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engineering
heat and mass transfer fundamentals and applications

Questions and Answers of Heat And Mass Transfer Fundamentals And Applications

Using the parametric table and plot features of EES, determine the squares of the number from 1 to 100 in increments of 10 in tabular form, and plot the results.
Solve this system of two equations with two unknowns using EES: x³y² = 10.5 3xy + y = 4.6
Heat treatment of metals is commonly done using electrically heated draw batch furnaces. Consider a furnace that is situated in a room with surrounding air temperature of 30°C and an average
Determine a positive real root of this equation using EES: 3.5x³10x0.5 - 3x = -4
Heat treatment is common in processing of semiconductor material. A 200-mm-diameter silicon wafer with thickness of 725 mm is being heat treated in a vacuum chamber by infrared heater. The
Consider a sealed 20-cm-high electronic box whose base dimensions are 50 cm × 50 cm placed in a vacuum chamber. The emissivity of the outer surface of the box is 0.95. If the electronic components
Reconsider Prob. 1–81. Using EES (or other) software, plot the convection heat transfer coefficient as a function of the wire surface temperature in the range of 100°C to 300°C. Discuss the
Reconsider Prob. 1–77. Using EES (or other) software, plot the rate of evaporation of liquid nitrogen as a function of the ambient air temperature in the range of 0°C to 40°C. Discuss the
Repeat Prob. 1–77 for liquid oxygen, which has a boiling temperature of 2183°C, a heat of vaporization of 213 kJ/kg, and a density of 1140 kg/m3 at 1 atm pressure.Data From Problem 77The boiling
The boiling temperature of nitrogen at atmospheric pressure at sea level (1 atm) is 2196°C. Therefore, nitrogen is commonly used in low temperature scientific studies since the temperature of liquid
Reconsider Prob. 1–74. Using EES (or other) software, plot the amount of power the transistor can dissipate safely as a function of the maximum case temperature in the range of 60°C to 90°C.
An AISI 316 stainless steel spherical container is used for storing chemicals undergoing exothermic reaction that provides a uniform heat flux of 60 kW/m2 to the container’s inner surface. The
A 5-cm-external-diameter, 10-m-long hot-water pipe at 80°C is losing heat to the surrounding air at 5°C by natural convection with a heat transfer coefficient of 25 W/m2·K. Determine the rate of
Reconsider Prob. 1–62. Using EES (or other) software, plot the rate at which ice melts as a function of the container thickness in the range of 0.1 cm to 1.0 cm. Discuss the results.Data from
Reconsider Prob. 1–70. Using EES (or other) software, plot the rate of heat transfer as a function of the heat transfer coefficient in the range of 20 W/m2 · K to 100 W/m2 · K. Discuss the
Silicon wafer is susceptible to warping when the wafer is subjected to temperature difference across its thickness. Thus, steps needed to be taken to prevent the temperature gradient across the wafer
Reconsider Prob. 1–54. Using EES (or other) software, plot the amount of heat loss through the glass as a function of the window glass thickness in the range of 0.1 cm to 1.0 cm. Discuss the
The inner and outer surfaces of a 4-m × 7-m brick wall of thickness 30 cm and thermal conductivity 0.69 W/m·K are maintained at temperatures of 26°C and 8°C, respectively. Determine the rate of
The inner and outer surfaces of a 0.5-cm thick 2-m × 2-m window glass in winter are 10°C and 3°C, respectively. If the thermal conductivity of the glass is 0.78 W/m·K, determine the amount of
A hair dryer is basically a duct in which a few layers of electric resistors are placed. A small fan pulls the air in and forces it to flow over the resistors where it is heated. Air enters a 900-W
The ducts of an air heating system pass through an unheated area. As a result of heat losses, the temperature of the air in the duct drops by 3°C. If the mass flow rate of air is 90 kg/min,
A 5-m × 6-m × 8-m room is to be heated by an electrical resistance heater placed in a short duct in the room. Initially, the room is at 15°C, and the local atmospheric pressure is 98 kPa. The room
1.2 kg of liquid water initially at 15°C is to be heated to 95°C in a teapot equipped with a 1200-W electric heating element inside. The teapot is 0.5 kg and has an average specific heat of 0.7
A house has an electric heating system that consists of a 300-W fan and an electric resistance heating element placed in a duct. Air flows steadily through the duct at a rate of 0.6 kg/s and
A room is heated by a baseboard resistance heater. When the heat losses from the room on a winter day amount to 9000 kJ/h, it is observed that the air temperature in the room remains constant even
In many manufacturing plants, individuals are often working around high temperature surfaces. Exposed hot surfaces that are potential for thermal burns on human skin tissue are considered to be
Liquid ethanol is a flammable fluid and can release vapors that form explosive mixtures at temperatures above its flashpoint at 16.6°C. In a chemical plant, liquid ethanol (cp = 2.44 kJ/kg∙K, ρ =
Water is heated in an insulated, constant diameter tube by a 5-kW electric resistance heater. If the water enters the heater steadily at 15°C and leaves at 60°C, determine the mass flow rate of
Consider a house with a floor space of 200 m2 and an average height of 3 m at sea level, where the standard atmospheric pressure is 101.3 kPa. Initially the house is at a uniform temperature of
A 60-gallon water heater is initially filled with water at 50ºF. Determine how much energy (in Btu) needs to be transferred to the water to raise its temperature to 120ºF. Evaluate the water
In a manufacturing plant, AISI 1010 carbon steel strips (ρ = 7832 kg/m3) of 2 mm thick and 3 cm wide are conveyed into a chamber at a constant speed to be cooled from 527ºC to 127°C. Determine the
A rigid closed tank is filled with 1 metric ton of liquid ammonia and is exposed to the sun. At 6 am, the liquid ammonia is at a temperature of 4°C. By 3 pm, the temperature of the liquid ammonia
A 15-cm-diameter aluminum ball is to be heated from 80°C to an average temperature of 200°C. Taking the average density and specific heat of aluminum in this temperature range to be ρ = 2700 kg/m3
Consider a 150-W incandescent lamp. The filament of the lamp is 5-cm long and has a diameter of 0.5 mm. The diameter of the glass bulb of the lamp is 8 cm. Determine the heat flux, in W/m2,(a) On the
What are the mechanisms of energy transfer to a closed system? How is heat transfer distinguished from the other forms of energy transfer?
What is heat flux? How is it related to the heat transfer rate?
Consider two identical rooms, one with a refrigerator in it and the other without one. If all the doors and windows are closed, will the room that contains the refrigerator be cooler or warmer than
When modeling an engineering process, how is the right choice made between a simple but crude and a complex but accurate model? Is the complex model necessarily a better choice since it is more
What is the importance of modeling in engineering? How are the mathematical models for engineering processes prepared?
How do the differential equations in the study of a physical problem arise?
What is the difference between the analytical and experimental approach to heat transfer? Discuss the advantages and disadvantages of each approach.
How do rating problems in heat transfer differ from the sizing problems?
How does transient heat transfer differ from steady heat transfer? How does one-dimensional heat transfer differ from two-dimensional heat transfer?
Why is it necessary to ventilate buildings? What is the effect of ventilation on energy consumption for heating in winter and for cooling in summer? Is it a good idea to keep the bathroom fans on all
What is asymmetric thermal radiation? How does it cause thermal discomfort in the occupants of a room?
How do (a) draft and (b) cold floor surfaces cause discomfort for a room’s occupants?
What is stratification? Is it likely to occur at places with low or high ceilings? How does it cause thermal discomfort for a room’s occupants? How can stratification be prevented?
Consider a house in Atlanta, Georgia, that is maintained at 22°C and has a total of 20 m2 of window area. The windows are double-door type with wood frames and metal spacers and have a U-factor of
The rate of heat loss through a unit surface area of a window per unit temperature difference between the indoors and the outdoors is called the U-factor. The value of the U-factor ranges from about
An ice skating rink is located in a building where the air is at Tair = 20°C and the walls are at Tw = 25°C. The convection heat transfer coefficient between the ice and the surrounding air is h =
Reconsider Prob. 1–125. Using EES (or other) software, plot the rate of heat loss through the window as a function of the U-factor. Discuss the results.Data From Problem 125The rate of heat loss
The critical heat flux (CHF) is a thermal limit at which a boiling crisis occurs whereby an abrupt rise in temperature causes overheating on fuel rod surface that leads to damage. A cylindrical fuel
A 4-m × 5-m × 6-m room is to be heated by one ton (1000 kg) of liquid water contained in a tank placed in the room. The room is losing heat to the outside at an average rate of 10,000 kJ/h. The
Reconsider Prob. 1–138. Using EES (or other) software, plot the rate of radiation heat transfer in winter as a function of the temperature of the inner surface of the room in the range of 8°C to
A 2-kW electric resistance heater in a room is turned on and kept on for 50 minutes. The amount of energy transferred to the room by the heater is(a) 2 kJ(b) 100 kJ(c) 6000 kJ(d) 7200 kJ(e) 12,000 kJ
A cold bottled drink (m = 2.5 kg, cp = 4200 J/kg · K) at 5°C is left on a table in a room. The average temperature of the drink is observed to rise to 15°C in 30 minutes. The average rate of heat
A 2-kW electric resistance heater submerged in 30-kg water is turned on and kept on for 10 min. During the process, 500 kJ of heat is lost from the water. The temperature rise of water is(a)
Eggs with a mass of 0.15 kg per egg and a specific heat of 3.32 kJ/kg · °C are cooled from 32°C to 10°C at a rate of 200 eggs per minute. The rate of heat removal from the eggs is(a) 7.3 kW(b) 53
Water enters a pipe at 20°C at a rate of 0.50 kg/s and is heated to 60°C. The rate of heat transfer to the water is(a) 20 kW(b) 42 kW(c) 84 kW(d) 126 kW(e) 334 kW
Steady heat conduction occurs through a 0.3-m-thick 9 m × 3 m composite wall at a rate of 1.2 kW. If the inner and outer surface temperatures of the wall are 15°C and 7°C, the effective thermal
Heat is lost steadily through a 0.5-cm thick 2 m × 3 m window glass whose thermal conductivity is 0.7 W/m · K. The inner and outer surface temperatures of the glass are measured to be 12°C to
Air enters a 12-m-long, 7-cm-diameter pipe at 50°C at a rate of 0.06 kg/s. The air is cooled at an average rate of 400 W per m2 surface area of the pipe. The air temperature at the exit of the pipe
A 10-cm-high and 20-cm-wide circuit board houses on its surface 100 closely spaced chips, each generating heat at a rate of 0.12 W and transferring it by convection and radiation to the surrounding
Heat is lost through a brick wall (k = 0.72 W/m · K), which is 4 m long, 3 m wide, and 25 cm thick at a rate of 500 W. If the inner surface of the wall is at 22°C, the temperature at the midplane
While driving down a highway early in the evening, the air flow over an automobile establishes an overall heat transfer coefficient of 18 W/m2 · K. The passenger cabin of this automobile exposes 9
Over 90 percent of the energy dissipated by an incandescent light bulb is in the form of heat, not light. What is the temperature of a vacuum-enclosed tungsten filament with an exposed surface area
On a still clear night, the sky appears to be a blackbody with an equivalent temperature of 250 K. What is the air temperature when a strawberry field cools to 0°C and freezes if the heat transfer
A 40-cm-long, 0.4-cm-diameter electric resistance wire submerged in water is used to determine the convection heat transfer coefficient in water during boiling at 1 atm pressure. The surface
A 3-m2 black surface at 140°C is losing heat to the surrounding air at 35°C by convection with a heat transfer coefficient of 16 W/m2 · K, and by radiation to the surrounding surfaces at 15°C.
A 25-cm-diameter black ball at 130°C is suspended in air, and is losing heat to the surrounding air at 25°C by convection with a heat transfer coefficient of 12 W/m2 · K, and by radiation to the
A person’s head can be approximated as a 25-cm diameter sphere at 35°C with an emissivity of 0.95. Heat is lost from the head to the surrounding air at 25°C by convection with a heat transfer
A room is heated by a 1.2 kW electric resistance heater whose wires have a diameter of 4 mm and a total length of 3.4 m. The air in the room is at 23°C and the interior surfaces of the room are at
A person standing in a room loses heat to the air in the room by convection and to the surrounding surfaces by radiation. Both the air in the room and the surrounding surfaces are at 20°C. The
Exhaust gases from a manufacturing plant are being discharged through a 10-m tall exhaust stack with outer diameter of 1 m, wall thickness of 10 cm, and thermal conductivity of 40 W/m·K. The exhaust
Consider a small hot metal object of mass m and specific heat c that is initially at a temperature of Ti. Now the object is allowed to cool in an environment at T∞ by convection with a heat
A 1200-W iron is left on the iron board with its base exposed to ambient air at 26°C. The base plate of the iron has a thickness of L = 0.5 cm, base area of A = 150 cm2, and thermal conductivity of
Consider a 20-cm-thick large concrete plane wall (k = 0.77 W/m · K) subjected to convection on both sides with T∞1 = 22°C and h1 = 8 W/m2·K on the inside, and T∞2 = 8°C and h2 = 12 W/m2 · K
Consider a steam pipe of length L, inner radius r1, outer radius r2, and constant thermal conductivity k. Steam flows inside the pipe at an average temperature of Ti with a convection heat transfer
When a long section of a compressed air line passes through the outdoors, it is observed that the moisture in the compressed air freezes in cold weather, disrupting and even completely blocking the
Consider a steam pipe of length L = 35 ft, inner radius r1 = 2 in, outer radius r2 = 2.4 in, and thermal conductivity k = 8 Btu/h · ft · °F. Steam is flowing through the pipe at an average
In a manufacturing plant, a quench hardening process is used to treat steel ball bearings (c = 500 J/kg·K, k = 60 W/m·K, r = 7900 kg/m3) of 25 mm in diameter. After being heated to a prescribed
Consider a water pipe of length L = 17 m, inner radius r1 = 15 cm, outer radius r2 = 20 cm, and thermal conductivity k = 14 W/m·K. Heat is generated in the pipe material uniformly by a 25-kW
Heat is generated uniformly at a rate of 4.2 × 106 W/m3 in a spherical ball (k = 45 W/m · K) of diameter 24 cm. The ball is exposed to iced-water at 0°C with a heat transfer coefficient of 1200
Consider a spherical reactor of 5-cm diameter operating at steady condition has a temperature variation that can be expressed in the form of T(r) = a - br2, where a = 850°C and b = 5 × 105 K/m2.
Consider a cylindrical shell of length L, inner radius r1, and outer radius r2 whose thermal conductivity varies in a specified temperature range as k(T) = k0(1 + βT2) where k0 and β are two
A pipe is used for transporting boiling water in which the inner surface is at 100°C. The pipe is situated in a surrounding where the ambient temperature is 20°C and the convection heat transfer
Consider a medium in which the heat conduction equation is given in its simplest forms as(a) Is heat transfer steady or transient?(b) Is heat transfer one-, two-, or three-dimensional?(c) Is there
The heat conduction equation in a medium is given in its simplest form asSelect the wrong statement below.(a) The medium is of cylindrical shape.(b) The thermal conductivity of the medium is
A metal spherical tank is filled with chemicals undergoing an exothermic reaction. The reaction provides a uniform heat flux on the inner surface of the tank. The tank has an inner diameter of 5 m
Consider a large plane wall of thickness L, thermal conductivity k, and surface area A. The left surface of the wall is exposed to the ambient air at T∞ with a heat transfer coefficient of h while
A solar heat flux q·s is incident on a sidewalk whose thermal conductivity is k, solar absorptivity is as, and convective heat transfer coefficient is h. Taking the positive x direction to be
A plane wall of thickness L is subjected to convection at both surfaces with ambient temperature T∞1 and heat transfer coefficient h1 at inner surface, and corresponding T∞2 and h2 values at the
Consider steady one-dimensional heat conduction through a plane wall, a cylindrical shell, and a spherical shell of uniform thickness with constant thermophysical properties and no thermal energy
The conduction equation boundary condition for an adiabatic surface with direction n being normal to the surface is(a) T = 0(b) dT/dn = 0(c) d2T/dn2 = 0(d ) d3T/dn3 = 0(e) -kdT/dn = 1
The variation of temperature in a plane wall is determined to be T(x) = 52x + 25 where x is in m and T is in °C. If the temperature at one surface is 38°C, the thickness of the wall is(a) 0.10 m(b)
The variation of temperature in a plane wall is determined to be T(x) = 110 - 60x where x is in m and T is in °C. If the thickness of the wall is 0.75 m, the temperature difference between the inner
The temperatures at the inner and outer surfaces of a 15-cm-thick plane wall are measured to be 40°C and 28°C, respectively. The expression for steady, one-dimensional variation of temperature in
The thermal conductivity of a solid depends upon the solid’s temperature as k = aT + b where a and b are constants. The temperature in a planar layer of this solid as it conducts heat is given
Hot water flows through a PVC (k = 0.092 W/m·K) pipe whose inner diameter is 2 cm and outer diameter is 2.5 cm. The temperature of the interior surface of this pipe is 50°C and the temperature of
Heat is generated in a long 0.3-cm-diameter cylindrical electric heater at a rate of 180 W/cm3. The heat flux at the surface of the heater in steady operation is(a) 12.7 W/cm2(b) 13.5 W/cm2(c) 64.7

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