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Detailed Design Review. P13681. Austin Frazer Role: Lead Engineer - Analysis Major: Mechanical Engineering Eileen Kobal Role: Lead Engineer – Mixtures of Gas Fluids Major: Chemical Engineering Ana Maria Maldonado Role: Team Manager Major: Industrial Engineering Marie Rohrbaugh

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Presentation Transcript
the team

Austin Frazer

    • Role: Lead Engineer - Analysis
    • Major: Mechanical Engineering
  • Eileen Kobal
    • Role: Lead Engineer – Mixtures of Gas Fluids
    • Major: Chemical Engineering
  • Ana Maria Maldonado
    • Role: Team Manager
    • Major: Industrial Engineering
  • Marie Rohrbaugh
    • Role: Project Manager
    • Major: Mechanical Engineering
The Team
agenda for the review
Agenda for the review
  • Overview of the Project
  • Our system designs
  • Part designs
  • Lab View layout
  • Bill of Materials
  • Test plans
  • Risk Assessment
  • Schedule for the rest of the Project
problem statement


Problem Statement

Fixtures interface between AGT can and UUT

Fixturing/leakage similar to other side

UUT leakage

Fixture leakage

To mass spectrometer

High pressure helium

High pressure helium

Leakage from Unit UnderTest

Leakage from Fixture

Leakage from room through lid and baseplate

the system

Flow Sensor

The System
  • We require a means to distinguish between the top two generated concepts. Consequently, a math model of the system was created.
    • Results must be an improvement from the baseline

0 psi (Vacuum)

Case 1) 14.7 psi (ambient)

Case 2) 0 psi (Vacuum)

Case 3) Variable pressure/vacuum (nitrogen)

3000 psi

simplification of the system

Orifices 1 and 2: Model Oring Leakage.

Simplification of the System

3000 psi

0 psi (To Mass Spectrometer)

Entire Vent Volume

Flow Sensor

  • Orings will be models as (very) small orifices
  • Molar percentages must be taken into consideration for all three cases (compare apples to apples)



Orifice 3 : Accurately simulates uniformly mixed flow out of vent.

parameters and equations

0 psi (To Mass Spectrometer)

3000 psi

Parameters and Equations

Entire Vent Volume

Ideal Gas Law:

Mixed Density Calculation:

Orifice area, Ao, is adjusted for the oring and vent orifices to produce accurate molar flow rates

  • Most Importantly: This is a pressure driven flow
    • Permeability considerations were made (Parker equations from design review). The leakage rates predicted through the Orings were too small.
  • Perfect gas mixture throughout the volume at all times
  • N2 and He are ideal gases
the simulation
The Simulation

Molar flow rate of helium into vent (3000 psi)

Molar flow rate of gas into can calculator

He Integrator

N2 Integrator

Molar flow rate of gas into/out of vent

Calculates % Moles

Calculates Mixed Density


Case 1: Ambient Vent Pressure

  • High vent pressure causes more total leakage than Case 2
  • More nitrogen is present; concentration of helium grows slower than in Case 2

Red Dots: Helium

Blue Dots: Nitrogen

≈ 14.8 psi

≈ 14.8 psi

14.7 psi

≈ 14.8 psi

14.7 psi

  • Case 2: Vacuum Vent Pressure
  • Low vent pressure causes less total leakage than Case 1
  • Less nitrogen is present; concentration of helium grows faster than in Case 1

Moderately High % Helium

14.7 psi

≈ 14.8 psi

≈ 1.1 psi

≈ 1.1 psi

1 psi

1 psi

Very High % Helium

1 psi

*Note: Hein remains (approximately) constant for both cases

total molar flow rate into can
Total Molar Flow Rate Into Can
  • Question arises: Is it better to have a lower total leakage (lower vent pressure) or a lower percentage of helium in the vent?
    • The simulation should answer this question
  • Below is a plot of the actual molar flow rates into the can

Note the order of magnitude

As expected, the total molar flow rate is less for Case 2

helium in can
% Helium in Can

Note the order of magnitude

  • The concentration of helium grows at a rapid rate when less N2 is present in the vent
  • At the beginning of the response, Case 2 exhibits a lower concentration of helium than Case 1
what does this tell us
What Does This Tell Us?

Graphed below are the results for the volume of the total leakage for cases 1 and 2:

  • Over the full interval, the model predicts that Case 2
  • An improvement is not expected for a constant vacuum scenario. A constant vacuum does show an improvement in can leakage for the full test duration
    • This duration of this improvement grows as the vent volume is increased

Full 6 Minutes

Early Region (2.5 seconds)

cases 1 and 2 with increased vent volume
Cases 1 and 2 With Increased Vent Volume
  • For a significantly increased volume:

The positive influence of Case 2 lasts for approximately 175 seconds (as opposed to 2 seconds). That being said, the remainder of the results will assume that the vent volume is the nominal calculated value (8.49E-7 m3)

cases 1 and 2 conclusions
Cases 1 and 2 Conclusions
  • Concentration of helium in vent dominates the response of the simulation
  • Case 2 would show a significant improvement over Case 1 if:
    • The % He was allowed to grow near 100% in both cases (within the allotted time interval)
    • The vent volume was significantly increased
  • A Case is needed which actively reduces the concentration of helium in the vent. A marked improvement over Case 1 is expected
case 3 concept
Case 3 Concept
  • Nitrogen is forced in at above ambient pressure: % Helium increases over time
  • Uniform mixture of gas molecules are removed from the vent: % Helium remains about same.

≈ 120 psi Mixture

120 psi N2

≈ 1 psi Mixture

case 3 concept continued
Case 3 Concept Continued
  • Nitrogen is once again forced into the vent: % Helium Drops (Note total percentage still > step 1)
  • Repeat step 2 and 3 throughout the 6 minute external leakage test. The percentage of helium will inevitably grow, but at a slower rate than cases 1 or 2.

≈ 120 psi Mixture

determining the frequency of pulse purge
Determining the Frequency of Pulse/Purge
  • Previous slides indicated that pulling a vacuum is only beneficial for approximately 2 seconds. Consequently the following duty cycles for varying input signal periods were calculated:
  • Values of 120 psi pulse pressure and 1 psi purge pressure were selected

120 psi

1 psi

1 Period

case 3 results
Case 3 Results


case 1 to case 3 comparison
Case 1 to Case 3 Comparison
  • The best curves of Case 3 are now compared to baseline:
  • A significant improvement is noted for Case 3
simulation conclusion
Simulation Conclusion
  • A case 3 scenario shows a marked improvement over the current setup
  • This model will be used as a tool in MSDII to fine tune the system to optimize can leakage prevention
areas of desired feedback
Areas of Desired Feedback
  • After seeing the results, is the magnitude of can leakage accurate?
    • If not, the size of the orifices will be adjusted accordingly
  • Is the 8.49E-7 m3 vent volume accurate? Note that this is 84.7 mm3
cycling valve
Cycling Valve


To the small o-ring


pipeline model
Pipeline model

Wires exit rear

2-way valve


3-way valve

Some type of relief structure will be in place here

2-way valve

From Nitrogen Source

From Vacuum Source

To large o-ring

To small vent

pressure vessel analysis plug
Pressure Vessel Analysis: Plug
  • A pressure vessel analysis was ran for the plug geometry. This geometry was selected due to the thin walls
    • Due to the thin walls this is considered the worst case geometry
  • Failure margins were calculated with a 1.1 factor of safety. Note all margins are positive.
material properties
Material Properties
  • Plugs assumed to be machined from structural steel (properties taken from ANSYS library):
    • Fty= 36.3 ksi
    • Ftu= 66.7 ksi
    • μ = 0.3
    • E = 2.9E7 psi
  • 472699 Nodes
  • 311215 Tetrahedral Elements (Overkill)

2 cells through thickness achieved

loads and boundary conditions
Loads and Boundary Conditions

Nominal Loading

Worst Case Loading

Fixed Support

nominal loading results
Nominal Loading Results

Maximum stress: 9675 psi

worst case loading results
Worst Case Loading Results

Maximum stress: 9675 psi

margin calculation
Margin Calculation
  • Margin for yield in the worst case loading scenario is negative. All others are positive
  • This is due to a high stress at the part surface. The net section stress will now be studied.
worst case loading net section stress
Worst Case Loading: Net Section Stress

Average stress is calculated for the load path shown. New margins are calculated


net section margins
Net Section Margins
  • Net section margins are positive
  • The part is deemed to be safe for cleanroom usage
wire diagram
Wire Diagram

Each valve has 2 leads for a circuit. They will be connected to a terminal block and then to a terminal block on the AGT system