The Influence of Surfactants, Dynamic and Thermal Factors on Liquid Convection after a Droplet Fall on Another Drop

Sergey Y Misyura,Oleg A Gobyzov,Vladimir S Morozov

doi:10.3390/app10124414

Abstract

The regularities of the processes and characteristics of convection in a sessile drop on a hot wall after the second drop fall are investigated experimentally. The movement of a particle on a drop surface under the action of capillary force and liquid convection is considered. The particle motion is realized by a complex curvilinear trajectory. The fall of droplet with and without surfactant additives is considered. Estimates of the influence of the thermal factor (thermocapillary forces) and the dynamic factor (inertia forces) on convection are given. The scientific novelty of the work is the investigation of the simultaneous influence of several factors that is carried out for the first time. It is shown that in the presence of a temperature jump for the time of about 0.01–0.1 s thermocapillary convection leads to a 7–8 times increase in the mass transfer rate in drop. The relative influence of inertial forces is found to be no more than 5%. The fall of drops with surfactant additives (water + surfactant) reduces the velocity jump inside the sessile drop 2–4 times, compared with the water drop without surfactant. Thermocapillary convection leads to the formation of a stable vortex in the drop. The dynamic factor and surfactant additive lead to the vortex breakdown into many small vortices, which results in the suppression of convection. The obtained results are of great scientific and practical importance for heat transfer enhancement and for the control of heating and evaporation rates.

Highlights

The dynamic factor and surfactant additive lead to the vortex breakdown into many small vortices, which results in the suppression of convection
Drop 2 evaporated in the mode of constant contact radius (CCR)
The dynamic factor was related to the inertial forces and the pressure jump inside drop 2

Summary

Introduction

Promising Technologies Based on the Interaction of Falling Liquid Drops and Heated Surfaces. Surface cooling by a spray (drop aerosol) is widely used in practice [1,2]. In this process, it is important to properly model the interrelated processes of heat and mass transfer, as this is what determines the efficiency of the technology as a whole. The continuous fall of drops of water–salt solution is realized on the tube walls in falling-film evaporators at desalination and cooling [4]. When the rate of the drop fall on a layer of burning fuel increases, three different modes are realized: spraying-injecting, splashing-injecting-secondary-injecting and bubble splashing [6]

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Results

Conclusion