An electric resistance furnace heats a charge through elements around an insulated chamber. This calculator models pure aluminum heated from 25°C in a crucible. Its animation follows solid heating, melting and liquid heating according to the selected target temperature.
Electric Furnace Power Sizing Interactive Calculator
Estimate a pure-aluminum charge heated from 25°C. Enter its mass, target rise, heating interval, charge-delivery efficiency and separate standing loss.
Equation Used
- Pure aluminum initially 25°C.
- Tabulated solid enthalpy; constant liquid heat capacity over entered range.
- A target at melting temperature means fully melted.
- Uniform temperature and constant average net charge power.
- No crucible or refractory heat storage.
Pure aluminum, uniform charge temperature and approximate tabulated enthalpy interpolation. Vessel and refractory storage excluded.
Heat passes from elements to the charge
The cutaway shows a steel shell, refractory insulation, resistance elements outside the crucible and the metal charge inside it. The probe shown above the crucible represents chamber sensing. There are no combustion flames, induction coils or electrode arcs in this particular illustration.
The phase shading follows the same absorbed-energy model as the calculator. Solid aluminum first heats to its melting point. Further energy melts it at constant temperature before the liquid rises above that temperature.
The loop is compressed for inspection. It does not predict temperature gradients, local hot spots, element temperature or how separate ingots physically settle.
Use an explicit charge and energy budget
The inputs are charge mass, target temperature rise, heating interval, efficiency and standing loss. The starting temperature is fixed at 25°C. A target below melting produces zero fusion energy.
Charge-delivery efficiency applies to the electrical input remaining after the separately entered standing loss. Do not enter an overall efficiency that already includes that same loss: doing so would count it twice.
The 250 kW output is only a numerical comparison. The illustration is not a dimensioned vessel and does not select a furnace model or establish a safe charge capacity.
Separate sensible heat from fusion
The material model uses NIST-JANAF aluminum enthalpy values with linear interpolation for the solid. At 933.45 K the tabulated solid and liquid enthalpies differ by 10.711 kJ/mol. Above that transition the liquid heat capacity used here is 31.751 J/(mol·K). Molar mass is 26.9815386 g/mol.
Mass divided by molar mass gives the number of moles. Multiplying molar enthalpy by that amount and dividing kJ by 3600 gives kWh. Sensible heat includes solid heating and any liquid superheat; fusion heat is added only for a target at or above 660.3°C.
For required charge energy Q, interval t in hours and efficiency η, average electrical power is P=Q/(ηt)+Pstanding. A target exactly at the melting point is interpreted as fully melted. The comparison percentage is 100 P/250.
Follow a 500 kg charge to 720°C
The default 695°C rise means a 720°C final temperature. The calculation heats the solid, supplies its fusion energy and then heats the liquid above 660.3°C.
During the melting portion, the orange phase region grows while the displayed temperature and curve remain on a plateau. After melting finishes, the temperature rises again.
Move the temperature-rise control to 100°C and the target becomes 125°C: the charge remains solid throughout and fusion heat is zero. A shorter heating interval raises required average power for the same charge energy.
Scope of this heat-budget model
Pure aluminum is an explicit material assumption. Alloys, oxidation, dross, evaporation, crucible heating and refractory heat storage are not calculated. Solid enthalpy is interpolated between published table points rather than inferred from one constant heat capacity.
The input power is an average energy requirement, not an element-design calculation. It does not give voltage, wiring, surface loading, furnace temperature or controller settings. The charge illustration holds a convenient visual volume and does not model thermal expansion or density change.
The required heat depends on the target phase as well as temperature. Actual furnace ratings and permissible operating conditions require equipment-specific data.
Electric-furnace questions
Why is fusion heat sometimes zero?
The target temperature is below the specified material’s melting point.
Why does the temperature pause during melting?
Energy is changing phase rather than raising the temperature in this pure-material equilibrium model.
Is the animation a real-time furnace simulation?
No. It compresses the entered heating interval into an inspection loop and uses a uniform-charge energy model.
Does 250 kW mean the design is approved?
No. It is only a numerical reference for comparing the calculated average power.
References
- NIST-JANAF Aluminum Table — solid/liquid enthalpy and phase transition.
- NIST Chemistry WebBook: Aluminum — molar mass and thermochemical data.
- Nabertherm electrically heated crucible furnaces — elements surrounding a crucible and chamber-temperature sensing. No manufacturer rating is inferred by this calculator.
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