# Hot water tank - help me please :)

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 January 13, 2007, 09:12 Hot water tank - help me please :) #1 Anthony Guest   Posts: n/a Hi everyone, my hot water tank has two inlets (one hot, one cold) with "mass-flow inlet" conditions and one outlet with "pressure outlet" condition. When i'm doing the simulation, Fluent says that there is a reversed flow on the outlet and don't even display the residuals but when I use "velocity inlet" conditions instead, everything is ok. The thing is I can't use "velocity inlet" conditions in my case because free convection has a big effect in a water tank and so density must not be constant. Do you have any idea to help me out? Thanks in advance for your answers

 January 13, 2007, 11:43 Re: Hot water tank - help me please :) #2 Ralf Schmidt Guest   Posts: n/a Hi! Are you shure, that the direction of the mass flow inlet is correct? The "reversed flow" on the outlet might come due to a negativ mass flow on the inlet. Set the mass flow "normal to bondary" Ralf

 January 13, 2007, 11:55 Re: Hot water tank - help me please :) #3 Anthony Guest   Posts: n/a Hi Ralf, you were right, the mass flow was set "Direction Vector" and now that it's set "normal to boundary", everything's fine. I was stucked on this for several days so thank you very much for your answer! Anthony

 January 16, 2007, 10:46 Re: Hot water tank - help me please :) #4 Venkatesh V Guest   Posts: n/a Following are mu suggestions. 1. First make sure in real life also what you are experiancing in CFD is not happening. 2. Try to extend (extrude) the outlet for 3 or 4 diameters.( follow this strategy if you find some re-circulation near outlet) 3. Check the value of pressure at outlet. Assign correct value of operating pressure. Check the gravity direction. Hope one of them should solve your problem

 January 16, 2007, 13:40 Re: Hot water tank - help me please :) #5 Anthony Guest   Posts: n/a Hi everyone, now that my boundary conditions problems are solved, I would like to simulate natural convection in my vertical hot water tank, which is adiabiatic, and I heard about Boussinesq approximation and density vs temperature fonction, which one should I use and how should I set it up? I'm supposed to get a clear boundary between hot and cold water but everything i tried, gave me a mix between the two temperature. Actually, i'm supposed to do an unsteady simulation but as I don't really know unsteady model, I wanted to be sure that natural convection was really working in a steady case before trying unsteady. Thank you very much for your help, I really appreciate. Anthony

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