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- Mass Transfer-I - MT1
- 2018
- PYQ
**Biju Patnaik University of Technology Rourkela Odisha - BPUT**- Chemical Engineering
- B.Tech
**25 Views**- Uploaded 10 months ago

Registration No : Total number of pages : 03 B.Tech PCE3I104 3rd Semester Regular/Back Examination 2018–19 MASS TRANSFER - I BRANCH : CHEM, PT Time : 3 Hours Max Marks : 100 Q.CODE : E929 Answer Question No.1 (Part-I) which is compulsory, any eight from Part-II, and any two from Part-III. The figures in the right-hand margin indicate marks. Assume suitable notations and any missing data wherever necessary. Answer all parts of a question at a place. Part – I Q1 Answer the following questions : (2 × 10) a) How does the binary gas phase diffusivity depend upon the total pressure and temperature? b) Give the physical significances of the dimensionless groups in mass transfer. c) What is equimolar counter-diffusion? d) Write the Gilliland’s equation and explain each terms used in it. Mention its importance. e) What is the physical significance of NTU? f) What are the factors that influence HtOG and NtOG of a packed tower? g) What happens if a column heated by open steam is operated at total reflux for a long time? h) What are the common packings and materials for a cooling tower? i) What is wet bulb depression? j) What are the important factors that influence the design and operation of a cooling tower? Part – II Focused-Short Answer Type Questions(Answer Any EIGHT out of TWELVE) Q2 Answer the following questions : a) Two vessels are connected by a tube 6 cm in diameter and 20 cm in length. Vessel 1 contains 70 % N2and 30 % O2while vessel 2 contains 30 % N2 and 70 % O2. The temperature is 200C and the total pressure is 2 atm. Calculate (i) the steady-state flux and the rate of transport of N2 from vessel 1 to 2 and (ii) the same quantities for O2. Given:Diffusivity of N2-O2 pair is 0.23 cm2/s at 316 K and 1 atm. (6 × 8)

b) In a reactor the gas (A) is sparged in an agitated suspension of catalyst particles, 0.5 mm in diameter, in a liquid (B). The gas dissolves in the liquid and is transported to the surface of the catalyst particles where it undergoes an instantaneous reaction. In a particular case the concentration of A in the liquid is 0.8kmol/m3, the rate of reaction is 3.0x10-6kmol/m2.s based on the external surface area of the catalyst particles, and the diffusivity of A in the liquid is 6.8x10-10 m2/s. If the diffusion of dissolved A to the catalyst surface occurs through a stagnant film surrounding a particle, calculate the thickness of the liquid film. c) Discuss in detail the types of mass transfer coefficients. d) Determine the relation between the gas-phase mass transfer coefficients kG and kY. e) Describe the penetration theory with a neat model. f) Discuss the important criteria for the selection of solvent and stripping medium for absorption. g) In the nth tray of an absorption column: Gs = 100 kmol/h; Ls = 120 kmol/h; yn+1 = 0.15; xn = 0.08; and xn-1 = 0.06. The equilibrium relation is linear in the form y = 1.02 x. If the liquid on the tray is well mixed, calculate the Murphree tray efficiency. h) Discuss about deviation from ideality and formation of azeotropes. i) Derive the Fenske’s equation. j) A charge of 52kmol of a mixture of benzene and chlorobenzene having 58mol % 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. The relative volatility of benzene in the mixture is 4.0. k) Discuss the construction and working of a counter flow induced draft cooling tower with a neat diagram. l) Discuss the hygrometer method of humidity measurement. Part – III Long Answer Type Questions (Answer Any Two out of Four) Q3 The gas phase mass transfer coefficient for the evaporation of a drop of ethyl alcohol in a stream of air at 300 K and 1.2 bar pressure is kG = 2.5 × 10-6kmol/s.m2.mmHg. Calculate the values of the mass transfer coefficient if the driving force is expressed in terms of difference in (i) mole fraction of alcohol in the gas phase, (ii) mole ratio of alcohol, (iii) concentration of alcohol in kmol/m3. Also calculate the coefficient FG. If the diffusivity of alcohol in air is 0.1 cm2/s at 00C, estimate the thickness of the stagnant gas-film. Vapour pressure of alcohol = 0.09 bar at 300 K. (16) Q4 SO2is scrubbed from an air stream in a small packed tower by contacting it with an organic solvent. The feed gas contains 2 % SO2 by volume and 90 % of it is to be absorbed. The total gas rate is 140 m3/h at 200C and 1 bar absolute pressure. The liquid enters the column at 1.2kmol/h. Given: the overall mass transfer coefficient KG = 3 × 10-4kmol/m2.s.∆p (∆p in bar); the effective gas-liquid contact area = 100 m2/m3 of packed volume; and slope of the equilibrium line m = 0.15. Determine the number of overall gas phase mass transfer units and the packed height if the column is 0.5 m in diameter. (16)

Q5 Q6 An aqueous solution of ethanol (29 mass % ethanol) is to be enriched into a top product having 90 mass % alcohol. The bottom product must not contain more than 3 mass % alcohol. The feed enters the column at 400C at a rate of 5100 kg/h. The reflux is at its bubble point and the reflux ratio is 1.2. Enthalpy of the feed = 4790 kJ/kmol. Determine: The number of ideal trays required using the Ponchon-Savarit method; The heat duty of the condenser and of the reboiler. The enthalpy concentration (kJ/kmol; reference states: pure liquids at 00C) and the VLE data at the operating pressure of 1 atm are given below. x, y 0.0 0.0417 0.0891 0.1436 0.207 0.281 HL 7540 7125 6880 6915 7097 7397 HV 48150 48250 48300 48328 48436 48450 x, y 0.37 0.477 0.61 0.779 1.0 - HL 7750 8105 8471 8945 9523 - HV 48450 48631 48694 48950 - - x 0.0 0.00792 0.016 0.0202 0.0417 0.0891 0.1436 0.281 0.37 y 0.0 0.0850 0.1585 0.191 0.304 0.427 0.493 0.568 0.603 x 0.477 0.61 0.641 0.706 0.779 0.86 0.904 0.95 1.0 y 0.644 0.703 0.72 0.756 0.802 0.864 0.902 0.9456 1.0 A sample of air has a dry bulb temperature of 350C and wet bulb temperature of 250C at a total pressure of 1 atm. Determine humidity, enthalpy, dew point, humid volume, and humid heat; If the sample of air is heated to 480C, what will be its wet bulb temperature? How much heat is rejected if 1 kg of air (dry basis) is cooled down from 35 to 180C? If the air sample is heated to 480C and its pressure doubled, what would be its relative humidity and dew point? (16) (16)

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