Understanding Heat Transfer
1
Conduction
Conduction takes place between substances that are in direct contact with each other. Heat transfer happens faster through substances that are good conductors, like metal, which is why proper loading techniques and insulation is important inside steel shipping containers.2
Convection
Convection occurs when warmer areas of a liquid or gas rise to cooler areas in the liquid or gas, and the cooler gas moves beneath. This creates a circular motion of heat transfer from high to low areas. When the sun heats a shipping container, circular motion of heat transfer exposes the top of the load to higher temperatures. Blankets and pallet covers help protect the load from this type of heat transfer by keeping the surrounding air away from the load.3
Radiation
Unlike conduction, radiant heat transfer occurs without any direct contact between the heat source and heated object. Heat can move through empty space by thermal radiation known as infrared radiation. Direct radiation from the sun can heat the steel surface of a shipping container which then conducts to the inside surface and radiates inside, turning them into traveling ovens. This is why a radiant barrier is crucial for temperature sensitive cargo.
