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engineering
mechanical engineering

Questions and Answers of Mechanical Engineering

A long, hemi cylindrical (l-m radius) shaped furnace used to heat treat sheet metal products is comprised of three zones. The heating zone (1) is constructed from a ceramic plate of emissivity 0.85
The bottom of a steam-producing still of 200-mm diameter is heated by radiation. The heater, maintained at 1000?C and separated 100 mm from the still, has the same diameter as the still bottom. The
A long cylindrical heater element of diameter D = 10 mm, temperature T1 = 1500 K, and emissivity ?1 = 1 is used in a furnace. The bottom area A2 is a diffuse gray surface with ?2 = 0.6 and is
A radiative heater consists of a bank of ceramic tubes with internal heating elements. The tubes are of diameter D = 20 mm and are separated by a distance s = 50 mm. A reradiating surface is
Consider a long duct constructed with diffuse, gray walls 1 m wide(a) Determine the net radiation transfer from surface A1 per unit length of the duct.(b) Determine the temperature of the insulated
The coating on aim by 2 m metallic surface is cured by placing it 0.5 m below an electrically heated surface of equivalent dimensions, and the assembly is exposed to large surroundings at 300 K. The
A cubical furnace 2 m on a side is used for heat treating steel plate. The top surface of the furnace consists of electrical radiant heaters that have an emissivity of 0.8 and a power input of 1.5 x
An electric furnace consisting of two heater sections, top and bottom, is used to heat treat a coating that is applied to both surfaces of a thin metal plate inserted midway between the heaters. The
A solar collector consists of a long duct through which air is blown; its cross section forms an equilateral triangle 1 m on a side. One side consists of a glass cover of emissivity ?1 = 0.9, while
The cylindrical peephole in a furnace wall of thickness L = 250 mm has a diameter of D = 125 mm. The furnace interior has a temperature of 1300 K, and the surroundings outside the furnace have a
A composite wall is comprised of two large plates separated by sheets of refractory insulation, as shown in the schematic. In the installation process, the sheets of thickness L = 50 mm and thermal
A small disk of diameter D1 = 50 mm and emissivity ?1 = 0.6 is maintained at a temperature of T1 = 900 K. The disk is covered with a hemispherical radiation shield of the same diameter and an
Consider a cylindrical cavity of diameter D = 100 mm and depth L = 50 mm whose sidewall and bottom are diffuse and gray with an emissivity of 0.6 and are at a uniform temperature of 1500 K. The top
Consider a circular furnace that is 0.3 m long and 0.3 m in diameter. The two ends have diffuse, gray surfaces that are maintained at 400 and 500 K with emissivities of 0.4 and 0.5, respectively. The
Consider the diffuse, gray, four-surface enclosure with all sides equal as shown. The temperatures of three surfaces are specified, while the fourth surface is well insulated and can be treated as a
A room is represented by the following enclosure, where the ceiling (1) has an emissivity of 0.8 and is maintained at 40?C by embedded electrical heating elements. Heaters are also used to maintain
Work Problem 13.23, part (b), except with wall and cylinder emissivity of ε w = 0.95 and εe = 0.12, respectively.Data from 13.23A long cylindrical rod of very high emissivity is heat treated
A cylindrical furnace for heat-treating materials in a spacecraft environment has a 90-mm diameter and an overall length of 180 mm. Heating elements in the 135-mm-long section (1) maintain a
In manufacturing semiconductors, rapid thermal processing (RTP) is used to rapidly heat a silicon wafer to an elevated temperature in order to induce effects such as ion diffusion, annealing, and
An observation cabin is located in a hot-strip mill directly over the line, as shown in the schematic. The cabin floor is exposed to a portion of the hot strip that is at a temperature of T ss =
An opaque, diffuse, gray (200 mm by 200 mm) plate with an emissivity of 0.8 is placed over the opening of a furnace and is known to be at 400 K at a certain instant. The bottom of the furnace having
A tool for processing silicon wafers is housed within a vacuum chamber whose walls are black and maintained by a coolant at Tvc = 300 K. The thin silicon wafer is mounted close to, but not touching,
Most architects know that the ceiling of an ice-skating rink must have a high reflectivity. Otherwise, condensation may occur on the ceiling and water may drip?onto the ice, causing bumps on the
Boiler tubes exposed to the products of coal combustion in a power plant are subject to fouling by the ash (mineral) content of the combustion gas. The ash forms a solid deposit on the tube outer
Consider two very large parallel plates. The bottom plate is warmer than the top plate, which is held at a constant temperature of T1 = 330 K. The plates are separated by L = 0.1m and the gap between
Coated metallic disks are cured by placing them at the top of a cylindrical furnace whose bottom surface is electrically heated and whose sidewall may be approximated as a reradiating surface. Curing
Electrical conductors, in the form of parallel plates of length L = 40 mm, have one edge mounted to a ceramic insulated base and are spaced a distance w = 10 mm apart. The plates are exposed to large
The spectral absorptivity of a large diffuse surface is ?? = 0.9 for A ? = 0.3 for ? > 1?m. The bottom of the surface is well insulated while the top may be exposed to one of two different
A long uniform rod of 50-mm diameter with a thermal conductivity of 15 W/m · K is heated internally by volumetric energy generation of 20 kW/m3. The rod is positioned coaxially within a larger
The cross section of a long circular tube, which is divided into two semi cylindrical ducts by a thin wall, is shown below. Sides 1 and 2 are maintained at temperatures of T1 = 600 K and T2 = 400 K,
A row of regularly spaced, cylindrical heating elements (1) is used to cure a surface coating that is applied to a large panel (2) positioned below the elements. A second large panel (3), whose top
In recent years there has been considerable interest in developing flat-plate solar collectors for home heating needs. The typical collector configuration consists of an absorbing surface that is
Applying high-emissivity paints to radiating surfaces is a common technique used to enhance heat transfer by radiation.(a) For large parallel plates, determine the radiation heat flux across the gap
Options for thermally shielding the top ceiling of a large furnace include the use of an insulating material of thickness L and thermal conductivity k, case (a), or an air space of equivalent
The composite insulation shown, which was described in Chapter 1 (Problem 1.72e), is being considered as a ceiling material. It is proposed that the outer and inner slabs be made from low-density
Hot coffee is contained in a cylindrical thermos bottle that is of length L = 0.3 m and is lying on its side (horizontally). The coffee container consists of a glass flask of diameter D1 = 0.07 m,
A vertical air space in the wall of a home is 0.1 m thick and 3 m high. The air separates a brick exterior from a plaster board wall, with each surface having an emissivity of 0.9. Consider
Consider a vertical, double-pane window for the conditions prescribed in Problem 9.96. That is, vertical panes at temperatures of T1 = 22° and T2 = - 20° C are separated by atmospheric air, and the
Consider the double-pane window of Problem 9.97, for which 1m x 1 m panes are separated by a 25-mm gap of atmospheric air. The window panes are approximately isothermal and separate quiescent room
A flat-plate solar collector consisting of an absorber plate and single cover plate, is inclined at an angle of T = 60° relative to the horizontal. Consider conditions for which the incident solar
Consider the tube and radiation shield of Problem 13.49, but now account for free convection in the gap between the tube and the shield.(a) What is the total rate of heat transfer per unit length
Consider the tube and radiation shield of Problem 13.49, but now account for free convection in the gap between the tube and the shield, as well as for the fact that the temperature of the shield may
Consider the flat-plate solar collector of Problem 9.100. The absorber plate has a coating for which ε1 = 0.96, and the cover plate has an emissivity of ε2 = 0.92. With respect to radiation
The lower side of a 400-mm-diameter disk is heated by an electric furnace, while the upper side is exposed to quiescent, ambient air and surroundings at 300 K. The radiant furnace (negligible
The surface of a radiation shield facing a black hot wall at 400 K has a reflectivity of 0.95. Attached to the back side of the shield is a 25-mm-thick sheet of insulating material having a thermal
The fire tube of a hot water heater consists of a long circular duct of diameter D = 0.07 m and temperature Ts = 385 K, through which combustion gases flow at a temperature of Tm, g = 900 K. To
Consider Problem 9.95 with N = 4 sheets of thin aluminum foil (εƒ = 0.07), equally spaced throughout the 50-mm gap so as to form five individual air gaps each 10 mm thick. The hot and cold surfaces
Consider the conditions of Problem 9.105. Accounting for radiation, as well as convection, across the helium-filled cavity, determine the mass rate at which gaseous nitrogen is vented from the
A special surface coating on a square panel that is 5 m by 5 m on a side is cured by placing the panel directly under a radiant heat source having the same dimensions. The heat source is diffuse and
A long rod heater of diameter D1 = 10 mm and emissivity ε1 = 1.0 is coaxial with a well-insulated, semi cylindrical reflector of diameter D2 = 1 m. A long panel of width W = 1 m is aligned with the
A radiant heater, which is used for surface treatment processes, consists of a long cylindrical heating element of diameter D1 = 0.005 m and emissivity ?1 = 0.80. The heater is partially enveloped by
A steam generator consists of an in-line array of tubes, each of outer diameter D = 10 mm and length L = 1m. The longitudinal and transverse pitches are each SL = S? = 20 mm, while the numbers of
The sketch shows a gas-fired radiant tube of the single- ended recuperative (SER) type. A mixture of air and natural gas is injected at the left end of the central tube, and combustion is essentially
A wall-mounted natural gas heater uses combustion on a porous catalytic pad to maintain a ceramic plate of emissivity Tc = 0.95 at a uniform temperature of Tc = 1000 K. The ceramic plate is separated
A furnace having a spherical cavity of 0.5-m diameter contains a gas mixture at 1 atm and 1400 K. The mixture consists of CO2 with a partial pressure of 0.25 atm and nitrogen with a partial pressure
A gas turbine combustion chamber may be approximated as a long tube of 0.4-m diameter. The combustion gas is at a pressure and temperature of 1 atm and 1000°C, respectively, while the chamber
A flue gas at 1-atm total pressure and a temperature of 1400 K contains CO2 and water vapor at partial pressures of 0.05 and 0.10 atm, respectively. If the gas flows through a long flue of 1-m
A furnace consists of two large parallel plates separated by 0.75 m. A gas mixture comprised of O2, N2, CO2, and water vapor, with mole fractions of 0.20, 0.50, 0.15, and 0.15, respectively, flows
In an industrial process, products of combustion at a temperature and pressure of 2000 K and 1 atm, respectively, flow through a long, 0.25-m-diameter pipe whose inner surface is black. The
Waste heat recovery from the exhaust (flue) gas of a melting furnace is accomplished by passing the gas through a vertical metallic tube and introducing saturated water (liquid) at the bottom of an
A radiant oven for drying newsprint consists of a long duct (L = 20 m) of semicircular cross section. The newsprint moves through the oven on a conveyor belt at a velocity of V = 0.2 m/s. The
(a) Neglecting convection heat transfer, determine the required temperature Tp of the heater plate. (b) If the water vapor is swept from the duct by the flow of dry air, what convection mass transfer
A novel infrared recycler has been proposed for reclaiming the millions of kilograms of waste plastics produced by the dismantling and shredding of auto-motive vehicles following their retirement. To
Assuming air to be composed exclusively of O2 and N2, with their partial pressures in the ratio 0.21: 0.79, what are their mass fractions?
A mixture of CO2 and N2 is in a container at 25°C, with each species having a partial pressure of 1 bar. Calculate the molar concentration, the mass density, the mole fraction, and the mass fraction
A He-Xe mixture containing 0.75 mole fraction of helium is used for cooling of electronics in an avionics application. At a temperature of 300 K and atmospheric pressure, calculate the mass fraction
Consider an ideal gas mixture of n species.(a) Derive an equation for determining the mass fraction of species i from knowledge of the mole fraction and the molecular weight of each of the n species.
Consider air in a closed, cylindrical container with its axis vertical and with opposite ends maintained at different temperatures. Assume that the total pressure of the air is uniform throughout the
Estimate values of the mass diffusivity DAB for binary mixtures of the following gases at 350K and 1 atm: ammonia-air and hydrogen-air.
A 100-mm-long, hollow iron cylinder is exposed to a 1000°C carburizing gas (a mixture of CO and CO2) at its inner and outer surfaces of radii 4.30 and 5.70 mm, respectively. Consider steady-state
An old-fashioned glass apothecary jar contains a patent medicine. The neck is closed with a rubber stopper that is 20 mm tall, with a diameter of 10 mm at the bottom end, widening to 20 mm at the top
Consider the evaporation of liquid A into a column containing a binary gas mixture of A and B. Species B cannot be absorbed in liquid A and the boundary conditions are the same as in Section 14.2.2.
An open pan of diameter 0.2 m and height 80 mm (above water at 27°C) is exposed to ambient air at 27°C and 25% relative humidity. Determine the evaporation rate, assuming that only mass diffusion
A spherical droplet of liquid A and radius ro evaporates into a stagnant layer of gas B. Derive an expression for the evaporation rate of species A in terms of the saturation pressure of species A,
The presence of a small amount of air may cause a significant reduction in the heat rate to a water-cooled steam condenser surface. For a clean surface with pure steam and the prescribed conditions,
A laboratory apparatus to measure the diffusion coefficient of vapor-gas mixtures consists of a vertical, small-diameter column containing the liquid phase that evaporates into the gas flowing over
Beginning with a differential control volume, derive the diffusion equation, on a molar basis, for species A in a three-dimensional (Cartesian coordinates), stationary medium, considering species
Consider the radial diffusion of a gaseous species (A) through the wall of a plastic tube (B), and allow for chemical reactions that provide for the depletion of A at a rate NA (k mol/s ∙ m3).
Beginning with a differential control volume, derive the diffusion equation, on a molar basis, for species A in a one-dimensional, spherical, stationary medium, considering species generation.
Gaseous hydrogen at 10 bars and 27°C is stored in a 100-mm-diameter spherical tank having a steel wall 2 mm thick. The molar concentration of hydrogen in the steel is 1.50k mol/m3 at the inner
A thin plastic membrane is used to separate helium from a gas stream. Under steady-state conditions the concentration of helium in the membrane is known to be 0.02 and 0.005k mol/m3 at the inner and
Consider the interface between atmospheric air and a body of water, both at 17°C.(a) What are the mole and mass fractions of water at the air side of the interface, at the water side of the
Oxygen gas is maintained at pressures of 2 bars and 1 bar on opposite sides of a rubber membrane that is 0.5 mm thick, and the entire system is at 25°C. What is the molar diffusive flux of O 2
Insulation degrades (experiences an increase in thermal conductivity) if it is subjected to water vapor condensation. The problem may occur in home insulation during cold periods, when vapor in a
Helium gas at 25°C and 4 bars is contained in a glass cylinder of 100-mm inside diameter and 5-mm thickness. What is the rate of mass loss per unit length of the cylinder?
Helium gas at 25°C and 4 bars is stored in a spherical Pyrex container of 200-mm inside diameter and 10-mm thickness. What is the rate of mass loss from the container?
Hydrogen at a pressure of 2 atm flows within a tube of diameter 40 mm and wall thickness 0.5 mm. The outer surface is exposed to a gas stream for which the hydrogen partial pressure is 0.1 atm. The
Consider the blister packaging material of Example 14.3.(a) Under the same conditions as in the example, determine the solubility of the polymer material (k mol/m3 bar) if the temperature is 295 K
An experiment is designed to measure the partition coefficient, K, associated with the transfer of a pharmaceutical product through a polymer material. The partition coefficient is defined as the
Ultra-pure hydrogen is required in applications ranging from the manufacturing of semiconductors to powering fuel cells. The crystalline structure of palladium allows only the transfer of atomic
Nitric oxide (NO) emissions from automobile exhaust can be reduced by using a catalytic converter, and the following reaction occurs at the catalytic surface: NO + CO → ½ N2 + CO2. The
Pulverized coal pellets, which may be approximated as carbon spheres of radius ro = 1 mm, are burned in a pure oxygen atmosphere at 1450 K and 1 atm. Oxygen is transferred to the particle surface by
To enhance the effective surface, and hence the chemical reaction rate, catalytic surfaces often take the form of porous solids. One such solid may be visualized as consisting of a large number of
A platinum catalytic reactor in an automobile is used to convert carbon monoxide to carbon dioxide in an oxidation reaction of the form 2CO + O2 → 2CO2. Species transfer between the catalytic
A novel process has been proposed to create a composite palladium tube for use as a hydrogen separation membrane in order to produce high-purity hydrogen. To fabricate the composite palladium tube, a
Consider combustion of hydrogen gas in a mixture of hydrogen and oxygen adjacent to the metal wall of a combustion chamber. Combustion occurs at constant temperature and pressure according to the
Consider a spherical organism of radius ro within which respiration occurs at a uniform volumetric rate of NA = –k0. That is, oxygen (species A) consumption is governed by a zero-order, homogeneous
Referring to Problem 14.34, a more representative model of respiration in a spherical organism is one for which oxygen consumption is governed by a first-order reaction of the form NA = – k1CA.(a)
Consider the problem of oxygen transfer from the interior lung cavity, across the lung tissue, to the network of blood vessels on the opposite side. The lung tissue (species B) may be approximated as
As an employee of the Los Angeles Air Quality Commission, you have been asked to develop a model for computing the distribution of NO2 in the atmosphere. The molar flux of NO2 at ground level, N''A2,

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