Thermodynamics: An Engineering Approach by Yunus A. Cengel and Michael A. Boles, 8th
Edition, McGraw-Hill, 2014
INTRODUCTION AND BASIC CONCEPTS
Thermodynamics and Energy:
It can be defined as the science of energy. Energy can be viewed as the ability to cause changes.
The name thermodynamics stems from the Greek words therme (heat) and dynamis (power), which
is most descriptive of the early efforts to convert heat into power.
Today it includes all aspects of energy and energy transformations, including power generation,
refrigeration, and relationships among the properties of matter.
Conservation of energy principle:
It is one of the most fundamental laws of nature which simply states that during an interaction,
energy can change from one form to another but the total amount of energy remains constant. That
is, energy cannot be created or destroyed.
1. a rock falling off a cliff, picks up speed as a result of its potential energy being converted
to kinetic energy (Fig. 1–1).
2. A person who has a greater energy input (food) than
energy output (exercise) will gain weight (store
energy in the form of fat.
The change in the energy content of a body or a system is
𝑬𝒊𝒏 −𝑬𝒐𝒖𝒕 = ∆𝑬
The first law of thermodynamics is simply an expression of
the conservation of energy principle, and it asserts that
energy is a thermodynamic property.
The second law of thermodynamics asserts that energy has
quality as well as quantity, and actual processes occur in the
direction of decreasing quality of energy.
For example, a cup of hot coffee left on a table eventually
cools, but a cup of cool coffee in the same room never gets
hot by itself (Fig. 1–3).