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 °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. [ABSTRACT FROM AUTHOR]