basic problem involving Internal energy and entropy of a vessel 1

[tech2580]

The problem is:

A 2ft^3 vessel is filled w/ 1 lbm of water at 100psia. What is the total internal energy and entropy of the vessel?

It's been a while since working a problem like this, any ideas?
Everything is greatly appreciated, many thanks in advance

 

[davefitz]

you need any 2 properties to determine the other properties.

You have P= 100psia, and v= 2./1. = 2 ft3/lbm.

so now use a steam table and obtain the rest.

 

[25362]

Since 0.5 lb/cf is not the density of the water at 100 psia, can you tell us the temperature?

 

[davefitz]

Another word for water that has already evaporated is "steam"

from the following online steam tables
<

http://www.steamtablesonline.com/steam97web.aspx>

p=100., T= 327.8, v= 2.0, h= 697.7, s=0.981216

units are english units, not metric.

 

[ione]

From the tables I’ve got at p = 100 psia and T = 327.87 °F the specific volume of steam v = 4.43313 ft3/lb.

 

[25362]

My steam tables didn't show a value for the given data. Therefore I had to assume it is a mixture of liquid and vapor.
It appears to be wet steam with a 44.9% quality as shown by the "calculator" suggested by davefitz.

 

[ione]

25362,

I was referring to dry steam. I agree with you that wet steam (44.9% dryness) has the values of enthalpy reported by davefitz

 

[gruntguru]

At the given pressure and specific volume it cannot be "dry steam". It is a "saturated mixture"

 

[25362]

One exception to the statement:

You need any 2 properties to determine the other properties.

It cannot apply when the two given properties are saturation pressure and temperature. In this case one needs an extensive property.

 

[25362]

Or, of course, the steam quality.

 

[25362]

Or specific volume, which is another intensive property.