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Author Topic: Why does dust settle yet smoke rises?  (Read 2246 times)

Offline Thebox

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Why does dust settle yet smoke rises?
« on: 31/12/2015 07:06:57 »
Smoke and dust, smoke always seem's to rise, a denser substance than air that should be less buoyant than air, dust always seem's to settle, what goes up generally falls back down unless there is something happening with the something.
So in dust and smoke there is an answer, but what is the question?
« Last Edit: 31/12/2015 08:41:36 by chris »


 

Offline Ophiolite

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What are the effects of density, size, geometry and surface area on settling rates of small particles in a gaseous medium?
 
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Offline Thebox

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What are the effects of density, size, geometry and surface area on settling rates of small particles in a gaseous medium?

What are the effects of gravity on small particles, when energy states are difference of the small particles,  different density, size, geometry and surface area   in a gaseous medium in which the mediums entropy of energy is variable to climate conditions?
« Last Edit: 31/12/2015 07:59:23 by Thebox »
 

Offline evan_au

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Re: Why does dust settle yet smoke rises?
« Reply #3 on: 31/12/2015 12:41:06 »
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Why does dust settle yet smoke rises?
Brownian motion causes small particles to be suspended in the air longer than large particles, all other things being the same.
- Combustion is a continual new source of very fine particles
- Very fine particles of dust blew away long ago, leaving only the coarser grains behind.

One thing that is different between smoke and dust is Density:
- Dust is picked up from the ground by moving air that is at air temperature.
- Air+dust is denser than air, and will start to settle out immediately
- Smoke is picked up from a fire by hot gases of combustion, at well above air temperature
- Smoke+combustion gases is lighter than air, and will not start to settle out until the temperature drops to around air temperature.
- If the air is not moving fast enough, it doesn't pick up any dust.
- If the air is not moving, smoke still rises.
 
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Offline RD

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Re: Why does dust settle yet smoke rises?
« Reply #4 on: 31/12/2015 12:45:09 »
Smoke and dust, smoke always seem's to rise, a denser substance than air that should be less buoyant than air ...

Smoke from the fire rises out of the chimney because the air it's in is hot , (from the fire). Hot-air is less dense than cooler air , (cf. hot-air balloon ).

The particles of smoke & dust "fallout" once the air cools down ...

http://www.manchestereveningnews.co.uk/news/manchesters-dark-history-archive-pictures-8722223
« Last Edit: 31/12/2015 12:46:58 by RD »
 

Offline vhfpmr

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Re: Why does dust settle yet smoke rises?
« Reply #5 on: 31/12/2015 13:07:48 »
Gravity causes hot air to rise because it's less dense than cold air, and gravity causes smoke to fall because it's more dense than air. If the hot air is rising faster than smoke particles fall, then the net direction of travel of the smoke is upwards.

The same applies to clouds, water droplets are heavier than air, but they're carried up by rising currents of warm air. The ability of the air to carry particles depends on wind resistance, which depends on cross sectional area, but as the mass goes up with the cube of the size and area by the square, larger particles are less able to be carried by the air than small ones. As the water droplets in a cloud coalesce and grow larger, the air becomes unable to support them and they fall as rain. Similarly, large dust particles will settle out of suspension quicker than small smoke particles.
 

Offline Thebox

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Re: Why does dust settle yet smoke rises?
« Reply #6 on: 01/01/2016 07:20:22 »
Gravity causes hot air to rise because it's less dense than cold air, and gravity causes smoke to fall because it's more dense than air. If the hot air is rising faster than smoke particles fall, then the net direction of travel of the smoke is upwards.

The same applies to clouds, water droplets are heavier than air, but they're carried up by rising currents of warm air. The ability of the air to carry particles depends on wind resistance, which depends on cross sectional area, but as the mass goes up with the cube of the size and area by the square, larger particles are less able to be carried by the air than small ones. As the water droplets in a cloud coalesce and grow larger, the air becomes unable to support them and they fall as rain. Similarly, large dust particles will settle out of suspension quicker than small smoke particles.


Interesting thoughts.

''gravity causes hot air to rise'' - gravity forces cold air to fall, it is more compressed and denser when cold, gravity does not cause hot air to rise, the ''hot'' forces air to rise and expand by molecule polarisation forcing opposing force.

Smoke also rises because it is ''hot''  , the ''charged'' gases and carbon etc of the burning fuel being ''convertual'' gravitational phase shifted to an opposite polarity.


This is what I observe, does nobody else observe this happens?


Dust also settle on vertical surfaces such has a television set by electrostatics, the dust defies gravity holding fixed to the mass of the television, does anybody also observe this?
 

Offline Thebox

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Re: Why does dust settle yet smoke rises?
« Reply #7 on: 01/01/2016 07:28:49 »
Quote
Why does dust settle yet smoke rises?
Brownian motion causes small particles to be suspended in the air longer than large particles, all other things being the same.
- Combustion is a continual new source of very fine particles
- Very fine particles of dust blew away long ago, leaving only the coarser grains behind.

One thing that is different between smoke and dust is Density:
- Dust is picked up from the ground by moving air that is at air temperature.
- Air+dust is denser than air, and will start to settle out immediately
- Smoke is picked up from a fire by hot gases of combustion, at well above air temperature
- Smoke+combustion gases is lighter than air, and will not start to settle out until the temperature drops to around air temperature.
- If the air is not moving fast enough, it doesn't pick up any dust.
- If the air is not moving, smoke still rises.

''Brownian motion of a big particle (dust particle) that collides with a large set of smaller particles (molecules of a gas) which move with different velocities in different random directions.''


Ke turns into heat?
 

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Re: Why does dust settle yet smoke rises?
« Reply #7 on: 01/01/2016 07:28:49 »

 

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