Cryogenic Pressure Transducer
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The Texas A&M Rocket Engine Design (RED) team is building our school's first liquid fueled bi-propellent rocket engine. Powered by liquid methane (CH4) and liquid oxygen (LOX), the rocket's propellent tanks and lines must be carefully monitored. This is being done with a pressure transducer (PT)
An off-the-shelf PT, capable of operating in cryogenic temperatures, can cost up to $4,000. As such, my team and I were tasked to design, manufacture, and test PTs capable of operating under -200° C while costing under $110.
Design Requirements
- Must operate at -200° C and measure up to 750 PSI
- Must be able to provide accurate and precise data (± 2 PSI)
- Must measure tank and fluid line pressures (CH4 & LOX)
- Must connect to fluid lines using the common flared fitting
- Must report pressure readings regularly
- Materials and fixtures must cost less than $110
Execution
Step 1: Brainstorming
I led a couple weeks worth of brainstorming sessions with my team. We discussed the design constraints and drew potential solutions on a large white board.
This was one of my favorite experiences because it taught me how diverse the ideas a group of students can come up with. It challenged my creativity and engineering ability.
Step 2: Draft Design
After brainstorming, a draft design was drawn and its design was verified via a Conceptual Design Review.
Initial prep started on the fixtures. One of the most critical characteristics of our design is that the electronics are protected from the extreme cold conditions. I had to research a lot about LOX heat transfer properties.
Step 3: CAD (Solidworks)
Several edits were made to the PT to make sure the system was compatible with the existing rocket design.
I designed the parts on CAD using Solidworks and some dimensional changes were implemented to ensure a good fit with the rest of the system. Fixtures to attach the piston to the loadcell was designed as well
Step 4: Preliminary Simulations
Interference simulations were ran on the part. After more dimensional tweaks, the design was considered computationally validated
Step 5: Research
I led another brainstorming session which involved materials selection, manufacturing techniques, and necessary fixtures.
After a few weeks of research into various materials for the piston-cylinder system and o-rings, my team and I decided to use Stainless Steel 304 as the core metal due to temperature ability, cost, and availability. The o-ring's material was chosen to be PTFE Teflon due to its operational temperature range and low cost.
The O-ring inserts design is altered to meet ASME standards
Minimum required dimensions to fit into recommended range:
Step 6: Critical Design Review
I led a Critical Design Review (CDR) for this system. After several hours of discussing my team's design choices, simulation results, material choices, manufacturing plan, and costs, our design was validated pending one change.
Step 7: Prototyping
Several design changes were made after the CDR. After these changes were made, prototyping began.
Our team utilized both a manual and a CNC lathe.
Video of the CNC Lathe threading the PT below
CNC Lathe Threading.mp4Google Sites
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