Technical data > Thermic calculations > Generalities
All below calculations are only given as an indication and we cannot
be held accountable for them in any way. You can make your own
estimations, seek our advice (please note that we will only carry out
product development studies if these are part of a signed detailed
agreement between both parties) or use an engineering and design company.
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Heating of liquids, gases or solids
(for calculation of amount
of material to be heated up)
F
= power in Watts M
= weight to be heated up in Kg Cp
= specific heat in Kcal/kg.K
DT
= temperature rise in °C or K
0,86 = conversion coefficient kcal/h into Watt
t = temperature rise time in hours
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Heat loss on side wall (natural convection)
(for insulation or
temperature maintenance calculations)
Φ = h . S . ΔT
F
= power in Watts
h = convection coefficient in W/m²
S = side wall surface area in m²
DT = temperature difference between side wall and air in °C ou K
Heat loss by natural convection
Heating surface in ambient air according to Mac Adams simplified
formula. DT = temperature difference between heating surface and ambient air
h1 = Convection coefficient of horizontal plate with heating side
upwards. h2 = Convection coefficient of horizontal plate with heating side
downwards. h3 = Convection coefficient of vertical plate that is higher than 0.3m. h4 = Convection coefficient of vertical plate that is lower than 0.3m.
Chart of convection dissipated heat in Watts/mē according to
DT and to surface area type :
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Conduction heat transfer
(for example for calculations
of heat losses through side wall)
flat side wall :
cylindrical side wall :
F = power in Watts
l = material conduction coefficient in W/m.K
S = material surface area in m²
DT = heat difference between the 2 side walls
in °C or K l
= length of cylindrical side wall in m R and r
= outside and inside radius of side wall.
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Radiation heat transfer
(for calculations of heat losses or energy input)
Generalized Kirchhoff’s law
or :
F = power in Watts
a =
absorption or emission coefficients of emitting surface s_{0} =
5,675 . 10^{8} W/m².K^{4} T = Absolute temperature in K
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Heat exchange by radiation between 2
surface areas
(Radiation heating)
ou :
F
= power in Watts s
=
s_{0}.a =
mutual radiation coefficient between the 2 surface areas W/m².K^{4}
T1 and T2 = absolute temperature of the 2 surface areas in K.
m = surface angle or shape factor
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Convection heating
There are many cases when convection thermal transfer is used.
It can be either natural (in the case of radiators or side wall heat losses) see above information or forced (in the case of process heaters, air heaters, etc…).
In any case, shapes and dimensions together with laminar or turbulent flow must be taken into account.
Our technical research department can help you to define your needs after you have submitted precise requirements.
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Change of state
(fusion or vaporization)
or :
F = power in Watts
M
= weight in kg r =
density in kg/dm^{3} V
= volume in dm^{3}
(or litre) L
= latent heat of fusion or vaporization kcal/kg. t = time
in hours
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