bluuebunny/crossref_metadata_2025_split huggingface dataset:
MPI Parallelization for Two-Way Coupled Euler-Lagrange Simulation of Microbubble Enhanced HIFU
Authors: Ma Jingsen , Gnanaskandan Aswin , Hsiao Chao-Tsung , Chahine Georges L. 
Published: October 2020

Abstract
Microbubble enhanced High Intensity Focused Ultrasound (HIFU) is of great interest to tissue ablation for tumor treatment such as in liver and brain cancers, in which ultrasonic contrast agent microbubbles are injected to the targeted region to promote local heating while reducing pre-focal damage. To accurately characterize the acoustic and thermal fields during this process, a compressible Euler-Lagrange model is used. The non-linear ultrasound field is modeled using compressible N-S equations on an Eulerian grid, while the microbubbles are tracked as discrete singularities in a Lagrangian fashion with their dynamics computed. Their intimate coupling is realized through the local void fraction, which is computed from the instantaneous bubble volumes and locations, and then fed to the fluid continuum model.
Owing to demanding computational cost in real applications, schemes for significant speedup are highly desirable. We present here a MPI parallelization scheme based on domain decomposition for both the continuum fluid and the discrete bubbles. The Eulerian computational domain is subdivided into several subdomains having each the same number of grids, while the bubbles are subdivided based on their locations corresponding to each subdomain. During each computation time step, MPI processors, each handling one subdomain, are 1) first used to execute the fluid computation, and 2) then to execute the bubble computations, 3) followed by the coupling procedure, which maps the void fraction from the Lagrangian bubble solutions into the Eulerian grids.
Steps 1) and 2) are relatively straightforward by routinely following regular MPI procedures. However, step 3) becomes challenging as the effect of the bubbles through the void fraction at an Eulerian point near a subdomain border will require information from bubbles located in different subdomains. Similarly, a bubble near a border between subdomains will spread its contribution to the void fraction of different subdomains. This is addressed by a special utilization of ghost cells surrounding each fluid subdomain, which allows bubbles to spread their void fraction effects across subdomain edges without the need of exchanging directly bubble information between subdomains and significantly increasing overhead. This void fraction implementation is verified by gas volume conservation before and after spreading the bubble effects. Other bubble effects such as thermal effects are handled in a similar way.
This parallelization scheme is validated and illustrated on a typical microbubble enhanced HIFU problem, followed by parallelization scaling tests and efficiency analysis.
Application of Advanced RANS Turbulence Models for the Prediction of Turbomachinery Flows
Authors: Casartelli Ernesto , Mangani Luca , Roos David , Del Rio Armando 
Published: October 2020

Abstract
The simulation models used in the design process of modern turbo-machines are becoming increasingly complex. Nevertheless, the steady-state RANS approach is still the mostly used method for CFD computations. However, detailed flow information is more and more required for further improving the performance and extend the operating range. Turbulence modeling has becoming therefore a key issue in this context. The increased computer power already available would enable the use of more sophisticated turbulence models than standard two equation ones, such as SST k-omega and k-epsilon. These, despite their shortcomings, are still predominant in the field, since more advanced models often lead to numerical instabilities in the simulations. The most important shortcomings can be related to either boundary layer effects or mixing process in the channels. In order to improve the predictions considering boundary layer effects, like impingement or large pressure gradients in flow direction, various derivations of four equations models were investigated. Using an additional transport equation for the wall normal Reynolds-stress component and an elliptic equation for near-wall effects, they improve the results for this kind of flows. Considering the accurate prediction of mixing processes, like (1) the interaction of tip-clearance vortices with the main flow or (2) off-design conditions, the focus was oriented to the anisotropy present in the turbulent structures. Standard models are often not sufficient to predict accurately vortices, which can have a huge impact on the performance, since based on the assumption of isotropic turbulence. Accordingly, they tend to dissipate and diffuse the vortices too quickly. Improved models, which take the anisotropic nature of the Reynolds-stresses into account, can help in this context. The models can thereby introduce the additional anisotropy via an explicit algebraic expression, or model directly the transport equations for the Reynolds-stresses. In order to improve the predictions using advanced turbulence models a particularly robust framework based on a pressure-based fully coupled approach was used.
The goal of this work is the development and testing of improved models for the application in turbo-machinery. The focus lies thereby on near-wall behavior and mixing / vortex dissipation. The assessment of the models is exemplarily used on the centrifugal compressor open-case Radiver with vaned diffuser.
Predicting Solid Particle Erosion and Uncertainty in Elbows by Artificial Intelligence Methods
Authors: Karimi Soroor , Xu Bohan , Asgharpour Alireza , Shirazi Siamack A. , Sen Sandip 
Published: October 2020

Abstract
AI approaches include machine learning algorithms in which models are trained from existing data to predict the behavior of the system for previously unseen cases. Recent studies at the Erosion/Corrosion Research Center (E/CRC) have shown that these methods can be quite effective in predicting erosion. However, these methods are not widely used in the engineering industries due to the lack of work and information in this area. Moreover, in most of the available literature, the reported models and results have not been rigorously tested. This fact suggests that these models cannot be fully trusted for the applications for which they are trained. Therefore, in this study three machine learning models, including Elastic Net, Random Forest and Support Vector Machine (SVM), are utilized to increase the confidence in these tools. First, these models are trained with a training data set. Next, the model hyper-parameters are optimized by using nested cross validation. Finally, the results are verified with a test data set. This process is repeated several times to assure the accuracy of the results. In order to be able to predict the erosion under different conditions with these three models, six main variables are considered in the training data set. These variables include material hardness, pipe diameter, particle size, liquid viscosity, liquid superficial velocity, and gas superficial velocity. All three studied models show good prediction performances. The Random Forest and SVM approaches, however, show slightly better results compared to Elastic Net. The performance of these models is compared to both CFD erosion simulation results and also to Sand Production Pipe Saver (SPPS) results, a mechanistic erosion prediction software developed at the E/CRC. The comparison shows SVM prediction has a better match with both CFD and SPPS. The application of AI model to determine the uncertainty of calculated erosion is also discussed.
Multiphase Flow Development on Single Particle Migration in Low Reynolds Number Fluid Domains
Authors: Pourghasemi Mahyar , Fathi Nima , Vorobieff Peter , Ahmadi Goodarz , Anderson Kevin R. 
Published: October 2020

Abstract
Here we present the results of the newly developed Eulerian-Lagrangian model to simulate both the primary and the secondary phases coupled in a transient analysis. A set of two a-dimensional, transient linear shear flow at low Reynolds numbers was considered, and the effect of shearing rate on a suspended buoyant spherical solid particle was analyzed. The rotation and displacement of the solid particle are considered in the model, and the effect of the secondary phase on the primary phase is also evaluated at each time step without any simplification. In order to overcome the existing discontinuity at the interface between secondary and primary phases in this Eulerian-Lagrangian approach, the interface between the solid particle and the fluid phase is replaced by a kernel function creating a smooth profile from the solid into the liquid with a predefined thickness. Several simulations were performed, and the reliability of the developed model was assessed. The global deviation grid convergence index (GCI) approach was employed to perform solution verification. The observed order of accuracy of the primary phase solver approaches 2, consistent with the formal order of accuracy of the applied discretization scheme. The obtained velocity profiles from the computational analyses show excellent agreement with the analytical solution confirming the reliability of the single-phase flow solver. To validate the computational results for the multiphase flow solver, we used the experimental data from our newly developed linear shear flow apparatus with suspended buoyant particles.
Effects of Taper Configurations on Heat Transfer and Pressure Drop in Single-Phase Flows in Microgaps
Authors: Moreira Debora C. , Ribatski Gherhardt , Kandlikar Satish G. 
Published: October 2020

Abstract
This paper presents a comparison of heat transfer and pressure drop during single-phase flows inside diverging, converging, and uniform microgaps using distilled water as the working fluid. The microgaps were created on a plain heated copper surface with a polysulfone cover that was either uniform or tapered with an angle of 3.4°. The average gap height was 400 microns and the length and width dimensions were 10 mm × 10 mm, resulting in an average hydraulic diameter of approximately 800 microns for all configurations. Experiments were conducted at atmospheric pressure and the inlet temperature was set to 30 °C. Heat transfer and pressure drop data were acquired for flow rates varying from 57 to 485 ml/min and the surface temperature was monitored not to exceed 90 °C to avoid bubble nucleation, so the heat flux varied from 35 to 153 W/cm2 depending on the flow rate. The uniform configuration resulted in the lowest pressure drop, and the diverging one showed slightly higher pressure drop values than the converging configuration, possibly because the flow is most constrained at the inlet section, where the fluid is colder and presents higher viscosity. In addition, a minor dependence of pressure drop with heat flux was observed due to temperature dependent properties. The best heat transfer performance was obtained with the converging configuration, which was especially significant at low flow rates. This behavior could be explained by an increase in the heat transfer coefficient due to flow acceleration in converging gaps, which compensates the decrease in temperature difference between the fluid and the surface due to fluid heating along the gap. Overall, the comparison between the three configurations shows that converging microgaps have better performance than uniform or diverging ones for single-phase flows, and such effect is more pronounced at lower flow rates, when the fluid experiences higher temperature changes.
Evolution of Heat Transfer in Pool Boiling in Contaminated Water
Authors: Graham Jacob , Hawa Angelo , Weisensee Patricia 
Published: October 2020

Abstract
Boiling heat transfer serves as an efficient mechanism to dissipate large amounts of thermal energy due to the latent heat of phase change. In academic studies, typically ultra-pure deionized (DI) water is used to avoid contamination. However, in industrial and commercial settings, the working fluid might be contaminated with sediments, dust, salts, or organic matter. Long-term boiling processes in non-DI water cause substantial build-up of a stable layer of deposit that dramatically reduces the heat transfer coefficient. Therefore, heating applications in a contaminated medium demand strategies to prevent such fouling. Here, we studied the use of lubricant infused surfaces (LIS) and their ability to possibly minimize the deposition of calcium sulfate. Aluminum samples were infused with Krytox 102 oil and the heat transfer coefficient was investigated at a vertical and horizontal surface orientation. Fouling effects were introduced by pool boiling for 7.5 hours in a 6.97 mM calcium sulfate solution at constant heat flux. Heat flux curves for both plain aluminum and LIS were calibrated before contamination. Initially, the LIS was unable to support a nucleate phase and transitioned directly from liquid convection to film boiling heat transfer. Upon partial degradation of the lubricant layer during long-run experiments, nucleate boiling ensued. Over 7.5 hours, the heat transfer coefficient of each sample (Al and LIS) degraded between 5.4% and 7.9% with no significant correlation with either lubricant treatment or surface orientation. Post boiling profilometry was conducted on each sample to characterize the thickness and distribution of the calcium sulfate layer. In these experiments, the plain aluminum surface outperformed the LIS at both orientations in minimizing calcium layer thickness. The LIS oriented vertically outperformed the LIS oriented horizontally.
A General Correlation for Frictional Pressure Drop of Flow Boiling in Plate Heat Exchangers
Authors: Tang Weiyu , Lv Tong , Zheng Boren , Li Wei 
Published: October 2020

Abstract
Plate heat exchangers are widely used in various industries for many years. The corrugated channels on the plates effectively enhance the turbulence of flow boiling and complicate the prediction of pressure drop. This paper presents a brief review about the influence factors of frictional pressure drop during flow boiling in plate heat exchangers. Experimental data points of frictional pressure drop were collected from previous literatures to develop a general correlation. The database contained 454 data points, covering eight refrigerants, mass flux range 5.5–137 kg m-2 s-1, heat flux 0–30 kW m-2, vapor quality 0.07–0.95, saturation pressure 0.11–2.7 MPa, chevron angle 30°–70° and hydraulic diameter 1.7–5.4 mm. In this work, several existing correlations were compared with the database, and all of them seem fail to give an acceptable prediction. A new correlation was proposed with multiple regression analysis in terms of two-phase Fanning friction factor. The new method showed good agreement and predicted 63.2% and 92.9% of data points within ±30% and ±50% errors, respectively.
Steam Flow Condensation on Superhydrophobic Surfaces in a High Aspect Ratio Microchannel
Authors: Mohammadpour Chehrghani Mirvahid , Abbasiasl Taher , Gharib Ghazaleh , Kosar Ali , Khalili Sadaghiani Abdolali 
Published: October 2020

Abstract
Steam flow condensation has a wide range of applications in the industry such as in air conditioning, refrigeration, and thermal power plants. Condensation of steam on highly hydrophobic surfaces has resulted in notable heat transfer improvement compared to conventional hydrophilic surfaces. Dropwise condensation and increased droplet mobility are the main reason for thermal performance enhancement of superhydrophobic surfaces. Although there are considerable reports of enhanced thermal transport behavior of highly hydrophobic surfaces on steam condensation, the literature lacks sufficient investigation on flow condensation of steam, such as the effect of average vapor quality change on heat transfer rate.
Unlike gravity-driven droplet departure in quiescent dropwise condensation, droplet departure sizes in flow condensation are governed by flow-droplet shear forces and droplet-surface adhesive forces. This work experimentally investigates steam flow condensation on nanotextured highly hydrophobic and slightly hydrophobic surfaces. The experimental setup consists of a reservoir, boiler, superheater, condensation chamber (test section), pre-condenser (to adjust the inlet quality), a post condenser, and a pump. A high aspect ratio microchannel was used as the test section. Different mass fluxes and inlet vapor qualities were used for the experimentations. Visualization studies were performed to analyze droplet dynamics such as droplet departure and coalescence in flow condensation. It is shown that for both surfaces increase condensation heat transfer coefficient were a function of both average quality and mass flux. Increase in mass flux from G = 8 kg/m2s to G = 14 kg/m2s, resulted in 65% and 60% enhancement in condensation heat transfer coefficient of slightly hydrophobic and highly hydrophobic surfaces respectively.
Numerical Prediction of Dropwise Condensation Performances Over Hybrid Surfaces, Under the Action of Gravity and Vapor Shear
Authors: Suzzi Nicola , Croce Giulio , D’Agaro Paola 
Published: October 2020

Abstract
A Lagrangian model following the history of every droplet belonging to an evolving droplets population, originally developed to simulate pattern evolution in the framework of in-flight icing phenomenon, is used in order to simulate dropwise condensation over different shaped micro-structured surfaces. Both the mechanical and the thermal energy balances are solved for every droplet, allowing to predict droplet velocity and condensing flow rate. Coalescence phenomenon is also implemented. The model in the present form is an evolution of the code presented at ICNMM 2019, introducing the effect of vapor shear, a physical model of the evolution of the dynamic contact angle during droplet growth and a prediction of condensing flow rate through the solution of thermal energy balance, thus taking into account the influence of the droplet size. Shared memory parallelization is also carried out decomposing the computational domain into different subdomains, allowing the efficient simulation of a larger number of droplets.
Here, the model is validated and used to predict the heat transfer performance of hybrid condensation surfaces, both plane and curved, under the action of both gravity and vapor shear. Starting from literature proposals, several patterns, each characterized by a complex composition of patches with different wettabilities, are numerically investigated and the configuration ensuring the best heat transfer performance and liquid drainage is identified. The sensitivity of the solution with respect to the uncertainty on the estimate of some parameters, such as nucleation density, is also discussed.
Effect of birth order on stereoacuity in Chinese preschool children: a cross-sectional study
Authors: Han Shu , Zhang Xiaohan , Li Rui , Tong Haohai , Zhao Xiaoyan , Wang Yue , Hao Qingfeng , Huang Dan , Zhu Hui , Zhang Xiaojun , Liu Hu 
Published: October 2020

ObjectiveThis study aimed to investigate the relationship between birth order and stereoacuity among Chinese children aged 60–72 months.DesignCross-sectional.Participants1342 children with complete data on the questionnaire, stereoacuity and refraction were included.ResultsThe mean stereoacuity was 53.2±1.7, 56.9±1.9 and 60.9±1.5 s of arc in the first-born group, second-born group and third-born group, respectively. Lower birth order was significantly correlated with better stereoacuity (p=0.036). Third-borns (OR=3.02, p=0.027) were at higher risk of having subnormal stereoacuity compared with first-borns in the multivariate analysis.ConclusionLater-borns had poorer stereoacuity than first-borns.
Population-based rapid assessment of avoidable blindness survey in Sohag governorate in Egypt
Authors: AlSawahli Heba , McCormick Ian , Mpyet Caleb D , Ezzelarab Gamal , Shalaby Mohammad 
Published: October 2020

ObjectivesTo determine the prevalence and causes of blindness and vision impairment, and the coverage and quality of cataract surgical services, among population aged 50 years and older in Sohag governorate in Egypt.DesignA population-based cross-sectional survey using two-stage cluster random sampling following the rapid assessment of avoidable blindness methodology.SettingA community-based survey conducted by six teams of ophthalmologists, assistants and local guides. Enrolment and examination were door-to-door in selected clusters.ParticipantsUsing 2016 census data, 68 population units were randomly selected as clusters (of 60 people) with probability proportionate to population size. Anyone aged 50 years and older, residing in a non-institutional setting in a cluster for at least 6 months, was eligible to participate.Primary and secondary outcome measuresThe prevalence and causes of blindness and vision impairment. Secondary outcomes were CSC and effectiveness and participant-reported barriers to cataract surgery.ResultsOf 4078 participants enrolled, 4033 (98.9%) were examined. The age-adjusted and sex-adjusted prevalence of blindness, severe vision impairment and moderate vision impairment were 5.9% (95% CI 4.8% to 6.9%), 4.7% (95% CI 3.8% to 5.7%) and 18.9% (95% CI 16.8% to 21.0%), respectively. Cataract caused most of blindness (41.6%), followed by non-trachomatous corneal opacity (15.7%) and posterior segment diseases (14.5%). Cataract surgical coverage (CSC) for persons for visual acuity <3/60 was 86.8%, the proportion of cataract surgeries with poor visual outcome was 29.5% and effective CSC (eCSC) was 44.9%. eCSC was lower in women than men. The most frequently reported barrier to surgery was cost (51.5%).ConclusionsThe prevalence of blindness in Sohag governorate is higher than districts in other middle-income countries in the region. CSC was high; however, women suffer worse quality-corrected CSC than men. The quality of cataract surgery needs to be addressed, while health system strengthening across government and private settings could alleviate financial barriers.
Asymmetric crypt fission in sessile serrated lesions
Authors: Rubio Carlos A , Schmidt Peter T 
Published: October 2020

ObjectiveSessile serrated lesions without dysplasia (SSL-ND) are epitomised by dilated crypts with epithelial serrations and architectural distortions portraying boot-shapes, L-shapes or inverted-T shapes. Recently, crypts in asymmetric fission were detected in SSL-ND. The purpose was to assess the frequency of crypts in asymmetric fission in a cohort of SSL-ND.MethodsThe frequency of crypts in fission was assessed in 60 SSL-ND, the distribution of cell proliferation in 48 SSL-ND and the expression of maspin, a tumour-suppressor protein, in 29 SSL-ND.ResultsOut of the 60 SSL-ND, 40 (66.7%) showed crypts in fission: 39 (65%) SSL-ND had crypts in asymmetric fission and one SSL-ND (1.7%), in symmetric fission (p<0.05). Of 1495 crypts recorded in the 60 SSL-ND, 73 (4.9%) were in asymmetric fission but only one (0.06%), in symmetric fission (p<0.05). Out of the 48 Ki67-immunostained SSL-ND,15 (31%) showed randomly distributed proliferating cell-domains. All 29 SSL-ND revealed maspin-upregulation (including crypts in asymmetric and symmetric fission). In contrast, the normal colon mucosa showed occasional single crypts in symmetric fission, proliferating cell-domains limited to the lower thirds of the crypts, absence of crypts in asymmetric fission and remained maspin negative.ConclusionsSSL-ND thrive with crypts in asymmetric fission displaying randomly distributed proliferating cell-domains and maspin-upregulation. These histo-biological aberrations disclose pathological cryptogenesis and suggest possibly unfolding somatic mutations in SSL-ND. The present findings may open new vistas on the parameters pertinent to the susceptibility of SSL-ND to develop dysplasia and carcinoma.