Page 59 - BASIC CONCEPTUAL OF THERMOFLUID

CHAPTER 5: SECOND LAW OF THERMODYNAMICS

CHAPTER 5

SECOND LAW OF

THERMODYNAMICS

The branch of physical science that
deals with the relations between heat
and other forms of energy such as
mechanical, electrical, or chemical
energy and by extension, of the
relationships between all forms of
energy.

5.1 Concept of Second Law of Thermodynamics

Whenever energy is converted from one form to another, some usable energy is lost in thermal energy that
disperses into the environment. The terms usable energy involved is entropy which measure disorder of
randomness. Fig. 5.1 below shown where the entropy occurred in the process ice cube change to liquid
causing the change of entropy increase and reversely process the entropy is decreased.

Fig. 5.1: Entropy, S in phase change processes [5]

5.2 Entropy in Heat Engine

There exist a useful thermodynamics variable called entropy, S. A natural process that starts in equilibrium
state and ends in another will go in the direction that causes the entropy of the system plus the environment
to increase for an irreversible process and to remain constant for a reversible process. The Fig. 5.2 below
represent the entropy in heat engine where from cold transfer to hot engine after heat, Q supplied to produce
work, W [6].

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