Peter C. Wayner, Jr.
The effect of interfacial phenomena on change-of-phase heat transfer in very thin liquid films is being studied. These films are sufficiently thin so that the average intermolecular force field is affected by the liquid film thickness. For example, the heat transfer characteristics of an evaporating interface in the shape of a constrained vapor bubble thermosyphon are being determined. Microscopic image processing equipment based on ellipsometry and interferometry have been developed and are being improved to obtain the important film thickness profile which gives the internal pressure field in the liquid. Complementary microscopic transport models are being developed. The results of these basic studies are then used to design small heat exchangers (e.g., heat pipes for the cooling of microelectronic devices).
The research is unique and important for at least two reasons: 1) Theoretically, we are developing techniques whereby the interfacial heat transfer coefficient of a thin film (during evaporation or condensation) can be obtained from the frequency dependent dielectric functions of the liquid/substrate system; 2) Experimentally, we have developed two microscopic image processing systems to measure the thickness profile of an evaporating thin film (an image scanning ellipsometer and an image analyzing interferometer). The thickness profile gives the pressure field. This research will lead to innovative heat transfer systems based on interfacial phenomena and an improved understanding of classical systems like boiling and the rewetting of a hot surface.