Self-propelled Jumping Research Articles

Numerical investigation of droplet condensation and self-propelled jumping on superhydrophobic microcolumned surfaces

This paper investigates the processes of droplet condensation and self-propelled jumping on microcolumn-structured superhydrophobic surfaces with various size parameters. Using a three-dimensional (3D) multiphase lattice Boltzmann method, a novel phenomenon of secondary coalescence jumping is identified, and the underlying mechanisms are analyzed in detail. The simulation results show that wettability has a significant influence on droplet jumping. As the hydrophobicity of the surface increases, the droplets tend to jump from the substrate. However, structure parameters, such as the microcolumn spacing and height, have non-monotonic effects on droplet jumping. The structure parameters determine whether droplet coalescence occurs under the bottom–bottom droplet coalescence mode or the bottom–top droplet coalescence mode. Bottom–bottom droplet coalescence is shown to promote droplet jumping. Based on the simulation results and kinetic analysis, the optimal spacing-to-width and height-to-width ratios of the microcolumns for droplet jumping are found to be approximately 0.6 and 1.0, respectively. We believe the results of this work will provide valuable guidance in the design of self-cleaning surfaces and enhancing heat transfer efficiency.

Not All Sizes of Dust can be Removed by Jumping Condensates on Superhydrophobic Surfaces.

It is well known that superhydrophobic surfaces (SHSs) possess self-cleaning ability, either by impacting or rolling water droplets or by self-propelled jumping condensate. However, contaminants that are present in the air are various. Is it possible that these contaminants can all be removed from SHSs by jumping condensate? In this study, hydrophilic SiO2 micro- or nanoparticles with diameters larger than, comparable to, and smaller than the width of the nanogaps of the SHS were first filled in the nanogaps or suspended on the nanostructures with the help of ethanol, and the resulting SHS was exposed to condensing water vapor. Direct observation through microscopy showed that jumping condensation was still obvious on the SHS that were capped or filled with micro- or nanoparticles. Scanning electron microscopy (SEM) imaging demonstrated that following jumping condensation, particles that possessed diameters significantly smaller or larger than the width of the nanogaps were both removed from the SHS. However, most particles possessing diameters comparable to the width of the nanogaps remained on the SHS. This confirms for the first time that not all contaminants or dust can be removed from an SHS by self-propelled jumping condensate. Furthermore, the study also simply demonstrates that vapor condensation occurs within the nanogaps of the SHS. This study is helpful in further understanding the mechanism of the self-cleaning caused by jumping condensate and exploring the initial formation of condensate droplets on the SHS.

Hierarchical microporous superhydrophobic surfaces with nanostructures enhancing vapor condensation heat transfer

A new hierarchical superhydrophobic surface with micropores and nanoblades (MN SHS) is proposed to strengthen the jumping ability of droplets and maintain the high-efficiency droplet jumping condensation at the larger subcoolings. The results demonstrate that the jumping frequency and the proportion of multidroplets merging (n ≥ 8) on the MN SHS are higher than those on the nanostructured superhydrophobic surfaces (Nano SHS). Moreover, the maximum diameter of condensate droplets is only 150 μm, which is approximately 50% smaller compared to the Nano SHS. Spontaneous jumping of condensate droplets is observed on the 40PPI MN SHS (PPI: the average number of pores per inch.) at a subcooling of 16 K; while the droplet jumping condensation occurs at a maximum of 5 K on the Nano SHS. As the subcooling ranges from 5 K to 16 K, the heat transfer coefficient of MN SHS is increased by at least 26.4% compared to the Nano SHS. In addition, lattice Boltzmann model is adopted to simulate the self-propelled jumping behaviors on different structured surfaces. The energy conversion efficiency of drops on the MN SHS is higher compared to that on the Nano SHS. This work will contribute to the potential development of dropwise condensation in energy utilization, petrochemical engineering, thermoelectric cooling and aerospace thermal management systems.

Fabrication of Metallic Superhydrophobic Surfaces with Tunable Condensate Self-Removal Capability and Excellent Anti-Frosting Performance.

Laser fabrication of metallic superhydrophobic surfaces (SHSs) for anti-frosting has recently attracted considerable attention. Effective anti-frosting SHSs require the efficient removal of condensed microdroplets through self-propelled droplet jumping, which is strongly influenced by the surface morphology. However, detailed analyses of the condensate self-removal capability of laser-structured surfaces are limited, and guidelines for laser processing parameter control for fabricating rationally structured SHSs for anti-frosting have not yet been established. Herein, a series of nanostructured copper-zinc alloy SHSs are facilely constructed through ultrafast laser processing. The surface morphology can be properly tuned by adjusting the laser processing parameters. The relationship between the surface morphologies and condensate self-removal capability is investigated, and a guideline for laser processing parameterization for fabricating optimal anti-frosting SHSs is established. After 120 min of the frosting test, the optimized surface exhibits less than 70% frost coverage because the remarkably enhanced condensate self-removal capability reduces the water accumulation amount and frost propagation speed (<1 μm/s). Additionally, the material adaptability of the proposed technique is validated by extending this methodology to other metals and metal alloys. This study provides valuable and instructive insights into the design and optimization of metallic anti-frosting SHSs by ultrafast laser processing.

Robust superhydrophobic and icephobic surface based on Teflon AF coated multiscale hierarchical ZnO/Cu2O nanostructures

We demonstrate hetero-nanostructured rough surface with solution based hydrophobic coating for robust superhydrophobic (SH) properties. The copper foil was anodically etched to generate Cu2O micro-needles and then ZnO nanorods were grown on Cu2O to create ZnO/Cu2O micro-nano hierarchical rough surface. A thin layer of Teflon AF was applied as a low surface energy coating on the top of the hierarchical surface. These surfaces were characterized for their structural phases using the X-ray diffraction technique and multiscale hierarchical surface morphology was confirmed using FESEM and AFM techniques. Wetting properties like static and dynamic water contact angle (CA) were analyzed using the advancing receding contact angle (ARCA) technique. This surface shows superhydrophobic properties with static CA of 157° and a roll-off angle of 3°. The durability of the SH surfaces was examined by water droplet impact for a range of velocities. The droplet rebounding is consistently seen up to Weber number, We ∼ 220. When the SH surface was cooled to −10 °C, dropwise condensation takes place. In this case, self-propelled jumping of droplets via multiple coalescences of microdroplets was observed. In the freezing rain condition, this surface exhibits poor adhesion to ice formation demonstrating an icephobic property. The surface retains SH properties even to the UVC exposure of about 12 J/cm2. The fabrication of the SH surface involves solution-based processes which are scalable to mass production for applications ranging from enhanced heat conduction to water-repellent coatings.

Numerical simulation of the coalescence-induced polymeric droplet jumping on superhydrophobic surfaces

Self-propelled jumping of two polymeric droplets on superhydrophobic surfaces is investigated by three-dimensional direct numerical simulations. Two identical droplets of a viscoelastic fluid slide, meet and coalesce on a surface with contact angle 180 degrees. The droplets are modelled by the Giesekus constitutive equation, introducing both viscoelasticity and a shear-thinning effects. The Cahn-Hilliard Phase-Field method is used to capture the droplet interface. The simulations capture the spontaneous coalescence and jumping of the droplets. The effect of elasticity and shear-thinning on the coalescence and jumping is investigated at capillary-inertial and viscous regimes. The results reveal that the elasticity of the droplet changes the known capillary-inertial velocity scaling of the Newtonian drops at large Ohnesorge numbers; the resulting viscoelastic droplet jumps from the surface at larger Ohnesorge numbers than a Newtonian drop, when elasticity gives rise to visible shape oscillations of the merged droplet. The numerical results show that polymer chains are stretched during the coalescence and prior to the departure of two drops, and the resulting elastic stresses at the interface induce the jumping of the liquid out of the surface. This study shows that viscoelasticity, typical of many biological and industrial applications, affects the droplet behaviour on superhydrophobic and self-cleaning surfaces.

The prediction of energy conversion during the self-propelled jumping of multidroplets based on convolutional neural networks

The energy conversion efficiency (the ratio of the maximum jumping kinetic energy to the maximum surface energy released from droplet coalescence) is an essential indicator of the self-propelled jumping of droplets, which determines its value for applications in various fields. In the practical condensation process, the initial states of the multidroplets with different sizes and distributions have a significant effect on the energy conversion efficiency, but the mechanism behind this effect remains unclear. This paper reveals the effect of the initial states of droplets on the energy conversion efficiency of multidroplet jumping (mainly three droplets) from the perspective of energy conversion and the internal flow of the merged droplets. Different initial states will lead to different flow directions of the liquid microclusters inside the merged droplets. The consistency between the flow direction and the jumping direction will affect the energy conversion efficiency. To characterize this effect quantitatively, we construct a machine learning model based on a convolutional neural network to predict the energy conversion efficiency of multidroplet jumping with different initial distribution angles and radius ratios. The input of the neural network is the images of the initial state of the droplets, and the output is the energy conversion efficiency. After training, the neural network can predict the energy conversion efficiency of multidroplet jumping with an arbitrary initial state.

Self-Propelled Nanodroplet Jumping Enhanced by Nanocone Arrays: Implications for Self-Cleaning and Anti-Icing Surfaces

Self-propelled jumping of droplets on solid surfaces is essential for many natural and engineering processes. Specifically, rational design based on micro-/nanostructures enables a merged droplet to jump spontaneously after the coalescence of two droplets. However, self-jumping is highly challenging for nanodroplets due to the significant energy dissipation. Herein, we show the enhancement of the nanodroplets’ self-propelled jumping with the properly designed nanocone arrays on hydrophobic surfaces using molecular dynamics simulation. The self-propulsion of nanodroplets could be triggered by the nanocone decoration on a graphene-like flat surface. With the reducing nanocone apex angle, the critical intrinsic contact angle that the merged droplet could successfully jump decreases to roughly 100°. Importantly, a strong droplet initial position dependence of the jumping velocity is revealed. As nanodroplets initially locate in the gap between the nanocones, an enhancement of ∼245% for the jumping velocity is obtained compared to that on the nanocone tip. Essentially, high-efficiency self-jumping dynamical behaviors are achieved by the small energy dissipation, which is strongly dependent on both the liquid–solid interaction area and time. This work confirms the crucial role of the nanostructure in boosting the self-propelled nanodroplet jumping and provides a feasible way to passively enhance the nanodroplets’ jumping, which has potential applications for controllable droplet movement on functional surfaces.

Synergistic dispersal of plant pathogen spores by jumping-droplet condensation and wind

Plant pathogens are responsible for the annual yield loss of crops worldwide and pose a significant threat to global food security. A necessary prelude to many plant disease epidemics is the short-range dispersal of spores, which may generate several disease foci within a field. New information is needed on the mechanisms of plant pathogen spread within and among susceptible plants. Here, we show that self-propelled jumping dew droplets, working synergistically with low wind flow, can propel spores of a fungal plant pathogen (wheat leaf rust) beyond the quiescent boundary layer and disperse them onto neighboring leaves downwind. An array of horizontal water-sensitive papers was used to mimic healthy wheat leaves and showed that up to 25 spores/h may be deposited on a single leaf downwind of the infected leaf during a single dew cycle. These findings reveal that a single dew cycle can disperse copious numbers of fungal spores to other wheat plants, even in the absence of rain splash or strong gusts of wind.

Solar anti-icing surface with enhanced condensate self-removing at extreme environmental conditions

The inhibition of condensation freezing under extreme conditions (i.e., ultra-low temperature and high humidity) remains a daunting challenge in the field of anti-icing. As water vapor easily condensates or desublimates and melted water refreezes instantly, these cause significant performance decrease of most anti-icing surfaces at such extreme conditions. Herein, inspired by wheat leaves, an effective condensate self-removing solar anti-icing/frosting surface (CR-SAS) is fabricated using ultrafast pulsed laser deposition technology, which exhibits synergistic effects of enhanced condensate self-removal and efficient solar anti-icing. The superblack CR-SAS displays superior anti-reflection and photothermal conversion performance, benefiting from the light trapping effect in the micro/nano hierarchical structures and the thermoplasmonic effect of the iron oxide nanoparticles. Meanwhile, the CR-SAS displays superhydrophobicity to condensed water, which can be instantly shed off from the surface before freezing through self-propelled droplet jumping, thus leading to a continuously refreshed dry area available for sunlight absorption and photothermal conversion. Under one-sun illumination, the CR-SAS can be maintained ice free even under an ambient environment of -50 °C ultra-low temperature and extremely high humidity (ice supersaturation degree of ∼260). The excellent environmental versatility, mechanical durability, and material adaptability make CR-SAS a promising anti-icing candidate for broad practical applications even in harsh environments.

Facile fabrication of high-aspect-ratio super-hydrophobic surface with self-propelled droplet jumping behavior for atmospheric corrosion protection

The super-hydrophobic surface with the self-propelled droplet jumping behavior has a promising application prospect in the field of atmospheric corrosion protection. Researchers have been devoted to realizing the self-propelled droplet jumping behavior by regulation of environmental and structure parameters. Unfortunately, these studies results are still lacking obviously. Herein, we facile fabricate the super-hydrophobic surface with high-aspect-ratio nanorod arrays by simple hydrothermal modification technique. The basic characteristics of the prepared surface are described by scanning electron microscopy, X-ray diffractometer, X-ray photoelectron spectroscopy and contact angle meter. In addition, the self-propelled droplet jumping behavior is observed and the behavior is analyzed by energy conservation and evaluated by droplet surface coverage. On this basis, the atmospheric corrosion protection performance of the surfaces is measured by electrochemical test. This work provides a new fabricate method and design strategy of super-hydrophobic surfaces with self-propelled droplet jumping behavior and excellent atmospheric corrosion protection performance.

A comparative study of the self-propelled jumping capabilities of coalesced droplets on RTV surfaces and superhydrophobic surfaces

Understanding the mechanism of coalescence-induced self-propelled jumping behavior provides distinct insights in designing and optimizing functional coatings with self-cleaning and anti-icing properties. However, to date self-propelled jumping phenomenon has only been observed and studied on superhydrophobic surfaces, other than those hydrophobic surfaces with weaker but fairish water-repellency, for instance, vulcanized silicon rubber (RTV) coatings. In this work, from the perspective of thermodynamic-based energy balance aspect, the reason that self-propelled jumping phenomenon does not happen on RTV coatings is studied. The apparent contact angles of droplets on RTV coatings can be less than the theoretical critical values therefore cannot promise energy surplus for the coalesced droplets onside. Besides, on RTV and superhydrophobic surfaces, the droplet-size dependent variation characteristics of the energy leftover from the coalescence process are opposite. For the droplets coalescing on RTV coatings, the magnitudes of energy dissipations are more sensitive to the increase in droplet size, compared to that of released surface energy. While for superhydrophobic coatings, the energy generated during the coalescence process can be more sensitive than the dissipations to the change in droplet size.

Exceptional atmospheric corrosion inhibition performance of super-hydrophobic films based on the self-propelled jumping behavior of water droplets

Super-hydrophobic surfaces have attracted much attention for their potential applications based on the lotus effect, especially in corrosion protection. However, the lotus effect has limited application given its high dependence on external forces, such as gravity and wind force. The self-propelled jumping behavior of water droplets, a newly found phenomenon over super-hydrophobic surfaces, would bring an alternative mechanism to atmospheric corrosion protection. Two different super-hydrophobic surfaces with a cone-shaped array microstructure and a flower-shaped hierarchical microstructure, respectively, were designed over copper substrate with an electrodeposition method. The dynamic growth and coalescence behavior of droplets were compared over the two super-hydrophobic surfaces. The cone-shaped array microstructure facilitates the self-jumping behavior of micro-droplets over the super-hydrophobic surface. In further, corrosion protection performance of the super-hydrophobic surfaces was examined after condensation in a simulated atmospheric environment. It was proven that the self-jumping behavior of micro-droplet helps remove the droplet over super-hydrophobic surfaces, thereby minimizing the likelihood of any subsequent corrosion behavior. This study demonstrates a novel corrosion protection mechanism for super-hydrophobic surfaces, and provides instructions for designing highly effective super-hydrophobic surfaces for corrosion protection.

Coalescence-induced self-propelled jumping of three droplets on non-wetting surfaces: Droplet arrangement effects

Coalescence-induced self-propelled droplet jumping has attracted extensive attention because of its huge potential for enhancing dropwise condensation heat transfer, anti-icing, and self-cleaning. Most previous studies focus on binary droplet jumping, with little research on the more complex and realistic multi-droplet jumping. As a result, the effect of the droplet arrangement on the multi-droplet jumping phenomenon remains unclear. In this paper, the self-propelled jumping of three droplets with different arrangements (two droplets are fixed, and the location of the third one is changed) is numerically simulated, and energy conversion efficiency is studied. Based on two different forming mechanisms, region I (the coalescence between the lateral droplets forms the central liquid bridge) and region II (the changed interface curvature of central droplets turns into the central liquid bridge under surface tension) are defined in three-droplet arrangements. The liquid bridges exhibit different dynamic behaviors in two particular regions, even the jumping velocity is determined by the moving synchronicity of liquid bridges in each region. The critical distribution angle that leads to the overall nonmonotonic change of jumping velocities ranges between 110° and 120° (0.02 ≤ Oh ≤ 0.16). Compared with the symmetry of the droplet configuration, the geometry of the droplet arrangement plays a dominate role in the nonmonotonic change. The maximum energy conversion efficiency is just over 6.5% and the minimum is just under 3%. The findings of this study not only reveal how the arrangement affects ternary droplet jumping and explain the phenomenon that cannot be explained before, but deepens our understanding of multi-droplet jumping as well.

Effect and relational analysis of physical parameters on coalescence-induced self-propelled jumping of droplets

Coalescence-induced self-propelled jumping of droplets on superhydrophobic surfaces has been widely concerned because of a great number of potential applications such as in the enhancement of condensation heat transfer, self-cleaning and anti-icing. The droplet jumping phenomenon exists in a gas-liquid two-phase system, and the physical parameters of fluid cannot be ignored. However, there are few reports on the influence of physical parameters on droplet jumping dynamics at present. In this paper, the three-dimensional volume-of-fluid method is used to simulate the coalescence-induced self-propelled jumping behaviors of droplets, then the energy terms are studied, and finally the grey relational analysis method is used to calculate the relation degree of the change of physical parameters (the viscosity and the density) to the real jumping velocity and the real solid-liquid contact time at the droplet departure time, respectively. Based on the changing trend of jumping velocity, the process of coalescence-induced self-propelled jumping can be divided into four stages, namely, the expansion of liquid bridge, the impact between the liquid bridge and the surface, the droplet departure from the surface, and the deceleration and oscillation in the air. Under the condition of dimensionless time, the dynamic characteristics of coalescence and jumping of droplets are affected only by &lt;i&gt;Oh&lt;/i&gt; number, which is independent of the viscosity and the density. In addition, the change of &lt;i&gt;Oh&lt;/i&gt; number only affects the above third stage of droplet departure from the surface. Under the condition of real time, the varied viscosity has no connection with the real time of droplet coalescence, and it only changes the real time of the third stage before droplet jumping. Meanwhile, the dimensionless jumping velocity decreases with &lt;i&gt;Oh&lt;/i&gt; number increasing, while the real jumping velocity increases when the viscosity and the density both descend. According to the calculated results of grey relational degree, the relation between the change of viscosity and the real jumping velocity is greater, while the relation between the change of density and the real contact time is greater. This work not only is favorable for a better understanding of droplet jumping, but also provides more ideas and theoretical bases for follow-up relevant studies.

Toward Passive Defrosting with Heterogeneous Coatings

A large amount of energy is lost in industrial active deicing. One problem is that water retention on the surface after ice melting decreases the overall heat-transfer coefficient by up to 20%. The Miljkovic group utilizes heterogeneous biphilic surfaces to enhance defrosting performance. They avoid water retention as the slush is rapidly drawn toward the hydrophilic regions before it completely melts.

Macrotextures-enabled self-propelling of large condensate droplets

On superhydrophobic surfaces, small condensate droplets exhibit a preferred self-propelled jumping by a coalescence-induced energy release, but large condensate droplets in several millimeters remain immobile. The accumulation of large condensate droplets leads to many problems such as shielding the growth of small droplets and increasing the thermal resistance of condensate. In this work, we present a largely unexplored strategy for enhancing the self-removal of large condensate droplets by the rational design of the millimetric macro-textured groove arrays (MGAs). In the condensation process, such macrotextures effectively create gradients in both concentration and diffusion flux of water vapor along the groove height, leading to a varying nucleation rate along the groove height. Facilitated by this preferential nucleation, large condensate droplets are objected to a Laplace pressure and undergo a self-propulsion to detach from the surface with ~50% decrease in diameter compared with the superhydrophobic surface without macro-textured groove arrays. Our findings enrich the fundamental understanding of how macrotextures regulate microscopic wetting state, and such macrotextures can be combined with the state-of-the-art micro/nano fabrication technologies for energy-water nexus applications.

Delayed Frost Growth on Nanoporous Microstructured Surfaces Utilizing Jumping and Sweeping Condensates.

Self-propelled jumping of condensate droplets (dew) enables their easy and efficient removal from surfaces and is essential for enhancing the condensation heat transfer coefficient and for delaying the frost growth rate on supercooled surfaces. Here, we report the droplet-jumping phenomenon using nanoporous vertically aligned carbon nanotube (VA-CNT) microstructures grown on smooth silicon substrates and coated with poly-(1H, 1H, 2H, 2H-perfluorodecylacrylate) (pPFDA). We also report droplet-sweeping phenomenon on horizontally mounted surfaces, concluding that the frost surface coverage area and the frost growth rates observed with the droplet-sweeping phenomenon are much lower than those that are observed with the droplet-jumping phenomenon alone. We also investigate the fundamentals of droplet-jumping and the frost growth phenomena using line-shaped, hollow-cylindrical, and cylindrical microstructures, comparing the frost surface coverage area and the ice-bridging times during condensation-frosting, prolonged condensation-frosting, and direct-frosting. We find that the closely spaced thin line-shaped microstructures and hollow-cylindrical microstructures are optimal for frost coverage reduction because of their ability to exhibit droplet-jumping and droplet-sweeping phenomena. We observe that adding nonuniform roughness on top of the microstructures leads to jumping-associated droplet-sweeping on supercooled surfaces. Here, we report the evaporation of an already frozen droplet because of freezing of a supercooled condensate droplet in its close vicinity, enabling the Cassie-Baxter state frost growth and enhancing defrosting efficiency. Finally, we discuss the dynamic defrosting behavior of the pPFDA-coated VA-CNT microstructures, concluding that the small gaps (spacings) between the microstructures not only enable dewetting transitions of droplets but also promote the Cassie-Baxter state frost formation.

Competing Effects between Condensation and Self-Removal of Water Droplets Determine Antifrosting Performance of Superhydrophobic Surfaces.

Preventing condensation frosting is crucial for air conditioning units, refrigeration systems, and other cryogenic equipment. Coalescence-induced self-propelled jumping of condensed microdroplets on superhydrophobic surfaces serves as a favorable strategy against condensation frosting. In previous reports, efforts were dedicated to enhance the efficiency of self-propelled jumping by constructing appropriate surface structures on superhydrophobic surfaces. However, the incorporation of surface structures results in larger area available for condensation to occur, leading to an increase in total amount of condensed water on the surface and partially counteracts the effect of promoted jumping on removing condensed water from the surface. In this paper, we focus on the competing effects between condensing and self-propelled jumping on promoting and preventing water accumulation, respectively. A series of micro- and nanostructured superhydrophobic surfaces are designed and prepared. The condensation process and self-propelled jumping behavior of microdroplets on the surfaces are investigated. Thousands of jumping events are statistically analyzed to acquire a comprehensive understanding of antifrosting potential of superhydrophobic surfaces with self-propelled jumping of condensed microdroplets. Further frosting experiments shows that the surface with the lowest amount of accumulated water exhibits the best antifrosting performance, which validates our design strategy. This work offers new insights into the rational design and fabrication of antifrosting materials.

Dynamic and energy analysis of coalescence-induced self-propelled jumping of binary unequal-sized droplets

The coalescence-induced self-propelled droplet jumping on superhydrophobic surfaces has a large number of potential applications such as enhancement of condensation heat transfer, self-cleaning, and anti-icing, which becomes a current hotspot. At present, most of the research studies focus on the self-propelled jumping of two identical droplets; however, the jumping induced by unequal-sized droplets is much closer to actuality. In this paper, the coalescence-induced self-propelled jumping of binary unequal-sized droplets is simulated and all energy terms are studied. The normalized liquid bridge width induced by unequal-sized droplets is a function of the square root of the normalized time, and the maximum jumping velocity is a function of the radius ratio as well. The maximum jumping velocity descends with the decrease in the radius ratio and contact angle, and the critical radius ratio shows an upward trend with the decrease in the contact angle. Furthermore, all energy terms decline with the decrease in the radius ratio. The effective energy conversion rate of binary equal-sized jumping is very low, less than 3% in our results. This rate of binary unequal-sized jumping further reduces due to the existence of asymmetric flow. This work helps for a better understanding of the characteristics of coalescence-induced self-propelled droplet jumping.