Experimental Study of the Effect of the Heating Profile on the Characteristics of the Geysering Instability

Abstract

Two-phase flow instabilities can be observed in diverse two-phase flow systems such as nuclear power, cryogenic fuel pipelines for aerospace engines, thermosyphon in solar energy collectors and during the transport of two-phase flows in pipelines. Under low flow rate and heat flux conditions a particular type of instability can occur named as geysering instability. The geysering instability is a compound relaxation instability driven by condensation and the changes in the hydrostatics pressure. In this work, we investigate the effect of non-uniform heat distribution in the dynamics of geysering or condensation-induced instability. By fixing the total power in the heated section, the control of the heating profile can influence the vapor generation. We study the characteristic of the oscillation wave shape, amplitude and period, and reversal flow magnitude. The test section consists of 2m horizontal heated section followed by a 5 m vertical inverted u-tube section. The heated section is divided into 5 independently controlled regions which allow to control the heating profile. The effect of the heat profile, peak value, and peak value location are discussed. Increasing the heat flux in the last segment of the test section, while maintaining the total power fixed, leads to the suppression of the instability. Contrary, increasing the heat flux in the first segment of the test section leads to a more pronounce oscillation.