A piston-and-cylinder device initially contains 50 L of liquid water at 25oC and 300 kPa. Heat is added to the water at constant pressure until the entire liquid is vaporized.
a.) What is the mass of the water in the cylinder in kg ?
b.) What is the final temperature of the water in the cylinder in oC ?
c.) Determine the total enthalpy change of the water for this process, in kJ.
d.) Show the process on a completely labeled TV Diagram.
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3 comments:
To help you figure out if you did the problem correctly, (and to reward those of you utilizing this blog), the answer to part C for the total change in enthalpy is 130613 kJ.
I am having trouble figuring out part A. It requires a double interpolation right? But I cannot figure out how to do this/set it up.
Anonymous at 10:57:
The good news is that part (a) does not require double interpolation! It is two interpolations, but not really a double interpolation. Here is why.
Since P > 1 atm and T < 100C, we KNOW the water is a subcooled liquid, right ? The weird part about this problem is that the first pressure entry in the subcooled liquid table is 5000 kPa and we are looking for properties (specific volume in this problem) at 300 kPa. So, what P do we use for the lower limit on P for interpolation ? We need to use the saturation pressure...the pressure associated with the saturated liquid. So, if you go to the saturation TEMPERATURE tables, you can get specific volume of the saturated liquid at 25C (and the rather low saturation pressure of a few kPa).
Next you need the upper limit for interpolation. This is the subcooled liquid at 25C and 5000 kPa. You must interpolate between 20C and 30C on the subcooled liquid table to get the specific volume.
Once you know specific volume at the lower pressure and 25C and the upper pressure, 5000 kPa, also at 25C, THEN you can interpolate on P to get the specific volume at 25C and 300 kPa and complete part (a).
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