Experimental investigation of heat transfer in coiled tube type molten salt steam generator

Abstract

Heat transfer performance of coiled tube type molten salt steam generator has been experimentally reported, and the wall temperature distribution, steam generation rate and thermal efficiency were comprehensively investigated. Heat transfer of the system was mainly determined by two phase flow inside coiled tube and molten salt convection outside tube. The coiled tube can be divided into three regions as liquid phase region, vapor-liquid two phase region and superheat steam region, and the wall temperature in two phase region first decreased for nucleate boiling with high heat transfer coefficient and then increased. When molten salt temperature increased, overall heat transfer coefficient and thermal efficiency first increased, and then dropped due to heat transfer deterioration for superheat steam and high heat loss. According to present experimental system, overall heat transfer coefficient had maximum of 290 W/m2 K at optimal molten salt temperature of 340 °C, while thermal efficiency approached to its maximum at molten salt temperature of 320 °C. When inlet water flow rate was increased, the superheat gradually decreased with the wall temperature dropping, and the overall heat transfer coefficient, steam generation rate and thermal efficiency first increased and then decreased. Moreover, molten salt forced convection can remarkably improve overall heat transfer coefficient.