Study on spacer-induced heat transfer deterioration of supercritical water in annular channel

Experimental and numerical investigations on spacer-induced heat transfer deterioration of supercritical water in annular channel have been carried out. The test section consists of a heated outer rod of 15.0 mm inner diameter and a concentric unheated inner rod of 7.41 mm outer diameter, forming a 3.80-mm-wide annular channel. A spacer with block ratio of 0.3 is equipped into the channel. The experimental conditions are the pressure of 23-25 MPa, mass flux of 450-1200 kg/(m(2)s), heat flux of 400-1000 kW/m(2) and fluid temperature of 240-450 degrees C. The spacer-induced heat transfer deterioration occurs at the conditions of mass flux 450 kg/(m(2) s), heat flux 400 kW/m(2) and specific fluid temperature region. Based on the experimental data, the criteria for the occurrence of deterioration are obtained. For the case that heat transfer deteriorates, the wall temperature experiences a couple of oscillations before recovering to the fully developed state. In order to study the mechanism of this complicated heat transfer behavior, numerical simulation has been performed with FLUENT and a reasonable explanation has been proposed. (C) 2018 Elsevier Ltd. All rights reserved.