Required Heating Power Calculator (kW)
Methodology
This calculator determines the minimum electrical power (kW) that the cartridge heater system must deliver to raise the temperature of a material from an initial value to the working value, within the available heating time. It is the first step in sizing any industrial heating installation.
Formula
P = (V × ρ × Cp × (t2 − t1) × 1.2) / (860 × T)
- V — Volume to heat (dm³ = litres)
- ρ — Material density (kg/dm³)
- Cp — Specific heat (kcal/kg·°C)
- t1 — Initial temperature (°C)
- t2 — Desired final temperature (°C)
- T — Available heating time (hours)
- 1.2 — 20% safety factor for heat losses to the surroundings
- 860 — Conversion factor kcal/kWh
Common material properties
- Steel: ρ = 7.8 kg/dm³ — Cp = 0.11 kcal/kg·°C
- Aluminium: ρ = 2.7 kg/dm³ — Cp = 0.22 kcal/kg·°C
- Bronze: ρ = 8.5 kg/dm³ — Cp = 0.09 kcal/kg·°C
- Cast iron: ρ = 7.2 kg/dm³ — Cp = 0.12 kcal/kg·°C
- Stainless steel: ρ = 7.9 kg/dm³ — Cp = 0.12 kcal/kg·°C
Worked example
Aluminium block of 2 litres to be heated from 20 °C to 180 °C in 30 minutes (0.5 h):
- P = (2 × 2.7 × 0.22 × (180 − 20) × 1.2) / (860 × 0.5)
- P = (2 × 2.7 × 0.22 × 160 × 1.2) / 430
- P = 228.1 / 430 = 0.53 kW (530 W)
Using this result, the number, diameter and power of the Maxiwatt cartridge heaters that fit the available bores in the block are selected, distributing the load evenly to optimise thermal uniformity.