Interfacial and plate temperature histories during dropwise condensation in the presence of non-condensibles

Measurements with a thermograph, spectral range 2,0-5,6 (µm, reveal temperature gradients in liquid drops that condense from a gas mixture with noncondensibles present. They indicate the presence of Marangoni convection that may explain the finding that the average thermal resistance of the condensate in plastic compact heat exchangers is lower than the expected value based on pure conduction. Histories of temperature fields of condenser plates exhibit, amongst other things, the importance of drainage by the large drops and the predicted linear decrease of the averaged interface temperature in the flow direction. Dedicated experiments with an initially homogeneous binary drop show that Marangoni flow can also be driven by concentration gradients at the interface, sustained by refreshing from the bulk liquid. It is unclear whether this effect manifests itself in heat exchangers.