Characteristics of bubble-induced liquid flows in a rectangular tank

Aliyu, Aliyu M.,Seo, Hyunduk,Kim, Hyogeun,Kim, Kyung Chun Elsevier 2018 Experimental thermal and fluid science Vol.97 No.-

<P><B>Abstract</B></P> <P>Bubbly flows are frequently encountered in many industrial applications where multiphase contact is used to promote heat, mass and momentum transfer. These include applications where both chemical and physical processes occur, such as wastewater treatment and biological aeration systems. We investigated the behaviour of underwater-generated bubble swarms, which were produced at the bottom of a 1-m<SUP>3</SUP> square tank from a 5-mm nozzle and allowed to rise by buoyancy in still water. Instantaneous velocity fields around the bubbles were obtained using Particle Image Velocimetry (PIV) seeded with 10–15-µm poly-dispersed fluorescent particles and gas flow rates ranging from 2 to 15 L/min (1.7–12.8 m/s). A continuous laser was used to obtain the time-resolved field, and a pulse laser was used to obtain the mean velocity fields. Images were captured at up to 2000 fps. After interrogation, a post-processing validation algorithm was employed to identify and remove vectors produced by bubbles and the interface, essentially producing vector fields of the liquid phase only. Proper orthogonal decomposition analysis was carried out on 1000 realisations of each gas flow case to identify dominant flow structures, and the flow was decomposed into its constituent spatial and temporal modes. We established that induced vortices in the liquid phase more clearly manifest at far streamwise locations shown by the spatial mode at lower gas flow rates and are clearer in the temporal mode at high gas flow rates. The mean streamwise and spanwise liquid velocities increased with the gas flow rate, and the streamwise bubble velocities can be well described by a top-hat profile curve. Finally, an analysis was done to estimate the bubble entrainment coefficient using the slip velocity and the gas buoyancy flux.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We investigated the behaviour of underwater-generated bubble swarms. </LI> <LI> Instantaneous velocity fields around the bubbles were obtained using PIV. </LI> <LI> POD analysis was carried out to identify dominant flow structures. </LI> <LI> The streamwise velocities can be well described by a top-hat profile. </LI> <LI> Bubble entrainment coefficient was estimated using the slip velocity and the gas void fraction. </LI> </UL> </P>

Upward gas–liquid two-phase flow after a U-bend in a large-diameter serpentine pipe

Aliyu, Aliyu M.,Almabrok, Almabrok A.,Baba, Yahaya D.,Lao, Liyun,Yeung, Hoi,Kim, Kyung Chun Elsevier 2017 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.108 No.1

<P><B>Abstract</B></P> <P>We present an experimental study on the flow behaviour of gas and liquid in the upward section of a vertical pipe system with an internal diameter of 101.6mm and a serpentine geometry. The experimental matrix consists of superficial gas and liquid velocities in ranges of 0.15–30m/s and from 0.07 to 1.5m/s, respectively, which cover bubbly to annular flow. The effects on the flow behaviours downstream of the 180° return bend are significantly reduced when the flow reaches an axial distance of 47 pipe diameters from the U-bend. Therefore, reasonably developed flow is attained at this development length downstream of the bend. Other published measurements for large-diameter film thickness show similar trends with respect to the superficial gas velocity. However, the trends differ from those of small-diameter pipes, with which the film thickness decreases much faster with increasing gas flow. As a result, only a few of the published correlations for small pipe data agreed with the experimental data for large pipe film thickness. We therefore modified one of the best-performing correlations, which produced a better fit. Qualitative and statistical analyses show that the new correlation provides improved predictions for two-phase flow film thickness in large-diameter pipes.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Gas–liquid flow experiments performed in a large diameter serpentine flow loop. </LI> <LI> Flow visualisation done using a wire mesh sensor to identify upward flow regimes. </LI> <LI> Conductance probes were used to measure film thickness in the annular regime. </LI> <LI> Asymmetrical films after a U-bend became symmetrical at middle and top positions. </LI> <LI> Improved film thickness correlation was developed and compared with existing ones. </LI> </UL> </P>

An experimental study on the characteristics of ejector-generated bubble swarms

Aliyu, Aliyu M.,Seo, Hyunduk,Kim, Minkyun,Kim, Kyung Chun Springer-Verlag 2018 JOURNAL OF VISUALIZATION Vol.21 No.5

Prediction of entrained droplet fraction in co-current annular gas-liquid flow in vertical pipes

Aliyu, A.M.,Almabrok, A.A.,Baba, Y.D.,Archibong, A.E.,Lao, L.,Yeung, H.,Kim, K.C. Elsevier 2017 Experimental thermal and fluid science Vol.85 No.-

<P>The entrained droplet fraction is an important parameter in annular two-phase flow, as its correlations are key inputs in flow simulation codes for the prediction of pressure drop and critical heat flux or dryout. Investigators have stressed the importance of extending the validity range of current correlations so that more conditions are covered. This could be achieved for example by including fluids with higher viscosities, a wider range of operating pressures, and increase in the size of pipes used for experiments (most of the data in the literature are from pipes of 50 mm diameter and below). In attempt to improve the latter, experiments were conducted in a 101.6 mm gas liquid flow loop at Cranfield University's Oil and Gas Engineering Laboratory and data on the fraction of droplets were collected in the annular flow regime by measuring the film velocity, from which the droplet fraction was calculated. Comparison of the film velocity by this method and by a mass balance showed close agreement. A capacitance Wire Mesh Sensor was used for flow visualisation in order to distinguish between annular and churn flow. In order to arrive at an improved correlation, over 1300 data points were gathered from other published works. These include air water studies where large pipes of up to 127 mm in diameter were used. The others were from small-diameter pipes and for refrigerant, steam water, air water, and air glycerine flows. Since in the annular regime, the gas flow entrains liquid droplets into the core, their presence alters the properties of the gas core. Therefore, accurate predictions are pivotal for the energy efficient design and operation of facilities in the petroleum and nuclear power industry. The correlation obtained here showed good agreement with the collected databank. (C) 2017 Elsevier Inc. All rights reserved.</P>

Development of a dual optical fiber probe for the hydrodynamic investigation of a horizontal annular drive gas/liquid ejector

Aliyu, A.M.,Kim, Y.K.,Choi, S.H.,Ahn, J.H.,Kim, K.C. Butterworth ; Elsevier Science Ltd 2017 Flow measurement and instrumentation Vol.56 No.-

A dual-channel optical fiber probe was developed to quantify the bubble characteristics (void fraction, velocity, and bubble size) in a gas-liquid annular ejector system. Water is pumped upstream of the ejector contraction. Since a low pressure region exists downstream in the ejector diffuser, this permits air to be sucked into the flowing liquid by jet pump action and the inlet air volumetric flow rate is measured by a flow meter. Verification of the void fraction (range 0.15-0.5) measured by the optical fiber probe was then possible and deviations were generally around +/- 5%. Also, bubble velocity was measured using the optical probe by cross-correlating signals from the two fibers whose tips are separated by a known distance. Alternatively measuring bubble velocity using a particle image velocimetry method provided validation for the optical fiber probe system where a high speed camera was used to capture instantaneous bubble images at time intervals of 0.125ms. Excellent agreement between the velocities using both methods is reported. For bubble size measurements, analyzing the temporal signals from a single probe enabled estimation of the size of a bubble. Bubble sizes measured ranged between 1.5 and 6.0mm and size distributions were constructed for different ejector water volumetric flow rates ranging from 0.0022 to 0.0063m<SUP>3</SUP>/s. LabVIEW provided a convenient platform for coding the algorithms for estimating the void fraction, bubble velocity and bubble size. For further comparison, a CFD study of the ejector system was done, and the vertical radial profiles of the void fraction were compared with those obtained by the optical fiber system and these showed good agreement.

Effect of liquid crossflow on the motion of underwater bubble swarms

Aliyu M. Aliyu(알리유 무사 알리유),Hyunduk Seo(서현덕),Kyung Chun Kim(김경천) 한국가시화정보학회 2017 한국가시화정보학회 학술발표대회 논문집 Vol.2017 No.11

Phenotypic Stability Analysis of Yield Components in Cashew (Anacardium occidentale L.) Using Additive Main Effect and Multiplicative Interaction (AMMI) and GGE Biplot Analyses

( Olawale M Aliyu ),( Oluwatosin O Adeigbe ),( Oluwafemi O Lawal ) 한국육종학회 2014 Plant Breeding and Biotechnology Vol.2 No.4

Perennial poor fruit-set and variability in tree yield are among major problems of cashew nut production. Thus, development of improved stable genotypes would be a sustainable strategy to address this perpetual problem in order to boost income and livelihood of many smallholder farmers of this important commodity crop. Here, we have applied additive main effect and multiplicative interaction (AMMI) and genotype, genotype by environment (GGE) biplot analysis to a 3-year multi-locational trial data on nine yield component characters of cashew to evaluate phenotypic stability across diverse environments. Variance analysis showed significant variability in the cashew genotypes and strong influence of genotype by environment (GxE) on tree yield as none of the genotypes was stable for any of the yield components across locations. GxE data showed that a substantial portion of the variation was explained by the genotype (highly heritable), accounting for between 10% and 87% of the variation, while the environment accounted for between 0.7% and 37%. Data showed significant higher values of interaction (GxE) than the respective values for environment, and were mostly captured and could be explained by the first principal component axis (IPCA 1) for all the yield component characters.There was an inverse relationship between stability and yield as the best three yielding genotypes (KT_26, IW_222 and IW_31) were found to be the most unstable. Among the yield component tested, hermaphrodite flowers per panicle, nuts per panicle, nuts per tree, nut weight, and tree fruiting efficiency were identified to be critical components for nut yield. Although there was wide variation between the three environments evaluated, the data effectively identified two mega-environments (ME), and two superior genotypes (IW_222 and KT_26) suitable for these two mega-environments. The GxE complex exposes the short-comings of broad recommendations of common agronomic-husbandry technologies across diverse cashew ecologies as each mega-environment would require specific adaptable technologies for optimal plant output. Above all, the data presented here underscore the importance of multi-locational evaluation of genotypes for varietal development in cashew.

Comparative Efficacy of Some Selected Plant Derived Biopesticides for the Control of Insect Pests of Cowpea (Vigna unguiculata (L.) Walp.) in Katsina State, Nigeria

Ahmed B. I.,Onu I.,Mudi L.,Aliyu M. 韓國作物學會 2007 Korean journal of crop science Vol.52 No.2

Field trial was conducted at the Research Farm of the Katsina State Agricultural and Rural Development Authority during the farming season of 2004 with a view to evaluate/determine the efficacy of some selected plant-derived biopesticides against the insect pests of cowpea as well as their effect on yield. The variety of the cowpea used was IT86D-719 and the plant derived biopesticides evaluated during the trial were chilli pepper, garlic, ginger, neem, sweetsop and tobacco. The experimental field was ploughed, harrowed and thereafter ridged before the commencement of the 2004 planting season. A total of twenty one (21) experimental plots were demarcated and arranged into seven treatment plots. The size of each plot was 5m~times4m while interspaces between adjacent plot and blocks were 1m and 2m, respectively. Results of the experiments showed that all the plant-derived biopesticide treatments were significantly (p>0.05) better than control treatment. The order of effectiveness of the treatments was tobacco (80-90%), sweetsop (75-85%), garlic (70-80), neem (72-78%), chilli pepper (60-70%) and ginger (30-50%). Furthermore, yield result corresponded positively with the effectiveness of the treatments. Results of the present finding suggest the use of tobacco, sweetsop and garlic as promising biopesticides in the control of cowpea insect pests.

Enhancement of momentum transfer of bubble swarms using an ejector with water injection

Seo, Hyunduk,Aliyu, Aliyu M.,Kim, Kyung Chun Elsevier 2018 ENERGY Vol.162 No.-

<P><B>Abstract</B></P> <P>This paper presents the application and a comparative study of two ejector configurations to enhance the momentum transfer of submerged bubble swarms generated in a water tank. High-speed photography was used to measure the bubble rise velocity profiles and bubble size distribution from captured images. The volumetric flowrate of air was varied from 2 to 15 L/min, and water was supplied at 70 L/min for the case with water injection. Three different cases were selected to conduct bubble swarm visualization: one with a plain nozzle, one with an air-driven ejector, and one with a water-driven ejector. Buoyancy experiments were also carried out to characterize momentum transfer capability. The plain nozzle and air-driven ejector cases make ergodically large bubbles. However, in the case with water injection, small bubbles were generated through the suction and mixing chamber inside the ejector, and evenly sized broken-up bubbles were produced. Due to the differences in bubble generating mechanisms, there were specific differences in the generated bubble characteristics such that the case with water injection showed significant buoyancy performance in interaction with a spherical model compared to the other cases.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Bubble swarms characteristics generated from ejectors are experimentally investigated. </LI> <LI> Digital image processing is carried out to obtain statistical data of bubble swarm. </LI> <LI> Momentum transfer is demonstrated by a buoyancy experiment with a spherical model. </LI> <LI> Uniform bubble swarm is realized by the proposed ejector with water injection. </LI> </UL> </P>

이젝터를 이용한 효율적인 공기방울 장벽 형성에 관한 연구

서현덕(Hyeon Deok Seo),Aliyu M. Aliyu,김경천(Kyung Chun Kim) 대한기계학회 2016 대한기계학회 춘추학술대회 Vol.2016 No.12

Bubble velocity and diameter in the water tank were experimentally studied with using a high-speed camera. Experiment was implemented with 3 cases, no ejector, two different configurations of ejector with 0 and 1.5 D (mixing section diameter) gaps between the nozzle exit and the ejector neck. Images were handled with MATLAB Image Processing tools and statistical methods. Bubble properties were analyzed with respect to the range of Reynolds number. At low Reynolds number case, the ejector acts as an obstacle. In the case of high Reynolds number larger than 21,100, the zero gap ejector shows the potential to produce smaller bubbles than the ‘no ejector’ case.