Experimental research of a two-phase nitrogen natural circulation loop

Abstract

Two-phase heat and mass transfer in nitrogen has been experimentally investigated in a natural circulation loop. The experiments were realized in steady-state conditions near atmospheric pressure with a 10 mm inner diameter vertical copper tube, uniformly heated over roughly 1 m in length. The vapor and total mass flow rates and the wall temperature were measured as a function of the tube heat flux density. The investigated ranges-limits are 40 g/s, 25% and 30 kW/m2 for the total mass flow rate, the vapor quality and the heat flux density respectively. Transition from single phase natural convection to nucleate boiling flow is evidenced by wall temperature measurements at five different locations along the heated tube. The measurements are compared to the numerical computations of the total mass flow rate that is simulated by a set of conservation equations based on a simple separated flow model. The model catches most of the features of the mass flow rate evolution as a function of the heat flux density. In addition, the wall temperature measurements are used to determine the heat transfer coefficients that are compared with known correlations in both single phase natural convection and boiling flow. A majority of the data falls within ±20% of the predicted values given by the correlations.