Desalination and Water Purification Technology Roadmap - A Report of the Executive Committee
USBR; Denver CO.
Report #96 - Summary -
The primary deficiencies of direct contact membrane distillation (DCMD) are flux reduction due to long-term pore wetting and reduced brine-side heat and mass transfer coefficients.
To overcome these, this research has made a preliminary investigation of the DCMD process where a number of changes were introduced:
(1) the porous hydrophobic hollow fiber membrane has a thin water-vapor permeable hydrophobic microporous coating of a silicone-fluoropolymer plasmapolymerized on the fiber outside diameter on the hot brine side to prevent pore wetting;
(2) to increase the brine-side heat transfer coefficient drastically, the hot brine feed is in a rectangular cross flow mode vis-a-vis the hollow fiber membranes;
(3) the hydrophobic porour hollow fibers had thick walls and high porosity; and
(4) the module design ensured that the temperature rise of the cold distillate was minimal.
It is known that the vacuum membrane distillation (VMD) technique, wherein there exists cavuum instead of cold distillate flow on one side of the membrane, the other side having hot brine flow, can illuminate many features of the brine side of the DCMD process.
Therefore extensive data were obtained for the DCMD as well as the VMD process.
For more information about the DWPR program, contact Kevin Price at: Bureau of Reclamation, 86-69000, PO Box 25007, Denver CO 80225; phone (303) 445-2260; or e-mail a message to MPrice@usbr.gov.