KEVOS® MAKEOS · Materials
Furnace Wall Design (Layers, Convection and Radiation from the Surface)
What outside surface temperature and heat loss will this layered furnace wall have, are the layer interfaces within their service temperatures, and what does the loss cost?
Heat loss through a layered furnace or oven wall with the outside surface losing heat by both convection and radiation: the surface temperature found by iteration so that conduction through the layers equals convection plus radiation (radiation as the radiant heat tool), the heat flux and loss for the wall area, the temperature at each interface (as the wall heat loss tool with the combined surface coefficient), the annual energy cost, and checks against the surface touch limit and the service limit of the insulating layer.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Hot face temperature | °C | Temperature of the hot face of the lining. |
| Ambient temperature | °C | Air temperature outside the furnace. |
| Layers (hot face first) | ||
| Layer 1 thickness | mm | Thickness of the hot-face layer (refractory brick or castable). |
| Layer 1 conductivity | W/m·K | Conductivity of layer 1 at its mean temperature. |
| Layer 2 thickness | mm | Thickness of the insulating layer. |
| Layer 2 conductivity | W/m·K | Conductivity of layer 2 at its mean temperature. |
| Layer 3 thickness (shell) | mm | Thickness of the steel shell (0 if none). |
| Layer 3 conductivity | W/m·K | Conductivity of the shell. |
| Outside surface | ||
| Convection coefficient | W/m²·K | Natural convection coefficient at the outer surface (about 5–10 indoors). |
| Surface emissivity | Emissivity of the outer surface (about 0.8 painted or oxidised steel). | |
| Wall area | m² | Area of wall. |
| Largest surface temperature | °C | Highest outside surface temperature you allow. |
| Service limit at the layer 1–2 interface | °C | Highest temperature the insulating layer may see (its service limit). |
| Hours per year | h | Hours per year at temperature. |
| Energy price | $/kWh | Energy price. |
Method and formulas
- Conduction resistance R = Σ t ÷ k per square metre; flux q = (T_hot − T_s) ÷ R.
- At the surface q = h_c (T_s − T_a) + ε σ (T_s⁴ − T_a⁴) (radiation as the radiant heat tool); solve for T_s by bisection.
- Interface temperatures fall by q × t ÷ k across each layer (as the wall heat loss tool with the combined coefficient).
- Loss = q × area; energy = loss × hours.
- Example: the shell runs at 62.288 °C, losing 514.16 W/m² (5.1416 kW); the insulation sees 850.73 °C.
Limitations
- Constant conductivities; real refractories vary strongly with temperature.
- Steady state; heat stored in the lining during start-up is not included.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Design a refractory and insulation lining
- Check a furnace shell surface for burn risk
- Estimate the running cost of wall losses
Who it is for
- Furnace engineers
- Plant engineers
- Energy managers
What you get
- Surface temperature, flux and heat loss
- Interface temperatures
- Annual energy cost and checks
Interpreting the result
- Most of the temperature drop should occur in the insulating layer; the brick protects it from the hot face.
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 Furnace Wall Design (Layers, Convection and Radiation from the Surface) calculator
