Experimental investigation of dropwise condensation on hydrophobic heat exchangers. Part II: Effect of coatings and surface geometry
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This is Part II of an experimental investigation of hydrophobic heat exchangers. Two plates were studied: (a) 0.127-mm-thick titanium grade 2 and (b) 0.203-mm-thick copper. Titanium plate had round-dimpled spacers. Copper had either round-dimpled spacers or round-shaped vertical-grooved spacers. Titanium was bare but copper had electroless Ni-P-PTFE hydrophobic coating. Two chemical compositions of the hydrophobic coating were employed: lead-containing and lead-free. For some studies, the coating thickness was varied from 0.635 to 127m. To measure the overall heat transfer coefficient, the plates were mounted in a sealed two-chamber apparatus with condensing saturated steam on one side and forced-convective boiling liquid water on the other. The best overall heat transfer coefficient was U=240kW/(m2C) (0.203-mm-thick copper plate, round-shaped vertical grooves, 2.54-m-thick lead-free Ni-P-PTFE, P=722kPa, T=160C, T=0.20C, saturated liquid velocity vliq=1.57m/s, shearing steam vsteam=0.23m/s, and flow ratio R0.6kg shearing steam/kg condensate). 2011.
