Electrical heating and cooling solutions
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    Heating a volume of liquid

    CALCULATION OF THE POWER REQUIRED FOR HEATING A VOLUME OF LIQUID

    The power to be installed in order to raise the temperature over a given time of a volume of liquid contained in a tank is the result of 2 calculations: The calculation of the power to raise the temperature of the liquid (Pch) and the calculation of the heat loss (Pth).

    Power to be installed (kW) = Heating power (Pch) + Heat loss (Pth)

    1/ Calculation of the power required to raise the temperature of a volume of liquid:

    – Heating power : Pch (kW)

    – Weight of liquid : M (kg)

    – Specific heat of liquid : Cp (kcal/kg×°C)

    – Starting temperature : t1 (°C)

    – Required end temperature : t2 (°C)

    – Heating time : T (h)

     1,2 : Safety coefficient linked to our manufacturing tolerances and variations in network power

    Pch = (M × Cp × (t2 − t1) × 1,2) ÷ (860 × T)

    a/ Calculation of the mass of liquid to be heated :

    – Weight of liquid : M (kg)

    – Volume of liquid to be heated : V (dm3 ou litre)

    – Density of the liquid : ρ (kg/dm3)

    M = V x p

    ρ / Cp values for a few liquids :

    Water : 1 / 1

    Mineral oil : 0,9 / 0,5

    Bitumen : 1,1 / 0,58

    Acetic acid : 1,1 / 0,51

    Hydrochloric acid : 1,2 / 0,6

    Nitric acid : 1,5 / 0,66

    b/ Calculation of the volume of liquid :

    In a cylindrical tank :

    – Volume of tank : (dm3)

    – Diameter of tank :  (dm)

    – Height of liquid : H1 (dm)

    V = π × (∅² ÷ 4) × H1

    In a rectangular tank : :

    – Volume of tank : (dm3)

    – Length of tank :  (dm)

    – Width of tank : W (dm)

    – Height of liquid : H1 (dm)

    V = L × W × H1

    2/ Calculation of the power required to compensate for heat loss :

    – Heat loss : Pth (kW)

    – Exchange surface area of the tank : S (m2)

    – Required end temperature : t2 (°C)

    – A temperature : ta (°C)

    – Exchange coefficient : K (kcal/h × m2 × °C)

     1,2 : Safety coefficient linked to our manufacturing tolerances and variations in network power

    Pth = (S × (t2 – ta) × K × 1,2) ÷ 860

    Exchange coefficient K as a function of the wind speed and insulation thickness :

    a/ Calculation of the exchange surface area of the tank

    Surface area of a cylindrical tank :

    – Surface area of the tank : (m2)

    – Diameter of tank :  (m)

    – Height of the tank : H2 (m)

    S = (π × (∅² ÷ 4)) + (π × ∅ × H2)

    Surface area of a rectangular tank :

    – Surface area of the tank : (m2)

    – Length of tank : L (m)

    – Width of tank : W (m)

    – Height of the tank : H2 (m)

    S = ((L + W ) × H2 × 2) + (L × W)