Optimization of reactor temperature according to radiation distribution characteristics

Abstract

Papers presented to the 11th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 20-23 July 2015.

Temperature stability inside a solar reactor is much more complex to achieve than that of traditional combustion based reactors. The main reason contributes to the transient nature of the solar radiation which serves as the source of high temperature process heat to run endothermic solar thermochemical reactions. One of the key factors to assure temperature stability inside a solar reactor is to understand the characteristics of the incoming solar radiation and design a solar reactor accordingly. This paper provides radiation distribution characteristics of 7 kW high flux solar simulator and design of a solar reactor according to that heat source. Flux characterization of the solar simulator was done by using a calorimetric calibration of a heat flux gage. The maximum and minimum peak flux output at the focal plane was obtained by moving the heat flux gage within the focal plane, but away from the focal point by 0.25 mm steps. Heat exchange between the gage and the Lambertian target was quantified by measuring the inlet and outlet temperatures. Flux map obtained per experimental measurements was used to determine corresponding aperture size of the solar reactor for various flux levels. Selection of representative flux levels were made based upon NREL database which was fit to the flux scale of the 7 kW solar simulator. An optimum aperture size for the solar simulator was calculated for various corresponding time of the day per incoming flux based on two different optimization methods and input parameters in order to maintain a constant reactor temperature. It was found that the maximum optimal aperture radius during sunset at 5 am varies between 1.8 cm and 3.52 cm for the methods used, whereas it decreases to 0.4 cm and 0.73 cm during midday. Optimal constant reactor temperatures for corresponding aperture sizes change between 1339 K and 854 K per method used and flux distribution measured.