Abstract
A Bubbling and Vacuum-enhanced direct contact membrane distillation (BVDCMD) is proposed to improve the water production rate of the direct contact membrane distillation (DCMD-)based seawater desalination process. Its heat and mass transfer mechanism are theoretically analyzed, and a CFD model is established, which is verified by the published data. Four types of the noncondensable gas, “O2,” “air,” “N2,” and “H2,” are adopted as the bubbling gas, and their process enhancements under different pressure of permeate side, temperature, and NaCl concentration of feed side and flow velocities are investigated. The results show that the permeate flux increased remarkably with the decrease in the viscosity of the bubbling gas, and hence, “H2” is the best option for the bubbling gas, with the permeate flux being enhanced by 144.11% and the effective heat consumption being increased by 20.81% on average. The effective water production rate of BVDCMD is predicted to be 42.38% more than that of DCMD, proving its feasibility in the seawater desalination.
Highlights
By 2025, approximately 70% of the world’s population will face water shortage [1], which has become a major environmental problem
Andres-Mañas et al [20] proposed and evaluated a novel seawater desalination system based on V-membrane distillation (MEMD), and the results showed that the four-effect configuration significantly improved the previous Vacuum-multieffect membrane distillation (V-MEMD) system, using the seawater feed flow as the cooling liquid of the condenser instead of a separate circuit
We proposed a novel Bubbling and Vacuum-enhanced direct contact membrane distillation process (BVDCMD) combining the Bubbling membrane distillation (BMD) and VEDCMD together to enhance the MD performance by the bubbling and transmembrane flow of noncondensable gas, and the enhancement is evaluated through CFD simulations of the MD process
Summary
By 2025, approximately 70% of the world’s population will face water shortage [1], which has become a major environmental problem. In Vacuum-enhanced direct contact membrane distillation (VEDCMD), a vacuum pump was added on the permeate side of the original DCMD to generate a vacuum state and a total pressure gradient between the feed and the permeate liquid, resulting in the increase of the membrane flux and decrease of the temperature polarization [14]. Bubbling membrane distillation (BMD) is designed to improve the traditional DCMD by bubbling air bubbles into the hot fluid, to enhance its disturbance by the gas-liquid two-phase flow, resulting in the change of the flow pattern from laminar to turbulent flow. We proposed a novel Bubbling and Vacuum-enhanced direct contact membrane distillation process (BVDCMD) combining the BMD and VEDCMD together to enhance the MD performance by the bubbling and transmembrane flow of noncondensable gas, and the enhancement is evaluated through CFD simulations of the MD process.
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