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November 2001

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Subject:
From:
Rummy Makmur <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 13 Nov 2001 06:11:46 -0600
Content-Type:
text/plain
Parts/Attachments:
text/plain (116 lines)
To prove that, you need combination of mass balance and mechanical energy
balance (i.e. bernoulli equation).

mass balance: mass rate in = mass rate out. Assuming incompressible fluid
(same density in and out), since mass rate = volume rate * density, density
get canceled out and the result is volume rate in = volume rate out. It is
also known that volume rate = velocity * Area. From this you can prove that,
if area is decreased (such as, putting your thumb on the hose), velocity
will increase.

Then you will need bernouli equation. Simplified Bernoulli Equation:
(P1/density) + (Velocity1^2/2)+ (gh1) = (P2/density) + (velocity2 ^ 2/ 2) +
(gh2)

Assuming h (height) is the same, they get canceled out. Then, you will have
an equation with only P (Pressure) and V (velocity) as variables which you
can use to prove that if V2 increases, P2 decreases, provided P1 and V1 are
constant.

So, volume rate at location 2 is not dependent on Pressure at location 2,
provided same pressure and volume rate coming in. It "feels" like pressure
increasing, but rather it's velocity that is increasing or kinetic energy
increases.

Check out these sites
http://physics.bu.edu/py105/notes/Bernoulli.html
http://rabi.phys.virginia.edu/HTW/water_distribution.html

For the second question, you might not be able to use same exact equations
for air, since air might be considered as compressible. It may involve more
complicated equations.

Rummy Makmur
Process Engineer
Ibiden Circuits of America

-----Original Message-----
From: Eric Christison [mailto:[log in to unmask]]
Sent: Tuesday, November 13, 2001 3:27 AM
To: [log in to unmask]
Subject: Re: [TN] Formula?


I think you're all barking up the wrong tree.

Bernoulli's equations shows the conservation of kinetic energy in fluids
and is generally used to calculate things like areodynamic lift on an
aerofoil or the forces exerted on a pipe wall as the the contents flows
round a corner.

I think you're searching for P1v1/T1 = P2v2/T2. However v is not volume
but specific volume ie m^3/Kg.

Spend a minute on a reality check. If you put your thumb on the end of a
hose pipe does the pipe get smaller? If not, how can the volume of the
pipe decrease?

Hope this helps,



[log in to unmask] wrote:
>
> Ray, try http://www.lmnoeng.com/Flow/bernoulli.htm
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]]On Behalf Of Golembiewski, Ray
> Sent: Monday, November 12, 2001 14:34
> To: [log in to unmask]
> Subject: [TN] Formula?
>
>         What is the formula that proves when I put my thumb on the end
> of a garden house, the pressure increases and volume decreases. Is the
> same formula used with air? Please help,
>
> Ray Golembiewski C.I.D.
> Manufacturing Test Engineer
> Projects Unlimited, Inc.
> (937) 918-2200
>
--
Eric Christison
Mechanical Engineer
STMicroelectronics
33 Pinkhill
Edinburgh
EH12 7BF

Tel: (0)131 336 6165
Fax: (0)131 336 6001

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