Heat transfer coefficients on smooth plate rotating evaporator-condensers are reliably predicted by equation (2). Radial machine grooving of the condensing surface improves the heat transfer coefficient in filmwise condensation on this surface by reducing the resistance up to 65 percent. The overall coefficient was improved some 13 percent. Surfaces radially scratched by coarse sandpaper exhibited higher coefficients than smooth surfaces. Sanding the condensation side improved the overall coefficient about 8 percent, and sanding the evaporation side improved it about 10 percent. Care should be used in applying grooves to the evaporation side, however, as they increase the tendency toward local overevaporation and, hence, scale formation. Machined grooves on the evaporation side reduced overall coefficients.

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