Thermodynamics - Find final pressure

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Discussion Overview

The discussion revolves around a thermodynamics problem involving the estimation of final pressure during a constant volume process of steam, transitioning from an initial state of 0.1 MPa and 350°C to a final temperature of 300°C. Participants are exploring the use of steam tables and linear interpolation to find the solution.

Discussion Character

  • Homework-related
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant initially calculated the final pressure using linear interpolation but arrived at 28.3 kPa, while the expected answer is stated to be 93.4 kPa.
  • Another participant suggests that steam tables should be used to solve the problem and asks which property is held constant in the system, providing multiple options for consideration.
  • Specific volume is identified as the constant property in the process by multiple participants.
  • Further inquiry is made into finding the specific volume of the steam at the initial state and looking up corresponding values in the steam tables at the final temperature of 300°C.

Areas of Agreement / Disagreement

Participants generally agree on the need to use steam tables and that specific volume is the constant property. However, there is no consensus on the correct final pressure, as differing calculations have been presented.

Contextual Notes

Participants have not resolved the discrepancies in the calculated final pressure and the expected answer, and there are indications of missing assumptions regarding the use of steam tables.

Ribz
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Homework Statement



An amount of steam undergoes a constant volume process from an initial state for which the pressure and temperature are 0.1MPa and 350°C respectively. The final temperature is 300°C. Using linear interpolation estimate the final pressure.

Homework Equations



Use Thermodynamics and Transport Properties of Fluids

The Attempt at a Solution



I used linear interpolation for the pressure at 100°C, which was 1.01325 bar. Got my answer which was 28.3 kPa. The answer stated is 93.4 kPa
 
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Ribz said:

Homework Statement



An amount of steam undergoes a constant volume process from an initial state for which the pressure and temperature are 0.1MPa and 350°C respectively. The final temperature is 300°C. Using linear interpolation estimate the final pressure.

Homework Equations



Use Thermodynamics and Transport Properties of Fluids

The Attempt at a Solution



I used linear interpolation for the pressure at 100°C, which was 1.01325 bar. Got my answer which was 28.3 kPa. The answer stated is 93.4 kPa
Hi Ribz. Welcome to Physics Forums!

Let me guess. You are supposed to be using steam tables to solve this, correct?

What is being held constant in this system:
(a) specific enthalpy?
(b) specific volume?
(c) specific internal energy?
(d) specific entropy?

Chet
 
Specific volume is constant
 
Ribz said:
Specific volume is constant
Good. So, from your steam tables, what is the specific volume of the steam initially? Now look in your steam tables for 300C, and find a condition as close as you can get to this specific volume. What is the specific volume at that point, and at the two adjacent pressures in the table? What are the pressures and volumes that go with the three points in your table?

Chet
 

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