Property Tables Question [Thermodynamics]

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Discussion Overview

The discussion revolves around a thermodynamics homework problem involving the determination of specific enthalpy (h) from given pressure and specific entropy values using property tables. The scope includes theoretical application of thermodynamic principles and the use of steam tables for superheated vapor states.

Discussion Character

  • Homework-related
  • Technical explanation

Main Points Raised

  • One participant states the problem and outlines their approach using property tables, identifying the state as superheated vapor based on specific entropy values.
  • The same participant notes the need for interpolation between property values at pressures of 0.6 MPa and 0.8 MPa to find specific enthalpy, but expresses uncertainty about how to find the temperature required for this calculation.
  • Another participant suggests looking up double interpolation as a potential method to resolve the issue.
  • Further replies indicate confusion about the suggestion to look up double interpolation, with one participant asking for clarification.
  • A later reply asserts that knowing pressure and specific entropy allows for complete determination of the state, including specific enthalpy and temperature, and emphasizes the need to understand how to use the superheated steam tables.

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus on the method to find specific enthalpy, with some suggesting double interpolation while others express confusion about the process. The discussion remains unresolved regarding the specific steps needed to complete the problem.

Contextual Notes

There are limitations regarding the clarity of the interpolation method and the specific use of steam tables, which may depend on the definitions and assumptions made in the context of the problem.

AfterSunShine
Messages
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Homework Statement


Given
Pressure=P=700 KPa
Specific Entropy = s = 7.6953 KJ / ( K Kg )

Find the Specific Enthalpy (h)

Homework Equations


No equation
Am using the property tables at the end of the following book :
Thermodynamics, an engineering approach, by Yunus A. Cengel and Michaek A.Boles 7th edition.


The Attempt at a Solution


By obtaining the values of s_f and s_g from Table A.5 and compare it to s, the state is Superheated Vapor.
This means I will use Table A.6
The pressure = 700 KPa = 0.7 MPa
But the most closest pressure to this pressure is 0.6 MPa and 0.8 MPa
So I will use interpolation like that
P (MPa) h
0.6 h1
0.7 h
0.8 h2

h1 and h2 must be calculated in order to apply interpolation to find h
To find h1,h2 Need to know T of the state
But I do not how to find it

Help please.
 
Physics news on Phys.org
Look up double interpolation.
 
I did not get it :\
 
Did not get what? Look it up on Google.
 
AfterSunShine said:

Homework Statement


Given
Pressure=P=700 KPa
Specific Entropy = s = 7.6953 KJ / ( K Kg )

Find the Specific Enthalpy (h)

Homework Equations


No equation
Am using the property tables at the end of the following book :
Thermodynamics, an engineering approach, by Yunus A. Cengel and Michaek A.Boles 7th edition.



The Attempt at a Solution


By obtaining the values of s_f and s_g from Table A.5 and compare it to s, the state is Superheated Vapor.
This means I will use Table A.6
The pressure = 700 KPa = 0.7 MPa
But the most closest pressure to this pressure is 0.6 MPa and 0.8 MPa
So I will use interpolation like that
P (MPa) h
0.6 h1
0.7 h
0.8 h2

h1 and h2 must be calculated in order to apply interpolation to find h
To find h1,h2 Need to know T of the state
But I do not how to find it

Help please.

If p and s are known, the state is known totally, including sp. enthalpy h and temperature T. Just need to know how to use your (superheated) steam tables.
 

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