Experimental study on a single-phase natural circulation loop and its steady-state solution

Abstract

A practical case of a single-phase natural circulation (SPNC) loop having a considerable circulation length and non-uniform structures is investigated via experimental and analytical approaches. The target facility (Facility to Investigate Natural Circulation in SMART, FINCLS) corresponds to the type of vertical heater and vertical cooler (VHVC), and the maximum height and total circulation length are 12.2 and 34.5 m, respectively. A series of SPNC tests comprising 29 steady-state conditions are performed under a wide range of working conditions: 0.5 MPa (60 °C) to 15.0 MPa (300 °C). Unexpected characteristics of the natural circulation (NC) flow rate are observed for two test groups under high-temperature conditions. An NC loop (NCL) model for a steady-state solution that reflects both heat-loss and heat-sink effects is developed by employing the lumped-component method and the moving-boundary algorithm. The NC flow rates for 29 steady-state conditions predicted by the NCL model agree well with measurements (within 5% error), and the unexpected characteristics of the NC flow rate are clearly demonstrated via analysis of the NCL model.