bluuebunny/crossref_metadata_2025 huggingface dataset:
Several Modifications to Improve Numerical Stability of Leishmen-Beddoes Dynamic Stall Model
Authors: Guo Jia , Meng Haoran , Zeng Pan , Lei Liping
Published: October 2020

Dynamic stall is dominant to aerodynamic performance of vertical axis wind turbines where angles of attack (AoAs) of blades vary periodically during operation. Therefore, dynamic stall models are necessarily employed in the simulation of wind turbines. Among them the Leishmen-Beddoes (LB) dynamic stall model are widely accepted nowadays. In the LB model, aerodynamic forces of blades are determined by AoAs and their rates of change. However, in consideration of the inevitable existence of numerical errors of AoAs, calculations of the rates of change may cause unexpected numerical problems. This paper focused on presence of fluctuations of blade forces due to minor numerical errors of AoAs in the LB model. Then three modifications, namely the implementation of filters of AoAs, alternative calculation of change of variables and scaling of time constants, were employed and their effect on numerical stability of the LB model was evaluated. It is found that the implementation of filters of AoAs can eliminate fluctuations of outcome forces but the phase delay is the side effect. In addition, alternative calculation of change of variables and scaling of time constants can reduce the maximum nominal fluctuations of results from 16.4% to 5.8% and 5.1%, respectively.
Parametric Optimization of a Dry Powder Inhaler
Authors: Kotteda V. M. Krushnarao , Badhan Antara , Kumar Vinod
Published: October 2020

In the present study, particles in cell method, a Eulerian-Lagrangian approach is used to simulate the flow in an inhaler. The number of uncertain parameters, including properties of particles, fluidizing agents’ properties, initial/boundary conditions, and numerical parameters related to PIC simulations, is fourteen. The residence time of 280 PIC simulations for different values of the uncertain parameters is used to test/train a data-driven framework. The values of the uncertain parameters are generated via the Latin Hypercube Sampling method and a normal distribution. The trained algorithm is used to predict the residence time for various unknown parameters. This framework is used to carry out the sensitivity analysis to find the most influential settings on the residence time of the particles in the inhaler. The optimum parameters of the influential parameters for a given residence time is calculated via the data-driven framework.
Influence of a Yield-Shear-Thinning Rheology on the Flow Behavior of Submerged Annular Jets
Authors: Hammad Khaled J.
Published: October 2020

The flow structure and decay characteristics of submerged annular yield-pseudoplastic jets are investigated. Numerical solutions to the governing mass and momentum conservation equations, along with the Herschel-Bulkley rheological model, are obtained using a finite-difference scheme. A parametric study is implemented to investigate the effects of annular nozzle diameter ratio, κ, the power-law index, n, and yield number, Y, over the following range: κ = {0, 0.5}; n = {1, 0.6}; and Y = {0, 1, 5}. The Reynolds number was fixed at Re = 100, which ensured steady and laminar jet flow conditions throughout the whole flow field. The selected yield number and power-law index values allowed for the investigation of the presence of yield stress and shear-thinning effects on the resulting structure and evolution of the flow field. The results demonstrate the substantial impact of the inflow conditions and rheology on the annular jet evolution, and on the extent of the outer recirculation region and recirculation strength of both the outer and central regions.
On the Boundary Condition for the Level Set Function in the Numerical Simulation of Moving Contact Lines
Authors: Gómez Pablo , Esteban Adolfo , Zanzi Claudio , López Joaquín , Hernández Julio
Published: October 2020

We present a method based on a level set formulation to reproduce the behavior of the contact line on solid walls in the simulation of 3D unsteady interfacial flows characterized by large density ratios. The level set method poses a particular difficulty, related to the reinitialization procedure, when used in the simulation of interfacial flows in which the interface intersects a solid wall, due to the appearance of a blind zone where standard reinitialization procedures produce inconsistent results. The proposed method overcomes this difficulty by introducing a boundary condition for the level set function on the solid surface based on the normal extension of the contact angle from the interface along the solid wall. In order to reproduce the dynamics of the contact line we use a simplified model that imposes a boundary condition on the interface curvature based on the static contact angle, and define a thin slip zone at the solid wall around the contact line. To assess the accuracy and robustness of the proposed method, we conducted several preliminary numerical tests in three dimensions, whose results are compared with analytical solutions and other results available in the literature.
Droplet Dynamics in Constricted Return Bends of Microfluidic Channels
Authors: Melbye Julie A. , Wang Yechun
Published: October 2020

Microfluidic delivery systems have been employed to facilitate cell seeding procedures in drug development for personalized medicine for cancer patients. Despite of the high-throughput nature and potential impact on clinical outcomes of these systems, the efficiency in cell trapping remains a challenge in the operation. Droplet-based microfluidics became one of the solutions due to the large size of the cell-enclosing droplets and their interfacial properties. This study is focused on the motion of the cell-enclosing droplet in a constricted return bends that help to restrict the release of the cells while maintaining the high-throughput nature of the device. In this preliminary study, a three-dimensional boundary element method is used to predict droplet shape, deformation and migration velocity under the influence of various fluid properties and operational conditions. A variety of channel geometries have been explored as well. The resulting computational framework will be used to guide the design of a droplet-based microfluidic delivery system for cell seeding in 3D tumor spheroid arrays.
Simulations of Flow Separation Control Using Different Plasma Actuator Models
Authors: Abdelraouf Hatem , Kassab Sadek Z. , Elmekawy Ahmed M. Nagib
Published: October 2020

This study investigates the active flow control on NACA0012 airfoil numerically by introducing dielectric barrier discharge (DBD) plasma actuators. The flow over the airfoil simulations were performed using ANSYS program for free-stream velocity 14.6 m/s with wide range of angle of attacks (from 0 to 20 degrees) on NACA0012 airfoil with applied voltage 16 kV across the electrodes. There are several plasma actuator models, which simulate the effect of the plasma actuator. This paper focuses on two numerical methods: Shyy model and Suzen model. They depend on calculating the induced body force of the plasma and import it in Navier Stokes equation as an external body force. Mesh independence study is performed on the airfoil and validate the results without plasma activation with the experimental results. Two actuators were added at positions 0.1 and 0.3 of the chord length to the airfoil and an investigation is performed on the lift CL and drag Cd coefficients of the airfoil without and with the activation of the plasma. Thereafter, a comparison between the numerical results of two different plasma simulation models that were applied.
Optimized Gun Barrel Based on Numerical Simulation to Produced Oil With Low BSW Content
Authors: Daza Silvia Araujo , Villamizar Urbano Montañez
Published: October 2020

This work presents the methodology and results of the optimization of the internals (Inlet distributor, oil and water collectors) of a 20,000 BPD (0.037 m3/s) gun-barrel tank starting from an existing design. Computational fluid dynamics (CFD) was applied to simulate and evaluate the performance of various internal configurations. These simulations were performed to determine the best configuration to ensure efficient separation of the oil-water mixture and oil with a low BSW content < 2% at the outlet. The simulations were carried out using the commercial software ANSYS Fluent under the two-phase flow VOF model and k-ε realizable turbulence model. Further CFD simulations were performed to evaluate the behavior of the gun barrel tank under different operating conditions (Different inlet flow rate) and to determine the maximum operation flow which allows obtaining the crude-oil with a maximum BSW content of 0.5%. From the simulation results, an operating curve (operating flow vs retention time) was constructed. This information allows, in practice, to identify the inlet flow rate based on the desired content of BSW in the separated oil.
Experimental and Numerical Modeling of Viscous Fluid Flow in Bifurcated Long Pipes for Oil Transport
Authors: Radulescu Victorita
Published: October 2020

The present paper presents some experimental and numerical modeling of the Newtonian and viscoelastic flows in bifurcated configurations of pipes, for stationary and non-permanent regimes. The main purpose of this study is to select an optimal design of the pipes ramifications, for minimizing the local pressure losses and to improve the efficiency of fluid transportation. The method is based on the transformation of the flow field obtained with particle image visualization technique, for different Reynolds numbers. Based on experimental results will be established optimum geometry of the ramifications. The results will be used as the boundary conditions for numerical modeling. The experimental measurements were performed into a closed circuit of pipes, with different diameters, consisting of a centrifugal pump supplied by a tank, sensors for estimating the pressure losses and devices for measuring the flow rate. It is detailed presented in a dedicated paragraph. The main pipe is connected to a transparent bifurcation with branches at different angles from the main pipe axis. The measurements illustrate that the flow has different aspects, depending on the bifurcation’s angle. The numerical simulations are performed with Fluent CFD based on the volume numerical method, to obtain the Navier-Stokes solutions for the Newtonian model in the laminar or turbulent flow conditions. A pre-processor has been used to create the geometry of the bifurcation and to generate the mesh. The 3D-flow domain contains 944390 volumes, tetrahedral hybrid. It was obtained the numerical solutions of the fluid flow in branching pipes for the Reynolds numbers from 1000 up to 40000. The governing equations were assumed from the k-ε model for turbulence flow, the equation of continuity, equation of fluid motion, and the transport equation. Finally, some conclusions and references are presented.
Particle Transport and Deposition in a Ventilated Room With a Standing Mannequin
Authors: Azhdari Mehrdad , Tavakol Mohammad Mehdi , Ahmadi Goodarz
Published: October 2020

This study presents the results of a series of numerical simulations for airflow field and particle dispersion and deposition around a mannequin standing inside a ventilated room. A 3-D airway model was constructed from the nostril inlet to the end of 4th lung generation and was integrated into the standing mannequin model in the room. The computational domain included the region around the mannequin and inside the respiratory system. The room was ventilated by a mixing air-conditioning system that supplied air with a speed of 3m/s from a diffuser mounted on the top of the sidewall and exited from a damper mounted at the bottom of the side or front walls. In the first mode, the diffuser and damper were located on the wall in front of the mannequin and in the second mode on the wall at the right side of the mannequin. The mean airflow field inside the room was obtained by solving the Navier-Stokes and continuity equations using the Ansys-Fluent software. The k-ω SST transitional model was employed for turbulence modeling. Then, spherical particles with 5, 10, 20, and 40 μm diameter and unit density were released into the room, and their trajectories were tracked by using the Lagrangian trajectory analysis approach. Aspiration efficiency and deposition of particles for inhalation flow rates of 15 and 30 lit/min were analyzed with the improved discrete random walk (DRW) stochastic model using a user-defined function (UDF) coupled into the Ansys-Fluent discrete phase model. Simulation results for the mean airflow showed the formation of a large recirculation zone inside the room. In the first mode, the main recirculation zone formed behind mannequin that carried the flow streamlines toward the mannequin breathing zone. In the second mode, the recirculation formed in front of the mannequin face that led the streamlines out of the breathing zone. The simulation results for particle inhalation showed that the aspiration efficiency of particles is higher in the first ventilation mode compared to the second mode. Results also showed that the total deposition of particles in the airway passage increases as particle size increases.
Volumetric Three-Componential Velocity Measurements (V3V) of Flow Structure Behind Mangrove-Root Type Models
Authors: Kazemi Amirkhosro , Castillo Eduardo E. , Curet Oscar , Hortensius Ruben , Stamatios Pothos
Published: October 2020

Mangrove roots produce complex flow structure interactions with their environment, which affect the nutrient, habitat and aquatic animals. Analysis of the flow structure behind the roots extends to a broad range of mangrove-inspired applications that provides understanding into complex flows encountered in unidirectional riverine flows. In this work, we modeled the mangrove roots with a cluster of rigid circular cylinders to investigate the vortex structure downstream of the models. The vortex organization of the patch of cylinder wakes was studied experimentally by time-resolved volumetric three-componential volumetric velocimetry (V3V) at Reynolds numbers 1014 and 3549. The results show that the vortex structure in the 3-D flow field reveals a regular shedding at Re = 1014, forming von Kármán vortices dominating the 3D motion. The flow structure behind rigid patches is coherent and the streamwise velocity remains unchanged. The regime for a flexible patch at Re = 3549 produces an intricate pattern where the multiple counter-rotating vortexes distorted substantially and forming a chain of rhombus-like vortex cells in the near wake. The information for the 3D flow feature provides useful information to a robust structure for Seawall erosion.
Uniform and Gaussian UV Light Intensity Distribution on Droplet for Selective Area Deposition of Particles
Authors: Li Tianyi , Kar Aravinda , Kumar Ranganathan
Published: October 2020

Particle transport through Marangoni convection inside a sessile droplet can be controlled by the UV light distribution on the surface. The photosensitive solution changes the surface tension gradient on the droplet surface and can induce clockwise and counter-clockwise circulations depending on the incident light distribution. In this paper, the stream function in the sessile drop has been evaluated in toroidal coordinates by solving the biharmonic equation. Multiple primary clockwise and counter-clockwise circulations are observed in the droplet under various concentric UV light profiles. The downward dividing streamlines are expected to deposit the particles on the substrate, thus matching the number of deposited rings on the substrate with the number of UV light rings. Moffatt eddies appear near the contact line or centerline of the droplet either due to a sharp change in the UV light profile or because the illuminated region is away from them.
Open-Source Accelerated Vortex Particle Methods for Unsteady Flow Simulation
Authors: Stock Mark J. , Gharakhani Adrin
Published: October 2020

A new open-source CFD solver is being developed based on the vorticity transport equations for simulation of unsteady incompressible flow in complex geometries. This is a hybrid approach, which uses a compact high-order finite-difference method to predict the flow in the near-boundary region and a Lagrangian Vortex Particle Method (LVPM) for the off-boundary vorticity-containing region. This paper focuses on the latter, presenting the particular LVPM implemented in the package and demonstrating selected benchmarks from simulations of flow in 2D lid-driven cavity, flow around a rotating cylinder (both at Re = 1,000), and impulsively started flow over a sphere at Re = 25, 40, 60, 80, 100. In addition, novel ideas on the development of an efficient and lightweight Graphical User Interface (GUI), as well as new approaches to cross-platform hardware acceleration for Teraflop/s computing on a desktop — achieving over two orders of magnitude speedup vs. an optimized serial code — are discussed.
Developing an Optimum Design of the Double Layer Microchannel Heat Sink for High Speed CPUs
Authors: Radwan Ali , Abo-Zahhad Essam M. , Abdelrehim O. , El-Shazly A. H. , Ookawara Shinichi , Awad M. M. , El-Kady M. F. , Elmarghany Mohamed R. , Salem Mohamed S. , Shouman Mahmoud A.
Published: October 2020

High speed CPUs and electronic chips usually dissipate relatively large quantities of energy in the form of heat. The limited available cooling space requires innovative and efficient thermal management techniques. These techniques must accomplish low operation temperatures along with uniform temperature distribution over the chip surface. Recently, several researches focused on developing different microchannel heat sink (MCHS) designs for this purpose. Among these designs is the double layer microchannel heat sink (DL-MCHS), which can be operated in either parallel flow (PF) or counter flow (CF) operation modes. The thermo-hydraulic characteristics of this heat sink was comprehensively investigated in the literature using numerical methods. However, based on the authors literature survey, all the previous numerical investigations considered the computational domain as a straight section with multi-channels in each layer. This approach assumes a uniform velocity for all the flow channels in each layer and neglect the effect of the inlet and outlet headers. In addition, the heat interaction between the coolant in both layers through the header section was not considered. These assumptions cause a considerable discrepancy between the numerical results in the literature and the realistic conditions. Therefore, in this work, a detailed 3D conjugate heat transfer model is developed. In this 3D model, DL-MCHS is designed with and without headers. The designed heat sinks are operated under PF and CF conditions. For a specific electronic chip with dimensions of 13 mm × 40 mm at a heat flux of 5 kW/m2. The model is validated with the experimental results in the literature. It is found that, including the header design in the simulation of the DL-MCHS must be considered in the simulation to predict the accurate thermo-hydraulic performance of the DL-MCHS specially in the CF. Further, using the DL-MCHS in PF operation accomplished a lower average chip temperature compared with the CF. Furthermore, at high coolant flowrate, neglecting the effect of the header in the CFD calculations can be approximated to predict the chip surface temperature. And finally, neglecting the header in the CFD calculations significantly affect the calculated pumping power for both PF and CF operated DL-MCHS.
Four Compartments Stepwise Varied Width Microchannels Cooling Approach for Densely-Packed Module of Concentration Photovoltaics
Authors: Abo-Zahhad Essam M. , El-Shazly A. H. , Ookawara Shinichi , El-Kady M. F. , Ali Abdallah Y. M. , Elqady Hesham I. , Elmarghany Mohamed R. , Salem Mohamed S. , Shouman Mahmoud A. , Radwan Ali
Published: October 2020

The high concentration of solar radiation on the multijunction solar cells used in the highly concentrated photovoltaic modules cases a very high cell temperature. Also, high cell temperature operations overall performance and increase thermal stresses. Therefore, an efficient cooling arrangement is mandatory to achieve a higher net output power from the high concentrator photovoltaic structures. In this work, the comprehensive three-dimensional (3D) model was developed and manipulated to investigate the performance of an HCPV system under the active cooling scheme to figure out its ability to handle effective heat dissipations. Various novel cooling microchannels manifold designs were numerically investigated and compared in the term of cooling down a densely packed high concentration photovoltaic. The solar cell type is the latest product of AZURSPACE triple junction of 3 × 3 mm2 solar cell. A 64 multijunction solar cells (electrical efficiency of 42.3% at cell temperature 25 °C) module were considered in this work. The influence heat sink design, channel dimensions, and inlet flow rate on the cooling performance of the manifold heat sink device were examined. The same external dimensions are considered, and the flow was laminar and the inlet temperature 25 °C for all designs for a reasonable comparison. the heat sink material the maraging steel. The concept of dividing the heat sink area to many segments is adopted to improve the heat removal capacity. The concept of channel width variation along the flow stream length was studied. The heat sinks including rectangular channels were adopted as they are easy to be fabricated. The limitations of 3D metal printing and pumping requirements were considered for all proposed designs where the minimum channel width is 0.8 mm. The comparison between all studied designs is highlighted concerning surface average temperature surface temperature uniformity and pressure drop.
Heat Transfer and Fouling Performance During Falling Film Evaporation in Vertical Porous Tubes
Authors: Wang Lei , Tang Weiyu , Zhao Limin , Li Wei
Published: October 2020

An experimental investigation was conducted on falling film evaporation along two porous tubes, which were sintered by stainless-steel powder with a diameter of 0.45 and 1 um, respectively. The test section is a 2 m long sintered tube with an outer diameter of 25 mm and a wall thickness of 2 mm. During the experiment, the pressure inside the tube was maintained at 1 atm, the inlet temperature was 373 K, and mass flux ranged from 0.51 to 1.36 kg/ (m s). Conditions of the steam outside the pipe, which was the heat source, were fixed, while the fouling tests were carried out at a constant mass flow of 0.74 kg/ (m s) using high-concentration brine as work fluid. The overall heat transfer coefficient under different working conditions was tested and compared with the stainless steel smooth tube of the same dimensions. The heat transfer coefficient of the two porous stainless tubes are about 35% and 20% lower than that of the smooth one, showing an inferior effect because the steam in the pores of the pipe wall during the infiltration process will reduce the heat conductivity. The heat transfer coefficient of the smooth tube deteriorated severely due to the deposition of calcium carbonate, which had little effect on the sintered tubes. Besides, the fouling weight of porous tubes is 2.01 g and 0 g compared with 5.52 g of the smooth tube.
Condensation Characteristics of Flows Inside the Three-Dimensional Enhanced Tubes
Authors: Zheng Boren , Shen Kunrong , Li Wei , Ma Xiang , Zhang Chuancai , He Yan , Ke Hanbing , Lin Yuansheng
Published: October 2020

This paper presents experimental condensation characteristics of R134a inside two three-dimensional enhanced heat transfer tubes (1EHT1 and 3EHT) and one equivalent smooth tube. The 1EHT1 tube has the primary elliptical dimples and secondary petal arrays, and the 3EHT tube has the grooves and square bulge. All the tested stainless-steel tubes have the same outer diameter of 15.88 mm. The test tubes are installed in a horizontal test section with an effective length of 2 m. In these experiments, condensation temperature is kept constant at 318K. The refrigerant qualities at the test section inlet and outlet are 0.8 and 0.2. Mass flux is varied from 70 kg/(m2s) to 170 kg/(m2s). In a comparison of condensation heat transfer performance, the 1EHT1 tube has the best heat performance followed by the 3EHT tube. Condensing coefficients of the 1EHT1 tube and the 3EHT tube are about 1.45 times and 1.16 times that of the smooth tube, respectively. The experimental results in this study are compared with other experiments conducted by R410A under similar experimental conditions to evaluate the thermal performance.
Review of Enhancement Techniques With Vapor Extraction During Flow Boiling in Microchannels
Authors: Moreira Debora C. , Ribatski Gherhardt , Kandlikar Satish G.
Published: October 2020

Flow boiling heat transfer in microchannels can remove high heat loads from restricted spaces with high heat transfer coefficients and minimum temperature gradients. However, many works still report problems with instabilities, high pressure drop and early critical heat flux, which hinder its possible applications as thermal management solutions. Much comprehension on the phenomena concerning flow boiling heat transfer is still missing, therefore many investigations rely on empirical methods and parametric studies to develop novel configurations of more efficient heat sinks. Nevertheless, investigations involving vapor extraction have successfully addressed all these previously reported issues while also increasing the heat transfer of heat sinks employing flow boiling in microchannels. In this sense, the objective of this review is to identify the main techniques employed for vapor extraction in microchannels-based heat sinks and analyze the physical mechanisms underneath the observed improvements during flow boiling, such that some design guidelines can be drawn. Three main strategies can be identified: passive vapor extraction, active vapor extraction, and membrane-based vapor extraction. All these strategies were able to dissipate heatfluxes higher than 1 kW/cm2, with the best performance achieved by a membrane-based heat sink, followed by active and passive designs. According to the present experimental and numerical data available in the literature, there is still room for improvement.
Insight to Innovation: An Overview of Research Journey of Dr. Satish Kandlikar
Authors: Raghupathi Pruthvik , Owens Alyssa , Steinke Mark , Lin Ting Yu , Kalani Ankit , Moreira Debora , Gonzalez-Hernandez Jose-Luis , Lu Zujie , Banerjee Rupak , Daino Michael , Jaikumar Arvind , Chauhan Aranya , Rishi Aniket , Perez-Raya Isaac , Emery Travis , Guimarães Aguilar Fernando
Published: October 2020

Professor Satish G. Kandlikar has been an outstanding researcher in the field of heat transfer having published some of the most widely cited publications over the last 30 years. Through the years he has co-authored 212 journal paper in various areas of heat transfer. The present paper provides a compressive look at Professor Kandlikar’s research work over the years. The research work has been broadly categorized into 1) flow boiling correlations, 2) fluid flow and heat transfer in microchannels, 3) roughness effect at microscale, 4) pool boiling heat transfer and CHF modeling, 5) surface enhancements for pool boiling, 6) numerical modeling of bubble growth in boiling, 7) modeling liquid-vapor and liquid-liquid interfaces, 8) water transport in PEM fuel cells and 9) infrared imaging to detect breast cancer. The research conducted in each of these areas has produced some landmark findings, some of the most widely used theoretical models and an abundance of high quality experimental data. The focus of this paper is to collate major finding and highlights some of the common themes that guided the research in Professor Kandlikar’s group. This will help the readers gain a comprehensive understanding of each of the areas of study in Professor Kandlikar’s group and place the findings of the paper in a larger context.
Microalgae Harvesting in a Microfluidic Centrifugal Separator for Enhanced Biofuel Production
Authors: Sharma Rohan , Shirley Scott , Farrukh Tahir , Kavosi Mohammadhassan , Kim Myeongsub
Published: October 2020

Biofuel is one of the renewable energy resources alternatives to fossil fuels [1]. Among various sources for biofuels, microalgae provide at least three-orders-of-magnitude higher production rate of biodiesel at a given land area than conventional crop-based methods. However, microalgal biodiesel still suffers from significantly lower harvesting performance, making such a fuel less competitive. To increase the separation performance of microalgae from cultivation solution, we used a spiral microchannel that enables the isolation of biofuel-algae particles from water and contaminants contained in the culturing solution. Our preliminary data show that separation performance in the microfluidic centrifugal separator is as high as 88% within a quick separation time of 30 seconds. To optimize separation performance, multiple parameters of algae behaviors and separation techniques were studied and were manipulated to achieve better performance. We found that changing these factors altered the separation performance by increasing or decreasing flocculation, or “clumping” of the microalgae within the microchannels. The important characteristics of the separator geometry, fluid properties, and environmental conditions on algae separation was found and will be further studied in the forthcoming tests. This introductory study reveals that there is an opportunity to improve the currently low performance of algae separation in centrifugal systems using much smaller designs in size, ensuring a much more efficient algae harvesting.
Effect of Wetted Microtexturing on Friction in Microchannel Flow
Authors: Rabiei Nastaran , Hidrovo Carlos
Published: October 2020

Microchannel flows are widely used in applications where small diffusion length scales are important. However, their inherent dimensional constrain also translates into high pumping power requirements. Inspired by nature, one possible method to reduce the large viscous pressure losses is to introduce textures in a microchannel. Depending on the interaction between the textured surface and the liquid, the microstructures can either be wetted or nonwetted. Less adhesion between solid and liquid in nonwetted state has made it popular in most of the friction reduction studies. However, in the nonwetted state, preventing liquid from penetrating into the grooves under pressurized conditions and the gas-liquid interface acting like a solid boundary open space to consider the wetted state for friction reduction as well. When dealing with the wetted state we should be aware that penetration of the flow inside the grooves can induce the pressure drag alongside the skin drag. Therefore, the wetted state will lead to a trade-off between skin and pressure drag. The aim of this work is to understand how different microtextures affect the total drag in a laminar microchannel flow. Textured microchannels with width-to-depth aspect ratios of 1, 10 and 50 and different width of the land region have been tested. In order to perform correct comparisons, the textured and baseline microchannels are designed to have the same volume. The results show that increasing the aspect ratio of the trenches introduces an extermum point in the hydraulic resistance of the microchannels. The optimum aspect ratio for the tested microchannels is 10, in which the trenches are not wide enough for streamlines to bend inside the trenches and increase the skin drag and they are not highly dense along the microchannel to reveal the negative effect of the pressure drag. On the whole, the hydraulic resistance of the textured channels is higher than the equivalent baseline for all the tested geometries.
Ice Formation due to Condensation of Moist Air on Commercial Wicks
Authors: Stallbaumer Emily , Cernas Adan , Betz Amy , Derby Melanie
Published: October 2020

Heat pipes are valuable heat transfer devices that can be used in space; however, when exposed to the extremely low temperature of space, the working fluid can freeze. Currently, there are different methods to help mitigate freezing effects, including non-condensable gas-charged heat pipes and understanding ice formation on surfaces (e.g., typically surfaces with hydrophobic coatings). However, there is limited research about ice formation on wicks. Different wicking structures may delay freezing or mitigate freezing effects. This paper will investigate ice formation on two surfaces — commercial sintered and grooved wicks. An indoor environmental chamber was used to control ambient air temperature (i.e., 22°C) and relative humidity (i.e., 60% RH) and a Peltier cooler was used to control the surface temperature (i.e., −5°C). The resulting condensation of water onto the surface and then freezing was recorded for an hour and analyzed for the time freezing began on the surface (i.e., ice is initially visible) and the time freezing was complete on the surface. Initial results indicate that the sintered wick begins to freeze first (on average at 10.73 minutes versus 13.66 for the grooved wick) and the freezing front propagates faster (taking on average 10.83 minutes versus 12.44 minutes for the grooved wick). From the analysis, it is seen that the wicking surface structure influences the initial freezing time and the rate the freezing front propagates across the surface. These differences and the causes are investigated in this paper. These differences can, in the future, be exploited to design an optimal freeze-tolerant heat pipe and heat pipe freezing models.
Nonoptimal Codon Usage Is Critical for Protein Structure and Function of the Master General Amino Acid Control Regulator CPC-1
Authors: Lyu Xueliang , Liu Yi
Published: October 2020

The general amino acid control response is critical for adaptation of organisms to amino acid starvation conditions. The preference to use certain synonymous codons is a universal feature of all genomes. Synonymous codon changes were previously thought to be silent mutations. In this study, we showed that the
Neurospora cpc-1
gene has an unusual codon usage profile compared to other genes in the genome. We found that codon optimization of the
cpc-1
gene without changing its amino acid sequence resulted in elevated CPC-1 expression, an altered protein degradation rate, and impaired protein functions due to changes in protein structure. Together, these results reveal the critical role of synonymous codon usage in regulation of CPC-1 expression and function and establish a genetic example of the importance of codon usage in protein structure.
Detrital zircon populations of the eastern Laurentian margin in the Appalachians
Authors: Kuiper Yvette D. , Hepburn J. Christopher
Published: October 2020

Newly compiled U-Pb detrital zircon data from eight geographic domains along the eastern Laurentian margin from Newfoundland (Canada) to Alabama (United States) show a highly consistent signature along strike, with only minor local variations. The Precambrian signature is characterized by a small ca. 2.7 Ga population and a major ca. 1.9–0.9 Ga population that peaks at ca. 1.2–1.0 Ga. Detrital zircon populations are from Laurentian Archean crust (ca. 2.7 Ga population), Paleoproterozoic orogens (ca. 1.9–1.6 Ga), the Granite-Rhyolite Province (ca. 1.5–1.4 Ga), and the Elzevir terrane and Grenville Province (ca. 1.3–0.9 Ga). The Mesoproterozoic populations vary in size depending on proximity to the ca. 1.5–1.4 Ga Granite-Rhyolite Province, the ca. 1245–1225 Ma Elzevir terrane, and the ca. 1.2–0.9 Ga Grenville Province. A middle Ordovician zircon population varies in size along strike depending on input from the Taconic orogenic belt, but it is strongest in the northern Appalachians. Because of the general along-strike consistency in detrital zircon age populations, the compilation of all 7534 concordant U-Pb detrital zircon data can be used in future U-Pb detrital zircon studies as an indicator for eastern Laurentian margin sources.
Childhood morbidity and its determinants: evidence from 31 countries in sub-Saharan Africa
Authors: Adedokun Sulaimon T , Yaya Sanni
Published: October 2020

Background

Although under-five mortality reduced globally from 93 per 1000 live births in 1990 to 39 in 2018, sub-Saharan Africa witnessed an increase from 31% in 1990 to 54% in 2018. Morbidity has been reported to contribute largely to these deaths. This study examined the factors that are associated with childhood morbidity in sub-Saharan Africa.

Methods

Demographic and Health Surveys of 31 countries in sub-Saharan Africa were used in this study. The study involved 189 069 children who had or did not have fever, cough or diarrhoea in the 2 weeks preceding the surveys. Descriptive statistics and binary logistic regression were applied in the analysis.

Results

About 22% of the children suffered from fever, 23% suffered from cough and 16% suffered from diarrhoea. While the odds of experiencing fever increased by 37% and 18%, respectively, for children from poorest and poorer households, children of women aged 15–24 and 25–34 years are 47% and 23%, respectively, more likely to experience diarrhoea. The probability of suffering from morbidity increased for children who are 12–23 months, of higher order birth, small in size at birth and from households with non-improved toilet facility.

Conclusions

This study has shown that childhood morbidity remains a major health challenge in sub-Saharan Africa with socioeconomic, maternal, child’s and environmental factors playing significant roles. Efforts at addressing this problem should consider these factors.
Spatial variations and associated factors of modern contraceptive use in Ethiopia: a spatial and multilevel analysis
Authors: Tegegne Teketo Kassaw , Chojenta Catherine , Forder Peta Michelle , Getachew Theodros , Smith Roger , Loxton Deborah
Published: October 2020

Objective

To assess spatial variations in modern contraceptive use and to identify factors associated with it among married women in Ethiopia.

Design

Cross-sectional analysis of population-based and health facility data.

Setting

Ethiopia Demographic and Health Survey data linked to Service Provision Assessment data.

Population

8473 married women and 1020 facilities that reported providing family planning services.

Methods

A linked secondary data analysis of population and health facility data was carried out. Both multilevel and spatial analyses were conducted to identify key determinants of women’s use of modern contraceptive and spatial clustering of modern contraceptive use.

Main outcome measure

Modern contraceptive use.

Results

About 24% of the variation in the use of modern contraception was accounted for by location. A one-unit increase in the mean score of health facilities’ readiness to provide short-term modern contraceptives in a typical region was associated with a 20-fold increase in the odds of modern contraceptive use (adjusted OR (AOR) 20.49, 95% CI 1.44 to 29.54). In the spatial analysis, it was found that Addis Ababa and the Amhara region had high clusters of modern contraceptive use rates. On the other hand, low rates of contraceptive use were clustered in the Afar and Somali regions.

Conclusion

There were significant variations in the use of modern contraceptives across the different regions of Ethiopia. Therefore, regions with low contraceptive rates and high fertility rates should be targeted for scaling up and tailoring of services to the culture and lifestyles of the population of those regions.
Prevalence and determinants of breast cancer screening in four sub-Saharan African countries: a population-based study
Authors: Ba Djibril M , Ssentongo Paddy , Agbese Edeanya , Yang Yanxu , Cisse Ramata , Diakite Brehima , Traore Cheick Bougadari , Kamate Bakarou , Kassogue Yaya , Dolo Guimogo , Dembele Etienne , Diallo Hama , Maiga Mamoudou
Published: October 2020

Objectives

Breast cancer is the most prevalent cancer and the second leading cause of cancer-related deaths among women after cervical cancer in much of sub-Saharan Africa. This study aims to examine the prevalence and sociodemographic–socioeconomic factors associated with breast cancer screening among women of reproductive age in sub-Saharan Africa.

Design

A weighted population-based cross-sectional study using Demographic and Health Surveys (DHS) data. We used all available data on breast cancer screening from the DHS for four sub-Saharan African countries (Burkina Faso, Ivory Coast, Kenya and Namibia). Breast cancer screening was the outcome of interest for this study. Multivariable Poisson regression was used to identify independent factors associated with breast cancer screening.

Setting

Four countries participating in the DHS from 2010 to 2014 with data on breast cancer screening.

Participants

Women of reproductive age 15–49 years (N=39 646).

Results

The overall prevalence of breast cancer screening was only 12.9% during the study period, ranging from 5.2% in Ivory Coast to 23.1% in Namibia. Factors associated with breast cancer screening were secondary/higher education with adjusted prevalence ratio (adjusted PR)=2.33 (95% CI: 2.05 to 2.66) compared with no education; older participants, 35–49 years (adjusted PR=1.73, 95% CI : 1.56 to 1.91) compared with younger participants 15–24 years; health insurance coverage (adjusted PR=1.57, 95% CI: 1.47 to 1.68) compared with those with no health insurance and highest socioeconomic status (adjusted PR=1.33, 95% CI : 1.19 to 1.49) compared with lowest socioeconomic status.

Conclusion

Despite high breast cancer mortality rates in sub-Saharan Africa, the prevalence of breast cancer screening is substantially low and varies gradually across countries and in relation to factors such as education, age, health insurance coverage and household wealth index level. These results highlight the need for increased efforts to improve the uptake of breast cancer screening in sub-Saharan Africa.
Implementing a triage tool to improve appropriateness of care for children coming to the emergency department in a small hospital in India
Authors: Joshi Neha , Wadhwani Rakhi , Nagpal Jitender , Bhartia Saru
Published: October 2020

Background

In 2015, senior consultants at Sitaram Bhartia Institute of Science and Research saw several sick children in their outpatient clinics for which they had been seen in the emergency department the previous day. These children seemed to require admission but were sent home. This prompted us to review the paediatric care provided in our emergency department.

Methods

A multidisciplinary team was formed to run this improvement initiative. Review of literature suggested that establishing a triage system around a prevalidated triage tool would help us deliver more appropriate care. The South African Triage Scale was selected and adapted.

Interventions

With the aim of delivering appropriate care to at least 50% of children, a series of sequential interventions were tested using the improvement methodology of Plan-Do-Study-Act (PDSA) cycles, an approach recommended by the Institute for Healthcare Improvement. Learnings from the PDSA cycle of the previous intervention helped decide the subsequent change idea. The interventions included training in use of tool, increasing nurse staffing levels, using team huddles as feedback opportunities, introducing nurse reminders, reducing non-productive work, developing local leadership and training a restricted group of locum paediatricians. Qualitative and quantitative information was analysed to retain or reject change ideas.

Results

At baseline only 16%–17% of children were receiving appropriate care. The sequential changes resulted in a gradual improvement to a median of 63% of children receiving appropriate care by the end of 20 months.

Conclusions

We succeeded in establishing a paediatric emergency triage system and culture in the given setting through a unique enriching experience. We worked on removing systemic barriers and facilitating change while facing several unexpected outcomes. A sustained iterative approach may be the best way to achieving significant improvement in difficult settings like ours.
Physical activity and sedentary time in a rural adult population in Malawi compared with an age-matched US urban population
Authors: Pratt Michael , Sallis James F , Cain Kelli L , Conway Terry L , Palacios-Lopez Amparo , Zezza Alberto , Spoon Chad , Geremia Carrie M , Gaddis Isis , Amankwah Akuffo , Friedman Jed , Kilic Talip
Published: October 2020

Objectives

This study was designed to assess patterns of objectively measured physical activity (PA) and sedentary behaviour in a sample of adults in a rural setting from a low-income Sub-Saharan African country (Malawi). The patterns of PA and sedentary behaviour in Malawi were compared with US data collected and analysed using the same methodology.

Methods

The Malawi PA data were collected as part of a survey experiment on the measurement of agricultural labor conducted under the World Bank Living Standards Measurement Study program. ActiGraph accelerometers (model GT3X) were worn on the right hip in a household-based sample of 414 working-age adults (15–85 years).

Results

Mean total and 95% CIs for PA by category in min/day for Malawi adults were: sedentary 387.6 (377.4–397.8), low-light 222.1 (214.7–229.5), high-light 136.3 (132.7–139.9), moderate 71.6 (68.8–74.5), vigorous 1.1 (0.5–1.8) and moderate-to-vigorous physical activity (MVPA) 72.8 (69.7–75.9). Mean of PA and sedentary behavior (min/day) summed across age and sex groups are compared between Malawi and US samples: sedentary behaviour, 387.6 vs 525.8 (p<0.001); low-light, 222.1 vs 217.0 (p=ns); high-light, 136.3 vs 45.6 (p<0.001); moderate, 71.6 vs 28.0 (p<0.001); vigorous, 1.1 vs 2.5 (p<0.001); MVPA, 72.8 vs 30.5 (p<0.001). Compared with the USA, Malawi participants averaged consistently less sedentary time/day and more minutes/day in all intensity levels of PA, except for low-light and vigorous PA.

Conclusion

Overall, levels of MVPA and high-light activity in adults in Malawi were substantially higher and sedentary time was substantially lower than those observed in US samples using near identical data collection, scoring and analysis.