Incipient Boiling of Sodium in Seven-Pin Bundle under Forced Convection Conditions

Abstract

Experimental studies were carried out on incipient boiling of sodium flowing in an electrically heated seven-pin bundle under forced convection. In the first series of experiments temperature distributions in the bundle were measured under non-boiling conditions. The measured temperature distributions agreed fairly well with the calculation by the NORMAL code. In the second series of experiments incipient-boiling (IB) phenomena were investigated, with particular reference to the IB superheat and the voiding patterns. The IB wall superheat decreased with increase in flow velocity. The observed coolant voiding was limited in the central subchannel because of the steep radial temperature gradient in the bundle. In order to describe this voiding process a two-dimensional voiding model was required.