Glossary
to accompany
Thermodynamics: An Engineering Approach, 5th edition
by Yunus A. Çengel and Michael A. Boles40Reciprocity relation shows that the inverse of a partial derivative is equal to its
reciprocal.
()
1
y / y
x
zzx
⎛⎞∂
⎜⎟=
⎝⎠∂∂∂Reduced pressure PR is the ratio of the pressure to the critical pressure.
Reduced temperature TR is the ratio of the temperature to the critical temperature.
Reference state is chosen to assign a value of zero for a convenient property or
properties at that state.
Refrigerant is the working fluid used in the refrigeration cycle.
Refrigerator is a cyclic device which causes the transfer of heat from a low-temperature
region to a high-temperature region. The objective of a refrigerator is to maintain the
refrigerated space at a low temperature by removing heat from it.
Refrigerator coefficient of performance is the efficiency of a refrigerator, denoted by
COPR, and expressed as desired output divided by required input or COPR = QL/Wnet, in.
Regeneration is the process of transferring energy with in a cycle from a working fluid
in a high temperature in part of the cycle to a lower temperature part of the cycle to
reduce the amount of external heat transfer required to drive the cycle.
Regenerator (see feedwater heater)
Regenerator effectiveness is the extent to which a regenerator approaches an ideal
regenerator and is defined as the ratio of the heat transfer to the compressor exit gas to
the maximum possible heat transfer to the compressor exit gas.
Reheat Rankine cycle is a modification of the Rankine cycle in which the steam is
expanded in the turbine in two stages and reheated in between. Reheating is a practical
solution to the excessive moisture problem in the lower-pressure stages of turbines, and it
is used frequently in modern steam power plants.
Reheating is a technique used to increase the expansion work for the gas turbine cycle.
The expansion process is completed in stages while reheating the working fluid between
stages. Since the steady-flow compression work is proportional to the specific volume of
the flow, the specific volume of the working fluid should be as large as possible during a
expansion process.
Relative density (see specific gravity)