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Simple heat exchanger model error
Posted 11.11.2015, 06:49 GMT-5 Fluid & Heat, Heat Transfer & Phase Change, Geometry, Mesh, Modeling Tools & Definitions, Parameters, Variables, & Functions Version 5.1 5 Replies
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I'm working on a heat transfer problem and could use some help. It concerns a large horizontal pipe containing an elongated u-shaped pipe (the 'loop'). The pipe contains air and the loop contains water. The water inside the u-shaped pipe is flowing and is laminar. The air in the larger pipe is initially at rest. There is heat being produced inside the u-shape. So heat is being transported from the loop through the pipe by convection and out of the model (using the external natural convection option inside the heat flux node). I'm interested in the steady state temperature in both pipe and u-shaped pipe.
Initially I started working on a simpler model which only contained 2 cylinders (ie. I used a cylinder instead of the loop). This model worked perfectly, but when I switched the smaller cylinder for the loop I started getting errors.
1. The direct solver gave the error of a singular matrix
2. the iterative solver returned a error message saying it ran into an undefined value.
I was wondering if these errors can be caused by poor meshing, since my boundary conditions are exactly the same for the working model and the non working model? Any help on solving my problem would be greatly appreciated!
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Steven Conrad, MD PhD
LSU Health
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Thanks for your reply. That's exactly why I'm puzzled. The only difference between the working and non working model is the path of the loop inside the pipe. The BC's are identically for both models, the only thing that is (slightly) different is the geometry.
kind regards
Jurriaan
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Division by zero.
- Function: /
Failed to evaluate variable.
- Variable: comp1.ht.rho
- Defined as: (Mw_a*comp1.spf.pA)/(comp1.ht.fluid1.minput_temperature*R_const)
Failed to evaluate expression.
- Expression: d((-comp1.ht.rho*comp1.ht.Cp*(comp1.ht.ux*comp1.Tx+comp1.ht.uy*comp1.Ty+comp1.ht.uz*comp1.Tz)*test(comp1.T)*comp1.ht.d)*(dvol),{test@3})
- Feature: Stationary Solver 1 (sol1/s1)
It seems that either comp1.ht.fluid1.minput_temperature or R_const is hitting zero. Don't have time to fully investigate why at this time, but hope that provides some clues to move forward.
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Steven Conrad, MD PhD
LSU Health
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I am having a similar error. Did you solve it? How?
Thank you!
José
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Yep, turned out my boundary conditions were ill-defined. It was necessary to add a pressure reference point to the model (laminar flow>point>pressure point constraint). This solved my problem.
Hope this helps!