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Investigation of the Phenomenon of Ferrofluid-Based Marble on a Surface under the Influence of a Magnetic Field

Akbari, Mohamad Javad | 2025

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 58491 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Shafii, Mohammad Behshad; Bijarchi, Mohammad Ali
  7. Abstract:
  8. Liquid marbles are droplets coated with hydrophobic particles that, due to their unique characteristics, have attracted considerable attention in recent studies in the field of fluid mechanics. These droplets can be used on both hydrophobic and even hydrophilic surfaces without breaking or undergoing significant deformation, thanks to their hydrophobic coating. This research is the first to comprehensively investigate the dynamics of liquid marbles’ impact and bouncing behavior on a surface. Additionally, it examines the effects of parameters such as impact velocity, marble diameter, core viscosity, and magnetic field on the parameters describing the dynamics of the marble during the bouncing phenomenon. In the first phase of this thesis, the behavior of simple marbles in the absence of a magnetic field upon impact with a hydrophilic surface is experimentally studied and analyzed. The impact regimes of marbles on the surface are initially examined at various Weber numbers, and the process continues with a focus on the bouncing behavior of the marbles from the surface. The transformation of the marble’s kinetic, gravitational, and surface potential energies during the continuous process of impact and bounce is thoroughly investigated. The effects of dimensionless Weber and gravitational Bond numbers on parameters describing the dynamic behavior of marbles during impact, including bounce time, maximum spreading time, maximum spreading ratio, maximum elongation ratio, and restitution coefficient, are analyzed. The differentiation in behavior at low and moderate Weber numbers is also considered. Additionally, relationships are proposed for predicting various parameters based on experimental data. Furthermore, using scaling analysis, relationships for bounce time and maximum spreading ratio are developed. The results indicate that different parameters exhibit distinct behaviors at lower and moderate Weber numbers, with differences particularly evident in bounce time, maximum spreading ratio, and restitution coefficient. In the second phase of the thesis, the oscillatory and bouncing behavior of liquid marbles in the post-bounce process after impact with a hydrophilic surface is experimentally investigated. The results are then compared with the outcomes from a mass-spring-damper model, and the effects of dimensionless Weber, gravitational Bond, and ohnesorge numbers on the parameters describing the oscillatory behavior are studied. The mass-spring-damper model is employed in two oscillatory phases for the marbles: (a) free oscillation after the marble bounces from the surface, continuing until the next impact, and (b) oscillation of the liquid marble after the last bounce from the surface until it comes to rest. The maximum error between the model results and experimental data is less than 5%. The findings show that increasing the ohnesorge number, gravitational Bond number, and Weber number increases, decreases, and increases the damping ratio, respectively. Moreover, the capability of this method to measure the physical properties of the marble's core fluid using its oscillatory behavior after bouncing is emphasized. In the final part of this phase, the number of successive bounces of the liquid marble is examined, and experimental results are matched with the developed analytical equations, which fully support the trends observed in the data. As the ohnesorge number increases, the number of bounces decreases due to increased viscous dissipation. In the third phase of this thesis, the dynamic behavior of liquid marbles based on ferrofluid when impinging on a surface (hydrophilic and hydrophobic) under the influence of a magnetic field is experimentally studied. Initially, the impact regimes of magnetic marbles at various Weber and magnetic Bond numbers are investigated, and three regimes — bouncing, non-bouncing, and rupture — are identified. The boundaries between these regimes are also recognized, and relationships among them are proposed. The effects of the magnetic field during the pre-impact phase, specifically on the impact velocity and the marble’s shape, are analyzed. An analytical relationship based on energy balance for predicting the impact velocity in the presence of a magnetic field is developed, which accurately follows the experimental data. The effects of the magnetic field on the maximum spreading time are then analyzed, and both the direct and indirect effects of the magnetic field are discussed. Finally, the most important impact parameter, the maximum spreading ratio, is considered. This section presents a novel analysis of the effect of the magnetic field on the results, as well as the development of an analytical model based on energy balance to estimate the maximum spreading ratio, alongside an analysis of the energy exchanges occurring during the impact process
  9. Keywords:
  10. Liquid Marbles ; Mass-Spring-Damper Model ; Ferrofluid Marble ; Weber Number ; Collision ; Magnetic Bond Number ; Marble Oscillation ; Marble Bouncing ; Magnetic Marble

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