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.
Thermal Gradient Mass Transfer
Internal Movement
Internal movement of water vapor through a porous medium driven by a temperature difference between two points causes moisture to accumulate in cold zones. In the storage of paper rolls or stacked boxes, thermal gradient mass transfer occurs when one side of the load is warmer than the other. This process leads to localized dampness even if the average moisture content of the material is within specification.
Vapor Pressure
Vapor pressure is higher at the warm end of the gradient, forcing water molecules to diffuse toward the cooler end where the pressure is lower. Once these molecules reach the cold surface, they often condense or are adsorbed by the fibers. This redistribution of water causes the board to expand at the cold side and shrink at the warm side, leading to structural distortions.
Temperature differences as small as five degrees Celsius trigger this movement over time.
Damage Consequence
Damage from this internal moisture movement is a common problem in warehouses with uninsulated walls or floor heating. The resulting uneven moisture profile makes the paper difficult to process and can lead to mold. Maintaining a uniform temperature across the storage area is the primary defense against this phenomenon.