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engineering
chemical engineering

Questions and Answers of Chemical Engineering

A number of polymers, including polyvinylchloride, polystyrene, and polymethylmethacrylate are made by suspension or emulsion polymerization, in which the product of polymerization reaction is finely
What are the advantages and disadvantages of superheated steam compared to air as the heating medium? Why might superheated steam be superior to air for the drying of lumber?
A direct-heat dryer is to operate with air entering at 250Â°F and 1 atm with a wet-bulb temperature of 105Â°F. Determine from the psychrometric chart and/or relationships of Table 18.3 the
Air at 1 atm, 200°F, and a relative humidity of 15% enters a direct-heat dryer. Determine the following from the psychrometric chart and/or relationships of Table 18.3.(a) Wet-bulb temperature.(b)
Repeat Example 18.1 if the air is at 1.5 atm instead of 1.0 atm.
n-Hexane is being evaporated from a solid with nitrogen gas. At a point in the dryer where the gas is at 70°F and 1.1 atm, with a relative humidity for hexane of 25%, determine:(a) Partial pressure
At a location in a dryer for evaporating toluene from a solid with air, the air is at 180°F, 1 atm, and a relative humidity of 15%. Determine the humidity, the adiabatic-saturation temperature, the
Repeat Example 18.5 for water only, with air entering at 180°F and 1 atm, with a relative humidity of 15%, for an exit temperature of 120°F. In addition, plot temperature through the dryer.
Air enters a dryer at 1,000°F with a humidity of 0.01 kg H2O/kg dry air. Determine the wet-bulb temperature if the air pressure is(a) 1 atm.(b) 0.8 atm.(c) 1.2 atm.
Paper is being dried with recirculating air in a two-stage drying system operating at 1 atm. The air enters the first dryer at 180"F, where the air is adiabatically saturated with moisture. The air
Before being recirculated to a dryer, air at 96oF, 1 atm, and 70% relative humidity is to be dehumidified to 10% relative humidity. Cooling water is available at 50°F. Determine a method for
Nitrocellulose fibers with an initial total water content of 40 wt% (dry basis) are dried in trays in a tunnel dryer operating at 1 atm. If the fibers are brought to equilibrium with air at 25?C and
The sucrose in ground coffee particles of an average diameter of 2 mm is to be extracted with water in a continuous, Counter current extractor at 25°C. The diffusivity of the sucrose in the
For the conditions of Example 16.8, determine the effect on leaching time of particle size over the range of 0.5 mm to 50 mm.
For the conditions of Example 16.8, determine the effect of % recovery of copper over the range of 50—100%.
Repeat Example 16.8, except that the ore contains 3 wt% Cu2O
For the shrinking-core model, if the rate of leaching is controlled by an interface chemical reaction that is first order in the concentration of reactant A, derive the expression,where k =
Estimate the sphericities of the following simple particle shapes:(a) a cylindrical needle with a height, H, equal to 5 times the diameter, D(b) a rectangular prism of sides a, 2a, and 3a
A certain circular plate of diameter, D, and thickness, t, has a sphericity of 0.594. What is the ratio oft to D?
A laboratory screen analysis for a batch of crystals of hypo (sodium thiosulfate) is as follows. Prepare both differential and cumulative-undersize plots of the data, using a spreadsheet. In
Derive expressions for the surface-mean and mass-mean diameter from a particle-size analysis based on counting, rather than weighing, particles in given size ranges, letting Ni be the number of
Using the screen analysis of Exercise 17.3, calculate, with a spreadsheet, the surface-mean, mass-mean, arithmetic-mean, and volume-mean crystal diameters, assuming that all particles have the same
A precipitation process for producing perfect spheres of silica has been developed. The individual particles are so small that most cannot be discerned by the naked eye. Using optical microscopy, the
A screen analysis for a sample of glauber's salt from a commercial crystallizer is as follows, where the crystals can be assumed to have a uniform sphericity and volume shape factor.Use a spreadsheet
1,000 grams of water is mixed with 50 grams of Ag2C03 and 100 grams of AgCl. At equilibrium at 25oC, calculate the concentrations in moles/liter of Ag+, C1–, and COT ions and the grams of Ag2CO3
5,000 lb/h of a saturated aqueous solution of (NH4)2SO4 at 80°C is cooled to 30°C. At equilibrium, what is the amount of crystals formed in lb/h. If during the cooling process, 50% of the water is
7,500 lb/h of a 50 wt% aqueous solution of FeC13 at 100°C is cooled to 20°C. At 100oC, the solubility of the FeC13 is 540 g/100 g of water. At 2PC, the solubility is 91.8 g/100 g water and crystals
The concentrate from an evaporation system is 5,870 lb/h of 35 wt% MgS04 at 180°F and 25 psia. It is mixed with 10,500 lb/h of saturated aqueous recycle filtrate of MgSO4 at 80°F and 25 psia. The
Urea is to be crystallized from an aqueous solution that is 90% saturated at 100°C. If 90% of the urea is to be crystallized in the anhydrous form and the final solution temperature is to be 30°C,
In Examples 17.3 and 17.5, heat addition to the crystallizer is by an external heat exchanger through which magma is circulated, as shown in Figure. If instead the heat is added to the feed,
For the conditions of Exercise 17.11, determine the rate at which heat must be added to the system.
For the conditions of Example 17.4, calculate the amount of heat in calories/100 grams of water that must be removed to cool the solution from 100 to 10.6oC.
Based on the following data, compare the effect of crystal size on solubility in water at 25°C for (1) KC1 (see Example 17.7), a soluble inorganic salt, with that for (2) BaS04, an almost insoluble
Determine the supersaturation ratio, S, required to permit 0.5-pm-diameter crystals of sucrose (MW = 342 and ρc = 1,590 kg/m3) to grow if σS,L 0.01 J/m2.
The Kelvin equation, (17-16), predicts that solubility increases to infinity as the crystal diameter decreases to zero. However, measurements by L. Harbury [J. Phys. Chem., 50, 190-199 (1946)] for
Using the following data, compare the effect of supersaturation ratio over the range of 1.005 to 1.02 on the primary homogeneous nucleation of AgNO3, NaNO3, and KNO3 from aqueous solutions at 25°C:
Estimate the effect of relative supersaturation on the primary, homogeneous nucleation of Bas04 from an aqueous solution at 25oC,if
Repeat parts (g) and (i) of Example 17.9 if the solution velocity past the crystal face is reduced from 5 cm/s to 1 cm/s.
The feed to a cooling crystallizer is 2,000 kg/h of 30 wt% Na2S04 in water at 40°C. This solution is to be cooled to a temperature at which 50% of the solute will be crystallized as the decahydrate.
Two tons per hour of the dodecahydrate of sodium phosphate (Na3PO4 ∙ 12H2O) is to be crystallized by cooling, in a cooling crystallizer, an aqueous solution that enters saturated at 40°C and
An aqueous feed of 10,000 kg/h, saturated with BaCl2 at 100°C, enters a crystallizer that can be simulated with the MSMPR model. However, crystallization is achieved with negligible evaporation. The
The feed to a continuous crystallizer that can be simulated with the MSMPR model is 5,000 kg/h of 40 wt% sodium acetate in water. Monoclinic crystals of the trihydrate will be formed. The pressure in
An MSMPR-type crystallizer is to be designed to produce 2,000 lb/h of crystals of the heptahydrate of magnesium sulfate with a predominant crystal size of 35 mesh. The magma will be 15 vol% crystals.
Refer to Example 17.12. In Run 15, Fitchett and Tarbell also made measurements of number density of crystals at 200 rpm, for which the data can be fitted well by the equationIn n = 26.3 – 0.407
Tai and Chen [AIChE J., 41, 68-77 (1995)] studied the precipitation of calcium carbonate by mixing aqueous solutions of sodium carbonate and calcium chloride in an MSMPR crystallizer with pH control,
Tsuge and Matsuo studied the precipitation of Mg(OH)2 by reacting aqueous solutions of MgCl2?and Ca(OH)2 in a 1-liter MSMPR crystallizer operating at 450 rpm and 25?C. Crystal sizes were measured by
The feed to the top of a falling-film crystallizer is a melt of 60 wt% naphthalene and 40 wt% benzene at saturation conditions. If the coolant enters at the top at 10°C, determine the crystal-layer
Paradichlorobenzene melts at 53°C, while orthodichlorobenzene melts at -17.6°C. They form a eutectic of 87.5 wt% of the ortho isomer at -23°C. The normal boiling points of these two isomers differ
Derive(17-67).
Derive the following expression for the average impurity concentration over a particular length of crystal layer, z2 – z1, after one pass or partial pass of zone melting.Using the results of
In Example 17.14, let the last 20% of the crystal layer be removed, following the first pass, to z/ℓ = 9. Calculate from (1), in Exercise 17.33, the average impurity concentration in the remaining
A bar of 98 wt% A1 with 2 wt% of Fe impurity is to be subjected to one pass of zone refining. The solid-liquid equilibrium distribution coefficient for the impurity is 0.29. If z /ℓ = 10 and
Wet lumber of the type in figure is slowly dried from an initial total moisture content of 50 wt% to a moisture content in equilibrium with atmospheric air at 25?C and 40% relative humidity.
Fifty pounds of cotton cloth containing 20% total moisture content (dry basis) are hung in a closed room containing 4,000 ft3 of air at 1 atm. Initially, the air is at 100°F at a wet-bulb
Raw cotton having an initial total moisture content of 95% (dry basis) and a dry density 43.7 lb/ft3 is to be dried batchwise to a final moisture content of 10% (dry basis) in a cross-circulation
Slabs of filter cake with a bone-dry density of 1,600 kg/m3 are to be dried from an initial free-moisture content of 110% (dry basis) to a final free-moisture content of 5% (dry basis) batchwise in
The filter cake of Exercise 18.28 is extruded into cylindrical-shaped pieces measuring 114 in. in diameter 318 in. long that are placed in trays that are 6 cm high x 1 m long x 0.5 m wide and through
It takes 5 h to dry a wet solid, contained in a tray, from 36 to 8% moisture content, using air at constant conditions. Additional experiments give critical- and equilibrium-moisture contents of 15%
A tunnel dryer is to be designed to dry, by crossflow with air, a wet solid that will be placed in trays measuring 1.5 m long x 1.2 m wide x 25 cm deep. Drying will be from both sides. The initial
A piece of hemlock wood measuring 15.15 x 14.8 x 0.75 cm is to be dried from the two large faces from an initial total moisture content of 90% to a final average total moisture content of lo%, with
When Case 1 of liquid diffusion is controlling during the falling-rate period, the time for drying can be determined from (3) under Example 18.13. Using that equation, derive an equation for the rate
In a cross-circulation tray dryer, the equations for the constant-rate period neglect radiation and assume that the bottoms of the trays are insulated so that heat transfer takes place only by
A tunnel dryer is to be used to dry 30 lb/h of raw cotton (dry basis) with a countercurrent flow of 1,800 lb/h of air (dry basis). The cotton enters at 70°F with a moisture content of 100% (dry
A 25 wt% solution of coffee in water at 70°F is spray dried to a final moisture content of 5% (dry basis) with air that enters at 450°F and 1 atm with a humidity of 0.01 lb/lb (dry basis) and exits
7,000 lb/h of wet, pulverized, clay particles with 27% moisture (dry basis) at 15°C and 1 atm enter a flash dryer where they are dried to a moisture content of 5% (dry basis) with a co-current flow
5,000 lb/h of wet isophthalic acid crystals with 30 wt% moisture (wet basis) at 30°C and 1 atm enter an indirect-heat, steam-tube rotary dryer, where they are dried to a moisture content of 2 wt%
The extruded filter cake of Examples 18.8 and 18.18 is to be dried under the same conditions as in Example 18.18 except that three drying zones 8 ft long each will be used, with flow upward in the
Repeat the calculations of Example 18.18 if the extrusions are 318 in. in diameter x ½ in. long. Compare your results with those of Example 18.18 and comment.
A direct-heat, countercurrent-flow, rotary dryer with a 6-ft diameter and 60-ft length is available to dry titanium dioxide particles at 70°F and 1 atm with a moisture content of 30% (dry basis) to
A fluidized-bed dryer is to be sized to dry 5,000 kg/h (dry basis) of spherical polymer beads that are closely sized to 1 mm in diameter. The beads will enter the dryer at 25°C with a moisture
Which of the following statements are true?(a) Feedback and feedforward control both require a measured variable,(b) The process variable to be controlled is measured in feedback control.(c)
Consider a home heating system consisting of a natural gas-flied furnace and a thermostat. In this case the process consists of the interior space to be heated. The thermostat contains both the
In addition to a thermostatically-operated home heating system, identify two other feedback control systems that can be found in most residences. Describe briefly how each of them works: include
Does a typical microwave oven utilize feedback control to set cooking temperature or to determine If the food is ‘cooked”? If not, what mechanism is used? Can you think of any disadvantages to
Driving an automobile safely requires a large amount of individual skill. Even if not generally recognized, the driver needs an intuitive ability to utilize feedforward and feedback control
The distillation column shown in the drawing is used to distill a binary mixture. Symbols x, y, and z denote mole fractions of the more volatile component, while B, D, R, and F represent molar flow
Two flow control loops axe shown in the drawing. Indicate whether each system is either a feedback or a feed-forward control system. Justify your answer. It can be assumed that the distance between
I. M. Appelpolscher, supervisor of the process control group of the Ideal Gas Company, has installed a 25 x 40 x 5-ft swimming poe1 in his backyard. The poo1 contains level and temperature sensors
A perfectly stirred, constant-volume lank has two input streams, both consisting of the same liquid. The temperature and flow rate of each of the streams can vary with time. (a) Derive a dynamic
A completely enclosed stirred-tank heating process is used to beat an incoming stream whose flow rate varies. The heating rate from this coil and the volume are both constant. (a) Develop a
Two tanks are connected together in the following unusual way in Figure.(a) Develop a model for this system that can be used to find h1, h2, w2, and w3 as functions of time for any given variations
Consider a liquid flow system consisting of a sealed tank with noncondensible gas above the liquid as shown in Figure. Derive an unsteady-state model relating the liquid Level h to the input flow
Two surge tanks are used to dampen pressure fluctuations caused by erratic operations of a large air compressor. (See Figure) (a) If the discharge pressure of the compressor is Pd(t) and the
A closed stirred-tank reactor with two compartments is shown in figure. The basic idea is to feed the reactants continuously into the first compartment where they will be preheated by energy
The Ideal Gas Company has built a stirred-tank chemical reactor with a paddle-type agitator. Dr. A. Quirk, head of the Chemical Kinetics and Reactor Design Group, is attempting to determine why his
A jacketed vessel is used to cool a process stream as shown in figure. The following information is available: (i) The volume of liquid in the tank V and the volume of coolant in the jacket Vi remain
A jacketed vessel similar to the one in Exercise 2.8 is used to heat a liquid by means of condensing steam. The following information is available:(i) The volume of liquid within the tank may
Irreversible consecutive reactions A ? B ? C occur in a jacketed, stirred-tank reactor as shown in Figure. Derive a dynamic model based on the following assumptions: (i) The contents of the tank and
A blending tank in figure is used to mix a process stream (Stream 1, pure A) with a liquid catalyst (Stream 2, pure B). The blending process outlet mixture then flows directly to a reactor. The flow
A process tank has two input streams—Stream 1 at mass flow rate w1 and Stream 2 at mass flow rate w2. The tank’s effluent stream, at flow rate w, discharges through a fixed valve to atmospheric
The liquid storage tank shown in figure has two inlet streams with mass flow rates w1 and w2 and an exit stream with flow rate w3. The cylindrical tank is 2.5 m tall and 2 m in diameter. The liquid
Consider a blending tank that has the same dimensions and nominal flow rates as the storage tank in Exercise 2.13 but incorporates a valve on the outflow line that is used to establish flow rate w3.
Suppose that the fed-batch bioreactor in figure is converted to a continuous, stirred-tank bioreactor (also called a chemostat) by adding an exit stream. Assume that the inlet and exit streams have
In medical applications the chief objectives for drug delivery are: (i) to deliver the drug to the correct location in the patient’s body, and (ii) to obtain a specified drug concentration profile
Bioreactions are often carried out in batch reactors. The fed-batch bioreactor model in Section 2.4.9 is also applicable to batch reactors if the feed flow rate F is set equal to zero. Using the
Use Eq. 3.1 to show that the Laplace transform of
A student has Laplace transformed an ordinary differential equation (ODE) and obtained the following transform: . The following facts are known: (i) The original ODE had all zero initial
Figure shows a pulse function. (a) From details in the drawing, calculate the pulse width, t. (b) Construct this function as the sum of simpler time elements, some perhaps translated in time, whose
Derive Laplace transforms of the input signals shown in Figs. a and b, by summing component functions found in Table3.1.

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