Natural Convection
Rayleigh number to Nusselt to heat rate for vertical plates, horizontal cylinders and horizontal plates — with optional radiation exchange to the surroundings, exactly as the textbook bath/pipe/absorber problems do it.
Body
Temperatures
Properties
Radiation
Frequently asked
- Which natural-convection correlation is used?
- Vertical plate: Nu = [0.825 + 0.387·Ra^⅙ / (1+(0.492/Pr)^(9/16))^(8/27)]². Horizontal cylinder (all-Ra Churchill–Chu): Nu = [0.6 + 0.387·Ra^⅙ / (1+(0.559/Pr)^(9/16))^(8/27)]². Horizontal plate: Nu = 0.54·Ra^¼ hot-up, 0.27·Ra^¼ hot-down.
- What is β for gases?
- For ideal gases β = 1/T_f with T_f in kelvin — evaluate it at the film temperature. Liquids take β from the property tables.
- Can I include radiation?
- Enter an emissivity and the calculator adds Q = ε·σ·A·(Ts⁴ − Tsurr⁴) (surroundings at T∞) to the convection duty and reports the total.