Hello,
I was trained to use a flutter tube to measure helium volume. I need to
double check this value based on the mass and am getting an absurd value,
hence, I am hoping someone can point out my mistake.
The tare weight on the dewar is 178.5. I am assuming this is in pounds based
on
https://www.cryofab.com/wp-content/uploads/2019/08/Cryofab_CMSH_Series_Specs_60.pdf
The vendor claims that at their facility the dewar's weight is 219 (pounds).
219 - 178.5 = 40.5 lbs
40.5 lbs / 2.2 lbs/kg = 18.4 kg
Helium density at 1 atm is 125 g/L (
https://en.wikipedia.org/wiki/Liquid_helium)
The liquid helium in the dewar is over-pressurized, however, I will ignore
this impact. (I assume the vendor measured the weight of the dewar with the
safety value is open, which is nominally 0.5 PSI or 0.03 atm. Can the change
in density associated with this change in pressure can be neglected for the
purposes of this calculation?)
18400 g / 125 g/L = 147.2 L
Given that the dewar capacity is 60 L, my conclusion is that the weight value
recorded by the vendor is not correct and their scale/balance is malfunctioning
or miscalibrated. Hence, the flutter tube is the only reliable measurement of u
helium volume in this case.
Thank you for your time,
Justin
Justin Douglas
he/him/his
NMR core lab
University of Kansas
justindouglas_at_ku.edu
justindo_at_gmail.com
Received on Wed Aug 17 2022 - 13:41:55 MST