Heating Up Applications - Energy Required and Heat Transfer Rates
Energy required to heat up a substance.
The energy required to heat up a substance - like a tank, swimming pool or similar - within a certain time can be calculated as
q = m cp dT / t (1)
where
q = mean heat transfer rate (kW)
m = mass of substance (kg)
cp = specific heat of the substance (kJ/kg oC)
dT = temperature difference (oC)
t = heat up time (s)
Note that heat loss to the surroundings will extend the heat up time.
Example - Heating up an Aluminum Saucepan filled with Cold Water
An aluminum saucepan with weight 2 kg is filled with 10 liter cold water with temperature 0 oC and heated to temperature 100oC (boiling) in one hour. The heat transfer rate (or required power) can be calculated as
q = [( (10 liter) (1 kg/liter) (4.2 kJ/kgoC) + (2 kg) (0.91 kJ/kgoC) ) ( (100 oC) - (0 oC) )] / [(1 h) 3600 (s/h)]
= 1.2 kW
The energy consumed can be calculated as
E = q t (2)
where
E = energy (kJ, kWs)
t = time (h)
- or, with values
E = (1.2 kW) (1 h)
= 1.2 kWh
