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effect extension inlet and outlet on Ground Heat Exchanger corrugated tube

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Old   March 27, 2020, 18:23
Default effect extension inlet and outlet on Ground Heat Exchanger corrugated tube
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Dear all,

I want to simulate Ground Heat Exchanger with corrugated tube in AnsysFluent 17.2. Due to temperature fluctuation in the ground, heat applied in the ground is transient. I find the inlet and outlet is too close to the corrugated tube. I am afraid the back flow could affect the simulation result. Hence, I lengthen the inlet section and outlet section (10 * Internal diameter of tube) to make sure that thermal and hydrodynamics flow is fully developed. but I put wall of the extension into Adiabatic condition. Because I want to see the effect heat transfer only in corrugated side. Is my extension methods correct?

Thank you

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Old   March 28, 2020, 15:38
Default Adiabatic
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It would not make much difference. If temperature field is a passive scalar, i.e., it does not affect the properties of the fluid, then it would not have any effect at all, except its own uniformity within the fluid, which you cannot control until you set diffusion coefficient to 0 in the extended region. In other words, heat transfer will be as per the boundaries where thermal interaction takes place, however, thermal field will keep on developing even in the extended outlet.
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Old   March 30, 2020, 19:59
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Dear vinerm

Thank you for your reply. The working fluid is water and temperature fluctuation is negligible hence water properties is constant.

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In other words, heat transfer will be as per the boundaries where thermal interaction takes place, however, thermal field will keep on developing even in the extended outlet.
In above sentence, the flow will be still developing in extension region. I'm curious whether the temperature will change in the extension region because the flow will still be developing.

Thank you for your help

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Old   March 31, 2020, 03:58
Default Temperature Change
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Since the walls are adiabatic in the extended region, the thermal energy will be conserved. However, the distribution of the temperature will keep on resolving. Adiabatic walls will cause an effect on the thermal field near the boundaries, so, for the rest of the length, thermal field will try to adjust to this new condition and will also try to become as uniform as possible due to diffusion.
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Old   April 9, 2020, 00:35
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Dear vinerm

I am sorry for late reply. Thank you for explaining the phenomenon. It helps me a lot.

Thank you
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corrugated pipe, fully developed condition, ground heat exchanger, transient

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