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Compound and simple droplets have been studied and appeared in many life applications, e.g., drug processing and microfluidic systems. Many studies have been conducted on the thermocapillary effects on simple droplets, but similar studies on compound droplets are quite rare. Filling this missing gap, this paper presents the front-tracking-based simulation results of the thermocapillary effects on compound droplets in a certain limited domain. The compound droplet consists of a single inner core that is initially concentric with the outer one. Various dimensionless parameters including Reynolds number from 1 to 50, Marangoni number from 1 to 100, droplet radius ratio from 0.3 to 0.8, and viscosity ratios from 0.1 to 6.4 are varied to reveal their influences on the migration of a compound droplet from cold to hot regions. Initially, the inner droplet moves faster than the outer one, and when the leading surface of the inner droplet touches the outer one, the inner and outer droplets migrate at the same speed. The effects of these parameters on the compound droplet eccentricity are also considered.

Compound droplets with different sizes are increasingly used in industrial production and academic research. This study aims to improve understanding of the dynamical behaviors of the compound droplet moving in microchannels. The compound droplet consisting of one inner core is initially concentric and placed at the entrance of a circular channel with a cone at the downstream region. Following this primary channel is a secondary channel that is circular and straight. Manipulation of the droplet is assisted by a flow introduced via the gap between two channels. The numerical results show that when passing through these confined channels, the droplet experiences a finite deformation or breakup mode. In each mode, the deformation or breakup of the compound droplet is also different when changing the values of the parameters including the capillary number, the ratio of the droplet radii, the ratio of the interfacial tension, the size of the secondary channel, the gap size and the cone angle. The finitely deformed droplet can be either nearly ellipsoidal with a deformation index D of around unity (i.e., first deformation mode) or highly elongated with a high D (i.e., second deformation mode). Breakup of the compound droplet happens to the outer droplet, and the breakup point is located either in front of the inner droplet (i.e., first breakup mode) or behind it (i.e., second breakup mode). The simple droplets yielded in the first breakup mode has a higher total volume than those in the second breakup mode. It is found that the droplet experiences the first deformation mode to the first breakup mode, then the second deformation mode and finally the second breakup mode when Ca increases. The regime diagrams of these modes, based on these parameters, are also presented.

A compound droplet deforming in a constricted tube widely appears in drug delivery and microfluidic devices. In such a constriction, an indentation can present at the trailing surface of the droplet. However, this aspect has not been fully investigated and understood so far. This study focuses on the effects of some dimensionless parameters on the negative curvature, i.e., indentation, at the trailing surface of a compound droplet moving through a constricted tube. The presence of the constriction at the middle of the tube length enhances the droplet indentation. Numerical results were obtained for the capillary number Ca (varied in range of 0.1–1.0), the inner-to-outer droplet radius ratio R21 (varied in range of 0.2–0.9), the droplet-to-tube radius ratio R10 (varied in range of 0.2–0.9), the inner-to-outer interfacial tension coefficient ratio σ21 (varied in range of 0.1–6.4), and the normalized depth of the constriction d/R (varied in range of 0.0–0.8). The results reveal that the most influencing factor is Ca, increasing its value leads to the increment of the maximum indentation at the trailing surface of the inner and outer droplets. The indentation is also increased with increasing the value of R10 and d/R. In contrast, increasing R21 results in a decrease in the indentation at the trailing surface of the outer droplet. When increasing σ21, the indentation at the trailing surface of the inner one is quickly suppressed, while the outer droplet is minorly affected. We also point out the patterns of the trailing surface of the inner and outer droplets and their transitions from one to the other patterns in the diagrams based on these parameters.

In this paper, we numerically investigate the dynamics of a compound droplet driven by surface tension variation induced by a thermal gradient in a sinusoidal constriction tube. Initially, the compound droplet with a concentric inner core is spherical and placed in the constriction's upstream region at a low temperature. As time progresses, it migrates downstream with a high temperature. Due to the constriction, the droplet is slowed down in the upstream region and accelerated again right after passing the constriction. This acceleration maximizes the eccentricity. However, the constriction results in an increase in the maximum eccentricity when increasing its depth to a value corresponding to the size of the tube neck, which is greater than or equal to the droplet size. Effects of various parameters, e.g., the Marangoni number Ma, the capillary number Ca, and the radius ratio Rio, are studied. It is found that increasing the Ma number or decreasing the Ca number reduces the maximum eccentricity and prolongs the travel time, i.e., the arrival time, from the upstream to the downstream. A similar reduction in the maximum eccentricity also occurs with the increased Rio ratio. Effects of these parameters on the migration velocity are also revealed.

Collisions of multi-core compound droplets have generated substantial interest in recent years because of their applications in the industry and academia. This study uses the front-tracking method to simulate the transition between the two collision modes of multi-core compound droplets in a simple shear flow. Compound droplets initially assumed identical have two sub-droplets of equal size. Given the shear flow, the droplets collide with one another and behave in two main modes, namely, passing-over and reversing. In the passing-over mode, the droplets pass over one another after coming into contact. The reversing mode appears with two compound droplets returning to their initial sides after the collision. During collision, the sub-droplets circulate approximately at the center of their enclosing outer droplets. Some parameters, including capillary number Ca, viscosity ratios μio and μmo, radius ratio Rio of the sub-droplets to the outer droplets, and sub-droplet angle a0, are investigated to determine their impact on these modes of collisions. We find that the transition from a reversing to passing-over mode occurs when we increase the value of Ca from 0.01 to 0.63}, {tiRio from 0.20 to 0.475, and μio and μmo in the range of 0.16-6.3. However, an increase in the value of a0 between -75° and 90° leads to a change from a passing-over to reversing mode. Diagrams of the colliding modes are also presented in this research.

In this study, the retraction and solidification of a fluid filament are studied by a front-tracking method/finite difference scheme. The interface between two phases is handled by connected points (Lagrangian grid), which move on a fixed grid domain (Eulerian grid). The Navier-Stokes and energy equations are solved to simulate the problem. Initially, the fluid filament has a shape as half of a cylindrical capsule contact with a cold flat surface. We consider the effect of the aspect ratio (Ar) on the solidification of the fluid filament. It is found that an increase in the aspect ratio (Ar) in the range of 2 – 14 causes the retraction length to increase. The rate of the solidification of a fluid filament decreases when the Ar ratio increases. The solidification time, the solidification height and the tip angle of the fluid filament under the influence of the aspect ratio are also considered. After complete solidification, a small protrusion on the top of the solidified fluid filament is found.

Introduction: Compound fluid filaments appear in many applications, e.g., drug delivery and processing or microfluidic systems. This paper focuses on the numerical simulation of an incompressible, immiscible, and Newtonian fluid for the contraction process of a fluid compound filament by solving the Navier-Stokes equations. The front-tracking method is used to solve this problem, which uses connected segments (Lagrangian grid) that move on a fixed grid (Eulerian grid) to represent the interface between the liquids. Methods: The interface points are advected by the velocity interpolated from those of the fixed grid using the area weighting function. The coordinates of the interface points are used to construct the indicators specifying the different fluids and compute the interfacial tension force. Results: The simulation results show that under the effects of the interfacial tension, the capsuleshaped filament can transform into a spherical compound droplet (i.e., non-breakup) or can break up into smaller spherical compound and simple droplets (i.e., breakup). When the density ratio of the outer to middle fluids increases, the filament changes from non-breakup to breakup upon contraction. Conclusion: Increasing the density ratio enhances the breakup of the compound filament during contraction. The breakup is also promoted by increasing the initial length of the filament.

Palliative care, specialized medical care for seriously ill people, has been demonstrated to reduce pain and symptoms while increasing satisfaction with health care, yet National U.S. surveys show that less than 10% of people are aware of palliative care. Equally concerning, among those that are familiar with palliative care, many believe it to be synonymous with hospice. The purpose of this study is to determine if theoretically driven videos of palliative care patients can improve knowledge of palliative care. The patient stories were modeled following key components of Theory of Reasoned Action and were edited to approximately three minutes in length. We recruited 161 adults age 50 and older from senior centers, assisted living, and other community-based sites. Each participant completed a survey of 18 questions about their knowledge of palliative care and intentions to elect palliative care services. After viewing three role model videos, participants completed a post-test comprised of the same set of questions. Results of the pre-post tests revealed that palliative care knowledge increased by 115%; t(126)=11.99, p