Accuracy of measurements of curvature and apparent contact angle in a constrained vapor bubble heat exchanger

Improved experimental and analytical techniques were developed to measure the liquid pressure field in a meniscus formed in the right angled corner of a Constrained Vapor Bubble (CVB) heat exchanger. Based on the definition of the curvature, an analytical expression for the curvature as a function of the film thickness profile and the apparent contact angle was obtained. The error associated with the resolution of the image processing system was defined and several imaging factors affecting the error are discussed. The error associated with the system resolution, Er, increases as the curvature increases; the apparent contact angle increases; the wavelength decreases; and the number of dark fringes used for the data fitting decreases. The accuracy of the data fitting can be used to also determine the region where the disjoining pressure and viscous stresses affect the results. Examples using pentane data are presented. The relatively large experimental cell size with regions of low capillary pressure was dictated by future use in microgravity.