Chapter 2

ENERGY, ENERGY TRANSFER, AND

GENERAL ENERGY ANALYSIS

| 51

W

hether we realize it or not, energy is an important
part of most aspects of daily life. The quality of life,
and even its sustenance, depends on the availabil-
ity of energy. Therefore, it is important to have a good under-
standing of the sources of energy, the conversion of energy
from one form to another, and the ramifications of these con-
versions.
Energy exists in numerous forms such as thermal,
mechanical, electric, chemical, and nuclear. Even mass can
be considered a form of energy. Energy can be transferred to
or from a closed system (a fixed mass) in two distinct forms:
heatand work. For control volumes, energy can also be
transferred by mass flow. An energy transfer to or from a
closed system is heatif it is caused by a temperature differ-
ence. Otherwise it is work, and it is caused by a force acting
through a distance.
We start this chapter with a discussion of various forms of
energy and energy transfer by heat. We then introduce vari-
ous forms of work and discuss energy transfer by work. We
continue with developing a general intuitive expression for the
first law of thermodynamics, also known as the conservation
of energy principle, which is one of the most fundamental
principles in nature, and we then demonstrate its use. Finally,
we discuss the efficiencies of some familiar energy conver-
sion processes, and examine the impact on energy conver-
sion on the environment. Detailed treatments of the first law
of thermodynamics for closed systems and control volumes
are given in Chaps. 4 and 5, respectively.

Objectives

The objectives of Chapter 2 are to:

• Introduce the concept of energy and define its various
  forms.


• Discuss the nature of internal energy.


• Define the concept of heat and the terminology associated
  with energy transfer by heat.


• Discuss the three mechanisms of heat transfer: conduction,
  convection, and radiation.


• Define the concept of work, including electrical work and
  several forms of mechanical work.


• Introduce the first law of thermodynamics, energy balances,
  and mechanisms of energy transfer to or from a system.


• Determine that a fluid flowing across a control surface of a
  control volume carries energy across the control surface in
  addition to any energy transfer across the control surface
  that may be in the form of heat and/or work.


• Define energy conversion efficiencies.


• Discuss the implications of energy conversion on the
  environment.