SIMULATION OF OSCILLATIONS IN BOILING FLOW IN A NATURAL CIRCULATION EVAPORATOR

This article presents both experimental and theoretical investigations on the nature of oscillations of void fraction and temperature in a boiling natural circulation loop of a short-tube natural circulation evaporator at low pressure and low heat flux conditions. The experimental study includes online measurement of void fraction and temperature in the loop. The proposed moving boundary model equations for boiling channel in the loop have been solved by a finite volume scheme and subsequently nonlinear ODEs have been solved by Gear's method. The proposed model equations have been validated with experimental data and the data taken from literature. The periodic nature of the pulse-variation of both void fraction and temperature has been identified. A comparison has been made on the applicability of homogeneous flow model and nonhomogeneous flow model to predict the void-fraction pulses and the temperature pulses. Measurement uncertainties and model uncertainties have also been discussed.