Introduction to Chemical Engineering Processes/Notation

Base Notation (in alphabetical order)

$[i]_{n}$ : Molarity of species i in stream n
a, b, c, d: Stoichiometric coefficients.
A: Area
C: Molar concentration (mol/L)
K: Equilibrium coefficient
m: Mass
MW: Molecular Weight (Molar Mass)
n: Moles
n: Number of data points (in statistics section)
N: Number of components
P: Pressure
r: Regression coefficient
R: Universal gas constant
T: Temperature
v: Velocity
V: Volume
x: Mole fraction in the liquid phase OR Mass fraction 
X: (molar) extent of reaction
y: Mole fraction in the gas phase
z: Overall composition
Z: Compressibility

Greek

$\rho$: Density
$\Sigma$: Sum

Subscripts

If a particular component (rather than an arbitrary one) is considered, a specific letter is assigned to it:

• [A] is the molarity of A
• $x_{A}$ is the mass fraction of A

Similarly, referring to a specific stream (rather than any old stream you want), each is given a different number.

• ${\dot {n}}_{1}$ is the molar flowrate in stream 1.
• ${\dot {n}}_{A1}$ is the molar flow rate of component A in stream 1.

Special subscripts:

If A is some value denoting a property of an arbitrary component stream, the letter i signifies the arbitrary component and the letter n signifies an arbitrary stream, i.e.

• $A_{n}$ is a property of stream n. Note ${\dot {n}}_{n}$ is the molar flow rate of stream n.
• $A_{i}$ is a property of component i.

The subscript "gen" signifies generation of something inside the system.

The subscripts "in" and "out" signify flows into and out of the system.

Embellishments

If A is some value denoting a property then:

${\bar {A}}_{n}$ denotes the average property in stream n

${\dot {A}}_{n}$ denotes a total flow rate in steam n

${\dot {A}}_{in}$ denotes the flow rate of component i in stream n.

${\hat {A}}$ indicates a data point in a set.

$A_{i}^{*}$ is a property of pure component i in a mixture.

Units Section/Dimensional Analysis

In the units section, the generic variables L, t, m, s, and A are used to demonstrate dimensional analysis. In order to avoid confusing dimensions with units (for example the unit m, meters, is a unit of length, not mass), if this notation is to be used, use the unit equivalence character ${\dot {=}}$ rather than a standard equal sign.