6. MIXING A radial flow impeller (disc turbine) is used for mixing glycerol and

Question

6. MIXING A radial flow impeller (disc turbine) is used for mixing glycerol and water with the final mixture volume of 3000 L Find the diameter and height of the tank. For the glycerol-water mixture containing 20 wt% b) Calculate the power and mixing time needed if a) PropertyUnit Species i water glycerol glycerol at 20 °C: kg im1000 1260 the mixing rate is 240 rpm. H4 CP As an alternative for this single mixing tank, 3 mixers with the same volume of 1000 L are suggested. c) By keeping the power per volume same as in "b)" estimate the dimension, power and mixing time and energy needed for mixing and discuss the results

Explanation / Answer

SOLUTION:

(a) Volume of the tank = 3000 L = 3000 m^3

Also, [V=pi r^2h]

For ideal radial flow impeller, D/H = 1/3 or H=3D

so, 3.14*(D/2)^2*3D = 3000

Diameter, D = 10.84 m

and Height, H = 3*10.84 = 32.52 m

(b) Power is given by,

[P=k ho n^3D^5]

For radial flow impeller(turbine), k = 4.80

1 RPM = 0.0167 rev/sec => 240 rpm = 4 rev/sec

So, P = 4.80*(0.2*1260+0.8*1000)*4^3*10.84^5

= 4.837*10^10 W

Mixing time, [t_{m}=1.54V/N*D]

= 1.54*3000/4*10.84

= 106.55 sec

(c) Power per volume is same.

So, 3*4.837*10^10/1000 = 4.80*(0.2*1260+0.8*1000)*4^3*D^5

So, Diameter, D = 3.392 m

Height, H = 3*3.392 = 10.176m

Power, P = 3*4.837/1000 = 1.451*10^8 W

Mixing time, 1.54*3*1000/4*3.392 = 340.51 sec

Energy required = Power*time = 1.451*10^8*340.51 = 4.941*10^10 J

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