1. What is the settling velocity in still air of a particle that is 40 µm in diameter and spherical? The particle has a density of 1400 Kg/m3. Use a density of 1.2 Kg/m3 and a viscosity of 10-5 Kg/m-sec for the air. (g = 9.8 m/sec2)
2. Pulverized coal (density = 980 kg/m3) is to be pneumatically conveyed from a storage bin to the burner of a power boiler. 10000 kg/hr of coal is to be fed to the burner. It is to be delivered to the burner at 2 bar through a 10 cm diameter pipe. If the maximum allowable pressure at the inlet of the pipe is 6 bar and the pipe is 35 m long, can the required flow of coal be delivered? The solids velocity is 6 m/s, and the gas velocity is 10 m/s. The measured terminal velocity of the coal dust is 1.65 m/s. Due to the short pipe length, it can be assumed that the pressure drop in the pipe is completely caused by friction between the solid and the pipe wall. The pipe is horizontal, and there are no bends. The solid/wall friction factor is given as:
3. The sphericity of a particle is defined as the ratio of the surface area of a sphere having the same volume as the particle to the surface area of the particle. What is the sphericity of a particle shaped as a cone having a base radius of 1 mm, and a height of 1 mm? Relations for cone volume and surface area are easily obtainable through a web search.
4. A packed bed reactor is 2 m in diameter with a packed height of 5 m. The catalyst pellets used are spheres 1 mm in diameter with a density of 2250 kg/m3. The reactor is to process 6 kg/s of a gaseous reactant stream with viscosity 2.5 x 10-5 kg/m-s and density 2 kg/m3. The void fraction is 0.4. What will be the pressure loss through the bed?
5. If the catalyst pellets of the previous problem are to be fluidized with the same gas, and the gas superficial velocity is to be 1.5 times the minimum fluidization velocity, what bed diameter would be needed to process 6 kg/s of gas?
6. In the production of a dye, batches of product slurry are filtered at a constant differential pressure of 300 kPa. This filtration takes 3 hours per batch
and 15 m3 of filtrate are collected. If the amount of filtrate collected per batch is to be 30 m3, but the batch time is to remain at 3 hours, what differential pressure would-be-required -to-use-the-same-filter? The resistanee-ofThealter medium is equivalent to 10 m3 of filtrate.
7. The following table contains particle separation data for an impingement device that separates particles from gas streams. The table shows the amount of material removed in each size range for a test operation.
(a) What is the total separation efficiency of this device?
(b) If the feed to this device is changed to contain a greater percentage of particles smaller than 100 pm in size, would you expect the total efficiency to increase, decrease, or remain constant?
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Size Range
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Feed
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Coarse Particles
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Fine Particles
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|
μm
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Kg/hr
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Kg/hr
|
Kg/hr
|
|
160 - 180
|
5
|
5
|
0
|
|
140 - 160
|
10
|
10
|
0
|
|
120 - 140
|
10
|
9
|
1
|
|
100 - 120
|
20
|
16
|
4
|
|
80 - 100
|
15
|
4
|
11
|
|
60 - 80
|
15
|
2
|
13
|
|
40 - 60
|
10
|
0
|
10
|
|
<40
|
15
|
0
|
15
|