Dear Spinlanders,
We recently installed Dwyer VFA gauges (calibrated for SCFH Air) on six magnets.
When I convert the observed flow rates to liquid helium boiloff (in mL/hr), I
consistently get values ~1.4-1.6x higher than what I would expect from BSMS
readings and fill history. I'm clearly making a mistake somewhere and would
be grateful for any guidance.
For example, our pumped 800 has a Dwyer VFA-3. The widest part of the ball
float is at 2.7 SCFH Air, which I convert to liquid mL/hr via the following
calculation:
* Multiply 2.7 SCFH Air by 2.69 to convert to helium (as per Dwyer
https://dwyer-inst.com/en/list/post/we-have-several-va-flowmeters-we-are-flowing-helium-through-them-and-need-to-know-what-the-flow-rate), resulting in a value of 7.26 SCFH helium.
* Convert to mL/hr (multiply by 28317), resulting in a value of 205666
gas mL/hr.
* Divide by the expansion ratio of 745:1, resulting in a value of 276 liquid mL/hr.
However, this is an impossible value! This magnet is filled with 250 L every
6.5 weeks; assuming 15% boiloff during fills, we are effectively putting 196 mL/hr
into the magnet. 196 mL/hr also agrees well with the electronic flow meter we
have for this magnet (BMPC), and with the rate I calculate based on the BSMS readings.
Thanks for reading! I'd be grateful for any advice and will gladly share the
corrected answer with AMMRL.
Sameer
--
Sameer Al-Abdul-Wahid, Ph.D. | Manager
Nuclear Magnetic Resonance Centre | University of Guelph
50 Stone Rd E | Guelph, ON | N1G 2W1 | CANADA
519-824-4120 Ext. 58914 | s.wahid_at_uoguelph.ca<mailto:s.wahid_at_uoguelph.ca>
http://nmr.uoguelph.ca/
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Received on Mon Sep 11 2023 - 11:05:28 MST