B.Tech. Industrial Biotechnology (V Semester) IB333 - MASS TRANSFER AND SEPARATION PART A Answer all the questions 10 X 2 = 20 marks 1. Write down the Ficks first law of diffusion 2. Predict diffusivity of ovalbumin at 298 oK in water as a dilute solution. Molecular weight of Ovalbumin is 44,000 Kg/Kgmol and viscosity at 25 oC = 0.8937 X 10-3 Pa.s. 3. Define Schimdt number 4. A strain of B.sphaericus is grown in 10 m3 fermenter. The maximum cell concentration achieved in the fermenter is 10 g/l. An improvement is made in the medium by precursor addition due to which the oxygen uptake rate of the organism is doubled. Determine the maximum cell concentration that can be achieved in the fermenter in the new medium. Assume the kLa and oxygen solubility is not changing due to the precursor addition. 5. Define relative volatility of vapor liquid system 6. Explain Pressure Swing cycle in Adsorption 7. Explain weeping and flooding in tray towers 8. A polyethylene film 0.00015m thick is being considered for use in packaging a pharmaceutical product at 30 C. If the partial pressure of oxygen outside is 0.21 atms and inside the package is 0.01 atms. Calculate the diffusionflux of oxygen at steady state. Permeability of film=4.17 X 10-12m3O2/s.m2.(atm/m) 9. What is meant by constant molal outflow in distillation. 10. Explain minimum boiling azeotroph mixture. Give an example. Part B Question no 11 is compulsory 5 X 16 = 80 marks 11. Aspergillus niger. is used to produce citric acid in the 30 kl fermenter. The total fermentation time is 168 hrs. Aspergillus niger mycelia will form pellets during the growth phase and the size of the pellet will be 4-6 mm. The amount of citric acid produced by the culture largely depend on the effective oxygen transfer from the medium to A.niger pellets. Explain different resistances acting in the transfer of oxygen from gas bubble to A.niger pellets. State which step is rate limiting step after the formation of pellet. 12. An ion exchange column containing 99.3 g of amberlite ion-exchange resin was used to remove Cu2+ from a solution where Co = 0.18 M CuSO4. The tower height = 30.5 cm and the diameter 2.59 cm. the flow rate was 1.37 cm3 solution/s to the tower. The breakthrough data are shown below t (S) 420 480 510 540 600 660 C (gmol Cu/l) 0 0.0033 0.0075 0.0157 0.0527 0.1063 t (S) 720 780 810 870 900 C (gmol Cu/l) 0.1433 0.1634 0.1722 0.1763 0.180 The concentration desired at the breakpoint is c/co = 0.010. Determine the break point time, fraction of total capacity used upto the breakpoint and length of unused bed. (OR) 13. A rectification column is fed 100 Kg mol /hr of a mixture of 50 mol% benzene and 50 mol% toluene. The feed is saturated vapor at dew point. The distillate is to contain 90 mol% benzene and the bottoms 10 mol% benzene. Calculate the Kg mol /h distillate & bottoms, minimum reflux ratio (Rm) and theoretical number of trays at an operating reflux ratio of 1.5 Rm. Equilibrium data are given below for the mole fraction Benzene x 1.000 0.780 0.581 0.411 0.258 0.130 0 y 1.000 0.900 0.777 0.632 0.456 0.261 0 14. Derive the flux equation for gas liquid mass transfer in aerobic fermentations. State how the flux equation will vary for highly soluble and poorly soluble solute.
(OR) 15. Calculate the maximum rate of absorption of oxygen in a fermenter from air bubbles at 1 atms pressure having diameters of 100 µm at 37 oC into water having zero concentration of dissolved oxygen. The solubility of oxygen from air in water at 37 oC is 2.26 X 10-4 Kg mole O2/m3. The viscosity and density of water are 6.947 X 10-4 Pa.s and 994 Kg/m3. The density of air is 1.13 Kg/m3. The Schmidt number for the system is 215. Agitation is used to produce the air bubbles. 16. Experiments are being conducted to determine the suitability of a cellophane membrane 0.029 thick for use in an artificial kidney device. In an experiment at 37oC using NaCl as the diffusing solute, the membrane separates two components containing stirred aqueous solutions of NaCl, where c1=1.0X10-4 g.mol/cm3 and c2=5.0 X 10-7 g.mol/cm3. The mass transfer coefficients on either side of the membrane have been estimated as equal and its value is 5.24 X 10-5 m/s. Experimental data obtained gave a flux 8.11 X 10-4 g.mol NaCl/s.m2 at pseudo steady state conditions. a) Explain different type of resistances and derive the equation for flux with series resistances in this membrane process. b) Calculate the permeability pM in m/s and DAB.K’ in m2/s c) Calculate the percent resistance to diffusion in the liquid films. (OR) 17. Derive the basic equations for the complete mixing model used for design of gas separation by membranes and the solution of equations for the calculating yp, q, and Am while all the other variables are known. 18. A drop of liquid toluene is kept at a uniform temperature of 25.9 oC and is suspended in air by a fine wire. The initial radius r1= 2.00 mm. The vapour pressure of toluene at 25.9oC is pA1= 3.84 kPa and rA = 866 Kg/m3 , P = 101.325 kPa , R=8314 m3.Pa/Kg mol. K , Molecular weight of toluene is 92.13 Kg/Kg mol , DAB = 0.086 X 10-4 m2/sec a) Derive the equation to calculate the complete time taken for evaporation of the liquid b) Calculate the time in secs for complete evaporation. (OR) 19. a) Derive the equation for the experimental determination of diffusivity of gas by two bulb method. b) Write the equation for converting kL to kx and kc’ to ky
ANNA UNIVERSITY, CHENNAI 25 MODEL QUESTION PAPER B.E. MECHANICAL ENGINEERING, VI SEMESTER ME340 – HEAT AND MASS TRANSFER TIME – 3 Hours MAXIMUM : 100 Marks (Use of steam table, Mollier Chart and HMT data book is permitted) PART – A (10 x 2 = 20 Marks) ANSWER ALL QUESTIONS 1. Write down the equation for heat conduction through a hollow
cylinder for one dimensional steady state without heat generation. 2. What is meant by critical radius of Insulation? 3. State the Wien’s displacement law. 4. Define radiation shape factor. 5. Give two examples of the application of free convection. 6. What is the significance of Nusselt Number? 7. What is the difference between film-wise and drop-wise condensation? 8. List out the different types of Heat exchangers.
9. Define Fick’s Law of Diffusion. 10. Give two practical examples of mass transfer. PART – B (5 x 16 = 80 Marks)
11. Water enters a cross flow Heat exchanger (both fluids unmixed) at 5oC and flows at the rate of 4600 kg/h to cool 4000 kg/h of air that is initially at 40oC. Assume the over all heat transfer coefficient value to be 150 W/m2K. For an exchanger surface area of 25m2, Calculate the exit temperature of air and water. (16) 12. a) A steel tube k=43.26 W/mK of 5.08 cm ID and 7.62 cm OD is covered with 2.54 cm of asbestos Insulation k=0.208 W/mK. The inside surface of the tube receives heat by convection from a hot gas at a temperature of 316oC with heat transfer coefficient ha=284 W/m2K while the outer surface of Insulation is exposed to atmosphere air at 38oC with heat transfer coefficient of 17 W/m2K. Calculate heat loss to atmosphere for 3 m length of the tube and temperature drop across each layer. (16)
( OR ) 12. b) (i) A plane wall 20 cm thickness generates heat at the rate of 5 x 104 W/m3 when an electric current is passed through it. The convective heat transfer coefficient between each face of the wall and the ambient air is 60 W/m2K. Determine. · The surface temperature (4) · The maximum temperature in the wall. Assume ambient air temperature to be 25oC and the thermal conductivity of the wall material to be 16 W/mK. (4) (ii) A steel ball 100 mm diameter was initially at 500oC and is placed in air which is at 35oC. Calculate time required to attain 400oC and 300oC. (8) k steel = 35 W/mK c = 0.46 kJ/ kgK p = 7800 kg/m3 h = 10 W/m2K 13. a) (i) Two parallel, infinite grey surface are maintained at temperature of 127oC and 227oC respectively. If the temperature of the hot surface is increased to 327oC, by what factor is the net radiation exchange per unit area increased?. Assume the emissivities of cold and hot surface to be 0.9 and 0.7 respectively. (8)
(ii) Two equal and parallel discs of diameter 25 cm are separated by a distance of 50 cm. If the discs are maintained at 600oC and 250oC. Calculate the radiation heat exchange between them. (8)
( OR ) b) Two large parallel planes with emissivities 0.35 and 0.8 5 exchange heat by radiation. The planes are respectively 1073K and 773K . A radiation shield having the emissivity of 0.04 is placed between them. Find the percentage reduction in radiation heat exchange and temperature of the shield. (16) 14. a) State the Buckingham’s p- Theorem. Explain the various parameters used in forced convection and using dimensional analysis obtain an expression for Nusselt number interms of Reynolds number and Prandtl number. (16) ( OR ) b) A circular disc heater 0.2m in diameter is exposed to ambient air at 25oC. One surface of the disc is insulated at 130oC. Calculate the amount of heat transferred from the disc when it is. (i) Horizontal with hot surface facing up (5) (ii) Horizontal with hot surface facing down (5) (iii) Vertical (6) 15. a) CO2 and air experience equimolar counter diffusion in a circular tube whose length and diameter are 1m and 50mm respectively. The system is at a toal pressure of 1 atm and a temperature of 25oC. The ends of the tube are connected to large chambers in which the species concentration are maintained at fixed values. The partial pressure of CO2 at one end is 190mm of Hg while at other end is 95mm of Hg. Estimate the mass transfer rate of CO2 and air through the tube. The diffusion coefficient for CO2 – air combination is 0.16 x 10 – 4 m2/s. (16) ( OR ) b) (i) Define the non dimensional numbers in mass transfer ( 6) (ii) Dry air at 27oC and 1 atm flows over a wet flat plate 50cm long at a velocity of 50m/sec. Calculate the mass transfer co-efficient of water vapour in air at the end of the plate. Take D=0.26x10 – 4 m2/sec. b = 1.1614 kg/m3 m = 184.6 10-7 Ns/m2 Pr = 0.707 (10)
B.E. /B.TECH DEGREE EXAMINATION, APRIL/MAY 2008. Sixth Semester (Regulation 2004) Mechanical Engineering ME1351 - HEAT AND MASS TRANSFER Time: Three hours Maximum: 100 marks
PART A - (10*2 = 20 MARKS) 1. A temperature difference of 500 C is applied across a fire-clay brick, 10cm thick having a thermal conductivity of 1W/mK. Find the heat transfer rate per unit area. 2. Write the general 3-D heat conduction equation in cylindrical coordinates. 3. Biot number is the ratio between _________and _________ 4. Define bulk temperature. 5. A vertical flat plate is maintained at a temperature lower than the surrounding fluid. Draw the velocity and temperature profiles assuming natural convection. 6. What is burnout point? Why is it called so? 7. What is a compact heat exchanger? Give examples. 8. What is thermal radiation and what is its wavelength band? 9. What are radiation shields? 10. Explain the physical meaning of Schmidt number?
PART B - (5*16 = 80 marks) 11. (a) A composite wall is formed of a 2.5 cm copper plate (k=355W/mK), a 3.2 mm layer of asbestos (k=0.110 W/mK) and a 5cm layer of fiber plate (k=0.049 W/mK). The wall is subjected to an overall temperature difference of 560 C (560 C on the Cu plate side and 0 C on the fiber plate side).Estimate the heat flux through this composite wall and interface temperature between asbestos and fiber plate. OR (b) When a thermocouple is moved from one medium to another medium at a different temperature, sufficient time must be given for the thermocouple to come to the thermal equilibrium with the new conditions before a reading is taken. Consider a 0.1 cm diameter copper thermocouple wire originally at 150 C. Find the thermometer response (i.e. an approximate plat of temperature vs time for intervals of 0, 40 and 120 seconds) when this wire is suddenly immersed in (i) water at 40 C (h=80 W/m2K) (ii) air at 40 C (h=40 W/m2K) Assume unit length of wire. 12. (a) Air at 400 K and 1atm pressure flows at a speed of 1.5 m/s over a flat plate of 2 m long. The plate is maintained at a uniform temperature of 300 K. If the plate has a width of 0.5 m, estimate the heat transfer coefficient and the rate of heat transfer from the air stream to the plate. Also estimate the drag force acting on the plate. OR (b) Cylindrical cans of 150 mm length and 65 mm diameter are to be cooled from an initial temperature of 20 C by
placing them in a cooler containing air at a temperature of 1 C and a pressure of 1 bar. Determine the cooling rates when the cans are kept in (i) Horizontal position (ii) Vertical position 13. (a) Water is to be boiled at atmospheric pressure in a mechanically polished stainless steel pan placed on top of a heating unit. The inner surface of the bottom of the pan is maintained at 108 C. The diameter of the bottom of the pan is 30 cm. Assuming Csf = 0.0130, calculate (i) the rate of heat transfer to the water, and (ii) the rate of evaporation of water. OR (b) Define effectiveness of a heat exchanger. Derive an expression for the effectiveness of a double pipe parallel flow heat exchanger. State the assumptions made. 14. (a) (i) Discuss briefly the variation of black body emissive power with wavelength of different temperatures. (8) (ii) The spectral emissive function of an opaque surface at 800 K is approximated as e1 = 0.30 0 = ? < 3µm e? = e2 = 0.80 3µm = ? < 7µm e3 = 0.10 7µm = ? < 8 Calculate the average emissivity of the surface and its emissive power. (8) OR (b) Explain the following: (5+5+6) (i) Specular and diffuse reflection (ii) Reflectivity and transmissivity (iii) Reciprocity rule and summation rule. 15. (a) Discuss briefly the following: (4+6+6) (i) Fick’s law of diffusion (ii) Equimolar counter diffusion (iii) Evaporation process in the atmosphere. OR (b) (i) What are the assumptions made in the 1-D transient mass diffusion problems? (4) (ii) An open pan, 20 cm diameter and 8 cm deep contains water at 25°C and is exposed to dry atmospheric air. Estimate the diffusion coefficient of water in air, if the rate of diffusion of water is 8.54 × 10-4 kg/h. (12) ------THE END-----ANNA UNIVERSITY :: CHENNAI – 600 025 MODEL QUESTION PAPER VI - SEMESTER B.TECH. CHEMICAL ENGINEERING CH340 – CHEMICAL REACTION ENGINEERING - I
Time: 3hrs Max Marks: 100 Answer all Questions PART – A (10 x 2 = 20 Marks) 1. Define F-type and K-type mass transfer coefficients and give its importance. 2. Explain the term flooding and loading in gas-liquid equipment where liquid is the dispersed phase. 3. Define Sherwood, Stanton and Schmidt number. 4. Explain the relationship between NTP and NTU? 5. State the basic assumptions made in film and penetration theory. 6. Define the term number of overall enthalpy transfer unit and height of enthalpy transfer unit. 7. What do you understand by the term fractional crystallization? 8. Define the term bound and unbound moisture content. 9. Define the super-saturation and state any four methods of achieving super-saturation. 10. Discuss briefly the term unsaturated surface drying. PART – B (5 x 16 = 80 Marks) 11. Water is to be cooled from 45 to 27°C in a counter-current cooling tower under conditions such HTU is 2.8m. Air enters at the bottom of the tower at 24°C and a wet-bulb temperature of 21°C. Find the height if 1.6 times the minimum air flow rate is used. Neglect the heat transfer resistance of the liquid phase. 12.a) An cylindrical tank of 6.0m in diameter contains benzene at 25°C which is exposed to the atmosphere in such a manner that the liquid is covered with a stagnant air film having an estimated thickness of 5mm. The concentration of benzene beyond the stagnant film is negligible. The vapour pressure of benzene 25°C is 100mm Hg. If the cost of benzene is Rs. 50 per litre what is the value of benzene lost from t his tank per day. The diffusivity of benzene is 7.71 x 10-6 m2/s and the density of benzene at 25°C is 880 kg/m3. OR 12.b) An ethanol (A)-water (B) solution in the form of a stagnant film 2.0 mm thick at 293 K is in contact at one surface with an organic solvent in which ethanol is soluble and water is insoluble. Hence, Ng = 0. At point 1 the concentration of ethanol is 16.8 wt% and the solution density is ?1 = 972.8 kg/m3. At point 2 the concentration of ethanol is 6.8 wt% and ?2 = 988.1 kg/m3. The diffusivity of ethanol is 0.74 x 10-9 m2/s. Calculate the steady state flux NA. 13.a) Naphthalene is submitted from a cylinder of naphthalene of 0.075m diameter and 0.5m long into a stream of pure carbon dioxide flowing at a velocity of 6 m/s and 1 atm. and 100° C. Calculate the mass transfer coefficient F. The vapor pressure of naphthalene at 100°C is 1320 N/m2.
Data Given: Viscosity of gas 0.018 x 10-3 kg/ms Density 1.43 kg/m3 Diffusivity 0.08 x 10-4 m2/s JD = 334.6 x 10-4 (Re)1-0.2 Where Reynolds number is based on the length of cylinder OR 13.b)i) State the difference between stage wise and differential contact gas-liquid equipment used in mass transfer operations. (8) ii) Derive the relationship between the overall and individual mass transfer coefficients. (8) 14.a) A continuous countercurrent dryer is being used to dry 453.6 kg dry solid /h containing 0.04 kg total moisture/kg dry solid to a value of 0.002 kg total moisture/kg dry solid. The granular solid enters at 26.7°C and is to be discharged at 62.8°C. The dry solid has a heat capacity of 1.465 kJ/kgK, which is assumed constant. Heating air enters at 93.3°C, having a humidity of 0.01 kg H2O / kg dry air and is to leave at 37.8°C, Calculate the air flow rate and the outlet humidity, assuming no heat losses in the dryer. OR 14.b) A porous solid under constant drying conditions takes 6.5 hours to reduce the moisture content from 30 to 10%. The critical moisture content is 14% and the equilibrium moisture content is 2.5%. If the rate of drying in the falling rate period is proportional to the free moisture content, how long will it take to dry a sample of the same solid 40 to 5%? 15.a)i) Explain briefly how crystal growth is controlled in a continuous crystallizer. (8) ii) Explain in detail the various factors governing the nucleation and crystal growth. (8) OR 15.b) Explain in detail the working of Swenson-Walker Continuous crystallizer with a neat diagram.
