Solving a Carnot Engine Problem: What Unit Do I Use?

[sophzilla]

I solved the problem, but I can't get the right unit for the answer.

A Carnot engine whose low-temperature reservoir is at 16°C has an efficiency of 31%. By how much should the temperature of the high-temperature reservoir be increased to increase the efficiency to 70%?

My numerical answer is 544.8. I tried Kelvin first - the most obvious choice - but that was wrong. Then I tried celcius and J/K.

I tried to work it out but I have no earthly idea - the other choices include:
- C0 (like the celcius sign but the circle is after the C)
-J/kg*K
-J/mol*K and
-kJ/kg

Any help would be grately appreciated.

 

[Andrew Mason]

My numerical answer is 544.8. I tried Kelvin first - the most obvious choice - but that was wrong. Then I tried celcius and J/K.

I tried to work it out but I have no earthly idea - the other choices include:
- C0 (like the celcius sign but the circle is after the C)
-J/kg*K
-J/mol*K and
-kJ/kg

Any help would be grately appreciated.

You have to use Kelvin for temperature in thermodynamics. I get 544.5 K as the increase (from 418.8 K to 963.33 K)

AM

 

[sophzilla]

Well...the thing is, I did use Kelvin. That was my first choice, but it was wrong. Any other sound possibilities?

 

[Andrew Mason]

Well...the thing is, I did use Kelvin. That was my first choice, but it was wrong. Any other sound possibilities?

Mind you, this temperature difference is also 544.5 degrees Celsius. It is just that you have to work out the thermodynamics part in K and then convert back to Celsius.

AM