Submit to Energies Review for Energies Edit a Special Issue

Journal Browser

► Journal Browser

Special Issue "Multiphase Flows"

Print Special Issue Flyer
Special Issue Editors
Special Issue Information
Keywords
Published Papers

A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "J: Thermal Management".

Deadline for manuscript submissions: closed (5 October 2021) | Viewed by 24323

Share This Special Issue

Special Issue Editors

Prof. Dr. Marek Ochowiak

E-Mail Website
Guest Editor

Department of Chemical Engineering and Equipment, Poznan University of Technology, 60-965 Poznan, Poland
Interests: multiphase flows; separation processes; atomization; sprays; mixing; chemical technology
Special Issues, Collections and Topics in MDPI journals

Dr. Szymon Woziwodzki

E-Mail Website
Guest Editor

Institute of Chemical Technology and Engineering, Poznan University of Technology, 60-965 Poznan, Poland
Interests: mixing; multiphase flows; process simulation; plant design; separation
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The term “multiphase flow” is used to refer to any fluid flow consisting of more than one phase. The flows could be classified according to the state of the different phases or components and therefore refer to gas/solids flows, liquid/solids flows, gas/particle flows, or bubbly flows and so on. Multiphase flow modelling and metering are key factors for optimal flow design and construction of efficient apparatuses. Over the last few decades, scientists have experimentally studied and developed the models of multiphase Newtonian and non-Newtonian fluid flows.

The present Special Issue invites contributions on the topic of multiphase flows, multicomponent flows, and chemical reactors of both experimental and computational studies. Of special interest are submissions from the fields of mechanical and energy engineering, environmental and chemical engineering, chemistry and environmental protection. We welcome both original research articles and review articles.

Prof. Marek Ochowiak
Dr. Szymon Woziwodzki
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Energies is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2200 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

multiphase flow
newtonian fluid
non-Newtonian fluid
rheology
sedimentation
fluidization
mixing
spray
reactors
bubbles
adsorption
heat transfer
mass transfer

Published Papers (18 papers)

Download All Papers

Research

Open AccessArticle

Gas Hold-Up and Mass Transfer in a Vessel with an Unsteady Rotating Concave Blade Impeller

Sebastian Frankiewicz

and

Szymon Woziwodzki

Energies 2022, 15(1), 346; https://doi.org/10.3390/en15010346 - 04 Jan 2022

Cited by 1 | Viewed by 694

Abstract

The steady mixing of gas-liquid systems is used where a large development of the interfacial area is required. However, the presence of gas in the liquid reduces the efficiency of mass transfer by reducing the mixing power, due to the creation of gas formations behind the impeller blades and the reduction in density. The efficiency of mass transfer can be increased by using a concave blade impeller or unsteady mixing. Mass transfer efficiency studies for these impellers and unsteady mixing are limited. This paper presents an analysis of the influence of the impeller construction on the gas hold-up and volumetric mass transfer coefficient k_La. Impellers with a different number of concave blades, and with alternatively arranged concave blades, were analyzed. The obtained results were compared with the standard flat blade turbine. The obtained results indicate that the arrangement of the concave blades has the greatest effect on reducing the gas hold-up and k_La. Higher values were obtained for the four-bladed and six-bladed impellers. A comparison of the gas hold-up rate for the unsteady and steady mixing has shown that for steady mixing greater gas hold-up is achieved. The volumetric mass transfer coefficient for unsteady mixing is also greater compared to steady mixing, indicating greater efficiency in mass transfer. Full article

(This article belongs to the Special Issue Multiphase Flows)

► Show Figures

Figure 1

Open AccessArticle

Oxygen Transfer Effects in a Two-Phase System of an Aqueous Phase and Liquid Perfluorochemical Subjected to Continuous Wave-Assisted Agitation in Disposable Bioreactor

Kamil Wierzchowski

Paweł Sobieszuk

and

Maciej Pilarek

Energies 2021, 14(14), 4381; https://doi.org/10.3390/en14144381 - 20 Jul 2021

Viewed by 967

Abstract

Systems of two immiscible liquid phases—aqueous phase (i.e., distilled water (dH₂O) or phosphate-buffered saline (PBS)) and liquid perfluorochemical (i.e., perfluorodecalin (PFD))—were subjected to wave-assisted agitation, i.e., oscillatory rocked, in a disposable bag-like container in a ReadyToProcess WAVE^TM25 bioreactor, to recognize oxygen transfer effects and effectivity of the surface aeration. According to the DoE methodology, values of the volumetric liquid-side mass transfer (k_La) coefficient for dH₂O, PBS, dH₂O-PFD, and PBS-PFD systems were determined for the whole range of operating parameters of the WAVE 25 bioreactor. A significantly higher maximal value of k_La was found for waving dH₂O than for dH₂O-PFD (i.e., 0.00460 s⁻¹ vs. 0.00331 s⁻¹, respectively) compared to more equal maximal values of k_La reached for PBS and PBS-PFD (0.00355 s⁻¹ vs. 0.00341 s⁻¹, respectively). The interface development factor (f) depended on the interfacial area a, and the enhancement factor (E^PFD), depending on k_La, was introduced to quantitatively identify the mass transfer effects in the systems of waving two immiscible liquids. The phase of PFD was identified as the reservoir of oxygen. Dimensional correlations were proposed for the prediction of the k_La coefficient, in addition to the f and E^PFD factors. The presented correlations, and the set of k_La values, can be directly applied to predict oxygen transfer effects reached under continuous oscillatory rocked systems containing aqueous phase and liquid perfluorochemical. Full article

(This article belongs to the Special Issue Multiphase Flows)

► Show Figures

Figure 1

Open AccessArticle

Influence of Spray Nozzle Operating Parameters on the Fogging Process Implemented to Prevent the Spread of SARS-CoV-2 Virus

and

Energies 2021, 14(14), 4280; https://doi.org/10.3390/en14144280 - 15 Jul 2021

Cited by 3 | Viewed by 1384

Abstract

This article reports the results of a study into the effect of operating parameters on the occurrence and course of gas–liquid two-phase phenomena during the fogging process carried out with the use of a conical pressure-swirl nozzle. Four alternatives of the stub regulation angles and four values of pressure of air supply to the nozzle were tested as part of the current research. The range of the investigated variables was common for the operation of fumigators used to prevent the spread of SARS-CoV-2 virus. The liquid flow rate (weighting method), the field of velocity, and turbulent flow intensity factor, as well as velocity profiles over the section of 1 m from the nozzle were determined using the particle image velocimetry (PIV) technique. The obtained results were correlated with the measurements of the diameters of spray droplets using the laser light scattering (LLS) technique. On the basis of this research, a dependence between the nozzle parameters and the spray cone pattern was identified in terms of dynamics and droplet diameter distribution. As a result of the research, a wide range of parameters were identified in which the fogging process was carried out in a stable and repeatable manner. There were exceptions to this rule only in the cases when there was a deficiency of the liquid necessary to generate a two-phase mixture. Full article

(This article belongs to the Special Issue Multiphase Flows)

► Show Figures

Graphical abstract

Open AccessArticle

Population Balance Application in TiO₂ Particle Deagglomeration Process Modeling

and

Energies 2021, 14(12), 3523; https://doi.org/10.3390/en14123523 - 13 Jun 2021

Cited by 4 | Viewed by 1257

Abstract

The deagglomeration of titanium-dioxide powder in water suspension performed in a stirring tank was investigated. Owing to the widespread applications of the deagglomeration process and titanium dioxide powder, new, more efficient devices and methods of predicting the process result are highly needed. A brief literature review of the application process, the device used, and process mechanism is presented herein. In the experiments, deagglomeration of the titanium dioxide suspension was performed. The change in particle size distribution in time was investigated for different impeller geometries and rotational speeds. The modification of impeller geometry allowed the improvement of the process of solid particle breakage. In the modelling part, numerical simulations of the chosen impeller geometries were performed using computational-fluid-dynamics (CFD) methods whereby the flow field, hydrodynamic stresses, and other useful parameters were calculated. Finally, based on the simulation results, the population-balance with a mechanistic model of suspension flow was developed. Model predictions of the change in particle size showed good agreement with the experimental data. Using the presented method in the process design allowed the prediction of the product size and the comparison of the efficiency of different impeller geometries. Full article

(This article belongs to the Special Issue Multiphase Flows)

► Show Figures

Figure 1

Open AccessArticle

Precise Evaluation of Gas–Liquid Two-Phase Flow Pattern in a Narrow Rectangular Channel with Stereology Method

Maciej Masiukiewicz

and

Stanisław Anweiler

Energies 2021, 14(11), 3180; https://doi.org/10.3390/en14113180 - 29 May 2021

Cited by 1 | Viewed by 1676

Abstract

The drive to increase the efficiency of processes based on two-phase flow demands the better precision and selection of boundary conditions in the process’ control. The two-phase flow pattern affects the phenomena of momentum, heat, and mass transfer. It becomes necessary to shift from its qualitative to quantitative evaluation. The description of the stationary structure has long been used in structural studies applied to metals and alloys. The description of a gas–liquid two-phase mixture is difficult because it changes in time and space. This paper presents a study of the precise determination of two-phase flow patterns based on stereological parameters analysis. The research area is shown against the flow map proposed by other researchers. The experiment was taken in the thin clear channel with dimensions of W = 50 × H = 1200 × T = 5 mm. The test method is based on the visualization of a two-phase air–water adiabatic flow pattern in the rectangular channel where superficial air velocities ranging from 0.006 to 0.044 m/s and the superficial water velocity ranged from 0.011 to 1.111 m/s. A high-speed camera was used for visualization. Images were analyzed with the use of stereological techniques. The study included the classification of structures according to generally accepted two-phase flow regime nomenclature for upwards co-current gas–liquid flow in a vertical rectangular channel. The result of the research was the determination of the stereological parameters’ changes with reference to the two-phase mixture flow hydrodynamics. The results were presented as waveform fluctuations in the values of stereological factors such as the volume fraction V_V, interfacial surface S_V, number of objects N_V, mean chord l′_m and the free distance λ. The description of how these parameters change with changes in phase fluxes is also presented. These waveforms help to distinguish the transient flow regimes, which allow for the automatic adjustment of the process stability. The authors found templates of the stereological parameters’ dependencies for flow pattern recognition. The research demonstrates wide possibilities of stereological methods’ application for the analysis of the two-phase gas–liquid process. The stereological model of two-phase pattern control enables the identification of process disorders. Full article

(This article belongs to the Special Issue Multiphase Flows)

► Show Figures

Graphical abstract

Open AccessArticle

Drag Reduction in the Flow of Aqueous Solutions of a Mixture of Cocamidopropyl Betaine and Cocamide DEA

Jacek Różański

Sylwia Różańska

Piotr Tomasz Mitkowski

Waldemar Szaferski

Patrycja Wagner

and

Adrianna Frankiewicz

Energies 2021, 14(9), 2683; https://doi.org/10.3390/en14092683 - 07 May 2021

Cited by 3 | Viewed by 1260

Abstract

The study presents results of rheological tests and measurements of pressure drops occurring during the flow of aqueous solutions of a mixture of drag reducing surfactants: cocamidopropyl betaine (CAPB, zwitterionic surfactant) and cocamide DEA (nonionic surfactant) through straight pipes. Tests were carried out at different CAPB/DEA weight ratios and different total concentrations of surfactants in the solution. Rheological measurements demonstrate the formation of a shear-induced structure (SIS) in the temperature range below 10 °C, which provides evidence for the presence of wormlike micelles in CAPB/DEA solutions. Drag reduction was observed during the flow of CAPB/DEA solutions in the temperature range from 3 to 45 °C, however, above 25 °C the degree of drag reduction was markedly decreased. The lower temperature limit at which drag reduction occurs depends on the CAPB and DEA weight ratio in the solution. In the range of higher temperatures, during the flow of CAPB/DEA solutions (similarly to flexible-chain polymer solutions) the onset of drag reduction is noted above a certain critical value of the Re_c_,0 number, whose value depends on the temperature of the solution, diameter of the pipe and the weight ratio of surfactants. At the same time, the critical value of wall shear stress τ_w,c₀ corresponding to the critical value of Re_c_,0 is approximately independent of pipe diameter. The critical value of the Re_c_,0 number has been linked to the clouding of CAPB/DEA solutions. Full article

(This article belongs to the Special Issue Multiphase Flows)

► Show Figures

Figure 1

Open AccessArticle

Void Fraction Prediction Method in Gas–Liquid Flow through Channel Packed with Open-Cell Metal Foams

Małgorzata Płaczek

and

Roman Dyga

Energies 2021, 14(9), 2645; https://doi.org/10.3390/en14092645 - 05 May 2021

Viewed by 1175

Abstract

This paper reports the results of a study concerned with air–water and air–oil two-phase flow in channels packed with open-cell metal foams. The research was conducted in horizontal channel with an internal diameter of 0.02 m and length of 2.61 m. The analysis applied three metal foams with pore density 20, 30, and 40 PPI and porosity typical for industrial applications, changing in the range of 92–94%. The experimental data were used to develop a new method for predicting void fraction in two-phase gas–liquid flow in channels packed with metal foams. A new gas void fraction calculating method based on drift-flux model was developed. This model gives a correct representation of changes in the gas void fraction value and good prediction accuracy. The average relative error in calculating the air void fraction in two-phase flow is less than 13%, and 86% of experimental points is characterized by an error less than 20%. Full article

(This article belongs to the Special Issue Multiphase Flows)

► Show Figures

Figure 1

Open AccessArticle

Impact of Process Parameters on the Diameter of Nanobubbles Generated by Electrolysis on Platinum-Coated Titanium Electrodes Using Box–Behnken Experimental Design

Karol Ulatowski

Radosław Jeżak

and

Paweł Sobieszuk

Energies 2021, 14(9), 2542; https://doi.org/10.3390/en14092542 - 28 Apr 2021

Cited by 3 | Viewed by 1153

Abstract

(1) The generation of nanobubbles by electrolysis is an interesting method of using electrical energy to form bubble nuclei, effectively creating a multiphase system. For every process, the effectiveness of nanobubble generation by electrolysis depends on various process parameters that impact should be determined. (2) In this work, the electrolytic generation of hydrogen and oxygen bubbles was performed in a self-built setup, in which a Nafion membrane separated two chambers. The generation of bubbles of both gases was investigated using Box–Behnken experimental design. Three independent variables were salt concentration, current density, and electrolysis time, while the dependent variables were Sauter diameters of generated bubbles. An ANOVA analysis and multivariate regression were carried out to propose a statistical and power model of nanobubble size as a process parameter function. (3) The generation of bubbles of hydrogen and oxygen by electrolysis showed that different factors or their combinations determine their size. The results presented in this work proved to be complementary to previous works reported in the literature. (4) The Sauter diameter of bubbles increases with salt concentration and stays constant with increasing current density in investigated range. The proposed correlations allow the Sauter diameters of nanobubbles generated during electrolysis to be predicted. Full article

(This article belongs to the Special Issue Multiphase Flows)

► Show Figures

Graphical abstract

Open AccessArticle

Two-Phase Liquid–Liquid Flow in the Aspect of Reduction of Pumping Power of Hydrophobic Substances with High Viscosity

Jerzy Hapanowicz

Energies 2021, 14(9), 2432; https://doi.org/10.3390/en14092432 - 24 Apr 2021

Cited by 2 | Viewed by 942

Abstract

The paper reports the results of a study into a method of estimating the level of power/energy reduction needed for pumping highly viscous hydrophobic liquids. The effect of reducing the flow resistance resulting from feeding an adequate volume of water into the flow tube is considered. The polar parameters of water selected for analysis are different than oil. Experimental studies were not carried out in this regard, since the commonly accessible equation expressing the resistance of two-phase liquid–liquid flow was utilized to develop the method discussed in this study. On its basis, simulations were carried out to determine the conditions and level of reduction of the two-phase flow resistance in comparison to the single-phase flow resistance of a highly viscous oily liquid. The analysis of the results provided means for determination of such ranges of variations in the flow parameters of the two-phase liquid–liquid system, in which the total power of pumps applied to pump both liquids is smaller than the power of one pump feeding oil into the pipeline in the conditions of single-phase flow. Calculations were performed for selected constant mass flux densities of oil with various viscosities as well as for water. The proposed method can be applied in the procedure of optimization calculations for pipeline installations and their feed systems. The given example of its use was preceded by a description of the reasons and effects associated with the reduction of flow resistance in liquid–liquid systems and a detailed presentation of how to use the equation that forms the essence of the described calculation method. Attention was also paid to other phenomena accompanying two-phase liquid–liquid flows, i.e., interfacial slip, phase inversion, specific flow structures, and the viscosity of the unstable mixture of two liquids flowing in the pipe. Full article

(This article belongs to the Special Issue Multiphase Flows)

► Show Figures

Graphical abstract

Open AccessArticle

Pressure Drops in Two-Phase Gas–Liquid Flow through Channels Filled with Open-Cell Metal Foams

Roman Dyga

and

Sebastian Brol

Energies 2021, 14(9), 2419; https://doi.org/10.3390/en14092419 - 23 Apr 2021

Cited by 3 | Viewed by 1314

Abstract

This paper describes experimental investigations of single-phase and two-phase gas–liquid flow through channels with a diameter of 20 mm and length of 2690 mm, filled with metal foams. Three types of aluminium foams with pore densities of 20, 30 and 40 PPI and porosities ranging from 29.9% to 94.3% were used. Air, water and oil were pumped through the foams. The tests covered laminar, transitional and turbulent flow. We demonstrated that the Reynolds number, in which the hydraulic dimension should be defined based on foam porosity and pore diameter d_e = ϕd_p/(1 − ϕ), can be used as a flow regime assessment criterion. It has been found that fluid pressure drops when flowing through metal foams significantly depends on the cell size and porosity of the foam, as well as the shape of the foam skeleton. The flow patterns had a significant influence on the pressure drop. Among other things, we observed a smaller pressure drop when plug flow changed to stratified flow. We developed a model to describe pressure drop in flow through metal foams. As per the proposed methodology, pressure drop in single-phase flow should be determined based on the friction factor, taking into account the geometrical parameters of the foams. We propose to calculate pressure drop in gas–liquid flow as the sum of pressure drops in gas and liquid pressure drop corrected by the drop amplification factor. Full article

(This article belongs to the Special Issue Multiphase Flows)

► Show Figures

Figure 1

Open AccessArticle

Application of Pseudohomogeneous and Heterogeneous Models in Assessing the Behavior of a Fluidized-Bed Catalytic Reactor

Katarzyna Bizon

Energies 2021, 14(1), 208; https://doi.org/10.3390/en14010208 - 03 Jan 2021

Viewed by 1132

Abstract

Comparative analysis of the steady-state and transient properties of a bubbling fluidized-bed catalytic reactor obtained according to different mathematical models of the emulsion zone was performed to verify the commonly used assumption regarding the pseudohomogeneous nature of this zone. Four different mathematical models of the fluidized-bed reactor dynamics were formulated, based on different thermal and diffusional conditions at the gas-solid interface and within the catalyst pellet, namely the model based on the assumption of pseudohomogeneous character for the emulsion zone, and a group of two-scale models accounting for the heterogeneous character of this zone. It was demonstrated that, while the pseudohomogeneous model of the emulsion zone predicts almost identical behavior of the reactor at steady-state as the proposed heterogeneous models, it may fail in the prediction of the reactor start-up behavior, especially when dealing with highly exothermic processes run at relatively high fluidization velocity. Full article

(This article belongs to the Special Issue Multiphase Flows)

► Show Figures

Graphical abstract

Open AccessArticle

Downward Annular Flow of Air–Oil–Water Mixture in a Vertical Pipe

and

Energies 2021, 14(1), 30; https://doi.org/10.3390/en14010030 - 23 Dec 2020

Cited by 2 | Viewed by 1301

Abstract

The paper presents the results of a study concerned with the hydrodynamics of an annular downward multiphase flow of gas and two mutually non-mixing liquids through a vertical pipe with a diameter of 12.5 mm. The air, oil and water were used as working media in this study with changes in superficial velocities in the ranges of j_g = 0.34–52.5 m/s for air, j_o = 0.000165–0.75 m/s for oil, and j_w = 0.02–2.5 m/s for water, respectively. The oil density and viscosity were varied within the ranges of ρ_o = 859–881 kg/m³ and η_o = 29–2190 mPas, respectively. The research involved the identification of multiphase flow patterns and determination of the void fraction of the individual phases. New flow patterns have been identified and described for the gravitational flow conditions of a two-phase water–oil liquid and a three-phase air–water–oil flow. New flow regime maps and equations for the calculation of air, oil and water void fractions have been developed. A good conformity between the calculated and measured values of void fraction were obtained. The map for the oil–water–air three-phase flow is valid for the following conditions: j_3P = 0.35–53.4 m/s (velocity of three-phase mixture) and oil in liquid concentration β_o* = 0.48–94% (oil in liquid concentration). In the case of a downward annular oil–water two-phase flow, this map is valid for liquid mixture velocity j_l = 0.052–2.14 m/s and β_o* = 0.48–94%. Full article

(This article belongs to the Special Issue Multiphase Flows)

► Show Figures

Figure 1

Open AccessArticle

Experimental and Numerical Analysis of Condensation Heat Transfer and Pressure Drop of Refrigerant R22 in Minichannels of a Printed Circuit Heat Exchanger

and

Energies 2020, 13(24), 6589; https://doi.org/10.3390/en13246589 - 14 Dec 2020

Cited by 5 | Viewed by 1201

Abstract

A Printed Circuit Heat Exchanger (PCHE) is a type of highly complete and efficient heat exchanger that consists of numerous mini/micro-channels and has been successfully applied to the Liquefied Natural Gas (LNG) regasification project. During the research presented in this paper, the condensation flow and heat transfer performance of the R22 in PCHE hot side minichannels are analyzed via experiments and numerical simulations, respectively. A liquid nitrogen–R22 experimental loop is established to examine the pressure difference and heat transfer coefficient of R22 in the minichannels of the PCHE hot side. The inlet pressures of the R22 range from 0.5 MPa to 0.65 MPa, the mass flux values are changed from 10.52

{kg m}^{- 2} s^{- 1}

to 109.42

{kg m}^{- 2} s^{- 1}

, and the inlet temperatures vary from 273 K to 289 K. The differences between experiments and simulations are analyzed by comparing the experimental values of the Nusselt number (Nu) and the friction pressure gradient with the numerical ones. Furthermore, the influences of pressure and mass flux on the Nu, as well as the friction pressure gradient, are analyzed in depth through condensation flow regimes to explore the underlying mechanism giving the results. Full article

(This article belongs to the Special Issue Multiphase Flows)

► Show Figures

Figure 1

Open AccessArticle

Optimization Method for the Evaluation of Convective Heat and Mass Transfer Effective Coefficients and Energy Sources in Drying Processes

Marcin Stasiak

Grzegorz Musielak

and

Dominik Mierzwa

Energies 2020, 13(24), 6577; https://doi.org/10.3390/en13246577 - 14 Dec 2020

Cited by 4 | Viewed by 933

Abstract

A new optimization method for the assessment of the coefficients existing in a model of drying kinetics is developed and presented in this article. This method consists of matching the drying kinetics resulting from the mathematical model with the drying kinetics resulting from the experiments. Both the heat and mass transfer coefficients, the critical relative humidity, and the additional ultrasound energy (heat) source are included in the optimization procedure. The Adams–Bashforth multistep method of solving nonlinear ordinary differential equations is used. The inverse problem of model parameter estimation is solved by the Rosenbrock optimization method. The methodology is illustrated by the example of the ultrasound-assisted convective drying of apple and carrot. A high level of agreement between the results obtained experimentally and numerically was found. The obtained results confirmed the great influence of ultrasound on the drying kinetics. It was found that ultrasound application improved the mass transfer by 20–80% and heat transfer by 30–90%. It was also found that the heating effect caused by the ultrasound’s absorption was very small, with a value below 1%. Full article

(This article belongs to the Special Issue Multiphase Flows)

► Show Figures

Figure 1

Open AccessArticle

Precise Determination of Liquid Layer Thickness with Downward Annular Two-Phase Gas-Very Viscous Liquid Flow

Krystian Czernek

and

Stanisław Witczak

Energies 2020, 13(24), 6529; https://doi.org/10.3390/en13246529 - 10 Dec 2020

Cited by 2 | Viewed by 1244

Abstract

The paper presents the characteristics of the original optoelectronic system for measuring the values of hydrodynamics of two-phase downward gas-very viscous liquid flow. The measurement methods and results of the research on selected values describing gas–oil two-phase flow are presented. The study was conducted in vertical pipes with diameters of 12.5, 16, 22, and 54 mm. The research was conducted with the superficial velocities of air j_g = 0–29.9 m/s and oil j_l = 0–0.254 m/s, which corresponded to the values of gas stream density g_g = (0–37.31) kg/(m²s) and of liquid g_l = (0.61–226.87) kg/(m²s), in order to determine the influence of air and oil streams on the character of liquid films. The variations in oil viscosity were applied in the range η_l = (0.055–1.517) Pas. The study results that were obtained with optical probes along with computer image analysis system revealed vast research opportunities in terms of the identification of gas–liquid two-phase downward flow structures that were generated as well as the determination of the thickness of liquid film with various level of interfacial surface area undulation. The designed and constructed proprietary measuring system is also useful for testing the liquid layer by determining the parameters of the resulting waves. It is considered that the apparatus system that is presented in the article is the most effective in examining the properties of liquid layers of oil and other liquids with low electrical conductivity and a significant degree of monochromatic light absorption. In view of noninvasive technique of measuring characteristic values of liquid films being formed, the above measuring system is believed to be very useful for industry in the diagnostics of the apparatus employing such flows. Full article

(This article belongs to the Special Issue Multiphase Flows)

► Show Figures

Figure 1

Open AccessArticle

Effect of Rheological Properties of Aqueous Solution of Na-CMC on Spray Angle for Conical Pressure-Swirl Atomizers

Krystian Czernek

Marek Ochowiak

and

Sylwia Włodarczak

Energies 2020, 13(23), 6309; https://doi.org/10.3390/en13236309 - 30 Nov 2020

Cited by 5 | Viewed by 1104

Abstract

Aerosol is a multiphase system, created as a result of the dispersion of a liquid in a gaseous medium. The atomized liquids are most often water and fuel; however, they can be any other substance. Even a small addition of a substance that changes the rheological properties (i.e., the nature of the flow) can change the properties of the resulting aerosol. The most important parameters that characterize the aerosol are the outflow rate, the droplet diameter, the spray spectrum, and the spray angle. The latter is important when selecting atomizers, especially those working in groups on the sprayer boom. The spray angle is an important parameter of the atomization process, providing a great deal of information about the quality of the spray. This study presents the results of rheological tests and the atomization of aqueous solutions with varying concentrations of sodium carboxymethylcellulose (Na-CMC). We found that the spray angle decreased with increasing Na-CMC concentration in the solution, which is attributable to an increase in shear viscosity. The design of the atomizer is also important. The largest spray angles were obtained for an atomizer with a diameter of 0.02 m and with the inlet port being placed at an angle to the atomizer axis. Based on the experimental results for various liquids and atomizer designs, a correlation equation describing the spray angle is proposed. Full article

(This article belongs to the Special Issue Multiphase Flows)

► Show Figures

Figure 1

Open AccessArticle

The Mathematical Model for the Secondary Breakup of Dropping Liquid

Oleksandr Liaposhchenko

Dobrochna Ginter-Kramarczyk

Radosław Olszewski

and

Bernard Michałek

Energies 2020, 13(22), 6078; https://doi.org/10.3390/en13226078 - 20 Nov 2020

Cited by 4 | Viewed by 1680

Abstract

Investigating characteristics for the secondary breakup of dropping liquid is a fundamental scientific and practical problem in multiphase flow. For its solving, it is necessary to consider the features of both the main hydrodynamic and secondary processes during spray granulation and vibration separation of heterogeneous systems. A significant difficulty in modeling the secondary breakup process is that in most technological processes, the breakup of droplets and bubbles occurs through the simultaneous action of several dispersion mechanisms. In this case, the existing mathematical models based on criterion equations do not allow establishing the change over time of the process’s main characteristics. Therefore, the present article aims to solve an urgent scientific and practical problem of studying the nonstationary process of the secondary breakup of liquid droplets under the condition of the vibrational impact of oscillatory elements. Methods of mathematical modeling were used to achieve this goal. This modeling allows obtaining analytical expressions to describe the breakup characteristics. As a result of modeling, the droplet size’s critical value was evaluated depending on the oscillation frequency. Additionally, the analytical expression for the critical frequency was obtained. The proposed methodology was derived for a range of droplet diameters of 1.6–2.6 mm. The critical value of the diameter for unstable droplets was also determined, and the dependence for breakup time was established. Notably, for the critical diameter in a range of 1.90–2.05 mm, the breakup time was about 0.017 s. The reliability of the proposed methodology was confirmed experimentally by the dependencies between the Ohnesorge and Reynolds numbers for different prilling process modes. Full article

(This article belongs to the Special Issue Multiphase Flows)

► Show Figures

Figure 1

Open AccessArticle

Influence of the Calcination Temperature of Synthetic Gypsum on the Particle Size Distribution and Setting Time of Modified Building Materials

and

Energies 2020, 13(21), 5759; https://doi.org/10.3390/en13215759 - 03 Nov 2020

Cited by 7 | Viewed by 2360

Abstract

The paper assesses the influence of the calcination temperature of synthetic gypsum binder on the binding properties of innovative gypsum pastes, as well as on masonry and plastering mortars. The calcination process of gypsum binder was carried out at four different temperatures ranging from 170 to 190 °C. The specimens for testing were prepared on the basis of the obtained raw material with a constant water to gypsum ratio of w/g = 0.75. It was noted that the calcination temperature influenced the setting time of the gypsum. Based on synthetic gypsum, mixtures of masonry and plastering mortars modified with tartaric acid and Plast Retard were designed. During the experiment, the particle diameter distribution of aqueous suspensions of building and synthetic gypsum particles (before and after calcination) was determined using the Fraunhofer laser method. The dimensions of the obtained artificial gypsum grains did not differ from the diameters of the gypsum grains in the reference sample. On the basis of the conducted research, it was found that the waste synthetic gypsum obtained in the flue gas desulphurization process met the standard conditions related to its setting time. Therefore, it may be a very good construction substitute for natural gypsum, and consequently, it may contribute to environmental protection and the saving and respecting of energy. Full article

(This article belongs to the Special Issue Multiphase Flows)

► Show Figures

Figure 1

Journal Menu

Journal Browser

Special Issue "Multiphase Flows"

Share This Special Issue

Special Issue Editors

Special Issue Information

Keywords

Published Papers (18 papers)

Research

Further Information

Guidelines

MDPI Initiatives

Follow MDPI