Absorptivity (radiation)

α

—

Amount of substance

N

mol

Molar flow rate
 
mol/s

Molar mass velocity(= N/A_{c})
 
mol/m^{2}s

Angle



Plane

α, β, γ, θ, Ø

rad

Solid

ω

sr

Area



Crosssectional

S

m_{2} 
Surface

A

m_{2} 
Coefficient of cubic expansion



(1/v)(∂v/∂T)_{p} 
β

K^{−1} 
Concentration



Mass (= M/V)

c

kg/m^{3} 
Molar (= N/V)
 
mol/m^{3} 
Contact angle

θ

rad.

Density



Mass (= M/V)

ρ

kg/m^{3} 
Molar (= N/V)
 
mol/m^{3} 
Diameter

D

m

Diffusion coefficient

D

m^{2}/s

Diffusivity

δ

m^{2}/s

Thermal (= λ/ρc_{p})

κ

m^{2}/s

Dryness fraction (quality)

x

—

Emissivity (radiation)

ε

—

Energy

E

J = kg m^{2}/s^{2} 
Enthalpy (= U + pV)

H

J = kg m^{2}/s^{2} 
Specific, molar

h,

J/kg, J/mol

Of phase change at constant p:



Melting

h_{sl},

J/kg, J/mol

Sublimation

h_{sg},

J/kg, J/mol

Evaporation

h_{lg},

J/kg, J/mol

Entropy

S

J/K = kg m^{2}/s^{2}K

Specific, molar

s,

J/kg K, J/mol K

Force

F

N = kg m/s^{2} 
Fraction



Mass, of species i

x_{i}y_{i} 
—

Mole, of species i
 
—

Phase

ε

—

Frequency

f

Hz, s^{−1} 
Frequency circular

ω

rad/s

Gas constant
 
J/mol K

Molar (universal)


= kg m^{2}/s^{2}· mol K

Specific, of species i

R_{i} 
J/kgK = m^{2}/s^{2}K

Gravitational acceleration

g

m/s^{2} 
Gibbs function (H – TS)

G

J = kg m^{2}/s^{2} 
Specific (h – Ts)

g

J/kg = m^{2}/s^{2} 
Molar (
–
)
 
J/mol



= Kgm^{2}/s^{2}mol

Heat



Quantity of

Q

J = kg m^{2}/s^{2} 
Rate
 
W = kg m^{2}/s^{3} 
Flux (
/A)
 
W/m^{2} = kg/s^{3} 
Heat capacity

c

J/K = kg m^{2}/s^{2} K

Specific, at constant volume or

c_{v}, c_{p} 
J/kg K = m^{2}/s^{2} K

pressure



Molar at constant volume or

,

J/mol K

pressure


= kg m^{2}/s^{2}mol K

Ratio c_{p}/c_{v} 
γ

—

Heat transfer coefficient

α

W/m^{2}K = kg/s^{3}K

Overall

U

W/m^{2}K = kg/s^{3}K

Internal energy

U

J = kg m^{2}/s^{2} 
Specific

u

J/kg = m^{2}/s^{2} 
Molar
 
J/mol = kg m^{2}/s^{2}mol

Joule Thompson coefficient



[(δT/δP)_{h}]

μ_{JT} 
m^{2}K/N = rns^{2}K/kg

Length

1(L)

m

Diameter

d(D)

m

Radius

r(R)

rn

Breadth

b(B)

m

Height

z(Z)

m

Thickness

δ

m

Liquid film thickness

δ

m

Liquid holdup

ε_{L} 
—

Mass

M

kg

Flow rate
 
kg/s

Mass velocity or mass flux
 
kg/m^{2}s

(
/A)



Flux of species i
 
kg/m^{2}s

Mass transfer coefficient

β

m/s

Molar mass
 
kg/kmol

Pressure

p

Pa = N/m^{2} 


= Kg/ms^{2} 
Drop

δp

Pa = N/m^{2} 


= kg/ms^{2} 
Reflectivity

p

—

Shear stress

τ

Pa = N/m^{2} 


= kg/ms^{2} 
Surface tension

σ

N/m = kgs^{2} 
Temperature



Absolute

T

K

Difference or interval

ΔT

K

Logarithmic mean difference

ΔT_{LM} 
K

Mean temperature difference

ΔT_{M} 
K

Thermal conductivity

λ

W/m K = kg m/s^{3}K

Time

t

s

Velocity

u

m/s

Component in Cartesian



coordinates x,y,z

u,v,w

m/s

View factor (geometric or

Ø_{12} 
sr

configuration factor)



Viscosity



Dynamic (absolute)

η

Pas = N s/m^{2} 


= kg/ms

Kinematic (= η/ρ)

ν

m^{2}/s

Void fraction

ε_{G} 
—

Volume

V

m^{3} 
Volumetric flow rate
 
m_{3}/s

Specific, molar volume

v,

m^{3}/kg

Work

W

J = kg m^{2}/s^{2} 
Rate (power)
 
W = kg m^{2}/s^{3} 
Wavelength

λ

m

Subscripts and Superscripts 


Solid or saturated solid

S (s)


Liquid or saturated liquid

L(l)


Gas or saturated vapor

G(g)


Change of phase at constant p:



Melting

SL (sl)


Sublimation

SG (sg)


Evaporation

LG (lg)


Critical state

c


Initial

o


Inlet

in,


Outlet

out,


At constant value of property

p,v,t. etc


Mean

–


Molar (per unit of amount of

~


substance)



Stagnation

o


Wall

W(w)


Heat & Mass Transfer, and Fluids Engineering