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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. [ABSTRACT FROM AUTHOR]

Experimental and numerical analyses have been carried out for single-phase natural convection thermally induced flow in an internally heated vertical annulus. The experiments are performed on an in-house setup having an internally heated annulus of aspect ratio 352 with the heat flux ranging from 2.5 kW/m2to 15 kW/m2. Water is used as the working fluid. The numerical simulations are carried out by a computational fluid dynamics (CFD) model developed using the commercial software package Ansys Fluent. The results of the present analysis are then compared with the experimental data. There is an excellent agreement between the numerical and the experimental results. The contour plots are presented for temperature, velocity, and thermal boundary layer. The thermal boundary layer thickness decreases while the thermal entry length increases with heat flux. An increase in the heat flux leads to the increase in the heat transfer coefficient and the Nusselt number. [ABSTRACT FROM AUTHOR]