Dropwise Condensation on Hydrophobic Wick Structures

The proposed SBIR project will develop an innovative heat transfer mechanism involving dropwise condensation promoted by a non-wetting self-assembled monolayer (SAM) on a porous metal wick. Dropwise condensation on a bare surface has shown the ability to increase condensation heat transfer coefficients by orders of magnitude over film condensation. By condensing on a wick, heat transfer coefficients are expected to be further increased over on bare surfaces because of the increased surface area of the porous metal wick and the more effective liquid removal from the cooled surface by a Laplace gradient mechanism. To promote dropwise condensation on the wick, the wick will be coated with a self-assembled monolayer with low surface energy, to make the surfaces non-wetting to low surface tension fluids such as fluorocarbons and refrigerants. The proposed condensation technology is applicable in pumped two-phase flow devices such as hybrid two-phase loops, passive two-phase flow devices such as loop heat pipes, and gravity aided heat pipes or thermosyphons. In Phase I, we will develop sintered metal wick with SAM fabrication procedure, experimentally demonstrate the improved condensation heat transfer coefficient, perform life test of SAM under thermal loading, and design liquid cooled condenser heat exchanger integrating dropwise condensation.