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Watt Density and Warm-Up Estimator
Enter volume, material, starting and target temperature to see the heat input the duty demands, then read it against the 1.0–3.0 W/cm² power density FlexBlanket builds custom silicone heaters to — power density on the specification table is the same quantity as watt density here. That band is a build envelope for custom heaters, not the power your duty needs, so fixed-area products such as the FLB-SDH-250 drum band sit below it by design. The estimator returns mass, energy, average power and watt density, then states whether that figure is below, inside or above the band.
Your Duty
Enter the duty and press Calculate.
Material Constants Used
These four values are the whole material model, and the estimator uses them exactly as printed. Specific heat is taken at the constant value shown rather than as a function of temperature, so a warm-up crossing a phase change is outside the model.
| Material | Specific heat c (kJ/kg·K) | Density (kg/L) | Mass of 200 L (kg) |
|---|---|---|---|
| Water | 4.18 | 1.00 | 200.0 |
| Mineral heat-transfer oil | 1.90 | 0.87 | 174.0 |
| Glycerine | 2.43 | 1.26 | 252.0 |
| Honey and syrup | 2.30 | 1.42 | 284.0 |
Where the Default Area Comes From
The 4350 cm² default is one FLB-SDH-250 drum band, which measures 1740 × 250 mm (68.5 × 9.8 in). Its published rating is 2000 W, and 2000 W divided by 4350 cm² works out at 0.46 W/cm² on the area it covers — a figure derived here from a published rating and a published band size, not a published rating in itself. Read it as the sanity check on what this tool returns for a 200 L drum: one band already carries that duty well under the custom band, and up to three bands stack on a single 200 L drum.
Reading the Verdict
The band is 1.0–3.0 W/cm² (6.5–19.4 W/in²), the power density we build to on custom silicone heaters only, and it is a construction envelope rather than the power a duty has to draw. Fixed-area products land below it by design — a drum band or a pipe jacket cannot shrink its area, because the container diameter fixes it — so a below-band result means the duty is met with room to spare. Only the above-band verdict forces a change before quotation; the other two are read as confirmations.
| Verdict | What it means | What to do with it |
|---|---|---|
| Below 1.0 W/cm² | The duty asks for less power than the bottom of the custom band over the area you entered, which is the normal result for a fixed-area product | Accept the lower figure: a standard FLB-SDH-250 band wraps a 200 L drum at a derived 0.46 W/cm², and up to three bands stack on one drum. On a custom heater only, cutting the heated area or shortening the warm-up time raises it |
| Inside 1.0–3.0 W/cm² | The average power fits the band we build custom silicone heaters to | Send the figure with the enquiry; the drawing fixes the final wattage |
| Above 3.0 W/cm² | The duty asks for more power per unit area than we build into one custom heater | Increase the heated area, lengthen the warm-up time, or split the load across more than one heater |
What This Model Leaves Out
Three real heat paths are absent from the arithmetic, and all three push the required power up rather than down.
- Standing heat loss from the container wall to ambient, which grows as the contents get hotter and as ambient falls.
- The thermal mass of the vessel itself — a steel drum absorbs heat that never reaches the contents.
- Insulation over the heater, which cuts the loss but drives the heater surface hotter for the same watt density.
The Margin to Send With Your Enquiry
Send the calculated figure with the ambient minimum, the container material and whether the heater is insulated, because each of those three moves the wattage the drawing fixes. Four inputs are enough to start that drawing — container dimensions, target temperature, operating conditions and local voltage — while the eight rows on the quotation input checklist are what let it come back quoted in one pass. The drawing is prepared at no charge before you order.
Send the Result
Quote the volume, material, temperatures, warm-up time and heated area you used, plus the watt density this page returned. The heater specification sheet prints those numbers in the row order of the published specification table, where the Family column marks the 1.0–3.0 W/cm² band as a silicone-heater figure. Full specifications, control options and lead times are on the silicone and flexible heaters page.
Send These Figures for a Heating Solution DrawingModel assumptions: mass = volume × density, rounded to two decimals; energy Q = mass × specific heat × (target − start), rounded to one decimal; average power P = Q ÷ warm-up time, using 1 kJ = 1000 J and 1 hour = 3600 s, rounded to one decimal; watt density = P ÷ heated area, rounded to two decimals. Constants used, and used at these values only: water 4.18 kJ/kg·K at 1.00 kg/L; mineral heat-transfer oil 1.90 kJ/kg·K at 0.87 kg/L; glycerine 2.43 kJ/kg·K at 1.26 kg/L; honey and syrup 2.30 kJ/kg·K at 1.42 kg/L. Scope: volume above 0 and up to 100,000 L, warm-up time above 0 and up to 720 hours; a zero entry, a value outside those bounds, or a target at or below the starting temperature returns no result.
The band thresholds are 1.0 W/cm² and 3.0 W/cm² inclusive, and they state what FlexBlanket builds custom silicone heaters to rather than what a duty must reach. Deliberately not modelled: standing heat loss to ambient, the thermal mass of the container, insulation over the heater, the attachment method, control overshoot, phase change, temperature-dependent specific heat, and any heat-up curve other than a constant average power. Every one of those pushes the real duty above this figure, so carry a margin on top of it into the enquiry.
