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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).

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.

Convection is the mode of energy transfer between a solid surface and the adjacent fluid
that is in motion, and it involves the combined effects of conduction and fluid motion.

Cycle is a process, or series of processes, that allows a system to undergo state changes
and returns the system to the initial state at the end of the process. That is, for a cycle
the initial and final states are identical.

Density is defined as mass per unit volume.

Diesel cycle is the ideal cycle for compress-ignition reciprocating engines, and was first
proposed by Rudolf Diesel in the 1890s. Using the air-standard assumptions, the cycle
consists of four internally reversible processes:
1-2 Isentropic compression,
2-3 Constant pressure heat addition,
3-4 Isentropic expansion,
4-1 Constant volume heat rejection.

Diffuser is a device that increases the pressure of a fluid by decreasing the fluid
velocity.

Efficiency is defined as the ratio of desired result for an event to the input required to
accomplish the event. Efficiency is one of the most frequently used terms in
thermodynamics, and it indicates how well an energy conversion or transfer process is
accomplished.

Energy Balance is the net change (increase or decrease) in the total energy of the system
during a process is equal to the difference between the total energy entering and the
total energy leaving the system during that process.

Enthalpy H (from the Greek word enthalpien, which means to heat) is a property and is
defined as the sum of the internal energy U and the PV product.

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