With the naphthalene sublimation technique, the mass transfer from hemispheres on a flat plate to air flowing between two parallel plates is measured. A length scale is introduced to render the correlation of the results independent of the drop size. Measured mass transfer from Bat plates is compared to measured heat transfer to Bat plates. With the aid of the findings, mean interface temperatures of condensate drops in a compact PVDF heat exchanger are predicted. The calculations are compared with temperatures measured with an infrared camera.