Heating water at constant volume and pressure

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SUMMARY

The discussion focuses on a thermodynamic problem involving a rigid tank with a volume of 0.01 m3 containing saturated water at 200°C and a quality of 0.4. The system is heated until all liquid vaporizes, requiring the calculation of the heat input (in kJ) necessary for this phase change. Jared utilizes steam tables to determine total molar volume and mass, while questioning the application of energy equations, specifically regarding the relationship between heat transfer (Q) and internal energy change (ΔU) in the context of vapor leaving the system.

PREREQUISITES
  • Understanding of thermodynamic properties of water and steam
  • Familiarity with steam tables and phase change calculations
  • Knowledge of the first law of thermodynamics
  • Concept of quality in saturated mixtures
NEXT STEPS
  • Study the application of the first law of thermodynamics in closed systems
  • Learn how to calculate heat transfer during phase changes using steam tables
  • Explore the concept of quality and its impact on energy calculations
  • Investigate methods for tracking energy leaving a system during phase transitions
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Thermodynamics students, mechanical engineers, and professionals involved in thermal system design and analysis.

debussie
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A rigid tank has a volume of 0.01m3. It initially contains saturated water at a temperature of 200°C and a quality of 0.4. The top of the tank contains a pressure-regulating valve that maintains the vapor at constant pressure. This system undergoes a process whereby it is heated until all the liquid vaporizes. How much head (in kJ) is required? You may assume that there is no pressure drop in the exit line.
 
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Please could you provide your attempt at the solution.

Jared
 
So far I have used the quality given, and the steam tables to calculate the total molar volume and total mass of the water:

Vm=(1-x)Vml+xVmv
m=V/Vm

I am assuming that the temperature of the system won't change because vapor will continue to leave as more vapor is created. I'm not sure where to go from here. Does Q=change in U? How do I keep track of the energy that is leaving with the vapor?
 

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