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Total Surface Heat Flux in a Volume

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Old   February 8, 2017, 03:56
Question Total Surface Heat Flux in a Volume
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Mickael Perrin
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Hello everyone,

I am a student and I actually work with ansys Fluent on an heat exchanger : Water Charge Air Cooler in cross flow. The fluids are water (52.5C) and air (220C). The goal is to transfer heat from air to the water so after simulation, I need to export the heat flux.

To avoid to research every contact surface, I use a volume integral to get the heat flux for every volume (air, water and aluminium) and then I multiply the heat flux (in W/m) by the surface (m) of each zone to get the real flux (W).

However when I proceeds, the energy balance isnt zero : the flux lost by air isnt the same gained by the water.

This is the geomtry i study :



To limit the number of cells, i do a planar symmetry according to the plan ZX in the middle of the air pass.

For exemple :
- thickness aluminium : 1 mm everywhere.

- lenght air : 30 mm
- height air : 6 mm
- width air : 2 mm

- lenght water = width air + 2*thickness alu = 4 mm
- height water = 1.6 mm
- width water = lenght air - 2*thickness alu = 28 mm

For this case, the air lose 0.87 W and the water get 0.86 W, (the aluminium at 0.0035 W is irrelevant acording to me) so there is a balance of 0.01W.
Can someone tell me where it come from ?

For this exemple the balance is about 0.01W but for some others, it can grow up to 0.3 W (the air lose 0.65 W but the water get 1,1W).

Thanks everyone for your help and your time

Cordially

Mickael
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heat exchanger, total surface heat flux, wcac

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