P15318: Gaseous Mass Flow Rate Controller

Build & Test

Table of Contents

Test Plans

The Microsoft Word Test Plan lays out all of the test plans in a single document, while the Microsoft Excel Test Plan lays them out over multiple sheets and includes data collected, as well as results and conclusions.

Test Plan (Microsoft Word)

Test Plan (Microsoft Excel)

Performance vs. Engineering Requirements

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Assembly and Fabrication Plans

Assembly Plan

Fabrication Plan

Preliminary Test Data

Velocity Distribution Profiles

Given that we are testing with a hot wire anemometer, we had to take some data to determine the flow characteristics at our measurement point; mainly determining if it was laminar or turbulent flow. The goal was to obtain turbulent flow so that there would be a blunt velocity distribution that would be easy to repeatedly measure. Instead, the data shows that the flow is a mixture of laminar/turbulent. To move forward with testing, we placed the hot wire anemometer probe in the position that we believed represented the bulk average of the blunt profile toward the center.

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Pressure vs MFR

Our goal for maximum mass flow rate was 20 g/s at 4 bar (60 psi). To check if we would be able to obtain this, we powered the valve to the fully opened position and increased the pressure. The data below shows that we were able to obtain 20 g/s at around 2.75 bar (40 psi). The data also shows that the MFR increased linearly with pressure, as expected.

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Leak Rate

To characterize the leak rate, we set up a test to measure the leak rate vs. input pressure for different output port spring forces. The results were as expected, showing that the higher the spring force, the lower the leak rate is at any given pressure. The downside of using a high spring force is that it means that the actuator will be harder to control. A compromise needs to be made between having a minimal leak rate and maximum actuator control.

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Actuator Position vs. Current

The initial thought on the rotary actuator was that it is a voltage controlled device. Since we were observing extreme non-linear behavior when controlling it with voltage, the purpose of this test was to see if the rotary actuator is actually a current controlled device. The results were still non-linear, just as before.

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Problems Encountered

Valve Friction

The delrin used for the output port and the aluminum used for the rotating disk is creating much more friction as anticipated. This is causing difficulties with regards to the actuator being able to provide enough torque to overcome the friction and rotate smoothly. To reduce this friction, the output port and rotating disk were lapped using diamond compound. The idea of the lapping is for the delrin surface to wear and form a perfect mating surface to the rotating disk. The pictures below illustrate the set-up that was used to show proof of concept before lapping our actual output port.

Lapping Set-up Delrin Wear

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Given that the results from out proof of concept test were promising, we went ahead and lapped our output port with a blank rotating disk. Although the output port did form to the rotating disk's surface, some particles in the diamond compound seemed to get trapped between the surfaces and dug into the output port. This caused the output port to have a somewhat smoother surface, but rough where the diamond compound dug into it.

Output Port "Blow Out"

When initially pressurizing our device to see if there were any leaks at high pressure, we determined that the pressure in the device was overcoming the spring force that was pushing the output port onto the disk. This meant that the device would not be able to used at pressures where this happened because it wouldn't be possible to control the flow. To solve this, we redesigned a new smaller output port. The reasoning behind it is that it has less exposed surface area for the pressure inside of the device to act on and therefore can handle a higher pressure before "blow out" occurs. The pictures below show the differences in exposed area between the original design and updated design.

Initial Exposed Surface Area Improved Exposed Surface Area

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