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High outlet temperatures with laminar flow

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Old   October 23, 2018, 04:02
Default High outlet temperatures with laminar flow
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Hi there!

I am modelling a simple geometry, where a pipe is heated with a constant heat flux and fluid (water) is flowing in the pipe.

When I model turbulent flow, the outlet temperature of the fluid corresponds to the amout of heat supplied to the pipe.
However, when I model laminar flow (no turbulence model) the outlet temperatures are too high. I get 20% more energy increase of the fluid than what is supplied to the pipe.

I extract the temperature and velocity as an area weighted average at an extended outlet and take the average density and heat capacity of the fluid. The inlet temperature is constant with a velocity inlet boundary condition. The outlet is fixed pressure and pipe is insulated where it is not supplied with heat from the constant heat flux.

Could this be caused by the way I extract the temperature? Could it have something to do with the length of the extended outlet?
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