A new methodology for experimental determination of liquid–gas interphase positions on a heated solid

In this paper a new methodology is presented to experimentally quantify liquid front positions on a heated solid when working under two-phase flow conditions. Applicable to solids, of which one dimension can be considered infinite (2D-solids), this methodology uses a unidimensional temperature profile measured inside the solid, which is interpreted with the aid of a newly defined parameter, cof∗h. The parameter cof∗h is an effective heat transfer coefficient in the framework of a unidimensional heat balance model. The values and profile of the parameter cof∗h reflect the different effectiveness in heat transfer of a heated surface when in contact with a liquid phase (wet surface) and when in contact with a gas phase (dry surface), thus making it possible to determine the position of the liquid front for every surface of such a 2D-solid. The accuracy of this method depends, mainly, on the conductivity of the solid and, secondly, on the distance between temperature gauges. The methodology has been validated with a commercial finite element analysis code and has been applied to locate experimentally the portion of the inner and outer wet surfaces of two horizontal pipe samples immersed in water under different operational temperatures. One of the samples is a normal smooth carbon steel pipe, while the other has microchannels grooved in its inner surface. The microchannels help to develop capillary forces that keep the inner surface wet above the horizontal water level at which the sample is immersed. The difference in liquid limit between the inner and outer surfaces can easily be determined by the parameter cof∗h. The method proposed is especially usefull when visual methods cannot be used.