| Description |
This thesis presents the design and optimization of a biologically inspired wet shape memory alloy (SMA) actuated pump that can provide thermal energy via fluidic convection to actuate external wet SMA subsystems. Furthermore, the pump draws from its own fluidic output to assist in the actuation of its own internal SMA actuators. A thorough analysis of the previous wet SMA robotic heart is conducted by searching for opportunities for improvement. Methods of improving the pump's output-to-input ratio included modifying the pumping chambers, actuation cycle timing, implementing electrical actuation, and continuously adding heat to the system. Dynamic modeling was performed to provide a baseline indicator of what was to be expected during actual implementation and testing. The effects of changing various parameters were explored to determine optimal configurations. Key parameters affecting performance include mechanical advantage, actuator length, flow durations, and water temperature. Implemented design changes and testing confirmed the modeling results. Continuous heating of the hot water within the pressurized accumulator greatly enhanced the pump's performance. Using only fluidic induced actuation, the output-to-input ratio peaked at 1.4. The pump reached an output-to-input ratio of 2.1 with the aid of electrical actuation. This is the first successful implementation of a self-sustaining thermofluidically powered SMA pump. Furthermore, unlike other SMA micropumps that typically output 1 mL/min or less, this pump is capable of a macroscale net output of 66 mL/min. While the pump's output exceeds the required input, the power efficiency and power density of the pump do not compare to that of the human heart due to the amount of power required to keep the hot water continuously heated. Viable options for improving efficiency and power density include minimizing pump mass, optimizing pumping chamber design, and reducing the amount of heat necessary to keep the hot water at an elevated temperature. |
