Calculation
Q = α·A·ΔT
Unlike conduction through a component, transfer between surface and fluid is captured directly via an empirical heat transfer coefficient, with no layer thickness involved.
Dubbel Thermodynamik D 10.2, Gl. (6) Newtonscher Ansatz Q̇ = α·A·(Tf − T0); Größenordnungen α nach Tab. 1
Convective heat transfer
Unlike conduction through a component, transfer between surface and fluid is captured directly via an empirical heat transfer coefficient, with no layer thickness involved.
MINTSI
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Result
Select a target and calculate.
Understand the inputs
- Heat flow Q — Heat flow transferred between surface and fluid.
- Heat transfer coefficient α in W/(m²·K) — Empirical coefficient; free convection in air about 5 to 25, forced convection in air about 25 to 250, water considerably higher.
- Transfer area A — Surface area involved in convection.
- Temperature difference ΔT — Difference between surface temperature and fluid temperature outside the boundary layer.
Example
α=25 W/(m²·K), A=2 m² and ΔT=8.4 K give Q=25·2·8.4=420 W.
Assumptions and limits
Constant, area-averaged heat transfer coefficient α and steady state; the actual determination of α from flow regime, fluid and geometry (Nusselt correlations) is outside this calculator.
Understand Convective heat transfer
This calculator determines the heat flow between a surface and a flowing fluid, complementing existing conduction through solid components with convective transfer.
What does this quantity describe?
The Newtonian approach describes convective heat transfer as Q=α·A·ΔT, where α is an empirical heat transfer coefficient dependent on flow regime, fluid and geometry.
Formula and variables
Q = α·A·ΔT
Q = α·A·ΔT
| Symbol / input | Meaning |
|---|---|
| Heat flow Q | Heat flow transferred between surface and fluid. |
| Heat transfer coefficient α in W/(m²·K) | Empirical coefficient; free convection in air about 5 to 25, forced convection in air about 25 to 250, water considerably higher. |
| Transfer area A | Surface area involved in convection. |
| Temperature difference ΔT | Difference between surface temperature and fluid temperature outside the boundary layer. |
Choose the inputs correctly
α is the heat transfer coefficient between surface and fluid, A the surface area involved, and ΔT the temperature difference between the surface and the fluid outside the boundary layer.
How to use the calculator
Take α from reference tables for the flow regime (free/forced, gas/liquid) and geometry involved, or compute it from a Nusselt correlation; take A and ΔT from the specific application.
Worked example
α=25 W/(m²·K), A=2 m² and ΔT=8.4 K give Q=25·2·8.4=420 W.
Understand the result and units
A higher heat transfer coefficient (e.g. from forced convection or a fluid with high thermal conductivity) raises heat flow proportionally, all else equal.
A is an area, ΔT a temperature difference. Q is output as a power; α is entered as a dimensionless numerical value with the unit W/(m²·K) noted in the help text.
Typical applications
Estimating heat loss or gain at surfaces in an air or water flow, heat-sink sizing, and building-envelope calculations with a known α.
Assumptions, limits and common mistakes
Constant, area-averaged heat transfer coefficient and steady state; the actual determination of α from flow regime, fluid properties and geometry via Nusselt, Reynolds and Prandtl numbers is outside this calculator.
Common mistake: Do not confuse α with the thermal conductivity λ of a solid; α describes transfer at the surface, λ conduction inside the component.
Frequently asked questions
What is “Convective heat transfer” used for?
Estimating heat loss or gain at surfaces in an air or water flow, heat-sink sizing, and building-envelope calculations with a known α.
Where do the input values come from?
α is the heat transfer coefficient between surface and fluid, A the surface area involved, and ΔT the temperature difference between the surface and the fluid outside the boundary layer.
What does the result not cover?
Constant, area-averaged heat transfer coefficient and steady state; the actual determination of α from flow regime, fluid properties and geometry via Nusselt, Reynolds and Prandtl numbers is outside this calculator.