Optimal Design of Thermal Actuated Valves Based on Level Set Based Topology Optimization

1. Abstract Recently there is a growing need for micro water cooling systems with the development of small-sized fuel cells for mobile electric devices. In general, a water cooling system requires a valve for controlling flow rate of coolant in order to keep targeted devices at appropriate working temperature. Traditional type of a flow control valve is driven by an external power source and a control system. However, for the realization of small-sized fuel cells, it is preferable that whole water cooling system is sufficiently small and can be driven by very little or no electricity. Therefore, in this paper, we focus on a thermal actuator as the successor to the traditional type of a flow control valve. A thermal actuator is a device which can generate motion using amplified thermal expansion effects. Thermal actuator can be driven by heat flowing into it and the amount of its deformation is decided by its temperature. Another advantage of a thermal actuator is that it can be designed as a compliant mechanism. A compliant mechanism can be monolithic structure and its monolithic structure also contributes miniaturization of a valve. Therefore, a thermal actuated compliant valve can be downsized and work with neither an external power source nor a control system. This is why we consider that a thermal actuated compliant valve is suitable for a flow control valve for the realization of a small-sized cooling system. To allow for efficient and effective design of such a thermal actuated compliant valve, we develop its optimal design method based on our two-stage design method that consists of topology and shape optimization. In the 1st stage, topology optimization creates an initial outline of a thermal actuated compliant valve. To allow for design of thermal actuator, we adopt level set based topology optimization and formulate the thermal actuator design problem as a topology optimization problem. In the 2nd stage, shape optimization then yields detailed shape of a thermal actuated compliant valve by considering various design requirements of a flow control valve such as ratio of valve opening due to temperature change and stress constraints. And then, to confirm the utility of the proposed method, we show a case study of a thermal actuated compliant valve design. 2.