Tek-Tips is the largest IT community on the Internet today!
Members share and learn making Tek-Tips Forums the best source of peer-reviewed technical information on the Internet!
-
Congratulations LittleInch on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!
particle velocity calculation
- Thread starter newmem
- Start date
btrueblood
Mechanical
An air stream that is accelerating/decelerating or constant velocity?
In either case, find the drag coefficient (CD) for the particle, and compute the drag force from
D = CD*(rho)*(V2)/2, (see definition of terms below)
and use F=ma to calculate the acceleration of the particle. Integrate to find the particle trajectory (velocity, position). Plots for the CD of spheres, cylinders, and some other shapes are available in published books on fluid dynamics. Most correlate the data to a parameter called the Reynold's number, which is typically (rho)*(V)*D/(mu), where rho is the fluid density, V the fluid velocity relative to the object, D is a characteristic dimension (like the diameter of a sphere), and mu is the dynamic viscosity of the fluid.
If the particles are very small, and the fluid not changing speed too rapidly, the particle velocity will be very close to the fluid speed (thus the principle of laser doppler velocimetry for experimentally measuring fluid velocities).
In either case, find the drag coefficient (CD) for the particle, and compute the drag force from
D = CD*(rho)*(V2)/2, (see definition of terms below)
and use F=ma to calculate the acceleration of the particle. Integrate to find the particle trajectory (velocity, position). Plots for the CD of spheres, cylinders, and some other shapes are available in published books on fluid dynamics. Most correlate the data to a parameter called the Reynold's number, which is typically (rho)*(V)*D/(mu), where rho is the fluid density, V the fluid velocity relative to the object, D is a characteristic dimension (like the diameter of a sphere), and mu is the dynamic viscosity of the fluid.
If the particles are very small, and the fluid not changing speed too rapidly, the particle velocity will be very close to the fluid speed (thus the principle of laser doppler velocimetry for experimentally measuring fluid velocities).
In still air, when the gravitational force equals the drag force one gets what is called the terminal velocity which is related to the Reynolds number (Re).
When the Re<10-5, "slip" between the gas molecules gives increased sedimentation rates and the mean free path of the molecules ([λ]) is used to estimate the terminal velocity.
The movement of particles of diameter less than 0.1[μ]m is dominated by Brownian motion, i.e. irregular movement due to impact with the fluid molecules.
If you are after fluidization velocities for small particles where sedimentation velocity depends on viscous forces, the Kozeny-Carman equation gives an estimate of the minimum fluidization velocity.
For pneumatic conveying used for granular and powder materials such as flour, seeds, grain, alumina, cement, and catalysts one may refer to the literature. For example:
Gluck, S.E.: Design tips for pneumatic conveyors Hydrocarbon Processing, 47 (Oct. 1958).
Gerchow, F.J.: How to select a pneumatic conveying system, Chem. Eng., Feb. 17, 72-86 (1975).
Gerchow, F.J.: Specifying components of pneumatic-conveying systems, Chem. Eng., March31, 88-96 (1975).
When the Re<10-5, "slip" between the gas molecules gives increased sedimentation rates and the mean free path of the molecules ([λ]) is used to estimate the terminal velocity.
The movement of particles of diameter less than 0.1[μ]m is dominated by Brownian motion, i.e. irregular movement due to impact with the fluid molecules.
If you are after fluidization velocities for small particles where sedimentation velocity depends on viscous forces, the Kozeny-Carman equation gives an estimate of the minimum fluidization velocity.
For pneumatic conveying used for granular and powder materials such as flour, seeds, grain, alumina, cement, and catalysts one may refer to the literature. For example:
Gluck, S.E.: Design tips for pneumatic conveyors Hydrocarbon Processing, 47 (Oct. 1958).
Gerchow, F.J.: How to select a pneumatic conveying system, Chem. Eng., Feb. 17, 72-86 (1975).
Gerchow, F.J.: Specifying components of pneumatic-conveying systems, Chem. Eng., March31, 88-96 (1975).
- Thread starter
- #4
The particles (in the order of a 30-100 micrometers) are introduced into a stream of high pressure air flowing through a tube. Does the velocity calculation using drag forces still hold good?
Is there any way to relate pressure of the air to its velocity?
Is there any way to relate pressure of the air to its velocity?
- Status
Similar threads
- Question
- Question
