bluuebunny/crossref_metadata_2025 huggingface dataset:
La agricultura urbana en Caracas: diagnóstico de los espacios agroproductivos desde una perspectiva socioecológica
Authors: Herrera Francisco
Published: October 2018

El incremento de la población urbana ha acarreado dificultades para el acceso a los alimentos, lo cual ha propiciado el surgimiento del fenómeno de la agricultura urbana. En Caracas, esta práctica se ha manifestado con la aparición de unidades de producción agrícola. El presente estudiocomprende un diagnóstico multidimensional que sugiere relaciones entre factores económicos, sociales y ecológicos, que se perfilan como aspectos determinantes de soberanía y sustentabilidad en trece unidades. Asimismo, se localizan varias fortalezas de dicha estructura, entre las cuales se sitúan la organización social, la diversidad cultural y el acceso a políticas públicas. En tanto, sus limitantes se centran en el acceso asemillas y la poca diversidad de rubros y prácticas. En suma, el diagnóstico expuesto representa un aporte metodológico para el seguimiento de unidades de agricultura urbana.
Cultura y conservación in situ de tubérculos andinos marginados en agroecosistemas de Boyacá: un análisis de su persistencia desde la época prehispánica hasta el año 2016
Authors: Clavijo Ponce Neidy Lorena
Published: October 2018

Con base en una indagación histórica, que tiene como complementada el estudio de caso de dos municipios del departamento de Boyacá, el presente estudio se propone identificar varios elementos culturales relacionados con tres especies andinas marginadas (Oxalis tuberosa Molina), (Tropaelum tuberosum Ruíz & Pavón) y (Ullucus tuberosus Caldas), los cuales surgen desde la época prehispánica y se sostienen hasta elpresente. Según ese marco, las evidencias muestran un sistema de conocimiento que corresponde a las creencias y las valoraciones que se organizan en torno a estas especies. Asimismo, es notorio que dicho esquema ha permanecido constante a lo largo del tiempo, al igual que tecnologías y prácticas de cultivo e intercambio, las cuales han permanecido y no sufrido mayores modificaciones desde la época precolombina,a pesar de la embestida de la revolución verde.
Desarrollo agrario y complejidad económica: estudio de caso de una empresa agrícola de Murcia, España
Authors: Noguera-Méndez Pedro
Published: October 2018

Desde la perspectiva de la complejidad económica se puede explicar el desarrollo a partir del proceso de acumulación de conocimiento incorporado a los bienes y servicios. A partir del estudio de la evolución de una empresa agrícola de Murcia (España), dedicada, desde 1995, a la producción, manipulación y comercialización de uva de mesa sin pepita y de su comparación con otras empresas agrícolas tradicionales, se examinan diversos conceptos de esta perspectiva; en particular la incorporación de conocimiento e información a los productos y la formación de redes tanto de personas como de empresas.
An Improved Thermal-Resistance-Capacitance Model for Vertical Single U-Tube Ground Heat Exchanger
Authors: Liao Quan , Fan Yongxiang , Zhu Xiaobo , Li Jintang
Published: October 2018

Based on four-thermal-resistance-capacitance network within a borehole, an improved thermal-resistance-capacitance model (TRCM), which takes into account the effect of nonuniform temperature distribution along the borehole perimeter, is proposed for vertical single U-tube ground heat exchanger. For a given geometric and physical parameters of ground heat exchanger, the numerical simulations of the conventional TRCM based on three-thermal-resistance-capacitance network within borehole, the improved TRCM based on four-thermal-resistance-capacitance network within borehole and three-dimensional (3D) finite volume computational fluid dynamics (CFD) model by using fluent software were conducted, respectively. Through the comprehensive comparisons of simulation results between these above-mentioned three models for vertical single U-tube ground heat exchanger, it could be concluded that the proposed improved TRCM could not only provide relatively high accurate results, but also remarkably decrease the solving time as compared to the benchmark 3D finite volume CFD model. Since the proposed TRCM has better performance than the one based on three-thermal-resistance-capacitance network within borehole and 3D finite volume CFD model, a new reliable and feasible TRCM for vertical single U-tube ground heat exchanger could be available for the design and optimization of ground heat exchanger, the data interpretation of thermal response test (TRT) and other applications of ground heat exchanger in real industrial engineering.
Development of Experimental Instrumentation for Measurement of Advection in Narrow Aperture in Granite Block
Authors: Kotowsk Jaroslav , Černoušek Tomáš , Jankovský Filip , Kůs Pavel , Polívka Petr , Skala Martin , Kovářová Hana , Zuna Milan
Published: October 2018

A granite block, acquired from a quarry Panská Dubenka located in the Czech Republic and used in presented experiments, is part of the same bedrock that can be potentially used for a deep geological repository. It is important to characterize advection in fractured rock to assess possible groundwater contamination. Newly used method—three-dimensional scanning using Hexagon Romer Arm was implemented to characterize the morphology of an examined fractured block with a aperture. The scanning technology provides the possibility to digitalize the rock surface. The scanning can be also used to determine any changes in the rock surface. The block was instrumented by tubing, and the aperture was sealed using a silicone. Flow paths were investigated by the comparison of fluid weights on the outlet on every output/site. The Hexagon Romer Arm is an ideal tool for the precise determination of a aperture's width in its full volume.
Interaction of Flow and Film-Cooling Effectiveness Between Double-Jet Film-Cooling Holes With Various Spanwise Distances
Authors: Yao Jiaxu , Xu Jin , Zhang Ke , Lei Jiang , Wright Lesley M.
Published: October 2018

The interaction of flow and film-cooling effectiveness between jets of double-jet film-cooling (DJFC) holes on a flat plate is studied experimentally. The time-averaged flow field in several axial positions (X/d = −2.0, 1.0, and 5.0) is obtained through a seven-hole probe. The downstream film-cooling effectiveness on the flat plate is measured by pressure sensitive paint (PSP). The inclination angle (θ) of all the holes is 35 deg, and the compound angle (β) is ±45 deg. Effects of the spanwise distance (p = 0, 0.5d, 1.0d, 1.5d, and 2.0d) between the two interacting jets of DJFC holes are studied, while the streamwise distance (s) is kept as 3d. The blowing ratio (M) varies as 0.5, 1.0, 1.5, and 2.0. The density ratio (DR) is maintained at 1.0. Results show that the interaction between the two jets of DJFC holes has different effects at different spanwise distances. For a small spanwise distance (p/d = 0), the interaction between the jets presents a pressing effect. The downstream jet is pressed down and kept attached to the surface by the upstream one. The effectiveness is not sensitive to blowing ratios. For mid-spanwise distances (p/d = 0.5 and 1.0), the antikidney vortex pair dominates the interaction and pushes both of the jets down, thus leading to better coolant coverage and higher effectiveness. As the spanwise distance becomes larger (p/d ≥ 1.5), the pressing effect almost disappears, and the antikidney vortex pair effect is weaker. The jets separate from each other and the coolant coverage decreases. At a higher blowing ratio, the interaction between the jets of DJFC holes happens later.
Effect of Density Ratio on Film-Cooling Effectiveness Distribution and Its Uniformity for Several Hole Geometries on a Flat Plate
Authors: Yao Jiaxu , Xu Jin , Zhang Ke , Lei Jiang , Wright Lesley M.
Published: October 2018

The film cooling effectiveness distribution and its uniformity downstream of a row of film cooling holes on a flat plate are investigated by pressure sensitive paint (PSP) under different density ratios. Several hole geometries are studied, including streamwise cylindrical holes, compound-angled cylindrical holes, streamwise fan-shape holes, compound-angled fan-shape holes, and double-jet film-cooling (DJFC) holes. All of them have an inclination angle (θ) of 35 deg. The compound angle (β) is 45 deg. The fan-shape holes have a 10 deg expansion in the spanwise direction. For a fair comparison, the pitch is kept as 4d for the cylindrical and the fan-shape holes, and 8d for the DJFC holes. The uniformity of effectiveness distribution is described by a new parameter (Lateral-Uniformity, LU) defined in this paper. The effects of density ratios (DR = 1.0, 1.5 and 2.5) on the film-cooling effectiveness and its uniformity are focused. Differences among geometries and effects of blowing ratios (M = 0.5, 1.0, 1.5, and 2.0) are also considered. The results show that at higher density ratios, the lateral spread of the discrete-hole geometries (i.e., the cylindrical and the fan-shape holes) is enhanced, while the DJFC holes is more advantageous in film-cooling effectiveness. Mostly, a higher lateral-uniformity is obtained at DR = 2.5 due to better coolant coverage and enhanced lateral spread, but the effects of the density ratio on the lateral-uniformity are not monotonic in some cases. Utilizing the compound angle configuration leads to an increased lateral-uniformity due to a stronger spanwise motion of the jet. Generally, with a higher blowing ratio, the lateral-uniformity of the discrete-hole geometries decreases due to narrower traces, while that of the DJFC holes increases due to a stronger spanwise movement.
Thermal Management and Characterization of High-Power Wide-Bandgap Semiconductor Electronic and Photonic Devices in Automotive Applications
Authors: Oh Seung Kyu , Lundh James Spencer , Shervin Shahab , Chatterjee Bikramjit , Lee Dong Kyu , Choi Sukwon , Kwak Joon Seop , Ryou Jae-Hyun
Published: October 2018

GaN-based high-power wide-bandgap semiconductor electronics and photonics have been considered as promising candidates to replace conventional devices for automotive applications due to high energy conversion efficiency, ruggedness, and superior transient performance. However, performance and reliability are detrimentally impacted by significant heat generation in the device active area. Therefore, thermal management plays a critical role in the development of GaN-based high-power electronic and photonic devices. This paper presents a comprehensive review of the thermal management strategies for GaN-based lateral power/RF transistors and light-emitting diodes (LEDs) reported by researchers in both industry and academia. The review is divided into three parts: (1) a survey of thermal metrology techniques, including infrared thermography, Raman thermometry, and thermoreflectance thermal imaging, that have been applied to study GaN electronics and photonics; (2) practical thermal management solutions for GaN power electronics; and (3) packaging techniques and cooling systems for GaN LEDs used in automotive lighting applications.
Design and Development of an Ultra Low Head Axial Hydro Turbine for Electricity Supply: Part I
Authors: Chen Jinbo , Engeda Abraham
Published: October 2018

As a major resource for electricity, hydropower is widely used around the world for renewable energy. Traditionally, large high-capital cost dam equipped with large turbine system is preferred to produce sufficient power supply. However, recently large hydropower system is questioned because of the impact of dams on the local environment, which could be a major barrier for development of large hydropower system. Besides, billions people remain without access to electricity and most of them are in remote and rural location where is not suitable for large hydropower system. Therefore, the utilization of ultra-low-head (ULH) water energy (situations where the hydraulic head is less than 3m or the water flow rate is more than 0.5m/s with zero head) has becomes more attractive. Part I of this paper focus on developing a design methodology for a low-impact, damless Kaplan turbine system for ULH water resource.
Experimental Study on Pressure Transients With Cavitation in Low Pressure Water-Hydraulic Pipeline
Authors: Jiang Dan , Ren Cong , Guo Qing
Published: October 2018

In this study, pressure transients are triggered by a steel ball, which is released from an upstream reservoir to hit a valve seat and shut off water flow in a horizontal straight copper pipeline. The pressure pulsations, cavitation and gas bubbles growth and collapse in the low pressure water-hydraulic pipeline are recorded by two pressure transducers and a high speed video camera, respectively. In addition, the influences of initial volume of gas bubbles in water and instant leakage in valve are investigated. The experimental results indicate that increasing initial gas bubble volume in water and the instant leakage of the valve will help to reduce magnitudes and numbers of pressure peaks during pressure transients. Then methods to reduce pressure pulsations in pipelines are put forward.
Turbulent Structure With Microbubbles Generated by Electrolysis in a Horizontal Channel Flow
Authors: Hiroi Takamichi , Hamada Tatsuya , Makino Masahiko , Kawakita Chiharu
Published: October 2018

The turbulent structure of flow field with microbubbles which is generated by electrolysis in a horizontal water channel is investigated at Reynolds number Rem = 24000 (based on the channel height). Firstly, Shadow Image Technique (SIT) is applied to investigate the relation between the shape and the velocity of microbubbles. The experiments have been carried out at the current value 100mA, 200mA, 300mA. The amount of gas generated by electrolysis per unit time is estimated 1.89–5.67 mm3/s. The void fraction is 0.95 × 10−5 – 2.93 × 10−4 %. The mode of the equivalent diameter is 5–10 μm regardless of the condition of the current value. In contrast the mean of the equivalent diameter increases with the increasing of the current value. The mean streamwise velocity of microbubbles increases with the current value. Secondly, Particle Image Velocimetry (PIV) is applied to investigate the turbulent structure in a microbubble channel flow. The experiments have been carried out at the current value 250mA, 300mA. The streamwise mean velocity decreases with the increasing of the current value. The velocity normal from the wall increases by microbubbles. The turbulent intensity with microbubble is bigger than that without microbubble. The Reynolds shear stress with microbubble, however, is smaller than that without microbubble. The decreasing of contribution to the friction coefficient of the turbulent component is calculated about 6.4 % using FIK identify at a low void fraction 2.93 × 10−4 %. The increasing of the frequency of inner interaction and outer interaction causes the decreasing of Reynolds shear stress is clarified by quadrant analysis.
Optimization of Piece-Wise Conical Nozzles: Theory and Application
Authors: Hasselmann Karsten , Bin Khamalrudin Muhammad Aiman , aus der Wiesche Stefan , Kenig Eugeny Y.
Published: October 2018

In this contribution, an optimization study based on computational fluid dynamics (CFD) in combination with Stratford’s analytical separation criterion was developed for the design of piece-wise conical contraction zones. The occurrence of flow separation can be formally described by a newly introduced dimensionless separation number. In the optimization process, the risk of flow separation is reduced by minimizing this separation number. It was found that the optimized piece-wise conical nozzle shape did not correspond to a simple geometric approximation of the ideal polynomial shape. In fact, it was beneficial to reduce the deflection in the outlet region for a piece-wise conical nozzle stronger than for a conventional one. In order to validate the new design method, large-scale tests for different nozzle designs were conducted. The measured velocity profiles and wall pressure distributions agreed well with the CFD predictions. The new method was applied for designing the contraction zone of a new closed-loop organic vapor wind tunnel (CLOWT) working at elevated pressure levels.
Water-Oil Flow in Square Microchannels With a Crossed Junction
Authors: Cao Zhen , Wu Zan , Qian Jin-yuan , Sunden Bengt
Published: October 2018

In the present study, water-oil flow patterns and slug hydrodynamics were experimentally studied in square glass microchannels with various hydraulic diameters (Dh = 600 μm, 400 μm, 200 μm). The aqueous phase is the continuous phase while the organic phase is the dispersed phase. The ranges of flow rates of the continuous phase and the dispersed phase are 0–200 ml/h and 0–12 ml/h, 0–120 ml/h and 0–6 ml/h, and 0–60 ml/h and 0–2 ml/h in the microchannels with Dh = 600 μm, 400 μm and 200 μm, respectively. The results show that the hydraulic diameter has significant effects on flow patterns and three main flow patterns are observed, i.e., annular flow, slug flow and droplet flow. Generally, annular flow appeared at high flow rates of the dispersed phase and low flow rates of the continuous phase, while droplet flow appeared at low flow rates of the dispersed phase and high flow rates of the continuous phase. However, slug flow existed at comparable flow rates of the continuous and dispersed phases. A dimensionless analysis is carried out and a new dimensionless group including Weber number and Reynolds number is derived. The new defined dimensionless group performs well to develop a general flow pattern map. In addition, slug flow hydrodynamics are investigated as well in the present study, considering the slug length and slug velocity. Based on the present experimental results, a new scaling law is proposed to predict the slug length and it shows a good agreement with the experimental results. It has been widely reported that slug velocities depend linearly on the total flow rates of the two phases, which is consistent with the present study. The linear law provides a good prediction of the experimental slug velocities but different slopes are suggested in microchannels with different hydraulic diameters.
Detailed Pressure Measurements During the Transition to Rotating Stall in an Axial Compressor: Influence of the Throttling Process
Authors: Margalida Gabriel , Dazin Antoine , Joseph Pierric , Roussette Olivier
Published: October 2018

This paper presents experimental unsteady pressure measurements gathered on a single stage axial compressor during pre-stall and transition to stall operations. The aim of this study is to analyze the transition from a stable operating point to the fully developed rotating stall regime, and more specifically, the effect of the throttling process on the development of the instabilities. To do so, experiments have been repeated leading the compressor to stall operations with various throttling speed.

On one hand, this paper analyses the effect of the throttling speed on the dynamic of the instability development from the first detection of spike type precursors to completely developed rotating stall.

On the other hand, a stall warning signal based on the correlation of the instantaneous pressure signal with a reference pressure signal is built. The influence of the location of the pressure transducer used for the warning signal is first analyzed. Then an analysis of the effect of the throttling process on the time between the warning signal and the effective stall development is proposed.
Data Compression Algorithms for Adjoint Based Sensitivity Studies of Unsteady Flows
Authors: Yang Liu , Nadarajah Siva
Published: October 2018

Adjoint based sensitivity studies are effective means to understand how flow quantities of interest and grid quality could affect the flow simulations. However, applying an unsteady adjoint method to three-dimensional complex flows remains a challenging topic. One of the challenges is that the flow variables at all previous time steps will be needed when solving the unsteady adjoint equation backwards in time. The straightforward treatment of storing all the previous flow solutions could be prohibitive for simulations with a large number of grid points and time steps. To avoid storing the full trajectory, the checkpointing method only stores the flow solutions at some carefully selected time steps called checkpoints, and re-computes the flow solutions between checkpoints when they are needed by the adjoint solver. However, the re-computation increases the computational cost by multiple times of the cost of solving the flow equations, which may be unacceptable for some applications. Alternatively, in this study, several data compression algorithms with much less extra cost were considered for alleviating the storage problem. In these data compression algorithms, the full flow solutions were projected onto a small set of bases which were either generated by the proper orthogonal decomposition (POD) method or by the Gram-Schmidt orthogonalization. Only a small set of bases and corresponding expansion coefficients need to be stored and they could recover the flow solutions at every time step with reasonable accuracy. The data compression algorithms were implemented in the numerical test cases, and the computed adjoint solutions were compared with that obtained by using full flow solutions. The comparisons demonstrated that the data compression algorithms were able to greatly reduce the storage requirements while maintaining sufficient accuracy.
Numerical Analysis of Thermal Effects Induced in the Hydrodynamics of the Heavy Oil Transport
Authors: Sánchez Salvador , Ascanio Gabriel , Aguayo Juan P. , Sánchez-Minero Felipe
Published: October 2018

In the present work, thermal effects induced in the hydrodynamics of heavy oil transport in pipelines are analyzed. Here, the thermal dependence of the dynamic viscosity and the mechanical heating caused by viscous dissipation are taking into account; therefore, the mathematical models that represent the study are solved in a coupled manner, evaluating at the same time both, the flow field inside of the pipeline, as well as, its corresponding heat transfer processes with respect to the environment. In order to conduct the analysis properly, numerical solutions are obtained in dimensionless way, and three main dimensionless parameters are defined; namely, β, Λ and Br, which represent the ratio of the internal radius to the length of the pipeline, the thermal conductivity for the diffusive heat transfer process in the conjugated system pipeline-thermal insulation (soil), and the Brinkman number associated to the mechanical heating, respectively. The main results reveal that, when heavy oils (extra-viscous fluids) are transported in pipelines, until a small reduction in their temperature generate substantial increment in the dynamic viscosity, and consequently, the flow rate is reduced in comparison with predictions considering a full thermal insulation condition (adiabatic process). Hence, we can conclude that during the transport of heavy oil the heat transfer and its effects over the flow field have to be estimated and controlled, this with the aim of having an efficient transport.
Research on the Solid-Liquid Two-Phase Flow in a Helical Groove Seal
Authors: Zhang K. , Wu D. Z.
Published: October 2018

Hydraulic machinery is widely used in delivering solid-liquid mixing medium. The abrasion and destruction caused by sediment particles occurs on the contact interface between the contacting seal elements, which has a considerable influence on the operational stability and safety.

Helical groove seal is a type of non-contacting dynamic seal. Relied on the reversed pressure produced by the rotary sealing element, the helical groove seal could reduce or prevent the leakage. Such seal has a good performance even if there is a big clearance between the sealing elements, so helical groove seal has its unique advantage on solid-liquid mixing medium. However, the study of helical groove seal on solid-liquid mixing flow is very poor.

In this paper, the certain conception and theoretical study of helical groove seal was introduced. With the commercial software FLUENT, the 3D internal flow of the seal was presented by using multiphase flow model. Based on the method of single variable model, the seals with different helical parameters were calculated to compare the characteristics of solid-liquid two phases flow in helical groove seals with different parameters, for example, the clearance and spiral groove depth. By this way, the relationship between structure and performance of particles-mixed helical groove seals is showed clearly, then the results can be used for design of helical groove seal structure.
Validation of a CFD Model Predicting the Effect of High Level Lateral Acceleration Sloshing on the Heat Transfer and Pressure Drop in a Small-Scale Tank in Normal Gravity
Authors: Kartuzova O. , Kassemi M.
Published: October 2018

A two-phase CFD model is developed to study the effects of sloshing with high level lateral acceleration on the heat transfer and pressure drop in a small scale tank. Computational results are compared to the data provided by a non-isothermal sloshing experiment without phase change conducted by T. Himeno et al. at the University of Tokyo and JAXA in 2011 [1]. The results of the current model are, also, compared to CFD predictions reported by Himeno et al. [2]. A step change in lateral acceleration was applied in the experiment. Different levels of lateral acceleration amplitude, varying between 0G and 0.5G, were considered. CFD results for interface movement and tank pressure are presented and compared in this paper to the experimental data for the case in which the value of lateral acceleration was set to 0.5G. The effects of initial and boundary conditions and turbulence modeling approach on the tank pressure change during sloshing are discussed in detail. The effect of conjugate heat transfer in the tank wall is also studied to show its important role in determining the tank pressure evolution. The results of the Reynolds Averaged Navier Stokes (RANS) models are compared to the results of the Large Eddy Simulation model (LES) to underscore the importance of correctly capturing the effects of turbulence for high fidelity predictions.
CFD Predictions and Experiments of Erosion of Elbows in Series in Liquid Dominated Flows
Authors: Sedrez Thiana A. , Rajkumar Yeshwanth R. , Shirazi Siamack A. , Khanouki Hadi Arabnejad , McLaury Brenton S.
Published: October 2018

Most previous studies of solid particle erosion in elbows considered an elbow for which the upstream length is long (L/D>100) and flow is well developed before reaching the elbow. But, in this study, experiments were conducted for two elbows in series, one in vertical upward-horizontal orientation and the second one placed after L/D = 6 in horizontal-vertical downward orientation. Erosion experiments were conducted with liquid-sand and liquid-gas-sand flow conditions in an experimental facility with two test section configurations: metallic elbows in series for erosion measurements and acrylic elbows in series for erosion pattern visualization. The experiments include erosion measurements of both metallic elbows with ultrasonic wall thickness (UT) measurements. All experiments including flow visualization of erosion pattern were conducted for both elbows for liquid dominated flows, and the results comparing the erosion ratio of the second elbow to the first elbow are presented. In addition, Computational Fluid Dynamics (CFD) simulations have been performed and compared to the experimental erosion patterns with both erosion pattern visualization and UT measurements. The results show good agreement between experiments and CFD simulations and experimental results provide a database for improving erosion modeling in liquid dominated flows.
Study on the Reduction of Pressure Fluctuation for a Double-Suction Centrifugal Pump With Staggered Blades
Authors: Li Qian-qian , Wu Da-zhuan
Published: October 2018

Due to the distinctive characteristic of massive flow rates, double-suction centrifugal pump has been extensively applied in lots of perspectives, such as drainage, irrigation, transportation projects and other hydraulic engineering realms. Nevertheless, the significance of the pressure fluctuation inside the double-suction centrifugal pump, which is getting more and more prominent under the soaring demands for low noise and comfortable living environment, could not be underestimated. Consequently, how to reduce the pressure fluctuation as far as possible and enhance the running stability of the pump is always the research hotspot. In this study, the double-suction centrifugal impeller with abominable vibration performance is redesigned to improve the internal flow and reduce the flow-induced noise. What’s addition, the two redesigned impellers wearing splitter blades were compared in staggered arrangement with different angles for the purpose of ulteriorly decreasing the pressure fluctuation. On the basis of Realizable k-ε model and SIMPLEC algorithm, the unsteady Reynolds-averaged Navier-Stokes equations (URANS) were resolved by means of CFD simulation and the flow performance and the vibration performance were validated with the experiments. The results illustrate that the redesigned impeller with multi-blade could raise the hydraulic performance and reduce the pressure fluctuation inside the pump. When the impeller of each side was laid with the staggered angle of 12 degrees, the pressure distribution tended to be more uniform and the pressure fluctuation was well ameliorated. Through the pressure fluctuation analysis in time domain and frequency domain, the pressure change inside the pumps could be evaluated quantitatively and accurately, hence different pumps could be contrasted in detail. The consequences of this paper could provide reference for pressure fluctuation reduction and vibration performance reinforcement of double-suction centrifugal pumps as well as other vane pumps.
A Numerical Study of Sand Particle Erosion in Elbow and a Series of Plugged Tees in Gas-Particle Two-Phase Flow
Authors: Farokhipour A. , Mansoori Z. , Saffar-Avval M. , Rasoulian M. A. , Rasteh A. , Shirazi S. A. , Ahmadi G.
Published: October 2018

Sand particle erosion is the main cause of the failure of bends in the natural gas pipelines. The rapid progress of computational power and modern numerical methods has provided the opportunity for developing realistic simulation of the erosion process. The goal of this paper is to predict the sand erosion rates with the use of computational fluid dynamics in the gas/solid flows in the plugged tees and standard elbows. For this purpose, the Eulerian-Lagrangian approach was used. To simulate the flow, the SIMPLE algorithm and the k-ω SST turbulence model were used. Particles were injected into the inlet pipe with different sizes. To predict more realistic results the Grant and Tabakoff stochastic rebound model was applied and the Oka model was used to calculate erosion. The results showed that, the use of plugged tee instead of a standard elbow would reduce the erosion rate only for fine particles. Also, for them, by increasing the plugged length the pipe will experience less erosion. For coarser particles, however, the vortex created in the plugged section did not affect the particles velocity; therefore, the erosion rate was not reduced.
Experiments of Tip Leakage Vortex Cavitation Cloud and Suction-Side-Perpendicular Cavitating Vortices in an Axial Flow Pump
Authors: Shen Xi , Zhang Desheng
Published: October 2018

The tip leakage vortex (TLV) cavitation mechanism of axial flow pump was investigated with the results of high speed photography and pressure pulsation measurement. The tip leakage vortex cavitation morphology and the transient characteristics of the TLV-induced suction-side-perpendicular cavitating vortices (SSPCV) were analyzed under different flow rates and different cavitation numbers which were combined with the time domain spectrum of pressure fluctuation to elucidate the relationship between the tip cavitation and pressure pulsation. The results showed that cavitation inception occurs earlier with more unstable tip leakage vortex cavitation shape under part-load flow rate condition, and the cavitation is more intense with the decrease of the cavitation number. The inception of SSPCV is attributed to the tail of the shedding cavitation cloud originally attached on the suction side (SS) surface of blade, moving toward the adjacent blade perpendicular to the suction surface, resulting in a flow blockage. With further decrease of pressure, the SSPCVs grow in size and strength, accompanied with a rapid degradation in performance of the pump. The cavitation images and the corresponding circumferential pressure distribution with the same phase showed that the lowest pressure coincides with the suction surface (SS) corner, The pressure was found to decrease along with the occurrence of the cavitation structure.
Numerical and Experimental Investigation of Heat Transfer Enhancement Using Heat Pipes for Electronic Cooling
Authors: Zhang Ning , Chandra Pankaj R. , Robledo Ryan , Balijepalli Sree Harsha
Published: October 2018

Computers are crucial to nearly every endeavor in the modern world. Some computers, particularly those used in military applications, are required to endure extreme conditions with limited maintenance and few parts. Units such as these will hereafter be referred to as “rugged computers.” This series of experiments aims to produce improvements to rugged computers currently in service. Using heat pipes and finned heat sinks on an enclosed box, a computer’s Central Processing Unit (CPU) is able to reject heat without suffering contamination from unforgiving environments. A modular prototype was designed to allow for three distinct cases; a case with no heat pipes and fins, a cast with heat-pipes mounted internally with exterior fins and a case with heat-pipes extended externally with exterior fins. Each case was tested at three different heat loads, with a copper plate heated by a silicone heat strip simulating the heat load generated by a CPU. Each case/load combination was run many times to check for repeatability. The aim of this research is to discover the ideal case for maximum heat transfer from the CPU to the external environment. In addition to the experiments, numerical simulation of these modular prototypes with different designs of heat pipes were conducted in this research. Creating an accurate model for computer simulations will provide validation for the experiments and will prove useful in testing cases not represented by the modular prototype. The flow and heat transfer simulations were conducted using Autodesk CFD. The aim here is to create a model that accurately reflects the experimentally-verified results from the modular prototype’s cases and loads, thereby providing a base from whence further designs can branch off and be simulated with a fair degree of accuracy.
Transient Simulation on Dynamic Motion of Mobile Perforated Plate in Two Stage Spring Linked Perforated Plates
Authors: Qian Jin-yuan , Hou Cong-wei , Gao Zhi-xin , Jin Zhi-jiang
Published: October 2018

In a piping system, due to the sudden opening or closing of valves and pumps etc., pressure inside can be changed both rapidly and suddenly, which may cause water hammer, noise, vibration, and even damage the whole piping system seriously. Thus, to stabilize pressure in piping system under a target value is very important. In this paper, a novel pressure regulation component, two-stage spring linked perforated plate (TSP), is proposed, which is mainly made up of a fixed perforated plate, a mobile perforated plate and a spring to link them. To begin with, a transient numerical model of a TSP is established and the simulation results are compared with the theoretical formula for the purpose of validation. Then, its dynamic flow and pressure characteristics are investigated under typical inlet pressure and outlet pressure to present its advantage on pressure stabilization. Meanwhile, different pressure ratios from 1 to 2 are all investigated on dynamic motion of mobile perforated plate. Under different working conditions, the displacement during the dynamic motion at different flow time, the response time to reach the final stabilization, and pressure characteristics are all figured out. This work can be useful for the further design work on two-stage spring linked perforated plates and similar pressure regulation components.
Experiments on the Injection of Elliptical Liquid Jets Into a Low Speed Airflow
Authors: Rezaei Yosef , Tadjfar Mehran
Published: October 2018

An experimental investigation was performed to study the physics of liquid jets injected into a low subsonic crossflow. The jets are issued from elliptical and circular injectors with equivalent exit area. The liquid jet was visualized using shadowgraph technique and a high speed camera was used to record the instantaneous status of the jet. The liquid / air momentum flux ratio and air Weber number were varied to examine their effects on different parameters of the flow like liquid jet column trajectory, breakup point and breakup regimes. The major axis of the elliptical nozzle was aligned parallel and perpendicular to the air crossflow direction. Two different breakup modes were observed, column breakup and bag breakup. Based on the obtained results some characteristics of injected liquid jets into the air crossflow such as penetration depth and the trajectory of liquid jet were affected by changing the nozzle exit shape.
Simulations of Hairpin Vortices in the Presence of a Passive Scalar
Authors: Handler Robert A. , Goldstein David B. , Suryanarayanan Saikishan
Published: October 2018

We have performed simulations of hairpin vortex evolution in a channel flow in which a passive scalar was present. The hairpin was created by disturbing the flow using an impulsive and spatially localized body force. Simultaneous with the introduction of the force, a passive scalar was introduced. The simulations were performed using a spectral code at a Reynolds numbers of 3000. The results show that a significant fraction of the scalar material is spontaneously trapped in the core of a hairpin vortex. This can be understood by recalling that vortex lines are material lines in flows for which the effects of diffusion are small. We will also discuss the possible implications of these observations with respect to the introduction of active scalars coincident with regions of concentrated vorticity.
Characterization of Cavitation During Pump Operation Based on Hilbert-Huang Transform
Authors: Sun Hui , Yuan Shouqi , Luo Yin , Gong Bo
Published: October 2018

Cavitation has negative influence on pump operation. In order to detect incipient cavitation effectively, experimental investigation was conducted to through acquisition of current and vibration signals during cavitation process. In this research, a centrifugal pump was modeled for research. The data was analyzed by HHT method. The results show that Torque oscillation resulted from unsteady flow during cavitation process could result in energy variation. Variation regulation of RMS of IMF in current signal is similar to that in axial vibration signal. But RMS of IMF in current signal is more sensitive to cavitation generation. It could be regarded as the indicator of incipient cavitation. RMS variation of IMF in base, radial, longitudinal vibration signals experiences an obvious increasing when cavitation gets severe. Such single variation regulation could be selected as the indicator of cavitation stage recognition. Hilbert-Huang transform is suitable for transient and non-stationary signal process. Time-frequency characteristics could be extracted from results of HHT process to reveal pump operation condition. The contents of current work could provide valuable references for further research on centrifugal pump operation detection.
Hemodynamics Characteristics of a Four-Way Right-Atrium Bypass Connector With an Optimized Central Diverter
Authors: Mack Elizabeth , Jagani Jakin , Untaroiu Alexandrina
Published: October 2018

The most common surgical procedure used to treat right ventricular heart failure is the Fontan procedure, which connects the superior vena cava and the inferior vena cava directly to the left and right pulmonary arteries bypassing the right atrium. Many studies have been performed to improve the Fontan procedure. Research has been done on a four-way connector that can both passively and actively improve flow characteristics of the junction between the Superior Vena Cava (SVC), Inferior Vena Cava (IVC), Left Pulmonary Artery (LPA) and Right Pulmonary Artery (RPA), using an optimized connector and dual propeller system. However, the configuration of these devices do not specify propeller motor placement and has a stagnation point in the center of the connector. This study focuses on creating a housing for the motor in the center of the connector to reduce the stagnation area and further stabilize the propellers. To do this, we created a program in ANSYS that utilizes the design-of-experiment (DOE) function to minimize power-loss and stagnation points in the connector for a given geometry. First, a CFD model is created to simulate the blood flow inside the connector with different housing geometries. The shape and size of the housing are used as parameters for the DOE process. In this study, an enhanced central composite design technique is used to discretize the design space. The objective functions in the DOE are red blood cell residence time and power loss. It was confirmed that the addition of the housing did decrease the size of the stagnation point. In fact, the housing added in stabilizing the flow through the connector by creating a more defined flow path. Because the flowrates from the IVC and SVC are not the same, the best configuration for the housing was found to be asymmetric along the axis of the pulmonary artery. While this is a continuation of previous studies, the creation of an optimized housing for the motors for the propellers makes implementation of the propeller idea more viable in a real life situation. The added stability of the propellers provided by the housing can also decrease the risk of propeller failure due to rotordynamic instability.
Modeling of Decelerated Descent of an Elongated Body With Vectored Thrust
Authors: Matveev Konstantin I. , Swensen John P. , Taylor Matthew E.
Published: October 2018

The subject of this study is a simplified model of an elongated body intended for controlled, low-speed landing after being released far above the ground. The envisioned system is structurally simple and compact. It comprises a cylindrical body with a vectored propulsor attached to its upper end. Far from the ground a low-magnitude thrust force directs the body toward the target site and maintains stable orientation, whereas near the ground higher thrust decelerates and directs the body to ensure low-speed landing near the target location. A 6-DOF dynamics model is applied for simulating the body descent. A strip approach is used for evaluating aerodynamic forces on the body. The thrust magnitude and direction are the controlled parameters. Results of simulations are presented for several scenarios of the body descending on the ground in calm air and in the presence of wind.
Interaction Between Surge Behavior and Internal Flow Field in an Axial-Flow Compressor
Authors: Sakata Yuu , Fujisawa Nobumichi , Ohta Yutaka
Published: October 2018

Interaction between surge behavior and internal flow field under coexisting phenomena of surge and rotating stall was experimentally investigated. In the experiment, the tank pressure of the compressor during surge was measured to detect the effect of the back-pressure fluctuation on the change in the internal flow field. Furthermore, the rotating stall in the compressor was investigated to define the influence of an unsteady internal flow field change on the surge behavior. From the tank pressure measurements, the amplitude of the tank pressure fluctuation was found to vary depending on the cycle. A larger maximal value for the tank pressure fluctuation led to a higher flow rate where the stall inception occurred. This difference in the flow rate indicated that the stall was induced by a severe adverse pressure gradient in the compressor. Then, the absolute rate of change in the flow coefficient was increased by both a large decrease in the compressor back pressure and performance degradation from stalling. In a case where the rate of decline in the flow rate was large, the scale of the stall cell developed up to a deep stall according to the movement of the operating point. Thus, a large trajectory for the surge cycle was selected, where the unsteady operating point went through the deep stall region. This development in the scale of the stall cell suggested to be influenced by the instability of the inner flow field caused by the rapid change in the flow rate.
Design of a Thermal Mass Flow Meter for Measurements Within the Rotor Rim Ducts of a Hydroelectric Generator
Authors: Venne Kevin , Mydlarski Laurent , Torriano Federico , Kirouac Mathieu , Charest-Fournier Jean-Philippe , Hudon Claude
Published: October 2018

To ensure the proper operation of hydroelectric generators, their cooling must be well understood. However, the airflow within such machines is difficult to characterize, and although Computational Fluid Dynamics (CFD) can be a reliable engineering tool, its application to the field of hydroelectric generators is quite recent and has certain limitations which are, in part, due to geometrical and flow complexities, including the coexistence of moving (rotor) and stationary (stator) components. For this reason, experimental measurements are required to validate CFD simulations of such complex flows. Of particular interest is the quantification of the flow within the rotor rim ducts, since it is directly responsible for cooling the poles (one of the most critical components of a hydroelectric generator). Thus, to measure the flow therein, an anemometer was designed. The anemometer had to be accurate, durable, cost-effective, easy to install, and able to withstand the extreme conditions found in hydroelectric generators (temperatures of 45°C, centrifugal forces of 300 g, etc.). In this paper, a thermal mass flow meter and a method for validating its performance, using hot-wire anemometry and a static model of a rotor rim, are described. Preliminary tests demonstrate that the thermal mass flow meter is capable of i) measuring the mass flow rate in the rotor rim ducts with an accuracy of approximately 10%, ii) fitting inside small rectangular ducts (12.2 mm by 51 mm), and iii) resisting forces up to 300 g.
Experimental Observation of Bubbles Released in Horizontal Water Flow
Authors: Kang Can , Ji Yanguang , Zhang Lili , Zhang Wei
Published: October 2018

To investigate the characteristics of the bubble which is exposed to the liquid cross flow, the method of ventilation was adopted and air was injected into the water flow. A water tunnel was used to provide uniform water flow with variable velocity magnitude. A high speed camera was used to record instantaneous bubble images. An image-processing code was developed to identify bubble profile and to calculate bubble parameters. The effects of water flow velocity and the flow rate of the injected air were considered. The results indicate that bubble size decreases as the water velocity increases; meanwhile, ellipsoidal bubble shape is transformed into rounded shape. The variation in the air flow rate leads to a slight change of bubble size as well the bubble shape. The bubble velocity fluctuates with the movement of the bubble, and the fluctuations are intensified as the water velocity decreases. As the balance between the forces exerted on the bubble is reached, an approximately linear relationship between the bubble velocity and the water flow velocity is proven. For a given bubble equivalent diameter, the bubble terminal velocity with the liquid cross flow is higher than that associated with stagnant water. For small Eötvös number, the consistency of the bubble aspect ratio in the cross flow and the stagnant water is manifested; however, large Eötvös number obtained here is beyond the range associated with the stagnant water, and the existing relationship is extended.