Glossary
to accompany
Thermodynamics: An Engineering Approach, 5th edition
by Yunus A. Çengel and Michael A. Boles3500(,)(,)
lim lim
xx
yyzzzxxyzxy
xxΔ→ Δ→ x
⎛⎞ ⎛⎞∂Δ +Δ−
⎜⎟ ⎜⎟==
⎝⎠ ⎝⎠∂Δ ΔPartial pressure of a component in a gas mixture is defined by Dalton’s law as the
product of the mole fraction and the mixture pressure. The partial pressure is identical to
the component pressure for ideal gas mixtures.
Partial volume of a component in a gas mixture is the product of the mole fraction and
the mixture volume. The partial volume is identical to the component volume for ideal
gas mixtures.
Pascal (Pa) is the unit of pressure defined as newtons per square meter (N/m
2
).Pascal’s law allows us to “jump” from one fluid column to the next in manometers
without worrying about pressure change as long as we don’t jump over a different fluid,
and the fluid is at rest.
Pascal’s principle, after Blaise Pascal (1623–1662), states that the consequence of the
pressure in a fluid remaining constant in the horizontal direction is that the pressure
applied to a confined fluid increases the pressure throughout by the same amount.
Path functions are functions whose magnitudes depend on the path followed during a
process as well as the end states.
Path of a process is the series of states through which a system passes during
a process.
Peltier effect is the cooling effect that occurs when a small current passes through the
junction of two dissimilar wires. This effect forms the basis for thermoelectric
refrigeration and is named in honor of Jean Charles Athanase Peltier, who discovered this
phenomenon in 1834.
Percent deficiency of air is the deficiency of air expressed as a percent of stoichiometric
air. For example, 90 percent theoretical air is equivalent to 10 percent deficiency of air.
Percent excess air or percent theoretical air is the amount of excess air usually
expressed in terms of the stoichiometric air. For example, 50 percent excess air is
equivalent to 150 percent theoretical air.
Perpetual-motion machine is any device that violates either the first or second law of
thermodynamics.
Perpetual-motion machine of the first kind PMM1 is a device that violates the first
law of thermodynamics (by creating energy).