Erick Tijerino

Structural morphology of acoustically levitated and heated nanosilica droplet

We study the vaporization and precipitation dynamics of a nanosilica encapsulated water droplet by levitating it acoustically and heating it with a CO2 laser. For all concentrations, we observe three phases: solvent evaporation, surface agglomeration, and precipitation leading to bowl or ring shaped structures. At higher concentrations, ring reorientation and rotation are seen consistently. The surface temperature from an infrared camera is seen to be dependent on the final geometrical shape of the droplet and its rotation induced by the acoustic field of the levitator. With nonuniform particle distribution, these structures can experience rupture which modifies the droplet rotational speed

Insight into morphology changes of nanoparticle laden droplets in acoustic field

Hollow structures with unique morphologies form due to particle agglomeration in acoustically levitated nanofluid functional droplets when subjected to external heating. The final diameter of the structure depends only on the ratio of agglomeration to evaporation time scales for various nanoparticle laden droplets, and not on the type of the suspended particles. These time scales depend only on nanoparticle concentration. This valuable information may be exploited to form microstructures with desired properties from ceramic compounds. Phase diagrams for alumina and silica droplets indicate the transition from a bowl to ring structure depending on concentration.

Nanoparticle agglomeration in an evaporating levitated droplet for different acoustic amplitudes

Radiatively heated levitated functional droplets with nanosilica suspensions exhibit three distinct stages namely pure evaporation, agglomeration, and finally structure formation. The temporal history of the droplet surface temperature shows two inflection points. One inflection point corresponds to a local maximum and demarcates the end of transient heating of the droplet and domination of vaporization. The second inflection point is a local minimum and indicates slowing down of the evaporation rate due to surface accumulation of nanoparticles. Morphology and final precipitation structures of levitated droplets are due to competing mechanisms of particle agglomeration, evaporation, and shape deformation. In this work, we provide a detailed analysis for each process and propose two important timescales for evaporation and agglomeration that determine the final diameter of the structure formed. It is seen that both agglomeration and evaporation timescales are similar functions of acoustic amplitude (sound ...

Acoustically Levitated Nanofluid Droplet Vaporization

The presence of nanometer size particles within an evaporating water droplet, affects the heat transfer and temperature distribution within the droplet. Levitating the droplet acoustically allows the study of this phenomenon without the heat transfer interference that occurs with the use of other techniques, such as capillary suspension [1]. In addition to the heat transfer effects, the remaining particle after the water in the droplet is completely evaporated, agglomerate together to form bowl shaped and ring shaped structures. The suspended droplet was heated using a Carbon Dioxide Laser. The process has been imaged in-situ with an Infrared (IR) camera, registering the temperature profile around the droplet surface. A high speed camera simultaneously captured the formation of nanoparticle structures. The experiments were conducted for a range of 0.1% to 5% nanosilica volume concentration solutions. Scanning Electron Microscopy was performed on the remaining structures to observe the inner portion and the outer surface of the formed structures.Copyright

IR Thermography and High Speed Imaging of Cerium Nitrate Precursor Droplets Heated by Monochromatic Irradiation

An experimental setup using radiative heating has been used to understand the thermophysical phenomena and chemical transformations inside acoustically levitated cerium nitrate precursor droplets. IR imaging in conjunction with high speed imaging shows presence of four distinct phases of heating. The droplet initially undergoes pure vaporization followed by surface precipitation. This results in a gelatinous phase due to precipitation of cerium nitrate which eventually goes though chemical transformation and forms a porous precipitate. Transmission Electron Microscopy (TEM) of the final precipitate revealed the presence of trapped gases in the form of bubbles. TEM also showed the presence of nano-ceria crystalline structures at 70°C. The current study also looks into the effect of different heating power on the process. At higher power each phase is sustained for smaller duration and higher maximum temperature. At all laser power, TEM showed the formation of nanoceria. In addition, the porosity of the final precipitate increased with power.Copyright

Human blood pressure simulation for photoelastic stress analysis in models of vasculature

The development of a numerical criterion to evaluate the stress on models of vasculature has applications in evaluation of human skills, robots and medical tools. This criterion will enable better medical training for endovascular surgery and the development of better medical techniques and tools. We propose to use the stress produced by human blood pressure simulation in the wall of the model of vasculature as this criterion; and to measure the principal component of stress magnitude using photoelastic effect. For that we simulated human blood pressure with a 5.6% of average error, we developed a shielded urethane model of vasculature enabling water circulation and avoiding plastic deformation with pressures below 182 mmHg. We developed software to calculate the stress of the model wall. Stress produced by human blood pressure simulation and a guide wire were compared numerically in four ranges.

Feedback Control with Hybrid Pump for Realistic Human Blood Pressure Reconstruction

Abstract Human blood pressure simulation is of particular interest for artificial blood vessel evaluation in regenerative medicine, and for endovascular surgery simulation to become more realistic. Conventional pumps do not offer a solution for the flow quality requirements; therefore we propose a hybrid pump that combines the best properties of lobe and piston pumps. Feedback control was applied to the hybrid pump, the system was tested using three different waveforms as reference. One of the waveforms is a polynomial approximation of pressure variation inside a coronary artery; when used a realistic human blood pressure simulation was produced. A scaffold for blood vessel regeneration was evaluated with the simulated human blood pressure.