Thermic calculations Generalities Basic rules for cartridge Adjustment of the CCHC Mould heating example Heat loss by natural convection

 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. Heating of liquids, gases or solids (for calculation of amount of material to be heated up) Heat loss of side wall (for insulation or temperature maintenance calculations) Heat transfer by conduction (for example for calculations of heat losses through side wall) -  flat side wall - cylindrical side wall Heat transfer by radiation (for calculations of heat losses or energy input) Heat exchange by radiation between 2 surface areas (radiation heating) Convection heating Change of state (fusion and vaporization) Back 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 Back 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
= 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/m² according to DT and to surface area type :  Back 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. Back 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
s0  = 5,675 .  10-8  W/m².K4
T = Absolute temperature in K Back Heat exchange by radiation between 2 surface areas ou :

F    = power in Watts
s = s0.a = mutual radiation coefficient between the 2 surface areas W/m².K4
T1 and T2 = absolute temperature of the 2 surface areas in K.
m = surface angle or shape factor Back 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. Back Change of state

(fusion or vaporization) or :

F = power in Watts
M = weight in kg
r = density in kg/dm3
V = volume in dm3 (or litre)
L = latent heat of fusion or vaporization kcal/kg.
t = time in hours Back © IVALDI 2004 - Home | About us | Contact us | Location | Customers | Legal informations Products : Introduction | Cartridge heaters | Coiled heaters | Band heaters | Strip heaters | Tubular heating elements | Immersion heaters | Air Heating Printed heaters | Temperature sensors | Temperature controllers | Accessories Technical data : Electrical calculation | Thermal calculation | Technical data