Droplet trampolining on heated surfaces in the transitional boiling regime. (July 2022)

• Record Type: Journal Article
• Authors: Agrawal, Pranjal; Dash, Susmita
• Is Part Of: International journal of heat and mass transfer. Volume 190(2022)
• Publication Date: 2022-07
• Subjects: Transitional boiling -- Bouncing -- Trampolining -- Bubble nucleation -- Momentum gain; Heat -- Transmission -- Periodicals; Mass transfer -- Periodicals; Chaleur -- Transmission -- Périodiques; Transfert de masse -- Périodiques; Electronic journals; 621.4022
• DOI: 10.1016/j.ijheatmasstransfer.2022.122811
• Languages: English
• ISSNs: 0017-9310

Abstract

Highlights: Surface morphology influences the Leidenfrost and transitional boiling regime. An unconstrained droplet shows a non-monotonic variation in the total evaporation time with temperature in the transitional boiling regime. An unconstrained droplet exhibits trampolining in the transitional boiling regime. The gain in momentum of the droplet resulting in trampolining is attributed to the bubble nucleation and escape prior to droplet take-off. Abstract: Droplet dynamics on a heated surface plays an important role in applications ranging from spray cooling to solidification and pharmaceuticals. Here, we show that in the transitional boiling regime, an unconstrained droplet exhibits trampolining where the droplet bounces to higher heights with each consecutive contact with the substrate. A water droplet of volume 1 μ L bounces to a height as high as 6-7 times of its diameter and the height of bounce increases to 18–20 times the diameter as the volume reduces to ∼ 0.1 μ L . The dynamics of the droplet in the transitional boiling regime results in a non-monotonic variation in the total evaporation time of the droplet with an increase in substrate temperature – an observation that is absent for a constrained droplet. We develop a force-based model to explain the trampolining behavior of the droplet and propose that the gain in momentum of the droplet that results in trampolining is caused by bubble nucleation and escape at the liquid-substrate interface prior to droplet takeoff.