-based direct contact and vacuum membrane distillation systems using aspen process simulation

Among four membrane distillation (MD) configurations, direct contact MD (DCMD) and vacuum MD (VMD) exhibit attractive characteristics from different perspectives and have great potential in treating reverse osmosis (RO) brine. Aiming at establishing a quick approach to predict the key output parameters associated with MD module performance and process efficiency, Aspen plus was employed to conduct systematic evaluation for both DCMD and VMD. Due to the lack of built-in MD operation models in Aspen Plus, one dimensional transport models were developed and complied as user customized units to simulate the hollow fiber-based DCMD and VMD modules. The corresponding programming was coded in FORTRAN language. The mathematical models for DCMD and VMD were verified by comparing the simulations results with the experimental and literature data, respectively.By incorporating the boundary-layer effect into the newly-established transport models, steady-state simulations of the respective DCMD and VMD flowsheets were carried out. The results showed that the DCMD presented much lower process efficiency than VMD in terms of permeation flux and specific energy consumption per kg distillate generated, even though it is considered as the simplest and most commonly employed configuration. With the same module specifications and operating conditions at equivalent energy cost, the VMD system demonstrated a minimal 2.5-fold higher average vapor flux (e.g., water recovery capacity) when compared to DCMD. The fundamental difference between the two configurations was revealed through MD mass- and heat-transfer analysis. Based on simulated temperature profiles, it was found that the VMD configuration presented a much higher driving force (transmembrane temperature difference) and negligible conductive heat loss to the membrane, which is a promising feature for achieving high thermal efficiency.

Numerical modeling and optimization of vacuum membrane distillation module for low-cost water production

A two-dimensional numerical model, involving energy conservation, momentum transport and continuity equations, was developed to provide the profiles of temperature, velocity and pressure of vacuum membrane distillation (VMD) process using hollow fiber module. The theoretical prediction was in good agreement with the experimental results from literature. Four design and operation variables, including feed temperature, hollow fiber length, feed volume flow rate and vacuum pressure, were optimized to minimize water production cost (WPC) using genetic algorithm (GA). A case study shows that the WPC can be decreased by 38.1% in comparison with the non-optimized VMD process. Meanwhile, a general guidance for reducing the WPC was also provided. The feed temperature should be adopted as high as possible, while the hollow fiber length cannot be too long to result in a decrease in water flux and an increase in pressure drop. The flow rate is recommended to take a lower bound value and the moderate degree of vacuum is preferable. This study indicates the importance of VMD system optimization to minimize water production cost.

Numerical modeling of the vacuum membrane distillation process

In this study, one-dimensional vacuum membrane distillation (VMD) model is suggested for predicting the performance of seawater desalination to evaluate the performance of hollow fiber type VMD module. The energy and momentum balance equations, as well as the heat and mass transfer equations, are simultaneously solved to determine the concentration of NaCl, temperature and velocity distribution of feed side along the module length, productivity of distilled water and specific energy consumption. The productivity increases with an increase in the inlet feed temperature and velocity, the number of fibers and the total module length. However, it decreases with an increase in the mass fraction of the feed. Specific heat energy consumption decreases with an increase in the inlet feed temperature and velocity and total module length, but it increases with an increase in mass fraction of the feed and number of fibers. The specific electrical energy consumption increases with an increase in mass fraction, velocity and total module length and a decrease in inlet feed temperature and number of fibers, but the specific electrical energy consumption is too small and negligible in comparison with the specific heat energy consumption (less than 2%) on various operating conditions and module dimensions.

Investigation of Shell Side Heat Transfer in Cross-Flow Designed Vacuum Membrane Distillation Module

This paper focuses on the investigation of heat transfer in a cross-flow designed vacuum membrane distillation (VMD) module. The employment of cross-flow membrane module could ensure significant reduction of temperature polarization effect at a relatively low range of Reynolds numbers. According to most literature on VMD, the heat transfer coefficients are usually estimated by the commonly used correlations for nonporous and rigid heat exchangers. However, due to the complex flow regime in module channel, the applicability of these formulas is questioned. In this work, the heat transfer in the shell side of VMD module was studied numerically and experimentally in the Reynolds range from 7.12 to 52.18. The experimental Nusselt numbers obtained in this work are relatively higher than those predicted in the literature for given conditions. The possible reasons leading to the considerable enhancement of heat transfer are analyzed and discussed.

Kinetic analysis of the vacuum membrane distillation of chloroform from aqueous solutions

In this work, the vacuum membrane distillation (VMD) technology has been applied to the removal of chloroform from a dilute aqueous stream. Microporous polypropylene hollow fiber membranes were used to immobilize the liquid–vapor interface. The influence of the following operational variables was experimentally studied: (i) initial chloroform concentration in the feed (212–2012 mg/l), (ii) feed flow rate in the laminar flow regime (0.23–0.98 l/min) and in the transition to the turbulent flow regime (2.7–8 l/min), (iii) temperature (5–47.5°C) and vacuum pressure in the permeate side (7 and 14 mm Hg). The mathematical model proposed to describe the kinetic results includes the mass balance to the feed tank and the mass balance to the VMD module. In the laminar regime the solution of the continuity mass conservation equation makes the diffusion coefficient of chloroform in the aqueous phase the only parameter needed to describe the separation rates. In the turbulent flow regime, a macroscopic mass balance including an overall mass transfer coefficient that accounts both for liquid film diffusion and membrane mass transport was developed. It was found that only at higher Reynolds numbers within the turbulent flow regime the resistance to mass transfer in the membrane had influence on the overall mass transfer coefficient.