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Jan 10, 2018
11:40 AM

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Jan 10, 2018
11:40 AM

Units

Hello,

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

9 REPLIES 9

Jan 10, 2018
11:49 AM

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Jan 10, 2018
11:49 AM

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

Jan 10, 2018
11:53 AM

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Jan 10, 2018
11:53 AM

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

Jan 10, 2018
11:59 AM

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Jan 10, 2018
11:59 AM

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

Jan 10, 2018
12:00 PM

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Jan 10, 2018
12:00 PM

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

Jan 10, 2018
12:15 PM

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Jan 10, 2018
12:15 PM

OK.

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

???????

Luc

Jan 10, 2018
12:26 PM

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Jan 10, 2018
12:26 PM

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.

Jan 10, 2018
12:45 PM

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Jan 10, 2018
12:45 PM

Better use here R and K not F and C

Jan 10, 2018
12:51 PM

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Jan 10, 2018
12:51 PM

Δ°F = R and Δ°C = K

The difference is merely display.

Jan 10, 2018
02:22 PM

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Jan 10, 2018
02:22 PM

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.