Heat and mass transfer fundamentals and
applications 5th edition solutions cengel
, 2-1
Solutions Manual
for
Heat and Mass Transfer: Fundamentals & Applications
5th Edition
Yunus A. Cengel & Afshin J. Ghajar
McGraw-Hill, 2015
Chapter 2
HEAT CONDUCTION EQUATION
PROPRIETARY AND CONFIDENTIAL
This Manual is the proprietary property of The McGraw- -
by copyright and other state and federal laws. By opening and using this Manual the user agrees to the following
restrictions, and if the recipient does not agree to these restrictions, the Manual should be promptly returned
unopened to McGraw-Hill: This Manual is being provided only to authorized professors and instructors for
use in preparing for the classes using the affiliated textbook. No other use or distribution of this Manual is
permitted. This Manual may not be sold and may not be distributed to or used by any student or other third
, 2-2
party. No part of this Manual may be reproduced, displayed or distributed in any form or by any means,
electronic or otherwise, without the prior written permission of McGraw-Hill.
, 2-3
Introduction
2-1 C The term steady implies no change with time at any point within the medium while transient implies variation with time or
time dependence. Therefore, the temperature or heat flux remains unchanged with time during steady heat transfer through a
medium at any location although both quantities may vary from one location to another. During transient heat transfer, the
temperature and heat flux may vary with time as well as location. Heat transfer is one-dimensional if it occurs primarily in one
direction. It is two-dimensional if heat tranfer in the third dimension is negligible.
2-2 C Heat transfer is a vector quantity since it has direction as well as magnitude. Therefore, we must specify both direction and
magnitude in order to describe heat transfer completely at a point. Temperature, on the other hand, is a scalar quantity.
2-3 C Yes, the heat flux vector at a point P on an isothermal surface of a medium has to be perpendicular to the surface at that point.
2-4 C Isotropic materials have the same properties in all directions, and we do not need to be concerned about the variation of
properties with direction for such materials. The properties of anisotropic materials such as the fibrous or composite materials,
however, may change with direction.
2-5 C In heat conduction analysis, the conversion of electrical, chemical, or nuclear energy into heat (or thermal) energy in solids is
called heat generation.
2-6 C the
conversion of some other form of energy into thermal energy. The phrase however, is vague since the form of
energy generated is not clear.
2-7 C The heat transfer process from the kitchen air to the refrigerated space is
transient in nature since the thermal conditions in the kitchen and the refrigerator, in
general, change with time. However, we would analyze this problem as a steady heat
transfer problem under the worst anticipated conditions such as the lowest thermostat
setting for the refrigerated space, and the anticipated highest temperature in the
kitchen (the so-called design conditions). If the compressor is large enough to keep the
refrigerated space at the desired temperature setting under the presumed worst
conditions, then it is large enough to do so under all conditions by cycling on and off.
Heat transfer into the refrigerated space is
three-dimensional in nature since heat will be entering through all six sides of the
refrigerator. However, heat transfer through any wall or floor takes place in the direction
applications 5th edition solutions cengel
, 2-1
Solutions Manual
for
Heat and Mass Transfer: Fundamentals & Applications
5th Edition
Yunus A. Cengel & Afshin J. Ghajar
McGraw-Hill, 2015
Chapter 2
HEAT CONDUCTION EQUATION
PROPRIETARY AND CONFIDENTIAL
This Manual is the proprietary property of The McGraw- -
by copyright and other state and federal laws. By opening and using this Manual the user agrees to the following
restrictions, and if the recipient does not agree to these restrictions, the Manual should be promptly returned
unopened to McGraw-Hill: This Manual is being provided only to authorized professors and instructors for
use in preparing for the classes using the affiliated textbook. No other use or distribution of this Manual is
permitted. This Manual may not be sold and may not be distributed to or used by any student or other third
, 2-2
party. No part of this Manual may be reproduced, displayed or distributed in any form or by any means,
electronic or otherwise, without the prior written permission of McGraw-Hill.
, 2-3
Introduction
2-1 C The term steady implies no change with time at any point within the medium while transient implies variation with time or
time dependence. Therefore, the temperature or heat flux remains unchanged with time during steady heat transfer through a
medium at any location although both quantities may vary from one location to another. During transient heat transfer, the
temperature and heat flux may vary with time as well as location. Heat transfer is one-dimensional if it occurs primarily in one
direction. It is two-dimensional if heat tranfer in the third dimension is negligible.
2-2 C Heat transfer is a vector quantity since it has direction as well as magnitude. Therefore, we must specify both direction and
magnitude in order to describe heat transfer completely at a point. Temperature, on the other hand, is a scalar quantity.
2-3 C Yes, the heat flux vector at a point P on an isothermal surface of a medium has to be perpendicular to the surface at that point.
2-4 C Isotropic materials have the same properties in all directions, and we do not need to be concerned about the variation of
properties with direction for such materials. The properties of anisotropic materials such as the fibrous or composite materials,
however, may change with direction.
2-5 C In heat conduction analysis, the conversion of electrical, chemical, or nuclear energy into heat (or thermal) energy in solids is
called heat generation.
2-6 C the
conversion of some other form of energy into thermal energy. The phrase however, is vague since the form of
energy generated is not clear.
2-7 C The heat transfer process from the kitchen air to the refrigerated space is
transient in nature since the thermal conditions in the kitchen and the refrigerator, in
general, change with time. However, we would analyze this problem as a steady heat
transfer problem under the worst anticipated conditions such as the lowest thermostat
setting for the refrigerated space, and the anticipated highest temperature in the
kitchen (the so-called design conditions). If the compressor is large enough to keep the
refrigerated space at the desired temperature setting under the presumed worst
conditions, then it is large enough to do so under all conditions by cycling on and off.
Heat transfer into the refrigerated space is
three-dimensional in nature since heat will be entering through all six sides of the
refrigerator. However, heat transfer through any wall or floor takes place in the direction
