Abstract
The present study pertains to the experimental impingement of two successive water drops on the solid surface. The drops were generated by a free-falling drop technique and a drop severance device with a velocity of 1.9 m/s at low Weber number. The initial drop diameter was fixed to either 930 μm or 1025 µm. Different from previous works, this study focused on four cases of drop impacts on stainless steel plates classified by the impingement timing of the leading drop deformation: case 1—single drop impingement for reference, case 2—the moment of the leading drop starting its spreading after impacting the surface, case 3—the instant of the leading drop reaching its maximum spreading, and case 4—the timing of the leading drop staying its maximum height. It is observed that the deformation behavior of two successive drops impacting on the surface is highly dependent on the impingement timing, which has minor effects on the change of the maximum drop spreading diameter, but affects significantly the change of the maximum height. The results reveal that the maximum spreading diameter of two drop impact for various cases is around 1.3 times larger than that of the single drop impingement. It is first observed that the maximum drop height for case 3 occurs at second recoil and is greater than those for case 2 and case 4 since the case 3 momentum effect at impingement timing acts in the inward direction, but the other two are in the outward direction.
Highlights
Drop impingements on a solid surface occur ubiquitously in nature and have many applications in industry and science, including power engineering,1,2 chemical engineering,3 agriculture,4,5 fire extinguishing,6 and forensic science.7,8 In such applications, it is frequently necessary to understand the mechanisms and phenomena involved in the impingement of single or multiple drops on dry surfaces
Different from previous works, this study focused on four cases of drop impacts on stainless steel plates classified by the impingement timing of the leading drop deformation: case 1—single drop impingement for reference, case 2—the moment of the leading drop starting its spreading after impacting the surface, case 3—the instant of the leading drop reaching its maximum spreading, and case 4—the timing of the leading drop staying its maximum height
The results reveal that the maximum spreading diameter of two drop impact for various cases is around 1.3 times larger than that of the single drop impingement
Summary
Drop impingements on a solid surface occur ubiquitously in nature and have many applications in industry and science, including power engineering, chemical engineering, agriculture, fire extinguishing, and forensic science. In such applications, it is frequently necessary to understand the mechanisms and phenomena involved in the impingement of single or multiple drops on dry surfaces. Drop impingements on a solid surface occur ubiquitously in nature and have many applications in industry and science, including power engineering, chemical engineering, agriculture, fire extinguishing, and forensic science.7,8 In such applications, it is frequently necessary to understand the mechanisms and phenomena involved in the impingement of single or multiple drops on dry surfaces. In investigating the drop impact onto either solid or liquid surfaces, a number of works have been devoted toward the case of only a single drop to simplify the modeling and to address underlying physical mechanisms, via theoretical analysis and experimental measurement.. The physics-based correlation of the heat transfer arising from drop impacts onto a dry substrate concerning the modeling of spray cooling at different boiling mechanisms was proposed in the review article by Breitenbach et al.. Yarin reviewed the single drop impact on thin liquid layers and dry surfaces with a focus on an explanation of practical motivations related to the fascinating phenomena of drop impacts. The complexity of the problem was attracting increased attention in unraveling the underlying physical mechanisms in the recent review by Josserand and Thoroddsen. Liang and Mudawar provided a comprehensive overview concerning heat transfer regimes, including film evaporation, nucleate boiling, transition boiling, and film boiling, of the liquid drop impact on a heated wall. Most recently, the physics-based correlation of the heat transfer arising from drop impacts onto a dry substrate concerning the modeling of spray cooling at different boiling mechanisms was proposed in the review article by Breitenbach et al. It can be concluded that the drop impinging on a solid surface is related to numerous parameters such as the type of working fluid, the impacted surface material, the initial drop diameter, the impact velocity, the impact direction, the impacted surface temperature, and so on
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