Glossary
to accompany
Thermodynamics: An Engineering Approach, 5th edition
by Yunus A. Çengel and Michael A. Boles20Ein - Eout =(Qin -Qout ) + (Win -Wout ) + (Emass, in- Emass, out ) = ΔEsystem
First law of thermodynamics for a closed system using the classical thermodynamics
sign convention is
Qnet, in - Wnet, out = ΔEsystem or Q - W =ΔE
where Q = Qnet, in = Qin - Qout is the net heat input and W = Wnet, out = Wout - Win is the net
work output. Obtaining a negative quantity for Q or W simply means that the assumed
direction for that quantity is wrong and should be reversed.
Flow energy (see flow work).
Flow exergy results from mass entering or leaving a system and carries exergy per unit
mass in the amount ψ = (h - h 0 ) - T 0 (s - s 0 ) +
2
Vr
/2 + gz with it. Therefore, the exergy ofa system increases by ψ when mass enters, and decreases by the same amount when mass
at the same state leaves the system.
Flow work (flow energy) is work required to push mass into or out of control volumes.
On a unit mass basis this energy is equivalent to the product of the pressure and specific
volume of the mass Pv.
Forced convection (convected energy) is convection heat transfer when the fluid is
forced to flow in a tube or over a surface by external means such as a fan, pump, or the
wind.
Forced-draft cooling tower, or induced-draft cooling tower, is a wet cooling tower in
which the air is drawn through the tower by fans.
Formal sign convention (classical thermodynamics sign convention) for heat and work
interactions is as follows: heat transfer to a system and work done by a system are
positive; heat transfer from a system and work done on a system are negative.
Four-stroke internal combustion engines are engines in which the piston executes four
complete strokes (two mechanical cycles) within the cylinder, and the crankshaft
completes two revolutions for each thermodynamic cycle.
Fourier’s law of heat conduction states that rate of heat conduction in a direction is
proportional to the temperature gradient in that direction.
Free convection (natural convection) is convection heat transfer when the fluid motion is
caused by buoyancy forces induced by density differences due to the variation of
temperature in the fluid.