Pneumatic System - Air flow

In summary, the conversation discusses the need for a formula to find the air velocity at the end of a nozzle in a piston-cylinder system, similar to a bicycle pump. The use of Bernoulli's principle is deemed ineffective due to dealing with compressible flow and uncertainty about pressure buildup. The unsteady flow equation is considered but not fully understood. A link is shared for modeling as a tire pump, although the goal is to pump air into the environment rather than a tire. The speaker asks for help from someone with more insight on fluid dynamics.
  • #1
scientist0523
4
0
Hi,

This is not homework, it's for myself. I'm trying to understand it for me only.

I have a piston that is translating in a cylinder and pushing/sucking air through a nozzle.
It's much comparable to a bicycle pump.
The piston is moving with non-linear (exponential) velocity until it slams against the cylinder wall.

I need a formula to find the air velocity at the end of the nozzle in function of time.

I have tried using Bernoulli's principle, but it does not apply because we are dealing with a compressible flow. And I'm not sure how pressure builds up, as the airflow through the nozzle 'negates' the pressure buildup
Also the volume and position (even velocity?) of the air particles in the cylinder change in time, so that means it's an unsteady flow?
I have looked at the unsteady flow equation but I can't seem to understand it either.

Help is appreciated.
 
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  • #3
Thank you very much for this link!
I knew it wasn't easy, but this will help me a lot.

EDIT: as useful as it may be, I'm not looking to pump the air into a tire, but to pump it in the environment with P=atm and so no pressure builds up as it's volume is infinitely big.
 
Last edited:
  • #4
Anyone with more insight of fluid dynamics?
 
  • #5


Hi there,

Thank you for reaching out for help with your understanding of pneumatic systems and air flow. I am happy to provide some guidance and information to help you better understand this topic.

Firstly, it is important to understand that pneumatic systems use compressed air to power mechanical movements, such as in the case of your piston and cylinder system. The movement of the piston creates changes in air pressure and flow, which can be harnessed to perform work.

In order to determine the air velocity at the end of the nozzle in function of time, you will need to consider a few factors. These include the initial conditions (such as the air pressure and flow rate at the start of the system), the geometry of the nozzle, and the properties of the air itself (such as its density and viscosity).

As you mentioned, Bernoulli's principle may not be applicable in this case as it assumes incompressible flow, whereas in pneumatic systems we are dealing with compressible flow. Instead, you may want to consider using the continuity equation and the conservation of energy equation to determine the air velocity at the nozzle exit.

The continuity equation states that the mass flow rate at any point in the system must remain constant, meaning that the product of the air density, velocity, and cross-sectional area must remain constant. This can help you determine the air velocity at the nozzle exit based on the initial conditions and geometry of the system.

The conservation of energy equation, also known as the Bernoulli equation for compressible flow, can help you determine the pressure and velocity changes along the length of the nozzle. This equation takes into account the changes in kinetic energy, potential energy, and internal energy of the air as it flows through the system.

As for the unsteady flow, you are correct in thinking that the volume and position of the air particles in the cylinder will change over time. This means that the flow is unsteady, and the equations used to analyze it are more complex. However, for a simple pneumatic system like the one you described, you may be able to make some simplifying assumptions to make the equations more manageable.

I hope this information helps you in your understanding of pneumatic systems and air flow. If you have any further questions, please don't hesitate to reach out. Best of luck with your studies!
 

1. What is a pneumatic system and how does it work?

A pneumatic system is a type of machinery that uses compressed air or gas to transmit and control energy. It works by using a compressor to compress air into a storage tank, and then releasing the compressed air through valves and actuators to power various mechanical components.

2. What are the benefits of using a pneumatic system?

There are several benefits to using a pneumatic system, including:

  • Low cost - air is a readily available and inexpensive resource
  • Ease of use - pneumatic systems are simple and require minimal training
  • Low maintenance - air is clean and does not require filtration or lubrication
  • Safe - air is non-toxic and non-flammable
  • High power-to-weight ratio - pneumatic systems can generate a lot of force without being heavy or bulky

3. How is air flow controlled in a pneumatic system?

Air flow in a pneumatic system is controlled through the use of valves. These valves can either be manually operated or automatically controlled by sensors and other devices. By controlling the opening and closing of valves, the amount and direction of air flow can be regulated to power different components of the system.

4. What are some common applications of pneumatic systems?

Pneumatic systems are used in a wide range of industries and applications, including:

  • Manufacturing - such as assembly lines and material handling
  • Transportation - including heavy machinery and vehicles
  • Construction - for powering tools and equipment
  • Medical - for tools and equipment used in surgeries and procedures
  • Aerospace - for flight control systems and landing gear

5. How can air flow be measured in a pneumatic system?

There are several ways to measure air flow in a pneumatic system, including:

  • Flow meters - these devices measure the volume or mass of air passing through a specific point in the system
  • Pressure gauges - by measuring the pressure of the air, the flow rate can be calculated
  • Orifice plates - these plates create a restriction in the air flow, allowing for measurement of the pressure difference before and after the restriction
  • Rotameters - these devices use a floating ball or other indicator to visually show the rate of air flow

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