Coalescence of two droplets on a solid substrate is an interfacial phenomenon that imposes the challenges of capturing the complex contact line motion and energy interaction between the solid-liquid interface. Recent investigations on the coalescence of polymeric droplets on a solid substrate have reported strong disagreements; the heart of the issue is whether coalescence of polymeric drops is similar to that of Newtonian fluid and is independent of molecular relaxation, or whether the role of entanglement of polymeric chains leads to a transition kinetics different from that of Newtonian fluid. Via this article, we resolve the disagreements through a discussion on the effects of merging method on the dominant forces governing the coalescence process, i.e., inertia, dissipation, and relaxation. In this regard, two methods of merging have been identified, namely droplet spreading method (DSM) and volume filling method (VFM). Our study unveils that the coalescence dynamics of polymeric drops is not universal and in fact, is contingent of the method by which the coalescence is triggered. Additionally, we demonstrate the spatial features of the bridge at different time instants by a similarity analysis. We also theoretically obtain a universal bridge profile by employing the similarity parameter in a modified thin film lubrication equation for polymeric fluids.

Twin fluid atomizers utilize the kinetic energy of high speed gases to disintegrate a liquid sheet into fine uniform droplets. Quite often, the gas streams are injected at unequal velocities to enhance the aerodynamic interaction between the liquid sheet and surrounding atmosphere. In order to improve the mixing characteristics, practical atomizers confine the gas flows within ducts. Though the liquid sheet coming out of an injector is usually annular in shape, it can be considered to be planar as the mean radius of curvature is much larger than the sheet thickness. There are numerous studies on breakup of the planar liquid sheet, but none of them considered the simultaneous effects of confinement and unequal gas velocities on the spray characteristics. The present study performs a nonlinear temporal analysis of instabilities in the planar liquid sheet, produced by two co-flowing gas streams moving with unequal velocities within two solid walls. The results show that the para-sinuous mode dominates the breakup process at all flow conditions over the para-varicose mode of breakup. The sheet pattern is strongly influenced by gas velocities, particularly for the para-varicose mode. Spray characteristics are influenced by both gas velocity and proximity to the confining wall, but the former has a much more pronounced effect on droplet size. An increase in the difference between gas velocities at two interfaces drastically shifts the droplet size distribution toward finer droplets. Moreover, asymmetry in gas phase velocities affects the droplet velocity distribution more, only at low liquid Weber numbers for the input conditions chosen in the present study.

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Low sensitivity to rheological properties of fluid and ability to produce fine sprays at low liquid pressure make airblast atomizers a preferred choice to process viscous liquids. Airblast atomizers essentially employ kinetic energy of coflowing gases to disintegrate a liquid sheet into fine spray. The present study employs the perturbation technique to carry out nonlinear investigation of the sinuous mode of instability in a thin planar viscous liquid sheet sandwiched between two inviscid gas streams moving at equal velocities. This paper analyzes temporal instability as well as droplet characteristics for a range of Reynolds numbers, Weber numbers, gas to liquid density ratios, and velocity ratios and reports the dual behavior of liquid viscosity at different operating conditions. For higher gas to liquid velocity ratios, this study identifies three regimes at all Weber numbers and gas to liquid density ratios: the first regime represents the stabilizing effect of viscosity at low Reynolds numbers, the second regime indicates the destabilizing effect of viscosity at intermediate Reynolds numbers, and the third regime further depicts the stabilizing effect of viscosity at high Reynolds numbers. However, for low gas to liquid velocity ratios, the third zone disappears at lower Weber numbers and gas to liquid density ratios, and the effect of viscosity is characterized by two regimes representing the weak stabilizing and destabilizing effect at low and relatively higher Reynolds numbers, respectively. Investigation of spray characteristics reveals that an increase in liquid viscosity produces relatively larger droplets at all flow conditions.

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The magnetic nanorobots, primarily composed of ferromagnetic materials, have been extensively investigated for their potential applications in cellular diagnostics and therapy. However, because of the substantial magnetic remanence exhibited by ferromagnetic materials, the magnetic stability of these nanorobots is a matter of serious concern. Here, we have designed and developed superparamagnetic iron oxide nanoparticles’(SPIONs) functionalized nanorobots (SPIONs-NR), a unique system that is highly stable against magnetic agglomeration. This kind of arrangement of random magnetic moments adhering to the nanorobot’s surface is relatively new and has not been previously explored in terms of fundamental physics and biomedical applications. We have carefully analyzed the various dynamical aspects of these functionalized nanorobots by studying their precession angle as a function of applied frequency at different magnetic fields. Furthermore, these functionalized nanorobots can be controllably maneuvered in the extracellular matrix by the application of rotating magnetic fields of comparatively lower magnitudes (usually < 50 G) to selectively target and annihilate malignant tissues via magnetic hyperthermia-induced localized heating, and therefore, making SPIONs-NR promising candidates in modernizing advanced nanomedicine research.

A numerical study is performed on simultaneous heat and mass transfer from a shrouded vertical nonisothermal variable height fin array, representing dehumidification process under natural convection. Fluid properties are treated as uniform, and the fluid is assigned to comply with Boussinesq approximation to include the effect of density variation with temperature and concentration. Semi-implicit method for the pressure linked equations revised (SIMPLER) algorithm is adopted to resolve pressure and velocity coupling. A detailed parametric investigation of fin spacing, variable fin height, and fin tip to shroud clearance for a range of thermal and mass Grashof number is undertaken. Results indicate that in case of smaller fin spacing, involving fin length of 0.3 m, coefficients of sensible and latent heat transfer increase with the decreasing variable height (H1*) of fin and become maximum at H1*=0.5, for all thermal and mass Grashof numbers considered presently. Further, total heat transfer analysis on a particular base length due to sensible heat shows a maximum of 24.4% enhancement, whereas same due to the latent heat shows a maximum of 25.8% enhancement, depending on the values of clearance. Induced velocities also increase with the decreasing variable height of fin (H1*), which influences the heat and mass transport. The output parameters of this analysis, like induced velocities and overall Nusselt numbers due to the sensible and latent heat, are correlated with the governing parameters. The correlation coefficients are found to be in a range from 0.97 to 0.99.