Learning Forum

[Oliver Taylor]

I have been trying to conduct the analysis of a water filled helical copper pipe wrapped around an exhaust pipe containing hot exhuast gases. I want the water to be pumped around the coil and analyse the transient heat transfer between the two fluids. 

So far I have resdesigned the model and mesh many times but still do not find the expected solution. I am fairly new to fluent so bare with. I will attach a screenshot of the model.  I have tapered one edge of the copper pipe to fit flush with the exhaust and make the contct region over which the heat transfer will occur. I know I must use thermal coupling but I am unsure on which walls / surfaces this is required , as well as what fluent is able to infer from the geometry and what I must define. Have been going in circles for a week since moving off solidworks ny help would be apprecaited. The screenshot does not include the exhuast in order to show the tapered contact surface.

 

 

 

 

[Rob]

You'll usually get a wall and wall:shadow in Fluent for walls with cells on both sides. How do you plan on accounting for the warmer air surrounding the coil?

[Oliver Taylor]

Hi Rob , thanks for this.

I am fairly new to CFD so am unsure, must I make a computationl boundary to analyse surronding air or can I assume het transfer only occurs due to the contact of the taper. 

When making named zones I created air/water inlet/outlet the bodies themselves and made the tapered wall its own named selection as the wall being heated. Which walls must I apply thermal coupling to and any other necessary conditions.

Many thanks,

Olly

[Rob]

I think your next step is the courses under learning (book icon on here) and tutorials under Help in the software. Modelling the air space may be useful, but equally we can make approximations: with some learning you'll know which option to use and why. 

[Oliver Taylor]

Hi Rob thanks.

I would normally do more research and begin with simpler geometry  first however this is a simple analysis for a project Im working on which I need to complete ASAP.

If I ignore the air around and only study the impact of the exhaust heating the tapered section , which areas would I used thermal coupling and how would I ensure inlet conditions= outlet during the transient analysis to see the overall het transfer to the fluid in a closed loop.

[Rob]

What closed loop? You've got two flow channels both of which have an inlet & outlet?  The thermal coupling is over the liquid-solid-solid-gas so use share topology or multibody parts (SpaceClaim or DesignModeler) so you have a conformal mesh and an easier time with the set up. You may want to review the "outside" thermal conditions too. 

Note, the advice about the courses and tutorials stands. Skipping that's not going to make your life any easier. 

[Oliver Taylor]

Hi Rob 

The image above is a simplified model whilst I get to grips with the setup. In reality the water will be pumped around the coil in a closed loop. I have read I can update the boundry conditions at each iteration to ensure the water is recirculated at the same temprature rather than say 600k at outlet and 300k at inlet.

Thank you I have tried using share topology but belive importing the assembly from cad has created some issues with sliding interfaces and non existant surfaces.

[Rob]

That sounds more like a complaint from Fluent. You shouldn't have any sliding interface zones. Do the coils touch axially? That may cause a problem. 

[Oliver Taylor]

No there is a gap between each coil. Would you recommend reproducing the assembly  within space claim ?

[Rob]

Probably not. I'd review the need to include the coil solid part through. Hence reading what Fluent does re "thin walls". I don't suggest doing tutorials without good reason.....