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This study examines the flow of the ternary nanofluid over a rotating stretchable cylinder with a torsional motion under the influence of a Cattaneo–Christov heat flux. In order to accomplish the goals of this simulation, a ternary hybrid nanofluid (THNF) that is based on water and incorporates nanoparticles with three distinct morphologies is considered. For assessing the colloidal mixture of spherical, cylindrical, and platelet shaped nanoparticles, the necessary models are used. By using appropriate similarity transformations, the modeled equations are reduced to a set of ordinary differential equations (ODEs). These ODEs are then solved using the finite element approach. The numerical integration's validity and reliability, as well as the newly obtained results, were thoroughly analyzed. Results reveal that the larger values of Reynolds number enhance the system's inertial force, which resists the liquid accelerating force and declines both velocities and heat transport. The rise in values of volume fractions and Reynolds number declines the skin friction coefficients along swirling and radial directions. The increase in values of both the thermal relaxation time parameter and Reynolds number improves the rate of heat transport. [ABSTRACT FROM AUTHOR]

Swirling flow at vertical shaft spillways results in flow fluctuations, reduces hydraulic system efficiency, and causes structural damage. Optimizing the shape of the inlet is a practical means to decrease the swirling flow strength. In the present study a comprehensive experimental investigation was performed to examine the effects of a new type of inlet over vertical shaft spillways, namely the circular piano-key (CPK) inlet, for free, orifice and full-pipe or black water flow regimes. Head-discharge relationships, threshold and critical submergence depths and the effects of different geometrical parameters of the CPK inlets on the spillway flow discharge coefficient were assessed. Results reveal that increases in the height of the inlet and outlet keys increase the released capacity of the shaft spillway. Given its increased total crest length and the effects of the radially placed walls of a CPK against the swirling flow, angles of the inlet and outlet keys of the CPK are found to significantly affect the spillway flow discharge. The effect of inlet and outlet overhangs on the efficiency of CPK inlets is not noteworthy, being negligible. Considering the destructive effects of swirling flow, the CPK inlets significantly decrease the range of submergence for an unfavourable swirling flow regime condition, increasing the threshold submergence depth and decreasing the critical submergence depth. The flow discharge through the CPK inlets is higher than those of the other circular-type spillways. The present modified CPK inlets more effectively divert water, serving as an economical alternative to the conventional circular spillways. [ABSTRACT FROM AUTHOR]

Achieving axisymmetric boundary conditions in turbulent swirl flows and predicting thermo-fluidic behaviours within a nozzle is often a challenge due to the difficulties of measurement diagnostics. Adding nanoparticles to ase fluids exacerbates the complexity because of the regeneration of effective properties of the fluid medium. As such, this study numerically investigates the flow and thermal characteristics for the effect of swirl and nanofluids of incompressible turbulent liquid jets. The results show that the axial and tangential velocity profiles for water-based nanofluids resemble to those for water in no-to-high swirl flows. The surface Nusselt number for strong swirl flow reduces with axial distances at isothermal wall condition, and the Nusselt number is strongly dependent on types of nanofluid for isoflux condition. Water-based nanofluids cause higher heat transfer compared to Dowtherm+Al2O3 and Syltherm800+ Al2O3. The average Nusselt number and the pressure drop are found to be the largest for 10% volume fraction. The increase of thermal-hydraulic performance factor for nanofluids after nozzle convergence is steeper for highly swirling flow than for non-swirling and medium swirling cases. A strong turbulent kinetic energy is observed immediately after the nozzle converging section for all nanofluid cases and Dowtherm+Al2O3 shows relatively uniform distributions across the nozzle. [ABSTRACT FROM AUTHOR]

A multidimensional numerical model was developed to simulate the operation of one cylinder of a 1.4-liter flex-fuel spark-ignition engine. Hydrous ethanol with 4.3%, 7.5%, 10%, 15%, and 20% water volumetric contents were the considered fuels for the engine. The full load engine operating point was analyzed at 3,875 rpm with a relative air-fuel ratio of 0.9 and a fixed ignition delay. A Grid Convergence Index study was conducted to guarantee the accuracy of the obtained numerical solutions. A six consecutive mechanical cycle simulation was performed for hydrous ethanol with 4.3% water content, and experimental data were used for validation purposes. Turbulent flame speeds were also evaluated and analyzed. Numerical results showed that 10% water content led to the highest engine-generated power output and flame propagation speeds and to the lowest CO and unburned ethanol emissions among the tested fuels. The flame shape and encompassed volume were also analyzed. The results also showed that the high swirl in the in-cylinder flow affects the initial development of the flame for all water contents considered. Fuels leading to lower flame distortions early after ignition showed higher reaction rates and better performance. [ABSTRACT FROM AUTHOR]

Supersonic separation technology is a cutting-edge method for efficient dehydration and hydrocarbon removal, yet challenges arise from the intricate flow dynamics within a supersonic nozzle. To address these challenges, a novel cascade drainage structure is proposed in this paper, combining the high swirl intensity of flush-type drainage with the extended drainage section, larger opening area, and reduced flow velocity of cylindrical drainage with oblique openings. Through comprehensive physical modeling and numerical analysis, this design is shown to enhance separation performance and mitigate fluid blockage within the nozzle. Through physical modeling and numerical analysis, we demonstrate its effectiveness in enhancing separation and mitigating fluid blockage. Experimental results confirm the cascade drainage structure's superiority, particularly at an optimal pressure ratio (${R_{np}}$ R np = 1.4). Ethanol vapor removal rate (${\delta _{steam}}$ δ steam ) and dew point drop ($\Delta {T_d}$ Δ T d ) reach 53.94% and 18.32°C, respectively, surpassing alternatives. Maintaining a 2 mm discharge clearance yields an outstanding dry gas ratio of approximately 85%. The findings contribute to advancements in dehydration and hydrocarbon removal processes, showcasing the potential for enhanced performance in supersonic separation technology within a concise framework. [ABSTRACT FROM AUTHOR]

The fully developed turbulent flow of pseudoplastic (n = 0:75) and Newtonian fluids in an isothermal axially rotating cylinder has been carried out using a large eddy simulation (LES) with an extended Smagorinsky model. The simulation Reynolds number of the present predictions has been assumed to be Res = 4000 at various rotation rates ð0 x N x 3Þ: This investigation seeks to assess the influence of the centrifugal force induced by the swirl on the mean flow quantities, turbulent statistics, and instantaneous turbulence structure to describe the rheological behavior and the turbulence features. The predicted results indicate that with increasing rotation rate, the pseudoplastic fluid tends to behave like a liquid when approaching the pipe center due to the lower apparent fluid viscosity in the logarithmic region as the pipe wall rotates. Moreover, the reduction in the pseudoplastic apparent viscosity in the core region induces a pronounced increase in the axial velocity profile further away from the pipe wall toward the core region. It is interesting to note that the growth of the centrifugal force induced by the swirl driven by the rotating pipe wall results in an apparent attenuation in turbulence intensities of the axial velocity fluctuation and, consequently, in the kinetic energy of turbulent fluctuations and the turbulent Reynolds shear stress of the axial-radial velocity fluctuations, as the pipe wall rotates. Moreover, the increased rotation rate leads also to a noticeable increase in the Root mean square (RMS) of the radial and tangential fluctuations. It can be said that the transport mechanism of turbulence intensities from the axial components to the other ones exhibits a marked increase with increasing pipe wall rotation. [ABSTRACT FROM AUTHOR]

The paper explores the use of swirling flow in the flotation process to enhance the removal of oil from oily sewage, thereby reducing environmental hazards. The study focuses on understanding the dynamic movement of dispersed oil droplets and their coalescence efficiency, as these factors play a crucial role in the overall flotation performance. By introducing a centrifugal force field into the air flotation flow, the collision and adhesion efficiency between oil droplets and bubbles, as well as the migration and separation efficiency, can be significantly improved. A laboratory swirling flotation cell was designed, and an experimental system was set up to conduct tests. The study employed a combination of experimental tests and CFD simulation, coupled with the Population Balance Model, to investigate the effects of swirling flow on the oil-water dynamic separation characteristics during the flotation process. The numerical simulation results were validated through online measurement of oil droplet size distribution using FBRM, ensuring a deviation within 3.0%. Additionally, the terminal velocity distribution of dispersed oil droplets under various swirl intensities in the annular space was analyzed. The study also examined the impact of turbulence intensity and swirl separation time on the oil-water separation process. The experimental result indicated that the tangential velocity attenuation is significant during swirling, and with an attenuation ratio of up to 84.8% when the oily sewage flows out of the annular space. The optimal turbulence intensity for promoting the collision coalescence process of oil droplets is found to be 6.5%, and the most suitable swirl separation time is 7.5 seconds. [ABSTRACT FROM AUTHOR]

In this paper, we consider the Cauchy problem of the 3D incompressible Keller–Segel–Navier–Stokes equations with partial diffusion, namely we remove the diffusion $ \Delta \rho $ Δ ρ. Using the damping effect of the growth term $ -\rho ^{3} $ − ρ 3 and the geometry of axisymmetric flow without swirl, we prove the global existence of weak solutions for the system. [ABSTRACT FROM AUTHOR]

Low-rank coal is currently widely used as fuel to cover the increasing needs of boilers. This kind of coal must be upgraded due to its high moisture content to increase its quality. The drying using a fluidized swirl bed has not been studied to reduce the moisture content of Low-Rank Coal. In contrast, the drying kinetic model has never been found. This study used the angle of guide vanes (AGV) 10°, 20°, and 30° to produce swirl flow. Experiments with varying temperatures used temperatures of 40°C, 45°C, and 50°C. The purpose of this work was to determine the drying characteristics, the best-drying kinetics models, the effective moisture diffusion value, SMER, MER, and SEC on swirl fluidized bed drying. The study results show that the Khazaei and Rational drying kinetic model was the most suitable for the two experimental variations. For experiments with varying AGV, the R2 values obtained are 0.9989–0.9992 and 0.9980–0.9983, while for the variable temperature, the values are 0.9990–0.9992 and 0.9983–0.9992 for each model. The research also found that the smaller AGV angle and higher temperature result in a faster drying rate and consume less energy. [ABSTRACT FROM AUTHOR]

This study aims to investigate the impact of activation energy on the flow of a hybrid nanofluid over a rotating stretching cylinder with torsional motion and a heat source/sink. The paraffin wax-sand-propylene glycol–water-based hybrid nanofluid has been used in the study. By adopting appropriate similarity transformations, the modeled partial differential equations are transformed into a set of ordinary differential equations, which are then solved using the finite element method. The numerical integration's validity and reliability, as well as the newly obtained discoveries, were thoroughly analyzed. Results reveal that the larger Reynolds number values enhance the system's inertial force, which resists the liquid accelerating force and declines both velocities and heat transport. The heat source/sink parameter has a favorable impact on the thermal profile, but larger Schmidt number values restrict mass transfer. The improved values of the chemical reaction rate parameter augment the mass transport rate, but nondimensional activation energy parameter has negative impact on Sherwood number. [ABSTRACT FROM AUTHOR]

Flow conditioners are widely utilized in pipeline systems to improve the precision of flow rate measurement in the pipeline systems of the offshore and subsea oil and gas industry. There is a lack of knowledge about the influences of the conditioners on the flow inside a bend pipe due to the measurement inaccuracy caused by geometries complexity. In this study, numerical simulations are carried out solving the three-dimensional Reynolds-averaged Navier-Stokes (RANS) equations with the κ--ω SST model to investigate the large-scale flow characteristics inside a double bend pipe and the performance of a conditioner with a bundle of 19 tubes. The obtained axial velocity inside a double bend pipe flow with no flow conditioner are compared with those of the previously published numerical simulations results and experimental data as the validation study. Helical flow structures are found behind the double bend and effectively removed by the flow conditioner. The performance of the flow conditioner is evaluated based on the axial flow velocity profiles, the swirl intensities and the deviation from the flow inside a straight pipe. The effects of Reynolds numbers and the lengths of the tube bundle on the flow downstream the flow conditioner are discussed. [ABSTRACT FROM AUTHOR]

Medical engineering is increasingly deploying nanotechnology and bio-inspired designs in the 21st century. Motivated by studying the spin coating of bio-nanofluid materials, gyrotactic bioconvection nanofluid swirling coating flow from a spinning disk to an isotropic permeable medium is analysed. The balance equations for mass, momentum, thermal, concentration and microorganism species including blowing effects are transformed into ordinary differential equations and then the solutions are obtained numerically through MATLAB bvp4c quadrature. These solutions are further validated with Adomian decomposition method (ADM). Increasing radial momentum slip reduces the radial skin friction and increasing tangential slip suppresses the tangential skin friction. Nusselt number, nanoparticle Sherwood number and micro-organism density number gradient are, respectively, decreased with increment in thermal slip, nanoparticle mass slip and micro-organism slip factors. Combinations of bioconvection and nanofluids provide excellent advantages in designing anti-bacterial and resilient bio-coatings for many devices. [ABSTRACT FROM AUTHOR]

The physical factors and conditions leading to the formation of stable vortex structures in internal turbulent swirling currents occurring in complex channels of various energy and heat exchangers are considered. The possibility of applying the theory of screw flows and the equation for the rate of helicity change to determine the critical conditions for the occurrence of a deterministic vortex structure of turbulent flows and to predict the effects of the occurrence of large-scale vortex formations in various elements of energy systems is substantiated. The phenomenon of the swirl flow crisis is described. It is shown that the use of thermodynamic stability analysis to describe complex vortex flows makes it possible to expand the applicability of mathematical modeling methods to describe the processes of formation of vortex structures. The results of computational and theoretical modeling of vortex formation processes during the flow of a swirl flow in pipelines of variable cross-section, which are elements of pipeline systems of a nuclear power installation, are presented. [ABSTRACT FROM AUTHOR]

Bidirectional vortex combustors are among the most efficient devices in terms of pollutants emission, fuel residence time, an extended range of stable operation. Despite many papers devoted to flow structure in the bidirectional chamber, their heat transfer and wall temperature distributions are not well-studied experimentally as well as most available calculation results are based on adiabatic or isothermal wall conditions. The present paper reports on new experimental and numerical results on flow and flame structures and surface temperature distributions obtained for a combustor with a toroidal vortex chamber. These results show a strong effect of the combustor operation mode and geometry configuration on its thermal conditions. Based on experimental validation, a reliable numerical approach for fluid dynamics, combustion, and heat transfer simulations in the bidirectional vortex chamber is suggested. This approach could assist in determining the most efficient parameters of the bidirectional combustor in terms of energy and environmental indicators as well as wall thermal conditions and service life. [ABSTRACT FROM AUTHOR]

Experimental study of unsteady swirling flows generated by special diverters in closed toroidal channels with different curvatures was carried out. The formation of a swirling flow in a toroidal channel is crucially different from the case of a straight cylindrical channel. It essentially depends on the curvature and is hindered by its increasing. The complex dynamics of swirling flow tightly connects with the interaction of jets after the diverter. Measurements of flow velocity using tracer's tracks showed that the evolution of the toroidal component in torus with one diverter can be divided into two-time intervals with different power laws. The evolution of the poloidal component is rather characterized by one slope "-2/3". [ABSTRACT FROM AUTHOR]

Heat transfer and flow resistance characteristics of a novel plate heat exchanger (PHE) with multi-chevron corrugate furrows have been studied experimentally and numerically for Reynolds Numbers (Re) ranging from 1200 to 5000. Numerical results obtained from 5 different turbulent models all show similar trends and good agreement with experimental values. Results indicate that the outlet temperature of the cold fluid, the heat transfer rate and pressure drops of both the cold and hot fluids decrease with an increase of Re. The opposite trends can be found for the outlet temperature of the hot fluid, while the friction factors of both the cold and hot fluids increase with increasing Re. Data obtained using the shear-stress transport k ∼ w (SST) model show the best agreement with experimental data and is recommended for PHE simulation. Hot temperature regions distribute mainly on the left side of the PHE as a result of the PHE flow arrangement, while cold temperature regions distribute on the right side; resulting in a "zigzag" flow pattern. Additionally, it also causes swirl flow to take place; creating an enhancement to heat transfer along with an increase to the pressure drop. [ABSTRACT FROM AUTHOR]

The strong increase in computational power observed during the last few years has allowed to use Large Eddy Simulation (LES) for industrial configurations. Nevertheless, the time-to-solution is still too large for a daily use in the design phases. The objective of this work is to develop a new time integration method to reduce the time-to-solution of LES of incompressible flows by allowing the use of larger time step. The projection method, probably the most commonly used method in the context of LES of incompressible flow, is generally applied using explicit time advancement which constrains the time-step value for stability reasons (CFL and Fourier constraints). The time step can then be small with respect to the physical characteristic times of the studied flow. In this case, an implicit time advancement method, which is unconditionally stable, can be used. However, this leads to non-linear resolution of momentum equation which can strongly increase time-to-solution because of non-linear iterations inside a physical iteration. To relax the stability constraints while minimising the computational cost of an iteration, a linearised implicit time advancement based on Backward Differentiation Formula (BDF) scheme is proposed in this work. The linearisation is performed using an extrapolated velocity field based on the previous fields. This time integration is first evaluated on a turbulent pipe test case. It is observed a time-to-solution up to five times lower than the explicit time integration while keeping the same accuracy in terms of mean and fluctuating velocity fields. To incorporate this new time advancement method in the automatic mesh convergence developed in Part I, a time-step control method based on the local truncation error is used. The resulting automatic time-step and mesh procedure is evaluated on a turbulent round jet case and on PRECCINSTA configuration, a swirl burner which is a representative case of an industrial aeronautical injection system. This new procedure leads to a time-to-solution up to three times lower than the previous procedure, presented in Part I. [ABSTRACT FROM AUTHOR]

With the constant increase of computational power for the past years, Computational Fluid Dynamics (CFD) has become an essential part of the design in complex industrial processes. In this context, among the scale resolving numerical methods, Large-Eddy Simulation (LES) has become a valuable tool for the simulation of complex unsteady flows. To generalise the industrial use of LES, two main limitations are identified. First, the generation of a proper mesh can be a difficult task, which often relies on user-experience. Secondly, the 'time-to-solution' associated with the LES approach can be prohibitive in an industrial context. In this work, these two challenges are addressed in two parts. In this Part I, an automatic procedure for mesh definition is proposed, whereas the Part II is devoted to numerical technique to reduce the LES 'time-to-solution'. The main goal of these works is then to develop an accurate LES strategy at an optimised computational cost. Concerning the mesh definition, because LES is based on separation between resolved and modelled subgrid-scales, the quality of the computed solution is then directly linked to the quality of the mesh. However, the definition of an adequate mesh is still an issue when LES is used to predict the flow in an industrial complex geometry without a priori knowledge of the flow dynamics. This first part presents a user-independent approach for both the generation of an initial mesh and the convergence of the mesh in the LES framework. An automatic mesh convergence strategy is proposed to ensure LES accuracy. This strategy is built to guarantee a mesh-independent mean field kinetic energy budget. The mean field kinetic energy is indeed expected to be mesh independent since only turbulent scales should be unresolved in LES. The approach is validated on canonical cases, a turbulent round jet and a turbulent pipe flow. Finally, the PRECCINSTA swirl burner is considered as a representative case of complex geometry. First, an algorithm for the generation of an unstructured mesh from a STL file is proposed to generate a coarse initial mesh, before applying the mesh convergence procedure. The overall strategy including automatic first mesh generation and its automatic adaptation paves the way to use LES approach as a decision support tool for various applications, provided that the 'time-to-solution' is compatible with the applications constraint. A second paper, referred as Part II, is devoted to the reduction of this time. [ABSTRACT FROM AUTHOR]

Several passive techniques can substantially improve the heat transfer performance of conventional heat exchangers. Passive methods persistently use heat transfer augmentation inside tubular sections, which tackle dominant thermal resistance. The thermal resistance in turbulent flow is primarily due to a thin viscous sublayer near the tube wall. This proliferates into the cross-section of the conduit in the case of laminar flows due to the existence of a relatively thicker boundary layer. This urges disturbance in the entire fluid throughout the cross-section in laminar flows, whereas augmentation devices are usually located close to the wall for turbulent flows. Most of these methods yield increased fluid residence time within the system by inducing swirling motion. The form of disturbance in the flow field is the characteristic of the passive technique used to prolong the fluid residence time and is exhibited differently in both flow regimes. The present article showcases a comprehensive review of heat transfer enhancement through thermo hydraulic performance assessment of these methods reported in the literature. The comparison is based on ratios of Nusselt numbers, first at the same Reynolds numbers, and then, at equal pumping power with constant heat transfer area. [ABSTRACT FROM AUTHOR]

The present study considers the effects of the electromagnetic field and pulsating flow on nanofluids heat transfer and flow characteristics in the three-start helically fluted tube. The experiments are performed using anofluids with the Reynolds number varying from 8000 to 13000, and with an Fe3O4/water nanofluids (Ferrofluid) concentration of 0.005% by volume with and without an electromagnetic field effect. The measured results are verified with the predicted results from the proposed correlations and the published experimental results. As a result of the disturbed flow boundary layer, higher swirling Brownian motion, higher local thermal conductivity, and the mixing of turbulent intensity, the heat transfer performance also increases. For a given pulsating flow of 30 Hz, the Nusselt number enhancement increases significantly to 137.7% and 156.7% for the helical depth ratios of 0.028 and 0.093, respectively. The helically fluted tube with a helical depth ratio of 0.093 and a helical pitch ratio of 0.93 yields the highest Nusselt number improvement. The Nusselt number under the electromagnetic field effect increases by 19.0% and 14.4% for the pulsating flow of 30 Hz and 20 Hz, respectively. Finally, a comprehensive evaluation index is applied to estimate thermo-hydraulic performance. It is found that the comprehensive evaluation index increases with the increasing Reynolds number at first and then decreases as the Reynolds number increases further. [ABSTRACT FROM AUTHOR]

In hydraulic turbines, either Francis or axial turbines, a high swirling flow is generated at PL conditions at the inlet of the draft tube resulting in the formation of a rotating vortex rope (RVR). This leads to pressure fluctuations which limit the operating range of single regulated turbines. In the present study, an axial hydraulic turbine has been numerically simulated by the k − ϵ and SST-based Scale-Adaptive Simulation model (SST SAS) turbulent models to capture helical RVR. Considering the formation of the RVR as the result of a global instability, linear global stability analysis of the time-averaged turbulent flow field has been conducted. For the first time in axial hydraulic turbines, how boundary conditions affect the unstable mode and which frequency, plunging or rotating, is related to the vortex rope instability have been studied. It is found that the flow inside the draft tube is sensitive to the asymmetrical disturbances with a frequency close to the rotational component. [ABSTRACT FROM AUTHOR]

The dry ice sublimation process of CO2 is a unique technique in which temperature ranges below the triple point of −56 °C can be achieved in a CO2 refrigeration system. However, during the evaporation process of the actual refrigeration system, the dry-ice blockage maybe happens in the evaporator, which causes a risk of system failure in the suction of the compressor. In order to overcome this problem, in this study, an ultra-low temperature CO2 cascade refrigeration system with a novel tapered evaporator/sublimator was designed and constructed. The novel evaporator/sublimator included a swirl promoter, which induces the swirling flow of solid-gas two-phase flow. Experiments were conducted for the investigation of solid-gas two-phase flow heat transfer characteristics in the evaporator/sublimator. According to the experimental results, it is verified that the CO2 refrigeration system can operate consistently and steadily without dry ice blockage in the evaporator/sublimator. In addition, the dry ice particles are uniformly distributed along the inner wall of the evaporator/sublimator by the installation of the swirl promoter, and the heat transfer coefficient is considerably improved. [ABSTRACT FROM AUTHOR]

Heat transfer enhancement is an essential parameter of heat exchangers, that can increase by increasing the value of heat transfer coefficient. So, researchers used different types of inserts, in which, single strip helical screw tape showed excellent enhancement in heat transfer, due to the formation of high-intensity swirl flow. However, to increase more intensity of swirl flow, Double strip helical screw tape inserts (DS-HST) used in present work. An experimental analysis is carried out to analyze thermal and friction factor characteristics of fluid flow in heat exchanger tube, with DS-HST, at twist ratio of 1.5, 2.5, and 3, in the range of Reynolds number from 4000 to 16000, at constant heat flux condition. Experimental results showed that Nusselt number and friction factor achieved excellent enhancement with double strip helical screw tape insert than single strip helical screw tape insert (SS-HST) with decreasing value of twist ratio. The correlation developed for Nusselt number at a range of Reynolds number, twist ratio and a number of strips. Moreover, Thermal performance factor achieved maximum value at twist ratio of 2.5 and 3 for DS-HST, than SS-HST inserts in the higher values of Reynolds number, at constant pumping power. So this range of turbulent flow showed the suitability of DS-HST inserts, which can reduce the size of heat exchangers or thermal applications, utilize energy resources, and decrease pollution in the environment. [ABSTRACT FROM AUTHOR]

The existing numerical research is concentrated on studying pressure drop, various velocity components, and heat performance behavior of heat exchanger pipe fitted with dimple on the inner pipe wall. Three-dimensional computational calculations using the CFD technique are conducted to study the influence of four geometrical parameters, including the distance between dimples, number of dimples, dimple diameter, and dimple pitch on the enhancement of thermo-hydraulic heat transfer. Also, the effects of the following parameters are optimized using the design of experiments (DOE) approaches combined with both Taguchi and Response Surface Methods. The results revealed different patterns of flow field and heat performance due to the use of dimples on the inner pipe surface. Moreover, utilized dimples can rise heat performance due to the interactions between the dimpled wall surfaces and swirling flow; hence, that can rise in area of heat transfer. Detailed flow analysis between dimples and pipe wall is demonstrated to describe the mechanisms of heat performance and pressure drop change. The orthogonal experiment outcomes revealed that the optimal design of the dimpled pipe has improved by about 35.75% and 36.1%. The numerical outcomes indicate that high value for the overall evaluation factor (PEF) is higher than 1. Based on the above findings, it can be found that hydrodynamic analysis flow, enhancement of heat transfer performance, and dimple optimization are required for different design applications. [ABSTRACT FROM AUTHOR]

The rate of diffusion-controlled corrosion of an annulus under swirl flow was studied by measuring the limiting current of the cathodic reduction of potassium ferricyanide depolarizer in the presence and absence of polyox WSR-301 drag-reducing polymer. It was found that the rate of diffusion-controlled corrosion of the inner cylinder of the annulus increases with increasing swirl flow solution velocity and decreases with increasing the active height of the cylinder. The data in the absence of polymer (blank solution) under swirl flow were fitted by a dimensionless equation. The importance of this equation in predicting the rate of diffusion-controlled corrosion and the corrosion allowance during the design of the swirl flow equipment was highlighted. For a given set of conditions, the rate of accelerated swirl flow corrosion was much higher than that of axial flow. Drag reducing polymer was found to inhibit the rate of diffusion-controlled corrosion by a maximum of 23%, if other benefits of the polymer are considered such as the decrease in the shear stress and the associated decrease in the erosion-corrosion tendency besides the decrease in pressure drop and pumping power requirement it may be concluded that the use of drag-reducing polymers in industry is worthwhile. [ABSTRACT FROM AUTHOR]

A fast RANS method for methane-air non-premixed combustion is proposed, using a k-ω SST model for turbulence, a transport species model for chemistry and eddy dissipation model for turbulence-chemistry interaction. The method is validated with experimental data from Sydney Swirl Flow and Flame Database. The same method is then used to simulate a two-dimensional axisymmetric combustor liner geometry, and finally a Design Exploration is proposed to optimize the Pattern Factor at the combustor outlet, obtaining the response surface for the entry variables, namely the Swirl Number and mass flows for each row of holes. An optimal combustor configuration is chosen. The results are then discussed and compared to similar works, showing the viability of the simplified CFD simulation and DoE optimization methodology. [ABSTRACT FROM AUTHOR]

Swirling gas flow is an important topic of research that helps in the design of rockets, atomizers,and gas turbine combustors. In the present work, swirl flow inside annular geometries with constant and varying cross-sectional areas are examined using computational fluid dynamics (CFD). Effects of changing the flow and geometric parameters on the swirl behaviour were studied. Reynolds number was found to increase the swirl number in straight and diverging cross-sectional geometries while no significant effect of Reynolds number was observed in converging cross-sectional geometry. Radius ratio, defined as the ratio of the inner to the outer radius of the annular geometry, was found to have a significant effect on the swirl number. Decreasing the radius ratio, in straight and diverging annular geometry decreases the swirl number, however, an opposite trend was observed in the case of converging annular geometry due to significant increase in axial velocity as a result of reduced cross-sectional area. Increasing the swirler vane angle increased the swirl number. At higher vane angles of 60° and 70°, a recirculation zone is developed near the exit of the swirler. Using small cone angles was found to lower the swirl decay rate in converging and diverging nozzles. [ABSTRACT FROM AUTHOR]

Swirling-flow nanobubble generator is an efficient hydrodynamic cavitation method that can continuously produce enormous quantities of bulk nanobubbles. However, the development of hydrodynamic models of nanobubble generation remains challenging and is rarely found in the literature due to the associated modeling complexity. In this work, a hydrodynamic model was developed to predict bubble size distribution in a swirling-flow type nanobubble generator using a combination of computational fluid dynamics (CFD) and population balance method (PBM). The proposed model was evaluated by considering several combinations of bubble coalescence, breakage, and turbulence models. The results show that the combination of the turbulence coalescence and Luo breakage models predicted better than any other model combination. The selection of appropriate turbulence models could improve the modeling accuracy. The standard k-Ω model provided better predictions than other turbulence models for high flow rates, while the standard k-ε model was more appropriate for low flow rates. The bubble number density was successfully predicted for a 30 min generation time. The turbulence dissipation rate influenced the bubble number density and mass transfer, and the results of simulation considering this relation corresponded to the experimental results. Therefore, the coupled CFD-PBM model can aid in the design of nanobubble generators using virtual prototypes and reduce the development costs required for broader applications. [ABSTRACT FROM AUTHOR]

A new rotational flamelet model with inward swirling flow through a stretched vortex tube is developed for sub-grid modelling to be coupled with the resolved flow for turbulent combustion. The model has critical new features compared to existing models. (i) Non-premixed flames, premixed flames, or multi-branched flame structures are determined rather than prescribed. (ii) The effects of vorticity and the related centrifugal acceleration are determined. (iii) The strain rates and vorticity applied at the sub-grid level can be directly determined from the resolved-scale strain rates and vorticity without a contrived progress variable. (iv) The flamelet model is three-dimensional. (v) The effect of variable density is addressed. (vi) The inward swirl is created by vorticity combined with two compressive normal strain components; this feature distinguishes the model from counterflow flamelet models. Solutions to the multicomponent Navier–Stokes equations governing the flamelet model are obtained. By coordinate transformation, a similar solution is found for the model, through a system of ordinary differential equations. Vorticity creates a centrifugal force on the sub-grid counterflow that modifies the molecular transport rates, burning rates, and flammability limits. Sample computations of the inward swirling rotational flamelet model without coupling to the resolved flow are presented to demonstrate the importance of the new features. Premixed, nonpremixed, and multi-branched flame structures are examined. Parameter surveys are made with rate of normal strain, vorticity, Damköhler number, and Prandtl number. The centrifugal effect has interesting consequences when combined with the variable-density field. Flow direction can reverse; burning rates can be modified; flammability limits can be extended. [ABSTRACT FROM AUTHOR]

Flow distortions from upstream combustors generate various and significant changes to the patterns of endwall heat transfer for an aircraft engine. In this study, to model engine-representative oncoming flows into the high-pressure turbine, turbulence and swirl generators are carefully designed at the inlet of a linear turbine cascade. Detailed heat transfer characteristics over the endwall are measured by using a steady thermochromic liquid crystal (TLC) method for various Reynolds numbers. Comparisons with a baseline case that has no upstream turbulence or swirl generators show that both turbulence and inlet swirl alter the heat transfer levels and distribution patterns, but their mechanism of action differs from one another. The turbulence alters the heat transfer by thinning the inlet boundary layer, while the inlet swirl generates the changed heat transfer due to the sweep effects of the swirl on the endwall, resulting in a much higher heat transfer enhancement than that by the turbulence. Additionally, the highest enhancement for both cases is found at the low Reynolds number of 1.0 × 105 and higher Reynolds numbers yield to a reduced enhancement. Specially, compared to the turbulence case, the enhancement by the inlet swirl drops much more rapidly, indicating that the inlet swirl effects have stronger links to the Reynolds number. [ABSTRACT FROM AUTHOR]

In the steam cracking industry of natural gas or naphtha, fouling of tubular heat exchangers by cokes is a major issue. This growing carboneous layer has two major negative effects: 1) it increases pressure drop and 2) reduces heat transfer from the tube wall to the processed fluid. Using the open-source Computational Fluid Dynamics software OpenFOAM, this study numerically investigates wall shear stress, pressure drop and heat transfer performances of swirl decaying flow generated by different elliptical cross-section twisted tube. One of the objectives is to determine if minor modifications of tube geometry can generate swirling flow which could enhance wall shear stress at a reduce pressure drop penalty. For a Reynolds number ranging from 10, 000 to 100, 000, it is shown that the investigated geometries could enhance heat transfer by 90% at an increased pressure drop of 128% which yields a Performance Evaluation Criterion (PEC) of 1.44. The comparison between the performances of the different geometries is carried out using a newly defined PEC based on the bulk temperature, along with the usual PEC. [ABSTRACT FROM AUTHOR]

Pre-swirl in the approach flow towards a pump leads to a decreased efficiency or even to malfunctioning of a pump. Especially for pumping stations with large rotodynamic pumps, the risk of malfunctioning should be minimized. For this reason, hydraulic investigations are performed prior to the construction of pumping stations to assess the amount of pre-swirl in the approach flow and if needed, to design local measures to decrease it. This article presents a test set-up of a simplified pump sump in which the pump performance characteristics are measured at a real pump for a wide range of predefined corotating and counterrotating swirl angles. The swirl angles are measured in a transparent model pump at scale 1:1 with a swirl meter at four bell diameters above the bell-mouth. The findings discussed in this paper provide insight in the relation between pre-swirl in the approach flow and pump performance. [ABSTRACT FROM AUTHOR]

Scroll vortex intakes are commonly used in water supply, drainage and sewerage systems. Water flows into the intake via an eccentric approach channel, forming a swirling vortex flow with a stable air core along the dropshaft. Previous design theories have largely been based on unjustified assumptions on the velocity and pressure distributions of the vortex flow at the intake bellmouth. To clarify these assumptions, a validated three-dimensional computational fluid dynamics model has been developed. Model predictions compare well with independent measurements of flow profile, velocity and air core size. While the vortex flow in the scroll chamber can be described by a free vortex with constant circulation equal to that at the inlet, the tangential velocity and the pressure distribution at the bellmouth outlet have to be approximated by a forced vortex. A revised theory is proposed, providing significant improvement to the prediction of air core sizes and head–discharge relationship. [ABSTRACT FROM AUTHOR]

The objective of the present research is to evaluate the effect of changing the length of the cylinder and cone such that the total cyclone length remains unaltered. For this purpose, five different cyclone models with increasing lengths of cylindrical section (Hc/D = 0.5, 1.0, 1.5, 2.0, and 2.5) have been considered. A comparison is made among different flow variables as well as the performance parameters. Unlike general engineering flows, cyclonic flows possess strong swirl, resulting in high streamlined curvatures and rapid change in strains that makes it anisotropic in nature. Therefore, we use the Reynolds stress model (RSM)—a closure model to Reynolds-averaged Navier-Stokes equation—to account for such anisotropies in the flow. The Navier-Stokes equations are discretized using finite volume methods and solved using commercial code Fluent. Conclusive results indicate that the collection efficiency, pressure drop, and tangential velocity are maximum for cyclone with Hc/D = 0.5 and minimum for Hc/D = 2.5. It has also been observed that at higher inlet velocities heavier dust particles accumulate near the cyclone roof, which may result in high rates of wall erosion. [ABSTRACT FROM AUTHOR]

Hydropower is a key energy conversion technology for stabilizing electrical power. When running at full load, a 3-D cavitation vortex rope develops in Francis turbines that acts as an internal source of energy and instability. 1-D models allow this phenomenon to be predicted and the range of safe operating points to be defined. These models involve three parameters: the mass flow gain factor, the wave speed and the second viscosity that must be calibrated. For the first time, the present work aims at identifying these parameters using 3-D URANS cavitating simulations. Two cavitation test cases are considered: a 2-D Venturi and a reduced scale model of a Francis turbine at full load operating conditions. RANS simulations allow the mass flow gain factor to be determined, whereas URANS simulations coupled with an optimization process allow the determination of the wave speed and the second viscosity. The new methodology shows its ability to identify the three parameters. [ABSTRACT FROM AUTHOR]

Supercritical water (SCW) as fluid with enough potential abilities such as high thermal efficiency can be replaced in water cooling systems. However, helical pipes are the most common type of swirl generators used for heat transfer enhancement, and their geometrical parameters contribute significantly to the compactness and efficiency of heat exchangers. In this study, for the Reynolds ranges of 8000–20000, a numerical study is performed to investigate SCW flow within circular tube, twisted oval tube and twisted multi-lobe tubes. Effects of such parameters as cross-section shapes and lobed numbers on heat transfer performance and flow physics of different spiral tubes were investigated. Results indicated SCW has a contradictory behavior with ordinary water. The results showed that twisted tri-lobed tubes had higher average Nusselt number than circular tube and twisted oval tube, which was 53% and 41%, respectively. Also in these tubes the larger radius of connecting arc and the smaller length of major axis conclude the higher amount like 4%-6% of heat flux due to the enhancement of swirling fluid flow in the pipe and the heat flux. By increasing the number of lobes, the swirling flow rate that is bounded by the lobes will increase. [ABSTRACT FROM AUTHOR]

This research focuses on the evaluation of the potential of conical strip inserts in absorber tube. Results of these experiment help in enhancing the heat transfer, friction, and thermal properties of parabolic trough collector. The novel design of conical strip insert produces swirl flows that boost the thermal properties of the parabolic trough collector. The heat transfer effect was found to be twist ratio dependent. Minimum enhancement in pressure drop due to the inclusion of inserts is observed. [ABSTRACT FROM AUTHOR]

Large-eddy simulation with the thickened flame model (LES/TFM) is conducted to simulate a three-dimensional dual swirl partially premixed methane/air gas turbine model combustor. Finite-rate chemistry is described by a skeletal chemical mechanism consisting of 16 species and 41 reactions. Flame sensors based on formyl radical (HCO) and chemical explosive mode analysis (CEMA) are proposed and implemented within the TFM framework. The two sensors are designed for multi-step chemical kinetic models to avoid thickening the low-intensity heat release rate (HRR) region. One-dimensional freely-propagating laminar premixed flames are first employed to assess the two new sensors. The HCO-based sensor can successfully avoid the low-intensity HRR region for lean flames, but can fail under fuel-rich conditions. The CEMA-based sensor can robustly avoid low-intensity HRR regions under both fuel-lean and fuel-rich conditions. A second test case using a hydrogen/air reheat burner further demonstrates the robustness of the CEMA-based sensor. The two new sensors are subsequently applied to the gas turbine model combustor, and effects of different flame sensors are studied. Baseline results from the HCO-based sensor are first compared with experimental measurements to validate the LES/TFM solver. The mean and r.m.s. velocity, temperature, and mass fractions of O 2 and CO agree reasonably well with the experiment, although the mixture fraction within the inner recirculation zone (IRZ) is under-predicted. The predicted mean and r.m.s. temperature and species profiles are comparable at most locations, except near the IRZ where the CEMA-based sensor predicts the largest fluctuations by only thickening the chemically explosive regions. After optimisation, only 15% of overhead in computational cost is imposed when the CEMA sensor is employed on-the-fly. Future work includes further reduction of the computational cost of the CEMA-based sensor. [ABSTRACT FROM AUTHOR]

Vortex is the dominant flow structure in hydro-energy machinery, and its swirling features are mainly determined by the rigid rotation part of vorticity. In this study, the rigid vorticity transport equation is proposed based on the vorticity decomposition. The vortex spatial evolution is described by the stretching term RST, the dilatation term RDT, the Lamb term RCT and the viscous term RVT. The shape change of a vortex tube is mainly affected by RST and RDT, while vortex production and dissipation are mainly reflected by RCT and RVT. Compared with the traditional vorticity transport equation, this new theoretical tool can distinguish between rigid rotation and shearing motion of local fluids, and it can better reveal the intuitive evolution characteristics of vortical structures. Two cases with clear engineering demands are analysed by using the transport equation, and the results show that it can provide a practical method for the analysis and control of vortical flows in hydro-energy machinery. [ABSTRACT FROM AUTHOR]

This study numerically investigates the combustion characteristics in a swirl burner for CO-H2 syngas by large eddy simulation. Firstly, experimental data are used to verify the applicability of the Boivin mechanism and the Sandia mechanism. The simulation results show that the Boivin mechanism predicts a more reasonable flame structure. Then, Syngas25, Syngas45, and Syngas100 (composed of 25%, 45%, and 100% H2 by volume, respectively) are set to numerically investigate the effect of hydrogen addition ratio on combustion characteristics by using the dynamic Smagorinsky model and the partially stirred reactor model. The detailed simulation data shows that the addition of hydrogen greatly influences the flame structure and flow field; with an increase in hydrogen addition, the flame length shortens, the temperature rises, and flashback caused by combustion induced vortex breakdown occurs. Furthermore, the precessing vortex core cannot exist stably in Syngas100, though it can be clearly observed in other cases. [ABSTRACT FROM AUTHOR]

Pre-swirl system is installed to minimize energy loss between the stationary and rotating parts of turbine secondary air system. Although various optimization studies were conducted to increase the pre-swirl efficiency, most of the studies were focused on a hole type pre-swirl nozzles. In this study, a vane type pre-swirl nozzle was optimized to increase mass flow rate and temperature drop for given boundary conditions. The system performance was analyzed by 3D CFD and the objective functions were used to maximize the discharge coefficient and the adiabatic effectiveness. After sensitivity analysis, seven design variables were chosen on the three planes of nozzle span-wise direction. The OLHD method was used to obtain the initial scattered test points, and the additional ones were supplied by the ALHD method. The Kriging model was constructed as the surrogate one, and refined iteratively until satisfying the convergence criteria between the estimated point and the CFD result. The optimized model improved the span-wise uniformity of the flow path and the discharge coefficient was increased by 2.57%, whilst the adiabatic effectiveness remained nearly constant. The performance was also analyzed for pressure ratio and off-design points, with the optimized model showing better performance at all boundary conditions. [ABSTRACT FROM AUTHOR]

Numerical modeling of turbulent impinging swirling jets involve complex flow physics that make their computation still very challenging. Thus, the literature on computational modeling of these nanofluid jets is really scarce, with most works on laminar impinging nanofluid jets or turbulent swirling/non-swirling air or water-only jets. In this paper a computational analysis of different configurations in the application of A l 2 O 3 nanoparticles to submerged high-Reynolds turbulent jet flows for cooling purposes is developed. Six volume fractions have been investigated ( ϕ = 0 , 2 , 4 , 6 , 8 and 10 % , which correspond to a Prandtl number of the nanofluid within the range P r n f ∈ [ 7 , 14.4 ]) along with two nozzle-to-plate distances ( H / D = 2 and 4) and several swirl numbers ( S = 0 , 0.16 , 0.27 , 0.45 , 0.77 and 0.83). The jet regime is fixed at a Reynolds number R e = 35,000. The computational study shows that the application of nanoparticles enhances forced convection for all the simulations carried out. However, the influence of swirl number and nozzle-to-plate distance is not that clear. Variations cause different effects on the performance. For instance, to vary the swirl intensity at large nozzle-to-plate separation has different effect than in short separations. Also, some ranges of variation of swirl may enhance heat transfer whilst others may worsen it. [ABSTRACT FROM AUTHOR]

In the context of emission-free electricity generation, the authors developed a novel hydrogen-oxygen combustor, which is based on swirl-stabilized combustion technology and steam dilution. Following previous burner characterization, the current study investigates the heat transfer conditions in the combustion chamber wall. To this end, a carefully controlled co-flow of air is used to cool the combustion chamber in an annular duct, which surrounds it. Temperature measurements enable the evaluation of the heat flux from the combustor flow to the walls, local wall temperatures, and the Nusselt numbers on the hot and the cold side. The extremely high wall temperatures, caused by the H2/O2 flame, can be reduced by steam dilution down to approximately 900 K. Even better cooling could be reached by using the dilution steam as the coolant before it flows to the plenum. The Nusselt numbers at the inner combustion chamber wall are in the order of 10–50 and increase with the thermal power and the steam dilution ratio. [ABSTRACT FROM AUTHOR]

Hydraulic characteristics of swirling flow at shaft spillways with an innovative inlet, namely the marguerite-shaped inlet, is investigated based on model experimentation. Detailed measurements of head–discharge relationship, flow regimes, water free-surface profiles, flow circulation, discharge coefficient and threshold and critical submergence depths were performed for shaft spillways with marguerite-shaped inlets. Results indicate that the strength of swirling flow through a marguerite-shaped inlet is significantly lower than that of a simple shaft and a morning glory spillway. Marguerite-shaped inlets increase the developed crest length by at least 6 times the global size of the original shaft spillway. Therefore, they produce exceptional hydraulic performances in increasing the weir overflow length without changing the global size of the shaft spillway, thereby increasing the flow discharge up to 6, 4 and 1.5 times the simple shaft, morning glory and circular piano-key spillways, respectively. Finally, based on the detailed experimental data, different empirical correlations are derived for estimating the threshold and critical submergence depths and discharge coefficient of the marguerite-shaped inlets for different flow regimes using regression analysis. [ABSTRACT FROM AUTHOR]

We present a systematic approach to extract the characteristic vortex region that contains the essential features of a complex flow field. The process involves the analysis of the complex eigenvalues of the velocity gradient tensor. In particular, we propose the analysis using the joint and marginal probability distributions of the complex eigenvalues of the velocity gradient tensor that preserves the sufficient swirling strength and the required orbital compactness of the swirling orbits defining the vortex region. We consider three complex flow scenarios for the application and the assessment of the proposed approach: (i) rotating Rayleigh–Benard convection, (ii) turbulent channel flow, (iii) turbulent flow field in a cylindrical cyclonic separator. While problem (i) is considered for the extraction of subsumed cyclonic structure, problems (ii) and (iii) are reminiscent of wall-bounded turbulent flows, relevant for different industrial applications. [ABSTRACT FROM AUTHOR]

Micromixers are being extensively used in micro total analysis systems (µTAS) and chemical processing. Passive micromixers are most preferable due to their robustness, ease of integration and low cost. However, it is difficult to achieve rapid mixing in passive mixers. Previous studies on passive T-mixer showed that convective effects at high Reynolds number improve mixing significantly. In the present study, a swirl component of velocity is imparted at inlets of T-mixer to enhance the convective effects. Numerical results have shown that the reverse orientation of the swirl (R-O-Swirl) in inlet channels favored earlier onset of engulfment regime which enhanced mixing at lower Reynolds number (66 < Re < 180). At high Reynolds number (Re > 266), swirl with same orientation (S-O-Swirl) in inlet channels increased the swapping of samples at junction which significantly improved mixing. Nearly three hundred to five hundred percent increase in mixing index is obtained with R-O-Swirl at 160 < Re < 180 and thirty to seventy percent increment with S-O-Swirl at 266 < Re < 372 as compared to T-mixer without swirl. Therefore, it is noted that the presence of swirl component at inlets can further enhance the engulfment regime and improve mixing efficiency of T-micromixer. [ABSTRACT FROM AUTHOR]

Numerical simulations were carried out to investigate the swirling decaying flow generated by a novel axial guide vane swirler with profiled blades and no supporting device in a tube and its effect on heat transfer and pressure drop compared to a developed turbulent flow in a no swirl tube. Reynolds number ranged from 10,000 to 200,000. Turbulence was modeled using a k − ω Shear Stress Transport model and a Low-Reynolds approach. The swirling flow enhances significantly the heat transfer locally especially in the developing swirling flow region and globally with an increase of Nusselt number from 1.57 to 1.34 respectively for Reynolds number of 10,000 and 200,000. Pressure drop is also increased up to 2.9 for a Reynolds number of 200,000, however this is relatively low compared to other axial guide vane swirler device encountered in the literature. Furthermore, the Performance Evaluation Criterion of the swirling flow is higher than 1 for both Reynolds number of 10,000 and 30,000. [ABSTRACT FROM AUTHOR]

The swirling flow is used to increase mixing and decrease nitrogen oxide emission in the combustor. Meanwhile, the swirling incoming flow has a significant effect on both aerodynamic and heat transfer characteristics of the downstream first-stage turbine. This paper conducts a numerical investigation on the influences of the inlet swirl core on the film cooling performance of a leading-edge model. Besides, the trenched holes are employed to improve the cooling performance under conditions of different swirl numbers and blowing ratios. The results show that the inlet swirl benefits the generation of downstream detrimental vortex structures and increases the mixing between coolant and mainstream. Although the trenched holes cannot absolutely change the flow patterns of swirling mainstream, they can guarantee the lateral spread of coolant and suppress the downstream coolant rotation. At different swirl numbers, the trenched cases all provide a better cooling performance, especially on the rows away from the stagnation line. Besides, the trenched cases show incremental cooling performance with the blowing ratio increasing from 1.0 to 3.0. However, for the round holes, the highest averaged cooling effectiveness is obtained at blowing ratio of 2.0, which is still lower than the trenched cases. [ABSTRACT FROM AUTHOR]

Accumulation of ice particles inside the pipes of an ice slurry refrigeration system is a problem that should be avoided to ensure the efficient performance of the system. In the present research, the swirling flow of ice slurry is numerically investigated using the Eulerian-Eulerian model coupled with the kinetic theory of granular flow. The swirling flow is generated by twisted tapes inserted into a smooth pipe. The results show that by swirling the flow, the ice particle diameter may be increased up to about three times larger than the typical particle diameter used in the ice slurry, without particle accumulation. Moreover, for the swirling flow of ice slurry with the ice particle diameter of 0.3 mm, the rate of mass transfer increases 25% while the ice volume fraction at the pipe outlet decreases 30%, compared to the non-swirling flow. Based on the obtained results of swirling flow, correlations for friction factor, mean Nusselt number, and performance parameter are proposed. [ABSTRACT FROM AUTHOR]

Lean-premixed combustion technology has been adopted widely for heavy-duty gas turbine application. The multiple-swirl structure might shorten the flame brush length and reduce emissions. However, the inlet flow cannot be set equally for each swirl burner. The inlet guiding ring structure should be carefully adjusted and validated to reach the design goal. This paper introduces a typical geometry of heavy-duty combustor, which is designed with multiple swirler structures. The inlet guiding ring is a semicircle type. The parametric analysis is trying to investigate the axial location of the inlet guiding ring effect on the downstream multiple-swirl flow structure. Computational results show that both the Counter-Swirl and Co-Swirl configurations possess quite well aerodynamics which can support the recirculation establishment and flame stabilization. As the axial distance between the inlet guiding ring and swirl nozzle increases from 16 mm to 37 mm, the width of the recirculation will increase, which intensify the turbulence mixing for the pilot and main stage. Meanwhile, the length of the recirculation also increases, and the turbulence intensity keeps relatively strong. When the gap distance increases from 37 mm to 51 mm, the flow phenomenon would return to the condition like the case with an axial distance equal to 16 mm. Therefore, the condition with the axial gap distance 37 mm is quite critical. Thus, the flow field is quite sensitive to the inlet guiding ring location. [ABSTRACT FROM AUTHOR]