Glossary
to accompany
Thermodynamics: An Engineering Approach, 5th edition
by Yunus A. Çengel and Michael A. Boles21Friction is a familiar form of irreversibility associated with bodies in motion which
results from the force that opposes the motion developed at the interface of the two
bodies in contact when the two bodies are forced to move relative to each other.
Frosting, which occurs in humid climates when the temperature falls below 2 to 5°C, is
the major problem with air-source systems. The frost accumulation on the evaporator
coils is highly undesirable since it seriously disrupts heat transfer. The coils can be
defrosted, however, by reversing the heat pump cycle (running it as an air conditioner).
This results in a reduction in the efficiency of the system.
Fuel is any material that can be burned to release energy.
Fuel–air ratio is the reciprocal of air–fuel ratio.
Fuel cells operate on the principle of electrolytic cells in which the chemical energy of
the fuel is directly converted to electric energy, and electrons are exchanged through
conductor wires connected to a load. Fuel cells are not heat engines, and thus their
efficiencies are not limited by the Carnot efficiency. They convert chemical energy to
electric energy essentially in an isothermal manner.
Fundamental dimensions (see primary dimensions)
Gage pressure is the difference between the absolute pressure and the local atmospheric
pressure.
Gas constant R is different for each gas and is determined from R = Ru/M.
Gas phase of a substance has molecules that are far apart from each other, and a
molecular order is nonexistent. Gas molecules move about at random, continually
colliding with each other and the walls of the container they are in.
Gas power cycles are cycles where the working fluid remains a gas throughout the entire
cycle. Spark-ignition automobile engines, diesel engines, and conventional gas turbines
are familiar examples of devices that operate on gas cycles.
Gas refrigeration cycle is based on the reversed Brayton cycle where the compressor
exit gases are cooled and then expanded in a turbine to further reduce the temperature of
the working fluid. The lower-temperature fluid is used to produce the refrigeration
effect.
Generalized compressibility chart shows that by curve-fitting all the data, gases seem
to obey the principle of corresponding states reasonably well.