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Quick
reference Formulas
Temperature
– °C
or °K
Pressure
SI unit – Pascal
1 Pa = 1 N/m2, too small a
unit
Common unit = Bar
1 Bar =105 N/m2= 0.1
Mpa
Atmospheric Pressure = 1 Bar abs at MSL
Vacuum = 0 Bar
abs
barg = kg/cm2g
Gauge pressure +
Atmospheric pressure = Absolute pressure
Density
in kg/m3
Specific Volume = 1 / Density in
m3/kg
Specific Gravity = Density ratio to water
Energy
SI unit = 1 Joule = 1 Nm = 4.186 cal
Common unit =
kilocalorie
1 kcal = heat reqd to raise 1 kg water by 1°C
1
kcal = 4186.8 Joules
Cp = sp. heat capacity in kcal/kg °C
Conversions
between SI and other units
mWC = meters
water column
1 Bar = 10 mWC
1 Bar = 14.23 PSI
(Lbs/in2)
150 psi = 10.54 Kg/cm2g
50
psi = 3.5 Kg/cm2g
10 bar g = 11 bar a = 10.2
Kg/cm2g = 11.2 Kg/cm2a
= 145 psig = 1 MPa = 106 N/m2
Where,
ρ=
Density(kg/m3)
m
= Mass (kg)
V= Volume (m3)
vg= Specific volume
(m3/kg)
Enthalpy
of saturated steam
hg
= hf + hfg
Where,
hg
= Total enthalpy or total heat of saturated steam (kJ/kg)
hf =
Liquid enthalpy (Sensible heat) (kJ/kg)
hfg = Enthalpy of
evaporation (Latent heat) (kJ/kg)
Heat
Balance in Process
Primary
Q = m x hfg
Where,
Primary
Q = Quantity of heat energy released (in kcals)
m = Mass of
steam releasing the heat (in kgs)
hfg = Specific enthalpy of
evaporation of steam (in kcals/kg)
Secondary
Q = m x cp x ΔT
Where,
Secondary
Q = Quantity of heat energy absorbed (in kcals)
m = Mass of the
substance absorbing the heat (in kgs)
cp = Specific heat
capacity of the substance (in kcals / kg °C )
ΔT =
Temperature rise of the substance (in °C)
Primary
Q = Secondary
Heat
transfer equation
Q
= U x A x ΔT
Where,
Q
= Heat transferred per unit time (kcals/hr)
U = Overall heat
transfer coefficient (kcals/hr / m²°C)
A = Heat
transfer area (m²)
ΔT = Temperature difference
between the primary and secondary fluid (°C)
Steam
line sizing
Where,
D
= Line size in mm
m = Mass flowrate of steam in kg/h
V =
Specific volume in m3/kg
π = a constant 3.14
c
= velocity m/s
Calculating
Steam Savings
Boiler
Heat Input = Qf x GCV
Where,
Qf
= Quantity of fuel (in kg/hr)
GCV (Gross Calorific Value)
=Energy contained in fuel in kcal/kg
Boiler
Heat Output = Qs x (Hs – Hw)
Where,
Qs
= Quantity of steam (in kg/hr)
Hs = Heat contained in steam
(Enthalpy of Saturated steam hg)
Hw = Heat already present in
the water from which steam is raised
Where,
Qc
= Quantity of condensate (in kg/hr)
Hc = Heat contained in
condensate (in kcal/kg)
Hw = Heat already present in the water
at ambient temperature (in kcal/kg)
GCV (Gross Calorific Value)
=Energy contained in fuel in kcal/kg
η = Boiler efficiency
ρ = Specific gravity of liquid/gas fuel
%
Flash steam Calculation
Where,
hf1
= Enthalpy of water at the higher pressure kcal/kg
hf2 =
Enthalpy of water at the flashing pressure kcal/kg
hfg2 =
Enthalpy of evaporation at the flash steam pressure
Actual
rating of a Boiler
Actual
Rating = F&A Rating X 540 / ( hg – hfFW)
Where,
hg
= enthalpy of steam at generation pressure
hfFW = Feed water
enthalpy
Blowdown
Where,
F
= Feedwater TDS in ppm
B = Boiler water set point in ppm
S =
Steam generation in kg/hr.
  
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