1-1
Solutions Manual for
Heat and Mass Transfer: Fundamentals & Applications
6th Edition
Yunus A. Çengel, Afshin J. Ghajar
McGraw-Hill Education, 2020
Chapter 1
INTRODUCTION AND BASIC CONCEPTS
PROPRIETARY AND CONFIDENTIAL
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1-2
Thermodynamics and Heat Transfer
1-1C Thermodynamics deals with the amount of heat transfer as a system undergoes a process from one equilibrium state to
1-3C The rating problems deal with the determination of the heat transfer rate for an existing system at a specified
1-4C The experimental approach (testing and taking measurements) has the advantage of dealing with the actual physical
1-5C Modeling makes it possible to predict the course of an event before it actually occurs, or to study various aspects of an
event mathematically without actually running expensive and time-consuming experiments. When preparing a mathematical
1-6C The right choice between a crude and complex model is usually the simplest model which yields adequate results.
1-9C The claim is false. The heater of a house supplies the energy that the house is losing, which is proportional to the
temperature difference between the indoors and the outdoors. A turned off heater consumes no energy. The heat lost from
1-3
1-4
1-16 The filament of a 150 W incandescent lamp is 5 cm long and has a diameter of 0.5 mm. The heat flux on the surface of
the filament, the heat flux on the surface of the glass bulb, and the annual electricity cost of the bulb are to be determined.
Assumptions Heat transfer from the surface of the filament and the bulb of the lamp is uniform.
Analysis (a) The heat transfer surface area and the heat flux on the surface of the filament are
2
cm 785.0)cm 5)(cm 05.0( ===
DLAs
26 W/m101.91==== 2
W150
Q
1-17 An aluminum ball is to be heated from 80C to 200C. The amount of heat that needs to be transferred to the aluminum
ball is to be determined.
Assumptions The properties of the aluminum ball are constant.
Q
1-5
1-18E A water heater is initially filled with water at 50F. The amount of energy that needs to be transferred to the water to
raise its temperature to 120F is to be determined.
Assumptions 1 Water is an incompressible substance with constant specific. 2 No water flows in or out of the tank during
heating.
Properties The density and specific heat of water at 85ºF from Table A–9E are:
1-19 An electrically heated house maintained at 22°C experiences infiltration losses at a rate of 0.7 ACH. The amount of
energy loss from the house due to infiltration per day and its cost are to be determined.
Assumptions 1 Air as an ideal gas with a constant specific heats at room temperature. 2 The volume occupied by the furniture
and other belongings is negligible. 3 The house is maintained at a constant temperature and pressure at all times. 4 The
infiltrating air exfiltrates at the indoors temperature of 22°C.
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1-7
1-21 A 2 mm thick by 3 cm wide AISI 1010 carbon steel strip is cooled in a chamber from 597 to 47°C to avoid
instantaneous thermal burn upon contact with skin tissue. The amount of heat rate to be removed from the steel strip is to be
determined.
Assumptions 1 Steady operating conditions exist. 2 The stainless steel sheet has constant specific heat and density. 3 Changes
in potential and kinetic energy are negligible.
1-22 Liquid water is to be heated in an electric teapot. The heating time is to be determined.
Assumptions 1 Heat loss from the teapot is negligible. 2 Constant properties can be used for both the teapot and the water.
Properties The average specific heats are given to be 0.7 kJ/kg·K for the teapot and 4.18 kJ/kg·K for water.
1-8
1-23 A water heater uses 100 kW to heat 60 gallon (0.2271 m3) of liquid water initially at 20°C. Determine the heating
duration such that the water exiting the heater would be in compliance with the ASME Boiler and Pressure Vessel Code
(ASME BPVC.IV-2015) service restrictions.
Assumptions1 Heating of the heater material is negligible (i.e. 100 kW is for heating the water only). 2 Constant properties
1-9
1-24 A boiler (10 kg) is used to heat 20 gallon (0.07571 m3) of liquid water with 50 kW for 30 minutes. Determine
whether this operating condition would be in compliance with the ASME Boiler and Pressure Vessel Code (ASME
BPVC.IV-2015) service restrictions.
Assumptions1 Heat loss from the boiler is negligible. 2 Constant properties are used for both the boiler and the water. 3 The
raise in temperature for the boiler and the water is equal. 4 No water flowing out of the boiler during the heating.
Properties The average specific heats are given to be 0.48 kJ/kg·K for the boiler material and 4.18 kJ/kg·K for the water. The
1-25 Water is heated in an insulated tube by an electric resistance heater. The mass flow rate of water through the heater is to
be determined.
Assumptions 1 Water is an incompressible substance with a constant specific heat. 2 The kinetic and potential energy
changes are negligible, ke pe 0. 3 Heat loss from the insulated tube is negligible.
1-10
1-26 It is observed that the air temperature in a room heated by electric baseboard heaters remains constant even though the
heater operates continuously when the heat losses from the room amount to 7000 kJ/h. The power rating of the heater is to be
determined.
Assumptions 1 Air is an ideal gas since it is at a high temperature and low pressure relative to its critical point values of –
1-11
1-12
1-13
1-14
1-30 Liquid water entering at 10°C and flowing at 10 g/s(0.01 kg/s) is heated in a circular tube by an electrical heater at
10 kW. Determine whether the water exit temperature would be below 79°C and comply with the ASME Code for Process
Piping, and the minimum mass flow rate to keep the exit temperature below 79°C.
Assumptions1 Water is an incompressible substance with constant properties. 2 Heat loss from the tube is negligible. 3
Steady operating conditions.
1-15
Heat Transfer Mechanisms
1-31C The thermal conductivity of a material is the rate of heat transfer through a unit thickness of the material per unit area
1-34C Superinsulations are obtained by using layers of highly reflective sheets separated by glass fibers in an evacuated
space. Radiation heat transfer between two surfaces is inversely proportional to the number of sheets used and thus heat loss
1-35C Most ordinary insulations are obtained by mixing fibers, powders, or flakes of insulating materials with air. Heat
1-36C The mechanisms of heat transfer are conduction, convection and radiation. Conduction is the transfer of energy from
the more energetic particles of a substance to the adjacent less energetic ones as a result of interactions between the particles.
1-37C Conduction is expressed by Fourier’s law of conduction as
dx
dT
kAQ−=
cond
where dT/dx is the temperature gradient,
k is the thermal conductivity, and A is the area which is normal to the direction of heat transfer.
1-16
1-44C The house with the lower rate of heat transfer through the walls will be more energy efficient. Heat conduction is
1-45C The rate of heat transfer through both walls can be expressed as
)(6.1
m 1.0
)C W/m16.0(
21
21
wood
21
woodwood
TTA
TT
A
L
TT
AkQ
−=
−
=
−
=
1-46C Emissivity is the ratio of the radiation emitted by a surface to the radiation emitted by a blackbody at the same
1-17
1-48 The thermal conductivity of a wood slab subjected to a given heat flux of 40 W/m2 with constant left and right surface
temperatures of 40ºC and 20ºC is to be determined.
Assumptions 1 Steady operating conditions exist since the surface temperatures of the wood slab remain constant at the
1-49 The inner and outer surfaces of a brick wall are maintained at specified temperatures. The rate of heat transfer through
the wall is to be determined.
Assumptions 1 Steady operating conditions exist since the surface
temperatures of the wall remain constant at the specified values. 2 Thermal
1-50E The inner and outer glasses of a double pane window with a 0.5-in air space are at specified temperatures. The rate of
heat transfer through the window is to be determined
Assumptions 1 Steady operating conditions exist since the surface temperatures
L
Brick wall
Glass
60F
48F
1-18
1-51 The inner and outer surfaces of a window glass are maintained at specified temperatures. The amount of heat transfer
through the glass in 5 h is to be determined.
Assumptions 1 Steady operating conditions exist since the surface temperatures of the glass remain constant at the specified
1-19
1-20
1-53 Heat is transferred steadily to boiling water in the pan through its bottom. The inner surface temperature of the bottom
of the pan is given. The temperature of the outer surface is to be determined.
Assumptions 1 Steady operating conditions exist since the surface temperatures of the pan remain constant at the specified
values. 2 Thermal properties of the aluminum pan are constant.
1-54E The inner and outer surface temperatures of the wall of an electrically heated home during a winter night are
measured. The rate of heat loss through the wall that night and its cost are to be determined.
Assumptions 1 Steady operating conditions exist since the surface temperatures of the wall remain constant at the specified
values during the entire night. 2 Thermal properties of the wall are constant.