Unit Exams 1

UNIT OPERATION

1.

Determine the height 124.1Kpa absolute, if absolute. a. b.

of a vertical column of fluid with a density of 641 kg/m that will be supported by a static pressure of the top of the column is open to the atmosphere. Atmospheric pressure may be taken as 101.1 Kpa 4.06 m 3.63 m

c. 3.15 m d. 4.6 m

e. none of the above

2.

A liquid with a density of 1121 kg/m flows through a straight steel pipe having an inside diameter of 0.0508 m at the rate of 45.4 kg/hr. The viscosity of the liquid is 0.9 Cp. Calculate the pressure drop in pascal due to friction if pipe is 1609m. a. 110 Pa c. 120 Pa e. none of the above b. 95 Pa d. 101 Pa

3.

Calculate the loss of mechanical energy as friction, expressed as lb f - ft/lbm due to sudden enlargement from a 2 in. inside diameter pipe to a 4 in. inside diameter for water at 65  F flowing at a rate of 1000 lb/min. a. 1.315 ft-lbf /lbm c. 13.15 ft-lbf -lbm b. 1.615 ft- lbf /lbm d. 15.36 ft-lbf /lbm

4.

Calculate the loss of mechanical energy as friction expressed as Joules/kg due to sudden contraction from a 0.0508 m inside diameter pipe to a 0.0254 m inside diameter pipe to a 0.0254 m inside diameter pipe for a liquid with a density of 641 kg/m 3 flowing at a rate of 22.7 kg/min. assume turbulent flow exist. a. 0.3J/kg c. 0.27J/kg e. none of the above b. 0.4 J/kg d. 0.20J/kg

5.

Calculate the Hp required for a pump assembly with an over all efficiency of 55%to deliver 200ft-lbf /lbm of fluid flowing to a system in which 100 lb of fluid flow per minute. a. 1.1 Hp c. 0.8 Hp e. none of the above b. 2.1 Hp d. 3.1 Hp

6.

A venturi meter is used to measure the flow of water from pumping installation. The venturi has 36 in. openings and an18in. throat. The venturi mercury manometer in which mercury and water are in contact has a reading of 3.1in. What is the flow in gallons per day? The temperature of water is 65  F. a. 15,700 gal/day c. 17,500 gal/day e. none of the above b. 16,000 gal/day d. 16,700 gal/day

7.

A liquid with a density of 75lb/ft3 flows through a 4 in sharp edge orifice in the bottom of a tank at the rate of 75 ft 3/min. The diameter of the tank is 10 ft. The orifice coefficient is 0.61. What is the depth of the liquid in the tank? The top of the tank is open to the atmosphere, and the water flows out of the tank to the atmosphere. a. 7.67 ft c. 9.57 ft e. none of the above b. 8.57 ft d. 8.27 ft

8.

A flat hard rubber (k ave. = 0.092 BTU/hr- ft F ) is 3 in. thick. If the difference in surface temperature from one side of the wallto the other is 100  F. Calculate the rate heat flow in BTU per hour per square foot wall surface. a. 35.8 BTU/hr-ft2 c. 38.8 BTU/hr-ft2 e. none of the above 2 b. 46.8 BTU/hr-ft d. 36.8 BTU/hr-ft2

9.

A copper rod is 3 ft long and 2 in. in diameter. The rod is insulated so that radial heat losses may be neglected. If one end of the rod has a temperature of 70  F and the other end is 220  F, calculate the rate of flow axially along the rod as: BTU per hr. For copper Kave may be taken as 220 BTU/hr-ft- F . a. 250 BTU/hr c. 230 BTU/hr e. none of the above b. 240 BTU/hr d. 220 BTU/hr

10.

A steam pipe with an outside diameter of 0.0838m is lagged with a cork insulation. The insulation is 0.0762mthick and k ave for the cork is 0.0433J/s-m- K . Thermocouples located at the inside and the outside surface of the cork indicate temperature of 383 K and 311 K respectively. Calculate the heat loss, as Joules per hour per meter. a. 68,000 J/hr-m c. 65,000 J/hr-m e. none of the above b. 70,000 J/hr-m d. 60,000 J/hr-m

11.

Water flow through a 2 in. standard (schedule40) steel pipe. The pipe is jacketed with steam at 230  F. The conditions are such that the over all heat transfer coefficient is 250 BTU/hr-ft2 of outside pipe area F . If the temperature of the water is 80  F at the pipe entrance and 180  F at the pipe exit, calculate the average amount of the heat gained by the water per hour four each foot of pipe length. a. 14,500 BTU/hr-ft c. 14,000 e. none of the above b. 14,140 BTU/hr-ft d. 13,140BTU/hr-ft

12.

An oil with a heat capacity at constant pressure 3559 J/kg K flows through a standard (schedule40) 0.0762 m diameter pipe at the rate of 1814 kg/hr. The pipe is 6.1 m long and jacketed with saturated steam at 383  k. The oil enters the pipe at 289  K and leave 361  K. Assuming a constant over all heat transfer coefficient for the system, calculate the value of the over all heat transfer coefficient based on the outside are of the pipe. a. 1620 J/s-K-m2 c. 1500 J/sK-m2 e. none of the above 2 b. 1720 J/s-K-m d. 1520 J/sK-m2

13.

Water flows through the copper wire with an outside diameter of 5in. and an inside diameter of 4.5 in. The pipe is jacketed with steam and over all coefficient of heat transfer is found to be 425 BTU/ hr-ft2 F inside are ( F ). The water film coefficient is 600 BTU/hr-ft2 F . Calculate the value of the steam film heat transfer coefficient. a. 1780 BTU/ hr-ft2- F c. 1720 BTU/ hr-ft2- F e. none of the above 2 b. 1750 BTU/ hr-ft - F d. 1700 BTU/ hr-ft2- F

14.

A standard (schedule 40) 2 in. diameter steel pipe carries water under such conditions that the water film coefficient is 450 BTU/hr-ft- F . The pipe is jacketed with steam having a film coefficient of 2000 BTU/hr-ft- F . What is the rate of heat transfer in BTU per hour per foot of pipe length if the mean over all temperature difference 100 F ? The average thermal conductivity of steel may be taken as 26 BTU/ hr-ft2- F /ft. a. 17,000 BTU/hr-ft c. 18,350 BTU/ hr-ft e. none of the above b. 17,250 BTU/hr-ft d. 17,350 BTU/ hr-ft

15.

Water is heated from 300 to 339 K in a 0.0762 m standard (schedule 40) steel pipe by saturated steam at 376 K considering outside the pipe. The water film coefficient is 2839J/s-m2- K and the steam film coefficient is 11, 356J/s-m2-F. What length of pipe is necessary if the water flows at a rate of 9072 kg/hr? a. 17.8 m c. 16.6 m e. none of the above b. 16.0 m d. 12.6 m

16.

A horizontal circular plate with a diameter of 8 in. is located in a room whose air temperature is 70  F. The upper surface of the plate has a temperature of 400  F. Calculate the amount of heat loss from the upper surface of the plate to the air by natural convention in BTU/hr. a. 180.5 BTU/hr c. 176.5 BTU/hr e. none of the above b. 186.5 BTU/hr d. 195 Btu/ hr

17.

A hot plate with an exposed area of 3 ft2 is placed in a room.. The emissivity of the metal making up the plate is 0.85. The plate surface is maintained at 500 F and the room temperature is kept at 90  F. Calculate the amount of heat lost from the plate by radiation in BTU over a period of 10 hours. .The non-black body correction factor (FAE)for this case is 0.85. a. 32,400 BTU/10 hr c. 35,000 BTU/ 10 hr e. none of the above b. 36,500 BTU/10 hr d. 33, 400BTU/ 10 hr

18.

The boiling temperature of a liquid at the liquid- vapor interface in an evaporator may be taken as 170  F. Calculate the standard over all heat transfer coefficient in the evaporator if 10, 000, 000 BTU/hr is transferred to the liquid through an area of 430ft2 . Saturated stem at a pressure of 20 lb/in2 gage is used as the heat source. a. 262 BTU/hr-ft2- F c. 270 BTU/hr-ft2- F e. none of the above b. 250 BTU/hr-ft2- F d. 265 BTU/hr-ft2- F

19.

A mixture containing 30 wt % sodium hydroxide and 70 wt% water is in equilibrium with a water-vapor pressure of 51.7Kpa. Determine the boiling temperature of the liquid at the liquid-vapor interface. a. 205 K c. 375 K e. none of the above b. 369 K d. 396 K

20.

A three effect evaporator uses original steam at a saturation pressure of 174.4 KPa gauge. The total boiling point rise is 8.3 K in the first effect, 13.9 K in the second effect and 22.2 K in the third effect. What is the limiting pressure which must be maintained in the vapor space of the third effect in order for the evaporator to operate? a. 60.7 Kpa c. 58.5 Kpa e. none of the above b. 68.7 Kpa d. 50.7 Kpa

21.

The vapor pressure of pure benzene is 986mmHg at a temperature of 89 8 C. The vapor pressure of pure to toluene is 392 mmHg at a temperature of 89  C. What will be the mole fraction of benzene in a binary liquid mixture of benzene and toluene, when the temperature is 89  C and the total equilibrium vapor pressure of benzene and toluene is 720 mmHg? a. 0.752 c. 0.663 e. none of the above b. 0.525 d. 0.552

22.

A liquid mixture of ethyl alcohol and water is in equilibrium with a vapor containing ethyl alcohol and water at a total pressure of 760 mmHg. A sample of the vapor indicates that it contains 3.3 mol of ethyl alcohol for every 1.7 mol of water. If the liquid has a mol fraction of 0.52 ethyl alcohol, what is the relative volatility for the mixture? a. 1.59 c. 1.79 e. none of the above b. 1.69 d. 1.89

23.

A liquid mixture of methyl alcohol and water contains0.41mol fraction methyl alcohol. The mixture is fed continuously to a unit where a simple equilibrium distillation occurs at atmospheric pressure. What will the concentration of the distillate be if 30 mol of distillate and 70 mol of the equilibrium liquid are withdrawn per 100mol of feed? a. 0.665 mol fraction CH3OH c. 0.775 mol fraction CH3OH e. none of the above b. 0.556 mol fraction CH3OH d. 0.456 mol fraction CH3OH

24.

A mixture containing 0.7 mol fraction a and 0.3 mol fraction b is subjected to a simple batch distillation until the instantaneous composition of the vapors leaving becomes 0.6 mol fraction a. If the relative volatility for the mixture is constant at  ab = 1.5, estimate the average composition of the total distillate collected. a. 0.825 mol fraction A c. 0.725 mol fraction A e. none of the above b. 0.925 mol fraction d. 0.625 mol fraction A

25.

An aqueous solution of ammonia containing 1 lb mol ofNH3 per 5 ft 3 of solution is in equilibrium with a gaseous mixture of NH 3 and air at 90  F when the partial pressure of NH3 is 0.0920 atm. Assuming Henry’s law is applicable to the NH3 over the range of contraction involved, what will be the equilibrium partial pressure of the NH 3 when the solution contains 1 mole % NH3 at 90  F may be taken as 61.9 lb/ft3. a. 0.0208 atm c. 0.0178 atm e. none of the above b. 0.0198 atm d. 0.0188 atm

26.

A continuous absorption tower is used for absorbing HCI in H 2O. Two hundred pound mols per hour of a gaseous mixture containing 5 mole oh HCI per 2 mols of air enters the bottom of the tower, and 15,000 lb of pure water enters the top of the tower per hour. The aqueous HCI solution leaving the bottom of the tower contains 1 mole of HCI for every7 moles of H2O. Assuming no water is vaporized I the tower, determine the mols of HCI per mol of all in the exit gas stream. a. 0.518 c. 0.318 e. none of the above b. 0.418 d. 0.618

27.

Ammonia is being absorbed in water at 70  F under such conditions that the Henry’s law applies. The value of the Henry’s constant H3is 3.03lbmol/ft3 –atm and the value of Kga for absorption is 3.0lbmol/h-ft3-atm. Determine the percent of the total resistance to mass transfer due to the gas film if the value of Kla is 5.1lbmol/h-ft3-(lbmol/ft3). a. 90.6 % c. 83.6 % e. none of the above b. 80.6 % d. 70.6 %

28.

A mixture of air and water vapor weighs 80 KG. Determine the humidity of the air if there is 1.4kg of water vapor in the mixture. a. 0.0178 kg water/kg dry air c. 0.0168 kg water/kg dry air e. none of the above b. 0.0188 kg water/kg dry air d. 0.0158 kg water/kg dry air

29.

The partial pressure of water vapor is 50 mmHg in a mixture of air and water vapor at 100  F and 1 atm pressure. How many BTU of heat must be added to 25lb of this mixture to raise the temperature to 12508  F? a. 90.4 BTU c. 93.4 BTU e. none of the above b. 83.4 BTU d. 98.4 BTU

30.

An adiabatic humidifier operates at atmospheric pressure under such conditions that the air leaving the unit is saturated at the adiabatic saturation temperature. If the air enters the humidifier at 80  F with a humidity of 0.005 lb of water vapor per pound of dry air, what will be the humidity of the air leaving the unit? a. 0.03 lb water vapor/lb dry air c. 0.018 lb water vapor/lb dry air e. none of the above b. 0.031 lb water vapor/lb dry air d. 0.011 lb water vapor/lb dry air

31.

A compressor delivers air at a total pressure at 40lb/in 2 , absolute and a temperature of 90  F. If this air is saturated with water vapor, what is the humidity of the air leaving the unit? a. 0.022 lb water/lb dry air c. 0.015 lb water/lb dry air e. none of the above b. 0.031 lb water/lb dry air d. 0.011 lb water/lb dry air

32.

Under conditions where a certain sand has reached its equilibrium moisture content, 50 kg of the sand and water contains 48.7kg dry sand. What is the equilibrium moisture content of the sand under these conditions? a. 0.0168 kg water/kg dry sand c. 0.0267 kg water/kg dry sand e. none of the above b. 0.0178 kg water/kg dry sand d. 0.0367 kg water/kg dry sand

33.

A tray drier is to be used for drying a solid material. Each tray is 3 ft wide by 4 ft long and the wet materials has a depth of 2 in. The density of the wet material is 50 lb/ft3. The wet materials contains 3 lb of water per pound of dry solid. How many trays are necessary to obtain 3,000 lb of a product containing 1 lb of water per pound of dry solid? a. 55 trays c. 50 trays e. none of the above b. 60 trays d. 65 trays

34.

A plate and frame filter press containing 20 frames is used to filter a slurry made up to 10 lb dry solids per 100 lb of liquid and solid mixture. The inside dimensions of each frame are 2 ft by 2 ft by 1 in thick. The caked formed in the filtration is non compressible and contains 0.7 lb of dry solids per pound of cake. How many pounds of solid free filtrate can be delivered before the press is filled with a wet cake having a density of lb/ft3? a. 3,600 lb c. 3,650 lb e. none of the above b. 3,500 lb d. 3,650 lb

35.

A rotary filter turns at the rate of 2 rpm. The fraction of total filtering area immersed in the slurry is 0.20. It has been observed that 1.5ft3 of filtration is delivered per minute per square foot of submerged area with a given slurry under these operating conditions. If 6 ft3 of the filtrate is delivered per revolution by this rotary filter, what is the total filtering area of the filter cloth on the drum? a. 59 ft2 c. 49 ft2 e. none of the above 2 b. 35ft d. 45 ft2

36.

Experimental filtration data for a compressible cake indicate that the specific cake resistance is 3.1 lb f – h/lb-ft when the pressure difference driving force is 2lb/in2 and 3.9 lbf –h/lb-ft when the pressure difference is 5lbf /in2. Estimate the value of the compressibility exponent for the cake. a. 0.15 c. 0.35 e. none of the above b. 0.20 d. 0.25

37.

A filtration is carried out in a plate and frame filter press at a constant pressure difference of 3lbf/in2. The total filtering area is 80ft2 and the specific cake resistance is 3.5 lb f –h/lb-ft. How many cubic feet of filtrate will be obtained in 1 hour if the filter cake contains10 lb of dry solids per cubic foot of filtrate? The resistance of the frame and the cloth may be assumed as negligible and the cake may be considered as non compressible. a. 397 ft3 c. 407 ft3 e. none of the above b. 387ft3 d. 366 ft3

38.

Drop of oil 15 microns in diameter are to be settled from their mixture with air. The specific gravity of the oil is 0.9and the air is at 70  F and 1 atm. A settling of 1 min. is available. How high should the chamber be to follow settling of these particles? The density of air at 70  F and 1 atm is 0.075 lb/ft3. The viscosity of the air is 0.018 Cp. a. 2.6 ft c. 1.7 ft e. none of the above b. 1.2 ft d. 2.2 ft

39.

A flotation plant produces 3,000 tons per dayofCUFeS2 (chalcopyrite). It produces 80 tons of Cu concentrate assaying 25% Cu. If the analyzes 0.7%, calculate the percentage recovery. a. 95.2% c. 85.3 % e. none of the above b. 93.2% d. 88.6 %

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