Electromechanical Conversion of Low-Temperature Waste Heat Via Helical Shape Memory Alloy Actuators

An energy harvesting prototype (EHP) was designed to convert low-temperature heat loss from fluid into electricity. The method for energy conversion uses two antagonistically connected shape memory alloy (SMA) actuators to rotate a shaft that is connected to a generator. Heat transfer equations for concentric annular flow are modeled. The relationship between SMA temperature and shaft angular rotation is derived from a semiempirical SMA stress-temperature model and Ozdemir's SMA stress-strain equations. The simulated generator shaft rotation and generator voltage are in close agreement with the corresponding experimental results. Additional experiments were conducted to compare the ability of spring and linear SMA wires to convert low-temperature heat lost from water into electricity. The linear SMA generated a peak 0.3 V, whereas the spring-shaped SMA generated a peak of nearly 5 V. On average, 7.4 mJ of energy per 2.5 s cycle was stored in a 6-F capacitor attached to the generator output. It is concluded that the EHP has a strong potential to recuperate low-temperature wasted heat.