# How to model the fluid flow from a pipe of variable temperature?

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 April 2, 2019, 12:03 How to model the fluid flow from a pipe of variable temperature? #1 Member   Priyanka P Join Date: Apr 2019 Location: Germany Posts: 40 Rep Power: 5 Hello Everyone, I am currently working on fluid dynamics and I have one question: I am studying about the fluid flow from a cylindrical pipe and I learnt how to find the velocity profile and flow rate. My question is what should be our approach when the pipe from which the fluid is passing, has a variable temperature? Means, the temperature of the pipe is getting increased due to some hardware components, which are attached outside the pipe at different positions along the length of the pipe. Which parameters of fluid can be affected and how to model them? Thank you

 April 2, 2019, 12:45 #2 Senior Member   Join Date: Dec 2017 Posts: 153 Rep Power: 7 Hello, you are asking about heat transfer, so first of all get a book and study the basics Regarding your question, temperature has an influence on density, viscosity and produces bouyancy effects to be added as body force. Strong temperature variation may require also compressible solvers, but in your case a boussinesq approximation could be appropriate. Regarding the model, you have to solve a transport eq for the temperature with suitable boundary conditions. If you know the temperature distribution then a dirichlet boundary condition at walls is fine, otherwise (and probably) you can fix the heat flux along the pipe which is a neumann like boundary condition. fresty and priyankap like this.

 April 2, 2019, 12:46 #3 Senior Member   Join Date: Aug 2014 Location: UK Posts: 213 Rep Power: 11 You would need to define the temperature at the pipe walls as a function (or a look up table if discontinuous) of axial coordinate i.e. T(pipeLength_axis). However, being said that, multiple other phenomenon such as: transient/ steady state, compressibility, phase change, etc. may need to be considered, in light of the simulation objectives. Would suggest to dig a bit further into relevant heat transfer theory. priyankap likes this.

 April 2, 2019, 12:47 #4 Senior Member   Filippo Maria Denaro Join Date: Jul 2010 Posts: 6,260 Rep Power: 67 The devices on the walls of the pipe introduce a heat flux as BCs. You need to know the values to set at the portion of the walls influenced by the devices. fresty and priyankap like this.

 April 10, 2019, 12:34 #5 Member   Priyanka P Join Date: Apr 2019 Location: Germany Posts: 40 Rep Power: 5 How can I assign the heat flux as a boundary condition. For example, If I am using the chtMultiRegionSimpleFoam solver. Then where and how can I mention my boundary condition of heat flux. Do I need to add an additional file in the '0' directory of my solver? OR is there already a booundary condition file for this?

 April 10, 2019, 12:42 #6 Senior Member   Join Date: Dec 2017 Posts: 153 Rep Power: 7 Fix the heat flux means fix k*dt/dn at some boundary. So you can use the bc called fixedGradient on a target patch. Since this bc will fix the gradient and not the flux, you have to pass your flux divided by the conductivity. For example if you have a flux 50w/m2 and k=10w/m*K then your gradient will be 50/10. priyankap likes this.

 Tags fluid dynamics, fluid flow, temperature calculation