Temperature Change in a Gas Flow

Good afternoon,

The problem which I wish to simulate comes down to gas flowing from a desorption surface to a pump port along a tube whose walls are colder than the gas when it leaves the desorption surface. However, no matter what temperattures I choose for the tube walls, the speed distribution of the gas look identical at any longitudinal position. How should configure my simulation to properly model the gas losing energy to the cold walls of the tube? Is the speed distribution (at transparent monitoring planes or the pumping port) the appropriate way to understand the temperature of the gas?

Best,

Alec

 

P.S. Many thanks for an elegant and effective program - and for the simplest setup process of any technical software I have ever installed!

Hello Alec and thanks for the nice words.

Indeed, the speed distribution is a good way to get info on gas temperature, an other way would be to look at the average molecule speed, displayed in the Facet Details window, calculated for all facets (even those without speed profiles).

As you say, the walls should thermalize rebounding particles. By default, perfect thermalization is assumed, which can be changed in the advanced facet parameters panel (parameter called Accomodation Factor).

Without seeing your geometry, the issue may be that much more directly desorbed molecules hit your measurement points than rebounding ones, or that the walls have sticking, thus thermalized particles are pumped.

If none of this is the case, if you wish, I can have a look at the geometry (which you can upload here, strip it down so it doesn't contain anything confidential).

Regards, Marton