Calculating Velocity in a Venturi Effect Nozzle: Converting Units

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Homework Help Overview

The discussion revolves around calculating the average velocity in a Venturi effect nozzle, with specific dimensions and a given flow rate. The problem involves unit conversion and application of the continuity equation.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants discuss the calculation of areas and velocities, questioning whether to convert dimensions from centimeters to meters before performing calculations. There is also a focus on maintaining consistent units throughout the calculations.

Discussion Status

Participants are exploring different approaches to unit conversion and discussing the implications of using different unit systems. Some guidance has been offered regarding unit consistency, but no explicit consensus has been reached on the preferred method of conversion.

Contextual Notes

The original poster expresses uncertainty about unit conversions and whether to convert all measurements to a single unit before calculations. There is an emphasis on understanding how units interact in the context of the continuity equation.

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Homework Statement


Venturi effect nozzle.. Starts off at 100cm and goes down to 40cm. The flow rate of the gas is 2.23 m3/s. What is the average velocity at the beginning and end of the nozzle.


Homework Equations


Continuity Formula, Bernelli = Q = A1V1=A2V2


The Attempt at a Solution


It's not the solution I am having trouble with so much, I am having a brain fart with units. I can take the area of 100cm and get 7850 cm2 and 40cm works out to 1256cm2 and you end up with a starting velocity of 0.000284 and an ending velocity of 0.001775 which I am assuming is cm/s.. Is that right or do I need to convert 100cm and 40cm to meters first and then do the calculation and then end up with meters/s?
 
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ISX said:
I can take the area of 100cm and get 7850 cm2 and 40cm works out to 1256cm2 and you end up with a starting velocity of 0.000284 and an ending velocity of 0.001775 which I am assuming is cm/s.

Hi ISX. No need to assume anything here. If you carry your units along in the calculation it will guide you. You have V = Q/A. You plugged in numbers as V = (2.23 m3/s)/(7850 cm2). So, what do the units reduce to here?
 
I guess I've never read it like you put it, just always had a guide to follow in the book. I see cubic meters and cm squared so I woulda thought you would make them both cm or both meters..so I'm still not sure.
 
ISX said:
I see cubic meters and cm squared so I woulda thought you would make them both cm or both meters..so I'm still not sure.

Right. You can go either way: convert the cm2 to m2 or convert the m3 to cm3.
 
Alright so both of these should be right then.

2cx650.jpg
 
Yes. Nice. :smile:
 
Schweeeeet. Thanks.
 

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