Abstract
The membrane distillation (MD) process for water desalination is affected by temperature polarization, which reduces the driving force and the efficiency of the process. To counteract this phenomenon, spacer-filled channels are used, which enhance mixing and heat transfer but also cause higher pressure drops. Therefore, in the design of MD modules, the choice of the spacer is crucial for process efficiency. In the present work, different overlapped spacers are investigated by computational fluid dynamics (CFD) and results are compared with experiments carried out with thermochromic liquid crystals (TLC). Results are reported for different flow attack angles and for Reynolds numbers (Re) ranging from ~200 to ~800. A good qualitative agreement between simulations and experiments can be observed for the areal distribution of the normalized heat transfer coefficient. Trends of the average heat transfer coefficient are reported as functions of Re for the geometries investigated, thus providing the basis for CFD-based correlations to be used in higher-scale process models.
Highlights
In regions where the existing freshwater sources do not meet the water demand, production of potable water from saline and brackish waters is needed [1]
membrane distillation (MD) is a thermally driven membrane-based process where the transport of water vapor is realized through a micro-porous hydrophobic membrane, which leads to a theoretical 100% rejection of salts
The separation process is driven by the vapor pressure difference at the membrane/liquid interfaces due to the temperature gradient existing between the two sides of the membrane
Summary
In regions where the existing freshwater sources do not meet the water demand, production of potable water from saline and brackish waters is needed [1]. The separation process is driven by the vapor pressure difference at the membrane/liquid interfaces due to the temperature gradient existing between the two sides of the membrane. MD is characterized by its compactness and low operational pressure requirement as well as low working temperature These features make it possible to power MD by low grade heat (waste heat) or renewable energy and boost its applicability in remote areas and small scale production [5,6,7]. Another important distinct feature of MD is its ability to desalinate highly saline brines and wastewater. One main advantage of MD technology is that evaporation and condensation surfaces are tightly packed, leading to a compact system with low capital cost per unit product
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