Expanding foam insulation

[floattuber]

We're having a thermal chamber extension built in-house and have found a problem with the expanding foam that was recommended to us.

The thermal analysis that was done suggests polyurethane foam (0.014 Btu/hr-ft-F) or cork board (0.025 Btu/hr-ft-F)for the insulation. The expanding foam that was suggested to us is rated at 0.12 Btu/hr-ft-F. The analysis and the foam suggestion were made by different people. As you can see, there is a magnitude of difference, however I can't imagine foam differing by that much.

Another problem is the manufacturer's english and metric rating. The english rating is 0.12 Btu/hr-ft-F while the metric rating is 0.017 W/mK. The conversion I've found says 1w/mK = 0.5779 Btu/Ft-hr-F. The english and metric versions don't match. The manufacturer says to divide the english value by 7 to convert it to metric. I don't know where they got this.

So my questions are:
1) which is the correct (ballpark) rating for polyurethane foam? 0.014 or 0.12 Btu/hr-ft-F?
2) am I missing something about the conversion?

I've gone online and looked for typical ratings for foam, but much of it is in metric and I can't do the conversion unless I know the answer to #2. I'm unsure of which is correct.

Here's the data sheet for the expanding foam with the english and metric values.

http://fomofoam.com/NEWPDFS/E84-TDS.pdf

 

[IRstuff]

see:

http://en.wikipedia.org/wiki/Building_insulation_materials#Categories

Note units at the top of the table. Note that many insulation numbers, even for SI units are expressed "per inch"

Your datasheet, I think, has incorrect units. Air is about 0.025 W/m*K (0.0144 BTU/*hr*ft*°F)

TTFN

FAQ731-376

 

[MintJulep]

Note also that the units in the Wiki table have length squared.

The length unit in thermal conductivity is a bastard unit because it is properly:

heat per time per unit thickness per unit area per unit temperature difference.

The length squared term in the area and the length term in the thickness result in a length unit to the first power - if the units are consistent.

Area in square feet and thickness in inches screws you up by 12.

Area in square meters and thickness in cm screws you up by 100.

Etc.

You very often see thermal conductivity messed up.

 

[StoneCold]

In another product sheet from the same company the K- factor is listed as 0.162 BTU·inch / ft²·h·°F (0.023 W/m·K)
Which is not consistant english to metric but does give you all the factors to check your product against.

Regards
StoneCold

 

[IRstuff]

That's because the SI quantity is the thermal conductivity, while the English quantity is the thermal conductance

TTFN

FAQ731-376

 

[IRstuff]

So, the SI quantity needs to be divided by 1 in (0.0254m) to get conductance and the correct conversion to English

TTFN

FAQ731-376

 

[ione]

I have tried to interpret your supplier data sheet another way, but still doesn’t work:

1. K factor (PER INCH) for English unit

0.12 Btu/[(ft *h *°F)*inch] = 0.12/0.083 Btu/[(ft* h* °F)*ft] = 1.446 Btu/[(ft^2 *h *°F)]

2. K factor (PER INCH) for SI

0.17 W/[(m*K)*inch] = 0.17/0.0254 W/(m^2*K) = 6.693 W/(m^2*K)


Unfortunately the conversion factor from Btu/[(ft^2 *h *°F)] to W/(m^2*K) is 5.674466 and so

1.446 Btu/[(ft^2 *h *°F)] = 5.674466 * 1.446 W/(m^2*K) = 8.162 W/(m^2*K)

 

[floattuber]

Thanks for the help guys. I finally got a hold of the thermal analysis guy here and he agrees there's something strange going on with the data sheet numbers.

 

[IRstuff]

see:

http://hyperphysics.phy-astr.gsu.edu/Hbase/Tables/thrcn.html

and:

http://cryogenics.nist.gov/MPropsMAY/Polyurethane/polyurethanerev.html

at 20°C, I get 0.022 W/m*K to 0.052 W/m*K (0.013 BTU/hr*ft*°F to 0.030 BTU/hr*ft*°F) using the NIST curve fits. The values vary according to the density and the fill gas.

TTFN

FAQ731-376

 

[ione]

Probably I got it: I mean I think I have found the reason why your supplier told you to divide by approx 7 (multiply by 0.143)

K factor (PER INCH) for English unit

0.12 Btu/[(ft ^2*h *°F)]*inch

Now to convert this to SI units:

Consider:
1. Btu/h = 0.294 W
2. ft = 0.3048 m
3. °F = 0.5555 (deltaT)
4. inch = 0.0254 m

0.12* [0.294/(0.3048 * 0.3048 * 0.5555) * 0.0254] W/(mK) = 0.12 * 0.1447 = 0.01736 W/(mK)