Question to all science boffins

[salem]

Can anybody help me with this scientific question:

1) Assume that if you attach the vacuum tube of a Venturi tube to a closed chamber, you find that at a specific airflow (x) the drop in pressure within the chamber is y.
2) Now assume that you attach two independent but identical Venturi tubes both subject to airflow x, to the same closed chamber.

Question: Will the drop in pressure in the closed chamber with two Venturi tubes attached to it, be y or 2y?

[justin.schoeman]

It will be 'y'.

Since air moves from a region of high pressure, to a region of low pressure, adding an identical venturi, producing the same pressure will result in no nett air flow, so the pressure will stay the same.

[Aerosan]

It will be 'y'.

Since air moves from a region of high pressure, to a region of low pressure, adding an identical venturi, producing the same pressure will result in no nett air flow, so the pressure will stay the same.

Korrek.

[salem]

I know I'm probably sounding stupid to all the scientists out there, but here is what I can't figure out:

If you are emptying a glass of water with two syringes, it will take half as long as if you tried emptying the glass with one syringe. Two syringes = twice the suction, therefore why should two venturi tubes not suck double the amount of air from the closed chamber and thus produce a combined suction force of 2y?

[Rudix]

I know I'm probably sounding stupid to all the scientists out there, but here is what I can't figure out:

If you are emptying a glass of water with two syringes, it will take half as long as if you tried emptying the glass with one syringe. Two syringes = twice the suction, therefore why should two venturi tubes not suck double the amount of air from the closed chamber and thus produce a combined suction force of 2y?

No, you will get double the "VOLUME" of suction but the "STRENGTH" will still be y.

You cannot add the 2 suction forces, the actual suction would be the average of the 2 (if they "suck" the same volume")

[Dish]

ya - thats what i would have said.....

[Morph]

Will the drop in pressure in the closed chamber with two Venturi tubes attached to it, be y or 2y?

My question is why?

[grostek]

Because both venturis produce an equal amount of suction.

With one venturi the drop in pressure will take place in x time

and with two venturies in half the time

So we have a reduction in time but not an additional reduction in pressure.

Take a bucket fill it with water drill a hole in the full bucket

measaure the time it takes to empty the water.

now repeat same experiment with two identical holes drilled in the same bucket, bucket should empty in half the time.

You cant empty more water out of the bucket because there is no more (unless you add more).Volume of bucket is fixed.

So the same for closed cylinder with attached venturi/venturies.

Kind regards,
Gunter Rostek

[salem]

Will the drop in pressure in the closed chamber with two Venturi tubes attached to it, be y or 2y?

My question is why?

The answer is also why (y)

[justin.schoeman]

Now take the same situation, but the two venturis have different pressures, 'x' and 'y'. What will the resultant pressure be in the closed chamber?

HINT: This is a trick question!

[Morph]

No, I mean why are you asking this question.

Are you looking at balancing your carbs etc?

[salem]

Now take the same situation, but the two venturis have different pressures, 'x' and 'y'. What will the resultant pressure be in the closed chamber?

HINT: This is a trick question!

It should be (x + y)/2

[justin.schoeman]

Now take the same situation, but the two venturis have different pressures, 'x' and 'y'. What will the resultant pressure be in the closed chamber?

HINT: This is a trick question!

It should be (x + y)/2

Nope. once the pressure differs, air will flow from the higher pressure pitot to the lower pressure pitot. The system is now a hydro-dynamic system, rather than hydro-static, so different rules apply. In all likelyhood, the pressure will be slightly less than (x+y)/2, but this depends on shape, size and interfaces of all the pipes and chambers.

Physics is a b*tch...

[salem]

No, I mean why are you asking this question.

Are you looking at balancing your carbs etc?

Hi Morph

It's for a project that I have in mind. I might pop in at Morningstar and discuss it with you on Saturday.

[Morph]

Cool, I'll be there all morning. Might be in the air for some of the time. Look for my burgandy Corsa Bakkie