4.-day-2-mockboards

SAINT LOUIS UNIVERSITY SCHOOL OF ENGINEERING AND ARCHITECTURE DEPARTMENT OF CHEMICAL ENGINEERING

MOCK BOARDS : CHEMICAL ENGINEERING PRINCIPLES 1.

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A wet material having a critical moisture content of 15% (d.b.) and an equilibrium moisture content of 3% (d.b.) took 6 hours to dry from 45% (d.b.) to 10% moisture. The time it will take to dry to 15% moisture dry bulb is a. 5 hrs b. 4.5 hrs c. 4 hrs d. 3.5 hrs Convert a moisture content of 85% wet basis to moisture content dry basis a. 156% b. 268% c. 567% d. 600% A wet food product contains 70% water. After drying, it is found that 80% of original water has been removed. Determine the mass of water removed per kilogram of wet food. a. 1.56 b. 0.56 c. 1.23 d. 0.23 Means the gaseous form of the component that is also present as liquid a. vapor b. vapor – free gas c. dry material d. liquid vapor The material (solid) that contains no liquid, its amount is constant during the process a. bone dry material b. wet solids c. dried solids d. bound moisture When a part of the solid is no longer wetted by the liquid, the transfer area available for direct heat and mass transfer decreases. a. initial rate period b. constant rate period c. 1st falling rate period d. 2nd falling rate period The removal of relatively small amounts of water or other liquid from the solid material to reduce the content of residual liquid to an acceptably low value. a. humidification b. air conditioning c. dehumidification d. drying A 100 kg batch granular solids containing 30% moisture is to be dried in a tray drier to 15.5% of moisture by passing a current of air at 350K tangentially across its surface at a velocity of 1.8 m/s. If the constant rate of drying under these conditions is 0.0007 kg/s-m2 and the critical moisture content is 15%, calculate the approximate drying time. Assume the drying surface to be 0.04 m2/kg dry mass. a. 3.26 hrs b. 2.44 hrs c. 1.15 hrs d. 0.98 hr This is water retained so that it exerts a vapor pressure less than that of free water at the same temperature. a. bound moisture b. equilibrium moisture c. critical moisture d. free moisture Raw cotton has been stored in a warehouse at 29C and 50% RH. For 200 kg of cotton from the warehouse, how many kilograms should appear in the woven cloth, neglecting lintage and thread losses? Regain of cotton cloth at 70%RH is 8.10. a. 202.8 b. 47.98 c. 187.62 d. 59.90 A single effect evaporator is used to concentrate 7 kg/s of solution from 10% to 50% of solids. The feed enters the evaporator at 294K and its specific heat is 3.76 kJ/kg-K. Steam is available at 205 kN/m 2 and evaporation takes place at 13.5 kN/m 2. The specific heat of the thick liquor is 3.14 kJ/kg-K. The overall heat transfer coefficient is 3 kW/m2-K. The condensate leaves the heating space at 352.7K. Calculate the amount of steam used in kg/s. a. 3.9 b. 4.7 c. 5.2 d. 6.5 Based from the preceding problem, estimate the heating surface required in m 2. a. 38 b. 52 c. 60 d. 69 When the pressure of the heating steam in an evaporator is increased, the steam consumption for a given duty and heat transfer area will a. increases b. decreases c. remains the same d. doubles It refers to any layer or deposit of extraneous material on a heat transfer surface, which can easily removed by mechanical means during maintenance. a. scaling b. salting c. fouling d. boiling The other term for long tube vertical rising film (LTVRF) evaporator is a. Rillieux b. Fairhurst c. Ballou d. Kestner If vapors are withdrawn from a given effect of the multiple-effect evaporator and used outside the evaporator system in place of the steam, the steam saving is number of withdrawal effect times amount of vapor withdrawal divided by the total number of effects. If one pound of vapor withdrawn from the second effect of a four-effect evaporator, how much steam would be saved?

SAINT LOUIS UNIVERSITY SCHOOL OF ENGINEERING AND ARCHITECTURE DEPARTMENT OF CHEMICAL ENGINEERING

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a. 0.50 b. 0.75 c. 1.0 d. 1.50 Based from the preceding problem, if one pound of vapor withdrawn from the third effect of a four-effect evaporator, how much steam would be saved? a. 0.50 b. 0.75 c. 1.0 d. 1.5 The primary purpose of evaporator design is to enable production of the necessary amount of satisfactory product at the a. higher total cost b. lowest total cost c. medium total cost d. NOTA An evaporator is used to concentrate 10,000 lb/h of a 20% solution of NaOH in water at 1400F using saturated steam at 25 psia at a rate of 7,000 lb/h. The OHTC is 275 Btu/h-ft2-0F when the pressure in the vapor is 1.7 psia. What is the steam economy? a. 0.83 b. 0.86 c. 0.89 d. 0.92 An evaporator is concentrating a feed (F) at 311K of a 20 wt% solution of NaOh to 50%. The saturated steam used for heating is 399.3K. The pressure in the vapor space of the evaporator is 13.3 kPa abs. The overall coefficient is 1420 W/m 2-K and the area is 86.4 m2. Calculate the feed rate of the evaporator (F) in kg/h. a. 8900 b. 8976 c. 9010 d. 9072 Diffusivity of ammonia (ft2/s) in air at 250C and 1 atm is a. 0.164 b. 0.229 c. 0.240 d. 0.320 Law governing mole – pressure relationships. a. ideal gas law b. dalton’s law c. amagat’s law d. raoult’s law Hydrogen will diffuse compared to oxygen a. half as fast b. 2 times slower c. 4 times faster d. 4 times slower In case liquid-liquid binary diffusion , diffusivity of one constituent into another is not dependent on a. temperature b. concentration c. pressure d. NOTA The value of Lewis number for air-water vapour system is around a. 1 b. 0.24 c. 3.97 d. 600 Ethyl alcohol is diffusing into an alcohol-water solution at 18 cm2/s. the concentration of alcohol in the bulk of the solution is negligible, while that at the surface of the solution is 0.12 g/cc. the film thickness is 0.15 cm and the diffusivity is 1x10-5 cm2/s. the mass of alcohol diffusing through 100 ft2 of interface per hour is a. 20 lbs b. 14 lbs c. 10 lbs d. 6 lbs How much faster will hydrogen diffuse than chlorine? a. 6x faster than Cl b. half the rate of Cl c. same as Cl d. twice as Cl The distribution coefficients for copper in aluminum at 500 and 600°C are 4.8x10-14 and 5.3x10-13 m2/s, respectively. Determine the approximate time (in hours) at 500°C that will produce the same diffusion result as a 10 hour heat treatment at 600°C. a. 9.10 b. 10.5 c. 110.4 d. 203.1 The diffusivity of benzene in air at 0°C and 1 atm is 0.299 ft2/hr. The diffusivity (in cm 2/s) of benzene in air at 25°C and 1 atm is a. 0.089 b. 0.261 c. 0.717 d. 0.277 At 750°K and 1 atm, the approximate value of Schmidt number for air is a. 0.01 b. 0.1 c. 1.0 d. 10 It is desired to increase the humidity of the air using a heater and adiabatic humidifier. The ambient air enters the heater at 800F dry bulb and 76.90F dew point temperature. The exhaust from the adiabatic humidifier has a dry bulb temperature of 1100F and 0.0265 lb water/lb dry air humidity. What is the wet bulb temperature (0F) of air entering the heater? a. 85 b. 80 c. 78 d. 74 At all humidities other than 0 and 100%, the percent humidity is _______ the RH a. more than b. less than c. equal to d. twice The mechanical – draft cooling towers are normally designed for liquid to gas (L/G) ratio with the corresponding values of KaV/L, which is defined as the cooling tower characteristics determined from the Merkel equation of Chesbyshev equation. What is the mechanical design range for L/G a. 0.65 – 1.5 b. 0.75 – 1.5 c. 0.5 – 1.5 d. 0.25 – 1.5

SAINT LOUIS UNIVERSITY SCHOOL OF ENGINEERING AND ARCHITECTURE DEPARTMENT OF CHEMICAL ENGINEERING

MOCK BOARDS : CHEMICAL ENGINEERING PRINCIPLES 34.

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Critical humidity of a solid salt means the humidity a. above which it will always become damp c. both (a) & (b) b. below which it will always stay dry d. NOTA The most efficient cooling tower out of the following is a. induced draft b. forced draft c. natural draft d. atmospheric For the cooling tower with a circulating water flowrate of 5000 gpm, six concentration cycle, 0.1% drift loss, inlet and outlet water temperature of 1000F and 800F respectively. The estimated amount of water loss due to evaporation is a. 25 gpm b. 85 gpm c. 100 gpm d. 150 gpm The difference of wet bulb temperature and adiabatic saturation temperature of unsaturated mixture of any system is a. positive b. negative c. zero d. NOTA Heat is BTU necessary to increase the temperature of 1 lb. of gas and its accompanying vapor by 1 o F is called the a. latent heat b. specific heat c. humid heat d. sensible heat The dew point of a saturated gas phase equals the a. gas temperature b. room temperature c. wet bulb temperature d. dry bulb temperature Refers to the ratio of the partial pressure to the vapor pressure at a specified temperature of the gas-vapor mixture. a. absolute humidity b. relative humidity c. percentage humidity d. saturation humidity Using antoine’s equation, the vapor pressure of tetrahydrofuran at 80 OC is estimated to be ____ psi. a. 49.55 b. 38.68 c. 29.36 d. 22.69 Establish the separation capability of a single stage batch still processing a mixture of two components having a relative volatility of 4. At the start of the batch separation, there are 600 mols of the more volatile compound A and 400 moles of the compound B in the kettle. When the remaining charge in the kettle is 80%B, how much total material has been boiled off? a. 500 b. 625 c. 650 d. 725 An ideal mixture of A and B is to be distilled continuously. If the relative volatility is constant at 1.75 and feed is saturated liquid with 50 mol% A, feed rate is 200 lbmols/h. Distillate composition of 90% A and bottoms composition of 10% A. Find the minimum number of stages. a. 6.8 b. 5.9 c. 6.1 d. 5.6 The liquid mixture of 60% benzene and 40% toluene is charged into a still pot where differential distillation is carried at 1.2 atm absolute pressure. How much of the charge must be boiled away to leave a liquid mixture containing 80% toluene? Assume the relative volatility to be 2.44 a. 14.41% b. 85.59% c. 41.14% d. 59.85% One hundred moles per hour of solution containing 80 moles of A, the rest B is subjected to a simple continuous distillation. D moles of distillate containing 72 moles A is obtained. If A is five times more volatile than B, the concentration of A in the distillate is a. 0.95 b. 0.85 c. 0.75 d. 0.65 A fractionating column is operating at 1 atm to produce a product of ethanol and water which leaves the top plate at 78.410C. The bottom product is to contain 1 mole percent ethanol. The feed contains 17 mole percent ethanol and is introduced at its boiling point. The feed rate is 44 moles per hour. Reflux is returned to the top plate at a rate of 31 moles per hour and at the top plate temperature . If plate efficiency is 60%, calculate the number of actual plates. a. 8 b. 16 c. 24 d. 35 Based from the preceding problem, calculate the rate of heat transfer in the reboiler in BTU/h a. 420,000 b. 531,000 c. 623,000 d. 754,000 Based from the preceding problem, calculate the rate of heat transfer in the condenser in BTU/h a. 672,000 b. 547,000 c. 495,000 d. 402,000

SAINT LOUIS UNIVERSITY SCHOOL OF ENGINEERING AND ARCHITECTURE DEPARTMENT OF CHEMICAL ENGINEERING

MOCK BOARDS : CHEMICAL ENGINEERING PRINCIPLES 49.

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A distillation column is composed of 7 theoretical stages in the enriching section and 8 theoretical stages in the stripping section. If the overall efficiency is 50%, then the number of actual stages is a. 15 b. 30 c. 16 d. 32 In distillation, the vapor generated by boiling the liquid is withdrawn from contact with the liquid and condensed as fast as it is formed. a. multi-step b. fractional c. differential d. flash Calculate the mass of the resulting solution if copper ore is to be leached with water in a single stage. 400 tons of copper ore containing 12% by mass copper sulfate and 88% by mass insoluble inert is leached with 1000 tons of water. The inerts will retain 1.3 tons of water per ton of inert. a. 568 tons b. 457 tons c. 542 tons d. 534 tons Roasted copper ore containing CuSO4 is to be extracted in a counter stage extractor. A feed consisting of 250 kg gangue, 50kg CuSO4 and 25 kg water is charged in the extractor. The strong solution produced consists of 85% water and 15% CuSO4 by mass. The recovery of CuSO4 is 90% of that in the ore. Pure water is to be used as a fresh solvent. After each stage, 1 kg of gangue retained 4 kg of solution. If equilibrium is attained in each stage, determine the weight of solution that leaves the first stage. a. 25 kg b. 255 kg c. 300 kg d. 1000 kg Based from the preceding problem, determine the percentage of CuSO 4 in the final discharge a. 0.2% b. 0.3% c. 0.4% d. 0.5% Based from the preceding problem, the number of stages required is close to a. 7 b. 8 c. 9 d. 10 A 120,000 ft3 leach bed contains 0.50% CuO. The bulk bed density is 105 lb/ft3 with a 0.33 void fraction. Leach acid is used to extract 92% of the copper content in 75 days. The average extraction rate (lb/h) of CuO is most nearly: a. 22 b. 32 c. 320 d. 3500 There are 30 kg of solute in 100 liters of water, the weight of solute that will be extracted by 35 liters of toluene. a. 30.0 kg b. 22.9 kg c. 15.0 kg d. 7.0 kg A series of pressure tanks operating with countercurrent solvent flow is called a. Kennedy Extractor b. Rotacel Extractor c. Diffusion Battery d. Percolation Used to obtain materials in attractive and uniform crystals of good purity, separating a solute from a melt or a solution and leaving impurities behind. a. gas absorption b. evaporation c. stripping d. crystallization A plait point is the point on the solubility curve, where the tie line reduces to a point. What is the number of plait point for a ternery system containing two pairs of partially miscible liquids? a. 0 b. 1 c. 2 d. 3 Degree of freedom for leaching and solvent extraction process is a. 0 b. 1 c. 2 d. 3 A pump delivers 40 gpm of water with a total head of 40 ft. The efficiency of the pump is 65%. What is its BHP? a. 0.62 b. 0.70 c. 2.0 d. 3.1 When two centrifugal pumps are connected in series, the discharge changes by a factor of a. 1/2 b. 1 c. 2 d. 4 What type of pump would you recommend if the capacity is 5000 gpm at a head of 15 ft of water? a. gear pump b. axial flow pump c. centrifugal pump d. screw pump What will be the rated capacity in gpm of a 4 ½ inch impeller centrifugal pump operating at a speed of 3450 rpm capable of generating a head of 40 ft of water? a. 320 b. 96 c. 248 d. 134 An axial flow pump operating at a speed of 880 rpm can supply water at a rate of 3000 gpm. The maximum head that this pump can deliver in ft. of water is a. 20 b. 87 c. 36 d. 62 When the impeller speed of an ideal centrifugal pump is doubled, the volumetric flow rate of the discharge is increased by a factor of

SAINT LOUIS UNIVERSITY SCHOOL OF ENGINEERING AND ARCHITECTURE DEPARTMENT OF CHEMICAL ENGINEERING

MOCK BOARDS : CHEMICAL ENGINEERING PRINCIPLES 67. 68.

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a. 2 b. 4 c. 3 d. 5 The rate of material __________ is zero in case of a steady state system. a. production b. accumulation c. input d. reaction Equal masses of CH4 and H2 are mixed in an empty container. The partial pressure of hydrogen in this container expressed as the fraction of total pressure is a. 1/9 b. 2/3 c. 5/9 d. 8/9 Separation of mixtures based on differences in volatilities by utilizing vapor and liquid phases at essentially the same temperature and pressure for the coexisting zones a. gas absorption b. distillation c. screening d. evaporation How many pounds of calcium fluoride rock is needed to produce 3000 lbs of a 60% HF per day if the yield is 90% and the rock contains 95% calcium fluoride? a. 4105 b. 3696 c. 3510 d. 4390 What horsepower is required to isothermally compress 800 ft3 of air per minute from 14.7 psia to 120 psia? a. 28 hP b. 108 hP c. 256 hP d. 13,900 hP Helium as the working fluid in an ideal Ericsson cycle operating between limits of 550 and 3000 R is being utilized. Calculate the thermal efficiency of this cycle. a. 77% b. 82% c. 87% d. 90% The food compartment of a refrigerator is maintained at 40C by removing heat from it at a rate of 360 kJ/min. If the required power input to the refrigerator is 2 kW, determine the performance of the refrigerator. a. 3 b. 0.33 c. 4 d. 0.25 Steam enters an adiabatic turbine at 8 MPa and 500 0C with a mass flowrate of 5 kg/s and leaves at 30 kPa. The adiabatic efficiency of the turbine is 0.85. Neglecting the KE change of the steam, determine the exit temperature in 0C. a. 41 b. 55 c. 69 d. 77 Based from the preceding problem, determine the power output of the turbine in KW. a. 1447 b. 4805 c. 12180 d. 16991 Isentropic process means a constant a. enthalpy process b. volume process c. pressure process d. entropy process An isolated system can exchange a. matter with its surroundings c. both matter and energy with its surroundings b. energy with its surroundings d. neither matter nor energy with its surroundings What is the degree of freedom for a system comprising liquid water equilibrium with its vapor? a. 0 b. 1 c. 2 d. 4 An irreversible process a. is the analog for linear frictionless motion in machines b. is an idealized visualization of behavior of a system c. yields the maximum amount of work d. yields the amount of work less than that of a reversible process If different processes are used to bring about the same chemical reaction, the enthalpy change is same for all of them. a. Hess’s Law b. Kirchoff’s Law c. Lavoisier Law d. Laplace Law It is a method of developing the design for a heat exchanger wherein the engineer assures the existence of an exchanger and makes calculations to determine if the exchanger would handle the process requirements under reasonable conditions. a. heat exchanger modeling c. heat transfer performance evaluation b. heat exchanger calculation d. rating of heat transfer The heat transfer radially across an insulated pipe per unit area a. remains constant c. increases from pipe wall to the insulated surface b. is inversely proportional to thermal conductivity d. decreases from pipe wall to the insulated surface In a heat exchanger, floating head is provided to

SAINT LOUIS UNIVERSITY SCHOOL OF ENGINEERING AND ARCHITECTURE DEPARTMENT OF CHEMICAL ENGINEERING

MOCK BOARDS : CHEMICAL ENGINEERING PRINCIPLES 84.

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a. relieve stresses caused by thermal expansion c. increase the heat transfer area b. facilitate cleaning of the exchanger d. increase log mean temperature gradient In a heat exchanger, hot fluid enters at 60OC and leaves at 48OC, where as the cold fluid enters at 35OC and leaves at 44OC. Calculate the mean temperature difference for cross flow (both fluids unmixed) a. 11.50 oC b. 13.58 oC c. 14.16 oC d. 14.45 oC O O A 5 cm diameter sphere at 600 C is placed near an infinite wall at 100 C. Both surfaces are black. Calculate the net radiant heat transfer between the two bodies. a. 125 W b. 175 W c. 250 W d. 31.8 W At 378.50C, the half-life for the first order thermal decomposition of ethylene oxide is 363 min and E = 52,000 cal/mole. Determine the specific rate of reaction at 4500C a. 0.101 / min b. 0.019 / min c. 0.011 /min d. 0.190 /min For the elementary step, (CH3)3CBr(aq) → CH3C+ (aq) + Br-(aq). The molecularity is a. 0 b. 1 c. 2 d. unpredictable Which statement is correct. a. Reactions with low activation energy are usually exothermic b. The rate law for a reaction is an algebraic expression relating the forward reaction rate to the product concentration c. The rate law sometimes enables to deduce the mechanism of a reaction d. Increase in the total pressure of a gas phase reaction increases the fraction of collisions effective in producing reactions States that the equilibrium is the state of the system consisting of the greatest number of equally likely molecular configuration which are macroscopically indistinguishable and can be considered to be identical. a. Thermodynamic equilibrium c. Kinetic view of equilibrium b. Statistical mechanics equilibrium d. Non-chain reaction mechanism For a reaction A  R, where R has autocatalytic effect CA0=1.0 mol/L. What is the time for 80% conversion if CR0 is 1/10 of CA0 and k for the autocatalytic reaction is 0.1/hr? a. 1 hr b. 2 hrs c. 3 hrs d. 4 hrs A steel rod on a bridge must be made to withstand a pull of 5000 lbs. Find the diameter of the rod assuming a factor of safety of 5 and ultimate stress of 64,000 psi. a. 0.75” b. 0.71” c. 0.84” d. 0.79” Conversion of sugar to alcohol with the aid of Saccharomyces cerevisiae produces a. beer b. wine c. yogurt d. rum This fatty acid has 12 carbons, no double bond and normally found in coconut oil and palm kernel oil a. Lauric acid b. Palmitic acid c. Stearic acid d. Myristic acid The process of hardening rubber is called a. Precipitation b. Polymerization c. Vulcanization d. Isomerization This is designated as the no.5 in the “big six” of plastics a. PET b. PVC c. PE d. PP Caustic soda is produced by reacting a 20% aqueous solution of sodium carbonate and 25% calcium hydroxide. Calcium carbonate is precipitated as the solution of caustic soda is produced. The precipitate is made up of 94% calcium carbonate, 5% water and 1% caustic soda. The number of grams of caustic soda formed per 100 grams of precipitate is a. 28.9 b. 75.2 c. 98.7 d. 212 It is a control system in which the control action is independent of the output. a. closed loop system c. feedback control system b. open loop system d. feedforward control system The amplitude ratio for the sinusoidal response of _________ is less than 1 a. first order system b. second order system c. transportation lag d. no answer The characteristic equation for a system is s3 + 9s2 + 26s + 12 (2+ KC) = 0. Using the Routh test, the value of KC that will keep the system on the verge of instability is

SAINT LOUIS UNIVERSITY SCHOOL OF ENGINEERING AND ARCHITECTURE DEPARTMENT OF CHEMICAL ENGINEERING

MOCK BOARDS : CHEMICAL ENGINEERING PRINCIPLES 100.

a. 20.9 b. 17.5 c. 13.2 d. 10.9 Which of the following relates the absorption and evolution of heat at the junctions of a thermocouple to the current flow in the circuit? a. Seebeck Effect b. Joule Heating Effect c. Thomson Effect d. Peltier Effect