An experimental and numerical study on the dynamics and temperature control of a solar reactor featuring human eye inspired mechanism

Despite of its high potential for use in wide range of industrial processes, solar energy is transient due to change in weather conditions and varying position of the Earth. Fluctuation of solar radiation from sunrise to sunset threatens consistent delivery of energy for endothermic solar thermal processes. Fluctuation of incident solar flux adversely effects the temperature stability of solar thermal receivers which in turn reduces the efficiency. Therefore, dynamic control of temperature is essential to maintain stable performance of solar receivers. This poster presents a novel reactor featuring an iris mechanism to control the entry of solar radiation into the receiver. The iris mechanism is made of eight stainless steel blades opening and closing the aperture in translational motion which changes the diameter size between complete closure to 10 cm. Performance of this mechanism was studied experimentally and numerically. Experimental work was done by using a 7 kW solar simulator as the high temperature heat source. Power level of the simulator was changed from 115 A to 155 A to mimic the changes in flux levels from sunrise to sunset. Radiation map of the flux intercepted on focal plane was experimentally determined using a heat gage, Lambertian target, and CCD camera. Results showed that the peak flux level reaches over 3000 kW/m2 providing concentration ratios exceeding 150 suns on 80 x 80 mm target. Optical and radiation characteristics of the solar simulator were numerically estimated by Monte Carlo (MC) ray tracing method. Comparison of numerical results and experimentally measured power levels was made to check the accuracy of the simulations. As the main goal of this work is to maintain semi-constant temperatures inside the solar receiver, a thorough numerical and experimental work were done to develop rigorous dynamic control of the system. Temperature inside the reactor was modeled via an in-house developed code where MC ray tracing module was coupled to unsteady energy balance equations for ring elements at the inner surface of the cavity receiver with the inclusion of radiation, convection and conduction heat transfer occurring within the control volume. Algebraic differential equations were solved via Runge-Kutta method to obtain dynamic temperature variation along the axial direction of the solar receiver. Validation of the simulation results were done by comparison with the experimentally measured temperature values taken at nine different locations of the solar receiver. Upon the validation of its accuracy, the heat transfer model was used to design a controller to regulate the gas temperature by adjusting the aperture size. Performance of the control system was evaluated via servo and regulatory approaches. The servo performance was evaluated by tracking two desired set points for outlet gas temperature at 450 K and 550 K. Monitoring test was performed by changing power levels of the solar simulator as an unmeasured disturbance to the process. It was observed that for both set point tracking and load rejection cases, the average settling time was less than 1 hour, and the maximum overshoot did not exceed 10%, which confirms the satisfactory performance of the designed controller.status: publishe