Can Brownian Motion Suspend Larger Particles in a Denser Fluid?

[Warpspeed13]

I was reading about ferrofluid and I was wondering how you would go about calculating the maximum size of a particle that could be suspended by Brownian motion in a fluid? Can a denser fluid suspend larger particles?

 

[mpelaez83]

The response is: kT>mgd, where kT is thermal energy, m the mass of the particle, g is gravity and s is the particle typical size. When thermal energy is smaller sedimentation will occur.

 

[Warpspeed13]

The response is: kT>mgd, where kT is thermal energy, m the mass of the particle, g is gravity and s is the particle typical size. When thermal energy is smaller sedimentation will occur.

Cool. How would the mass of the carrier fluid particles be accounted for? It seems mercury would be different than water.

 

[mpelaez83]

You actually account for that through viscosity in some way. The carrier fluid as you call it is accountef by a viscosity and a temperature, the system temperature

 

[mpelaez83]

These are deep questions people don't ask so there are a lot of reasonable misconceptions.

 

[Warpspeed13]

Cool thanks for the help

 

[Warpspeed13]

You actually account for that through viscosity in some way. The carrier fluid as you call it is accountef by a viscosity and a temperature, the system temperature

Sorry but what units were you're original equation in, I assumed it was jules> kg* 9.82* surface area in m^2

 

[mpelaez83]

g has units of m/s^2, d is in meters and m is in kg. Then you get joules.

 

[Warpspeed13]

g has units of m/s^2, d is in meters and m is in kg. Then you get joules.

Is kT the energy of one carrier fluid atom or the energy of the system?

 

[mpelaez83]

kT is the energy associated to one particle. When i say particle you can think on both the solvent molecules or the dispersed particles. The energy of a thermodynamic system it depends on and adittional thermodynamic variable, partiole number N. For example in an ideal gas the energy of the system is ~NkT

 

[Warpspeed13]

Cool thanks for the help

 

[mpelaez83]

No problems. Physics is cool.

 

[Warpspeed13]

Yep.