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Heat flux in ansys cfx

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Old   April 13, 2009, 20:09
Default Heat flux in ansys cfx
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Julio Mendez
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Good Evening everyone, I`m a new user of ansys cfx and I`m practicing with a problem of ventilation.
The point is that šI have doubt about the term oh heat flux in cfx, that term is about W/m2, but the problem that I have is that I have the heat flux in Btu/h.
Thaht heat flux (btu/h) i got calculating the total heat flux through a wall that has 30 m2, should i supposse that the "wall" has just 1 m2 to adjust the terms?, i mean to calculate the heat flux through 1 m2 of wall, in that sense i"ll have a pseudo heat per unit of area, off course in Btu/ h, but i can it converter to W /"m2"

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Old   April 14, 2009, 13:55
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Bernhard Gschaider
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Quote:
Originally Posted by juliom View Post
Good Evening everyone, I`m a new user of ansys cfx and I`m practicing with a problem of ventilation.
The point is that šI have doubt about the term oh heat flux in cfx, that term is about W/m2, but the problem that I have is that I have the heat flux in Btu/h.
Thaht heat flux (btu/h) i got calculating the total heat flux through a wall that has 30 m2, should i supposse that the "wall" has just 1 m2 to adjust the terms?, i mean to calculate the heat flux through 1 m2 of wall, in that sense i"ll have a pseudo heat per unit of area, off course in Btu/ h, but i can it converter to W /"m2"

Hi Juliom!

I'm sure you've seen this scene in one form or another in a "funny movie": A guy stumbles into a bikers bar full of Hell's Angles and asks if they play any Donna Summers records around here (or whether they serve Cappuccinos, or ...). Usually there is a cut indicating that something violent happens. Next scene is the guy sitting with a torn shirt in front of the bar and mumbling "Obviously not".

The difference here is: Guy stumbles into an OpenFOAM-forum and asks for unit conversions in a commercial solver. Everyone will politely tell him that the CFX-Forum is next door. But if he wants to stay and try it in OpenFOAM questions about calculating the the heat-flux in OpenFOAM will be gladly answered

Bernhard
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Old   April 14, 2009, 14:30
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James Nally
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Quote:
Originally Posted by juliom View Post
Good Evening everyone, I`m a new user of ansys cfx and I`m practicing with a problem of ventilation.
The point is that šI have doubt about the term oh heat flux in cfx, that term is about W/m2, but the problem that I have is that I have the heat flux in Btu/h.
Thaht heat flux (btu/h) i got calculating the total heat flux through a wall that has 30 m2, should i supposse that the "wall" has just 1 m2 to adjust the terms?, i mean to calculate the heat flux through 1 m2 of wall, in that sense i"ll have a pseudo heat per unit of area, off course in Btu/ h, but i can it converter to W /"m2"

One btu = 1055 Joules (J)
One watt = 1 Joule per second (J/s)
One hour is 3600 seconds
therefore 1 btu/hr is equivalent to 1055 J/hr or 1055/3600 J/s which is 0.29 W
Now this value is measured over the whole 30 m^2 wall so to get a heat flux in W/m^2 we just divide by 30 to give 0.01 W/m^2.

You had better calculate this yourself if you want more significant figures though.

I hope that this is what you were looking for.

James
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