Physical symbols

Fundamental physical variables
 

Symbol

Designation

Unit

n

Quantity

 

l

Length

mm; m

r

Radius

mm

d

Diameter

mm

s

Wall thickness

mm

u

Velocity

m/s

A

Area

mm²; m²

V

Volume

Volume flow rate

m³/h

n

Standard volume flow rate

mn³/h

m

Mass

kg; t

Mass flow rate

kg/h; t/h

Q

Heat quantity

kJ; kWh; MJ; MWh

Heat flow rate

kW; MW

t

Time

s; h; a

T

Temperature

K; °C

p

Excess pressure

Pa; mbar; bar

pabs

Absolute pressure

bara

ρ

Density

kg/m³

ρn

Standard density

kg/mn³

h

Specific enthalpy

kJ/kg

r

Specific evaporation enthalpy

kJ/kg

cp

Specific heat capacity

kJ/kgK


Combustion
 

Symbol

Designation

Unit

Hi

Net calorific value

kWh/kg; kWh/mn³

Hs

Gross calorific value

kWh/kg; kWh/mn³

α

Flue gas condensation ratio

kg/kg

λ

Excess air

kg/kg


Efficiency
 

Symbol

Designation

Unit

ƞ

Efficiency

%

qA

Flue gas loss relative to Hi

%

ηa

Annual degree of utilisation

%


Heat transfer
 

Symbol

Designation

Unit

λ

Heat conductivity

W/mK

α

Heat transfer coefficient

W/m²K

k

Heat transition coefficient

W/m²K


Fluid mechanics
 

Symbol

Designation

ζ

Pressure loss coefficient

λ

Pipe friction coefficient


Other
 

Symbol

Designation

Unit

α

Coefficient of thermal expansion

mm/(m ⋅ 100K)

L

Electrical conductivity

μS/cm