# Operating Pressure (Natural Convection problem)

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 July 2, 2006, 14:56 Operating Pressure (Natural Convection problem) #1 Andrew Tress Guest   Posts: n/a Hi all I am simulating a closed vesel natural convection problem in Fluent. My task is to check the heat transfer coffecient variation with the change in initial pressure. There are no inlet or outlet boundary conditions and the only condition impose on the system is isothermal condition on the wall of the vessel and heat generation in the fluid. I have used Boussinesq approximation for density specification and I need to do transient state analysis. My problem is when I plot the pressure variation along X dimension of vessel it show almost zero value of pressure (dynamic pressure) in the whole domain even if I set operating pressure as high as 5 bar. I assume I am missing somewhere in specifying the operating pressure condition. Kindly let me know if the experimental pressure condition was 5 bar how should I specify the operating pressure to reproduce the experimental results. Please help me in the same.... Thanks in advance Regards. Andrew

 July 3, 2006, 16:00 Re: Operating Pressure (Natural Convection problem #2 V. Kumar Guest   Posts: n/a You said that is a natural convection problem, then from where pressure variations is coming into picture? It seems to be a forced convection problem (driven by pressure gradient) according to your explaination. Usually isothermal wall is not a good boundary condition for practical applications (except in very carefully done experiemnts where walls are const. maintained at a particular temperature). If Delta T is quite large in your domain you may use density as a function of temperature. Do not plot dynamic pressure. You should look at absolute or static or thermodynamic pressure. The value of static pressure may be small but not zero. Most probably, your flow is incompressible. In incompressible flow problems, absolute pressure has no meaning since it is no longer a thermodynamic variable. For such problems you should set a reference pressure at some point in your computational domain. In your problem reference pressure will be 5 bar. have fun

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