Increasing heat transfer during condensation on surfaces via lubricant impregnation

The low contact angle hysteresis shown by superhydrophobic surfaces towards water has many interesting applications including condensation. However these useful properties can be lost during condensation. Water droplets randomly nucleate anywhere on the surface including in between the surface textures and grow while still remaining entrained in the texture. By using specially crafted textures, coalescence induced self-propulsion of droplets to eject them from the surface can be achieved; however surface textures are vulnerable to damage and defects. A new approach to prevent a droplet from attaining pinned state on surfaces with nano/micro textures has recently been introduced by impregnating surfaces with a liquid immiscible with the droplet such that the `Impregnating Lubricant' remains trapped on the surface forming a hybrid surface of liquid and solid. This work will focus on mechanics of condensation on such lubricant impregnated surfaces. We show that lubricants despite having ultra-smooth surfaces nevertheless show significant enhancement in nucleation as compared to solid surfaces with similar surface energy. Further we discuss the mechanisms behind the increase in heat transfer during condensation on such surfaces. Longevity of lubricant is a key aspect in application of these surfaces for industrial applications such as condensers, cooling systems, heat pipes etc. We report the mechanics of lubricant loss and how such losses can be minimized for long-term usage of such surfaces.