Glossary
to accompany
Thermodynamics: An Engineering Approach, 5th edition
by Yunus A. Çengel and Michael A. Boles38Propulsive efficiency of an aircraft turbojet engine is the ratio of the power produced to
propel the aircraft and the thermal energy of the fuel released during the combustion
process.
Propulsive power is the power developed from the thrust of the aircraft gas turbines and
is the propulsive force (thrust) times the distance this force acts on the aircraft per unit
time, that is, the thrust times the aircraft velocity.
Pseudo-reduced specific volume vR is used with the generalized compressibility chart to
determine the third property when P and v, or T and v, are given instead of P and T.
Psychrometric chart presents the properties of atmospheric air at a specified pressure
and two independent intensive properties. The psychrometric chart is a plot of absolute
humidity versus dry-bulb temperature and shows lines of constant relative humidity, wet-
bulb temperature, specific volume, and enthalpy for the atmospheric air.
Pump is a steady flow device used to increase the pressure of a liquid while compressors
increase the pressure of gases.
Pump efficiency is defined as the ratio of the mechanical energy increase of the fluid as
it flows through the pump to the mechanical energy input to the pump.
Pure substance is a substance that has a fixed chemical composition throughout.
P-v-T surface is a three-dimensional surface in space which represents the P-v-T
behavior of a substance. All states along the path of a quasi-equilibrium process lie on
the P-v-T surface since such a process must pass through equilibrium states. The single-
phase regions appear as curved surfaces on the P-v-T surface, and the two-phase regions
as surfaces perpendicular to the P-T plane.
Quality x is the ratio of the mass of vapor to the total mass of a saturated mixture. The
quality lies in the range 01 ≤≤x.
Quality of energy is a measure of how much of the energy can be converted to work.
More of energy at high temperatures can be converted to work. Therefore, the higher the
temperature, the higher the quality of the energy.
Quasi-equilibrium process (see quasi-static process).
Quasi-static, or quasi-equilibrium, process is a process which proceeds in such a
manner that the system remains infinitesimally close to an equilibrium state at all times.
A quasi-equilibrium process can be viewed as a sufficiently slow process that allows the
system to adjust itself internally so that properties in one part of the system do not change
any faster than those at other parts.