Volumetric Flux Research Articles

Influence of welding sequences on induced residual stress and distortion in pipes

A three-dimensional (3D) finite element (FE) model based on thermal-elastic-plastic approach in SYSWELD® was employed to investigate the effects of welding sequences on induced residual stresses and radial distortion in AISI 316L stainless steel welded pipes. To mesh the model, the HYPERMESH® processor was utilized and the model was then exported to SYSWELD® for further thermo-mechanical analysis. The Goldak's double ellipsoidal moving heat source model was employed in SYSWELD® to obtain the volumetric heat flux density in the Gas Metal Arc Welding (GMAW) simulation process. A neural-network program was suitably trained and used to predict the parameters of Goldak's model. The obtained numerical models using predicted Goldak’s parameters were then successfully validated by experimental results in terms of size of welding pool and the temperature distribution. Four different welding sequences (concepts) were investigated and compared: three quarters and one full circumferential welding. These welding sequences were anticipated to create the least residual stress and distortion in pipe welding. The results demonstrate that the welding sequences significantly influence induced residual stresses and distortions in magnitude and in distribution. For the full circumferential welding concept, which was proposed in this study, the residual stresses and distortion present more uniform distribution along the circumferential direction than those in quarter welding sequences. The magnitude of welding distortion was also significantly lower in the full circumferential concept when compared to the quarter welding concepts. The FE results of residual stresses in the full circumferential welding sequences were accurately validated by experimental tests.

A quantitative study of salinity effect on water diffusion in n-alkane phases: From pore-scale experiments to molecular dynamic simulation

Numerous mechanisms have been proposed to untangle the effect of a low concentration of dissolved salts in the water flooding medium. One potential mechanism for enhanced oil movement is proposed with osmosis effect, however, the process of water transport through the oil phase, due to a salinity contrast, is not fully understood. In our study, we used three aqueous solutions and two alkanes in a series of microfluidic experiments with hydrophobically coated glass micro-chips for mimicking the low-salinity waterflooding process in an oil-wet rock formation. We created multiple systems of low-salinity water-alkane/high-salinity water in the porous micromodel, and afterward, continuously monitored the domain for 70 h. We noted that ionic strength and the hydrocarbon chain length both played important roles in water diffusion. A salinity contrast of 1.7 g/L-170 g/L caused a higher water volumetric flux than 50 g/L-170 g/L for both alkanes. The difference in water volumetric fluxes for those two contrasts were not proportional to the salinity contrast during the experimental period. There was no simple relationship between the chain length of hydrocarbon and water volumetric flux. Moreover, to investigate the effect of salinity on water behavior in heptane, we conducted molecular dynamic (MD) simulations by considering three different concentrations in the high-salinity water region featuring our experiments. The results indicated that high salinity limited the water diffusion from high-salinity phase into the oil phase and reduced the possibility of water entering the heptane phase. Therefore, the net flux of water from the pure water side to the salty waterside was enhanced.

Numerical and experimental analysis of temperature distribution and melt flow in fiber laser welding of Inconel 625

In these days, laser is a useful and valuable tool. Low input heat, speed, accuracy, and high controllability of laser welding have led to widespread use in various industries. Nickel-based superalloys are creep-resistant materials used in high-temperature conditions. Also, these alloys have high strength, fatigue, and suitable corrosion resistance. Inconel 625 is a material that is strengthened by a complex deposition mechanism. Therefore, the parameters related to laser welding affect the microstructure and mechanical properties. Therefore, in this study, the effect of fiber laser welding parameters on temperature distribution, weld bead dimensions, melt flow velocity, and microstructure was investigated by finite volume and experimental methods. In order to detect the temperature history during continuous laser welding, two thermocouples were considered at a distance of 2 mm from the welding line. The heat energy from the laser beam was modeled as surface and volumetric heat flux. The results of numerical simulation showed that Marangoni stress and buoyancy force are the most important factors in the formation of the flow of liquid metal. Enhancing the laser power to 400 W led to the expansion of the width of the molten pool by 1.44 mm, which was in good agreement with the experimental results. Experimental results also showed that increasing the temperature from 500 °C around the molten pond leads to the formation of a coarse-grained austenitic structure.

Effect of binary mixed-surfactants and hybrid nanofluid on spray cooling heat transfer

The present study emphasizes the spray-cooling enhancement of a copper heater block of 10 mm2 cross-sectional area with binary mixed surfactant based fluid and hybrid nanofluid using a pressure swirl nozzle with an orifice size of 0.51 mm. The experiments have been carried out at two distinct fluid input temperatures of 27 °C and 42 °C, with a volumetric flux of 3.50 cm3/cm2s. Polyvinyl pyrrolidone (polymer surfactant), Sodium dodecyl sulfate (an anionic surfactant), Tween-20 (a nonionic surfactant) have been used as binary mixed surfactant systems in distilled water. The best performance has been obtained with SDS:Tween-20, which resulted in a maximum heat flux of 264 W/cm2 and a heat transfer coefficient of 3.59 W/cm2K. When compared to distilled water, the heat transfer coefficient increased by 32.2%, but only by 25.2% and 18.1% with PVP:Tween-20 and SDS:PVP surfactant solutions. Further, the effect of a hybrid nanofluid, which is a colloidal mixture of Titanium dioxide (TiO2) and MWCNTs (multi-walled carbon nanotubes) in distilled water, has been studied to better understand spray cooling heat transfer enhancement. Heat transfer was first enhanced by the hybrid nanofluid and then decreased as the volume concentration was increased from 0.1% to 0.3%. A maximum heat flux of 234 W/cm2 and a heat transfer coefficient of 3.15 W/cm2K has been achieved, with a heat transfer coefficient improvement of nearly 27.3% compared to distilled water. However, the mixed surfactant system outperformed, giving nearly 12.8% improvement in heat flux values. It has been observed that low surface tension resulted in high heat transfer rates. Furthermore, the effect of 15 °C subcooling on heat transfer performance has been investigated. A new correlation to find Nusselt number is proposed in terms of Reynolds number, Weber number and Prandtl number with a mean absolute error of 7.16%.

Experimental study on spray cooling heat transfer enhancement using MWCNT and TiO2 hybrid nanofluid

In the present study, two nanofluids namely Multi-walled carbon nanotubes and Titanium dioxide dispersed in distilled water, have been used with three different concentrations; 0.1%, 0.2%, and 0.3% by volume, to investigate heat transfer enhancement in spray cooling applications. A square copper specimen of 10 mm2 has been spray cooled with a volumetric flux of 2.5 cm3/cm2s using a 0.4 mm diameter pressure nozzle. The results revealed that the average heat transfer coefficient and corresponding critical heat flux enhanced significantly at 0.2 vol% for both nanofluids in contrast to distilled water. The results showed an improvement of 21.9% and 26.3% in heat transfer coefficient for Multi-walled carbon nanotubes and Titanium dioxide nanofluid, respectively. The effect of hybrid nanofluid in various concentrations has also been investigated on heat transfer performance. The results obtained showed a maximum value of 425 W/cm2 for critical heat flux and 4.42 W/cm2K for heat transfer coefficient, with a heat transfer coefficient improvement of nearly 40.31% in comparison to distilled water. This results in an enhancement ratio of 1.6 for critical heat flux and 1.4 for heat transfer coefficient. In contrast to single nanoparticle nanofluid, the hybrid nanofluid indicated a moderate improvement in heat transfer coefficient of 11.7% and 7.8% for Multi-walled carbon nanotube and Titanium dioxide nanofluids, respectively. It has been observed that heat transfer performance was first enhanced and then declined as the volume fraction increased from 0.1% to 0.3% for all the nanofluids.

A finite volume coupled level set and volume of fluid method with a mass conservation step for simulating two‐phase flows

AbstractThis article presents a finite volume method for simulating two‐phase flows using a level set approach coupled with volume of fluid method capable of simulating sharp fluid interfaces. The efficiency of the method is a result of the fact that the interface is calculated in order to satisfy mass conservation with no explicit interface reconstruction step and the mass fluxes across cell‐faces are corrected to respect the recovered volume fraction. The mass‐conservation correction step proposed here, is utilized using an iterative algorithm which solves a reaction‐diffusion equation for the mass correction of the level set. The re‐sharpened volume fraction is used for the new volumetric fluxes at each cell which are calculated through the proposed algorithm that guarantees that they satisfy mass conservation. The algorithm is not limited in representing the interface with the 0.5‐contour and is applicable for arbitrary polyhedral cells. Good accuracy and mass conservation are achieved when compared to other conservative approaches.

Euler-Euler numerical simulations of upward turbulent bubbly flows in vertical pipes with low-Reynolds-number model

In this work, numerical simulations of upward turbulent bubbly flows in vertical pipes are conducted in the Euler-Euler framework with a low-Reynolds-number (LRN) model for liquid. It is found that the existing correlation for the drag coefficient of a single bubble in a shear flow, which has been successfully used along with the high-Reynolds-number (HRN) models, cannot be used with the LRN model. The reason is that drag forces of bubbles calculated using such correlation are enormous in near-wall cells (order of [Formula: see text]), which causes a divergence of numerical simulations with LRN. Therefore, a modified correlation for the drag coefficient of a single bubble in shear flow, that can be used successfully with the LRN model, has been proposed. The results of numerical simulations, performed with a new correlation for the drag coefficient, are analysed and compared to selected experimental measurements for different pipe diameters and different flow conditions of gas and liquid. It is shown that the largest effect of the application of the new correlation for the drag coefficient of a single bubble in shear flow in numerical simulations can be achieved on the reduction of the relative velocity between gas and liquid. The degree of this reduction depends on the pipe diameter and liquid volumetric flux.

Power generation cell driven by osmotic pressure in microchannels with hydrophobic surfaces and viscoelectric effects

A theoretical study that explores power generation via streaming potential and osmotic gradients is proposed. The system is compounded by an osmotic membrane that has different saline concentrations on each side. This concentration gradient promotes a volumetric flux rate inside a microchannel with parallel plates whose surfaces are made of modified hydrophobic fumed silica, thus, the no-slip condition is no longer sustained. Aside from these characteristics, we consider viscoelectric effects in the analysis. The set of equations is written in dimensionless variables, which are solved with integrodifferential methods, permitting us to obtain semi-analytical solutions for velocity, pressure fields, and the most important: the electric potential generated for the system. This setup converts concentration gradients into electric energy in the form of streaming potential. Besides, we demonstrate that hydrophobic surfaces promote a greater induced streaming potential, nonetheless, for high potentials appears a saturation phenomenon which avoids the growth of the induced electric potential no matter how large the slip-conditions could be.

Quantifying the Effects of Bed Roughness on Transit Time Distributions via Direct Numerical Simulations of Turbulent Hyporheic Exchange

AbstractWe report direct numerical simulation (DNS) results of hyporheic exchange for a flat river bed with two different particle roughness textures, at a surface flow friction Reynolds number of 395 and a bed permeability Reynolds number of 2.6. Transit time distributions (TTDs), subsurface flow patterns, and the interfacial volumetric fluxes are discussed. The transit time was quantified using a forward particle tracking method based on pure advection by three‐dimensional, pore‐resolved, time‐mean velocities. Results show that bed roughness induces deep subsurface flow paths that yield a TTD with a power‐law tail. Roughness obstructs the surface flow, creating interfacial pressure variations which induce subsurface flow. Next, the molecular diffusion is accounted for based on a random walk method and is shown to increase transit times regardless of roughness texture. This work demonstrates that particle roughness on a macroscopically flat sediment bed can induce significant hyporheic exchange that is fundamentally similar to that induced by bedforms.

Numerical simulation and optimization of semi-dry flue gas desulfurization in a CFB based on the two-film theory using response surface methodology

Semi-dry circulating fluidized bed flue gas desulfurization(CFB-FGD) is a major industrial FGD technology. Assuming that only one desulfurizer particle is wrapped in each droplet for mass transfer and dissolution, this study proposed a two-film theory-based simplified desulfurization model, with which CFB desulfurization was performed. After model verification, this study simulated the hydrodynamics and desulfurization reaction characteristics and explored the effects of inlet SO2 concentration(A), gas velocity(B), circulating particle mass flux(C), and jet water volumetric flux(D) on the desulfurization efficiency. Simulation results coupling with response surface methodology (RSM) analysis could not only quantitatively reflect the effect degree of a single variable but also apply to the interaction between parameters, thus determining the optimal parameters. RSM results showed that D and CD were the independent and interaction parameters, respectively, that most significantly affected desulfurization efficiency. The simulation under the optimal operating parameters showed that the desulfurization efficiency was greatly improved, reaching 99.69%.

An Application of Homotopy Perturbation Method to Fractional-Order Thin Film Flow of the Johnson–Segalman Fluid Model

Thin film flow is an important theme in fluid mechanics and has many industrial applications. These flows can be observed in oil refinement process, laser cutting, and nuclear reactors. In this theoretical study, we explore thin film flow of non-Newtonian Johnson–Segalman fluid on a vertical belt in fractional space in lifting and drainage scenarios. Modelled fractional-order boundary value problems are solved numerically using the homotopy perturbation method along with Caputo definition of fractional derivative. In this study, instantaneous and average velocities and volumetric flux are computed in lifting and drainage cases. Validity and convergence of homotopy-based solutions are confirmed by finding residual errors in each case. Moreover, the consequences of different fractional and fluid parameters are graphically studied on the velocity profile. Analysis shows that fractional parameters have opposite effects of the fluid velocity.

The Effect of Weber Number on Spray and Vaporization Characteristics of Liquid Jets Injected in Air Crossflow

AbstractThis paper details a numerical investigation conducted to systematically evaluate the effects of aerodynamic Weber number, in the range from 68 to 136, on spray characteristics and gaseous fluid dynamics when liquid jets are injected in high-temperature air crossflow. The momentum flux ratio and air temperature for all the cases studied in this research effort are 9 and 573 K, respectively. The computations are conducted using an Eulerian–Lagrangian framework, where the gas phase is modeled by the compressible form of the Navier–Stokes equations and the liquid phase is treated in the Lagrangian frame with appropriate models to account for jet injection and breakup phenomena. A modified version of two-way coupling, which takes into account the finite size of the dispersed phase, is used to account for the exchange of mass, momentum, energy and species between the two phases. Turbulence closure is achieved using the large eddy simulation technique. As a first step, the framework is validated against measurements for non-vaporizing and vaporizing conditions—our results agree well with experimental data. Next, three computations in the range of Weber numbers mentioned above are conducted—the effect of Weber number is quantified in terms of the spatiotemporal evolution of the mass fraction of the vaporized liquid, detailed distributions of droplet sizes, their velocities, and volumetric fluxes. It is found that with an increase in the Weber number, the droplet sizes and the penetration depth monotonically decreased. As a result, at higher Weber number conditions, the vaporized liquid in the domain increases due to the overall enhancement in the effective surface area of the liquid phase.

Interannual Relationship between Haze Days in December–January and Satellite-Based Leaf Area Index in August–September over Central North China

Haze pollution in central North China has become a hot topic in recent decades due to its serious environmental and health effects. In this work, the interannual relationship between haze days in December–January (DJ_HD) and leaf area index in August–September (AS_LAI) over central North China, along with the possible physical mechanisms involved, are investigated. The relationship varies in different periods, being significant during 1982–2000 (P1) but insignificant during 2001–2014 (P2). During P1, there is an in-phase relationship between AS_LAI and surface evaporation, and an out-of-phase relationship between AS_LAI and surface albedo in August–September. The surface evaporation and albedo anomalies persist to October–November and are associated with lower top-layer volumetric soil water, upward sensible heat flux and downward latent heat flux anomalies in October–November, which act as the bridge in the relationship between AS_LAI and DJ_HD. Both the volumetric soil water and heat fluxes anomalies persist to December–January and correspond to atmospheric circulations similar to the weakened East Asian winter monsoon pattern, which is the dominant system for winter haze events. Thus, the ventilation conditions in December–January are favorable for the accumulation of haze particles. However, during P2, the relationships are not significant between AS_LAI and volumetric soil water or surface soil temperature during October–January. Meanwhile, the East Asian winter monsoon is likely strengthened and tends to be more significantly affected by factors including Arctic sea ice, Arctic Oscillation, etc. Therefore, the effects of AS_LAI on the monsoon may become insignificant and, in turn, the relationship between AS_LAI and DJ_HD becomes insignificant during P2.

Intrinsic Dependence of Groundwater Cation Hydraulic and Concentration Features on Negatively Charged Thin Composite Nanofiltration Membrane Rejection and Permeation Behavior.

Commercial nanofiltration membranes of different molecular weight cut-offs were tested on a pilot plant for the exploration of permeation nature of Ca, Mg, Mn, Fe, Na and ammonium ions. Correlation of transmembrane pressure and rejection quotient versus volumetric flux efficiency on nanofiltration membrane rejection and permeability behavior toward hydrated divalent and monovalent ions separation from the natural groundwater was observed. Membrane ion rejection affinity (MIRA) dimension was established as normalized TMP with regard to permeate solute moiety representing pressure value necessary for solute rejection change of 1%. Ion rejection coefficient (IRC) was introduced to evaluate the membrane rejection capability, and to indicate the prevailed nanofiltration partitioning mechanism near the membrane surface. Positive values of the IRC indicated satisfactory rejection efficiency of the membrane process and its negative values ensigned very low rejection affinity and high permeability of the membranes for the individual solutes. The TMP quotient and the efficiency of rejection for individual cations showed upward and downward trends along with flux utilization increase. Nanofiltration process was observed as an equilibrium. The higher the Gibbs free energy was, cation rejection was more exothermic and valuably enlarged. Low Gibbs free energy values circumferentially closer to endothermic zone indicated expressed ions permeation.

Study on Accurate Estimation of Positions and Volumetric Fluxes of Co2 Seepage from the Seafloor

Study on Accurate Estimation of Positions and Volumetric Fluxes of Co2 Seepage from the Seafloor

Experimental investigation on the coolability of nuclear reactor debris beds using seawater

During the Fukushima nuclear reactor accident, seawater was injected into the reactor core to cool the decay heat from the heat generating porous debris bed. However, the impact of dissolved salts in water on the coolability of a debris bed is not well understood. This paper is one of the first works to investigate the cooling mechanisms for debris bed using seawater. An experimental system was built where the packed bed test section was volumetrically heated via a high frequency induction heater. The temperature along the axis of the test section was measured using a high resolution temperature sensor based on Optical Frequency Domain Reflectometry. Experimental results show that the dryout heat flux increases with an increase in concentration, with pure water having a dryout volumetric heat flux of 1.8 MW/m3 and salt water of concentration 7% having a dryout volumetric heat flux of 2.8 MW/m3. However, this enhanced coolability using salt water is short term, as the crystallization fouling mechanism becomes significant over time and leads to gradual temperature excursion in the bed. The fouling mechanism eventually leads to a cross section of the debris bed to plug with the deposited salts, and this leads to a pressure build up in the lower regions of the debris bed.

Clarification of yeast cell suspensions by a highly porous polyamide nanofiber sponge

Depth filtration is an attractive method for initial clarification of broth for removing cells and cell debris. Electrospun nanofibers with their large specific surface area and a porous structure are known as attractive materials in filtration processes. However, dead-end filtration of cells through nanofiber mats (NFM) always leads to cake formation and increasing resistance. In this study, for the first time, a nanofiber sponge (NFS) or nanofiber aerogel was synthetized from polyamide 6 (PA6) building blocks. The NFS was flexible, highly porous and mechanically stable. The pore size of the NFS was tuned between 8 and 26 µm during the cryogenic processing step. Volumetric flux and filtration efficiency of the NFS depended on the pore size and the results were compared with those for NFM from the same PA6 nanofiber material. Dead-end filtration of Saccharomyces cerevisiae was feasible at a low differential pressure of 3.5 kPa and cell filtration efficiency was > 99 %. Modelling of the filtration process revealed that cake formation is prevented by NFS filters since cells are able to penetrate into the filter and to adsorb on their internal surface. The filtration characteristics were also compared with commercial depth filters and revealed the high flux of NFS filters along with the possibility to avoid filter aids and a low environmental impact. PA6-NFS filters may become a new and cost effective generation of filters for removing different cells or cell debris from broth and other applications.

Improving membrane filtration performance through time series analysis

For ultrafiltration, and membrane filtration more generally, the quantitative determination of the modes of fouling remains a subject of great interest. Herein an integral method for determining the modes from a time series of volumetric flux Jleft(tright) is given and illustrated with previously published filtration data of bergamot juice (Ruby-Figueroa et al (J Membr Sci 524:108-116, 2017)). The integral method of fouling analysis has the potential to become the cornerstone of a robust empirical process. In addition to determining, in a clear-cut manner, the point at which there is a switch from one mode to another, the robust methodology yields characteristic Jleft(tright) equation for each mode that are an excellent fit to the data. The emphasis is upon the creation of a robust methodology which is best viewed as being a semi-empirical method that is indicative of the modes of fouling. For the example chosen, the initial 4 L/m2 generates some pore blocking after which the main mode of fouling is cake build-up. The variation of overall resistance with time is also informative and analysis of this series was used to check the result for the initial phase of fouling as determined from the time series of volumetric flux. A comparison against the ARIMA (Autoregressive integrated moving average) method, which has never been previously undertaken, is given herein. The integral method of fouling analysis was found to be superior, in part because of the quality of fit to the data and in part because it enables one to establish whether the initial fouling is different in character from the subsequent fouling. Having this information can improve membrane selection and overall membrane filtration performance.

A green vapor suppressing agent for aqueous ammonia carbon dioxide capture solvent: Microcontactor mass transfer study

Aqueous ammonia is a promising carbon dioxide capture solvent and has recently attracted significant attention, but its main problem is high evaporation rate of ammonia in the absorber. Glycerol, which is a by-product of biodiesel, has hydroxyl groups that bind to ammonia molecules. Hence, it can reduce the vaporization of ammonia as an additive and improve the CO2 absorption properties. In this work, the mass transfer performance of glycerol, as an ammonia vaporization reduction additive, was investigated. Carbon dioxide absorption experiments using ammonia-glycerol hybrid solvent have been done in a T-shaped microchannel. The impact of process condition, including ammonia concentration (4–10 wt%), glycerol concentration (1–3 wt%), liquid flow rate (3–9 ml/min) and temperature (20–40 °C) was investigated on the volumetric overall mass transfer coefficient (KGaV), absorption percentage (AP) and volumetric molar flux (NAaV). According to the results, rising the glycerol concentration in the range of 2–3 wt% leads to an increase in KGaV by 4.8%. Hence, the addition of glycerol to aqueous ammonia not only increases the mass transfer coefficient but also reduces the vapor pressure of ammonia as a green vapor suppressing agent and diminishes the ammonia loss in the absorption tower.

Circumferential incoherent distribution of film thickness for multi-dimensional two-phase annular flow

Annular flow in rod bundle geometry is characterized by multi-dimensional properties in terms of two distinct length scales, rendering no consensus yet on an available model for predicting the circumferential incoherent distribution of film thickness. Current paper presents a semi-empirical but original correlation based on pertinent underlying physics. Gas phase Reynolds number is used to illustrate the gas–liquid interfacial shear-off mechanism. Liquid source term is scaled by the combination of void fraction and liquid volumetric flux. Circumferential shear stress produced by secondary flow is employed to denote mass transport in subchannel. Four available datasets including 189 data points are collected to develop and validate the proposed correlation from both cross-sectional and subchannel local regions perspectives. The majority of data can be correlated with the maximum relative error of ± 20.0%. Based upon the heuristic correlation, the circumferential incoherent distribution of film thickness is analyzed. The average film thickness on center rod increases slightly as the liquid velocity increased, since most of liquid phase migrates to corner region leading to a dramatically increase in film thickness on rod nearby duct wall. Two dependent factors are mainly responsible for the rod peripheral distribution of liquid thickness, in which the hydrodynamic effect dominates over the secondary flow factor, but the secondary flow makes the peripheral distribution of film thickness more uniform. Among the hydrodynamic parameters, both void fraction and gas velocity contribute to the thinning of the liquid film, but the increasing of liquid thickness along with rod periphery is attributed to the variation of subchannel characteristic length.