Mixed Flow Research Articles

Analysis of Hydrothermal Flow and Performance of Heat Transfer in 3D Pipes Based on Varying Dimple Structure Configurations

ABSTRACTIn the current work, the study examines the flow patterns and heat transfer capabilities of tubes with various spherical dimple configurations. A numerical analysis, supported by experimental validation on a reference model, was conducted on a circular tube with an alternating flow path. The primary goal was to enhance the thermal performance of circular tubes by inducing mixing and vortex flows. The impact of three design factors on thermal–hydraulic performance was investigated, dimple pipe diameter (DPD), dimple group number (DGN), and number of dimples (NODs). Dimpled tubes consistently outperformed smooth tubes in heat transfer due to increased flow mixing and separation. Both increasing the Reynolds number and decreasing the design factors led to the formation of mixing and vortex patterns. The performance evaluation factor (PEF) varied across different dimple configurations. For DPD, PEF ranged from 1.14 to 1.33; for DGN, it ranged from 1.15 to 1.28; for NOD, it ranged from 0.95 to 1.21, all within a Reynolds number range of 4000–15,000. At a Reynolds number of 6000, all three configurations of DPD, DGN, and NOD outperformed the smooth pipe in terms of the Nusselt number. For DPD, Nusselt number improvements ranged from 25.7% to 30.8%, and friction factors increased by 21% to 67%. DGN configurations exhibited a wider range of Nusselt number enhancement from 25% to 49.6%, and friction factor increase from 37% to 72%. NOD configurations also demonstrated consistent improvements, with Nusselt number increases ranging from 27.35% to 31% and friction factor increases from 42% to 74%. Spherical dimples can significantly enhance the thermal–hydraulic performance of tubes, so the best configuration depends on the specific application, and the highest performance, with a 1.33 increase in PEF, was achieved with a dimple diameter of 2 mm (DPD = 2 mm) and a dimple density of four dimples per unit area (NOD = 4).

Application of oscillating elastic surfaces for heat transfer enhancement from heat dissipating electronic chips

The present study investigates the possibility of heat transfer enhancement from discrete heat sources by an oscillating elastic surface. The three liquid cooled heat sources are located on the bottom surface of a rectangular channel and are influenced by oscillation of the upper surface. Finite element simulations are carried out at several Reynolds numbers in the laminar flow regime for two different cases of oscillation by cosine and step loads with various periods and amplitudes. It is observed that oscillation of the channel surface alters the direction of the pressure gradient and causes backflow and several vortices along the channel. It also leads to the thermal boundary layer disturbance and flow acceleration on the heat sources and consequently intensifies the heat transfer. Results indicate that reducing the period of the oscillations improves the flow mixing and thus increases the heat transfer rate to an optimum value. Further decrease in the period has a reverse effect on the heat transfer enhancement. Maximum heat transfer enhancement of 223.4 %, 162.2 %, 137.8 %, and 150.5 % are obtained for Reynolds numbers of 200, 600, 1000, and 1400, respectively. It is worth mentioning that the heat transfer enhancement is achieved at the expense of a considerable pressure drop increase. The overall performance factor implies that the heat transfer enhancement dominates the pressure drop increase only at low amplitudes and periods of oscillations. Comparison between the cosine and step loads reveals that the cosine and step forces exhibit better heat transfer performance at low and high periods, respectively.

Levenberg–Marquardt back-propagation algorithm for a developing unsteady hybrid nanofluid mixed convective flow across a revolving sphere: irreversibility analysis

Levenberg–Marquardt back-propagation algorithm for a developing unsteady hybrid nanofluid mixed convective flow across a revolving sphere: irreversibility analysis

The Impact of Variable Viscosity and Variable Thermal Conductivity on the Mixed Convective Flow of Casson Nanofluid in a Channel with Chemical Reaction

A theoretical analysis has been conducted on the mixed convective Casson nanofluid flow in a vertical channel that contains a first-order chemical reaction. The energy equation takes into account the combined effects of variable viscosity and variable thermal conductivity and the viscous dissipation. Nanofluids have different nanoparticles such as Aluminum oxide (), Copper (), Silver (), Titanium oxide () and Iron oxide () are suspended nanoparticles in water () and Ethylene Glycol () as base fluids. The governing equations are solved by perturbation method analytically like the momentum, energy, and diffusion equations, semi-numerically using differential transform method and numerically using BVP5C method. The obtained numerical values are agreed well for all the three methods and is shown in tabular form. For each of the several governing factors, the contours of velocity, temperature, and concentration are shown graphically. Additionally, data is tabulated for skin friction, Nusselt number. The results found that the silver nanoparticles enhance the thermal conductivity considerably in the flow. The variable viscosity regulates the flow while the variable thermal conductivity suppresses the flow.

Numerical computations of magnetohydrodynamic mixed convective flow of Casson nanofluid in an open-ended cavity formed by earthquake-induced faults

Numerical computations of magnetohydrodynamic mixed convective flow of Casson nanofluid in an open-ended cavity formed by earthquake-induced faults

Outlining the impact of electro-osmotic force and mixed convection flow of EMHD nanofluid flow on the stretched cylinder: a computational layout

Abstract This research has focused on studying the electro-magneto-hydrodynamic (EMHD) nanofluid flow over a stretched cylinder in the presence of electro-osmotic force and mixed convection. This inquiry shows a novel approach through the use of thermophoresis and Brownian motion and nanofluid is comprised of water and copper nanoparticles. Similarity transformations simplified the mathematical model and produced nonlinear ordinary differential equations with suitable boundary conditions, which the MAPLE-21 software numerically solved using the RK-4 shooting criteria. Tables and graphs have been used to illustrate the impact of the key flow factors on Electric potential profiles, velocity profiles, temperature outlines, and concentration distribution. Following the physical deliveries, we have calculated the Sherwood number, Nusselt number, and skin friction. The electro-osmotic parameter diminishes the electric potential profiles and a dual effect occurs for the curvature parameter. The Nusselt number declined by 5.91 % for the electro-osmotic parameter but the Sherwood number enhanced by 30.7 % at a rate. The practical applications of this model shed light on thermal management in electronics and nuclear reactors, plasma physics, various chemical processes, filtration, separation, and fuel cells, as well as the manipulation of biological fluids in lubrication or medical devices.

Real-time executable platoon formation approach using hierarchical cooperative motion planning framework

While connected and automated vehicle (CAV) platooning holds promise for enhancing traffic efficiency and reducing energy consumption, we still lack efficient algorithms for guiding the local movements of CAVs to form a platoon on a road due to significant computational and control challenges. This study addresses this gap by designing a real-time executable Hierarchical and Recursive Platoon Formation (HR-PF) framework tailored to mixed flow traffic conditions that encompass both Human-Driven Vehicles (HDV) and CAVs. The HR-PF framework comprises three hierarchical mathematical models (modules) designed to optimize platoon formation while considering both macroscopic traffic conditions and microscopic traffic safety. Module-I formulates a mixed integer quadratic program to determine the timing, location, and state of platoon formation. It is further extended to a mixed integer nonlinear program so that we can also select the optimal size of the target platoon. Module-II designs a Hybrid State-Lattice Motion planner to generate optimal trajectory references for CAVs to approach the target platoon state, ensuring microscopic traffic safety. Module-III develops longitudinal and lateral controllers to enable CAVs to track trajectory references accurately. These models function recursively at varying frequencies to balance mathematical rigor with practical application. Numerical experiments demonstrate that HR-PF facilitates efficient platoon formation in real-time across diverse traffic scenarios and road geometries while sustaining traffic efficiency. Furthermore, the performance of platoon formation is affected by surrounding traffic density and CAV penetrations, with prompt formation observed under LOS C and D traffic environments and slightly more traffic impacts under LOS E and F. These findings provide robust support for exploring advanced platoon formation and platooning strategies for CAVs under complicated traffic environments.

Unsteady Flow Mechanism of Corner Separation Control Using Blade End Slots in a Highly Loaded Compressor Cascade

Abstract Blade end slots has been proved to be an effective method to suppress the corner separation, thereby improving the aerodynamic performance of compressor. The unsteady effects of blade end slots affiliated with a highly-loaded compressor cascade on corner separation control are investigated based on delayed detached eddy simulation under the Mach number of 0.59. The corner separation vortex structures between the datum blade and the end slotted blade are compared. The vortex topologies are markedly reorganized and suppressed by the blade end slots. Unsteady flow behaviors of separation vortex and the corresponding dynamic mechanisms are analyzed in both time and frequency domains. The interaction of the self-adaptive jet flow from the blade end slots to the corner separation flow results in smaller-scale vortices in the blade end region with a higher characteristic frequency. Consequently, the unsteady effects caused by corner separation vortices are significantly reduced in range and intensity through the enhancement of flow mixing and the rapid dissipation of corner separation vortices into larger-scale lower-frequency features. Furthermore, spatiotemporal features and dynamics of corner separation flow with blade end slot control are investigated using the enhanced dynamic mode decomposition method. Results show that the dominant unsteady flow behavior develops with better stability, and the intermittency of low-frequency and large-scale behavior is reduced via the blade end slot control.

Analysis of irregular heat source/sink of a stagnation-point flow toward a vertical plate induced by spherical hybrid nanofluids

Heat transfer technology is quickly increasing as a result of the demand for well-organised heating and cooling systems (HGS and CGS) in the necessary chemical, automotive, and aerospace sectors. Thus, the current study aims to observe mixed convective flow of a Williamson fluid near the stagnation point in the presence of hybrid nanoparticles (Al2O3 and Cu) across a vertical flat plate with the Hall effect. The water-based alumina (Al2O3) and copper (Cu) nanoparticles that have been convectively heated are evaluated for their suitability in industry. The primary equations are non-dimensionalized employing the relevant similarity factors before being solved numerically by the bvp4c solver in MATLAB software. We examine the impacts of several pertinent parameters on transverse and axial velocities, drag force, temperature, and heat transfer. In the case of opposing flow, two different outputs are obtained, whereas just one is procured in the case of assisting flow. The impact of Lorentz force can also be used to alter the flow and physical properties of heat transfer.

Capacity modeling for mixed traffic with connected automated vehicles on minor roads at priority intersections

ABSTRACT As connectivity technology advances, connected automated vehicles (CAVs), connected vehicles (CVs), and regular vehicles (RVs) form mixed traffic traffic at priority intersections. This paper presents an analytical capacity model to evaluate the impacts of such mixed flow on minor roads. We define two platoon types based on the leading vehicle: CAV-led and CV/RV-led platoons. Assuming headway distribution on the major roads follows the M3 distribution, we derive probabilities of these platoons passing through the intersection during a single time gap on a major road. According to the expected probabilities of different vehicle types, the probabilities of these two types of platoon configurations are obtained. Based on this, we establish a mixed traffic capacity model. The capacity model’s effectiveness is validated through numerical experiments. The results demonstrate that the proposed model can analyze the impacts of key factors on mixed traffic capacity, including CAV penetration rate, CV proportion, traffic volume on major roads, and vehicle headway. HIGHLIGHTS Propose an analytical capacity model for mixed traffic on minor roads at priority intersections. Conduct numerical experiments to validate the effectiveness of the proposed mixed traffic capacity model. The proposed model can be applied to evaluate the capacity impacts of connected automated vehicle penetration rate, connected vehicle proportion, traffic volume on major roads, and vehicle headway at priority intersections.

Experimental and simulation study of pounding tuned mass damper on jumper flow induced vibration

Subsea jumpers carrying gas-liquid mixed flows can experience flow-induced vibration (FIV), potentially shortening their service life. The pounding tuned mass damper (PTMD), impact at the viscoelastic boundary can be used to dissipate energy. This paper focuses on a rigid m-shaped jumper to evaluate the specific damping effects of PTMD on the jumper under gas-liquid flow. Three PTMD configurations with significant damping effects are tailored based on the natural frequency of the jumper. Vibration tests are carried out to assess the damping effectiveness of each configuration, and the most effective PTMD is selected. Subsequently, the damping efficacy of PTMD on FIV within the jumper under varying flow conditions is investigated using both experimental methods and numerical simulations (VOF and FIS model). The results show that PTMD has obvious damping effects on free vibration and the main frequency and high-frequency jumper vibrations caused by FIV. Subsequent to the installation of PTMD, a substantial reduction in displacement has been observed across all components of the jumper. The suspension span exhibits the most pronounced decrease, exceeding 60%, while the displacement at the elbow joint is reduced by over 40%.

Analytical Investigation on Flow Reversal in a Fully Developed Steady Mixed Convection Flow With Boundary Condition of the Third Kind

ABSTRACTThis work presents exact solutions to analyze the effect of the Biot number on mixed convection flow in a vertical channel with asymmetric heating and flow reversal. The equations governing flow formation and temperature distributions are offered with convective boundary conditions. Closed‐form solutions for temperature, velocity, and skin friction are found and simulated graphically.

Developing a jam-absorption strategy for mixed traffic flow at signalized intersections using deep reinforcement learning

ABSTRACT Jam-absorption driving (JAD) can effectively prevent the generation and propagation of traffic oscillation. To alleviate the traffic congestion in the signalized intersection with mixed traffic flow, including human driving vehicles (HDVs) and connected and automated vehicles (CAVs), this study provides a jam-absorption driving strategy based on the traffic delay prediction of the mixed platoon under traffic congestion. An online traffic congestion prediction method with the objective of JAD is proposed and focuses on the leaving state of the trajectory to achieve fast capture of congestion features. Then, with real-time status and prediction information, we develop a Jam-absorption driving strategy based on a deep reinforcement learning (DRL) model to improve adaptability to the mixed traffic environment. The results show that this strategy can suppress more than 70% of traffic oscillations with excellent execution efficiency, improving traffic safety and efficiency.

Numerical study of an electrically conducting nanofluid flow past a vertical stretching Riga plate

The heat and mass transfer through electrically conducting and mixed convective nanofluid flow across an elongating Riga plate is studied. Riga plate is an electromagnetic sheet, in which electrodes are assembled alternatively. The arrangement of Riga plate produces electromagnetic behavior in the fluid flow. In the current analysis, the influence of Arrhenius activation energy, viscous dissipation and heat source/sink over the surface of Riga sheet is considered. The heat and mass transfer are examined by convective boundary conditions and nanoparticles (NPs) zero-mass flux. The Brownian motion and thermophoretic diffusion of fluid molecules are applied via Buongiorno's approach. Von Karman's similarity approach is implemented to reset the modeled equations into the dimensionless form of ordinary differential equations (ODEs). The system of ordinary differential equations is solved numerically via PCM (parametric continuation method). The fluid velocity, temperature field, and concentration gradients are analyzed by varying various flow parameters and graphically portrayed. The numerical results are validated by comparing them with the published studies. It can be resolved form the results that the flow rate decilnes with the effect of power index m, whereas enhances with the consequence of Hartmann number. The significance of thermophoresis term augments the temperature curve of the fluid.

Evaluating the mixed convection flow of Casson fluid from the semi-infinite vertical plate with radiation absorption effect

This study examines a steady laminar Casson fluid flow induced by a semi-infinite vertical plate under the impact of the Darcy-Forchheimer relation and thermal radiation. The features of mixed convection, cross-diffusion, radiation absorption, heat generation, chemical reactions and viscous dissipation are also considered to explain the transport phenomenon. The resultant system of equations, concerned with the problem under consideration, is transformed into a group of non-linear ordinary differential equations (ODEs) by means of similarity variables. The bvp4c method, an instrument popular for its numerical accomplishments, is utilized to solve this problem. The effect of flow parameters on heat transfer, concentration and velocity is evaluated via diagrams. To validate our code, we have compared the present outcomes to the prevenient literature, and stable consent has been detected. Moreover, the friction coefficient Cfx, Nusselt number Nux, and Sherwood number Shx are also computed to assess velocity gradient, efficiency of heat transfer and mass transfer process, respec-tively.

Temperature-dependent density effects on oscillatory mixed convective flow across a non-conducting horizontal circular cylinder embedded in a porous medium

Temperature-dependent density and aligned magnetic field influence on mixed thermal convection heat and current density aspects over a non-conducting porous circular horizontal cylinder is the novelty of this investigation. The magnetic effects over the surface are minimal but maximum away from the surface. The density of the fluid is assumed as an exponential variable of temperature to record the heat and current density rates. The pertinent form of partial differential equations is designed using suitable dimensionless quantities. The computational outputs of fluid velocity, magnetic fields and temperature variations are drafted using fluctuating-stokes quantities. The primitive quantities are utilised to make similar and asymptotic programs in FORTRAN for geometrical and numerical outcomes. The transient and oscillating behaviour of gradient values is sketched by using steady results in the oscillating formula. The finite difference methodology is applied to examine the physical properties with the Gaussian elimination matrix scheme. Effects of buoyant force ( λ ), Prandtl (Pr), magnetic force ( ξ ), density factor ( m ) and MHD Prandtl factor ( γ ) on the thermal behaviour of magneto-hydrodynamic analysis are applied. Results are explored around three angles π / 6 , π / 3 , π of the cylinder. Increasing magnitude in fluid velocity is deduced with high amplitude as porosity, buoyant and density parameters are enhanced.

Validation through internal flow physics of response surface methodology optimized mixed flow pump as turbine

In order to determine the optimal working efficiency of mixed flow pumps as turbine (MF-PAT) under a design condition of 10m3kw, this study takes the number of blades, blade wrap angle, impeller outer diameter, and impeller inlet width as design variables. Based on the center combination design method, experimental scheme design is carried out, and the head, shaft power, and efficiency of the turbine are used as evaluation indicators. A response surface model is constructed for optimization analysis, and the optimal geometric parameter combination of the impeller for MF-PAT is determined. For MF-PAT with forward-curved blade impeller in this paper, the optimal parameter combination is recommended as blade number Z = 6, blade wrap angle α = 47°, impeller outer diameter D2 = 140 mm and impeller inlet width b2 = 34 mm. The results show that compared with the original scheme, its efficiency has increased by 7.8 %. The established response surface model can reflect the relationship between evaluation indicators and design variables, and can be used for optimizing the geometric parameters of MF-PAT impellers. It can effectively enhance the blade's constraint ability on liquid flow, reduce hydraulic losses, and improve the performance of MF-PAT. Apply the ns-ds methodology for this and future mixed flow optimized pumps as turbines.

The effects of communication topology on mixed traffic flow: modelling and analysis

This paper aims to evaluate the combined impact of the communication topology (CT) and vehicular spatial distribution (SD) on mixed traffic of human-driven vehicles (HDVs) and connected and autonomous vehicles (CAVs). A generalized car-following (CF) model is presented to capture mixed traffic dynamics, integrating the effects of the CT, human reaction time, information delay and the optimal velocity changes with memory. Then, the linear stable condition of the model is derived using the perturbation method. Finally, extensive simulations are conducted under different CTs (i.e., multiple-predecessor leader following (MPLF) topology, predecessor following (PF) topology, and predecessor-leader following (PLF) topology) and six kinds of SDs. The results reveal that the MPLF topology demonstrates the best steady performance (i.e., stability) and dynamic performance (i.e., smoothness), and that the SD where CAVs are concentrated at the front of the traffic flow shows superior dynamic performance.

Parametric influences on flow, heat transfer, and nutrient transport in the knee joint cavity, a numerical approach

A novel aspect of this study is the investigation of the impact of temperature-dependent Arrhenius reactions and metabolic heat generation on the overall heat transfer within a knee joint cavity. This is a unique contribution where the interaction between thermal effects and metabolic activity is shown to influence the transport of nutrients and the removal of waste products. For the first time, the study also aims to examine the influence of key non-dimensional numbers on the characteristics of mixed convection flow, providing new insights into the dominant physical mechanisms at play. An innovative feature of the model is the incorporation of a non-linear reaction term to address the balance between protein synthesis and degradation. By integrating both thermal and biochemical dynamics, this approach offers a comprehensive analysis of protein aggregation in the knee joint, with potential implications for understanding and treating joint diseases, particularly those related to the health of synovial fluid and cartilage, such as osteoarthritis. The findings have the potential to inform the development of improved therapeutic strategies for managing these conditions. In the context of knee joint cavity dynamics, a low Cauchy number Ca plays a crucial role in ensuring steady and laminar flow, which reduces inertia and ensures that the continuity equation is satisfied. This laminar nature of the flow is essential for maintaining stable synovial fluid movement within the cavity, which aids in the smooth transport of nutrients and waste products. Additionally, higher Peclet number Pe values indicate an increased dominance of convective transport over diffusion, thereby enhancing the supply of essential nutrients to cartilage and bone, while also facilitating the removal of waste products and inflammatory mediators. This efficient convective transport mechanism is vital for the overall health of the joint and for mitigating inflammation. Furthermore, the Zeldovich number β significantly influences the temperature sensitivity of the Arrhenius reaction term within the cavity, where higher values reflect increased reactivity to temperature changes. This temperature dependence impacts metabolic heat generation and protein dynamics, further influencing the biochemical processes that occur within the joint. Collectively, these non-dimensional parameters highlight key aspects of synovial fluid dynamics, nutrient transport, and biochemical reactions that are essential to the functioning and health of the knee joint.

Analysis of fluid forces impacting on the impeller of a mixed flow blood pump with computational fluid dynamics.

This study presents four different impeller designs to compare hydrodynamic forces. Numerical simulation studies are performed via computational fluid dynamics to specify and investigate the hydraulic forces impacting the impeller of the mixed-flow blood pump with a volute. The design point of this pump is that the flow rate is 5 L/min, the rotational speed is 8000 rpm, and the manometric head is 100 mmHg. The designed impellers are placed in the same volute and simulation studies are performed with the same mesh size (17.3 million cells) of the pumps. The simulation studies have been conducted in setting 1050 kg/m3 blood density, 35 cP fluid viscosity, and SST-kω turbulence model. Additionally, this study examines the changes in hydraulic forces and hydraulic efficiency with fluid viscosity. As a result of experimental simulation studies, the highest hydraulic efficiencies of 40.87% and 39.5% are achieved in the case of the shaftless-grooveless and shafted-grooveless impeller, respectively. The maximum axial forces are obtained from the pump with the shaftless-grooveless impeller. Whereas radial forces, maximum values are calculated in the pump with the shaftless-outer groove impeller for all flow rates. Finally, the wall shear stresses, which are important for blood pump designs, are evaluated and the maximum value of 227 Pa is observed in the pump impeller with a shaftless-grooved.