What is the exit steam velocity?

Click For Summary

Discussion Overview

The discussion revolves around calculating the exit steam velocity from a nozzle given specific conditions of steam, including pressure, temperature, initial velocity, enthalpy at the exit, and heat loss. The context is primarily homework-related, focusing on the application of thermodynamic equations and steam properties.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • One participant presents a problem statement involving steam entering a nozzle and seeks assistance in determining the exit velocity.
  • Another participant suggests using steam tables to find specific volume and specific enthalpy for the given conditions.
  • Participants discuss the enthalpy of steam at the nozzle inlet and the implications of heat loss during the steam's passage through the nozzle.
  • There is a clarification that the problem can be solved per unit mass, indicating that mass flow rate and area may not be necessary for the calculations.
  • One participant expresses uncertainty about how to start solving the problem due to having two unknowns.
  • Another participant confirms the enthalpy and specific volume values obtained from the steam tables.
  • One participant indicates they have solved the problem after receiving input from others.

Areas of Agreement / Disagreement

There is no explicit consensus on the approach to the problem, as participants provide varying levels of assistance and clarification. Some participants agree on the method of solving per unit mass, while others express uncertainty about the initial conditions and calculations.

Contextual Notes

Participants mention the need to consider heat loss and the specific properties of steam, indicating that assumptions about ideal gas behavior do not apply. The discussion reflects the complexity of the problem and the need for accurate data from steam tables.

Who May Find This Useful

This discussion may be useful for students or individuals studying thermodynamics, particularly those working on problems involving steam properties and nozzle flow calculations.

Nemo's
Messages
69
Reaction score
0

Homework Statement


Steam, at 15 bar and 280oC, enters a nozzle with an initial velocity of 125 m/s. The steam enthalpy at the exit section is 2800 kJ/kg and the heat loss is 25 kJ/kg. What is the exit steam velocity?.

Homework Equations


1)Qin - Qout = m [h2-h1+((c22-c12))/2]
2)h = Pv + u
3)A1c1/ρ1 = A2c2/ρ2

The Attempt at a Solution


0-25k = m((2800-h1)+-125^2/2)

Steam is not an ideal gas so I can't use Pv=mRT. I have two unknowns and I don't know where to start. I hope you can help.
 
Physics news on Phys.org
For steam at 15 bar and 280 C, from your steam tables, what is the specific volume and the specific enthalpy?
 
Nemo's said:

Homework Statement


Steam, at 15 bar and 280oC, enters a nozzle with an initial velocity of 125 m/s. The steam enthalpy at the exit section is 2800 kJ/kg and the heat loss is 25 kJ/kg. What is the exit steam velocity?.

Homework Equations


1)Qin - Qout = m [h2-h1+((c22-c12))/2]
2)h = Pv + u
3)A1c1/ρ1 = A2c2/ρ2

The Attempt at a Solution


0-25k = m((2800-h1)+-125^2/2)

Steam is not an ideal gas so I can't use Pv=mRT. I have two unknowns and I don't know where to start. I hope you can help.
1. What's the enthalpy of the steam in the nozzle inlet?
2. What have you done with the heat loss of 25 kJ/kg which occurs while the steam passes thru the nozzle?
 
Chestermiller said:
For steam at 15 bar and 280 C, from your steam tables, what is the specific volume and the specific enthalpy?
Thanks for letting me pay attention to the tables.
h1=2789.88
v=0.132
Now if I can only get the area I can use m= A*c1/ρ1 to get m and then substitute in 1 to get c2.
 
Nemo's said:
Thanks for letting me pay attention to the tables.
h1=2789.88
v=0.132
Now if I can only get the area I can use m= A*c1/ρ1 to get m and then substitute in 1 to get c2.
You don't need to determine m or A, because you are going to solving the problem per unit mass. The 25 kJ/kg is already per unit mass. So the m should not be in your equation.
 
Chestermiller said:
You don't need to determine m or A, because you are going to solving the problem per unit mass. The 25 kJ/kg is already per unit mass. So the m should not be in your equation.
O.k thanks a lot
 
I solved it . Thank you anyway
 

Similar threads

  • Poll Poll
  • · Replies 9 ·
Replies
9
Views
6K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 11 ·
Replies
11
Views
2K
Replies
25
Views
4K
Replies
9
Views
2K
Replies
1
Views
3K
  • · Replies 1 ·
Replies
1
Views
13K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 1 ·
Replies
1
Views
3K
Replies
1
Views
5K