Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.
Solar energy is an abundant renewable energy resource that can
be used to provide high process heat necessary to run thermo
chemical processes for production of various solar fuels and
commodities. In a solar reactor, sunlight is concentrated into a
receiver through a small opening called the aperture. However,
obtaining and maintaining semi-constant high temperatures
inside a solar reactor is a challenge. This is because the incident
solar radiation can fluctuate depending on the position of the
sun and the weather conditions. For fixed aperture size reactors,
changes in incident solar flux directly affect the temperature
inside the reactor. This paper presents a novel solar reactor with
variable aperture mechanism which is designed and
manufactured at our lab. Radiation heat transfer analysis of this
reactor concept is studied via Monte Carlo (MC) ray tracing.
MC ray tracing module is coupled to a steady state onedimensional
energy equation solver. Energy equation is solved
for the wall and gas, accounting for the absorption, emission,
and convection. Incoming direct flux values for a typical day
are obtained from National Renewable Energy Lab (NREL)
database. Results show that for a perfectly insulated reactor, the
average temperature of the working fluid may be kept
appreciably constant throughout the day if aperture diameter is
varied between 3 cm and 1.5 cm for incoming fluxes starting
with 400 W/m2 at 05:12 am in the morning, reaching peak
value of 981 W/m2 at noon, and eventually receiving 400 W/m2
at 6:58pm in the evening, which can make the solar reactor run
about 13 hours continuously at 1500K semi-constant
temperature.
