Numerical and experimental analysis of natural convection flow boiling of water in internally heated vertical annulus

Numerical and experimental analysis of natural convection subcooled boiling flow in a high aspect ratio narrow vertical annulus operating at atmospheric pressure is carried out. The computational model is developed using RPI wall boiling model. The annular gap is 3.5 mm and aspect ratio is 352. A new empirical relation for nucleation site density is developed for the present geometrical configuration and implemented in the Fluent code with the help of user-defined function (UDF). The results from the numerical analysis are then compared with the experimental results which show excellent agreement. The wall superheat is found to be maximum at the point of boiling incipience which increases with heat input. The wall temperature shows a gradual decrease in the boiling region. The average heat transfer coefficient increases almost linearly for both subcooled and saturated boiling region.