FILTRATION 1. Water is filtered through a sand bed 150 mm thick.The depth of water on top of the bed is 120 mm. the porosity is 0.4 and the mean particle diameter is 0.25 mm. The dynamic viscosity is 0.89 cP and the density is 998 kg/m3. Calculate the flow rate per square meter of area. a. b. c. d. 2.72 x 10-2 m3/s 0.543 x 10-3 m3/s 15.50 m/s 0.543 x 10-3 m/s for 2. (29.7) The following relation between α and superlight CaCO3 has been determined to be Where is in pounds for per square foot. This relation is followed over a pressure range from 0 to 1,000 lb/in2. A slurry of this material giving 3.0 lb of cake solid per cubic foot of filtrate is to be filtered at a constant pressure drop of 70 lbf/in2 and a temperature of 70°F. Experiments on this sludge and the filter cloth to be used gave a value of Rm= 1.2 x 1010 ft-1. A pressure filter of the tank type is to be used. How many square feet of filter surface are needed to give 1,400 gal of filtrate in a 1-h filtration? The viscosity is that of water at 70°F. a. b. c. d. 71.71 ft2 71.44 ft2 71.44 ft2 71.44 ft2 3. (29.8) The filter of Prob. 29.7 is washed at 70°F and 70 lbf/in2 with a volume of wash water equal to one-third that c. the rate of filtration follows the relation (v – filtrate volume. b.34 ft2 26. c. d. 2812. k and c – constants) ε = 0.40? . 29. d.775 hr 2798.12 s or 0.time.777 hr 4.73 ft2 5.7. How thick a layer of particles would be needed to account for the gel-layer resistance if a. The washing rate is 85 percent of the theoretical value.780 hr 2791. (29. d. Under the same conditions.1 atm. b. 483 ft2 34.21 s or 0.73 s or 0. The pressure drop is limited to a maximum of 50 lbf/in2. t. 6. b.of the filtrate. c.8 micrometer spherical particles has a permeate flux of 150 L/m2-h at 30°C and a pressure drop of 2. the pure water flux was 280 L/m2-h. How much filter area must be provded if the cycle time is 3 min and the drum submergence is 50 percent? a.40 s or 0.09 ft2 27. (29.17) A microfiltration unit is used to concentrate a suspension of 0. How long should it take to wash the cake? a. In constant pressure filtration.400 gal/h of filtrate from the slurry described in Prob.781 hr 2808.10) A continuous pressure filter is to yield 1. b. maximum optimum minimum and greater the zero zero . the filtration time will be reduced by a factor of: a. a. the solids concentration in the feed slurry is increased by evaporating half the solvent. c. c. To reduce the time of If the filtration. resistance decreases with time resistance increases with time rate of filtration increases with time rate of filtration decreases with time 9. A filtration is conducted at constant pressure to recover solids from the dilute slurry. resistance of the filter medium is negligible. d. d. b. c.a. In constant pressure filtration. the cake resistance is : a. 7. At the beginning of filtration. b. 1 2 4 8 8. d. c. d. b. If one quarter of the total value of Assume that the cake is the filtrate is collected during the constant rate period. 12. the time taken for the collection of 20 m3 of filter is __________ minutes and for the collection of 30 m3 is _______ minutes. 90 minutes. 10 minutes. 60 minutes. 270 minutes. respectively (proper use of solution) . is: a. 15 minutes. a. d. 600 minutes. 120 minutes. what is the total filtration time? negligible. a. d. The filter medium resistance of an old. respectively(V2/V1 is used) b. 55 minutes 60 minutes 50 minutes 57 minutes A vacuum leaf filter gives a total value of 10 m3 of If the resistance of the filter incompressible and the filter medium resistance is filtrate of 30 minutes. cloth is negligible. c. b. respectively ((V1/V2) squared is used) d. 300 minutes. used filter much smaller than that of a new filter much larger than that of a new filter equal to that of new filter infinitely large A filtration is carried out for 10 min at a constant rate in a leaf filter and thereafter it is continued at constant pressure which is attained at the end of the constant rate period. 11. respectively (V1 used is 1 cubicmeter) c. b. c.10. A is the filtration area. c.5 L of filtrates at a filtration pressure twice that is used in the test? a. and C is the concentration of solids in the feed slurry.3. Constant rate filtration.t=seconds) If the resistance of the filter medium is assumed unaffected with pressure drop and the compressibility coefficient of the filter cake is 0. a. 10 20 25 30 A centrifugal filtration unit at a rotational speed of ρL) located at a ω has inner surface of the liquid (density radial distance R from the axis of rotation.3V + 8. 15. Where V is the filtrate. what will be the time taken for the collection of 3. 55 s 58 s 50 s 53 s 14. Rmi assume incompressible cake. c.5 (V = liters. The thickness . μ is viscosity of the filtrate. In a 20 min.13. A constant pressure filtration test gave data that can fit an expression:dt/dv = 9. 5m3 of filtrate was obtained. d. b. b. d. how much more time in minutes will it take for another 5m3 of filtrate to be produced? Neglect filter medium resistance. If this is followed by a constant pressure filtration. The basic filtration equation is given as . α is specific cake resistance. d. 18. The initial pressure drop during filtration is__________. For laminar flow conditions. c. information on process conditions filtration in order to form ________________. and filter medium is necessary . b. c.of the liquid film is δand no cake s formed. the liquid fl. the relationship between the pressure (∆Pc) across an incompressible filter cake and the specific surface area (So) of the particles being filtered in given by ONE of the following: a. d. 16. b. (∆Pc)is proportional to (So) (∆Pc)is proportional to 1/(So) (∆Pc)is proportional to (So)2 (∆Pc)is proportional to 1/(So)2 Filter aids are added to the slurry prior to compact cakes of low porosity cakes of increased crystalline cakes none of the above In a filter bed. 17. a. a. b. a. d. b. c.ow is laminar is turbulent is between laminar and turbulent cannot be predicted. c. d. The rate of filtration in a rotary-drum filter increases with an increase in drum speed decreases with an increase in drum speed is independent of the drum speed increases with an increase in drum speed up to a certain critical value and thereafter. Discontinuous pressure filter Continuous vacuum filter Discontinuous vacuum filter none of the above The filter medium resistance usually is important only during the early stages of filtration only during the final stages of filtration all through the filtration process none of these. d. c. d. which filter do you recommend? a. a. b. a. b. In order to achieve rapid filtration of viscous liquids or slurries containing fine solids. a. c. d. b. b. 22. c. Which of the following statement is true about vacuum the solids in the slurry are very fine the liquid has a high vapour pressure the liquid has a low viscosity the liquid is a saturated solutions which will filtration is incorrect? crystallize on cooling 20. filtration rate no longer increases with drum speed . 21. c.19. d. 25. a. d.1 to 2 RPM 25 to 50 RPM 50 to 100 RPM 100 to 200 RPM filter is . 24.23. b. d. c. c. The flow of filtrate through cake deposited on septum is usually which equation will use to calculate pressure drop for this situation? a. b. a. d. b. Leva’s equation Kozeny-Carman equation Blake-Plummer equation Bernoulli’s equation A rotary drum filter is – Continuous Vacuum filter A Discontinuous Vacuum Filter A Continuous Pressure Filter None of the above The speed of rotation of an industry rotary – drum 0. c.