MicroBooNE Document 3846-v1

MicroBooNE Argon Purge Simulation

Document #:
MicroBooNE-doc-3846-v1
Document type:
Design or Technical Note
Submitted by:
Erik A. Voirin
Updated by:
Erik A. Voirin
Document Created:
27 Oct 2014, 13:45
Contents Revised:
09 Nov 2015, 15:55
Metadata Revised:
09 Nov 2015, 15:55
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Abstract:
In this document we simulate the argon purge of the MicroBooNE cryostat using an achievable flow rate of argon gas through the sparger holes at the bottom of the cryostat. Previous purges have been done with diffusers to distribute flow evenly and slowly into the bottom of the cryostat. Previous purges have also been done with a 1.2 meter per hour upward velocity. That high of a flow rate is not achievable without significant pressure rise in this vessel, so several flow rates were compared analytically and a flow rate of 480 SCFH was determined to be acceptable. This scenario was simulated using Computational Fluid Dynamics (CFD) software, where argon flowed out each sparger holes at a flow rate of 2.273 SCFH, and 1.0036 meters per second. Calculations for this flow rate show roughly 4 psig of back pressure through exhaust pipes, and 1 volume change every 12.5 hours. Simulation results show the sparger pipe holes cause some advective mixing of the gasses in the cryostat and performance is not as good as if a diffuser was used. However, we still see a maximum of 10 ppm original air after 50 hours of purging (4 volume changes) and a maximum of 1 ppm original air after 80 hours of purging (6.5 volume changes).
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