Dimensional analysis, conversion of units in an equation

AI Thread Summary
The discussion revolves around converting an equation involving heat transfer from one set of units to another, specifically from kcal to Btu and from Celsius to Fahrenheit. The main confusion arises regarding the correct temperature conversion factor to use, with differing opinions on whether to apply the linear conversion formula or the factor for temperature differences. Participants emphasize the importance of maintaining dimensional homogeneity throughout the conversion process. The original equation's constant is analyzed to ensure the units align correctly with the desired equation. Ultimately, clarity is sought on the appropriate temperature conversion method, highlighting a potential misunderstanding in the professor's guidance.
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We are asked to transform this equation:

h=1147(1+0.05625T)\frac{V^{0.6}}{D^{0.4}}

where the units of each variable h, T, V and D are:

h->\frac{kcal}{h·m^{2}·ºC}
T->ºC
V->\frac{m}{s}
D->cm

into another equation where the units of each variable h, T, V and D now are:

h->\frac{Btu}{h·ft^{2}·ºF}
T->ºF
V->\frac{ft}{s}
D->inches

Data:
1 Btu <> 0.252 kcal
1 ft <> 0.3048m
1 ft <> 12 inches
1 ºC <> 1.8 ºF
(ºF) = 1.8(ºC)+32

The professor said the solution is

h=2.479T\frac{V^{0.6}}{D^{0.4}}

however I've tried the very same solution method which had worked for me in the past to solve other conversion problems but I can't seem to get the answer right, I'm confused as to which temperature conversion "factor" should we use, 1 ºC<>1.8 ºF or (ºF)=1.8(ºC)+32? I have really given up on this. :confused:
 
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Show your work.

In your unit conversions, you have something per degree C. You are not trying to find a particular temperature, so F = 1.8C + 32 is not the correct conversion.
 
Well what i did first is find out the units of the constant 1147 in the original equation so the principle of dimensional homogeneity at both sides of the = sign is satisfied:

\frac{kcal}{h·m^{2}·ºC}=\frac{kcal·cm^{0.4}·s^{0.6}}{h·m^{2.6}·ºC^{2}}·ºC·\frac{m^{0.6}}{cm^{0.4}·s^{0.6}}

Then I repeated the same process for the units of the new desired equation:

\frac{Btu}{h·ft^{2}·ºF}=\frac{Btu·inches^{0.4}·s^{0.6}}{h·ft^{2.6}·ºF^{2}}·ºF·\frac{ft^{0.6}}{inch^{0.4}·s^{0.6}}

Then I made an attempt to convert the constant with its units from the original equation into a constant with the units from the desired equation:

1147\frac{kcal·cm^{0.4}·s^{0.6}}{h·m^{2.6}·ºC^{2}}·\frac{Btu}{0.252kcal}·\frac{0.394^{0.4}inches^{0.4}}{cm^{0.4}}·\frac{0.3048^{2.6}m^{2.6}}{ft^{2.6}}· This is where I don't know how to proceed in order to convert the temperature units from ºC^{2} to ºF^{2}, the professor said we should use the factor 1ºC <> 1.8ºF when we have ΔT in an equation BUT when we have a specified T we should use (ºF)=1.8(ºC)+32, but SteamKing disagrees so I don't know how to proceed at all. I have a hunch my professor made a mistake but I'm not sure.
 
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