Fraction Of Bubbles Research Articles

Numerical Measurement of the Effective Electrical Conductivity of Electrolyte-Gas Bubble Dispersions

Bubble formation during water electrolysis is inevitable. Apart from mass and heat transfer limitations, the presence of these bubbles causes a decrease in the local electrical conductivity of the electrolyte, thereby contributing further to the ohmic resistance of the system. Experimental and theoretical studies have shown that the effective electrical conductivity of an electrolyte-gas bubble dispersion depends on the volume fraction of gas bubbles. However, these studies do not provide insight into the dependence of conductivity on the geometric and spatial parameters of the dispersion, such as the size distribution of the bubbles or their spatial arrangement.Experimentally, the conductivity of such dispersions can be measured using the four-electrode conductivity measurement technique. In this talk, I will present a numerical rendition of this experimental technique to measure the conductivity of an electrolyte dispersed with gas bubbles, using the lattice Boltzmann method. The computational nature of the method lends itself well to investigating systems with different bubble size distributions and spatial configurations. The model also offers the flexibility to specify the surface charge density of the dispersed bubbles. The visualization of the ionic flux around these dispersed bubbles provides insights into the motion of ions along the paths of least resistance, and therefore a better understanding of the behavior of such systems.The effective conductivity of bubble dispersions with varying degrees of randomness in their spatial arrangement has been measured, ranging from a regularly packed array of bubbles to a completely random packing. We observed that the numerically measured conductivity deviates from that predicted theoretically at high bubble volume fractions. Moreover, for the same bubble volume fraction, different spatial arrangements yield different values of conductivity, thus highlighting the influence of spatial arrangement of the bubbles on the effective conductivity of the dispersion. Additionally, the spread (standard deviation) of the numerically measured conductivity about the mean value for a given bubble volume fraction is observed to be larger at moderate volume fractions, in comparison to very dilute and densely packed dispersions. This can be explained by the fact that at moderate bubble volume fractions, there is a larger probability for the formation of random bubble clusters that hinder the movement of ions. Such clusters are unlikely in dilute cases and are universal in the dense limit, and as a consequence, less variation in the resulting effective conductivity is observed for the two limiting cases. This furthermore indicates the importance of spatial arrangement on the effective conductivity of such dispersions.

Heat transfer coefficients for bubbly molten salt nuclear reactors

Modeling the heat transfer process in a molten salt nuclear reactor is challenging due to the non-uniform distribution of fuel material and cooling fluid. Developing theoretical tools to calculate effective parameters and temperature distribution is essential for ensuring the safety of reactor design. In this study, we utilized the theory of volume averaging to upscale the local model for heat transport in a fluid fuel reactor, known as the Molten Salt Fast Reactor (MSFR). This upscaled model, which is valid for the bulk of the reactor core, combines the heat transport physics that occurs at the microscale through mathematically derived effective coefficients. These coefficients can be obtained by solving related boundary-value problems. The standalone core of the MSFR with inert gas bubbles was studied and the local thermal equilibrium (non-equilibrium) condition between the fluid and bubbles was found to be achievable for small (large) bubbles volume fractions. We present the numerically calculated values of the effective coefficients in terms of the volume fraction of bubbles under operating conditions and provide correlations to facilitate their use in computational codes.

Characterizing bubble behavior in a pseudo‐2D fluidized bed of wet particles

AbstractBy applying digital image analysis on the bubble characteristics in a two dimensional wet‐particle fluidized‐bed, we report two‐stage evolution of bubble characteristics with increasing liquid content. In the first stage, bubble number and uniformity of bubble fraction increase, while bubble average diameter and aspect ratio decrease. In the second stage, these characteristics shift toward an opposite direction. This two‐stage evolution of bubble characteristics are analogous to that of reducing particle size in dry‐particle fluidization, and the fluidizing properties of particles shifts from Geldart Group B to Group A and then to Group C. Furthermore, liquid addition causes a continuous decrease of bubble fraction and bubble flow rate. This is different from dry‐particle fluidization, in which reducing particle size causes an increase trend. An explanation for this difference is that liquid addition increases the equivalent size of agglomerates in wet‐particle fluidization, which is opposite to the effect of reducing particle size.

Effects of pressure and particle size on bubble behaviors in a pseudo 2D pressured fluidized bed with Geldart A/B, B and D particles

Bubble behaviors of three types of particles from Geldart A/B, B and D groups were comprehensively investigated in a pseudo 2D pressurized fluidized bed via digital image analysis. Based on the analysis of a large quantity of experimental data, the effects of pressure and particle size on the spatial distribution of bubbles, bubble diameter, rise velocity, bubble fraction and flow regimes were obtained. Results show that bubbles are smaller and uniformly dispersed throughout the bed of Geldart A/B particles, while they become densely populated and grow into much larger sizes in the bed of Geldart B particles. A single peak of large bubbles in the center and emptying of bubble near the walls is formed in the bed of Geldart D particles due to the preferable rising path of bubbles towards the center and the significant coalescence of bubbles. Bubble diameter decreases with increasing pressure, and the effect of pressure is more pronounced on Geldart D particles. Bubble rise velocity increases with the increasing particle size and decreases as pressure rises. Large bubbles/slugs hardly appear in the bed of Geldart A/B particles, while they are clearly visible in the bed of Geldart B and D particles. The flow regime transition from slugging to fast fluidization shifts to the lower gas velocity for Geldart D particles compared with Geldart B particles.

A hybrid drag model for studying hydrodynamics in a 2D gas-solid tapered fluidized bed

The present work proposes a hybrid drag model by combining homogeneous Ergun correlation and heterogeneous bubble-based drag formulation. The predictions of bubble size, bubble fraction, bed expansion ratio, particulate fluidized area fraction, and solid volume fraction in a 2D gas-solid tapered fluidized bed using the hybrid, Gidaspow, and Energy Minimization Multi-Scale (EMMS) drag models have been compared with the experimental results. The hybrid drag model predicts these parameters closer to the experimental findings. A heterogeneous flow structure has been observed in simulations similar to experiments for the tapered fluidized bed. The bed shows larger solid volume fraction values near its periphery compared to its center. The solid particles show a central-upward and peripheral-downward flow pattern in the tapered fluidized bed.

Feasibility of melt segregation from a crystal mush in response to the 2011–2012 eruption at Cordón Caulle, Chile

SUMMARY The 2011–2012 eruption at Cordón Caulle in Chile produced crystal-poor rhyolitic magma with crystal-rich mafic enclaves whose interstitial glass is of identical composition to the host rhyolite. Eruptible rhyolites are thought to be genetically associated with crystal-rich magma mushes, and the enclaves within the Cordón Caulle rhyolite support the existence of a magma mush from which the erupted magma was derived. Moreover, towards the end of the 2011–2012 eruption, subsidence gave way to inflation that has on average been continuous through at least 2020. We hypothesize that magma segregation from a crystal mush could be the source of the observed inflation. Conceptually, magma withdrawal from a crystal-poor rhyolite reservoir caused its depressurization, which could have led to upward flow of interstitial melt within an underlying crystal mush, causing a new batch of magma to segregate and partially recharge the crystal-poor rhyolite body. Because the compressibility of the crystalline matrix of the mush is expected to be lower than that of the interstitial melt, which likely contains some fraction of volatile bubbles, this redistribution of melt would result in a net increase in volume of the system and in the observed inflation. We use numerical modelling of subsurface magma flow and storage to show under which conditions such a scenario is supported by geodetic and petrologic observations.

Impact of Salinity and Temperature on Removal of PFAS Species from Water by Aeration in the Absence of Additional Surfactants: A Novel Application of Green Chemistry Using Adsorptive Bubble Fractionation

Impact of Salinity and Temperature on Removal of PFAS Species from Water by Aeration in the Absence of Additional Surfactants: A Novel Application of Green Chemistry Using Adsorptive Bubble Fractionation

Bubble Loading in a Fluidized Column: Effects of Bubble Size, Particle Size, Contact Angle and Particle Density

ABSTRACT The size of bubbles and particle properties (including particle size, density and contact angle) play an important role on the degree of particle loading on bubbles and this has been studied extensively. However, experimental results on the influence of these properties on bubble loading under fluidized-bed flotation conditions (where the probability of detachment is expected to be negligible) are scarce. In this work, the loading fraction (L) of individual bubbles was studied using a high-speed video camera (Phantom Miro LC111). Particles of silica (−75 + 53 µm to −1018 + 850 µm) and magnetite (−425 + 300 µm) were fluidized in a specially designed perspex column. Specific sizes of air bubbles were generated using a combination of a syringe pump and nozzles with different internal diameters. The generated bubbles rose through a bed of fluidized particles, which resulted in bubble loading. The results indicate that fractional bubble loading decreased with an increase in both bubble and particle size. With a 2 mm bubble, the loading fraction of silica declined from circa 0.9 to circa 0.1. However, with coarse particles (−850 + 600 µm and −1018 + 850 µm), bubble loading increased with an increase in bubble size, until an optimum bubble size of 2 mm and then started to decrease as bubble size increased. An increase in particle contact angle showed a corresponding increase in loading fraction, while the density of the material seemed to play no role in terms of the loading fraction. An increase in loading fraction had a negative effect on bubble rise velocity.

X‐ray Computed Tomography Characterization of Slag Crust and the Effect of Bubbles and Metallic Iron in Slag on Heat Transfer to Copper Stave

Understanding the heat transfer properties of the slag crust is critical to the safe operation of copper staves. The distribution of metallic iron and bubbles in the slag crust is detected by X‐ray computed tomography. The thermal conductivity of the slag crust is modified based on an effective thermal conductivity model and laser thermal conductivity measurements to predict the effect of metallic iron and bubbles on the heat transfer in the slag crust. The results show that the average volume fractions of metallic iron and air bubbles in the slag crust are 3% and 4.5%, respectively. The measured value is consistent with the trend of the effective thermal conductivity calculation model, and the calculation result of the Maxwell–Eucken effective thermal conductivity model is very accurate. Variations in the volume fraction of metallic iron in the slag crust have a greater effect on the thickness of the slag crust, while variations in the volume fraction of bubbles have a smaller effect on the thickness of the slag crust. It is recommended to keep it between 10 and 30 mm in blast furnace production to help improve the operational life of the copper stave.

PHANGS–JWST First Results: A Statistical View on Bubble Evolution in NGC 628

The first JWST observations of nearby galaxies have unveiled a rich population of bubbles that trace the stellar-feedback mechanisms responsible for their creation. Studying these bubbles therefore allows us to chart the interaction between stellar feedback and the interstellar medium, and the larger galactic flows needed to regulate star formation processes globally. We present the first catalog of bubbles in NGC 628, visually identified using Mid-Infrared Instrument F770W Physics at High Angular resolution in Nearby GalaxieS (PHANGS)–JWST observations, and use them to statistically evaluate bubble characteristics. We classify 1694 structures as bubbles with radii between 6 and 552 pc. Of these, 31% contain at least one smaller bubble at their edge, indicating that previous generations of star formation have a local impact on where new stars form. On large scales, most bubbles lie near a spiral arm, and their radii increase downstream compared to upstream. Furthermore, bubbles are elongated in a similar direction to the spiral-arm ridgeline. These azimuthal trends demonstrate that star formation is intimately connected to the spiral-arm passage. Finally, the bubble size distribution follows a power law of index p = −2.2 ± 0.1, which is slightly shallower than the theoretical value by 1–3.5σ that did not include bubble mergers. The fraction of bubbles identified within the shells of larger bubbles suggests that bubble merging is a common process. Our analysis therefore allows us to quantify the number of star-forming regions that are influenced by an earlier generation, and the role feedback processes have in setting the global star formation rate. With the full PHANGS–JWST sample, we can do this for more galaxies.

気泡塔内大・小気泡群のボイド率に関する研究

The void fractions of large and small bubbles, αG,L and αG,S, in a bubble column were measured by means of the DGD (Dynamic Gas Disengagement) method. The column diameter was 200 mm and the initial liquid heights H0 were 800, 1600, 2400, and 3000 mm. We dealt with heterogeneous bubbly flows with the superficial gas velocity JG from 0.06 to 0.30 m/s. Three kinds of liquids were used as the liquid phase to understand effects of the liquid viscosity on the void fractions. The following conclusions were obtained: (1) an experimental database of the void fractions of large and small bubbles was obtained at various initial liquid heights and liquid viscosities, (2) the void fractions of large and small bubbles increase with increasing JG at constant H0, (3) the void fraction of large bubbles for JG ≤ 0.10 m/s decreases with increasing H0 for H0 < 2400 mm and is almost constant for H0 ≥ 2400 mm while αG,L is independent of H0 for JG ≥ 0.20 m/s, (4) the liquid viscosity does not affects αG,L, (5) the void fraction of small bubbles slightly increases at JG = 0.06 m/s, whereas it is almost constant at JG = 0.10 m/s, and decreases for JG ≥ 0.20 m/s as H0 increases, and (6) the void fraction of small bubbles decreases with increasing the liquid viscosity and dependence of αG,S on H0 is not so different.

Computational Analysis of Machining Induced Stress Distribution during Dry and Cryogenic Orthogonal Cutting of 7075 Aluminium Closed Cell Syntactic Foams.

The addition of hollow aluminium oxide bubbles to the 7075 aluminium matrix results in a lightweight syntactic foam with a reduced density and an increased peak compression strength. The presence of ceramic bubbles also aids in a reduced coefficient of thermal expansion and thermal conductivity in comparison to aluminium alloys. In spite of their enhanced material properties, the inclusion of hollow aluminium oxide bubbles presents the challenge of poor machinability. In order to elucidate the problem of poor surface machinability, an attempt has been made to develop a thermo-mechanical finite element machining model using AdvantEdgeTM software with which surface quality and machined syntactic foam material can be analyzed. If the novel model developed is combined with virtual reality technology, CNC technicians can observe the machining results to evaluate and optimize the machining program. The main novelty behind this software is that the material foam is assumed as a homogeneous material model for simplifying the material model as a complex heterogeneous material system. The input parameters used in this study are cutting speed, feed, average size and volume fraction of hollow aluminium oxide bubbles, and coolant. For the output parameters, the numerical analysis showed a 6.24% increase in peak tensile machining induced stress as well as a 51.49% increase in peak cutting temperature as cutting speed (25 m/min to 100 m/min) and uncut chip thickness (0.07 mm to 0.2 mm) were increased. The average size and volume fraction of hollow aluminium oxide bubbles showed a significant impact on the magnitude of cutting forces and the depth of tensile induced stress distribution. It was observed on the machined surface that, as the average size of hollow aluminium oxide bubbles became coarser, the peak machining induced tensile stress on the cut surface reduced by 4.47%. It was also noted that an increase in the volume fraction of hollow aluminium oxide bubbles led to an increase in both the peak machining induced tensile stress and the peak cutting temperature by 29.36% and 20.11%, respectively. This study also showed the influence of the ceramic hollow bubbles on plastic deformation behavior in 7075 aluminium matrix; the machining conditions for obtaining a favorable stress distribution in the machined surface and sub-surface of 7075 closed cell syntactic foam are also presented.

Computational fluid dynamics investigation of bitumen residues in oil sands tailings transport in an industrial horizontal pipe

Pipeline transport is commonly used in the oil sand industry to convey crushed oil sand ores and tailings. Bitumen residues in the oil sand tailings can be a threat to the environment that separating them from tailings before disposal is crucial. However, low bitumen concentration in the tailing slurry and the complex transport characteristics of the four-phase mixture make the process difficult. This study establishes an Eulerian–Eulerian (E–E) computational fluid dynamics model for an industrial-scale oil sand tailings pipeline. A comprehensive sensitivity analysis was conducted on the selection of carrier-solid and solid-bitumen drag models. The combination of small and large particle sizes (i.e., 75 and 700 μm) and bitumen droplet size (i.e., 400 μm) provided good agreement with field data in velocity profiles and pressure drop. The validated model was subsequently extended to investigate the influence of the secondary phase (i.e., bitumen droplets and bubbles) on flow characteristics in a tailing pipeline. The investigation covered a range of bitumen droplet size (100–400 μm), bitumen fraction (0.0025–0.1), bubble size (5–1000 μm), and bubble fraction (0.0025–0.3) and their influences on the velocity, solids, and bitumen distribution are revealed. For an optimum bubble size of 500 μm, a maximum recovery of 59% from the top 50% and 83% from the top 75% of the pipe cross section was obtained. The present study demonstrates the preferential distribution of bitumen and provides valuable insight into bitumen recovery from an industrial-scale tailing pipeline.

Effect of the Inclined Part Length of an Inclined Blade on the Cavitation Characteristics of Vortex Pumps

To study the effect of the length of the second inclined section of the inclined vane on the vortex structure and pressure distribution inside a vortex pump, this paper uses a combination of numerical simulations (CFD) and experimental verification methods to analyze the static pressure distribution of the internal flow field and the volume fraction distribution of the impeller bubble at different total inlet pressures as well as to analyze the volume and streamline of the distribution of the impeller bubble of the vortex pump at different instants. The results show that as the length of the second inclined section of the inclined vane increases, both the low-pressure area and the volume fraction of the vapor bubbles inside the impeller of the vortex pump increase, and the resistance to cavitation becomes worse. When the total inlet pressure of the impeller is low, a large number of vortices will be generated inside the flow channel of the vortex pump, leading to vortex cavitation; the longer the length of the inclined section, the larger the velocity gradient of the fluid and the more serious the phenomenon of deliquescence, leading to more intense cavitation, while a shorter inclined section length can effectively improve the anti-cavitation performance of the vortex pump.

Bubble behaviors of geldart B particle in a pseudo two-dimensional pressurized fluidized bed

Pressurized fluidized beds have been developed in quite a few industrial applications because of intensified heat and mass transfer and chemical reaction. The bubble behaviors under elevated pressure, strongly influencing the fluidization and reaction conversion of the whole system, are of great research significance. In this work, the bubble behaviors of Geldart B particle in a pseudo two-dimensional (2D) pressurized fluidized bed were experimentally studied based on digital image analysis technique. The effects of pressure and fluidization gas velocity on the general bubble behaviors (i.e., size, shape and spatial distribution) and the dynamic characteristics, such as the time-evolution of voidage distribution and local flow regimes, were comprehensively investigated. Results show that increasing pressure reduces the stability of bubbles and facilitates gas passing through the emulsion phase, resulting in the “smoother” fluidization state with smaller bubbles and declined bubble fraction and standard deviation. The equivalent bubble diameter and bubble aspect ratio increase with the increasing gas velocity while decrease as pressure rises. The elevated pressure reduces bubbles extension in the vertical direction, prohibits the “short pass” of fluidization gas in large oblong bubbles/slugs and benefits the gas–solid interaction. The flow regimes variation with gas velocity is affected by the elevated pressure, and demonstrates different features in different local positions of the bed.

Study of an air bubble curtain along a wall in water and radiated noise mitigation

The injection of air bubbles into the liquid phase of a freestream flow has several impacts on the flow structure, which depends on the volume and size of the bubbles. This work experimentally investigates the characteristics of air bubble injection into freestream flow using three different injector models. The effects of the bubble curtain on the sound wave attention are studied. A wide range of air injection rates from 2 to 50 standard liters per minute is injected into the freestream water at Froude numbers (Fr) of 50.5, 70.7, and 90.9. The injector model is placed on the sidewall, which is where the bubble curtain is generated. High-speed cameras and an image processing technique are used to visualize and quantify the projected void fraction (PVF) of air bubbles. The sound measurement system consists of two hydrophones. The first hydrophone projects sound waves at discrete frequencies ranging from 17 to 50 kHz, and the second receives the transmitted sound waves. The bubble PVF is observed to increase with the air injection rate as the Froude number increases. There is no significant increment in the thickness of the bubbly curtain when the air injection rate or Froude number increases. The different air injector models produce various air bubble flow patterns, and model II provides the highest PVF. The bubble curtain greatly suppresses sound waves at all frequency ranges. However, the sound attenuation rate varies along the frequency range. The insertion loss increases depending on the PVF of the bubbles, freestream velocity, and frequency range. At a high Froude number of 90.9, the increased air injection rate does not affect the insertion loss. Model II has a relatively higher insertion loss rate at frequencies &amp;gt;26 kHz.

Effects of different He+ irradiating ion energies on the evolution behavior of helium bubbles in dispersion-strengthened NiMo–Y2O3NP alloys

The nickel-based NiMo–Y2O3NP alloy has been identified as a potential structural material to be used for advanced reactors. In this study, the microstructural evolution behavior of oxide-dispersion-strengthened NiMo–Y2O3 alloys irradiated with He+ ions possessing different incident particle energies (0.5, 1.0, and 2.0 MeV) was investigated by transmission electron microscopy, simulation calculations, and nanoindentation tests. The experimental results showed that helium bubbles were generated in all three irradiated samples of the NiMo–Y2O3NP alloy, where more than half of the bubbles were smaller than 4 nm in diameter. As the energy of the incident He+ irradiating ion increased, the number density of helium bubbles decreased, but their average size increased within the tolerance of the error, inducing an increase in the volume fraction of helium bubbles in the damage peak region. This could be attributed to the decrease in helium concentration and increase in the ratio of vacancies to helium atoms (Vac./He) in helium bubbles in the damage peak region. In addition, the average nanohardness of the irradiated samples S1, S2, and S3 was higher than that of the unirradiated sample S0. In this study, we evaluated the effects of He+ irradiating ion energy on the evolution behavior of helium bubbles in the alloy, providing a reference for further research on the evolution behavior of helium-induced damage defects of structural materials.

Modelling the Electrochemical Reduction of CO2 Under Gas-Liquid Channel Flow

Electrochemical reduction of CO2 using renewable energy sources is a promising avenue for sustainable production of bulk chemicals. The feasibility of electrochemical CO2 conversion has been demonstrated at lab scale, leading researchers to propose several reactor designs. However, CO2 electrolysis in aqueous systems is severely limited by mass transfer leading to performance parameters insufficient for industrial application. A strategy to enhance mass transfer is to actively introduce CO2 as a gas flow, while keeping diffusion paths between reactants and catalyst short, by separating the gas flow from the liquid electrolyte through a gas diffusion electrode. However, flooding, salt formation, or drying out of the gas diffusion electrode are common problems and present a major obstacle towards commercialisation. A promising reactor concept that enhances mass transfer without the complexity of a gas diffusion electrode is a structured reactor operated under gas-liquid Taylor flow: gas–liquid flow consisting of elongated bubbles in micro- or milli-channels. While this is a proven concept to enhance mass transfer for heterogeneous catalysis in flow cells, literature on this approach for electrochemical processes is scarce and the effect of process conditions on the reactor performance are poorly understood.In this work, we propose a tubular cell design, inspired from the field of fuel cells, for CO2 electrolysis with a zero-gap membrane electrode assembly. We further, develop a simple analytical model revealing how reactor performance in terms of faradaic efficiency and current density is governed by the key features of Taylor flow. These features film thickness, bubble velocity, and volume fraction of CO2 bubbles over aqueous electrolyte, for a given cathode potential.We find that the film thickness and the volume ratio of CO2/electrolyte fed to the reactor significantly affect the limiting current density and the faradaic efficiency. Additionally, we find industrially relevant performance with faradaic efficiencies (> 90 %) at current densities of up to 500 mA cm-2, when operating the reactor at elevated pressure beyond 5 bar. This demonstrates the general potential of this reactor concept to overcome mass transfer limitations in the field of electrolysis. We compare our predictions with numerical simulations, showing good agreement for a large window of operation conditions, illustrating when the simple predictive expressions for the current density and faradaic efficiency can be applied. We will discuss the importance of including interdependencies on the reactor scale to assess the economic viability of a reactor design and presents a tool to evaluate reactor design choices. We expect that the simple predictive expressions are instrumental in guiding experimental studies and reactor design choices, taking into account both technical and economic considerations.

Atomistic simulation and continuum modeling of the dynamic tensile fracture and damage evolution of solid single crystalline Al with He bubble

The dynamic tensile fracture mechanism and damage evolution characteristics of solid single crystalline Al with He bubble are investigated by molecular dynamics (MD) simulations and continuum modeling. The physical mechanism leading to fracture is found to be dominated by He bubble growth, in wide ranges of strain rate and initial bubble volume fraction. The bubble growth process can be divided into three stages and the microscopic mechanism is related to the plastic deformation of surrounding metallic material predominated by dislocation growth and movement. It is further revealed that the evolution characteristics of He bubble are independent on strain rate or initial bubble volume fraction, but the growth rate increases significantly with increasing strain rate or decreasing bubble fraction. Additionally, the critical stress for bubble growth and dynamic tensile strength at the strain rates from 106 /s to 1010 /s are obtained, showing strain rate hardening effect. Finally, a continuum model based on the understanding derived from MD simulations is proposed to describe the damage evolution of the metal with He bubble, including the new strength softening effect induced by bubble growth. The dynamic tensile processes at the strain rates from 104 /s to 1010 /s are calculated by this model, and the obtained pressure and bubble evolutions and dynamic tensile strength are in good agreement with available MD results. We suppose that the present study sheds some light on the dynamic fracture of solid metals containing He bubble.

Evaluations on effect of volume fraction of injected air on exergo-economic performance of a shell and tube heat exchanger

Increasing heat transfer rate in heat exchangers is one of the topics interested by researchers which leads to economic savings. Various methods have been proposed in this field which are categorized into two main groups of active and passive techniques. Despite numerous investigations were conducted in this regards, very rare investigations have probed these methods from the economic viewpoints. Present study was carried out to investigate the effect of volume fraction (VF) of air bubbles on exergo-economic performance of horizontal shell and helically coiled tube exchanger (HSHTE). The air bubbles were injected into shell side via especial method. Holes with certain properties were fabricated on a plastic pipe with diameter of 3 mm for injecting air bubbles. Both counter flow and parallel flow were considered in this investigation. Present study showed that air injection has significant effect on thermal efficiency, exergy destruction and economic performance of the HSHTE. It was found that increment of VF increases number of thermal units, first law efficiently and exergy destruction increase by 4.5, 2.4 and 12.5 times, respectably. Furthermore, best values of Net profit per unit transferred heat load (դ p ) was about 9.3 × 10 −5 ($/J) which presented up to 13% better financial performance in comparison with parallel flow.