The effect of the angle of inclination of a condenser on the gas-to-plate heat resistance in dropwise condensation

In a previous study [1] it was shown that tilting a compact plate condenser may increase the heat flux to the coolant by about 8%, depending on the inlet humidity. The explanation for this is enhanced drainage: the length of the paths of large drainage drops is increased, and the re-initiation of condensation at the ‘dry’ tracks decreases the mean gas-to-plate heat resistance. In the present study this explanation is verified, using infrared thermography and the following strategy of analysis [2]. The spatial temperature variations that occur in dropwise condensation on a condenser plate are measured instantaneously. They are averaged in time only in the direction parallel to the coolant flow (not vertical in a tilted exchanger). An assessment of extreme values leads to determination of the gas-to-plate heat resistance. The parameter Fcond quantifies the deviation of actual heat transfer from purely conductive heat transfer through the condensate. Mixing in the condensate, and the continual refreshing of liquid in contact with the gas, causes Fcond to be about 4 in a vertical condenser with dropwise condensation [2]. In the inclined condenser Fcond is found to be about 5, showing that tilting the exchanger affects the mean gas-to-plate heat resistance in the expected way.