MOMENTUM TRANSFER September 21, 2015FLOW OF SOLIDS IN LIQUIDS AND AGITATION

FREE SETTLING1. The Reynold’s number of a cylindrical settling through a liquid is 1.0. The estimated drag coefficient

of cylinder isA. 10 B. 3.0 C. 20 D. 1.0

2. What will be the terminal falling velocity of a particle diameter 10 microns and of density 1600 kg/m3 settling in a liquid of density 1000 kg/m3 and viscosity 0.001 Pa-s?

A. 0.033 mm/s B. 0.00005 mm/s C. 1.25 mm/s D. 154 mm/s3. From the data in problem 2, if Stokes law applies for particle Reynold’s number up to 0.2, what is

the diameter of the largest particle whose behavior is governed by Stokes’ law for this solid and liquid?

A. 10 microns B. 85 microns C. 380 microns D. 540 microns

4. Drops of oil 15 microns in diameter are to be settled from their mixture with air. The specific gravity of the oil is 0.90, and the air is at 70°F and 1 atm and a settling time of 1 min is available. How high should the chamber be to allow settling of these particles?

A. 1.2 ft B. 1.5 ft C. 2 ft D. 2.4 ft5. What is the mass of a sphere of material of density 7500 kg/m3 whose terminal velocity in a large

deep tank of water is 0.6 m/s?A. 0.000054 g B. 0.029 g C. 5.4 g D. 29.0 g

HINDERED SETTLING6. Solid spherical particles having a diameter of 0.09 mm and a solid density 2, 002 kg/m3 are settling

in a solution of water at 26.7°C. The volume fraction of the solids in the water is 0.45. The settling velocity is

A. 3.3 x 10-5 m/s B. 3.269 x 10-3 m/s C. 2.369 x 10-4 m/s D. 3 x 10-2 m/s7. A glass sphere having a diameter of 1.554 x 10-4 m in H2O at 293.2 K and the slurry contains 60 wt

% solids. The density of the glass spheres is 2467 kg/m3. The settling velocity of glass sphere in m/s is

A. 3.05 x 10-2 B. 0.265 C. 1.525 x 10-3 D. 5.125 x 10-4

AGITATION8. It is desired to agitate a liquid having a viscosity of 1.5 x 10-3 Pa-s and a density of 969 kg/m3 in a

tank having a diameter of 0.91 m. The agitator will be a six blade open turbine having a diameter of 0.305 m operating at 180 rpm. The tank has four vertical baffles each with a width of 0.076 m. Also, W=0.0381 m. Calculate the required kW.

A. 0.120 B. 0.142 C. 0.172 D. 0.190

BRINGHOME EXAM:1. What will be the terminal falling velocity of glass sphere 1 mm in diameter in water if the density of

glass is 2500 kg/m3?A. 0.000145 m/s B. 0.00145 m/s C. 0.145 m/s D. 1.45 m/s

2. What is the mass of sphere of density 7500 kg/m3 which has a terminal velocity of 0.7 m/s in a large tank of water?

A. 0.066 g B. 4.22 g C. 0.00078 g D. 1.28 g3. Calculate the terminal settling velocity of dust particles having a diameter 30μm falling through air

at 1bar and 240 K. The density of the dust particles is 1280 kg/m3.A. 0.0432 m/s B. 0.0132 m/s C. 0.0248 m/s D. 0.0358 m/s

4. An agitation vessel is equipped with a turbine impeller having a diameter of 30 cm. If water (density=1000 kg/m3; viscosity=1 E-3 Pa-s) is agitated in this tank at an impeller speed of 100 rpm, what would be the Reynold’s number of the agitated water?

A. 150, 000 B. 700, 000 C. 650, 000 D. 600, 0005. An oil water separator for coconut oil mill is being designed by the plant’s chemical engineer to

remove coconut oil from the mill’s effluent water. Experiments have shown that with the specific gravity differential between the coconut oil and water the rising velocity of the coconut oil globules in water is 0.0945 m/min. Practice has shown that for the separator to be effective the following parameters hold: water velocity along the separator=0.91 m/min; depth of water in separator=0.3

times the width of separator. If 230 cubic meters of effluent water is to be handled per hour, the length of the separator in meters is

A. 11 m B. 15 m C. 9 m D. 1.125 m