Adiabatic Process: 1kg H2O from 220kPa, 200C to 50C

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Discussion Overview

The discussion revolves around a homework problem involving a reversible adiabatic process for 1 kg of water transitioning from an initial state of 220 kPa and 200°C to a final state of 50°C. Participants explore how to determine the final pressure and volume of the water.

Discussion Character

  • Homework-related

Main Points Raised

  • One participant states the initial condition and asks for the final pressure and volume, assuming entropy remains constant (S1 = S2).
  • Another participant introduces a formula relating temperatures and pressures in an adiabatic process but expresses uncertainty about the meaning of the gamma values in the equation.
  • A third participant suggests using steam tables or a temperature-entropy diagram to find the necessary properties, noting that the initial condition is superheated and that interpolation may be required for accurate entropy values.
  • A later reply acknowledges a previous misunderstanding and mentions calculating the specific volume multiplied by the mass to find the volume, indicating a realization of a simpler approach.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the final pressure and volume, and multiple approaches are discussed without resolution of the problem.

Contextual Notes

There is a reliance on steam tables and potential interpolation, which may introduce limitations based on the accuracy of the tables and the specific conditions of the problem.

BooGTS
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Homework Statement


1 kg of H20 goes through a reversible adiabatic proces from 220kPa, 200C to 50C in the final state. What is the pressure final and volume final?

Assume S1=s2


Homework Equations



Conservation of Energy

The Attempt at a Solution



Found S to be 7.5080, was thinking I could find this relating to 30°C, but missing something.
 
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T_2 = T_1 \left( \frac{P_2}{P_1} \right)^{\frac{\gamma-1}{\gamma}}

Found that, but don't really know what the gammas represent?

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Use your steam tables or temperature-entropy diagram for water. Your initial condition is super heated. So you will need to look in the super heated steam tables. Find P1 and T1 in the tables to determine entropy (s1). You might need to do some interpolation to find S1 because the pressures in the tables may not be the exactly what you are looking for. Go to the saturated water tables for T2 and S1. You are saturated if S1 is between Sf and Sg for that temperature. It looks like you are. Read P2 from the table.
 
Wow, I was way over complicating that, thanks so much RTW69!

Then I took the specific volume X the mass of the water and got the volume (just in case someone looks at this in the future).
 

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