Model buoyancy driven heat transfer for plates and cylinders. Check air or liquid regime behavior. Compare results, export reports, and refine thermal decisions confidently.
| Geometry | Surface Temp (deg C) | Ambient Temp (deg C) | Length (m) | Area (m^2) | Beta (1/K) | Nu (m^2/s) | Alpha (m^2/s) | k (W/m-K) |
|---|---|---|---|---|---|---|---|---|
| Vertical plate | 80 | 25 | 0.50 | 1.20 | 0.0032 | 0.0000189 | 0.0000220 | 0.028 |
| Horizontal cylinder | 120 | 35 | 0.08 | 0.45 | 0.0030 | 0.0000210 | 0.0000250 | 0.031 |
| Sphere | 60 | 20 | 0.15 | 0.32 | 0.0033 | 0.0000175 | 0.0000215 | 0.027 |
1. Temperature difference: Delta T = Ts - Tinf
2. Prandtl number: Pr = nu / alpha
3. Grashof number: Gr = g beta Delta T L3 / nu2
4. Rayleigh number: Ra = Gr x Pr
5. Nusselt number: A geometry-specific empirical correlation estimates buoyancy-driven convection strength.
6. Heat transfer coefficient: h = Nu k / L
7. Heat transfer rate: Q = h A Delta T
The selected relation depends on geometry and Rayleigh range. Accuracy improves when fluid properties are evaluated at the film temperature.
Natural convection occurs when density differences drive motion without fans or pumps. Hotter fluid rises, cooler fluid sinks, and the resulting circulation changes the convective coefficient.
The Rayleigh number combines buoyancy, viscosity, and thermal diffusion effects. Lower values usually indicate stable laminar motion, while higher values imply stronger mixing and possible turbulence.
Characteristic length depends on geometry. For a vertical wall, height is common. For cylinders and spheres, the outside diameter often serves as the working length scale.
This tool focuses on free convection only. If forced flow, radiation dominance, or phase change exists, combine this estimate with additional thermal models.
It estimates natural convection performance from geometry, temperature difference, and fluid properties. Outputs include Rayleigh number, Nusselt number, heat transfer coefficient, and heat transfer rate.
Free convection correlations assume properties evaluated near the average boundary layer condition. Using film-temperature values reduces error when the surface and ambient temperatures differ meaningfully.
Use the length associated with the selected geometry and the published correlation. A wall typically uses height, while a cylinder or sphere often uses outside diameter.
A negative value means the surface is cooler than the surroundings, so heat flows from the fluid toward the surface. The sign indicates direction only.
Yes. Enter the correct liquid properties at the film temperature. Large Prandtl differences can strongly change Rayleigh and Nusselt predictions, so property quality matters.
No. Radiation is not added to the reported heat transfer rate. For hot surfaces, combine this result with a separate radiation model for total heat loss.
The check compares your entered thermal diffusivity with k divided by rho times cp. It helps catch inconsistent property sets before using the output in design work.
It is best for preliminary sizing, screening, and sanity checks. Final certification should rely on validated standards, detailed simulation, or measured thermal test data.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.