Glossary
to accompany
Thermodynamics: An Engineering Approach, 5th edition
by Yunus A. Çengel and Michael A. Boles10Conduction is the transfer of energy from the more energetic particles of a substance to
the adjacent less energetic ones as a result of interaction between particles.
Conservation of energy principle states that during an interaction, energy can change
from one form to another but the total amount of energy remains constant. That is, energy
cannot be created or destroyed (see first law of thermodynamics).
Conservation of mass principle is expressed as net mass transfer to or from a control
volume during a time interval is equal to the net change (increase or decrease) in the total
mass within the control volume during the time interval.
Conservation of mass principle for combustion (or the mass balance) is the principle
used to balance chemical reaction equations. It can be stated as the total mass of each
element is conserved during a chemical reaction. The total mass of each element on the
right-hand side of the reaction equation (the products) must be equal to the total mass of
that element on the left-hand side (the reactants) even though the elements exist in
different chemical compounds in the reactants and products. Even though the mass must
be conserved, the total number of moles is not necessarily conserved during a chemical
reaction.
Constant-volume gas thermometer measures the temperature on the ideal-gas
temperature scale using a rigid vessel filled with a gas, usually hydrogen or helium, at
low pressure. The temperature of a gas of fixed volume varies linearly with pressure at
sufficiently low pressures.
Continuity equation is the conservation of mass equation as it is often referred to in
fluid mechanics.
Continuum is a view of mass as continuous, homogeneous matter with no holes. Matter
is made up of atoms that are widely spaced in the gas phase. Yet it is very convenient to
disregard the atomic nature of a substance. The continuum idealization allows us to treat
properties as point functions, and to assume the properties to vary continually in space
with no jump discontinuities. This idealization is valid as long as the size of the system
we deal with is large relative to the space between the molecules. This is the case in
practically all problems, except some specialized ones.
Control mass (see closed system)
Control surface is the boundary of a control volume, and it can be real or imaginary.
Control volume (also see open system) is any arbitrary region in space through which
mass and energy can pass across the boundary. Most control volumes have fixed
boundaries and thus do not involve any moving boundaries. A control volume may also
involve heat and work interactions just as a closed system, in addition to mass interaction.