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engineering
heat and mass transfer fundamentals and applications

Questions and Answers of Heat And Mass Transfer Fundamentals And Applications

In a cogeneration plant, combustion gases at 1 atm and 800 K are used to preheat water by passing them through 6-m-long, 10-cm-diameter tubes. The inner surface of the tube is black, and the partial
A flow-through combustion chamber consists of 15-cm diameter long tubes immersed in water. Compressed air is routed to the tube, and fuel is sprayed into the compressed air. The combustion gases
Repeat Prob. 13–106 for a total pressure of 3 atm.Data from problem 106A flow-through combustion chamber consists of 15-cm diameter long tubes immersed in water. Compressed air is routed to the
A gas at 1200 K and 1 atm consists of 10 percent CO2, 10 percent H2O, 10 percent O2, and 70 percent N2 by volume. The gas flows between two large parallel black plates maintained at 600 K. If the
Explain all the different mechanisms of heat transfer from the human body(a) Through the skin(b) Through the lungs.
How is the insulating effect of clothing expressed? How does clothing affect heat loss from the body by convection, radiation, and evaporation? How does clothing affect heat gain from the sun?
Consider a person who is resting or doing light work. Is it fair to say that roughly one-third of the metabolic heat generated in the body is dissipated to the environment by convection, one-third by
What is operative temperature? How is it related to the mean ambient and radiant temperatures? How does it differ from effective temperature?
A person feels very comfortable in his house in light clothing when the thermostat is set at 22°C and the mean radiation temperature (the average temperature of the surrounding surfaces) is also
Repeat Prob. 13–117 for a mean radiation temperature of 10°C.Data from problem 117A person feels very comfortable in his house in light clothing when the thermostat is set at 22°C and the mean
The convection heat transfer coefficient for a clothed person while walking in still air at a velocity of 0.5 to 2 m/s is given by h = 8.6V 0.53, where V is in m/s and h is in W/m2 · K. Plot the
A car mechanic is working in a shop whose interior space is not heated. Comfort for the mechanic is provided by two radiant heaters that radiate heat at a total rate of 4 kJ/s. About 5 percent of
Consider a large classroom with 90 students on a hot summer day. All the lights with 2.0 kW of rated power are kept on. The room has no external walls, and thus heat gain through the walls and the
An average person produces 0.50 lbm of moisture while taking a shower and 0.12 lbm while bathing in a tub. Consider a family of four who shower once a day in a bathroom that is not ventilated. Taking
A simple solar collector is built by placing a 6-cm-diameter clear plastic tube around a garden hose whose outer diameter is 2 cm (Fig. P13–127). The hose is painted black to maximize solar
Consider a 1.5-m-high and 3-m-wide solar collector that is tilted at an angle 20° from the horizontal. The distance between the glass cover and the absorber plate is 3 cm, and the back side of the
A clothed or unclothed person feels comfortable when the skin temperature is about 33°C. Consider an average man wearing summer clothes whose thermal resistance is 1.1 clo. The man feels very
A long cylindrical black surface fuel rod of diameter 25 mm is shielded by a surface concentric to the rod. The shield has diameter of 50 mm and a constant surface temperature of 320 K. Both inner
A solar collector consists of a horizontal copper tube of outer diameter 5 cm enclosed in a concentric thin glass tube of diameter 12 cm. Water is heated as it flows through the tube, and the annular
A solar collector consists of a horizontal aluminum tube having an outer diameter of 2.5 in enclosed in a concentric thin glass tube of diameter 5 in. Water is heated as it flows through the tube,
A thin aluminum sheet with an emissivity of 0.12 on both sides is placed between two very large parallel plates maintained at uniform temperatures of T1 = 750 K and T2 = 400 K. The emissivities of
A thermocouple used to measure the temperature of hot air flowing in a duct whose walls are maintained at Tw = 500 K shows a temperature reading of Tth = 850 K. Assuming the emissivity of the
In a natural-gas fired boiler, combustion gases pass through 6-m-long 15-cm-diameter tubes immersed in water at 1 atm pressure. The tube temperature is measured to be 105°C, and the emissivity of
Repeat Prob. 13–144 for a total pressure of 3 atm for the combustion gases.Data from problem 144In a natural-gas fired boiler, combustion gases pass through 6-m-long 15-cm-diameter tubes immersed
Consider an infinitely long three-sided triangular enclosure with side lengths 2 cm, 3 cm, and 4 cm. The view factor from the 2 cm side to the 4 cm side is(a) 0.25(b) 0.50(c) 0.64(d) 0.75(e) 0.87
Consider a 15-cm-diameter sphere placed within a cubical enclosure with a side length of 15 cm. The view factor from any of the square-cube surfaces to the sphere is(a) 0.09(b) 0.26(c) 0.52(d)
A 70-cm-diameter flat black disk is placed in the center of the top surface of a 1-m × 1-m × 1-m black box. The view factor from the entire interior surface of the box to the interior surface of
Consider two concentric spheres with diameters 12 cm and 18 cm forming an enclosure. The view factor from the inner surface of the outer sphere to the inner sphere is(a) 0(b) 0.18(c) 0.44(d) 0.56(e)
The number of view factors that need to be evaluated directly for a 10-surface enclosure is(a) 1(b) 10(c) 22(d) 34(e) 45
Consider two concentric spheres forming an enclosure with diameters of 12 cm and 18 cm and surface temperatures 300 K and 500 K, respectively. Assuming that the surfaces are black, the net radiation
Consider a vertical 2-m-diameter cylindrical furnace whose surfaces closely approximate black surfaces. The base, top, and side surfaces of the furnace are maintained at 400 K, 600 K, and 900 K,
Consider a vertical 2-m-diameter cylindrical furnace whose surfaces closely approximate black surfaces. The base, top, and side surfaces of the furnace are maintained at 400 K, 600 K, and 900 K,
A solar flux of 1400 W/m2 directly strikes a space vehicle surface which has a solar absortivity of 0.4 and thermal emissivity of 0.6. The equilibrium temperature of this surface in space at 0 K
A 70-cm-diameter flat black disk is placed at the center of the ceiling of a 1-m × 1-m × 1-m black box. If the temperature of the box is 620°C and the temperature of the disk is 27°C, the rate of
Consider two infinitely long concentric cylinders with diameters 20 and 25 cm. The inner surface is maintained at 700 K and has an emissivity of 0.40, while the outer surface is black. If the rate of
Consider a surface at 0°C that may be assumed to be a blackbody in an environment at 25°C. If 300 W/m2 of radiation is incident on the surface, the radiosity of this black surface is(a) 0 W/m2(b)
Consider a gray and opaque surface at 0°C in an environment at 25°C. The surface has an emissivity of 0.8. If the radiation incident on the surface is 240 W/m2, the radiosity of the surface is(a)
Consider a 3-m × 3-m × 3-m cubical furnace. The base surface is black and has a temperature of 400 K. The radiosities for the top and side surfaces are calculated to be 7500 W/m2 and 3200 W/m2,
The base surface of a cubical furnace with a side length of 3 m has an emissivity of 0.80 and is maintained at 500 K. If the top and side surfaces also have an emissivity of 0.80 and are maintained
Two gray surfaces that form an enclosure exchange heat with one another by thermal radiation. Surface 1 has a temperature of 400 K, an area of 0.2 m2, and a total emissivity of 0.4. Surface 2 has a
The surfaces of a two-surface enclosure exchange heat with one another by thermal radiation. Surface 1 has a temperature of 400 K, an area of 0.2 m2, and a total emissivity of 0.4. Surface 2 is
Two concentric spheres are maintained at uniform temperatures T1 = 45°C and T2 = 280°C and have emissivities ε1 = 0.25 and ε2 = 0.7, respectively. If the ratio of the diameters is Δ1/Δ2 = 0.30,
Consider a 3-m × 3-m × 3-m cubical furnace. The base surface of the furnace is black and has a temperature of 400 K. The radiosities for the top and side surfaces are calculated to be 7500 W/m2 and
Two very large parallel plates are maintained at uniform temperatures T1 = 750 K and T2 = 500 K and have emissivities ε1 = 0.85 and ε2 = 0.7, respectively. If a thin aluminum sheet with the same
Consider an enclosure consisting of N diffuse and gray surfaces. The emissivity and temperature of each surface as well as the view factors between the surfaces are specified. Write a program to
How is the concentration of a commodity defined? How is the concentration gradient defined? How is the diffusion rate of a commodity related to the concentration gradient?
Consider an aperture of 10-mm diameter through which radiation is emitted as a blackbody with an emissive power of 2.87 × 105 W/m2. A radiation sensor is positioned with a 30° tilt off the normal
A small circular surface of area A1 = 2 cm2 located at the center of a 2-m-diameter sphere emits radiation as a blackbody at T1 = 1000 K. Determine the rate at which radiation energy is streaming
Repeat Prob. 12–47 for a 4-m-diameter sphere.Data from problem 47A small circular surface of area A1 = 2 cm2 located at the center of a 2-m-diameter sphere emits radiation as a blackbody at T1 =
A small surface of area A1 = 8 cm2 emits radiation as a blackbody at T1 = 800 K. Part of the radiation emitted by A1 strikes another small surface of area A2 = 8 cm2 oriented as shown in the figure.
A small surface of area A = 1 cm2 emits radiation as a blackbody at 1800 K. Determine the rate at which radiation energy is emitted through a band defined by 0 ≤ ϕ ≤ 2π and 45 ≤ θ ≤ 60°,
Consider the intensity of solar radiation incident on earth’s surface can be expressed as Ii = 100 cosθ, where Ii has the units of W/m2 · sr. Determine the peak value for the intensity of
A small surface of area A = 1 cm2 is subjected to incident radiation of constant intensity Ii = 2.2 × 104 W/m2 · sr over the entire hemisphere. Determine the rate at which radiation energy is
A small surface of area A1 = 3 cm2 emits radiation as a blackbody with total emissive power of Eb = 5.67 × 104 W/m2. Part of the radiation emitted by A1 strikes another small surface of area A2 = 8
A small surface of area A1 = 3 cm2 emits radiation as a blackbody at T1 = 1000 K. A radiation detector (A2) is placed normal to the direction of viewing from surface A1 at a distance L, as shown in
An ordinary egg can be approximated as a 5.5-cmdiameter sphere whose properties are roughly k = 0.6 W/m · K and α = 0.14 × 10-6 m2/s. The egg is initially at a uniform temperature of 8°C and is
A thick wall made of refractory bricks (k = 1.0 W/m · K and α = 5.08 × 10-7 m2/s) has a uniform initial temperature of 15°C. The wall surface is subjected to uniform heat flux of 20 kW/m2. Using
A stainless steel slab (k 5 14.9 W/m · K and a = 3.95 × 10-6 m2/s) and a copper slab (k = 401 W/m · K and α = 117 × 10-6 m2/s) are subjected to uniform heat flux of 10 kW/m2 at the surface. Both
How does the rate of freezing affect the tenderness, color, and the drip of meat during thawing?
The chilling room of a meat plant is 15 m × 18 m × 5.5 m in size and has a capacity of 350 beef carcasses. The power consumed by the fans and the lights in the chilling room are 22 and 2 kW,
Consider steady one-dimensional heat conduction in a composite plane wall consisting of two layers A and B in perfect contact at the interface. The wall involves no heat generation. The nodal network
A 10 cm × 10 cm horizontal flat heater is used for vaporizing refrigerant-134a at 350 kPa. The heater is supplied with 0.35 MW/m2 of heat flux, and the surface temperature of the heater is 25°C. If
In a gas-fired boiler, water is boiled at 150°C by hot gases flowing through 50-m-long, 5-cm-outer-diameter mechanically polished stainless-steel pipes submerged in water. If the outer surface
Repeat Prob. 10–36 for a boiling temperature of 155°CData from problem 36In a gas-fired boiler, water is boiled at 150°C by hot gases flowing through 50-m-long, 5-cm-outer-diameter mechanically
A 2-mm-diameter cylindrical metal rod with emissivity of 0.5 is submerged horizontally in water under atmospheric pressure. When electric current is passed through the metal rod, the surface
A 1 m × 1 m horizontal flat heater is used for generating steam by boiling water at 1 atm. The boiling occurs at an excess temperature above 300°C, but is maintained below the burnout point.
Water is boiled at 90°C by a horizontal brass heating element of diameter 7 mm. Determine the surface temperature of the heater for the minimum heat flux case.
Water is boiled at atmospheric pressure by a horizontal polished copper heating element of diameter D = 0.5 in and emissivity ε = 0.05 immersed in water. If the surface temperature of the heating
Repeat Prob. 10–41E for a heating element temperature of 988°F.Data from problem 41Water is boiled at atmospheric pressure by a horizontal polished copper heating element of diameter D = 0.5 in
A 20-mm-diameter metal sphere has an emissivity of 0.75. The sphere was removed from a furnace when it reached a uniform temperature of 700°C and was suddenly submerged in a water bath at
A 20-mm-diameter cylindrical steel rod with a length of 200 mm has an emissivity of 0.9. The steel rod was removed from a furnace when it reached a uniform temperature of 500°C and was suddenly
A long cylindrical stainless steel rod (cp = 450 J/kg ∙ K, ρ = 7900 kg/m3, ε = 0.30) with mechanically polished surface is being conveyed through a water bath to be quenched. The 25-mm-diameter
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
Cylindrical stainless steel rods are heated to a uniform temperature of 700°C and then quenched in water at 1 atm. The rods are 25 cm in length, 25 mm in diameter, and their surface have an
A cylindrical rod is used for boiling water at 1 atm. The rod has a diameter of 1 cm and its surface has an emissivity of 0.3. Determine the film boiling convection heat transfer coefficient at the
A 3-mm-diameter cylindrical heater is used for boiling water at 100°C. The heater surface is made of mechanically polished stainless steel with an emissivity of 0.3. Determine the boiling convection
Saturated refrigerant-134a vapor at a pressure of 888 kPa is condensed as it is flowing through a 0.25-m-long tube with a diameter of 12 mm. The tube wall temperature is maintained uniform at 15°C.
Draw a 1-shell-pass and 6-tube-passes shell-and-tube heat exchanger. What are the advantages and disadvantages of using 6 tube passes instead of just 2 of the same diameter?
Draw a 2-shell-passes and 8-tube-passes shell-and tube heat exchanger. What is the primary reason for using so many tube passes?
What are the restrictions on the relation UAs = Ui Ai = Uo Ao for a heat exchanger? Here As is the heat transfer surface area and U is the overall heat transfer coefficient.
Reconsider Prob. 11–18. Using EES (or other) software, plot the overall heat transfer coefficient as a function of the limestone thickness as it varies from 1 mm to 3 mm, and discuss the
Reconsider Prob. 11–24. Using EES (or other) software, plot the overall heat transfer coefficient based on the inner surface as a function of fouling factor as it varies from 0.0001 m2 · K/W to
A double-pipe heat exchanger is constructed of a copper (k = 380 W/m · K) inner tube of internal diameter Di = 1.2 cm and external diameter Do = 1.6 cm and an outer tube of diameter 3.0 cm. The
Reconsider Prob. 11–26. Using EES (or other) software, investigate the effects of pipe conductivity and heat transfer coefficients on the thermal resistance of the heat exchanger. Let the thermal
Reconsider Prob. 11–45. Using EES (or other) software, investigate the effects of temperature and mass flow rate of geothermal water on the length of the tube. Let the temperature vary from 100°C
Engine oil (cp = 2100 J/kg · K) is to be heated from 20°C to 60°C at a rate of 0.3 kg/s in a 2-cm-diameter thin walled copper tube by condensing steam outside at a temperature of 130°C (hfg =
Reconsider Prob. 11–54. Using EES (or other) software, investigate the effects of oil exit temperature and water inlet temperature on the overall heat transfer coefficient of the heat exchanger.
Reconsider Prob. 11–59E. Using EES (or other) software, investigate the effect of the condensing steam temperature on the rate of heat transfer, the rate of condensation of steam, and the mass flow
Reconsider Prob. 11–61. Using EES (or other) software, investigate the effect of the exhaust gas inlet temperature on the rate of heat transfer, the exit temperature of exhaust gases, and the rate
Geothermal water (cp = 1.03 Btu/lbm · °F) is to be used as the heat source to supply heat to the hydronic heating system of a house at a rate of 40 Btu/s in a double-pipe counter-flow heat
A 1-shell-pass and 8-tube-passes heat exchanger is used to heat glycerin (cp = 0.60 Btu/lbm · °F) from 65°F to 140°F by hot water (cp = 1.0 Btu/lbm · °F) that enters the thin walled
Oil is being cooled from 180°F to 120°F in a 1-shell and 2-tube heat exchanger with an overall heat transfer coefficient of 40 Btu/h ft2 · °F. Water (cpc = 1.0 Btu/lbm · °F) enters at 80°F and
Reconsider Prob. 11–69. Using EES (or other) software, investigate the effect of the mass flow rate of water on the rate of heat transfer and the tube-side surface area. Let the mass flow rate vary
Consider a shell and tube heat exchanger in a milk pasteurizing unit in which the milk flowing is to be heated from 20°C by hot water initially at 140°C and flowing at a rate of 5 kg/s. The milk
Repeat Prob. 11–72 for a mass flow rate of 3 kg/s for water.Data from problem 72A shell-and-tube heat exchanger with 2-shell passes and 12-tube passes is used to heat water (cp = 4180 J/kg · K) in
Glycerin (cp = 2400 J/kg · K) at 20°C and 0.3 kg/s is to be heated by ethylene glycol (cp = 2500 J/kg · K) at 60°C and the same mass flow rate in a thin-walled double-pipe parallel-flow heat
Reconsider Prob. 11–97. Using EES (or other) software, investigate the effects of the mass flow rate of water and the tube length on the outlet temperatures of water and air. Let the mass flow rate
Reconsider Prob. 11–99. Using EES (or other) software, investigate the effects of the inlet temperature of hot water and the heat transfer coefficient on the rate of heat transfer and the surface
In an industrial facility, a countercurrent double pipe heat exchanger is used to heat the glycerin flowing at a rate of 1.5 kg/s from 10°C to 50°C by passing hot water at an inlet temperature of
Cold water (cp = 4180 J/kg · K) enters the tubes of a heat exchanger with 2-shell passes and 23-tube passes at 14°C at a rate of 3 kg/s, while hot oil (cp = 2200 J/kg · K) enters the shell at

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