Finding the internal energy using a steam table

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Discussion Overview

The discussion revolves around the process of finding the entropy of water at a pressure of 5 Bar and an internal energy of 2724 kJ/kg using steam tables. Participants explore how to navigate the tables and relate internal energy to entropy, focusing on the use of different tables for superheated and saturated steam.

Discussion Character

  • Homework-related
  • Technical explanation
  • Exploratory

Main Points Raised

  • One participant expresses uncertainty about how to use the steam tables after finding the pressure of 500 kPa.
  • Another participant seeks clarification on whether the initial understanding of the problem is correct, confirming the parameters given.
  • A participant identifies that the relevant table is for superheated steam and asks about the column headings present in the table.
  • After some back and forth, a participant realizes they have two tables and explains their approach to find the temperature using internal energy from one table and then using that temperature to find entropy from another table.
  • The calculated value of entropy is reported as 7.272, with a participant expressing gratitude for the assistance received.

Areas of Agreement / Disagreement

There is no explicit consensus on the method of using the steam tables, as participants clarify and refine their understanding of the tables and their contents. The discussion reflects a collaborative effort to navigate the problem rather than a resolution of differing viewpoints.

Contextual Notes

Participants mention having two different tables, which may lead to confusion regarding which table to use for specific properties. The relationship between internal energy and entropy is explored but not fully resolved in terms of methodology.

smoothie king
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Homework Statement


What is entropy of water at 5 Bar and an internal energy of 2724 kJkg-1?

The Attempt at a Solution


I have looked at the steam tables, i found where the pressure is 500kpa, then i do not know where to go from there.

Thank You
 
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So you will be supplied with tables that no one has told you how to use? Really?
 
phinds said:
So you will be supplied with tables that no one has told you how to use? Really?

i have changed the question around
 
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smoothie king said:
i have changed the question around

sorry for double post, i pressed something wrong by accident.
 
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Let me understand correctly. You have steam tables, and you know that you have water at 5 bars with an internal energy of 2724 kJ/kg, and you are asked to determine its entropy. Is that right?

Chet
 
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Chestermiller said:
Let me understand correctly. You have steam tables, and you know that you have water at 5 bars with an internal energy of 2724 kJ/kg, and you are asked to determine its entropy. Is that right?

Chet

Yes, that's exactly what I'm trying to do, i didnt know how to change the title and i didnt want to start a new thread.
 
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You found a place in the tables where the pressure is 500 kPa. What is the heading on the top of the page (e.g., saturated steam or superheated steam)?

Chet
 
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Chestermiller said:
You found a place in the tables where the pressure is 500 kPa. What is the heading on the top of the page (e.g., saturated steam or superheated steam)?

Chet
Superheated Steam
 
smoothie king said:
Superheated Steam
OK. Now there are columns of numbers on the page. What are the headings on the columns of numbers?

Chet
 
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  • #10
Chestermiller said:
OK. Now there are columns of numbers on the page. What are the headings on the columns of numbers?

Chet

They are all temperatures from 100°c to 700°c
 
  • #11
smoothie king said:
They are all temperatures from 100°c to 700°c
What are the headings on the other columns (or rows?)?

Chet
 
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  • #12
Chestermiller said:
What are the headings on the other columns (or rows?)?

Chet

there is t(sat), then h and s for all the temperatures above. also hg and sg for saturation
 
  • #13
smoothie king said:
there is t(sat), then h and s for all the temperatures above. also hg and sg for saturation
I thought you said that the part of the table you were open to was for superheated steam. This table is for saturated steam. What gives?

Chet
 
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  • #14
Chestermiller said:
I thought you said that the part of the table you were open to was for superheated steam. This table is for saturated steam. What gives?

Chet

i have two tables and i didn't notice, i have one with h and s, another with u and v, i just realized that i have to find the value for temperature in the u and v table using internal energy, then use that temperature to find the value of entropy in the h and s table. I got the value of entropy to be 7.272.

Thank you very much!
 
  • #15
smoothie king said:
i have two tables and i didn't notice, i have one with h and s, another with u and v, i just realized that i have to find the value for temperature in the u and v table using internal energy, then use that temperature to find the value of entropy in the h and s table. I got the value of entropy to be 7.272.

Thank you very much!
Sounds about right.

Chet
 
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