Introduction to Chemical Engineering Processes/Notation

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A Note on Notation[edit]

Base Notation (in alphabetical order)[edit]

 [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 [1]
X: (molar) extent of reaction
y: Mole fraction in the gas phase
z: Overall composition
Z: Compressibility
  1. Unless specified explicitly, assume that a given percent composition is in terms of the overall flowrate. So if you're given a flowrate in terms of kg/s and a compositoin of 30%, assume that the 30% is a mass fraction. If a given equation requires one or the other, it will explicitly be stated near the equation which is necessary.


 \rho : Density
 \Sigma : Sum


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.


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[edit]

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.