Thermodynamics adiabatic diffuser question

Click For Summary

Discussion Overview

The discussion revolves around solving a problem related to an adiabatic diffuser, specifically focusing on determining the exit area of the diffuser given certain inlet conditions and an exit pressure. The scope includes theoretical and mathematical reasoning related to thermodynamics and fluid dynamics.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • One participant presents the initial conditions of the airstream and expresses confusion about how to determine the exit area using the equations related to mass flow and thermodynamic properties.
  • Another participant asks for clarification on how to find the exit area, indicating a need for further guidance.
  • Several participants inquire about the meaning of "adiabatic" and its implications for relating inlet and outlet properties, with one defining it as zero heat transfer.
  • One participant suggests using the conservation of energy equation for open systems to find the outlet temperature and subsequently the outlet density, which could then be used to solve for the exit area.
  • Another participant notes that there may be simpler methods to solve the problem, implying that the current approach may be unnecessarily complex.
  • There is a request for more specific guidance on applying the conservation of energy equation to find the final temperature, indicating uncertainty in the application of the theory.
  • A participant advises reviewing textbooks or lecture notes for foundational understanding, suggesting that the forum may not be the best format for comprehensive learning.

Areas of Agreement / Disagreement

Participants express varying levels of understanding and approaches to the problem, with no consensus on the best method to determine the exit area. Some participants agree on the use of conservation of energy, while others express confusion about its application.

Contextual Notes

Participants mention various equations related to conservation of energy and mass flow, but there are unresolved steps and assumptions regarding how to apply these equations to find the exit area. The discussion reflects a reliance on specific definitions and interpretations of thermodynamic principles.

Superhawkkodaka
Messages
14
Reaction score
0
An adiabatic diffuser is employed to decrease the velocity of an airstream from 220 to 30 m/s. The air enters the diffuser at a rate of 8 kg/s with a temperature of 300c and a pressure of 100kpa. Determine the exit area of the diffuser if the exit pressure is 125kpa.

Answer is 0.37 m^2

Guys I am really lost with this one.. I used equations pv=mrt, m=p'v'a, v=v'a
Note (v' is velocity as in> m/s and p' is density) just to prevent confusion

What i only got are the initial values v1, a1, p'1..
 
Engineering news on Phys.org
I can't get a2(exit area) have any ideas guys?
 
What does adiabatic mean? How can you use this information to relate the inlet and outlet properties?
 
billy_joule said:
What does adiabatic mean? How can you use this information to relate the inlet and outlet properties?
i for got to add the equation for conservation of energy on open system
q=∑(exi
billy_joule said:
What does adiabatic mean? How can you use this information to relate the inlet and outlet properties?

adiabatic mean
billy_joule said:
What does adiabatic mean? How can you use this information to relate the inlet and outlet properties?

adiabatic means heat transfer is zero (Q=0)

i forgot to add the equation for open systems
Q= ΔH + ΔPE + ΔKE + W --- in this equation Q, W, & PE is equal to zero..
and
ΔH = ΔU + Δ(PV)

this equations might be usable.. my question is how do i use these equations to determine exit area
 
You can find the outlet temp. via conservation of energy. Then you can find outlet density as you have temp. & pressure.
Then use the mass flow equation you gave in your first post to solve for area.
 
I must add that there are probably other, potentially simpler ways to solve the problem.
 
billy_joule said:
You can find the outlet temp. via conservation of energy. Then you can find outlet density as you have temp. & pressure.
Then use the mass flow equation you gave in your first post to solve for area.

conservation of energy equation? i don't know how to get the final temperature.. can you be more specific with equation for conservation of energy?
i only know this equation for conservation of energy for open system : Q= ΔH + ΔPE + ΔKE + W
i can' simplify tthe equation that i gave to input the temperature in the equation
 
Last edited:
Superhawkkodaka said:
i only know this equation for conservation of energy for open system : Q= ΔH + ΔPE + ΔKE + W
You have one unknown in that equation so you should be able to solve it.
If you have no idea how to proceed it's generally best to review your textbook and/or lecture notes. We can help with specific problems but a forum is a poor format to learn course material from.
 

Similar threads

  • · Replies 9 ·
Replies
9
Views
12K
  • · Replies 22 ·
Replies
22
Views
6K
  • · Replies 20 ·
Replies
20
Views
11K
Replies
25
Views
4K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 14 ·
Replies
14
Views
3K
  • · Replies 3 ·
Replies
3
Views
3K
Replies
1
Views
2K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K