What is the air velocity from a tyre pumped to 200 kPa?

Click For Summary

Discussion Overview

The discussion revolves around calculating the velocity of air exiting a tyre valve when the tyre is inflated to a pressure of 200 kPa. Participants explore various equations and assumptions related to fluid dynamics, particularly focusing on the Bernoulli equation and flow conditions.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant asks for the velocity of air from a tyre valve at 200 kPa and inquires about the relevant equations.
  • Another participant suggests using the Bernoulli equation for the calculation.
  • There is a mention of incompressible flow, with some participants debating the applicability of the Bernoulli equation under this assumption.
  • One participant asserts that the flow will be choked at the valve and proposes plotting density over time to calculate mass flow based on the valve's flow area.
  • Another participant challenges the choking flow assumption, noting that 200 kPa (29 psi) is not near the choking pressure, which they recall to be around 65 psi.
  • A participant introduces a related question about the velocity at which the tyre would be propelled forward, suggesting that the mass of escaping air would affect the tyre's motion and eventually lead to a stop.

Areas of Agreement / Disagreement

Participants express differing views on the applicability of the Bernoulli equation and the choking flow condition, indicating that multiple competing perspectives remain unresolved.

Contextual Notes

There are assumptions regarding flow conditions, such as incompressibility and choking flow, that are not fully explored or agreed upon. The discussion also includes varying interpretations of pressure effects on flow dynamics.

Paul245
Messages
13
Reaction score
0
Can anyone tell me what the velocity of air coming out a valve of a tyre pumped to 200 kPa would be?

What equations to you use?
 
Physics news on Phys.org
Bernoulli equation...
 
incompressable flow
 
What do you mean? The bernoulli equation can always be applied.. (i'm not talking about the "original" bernoulli equation proposed by bernoulli but the general one where we don't integrate the pressure function at once..)
 
I think that was Bernoulli with the incompressible flow assumption...
 
The flow will certainly be choked at the valve. All you need to do is plot the density as a function of time and find the flow area of the valve and you can calculate the mass flow.
 
200 kpa is 29 psi, isn't it? So it isn't anywhere near choked flow, which, iirc, is somwhere around 65 psi.
 
Can i twist this a bit and ask this question

At what velocity what the tyre be propelled forward, what would be the limiting conditions

Till what time would this actually keep moving.

My guess: (i am still working on the math)

At some bore radius where the force is large enough to push the tyre along.

So as the tyre keeps moving its mass decreases(air is escaping) and at some point the mass going out(change in mass) would equal the pressure(now decreasing)

At that point the tyre would stop, am i right here
 
russ_watters said:
200 kpa is 29 psi, isn't it? So it isn't anywhere near choked flow, which, iirc, is somwhere around 65 psi.
I suppose I should have paid attention to the pressures. Whoops.
 

Similar threads

Undergrad Can I suck myself forward with a straw when floating in air?
  • · Replies 19 ·
Replies
19
Views
2K
Undergrad Lift Force of a Rotating Sphere in the Air
  • · Replies 7 ·
Replies
7
Views
3K
Graduate How does a 1-wheeled motorcycle turn?
  • · Replies 16 ·
Replies
16
Views
3K
Undergrad Drag equation - relative flow velocity
  • · Replies 11 ·
Replies
11
Views
4K
Undergrad In a closed loop system with a pump, how can we control the pressure?
  • · Replies 26 ·
Replies
26
Views
8K
Undergrad Dynamics of pumping fluid into a cylinder with an air hole?
  • · Replies 4 ·
Replies
4
Views
2K
Undergrad Does a rotating accelerometer moving linearly measure linear velocity?
  • · Replies 47 ·
2
Replies
47
Views
5K
High School Problems with modelling the vertical motion of a dust particle
  • · Replies 15 ·
Replies
15
Views
1K
How to determine air velocity in open ended tube?
  • · Replies 9 ·
Replies
9
Views
2K
High School Time to fall from 200 miles
  • · Replies 8 ·
Replies
8
Views
2K