Bubbles in water, need a method/equations

  • Context: Undergrad 
  • Thread starter Thread starter NCStarGazer
  • Start date Start date
  • Tags Tags
    Bubbles Water
Click For Summary

Discussion Overview

The discussion revolves around the dynamics of gas bubbles rising through water from a variable depth, specifically focusing on the factors that influence their speed and acceleration. Participants explore theoretical approaches, relevant equations, and the impact of different gases and conditions on bubble behavior.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant seeks a general guideline for calculating the time it takes for gas bubbles to travel to the surface from different depths, emphasizing the need for equations that account for various factors such as liquid density and gas type.
  • Another participant suggests that the speed of the bubbles may primarily depend on density, proposing that the relationship between bubble speed and fluid density should be explored, particularly with temperature variations.
  • A different viewpoint introduces the concept of Stokes flow for small, nearly spherical bubbles, indicating that the forces acting on the bubbles can be analyzed using Newton's second law, considering buoyancy and drag forces.
  • One participant discusses the effect of pressure on bubble volume at depth, noting that as bubbles rise, they expand due to decreasing pressure, which could influence their ascent speed. They mention the relevance of adiabatic and ideal gas laws in this context.

Areas of Agreement / Disagreement

The discussion contains multiple competing views regarding the factors influencing bubble dynamics, and no consensus has been reached on a definitive method or equation for calculating bubble ascent speed.

Contextual Notes

Participants acknowledge various assumptions, such as the effects of temperature on fluid density and the conditions under which Stokes flow applies. There are also references to the complexities of gas expansion and pressure changes that may not be fully resolved.

NCStarGazer
Messages
7
Reaction score
0
I have a need to know how fast gas bubbles will travel from a variable depth in a liquid to the surface. I realize there are a lot of variables here, liquid density, gas density, temp. etc... What I need is a general guideline for calculating the time with different gases through a homogenesis liquid. Any direction to a good article / study or equations is appreciated. Bottom line is probably stated as needing to know the rate of acceleration of a gas in a liquid to the surface, it will be important to be able to calculate the max velocity of the gas too. Example, if I had oxygen at 100 m under water and Helium 100 m under water at what rate will oxygen accelerate to the surface compared to Helium.

Thanks!
 
Physics news on Phys.org
I'm not an expert in fluid dynamics, but it makes sense to me that your bubbles' speeds should only be a function of density. And if the density of fluids changes minimally with respect to temperature, you would need a function of density with the variable temperature.

I'm also not sure about this, but how quickly a bubble rises might be equivalent to how quickly water would fall in air but reversed. so if water falls in air at say 9.6 m/s^2, maybe air rises in water at that same acceleration
 
You may be able to use Stokes flow, if the bubble is small enough to be nearly spherical. Then, the idea is simply F = ma, with the total force being a sum of buoyancy and drag forces.

http://en.wikipedia.org/wiki/Stokes'_law
 
Given the bubbles are placed in the water at depth, i think you mentioned 100 M, they will start with a volume based on the pressure at this depth. I think one foot of depth is around .433 pounds for water, so 100 feet would be 43.3 psi and 300 feet (100 meter) 129.3 psi. The original pressure being 14.7 psi. the new pressure being 129.3 psi the volume at the top of water column will be 129.3/14.7 x (original volume of bubble). So its going to float faster as it expands up. That was a temperature constant observation, if the gas is allowed to expand rapidly the internal temperature of gas will drop retarding the volume expansion; less volume means less speed floating. Check out adiabatic gas laws and ideal gas laws.
 

Similar threads

  • · Replies 8 ·
Replies
8
Views
2K
  • · Replies 41 ·
2
Replies
41
Views
7K
  • · Replies 4 ·
Replies
4
Views
3K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 12 ·
Replies
12
Views
7K
Replies
9
Views
2K
  • · Replies 13 ·
Replies
13
Views
2K
  • · Replies 12 ·
Replies
12
Views
18K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K