Btu/hr.ft.F to W/m.K

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Btu/hr.ft.F to W/m.K

Postby Willmot » Mon Mar 15, 2004 9:09 pm

Can anyone help me convert British Thermal Units per hour foot farhenheit, Btu/hr.ft.F, to Watts per metre Kelvin, W/m.K.
Regards
Willmot
Willmot
 

Re: Btu/hr.ft.F to W/m.K

Postby Knight » Tue Mar 16, 2004 12:54 am

Willmot wrote:Can anyone help me convert British Thermal Units per hour foot farhenheit, Btu/hr.ft.F, to Watts per metre Kelvin, W/m.K.
Regards
Willmot
On a quick pass, you can convert convert BTU/hr to Watts by multiplying by 0.2931. You can convert feet to meters by multiplying by 0.3048.
Code: Select all
BTU      | 0.2931 W | 0.3048 Ft |
---------------------------------
Hr·Ft·°f | BTU/Hr   |    m      |
Cancel your terms, and this gives us W/m·°f

Getting °f to Kelvins, you'd first convert °f to °c using °c = (°f-32)·0.5556, then adding 273.1

So, you'd have:
Code: Select all
               W
--------------------------
m·[(0.5556·(°f-32))+273.1]

which will leave you with:
Code: Select all
 W
----
m·K
William J. Knight
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Los Alamos National Labs
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Thermal conductivity

Postby mike.wright2@networkrail. » Thu Jun 24, 2004 9:58 pm

These are units of thermal conductivity. The rate of heat flow (BTU/h or watts) divided by the thickness of the substance (ft or m) divided by the temperature gradient (degrees f or K). As it is a temperature gradient the correct SI unit is not K but degrees K, therefore you do not add 273.1, neither do you subtract 32 from degrees f for the same reason
According to my reference book you just multiply by 1.731 to do the conversion, which is much simpler. It comes from 1.8(degrees f to K) x 0.2931(BTU/h to Watts)/0.3048(ft to m).
mike.wright2@networkrail.
 


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