A Transport Phenomena View of the Teapot Effect: Fluid Adhesion, Momentum Transport, and Wettability Control

Aditya Singal, Avishi Jain

Abstract: The "teapot effect" refers to the propensity of a poured liquid stream to wrap around the underside of a spout and trickle down rather than separate cleanly. The present work revisits this behaviour within the framework of transport phenomena, joining classical free-surface hydrodynamics to contemporary ideas of wettability and capillary adhesion. The foundational work of Reiner (vortex-driven film attachment), Keller (exact free-boundary potential-flow solutions), and Bocquet and colleagues (hydro-capillary adhesion) is surveyed and recast in terms of momentum transport, stress analysis, and interfacial boundary conditions. We outline a complex-potential treatment in which the velocity potential ϕ and stream function ? capture the flow as it bends around the lip, with Bernoulli suction permitting attachment. A cloud-hosted computational fluid dynamics (CFD) study run at three inlet velocities recovers the anticipated rise of lip suction with flow rate. In addition, we describe a wetting-history (hysteresis) effect: on a previously wetted surface the velocity needed for clean detachment is about twelve percent above that of a dry surface, which implies that the critical Weber number Wec carries a dependence on surface history.

Keywords: Boundary layer, capillary adhesion, computational fluid dynamics, contact-angle hysteresis, free-surface flow, momentum transport, teapot effect, wettability