EVAPORATION CHARACTERISTICS OF A CONFINED NANOFLUID BRIDGE BETWEEN TWO HEATED PARALLEL PLATES

This paper focusses on understanding the thermophysics and contact line dynamics of evaporating liquid bridges of pure water and nanofluids (0.1% and 0.5% v/v of CuO nanoparticles of average particle size < 50 nm), confined between two heated parallel glass substrates, maintained at a fixed distance, under near constant temperature boundary conditions (60 degrees C and 80 degrees C, respectively). Externally controlled, thin film indium-tin oxide (ITO) coated heaters were fabricated on the glass substrate to maintain the thermal boundary condition. High-resolution images of the liquid bridges were obtained during the evaporation process and later digitally analyzed to find the temporal evolution of relevant geometrical parameters. Subsequently, different thermal resistances involved were estimated, leading to the overall heat transfer coefficient. The order of magnitude of the interfacial resistance was found negligible as compared to the internal thermal resistance of the liquid bridge. Nanofluids evidently showed enhanced diffusional conductivity, and hence increased overall heat transfer coefficient, with a unique contact line motion, involving stick-slip behavior. Strong pinning effect at the contact line was observed during nanofluid evaporation, as a result of deposition of the particles, due to which the life span of nanofluid liquid bridge was much shorter than that of pure water. The rate of evaporation was dependent on the nanoparticle loading.