Input Data
Plotly Graph
This chart plots the resistance contribution of each active component. It updates after calculation and shows a sample profile before submission.
Example Data Table
| Case | Inputs | Thermal Resistance | Heat Rate | Notes |
|---|---|---|---|---|
| Single slab | A = 2.5 m², L = 0.12 m, k = 0.8 W/m·K, hi = 10, ho = 25, Th = 120, Tc = 35 | 0.116 K/W | 732.759 W | Includes both convection films and conduction through one wall. |
| Composite wall | A = 4 m², layers = (0.08/0.7), (0.05/0.04), (0.013/0.16), hi = 8, ho = 20, Th = 22, Tc = -5 | 0.405134 K/W | 66.645 W | Useful for insulation stacks, walls, doors, and panels. |
| Hollow cylinder | ri = 0.03 m, ro = 0.06 m, L = 1.5 m, k = 16 W/m·K, hi = 50, ho = 12, Th = 200, Tc = 40 | 0.222698 K/W | 718.462 W | Appropriate for pipes, ducts, and insulated process lines. |
Formula Used
Planar conduction and composite wall
Single slab: R = L / (kA)
Composite wall: Rtotal = Σ[L / (kA)] + 1 / (hiA) + 1 / (hoA)
Heat rate: Q = ΔT / Rtotal
Cylinder and sphere
Cylinder: R = ln(ro/ri) / (2πkL)
Sphere: R = [(1/ri) - (1/ro)] / (4πk)
Add film resistances when convection exists on inner or outer boundaries.
Convection film
Film resistance: R = 1 / (hA)
Heat flux: q" = Q / A = hΔT
Contact resistance
Area-specific contact resistance input: R"c (m²·K/W)
Converted value: Rcontact = R"c / A
How to Use This Calculator
- Choose the geometry or resistance model that matches your engineering case.
- Enter hot-side and cold-side temperatures using the same temperature scale.
- Fill in geometry, material properties, and optional convection coefficients.
- For composite walls, set the active layer count and provide thickness and conductivity for each active layer.
- Click the calculate button to display total resistance, heat-transfer rate, U-value, and interface temperatures.
- Use the CSV or PDF buttons to save the generated result block for reports, audits, or design reviews.
Heat Flow Starts With Resistance
Thermal resistance translates geometry and material data into a direct heat-flow barrier. Lower total resistance means higher heat transfer for the same temperature difference. For a wall with 85 K across it, a total resistance of 0.20 K/W gives 425 W, while 0.40 K/W cuts heat flow to 212.5 W. That is why insulation matters.
Conductivity Strongly Changes Performance
Thermal conductivity is often the fastest way to compare materials. A mineral wool layer near 0.04 W/m·K resists heat far better than concrete near 1.4 W/m·K or steel above 40 W/m·K. If area stays constant, doubling conductivity halves conductive resistance. Selecting a low-k insulation product can produce a larger thermal improvement than increasing thickness in a highly conductive layer.
Thickness And Area Move Results Predictably
Planar conduction follows R = L divided by kA, so resistance rises linearly with thickness and falls as area increases. If thickness grows from 0.05 m to 0.10 m, resistance doubles. If area increases from 1 m² to 2 m², resistance becomes half. These trends help engineers check whether size changes or insulation upgrades reduce the load more effectively.
Surface Films Can Dominate Light Constructions
Convection coefficients can change total resistance, especially for thin panels or metal walls. With h equal to 10 W/m²·K and area of 2 m², a single film adds 0.05 K/W. Raising h to 25 lowers that film resistance to 0.02 K/W. In still air, surface films become a major share of total resistance.
Composite Assemblies Need Layer By Layer Checks
Real systems rarely use one material only. Roofs, ducts, ovens, and chilled panels may include metal skins, insulation cores, air gaps, and contact interfaces. A three-layer wall might add 0.03, 0.31, and 0.02 K/W from conduction terms, showing the insulation core dominates performance. Layer accounting also reveals where marginal spending produces the highest thermal benefit.
Design Decisions Improve With Clear Outputs
The most useful outputs are total resistance, U-value, heat-transfer rate, and interface temperatures. U-value standardizes performance per unit area, while interface temperatures help identify condensation, burn risk, or material limits. Exported result tables support documentation, supplier comparison, and review meetings. Used early, the calculator helps engineers compare alternatives and justify thermal upgrades before fabrication begins.
FAQs
1. What does thermal resistance tell me?
It shows how strongly a material layer, surface film, or assembly resists heat flow. Higher resistance means lower heat transfer for the same temperature difference.
2. When should I use composite wall mode?
Use composite mode when heat passes through multiple solid layers in series, such as insulated walls, sandwich panels, doors, roofs, ducts, or furnace linings.
3. Why are convection coefficients optional in some modes?
They are optional because some checks focus only on solid conduction. When known, adding inside and outside film coefficients gives a more realistic total resistance.
4. Can I enter temperatures in Celsius?
Yes. Enter both temperatures using the same scale. Because the calculation uses temperature difference, consistent Celsius or Kelvin inputs both work correctly.
5. What is the benefit of interface temperatures?
Interface temperatures help identify condensation risk, insulation weak points, and surfaces that may exceed operating, handling, or material service limits.
6. How should I interpret the Plotly graph?
The bar heights show which resistance components dominate the total. Larger bars indicate the layers or films where design changes will have the biggest thermal impact.