# How to set initial pressure

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 February 14, 2020, 09:24 How to set initial pressure #1 New Member   KevNo Join Date: Oct 2019 Location: Germany Posts: 2 Rep Power: 0 Hello! I'm a newby in Fluent and have a question: I want to model a countercurrent-flow tube heat exchanger. The flow through the tubes has an initial pressure of 250000 Pascal (temperature 40 degrees) - velocity inlet. The flow around the tubes has an initial pressure of 450000 Pascal (temperature 15 degrees) - velocity inlet. I have two corresponding pressure outlets. I want to simulate the flow and the temperature gradient (energy equation and viscous flow are activated). I'm using a pressure-based solver in the steady case. So, where can I set the initial pressure? In the inlets are only supersonic pressure and in the outlets backflow pressure given... Thank you!

 February 14, 2020, 12:02 #2 Senior Member   Lucky Tran Join Date: Apr 2011 Location: Orlando, FL USA Posts: 3,744 Rep Power: 45 In the initialization pane. It looks like so.

 February 14, 2020, 14:29 Initial Pressure #3 Senior Member     Vinerm Join Date: Jun 2009 Location: Nederland Posts: 539 Rep Power: 16 There are multiple ways to initialize at different pressure values, however, the initialization would have no effect if the system is incompressible. You can initialize with same pressure. If the system, however, is compressible, you have to initialize all domains at same pressure, say lower of the two, using the initialization dialogue box, as shown by Lucky and then use the patch within the same dialogue box to initialize the other domain at higher pressure. __________________ Regards, Vinerm PMs only for private content

 February 17, 2020, 06:59 #4 New Member   KevNo Join Date: Oct 2019 Location: Germany Posts: 2 Rep Power: 0 Thank you both! I have incompressible flow with water on both sides. So, I don't need to initializie with the pressure? But where can I setup this information?

 February 17, 2020, 08:09 Incompressible #5 Senior Member     Vinerm Join Date: Jun 2009 Location: Nederland Posts: 539 Rep Power: 16 For an incompressible system, pressure has no relevance. Only its drop is important. Therefore, you do not need to set different pressure values. However, if you have some model, e.g., evaporation-condensation or cavitation, where value of pressure is important, then you have to set pressure accordingly. You can use patch option for the same. __________________ Regards, Vinerm PMs only for private content

 February 17, 2020, 13:19 #6 Senior Member   Lucky Tran Join Date: Apr 2011 Location: Orlando, FL USA Posts: 3,744 Rep Power: 45 You still need to initialize the pressure field. The point is that the value of pressure has a slightly different meaning for an incompressible fluid. Regardless, Fluent is a compressible N-S solver even when the Fluid is incompressible.

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