Thermodynamics -- Calculate the pressure and temperature

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Discussion Overview

The discussion revolves around a thermodynamics problem involving a rigid vessel containing water and steam at a specified temperature. Participants are tasked with calculating the pressure and temperature after heating the vessel until all water has evaporated, while maintaining constant volume. The focus is on understanding the phases of water present and the properties of steam at the given conditions.

Discussion Character

  • Homework-related
  • Technical explanation
  • Exploratory

Main Points Raised

  • One participant states the initial conditions, including the volume, mass of water, and temperature.
  • Another participant emphasizes the importance of recognizing that the volume is constant due to the rigid nature of the vessel.
  • There is a suggestion that the system should be in the superheated vapor state after complete evaporation of water.
  • A participant points out a potential typo in the mass of liquid water provided in the initial post, suggesting it should be 0.9185 kg instead of 0.0185 kg.
  • Participants discuss the need to find the specific volume of the vapor and how to use steam tables for determining corresponding temperature and pressure.
  • There is mention of using interpolation with steam tables to find the temperature and pressure based on the specific volume of 50 m³/kg.

Areas of Agreement / Disagreement

Participants express uncertainty regarding the correct mass of liquid water and the implications for the calculations. There is no consensus on the final values for pressure and temperature, as the discussion remains exploratory with multiple viewpoints on how to approach the problem.

Contextual Notes

Participants have not fully resolved the implications of the specific volume and its relation to the state of the water vapor. There are also unresolved questions regarding the calculations needed to find the temperature and pressure from the steam tables.

ps3stephen
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Homework Statement


A rigid vessel of volume 5m^3 contains 1.0 kg of water and steam at 19 degree C.Find the pressure and the mass of liquid and vapour in the vessel.

The vessel is now heated unit the water is just evaporated. Calculate the the pressure and temperature of this process. The volume should be constant since it is a rigid vessel. Please help with this part. Thank you.

T= 19 degree C
v=50m^3/kg
Psat=0.02196 bar (from steam tables)
vf=0.100164*10^-2 m^3/kg
vg=61.34 m^3/kg
mvapour=0.0815 kg
mliquis=0.0185 kg

Homework Equations


v = (1 – x)vf + x vg

The Attempt at a Solution

 
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ps3stephen said:
Please help with this part
You're going to have to move your feet at least one step --- what is one thing you know?
ps3stephen said:
the water is just evaporated
 
Bystander said:
You're going to have to move your feet at least one step --- what is one thing you know?

Well, the volume is constant.
 
Anything else?
 
Bystander said:
Anything else?
everything i know is stated up there.
 
How many phases?
 
It should be at the superheated vapour state since it state the water is just evaporated.
 
ps3stephen said:
superheated vapour
Mass, volume, number of phases --- need anything else?
 
Mass and volume are given. I just have no clue about what its about when it just evaporated. Volume should be constant since it is a rigid tank.
 
  • #10
Your answer for liquid water in part 1 should be 0.9185 kg. You must have a typo in post #1.

For part 2, if there is no liquid water remaining in the container, what does the specific volume of the water vapor have to be?

Chet
 
  • #11
specific volume should be 50m^3/kg. so i should be find the temperature and pressure from the steam table?
 
  • #12
ps3stephen said:
specific volume should be 50m^3/kg. so i should be find the temperature and pressure from the steam table?
Sure
 
  • #13
so, i have specific volume of 50 m^3/kg from the steam table and do interpolation to find the temperature and pressure correspond to the specific volume of 50 m^3/kg?
 
  • #14
ps3stephen said:
so, i have specific volume of 50 m^3/kg from the steam table and do interpolation to find the temperature and pressure correspond to the specific volume of 50 m^3/kg?
Sure
 

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