Handbook of Turbomachinery Second Edition Revised - Ventech!

First Law of Thermodynamics
The first law of thermodynamics or the law of conservation of energy states
that energy can neither be created nor destroyed. It describes the change of
energy between forms (heat to work and work to heat) and allows for
accounting for the transfer of energy to and from a system and changes of
energy within a system. One typical form of the first law is
Where
DQ ¼ W* þ DU ð1Þ
DQ ¼ heat added to the system.
W ¼ work done by the system to the surroundings.
DU ¼ increase in energy storage within the system.
A useful property for flow processes, such as in steam turbines, is the
concept of enthalpy. Enthalpy per unit mass is defined as
Where
H*%u þ Pv ð2Þ
H* ¼ enthalpy.
u ¼ internal energy per unit of mass.
P ¼ pressure.
v ¼ volume per unit mass.
In the case of an ideal flow system with no heat exchange with the
surroundings or change in potential or kinetic energy, the work done by the
system is the change in enthalpy between two states:
W ¼ Dh ð3Þ
Second Law of Thermodynamics
Simply stated, the second law of thermodynamics is that not all of a given
quantity of heat can be converted to useful work. The second law of
thermodynamics places strict limits on the available performance of any
heat engine, including a steam turbine. For example, one of the implications
of the second law is that all real cycles must reject heat. The second law is
typically discussed by considering the entropy of a thermodynamic system.
Entropy is defined as the quantity of heat added during a reversible process
Copyright © 2003 Marcel Dekker, Inc.