What is the Cv for water at different temperatures?

[Curl]

I thought about an interesting steam cycle but to calculate efficiency etc. I need to find out the Q absorbed when 1kg water is heated at constant volume from 1atm and 100C to 500C.

For this I need Cv(T), energy capacity as a function of temperature (with V constant). Maybe there is no elementary formula because of the phase change and also it will go past the critical point, so at least does anyone know any good steam tables that will have values in this range? Most of them stop a the critical point.

I can't figure out what enthlapy is for water above the critical point.

 

[gmax137]

Sorry about the units, I'm a Btu guy
at 100C (212F) and 1 atm (14.7 psia) enthalpy is 180.2 Btu/lb (liquid) and 1150.3 (vapor)
at 500C (932F) and 1 atm (14.7 psia) enthalpy is 1499.9 Btu/lb

from subcooled/superheat steam tables (ASME)

does that help?

 

[Dickfore]

Whatever cycle you had invented, it cannot have an efficiency coefficient higher than 60%.

 

[Curl]

Sorry about the units, I'm a Btu guy
at 100C (212F) and 1 atm (14.7 psia) enthalpy is 180.2 Btu/lb (liquid) and 1150.3 (vapor)
at 500C (932F) and 1 atm (14.7 psia) enthalpy is 1499.9 Btu/lb

from subcooled/superheat steam tables (ASME)

does that help?

At 500C, the pressure will not be 1 atm, it might be something like 60 atm. I'm heating this at constant volume, then expanding adiabatically back to 1 atm.

When I'm back to 1 atm, the water will be cooler (because of the work). So at this point I don't know temperature or enthlapy.

Maybe this problem is too tough to figure out.

 

[russ_watters]

First hit on google: http://www.efunda.com/materials/water/steamtable_sat.cfm

 

[Andy Resnick]

Whatever cycle you had invented, it cannot have an efficiency coefficient higher than 60%.

That's what I got, too.

 

[Curl]

First hit on google: http://www.efunda.com/materials/water/steamtable_sat.cfm

I already tried that.

* Out of range error: The maximum temparature in the database is 189.97C (373.946F)

 

[Curl]

That's what I got, too.

Can you show how you got this? Just telling me the answer ruins the point of the exercise.

 

[rock.freak667]

From my steam tables, at 101.325 kPa (0.1MPa) I have the following

at 100°C, h_f=419.1, h_g=2676, h_fg=2256.9 (all in kJ/kg)

I assume at 100°C your steam is dry and saturated so the enthalpy is h_g

at 500°C and 0.1MPa, the enthalpy is3488 kJ/kg'

As for the maximum efficiency, look up 'carnot efficiency'