Modeling and calculation of temperature-concentration polarisation in the membrane distillation process (MD)
ABSTRACT A model for a membrane distillation process in a plate-and-frame unit has been developed. It is based on a mass and energy balance equation for hydrodynamic, temperature and concentration boundary layers. The model takes into account energy interdependence between flow in feed and in permeate channels. A model taking into consideration temperature-concentration polarisation (TCP) predicts temperature and concentration values at the membrane surface. The model consists of an analytical equation and permits simulation or analysis of the influence of various factors to permeate flux.
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ABSTRACT: New membrane distillation configurations and a new membrane module were investigated to improve water desalination. The performances of three hydrophobic microporous membranes were evaluated under vacuum enhanced direct contact membrane distillation (DCMD) with a turbulent flow regime and with a feed water temperature of only 40 °C. The new configurations provide reduced temperature polarization effects due to better mixing and increased mass transport of water due to higher permeability through the membrane and due to a total pressure gradient across the membrane. Comparison with previously reported results in the literature reveals that mass transport of water vapors is substantially improved with the new approach. The performance of the new configuration was investigated with both NaCl and synthetic sea salt feed solutions. Salt rejection was greater than 99.9% in almost all cases. Salt concentrations in the feed stream had only a minor effect on water flux. The economic aspects of the enhanced DCMD process are briefly discussed and comparisons are made with the reverse osmosis (RO) process for desalination.Journal of Membrane Science 01/2004; · 4.09 Impact Factor
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ABSTRACT: To maximize the desalination performance of both productivity and thermal efficiency, model-based optimal design of a hollow fiber direct contact membrane distillation (DCMD) module is proposed. The mathematical model equations for the entire module are derived by integrating the permeate flux across the membrane with the mass, momentum and energy balances on both feed and permeate sides. The property variations of feed and permeate sides along the length of the membrane module are simulated. It is found that there is a trade-off between the permeate flux (productivity) and thermal efficiency. The trade-off depends on not only the operating variables, such as the temperature and the flow rate of the cold solution, but also the fiber dimensions, such as the fiber length and the packing density. Based on the above decision variables, optimization of the hollow fiber DCMD module is carried out using the Pareto genetic algorithm. It is demonstrated that the optimal values of the inlet cold flow rate and the fiber length are more sensitive than the module packing density. With the synchronous increase in the inlet cold flow rate and the fiber length, the productivity increases at the cost of higher thermal efficiency.Journal of Membrane Science. 01/2008;
Chapter: Membrane Distillation[Show abstract] [Hide abstract]
ABSTRACT: This paper provides a state-of-the-art review of the separation process known as membrane distillation, MD. An introduction to the terminology and fundamental concepts associated with MD as well as a historical review of the developments in MD are presented. Membrane properties, transport phenomena, and module design are discussed in detail. A critical evaluation of the MD literature is incorporated throughout this review.12/2008: pages 297 - 369; , ISBN: 9780470276280