Heat in a const. pressure/volume calculation

[guideonl]

Hi guys,
I am back, because I found properties tables in the web, which aprove my 1st Cp value (1.875KJ/Kg K).
russ_watters asked where did I find this value?
Actully I got this value from calculation a formula for Cp(T), but recently I found it also in a textbook tables. So, now I am confused .. from one side I've got the same value as in the table, but from the other side I wonder if 300 deg K water could be considered as an ideal gas (water steam is appeared in the table under the title of ideal gas !)
Hereby the tables I used, see table A-2 (a) last row (also Cv value for that Temp is noted).

 

[Chestermiller]

Hi guys,
I am back, because I found properties tables in the web, which aprove my 1st Cp value (1.875KJ/Kg K).
russ_watters asked where did I find this value?
Actully I got this value from calculation a formula for Cp(T), but recently I found it also in a textbook tables. So, now I am confused .. from one side I've got the same value as in the table, but from the other side I wonder if 300 deg K water could be considered as an ideal gas (water steam is appeared in the table under the title of ideal gas !)
Hereby the tables I used, see table A-2 (a) last row (also Cv value for that Temp is noted).

That's the heat capacity of water vapor, and you are dealing with liquid water.

 

[guideonl]

That's the heat capacity of water vapor, and you are dealing with liquid water.

Sorry, I don't understand. The table's values are for 300 deg K ! Does it mean that the pressure is not atmospheric but lower than the atmospheric pressure? (to be at the vapor region associated to vapor at that temp.)

 

[Chestermiller]

Sorry, I don't understand. The table's values are for 300 deg K ! Does it mean that the pressure is not atmospheric but lower than the atmospheric pressure? (to be at the vapor region associated to vapor at that temp.)

Are you saying you can’t have liquid water at 100 C?

 

[PeterDonis]

Are you saying you can’t have liquid water at 100 C?

He said 300 K, which is about 27 C. I assume he's looking at saturation pressure values and mistaking the vapor one for the liquid one.

 

[guideonl]

Are you saying you can’t have liquid water at 100 C?

No! That's not what I'm saying. Unless you did'nt notice, the A-2 table is related to 300 deg K!

 

[guideonl]

He said 300 K, which is about 27 C. I assume he's looking at saturation pressure values and mistaking the vapor one for the liquid one.

Please refer to A-2 table (I've attached above), and explain what for Cp & Cv values stand? The title is odd, its for ideal gases @ 300 deg K (27 deg C). Water at this temp. are not vapor but liquid, unless you assume pressure is lower than atm. pressure.

 

[Chestermiller]

He said 300 K, which is about 27 C. I assume he's looking at saturation pressure values and mistaking the vapor one for the liquid one.

Oops. Sorry that was a typo on my part. I meant 300 K. But, even at 100 C (373 K) liquid water could, of course, still exist. But anyhow, what I am saying is that the value in the table from Moran et al, Introduction to Engineering Thermodynamics that the OP presented is for water vapor, not liquid water.

 

[russ_watters]

Please refer to A-2 table (I've attached above), and explain what for Cp & Cv values stand? The title is odd, its for ideal gases @ 300 deg K (27 deg C). Water at this temp. are not vapor but liquid, unless you assume pressure is lower than atm. pressure.

You most certainly can have water as vapor or liquid at 300K. You are dealing with liquid water and your table is for vapor, so clearly you are using the wrong table.

[edit] Look at table A-3 or A-4.

 

[PeterDonis]

You most certainly can have water as vapor or liquid at 300C

300 K, not 300 C. Your statement is still true at 300 K, of course.

 

[russ_watters]

300 K, not 300 C. Your statement is still true at 300 K, of course.

Yep, fixed.