Numerical simulation of heat and mass transfer in direct membrane distillation in a hollow fiber module with laminar flow
Fane, Anthony Gordon
Date of Issue2011
School of Civil and Environmental Engineering
Singapore Membrane Technology Centre
The heat and mass transfer processes in direct contact membrane distillation (MD) under laminar ﬂow conditions have been analyzed by computational ﬂuid dynamics (CFD). A two-dimensional heat transfer model was developed by coupling the latent heat, which is generated during the MD process, into the energy conservation equation. In combination with the Navies–Stokes equations, the thermal boundary layer build-up, membrane wall temperatures, temperature polarization coefﬁcient (TPC), local heat transfer coefﬁcients, local mass ﬂuxes as well as the thermal efﬁciency, etc. were predicted under counter-current ﬂow conditions. The overall performance predicted by the model, in terms of ﬂuxes and temperatures, was veriﬁed by single hollow ﬁber experiments with feed in the shell and permeate in the lumen. Simulations using the model provide insights into counter-current direct contact MD. Based on the predicted temperature proﬁles, the local heat ﬂuxes are found to increase and then decrease along the ﬁber length. The deviation of the membrane wall temperature from the ﬂuid bulk phase on the feed and the permeate sides predicts the temperature polarization (TP) effect. The TP coefﬁcient decreases initially and then increase along the ﬁber length. It is also found that the local Nusselt numbers (Nu) present the highest values at the entrances of the feed/permeate sides. Under the assumed operating conditions, the feed side heat transfer coefﬁcients hf are typically half the hp in the permeate side, suggesting that the shell-side hydrodynamics play an important role in improving the heat transfer in this MD conﬁguration. The model also shows how the mass transfer rate and the thermal efﬁciency are affected by the operating conditions. Operating the module at higher feed/permeate circulation velocities enhances transmembrane ﬂux; however, the thermal efﬁciency decreases due to the greater heat loss at a higher permeate velocity. The current study suggests that the CFD simulations can provide qualitative predictions on the inﬂuences of various factors on MD performance, which can guide future work on the hollow ﬁber module design, module scale-up and process optimization to facilitate MD commercialization.
DRNTU::Engineering::Environmental engineering::Water treatment
Journal of membrane science
© 2011 Elsevier. This is the author created version of a work that has been peer reviewed and accepted for publication by Journal of Membrane Science, Elsevier B.V. It incorporates referee’s comments but changes resulting from the publishing process, such as copyediting, structural formatting, may not be reflected in this document. The published version is available at: [DOI: http://dx.doi.org/10.1016/j.memsci.2011.09.011].