Drag Coefficients Associated With a Moving Drop Experiencing Condensation

For a moving liquid drop experiencing condensation, three different drag coefficients govern the motion and the transport. These coefficients are associated with friction, pressure, and condensation. Unlike situations involving the motion of a rigid sphere or a liquid drop without the presence of condensation, there is a large pressure recovery in the rear of a moving drop experiencing condensation. As a consequence, the pressure drag coefficient exhibits interesting behavior. While the coefficients for the friction drag and the condensation drag increase with the level of condensation, the pressure drag coefficient decreases rapidly. In this note, the roles played by the various drag forces in condensing situations are delineated. Results for the variation of average condensation heat transfer with vertical-fall height of the drop are presented.