Questions and Answers of Unit Operations Of Chemical Engineering

Results have been reported on the performance of a crystallizer operating on sodium chloride. Results from one experiment are Tip speed uT = 1.350 ft/min Retention time = 1.80
Examine the data shown in Fig. 13.9 for nucleate boiling of a normal paraffin on a single horizontal tube. (a) Calculate the heat transfer coefficient for several values of ΔT, and compare the
If the filter cake of Example 24.1 is placed on an uninsulated metal pan, conduction through the pan and the wet cake would increase the surface temperature and the drying rate. (a) If the change in
Spherical alumina catalyst particles with 30 percent moisture and an average size of 300 μm are dried in a batch fluidized bed with air entering at 250°F, a superficial velocity of 1.2 ft/s, and a
A hollow-fiber membrane separator with an O2/N2 selectivity of 6.0 is operated with feed and permeate pressures of 5.0 and 1.0 atm. (a) What is the maximum oxygen concentration that could be
Reverse osmosis is used to produce pure water from sea water that has a salt concentration of 35,000 ppm and an osmotic pressure of 10 lbƒ/in.2 per 1.000 ppm. The inlet pressure is 900 lbƒ/in.2
A spiral-wound membrane used for concentrating apple juice by reverse osmosis was first tested with pure water at temperatures from 20°C to 40°C. The flux was proportional to the transmembrane
A brochure from the Permea Corporation claims that increasing the operating pressure from 90 to 180 lbƒ/in.2 raises the nitrogen productivity of their air separation membrane units by a factor of
The separation of toluene-ethanol mixtures was studied using a polyethylene membrane in a small pervaporation cell. With one atmosphere pressure and 30°C on the 361 upstream side and full vacuum on
Plot the cumulative distribution given in Table 28.1 on logarithmic-probability paper. Is the plot linear over any range of particle sizes? How does the amount of fine material (smaller than 20-mesh)
An ideal product classification in a continuous vacuum crystallizer would achieve the retention of all crystals within the crystallizer until they attained a desired size and then discharge them from
CuSO4·5H2O containing 3.5 percent of a soluble impurity is dissolved continuously in sufficient water and recycled mother liquor to make a saturated solution at 80°C. The section is then cooled to
A solution of MgSO4 containing 43 g of solid per 100 g of water is fed to a vacuum crystallizer at 220°F. The vacuum in the crystallizer corresponds to an H2O boiling temperature of 43°F, and a
Calculate the arithmetic mean diameter D̅g for the -4- to + 200-mesh fractions of the material analyzed in Table 28.1. How does D̅g differ qualitatively from the volume mean diameter D̅v?Table
Assume that CuSO4·5H20 is to be crystallized in an ideal product-classifying crystallizer. A 1.4-mm product is desired. The growth rate is estimated to be 0.2 μm/s. The geometric constant a is
A potassium chloride crystallizer that operates at 100°F has a fines dissolution loop where the slurry temperature is 130°F. The solubility of KCI is 39.3 g/100 g H2O at 100°F and 44 g/100 g H2O
A small stirred tank used for batch crystallization of an antibiotic gave satisfactory results when the 10-cm turbine was operated at 550 r/min. The tank was 30 cm in diameter with an average depth
Use the nomograph in App. 8 to determine the value of n in the equation for gas viscosity, Eq. (3.6), for carbon monoxide and for helium over the ranges 0 to 300°C and 300 to 600°C.Eq. 3.6where μ
For the MgSO4 crystallizer of Example 27.5, the expected growth rate is 0.055 cm/h for a 20-mesh crystal. If the supersaturation is about 3 percent and the mass transfer coefficient is twice that for
Under the conditions given in Prob. 15.9, how long would it take to heat the vessel contents (a) from 20 to 60C, (b) from 60 to 100C?Prob. 15.9A turbine-agitated vessel 2 m in diameter contains 5,500
If the desired production rate in the crystallizer of Example 27.5 is 4.200 kg/h of MgS4·7H2O, the volume of liquid in the crystallizer is 7.7 m3, and the nucleation rate is 2.7 x 109 nuclei/m3·h,
Crystallization of gypsum takes place in a 200,000-gal stirred tank that is part of a process for flue gas desulfurization. With a single outlet to a settling tank and filter. the slurry has 15
What heat-transfer coefficient would be expected for natural convection to water at 212°F and 1 atm, outside a 1-in. horizontal pipe with a surface temperature of 213°F? Compare with Fig. 13.5 and
Calculate the temperatures of the inside and outside surfaces of the metal pipe or tubing in cases 1 to 3 of Prob. 11.1.Cases 1 to 3 of Prob. 11.1Calculate the overall heat-transfer coefficients
A turbine-agitated vessel 2 m in diameter contains 5,500 kg of a dilute aqueous solution. The agitator is 2/3 m in diameter and turns at 140 r/min. The vessel is jacketed with steam condensing at
A slab with a wet weight of 5 kg originally contains 50% moisture (wet basis). The slab is 600 by 900 by 75 mm thick. The equilibrium moisture content is 5% of the total weight when in contact with
(a) If the 6-ft tank described in Example 9.6 is equipped with a large impeller (Da/Dt = 2/3 instead of 1/3), what impeller speed will be needed to give the same power input of 2 hp per 1,000
A triple-effect evaporator of the long-tube type is to be used to concentrate 35.000 gal/h of a 17 percent solution of dissolved solids to 38 percent dissolved solids. The feed enters at 60°F and
Fluorspar (CaF2) is to be dried from 6 to 0.4 percent moisture (dry basis) in a countercurrent adiabatic rotary dryer at a rate of 18.000 lb/h of bone-dry solids. The heating air enters at 1,000°F
Data for a heat pipe designed to preheat air for a boiler are given below. (a) Check the heat balance for the unit and calculate the average heat transfer rate in kW for a single pipe. (b) Estimate
Set up and solve the differential equation for mass transfer from a small sphere of a pure slightly soluble solid suspended in a large mass of stagnant water.
A porous solid is dried in a batch dryer under constant drying conditions. Seven hours are required to reduce the moisture content from 35 to 10 percent. The critical moisture content was found to be
(a) Show that for a small drop of dilute slurry evaporating in a spray dryer, the drying time is proportional to the square of the initial size of the droplet. (b) What is the approximate drying
(a) Calculate the mean droplet diameter for a spray dryer with a 6-in. rotary atomizer turning at 10,000 rpm. The feed rate is 30 lb/min at 120°F. Assume the slurry density is 70 lb/ft3 and the
A continuous countercurrent dryer is to be designed to dry 800 lb of wet porous solid per hour from 140 percent moisture to 20 percent, both on the dry basis. Air at 120°F dry-bulb and 70°F
A food product containing 65 percent moisture is to be freeze-dried in a vacuum dryer operating at 0.5 mm Hg and a condensing temperature of -25°C. The material is 1.0 cm thick, and drying is to
Fine particles from a centrifuge are spread in layers 4.0 cm thick on 0.8 x 0.8 m metal trays in a tray dryer. The initial moisture content is 0.25 kg/kg of dry solid. The gas velocity in the dryer
Calculate the thermal efficiency of the rotary dryer described in Example 24.3. Assume air was heated from 70 to 260°F before entering the dryer.Example 24.3Calculate the diameter and length of an
A fluidized bed dryer is charged with a batch of spherical catalyst particles with an average diameter of 800 m and a wet particle density of 1,700 kg/m3. The initial bed height is 1.2 m. (a) With
(a) Use the correlation in Fig. 25.4 to predict the amount of n-butanol adsorbed on carbon for the conditions of Example 25.2, and compare with the experimental data. (b) Estimate the saturation
Granular carbon is used to remove phenol from an aqueous waste. If 10 x 20-mesh carbon is used with a superficial velocity of 0.03 m/s, estimate the number of transfer units in a bed 4 m deep. The
Adsorption on 6 x 10-mesh activated carbon is being considered to recover methyl ethyl ketone (MEK) from an airstream at 25°C and 1 atm. The airflow is 12,000 std ft3/min, and the air has 0.40 lb
The preliminary design for a vapor-phase adsorber specified a bed of 6 x 16-mesh carbon 6 ft in diameter and 4 ft deep, with a superficial velocity of 60 ft/min. However, the estimated pressure drop
Data for drying nitrogen with molecular sieve type 4A are given by Collins. Calculate the saturation capacity from the breakthrough curve, and determine the length of un- used bed based on a
Air with relative humidity of 50 percent at 20°C is compressed to 8 atm, cooled to 30°C to condense some of the water, and dried in a silica-gel dryer. What fraction of the water in the air is
A molecular sieve adsorbent used for air separation has a maximum capacity for N2 of 0.046 g/g at 30°C, and the data can be fitted to a Langmuir isotherm with K = 0.50 atm-1 (a) What is the
Granular activated carbon impregnated with sulfur is used to remove mercury vapor from natural gas and from air. Because chemical reaction converts the mercury to mercuric sulfide, the adsorption is
An adsorber for removing vinyl chloride monomer (VCM) from air has two beds of BPL carbon that are 4 ft deep, and at breakthrough, the beds have 0.09 lb VCM carbon. The average bed temperature is
A water softener has a resin bed 1 ft in diameter and 1.5 ft long. If the water contains 20 ppm Ca2+, 10 ppm Mg2+, and 300 ppm Na+, how many gallons can be treated before the resin needs regeneration?
A bed of 2-mm ion exchange beads with a particle density of 1.2 g/cm3 is back-washed with water at 15 C. (a) Predict the minimum fluidization velocity. (b) Estimate the bed expansion for V̅0 = 3
A filter cake 2 in. thick in a tray dryer is exposed to a stream of air at 160°F. Estimate the effective coefficient for radiant heat transfer from the tray above, and compare this with the
Tests in a laboratory adsorption column 1/4 in. in diameter and 12 in. long, packed with 20 x 32 mesh particles of activated carbon, gave good removal of solvent from an air stream, but tb was too
Laboratory tests of a membrane for H2/CH4 separation gave a permeate composition of 80 percent H2 and a residue of 42 percent H2 when the feed had 50 percent H2 and the feed and permeate absolute
(a) If a membrane has a selectivity of 8 for air separation, what is the maximum oxygen concentration that can be obtained for a single-stage device? (b) What is the approximate permeate composition
Preliminary analysis of a binary gas mixture by GC showed overlapping peaks, with t*A ≅ 15 min, t*B ≅ 21 min, and σA ≅ 2.1 min. (a) What are the values of N and α? (b) If the column length
Dialysis is being considered to recover a product A with molecular weight 150 from a dilute aqueous stream. The principal contaminant is a polymer B with molecular weight 15,000. Predict the initial
A hollow-fiber separator used for reverse osmosis is suspected of having flaws in the 0.1-μm dense layer, since the salt rejection is only 97 percent when tested with sea-water at 1,000 lbƒ/in.2
Pervaporation is used to produce nearly pure ethanol from a feed with 90 percent ethanol and 10 percent water. The feed enters at 80°C, and the design calls for reheating the liquid after the
Show how the water flux and salt rejection would change with upstream pressure for a perfect cellulose acetate asymmetric membrane and a feed with an osmotic pressure of 20 atm. Use the diffusivity
(a) Calculate the internal pressure drop for an oxygen-nitrogen hollow-fiber separator that has 600-m outside-diameter and 400-μm inside-diameter fibers 1.0 m long. When P1 ≅ 75 lbƒ/in.2 abs and
(a) Use the data in Table 26.2 to estimate the membrane selectivity for N2/CH4 based on the average driving force. (b) Explain why the same method cannot be used to estimate the H2/CH4
The permeation rates of CH4 and CO2 in a GASEP membrane at 80°F were given as 0.00205 and 0.0413 ft3 (std conditions)/ft2·h·(lbƒ/in.2), respectively. At 100°F the corresponding values were
A three-component mixture at 600 lbƒ/in.2 abs is fed to a membrane separator with a permeate pressure of 120 lbƒ/in.2 abs. The mixture has 50 percent A, 30 percent B, and 20 percent C. and the
A membrane system treating air with 1 percent CFC-11 produces a residue with 0.1 percent CFC-11 and a permeate of 4.9 percent CFC-11 with a stage cut of 19 percent. R 0.05. (a) What is the
The hollow-fiber separator of Example 26.1 has 300 x 600 μm fibers 1 m long and an external area of 5.2 m2. (a) With a permeate flow of 3.1 L. (STP)/min, what are the exit velocity and the pressure
Data on the rate of mixing of sand and salt particles in an air-fluidized bed are given in Table 28.3. The number of particles in each spot sample was about 100. (a) For each run. calculate the
The slurry of Prob. 29.3 is to be filtered in a press having a total area of 8 m2 and operated at a constant pressure drop of 2 atm. The frames are 36 mm thick. Assume that the filter medium
The slurry of Prob. 29.3 is to be filtered in a press having a total area of 8 m2 and operated at a constant pressure drop of 2 atm. The frames are 36 mm thick. Assume that the filter medium
A continuous rotary vacuum filter operating with a pressure drop of 0.7 atm is to handle the feed slurry of Prob. 29.3. The drum submergence is to be 15 percent. What total filter area must be
A continuous rotary vacuum filter operating with a pressure drop of 0.7 atm is to handle the feed slurry of Prob. 29.3. The drum submergence is to be 15 percent. What total filter area must be
A batch centrifugal filter having a bowl diameter of 750 mm and a bowl height of 450 mm is used to filter a suspension having the following properties:The final cake is washed with water under such
The screens used in Prob. 29.1 are shaking screens with a capacity of 4 metric tons/m2-h-mm mesh size. How many square meters of screen are needed for each of the screens in Prob. 29.1 if the feed to
A batch centrifugal filter having a bowl diameter of 750 mm and a bowl height of 450 mm is used to filter a suspension having the following properties:Liquid, water
What is the capacity in cubic meters per hour of a clarifying centrifuge operating under the following conditions? Diameter of bowl, 600 mm Specific gravity of
The filter of Prob. 29.7 is operated at a constant rate of 0.6 gal/ft2-min from the start of the run until the pressure drop reaches 70 lbƒ/in.2 and then at a constant pressure drop of 70 lbƒ/in.2
Show that at the critical speed the centrifugal force on a ball on a ball mill is equal to the force of gravity.
Trap rock is crushed in a gyratory crusher. The feed is nearly uniform 2-in. spheres. The differential screen analysis of the product is given in column,(1) of Table 28.4. The power required to crush
It is desired to separate a mixture of crystals into three fractions, a coarse fraction retained on an 8-mesh screen, a middle fraction passing an 8-mesh but retained on a 14-mesh screen, and a fine
The dust-laden air of Prob. 29.11 is passed through an impingement separator at a linear velocity of 8 m/s. The separator consists essentially of ribbons 25 mm wide. What is the maximum fraction of
The data in Table 29.6 were taken in a constant-pressure filtration of a slurry of CaCO3 in H2O. The filter was a 6-in. filter press with an area of 1.0 ft2. The mass fraction of solids in the feed
Assuming that the actual rate of washing is 85 percent of the theoretical rate, how long will it take to wash the cake in the press of Prob. 29.4 with a volume of wash water equal to that of the
A large Banbury mixer masticates 1.800 lb of scrap rubber with a density of 70 lb/ft3 The power load is 6,000 hp per 1,000 gal of rubber. How much cooling water, in gallons per minute, is needed to
What rotational speed, in revolutions per minute, would you recommend for a ball mill 1,200 mm in diameter charged with 75-mm balls?
The following relation between α and Δp for superlight CaCO3 has been determined to be a = 8.8 x 1010 [1 + 3.36 x 10-4 (Δp)0.86]where Δp is in pounds force per square foot. This relation is
Air carrying particles of density 1.800 kg/m3 and an average diameter of 20 μm enters a cyclone at a linear velocity of 18 m/s. The diameter of the cyclone is 600 mm. (a) What is the approximate
The filter of Prob. 29.7 is washed at 70°F and 70 lbƒ/in.2 with a volume of wash water equal to one-third that of the filtrate. The washing rate is 85 percent of the theoretical value. How long
A continuous pressure filter is to yield 1.400 gal/h of filtrate from the slurry described in Prob. 29.7. The pressure drop is limited to a maximum of 50 lbƒ/in.2 How much filter are must be
(a) Calculate the apparent mass-transfer coefficient for latex from the ultrafiltration results shown in Fig. 29.25. (b) Using the corresponding data for albumin as a reference, estimate the
Microfiltration is used to concentrate a suspension of latex particles from 2.5 wt percent to 20 percent. The particles are spheres with an average diameter of 0.2 μm. The membrane has a pure water
Diafiltration is used to purify 40 L of dilute protein solution produced in a pilot plant. The solution has 0.8 percent protein and 3.2 percent salts, and the protein/salt ratio should be 50:1 after
Data for washing a filter cake containing the antibiotic lincomycin are given by Belter, Cussler, and Hu.4 What wash ratio would be required to recover 95 percent of the antibiotic originally in the
A microfiltration unit used to concentrate a suspension of 0.8-µm spherical particles has a permeate flux of 150 L/m2·h at 30°C and a pressure drop of 2.1 atm. Under the same conditions, the pure
(a) Predict the effect of pressure drop on the permeate flux for the ultrafiltration of cheese whey in a 2-cm-diameter tubular membrane at a solution velocity of 3 m/s. Assume the membrane
A gas-phase exothermic reaction is carried out in a multitube reactor with the catalyst in 1-in. tubes and boiling water in the jacket. The feed temperature and the jacket temperature are 240°C. The
Air for a pilot-plant reactor is passed through a 50-mm pipe equipped with electric heaters strapped to the outside. By what factor could the overall heat-transfer coefficient be increased by filling
A shell-and-tube exchanger with two tube passes is used to heat ethanol from 60°F to 140°F with steam condensing at 230°F in the shell. The BWG 14 steel tubes are in. OD. The design overall
A shell-and-tube exchanger with 1-in. BWG 14 tubes will be used to cool a heavy oil from 120 to 50C, using cooling water at 25C. The oil properties are: (a) To help decide which fluid to put in the
Calculate FG for a 1-2 exchanger with Z = 1.0 and ηH = 0.50 using Eq. (15.1) and check with the value from Fig. 15.6.Eq. 15.1Fig. 15.6 FG = 1-H 1-ZnH 2 – nh(Z+1 (Z +D)?) 2-1H
Compare the outside coefficient in a crossflow exchanger [Eq. (15.8)] with that predicted by the Donohue equation [Eq. (15.6)] for typical values of Re and Pr. Why are the values from the Donohue
A hydrocarbon oil with the properties given in Problem 15.15 is to be cooled from 120 to 60°C in a plate-type exchanger. Cooling water at 30°C enters the exchanger at twice the mass flow rate of

Showing 1 - 100 of 432