Investigation of the Teapot Effect

Abstract

It is an annoying event when the tea or any liquid spilling from the teapot flows outside the spout surface onto the table instead of into a cup. In this study, this event, which is called the teapot effect, is investigated experimentally and numerically using a porcelain teapot. The liquid was poured from the teapot at different flow rates, while the teapot was positioned at an angle of 5–25° to the ground. Therefore, the liquid flow was provided from the teapot's spout at different flow rates (in the range of 0.2–0.54 l/min). Experiments and simulations were performed using two types of teapot spouts: one with a hydrophilic surface and the other with a superhydrophobic spout surface. While the liquid's momentum ensures that the liquid tends to maintain its flow direction, the liquid adjacent to the spout surface is slowed down by the capillary adhesion force. The balance between the liquid's forward momentum and the capillary adhesion force determines the flow direction. The liquid flowing from the superhydrophobic spout flows without creating the teapot effect. In the case of a hydrophilic spout, the velocity of the liquid is the dominant factor in the teapot effect. The capillary adhesive force of the spout surface is the dominant parameter for the teapot effect. Pressure has a second-order effect due to the velocity gradient created by the change in the direction of the liquid flow due to the capillary adhesion force.