Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.
The successful design and operation of a small-scale solar
thermal Brayton cycle depend on the successful understanding
of the losses or irreversibilities in the system which are mainly
due to heat transfer and fluid friction. The small-scale open
solar thermal Brayton cycle uses air as working fluid which is
heated in a cavity receiver which captures the solar radiation
focused onto it from a parabolic concentrator. The goal of this
work is to determine the optimum receiver tube diameter and
counter-flow recuperator geometries of a small-scale open and
direct solar thermal Brayton cycle with 4.8 m diameter
parabolic dish, so that the net power output of the system is a
maximum. In this work an updated receiver model is used. An
open rectangular cavity receiver is used instead of a spherical
receiver as was used in previous work. SolTrace is used to
determine the solar heat flux rates on the receiver inner walls.
The temperatures and net absorbed heat rates at different parts
of the receiver tube are found by solving multiple equations
using numerical methods. The model describing the heat loss
rate from the recuperator to the environment is also updated in
this work. Five different turbo-machines with different
operating points are considered in this study. The results show
the optimum geometries of the proposed system. It is shown
that for the 4.8 m diameter solar dish with 0.25 x 0.25 m
receiver aperture area, a receiver tube diameter of 83.3 mm will
give the best results.
