Sanity Check - Unit Conversion

[Wecos]

Hey people,

I'm working with a problem that may involve radiation effect and I need to apply the Stephan-Boltzmann constant in english units (BTU/s/in^2/oF^4). the constant is generally know as 5.67E-8 W/m^2/K^4.

So I just convert by (1BTU/s = 1054.1175W), (1m^2 = 1550.0031in^2), and (1 deltaK^4 = 10.4976 deltaF^4). Which gives me 3.306E-15 BTU/s/in^2/oF^4.

While browsing online I find a reference for S-B = 1.714E-9 BTU/hr/ft^2/oF^4 which converts to 1.984 BTU/s/in^2/oF^4, not even in the same ballpark as my conversion.

Could you please check my math and possible snaity on this issue. Hopefully I just found a shotty website. Thanks all

 

[Wecos]

Sorry, that last number should be 1.984E-13 BTU/s/in^2/oF^4

 

[zdas04]

You did good. I typed your constant into MathCad and told it to convert to your units and got 3.303E-15 BTU/(s*in^2*R^4). Since you are using dT instead of T, it doesn't matter if you use F or R and using F in MathCad is a little tricky.

When I put in 1 W/(m^2*K^4) I get 5.825E-8 BTU/(s*in^2*R^4).

This looks like a good example of the

http://WWW being

a Cavet Emptor kind of place. I'm always a little leary of using a number from the internet that I can't confirm independently. I had a mistake on my web page once and when I started searching for the authoritative answer I found 10 links back to my page with the wrong number on it.

David

 

[Wecos]

David,

Thanks for double checking me. Wierd thing is that I found another site with the same english units results that don't match mine: 0.1714E-8 BTU/hr/ft^2/oF^4.

I can feel confident with my own conversion against one rogue site, but when 2 sites don't match my work I start to wonder.

 

[Wecos]

Well now that I feel like a complete idiot... My second conversion, the check value, was wrong on my account. The values do match up correctly. Thanks again for your time.

 

[IRstuff]

Yes, in Mathcad, 3.3031E-15 BTU/s/in^2/R^4 equates to 1.7123E-9 BTU/hr/ft^2/R^4



TTFN

FAQ731-376

 

[25362]

...and, of course, 0.1714E-8 = 1.714E-9