3. A closed system containing 75 kg of water in 20 m3 at undergoes a constant vo

Question

3. A closed system containing 75 kg of water in 20 m3 at undergoes a constant volume process from an initial temperature of 100°C until the pressure is 1500 kPa. a. Determine whether point 1 is a compressed liquid, a superheated vapor, or a mixture.Be b. Determine whether point 2 is a compressed liquid, a superheated vapor, or a mixture. Be c. Find the specific heat transfer for this process (10 points). specific about how you found your result (5 points) specific about how you found your result (5 points). (No credit for unsupported answers.)

Explanation / Answer

a. Initial temperature = 100 C which is the boiling point of water. So, at this point the system contains a micture of both water vapours and the liquid water, instead of pure compressed liquid or a superheated vapor.

b. Final temperature, T = PV/nR

number of moles of water = 75*10^3/18.01 = 4.164*10^3 moles

So, T = 1500*10^3 *20/4.164*10^3*8.314 = 867 K

= 593.32 C

So, at this point the system will be in a superheated vapor.

c. Specific heat transfer = n(change in specific heat)dT

= 4.164*(4.187-1.996)*(593.32-100)

= 4500 kJ

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