Thermodynamics and steam, temperature etc tables

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Homework Help Overview

The problem involves 2000 kg of water, initially in a saturated liquid state at 150 ºC, which is heated in a closed container of constant volume until the pressure reaches 2.5 MPa. Participants are tasked with finding the final temperature and the volume of the container, while considering the state of the water during the heating process.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants discuss the necessity of determining whether the water transitions to a superheated vapor or remains as a saturated liquid/vapor mixture. There is also a focus on using steam tables to find specific volumes and pressures, and the implications of constant volume heating on the state of the water.

Discussion Status

Some participants have offered guidance on using steam tables and interpreting the P-v diagram, while others have raised questions about the assumptions regarding the volume of the liquid and its relationship to the container's volume. There is an acknowledgment of the need to clarify the state of the water at the final pressure.

Contextual Notes

Participants note that the problem does not explicitly state whether the liquid occupies the entire container, leading to discussions about the implications of this assumption on the uniqueness of the solution.

Cozy_Powell
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Homework Statement



2000 kg of water, initially in a saturated liquid state and at 150 ºC, are heated in a closed container of constant volume, until the pressure is 2,5 MPa.
Find the final temperature and the volume of the container.

Homework Equations



I believe it is a matter of consulting the tables... but I am missing something because I don't know how to do it!

The Attempt at a Solution



I believe it is necessary to know if the water, in the final state, is superheated vapor ou saturated liquid/ vapor... is it? How do we know that?

Many thanks!
 
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I think it's safe to assume that all of the water becomes vapor, because it asks to find the volume of the container, which might mean you will have to find the volume of the gaseous H2O.
 
Cozy_Powell said:

Homework Statement



2000 kg of water, initially in a saturated liquid state and at 150 ºC, are heated in a closed container of constant volume, until the pressure is 2,5 MPa.
Find the final temperature and the volume of the container.

Homework Equations



I believe it is a matter of consulting the tables... but I am missing something because I don't know how to do it!

The Attempt at a Solution



I believe it is necessary to know if the water, in the final state, is superheated vapor ou saturated liquid/ vapor... is it? How do we know that?

Many thanks!

The initial state is saturated liquid at T=150 C.

(1) Can you use the steam tables to find the specific volume of this state? While you're at it, what is the initial pressure?

(2) If you know the mass and specific volume, can you find the volume?

The liquid is heated at constant volume. Think about what the saturation curve looks like on a P-v diagram. Which direction are you headed if you start with a saturated liquid and add heat? What state is the fluid in when it reaches 2.5 MPa? (Hint: Does the saturation specific volume of pure liquid increase or decrease as temperature and pressure are increased? Is 2.5 MPa above or below the critical pressure?) Which table do we use for water in this state?

BBB
p.s. cryora's speculation is inapt.
 
Thank you very much bbbeard!

Regarding to (2)... I've done that, but can we assume that the volume of the liquid is equal to the volume of the container?
 
Cozy_Powell said:
can we assume that the volume of the liquid is equal to the volume of the container?

Well, if you don't assume that that liquid takes up the entire container, then the problem does not have a unique solution. My take, as someone who has taught thermo many times, is that they intend for you to assume that the process is a constant volume process, i.e. that the liquid takes up the entire container and that the container is perfectly rigid.

BBB
 
oh... I'll assume that then! I didn't know we could do it because nothing in the problem tells us that.

Thank you very much for your previous hint on the P-v diagram!
I was making the huge mistake of thinking that the saturated liquid would get into vapor and that was driving me mad! Thanks to you, now I understand that it becomes a compressed liquid ;)

Thank you!
 

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