## What is/are Void Fraction?

Void Fraction - Due to the complexity of the shape, the studies on the void fraction of the cylindrical particles are not as thorough as the spherical particles.^{[1]}Taking into account new problems arising in the transportation of a steam-water heat carrier to support operation of geothermal power plants (GeoPP), a procedure is outlined for determining the void fraction considering the gravity component of the pressure drop in the hydraulic design calculations of steam-water piping.

^{[2]}correlations for the drift-flux parameters of the distribution parameter and the drift velocity to predict the void fractions in the 5 flow regimes, together the newly-developed transition criteria, in the vertical rod bundle flow channels.

^{[3]}The impact of important model parameters, such as the void fraction and the friction coefficient between strands, on the mechanical behavior of the conductor is investigated.

^{[4]}25 mm for the iron electrode with optimal electrode porosities in the range of void fraction of 0.

^{[5]}The findings are used to explain the observed heat transfer enhancement that occurred concurrently with the reduction in the void fraction.

^{[6]}The effect of electrical charge used for plating Sn–Cu solder, void fraction in the joint, Sn–Cu solder composition on the joining characteristics, and shear strength of the Si-DBC system were analyzed.

^{[7]}A heated horizontal pipe with stainless steel, Aluminum, and Zircalloy surface materials are used to numerically predict the field temperature and void fraction.

^{[8]}A new algorithm based on an implicit fractional step method is used to solve the time-dependent mass, momentum and transport equation for the void fraction.

^{[9]}The axial and radial spatial-temporal distribution of void fraction and time series of differential pressure fluctuation was presented.

^{[10]}A parametric study was instigated to account for the influence of void fraction and particle size on predicted broadband sound absorption properties targeting permeability values in the range of 0.

^{[11]}The flow influencing parameters such as pressure drop, turbulence intensity, design of packed beds, the surface area of packed beds, the void fraction of the system discussed.

^{[12]}The void fractions of reactors C and D were decreased by adding extra gravel.

^{[13]}43%; when foaming was carried out at a temperature of 150 °C in boiled glycerin, the foaming ratio, cell size, cell density, and void fraction were found to be 43.

^{[14]}A negative feedback connection between void fraction and mass flow rate is the reason for the oscillation in its initial process.

^{[15]}Numerical and empirical commentary of cocurrent gas–non-Newtonian flows and non-Newtonian bubbly flow reactors has been expressed in view of their flow regimes, transition boundaries of flow regimes, void fraction, and pressure drop modeling because of importance of such details related to the industries within broad spectrum of chemical engineering and technology.

^{[16]}The void fraction result shows liquid mainly flows in the half of the header without microchannel tube intrusions.

^{[17]}A study was conducted to investigate the void fraction and pressure drop characteristics of methane/propane under different mass flux, saturation pressure and heat flux in a helically coiled tube, and the effects of distribution ratio (methane/propane) 50/50, 66/34 and 80/20 mole% were also analyzed.

^{[18]}Void fraction distributions in helical coils of various diameters are computationally estimated with inlet mass flux, degree of subcooling and wall superheat as inputs.

^{[19]}The results show that after the fluid flows through the orifice plate, the void fraction and liquid velocity increase.

^{[20]}A comparison of the CFD simulation results with the high-resolution experimental data from a helical coil experimental setup operated with a mixture of water and air is discussed, with special emphasis on two-phase pressure drops and void fraction distributions (Che et al.

^{[21]}A significant issue for them is the void fraction function induced by superficial velocity, fluid viscosity, and slope.

^{[22]}Besides, considering the gap-graded feature of basal, the traditional coarse-grain method that accounts for porosity based on particle centres may result in inaccuracy in void fraction determination.

^{[23]}The test results affirmed that the MHD convection approach evacuated the gas bubbles more rapidly and improved the void fraction in the gas bubble scattering layer.

^{[24]}In this article, the void fraction along the length of coolant channel in a reactor and mechanical performance of Zr cladding enwrapping UO2 fuel are investigated by establishing a fully coupled multiphysics model based on the CAMPUS code.

^{[25]}Void fraction of cylindrical particles greatly influences heat and mass transfer and resistance characteristics involved in the processes.

^{[26]}We consider two distinguished limits and, for one of them, 13 obtain an explicit solution for the sulphur dioxide concentration and the void fraction in the filter.

^{[27]}The normalized flow rate, pressure, and void fractions were predicted to describe the overall behavior of the pipe break phenomena.

^{[28]}The void fraction, flexural modulus and strength of different regions of 3D CFRP parts fabricated by P–HF–P and autoclave processes were evaluated.

^{[29]}And the phenomena were explained from mechanism and the change of void fraction.

^{[30]}% to analyze the physical (experimental and theoretical densities, void fraction and hardness), mechanical (tensile strength, tensile modulus, flexural strength, flexural modulus, impact strength), thermo-mechanical (dynamic mechanical analysis, DMA), and three-body abrasive wear rate, respectively.

^{[31]}The void fraction of the foams ranged from 50 to 92%, and they demonstrated a high degree of closed cell content (>98%).

^{[32]}The position of flashing front and the distribution of void fraction in the riser are never fixed.

^{[33]}Simultaneous pressure and void fraction measurements reveal that extreme events are associated with a change from a shear layer mode to a wake mode, with a temporal signature that is heavily affected by the presence of the vapor phase.

^{[34]}This study is devoted to quantify the void fraction which is an important parameter for the driving force of natural circulation flow, and to evaluate the effect of the void fraction correlation on the prediction accuracy of the natural circulation flow rate.

^{[35]}The mercury intrusion porosimetry test indicates that 3D printing provides a favorable squeezing effect to decrease concrete porosity, reducing the void fraction from 17.

^{[36]}Multilayered membrane filters, which consist of a stack of thin porous membranes with different properties (such as pore size and void fraction), are widely used in industrial applications to remove contaminants and undesired impurities (particles) from a solvent.

^{[37]}However, the phase distribution of wet gas with a high gas volume fraction (GVF) in a horizontal pipe is non-homogeneous and causes uncertainty in the measurement of void fraction using the single-beam gamma-ray method.

^{[38]}The temperature distribution, void fraction and pressure drop for two-phase subcooled boiling water flow were obtained.

^{[39]}Keywords : pipe, heavy fluid, numerical modelling, circumferential admittance approach, cylindrical shell, resonance frequency, void fraction.

^{[40]}Larger superficial gas velocity and hard-sphere model respectively cause more vigorous inter-phase momentum exchange and more frequent collision events, indicating the more intense bubble evolution and the resulting fluctuations of void fraction.

^{[41]}The void fraction increases at first and tends to a stable value finally.

^{[42]}The criteria of the initiation of drastic intergroup transfer in small diameter tubes in terms of the bubble relative diameter and the void fraction are developed.

^{[43]}On the other hand, more charge transfer and void fraction are presented, opening band gaps and leading to different electronic and optical properties.

^{[44]}Therefore, the void fraction distribution behind the obstacle that simulates the grid spacer shape simply was measured by using a wire mesh sensor (WMS) system.

^{[45]}The calculated results demonstrated that even in the case of cohesive particles, an increase in the particle size ratio reduced the void fraction of the powder bed during the packing and compression processes.

^{[46]}In many industrial applications prediction on two phase parameters such as void fraction, bubble shape, phase velocities are important.

^{[47]}The behavior of bubble coalescence in subcooled boiling has a significant influence on the void fraction and heat transfer capacity.

^{[48]}9; the frictional pressure drop always decreases with the increasing saturated pressure when the void fraction is higher than 0.

^{[49]}We find that the Reynolds number ( R e ) and the void fraction ( α ) essentially determine the onset of self-sustained oscillations in the two-fluid/pipe system.

^{[50]}

## two phase flow

Capacitance sensor is a non-intrusive devices used for the void fraction measurement in two-phase flows.^{[1]}In this study, the past experimental studies performed in the gas-liquid metal two-phase flow are reviewed, and the void fraction and interfacial area concentration (IAC) database taken in the N2-Pb/Bi (nitrogen and lead/bismuth eutectic alloy) two-phase flow in a vertical circular flow channel are collected.

^{[2]}In this article, we develop a novel deep learning based soft measure technique to predict the gas void fraction, which is one key parameter in a gas–liquid two-phase flow.

^{[3]}Measurement of oil-gas two-phase flow parameters such as Gas Void Fraction (GVF) and phase distribution plays a vital role in oil and gas industries.

^{[4]}Since the responses of the electromagnetic flowmeter (EMF) can be affected by the flow characteristics, the combination of the EMF and the void fraction meter is always necessary for the two-phase flow measurement.

^{[5]}The improved model was validated systematically by the adiabatic two-phase flow data for different interface morphologies and the boiling flow data with different void fraction.

^{[6]}The study of geyser-boiling phenomena, which occurs inside the thermosyphon is of extreme importance, therefore the experimental analysis of the parameters related to the two-phase flow (liquid-steam), such as void fraction, bubble frequency, bubble velocity, and bubble length are necessary, since these parameters have a significant influence on heat transfer.

^{[7]}Both two-phase flow patterns and the void fraction measurements were used to evaluate the dissolved oxygen mass transfer mechanism through the airlift pump.

^{[8]}Predicting the void fraction of a two-phase flow outside of tubes is essential to evaluate the thermohydraulic behaviour in steam generators.

^{[9]}The air-water two-phase flow was more mal-distributed as the void fraction increased.

^{[10]}Based on available knowledge on the two-phase flow regime transition from bubbly to slug flows, it was postulated that bubble coalescence is intensified substantially when the local void fraction near the heated wall exceeds a critical value.

^{[11]}The paper presents a method for the measurement of void fraction in two-phase flow of liquid and gas phases in small channels by means of capacitance sensor.

^{[12]}Although sectional void fraction of the two-phase flow can be detected in several ways, the quality of the two-phase flow is hardly obtained from the sectional void fraction since velocities of liquid- and gas-phase in the pipe are different from each other.

^{[13]}In this context, this article presents an electrical impedance tomography (EIT)-based eigenvalue correlation method that allows extracting two-phase flow features, namely, the void fraction and the flow regime, which are used in turn to improve flow visualizations.

^{[14]}The goal of this study is to propose a dual-energy gamma attenuation method with radial basis function neural network (RBFNN) to determine scale thickness in petroleum pipelines in which two-phase flows with different symmetrical flow regimes and void fractions exist.

^{[15]}It is observed that 1) the pipe wall effect can alter the non-uniform radial two-phase distribution; 2) the bubbly-to-slug flow regime transition in a small diameter pipe happens in a smaller void fraction than in a large diameter pipe; 3) the bubble coalescence phenomenon can be more dominant for small pipe flow, and an intensive intergroup transfer can happen for the two-group interfacial area transport in two-phase flows.

^{[16]}Currently, there are no universal methods for calculating the heat transfer and pressure drop for a wide range of two-phase flow parameters in mini-channels due to changes in the void fraction and flow regime.

^{[17]}Also, tomographic images and probability density functions were used to capture the cross- section void fraction and its distribution for the two-phase flow patterns.

^{[18]}Precise measurement of total rate and void fraction, key parameters in two-phase flows, can significantly improve the industrial efficiency, which is still a challenging issue due to their complex characteristics.

^{[19]}A high-speed video camera equipped with synchronous movement system was applied to combine the recording of two-phase flow images with simultaneous local void fraction measurements both based on the same photographic data set.

^{[20]}In the current article, a novel system consists of an X-ray tube and one sodium iodide crystal detector with ability of determining type of flow regime as well as void fraction percentage of a two phase flow, is proposed.

^{[21]}In the present paper, high-resolution measurements of the void fraction distribution for an adiabatic upward air–water two-phase flow were conducted in a transparent helically coiled acrylic pipe by means of high-speed X-ray radiography at ambient conditions.

^{[22]}The void fraction is a key parameter of the two-phase flow in vertical downward pipes, particularly for calculating the mixture density, mixture velocity, mixture viscosity, heat transfer coefficient, and pressure gradient of the flow.

^{[23]}In two-phase flow, bubbles are entrained by the secondary flow to form double-peaked void fraction and interfacial area concentration distributions.

^{[24]}Since the void fraction is one of the most critical design parameters for the RBWR, this study developed the drift-flux correlation applicable to two-phase flow in the tight-lattice rod bundle.

^{[25]}Meanwhile, a combined method of impeller Euler head distribution and entropy generation rate analysis are applied for the head degradation of ACP100 reactor coolant pump under gas–liquid two-phase flow condition, and 70% of gas void fraction (GVF) is shown as the maximum degradation point.

^{[26]}Diode based liquid level sensors have been developed to measure the void fraction of the two-phase flow.

^{[27]}

## interfacial area concentration

In the current nuclear reactor system analysis codes, the interfacial area concentration and void fraction are mainly obtained through empirical relations based on different flow regime maps.^{[1]}Three kinds of the state-of-the art measurement techniques were applied to quantify key parameters such as radial and vertical distributions of void fraction, bubble velocity, interfacial area concentration (IAC), Sauter mean diameters, high-resolution temperature distribution on rod surface, bubble transport behavior, and turbulent velocity components as well as onset of nucleate boiling (ONB), and onset of significant void (OSV).

^{[2]}The benchmark shows that the most suitable semi-empirical or empirical correlations chosen to predict the interfacial area concentration are different in the low void fraction region and high void fraction region.

^{[3]}Five measurement ports in this unheated section provide measurement of pressure and local measurements of void fraction, interfacial area concentration, gas velocity, Sauter mean diameter, and liquid temperature.

^{[4]}

## heat transfer coefficient

The fluid thermodynamic state along the heat exchangers is evaluated based on the energy and momentum balance considering predictive methods available in the open literature for heat transfer coefficient, pressure drop and void fraction.^{[1]}Inaccurate battery material properties are shown to play only a small part in the predicted thermal runaway behavior while initial temperature of simulation, applied heat transfer coefficient and electrode void fraction have a large effect on the thermal runaway response.

^{[2]}The void fraction in headers of microchannel heat exchangers (MCHEs) affects the refrigerant charge, distribution, pressure drop, and heat transfer coefficient of MCHEs.

^{[3]}A summary of observed experimental behaviors observed in literature for heat transfer coefficient, pressure drop, flow pattern and void fraction is presented.

^{[4]}

## gas liquid two

The interphase forces of gas-liquid two-phase flow produce flow noise, which contains abundant two-phase flow information, such as two-phase flow rate, flow pattern, void fraction, etc.^{[1]}As one of the important characteristic parameters of gas-liquid two-phase flow, liquid film thickness is closely related to pressure drop, void fraction and velocity.

^{[2]}Based on a simulation of a gas-liquid two-phase flow field, the effects of grinding head rotational speed and superimposed linear and circular translational movements on the flow velocity and void fraction were investigated.

^{[3]}

## two fluid model

Since flashing scenarios often accompanying with high void fraction and broad bubble size range, a poly-disperse two-fluid model is recommended.^{[1]}Void fraction prediction of the one-dimensional two-fluid model has been evaluated utilizing a computational tool developed in MATLAB.

^{[2]}Current predictive tools are based on the mechanistic two-fluid model, which requires the use of closure relations to predict integral flow parameters such as liquid holdup (or void fraction) and pressure gradient.

^{[3]}

## interfacial friction factor

The influence of estimates obtained from nine interfacial friction factor models on the accuracy of predicting pressure gradient, film thickness and gas void fraction was investigated by utilising a two-fluid model.^{[1]}The influence of estimation of interfacial friction factor on accurate determination of film thickness, void fraction and pressure gradient was investigated using a two-fluid model.

^{[2]}The trend of the interfacial friction factor indicates that the transition from the smooth to wavy IAFB regions occurs at a void fraction range of 0.

^{[3]}

## interfacial momentum transfer

Precise modeling of the area-averaged interfacial drag force in the interfacial momentum transfer term is essential in predicting void fraction accurately.^{[1]}The main focus of the paper is interfacial momentum transfer, which essentially governs the void fraction distribution in the flow, and turbulence modelling closures.

^{[2]}Important effects to model also include void fraction dispersion and turbulent diffusion; then, it is necessary to model the relative velocity, including the drift velocity orthogonal to gravity induced by the complex interactions between turbulent velocity fluctuations and the interfacial momentum transfer.

^{[3]}

## gas flow rate

The catalyst textural properties (particle size and void fraction) and reaction conditions (gas flow rate and radiative power input) were investigated in the CeO2 reduction reaction.^{[1]}Such flow depends on the gas flow rate, bubble size (mean bubble diameter), void fraction, bubble velocity, the distance between bubble generator and free surface (i.

^{[2]}In this experiment, the distribution of oil flow rate is 1- $10~ m^{3}/h $ , the distribution of gas flow rate is 20- $150~ m^{3}/h $ , and the distribution of GVF (gas void fraction) is 0.

^{[3]}

## Ga Void Fraction

In the second part, the above-mentioned results were compared with those obtained from gas-liquid mixtures under various gas void fraction conditions.^{[1]}In this article, we develop a novel deep learning based soft measure technique to predict the gas void fraction, which is one key parameter in a gas–liquid two-phase flow.

^{[2]}Bubble size, number of bubbles, gas void fraction, and IAC were calculated using an Open-CV Python algorithm.

^{[3]}Measurement of oil-gas two-phase flow parameters such as Gas Void Fraction (GVF) and phase distribution plays a vital role in oil and gas industries.

^{[4]}The influence of estimates obtained from nine interfacial friction factor models on the accuracy of predicting pressure gradient, film thickness and gas void fraction was investigated by utilising a two-fluid model.

^{[5]}For enhanced natural circulation of alkali and heavy liquids metals of Na, Pb and LBE, the determined average gas void fraction in the bubbly flow regime is.

^{[6]}, gas void fraction or liquid hold-up.

^{[7]}The suggested system may constitute a breakthrough in the field of multiphase flow metering since it allows simultaneous visualization of the flow, in addition to accurately determine the flow rate of individual phases even in challenging situations such as the case for high gas void fraction (GVF) multiphase flow (i.

^{[8]}Simulation results showed that the electrolyte flowed into and out IEG periodically, gas bubbles were easy to squeeze out and the gas void fraction deceased about 16% to 54%, the maximum current density increased by 1.

^{[9]}The characteristics of phase interaction and gas holdup were analyzed at different inlet gas void fractions (IGVFs), and inlet bubble diameters.

^{[10]}Combined with an example of drilling, the gas void fraction distribution, migration and bottom-hole pressure change law is given, which provides theoretical basis for low permeability gas reservoirs in underbalanced pressure drilling borehole designing.

^{[11]}In this experiment, the distribution of oil flow rate is 1- $10~ m^{3}/h $ , the distribution of gas flow rate is 20- $150~ m^{3}/h $ , and the distribution of GVF (gas void fraction) is 0.

^{[12]}The inlet gas void fraction (IGVF) has a great effect on the power performance of the multiphase pump, and the effect is even greater under the cavitation condition.

^{[13]}Meanwhile, a combined method of impeller Euler head distribution and entropy generation rate analysis are applied for the head degradation of ACP100 reactor coolant pump under gas–liquid two-phase flow condition, and 70% of gas void fraction (GVF) is shown as the maximum degradation point.

^{[14]}

## Local Void Fraction

This paper presents test facility design, probe fabrication, calibration details and test procedures along with preliminary attempts to estimate local void fractions.^{[1]}Also, two major discrepancies are found in the local void fraction profile prediction as well as the wall temperature profile prediction: 1.

^{[2]}Synchronized flow visualization images, along with local void fraction and vibration measurements, were used to evaluate the response of the structure as the slug flow passed through the orifices.

^{[3]}Based on available knowledge on the two-phase flow regime transition from bubbly to slug flows, it was postulated that bubble coalescence is intensified substantially when the local void fraction near the heated wall exceeds a critical value.

^{[4]}Radial distributions of local void fraction, gas velocity and liquid velocity have been used for comparison of different models in different cases.

^{[5]}Determination of the local void fraction in BWRs from in-core neutron noise measurements requires the knowledge of the axial velocity of the void.

^{[6]}More importantly, extensive data on local void fraction in liquid slugs (αl,LS) and in continuous slug units (αl), gas-phase velocity of Taylor bubble (UTB) and liquid slug (ULS), length of Taylor bubble (LTB) and liquid slug (LLS), were obtained.

^{[7]}The experimental data of the jet thickness related to a local void fraction of 50% seemed to be similar to the jet thickness due only to gravitational effects until the break-up length was reached.

^{[8]}A high-speed video camera equipped with synchronous movement system was applied to combine the recording of two-phase flow images with simultaneous local void fraction measurements both based on the same photographic data set.

^{[9]}LIDAR-derived free-surface elevations were compared with typical point-source measurements using air–water conductivity probes, showing that the elevations measured with LIDAR consistently corresponded to locations of strongest air–water flow interactions at local void fractions of approximately 50%.

^{[10]}In the present work, we have developed a new technique that makes it possible to measure the local void fraction, size of characteristic regions of the liquid films on the upper and lower walls of microchannel, frequency of bubble formation, and other quantitative characteristics.

^{[11]}The X-ray radiography offers an effective method for determining the local void fraction and allows for an estimation of the bubble volume.

^{[12]}

## Averaged Void Fraction

In this study, we investigated a behavior of time-averaged void fraction in five flat microchannels with cross sectional area of 0.^{[1]}The time-averaged void fraction shows a gap region peak in bubbly flow.

^{[2]}In the bubble plume problem, we compared the bubble plume behavior and the time-averaged void fraction of the simulation results with those of previously reported experiments, and found good agreement between them.

^{[3]}The experimental results presented and analyzed in this study are the local time-averaged void fraction and bubble velocities at three axial positions L/D = 14.

^{[4]}The simulated surface averaged void fraction agree well with the experimental data, which indicate the promising application of the present method for modeling the boiling flow in the fuel rod bundle.

^{[5]}High-order integration in time is performed using strong stability-preserving Runge-Kutta schemes and we propose conditions on the numerical parameters for the positivity of the cell-averaged void fraction and partial densities.

^{[6]}As a result, the nose position, local time-averaged axial velocity, and area-averaged time-averaged void fraction for plug bubbles can be obtained with this newly developed image analysis technique.

^{[7]}

## High Void Fraction

Since flashing scenarios often accompanying with high void fraction and broad bubble size range, a poly-disperse two-fluid model is recommended.^{[1]}Downhole gas separators are usually installed upstream of the pump in oil production wells to avoid free gas, but they cannot handle high void fraction.

^{[2]}Structured packings are widely used in oil & gas industries, as they can provide substantial surface area and high void fraction, thus enabling high mass transfer efficiency at a low pressure drop.

^{[3]}This makes possible the application of the procedure to high void fraction bubbly flows.

^{[4]}With high void fraction of 42.

^{[5]}In zones with a high void fraction under the SPS and above the SPS, mist flow occurs as a result of steam escaping from the interface with water droplets being captured and carried up.

^{[6]}

## Sectional Void Fraction

These measurements have enabled accurate calculation of the cross-sectional void fraction, vapor quality, interfacial shear stress and superficial velocities, which form the coordinates of the existing flow regime maps.^{[1]}ABSTRACT This paper presents new capacitive sensors built and calibrated to measure cross-sectional void fraction between tubes in vertical headers of microchannel heat exchangers (MCHEs).

^{[2]}The study used this method to determine the cross-sectional void fraction of two-phase water flow through a Polyvinyl chloride (PVC) pipechannel.

^{[3]}Although sectional void fraction of the two-phase flow can be detected in several ways, the quality of the two-phase flow is hardly obtained from the sectional void fraction since velocities of liquid- and gas-phase in the pipe are different from each other.

^{[4]}

## Bubble Void Fraction

The increase of bubble void fraction caused by continuous wave exposure were found to be consistent with the experimental observation.^{[1]}Crank Nicolson implicit scheme is used for discretizing the scalar convection equation for bubble void fraction and transforming into algebraic equation.

^{[2]}Ceccio (Annu Rev Fluid Mech 42:183–203, 2010) and Murai (Exp Fluids 55(7):1–28, 2014) have compiled drag reduction data from a number of different studies and facilities, and highlighted the large differences and scatter in the data even at the same bubble void fraction.

^{[3]}

## Different Void Fraction

The improved model was validated systematically by the adiabatic two-phase flow data for different interface morphologies and the boiling flow data with different void fraction.^{[1]}0 m/s and 8 different void fractions ranging from 0.

^{[2]}The numerical results indicated that, when the flow pitch velocity is larger than the critical velocity, the tube array system is undergoing a limit cycle motion, and the dynamic characteristics of the tube array are almost similar for different void fractions.

^{[3]}

## Low Void Fraction

At relatively low void fractions (up to ~20%), the growth of bubbles with size comparable to the MWCNT length increased the conductivity.^{[1]}The benchmark shows that the most suitable semi-empirical or empirical correlations chosen to predict the interfacial area concentration are different in the low void fraction region and high void fraction region.

^{[2]}An experimental study was conducted on the flow characteristics and turbulence suppression in vertically issued bubbly jets with low void fraction (less than 1%, Re = 3,172).

^{[3]}

## Predicting Void Fraction

Precise modeling of the area-averaged interfacial drag force in the interfacial momentum transfer term is essential in predicting void fraction accurately.^{[1]}The interfacial drag force governs the momentum exchange between gas and liquid phases and is a key parameter in predicting void fraction using a one-dimensional thermal-analysis code.

^{[2]}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.

^{[3]}

## Smaller Void Fraction

Also, most of the results showed smaller void fraction than the experimental data near the heated wall as well as the bulk region.^{[1]}It is observed that 1) the pipe wall effect can alter the non-uniform radial two-phase distribution; 2) the bubbly-to-slug flow regime transition in a small diameter pipe happens in a smaller void fraction than in a large diameter pipe; 3) the bubble coalescence phenomenon can be more dominant for small pipe flow, and an intensive intergroup transfer can happen for the two-group interfacial area transport in two-phase flows.

^{[2]}However, the flow instabilities that improve mass transfer are weakened in channels with smaller void fraction, leading to smaller flux enhancement.

^{[3]}

## Average Void Fraction

The experimental two-phase data classifies the flow patterns using the probability density function (PDF) and shows the important flow variables such as average void fraction, pressure gradient, slug body void fraction, liquid slug, Taylor bubble and slug unit lengths, structural velocity and frequency obtained by electrical capacitance tomography (ECT) and a wire mesh sensor (WMS).^{[1]}A simple flow visualisation technique was applied to retrieve the two-dimensional side-looking profile of the roller edge and average void fraction.

^{[2]}

## Wall Void Fraction

Compared to other components, mixing vanes exhibited a stronger and more lasting influence on the generation of lateral disturbance, which resulted in a substantial decrease in the values of wall superheat and near-wall void fraction.^{[1]}Critical near-wall void fraction was used as the criterion of dryout.

^{[2]}

## Water Void Fraction

By varying the oil-in-water void fraction, catastrophic phase inversion between oil-in-water and water-in-oil emulsions can be triggered, changing the morphology, including droplet sizes, and rheological properties of the mixture, dramatically.^{[1]}Results on overall pump head and efficiency performance, pressure pulsation and high speed camera visualization of flow patterns behavior are presented for different inlet air-water void fractions at a given rotational speed.

^{[2]}

## Substantial Void Fraction

removed perovskite films with dimethyl sulfoxide solvent from the hole-transfer layer and observed a substantial void fraction that degraded film performance.^{[1]}org P H O T O : B L IC K W IN K E L /A L A M Y S T O C K P H O T O sulfoxide solvent from the holetransfer layer and observed a substantial void fraction that degraded film performance.

^{[2]}

## Larger Void Fraction

Hydraulic jumps with fully developed inflow conditions had comparatively larger void fractions in the first half of the jump roller and larger bubble count rates throughout, while a comparatively larger number of smaller bubble sizes suggested a stronger break-up of bubbles.^{[1]}Numerical and theoretical analysis results show that the improvement of temperature uniformity and better heat transfer performances are highly related, which can be improved with larger void fraction and smaller fluid channel diameter.

^{[2]}

## Air Void Fraction

Therefore, with the aim of exploring the internal flow features and noise characteristics of drainage pumps during empty discharge period, the energy performance test was processed under pure water condition as well as under different air void fraction and part load conditions.^{[1]}A linear relationship was achieved between the cubic root of air void fraction (porosity) and the simulated compressive strength.

^{[2]}