Experimental and numerical analysis of transient natural convection of water in a high aspect ratio narrow vertical annulus

Experimental analysis and numerical simulation of transient natural convection flow of distilled water in a high aspect ratio narrow vertical annulus are presented. For the numerical simulation, a CFD model is developed which is solved using ANSYS Fluent and validated with the previous available data. The experimental analysis and numerical simulation have been performed for a heat input range of 300 W-1800 W. The annulus internal diameter is 38 mm and external diameter is 45 mm that results in the annular gap of 3.5 mm while the aspect ratio is 352 and radius ratio is 1.184. The objective of the present work is to develop a CFD model for the prediction of dynamic behaviour of natural convection in a vertical annulus and validate it with experiments. The transient period seems to increase gradually with annulus height. With an increase in heat input, a drop in the transient period is observed. The transient period is predicted fairly well by the computational model. The novelty of the present work is that a very simple CFD model is developed for transient natural convection in a high aspect ratio vertical annulus that can be used in the design of control system for cooling of nuclear reactor cores.