Thermodynamic Boundary Layer Mechanics inside Wrapped Unitized Pallet Containers
Thermal boundary layers inside stretch-wrapped pallets drive vapor condensation and localized corrugated compression strength failure during temperature transitions.
Closed Container Condensation
Atmospheric Event
Atmospheric phenomenon occurring within sealed transport units involves the transition of water vapor into liquid droplets on the interior surfaces or the cargo itself. In the context of maritime shipping, closed container condensation occurs when the temperature of the air inside the steel box drops below its dew point. This event leads to container rain or cargo sweat.
Thermal Cycle
Thermal cycles during day and night drive the movement of moisture between the internal air and the packaged goods. When the sun heats the roof of the container, air temperature rises and its capacity to hold water increases. As night falls, the metal skin cools rapidly, causing moisture to condense and fall onto the stacks of paper or board.
Damp pallets or high moisture content in the packaging materials themselves provide the reservoir of vapor that feeds this cycle throughout the voyage. Fluctuating humidity levels inside the unit weaken the structural integrity of corrugated containers.
Moisture Protection
Protection against moisture damage involves the use of desiccants or thermal liners to moderate the internal environment. Damage from liquid water stains the board and weakens the adhesive bonds. Proper ventilation or humidity control remains necessary for long distance shipping through varying climates.