Stabilization of single phase rectangular natural circulation loop of larger diameter using orifice plate

Abstract

Experimental investigations on the dependence of the stability threshold on different operating procedures have been carried out in a uniform diameter rectangular loop with orifice plates. The investigations revealed that there is no unique stability threshold for the different operating procedures with orifice confirming the existence of a hysteresis region just as in the loop without orifice. The hysteresis region can be further categorized into unconditionally stable, conditionally stable and unconditionally unstable regions even with the orifice plates. The stability region is found to increase with the introduction of the orifices. The predicted dimensionless steady state flow rate with orifice is found to be in good agreement with the data. One dimensional linear stability analysis accounting for the effective length of the orifices and elbows have been used to predict the stability map. The 1-D analysis can qualitatively predict the stabilizing effect of the orifice plates. However, the stable experimental data is not well characterized by the stability map predicted by the 1-D linear stability analysis which is attributed to the 3-D nature of the flow, the heat losses and the wall thermal inertia which are neglected in the 1-D analysis.