How does temperature in Celcius affect enthalpy in a compressed liquid?

[MariusM]

Hello!

I was playing around with a problem and while I was doing it I noticed a similarity between

C_v*T=h by using celsius and not Kelvin.

So if I have a compressed liquid at say 50°C, looking up at a property table I find the h_f to be 209.34 kJ/kg (the pressure is considered to be low). If you take the equation C_v*T, where C_v≈4.18 and T=50°C you get 209 kJ/kg. Doing this with kelvin instead gives a much larger number.

My question is why is the relation here celsius? Does it have something to do with the saturated water tables being celsius dependent?

 

[Chestermiller]

Hello!

I was playing around with a problem and while I was doing it I noticed a similarity between

C_v*T=h by using celsius and not Kelvin.

So if I have a compressed liquid at say 50°C, looking up at a property table I find the h_f to be 209.34 kJ/kg (the pressure is considered to be low). If you take the equation C_v*T, where C_v≈4.18 and T=50°C you get 209 kJ/kg. Doing this with kelvin instead gives a much larger number.

My question is why is the relation here celsius? Does it have something to do with the saturated water tables being celsius dependent?

The reference state for zero enthalpy is typically not taken as absolute zero. You have to look up in your table the specific reference state that they use for zero enthalpy. This information is usually given on the first page of the table at the very top. Or, you can look at the numbers in the table until you find a set of conditions where h is zero.

Chet

 

[MariusM]

Thank you very much for your informative reply! I will read more upon the subject of reference state regarding zero enthalpy so I'll hopefully get a full comprehension of this.