What Is the Correct Equation for Fluids Momentum Balance?

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Discussion Overview

The discussion revolves around the correct formulation of the momentum balance equation for fluid dynamics, particularly in the context of a sieve tray operating under specific flow conditions. Participants are exploring the relationship between liquid depths and flow velocities in different regions of the tray.

Discussion Character

  • Homework-related
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant presents a momentum balance equation involving mass flow rates and pressure differences but indicates difficulty in achieving the correct final equation.
  • Another participant describes a flow pattern on a sieve tray, detailing the velocities and densities in different regions and proposes a relationship between liquid depths in these regions.
  • A request is made for a physical interpretation of the problem and for the equations used to reflect this understanding.

Areas of Agreement / Disagreement

There appears to be no consensus on the correct equation for the momentum balance, as participants are presenting different aspects of the problem and seeking clarification on physical interpretations.

Contextual Notes

The discussion includes an unresolved mathematical relationship and lacks clarity on certain assumptions regarding flow conditions and properties of the fluids involved.

chemengineer23
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Homework Statement


Attached document

Homework Equations


m(flow)*(v1-v2)+P1A1-P2A2

The Attempt at a Solution


I did a mass balance to plug into the momentum balance, but I am not getting the final equation correct.
 
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Sorry, there was no document attached to your post. :(
 
The figure below illustrates the flow pattern on a sieve tray operating at a high liquid flow rate with a gas that is negligibly absorbed in the liquid. The liquid flows from left to right across the tray. the region AB is where the velocity of the clear liquid is uL and the density is pL. The perforations I the sieve part of the tray) begin at point B, and BC is the froth zone with velocity uF and density pF. Show that the liquid depths in the two regions are related by (hF/hL)^3*(pF/pL)-hF/hL(1+(2uL^2/ghL))+2(uL^2)pL/ghFpF=0

What is the value hF when hL= 0.2 ft, uL= 0.5 ft/s, pF/pL= 0.5
 

Attachments

Please tell us what is happening physically, as you assess it. Please also show us what you did to capture this physical assessment in terms of equations.

Chet
 

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