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Thermodynamics involves the study of
various systems. A system in thermodynamics is
nothing more than the
collection of matter that is being studied. A system could
be the water within one side
of a heat exchanger, the fluid inside a length of pipe, or
the entire lubricating oil system for a
diesel engine.
Determining the boundary to solve a
thermodynamic problem for a system will depend
on what information is known about the system and what
question is asked about the system. Everything external to the
system is called the thermodynamic surroundings,
and the system is separated
from the surroundings by the system boundaries.
These boundaries may either be fixed or
movable. In many cases, a thermodynamic analysis must be
made of a device, such as a heat exchanger,
that involves a flow of mass into and/or out of the
device. The procedure that is followed
in such an analysis is to specify a control surface, such
as the heat exchanger tube walls.
Mass, as well as heat and work (and momentum), may flow
across the control surface.
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