Energy Balance on an Open System

W
Sign convention arrow.
Q
Sign convention arrow.
Closed
System
Mass In
Mass Out
This diagram shows a closed system with a system boundary enclosing it and sign convention arrows showing that heat transfer is positive when heat flow into the system and work is positive when it is done by the system.

Differential Energy Balance Equation

for an open system:
Mass flowing across the system boundary carries energy with it.
Remember:
A water heater with cold water entering and hot water leaving.
Equation.
Equation.
Equation.
Rate of change of the
total energy of the system
Rates at which energy
flows into and out of
the system
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Ch 5, Lesson B, Page 2 - Energy Balance on an Open System