Free Surface Effect

Also referred simply as ‘sloshing,’ this effect represents the tendency of liquids or unconstrained aggregates of small solid objects, such as seeds, gravel, or crushed ore, as contents or cargo of a tanker truck move around. Whether fluid or small solids, the action is similar to that of fluids, moving around resulting from variations of a vehicle’s orientation inside the cargo as a counterpoint to the operator’s motions. The state of a tank that’s not completely filled is known as a “slack tank,” when referring to the free surface effect and can be prevented by installing baffles. A full tank is known to be “pressed up.”

Baffles mitigating the free surface effect of liquids