Is it possible to increase fluid pressure by blowing air through a straw?

[BWElbert]

Hello everyone, this actually happens to be my first post on PF. So, this question is a rather basic one, however the conversion between theoretical and experimental is not going so well. So, here is the initial question/dilemma:

Is it possible to blow across the top of a straw so fast that the fluid inside rises up and follows the path of your exhalation? If not, at what velocity does the air have to flow in order to decrease the pressure enough to allow the fluid to rise up and out of the straw?

Well then, that is the problem and I have been occasionally dabbling back into the problem (last summer I spent two weeks developing ways to provide solutions to this problem and how to compare this to what the max velocity of human exhalation may be), but recently it has been brought back up by my roommate. I am going to rework some equations, but I was curious if anyone had any suggestions for ways to experiment using an air compressor and how to convert gauge PSI to velocity.

Hopefully, one of you have tackled a similar or the same problem and can lend some help either in ideas or new looks at it, or even data that could help.

Thank you all very much, and if you would like I can post some of my equations and work up to now.

B.W. Elbert
Ohio University

 

[eljose79]

Dear B.W. Elbert,

Thank you for bringing up this interesting question on our forum. I am always fascinated by such curious inquiries and am happy to offer my insights on the matter.

Firstly, to answer your initial question, yes it is possible to blow across the top of a straw with enough force that the fluid inside rises up and follows the path of your exhalation. This phenomenon is known as the Bernoulli's principle, which states that as the velocity of a fluid increases, its pressure decreases. This decrease in pressure allows the fluid to rise up and out of the straw.

To determine the required velocity of air flow to achieve this, we can use the Bernoulli's equation, which relates the pressure, velocity, and height of a fluid. However, this equation is for idealized conditions and may not accurately represent real-world scenarios. That is why it is important to conduct experiments to validate our theoretical predictions.

One way to experimentally test this phenomenon is by using an air compressor and a pressure gauge. By adjusting the pressure and flow rate of the air, you can observe the behavior of the fluid inside the straw and determine the minimum velocity required to cause it to rise up.

Another approach could be to use high-speed cameras to record the behavior of the fluid inside the straw at different air flow velocities. This will provide visual evidence and allow for more accurate measurements.

In terms of converting gauge PSI to velocity, it is important to note that pressure and velocity are two different parameters and cannot be directly converted. However, you can use the Bernoulli's equation to determine the velocity based on the pressure and other relevant parameters.

I hope this helps in your experimentation and I look forward to seeing your findings. Best of luck!

 

[charng]

Hello B.W. Elbert,

Thank you for sharing your question and dilemma with us. It is a very interesting and relevant topic, especially for those studying fluid mechanics.

To answer your initial question, yes, it is possible to increase fluid pressure by blowing air through a straw. This is due to the Bernoulli's principle, which states that as the velocity of a fluid increases, its pressure decreases. When you blow air through a straw, the air molecules are moving faster and therefore exerting less pressure on the fluid inside the straw. This decrease in pressure allows the fluid to rise up and follow the path of your exhalation.

The velocity at which the air needs to flow to decrease the pressure enough for the fluid to rise up and out of the straw will depend on factors such as the diameter of the straw, the density of the fluid, and the atmospheric pressure. It would be best to experiment and gather data to determine the exact velocity needed in your specific case.

As for your experimentation, using an air compressor to control the velocity of the air and a pressure gauge to measure the pressure would be a good approach. To convert gauge PSI to velocity, you can use the equation v = √(2(P1 - P2)/ρ), where v is the velocity, P1 is the initial pressure, P2 is the final pressure, and ρ is the density of the fluid.

I hope this helps and good luck with your experiments! If you have any further questions or would like to discuss your equations and work, please feel free to post them here. Best of luck in your research.