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Convective heat transfer coefficient for air
6

Convective heat transfer coefficient for air

Convective heat transfer coefficient for air

(OP)
Where could I find some values for the heat transfer coefficient for air under natural convection?  I have to believe that this has been worked out many times somewhere.

RE: Convective heat transfer coefficient for air

I typically use about 5 BTU/(hr-ft^2-F) for pipe to still air.  Hasn't got me into trouble yet.

Regards,

SNORGY.

RE: Convective heat transfer coefficient for air

Natural convection to air depends on the surface orientation as well as the temperature difference between the surfae and fluid.

I use formulae from McAdams Heat Transmission, which gives h=1.776(DT)^0.25 for air for a vertical surface.

corus

RE: Convective heat transfer coefficient for air


J.P.Holman's Heat Transfer McGraw-Hill, Para. 7-9 (Table 7-2) gives simplified equations for free convection from various surfaces for laminar and turbulent flow.

RE: Convective heat transfer coefficient for air

Sorry, I was using SI units.

corus

RE: Convective heat transfer coefficient for air

The "Standard" way of calculating this can be found in the ASTM C680 Standard.

The formulae, calculations, etc, are from Fundamentals of Heat and Mass Transfer by Incropera and DeWitt.

RE: Convective heat transfer coefficient for air

I tend to use Holman too.

 

RE: Convective heat transfer coefficient for air

Depending on your conservative slant, I would say 1 BTU/hr ft^2 F is a safe bet for free convection of air.  If your conservative slant is at the high side, I think the 5 BTU/hr ft^2 F is a good number.  Depending on what you are calculating, you may not need to use any formulas.

RE: Convective heat transfer coefficient for air

With a 7-month winter, with 2 of those months having frequent excursions into the -35 C range, I tend to predict a high heat transfer coefficient to make sure we insulate and trace the heck out of stuff.

There's nothing like starting up a sulphur plant in central Alberta in January, for example.

Regards,

SNORGY.

RE: Convective heat transfer coefficient for air

(OP)
What a great resource.  Thanks.  By the way I found a copy of Holman's book at Albris for $1.99!

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