Calculator
Formula used
The calculator uses the steady, one‑dimensional thermal resistance method for a plane wall. For each conduction layer: R''cond = L / k. If convection is included at the boundaries: R''conv = 1 / h. Optional contact resistance is added as R''c.
Total per‑area resistance: R''total = Σ(L/k) + (1/hhot) + (1/hcold) + R''c. Heat flux: q" = ΔT / R''total. Heat rate: q = q" × A.
Assumptions: constant properties, no internal heat generation, negligible edge effects, and normal heat flow through the wall.
How to use this calculator
- Select a model: single-layer, with convection, or composite layers.
- Enter hot and cold temperatures, then choose the unit.
- Fill in each layer’s thickness and conductivity values.
- Include convection coefficients and contact resistance if needed.
- Press Calculate, then download CSV or PDF if desired.
Example data table
| Case | A (m²) | Thot (°C) | Tcold (°C) | Layers (L, k) | Convection (hhot, hcold) | Estimated q" (W/m²) |
|---|---|---|---|---|---|---|
| Single wall | 2.0 | 60 | 20 | 0.12 m, 1.4 W/m·K | — | 466.67 |
| Wall + insulation | 1.5 | 55 | 25 | 0.12 m, 1.4; 0.05 m, 0.035 | — | 20.41 |
| With convection | 1.5 | 60 | 20 | 0.12 m, 1.4 | 10, 25 | 206.42 |
Numbers are illustrative and rounded; your results will depend on inputs and model choice.
FAQs
1) When should I use the convection option?
Use it when the wall surfaces exchange heat with fluids by convection. It helps estimate surface temperatures and a more realistic heat flux when h values are known.
2) What does R'' mean in the results?
R'' is thermal resistance per unit area, with units m²·K/W. It lets you compute heat flux directly using q" = ΔT / R'' without needing the area.
3) Why is my heat flux negative?
Negative heat flux means the temperature you labeled “hot” is actually lower than the “cold” side. The magnitude is still correct; the sign indicates direction.
4) Can I model multiple materials in one wall?
Yes. Choose the composite wall model and set 2 or 3 layers. Enter each layer’s thickness and conductivity to get the combined resistance and heat flow.
5) What if I only need heat flux, not heat rate?
Select “Heat flux q"” in Solve for. You may leave the area blank because q" depends only on ΔT and the per‑area resistances.
6) How do I pick conductivity values?
Use published material property tables for the expected operating temperature. If conductivity changes strongly with temperature, use an average or run separate cases.
7) What does contact resistance represent?
It models imperfect contact between layers, such as rough surfaces or gaps. Enter R''c if known; otherwise set it to zero for ideal contact.
8) Does this handle radiation or transient conduction?
No. This tool is for steady, one‑dimensional conduction with optional convection. For radiation or time‑varying cases, use a more detailed heat transfer model.