Effect of Adding Horizontal Rings on the Thermal Behavior of Cylindrical Liquid Enclosure Exposed to High Heat Flux

Abstract

Power generation by using concentrated solar thermal energy on liquid enclosures is one
of the most promising renewable energy technologies. In this work, a developed liquid
enclosure fitted with various number and configurations of horizontal metal rings have been
analyzed, fabricated and tested. The influence of adding metal rings arrangement is
investigated for its potential to enhance radial heat conduction to the center-line of the
enclosure from the side-walls. Experiments were carried out for fluid in both static and
dynamic modes of operation inside the enclosure that subjected to high heat flux.
A developed two-dimensional CFD model to predict the transient flow and thermal fields
within liquid enclosure subjected to heat flux has been developed and tested. The developed
numerical model takes into consideration energy transport between the liquid inside enclosure
and the solid material of the enclosure. The numerical simulations have been compared with
experimental measurement. The computational code has been found in a good level of
agreement with the experimental data except for liquid at the peak part of the enclosure.
The results indicate that adding metal rings produce significant impact on the transient
temperature difference inside enclosure during both static and dynamic modes. The six-ring
model is found to be more effective for enhancing radial heat transfer than other three models
that have been tested. The in-line arrangement is found to provide better thermal effect as
compared to the staggered rings.
Two new correlations for natural heat transfer inside liquid enclosures subjected to high
heat flux have been formulated (one for no-ring model and the other for six-ring model). The
natural Nusselt number is found to be around a constant value for Rayleigh number less than
(5 x 10
8
).
The recommended use of metal rings inside liquid enclosures subjected to heat flux, and
the predicted Nusselt number correlation, will add to local knowledge a significant mean to
gain more heat in large scale concentrated solar power plants.