abstract
In this work, an extensive analysis on direct contact membrane distillation (DCMD) performance was
developed to estimate the mass flux and the heat efficiency, considering transport phenomena, membrane
structural properties and most sensitive process parameters, with the aim to provide optimization
guidelines for materials and methods. The results showed that an increase of the temperature gradient
resulted in the enhancement of both transmembrane flux and thermal efficiency. The investigation of
the effects of membrane properties confirmed that better DCMD performance was achieved when using
polymeric membranes characterized by low thermal conductivity (flux and thermal efficiency declined
by 26% and 50%, respectively, when increasing thermal conductivity from 0.1 to 0.5W/mK), and high
porosity. An optimal thickness value (around 0.7mm) was identified when operating at low temperature
gradient (<5 ◦C). However, at higher temperature gradient (>10 ◦C), increasing the membrane thickness
from 0.25 to 1.55mm resulted in a flux decay of about 70% without a significant improvement in thermal
efficiency.
Exergy analysis, sensitivity study and economical evaluation were carried out to assess the feasibility
of DCMD process. For DCMD with heat recovery, the estimated water cost was $1.17m−3, which was
comparable to the cost of water produced by conventional thermal processes: i.e. around $1.00m−3 for
multiple effect distillation (MED) and $1.40m−3 for multi-stage flash (MSF). However, significant savings
are expected when using a low-grade thermal energy source, decreasing the cost of DCMD to values
approaching the cost of water produced by reverse osmosis (RO), which is about $0.50m−3.
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