Feasibility of using Shape Memory Alloy (SMA) spring to facilitate actuation of an iris coupled to a solar reactor

Variation in incoming solar energy adversely affects the temperature inside the reactor and lowers its efficiency. Therefore, it is important to develop a mechanism that can maintain semi-constant temperatures inside the reactor from sunrise to sunset. In this paper, we present a promising aperture mechanism that contracting and enlarging its circular opening with the use of Nickel-Titanium Shape Memory Alloy (SMA) springs. SMA springs possess memory of their shapes at certain temperatures, and therefore, by controlling the temperature of the spring, it is possible to exert different forces. These forces may be then transferred to the variable aperture mechanism. In this study, variation of the force exerted by an SMA spring with respect to temperature was experimentally tested and viability of SMA spring use in actuating an iris mechanism aperture was examined. In order to simulate conditions under fluctuation solar radiation, a 7 kW solar simulator was used in experiments at varying power levels. It was observed that SMA springs are promising as a replacement to the actuation mechanism driven by a motor.