KEVOS® MAKEOS · Materials
Electric Tank Heater Sizing (Heat-up, Losses and Watt Density)
How much heater power will bring this tank up to temperature in time, and is the installed heater’s surface loading safe for the liquid?
Sizing of an electric immersion heater for a tank: energy to heat the liquid and the vessel (as the heating energy tool), average surface loss during heat-up and holding loss at temperature from an overall loss coefficient, the power needed for the heat-up time with a margin, the heat-up time with the installed heater, holding duty and the element surface watt density against your limit for the liquid.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Tank and liquid | ||
| Liquid volume | L | Volume of liquid heated. |
| Liquid density | kg/m³ | Density of the liquid. |
| Liquid specific heat | kJ/kg·K | Specific heat of the liquid (4.18 water, about 1.9–2.1 oils). |
| Vessel mass heated | kg | Mass of tank steel that heats up with the liquid. |
| Vessel specific heat | kJ/kg·K | Specific heat of the vessel material (about 0.5 steel). |
| Starting temperature | °C | Temperature at the start of heat-up. |
| Set temperature | °C | Working temperature. |
| Ambient temperature | °C | Surrounding air temperature. |
| Tank surface area losing heat | m² | Outside area of walls, bottom and liquid surface that lose heat. |
| Overall loss coefficient | W/m²·K | Overall loss coefficient (about 1–2 insulated, 5–10 bare steel in still air; an open liquid surface loses far more). |
| Heat-up time wanted | h | Time allowed to reach the set temperature. |
| Power margin | % | Margin on the power found. |
| Heater | ||
| Installed heater power | kW | Rated power of the heater fitted or considered. |
| Number of elements | Number of heater elements. | |
| Heated surface per element | cm² | Heated (sheath) surface of one element. |
| Largest watt density for the liquid | W/cm² | Highest surface watt density the liquid accepts (your value from the heater maker; much lower for oils and viscous liquids than for water). |
Method and formulas
- Heat-up energy Q = (m c + m_v c_v)(T_s − T₀), with m = V ρ.
- Loss during heat-up ≈ U A [(T₀ + T_s) ÷ 2 − T_amb]; holding loss = U A (T_s − T_amb).
- Power needed = (Q ÷ t + heat-up loss) × (1 + margin); heat-up time with the installed heater = Q ÷ (P − heat-up loss).
- Watt density = installed power ÷ (elements × heated surface per element).
- Example: heating 1000 L from 15 to 60 °C in 3 h needs 19.848 kW; the 21 kW heater does it in 2.5734 h.
Limitations
- Uniform liquid temperature; poorly stirred tanks stratify.
- Evaporation from an open hot surface can dominate the losses and is not included in a simple U value.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Size a heater for a wash, plating or oil tank
- Check an existing heater’s heat-up time
- Check watt density so oil or solutions do not burn on the elements
Who it is for
- Plant engineers
- Maintenance engineers
- Process engineers
What you get
- Heat-up energy and losses
- Power needed and actual heat-up time
- Holding duty and watt density
Interpreting the result
- If the holding duty is very low, a smaller heater with a longer heat-up time may be acceptable.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 371–378. Topic reference; no source tables or recommended settings are reproduced.
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Open the Electric Tank Heater Sizing (Heat-up, Losses and Watt Density) calculator
