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engineering
heat and mass transfer fundamentals and applications

Questions and Answers of Heat And Mass Transfer Fundamentals And Applications

Water is boiled at 100°C electrically by an 80-cm-long, 2-mm-diameter horizontal resistance wire made of chemically etched stainless steel. Determine(a) The rate of heat transfer to the water and
During a heat treatment process, a 20-mm diameter cylindrical steel rod with a length of 200 mm was removed from a furnace when it reached a uniform temperature of 500°C and was suddenly submerged
Electric current is passed through a 2-mm diameter cylindrical metal rod with emissivity of 0.5. The rod is submerged horizontally in water under atmospheric pressure and the rod surface temperature
Water is boiled at 100°C by a spherical platinum heating element of diameter 15 cm and emissivity 0.10 immersed in the water. If the surface temperature of the heating element is 350°C, determine
In a heat treatment process, 20-mm-diameter steel ball bearings are being heated to a uniform temperature of 700°C. The ball bearings are then being removed and immediately submerged in a water bath
Saturated steam at 100°F is condensed on a 4-ft-high vertical plate that is maintained at 80°F. Determine the rate of heat transfer from the steam to the plate and the rate of condensation per foot
Saturated ammonia vapor at 25°C condenses on the outside of a 2-m-long, 3.2-cm-outer-diameter vertical tube maintained at 15°C. Determine(a) The average heat transfer coefficient,(b) The rate of
Saturated refrigerant-134a vapor at 35°C is to be condensed on the outer surface of a 7-m-long, 1.5-cm-diameter horizontal tube that is maintained at a temperature of 25°C. Determine the rate at
Repeat Prob. 10–110 for a tube diameter of 3 cm.Data from problem 110Saturated refrigerant-134a vapor at 35°C is to be condensed on the outer surface of a 7-m-long, 1.5-cm-diameter horizontal tube
A 1.2-cm-diameter silver sphere initially at 25°C is suspended in a room filled with saturated steam at 100°C. Using the lumped system analysis, determine how long it will take for the temperature
Repeat Prob. 10–113 for a 3-cm-diameter copper ball.Data from problem 113A 1.2-cm-diameter silver sphere initially at 25°C is suspended in a room filled with saturated steam at 100°C. Using the
Saturated isobutane vapor in a binary geothermal power plant is to be condensed outside an array of eight horizontal tubes. Determine the ratio of the condensation rate for the cases of the tubes
Shown in Fig. P10–118 is the tube layout for a horizontal condenser that is used for liquefying 900 kg/h of saturated ammonia vapor at 37°C. There are 14 copper tubes, each with inner diameter Di
The condenser of a steam power plant operates at a pressure of 0.95 psia. The condenser consists of 144 horizontal tubes arranged in a 12 × 12 square array. The tubes are 15 ft long and have an
Repeat Prob. 10–116E for a tube diameter of 2 in.Data from problem 116The condenser of a steam power plant operates at a pressure of 0.95 psia. The condenser consists of 144 horizontal tubes
Saturated ammonia vapor at 25°C condenses on the outside surface of 16 thin-walled tubes, 2.5 cm in diameter, arranged horizontally in a 4 × 4 square array. Cooling water enters the tubes at 14°C
Saturated steam at 270.1 kPa condenses inside a horizontal, 10-m-long, 2.5-cm-internal-diameter pipe whose surface is maintained at 110°C. Assuming low vapor velocity, determine the average heat
When boiling a saturated liquid, one must be careful while increasing the heat flux to avoid burnout. Burnout occurs when the boiling transitions from _____ boiling.(a) Convection to nucleate(b)
Heat transfer coefficients for a vapor condensing on a surface can be increased by promoting(a) Film condensation(b) Dropwise condensation(c) Rolling action(d) None of them
When a saturated vapor condenses on a vertical, isothermal flat plate in a continuous film, the rate of heat transfer is proportional to (a) (Ts - Tsat)¹/4 (c) (T₁-T3/4 sat (e)
At a distance x down a vertical, isothermal flat plate on which a saturated vapor is condensing in a continuous film, the thickness of the liquid condensate layer is d. The heat transfer coefficient
Saturated water vapor is condensing on a 0.5 m2 vertical flat plate in a continuous film with an average heat transfer coefficient of 7 kW/m2 · K. The temperature of the water is 80°C (hfg = 2309
Steam condenses at 50°C on a 0.8-m-high and 2.4-mwide vertical plate that is maintained at 30°C. The condensation heat transfer coefficient is(a) 3975 W/m2 · K(b) 5150 W/m2 · K(c) 8060 W/m2 ·
An air conditioner condenser in an automobile consists of 2 m2 of tubular heat exchange area whose surface temperature is 30°C. Saturated refrigerant-134a vapor at 50°C (hfg = 152 kJ/kg) condenses
Steam condenses at 50°C on the outer surface of a horizontal tube with an outer diameter of 6 cm. The outer surface of the tube is maintained at 30°C. The condensation heat transfer coefficient
Saturated water vapor at 40°C is to be condensed as it flows through a tube at a rate of 0.2 kg/s. The condensate leaves the tube as a saturated liquid at 40°C. The rate of heat transfer from the
Steam condenses at 50°C on the tube bank consisting of 20 tubes arranged in a rectangular array of 4 tubes high and 5 tubes wide. Each tube has a diameter of 6 cm and a length of 3 m, and the outer
Design the condenser of a steam power plant that has a thermal efficiency of 40 percent and generates 10 MW of net electric power. Steam enters the condenser as saturated vapor at 10 kPa, and it is
The refrigerant in a household refrigerator is condensed as it flows through the coil that is typically placed behind the refrigerator. Heat transfer from the outer surface of the coil to the
A manufacturing facility requires saturated steam at 120°C at a rate of 1.2 kg/min. Design an electric steam boiler for this purpose under these constraints:• The boiler will be in cylindrical
Water-cooled steam condensers are commonly used in steam power plants. Obtain information about water-cooled steam condensers by doing a literature search on the topic and also by contacting some
Repeat Prob. 10–134 for a boiler that produces steam at 150°C at a rate of 2.5 kg/min.Data from problem 134 A manufacturing facility requires saturated steam at 120°C at a rate of 1.2 kg/min.
Conduct this experiment to determine the boiling heat transfer coefficient. You will need a portable immersion-type electric heating element, an indoor-outdoor thermometer, and metal glue (all can be
A typical section of a building wall is shown in Fig. P3–66. This section extends in and out of the page and is repeated in the vertical direction. The wall support members are made of steel (k =
Reconsider Prob. 4–15. Using EES (or other) software, investigate the effects of the heat transfer coefficient and the final plate temperature on the time it will take for the plate to reach this
A 6-mm-thick stainless steel strip (k = 21 W/m · K, ρ = 8000 kg/m3, and cp = 570 J/kg · K) exiting an oven at a temperature of 500°C is allowed to cool within a buffer zone distance of 5 m. To
After heat treatment, the 2-cm thick metal plates (k = 180 W/m · K, ρ = 2800 kg/m3, and cp = 880 J/kg · K) are conveyed through a cooling chamber with a length of 10 m. The plates enter the
A person is found dead at 5pm in a room whose temperature is 20°C. The temperature of the body is measured to be 25°C when found, and the heat transfer coefficient is estimated to be 8 W/m2 · K.
Carbon steel balls (ρ = 7833 kg/m3, k = 54 W/m · K, cp = 0.465 kJ/kg·°C, and a = 1.474 × 10-6 m2/s) 8 mm in diameter are annealed by heating them first to 900°C in a furnace and then allowing
Reconsider Prob. 4–34. Using EES (or other) software, investigate the effect of the initial temperature of the balls on the annealing time and the total rate of heat transfer. Let the temperature
A heated 6-mm-thick Pyroceram plate (ρ = 2600 kg/m3, cp = 808 J/kg · K, k = 3.98 W/m · K, and a = 1.89 × 10–6 m2/s) is being cooled in a room with air temperature of 25°C and convection heat
A hot brass plate is having its upper surface cooled by impinging jet of air at temperature of 15°C and convectionheat transfer coefficient of 220 W/m2 · K. The 10-cm thick brass plate (ρ = 8530
An electronic device dissipating 20 W has a mass of 20 g, a specific heat of 850 J/kg · K, and a surface area of 4 cm2. The device is lightly used, and it is on for 5 min and then off for several
Reconsider Prob. 4–60. Using EES (or other) software, investigate the effect of the cooling time on the final center temperature of the shaft and the amount of heat transfer. Let the time vary from
A 65-kg beef carcass (k = 0.47 W/m · K and α = 0.13 × 10-6 m2/s) initially at a uniform temperature of 37°C is to be cooled by refrigerated air at 210°C flowing at a velocity of 1.2 m/s. The
Reconsider Prob. 4–68. Using EES (or other) software, investigate the effect of the final center temperature of the egg on the time it will take for the center to reach this temperature. Let the
Chickens with an average mass of 1.7 kg (k = 0.45 W/m · K and α = 0.13 × 10-6 m2/s) initially at a uniform temperature of 15°C are to be chilled in agitated brine at 27°C. The average heat
Consider a mixture of air-water flow in a tube. Suddenly the air flow is shut off, so that only water is flowing in the tube. Starting with the two-phase non-boiling heat transfer correlation, find
Hailstones are formed in high altitude clouds at 253 K. Consider a hailstone with diameter of 20 mm and is falling through air at 15°C with convection heat transfer coefficient of 163 W/m2 · K.
In a chicken processing plant, whole chickens averaging 5 lbm each and initially at 65°F are to be cooled in the racks of a large refrigerator that is maintained at 5°F. The entire chicken is to be
A large cast iron container (k = 52 W/m · K and α = 1.70 × 10-5 m2/s) with 5-cm-thick walls is initially at a uniform temperature of 0°C and is filled with ice at 0°C. Now the outer surfaces of
Reconsider Prob. 4–96. Using EES (or other) software, plot the soil temperature as a function of the distance from the earth’s surface as the distance varies from 0 m to 1m, and discuss the
In a vacuum chamber, a thick slab is placed under an array of laser diodes with an output constant pulse. A thermocouple is inserted inside the slab at 25 mm from the surface and the slab has an
Thick slabs of stainless steel (k = 14.9 W/m · K and α = 3.95 × 10-6 m2/s) and copper (k = 401 W/m · K and α = 117 × 10-6 m2/s) are placed under an array of laser diodes, which supply an energy
A stainless steel slab (k = 14.9 W/m · K and α = 3.95 × 10-6 m2/s) and a copper slab (k = 401 W/m · K and α = 117 × 10-6 m2/s) are placed under an array of laser diodes, which supply an energy
Repeat Prob. 4–107 with the heat transfer coefficient at the top and the bottom surfaces of each block being doubled to 80 W/m2·K.Data From Problem 107Consider a cubic block whose sides are 5 cm
A 5-cm-high rectangular ice block (k = 2.22 W/m · K and α = 0.124 × 10-7 m2/s) initially at 220°C is placed on atable on its square base 4 cm × 4 cm in size in a room at 18°C. The heat transfer
Reconsider Prob. 4–110. Using EES (or other) software, investigate the effect of the initial temperature of the ice block on the time period before the ice block starts melting. Let the initial
Reconsider Prob. 4–113. Using EES (or other) software, investigate the effect of the cooling time on the center temperature of the cylinder, the center temperature of the top surface of the
A 20-cm-long cylindrical aluminum block (ρ = 2702 kg/m3, cp = 0.896 kJ/kg · K, k = 236 W/m · K, and α = 9.75 × 10-5 m2/s), 15 cm in diameter, is initially at a uniform temperature of 20°C. The
10-m-long copper tube with a diameter of 25 mm is used for transporting cold fluid. The cold fluid flow inside the tube causes the tube surface temperature at 3°C to be colder than the ambient
Repeat Prob. 4–116 for the case where the aluminum block is inserted into the furnace on a low-conductivity material so that the heat transfer to or from the bottom surface of the block is
Reconsider Prob. 4–116. Using EES (or other) software, investigate the effect of the final center temperature of the block on the heating time and the amount of heat transfer. Let the final center
What are the common kinds of microorganisms? What undesirable changes do microorganisms cause in foods?
How does refrigeration prevent or delay the spoilage of foods? Why does freezing extend the storage life of foods for months?
What are the environmental factors that affect the growth rate of microorganisms in foods?
What is the effect of cooking on the microorganisms in foods? Why is it important that the internal temperature of a roast in an oven be raised above 70°C?
How can the contamination of foods with microorganisms be prevented or minimized? How can the growth of microorganisms in foods be retarded? How can the microorganisms in foods be destroyed?
How does(a) The air motion(b) The relative humidity of the environment affect the growth of microorganisms in foods?
The cooling of a beef carcass from 37°C to 5°C with refrigerated air at 0°C in a chilling room takes about 48 h. To reduce the cooling time, it is proposed to cool the carcass with refrigerated
Consider the freezing of packaged meat in boxes with refrigerated air. How do(a) The temperature of air,(b) The velocity of air,(c) The capacity of the refrigeration system,(d) The size of the meat
It is claimed that beef can be stored for up to two years at –23°C but no more than one year at –12°C. Is this claim reasonable? Explain.
What is a refrigerated shipping dock? How does it reduce the refrigeration load of the cold storage rooms?
How does immersion chilling of poultry compare to forced-air chilling with respect to(a) Cooling time,(b) Moisture loss of poultry,(c) Microbial growth.
What is the proper storage temperature of frozen poultry? What are the primary methods of freezing for poultry?
What are the factors that affect the quality of frozen fish?
In a meat processing plant, 10-cm-thick beef slabs (ρ = 1090 kg/m3, cp = 3.54 kJ/kg · K, k = 0.47 W/m · K, and α = 0.13 × 10–6 m2/s) initially at 15°C are to be cooled in the racks of a large
Chickens with a water content of 74 percent, an initial temperature of 32°F, and a mass of about 7.5 lbm are to be frozen by refrigerated air at 240°F. Using Figure 4–55, determine how long it
A watermelon initially at 35°C is to be cooled by dropping it into a lake at 15°C. After 4 h and 40 min of cooling, the center temperature of watermelon is measured to be 20°C. Treating the
In an event of a volcano eruption, lava at 1200°C is found flowing on the ground. The ground was initially at 15°C and the lava flow has a convection heat transfer coefficient of 3500 W/m2 · K.
Consider the engine block of a car made of cast iron (k = 52 W/m · K and α = 1.7 × 10-5 m2/s). The engine can be considered to be a rectangular block whose sides are 80 cm, 40 cm, and 40 cm. The
A man is found dead in a room at 16°C. The surface temperature on his waist is measured to be 23°C and the heat transfer coefficient is estimated to be 9 W/m2 · K. Modeling the body as 28-cm
The Biot number can be thought of as the ratio of(a) The conduction thermal resistance to the convective thermal resistance.(b) The convective thermal resistance to the conduction thermal
Lumped system analysis of transient heat conduction situations is valid when the Biot number is(a) Very small(b) Approximately one(c) Very large(d) Any real number(e) Cannot say unless the Fourier
Polyvinylchloride automotive body panels (k = 0.092 W/m · K, cp = 1.05 kJ/kg · K, ρ = 1714 kg/m3), 3-mm thick, emerge from an injection molder at 120°C. They need to be cooled to 40°C by
A steel casting cools to 90 percent of the original temperature difference in 30 min in still air. The time it takes to cool this same casting to 90 percent of the original temperature difference in
An 18-cm-long, 16-cm-wide, and 12-cm-high hot iron block (ρ = 7870 kg/m3, cp = 447 J/kg · K) initially at 20°C is placed in an oven for heat treatment. The heat transfer coefficient on the surface
A 10-cm-inner diameter, 30-cm-long can filled with water initially at 25°C is put into a household refrigerator at 3°C. The heat transfer coefficient on the surface of the can is 14 W/m2 · K.
A 6-cm-diameter 13-cm-high canned drink (ρ = 977 kg/m3, k = 0.607 W/m · K, cp = 4180 J/kg · K) initially at 25°C is to be cooled to 5°C by dropping it into iced water at 0°C. Total surface area
Copper balls (ρ = 8933 kg/m3, k = 401 W/m · K, cp = 385 J/kg·°C, α = 1.166 × 10-4 m2/s) initially at 200°C are allowed to cool in air at 30°C for a period of 2 minutes. If the balls have a
Repeat Prob. 4–178 using a banana instead of an apple. The thermal properties of bananas are practically the same as those of apples.Data from problem 178Conduct the following experiment at home to
Saturated ammonia vapor at 30°C is passed over 30 vertical flat plates, each of which is 10 cm high and 25 cm wide. The average surface temperature of the plates is 10°C. Estimate the average heat
A vertical 0.5 m × 0.5 m square plate is used in a process to condensate saturated water vapor. If the desired rate of condensation is 0.016 kg/s, determine the necessary surface temperature of the
Carbon steel balls (ρ = 7830 kg/m3, k = 64 W/m · K, cp = 434 J/kg · K) initially at 150°C are quenched in an oil bath at 20°C for a period of 3 minutes. If the balls have a diameter of 5 cm and
In a production facility, large plates made of stainless steel (k = 15 W/m · K, α = 3.91 × 10-6 m2/s) of 40 cm thickness are taken out of an oven at a uniform temperature of 750°C. The plates are
A long 18-cm-diameter bar made of hardwood (k = 0.159 W/m · K, α = 1.75 × 10-7 m2/s) is exposed to air at 30°C with a heat transfer coefficient of 8.83 W/m2·K. If the center temperature of the
Consider a 7.6-cm-long and 3-cm-diameter cylindrical lamb meat chunk (ρ = 1030 kg/m3, cp = 3.49 kJ/kg · K, k = 0.456 W/m · K, α = 1.3 × 10-7 m2/s). Fifteen such meat chunks initially at 2°C are
Consider a 7.6-cm-diameter cylindrical lamb meat chunk (ρ = 1030 kg/m3, cp = 3.49 kJ/kg · K, k = 0.456 W/m · K, a = 1.3 × 10-7 m2/s). Such a meat chunk intially at 2°C is dropped into boiling
A potato that may be approximated as a 5.7-cm solid sphere with the properties ρ = 910 kg/m3, cp = 4.25 kJ/kg · K, k = 0.68 W/m · K, and α = 1.76 × 10-7 m2/s. Twelve such potatoes initially at
A small chicken (k = 0.45 W/m · K, α = 0.15 × 10-6 m2/s) can be approximated as an 11.25-cm-diameter solid sphere. The chicken is initially at a uniform temperature of 8ºC and is to be cooked in

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