Heat and mass transport resistances in vacuum membrane distillation per drop

Vacuum membrane distillation (VMD) is a separation process based on the use of microporous hydrophobic membranes. The membrane is located between an a queous phase and a permeate, which is kept under vacuum at pressure values below the equilibrium vapor pressure of the feed. The liquid stream vaporiz es at one side of the membrane, and the vapors diffuse through the gas phas e inside the membrane pores. The process rate and performance are affected highly by the transport phenomena both in the liquid phase and through the membrane. Heat- and mass-transfer resistance in the liquid phase, as well a s mass-transfer resistance through the membrane, play an important role in determining the process performance. Based on VMD experimental data for sev eral binary aqueous mixtures containing volatile organic compounds, a simpl e criterion to investigate the role of each transport resistance on the sep aration efficiency is discussed.