A detailed rigorous theoretical model has been developed to
predict the transmembrane flux of a shell-and-tube type
vacuum membrane distillation (VMD) module for seawater
desalination. There are primarily two modes of operation to
carry out VMD: lumen-side feed (in-out configuration) and
shell-side feed (out-in configuration). In this study, detailed
mathematical formulations are derived, not for in-out
configuration since it has been observed to be restricted by
operational constraints such as crystallization in the lumen side
of the hollow fiber at high seawater concentrations, but for outin
configuration commonly used in seawater desalination
applications. For the out-in configuration VMD module, in
spite of the much lower viscosity of water vapor than liquid
phase, the pressure build-up of water vapor in the lumen should
not be overlooked as the pressure build-up directly reduces the
driving force for vapor permeation through the membrane pores.
Experimental results and model predictions for mean permeate
flux are compared and shown to be in good agreement. The
property variation of feed and permeate sides along the axial
direction is also examined. Further, the influences of operating
parameters (feed temperature and flow rate, hollow-fiber length)
on the permeate flux are evaluated, and the pressure build-up of
the water vapor in the lumen side is also investigated.
Papers presented at the 13th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Portoroz, Slovenia on 17-19 July 2017 .