bluuebunny/crossref_metadata_2025 huggingface dataset:
Výchova a udržateľný rozvoj
Authors: Virághová Silvia
Published: October 2021

ŠEBEN ZAŤKOVÁ, T., MRAVCOVÁ, A., BARANOVIČ, Š. 2020. Výchova a udržateľný rozvoj. Kraków: Spolok Slovákov v Poľsku, 174 s. ISBN 978- 83-8111-188-1.
Optimum Torrefaction Range for Macaw Husks Aiming Its Use as a Solid Biofuel
Authors: Silva R. L. , Seye O. , Schneider P. S.
Published: October 2021

Biomass feedstock is broadly available in many countries, and a significant amount of residual biomass comes from agriculture and forest crops. This study aims to identify a consistent criteria for optimize Macaw husks torrefaction process maximizing the energy content and minimizing the mass loss. The optimization criteria is based on the severity factor (SF), HHVTorrefied, and ηSolid-Yield. The energy density (ρEnergy) does not provide consistent and indisputable evidence as an optimization criteria; the same applies to energy-mass co-benefit index (EMCI) and ηEnergy-Yield. This investigation combined few temperatures (180 °C, 220 °C, and 260 °C) with different residence times (20, 40, and 60 min) and found that the optimum torrefaction range for Macaw husk is 220 < T (°C) < 240 and 10 < t (min) < 40. The best experimental result was 220-40 (dry torrefaction at T = 220 °C and t = 40 min) corresponding to SF ∼ 5.14 and HHVTorrefied ∼ 21.71 MJ/kg (ηSolid-Yield ∼ 0.86 and HHVRatio ∼ 1.14). As the raw material has small ρBulk or ρEnergy, the authors suggest the use of a densification process previously to torrefaction. The obtained solid final product had high-quality biofuel following properties: FCdb, H/C, and O/C ratios, high heating value (HHV). The gain and loss optimization method seems promising to identify the optimum torrefaction parameters for any biomass species and the obtained optimum temperature is not far from the ones available as waste heat in industrial processes.
How Work From Home Has Affected the Occupant's Well-Being in the Residential Built Environment: An International Survey Amid the Covid-19 Pandemic
Authors: Pang Zhihong , Becerik-Gerber Burçin , Hoque Simi , O’Neill Zheng , Pedrielli Giulia , Wen Jin , Wu Teresa
Published: October 2021

This paper presents the results from an international survey that investigated the impacts of the built environment on occupant well-being during the corona virus disease 2019 (COVID-19) pandemic when most professionals were forced to work from home (WFH). The survey was comprised of 81 questions focusing on the respondent's profiles, residences, home indoor environmental quality, health, and home working experiences. A total of 1460 responses were collected from 35 countries, and 1137 of them were considered complete for the analysis. The results suggest that home spatial layout has a significant impact on occupant well-being during WFH since home-life distractions and noises due to the lack of a personal workspace are likely to prevent productive work. Lack of scenic views, inadequate daylighting, and poor acoustics were also reported to be detrimental to occupant productivity and the general WFH experience. It is also revealed from this survey that temperature, relative humidity, and indoor air quality generally have higher satisfaction ratios compared with the indoor lighting and acoustic conditions, and the home layout. Hence, home design for lighting, acoustics, and layout should also receive greater attention in the future.
Experimental Testing and Numerical Modeling of Small-Scale Boat With Drag-Reducing Air-Cavity System
Authors: Collins Jeffrey M. , Whitworth Phillip R. , Matveev Konstantin I.
Published: October 2021

Hydrodynamic performance of ships can be greatly improved by the formation of air cavities under ship bottom with the purpose to decrease water friction on the hull surface. The air-cavity ships using this type of drag reduction are usually designed for and typically effective only in a relatively narrow range of speeds and hull attitudes and sufficient rates of air supply to the cavity. To investigate the behavior of a small-scale air-cavity boat operating under both favorable and detrimental loading and speed conditions, a remotely controlled model hull was equipped with a data acquisition system, video camera and onboard sensors to measure air-cavity characteristics, air supply rate and the boat speed, thrust and trim in operations on open-water reservoirs. These measurements were captured by a data logger and also wirelessly transmitted to a ground station and video monitor. The experimental air-cavity boat was tested in a range of speeds corresponding to length Froude numbers between 0.17 and 0.5 under three loading conditions, resulting in near zero trim and significant bow-up and bow-down trim angles at rest. Reduced cavity size and significantly increased drag occurred when operating at higher speeds, especially in the bow-up trim condition. The other objective of this study was to determine whether computational fluid dynamics simulations can adequately capture the recorded behavior of the boat and air cavity. A computational software Star-CCM+ was utilized with the VOF method employed for multi-phase flow, RANS approach for turbulence modeling, and economical mesh settings with refinements in the cavity region and near free surface. Upon conducting the mesh verification study, several experimental conditions were simulated, and approximate agreement with measured test data was found. Adaptive mesh refinement and time step controls were also applied to compare results with those obtained on the user-generated mesh. Adaptive controls improved resolution of complex shedding patterns from the air cavity but had little impact on overall results. The presented here experimental approach and obtained results indicate that both outdoor experimentation and computationally inexpensive modeling can be used in the process of developing air-cavity systems for ship hulls.
Experimental and Numerical Investigation of Small Particle Erosion in Gas Dominated Multiphase Flow
Authors: Haider G. , Othayq M. , Shirazi S. A.
Published: October 2021

Sand production is a significant challenge in petroleum engineering, and specifically in multiphase gas condensate wells where small amount of liquid is present with the gas. Sand particles entrained in multiphase flow can severely affect the integrity of fluid transportation structures such as pipelines, elbows, and reducers. Traditionally, sand management techniques such as sand screens and gravel packs are used to control sand. However, small particles can pass through these controls. Furthermore, small particles can block a part of the sand screen, causing high velocities in other sections which can cause erosion of the sand screen openings allowing larger particles to pass through which in turn cause more erosion. Furthermore, these small particles are highly susceptible to turbulent regions of flow and can cause severe erosion in these regions. Hence, it is critically important to understand the erosion caused by small particles. This study investigates the effect of small particles on erosion. Small particle erosion is more severe in gas dominated multiphase flows such as annular and mist flows than liquid dominated bubbly and slug flows. A 90-degree standard elbow is used in the experimental and numerical analyses because of its high erosion vulnerability and its importance in pipeline applications. This is because the flow changes direction in this geometry which has complex implications on erosion. This study follows the below mentioned research method:

1) Flow Visualization Study: To understand the flow behavior in bend.

2) Paint-Removal Study: To visualize the progress of paint-removal pattern and to identify the erosion hot spots caused by sand particles.

3) Multiphase Erosion Experiments: To determine the wall thickness loss on identified hot spots using fix-mounted temperature compensated ultrasonic measurement technique.

4) Computational Fluid Dynamics (CFD) Study: To compare erosion patterns with CFD simulations of multiphase flow.

Furthermore, the effects of particle size on erosion ratio and its distribution in pipe bends are discussed. The CFD results of larger particles agree better with experimental data than for smaller particles using existing erosion models.
Low Temperature Testing of Ultrasound Sensors in Liquid Nitrogen
Authors: Chung Joseph Chul , Lee Michael Myung-Sub , Chun Sejong , Yang Inseok
Published: October 2021

Ultrasonic flow metering is one of flow measurement techniques applicable to low temperature environment. Unlike pipe provers or Coriolis mass flowmeters, ultrasonic flowmeters require waveguides in front of ultrasound sensors. The waveguides can prevent heat conduction from the ultrasound sensors to low temperature liquids, such as liquid nitrogen. The ultrasound sensors can maintain its piezoelectricity within the specified temperature ranges by thermal insulation of the waveguides.

In this study, low temperature testing on a pair of ultrasound sensors was performed to see if ultrasound waves could be transmitted normally through liquid nitrogen. A flowmeter cell with diameter of 300 mm (equivalently, 12”) was used as a container for liquid nitrogen. Three pairs of ultrasound sensors were installed in the flowmeter cell. Fiber-optic sensors were also attached on its inner wall to measure the temperature of liquid nitrogen. As a result, ultrasound waves were successfully transmitted between a pair of ultrasound sensors by using a preamplifier. The fiber-optic sensors could measure the temperature of liquid nitrogen although the sensors were not calibrated by the reference temperature scale at KRISS.
Movement of Cell Flowing Over Oblique Micro Grooves in Flow Channel
Authors: Hashimoto Shigehiro , Yonezawa Hiroki
Published: October 2021

A micro flow-channel with bottom-microgrooves has been manufactured by photolithography technique for cell sorting. The movement of each cell passing over microgrooves has been analyzed in relation to cell deformation and alignment in vitro. The flow path (height 0.05 mm × width 1 mm × length 25 mm) between the two transparent PDMS disks has rectangular microgrooves (4.5 μm deep, 0.2 mm long) on the bottom. Variations are made in groove widths (0.03 mm, 0.04 mm, and 0.05 mm). The angle between the flow direction and the longitudinal axis of the groove is 45 degrees. Myoblasts (C2C12: mouse myoblast line) were used in the flow test. The main flow velocity of the medium (0.02 mm/s < vx < 0.23 mm/s) was controlled by the pressure difference between the inlet and the outlet. The shape of each flowing cell was tracked in a movie recorded by a camera attached to the eyepiece of the microscope. Experimental results show that the movement perpendicular to the main flow direction in the micro-groove can distinguish cells in relation to smaller deformations and larger alignment changes.
Frequency Response of Synthetic Jets Emanating From an Array of Circular Orifices
Authors: Arafa Nadim , Sullivan Pierre , Ekmekci Alis
Published: October 2021

The effect of the excitation frequency of synthetic jet actuators on the mean jet velocity of synthetic jets issuing from an array of circular orifices is investigated experimentally. Herein, the focus is placed on an array of circular orifices, rather than a single orifice, as it brings the advantage of covering long-span airfoils. The array consists of 16 circular orifices, each having a diameter of 3.42 mm, distributed over a span of 300 mm. The jets are generated by the excitation of a single cavity via 16 piezoelectric elements. Localized velocity measurements at the exit of the orifices show that the mean jet velocity varies with the excitation frequency. Several distinct resonant peaks were observed in the frequency response. Acoustic simulations of the cavity showed that these peaks correspond to acoustic mode shapes of the cavity. Due to the high-aspect ratio of the cavity, several acoustic mode shapes exist in the excitation frequency range aside from the Helmholtz resonance frequency. Moreover, the mean jet velocity emanating from the array shows a variation from orifice to orifice, depending on the excited acoustic mode.
Different Clogging Behavior of Wastewater Pumps
Authors: Beck David , Holzbauer Yvonne , Thamsen Paul Uwe
Published: October 2021

The transport of wastewater presents operators with increasing challenges for their wastewater pumps due to an increasing proportion of tear-resistant fibrous materials and new types of hygiene articles (e.g. wet wipes) in the wastewater. This paper describes the different clogging behavior of wastewater pumps, which were recorded during the functional performance tests. In addition to the findings of the points susceptible to clogging, the maximum uptake of solids by an impeller is also discussed. The maximum uptake of solids is defined as the degree of saturation. Furthermore, it is shown to what extent the different clogging behavior influence the hydraulic performance and the resulting efficiency changes.

In these tests, it became apparent that wastewater pumps react very differently to clogging. On the one hand, it can lead to a reduction in hydraulic function, which reduces the efficiency of the system. A distinction must be made here as to whether the pumps with a certain number of solids, a defined degree of saturation, retain their function or are brought to a standstill. On the other hand, the hydraulic performance can remain almost constant or, in some cases, be increased despite the clogging that occurs, but this is accompanied by an increased power requirement and can thus reduce the service life and the efficiency of the system.
Visualisation of Interactions Between Impeller and Textile in a Wastewater Pump
Authors: Steffen Matthias , Thamsen Paul Uwe
Published: October 2021

In order to characterize wastewater pumps regarding their clogging behaviour, a wide variety of test procedures with artificial wastewater exist. These tests provide a good insight into the clogging characteristics of a pump. However, conclusions about the clogging mechanisms and their sources cannot be drawn.

This paper deals with the design and implementation of an optical access on the suction side of a wastewater pump to allow visualisation of the interaction between impeller and textile via high-speed recordings. The optical access is realized by an endoscope and a connected high-speed camera with a frame rate of 2000 fps and a resolution of 1024 × 1024 pixels. To ensure sufficient illumination of the impeller, a light ring assembled from 12 high power LEDs with a luminous flux of 5595 lumen are circumferentially arranged around the suction side of the pump. The light ring concept is scalable to fit any pump size. A clogging-affine impeller is developed, 3D printed and used for experimental investigations. For the investigated impeller, the blade’s upper area is identified to be crucial for pump clogging. Optical accessibility provides an important contribution to develop non-clogging impellers.
Vorticity Growth Formed in Vicinity of a Wall on a Moving Elastic Airfoil
Authors: Fuchiwaki Masaki
Published: October 2021

The flow field around moving airfoils capable of flexible elastic deformation has become a focus of attention. These flow fields may be understood as a fluid-structure interaction (FSI) problem, and the motion and deformation of elastic airfoils, as well as the associated vortex flow phenomena in their vicinity, are complicated. Many studies on the flow filed around the elastic moving airfoil have been investigated by experimental and numerical approached. The macro scale vortex structure and the dynamic forces acting on the elastic moving airfoil have been understood. However, the growth process of the vorticity in a vicinity of the wall of an elastic airfoil has not been clarified sufficiently. In this study, the authors focus on the dynamic behaviors of vorticity in the vicinity of the wall on the elastic heaving airfoil and investigate the growth process of the vorticity in a vicinity of the wall of an elastic airfoil by the fluid structure interaction and LES simulations using ANSYS 17.0/ANSYS CFX 17.0. The vorticity in the vicinity of a wall of the elastic airfoil spreads along the wall simultaneously with the increase of the spatial gradient of the wall, and discrete vorticity regions coalesce into a single layer. The time variation in spatial gradient contribute greatly to the growth and development of vorticity.
Boundary Layer Multi-Property Flow Measurements Using a Micro-Plasma Sensor
Authors: Papadopoulos George , Bivolaru Daniel , Martin Nicholas , Dawideit Timothy
Published: October 2021

When voltage is applied between two electrodes situated in close proximity to each other (10–100 μm), a weakly ionized, low temperature plasma discharge can be generated. This in turn creates a plasma sheath, an electrically ionized boundary layer (typically of the order of 10’s to 100’s of microns), where space charge effects dominate. The sheath acts like a virtual capacitor, with the plasma behaving as an inductor. Aerodynamic effects influence the plasma morphology (shape, thickness), thus making the plasma the transduction mechanism. The attraction to the use of plasma discharge as a transduction method for fluid flow property measurement stem from the fact that it lends itself to a probe implementation that is simple in design, can be miniaturized, and at the same time offers unmatched capability for handling ultra-high temperature environments. Sensing plasma discharge characteristics and their variation due to flow interaction can be done electrically, but also optically to yield time-varying intensity and spectral information from fluid-plasma interaction. The current paper focuses on the deployment of a micro-plasma sensor system as a new novel multi-parameter sensing approach for surface flow measurement. Results on pressure dynamics, shear flow, and other possible engineering parameters will be discussed in the context of results from several bench-level experiments.
Second Moment Closure Modeling and DNS of Stratified Shear Layers
Authors: Jain Naman , Huang Xinyi , Yang Xiang , Kunz Robert , Pham Hieu T. , Sarkar Sutanu
Published: October 2021

Buoyant shear layers are encountered in many engineering and environmental applications, and have been studied by researchers in the context of experiments and modeling for decades. Often, these flows have high Reynolds and Richardson numbers, and this leads to significant/intractable space-time resolution requirements for DNS or LES modeling. On the other hand, many of the important physical mechanisms in these systems, such as stress anisotropy, wake stabilization, and regime transition, inherently render eddy viscosity-based RANS modeling inappropriate. Accordingly, we pursue second-moment closure (SMC), i.e., full Reynolds stress/flux/variance modeling, for moderate Reynolds number non-stratified, and stratified shear layers for which DNS is possible. A range of sub-model complexity is pursued for the diffusion of stresses, density fluxes and variance, pressure strain and scrambling, and dissipation. These sub-models are evaluated in terms of how well they are represented by DNS in comparison to the exact Reynolds averaged terms, and how well they impact the accuracy of the full RANS closure.

For the non-stratified case, the SMC model predicts the shear layer growth rate and Reynolds shear stress profiles accurately. Stress anisotropy and budgets are captured only qualitatively. Comparing DNS of exact and modeled terms, inconsistencies in model performance and assumptions are observed, including inaccurate prediction of individual statistics, non-negligible pressure diffusion, and dissipation anisotropy. For the stratified case, shear layer and gradient Richardson number growth rates, and stress, flux and variance decay rates, are captured with less accuracy than corresponding flow parameters in the non-stratified case. These studies lead to several recommendations for model improvement.
Simple, Cost-Effective Fabrication, and Flow Dynamics Analysis of a Passive Microfluidic Mixer Using 3D Printing and Soft Lithography
Authors: Rubby Md Fazlay , Parvez Mohammad Salman , Islam Nazmul
Published: October 2021

Simple and low-cost fabrication of microfluidic devices has attracted considerable attention among researchers. The traditional soft lithography fabrication method requires expensive equipment like a UV exposure system and mask fabrication facility. In this work, an alternative and low-cost UV exposure system was introduced along with an alternative mask fabrication system. A previously reported passive microfluidic mixer was fabricated successfully using this modified soft lithography method. Challenges were presented during this modified fabrication method. Another emerging potential alternative for the fabrication of microfluidic mixers is 3D printing. It was also used in this experiment to fabricate a passive micromixer. This method is well known for rapid prototyping and the creations of complex structures. However, this method has several disadvantages like optical transparency, lower resolution fabrication, difficulties in flow characterization, etc. These problems were addressed, and the solutions were discussed in this work. Comparative analysis between 3D printing and soft lithography fabrication was presented. Flow characterization inside the 3D printed micromixer was carried out using the microparticulate image velocimetry (micro-PIV) system. It explains how the geometrical shape of the micromixer accelerates the natural diffusion process to mix the different fluid streams. Finally, a 3D numerical simulation of the passive micromixer was carried out to visualize the flow dynamics inside the micromixer. The flow pattern found from the numerical simulation and the experimental flow characterization is analogous. These observations could play an important role to design and fabricate cost-effective micromixers for lab-on-a-chip devices.
Fluid-Structure Interaction Simulations of Parachute Deployment and Inflation
Authors: Wang Liwu , Tang Mingzhang , Liu Yu , Zhang Sijun
Published: October 2021

The numerical simulation of the parachute deployment/inflation process involves fluid structure interaction problems, the inherent complexities in the fluid structure interaction have been posing several computational challenges. In this paper a high fidelity Eulerian computational approach is proposed for the simulation of parachute deployment/inflation. Unlike the arbitrary Eulerian Lagrangian (ALE) method widely employed in this area, the Eulerian computational approach is established on three computational techniques: computational fluid dynamics, computational structure dynamics and computational moving boundary. A set of stationary, non-deforming Cartesian grids is adopted in our computational fluid dynamics, our computational structure dynamics is enhanced by non-linear finite element method and membrane wrinkling algorithm, instead of conventional computational mesh dynamics, an immersed boundary method is employed to avoid insurmountable poor grid quality brought in by moving mesh approaches. To validate the proposed numerical approach the deployment/inflation of C-9 parachute is simulated using our approach and the results show similar characteristics compared with experimental results and previous literature. The computed results have demonstrated the proposed method to be a useful tool for analyzing dynamic parachute deployment and subsequent inflation.
Shape Optimisation of NACA4412 In-Ground Effect- Selection of a Turbulence Model
Authors: P. N. Jithin , Arumugham-Achari Ajith Kumar
Published: October 2021

Shape optimisation of a wing-in-ground airfoil would be required to improve its aerodynamic characteristics under various flight conditions. Identification of an optimised shape at various heights above ground (h/c) and angles of attack (α) could be helpful in developing morphing wing capabilities for such airfoil. Prior to conducting shape optimisation a suitable turbulence model have to be selected for such studies. We have performed In-ground-effect (IGE) simulations using four turbulence models, viz., Spalart Allmaras, SST k-ω, Standard k-ε and Transition SST model, to compare their advantages and disadvantages during such analysis. For an unaltered NACA4412 airfoil, while all the models predicted coefficient of lift (Cl) in close agreement with experimental results, Transition SST model was able to predict fine details like laminar separation bubble formation. There was a generic discrepancy in predicting drag coefficients (Cd) with all these turbulence models. However results from Transition SST were the closest to experiments. Spalart Allmaras and SST k-ω were better in the prediction of Cd when compared to standard k-ε model. We consider such studies would be helpful to generate a database of optimised airfoils for a variety of flight conditions near to ground.
Solution-Responsive Particle Size Adaptivity in Lagrangian Vortex Particle Methods
Authors: Stock Mark J. , Gharakhani Adrin
Published: October 2021

In order to minimize the computational resources necessary for a given level of accuracy in a Lagrangian Vortex Particle Method, a novel particle core size adaptivity scheme has been created. The method adapts locally to the solution while preventing large particle size gradients, and optionally adapts globally to focus effort on important regions. It is implemented in the diffusion solver, which uses the Vorticity Redistribution Method, by allowing and accounting for variations in the core radius of participating particles. We demonstrate the effectiveness of this new method on the diffusion of a δ-function and impulsively started flow over a circular cylinder at Re = 9,500. In each case, the adaptive method provides solutions with marginal loss of accuracy but with substantially fewer computational elements.
Elementary Numerical Analysis of Wet Foam Formation and Study of Its Flow Structures and Physical Behavior
Authors: Shirani Ebrahim , Nasirzade Sima , Aloui Fethi
Published: October 2021

The purpose of this study is to analyze the flow of wet foam and to study the effect of volume fraction, velocity and surface tension and other physical parameters on the foam flow. The most numerical researches done in this area are for single-phase flows. The numerical simulation in this study is the first simulation in the foam flow, in which both the bubbles and the water are simulated as two-phase flow. In this study, fluid containing a surfactant and bubbles are flowing in a duct. The dimensions of the duct cross section is 15 × 60 in millimeters. The numerical solution is performed for three Reynolds numbers of 50, 100 and 1000, three volume fractions of 48, 41 and 28, and three Weber numbers of 0.405, 0.27 and 0.203 (27 different modes), and the effect of the above parameters on the flow behavior and its physical properties have been investigated.

It was found that in foam flow, the velocity fluctuations, due to the movement of bubbles in the flow, is in the order of magnitude of the mean velocity. The same is true for wall shear stress. By increasing the Reynolds number, the pressure loss increases, the magnitude of the velocity fluctuations decreases and the frequency of the velocity fluctuations increases. By increasing the Weber number, the pressure loss and the magnitude of the velocity fluctuations decrease and the mean shear stress increases. By increasing the foam quality, pressure loss increases, the mean shear stress and the magnitude of the velocity fluctuations decrease and its frequency increases. And the phenomenon of coalescence causes a sudden increase in momentum speed.
A Hybrid High-Order Vorticity-Based Eulerian and Lagrangian Vortex Particle Method, the 2-D Case
Authors: Stock Mark J. , Gharakhani Adrin
Published: October 2021

Hybrid Lagrangian-Eulerian solvers combine the convective and compactness advantages of vortex methods with the spatial anisotropy and boundary-resolving advantages of Eulerian methods to create flexible solvers capable of adequately capturing thin boundary layers while still maintaining wake vortex coherency for unsteady incompressible flow in complex geometries. The present paper details a new hybrid method which combines, in one open-source package, a novel, compact, high-order Eulerian scheme for vorticity transport to predict the flow in the near-boundary region with a grid-free, unremeshed, Lagrangian Vortex Particle Method (LVPM) for the off-boundary vorticity-containing region. This paper focuses on the hybridization of the two methods and demonstrates its effectiveness on two canonical benchmarks: flow in 2-D lid-driven cavity at Re = 1,000 and impulsively started flow over a circular cylinder at Re = 9,500. In each case, the hybrid method improves upon a pure LVPM and uses far fewer cells than a purely Eulerian scheme. In addition, the size of the associated Eulerian region is greatly reduced compared to previous hybrid methods.
Modified Operating Parameter-Based Iyer Correlation for the Coefficient of Performance (COP) Prediction of Different Fluid Pairs in Double-Effect Vapor Absorption Refrigeration (VAR) Cycles
Authors: Khan Muhammad Saad , Kadam Sambhaji T. , Kyriakides Alexios-Spyridon , Hassan Ibrahim , Papadopoulos Athanasios I. , Rahman Mohammad Azizur , Seferlis Panos
Published: October 2021

Vapor absorption refrigeration (VAR) is a sustainable alternative to the conventional vapor compression refrigeration (VCR) cycle, owing to its lower non-renewable energy requirements and potentially for exploitation of renewable energy sources. Traditionally, the coefficient of performance (COP) of the conventional single effect VAR cycle is considerably lower than VCR cycles. This provides room for improvement which can be attained through double effect VAR cycles that provide relatively higher performance. The COP of the dual effect VAR cycle is enhanced due to the waste/rejected heat energy utilization from the condenser or the absorber into a secondary generator. Models that correlate the COP of the double effect VAR cycle with operating parameters are not available in the open literature, with Iyer’s correlation being the only exception. This work applies this COP correlation using literature data for double effect VAR that operate with a variety of refrigerant and absorbent pairs. A comprehensive Mean Absolute Percentage Error (MAPE) analysis is performed for more than 2028 data points of various fluid pairs. Results reveal that MAPE (86.6–839%) values appear to be quite high for the reported correlation. Furthermore, the model is optimized using the proposed data set, considerably reducing the MAPE up to 36.03%. The results also indicate that due to the lack of fluid-specific parameters, the application of this correlation may not support the development of new double effect VAR cycles. Therefore, it is crucial to establish a performance-based correlation that considers both operational parameters and fluid parameters to assess the performance of new and efficient dual effect VAR cycles.
CFD Analysis on Biogas Bubble Creation Within a Stirred Tank of a Wastewater Treatment Plant
Authors: Dabiri Soroush , Rauch Wolfgang
Published: October 2021

A mixing strategy for assuring a homogeneous fluid flow inside wastewater treatment plants (WWTPs) is a necessity, in order to keep continuous contacts of substrates and degraders. On the other hand, mixing is an energy-demanding process. Therefore, the power consumption for mixing the fluid flow within bioreactors affects the overall efficiency of WWTPs. The current study aims at evaluating the incorporation of biogas bubble creation on the mixing of WWTP tanks. Computational fluid dynamics (CFD) enables simulating hydrodynamics of multiphase fluid flows injected with bubble parcels. The case is a cylindrical stirred tank, in which the fluid flow is agitated via a rotating mixer. Mixer rotates at various speeds; and for each case, the ultimate fluid flow is captured both with and without bubble creation. Non-Newtonian characteristics of the fluid flow within the tank are considered and k–ε turbulence closure is selected for the model. By a two-way coupling of an Eulerian-Lagrangian platform, velocity fields and the amount of dead volume are analyzed and discussed.

Our key finding is that the biogas bubble creation contributes to the reduction of dead volume inside the WWTP tank, when there is no external rotating mixing, or once the amount of mixer rotation speed is low.
Computational Fluid Dynamic Analysis of the Flow Around a Propeller Blade of Multirotor Unmanned Aerodynamic Vehicle
Authors: Martinez Victor H. , Bhaganagar Kiran
Published: October 2021

Multirotor Unmanned Aerodynamic Vehicles (MUAV) have been a high interest topic in the aerodynamic community for its many applications, such as, logistics, emergency rescue, agriculture data collection, and environmental sensing to name a few. MUAV propeller blades create a highly complex turbulent fluid flow around the body and the environment around it. The flow physics generated from the rotation of the propeller blades were studied in this paper along with the analysis of aerodynamic characteristics. A Reynolds Average Navier-Stokes (RANS) Computational Fluid Dynamics (CFD) analysis of a propellor blade from a MUAV has been performed to quantify the aerodynamic effects. For this purpose, the verification and validation of the commercially available CFD solver COMSOL Multiphysics v5.5 was performed using the NACA 0012 airfoil which is one of the most highly studied of the NACA family. With this validation it created confidence on the results for simulating a MUAV propeller and evaluate the aerodynamic characteristics of thrust coefficient (KT), power coefficient (KP), and Efficiency (η). These characteristics were compared against experimental data and results showed to have a similar trend. This showed that the CFD solver is capable of solving the aerodynamic characteristics of any propeller blade geometry.
Aerodynamic Performance of Design for a CO2 Dragster
Authors: Paez Brandon , Rodriguez Arturo , Dudu Nicholas , Terrazas Jose , Adansi Richard , Kotteda V. M. Krushnarao , Aguilar Julio C. , Kumar Vinod
Published: October 2021

The CO2 Dragster competition is performed at a national level as part of the Technology Student Association (TSA), and it seeks to increase and implement STEM skills for high school students. Students are expected to create CO2-powered Dragsters, which are placed on a 20-meter track to compete against each other. The CO2 Dragster consists of a pressure vessel containing CO2, which is placed in a pre-drilled cartridge located at the back of the vehicle. The CO2 propellant is used to provide thrust to the Dragster during the race, and sand smoothed balsawood material is used for the solid body of the Dragster. The CO2 Dragster competition is introduced at the high school level to provide students with a hands-on activity that allows them to learn and apply the fundamentals of fluid dynamics and solid mechanics. The students are placed in charge of designing a 3D model of their Dragster and are required to submit the 3D model with their respective drawings. In this paper, a mathematical, computational, and experimental analysis of a CO2 Dragster is provided. This research consisted of creating a shell model on NX 10, then inserted into ANSYS Fluent to simulate the flow around the model to identify and track the stagnation points, pressure loadings, and flow separation effects caused by the fluid interaction with the Dragster. Mathematical formulas were implemented to find the fracture of slim body CO2 Dragsters, using a coupling between fluid mechanics and solid mechanics, Fluid-Structure Interactions (FSIs). In conclusion, by creating a computational model, it is possible to drive dragster design by simulating different dragster designs’ computationally to improve its performance. Creating a computational functional model to simulate the Dragster, implementing mathematical formulas to understand the behavior, and experimentally evaluating the parameters based on performance will lead to more innovative practices of creating better Dragsters for this competition.
Experimental Evaluation of Novel Swirl Flow Air-Water Separation Apparatus for Desalination/Water Remediation Applications
Authors: Thyagarajan Ashok , Banerjee Debjyoti , Dhir Vijay
Published: October 2021

A novel apparatus that is capable of dynamic flash evaporation and phase separation using centrifugal flow (i.e., using a Hydro-Cyclone Apparatus/HCA) is evaluated in this study. The objective of this study is to evaluate the performance of a novel phase separator apparatus that forms a stable air core at the center from a premixed air-water mixture. The air core is retrieved using a retrieval tube placed at the center of the test section. Experiments were performed by varying the inlet volume flow rates of air and water to determine the maximum separation efficiency and plot its variation as a function of inlet air and water flow rates. The data obtained from this study is used as a preliminary indicator of the anticipated range of separation efficiencies for the system during experiments involving phase change for the production of potable water from saline water for water remediation applications.
Experimental Measurement of Oil Droplets Size and Velocity Above the Rotor/Stator in a Rotary Compressor
Authors: Wu Puyuan , Chen Jun , Sojka Paul E. , Li Yang , Cao Hongjun
Published: October 2021

Hundreds of millions of Air conditioning (AC) systems are produced each year. Many of them, especially small AC appliances, use rotary compressors as the system’s heat pump due to their simple structure and high efficiency in a small system. Lubricant oil is used in the rotary compressor to lubricate the moving parts, such as the crankshaft and the rolling piston, and to seal the clearance between the sliding parts, e.g., the clearance between the rolling piston and the cylinder, and the vane and the cylinder. As the compressed refrigerant vapor is discharged from the cylinder through the discharge port, part of lubricant oil in the cylinder would be carried by the vapor and atomize into small droplets in the lower cavity during the discharge process, which is complicated and highly-coupled. Some of these oil droplets would ultimately be exhausted from the compressor and enter other parts in the system, reducing the compressor reliability and deteriorating the heat transfer of the condenser and the evaporator in the system. Our previous research studied the atomization of the lubricant oil during the discharge process in the compressor’s lower cavity. However, the oil droplets’ behavior downstream of the lower cavity is unknown. Thus, studying the oil droplets’ behavior after passing through the rotor/stator can help understand how the rotor/stator would affect the droplet size distribution and movement, thus controlling the flow rate of escaped oil droplets. In this study, a hot gas bypass test rig is built to run a modified rotary compressor with sapphire windows right above the rotor/stator. The oil droplets’ size distribution and movement along the radial direction are obtained at the shaft’s rotating frequency of 30 and 60 Hz by shadowgraph. It is found that droplet size at 30 and 60 Hz varies little in the inner region of the rotor/stator clearance and would increase sharply above the clearance and keep increasing in the outer region of the clearance. More importantly, droplet velocity has a downward velocity component at the inner region and an upward velocity component at the outer region of the rotor/stator clearance. With the result of droplet size distribution and droplet velocity above the rotor/stator, we propose the model of the oil droplet’s path above the rotor/stator, which can be understood as the coupling of a swirling jet and a rotating disk.
A Comprehensive Review of Three-Dimensional Neuro-Organoids and Engineering Brain-on-a-Chip Microfluidic Devices
Authors: El Nihum Lamees , Shettigar Nandan , Banerjee Debjyoti , Krencik Robert
Published: October 2021

The focus of this review is to describe advances in three-dimensional (3D) organoids reported in the literature with an emphasis on the engineering of microfluidic device platforms for investigating neuro-organoids. Furthermore, the paper will assess current limitations in microfluidic design that must be addressed for realizing the full potential of brain-on-a-chip devices.
Turbulent Flow Simulation of Supercritical Hydrothermal Synthesis in T-Shaped Channel
Authors: Furusawa Takashi , Matsui Kenta , Yatsuyanagi Shuto , Yamamoto Satoru , Yoko Akira , Adschiri Tadafumi
Published: October 2021

Turbulent mixing flows of supercritical water and a metal-salt solution were investigated using Reynolds-averaged Navier–Stokes (RANS) simulations. The mass conservation equations for metal-salt and metal-oxide in an aqueous solution, which were coupled with Navier–Stokes equations and the Shear Stress Transport (SST) turbulence model, were solved by considering production by the hydrothermal reaction. The reaction rate in the numerical simulation was interpolated linearly using the experimental data. The mixing flows in a T-shaped channel for various Reynolds numbers were simulated numerically. Fluid mixing causes a hydrothermal reaction in a high temperature region. In a situation with a low temperature and low Reynolds number, the mixing became a steady state, and the metal oxide was generated along the channel wall. For a high Reynolds number, the periodic vortexes were observed at the mixing point and the fluid temperature increased rapidly. A numerical simulation reproduced the apparent reaction rate of the experimental measurements, except for the low Reynolds number case. The time-averaged temperature distributions indicated that the increasing temperature rate in the mixing reactor depends on the inlet supercritical water temperature, which affects the distribution of the concentration of metal oxide. If the turbulence effects were ignored in low-temperature instances, the apparent reaction rate was estimated to be quite low. The turbulent diffusivity and thermal conductivity crucially affected the conversion rate, especially for conditions with a low Reynolds number.
Large Scale Structures in Elevated Jet Normal to Crossflow
Authors: Gupta Jyoti , Saha Arun K.
Published: October 2021

Transverse jet from elevated source is found in various environmental and industrial field which include smoke exhausting from stack into atmosphere and sewage water disposal in deep-ocean. The experiment is carried out in water tunnel using flow visualization and Laser Doppler Velocimetry. Analysis has been performed for axisymmetric round jet of aspect ratio of 9.0 with the velocity ratio varying up to 2.5 at Reynolds number (based on free stream crossflow velocity and jet external diameter) of 1000. Result shows the formation of different jet shear layer vortices with varying velocity ratio are: (i) clockwise-downwash vortices (velocity ratio less than 0.3), (ii) delayed-regular-clockwise vortices (between 0.3 to 0.7), (iii) regular-clockwise vortices (between 0.7 to 1.4) at the lee side of the jet shear layer, (iv) irregular-anticlockwise vortex at the upstream along with clockwise vortices at the lee side of the jet shear layer that together forms mushroom vortices (between 1.4 to 1.9) and (v) regular-mushroom vortices (above 1.9). The other vortices found are stack-end vortex (less than 0.9) in the wake near free end, upright vortices (above 0.9) in jet-wake and hairpin vortices (between 0.3 to 0.6) in downstream which is the stretched part of evolving shear layer.
Inverse Problems in Magnetic Resonance Velocimetry: Shape, Forcing and Boundary Condition Inference
Authors: Kontogiannis Alexandros , Juniper Matthew
Published: October 2021

We derive and implement an algorithm that takes noisy magnetic resonance velocimetry (MRV) images of Stokes flow and infers the velocity field, the most likely position of the boundary, the inlet and outlet boundary conditions, and any body forces. We do this by minimizing a discrepancy norm of the velocity fields between the MRV experiment and the Stokes problem, and at the same time we obtain a filtered (denoised) version of the original MRV image. We describe two possible approaches to regularize the inverse problem, using either a variational technique, or Gaussian random fields. We test the algorithm for flows governed by a Poisson or a Stokes problem, using both real and synthetic MRV measurements. We find that the algorithm is capable of reconstructing the shape of the domain from artificial images with a low signal-to-noise ratio.
Liutex and Third Generation of Vortex Identification
Authors: Yu Yifei , Nottage Charles , Alvarez Oscar , Liu Chaoqun
Published: October 2021

Scientists developed many vortex identification methods and Liu classified the traditional vortex identification methods into two generations. Vorticity and vorticity-based methods belong to the first generation while eigenvalues-based methods are considered as the second generation, such as Q criterion and λci method. However, although these methods are widely used, there is still room for improvements. People used to consider direction of vorticity is the swirling axis and the magnitude of it is the rotation strength, but the predictions by vorticity does not match the experiment very well which drove scientists to develop the second-generation methods. All the second-generation methods are scalar-valued and as a result they are unable to locate the swirling. Another problem is even though second-generation methods can predict vortex better than vorticity, they are more or less contaminated by shear. To solve these problems, Liu innovated Liutex recently. Liutex is a vector quantity whose direction represents rotation axis and whose magnitude represents rotation strength. Firstly, the physical essence of rotation axis is provided coming with the mathematical definition of swirling axis which is the direction of Liutex. Secondly, orthogonal transformations are used to find out the rigid rotation speed and that speed is defined as the strength of Liutex. Wang later proposed an explicit formula to calculate Liutex strength without doing orthogonal transformations which makes it much easier to apply Liutex method. Some theories dependent on Liutex concept have been proposed these years. Liutex core lines represent the core of vortex which can uniquely and clearly show vortex structure. Principal coordinate is a special coordinate in which it is easy to decompose the velocity gradient tensor into rotation, shear and stretching parts correctly. And principal decomposition is the decomposition in principal coordinate. The Liutex theory system is gradually formed and they are considered as the third generation by Liu.
Harnessing the Power of the Cloud - Computational Fluid Dynamics With SimScale
Authors: Murad Jousef
Published: October 2021

Computational fluid dynamics is a computational method that enables engineers and designers to study the motion of fluids through computer simulations and modelling. Many tools on the market are so-called “in-house” tools requiring a certain level of expertise and upfront investment before proving their added value. Facilitated by the emergence of cloud computing, computer-aided engineering (CAE) technology is now offered as a software as a service (SaaS) solution, which increases its accessibility and ease of use. Online fluid flow (CFD) simulation is used in addressing a broad variety of problems like electronics design or pedestrian wind comfort (PWC), allowing engineers to accurately predict fluid flow behaviour guiding them towards smarter design decisions. SimScale is creating a paradigm shift for high-performance computing which can solve several problems that are faced when using on-premises software.