I have a project which consists of 2 tubes (tube A and Tube
b) of equal lengths. Tube B is smaller than Tube A and is placed
inside Tube A concentrically. Cryogenic liquid flows through the
inner tube (Tube B). The space between The outer wall of Tube B and
Inner wall of Tube A is vacuum (Air at low pressure) with no flow
and at room temp initially. Lids are placed at both ends and they
are set to insulation material. I put a heat load (heat transfer
coefficient) on the outer wall of the outer tube A.
I put boundary conditions on the inlet & outlet of the inner tube B that has cryo fluid flowing through it. And The outer wall bounder condition is set on Tube A.
The model solves nicely with no warnings BUT the vacuum air does not seem to insulate as it should. I am measuring the average surface temperature of the outer tube A as a goal. I change the air pressure between the 2 shafts but I get the same result. No matter what pressure I'm putting for the air, the outer shaft temperature is the same.
what can I do to troubleshoot this problem?
thanks in advance
I put boundary conditions on the inlet & outlet of the inner tube B that has cryo fluid flowing through it. And The outer wall bounder condition is set on Tube A.
The model solves nicely with no warnings BUT the vacuum air does not seem to insulate as it should. I am measuring the average surface temperature of the outer tube A as a goal. I change the air pressure between the 2 shafts but I get the same result. No matter what pressure I'm putting for the air, the outer shaft temperature is the same.
what can I do to troubleshoot this problem?
thanks in advance
try using 'X-Y plot' to obtain the values of the low pressure air properties, just to see if they make sense physically. Start with air pressure at ambient and then keep lowering the pressure, to see if the physical properties make sense.
You'll have to add a line through your Tube A, perhaps one on 'centerline' of the outer cylinder and another on the interface surface, and then create the x-y plot using one of the lines.
rich.