Thermal energy transfers faster when the temperature difference is large, the path for heat is easy to travel through, and there is lots of area for transfer; it slows down when the material or conditions resist heat flow.
Main factors
- Temperature difference ( ΔT\Delta TΔT): A bigger temperature difference between two regions or between an object and its surroundings gives a higher rate of heat transfer in all three modes (conduction, convection, radiation).
- Thermal conductivity of the material : Good conductors (metals) transfer heat quickly, while insulators (wood, plastic, foam) transfer heat slowly.
- Surface area in contact : A larger contact area (e.g. fins on a radiator) allows more heat to be transferred per second by conduction, convection, and radiation.
- Thickness / distance : A thicker layer of material or a longer distance reduces the rate of conduction; heat flows more slowly through thick insulation than through thin material.
Extra factors by heat transfer type
- For conduction : Rate increases with higher thermal conductivity, larger cross‑sectional area, and larger temperature gradient, and decreases with greater thickness.
- For convection : Rate increases with stronger fluid motion (wind, stirring), larger temperature difference between surface and fluid, and greater surface area exposed to the fluid.
- For radiation : Rate increases with higher surface temperature, larger surface area, higher emissivity (dark, matte surfaces), and decreases with greater distance (intensity falls roughly with the square of distance).
Object-related factors
- Surface nature and color : Dark, matte surfaces are better emitters and absorbers of thermal radiation; shiny, light surfaces emit and absorb less.
- Shape and size (surface area to volume) : Objects with a high surface-area-to-volume ratio (small or thin objects) lose or gain heat faster than bulky ones of the same material.
