Effect of Strip Orientations and Geometry on the Critical Heat Flux in Pool Boiling

Abstract

The objective of this research work is to experimentally determine and analyze the effect of geometry and orientation of strips (heating element) on critical heat flux (CHF) in pool boiling under atmospheric pressure. Studies concerning the effect of geometry, orientation, and thermophysical properties of the heating element on CHF are limited. In the present work, Stainless Steel 304 is used as strip material. The experiments are conducted with strips of length 50, 75, 100, and 150 mm each having width 5, 10, and 15 mm. The experiments are performed with strips of two thicknesses 0.1 and 0.2 mm. For each of the aforementioned combination of dimensions, the experiment is conducted by orienting it in horizontally, vertically over width and vertically over length, respectively. DC power supply is used to supply controlled amount of heat accurately. K-type thermocouples are used to measure the temperature of fluid. Datalogger is used to record the current, voltage, and temperature values. DSLR video camera is used to record the boiling mechanism as well as the location of critical heat flux on strips. The experimental setup was tested for repeatability, and it was observed that under same experimental conditions, CHF value obtained was within a relative deviation of ±6%. It is observed that thickness of strip has negligible effect on CHF for given dimensions and orientation. However, for a fixed length of strip, the magnitude of CHF decreases with increase in its width. It is observed that CHF decreases with increase in the length of strip for a fixed width irrespective of orientation. Out of the three orientations of strip, vertical over width has maximum CHF followed by horizontal and vertical over length, respectively.