Experimental investigation and modeling of onset of condensation induced water hammer in equal-height-difference natural circulation system

Abstract

Condensation induced water hammer (CIWH) in equal-height-difference natural circulation systems (EHDNCS) can lead to significant damage to associated equipment. To investigate the mechanism and the prediction of the onset of CIWH in EHDNCS, a small-scale experiment of EHDNCS was conducted under different water temperatures, heat transfer powers, and resistance coefficients of the water-side inlet. This study analyzed the thermal hydraulics, flow regimes, and the onset mechanism of CIWH through temperature and pressure measurement, U-Net image segmentation, and analytical modeling. Four distinct flow regimes were observed in the horizontal pipe: single-phase flow, non-periodic bubble, periodic bubble, and CIWH. Flow regime maps based on water temperature and heat transfer power were obtained under different inlet resistance coefficients. When the steam bubble length is smaller than the pipe length, no CIWH occurs. When the steam bubble length reaches the pipe outlet to form stratified flow, CIWH occurs at a high steam channel height. The occurrence of stratified flow and reverse flow of subcooled water in the steam channel causes the onset of CIWH in EHDNCS. A dimensionless criterion has been developed to predict the onset of CIWH when the saturated steam-water mixture is discharged through a horizontal pipe in EHDNCS. This criterion effectively predicted the transition from periodic bubble to CIWH in the experiment.