Hello Everyone,
I have a question related to the generation of vacuum.
Suppose I have a region Air, and that air has some thermal conductivity, viscosity and heat capacity etc. Air is at room temperature and at atmospheric pressure.
Now, If we generate a vacuum there by lowering the pressure to a very very small value.
Now what will happen with the other parameters (thermal conductivity, specific heat and viscosity)?
They will increase or decrease OR do we have a relationship of all these parameters with pressure?
Any help would be highly appreciated.
Thank you
All these properties will decrease more or less and this depends on the pressure. This should be written in many publications. Best Regards Steffen.
Steffen Feja Thank you so much for your reply.
I tried a lot looking for that, but couldn't find any helpful information about the magnitude of change in these parameters.
For example, If I am decreasing my pressure from 100000 pascal to 1 pascal, then how can I calculate the other parameters mentioned above. Is there any mathematical relationship between them?
Refprop by NIST can calculate this.
for instance (at 25 °C):
cP at 0.01 MPa = 1.0048 instead of 1.0064 (KJ/kg·K)at 0.1 MPa
Therm.Cond.: 26.218 instead of 26.250 (mW/m·K)
Dyn. Visc: 18.435 instead of 18.449 (µPa·s)
!Attention! Kinematic viscosity is increasing due to decreasing density and η = ν ⋅ ρ .
Best Regards
Steffen.
Steffen Feja Thank you so much for your reply.
I didn't use this tool, but It seems like this software can calculate most of thermophysical parameters.
I tried looking for this tool, but couldn't find it. Do we have a limited trial version for that or NOT?
Thank you
It is not complicate: https://trc.nist.gov/refprop/MINIREF/MINIREF.HTM
Regards (Grüße)
Steffen.
Steffen Feja Thank you for the installation link. It is working fine.
I have one question here:
We have different gases in thi tool like (carbon dioxide, nitrogen, oxygen etc.).
And I want to see the cP, thermal cond. and viscosity of Air at low pressure.
Is it possible to select Air, OR we can select multiple gases, because air is a mixture of different gases.?
Thank you
I am not allowed to execute the MiniRef, but as written: it contains a limited number of pure fluids (water, CO2, R134a, nitrogen, oxygen, methane, propane, helium, hydrogen, and dodecane), along with air as a pseudo-pure fluid. You can have a try. Perhaps I will try it at my home computer in the next couple of days.
Best Regards
Steffen.
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