Paper presented to the 3rd Southern African Solar Energy Conference, South Africa, 11-13 May, 2015.
The open solar thermal Brayton cycle uses air as working
fluid, which makes this cycle very attractive for use in waterscarce
countries, such as South Africa. An open-cavity tubular
solar receiver may be used in a dish-mounted solar thermal
Brayton cycle. This solar receiver has been optimised in recent
work using the method of entropy generation minimisation. The
performance of the optimised open-cavity tubular receiver can
be modeled analytically, but this model should be validated.
The purpose of the study was to test the receiver in an
experimental setup to validate a heat loss model which
considers the errors associated with the collector. A 4.8 m
diameter aluminium parabolic dish with 45° rim angle was
constructed on a two-axis solar tracking system. An optical
error of 5 mrad was measured. The receiver had an aperture
area of 0.25 m x 0.25 m and was constructed from 88.9 mm
diameter stainless steel 316 tube sections. The solar tracking
was done manually to provide a tracking error of less than 1°. A
blower was used to blow air through the receiver tube to
determine the net heat transfer rate to the air. A hightemperature
test was also done wherein the receiver was heated
up to steady state to determine the convection heat transfer
coefficient. The temperatures on the receiver surface were
measured with K-type thermocouples. The maximum
temperature reached was around 650 K. It is shown that the
insulation arrangement around the receiver tube is important.
