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Previous Year Exam Questions of Mass Transfer-I of BPUT - MT1 by Verified Writer

  • Mass Transfer-I - MT1
  • 2017
  • PYQ
  • Biju Patnaik University of Technology Rourkela Odisha - BPUT
  • Chemical Engineering
  • B.Tech
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Registration No. Total number of pages: 03 B.Tech. PCE3I104 3rd Semester Regular/Back Examination 2017-18 MASS TRANSFER - I BRANCH : CHEM, PT Time : 3 Hours Max Marks : 100 Q.CODE : B1192 Answer Question No.1 and 2 which are compulsory and any four from the rest. The figures in the right hand margin indicate marks. Assume suitable notations and any missing data wherever necessary. Use of Humidity Chart is permitted. Answer all parts of a question at a place. 1. (a) (b) (c) (d) (e) (f) (g) Answer the following questions : Which of the following solutes has the highest diffusivity in water ? i. tert-butanol ii. iso-propanol iii. methanol iv. none of these The breathing process within the lungs involves: i. diffusion of A through non-diffusing B ii. equimolar counter diffusion iii. multicomponent non-equimolar counter diffusion iv. none of these The optimum ratio of the actual liquid rate to the minimum liquid rate for gas absorption generally lies between: i. 0.0 and 1.0 ii. 0.5 and 1.5 iii. 1.2 and 2.0 iv. none of these With the increase of liquid viscosity, the tray efficiency generally: i. increases ii. decreases iii. remains unchanged iv. increases then decreases Which of the following quantities is appreciably dependent on the solubility of a gas in the solvent ? i. HTU ii. NTU iii. Specific interfacial area iv. All of these The relative volatility of A in a mixture of A and B is 1.5. What is the mole fraction of B in the first droplet condensed from an equimolar saturated vapour mixture of A and B ? i. 0.4 ii. 0.5 iii. 0.6 iv. none of these For decolourization/deodorization of vegetable oils which method is preferred? i. batch distillation ii. steam distillation iii. flash distillation iv. none of these (2x10)

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(h) (i) (j) 2. (a) (b) (c) (d) (e) (f) (g) (h) (i) (j) 3. (a) (b) 4. (a) (b) The q values for a feed of saturated liquid and saturated vapour are: i. > 1 and < 1 ii. = 1 and < 1 iii. = 0 and = 1 iv. = 1 and = 0 Which type of tower is most favoured in the chemical process industries ? i. Induced draft tower ii. Hyperbolic tower iii. Spray tower without a fill iv. none of these What is the maximum possible humidity of air at 300C and 1.3 atm pressure in kg/kg dry air? i. 0.042 ii. 0.009 iii. 0.0207 iv. None of these Answer the following questions : Under what conditions are the mass average velocity and the molar average velocity of the components of a mixture equal ? How does the binary gas-phase diffusivity depend upon the total pressure and temperature ? Mention the physical significance of HTU and NTU. What do you understand by absorption and stripping factors ? Which solventsare recommended for drying of air in a H2SO4 plant and drying of natural gas ? What are the important factors that determine the selection of a batch distillation column for the separation of a liquid mixture ? What happens if a distillation column heated by open steam is operated at total reflux for a long time ? Discuss about optimum reflux ratio in distillation. What are the important factors that influence the design and operation of a cooling tower ? What are the common packings and materials for a cooling tower ? (2x10) Derive the Stefan’s method for the determination of diffusivity with a neat sketch. A tube of small diameter was filled with acetone (ρ = 0.80 gm/cm3) upto 1.15 cm from top and maintained at a temperature of 200C in a gentle current of air. After 6 hours the level of liquid fell to 2.25 cm from the top. Calculate the diffusivity of acetone in air if the barometric pressure was 750 mm Hg. Vapour pressure of acetone at 200C is 180 mm Hg. R = 82.06 cm3.atm/gmol.K. (7) In a chemical plant, a gas containing 4 % cyclo-hexane and 96 % inerts has to be treated with a non-volatile absorption oil in a packed tower. It is required to remove 98 % of the cyclo-hexane of the feed gas. The feed solvent is free from cyclo-hexane. If the feed gas rate is 80 kmol /hr, calculate the minimum solvent rate. The equilibrium relation is given by: Y = 0.2 X / (1 + 0.8 X) Discuss in detail about the minimum liquid rate for absorption with suitable diagrams. (7) (8) (8)

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5. 6. (a) (b) 7. 8. (a) (b) 9. (a) (b) (c) A gas mixture containing 12mol % SO2 and88mol % air at 1 atmtotal pressure and 300C is to be scrubbed with water to remove 95 % of the SO2 in a tower packed with 30 mm ceramic rings. The feed gas rate is 1400 kg/hr. Calculate: i. The minimum liquid rate and ii. The tower diameter if the liquid rate is 1.2 times the minimum and the tower operates at 75 % of the flooding velocity. For the calculation of the tower diameter, the liquid may be assumed to have properties like water. The equilibrium data for SO2-water system in mole fraction unit (300C and 1 atm total pressure) are: 104x 0 0.56 1.40 2.8 4.22 8.42 14.0 19.6 27.9 2 3 3 5 103y 0 0.79 2.23 6.19 10.6 25.9 47.3 68.5 104 0 5 (15) A charge of 60 kmol of a mixture of benzene and chlorobenzene having 50mol % of the less volatile is to be batch-distilled. If 30 moles of the solution is vaporized and condensed as the distillate, calculate the concentration of the accumulated distillate. Also, if the concentration of the accumulated product is found to be 70mol % benzene, calculate its amount. The relative volatility of benzene in the mixture is 4.0. Discuss in detail the Ponchon-Savarit method. (6) 1000 kg/hr of an ethanol-water solution containing 0.28 mole fraction of ethanol is to be separated in a distillation column to produce a distillate containing 0.85 mole fraction ethanol and a residue containing 0.08 mole fraction ethanol. The feed enters the column at its boiling point. Using an operating reflux of 3.2 times the minimum, determine the moles of vapour leaving the top plate and the composition of vapour and liquid leaving 2nd and 3rd plates counted from the top of the column, using the following equilibrium data: Mole fraction 0 0.10 0.20 0.30 0.40 0.50 ethanol in vapour (y1) Mole fraction 0 0.01 0.025 0.04 0.08 0.16 ethanol in liquid (x1) y1 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 x1 0.25 0.375 0.50 0.60 0.70 0.78 0.85 0.90 (15) Determine the following psychrometric properties of a moist air sample having a dry-bulb temperature 270C and a humidity of 0.015 kg/kg dry air using the psychometric chart and/or the vapour pressure equation for water: i. relative humidity, ii. Dew point, iii. Adiabatic saturation temperature, iv. Wet-buld temperature, v. humid volume, and vi. humid heat. The Antoine equation for water is: ln PA0 (bar) = 11.9 -3984.9/(T-39.7). The total pressure is 1 atm. Discuss the construction and operation of a natural draft cooling tower with a neat diagram. (8) Write short notes on: Selection of solvent for absorption McCabe-Thiele’s method Sling psychrometer (9) (7) (5) (5) (5)

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