Mass Transfer PDF

MASS TRANSFER b. forced c. induced SECTION 1 d. non...

MASS TRANSFER b. forced c. induced SECTION 1 d. none of these 1. Mass transfer rate between two fluid phases does not necessarily depend 11. Pick out the correct statement. on the __________ of the two phases. a. In case of liquid-liquid extraction, no separation is possible, if the a. chemical properties selectivity of the solvent used is unity. b. physical properties b. With increase in temperature, the selectivity of the solvent used in c. degree of turbulence solvent extraction decreases. d. interfacial area c. The selectivity of solvent used in solvent extraction is unity at the plait point. 2. In a solution containing 0.30 Kg mole of solute and 600 kg of solvent, the d. all (a), (b) and (c). molality is 12. __________ columns are used for liquid dispersion in a continuous gas a. 0.50 phase. b. 0.60 c. 2 a. Packed d. 1 b. Pulse c. Bubble cap 3. Fenske equation determines the d. Sieve plate a. maximum number of ideal plates. 13. Overall efficiency of the distillation column is b. height of the distillation column. c. minimum number of theoretical plates. a. the ratio of number of ideal plates to actual plates. d. optimum reflux ratio. b. the ratio of number of actual plates to ideal plates. c. same as the Murphree efficiency. 4. The term "co" in a cooling tower refers to the difference in the temperature d. always more than the point efficiency. of 14. On addition of solute in the solvent, the __________ of the solution a. cold water leaving the tower and the wet bulb temperature of the decreases. surrounding air. b. hot water entering the tower and the wet bulb temperature of the a. boiling point surrounding air. b. freezing point c. hot water entering the tower and the cooled water leaving the c. vapour pressure tower. d. both (b) and (c) d. none of these 15. Which is the controlling factor for a drum drier? 5. Which of the following is the most suitable for extraction in a system having very low density difference? a. Diffusion b. Heat transfer a. Mixer-settler extractor c. Both (a) and (b) b. Centrifugal extractor d. Neither (a) nor (b) c. Pulsed extractor d. Packed extraction tower 16. Drying operation under vacuum is carried out to 6. Total reflux in a distillation operation requires minimum a. dry those materials which have very high unbound mositure content. a. reboiler load b. reduce drying temperature. b. number of plates c. increase drying temperature. c. condenser load d. dry materials having high bound moisture content. d. all (a), (b) and (c) 17. Air initially at 101. 3 kPa and 40°C and with a relative humidity of 50%, is 7. The amount of steam required per unit quantity of distillate in case of steam cooled at constant pressure to 30°C. The cooled air has a distillation will be reduced by a. higher dew point. a. raising the temperature. b. higher absolute (specific) humidity. b. lowering the total pressure. c. higher relative humidity c. both (a) and (b). d. higher wet bulb temperature. d. neither (a) nor (b). 18. Separation of two or more components of a liquid solution can not be 8. The difference of wet bulb temperature and adiabatic saturation temperature achieved by of unsaturated mixture of any system is a. fractional crystallisation a. +ve b. liquid extraction b. -ve c. absorption c. zero d. evaporation d. none of these 19. Stefan's law describes the mass transfer by 9. Fenske's equation for determining the minimum number of theoretical stages in distillation column holds good, when the a. diffusion b. bulk flow a. relative volatility is reasonably constant. c. both 'a' & 'b' b. mixture (to be separated) shows negative deviation from ideality. d. neither 'a' nor 'b' c. mixture (to be separated) shows positive deviation from ideality. d. multicomponent distillation is involved. 20. At minimum reflux ratio for a given separation 10. When the temperature and humidity of air is low, we usually use a. number of plates is zero. __________ draft cooling tower. b. number of plates is infinity. c. minimum number of the theoretical plates is required. a. natural  d. separation is most efficient. d. velocity is more than the loading velocity. 21. Relative humidity is the ratio of the 31. As the reflux ratio in a distillation coloumn is increased from the minimum, the a. partial pressure of the vapour to the vapour pressure of the liquid at room temperature. a. slope of the operating line in stripping section decreases. b. partial pressure of the vapour to the vapour pressure of the liquid at b. number of plates decreases very slowly first and then more and gas temperature. more rapidly. c. actual humidity to saturation humidity. c. total cost first decreases and then increases. d. none of these d. liquid flow increases while the vapor flow decreases for a system. 22. In batch distillation with constant reflux, overhead product composition 32. Absorption factor is defined as (where, S1 = slope of the operating line S2 __________ with time. = slope of the equilibrium curve) a. increases a. S2/S1 b. decreases b. S1/S2 c. does not vary c. S1 - S2 d. may increase on decrease, depends on the system. d. S1 x S2 23. Psychrometry deals with the properties of gas-vapor mixture. Humidity 33. A plait point is the point on the solubility curve, where the tie line reduces can be determined by the measurement of the __________ of a fibre. to a point. What is the number of plait point for a ternery system containing twopairs of partially miscible liquids? a. electrical resistance b. thermal conductivity a. 0 c. strength b. 1 d. none of these. c. 2 d. 3 24. Heat in BTU necessary to increase the temperature of 1 lb of gas and its accompanying vapour by 1°F is called the 34. Which of the following remains constant during sensible cooling process ? a. latent heat a. Specific humidity b. humid heat b. Partial pressure of vapour c. specific heat c. Both (a) and (b) d. sensible heat d. Neither (a) nor (b) 25. To increase the absorption factor, (where, G = gas flow rate, S = solvent 35. Physical absorption is flow rate) a. an irreversible phenomenon. a. increase both 'G' and 'S'. b. a reversible phenomenon. b. decrease both 'G' and 'S'. c. accompanied by evolution of heat. c. increase 'S' and decrease 'G'. d. both (b) and (c) d. increase 'G' and decrease 'S' 36. Make up water is required in a cooling tower to replace the water lost by 26. The mass diffusivity, the thermal diffusivity and the eddy momentum diffusivity are same for, NPr = NSc = __________ a. evaporation b. drift a. 1 c. blowdown and leakage b. 0.5 d. all (a), (b) and (c) c. 10 d. 0 37. Which of the following quantities need not be fixed before starting the design of a co-current absorber? 27. Dew point of a gas-vapour mixture a. Heat gain or loss a. increases with temperature rise. b. Flow rate of entering liquid b. decreases with temperature rise. c. Flow rate of gas c. decreases with decrease in pressure. d. None of these d. increases with increase in pressure. 38. Mass transfer co-efficient of liquid is 28. In a packed absorption tower, if the equilibrium and operating lines are both straight lines, then the ratio, HETP/HTUOG __________ the absorption a. affected more by temperature than that for gases. factor. b. affected much less by temperature than that for gases. c. not affected by the temperature. a. increases with increase in d. none of these. b. is one at unity value of c. both (a) and (b) 39. Absorption accompanied with chemical reaction is exemplified by the d. neither (a) nor (b) absorption of 29. Which of the following plays an important role in problems of a. ammonia in water. simultaneous heat and mass transfer ? b. benzol present in coke oven gas by wash oil. c. SO2 in alkaline solution. a. Lewis number d. all (a), (b) and (c). b. Schmidt number c. Prandtl number 40. Which of the following unit operations makes use of Thiele-Geddes d. Sherwood number equation ? 30. In case of an absorber, the operating a. Liquid-liquid extraction b. Solid-liquid extraction a. line always lies above the equilibrium curve. c. Multicomponent absorption with chemical reaction b. line always lies below the equilibrium curve. d. Multicomponent distillation. c. line can be either above or below the equilibrium curve. 41. Which of the following liquid-vapor contacting devices provides a. molar heats of vaporisation of components are nearly equal. maximum contact surface area for a particular duty? b. linear crystal growth rate depends on the degree of supersaturation. c. linear crystal growth rate does not depend on the crystal size. a. Sieve plate column d. linear crystal growth rate depends on the crystal size. b. Bubble cap column c. Randomly packed column 2. Bollman extractor d. Wetted wall column a. is a static bed leaching equipment. 42. The equipment frequently used for adiabatic humidification-cooling b. is used for extraction of oil from oilseed. operation with recirculating liquid is c. is a centrifugal extractor. d. employs only counter-current extraction. a. natural draft cooling tower b. induced draft cooling tower 3. The relation, Sc = Pr = 1, is valid, when the mechanism of __________ c. spray chamber ansfer is same. d. none of these a. heat and mass 43. Chemisorption (chemical adsorption) is b. mass and momentum c. heat and momentum a. same as "Van der Waals" adsorption. d. heat, momentum and mass b. characterised by adsorption of heat. c. an irreversible phenomenon. 4. A coalescer in a mixer-settler liquid-liquid extraction coloumn d. a reversible phenomenon. a. comprises of thin bed of substances of extended surface having 44. The rate of solid-liquid extraction is limited by the high porosity. b. helps in increasing the bubble size entering the settler. a. phase change of the solute as it dissolves in the solvent. c. helps in increasing the settling rate of the bubbles. b. diffusion of the solute through the solvent in the pores to the d. all 'a', 'b', & 'c'. outside of the particle. c. diffusion of the solute from the solution in contact with the particle 5. For the same feed, feed quality and separation (in a distillation column), to the main bulk of the solution. with the increase of total pressure, the number of ideal plates will d. all 'a', 'b' & 'c'. a. increase 45. Raoult's law applies to the b. decrease c. remain same a. all liquid solutions d. data insufficient, can't be predicted b. non-ideal solution only. c. non-volatile solute. 6. Pick out the correct statement. d. solvents. a. Ponchan-Savarit method is more accurate than McCabe-Thiele 46. In distillation columns, the number of bubble caps per tray primarily method to determine the number of theoretical stages required for depends upon the the separation of non-ideal binary system by distillation. b. A sharp decrease in pressure drop is an indication of flooding in a a. allowable liquid velocity. distillation coloumn. b. allowable gas velocity. c. Solvent used in extractive distillation should be of high volatility. c. allowable gas and liquid velocities. d. Flash distillation is suitable for separating components which have d. feed composition. very close boiling temperature. 47. In distillation, overhead product contains 7. When the liquid phase and vapour phase of a binary system obeys Raoult's and Dalton's law respectively, the relative volatility is the ratio of a. only one component b. two components a. vapour pressure of component A to that of component B. c. any number of components b. vapour pressure of component A to the total pressure. d. only saturated liquid c. vapour pressure of component A to the partial pressure of A. d. partial pressure of component A to the total pressure. 48. With increase in pressure, the relative volatility for a binary system 8. The operation involved when the soluble material is largely on the surface a. increases. of an insoluble solid and is merely washed off by the solvent is called b. decreases. c. remains same. a. decoction d. either (a) or (b), depends on the system. b. percolation c. elutriation or elution 49. Low viscosity absorbent is preferred for reasons of d. none of these a. rapid absorption rates and good heat transfer characteristics. 9.In the constant rate period of the rate of drying curve for batch drying, b. improved flooding characteristics. c. low pressure drop on pumping. a. cracks develop on the surface of the solid. d. all (a), (b) and (c). b. rate of drying decreases abruptly. c. surface evaporation of unbound moisture occurs. 50. Mass transfer co-efficient (K) and diffusivity (D) are related according to d. none of these. film theory as 10. It takes 6 hours to dry a wet solid from 50% moisture content to the a. K∝D critical moisture content of 15%. How much longer it will take to dry the solid b. K ∝(D)^1/2 to 10% moisture content, under the same drying conditions? (The equilibrium c. K ∝ D1.5 moisture content of the solid is 5%). d. K ∝ D2 a. 15 min b. 51 min c. 71 min SECTION 2 d. 94 min 1. The McCabe Δ L law states that the 11. Agitator is provided in a crystalliser for 20. Weeping in a distillation column a. avoiding deposition on cooler surfaces. a. increases tray efficiency. b. formation of nuclei. b. provides large interfacial surface for mass transfer. c. crystal growth. c. results due to very high gas velocity. d. all (a), (b) and (c). d. results due to very low gas velocity. 12. __________ diffusion is used for separating the isotopes of methane. 21. In case of binary distillation, increasing the reflux ratio above optimum does not result in the increase of a. Thermal b. Pressure a. area between operating line and 45° diagonal x-y diagram. c. Concentration b. condenser and reboiler surfaces. d. Force c. tower cross-section. d. none of these. 13. Ordinary diffusion process is also called __________ diffusion. 22. Wetted wall tower experiment determines the a. pressure b. thermal a. molal diffusivity. c. concentration b. volumetric co-efficient. d. forced. c. mass transfer co-efficient. d. none of these. 14. Pick out the wrong statement. 23. In McCabe-Thiele method, at infinite reflux ratio a. Different solids have different equilibrium moisture curves. b. Total condenser or reboiler is considered equivalent to one a. the overhead product is minimum. theoretical plate in McCabe-Thiele method of theoretical plate b. both the operating lines coincide with diagonal. calculation for distillation column. c. both (a) and (b). c. Heat removal load on cooler remains constant, even with increase d. neither (a) nor (b). of the reflux ratio in a distillation column. d. Even a forced draft cooling tower can not cool water below the wet 24. With decrease in the throughput (compared with the design capacity) for a bulb temperature. bubble cap distillation column, its efficiency 15. Pick out the wrong statement pertaining to the rotary dryer. a. increases b. decreases a. Flights (located in the inside shell of rotary dryer) lift the material c. remains same being dried and shower it down through the current of hot d. may increase or decrease; depends on individual design. air/gases. It extends from the wall to a distance which is about 8- 12% of the inside diameter of shell. 25. Plate towers are preferred to packed towers, when large temperature b. Hold up of a rotary drier is defined as the fraction of the dryer changes are involved, because of the reason that the volume occupied by the solid at any instant. The best performance for rotary drier is obtained, when the hold up is in the range of 0.05 a. packing may be crushed due to thermal expansion/contraction of to 0.15. the components of the equipments. c. Rotary dryer is suitable for drying sticky material. b. pressure drop in the equipment will be. very high. d. Recommended peripherial speed of a rotary drier is in the range of c. viscosity variation of the fluids may cause channeling/flooding. 10 to 30 metres/minute. d. none of these. 16. The reason for preferring packed towers over plate towers in distillation 26. The equilibrium liquid composition compared to the vapor composition in practice is that the packed tower operation gives case of azeotropic mixture is a. low pressure drop and high hold up. a. more b. high pressure drop and low hold up. b. less c. low pressure drop and low hold up. c. same d. high pressure drop and high hold up. d. either more or less; depends on the system 17. If the path of liquid across the plate is very long as in case of large 27. Out of the following gas-liquid contacting devices, for a given set of diameter tower, Murphree efficiency can be __________ percent. operating conditions, gas pressure drop is the least in __________ tower. a. 100 a. wetted wall b. >100 b. bubble cap c. < 100 c. perforated tray d. none of these d. packed 18. Compound A is extracted from a solution of A + B into a pure solvent S. A 28. Pick out the system with minimum boiling azeotrope at 1 atm. Co-current unit is used for the liquid-liquid extraction. The inlet rate of the solution containing A is 200 moles of B/hr.m2 and the solvent flow, rate is 400 a. benzene-toluene moles of S/m2. hr. The equilibrium data is represented by Y = 3X2 , where Y b. ethyl alcohol-water is in moles of a A/moles of B and X is in moles A/moles of S. The maximum c. hydrochloric acid-water percentage extraction achieved in the unit is d. all (a), (b) and (c) a. 25% 29. Free flowing granular materials can be best dried in a __________ drier. b. 50% a. rotary c. 70% b. cylinder d. 90% c. drun 19. Raoult's law is applicable to the d. freeze a. ideal solutions 30. In case of an ideal solution, the total vapor pressure varies __________ b. real solutions with the composition expressed as mole fraction, c. mixture of water and alcohol a. inversely d. non-ideal gases b. linearly  c. exponentially d. none of these 31. Corresponding to Nusselt number in heat transfer, the dimensionless group in mass transfer is the __________ number. a. Sherwood b. Schmidt c. Peclet d. Stanton c. d. 32. If the specific heats of a gas and a vapor are 0.2KJ/Kg.°K and 1.5 39. An aqueous solution of methanol is to be distilled in a tray column. High KJ/Kg.°K respectively, and the humidity is 0.01; the humid heat in KJ/°Kg. is pressure steam is available as a source of heat. For a given reflux ratio and overhead composition, two options are being explored; (i) a reboiler is used a. 0.31 and (ii) no reboiler is used but steam is fed directly to the bottom of the b. 0.107 column. As compared to option (i), in option (ii) c. 0.017 d. 0.215 a. less number of trays are required. b. composition of the residue remains unchanged. 33. Liquid diffusivity is of the order of __________ cm2 /second. c. more number of trays are required but the residue composition remains unchanged. a. 0.01 d. more number of trays are required and the residue composition is b. 0.1 more dilute in methanol. c. 10^-5 to 10^-6 d. >1 40. The partial pressure distribution of an ideal gas diffusing through another stagnant ideal gas at steady state follows a/an __________ law. 34. The solvent used in liquid extraction should not have high latent heat of vaporisation, because a. exponential b. parabolic a. the pressure drop and hence the pumping cost will be very high. c. linear b. it cannot be recovered by distillation. d. cubic c. its recovery cost by distillation may be prohibitatively high. d. it will decompose while recovering by distillation. 41. Which of the following binary systems is an example of a maximum boiling azeotrope ? 35. At the same gas flow rate, the pressure drop in a packed tower being irrigated with liquid __________ that in dry packed tower. a. Water-hydrochloric acid. b. Acetone-carbon disulphide. a. is greater than c. Water-ethyl alcohol. b. is lower than d. n-heptane-n-octane c. is same as d. cannot be predicted as data are insufficient. 42. (NRe. NSc) is termed in mass transfer operation as the __________ number. 36. Molarity is defined as the number of gm moles of solute per __________ of solvent. a. Stanton b. Sherwood a. litre c. Peclet b. kg d. none of these c. gm d. c.c 43. The binary diffusivity in gases and liquids vary respectively as 37. The value of Lewis number (Le = Sc/Pr) for air-water vapour system is a. T3/2 and T around b. T and T3/2 c. T1/2 and T3/2 a. 1 d. T3/2 and T1/2 b. 0.24 c. 3.97 44. Pick out the correct statement. d. 600 a. The slope of the stripping line is always less than unity. 38. Which of the following T-H diagram is valid for dehumidification b. For a given separation in a binary distillation column, with increase operation ? in reflux ratio (above the minimum reflux ratio), the fixed cost of the distillation column first increases and then decreases. c. In Ponchon-Savarit method of no. of theoretical plate determination, the stripping and rectifying operating lines are vertical at total reflux. d. Kremsor-Brown-Souder's equation is used to calculate the efficiency of a plate tower. 45. Pick out the correct statement. a. b. a. Dialysis process is used for the production of fresh water from brine. b. Electrodylsis is used in the manufacture of NaOH. c. Electrodylsis is used for the refin-ning/purification of petrol. d. both (b) and (c). 46. Pick out the correct statement. a. Bound moisture is removed during constant rate drying period. b. Free moisture is removed during falling rate drying period.  c. The sum of free moisture and equilibrium moisture in a solid is d. The relative volatility of a binary mixture at the azeotropic called the critical moisture. composition is 1. d. The driving force for mass transfer in a wet solid is its free moisture content. 6. A minimum boiling azeotrope is exemplified by 47. Very tall packed towers are divided into series of beds to a. toluene-benzene b. acetone-carbon disulphide a. reduce the overall pressure drop c. water-isobutyl alcohol b. avoid channelling d. none of these c. reduce liquid hold-up d. avoid flooding 7. Which of the following solutions will follow Raoult's law most closely ? 48. Moisture contained by a substance in excess of the equilibrium moisture is a. A solution of benzene, toluene and oxylene. called the __________ moisture. b. 35% solution of camphor in water. c. 35% solution of NH3 in water. a. unbound d. A solution of polar organic compounds (not of homologs of a b. free series). c. critical d. bound 8. Use of raschig rings in place of crushed stones as packing in packed beds (other things being same) 49.With increase in temperature, the solubility of gases in liquids, at fixed pressure a. increases pressure drop, increases surface area. b. increases pressure drop, decreases surface area. a. increases c. decreases pressure drop, increases surface area. b. decreases d. decreases pressure drop, decreases surface area. c. remains same d. either (a) or (b), depends on the system. 9. Critical humidity of a solid salt means the humidity 50. In most of the vacuum crystalliser, vacuum is generally produced by a. above which it will always become damp. means of a b. below which it will always stay dry. c. both (a) and (b). a. suction pump d. above Which it will always become dry and below which it will b. compressed air jet always stay damp. c. steam jet ejector with a barometric condenser d. none of these 10. The assumption made in Elis method in distillation is that enthalpy concentration lines of vapor and liquid are a. parallel SECTION 3 b. straight c. both parallel and straight 1. On moving the feed line (q-line) from saturated liquid feed (vertical d. neither parallel nor straight position) to saturated vapor feed (horizontal feed), if the slope of both the operating lines are to be increased, then it will result in 11. As complete saturation of an adsorbent is approached, the differential heat of adsrop-tion approaches a. greater degree of separation with a fixed number of trays b. increased reboiler load a. that of normal condensation. c. increased reflux ratio b. integral heat of adsorption. d. None of these c. zero. d. none of these. 2. __________ column is the most suitable for achieving the best performance for mass transfer operations involving liquid with dispersed solids. 12. 'Absorption with chemical reaction' is involved in the removal of a. Watted wall a. carbon dioxide from gaseous stream using alkaline solution. b. Packed b. benzol from coke oven gas using solar oil/wash oil. c. Plate c. ammonia from coke oven gas using refrigerated water. d. Spray d. tar from coke oven gas in primary gas coolers using chilled water. 3. Deairation (removal of O2) of water is done by 13. The-relative volatility for separation of a non-ideal binary mixture by distillation should be a. rectification b. absorption a. 0 c. ion-exchange b. 1 d. adsorption c. >1 d. 500 22. Which of the following is the most commonly used leaching solvent in d. >1000 vegetable oil industry ? 12. In continuous distillation, the internal reflux ratio (Ri) and the external a. Phenol reflux ratio (Re) are related as b. Hexane c. Furfurol d. Liquid SO2 a. b. 23. In an absorber, HETP does not vary with the a. flow rate of liquid b. flow rate of gas c. type and size of packing d. none of these c. Ri = Re d. 24. Large quantity of silica gel is normally dried in a __________ dryer. 13. In a counter-current extractor, as the axial mixing increases, the extraction efficiency a. freeze b. through circulation a. increases c. rotary vacuum b. decreases d. tray c. remains unchanged d. depends on the pressure of the system 25. For the same system, if the same liquid used in an absorber is decreased, the tower height will 14. Heat sensitive materials like certain pharmaceuticals and food stuffs can be dried in a/an __________ dryer. a. increase b. decrease a. indirect tray c. remain unaffected b. spray d. decrease or increase ; depends on the type of liquid c. freeze d. none of these 26. Hydrogenation of oil is carried out in a/an __________ in Vanaspati manufacturing plant. 15. In extractive distillation, solvent is a. agitated vessel a. added to alter the relative volatility of the mixture. b. sieve tray column b. of high volatility. c. bubble cap column c. present in overhead stream. d. packed tower d. of high viscosity to give high tray efficiency. 27. Sides of equilateral-triangular co-ordinates (on which ternary liquid 16. Radioactive nuclear waste is treated in system is plotted) represent a. mixer-settler extractor a. a pure component. b. rotating-disc contactor b. a binary mixture. c. pulsed column extractor c. a ternary mixture. d. Bollman extractor d. partially miscible ternary system. 17. Large scale drying of sugar is done in a __________ dryer. 28. In distillation column design, the McCabe-Thiele procedure is inadequate a. spouted bed and a Ponchan-Savarit procedure is needed, when b. tray a. saturated feed is not used. c. rotary b. an azeotrope forms. d. truck c. the latent heat of vaporisation of the more and less volatile 18. __________ temperature is the steady state temperature attained by a components are greatly different. small amount of liquid evaporating into a large quantity of unsaturated gas- d. a total condenser is used. vapor mixture. 29. In an interphase mass transfer process, the lesser the solubility of a given a. Dry bulb solute in a liquid, the higher are the chances that the transfer process will be b. Wet bulb a. liquid phase resistance-controlled. c. Dew point b. gas phase resistance controlled. d. none of these c. impossible. 9. The drying time between fixed moisture contents within the 'constant rate d. driven by a non-linear driving force. period' is proportional to (assuming that drying occurs from all surfaces of the 30. As the reflux ratio decreases, the solid) (where, T = thickness of the solid ) a. a. separation becomes more efficient. T1/2 b. number of plates increases. b. T c. column diameter increases. c. T 1.5 d. none of these. d. T3 31. Which of the following equipments is not used for gas dispersion ? 20. __________ equation applies to diffusivities in liquids. a. Agitated vessels a. Gilliland b. Bubble cap tray towers b. Hirschfelder c. Perforated sieve tray towers c. Wilke and Chang d. Spray towers d. none of these 32. One mole feed of a binary mixture of a given composition is flash 21. A packed tower compared to a plate tower for a particular mass transfer vaporised at a fixed P and T. If Raoult's law is obeyed, then changing the feed operation composition would effect  a. the product composition but not the fraction vaporised. c. both (a) and (b) b. the product composition as well as the fraction vaporised. d. vapour pressure of the solution c. the fraction vaporised but not the product composition. d. neither the product composition nor the fraction vaporised. 44. Operating velocity in a packed tower is usually __________ the flooding velocity. a. half b. twice c. equal to 33. The equation, is for d. more than a. steady state equimolar counter diffusion b. Fick's first law of diffusion 45.The Knudsen diffusivity is dependent on the c. steady state diffusion for stagnant case d. liquid M.T.C. by penetration theory. a. molecular velocity only. 34. With increase in the liquid flow rate at a fixed gas velocity in a randomly b. pore radius of the catalyst only. packed counter current gas-liquid absorption column, the gas pressure drop c. molecular mean free path only. a. decreases d. molecular velocity and por radius of the catalyst. b. remains unchanged 46. Minimum possible diameter of a packed coloumn is decided mainly by the c. increases d. decreases exponentially a. flooding b. gas viscosity c. liquid density d. liquid hold up 35. The equation, is for 47. Solvent used in extractive distillation a. Fick's second law of diffusion. b. stready state diffusion for stagnant case. a. is of low volatility. c. liquid M.T.C. by Higbie penetration theory. b. forms a low boiling azeotrope. d. none of these. c. forms a high boiling azeotrope. 36. Which of these columns incurs the lowest pressure drop ? d. does not alter the relative volatility of the original components. a. Packed column (with stacked packing) b. Packed column (with dumped packing) 48. Capacity of a rotary dryer depends on its c. Bubble plate column a. r.p.m d. Pulse column b. inclination with ground surface 37. In the desorption of highly soluble gas from the liquid, the main resistance c. both (a) and (b) will be in the __________ phase. d. neither (a) nor (b) a. gas b. liquid 49. The cooling effect in a cooling tower can be speeded up by c. both (a) & (b) d. neither (a) nor (b) a. increasing the air velocity and area of exposed wet surface. 38. If G = insoluble gas in gas stream and L = non-volatile solvent in liquid b. reducing the barometric pressure. stream, then the slope of the operating line for the absorber is c. reducing the humidity of the air. d. all (a), (b) and (c). a. L/G b. G/L 50. The following plot gives the saturated humidity (He) versus temperature c. always < 1 (T).Line joining (H1, T1) and (H2, T2) is the constant enthalpy line. Choose d. none of these the correct one from among the alternatives A, B, C and D. 39. Which of the following remains constant during evaporative cooling process with recirculated water supply ? a. Relative humidity b. Partial pressure of vapour c. Wet bulb temperature d. None of these 40. For stripping of a gas in a counter current stripper, the operating line a. lies above the equilibrium curve. b. lies below the equilibrium curve. c. can lie above or below the equilibrium curve. d. is always parallel to the equilibrium curve. 41. Which of the following same diameter columns gives lowest pressure drop per unit height ? a. Bubble-cap column b. Sieve-plate column c. Packed column (stacked) d. Randomly packed column a. T1-Dew point temp; T2-Dry bulb temp; T3-Wet bulb temp. 42. Diffusion in concentrated solutins differs from that in dilute solutions, b. T1-Dew point temp; T2-Wet bulb temp; T3-Dry bulb temp. because of the change in the __________ with the concentration of the c. T1-Wet bulb temp; T2-Dry bulb temp; T3-Dew point temp. solution. d. T1-Dry bulb temp; T2-Wet bulb temp; T3-Dew point temp. a. degree of ideality b. viscosity SECTION 6 c. both 'a '& 'b' 1. When both the fluids flow concurrently in an absorber, the slope of the d. neither 'a' nor 'b' operating line is a. - ve 43. Stage efficiency in a leaching process depends on the b. + ve c. 1 a. time of contact between the solid and the solution d. -1 b. rate of diffusion of the solute through the solid and into the liquid 2. The percentage humidity is less than the relative humidity only at __________ percent humidity. a. zero b. hundred a. c. both zero and hundred d. none of these 3. Back-trapping in a distillation column b. a. increases tray efficiency. b. decreases tray efficiency. c. reduces pressure drop. c. d. is desirable, as it provides improved vapour-liquid contact. d. None of these 12. The falling rate period in the drying of a solid is characterised by 4. Flooding in a vapor-liquid contacting equipment occurs in a tray, when the pressure drop through a tray is __________ the liquid head available in the a. increase in rate of drying. downcomer. b. increasing temperatures both on the surface and within the solid. c. decreasing temperatures. a. less than d. none of these. b. more than c. same as 13. In which of the following unit operations, the selectivity is an important d. very much less parameter ? 5. Milk is dried usually in a __________ dryer. a. Distillation b. Solvent extraction a. freeze c. Absorption b. spray d. None of these c. tray d. rotary 14. Which of the following is an undesirable characteristic for the solvent used in gas absorption ? 6. At a given equilibrium pressure, with increase in temperature, the concentration of adsorbed gas on solid adsorbant a. Low vapor pressure b. Low viscosity a. increases c. High gas solubility b. decreases d. None of these c. remains unchanged d. increases exponentially 15. Which of the following equipments is not used for liquid dispersion ? 7. Which of the following adsorbent is used to decolourise yellow glycerine ? a. Wetted wall towers b. Packed towers a. Silica gel c. Venturi scrubbers b. Alumina d. Agitated vessels c. Fuller's earth d. Activated carbon 16. Diameter of raschig rings used in packed tower in industry is normally around __________ inches. 8. Which of the following liquid temperature (T) Vs. vapor-gas mixture enthalpy (H) diagram is valid for humidification operation? a. 2 b. 8 c. 12 d. 18 17. The diffusion co-efficient in m2 /s. of acetic acid in benzene (liquid in liquid) is a. b. a. 2.09 x 10-4 b. 2.09 x 10-5 c. 2.09 x 10-9 d. 2.09 x 10-12 18. Pick out the wrong statement. a. The Reynolds analogy for mass transfer is given by Lewis relation c. d. none of these and is applicable, when Schmidt number is one. b. Sherwood number for flow in pipes can be expressed as the ratio of 9. In a distillation column, with increase in the reflux ratio, the heat removed the concentration gradient at wall to the overall concentration in the cooler difference. a. increases. c. According to film theory for equimolar counter diffusion, the mass b. decreases. transfer coefficient is given by DAB(b)P - 3, Q - 2 c. remains unaffected. d. The z-component of the total mass flux of a component A in binary d. and the heat required in reboiler decreases. mixture of A and B is given by - Dab'.dCA/dz. 10. Pick out the wrong statement. 19. In case of non-ideal gases and liquids, the molal diffusivity a. Constant pressure distillation can not separate an azeotropic a. varies inversely as the pressure. mixture. b. varies directly as the pressure. b. Relative volatility of a binary mixture changes appreciably with the c. is independent of pressure. minor change in temperature. d. is equal to the volumetric diffusivity. c. The relative volatility of a binary mixture at azeotropic 20. Condensation of a vapour-gas mixture just begins, when (where, p = composition is unity. partial pressure of the vapour P = vapour pressure of the liquid ) d. Flash distillation is practised on wide spread scale in petroleum refinery. a. p=P b. p >>P 11. Which of the following is not a unit of mass transfer co-efficient ? c. p1 38. In a shell and tube type heat exchanger, the floating tube bundle heat c. 0.6 c. Air d. < 0.1 d. All have the same conductivity 9. 21. A sphere of radius 'R1' is enclosed in a sphere of radius 'R2'. The view (or shape) Maximum heat transfer rate is obtained in __________ flow. factor for radiative heat transfer of the outer sphere with respect to the inner sphere is a. laminar a. 0 b. turbulent b. R2/(R1+R2) c. creeping c. 1 d. (R1/R2)2 The capacity of double-effect evaporator is less than half of the capacity of two single effects, each of which is operating over same terminal temperature difference, when 22. the For a laminar flow of fluid in a circular tube, 'h1' is the convective heat transfer co- a. solution has an elevation of boiling point. efficient at velocity 'V1'. If the velocity is reduced by half and assuming the fluid b. evaporators operate under vacuum. properties are constant, the new convective heat transfer co-efficient is c. evaporators opreate at atmospheric pressure. a. 1.26 h1 d. none of these. b. 0.794 h1 c. 0.574 h1 35. d. 1.741 h1 Peclet number (Pe) is given by a. Pe = Re.Pr 23. b. Pe = Re/Pr The main purpose of providing fins on heat transfer surface is to increase the c. Pe = Pr/Re a. temperature gradient. d. Pe = Nu.Re b. mechanical strength of the equipment. c. heat transfer area. 36. d. heat transfer co-efficient. Nusselt number is the ratio of the a. temperature gradient of the wall to that across the entire pipe. 24. b. temperature difference to the temperature gradient at the wall. A BTU/hr.ft.2 °F is equal to c. heat flux at the wall to that across the entire pipe. a. 1 kcal/hr. m2°C. d. none of these b. 4.88 kcal/hr. m.2°C. c. 1 kcal/hr. m2.°K. 37. d. none of these. Prandtl number is the ratio of a. momentum diffusivity to mass diffusivity. 25. b. momentum diffusivity to thermal diffusivity. Which of the following has the lowest Prandtl number ? c. thermal diffusivity to mass diffusivity. a. Molten sodium (a coolant used in fast breeder reactor) d. thermal diffusivity to momentum diffusivity. b. Water c. Transformer oil 38. d. Dilute H2SO4 Which of the following parameters is increased by use of finned tube in a multipass shell and tube heat exchanger ? a. Tube side pressure drop and the heat transfer rate. 26. b. Convective heat transfer co-efficient. In SI units, fouling factor is expressed in c. Effective tube surface area for convective heat transfer. a. m2°K/W d. All (a) (b) and (c). b. W/m2°K c. m2°K 39. d. m°K/W Forced circulation evaporators are useful for the concentration of viscous, salting and scale forming liquors. Which of the following is a forced circulation evaporator? 27. a. Long vertical evaporator An ejector is used to b. Horizontal tube evaporator a. increase pressure c. Agitated film evaporator b. increase temperature d. Calenderia vertical tube evaporator c. remove condensate d. none of these 40. "The ratio of the total emissive power to the absorptivity for all bodies is same at ther- 28. mal equilibrium". This is __________ law. Extremely large or small volumes of fluids are generally best routed through the shell a. Kirchoffs side of a shell and tube heat exchanger, because of the b. Planck's a. less corrosion problems. c. Wien's displacement b. flexibility possible in the baffle arrangement. d. Stefan-Boltzman c. low pressure drop. d. high heat transfer co-efficient. 41. View factor is important in heat transfer by 29. a. steady state conduction All analogy equations connecting friction factor and heat transfer co-efficient apply b. natural convection only to c. forced convection a. wall or skin friction d. radiation b. form friction c. both (a) and (b) 42. d. turbulent flow The advantage of using a 1 - 2 shell and tube heat exchanger over a 1 - 1 shell and tube heat exchanger is 30. a. lower tube side pressure drop. Electro-magnetic spectrum range, which is important for radiation varies from b. lower shell side pressure drop. __________ microns. c. higher tube side heat transfer co-efficient. a. 1 to 100 d. higher shell side heat transfer co-efficient. b. 0.5 to 50 c. 10 to 100 43. d. 100 to 1000 For a multipass shell and tube heat exchanger, the LMTD correction factor is always a. 1 b. >1 31. The characteristic dimensionless groups for heat transfer to a fluid flowing through c. wall temperature. c. suspended solids content b. exit fluid temperature < wall temperature. d. all (a), (b) and(c) c. exit fluid temperature = wall temperature. 20.At steady state the temperature variation in a plane wall, made of two different solids I & II is shown below : d. Graetz number > 100. 29.1000 kg of wet solids are to be dried from 60% to 20% moisture (by weight). The mass of moisture removed in kg is a. 520 b. 200 c. 400 d. 500 30.Which is the most suitable for the con-certration of highly concentrated solution? a. Open pan evaporation b. Long tube vertical evaporator The thermal conductivity of material I a. is smaller than that of II. c. Agitated film evaporator b. is greater than that of II. d. None of these c. is equal to that of II. 31.Unsteady state heat conduction occurs, when d. can be greater than or smaller than that of II. a. temperature distribution is independent of time. b. temperature distribution is dependent on time. 21. Duhring rule is important in solving problems on a. distillation c. heat flows in one direction only. b. crystallisation d. three dimensional heat flow is concerned. c. evaporation 32.What is the absorptivity of a black body ? a. 1 d. humidification b. 0 22. In a shell and tube heat exchanger, the height of 25 percent cut baffles is equal to (where, D = inside diameter of shell) c. 0.78 a. 0.25 D d. 0.95 b. 0.75 D 33.Mode of heat transfer in which the fluid moves under the influence of c. 0.50 D changes in fluid pressure produced by external work is called a. radiation d. none of these b. natural convection 23. Multiple effect evaporation is generally recommended, when the a. large scale evaporation of liquor is needed. c. forced convection d. conduction a. maximum resistance in the series. b. sum of all resistances. c. average of all resistances. 34.Baffle spacing a. is not the same as baffle pitch. d. minimum resistance presents in the series. b. should be less than one fifth the diameter of the shell. 44.Double pipe heat exchangers are preferably useful, when c. should be less than the inside diameter of the shell. a. high viscosity liquid is to be cooled. d. none of these. b. requirement of heat transfer area is low. 35.Boiling point elevation of a solution of NaOH c. overall heat transfer co-efficient is very high. a. increases rapidly with temperature rise. d. a corrosive liquid is to be heated. b. is almost independent of temperature. 45.Removal of __________ heat is involved in the condensation of a vapor c. is almost independent of pressure. under saturated conditions. d. both (b) and (c). a. super b. sensible 36.The advantage of backward feed multiple effect evaporators over forward c. latent feed units is that a. heat sensitive material can be handled. d. both(b) & (c) b. there is no additional cost of pumping. 46.The rate of heat transfer from a vertical plate by natural convection depends c. most concentrated liquid is at highest temperature. upon the temperature differences (ΔT) between wall and outside bulk. The d. equal heat transfer co-efficients exist in various effects. proportionality is given as a. (ΔT)1/4 37.Which of the following is the most controlling factor for the rate of bubble b. ΔT1/2 detachment from the hot solid surface ? a. Liquid density c. (ΔT)5/4 b. Liquid viscosity d. (ΔT)3/4 c. Hot surface temperature 47.If air (a non-condensing gas) is present in a condensing vapor stream, it will d. Interfacial tension __________ the condensation rate of vapor. a. increase 38.Which characteristic of a fluid is not important in deciding its route in a shell b. decrease and tube heat exchanger ? a. Corrosiveness c. not affect b. Fouling characteristic d. increase the condensing film co-efficient as well as c. Viscosity 48.Prandtl and Reynold's analogies are identical for Prandtl number value of d. None of these a. 0 b. 0.5 39.Thermal conductivities of most of the liquids __________ with rise in temperature. c. 1 a. increases d. 5 b. decreases 49.The outlet temperature of cooling water in a heat exchanger is generally not c. remains unchanged allowed to exceed above 50°C in industrial practice mainly to avoid d. may increase or decrease; depends on the liquid a. its evaporation loss b. excessive corrosion 40.A metal ball of radius 0.1 m at a uniform temperature of 90°C is left in air at 30°C. The density and the specific heat of the metal are 3000 kg/m3 and 0.4 c. uneconomic LMTD kJ/kg.K respectively. The heat transfer co-efficient is 50 W/m2.K Neglecting the temperature gradients inside the ball, the time taken (in hours) for the ball to d. decrease in heat exchanger efficiency cool to 60°C is a. 555 50.In evaporators, lowering the feed temperature a. increases the heating area required. b. 55.5 b. reduces the economy. c. 0.55 c. both (a) and (b). d. 0.15 d. decreases the heating area required. 41.The purpose of floating head in a heat exchanger is to a. avoid buckling of tubes. b. provide support for tubes. SECTION 8 c. decrease the pressure drop. 1. The type of liquor circulation system to be ' employed in evaporators (viz. d. facilitate its lengthening, if needed. natural or forced circulation) is determined mainly by the __________ of the liquid. 42.1000 Kg of liquid at 30°C in a well stirred vessel has to be heated to 120°C, a. viscosity using immersed coils carrying condensing steam at 150°C. The area of the b. density steam coils is 1.2 m2 and the overall heat transfer co-efficient to the liquid is c. thermal conductivity 1500 W/m2.°C. Assuming negligible heat loss to the surrounding and specific d. corrosive nature heat capacity of the liquid to be 4 kJ/kg.°C, the time taken for the liquid to reach desired temperature will be 2.In case of surface condensers, a straight line is obtained on a. 15 min b. 22 min plotting __________ on an ordinary graph paper. a. 𝟏/𝑽 ̅ −𝟎.𝟖 c. 44 min b. 𝑉̅ −0.8 d. 51 min c. 𝑉̅ −2 d.. 1/𝑉̅ −2 43.Overall thermal resistance for conductive heat transfer through a series of 3. Thermal diffusivity is the most important in heat transfer by flat resistances is equal to the a. conduction b. radiation c. condensation d. natural convection 14. In a boiling curve, the peak heat flux is called the __________ point. a. Nusselt 4.(NGr x NPr) is called the __________ number. b. Leidenfrost a. Graetz c. boiling b. Reyleigh d. burnout c. Nusselt d. Stanton 15. Pick out the wrong statement. a. Heat transfer from a hot body to cold body by the emission of heat waves is 5.A dephlegmator is a called radiation: a. total condenser b. Filmwise condensation takes place on non-wettable surfaces. b. vacuum evaporator c. The boiling point of a solution is affected by liquid head as well as boiling point c. partial condenser elevation. d. double pipe heat exchanger d. none of these. 6.A tank painted with which of the following coloured paints, would heat up 16. h.D/K is called the __________ number. maximum by radiation from sun ? a. Nusselt a. Yellow paint b. Peclet b. White paint c. Rayleigh c. Black paint d. Grashoff d. Grey paint 17. Prandtl number is the ratio of 7. The separation of liquid droplets from the vapor is done by a/an __________ a. mass diffusivity to thermal diffusivity. , in the evaporators. b. momentum diffusivity to thermal diffusivity. a. steam ejector c. thermal diffusivity to mass diffusivity. b. entrainment separator d. thermal diffusivity to momentum diffusivity. c. compressor d. vacuum pump 18. Conductance is given by(where, x = thickness, A = heat flow area, K = thermal conductivity.) 8. Fouling factor for a heat exchanger is given by (where, U1 = heat transfer co- a. x/KA efficient of dirty surface U2 = heat transfer co-efficient of clean surface) b. KA/x a. U1 - U2 c. K/Ax d. A/Kx 19. Heat flux, as defined in heat flow is analogous to __________ in electricity flow. b. a. current b. voltage c. resistance d. none of these c. d. U2 - U1 20. The wavelength at which the maximum monochromatic emissive power occurs for a black body, is (where, T = absolute temperature of the black body) 9.If a single tube pass heat exchanger is converted to two pass, then for the a. αT same flow rate, the pressure drop per unit length in tube side will b. α 1/T a. increase by 1.8 times c. α T4 b. decrease by 22 d. independent of T c. increase by 216 d. remain unchanged 21. In a shell and tube heat exchanger, putting a longitudinal baffle across the shell, forces the shell side fluid to pass __________ through the heat 10. A steel sphere of radius 0.1 m at 400°K is immersed in an oil at 300°K. If the exchanger. centre of the sphere reaches 350°K in 20 minutes, how long will it take for a a. once 0.05 m radius steel sphere to reach the same temperature (at the centre) under b. twice identical conditions ? Assume that the conductive heat transfer co-efficient is c. thrice infinitely large. d. four times a. 5 minutes b. 10 minutes 22. When the ratio of the Grashoff number and to the square of Reynolds c. 20 minutes number is one, the dominant mechanism of heat transfer is d. 40 minutes a. free convection b. entry length problem in laminar forced conduction (developing thermal 11. Fluid motion in the natural convection heat transfer between a solid surface boundary layer) and a fluid in contact with it, results from the c. mixed convection (both free and forced) a. existence of thermal boundary layer. d. forced convection b. temperature gradient produced due to density difference c. buoyancy of the bubbles produced at active nucleation site. 23. The purpose of providing bleed points in the evaporator is to d. none of these. a. admit the feed b. remove the product 12. Evapo