Glossary
to accompany
Thermodynamics: An Engineering Approach, 5th edition
by Yunus A. Çengel and Michael A. Boles45related to the changes in internal energy. It would be more proper to define Cv as the
change in the internal energy of a substance per unit change in temperature at constant
volume.
Specific heat ratio k is defined as the ratio Cp/Cv.
Specific heats for solids and liquids, or incompressible substances, are equal.
Specific humidity (see absolute humidity)
Specific properties are extensive properties per unit mass. Some examples of specific
properties are specific volume (v=V/m) and specific total energy (e= E/m).
Specific volume is the reciprocal of density and is defined as the volume per unit mass.
Specific weight w is the weight of a unit volume of a substance and is determined from
the product of the local acceleration of gravity and the substance density.
Speed of sound (sonic speed) is the speed at which an infinitesimally small pressure
wave travels through a medium.
Spray pond is a pond where warm water is sprayed into the air and is cooled by the air
as it falls into the pond. Spray ponds require 25 to 50 times the area of a cooling tower
because water loss due to air drift is high.
Spring work is the work done to change the length of a spring.
Stable form of an element is the chemically stable form of that element at 25°C and 1
atm. Nitrogen, for example, exists in diatomic form (N 2 ) at 25°C and 1 atm. Therefore,
the stable form of nitrogen at the standard reference state is diatomic nitrogen N 2 , not
monatomic nitrogen N.
Stagnation enthalpy (total enthalpy) is the sum of the enthalpy and kinetic energy of the
flow and represents the total energy of a flowing fluid stream per unit mass. It represents
the enthalpy of a fluid when it is brought to rest adiabatically with no work. The
stagnation enthalpy equals the static enthalpy when the kinetic energy of the fluid is
negligible.
Stagnation pressure is the pressure a fluid attains when brought to rest isentropically.
For ideal gases with constant specific heats, the stagnation pressure is related to the static
pressure of the fluid through the isentropic process equation relating pressure and
temperature.