Computational Modeling of Drug Dissolution in the Human Stomach

A computational model of drug dissolution in the human stomach is developed to investigate the interaction between gastric flow and orally administrated drug in the form of a solid tablet. The stomach model is derived from the anatomical imaging data and the motion and dissolution of the drug in the stomach are modeled via fluid-structure interaction combined with mass transport simulations. The effects of gastric motility and the associated fluid dynamics on the dissolution characteristics are investigated. Two different pill densities are considered to study the effects of the gastric flow as well as the gravitational force on the motion of the pill. The average mass transfer coefficient and the spatial distributions of the dissolved drug concentration are analyzed in detail. The results show that the retropulsive jet and recirculating flow in the antrum generated by the antral contraction wave play an important role in the motion of the pill as well as the transport and mixing of the dissolved drug concentration. It is also found that the gastric flow can increase the dissolution mass flux, especially when there is substantial relative motion between the gastric flow and the pill.

Undulatory Swimming Performance Explored With a Biorobotic Fish and Measured by Soft Sensors and Particle Image Velocimetry

Due to the difficulty of manipulating muscle activation in live, freely swimming fish, a thorough examination of the body kinematics, propulsive performance, and muscle activity patterns in fish during undulatory swimming motion has not been conducted. We propose to use soft robotic model animals as experimental platforms to address biomechanics questions and acquire understanding into subcarangiform fish swimming behavior. We extend previous research on a bio-inspired soft robotic fish equipped with two pneumatic actuators and soft strain sensors to investigate swimming performance in undulation frequencies between 0.3 and 0.7 Hz and flow rates ranging from 0 to 20 cms in a recirculating flow tank. We demonstrate the potential of eutectic gallium–indium (eGaIn) sensors to measure the lateral deflection of a robotic fish in real time, a controller that is able to keep a constant undulatory amplitude in varying flow conditions, as well as using Particle Image Velocimetry (PIV) to characterizing swimming performance across a range of flow speeds and give a qualitative measurement of thrust force exerted by the physical platform without the need of externally attached force sensors. A detailed wake structure was then analyzed with Dynamic Mode Decomposition (DMD) to highlight different wave modes present in the robot’s swimming motion and provide insights into the efficiency of the robotic swimmer. In the future, we anticipate 3D-PIV with DMD serving as a global framework for comparing the performance of diverse bio-inspired swimming robots against a variety of swimming animals.

Microscale impeller pump for recirculating flow in organs-on-chip and microreactors

Fluid flow is an integral part of microfluidic and organ-on-chip technology, ideally providing biomimetic fluid, cell, and nutrient exchange as well as physiological or pathological shear stress. Currently, many of...

Critical Examination of Variables Effecting Friction Loop Results for Friction Reducer Selection

Friction reducer evaluations for field application selection are conducted in laboratory benchtop recirculating flow loops or once-through systems. Industry standard procedures and benchtop flow loop (loop) system specifications for friction reduction assessment are nonexistent, though standardization efforts are recently documented. Research and papers correlating friction reducer performance to brine and additives have been published, however other key variables can significantly affect performance and therefore must be addressed to maximize product recommendation accuracy. This paper illustrates how variances affect results. Benchtop recirculating loops used for testing friction reduction products for a specific field's application vary significantly in system components, configurations, and test analyses. Crucial loop system variance examples include differing pipe diameters, pump configurations, flow meter types and placement, differential pressure section and full run lengths, reservoir designs, mixing conditions, and end performance calculations. Oil and gas producers and service companies are trending towards outsourcing friction reducers to independent testing laboratories for loop assessment results prior to recommending friction reducers for end use field applications. These recommendations may have inherent selection bias depending upon the loop system's components and configuration. Friction reduction calculations during loop testing do not consistently consider changes in viscosity and temperature, thereby altering absolute results when evaluating performance. To apply the simplified assumptions in standard pressure, drop methodology, equivalency in flow rate, density, viscosity, and temperature within the run must be maintained. Performance of the friction reducer in a specific brine and additive test run should primarily be dependent upon dosage and method of injecting friction reducer into the loop, however other variables can contribute to performance results. We presume equivalency in pipe roughness and proper loop cleansing. The effects of these variables on friction reduction response applying wide-ranging factors of flowrate, density, viscosity, and temperature are evaluated using designed experiments with responses plotted and illustrated in Cartesian and contour graphs. The result of these designed experiments identified that certain variables are more influential on friction reducers’ measured performances in standard loop experiments and require observation and documentation during performance testing. The final study in this work generated vastly different performance curves when all of the aspects of loop design, entry and differential run lengths, flow rate, injection method, friction reducer types and loadings, and brine types, densities, viscosities, and temperatures were held constant. The goal of benchtop loop testing is scaling for actual field applications. Scaling discrepancies persist however due to differing pipe diameters, fluid circuit designs, and pump types and rates combined with changing brine compositions, proppant, and chemical additive effects on friction reducer products. Understanding that different benchtop loops, or potentially the same benchtop loop, will generate differing results is intriguing, yet unsettling.

A Study of Recirculating Flow Fields Downstream of a Diverse Range of Axisymmetric Bluff Body Geometries Suitable for Flame Stabilization

This work investigates the non-reacting time averaged and fluctuating flow field characteristics downstream of a variety of axisymmetric baffles, operating in combination with an upstream double-cavity premixer arrangement. The study aims to broaden knowledge with respect to the impact of different bluff body shapes, leading and trailing edge flow contours, blockage ratios and incoming flow profiles impinging on the bluff body, on the development and properties of the downstream recirculating wake. Particle Image Velocimetry (PIV) measurements have been employed to obtain the mean and turbulent velocity fields throughout the centrally located recirculation zone and the adjacent developing toroidal shear layer. The results are helpful in demarcating the cold flow structure variations in the near wake of the examined baffles which support and, to some extent, determine the flame anchoring performance and heat release disposition in counterpart reacting configurations. Additionally, such results could also assist in the selection of the most suitable flame stabilization configuration for fuels possessing challenging combustion behavior such as multi-component heavier hydrocarbons, biofuels, or hydrogen blends.

Cavitation on top of collision breaks the cover of coronary plaques and triggers acute coronary syndrome

Background Coronary injuries are hypothesized to be caused by the cavitation phenomenon (explosion of air bubbles) which is seen frequently in industrial pipes. Based on hydraulics principles applied to the coronary circulation. during distal negative suctioning in diastole, if the coronary static pressure decreases below the vapor pressure (VP), bubbles will form. They explode when the coronary static pressure recovers > the VP during systole. These explosions create jet waves weakening and rupturing the cover of the coronary plaques, triggering acute coronary syndrome (ACS). How could these events be observed, recorded and compared? Methods Coronary angiograms of patients with ACS and stable coronary artery disease (CAD) (control) were selected. The arteries were recorded at 15 frames per second and saved in the electronic health records and reviewed image by image. After the index artery was completely filled with contrast, the following images showed the blood in white moving in on a background of black contrast. The flow could be laminar, turbulent (mixing of blood in white and contrast in black), antegrade or RETROGRADE (black column traveling backward). At the same time, an artificial intelligence (AI) program was used to detect and identify the flow. Results There were 104 patients with ACS enrolled and 20 patients with stable CAD as control. First, in the ACS group, 84 lesions (80%) were in the end of the proximal segment of the left anterior descending artery (LAD) and mid-segment of the right coronary artery (RCA). 20 lesions (19%) were at the distal RCA. Second, during diastole, 95% of the flow were laminar. The flow became turbulent at the beginning of systole. The turbulence was caused by the COLLISION of the antegrade flow (end of diastole) and the retrograde flow (at the beginning of systole). These collisions were seen in 95% at the location of vulnerable plaques of patients with ACS. In the control patients, there were only 2 cases (10%) with collision. Third, in the 20 patients with lesions at the distal RCA, the lesions were seen to be located at the areas of recirculating flow, at the ostium of the posterior descending artery (PDA) or proximal to the origin of the PDA. The cause of turbulence was most likely due to cavitation on top of collision. The cavitation happened because of continuous steady forward flow (of the PDA) in the myocardium during systole, while at the proximal RCA the blood flew forward more slowly. (Fig.1) The DSICREPANCY of velocities at the proximal and distal RCA allowed the formation of an empty gap (bubble of air). When the flow reversed during systole, this retrograde flow slammed on the bubble which collapsed violently, injured, ruptured the cover of the plaque and started ACS. Conclusions Rupture of bubbles (cavitation) on top of collision was most likely the cause of injury to the cover of vulnerable plaques, triggering ACS. Understanding the mechanism will help to better manage ACS. FUNDunding Acknowledgement Type of funding sources: None. Cavity formation and collision Formation of cavitation at the PDA

Droplet Evaporation in a Gas-Droplet Mist Dilute Turbulent Flow behind a Backward-Facing Step

The mean and fluctuation flow patterns and heat transfer in a turbulent droplet-laden dilute flow behind a two-dimensional single-side backward-facing step are numerically studied. Numerical simulations are performed for water droplets, with the inlet droplet diameters d1 = 1–100 μm; they have a mass fraction of ML1 = 0–0.1. There is almost no influence of a small number of droplets on the mean gas flow and coefficient of wall friction. A substantial heat transfer augmentation in a droplet-laden mist-separated flow is shown. Heat transfer increases both in the recirculating flow and flow relaxation zones for fine, dispersed droplets, and the largest droplets augment heat transfer after the reattachment point. The largest heat transfer enhancement in a droplet-laden flow is obtained for small particles.

Electrokinetic instability due to streamwise conductivity gradients in microchip electrophoresis

We present an experimental and numerical investigation of electrokinetic instability (EKI) in microchannel flow with streamwise conductivity gradients, such as those observed during sample stacking in capillary electrophoresis. A plug of a low-conductivity electrolyte solution is initially sandwiched between two high-conductivity zones in a microchannel. This spatial conductivity gradient is subjected to an external electric field applied along the microchannel axis, and for sufficiently strong electric fields an instability sets in. We have explored the physics of this EKI through experiments and numerical simulations, and supplemented the results using scaling analysis. We performed EKI experiments at different electric field values and visualised the flow using a passive fluorescent tracer. The experimental data were analysed using the proper orthogonal decomposition technique to obtain a quantitative measure of the threshold electric field for the onset of instability, along with the corresponding coherent structures. To elucidate the physical mechanism underlying the instability, we performed high-resolution numerical simulations of ion transport coupled with fluid flow driven by the electric body force. Simulations reveal that the non-uniform electroosmotic flow due to axially varying conductivity field causes a recirculating flow within the low-conductivity region, and creates a new configuration wherein the local conductivity gradients are orthogonal to the applied electric field. This configuration leads to EKI above a threshold electric field. The spatial features of the instability predicted by the simulations and the threshold electric field are in good agreement with the experimental observations and provide useful insight into the underlying mechanism of instability.

Investigation of the Wind-Induced Airflow Pattern Near the Thies LPM Precipitation Gauge

The airflow velocity pattern generated by a widely used non-catching precipitation gauge (the Thies laser precipitation monitor or LPM) when immersed in a wind field is investigated using computational fluid dynamics (CFD). The simulation numerically solves the unsteady Reynolds-averaged Navier–Stokes (URANS) equations and the setup is validated against dedicated wind tunnel measurements. The adopted k-ω shear stress transport (SST) turbulence model closely reproduces the flow pattern generated by the complex, non-axisymmetric outer geometry of the instrument. The airflow pattern near the measuring area varies with the wind direction, the most intense recirculating flow and turbulence being observed when the wind blows from the back of the instrument. Quantitative parameters are used to discuss the magnitude of the airflow perturbations with respect to the ideal configuration where the instrument is transparent to the wind. The generated airflow pattern is expected to induce some bias in operational measurements, especially in strong wind conditions. The proposed numerical simulation framework provides a basis to develop correction curves for the wind-induced bias of non-catching gauges, as a function of the undisturbed wind speed and direction.