Membrane and Desalination Technologies - TCE Moodle Website

536 J.P. Chen et al.
produced by turning heat into latent heat of evaporation, the MED technique uses latent heat
to produce secondary latent heat in each chamber. This use of double condensing-evaporation
heat transfer mechanisms is highly efficient and energy saving.
MED was developed earlier than MSF; however, it has not been extensively utilized for
water production. A new type of low-temperature, horizontal-tube MED process has been
successfully developed and used in the Caribbean. These plants appear to be very rugged,
easy to operate, and economical, as they can be made of aluminum or other low-cost materials
(10). The cost for O&M of MED is slightly higher than that for RO.
2.5. Vapor Compression
VC process uses mechanical energy rather than direct heat as a source of thermal energy.
Figures 12.7 and 12.8 demonstrate the VC process. Water vapor is drawn from the evaporation
chamber by a compressor. Except in the first stage, the vapor is condensed on the outsides of
tubes in the same chambers. The heat of condensation is used to evaporate a film of saline water
applied to the inside of the tubes within the evaporation chambers. VC normally has a low fresh
water production capacity, i.e.