Designing a Wind Tunnel: Homework Assignment and Bernoulli Principle Explanation

[shinnsohai]

Homework Statement

Recently I've been given an assignment
Build a Wind Tunnel(That can generated wind speed of 20m/s)
-Izzit the chamber(whole tunnel) must be sealed ?
-The material of the wind tunnel must be transparent(something like plastic?)on the test section??

Homework Equations

Bernoulli EQN
http://hyperphysics.phy-astr.gsu.edu/%E2%80%8Chbase/imgmec/bernoul.gif
Copyrights towards hyperphysics

Is there any relevant equation that I left out?

The Attempt at a Solution

Due to not enough money$$
I am planning to use ordinary standing fan to do so...but will it reach 20m/s ??
Just now at the lab, I've taken a stationary fan and test it with a anemometer
the maximum that i can get is 6 to 7m/s(tested just on putting infront of the fan)
http://www.tecpel.com/My%20Pictures/avm-702s.jpg

-Based on the Bernoulli principle, by decreasing the cross-sectional area it will increase the speed of air(or other flows). Perhaps it will increase the speed as the area close down

Currently Drawing the concept...To Be updated soon.:tongue2:

Sorry for the broken language
@_@

 

[mfb]

To use such a tunnel, the fan has to establish some pressure difference to account for friction... but it might be possible.

 

[shinnsohai]

Thanks for replying mbf
From what you wrote, I do think that the fan could actually establish a pressure difference as if the wind tunnel are totally closed and fan output is fixed closely on the input of the tunnel
But is it okay to use fan? due to the fan cross-sectional area kind ar BIG and to find a tube that fix the fan is quite hard, can't seen over the hardware shop.

I'd have an another idea...
Instead of using fan, can i just use a compressor ? but how do I covert the compressor's pressure to m/s ??

Something like this ??
But the output of this kind of compressor is so small
only few inch @@

 

[mfb]

I'm not sure if the compressor gets enough air flow for a reasonable wind tunnel. It is possible to get 20m/s easily with a small pipe, however.

due to the fan cross-sectional area kind ar BIG and to find a tube that fix the fan is quite hard, can't seen over the hardware shop.

Well, that is an engineering problem. Maybe you can use something like a box where one side gets the fan and the other side gets the tunnel.

 

[shinnsohai]

I think , I could Predict the output velocity(that I wanted to calculate)
by using
Continuity Equation ??
as
ρ x A1 x V1 = ρ x A2 x V2
(Since the liquid/air density should be the same)
A1 x V1 = A2 x V2
So I Have Area 1 and Area 2
and of coz the Velocity at the beginning

Am I Using the Correct Equation for this case?
IM Still A Newbie in applying formulae to real cases

 

[mfb]

ρ does not have to be constant, but for most setups this should be a good approximation.

and of coz the Velocity at the beginning

Well, that velocity will be influenced by your pipe design.

 

[shinnsohai]

BUMP!
Sorry for super duper late reply due to no internet connection:tongue:

Anyway I'd comeup with two design. which is better?

I am thinking of it , the chocolate part is made up of wood?
will wood eventually works?(FINE wood boards)

something like this.

As if for the test part, it should be made up of acrylic(Perspex)

for the fan.

http://images.buzzillions.com/images_products/10/12/flowpro-q-standard-premium-cooling-fan-25in-2-3-hp-9500-cfm-model-11409_3197984_100.jpg
http://www.buzzillions.com/reviews/flowpro-premium-cooling-fan-25in-2-3-hp-9500-cfm-model-11409-reviews#Description

With Air Delivery CFM 8,100-9,500
And The Volume of test area of 15cm x 15cm x15cm
I'll get the max of 70m/s?
is this for real?
By using the converter

 

[mfb]

Your air delivery value requires the full cross-section of the fan - with your wind tunnel design, air flow will be reduced (as air pressure builds up behind the fan).