The final design solution integrates a modified aluminum valve housing compatible with the process fluid and testing chamber with a stepper motor actuator system using a Bowden cable mechanical linkage. The Bowden cable is a mechanical linkage that, in this case, is composed of a FEP coated steel inner wire that transfers loading from the driving end to the driven end. The path of the wire is determined by an outer PTFE tubing, which is statically fixed at both ends. This design solution separates the sensitive electronics in the actuator from the extreme temperatures experienced within the test chamber.

The stepper motor actuator directly interfaces with the steel cable in the Bowden Cable through a wheel mount. Incremented turns by the stepper motor pull on the Bowden cable which transmits the force to the valve housing armature. The armature is pulled against the spring in the valve, causing the stop to be pulled away from the valve nozzle and permit the process fluid to flow through. As the force of the actuator is increased, a greater force is exerted on the armature causing it to displace further from the nozzle and increasing the flow rate through the valve.

A flowmeter measures volumetric flow rate through the system to provide real-time feedback on refrigerant fluid moving through the valve. Based on a user or system specified cooling rate that is proportional to the flow rate of fluid, the measured flow rate can be adjusted to match the desired flow rate. In the final design solution, two separate Arduino controllers are used, one to receive digital output from the flowmeter, and another to manually direct the stepper motor’s movement. The final hardware prototype does not incorporate the real-time feedback system. However, it does possess the hardware required to do so.