Preliminary Detailed Design
Table of Contents
Updated SimulationOne of the important customer requirements is pressurizing and depressurizing the vessel in a way that it follows the compression cycle. The Simscape model was updated to match the system requirements.
The system is consisted of an inlet, suction, and outlet valve (which is the valve that will be designed by the team). The vessel size is changed to 0.1ft^3. The pressure is entering at 50 psig and pressurizes the vessel to 5 psig. Once the vessel reaches 5 psig, the outlet valve opens and lets the compressed air out. After the outlet valve closes, the suction valve opens until the pressure inside the vessel is back to 0 psig. Notice that the system has an overshoot value of about 1 psi, meaning that the pressure in the vessel reaches 6 psig instead of 5. However the results are close to ideal and the overshoot can be neglected. The compression cycle repeats at a frequency of 4HZ, which is the customer's requirement.
The orifice area and mass flow rate values of inlet and suction valve that's obtained from this simulation model will assist the team in purchasing the suitable valves. Most importantly, the orifice area value of the outlet valve obtained from this simulation will play a significant role in designing the active valve.
PiezoPiezo materials have a nearly infinite resolution and consume little power. However, piezo materials have not overtaken solenoid technologies in fluid control applications. A study done by the National Physical Laboratory shows the results of using piezo materials in high frequency applications for a long period of time. (Link to article: http://publications.npl.co.uk/npl_web/pdf/cmmt148.pdf). Overall, long periods of use result in mechanical and electrical degradations of the piezo material. These changes to the piezo material also change the properties of the material which may result in different actuation lengths. Given that our project requires a small amount of precision, piezo materials were not chosen has our actuator.
The shift of the resonance peak of the length extensional mode of a piezo. cylindrical sample with repeated exposure to a 160MPa stress. The height of the peak also reduces with repeated cycling, and this is reflected in the general degradation of all the piezoelectric parameters. Model
The load applied has spread unevenly and is difficult to control the homogeneity of the stress levels throughout the sample. Thus making its fatigue and functionality unpredictable and decreasing substantially over the number of cycles Model
Updated Actuation Pugh ChartBased on the research done on piezo material and its fatigue behavior, the actuation subsystem pugh chart was redone. After considering the results of this pugh chart, the team selected an electromagnetic solution (solenoid) for actuating the active valve.
Drawings & SchematicsAfter combining all the subsystem level concepts, two distinct design options were generated. In both designs, the active valve is consistent of four valves that open and close using solenoid actuated poppets. Adding up the orifice areas of these valves will be equivalent to the orifice area of the active valve obtained from the simulation section.
In the first design, only one solenoid is used to actuate a plate that includes the four poppets. This will make it easier to control all four orifice areas simultaneously. However, if the solenoid fails so does all four valves. On the other hand, in the second design, each valve has it's own solenoid which decreases the chance of system failure. If one solenoid fails, the 3 other valves will continue operating.
Below are the drawings for both designs.