Bubbling and jetting regimes in planar coflowing air–water sheets

The dynamics of a plane air sheet surrounded by a coflowing water film, discharging into stagnant air, is investigated by means of experiments and linear stability theory. For fixed values of the water-to-air thickness ratio, h = hw,0*/ha,0* ≃ 5.27, and of the air-to-water density ratio, S = ρa/ρw ≃ 0.0012, two different flow regimes are experimentally observed depending on the values of two control parameters, namely the Weber number, defined as We = ρwuw,0*2ha,0*/σ, and the velocity ratio, Λ = uw,0*/ua,0*, where uw,0* and ua,0* are the water velocity and the mean air velocity at the exit slit, respectively, and ha,0* and hw,0* are the half-thicknesses of the air and water sheets at the exit. The study focuses on the characterization of the transition between the two regimes found experimentally: a bubbling regime, leading to the periodic breakup of the air sheet, and a jetting regime, where both sheets evolve slowly downstream without breaking. With the aim of exploring whether the transition from the jetting to the bubbling regime is related to a convective/absolute instability transition, we perform a linear spatiotemporal stability analysis. The base flow is described by a simple model that incorporates the downstream evolution of the sheets, which shows excellent agreement with our experiments if the existence of a sufficiently long region of absolute instability, of the order of one absolute wavelength evaluated at the nozzle exit, is imposed as an additional requirement. Finally, we show that the transition is also properly captured by two-dimensional numerical simulations using the volume of fluid technique.

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STABILITY CHARACTERISTICS OF COMPRESSIBLE BINARY PLANAR JETS

Revista de Engenharia Térmica ◽

10.5380/reterm.v19i1.76438 ◽

2020 ◽

Vol 19 (1) ◽

pp. 80

Author(s):

M. T. Mendonca ◽

M. M. Vargas

Keyword(s):

Density Gradient ◽

Velocity Ratio ◽

Density Ratio ◽

Chemical Species ◽

Phase Speed ◽

Linear Stability Theory ◽

Density Gradients ◽

Lower Phase ◽

External Mode ◽

The Stability

The present work investigates the stability of compressible binary planar jets. Different from a homogeneous jet, where a single chemical species is present, the binary jet may have strong density gradients due to the choice of the chemical species considered in each stream. The goal is to identify the possible instability modes for simple and co-flowing jets and investigate the effect of density gradients on the flow structure, growth rates, unstable frequency range and disturbance phase speed for each mode. The effect of species concentration on free shear layer stability has been reported previously in the literature, but detailed comparisons between stability modes and characteristics for a range of density ratios typical of oxygen and hydrogen mixtures as well as the identification of inner and outer sinuous and varicose modes are new. Linear stability theory is used to determine the stability characteristics of the different configurations. For the co-flowing jet four different modes are found, the inner and outer shear layers both have sinuous and varicose modes. Both for the sinuous and varicose modes the simple jet is more unstable when the fluid with the highest density is at the inner jet, with amplification rates twice as high as the lowest density ratio considered, but the range of unstable frequencies can be four times lower. The sinuous mode is less dispersive than the varicose and the disturbance speeds may vary by one order of magnitude with density ratio. For co-flowing jets the external mode is up to seven times more unstable, but this is due to the choice of the velocity ratio considered. For the inner mode the density gradient has a stabilizing effect regardless of which species is at the center. The co-flowing jet is more dispersive, except for the varicose inner mode. The variation of phase speed with density gradient is not as strong as in the simple jet. The ratio of larges to lower phase speeds are of the order of 2 for the co-flowing jet and 4 for the simple jet.

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Characterization of the Effect of Moisture on Tribology of Titanium Rubbed Against Different Pin Materials

Chemical Science International Journal ◽

10.9734/csji/2020/v29i230158 ◽

2020 ◽

pp. 1-10

Author(s):

Bodhi R. Manu ◽

Adam M. Schroeder ◽

Ahalapitiya H. Jayatissa

Keyword(s):

Friction Coefficient ◽

Relative Humidity ◽

Coefficient Of Friction ◽

Water Film ◽

Interfacial Surface ◽

The Coefficient Of Friction ◽

The Mean ◽

Machine Parts ◽

Pin On Disk

Tribology investigations were conducted to understand the effect of humidity and water adsorption at the interfacial surface on the friction coefficient of titanium. Pin-on-disk tribometer tests were conducted at different levels of humidity ranging from 0% to 71% RH using aluminum and steel pins on a titanium plate. The variation of the mean coefficient of friction was plotted as a function of relative humidity. The friction coefficient slightly decreased when the relative humidity was increased from 0% to 10% RH. However, it increased with a further increase in humidity. The maximum friction coefficients were observed at 55% and 65% RH for steel and aluminum, respectively. The thickness of the wear tracks also showed the same trend as the friction coefficient. Under high humidity conditions, water vapor can condense on the surface of the moving machine parts. To understand the influence of this water film, a pin-on-disk test was carried out on a sample where a thin film of water masks metal surfaces from contact. Although the coefficient of friction was similar for both the aluminum and steel pins’ interaction with titanium (~0.36), the wear tracks were not formed for steel pin/titanium interaction even though this experiment was conducted for more cycles.

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Caracterização da Peneira Média em Clones de Coffea canephora

REVISTA FIMCA ◽

10.37157/fimca.v5i2.58 ◽

2018 ◽

Vol 5 (2) ◽

pp. 28-31

Author(s):

Darlan Darlan Sanches Barbosa Alves ◽

Victor Mouzinho Spinelli ◽

Marcos Santana Moraes ◽

Carolina Augusto De Souza ◽

Rodrigo da Silva Ribeiro ◽

...

Keyword(s):

Genetic Improvement ◽

Block Design ◽

Coffea Canephora ◽

Coffee Production ◽

Randomized Block Design ◽

Significant Difference ◽

The Mean ◽

Four Blocks ◽

Selection Of

Introdução: O estado de Rondônia se destaca como tradicional produtor de café, sendo o segundo maior produtor brasileiro de C. canephora. No melhoramento genético de C. canephora, a seleção de plantas de elevada peneira média está associada à bebida de qualidade superior. Objetivos: O objetivo desse estudo foi avaliar a variabilidade genética de clones de C. canephora para o tamanho dos grãos, mensurado a partir da avaliação da peneira média (PM). Materiais e Métodos: Para isso, foi conduzido ao longo de dois anos agrícolas experimento no campo experimental da Embrapa no município de Ouro Preto do Oeste-RO, para a avaliação da peneira média de 130 genótipos (clones) com características das variedades botânicas Conilon, Robusta e híbridos intervarietais. O delineamento experimental utilizado foi de blocos ao acaso, com quatro repetições de quatro plantas por parcela. Resultados: Não houve resultados significativos para a interação clones X anos, indicando uma maior consistência no comportamento das plantas ao longo do tempo. Porém foram observadas diferenças significativas para o tamanho dos grãos entre os genótipos avaliados, possibilitando selecionar genótipos superiores. Conclusão: Os genótipos agruparam-se em cinco classes de acordo com o teste de média, subsidiando a caracterização de um gradiente de variabilidade da característica avaliada ABSTRACTIntroduction: Coffea canephora accounts for approximately 35% of the world's coffee production. The state of Rondônia stands out as a traditional coffee producer, being the second largest Brazilian producer of C. canephora. In the classical genetic improvement of C. anephora, the selection of plants of high average sieve is associated with a drink of superior quality. Objectives: The objective of this udy was to evaluate the genetic variability of Coffea canephora clones for the agronomic medium sieve (PM). Materials and Methods: The experiment was conducted in the experimental field of Embrapa, municipality of OuroPreto do Oeste-RO, located at coordinates 10º44'53 "S and 62º12'57". One hundred thirty genotypes (clones) of botanical characteristics Conilon, Robusta and intervarietal hybrids were evaluated in the agricultural years 2013-2014 and 2014-2015. The experimental design was a randomized block design with four blocks and four plants per plot, spacing 3.5 x 1.5 meters between plants. Results: Significant difference was found for the grain size. According to the F test, at 5% probability, the genotypes were grouped into five classes according to the mean test. Conclusion: The results obtained subsidized the characterization of a variability gradient of the evaluated trait.

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Characterization of Maize Genotypes (Zea mays L.) for Resistance to Striga asiatica and S. hermonthica and Compatibility with Fusarium oxysporum f. sp. strigae (FOS) in Tanzania

Agronomy ◽

10.3390/agronomy11051004 ◽

2021 ◽

Vol 11 (5) ◽

pp. 1004

Author(s):

John Lobulu ◽

Hussein Shimelis ◽

Mark D. Laing ◽

Arnold Angelo Mushongi ◽

Admire Isaac Tichafa Shayanowako

Keyword(s):

Grain Yield ◽

Fusarium Oxysporum ◽

Biocontrol Agent ◽

Zea Mays L ◽

Control Treatment ◽

Yield Reduction ◽

Maize Genotypes ◽

Significant Yield ◽

The Mean

Striga species cause significant yield loss in maize varying from 20 to 100%. The aim of the present study was to screen and identify maize genotypes with partial resistance to S. hermonthica (Sh) and S. asiatica (Sa) and compatible with Fusarium oxysporum f. sp. strigae (FOS), a biocontrol agent. Fifty-six maize genotypes were evaluated for resistance to Sh and Sa, and FOS compatibility. Results showed that FOS treatment significantly (p < 0.001) enhanced Striga management compared to the untreated control under both Sh and Sa infestations. The mean grain yield was reduced by 19.13% in FOS-untreated genotypes compared with a loss of 13.94% in the same genotypes treated with FOS under Sh infestation. Likewise, under Sa infestation, FOS-treated genotypes had a mean grain yield reduction of 18% while untreated genotypes had a mean loss of 21.4% compared to the control treatment. Overall, based on Striga emergence count, Striga host damage rating, grain yield and FOS compatibility, under Sh and Sa infestations, 23 maize genotypes carrying farmer preferred traits were identified. The genotypes are useful genetic materials in the development of Striga-resistant cultivars in Tanzania and related agro-ecologies.

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Characterization of Deleterious Mutations in Outcrossing Populations

Genetics ◽

10.1093/genetics/150.2.945 ◽

1998 ◽

Vol 150 (2) ◽

pp. 945-956 ◽

Cited By ~ 4

Author(s):

Hong-Wen Deng

Keyword(s):

Genetic Variation ◽

Genetic Variance ◽

Estimation Bias ◽

Deleterious Mutations ◽

Environmental Variance ◽

Higher Power ◽

Sib Mating ◽

The Mean ◽

Simulation Results

Abstract Deng and Lynch recently proposed estimating the rate and effects of deleterious genomic mutations from changes in the mean and genetic variance of fitness upon selfing/outcrossing in outcrossing/highly selfing populations. The utility of our original estimation approach is limited in outcrossing populations, since selfing may not always be feasible. Here we extend the approach to any form of inbreeding in outcrossing populations. By simulations, the statistical properties of the estimation under a common form of inbreeding (sib mating) are investigated under a range of biologically plausible situations. The efficiencies of different degrees of inbreeding and two different experimental designs of estimation are also investigated. We found that estimation using the total genetic variation in the inbred generation is generally more efficient than employing the genetic variation among the mean of inbred families, and that higher degree of inbreeding employed in experiments yields higher power for estimation. The simulation results of the magnitude and direction of estimation bias under variable or epistatic mutation effects may provide a basis for accurate inferences of deleterious mutations. Simulations accounting for environmental variance of fitness suggest that, under full-sib mating, our extension can achieve reasonably well an estimation with sample sizes of only ∼2000-3000.

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Correlation of Global Quantities at Material Characterization of Pressure-Sensitive Materials Using Sharp Indentation Testing

Lubricants ◽

10.3390/lubricants9030029 ◽

2021 ◽

Vol 9 (3) ◽

pp. 29

Author(s):

Carl F. O. Dahlberg ◽

Jonas Faleskog ◽

Per-Lennart Larsson

Keyword(s):

Finite Element ◽

Material Characterization ◽

Pressure Sensitivity ◽

Pressure Sensitive ◽

The Mean ◽

Sharp Indentation ◽

Von Mises ◽

Von Mises Plasticity ◽

Hardness Values

Correlation of sharp indentation problems is examined theoretically and numerically. The analysis focuses on elastic-plastic pressure-sensitive materials and especially the case when the local plastic zone is so large that elastic effects on the mean contact pressure will be small or negligible as is the case for engineering metals and alloys. The results from the theoretical analysis indicate that the effect from pressure-sensitivity and plastic strain-hardening are separable at correlation of hardness values. This is confirmed using finite element methods and closed-form formulas are presented representing a pressure-sensitive counterpart to the Tabor formula at von Mises plasticity. The situation for the relative contact area is more complicated as also discussed.

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Effect of Mean Velocity-to-Critical Velocity Ratios on Bed Topography and Incipient Motion in a Meandering Channel: Experimental Investigation

Water ◽

10.3390/w13070883 ◽

2021 ◽

Vol 13 (7) ◽

pp. 883

Author(s):

Nargess Moghaddassi ◽

Seyed Habib Musavi-Jahromi ◽

Mohammad Vaghefi ◽

Amir Khosrojerdi

Keyword(s):

Experimental Investigation ◽

Critical Velocity ◽

Velocity Ratio ◽

Scour Depth ◽

Incipient Motion ◽

Mean Velocity ◽

Straight Path ◽

Meandering Channel ◽

Bed Topography ◽

The Mean

As 180-degree meanders are observed in abundance in nature, a meandering channel with two consecutive 180-degree bends was designed and constructed to investigate bed topography variations. These two 180-degree mild bends are located between two upstream and downstream straight paths. In this study, different mean velocity-to-critical velocity ratios have been tested at the upstream straight path to determine the meander’s incipient motion. To this end, bed topography variations along the meander and the downstream straight path were addressed for different mean velocity-to-critical velocity ratios. In addition, the upstream bend’s effect on the downstream bend was investigated. Results indicated that the maximum scour depth at the downstream bend increased as a result of changing the mean velocity-to-critical velocity ratio from 0.8 to 0.84, 0.86, 0.89, 0.92, 0.95, and 0.98 by, respectively, 1.5, 2.5, 5, 10, 12, and 26 times. Moreover, increasing the ratio increased the maximum sedimentary height by 3, 10, 23, 48, 49, and 56 times. The upstream bend’s incipient motion was observed for the mean velocity-to-critical velocity ratio of 0.89, while the downstream bend’s incipient motion occurred for the ratio of 0.78.

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Preparation and Characterization of Carbon Supported Nano-Nickel and its Sorption Behavior for Zinc from Aqueous Solutions

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.510-511.271 ◽

2012 ◽

Vol 510-511 ◽

pp. 271-276 ◽

Cited By ~ 1

Author(s):

Tayyaba Asim ◽

R. Ahmed ◽

M.S. Ansari

Keyword(s):

Morphological Study ◽

Aqueous System ◽

Effect Of Temperature ◽

Vacuum Drying ◽

Sorption Behavior ◽

Nickel Deposition ◽

Adsorption Data ◽

Nano Nickel ◽

The Mean

Nickel deposited on carbon has been used as adsorbent to recover Zn (II) from aqueous system. The adsorbent was synthesized by depositing nickel nitrate on carbon under inert conditions and decomposing it to nickel by raising the temperature, washing and vacuum drying. Various techniques including XRD, FTIR, and SEM were employed for its characterization. FTIR showed that the nickel deposition enhanced the carbon functionalization due to presence of OH, C=O and C-O groups.Average crystallite size ofabout 9 nm was determined from XRD. Nickel deposition resulted in further division particles as indicated from the morphological study. Zn (II) was subjected to adsorptionon the synthesized adsorbent. It was observed that the rate of adsorption increased significantly on the nickel deposited carbon than the carbon alone. Morris-Weber, Lagergren and Reichenberg models were applied to find out the type and rate of adsorption employingfirst and second order rate equations.The adsorption data were applied toLangmuir, Freundlich and D-R isotherms and values of isotherm constants were calculated and were higher for Ni/C than carbon alone. The mean free energy of zinc sorption on carbon and Ni/C are 16.67 and 18.26 kJmol-1 which shows chemisorption. Thermodynamic studies were done to find out the effect of temperature on sorption. Positive values of ΔH and negative values of ΔG show endothermic and spontaneous type of sorption.

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Ribbing Instability Analysis of Forward Roll Coating

Journal of Mechanics ◽

10.1017/s1727719100002628 ◽

2009 ◽

Vol 25 (2) ◽

pp. 167-175

Author(s):

K. N. Lie ◽

Y. M. Chiu ◽

J. Y. Jang

Keyword(s):

Surface Coating ◽

Velocity Ratio ◽

Rolling Process ◽

Linear Stability Theory ◽

Wave Number ◽

Roll Coating ◽

Critical Capillary Number ◽

Roll Velocity ◽

Forward Roll Coating ◽

Numerical Program

AbstractThe ribbing instability of forward roll coating is analyzed numerically by linear stability theory. The velocity ratio of two rolls is fixed to be 1/4 for practical surface coating processes. The base flows through the gap between two rolls are solved by use of powerful CFD-RC software package. A numerical program is developed to solve the ribbing instability for the package is not capable of solving the eigenvalue problem of ribbing instability. The effects of the gap between two rolls, flow viscosity, surface tension and average roll velocity on ribbing are investigated. The criterion of ribbing instability is measured in terms of critical capillary number and critical wave number. The results show that the surface coating becomes stable as the gap increases or as the flow viscosity decreases and that the surface coating is more stable to the ribbing of a higher wave number than to the ribbing of a lower wave number. The effect of average roll velocity is not determinant to the ribbing instability. There are optimum and dangerous velocities for each setup of rolling process.

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Potentiality of Mean-Field Approaches for Recrystallisation: Characterization of the Deformed State of Polycrystals

Materials Science Forum ◽

10.4028/www.scientific.net/msf.467-470.33 ◽

2004 ◽

Vol 467-470 ◽

pp. 33-38 ◽

Cited By ~ 1

Author(s):

Rénald Brenner ◽

O. Castelnau ◽

Brigitte Bacroix

Keyword(s):

Mean Field ◽

Mechanical State ◽

Microstructural Parameters ◽

Deformed State ◽

The Mean ◽

Field Approaches

The description of the mechanical state of a polycrystal is presented in the framework of the mean-field approaches and attention is paid to the fields heterogeneity. For nonlinear behaviours, the importance of the chosen model is emphasized with respect to relevant microstructural parameters for recrystallisation.

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