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So, I must do the following conversion from my engineering textbook:

$0.155 \frac{m^2 * ^{\circ} C}{W}$ to $\frac{^{\circ}F * ft^2 * hr}{Btu}$

I can get as far as:

$0.155 \frac{m^2 * ^{\circ} C}{W} * (\frac{1 ft}{0.3048 m})^{2} * \frac{1 W}{3.4123 \frac{Btu}{h}} = .39108 \frac{ft^2 * ^{\circ}C *hr}{Btu}$, but I can't figure out how to do the final conversion properly, which involves converting that from

$.39108 \frac{ft^2 * ^{\circ}C *hr}{Btu}$ to $\frac{^{\circ}F * ft^2 * hr}{Btu}$.

FabulousGlobe
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  • Welcome to engineering.SE! Can you confirm the 0.39108? Just following your calculation I would get 0.4889... – idkfa Oct 02 '15 at 00:53
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    So you have one unit left to convert. Convert that unit... – hazzey Oct 02 '15 at 01:01
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    @hazzey. The problem for me is that I'm not sure how converting temperature inside of a compound unit works, due to the fact that I'm not familiar with any one number that I can multiply a compound unit containing degrees Celsius to get degrees Fahrenheit. I don't know if I can simply use a stretch factor of $\frac{9}{5}$ as a conversion factor, or if I should plug it my final result into $F = \frac{9*C}{5} + 32$. – FabulousGlobe Oct 02 '15 at 01:35
  • @idkfa, Could you tell me what you used to get that number? – FabulousGlobe Oct 02 '15 at 01:36
  • I just used the equation and numbers you provided. – idkfa Oct 02 '15 at 01:39
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    I think this question is more valuable than it may seem at first; the conversion of temperature differences vs. specific temperatures seems to befuddle many people, including those in the sciences. I remember taking a final exam in my last semester of engineering school, where in one question it was necessary to do a temperature difference conversion. So many students were confused by this that the instructor had to stop the test and spell it out for them. These were people about to receive their B.S. in chemical engineering, by the way. – Carlton Oct 02 '15 at 13:33
  • A similar question is Problem with energy transfer rate conversion – MechtEngineer Dec 20 '18 at 00:30

1 Answers1

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I suspect you're converting a value of thermal resistance, which means that the temperature units represent a temperature difference, rather than specific values of temperature. In this case, the constant 32 drops out of the conversion and you would just just multiply by $\frac{1.8^\circ F}{^\circ C}$. Also, I agree with idkfa that your math is wrong in the conversion of power and area. I get 0.489.

Carlton
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