## Fluids

#### Heat transfer and fluid flow in Pipe

• jhjang
Subscriber

Hello everyone,

I am trying to simulate 2D laminar developing flow and heat transfer in grooved enhanced pipe. The details are

Diameter 40mm, Length of pipe 400mm

Inlet velocity 0.0125375m/s

pressure outlet

heat flux  50w/m^2

Results

When I calculate Nusselt number in this way…

Surface integral, Area-weighted average, wall fluxes, Nusselt number & Skin friction factor, I feel these results are not in the right pattern...

Area-Weighted Average

Skin Friction Coefficient

wall 0.048432428    (Smooth)             0.37105531  (grooved)

Area-Weighted Average

Surface Nusselt Number

wall 15.567972          (smooth)             14.906946   (grooved)

here the trend of results for both Nu and skin friction is in opposite order.

Please help me to calculate local and average Nusselt number and friction factor

• DrAmine
Ansys Employee

Please stop creating several threads for the same issue especially as we have started answering in the other thread. Are you now doing a 2D or 3D?

• jhjang
Subscriber

Thankyou Abenjadj sir,

I am doing on 3D but since i was getting wrong results so i tried 2D also.

• DrAmine
Ansys Employee

Just focus on what I have already asked: Have you adjusted the reference values to match your case. The default values are not valid for every case.

Moreover what do you mean with "here the trend of results for both Nu and skin friction is in opposite order." Do you have exp. results or references?

Just to remind: Simple laminar flow you will have Cf to be proportional to the inverse of the square root of Reynolds number at external flat surface. Whereas the Nu number is proportional to the square root of the Reynolds number.

For simple basic geometries we can refer to some well know correlations.

• seeta gunti
Ansys Employee

Hi,

Following video tutorial will help you on how to model the heat transfer in pipes from geometry to post processing. Please go through the following links.

Regards,

Seeta

• jhjang
Subscriber

Hi, Seeta Gunti

Thank you for this video. I have seen this video and know some more things but still, I have the problem how to get friction factor and Nu over the curve.

• jhjang
Subscriber

Hello Amin sir,

I do not have experimental or reference results. here what I have the opposite trend means friction factor and Nusselt number is less for the enhanced surface than the smooth surface. when I change the reference value of length as the diameter of the pipe then nusselt number start from around 10 but when I keep the reference length as default then nusselt number start around 800-900.

I just extract the results directly using area weighted average, wall heat flux, nusselt number, and skin friction coefficient.

• DrAmine
Ansys Employee

Ensure for well resolved boundary layer for your laminar case. You need to carry out a mesh sensitivity analysis to see if the trend is mesh dependent or not.

How big is the device Reynolds number?

• jhjang
Subscriber

I have checked for Re 500 and 1000.

Sir, will you please elaborate me on how to get Friction factor and Nu number directly from the software for any case.

• atulsingh92
Subscriber

Hello @Abenhadj,

A question about reference values, here. (I am doing a similar case of enhanced wall tubes with grooves, in 3D and turbulent along with periodic bc)

I wanted to know exactly "how" can I tune this reference value to my case. Changing the reference value pretty much changes the Nusselt. So essentially I could end up having any nusselt nunmber, for any reference temperature.

Now when you mention "adjusted to your case", does this mean, I should look at a similar experimental setup, for a particular reynolds, know what Nusselt does the experiments show, and then reverse calculate the neccessary reference temperature to input for my case?
Or is there some other method to tune this value?

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