Question About Thermal Expansion.

[Chewbalka]

Iron Thermal expansion (25 °C) 11.8 µm·m−1·K−1

 

Can someone explain this i got it off off wiki. http://en.wikipedia.org/wiki/Iron

 

What i think its saying is at twentyfive degrees celsius expansion is 11.8 micrometers times m??-1? Times k??-1? Equals?? I must have this wrong plus i have no clue what the values of m and k are.

[belovelife]

me too i work glass, and while i understand how it works, the formulas are all greek'

 

i know that when things cool , they shrink

 

must be some sort of exagerated electron shell at the atomic level, that limits the quanta release of the added photons

or something

[Chewbalka]

Its all crazy man lol. But at the moment i am attempting to work out some math to help prove my other hypothesis and i need to find patterns to verify my findings lol and this is something thats holding me back lol

[Chewbalka]

K whats going on lol i think i got it but i am consistently off by 0.0041...

The math i found at this site http://www.engineeringtoolbox.com/linear-thermal-expansion-d_1379.html

I rewrote the formula this way

 

Length plus length times coefficient times ( end temperature minus start temperature) plus length equals Answer

 

L + L x Coe x ( ET -ST) + L = A

 

6+6 x 0.000023 x (-30 - 20) + 6 =

12 x 0.000023 x (-10) + 6 =

0.000276 x -10 + 6 =

-0.00276 + 6 =

My answer 5.99724

Their answer 5.9931?

[Chewbalka]

Lol i guess no one else gets it either! Thats ok this is why they invented the internet for, i was only hoping to cut a corner and speed this process up lol. Back to researching i suppose!

[GeorgeG]

Iron Thermal expansion (25 °C) 11.8 µm·m−1·K−1

 

In plain English, that is saying "the thermal expansion of iron at 25°C is 11.8 micro meters per meter [of material diameter or thickness] per degree Kelvin [or per Kelvin in current terminology] of temperature difference."

 

" 11.8 µm·m−1·K−1 " should be written " 11.8 µm · m⁻¹ · K⁻¹ " or " 11.8 µm / m / K "

 

I can't explain why you get a different value than "they" do because I can't tell what values you are using for the distance (m in meters) and the temperature difference K (in Kelvins.) It's all multiplication and division, no addition or subtraction involved.

 

Sample: At 50°C, what would the increase in length of a piece of iron that is 10m long at 25°C be?

 

The formula for figuring this would be ΔL = Coeff_{thermal expansion Fe} * L * ΔT

 

So L = 10m and ΔT = 50 - 25 = 25K (so there is some subtraction)

 

So the thermal expansion (ΔL) = 11.8µm/m/K · 10m · 25K = 2950µm (or 2.95mm), note that both m and K cancel out.

Edited October 3, 2013 by GeorgeG

[Mountain]

According to my pocket reference third edition by Thomas J Glover the thermal expansion rates of iron are thus.

 

Iron..... per Degree C.... 0.0000120 per Degree F..... 0.0000067

 

I at first was thinking this would be a measurement per degree, but you have to have the length of the iron to know that, this number would have to be a percentage of your length.

 

Iron cast.. per C... 0.0000106 per F 0.0000059

 

Iron wrought,, per C...0.0000120 per F 0.0000067

 

These books are pretty dang handy, I have right here expansion rates of everything from Acetal to zirconium.

Edited September 9, 2013 by Mountain

[richard tj]

for every 1 degree change in kelvin, a piece of steel will expand by 11.8 micro meter for every meter. So, increase the temp 1 degree kelvin and the steel will expand by 11.8x(your lenth of steel measured in meters)

[richard tj]

cn also re-arrange the equation to make: 11.8/m/k is exactly the same as 11.8 x k / m (k is the change in temp and m must be measured in units of meters)