| Network | Inputs | Equivalent Resistance (K/W) | Heat Rate (W) | Notes |
|---|---|---|---|---|
| Pre + (A||B) + Post |
Thot=80°C, Tcold=20°C Pre: 0.05, 0.08 Branch A: 0.22, 0.15 Branch B: 0.35, 0.10 Post: 0.12 |
≈ 0.412 | ≈ 145.63 | Parallel block splits heat by branch resistances. |
- Series: Req = Σ Ri
- Parallel: 1/Req = Σ (1/Ri)
- Heat rate: Q = (Thot − Tcold) / Req
- Temperature drop: ΔTi = Qi · Ri
- Common element models: Conduction plane wall R = L/(kA), convection R = 1/(hA), contact resistance R = 1/(hcA).
- Choose a network type that matches your heat-flow paths.
- Select a solve mode: compute Q, or compute a boundary temperature.
- Enter temperatures (°C or K) and/or heat rate (W) as required.
- Fill resistances (K/W) using your geometry and material data.
- Click Calculate to see results above the form.
- Use CSV/PDF export to document scenarios and share outputs.
1) Why thermal resistance networks matter
Thermal resistance networks compress complicated heat paths into a few K/W elements that behave like electrical resistors. Once mapped, you can predict heat rate, temperature drops, and margins against material limits.
2) Building blocks: conduction, convection, and contact
For plane-wall conduction use R = L/(kA). Typical conductivity ranges: air about 0.024 W/m·K, plastics near 0.2, stainless steel about 15, copper around 400. Convection uses R = 1/(hA): natural convection is often 5–25 W/m²·K, forced air frequently 25–250, and many liquids reach 200–5000+ in compact cooling channels. Contact resistance can be modeled as R = 1/(h_cA), with h_c commonly spanning 500–20000 W/m²·K depending on pressure and surface finish.
3) Series networks: stacked layers and films
Series networks represent one heat-flow path: for example inner film, wall conduction, then outer film. The total resistance is the sum, and the largest element usually produces the biggest temperature drop. That is often the best starting point for improvement.
4) Parallel networks: multiple heat-flow paths
Parallel networks split heat among branches that share the same ΔT. Heat sinks, bypass routes, and competing materials can behave this way. Lower-resistance branches carry a larger share of heat, and the tool reports each branch contribution.
5) Series–parallel: realistic assemblies
Many assemblies have a shared upstream path, a split into two routes, then a shared downstream path. The series–parallel option models Pre + (A||B) + Post and reports split-node temperatures to help you pinpoint hot spots.
6) Temperature units and what ΔT means
Enter boundary temperatures in °C or K, but differences are always Kelvin-based. Because Δ°C = ΔK, the heat-rate equation stays consistent. Keep resistances in K/W and heat rate in watts for clean interpretation.
7) Turning results into design decisions
After computing Req and Q, run “what-if” cases: increase area, reduce thickness, switch materials, or improve h to lower resistance. Use element-level ΔT values to check a thermal budget at each interface and confirm your hottest component stays within limits. Export files to compare scenarios, track revisions, and communicate trade-offs.
8) Practical checks before trusting a model
If Q looks extreme, re-check units for area and thickness, and ensure every element is K/W. Radiation is nonlinear; if you linearize it, use an effective resistance valid for your temperature range and treat it as the correct series or parallel element.
1) What does K/W mean for thermal resistance?
K/W means how many kelvin of temperature drop you get per watt of heat flow. If an element is 0.2 K/W and 50 W passes through it, the drop across it is 10 K.
2) Can I enter temperatures in Celsius?
Yes. Celsius is fine for boundary temperatures. The calculator uses Kelvin for temperature differences, but Δ°C equals ΔK, so the heat-rate calculation remains consistent and physically correct.
3) How do I convert a convection coefficient into a resistance?
Use R = 1/(hA). Enter the result in K/W, where h is in W/m²·K and A is in m². Larger area or higher h reduces the resistance.
4) Why does the parallel option report different branch heat rates?
All parallel branches share the same ΔT, so each branch heat rate is ΔT divided by its branch resistance. Lower-resistance branches carry more heat, and totals add to the overall heat rate.
5) What if one branch in series–parallel is much larger resistance?
The higher-resistance branch carries less heat. In the limit of a very large resistance, its heat flow approaches zero and the parallel block behaves almost like the lower-resistance branch alone.
6) Does this include radiation automatically?
Not automatically. If you have an effective linearized radiation resistance for your temperature range, you can add it as another K/W element in series or as a parallel path, depending on geometry.
7) What should I do if the heat rate looks unrealistically high?
Re-check thickness, area, and coefficient units. A small area or missing thickness conversion can shrink resistance drastically. Also verify you did not enter resistances as W/K; this tool expects K/W.