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1

Effect of flow orientation in experimental studies on FC-770 boiling heat transfer in asymmetrically heated minichannels

Piasecka Magdalena, Strąk Kinga

Archives of Thermodynamics

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2024

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Vol. 45, no 2

29--39

EN

The article presents experimental results of boiling heat transfer during FC-770 flow in a group of five minichannels with a common heated wall. The flow orientation was changed from 0º to 180º, with a 15° increment. During the experiments, the temperature of its outer heated wall surface was measured by an infrared camera. At the same time, flow patterns were captured through the glass plate opposite the heated wall using a high-speed camera. The purpose of the calculations was to determine local heat transfer coefficients on the contact surface between the working fluid and the heated surface in the central minichannel, using a simplified 1D calculation method. The results in the form of dependences of the temperature of the heated wall and the heat transfer coefficient as a function of the distance from the channel inlet for various flow orientations were analysed. Furthermore, typical boiling curves and two-phase flow patterns were presented. The mean relative error of the heat transfer coefficient was determined for various flow orientation. The dependence of the void fraction as a function of heat flux was illustrated for various angles of minichannel inclination to the horizontal plane. It was observed that the void fraction increased with heat flux and with increasing angle of inclination of the minichannel to the horizontal plane.

2

Verification of Dead Zones Generated in Bioreactors as a Proactive Stage in Bioreactor Design

Al-Mashhadani Mahmood K. H.

Journal of Ecological Engineering

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2023

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Vol. 24, nr 6

65--74

EN

The activity and growth of microorganisms for renewable energy production are still influenced by the dead zones created in bioreactors. These areas form a nutrient and thermal gradient, causing an abundance of food in certain areas compared to famines in other areas of same bioreactor. The current study is a step in identifying those dead zones, followed by another step in improving the flow of media inside the reactor. The results indicated that the inner parts of the bioreactor may be a crucial factor in the creation and spread of such dead zones. For example, the position of the disc-type diffuser contributes to the generation of those areas at the bottom of the reactor. It was inferred from the fluid movement in reactors using the annular-type diffuser proposed in the current study. The bubble size, gas mass flux, and radiuses of fillet, as the most important factors, were examined in both bioreactors. The results revealed a noticeable improvement in these parameters in this area of the reactor when the disc diffuser was replaced by the annular diffuser. For example, the average liquid velocity was recorded in the lower part of the modernized reactor at 0.0198 m/s, while the velocity was recorded in the conventional reactor at 0.00077 m/s under same bubbles diameter used in both reactors (0.125 mm). The inclusion of the effect of the presence of microorganisms in mathematical models was also addressed in the current study. The results showed that the amount of oxygen remaining at the bottom of the reactor after bio-consumption in the presence of the annular diffuser was higher than that in the conventional reactor. This clearly emphasizes the importance of the design of the internal parts of the bioreactor.

3

Experimental investigation of flow pattern over a fully developed bed at a 60° river confluence in large foods

Balouchi Behnam, Shafai Bejestan Mahmood, Ruther Nils, Rahmanshahi Mostafa

Acta Geophysica

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2022

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Vol. 70, no 5

2283--2296

EN

River confluences have a complex flow and sedimentation pattern that have vital influences on the hydraulic and bed morphology of river reach and the surrounding area. Confluences can be observed in waterways with various situations such as live bed conditions. This condition is a hydro-morphological situation with a high densiometric Froude number, i.e., bed load transport is supplied from upstream. According to the literature review, most of the experimental studies investigate the flow pattern on the flatbed and not on the developed riverbed, or/and in the low densiometric Froude number, or/and without supplying the sediment from upstream. Therefore, in the present study for the quantification of the flow pattern under these conditions, each developed bed was fixed with the cement blanket method in the laboratory. Then, the 3D velocity was measured at specific points at the confluence. The current study was designed to understand the flow pattern corresponding to the river bed behavior in the case of large foods. It is expected that the morphological features downstream of the confluence have a different pattern than the ones in the condition described in other literature. Thus, this paper describes briefly what are the different bed features and investigates the corresponding flow pattern. The results of the flow pattern on the developed bed show that all zones at the river confluence can be observed except the point bar due to the approximate equality of the mean longitudinal velocity of the separation zone and the main channel upstream of the confluence. Moreover, results show that by increasing the bedload ratio (sediment discharge to water discharge of the main channel of upstream of the confluence) from 0 to 3× 10−4, for defection to the outer bank of the channel decreased down to 45%, the stagnation equivalent area decreased down to 2.5 times, and bed shear stress decreased down to 40%. Hence, the momentum of lateral flow decreased with increasing bedload. Besides, the recovery zone occurred at a longer distance after the confluence compared to the case without bedload. Hence, the location of the maximum velocity zone, vortices, and secondary flows changed downstream of the confluence, by changing the bed load value.

4

Coastal Water Properties and Hydrodynamic Processes in the Malacca Strait: Case Study Northeastern Coast of Sumatra, Indonesia

Koropitan Alan Frendy, Barus Ternala Alexander, Cordova Muhammad Reza

Journal of Ecological Engineering

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2021

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Vol. 22, nr 11

16--29

EN

Dynamic processes in the coastal waters play an important role in regulating the marine pollution distribution caused by riverine inputs and are relevant for coastal management. Here, the coastal water properties were investigated from field measurements and modeling hydrodynamic processes in the northeastern coast of Sumatra. The present study found that the river discharges affect a low salinity of 28–29 psu in the surface waters along near the coastal line. The river discharge might influence by strong La Niña with high rainfall in December 2010. However, the authors suggested that the effect of tidal mixing is stronger than the freshwater discharges, resulting in vertically well-mixed coastal waters in the region. The observed tidal range of 200 cm indicates a strong tidal mixing in the waters. The tidal elevation contributes more than 70% of the total measured sea elevation. The tidal current signal in which the flow pattern simulations show no significant differences among tide and wind-tide driven currents, is also dominant (77%).

5

The rectangular two-phase closed thermosyphon: A case study of two-phase internal flow patterns behaviour for heat performance

Chompookham Teerapat, Sichamnan Surachet, Bhuwakietkumjohn Nipon, Parametthanuwat Thanya

Archives of Thermodynamics

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2020

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Vol. 41, no 3

223--254

EN

This research explored different types of two-phase flow patterns that influenced heat transfer rate by assessing rectangular two-phase closed thermosyphon (RTPCT) made from glass with the sides of equal length of 25.2 mm, aspect ratio 5 and 20, evaporation temperature of 50, 70, and 90°C, working substance addition rate of 50% by volume of evaporator, and water inlet temperature at condensation of 20°C. Upon testing with aspect ratios 5, three flow patterns emerged which were: bubble flow, slug flow and churn flow respectively. As per the aspect ratio 20, four flow patterns were discovered which were: bubble flow, slug flow, churn flow and annular flow, respectively. Aspect ratio 5 pertains characteristic which resulted in a shorter evaporation rate of the RTPCT than that of the aspect ratio 20, thus, a shorter flow distance from the evaporator section to heat releaser was observed. Therefore, flow patterns at aspect ratio 5 exhibited a faster flow velocity than that of the aspect ratio 20. Furthermore, changes of flow pattern to the one that is important for heat transfer rate can be easily achieved. Churn flow was the most important type of the flow for heat transfer, followed by slug flow. Moreover, with aspect ratio 20, annular flow was the most important flow for the heat transfer, followed by churn flow, respectively. Throughout the test, average heat flux as obtained from the aspect ratio 5 were 1.51 and 0.74 kW/m2 which were higher than those of the aspect ratio 20. The highest heat flux at the operating temperature of the evaporator section was 90°C, which was equivalent to 2.60 and 1.52 kW/m2, respectively.

6

Metal foams as structural packing in the construction of process equipment

Dyga R.

Technical Transactions

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2017

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Vol. 4(114)

165--178

EN

The paper presents possibilities of the application of open-cell metal foams in the construction of process equipment. The article also describes results of own experimental studies on hydrodynamic and thermal phenomena occurring during fluid flow through channels packed with aluminium alloy foams. The collected experimental data enabled to determine, among others, pressure drops and the heat transfer coefficient, and to indicate main gas–liquid flow patterns.

PL

W artykule przedstawiono możliwości wykorzystania otwartokomórkowych pian metalowych w budowie aparatury przemysłowej. Opisano wyniki własnych badań doświadczalnych dotyczących zjawisk hydrodynamicznych i cieplnych zachodzących podczas przepływu płynu przez kanały wypełnione pianami ze stopów aluminium. Zebrane dane eksperymentalne pozwoliły określić m.in. wartości oporów przepływu i współczynnika wnikania ciepła oraz wskazać podstawowe struktury przepływu gaz–ciecz.

7

Hydrodynamics of two-phase flow in tubular reactor

Czernek K., Płaczek M.

Technical Transactions

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2017

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Vol. 4(114)

101--114

EN

In the paper, the possibility of using an optoelectronic system for measuring the parameters relating to the hydrodynamics of liquid film in two-phase flow of highly viscous liquids and gas was evaluated. The methodology of the measurement and experimental results in relation to the annular co-current air–oil falling flow was given.

PL

W pracy dokonano oceny możliwości wykorzystania układu optoelektronicznego do pomiaru wielkości opisujących hydrodynamikę filmu cieczy przy dwufazowym przepływie cieczy bardzo lepkiej i gazu. Podano metodykę prowadzenia pomiarów oraz ich wyniki w odniesieniu do współprądowego opadającego przepływu pierścieniowego powietrze–olej.

8

Flow structures during refrigerants condensation

Sikora M.

Journal of Mechanical and Energy Engineering

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2017

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Vol. 1, No 1

101--106

EN

For several years, in the world are carried out studies on the refrigerants condensation in minichannels. These studies are aimed at understanding the condensation process and facilitate the design of mini heat exchangers. It is very important to optimize heat transfer and drive power consumption of the is the knowledge of the processes occurring during refrigerants condensation in pipe minichannels. It is important in this case to make a individual flow structures maps for the refrigerants, due to the significant effect of flow structured formed in the minichannel on the heat transfer and flow resistance. Unfortunately, in relation to the number of publications about condensation in minichannels, the number of published flow maps is relatively small. Due to the fact that the condensation process takes place differently in the minichannels and conventional channels, there is no possibility of using the flow maps for conventional channels to identification flow patterns in minichannels. One of the most popular flow maps for the condensation in minichannels is the map created by Colleman and Garimella, which was made for the R134a refrigerant. The authors conducted their own experimental studies of refrigerants R134a, R404A and R407C condensation in pipe minichannels with an internal diameter d = 3.3 - 0.31 mm. These studies results were subjected to calculation identification of flow structures using the map of Colleman and Garimella. These results are compared with the criteria published on Thome and Cavallini flow maps.

9

Physical Modelling of Tundish Slag Entrainment under Various Technological Conditions

Michalek K., Gryc K., Socha L., Tkadlečková M., Saternus M., Pieprzyca J., Merder T., Pindor L.

Archives of Metallurgy and Materials

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2017

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Vol. 62, iss. 3

1467--1471

EN

This paper deals with the issue of physical modelling of vortexes creation and tundish slag entrainment over the mouth of the nozzle into the individual casting strands. Proper physical model is equivalent to the operational continuous casting machine No. 2 in TŘINECKÉ ŽELEZÁRNY, a.s. Physical modelling methodology and simulated operational conditions are shortly described. Physical modelling was used for the evaluation of current conditions of steel casting at the application of different impact pads in the tundish. Further, laboratory measurement on the physical model aiming the determination of exact critical periods of vortexes creation and study of the slag entrainment as a consequence of changes in surface level during the tundish refilling to standard level were realised. The obtained results were analysed and discussed.

10

3D numerical simulation of flow field around twin piles

Amini A., Parto A. A.

Acta Geophysica

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2017

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Vol. 65, no. 6

1243--1251

EN

In this study to identify the flow pattern and local scour mechanism around pile groups, the flow field was simulated using FLOW-3D software. A pair of pile on a flat-bed channel with side by side and tandem arrangements was investigated. To establish Navier–Stokes equations, the RNGk-ε turbulence model was used and the results were verified using experimental data. In case of FLOW-3D capability, it was found that the software was able to properly simulate the expected interaction between the pile groups. The results of flow field simulation showed that Reynolds number and the pile spacing are the most influential variables in forming vortices. The flow around tandem pile and the downward flow around wake vortices were more intense and complicate in comparison with side by side arrangements and single pile.

11

Some problems of hydrodynamics of two-phase flow mixtures in minichannels

Wengel M., Miłaszewicz B., Ulbrich R.

Archives of Thermodynamics

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2014

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Vol. 35, no. 2

93--101

EN

Gas-liquid two-phase flow in minichannels has been the subject of increased research interest in the past few years. Evaluation, however, of today's state of the art regarding hydrodynamics of flow in minichannels shows significant differences between existing test results. In the literature there is no clear information regarding: defining the boundary between minichannels and conventional channels, labelling of flow patterns. The review of literature on the hydrodynamics of gas-liquid flow in minichannels shows that, despite the fact that many research works have been published, the problem of determining the effect of diameter of the minichannel on the hydrodynamics of the flow is still at an early stage. Therefore, the paper presents the results of research concerning determination of flow regime map for the vertical upward flow in minichannels. The research is based on a comprehensive analysis of the literature data and on the research that has been carried out. Such approach to the mentioned above problems concerning key issues of the two-phase flow in minichannels allowed to determine ranges of occurrence of flow structures with a relatively high accuracy.

12

Rock grade control structures and stepped gabion weirs: Scour analysis and flow features

Pagliara S., Palermo M.

Acta Geophysica

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2013

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Vol. 61, no. 1

126--150

EN

Rock and stepped gabion weirs are peculiar hydraulic structures that received relatively little attenti on in technical literature. Neverthe- less, they can be successfully used for river restoration instead of tradi- tional hydraulic structures. They have the advantage of being elastic structures and to preserve the natura l environment. They can easily adapt to the in situ conditions and can be effortle ssly modified according to the different hydraulic or geometric cond itions which can occur in a natural river. The present study aims to anal yze the effects of their presence on flow pattern and on the scour hole occurring downstream. The analysis involved scour processes, hydraulic jump types, stilling basin morphol- ogy and flow patterns. Two different hydraulic jump types were distin- guished and classified. It was show n that the flow regime deeply influences the scour process, which evolves much more rapidly when a Skimming Flow regime takes place. Empirical relationships are pro- posed to evaluate maximum scour depth, maximum axial length, and non dimensional axial profiles.

13

Comparison of experimental data and numerical simulation of two-phase flow pattern in vertical minichannel

Sowiński J., Krawczyk M., Dziubiński M.

Chemical and Process Engineering

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2012

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Vol. 33, nr 1

63-70

EN

The aim of the study was the implementation of a numerical simulation of the air-water two-phase flow in the minichannel and comparing results obtained with the values obtained experimentally. To perform the numerical simulations commercial software ANSYS FLUENT 12 was used. The first step of the study was to reproduce the actual research installation as a three-dimensional model with appropriate and possible simplifications - future computational domain. The next step was discretisation of the computational domain and determination of the types of boundary conditions. ANSYS FLUENT 12 has three built-in basic models with which a two-phase flow can be described. However, in this work Volume-of-Fluid (VOF) model was selected as it meets the established requirements of research. Preliminary calculations were performed for a simplified geometry. The calculations were later verified whether or not the simplifications of geometry were chosen correctly and if they affected the calculation. The next stage was validation of the chosen model. After positive verification, a series of calculations was performed, in which the boundary conditions were the same as the starting conditions in laboratory experiments. A satisfactory description of the experimental data accuracy was attained.

14

Fyzikální a numerické modelové studium charakteru proudění kovové taveniny v průtočném metalurgickém agregátu při různých okrajových podmínkách

Michalek K., Gryc K., Strasak P.

Prace Instytutu Metalurgii Żelaza

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2009

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T. 61, nr 5

98-101

EN

The paper is devoted to a study of metal melt flow pattern in the through-flow metallurgical aggregate (tundish) under different boundary conditions. For evaluating of flow conditions in the tundish a permanent concentration change (Heaviside unit step) was used. Experiments carried out by physical model in the geometric scale 1:5 to the real tundish and simultaneously carried out by numerical simulations was done for one type of impact pad design under isothermal flow conditions. Physical modelling was done by changing of KCl water solution concentration during experiments and by measuring of conductibility in the inlet and outlets areas (thermal and conductibility probes). Obtained data was recalculated based upon Freude’s criterion to the real tundish conditions. For mathematical identification of individual F-curves the authentic approximate method was used. Numerical modelling was realized by CFD program Fluent. Results obtained from both modelling methods are compared by defined dimensionless concentration value (0,1) under conditions of three different surface highs for three different casting speeds. It could be noted that results obtained from both modelling methods are comparable – the methodology is set correctly.

15

Simulations of flow patterns in silos with a cellular automaton: Part 1

Kozicki J., Tejchman J.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2005

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Vol. 9, No 1

81-102

EN

A simplified cellular automaton was used to calculate the kinematics of non-cohesive granular materials during confined flow in silos. In this model, granular flow was assumed to be an upward propagation of holes through a lattice composed of cells representing single particles. Calculations were carried out with different silo shapes and inserts, transition probabilities, migration rules, outflow schemes, grid types, wall roughness and cell numbers. To visualize the calculation process, horizontal layers of various shades were introduced. The simulation results were compared with laboratory tests in model silos.

16

Simulations of flow patterns in silos with a cellular automaton: Part 2

Kozicki J., Tejchman J.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2005

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Vol. 9, No 1

103-114

EN

An improved cellular automaton has been used to calculate the kinematics of non-cohesive granular materials during confined flow in mass and funnel flow model silos. In this model, based on a gas model of hydrodynamics, collisions and dissipation of particles were taken into account during granular flow. The model allowed for investigations of dilatant zones in granular material during silo flow.

17

Experimental study on bubble pump performance with organic working fluids

Koyfman A., Jelinek M., Levy A., Borde I.

Zeszyty Naukowe Politechniki Świętokrzyskiej. Mechanika

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2003

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Z. 77

25-32

EN

The performance of a diffusion absorption refrigeration system is dependig primarily on the performance of the bubble pump. The bubble pump is a vertical tube with a heating element at the botton, in which a flow is induced by a boiling and segregation process of a binary solution. The supplied heat, generated gas that lift up the binary mixture through the verticaltube in various two-phase modesof flow. In the present study, the performance of a bubblepump with organic working fluids was carried out experimentally. During the investigation pictures were taken showing that the bubble pump operates at slug flow regime with a churn floow regime at the entrance of the bubble pump tube and that performance of the bubble pump depends mainly on the motive head and on the heat input to the bubble pump.

18

Wykorzystanie analizy obrazu do rozpoznawania struktur przepływu dwufazowego gaz–ciecz w złożu dwuwymiarowym

Masiukiewicz M., Zając D., Ulbrich R.

Inżynieria Chemiczna i Procesowa

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2001

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T. 22, z. 3D

917--922

PL

Praca stanowi ocenę możliwości zastosowania metody analizy obrazu w odniesieniu do przepływu dwufazowego gaz-ciecz w złożu dwuwymiarowym. Idea zaproponowanej metody opiera się na analizie zmian poziomu szarości zarejestrowanych kamerą video struktur przepływu w czasie. Natomiast zmiana poziomu szarości to w praktyce zmiana udziału objętościowego fazy ciekłej i gazowej.

EN

This paper reports results of the use of image analysis method applied to two-phase gas-liquid flow in two-dimensional bed. Idea of proposed method is based on gray level value change of recorded flow structures by CCD camera. The change of gray level value is the change of volume fraction of liquid and air phase.