| The Constrained Vapor Bubble, CVB, which utilizes the intermolecular force gradient of thin liquid film to return the liquid back to the evaporator from the condenser, is a passive, change of phase heat transfer system. A low capillary pressure design is particularly suitable for use in microgravity conditions as a heat transfer device. Current ground based studies are a precursor to microgravity studies.; An experimental setup was built to study the fluid flow, mass and heat transfer of thin film in a vertical CVB. A new image analyzing technique was developed to obtain the curvature and apparent contact angle simultaneously for the concave thin film. Using a coordinate transformation, the technique can also be applied to the convex drop. Using the new technique and experimental data for the thickness profile of the thin film, the curvature and apparent contact angle of a growing sessile drop were analyzed.; A theoretical model describing fluid flow, heat and mass transfer of the thin film was developed to predict the parameters that are key to the transport processes of the CVB. The coupled ordinary differential equations were solved numerically to yield the temperature, curvature, pressure and velocity variations along the axial distance of the CVB. The modeling results were in good agreement with the experimental results.; In the condenser region, the movement of a single condensed ethanol sessile drop into a concave thin film was studied. The intermolecular force for small drops is found to be much larger than the gravitational force and dominates condensate removal. A dimensionless force balance model for viscous shear stress demonstrates the effect of changes in the contact angle and curvature of the thin film. |
