Experimental study of boiling incipience in a closed loop vertical annular thermosiphon

The present study aims to identify the conditions of boiling incipience experimentally and relate them to the important relevant parameters such as heat flux, liquid submergence level and physical properties during boiling of liquids in an internally heated vertical annulus. The heating surface and liquid temperature distributions were therefore obtained with distilled water as a test fluid in the annulus. The test section is an annulus made of two concentric tubes, the inner made of stainless steel while the outer of corning glass through which flow during the boiling and non-boiling phenomenon along the annulus can be visualized. The maximum wall superheat, attained around boiling incipience, was taken from the wall temperature distributions. The computed values of (δ°/rc), which is ratio of the superheated layer to the radius of cavity on the heating surface, come out to be in the range of 8-18, which is quite comparable to the reported values in the literature. Correlations have been proposed in terms of the heat flux, physical properties of water and liquid submergence level.