Driven by buoyancy or external flow respectively.
Forced convection: flow driven by fans or pumps; Nu=f(Re,Pr). Natural convection: buoyancy drives flow; Nu=f(Ra) with Rayleigh number Ra=gβΔTL³/(να). Natural convection is weaker but needs no power, used in passive cooling and radiators.
A heated vertical plate in still air has h around 5–10 W/m²K.
Natural and forced convection describe the two ways fluid moves, so they affect cooling design, heating and ventilation choices.
Driven by buoyancy or external flow respectively.
Natural and forced convection describe the two ways fluid moves, so they affect cooling design, heating and ventilation choices.
A fan or pump increases fluid velocity, which increases the heat transfer coefficient and the heat removed.
Buoyancy from density changes caused by temperature differences, so hot fluid rises and cold fluid sinks.
Typical applications include designing a passive heat sink that relies on natural convection, sizing a fan for forced air cooling of an electronics cabinet and estimating heat loss from a radiator in a room.
Study "Convection" first (topic 86 of 105 in Thermodynamics & Fluids). It covers the groundwork this topic builds on.
Grashof number. Mixed convection. Chimney effect.
A heated vertical plate in still air has h around 5–10 W/m²K.
The next topic is "Nusselt number", which builds directly on this one.
It is classed as Advanced in Thermodynamics & Fluids (topic 87 of 105). It is an advanced topic. It assumes you are comfortable with the intermediate topics in Thermodynamics & Fluids.
Want to practise? Open the interactive course for quick checks, quizzes, simulations and progress tracking.