Glossary
to accompany
Thermodynamics: An Engineering Approach, 5th edition
by Yunus A. Çengel and Michael A. Boles49Therm is defined as an amount of energy produced by the combustion of natural gas and
is equal to 29.3 kWh.
Thermal conductivity is defined as a measure of the ability of a material to conduct
heat.
Thermal efficiency ηth is the ratio of the net work produced by a heat engine to the total
heat input, ηth = Wnet/Qin.
Thermal efficiency of a heat engine is the fraction of the thermal energy supplied to a
heat engine that is converted to work.
Thermal efficiency of a power plant is defined as the ratio of the shaft work output of
the turbine to the heat input to the working fluid.
Thermal energy is the sensible and latent forms of internal energy.
Thermal energy reservoir, or just a reservoir is a hypothetical body with a relatively
large thermal energy capacity (mass specific heat) that can supply or absorb finite
amounts of heat without undergoing any change in temperature.
Thermal equilibrium means that the temperature is the same throughout the entire
system.
Thermodynamic equilibrium is a condition of a system in which all the relevant types
of equilibrium are satisfied.
Thermodynamic system, or simply a system, is defined as a quantity of matter or a
region in space chosen for study.
Thermodynamic temperature scale is a temperature scale that is independent of the
properties of the substances that are used to measure temperature. This temperature scale
is called the Kelvin scale, and the temperatures on this scale are called absolute
temperatures. On the Kelvin scale, the temperature ratios depend on the ratios of heat
transfer between a reversible heat engine and the reservoirs and are independent of the
physical properties of any substance.
Thermodynamics can be defined as the science of energy. Energy can be viewed as the
ability to cause changes. The name thermodynamics stems from the Greek words therme
(heat) and dynamis (power), which is most descriptive of the early efforts to convert heat
into power. Today the same name is broadly interpreted to include all aspects of energy
and energy transformations, including power production, refrigeration, and relationships
among the properties of matter.