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engineering
mechanical engineering

Questions and Answers of Mechanical Engineering

Consider the packed bed of aluminum spheres described in Problem 5.12 under conditions for which the bed is charged by hot air with an inlet velocity of V = 1 m/s and temperature of Tg,i = 300°C,
The use of rock pile thermal energy storage systems has been considered for solar energy and industrial process heat applications. A particular system involves a cylindrical container, 2 m long by 1
The cylindrical chamber of a pebble bed nuclear reactor is of length L = 10m and diameter D = 3 m. The chamber is filled with spherical uranium oxide pellets of core diameter Dp = 50 mm. Each pellet
Latent heat capsules consist of a thin-walled spherical shell within which a solid-liquid, phase-change material (PCM) of melting point T mp and latent heat of fusion hsf is enclosed. As shown
Consider the packed bed (ε = 0.5) of latent heat capsules (Dc = 50 mm) described in Problem 7.102, but now for an application in which ambient air is to be heated by passing it through the bed. In
Consider mass loss from a smooth wet flat plate due to forced convection at atmospheric pressure. The plate is 0.5 m long and 3 m wide. Dry air at 300 K and a free stream velocity of 35 m/s flows
Consider dry, atmospheric air in parallel flow over a 0.5-m-long plate whose surface is wetted. The air velocity is 35 m/s, and the air and water are each at a temperature of 300 K.(a) Estimate the
A flat plate coated with a volatile substance (species A) is exposed to dry, atmospheric air in parallel flow with T∞ = 20°C and u∞ = 8 m/s. The plate is maintained at a constant temperature of
Dry air at atmospheric pressure and 350 K, with a free stream velocity of 25 m/s,flows over a smooth, porous plate 1 m long(a) Assuming the plate to be saturated with liquid water at 350 K, estimate
A scheme for dissipating heat from an array of N = 100 integrated circuits involves joining the circuits to the bottom of a plate and exposing the top of the plate to a water bath. The water
A series of water-filled trays, each 222 mm long, experiences an evaporative drying process. Dry air at T∞ = 300 K flows over the trays with a velocity of 15 m/s, while radiant heaters maintain the
Consider the physical system of Problem 7.109 la series of water-filled trays heated radiatively), but under operating conditions for which each tray is 0.25 m long by 1 m wide and is uniformly
The apparatus described in Problem 7.40 is used by our students to experimentally determine convection heat and mass transfer coefficients, to confirm the heat-mass analogy, and to compare measured
Dry air at 35°C and a velocity of 20 m/s flows over a wetted plate of length 500 mm and width 150 mm, an imbedded electrical heater supplies power to maintain the plate surface temperature at
A minivan traveling 90 km/h has just passed through a thunderstorm that left a film of water 0.1 mm thick on the top of the van. The top of the van can be assumed to be a flat plate 6 m long. Assume
Benzene, a known carcinogen, has been spilled on the laboratory floor and has spread to a length of 2 m. If a film 1 mm deep is formed, how long will it take for the benzene to completely evaporate?
Atmospheric air of 40% relative humidity and temperature T∞ = 300 K is in parallel flow over a series of water-filled trays, with U∞ = 12 m/s.What is the rate at which energy must be supplied to
A stream of atmospheric air is used to dry a series of biological samples on plates that are each of length Li = 0.25 m in the direction of the airflow. The air is dry and at a temperature equal to
Condenser cooling water for a power plant is stored in a cooling pond that is 1000 m long by 500 m wide. However, because of evaporative losses, it is necessary to periodically add "makeup" water to
Consider the plate conveyor system of Problem 7.24, but now under conditions for which the plates are being transported from a liquid bath used for surface cleaning. The initial plate temperature is
In a paper drying process, the paper moves on a conveyor belt at 0.2 m/s, while dry air from an in-line array of round jets (Figure 7.17 b) impinges normal to its surface. The nozzle diameter and
In a paper mill drying process, a sheet of paper slurry (water-fiber mixture) has a linear velocity of 5 m1s as it is rolled. Radiant heaters maintain a sheet temperature of Ts = 330 K, as
A channel of triangular cross section, which is 25 m long and 1 m deep, is used for the storage of water.The water and the surrounding air are each at a temperature of 25°C, and the relative
Mass transfer experiments have been conducted on a naphthalene cylinder of 18.4-mm diameter and 88.9-mm length subjected to a cross flow of air in a low-speed wind tunnel. After exposure for 39 min
Dry air at l-atm pressure and a velocity of 15 m/s is to be humidified by passing it in cross flow over a porous cylinder of diameter D = 40 mm, which is saturated with water.(a) Assuming the water
Dry air at 35°C and a velocity of 15 m/s flows over a long cylinder of 20-mm diameter, the cylinder is covered with a thin porous coating saturated with water, and an imbedded electrical heater
Dry air at 20°C and a velocity of 15 m/s flows over a 20-mm-diameter rod covered with a thin porous coating that is saturated with water. The rod (k = 175 W/m ∙ K) is 250 mm long and its ends are
Approximate the human form as an unclothed vertical cylinder of O.3-m diameter and 1.75-m length with a surface temperature of 30°C.(a) Calculate the heat loss in a 10-m/s wind at 20°C.(b) What is
It has been suggested that heat transfer from a surface can be augmented by wetting it with water. As a specific example, consider a horizontal tube that is exposed to a transverse stream of dry air.
In the first stage of a paper drying process, a cylinder of diameter 0.15 m is covered by moisture-soaked paper. The temperature of the paper is maintained at 70°C by imbedded electrical heaters.
Cylindrical dry-bulb and wet-bulb thermometers are installed in a large-diameter duct to obtain the temperature T∞, and the relative humidity ϕx of moist air flowing through the duct at a velocity
The thermal pollution problem is associated with discharging warm water from an electrical power plant or from an industrial source to a natural body of water. Methods for alleviating this problem
Cranberries are harvested by flooding the bogs in which they are grown and raking them into troughs for transport. At the processing plant, the surface moisture on the berries is removed as they roll
A spherical drop of water, 0.5 mm in diameter, is falling at a velocity of 2.15 m/s through dry still air at l-atm pressure. Estimate the instantaneous rate of evaporation from the drop if the drop
A spherical droplet of alcohol, 0.5 mm in diameter, is falling freely through quiescent air at a velocity of 1.8 m/s. The concentration of alcohol vapor at the surface of the droplet is 0.0573 kg/m3,
As described in Problem 7.77, the second step in tissue engineering is to seed the top surface of the scaffold with human cells that subsequently grow into the pores of the scaffold. A seeding method
Motile bacteria are equipped with flagella that are rotated by tiny, biological electrochemical engines which, in turn, propel the bacteria through a host liquid.Consider a nominally spherical
In a home furnace humidification system, water droplets of diameter D are discharged in a direction opposing the motion of warm air emerging from the heater. The air is humidified by evaporation from
Evaporation of liquid fuel droplets is often studied in the laboratory by using a porous sphere technique in which the fuel is supplied at a rate just sufficient to maintain a completely wetted
Fully developed conditions are known to exist for water flowing through a 25-mm-diameter tube at 0.01 kg/s and 27°C. What is the maximum velocity of the water in the tube? What is the pressure
What is the pressure drop associated with water at 27°C flowing with a mean velocity of 0.2 m/s through a 600-m-long cast iron pipe of 0.15-m inside diameter?
Water at 27°C flows with a mean velocity of 1 m/s through a l-km-long pipe of 0.25-m inside diameter.(a) Determine the pressure drop over the pipe length and the corresponding pump power
An engine oil cooler consists of a bundle of 25 smooth tubes, each of length L = 2.5 m and diameter D = 10 mm.(a) If oil at 300 K and a total flow rate of 24 kg/s is in fully developed flow through
For fully developed laminar flow through a parallel-plate channel, the x-momentum equation has the form μ(d2u/dy2) = dp/dx = constant. The purpose of this problem is to develop expressions for the
Consider pressurized water, engine oil (unused), and NaK (22%/78%) flowing in a 20-mm-diameter tube.(a) Determine the mean velocity, the hydrodynamic entry length, and the thermal entry length for
Velocity and temperature profiles for laminar flow in a tube of radius ro = 10 mm have the form u (r) = 0.1 [1 – (r/ro)2] T(r) = 344.8 + 75.0(r/ro)2 – 18.8(r/ro)4 with units of m/s and K.
At a particular axial station, velocity and temperature profiles for laminar flow in a parallel plate channel have the form u(y) = 0.75[1 – (y/yo) 2] T(y) = 5.0 + 95.66(y/yo) 2 –
In Chapter 1, it was stated that for incompressible liquids, flow work could usually be neglected in the steady-flow energy equation (Equation 1.11d). In the trans-Alaska pipeline, the high viscosity
When viscous dissipation is included, Equation 8.48 (multiplied by pcp) becomesThis problem explores the importance of viscous dissipation. The conditions under consideration are laminar, fully
Water enters a tube at 27°C with a flow rate of 450 kg/h. The heat transfer from the tube wall to the fluid is given as q's (W/m) = ax, where the coefficient a is 20 W/m2 and x (m) is the axial
Consider flow in a circular tube within the test section length (between 1 and 2) a constant heat flux q"s is maintained.(a) For the following two cases, sketch the surface temperature Ts(x) and the
Consider a cylindrical nuclear fuel rod of length Land diameter D that is encased in a concentric tube. Pressurized water flows through the annular region between the rod and the tube at a rate m,
In a particular application involving fluid flow at a rate nz through a circular tube of length L and diameter D, the surface heat flux is known to have a sinusoidal variation with x, which is of the
A flat-plate solar collector is used to heat atmospheric air flowing through a rectangular channel. The bottom surface of the channel is well insulated, while the top surface is subjected to a
Atmospheric air enters the heated section of a circular tube at a flow rate of 0.005 kg/s and a temperature of 20°C. The tube is of diameter D = 50 mm, and full developed conditions with h = 25 W/m2
Water at 300 K and a flow rate of 5 kg/s enters a black, thin-walled tube, which passes through a large furnace whose walls and air are at a temperature of 700 K. The diameter and length of the tube
Slug flow is an idealized tube flow condition for which the velocity is assumed to be uniform over the entire tube cross section. For the case of laminar slug flow with a uniform surface heat flux,
Superimposing a control volume that is differential in x on the tube flow conditions of Figure 8.8, derive Equation 8.45a.
An experimental nuclear core simulation apparatus consists of a long thin-walled metallic tube of diameter D and length L, which is electrically heated to produce the sinusoidal heat flux
Water at 20°C and a flow rate of 0.1 kg/s enters a heated, thin-walled tube with a diameter of 15 mm and length of 2 m. The wall heat flux provided by the heating elements depends on the wall
Engine oil is heated by flowing through a circular tube of diameter D = 50 mm and length L = 25 m and whose surface is maintained at 150°C.(a) If the flow rate and inlet temperature of the oil are
Engine oil flows through a 25-mm-diameter tube at a rate of 0.5 kg/so The oil enters the tube at a temperature of 25°C, while the tube surface temperature is maintained at 100°C.(a) Determine the
An oil pre-heater consists of a ingle tube of 10 mm diameter and 5m length, with its surface maintained at 175°C by swirling combustion gases. The engine oil (new) enters at 75°C. What flow rate
Engine oil flows at a rate of I kg/s through a 5-mm-diameter straight tube. The oil has an inlet temperature of 45°C and it is desired to heat the oil to a mean temperature of 80°C at the exit of
Ethylene glycol flows at 0.0 I kg/s through a 3-mm-diameter, thin-walled tube. The tube is coiled and sub-merged in a well-stirred water bath maintained at 25°C. If the fluid enters the tube at
In the final stages of production, a pharmaceutical is sterilized by heating it from 25 to 75°C as it moves at 0.2 m/s through a straight thin-walled stainless steel tube of 12.7-mm diameter. A
Batch processes are often used in chemical and pharmaceutical operations to achieve a desired chemical composition for the final product. Related heat transfer processes are typically transient,
The mold that is used in an injection molding process is constructed of metal (p = 7800 kg/m3, c = 450 J/kg ∙ K). The mold, to be heated to 190°C prior to injection of the thermoplastic material,
The evaporator section of a heat pump is installed in a large tank of water, which is used as a heat source during the winter. As energy is extracted from the water, it begins to freeze, creating an
To cool a summer home without using a vapor-compression refrigeration cycle, air is routed through a plastic pipe (k = 0.15 W/m ∙ K, Di = 0.15 m, Do = 0.17 m) that is submerged in an adjoining body
Water flowing at 2 kg/s through a 40-mm-diameter tube is to be heated from 25 to 75°C by maintaining the tube surface temperature at 100°C.(a) What is the required tube length for these conditions?
Consider the conditions associated with the hot water pipe of Problem 7.56, but now account for the convection resistance associated with water flow at a mean velocity of U m = 0.5m/s in the pipe.
A thick-walled, stainless steel (AISI 316) pipe of inside and outside diameters D; = 20 mm and Do = 40 mm is heated electrically to provide a uniform heat generation rate of q = 10 6 W/m3.The outer
Consider the encased pipe of Problem 4.29, but now allow for the difference between the mean temperature of the fluid, which changes along the pipe length, and that of the pipe.(a) For the prescribed
Water flows through a thick-walled tube with an inner diameter of 12 mm and a length of 8 m. The tube is immersed in a well-stirred, hot reaction tank maintained at 85°C, and the conduction
Atmospheric air enters a100-m-long, 150-mm-diameter uninsulated heating duct at 60°C and 0.04 kg/s. The duct surface temperature is approximately constant at Ts = 15°C.(a) What are the outlet air
An air heater for an industrial application consists of an insulated, concentric tube annulus, for which air flows through a thin-walled inner tube. Saturated steam flows through the outer annulus,
The products of combustion from a burner are routed to an industrial application through a thin-walled metallic duct of diameter D; = I m and length L = 100 In. The gas enters the duct at atmospheric
Liquid mercury at 0.5 kg/s is to be heated from 300 to 400 K by passing it through a 50-mm-diameter tube whose surface is maintained at 450 K. Calculate the required tube length by using an
The surface of a 50-mm-diameter, thin-walled tube is maintained at 100°C. In one case air is in cross flow over the tube with a temperature of 25°C and a velocity of 30 m/s. In another case air is
Cooling water flows through the 25.4-mm-diameter thin-walled tubes of a steam condenser at 1 m/s, and a surface temperature of 350 K is maintained by the condensing steam. The water inlet temperature
The air passage for cooling a gas turbine vane can be approximated as a tube of 3-mm diameter and 75-mm length. The operating temperature of the vane is 650°C, and air enters the tube at 427°C.(a)
The core of a high-temperature, gas-cooled nuclear reactor has coolant tubes of 20-mm diameter and 780-mm length. Helium enters at 600 K and exits at 1000 K when the flow rate is 8 x 10-3 kg/s per
Air at 200 kPa enters a 2-m-Iong, thin-walled tube of 25-mm diameter at 150°C and 6 m/s Steam at 20 bars condenses on the outer surface.(a) Determine the outlet temperature and pressure drop of the
Heated air required for a food-drying process is generated by passing ambient air at 20Â°C through long, circular tubes (D = 50 mm, L = 5 m) housed in a steam condenser. Saturated steam at
Consider a horizontal, thin-walled circular tube of diameter D = 0.025 m submerged in a container of n-octadecane (paraffin), which is used to store thermal energy. As hot water flows through the
A common procedure for cooling a high-performance computer chip involves joining the chip to a heat sink within which circular micro channels are machined. During operation, the chip produces a
One way to cool chips mounted on the circuit boards of a computer is to encapsulate the boards in metal frames that provide efficient pathways for conduction to supporting cold plates. Heat generated
Refrigerant -134a is being transported at 0.1 kg/s through a Teflon tube of inside diameter D; = 25 mm and outside diameter Do = 28 mm, while atmospheric air at V = 25 m/s and 300 K is in cross flow
Oil at 150°C flows slowly through a long, thin-walled pipe of 30-mm inner diameter, the pipe suspended in a room for which the air temperature is 20°C and the convection coefficient at the outer
Exhaust gases from a wire processing oven are discharged into a tall stack, and the gas and stack surface temperatures at the outlet of the stack must be estimated. Knowledge of the outlet gas
A hot fluid passes through a thin-walled tube of 10-mm diameter and 1-m length and a coolant at T∞ = 25Â°C is in cross flow over the tube. When the flow rate is m = 18 kg/h and the inlet
Consider a thin-walled tube of 10-mm diameter and 2-m length. Water enters the tube from a large reservoir at in = 0.2 kg/s and Tm,i = 47°C.(a) If the tube surface is maintained at a uniform
Water at a flow rate of m = 0.215 kg/s is cooled from 70°C to 30°C by passing it through a thin-walled tube of diameter D = 50 mm and maintaining a coolant at T∝ = 15°C in cross flow over the
Consider a thin-walled, metallic tube of length L = 1 m and inside diameter Di = 3 mm. Water enters the tube at m = 0.015 kg/s and Tm.i = 97°C.(a) What is the outlet temperature of the water if the
A thick-walled steel pipe (k = 60 W/m ∙ K) carrying hot water is cooled externally by a cross-flow airstream at a velocity of 20 m/s and a temperature of 25°C. The inner and outer diameters of the
Heat is to be removed from a reaction vessel operating at 75°C by supplying water at 27°C and 0.12 kg/s through a thin-walled tube of 15-mm diameter. The convection coefficient between the tube
A heating contractor must heat 0.2 kg/s of water from 15Â°C to 35Â°C using hot gases in cross flow over a thin-walled tube.Your assignment is to develop a series of design graphs that can be used
A thin-walled tube with a diameter of 6 mm and length of 20 m is used to carry exhaust gas from a smoke stack to the laboratory in a nearby building for analysis. The gas enters the tube at 200°C
A 50-mm-diameter, thin-walled metal pipe covered with a 25-mm-thick layer of insulation (0.085 W/m ∙ K) and carrying superheated steam at atmospheric pressure is suspended from the ceiling of a

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