301 research outputs found
Complementary technologies required for 21st century additive manufacturing product insertion.
Microfluidos: ¿cuánto hay de nuevo?
Microfluidic groups many branches of Physics ranging from Fluid Dynamics to Electronics and closely linked with Biology Sciences. Its interdisciplinary character is a distinctive feature, as the times we are living today. In the last ten years, along with the development of biotechnology, microelectronics, materials science and many others, the use of microfluidic devices has increased remarkably. Few scientists in Cuba have worked in topics related with Microfluidics; nevertheless, there is no reference in which this activity has been pointed out explicitly. This article aims to introduce some terms and divulge basic aspects of Microfluidics; besides this, another article will be published with most applications of Microfluidics that could be of interest for Cuba
A Comparison of Drug Delivery into Skin Using Topical Solutions, Needle Injections and Jet Injections
Microfluidic jet impacts on deep pools: transition from capillary-dominated cavity closure to gas-pressure-dominated closure at higher Weber numbers
Studying liquid jet impacts on a liquid pool is crucial for various engineering and environmental applications. During jet impact, the free surface of the pool deforms and a cavity is generated. Simultaneously, the free surface of the cavity extends radially outward and forms a rim. Eventually the cavity collapses by means of gas inertia and surface tension. Our numerical investigation using an axisymmetric model in Basilisk C explores cavity collapse dynamics under different impact velocities and gas densities. We validate our model against theory and experiments across a previously unexplored parameter range. Our results show two distinct regimes in the cavity collapse mechanism. By considering forces pulling along the interface, we derive scaling arguments for the time of closure and maximum radius of the cavity, based on the Weber number. For jets with uniform constant velocity from tip to tail and, the cavity closure is capillary-dominated and happens below the surface (deep seal). In contrast, for the cavity closure happens above the surface (surface seal) and is dominated by the gas entrainment and the pressure gradient that it causes. Additionally, we monitor gas velocity and pressure throughout the impact process. This analysis reveals three critical moments of maximum gas velocity: before impact, at the instant of cavity collapse and during droplet ejection following cavity collapse. Our results provide information for understanding pollutant transport during droplet impacts on large bodies of water, and other engineering applications, like additive manufacturing, lithography and needle-free injections.</p
Gas density influences the transition from capillary collapse to surface seal in microfluidic jet impacts on deep pools
Studies of liquid jet impacts onto a deep liquid pool are of great significance for a multitude of engineering and environmental applications. During jet impact, the free surface of the pool deforms and a cavity is generated. Simultaneously, the free surface of the cavity extends radially outward and forms a rim. Eventually the cavity collapses by means of gas inertia and surface tension. In this work we study numerically such cavity collapse, under different impact velocities and ambient gas density conditions. An axisymmetric numerical model, based on the volume of fluid method is constructed in Basilisk C. This model is validated by qualitative and quantitative comparison with theory and experiments, in a parameter range that has not been previously explored. Our results show two distinct regimes in the cavity collapse mechanism. By considering forces pulling along the interface, we derive scaling arguments for the time of closure and maximum radius of the cavity, based on the Weber number. For jets with uniform constant velocity from tip to tail and the cavity closure is capillary dominated and happens below the surface (deep seal). In contrast, for the cavity closure happens above the surface (surface seal) and is dominated by the gas entrainment and the pressure gradient that it causes. Our results provide information for understanding pollutant transport during droplet impacts on large bodies of water, and other engineering application, like additive manufacturing, lithography and needle-free injections
Cavitation induced by pulsed and continuous-wave fiber lasers in confinement
Bubbles generated with lasers under confinement have been investigated for
their potential use as the driving mechanism for liquid micro-jets in various
microfluidic devices, such as needle free jet injectors. Here, we report on the
study of bubble formation by a continuous-wave (CW) and a pulsed laser inside
an open-ended microfluidic capillary. This results in a direct comparison
between bubbles generated by laser sources emitting light in different time
scales (ms and ns). The bubble kinetics represents an important parameter
because it determines the available kinetic energy for a subsequent liquid jet.
We show that the bubble growth rate increases linearly with the delivered
energy for both the CW and the pulsed laser. Experiments show that at equal
absorption coefficient, the bubble growth for both lasers is similar, which
indicates that they can be used interchangeably for a jet generation. However,
bubbles generated by a CW laser require more optical energy, which is due to
heat dissipation. Furthermore, the bubbles generated by the CW laser show a
slightly larger variation in size and growth rate for identical initial
conditions, which we attribute to the stochastic nature of thermocavitation
Laser beam properties and microfluidic confinement control thermocavitation
Thermocavitation, the creation of a vapor bubble by heating a liquid with a continuous-wave laser, has been studied for a wide range of applications. Examples include the development of an actuator for needle-free jet injectors, as the pumping mechanism in microfluidic channels and nanoparticle synthesis. Optimal use in these applications requires control over the bubble dynamics through the laser power and beam radius. However, the influence of the laser beam radius on the bubble characteristics is not fully understood. Here, we present a way to control the beam radius from an optical fiber by changing the distance from the glass-liquid interface. We show that the increase in the beam size results in a longer nucleation time. Numerical simulations of the experiment show that the maximum temperature at nucleation is 237 ± 5 °C and independent of laser parameters. Delayed nucleation for larger beam sizes results in more absorbed energy by the liquid at the nucleation instant. Consequently, a larger beam size results in a faster growing bubble, producing the same effect as reducing the laser power. We conclude that the bubble energy only depends on the amount of absorbed optical energy and it is independent of the beam radius and laser power for any amount of absorbed energy. This effect contrasts with pulsed lasers, where an increase in the beam radius results in a reduction of bubble energy. Our results are of relevance for the use of continuous-wave laser-actuated cavitation in needle-free jet injectors as well as other applications of thermocavitation in microfluidic confinement.</p
Gas density influences the transition from capillary collapse to surface seal in microfluidic jet impacts on deep pools
Studies of liquid jet impacts onto a deep liquid pool are of great
significance for a multitude of engineering and environmental applications.
During jet impact, the free surface of the pool deforms and a cavity is
generated. Simultaneously, the free surface of the cavity extends radially
outward and forms a rim. Eventually the cavity collapses by means of gas
inertia and surface tension. In this work we study numerically such cavity
collapse, under different impact velocities and ambient gas density conditions.
An axisymmetric numerical model, based on the volume of fluid method is
constructed in Basilisk C. This model is validated by qualitative and
quantitative comparison with theory and experiments, in a parameter range that
has not been previously explored. Our results show two distinct regimes in the
cavity collapse mechanism. By considering forces pulling along the interface,
we derive scaling arguments for the time of closure and maximum radius of the
cavity, based on the Weber number. For jets with uniform constant velocity from
tip to tail and the cavity closure is capillary dominated and
happens below the surface (deep seal). In contrast, for the
cavity closure happens above the surface (surface seal) and is dominated by the
gas entrainment and the pressure gradient that it causes. Our results provide
information for understanding pollutant transport during droplet impacts on
large bodies of water, and other engineering application, like additive
manufacturing, lithography and needle-free injections
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