Shape Memory Alloy Actuator with Sharp Phase Change

Problem: Thermally-actuated gas valves require a gas-oil temperature difference of at least 6┬░C to completely actuate, based on commercially available SMA wire material properties. Some wells may have less than 6┬░C temp difference, and thus the current safety valve design could not be applied. Technology: This invention describes a way to decrease the temperature difference required for the SMA wire to fully actuate. The SMA wire actuates when it is heated from As (Austenite Start Temperature) to Af (Austenite Finish Temperature), which are both dependent on the stress applied to the wire. Higher stress increases both As and Af, while lower stress decreases both. A negative differential spring displaced can decrease the As-Af temperature difference. Christopher Noble crn@mit.edu

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