(144j) Microscale Heat Transfer and Fluid Flow in an Evaporating Moving Extended Meniscus

Due to the large ratio of interfacial area to system volume, interfacial forces can have a controlling effect on phase change processes in microscale systems. For example, the interfacial pressure jump gradient due to varying disjoining and capillary pressures is used extensively for fluid control and stability in passive heat pipes with and without wicks. To optimize the design and use of microscale systems, experimental data on the microscopic details of phase change heat transfer, fluid flow, and stability in an extended meniscus are needed. Herein, the results of experiments on an evaporating extended meniscus of pure pentane on a quartz surface in a constrained vapor bubble (an heat exchanger) are presented.

The evaporative heat flux distribution in the leading edge region of a moving evaporating thin liquid film of pentane on quartz was obtained by analyzing the measured thickness profile for thicknesses, δ < 2 μm. The profiles in a constrained vapor bubble were obtained using image analyzing interferometry. Although the evaporating meniscus appeared to be benign, high heat fluxes were obtained. Significantly higher heat fluxes are possible. The interfacial slope, curvature, interfacial shear stress, and liquid pressure profiles were also obtained. The results obtained using a continuum model were consistent with those obtained using a control volume model. The measured pressure field profile of the isothermal extended meniscus agreed with the constant pressure field predicted by the augmented Young-Laplace model. For the nonisothermal case, measured thickness gradients lead to disjoining pressure and curvature gradients for fluid flow and evaporation. The experimental results confirm that disjoining pressure at the contact line controls fluid flow within an evaporating completely wetting thin curved film and is, therefore, a useful boundary condition [1]. However, in small interfacial systems, non-idealities can have a dramatic effect.

Reference

[1] S. S. Panchamgam, S. J. Gokhale, S. DasGupta, J. L. Plawsky, and P. C. Wayner Jr., ?Experimental Determination of the Effect of Disjoining Pressure on Shear in the Contact Line Region of a Moving Evaporating Thin Film,? J. Heat Transfer, 127 (3), 231 (2005).