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J
jdesai-21-Visitor
1-Visitor
January 10, 2018
Question

Units

  • January 10, 2018
  • 3 replies
  • 5572 views

Hello,

Could someone please tell me what is wrong with these units. I hit the * and then inserted temp units (F)DUH ???DUH ???

3 replies

L
LucMeekes23-Emerald IV
23-Emerald IV
January 10, 2018

That's Prime... Note that many of the temperature units are functions rather than 'simple' units, due to the fact that conversion requires more than simple multiplication with a constant.

 

Success!
Luc

J
jdesai-21-VisitorAuthor
1-Visitor
January 10, 2018

so what do I do? How do I insert units in alpha (co-eff of thermal expansion in/in*degF)

D
DJF16-Pearl
16-Pearl
January 10, 2018

You need the delta temp, which is available in the temperature units.

 

2018-01-10_10-58-07.jpg

M
MJG1-Visitor
1-Visitor
January 10, 2018

What you want is change in °F (Δ°F), not °F.

L
LucMeekes23-Emerald IV
23-Emerald IV
January 10, 2018

OK.

 

But then why does it produce an error message: "This value must be a scalar or a matrix".

???????

 

Luc

 

M
MJG1-Visitor
1-Visitor
January 10, 2018

Short answer:

Because of poor error handling.

 

Slightly longer answer:

Because (as you noted) °F is a function.  You can't multiply by °F for the same reason you can't multiply by any other function (numerically).  You can only multiply by a scalar or matrix.  The °F function can only be applied to a scalar or matrix, not multiplied by one.

V
24-Ruby IV
ValeryOchkov24-Ruby IV
24-Ruby IV
January 10, 2018

Better use here R and K not F and C

RK.png

M
MJG1-Visitor
1-Visitor
January 10, 2018

Δ°F = R   and   Δ°C = K

The difference is merely display.

V
24-Ruby IV
ValeryOchkov24-Ruby IV
24-Ruby IV
January 10, 2018

I asked my colleague from NIST why you have R in the unit of entropy, and in thermal conduction unit F. He answered that it is easier to change the US Constitution than to teach American engineers to use R in the thermal conductivity unit, rather than F.

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