Performance improvements by embedded spacer in direct contact membrane distillation – Computational study

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.

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“…They are calculated as a function of local temperature and salt concentration using the modified Antoine equation [ 35 ]

…”

Section: Methodsmentioning

confidence: 99%

Theoretical Investigation of Vapor Transport Mechanism Using Tubular Membrane Distillation Module

Alanezi

Bassyouni

Abdel-Hamid³

et al. 2021

Membranes

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“…Recently, the use of feed spacers has attracted attention as an effective method for improving flux and removing fouling by increasing the turbulence of the feed flow. Alwatban et al [ 21 ] reported that both CP and TP were mitigated significantly, and the water flux was enhanced by approximately 40% with a module containing embedded spacers of the larger strand.…”

Section: Introductionmentioning

confidence: 99%

Fouling Control Strategies for High Concentrated Liquid Desiccants Concentrating Using Membrane Distillation

Lee

Jeong

et al. 2023

Membranes

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Air conditioning using a liquid desiccant (LD) is an energy-efficient air purification and cooling system. However, high energy is required to concentrate or regenerate the LD. This study aimed to investigate the characteristics of membrane fouling in more detail and determine control strategies for LD concentrating using membrane distillation (MD). Two different LDs—lithium chloride (LiCl) and potassium formate (HCOOK)—were used. Because LDs require high concentrations by nature (i.e., 40 wt% for LiCl and 70 wt% for HCOOK), the concentration was started from half of those concentrations. This resulted in a flux decline with severe membrane fouling during the concentration using MD. Different membrane fouling mechanisms were also observed, depending on the LD type. Three different physical membrane fouling control methods, including water flushing (WF), air backwashing (AB), and membrane spacer (SP), were introduced. Results showed that WF was the most effective. Both AB and SP showed a marginal change to no cleaning; however, an initial flux with SP was about 1.5 times higher than no cleaning. Therefore, WF combined with the SP could maintain a high flux and a low fouling propensity in the treatment of a high-concentration solution using MD.

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“…Another route to mitigating the polarization effects is increasing the chaotic state of the flow near the membrane surface, such as increasing the feed velocity and using pulse flow [22,23] or filling the spacers in the flow channels [24][25][26][27]. It has been reported that changing the geometry of the MD module channel is an effective approach to increasing the chaotic state of feed and coolant [28][29][30][31].…”

Section: Introductionmentioning

confidence: 99%

Optimizing Membrane Distillation Performance through Flow Channel Modification with Baffles: Experimental and Computational Study

Zhang,

Mu,

Sun

et al. 2023

Separations

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It has been identified that temperature polarization and concentration polarization are typical near-surface phenomena limiting the performance of membrane distillation. The module design should allow for effective flow, reducing the polarization effects near the membrane surfaces and avoiding high hydrostatic pressure drops across and along the membrane surfaces. A potential route to enhancing the membrane distillation performance is geometry modification on the flow channel by employing baffles as vortex generators, reducing the polarization effects. In this work, various baffles with different structures were fabricated by 3D printing and attached to the feed flow channel shell in an air gap membrane distillation module. The hydrodynamic characteristics of the modified flow channels were systematically investigated via computational fluid dynamics simulations with various conditions. The membrane distillation tests show that adding the baffles to the feed channel can effectively increase the transmembrane flux. The transmembrane flux with rectangular baffles and shield-shaped baffles increases by 21.8% and 28.1% at the feed temperature of 70 °C. Moreover, the shield-shaped baffles in the flow channel not only enhance the transmembrane flux but also maintain a low-pressure drop, making it even more significant.

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Performance improvements by embedded spacer in direct contact membrane distillation – Computational study

Cited by 30 publications

References 48 publications

Theoretical Investigation of Vapor Transport Mechanism Using Tubular Membrane Distillation Module

Theoretical Investigation of Vapor Transport Mechanism Using Tubular Membrane Distillation Module

Fouling Control Strategies for High Concentrated Liquid Desiccants Concentrating Using Membrane Distillation

Optimizing Membrane Distillation Performance through Flow Channel Modification with Baffles: Experimental and Computational Study

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