×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

vaccum pumping+bernoulli's eq

vaccum pumping+bernoulli's eq

vaccum pumping+bernoulli's eq

(OP)
In laboratories, there is a common “vacuum suction”  thing (looks like a “T” working on the principle that tap water moving past a junction (T-junction) don’t know the name for it) will case a low pressure due to the high velocity  (Bernoulli’s eq). This I can understand intuitionally, but with time as the pressure falls in the vacuum chamber, why doesn’t water flow into this part of the system as well since the pressure in the vacuum chamber is way lower than the atmospheric pressure?
What law of physics can be applied to explain this in a proper way?

Maybe it’s a similar problem as why a liquid will keep on flowing if you create a low pressure in the end of a hose and if the end part of the hose is lower than the part sucking the liquid. Could anyone explain this?

RE: vaccum pumping+bernoulli's eq

That is called an ejector, but it is rather new for me that they are used in labs for evacuating chambers. Mostly, we use vacuum pumps.

The only and one physics law(or natural law rather) that can be applied here is that flow always occurs from high head(don't dilute this with pressure) to a low head region. The throat of the venturi (or the connecting point of horizontal and vertical bars of T) has the lowest head, lower than the chamber.

Please read the rules carefully. We generally don't discuss these kind of fundamentals.

RE: vaccum pumping+bernoulli's eq


Dramarc, quark's explanation is clear and sufficient. One of your examples is an eductor (=ejector) and the other is a siphon.

I reckon the following quote applies.
 

Quote:

It's elementary, my dear Watson.
Sherlock Holmes.

RE: vaccum pumping+bernoulli's eq

They're called aspirators...at least the ones that connect directly to lab faucets.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources