Reynolds Number Flow Research Articles

Predictions of windage heating and flow characteristics in a high-speed rotating seal of aero-engine

The labyrinth seal plays a crucial role within the secondary air system of an aeroengine, significantly impacting its safety and reliability. This paper presents a comprehensive evaluation of the complex windage heating phenomenon within a high-speed rotating labyrinth seal system. Employing similarity criteria and dimensional analysis, the multifactorial influences on the seal system are thoroughly characterized. A dedicated high-speed rotating labyrinth seal test rig was constructed to conduct an experimental investigation into the windage heating characteristics of a four-tooth, stepped-slanted labyrinth seal. The results demonstrate a peak windage heating of 11.8 K and windage heating coefficient of 1.14 when the inlet temperature rose from ambient to 100 °C, under the rotating Mach number of 0.418 and pressure ratio of 1.1. Conversely, as the seal clearance increased from 0.2 mm to 0.6 mm, with a rotating Mach number of 0.487 and a pressure ratio of 2.0, the windage heating coefficient decreased to 0.57. Furthermore, five dimensionless operating cases were analyzed using similarity principles to elucidate the correlation between system performance and the combined effects of strong rotating flow and windage heating characteristics. The analysis revealed that the windage heating coefficient exhibited a decreasing trend with increasing flow Reynolds number, effective pressure ratio, inlet swirl ratio, and dimensionless clearance, as the effective pressure ratio increase from 1.1 to 5.0, with the rotating Mach number of 0.624 and flowing Reynolds number of 9600, the windage heating coefficient decrease from 1.831 to 0.797, representing a 56 % reduction. Conversely, the windage heating coefficient increased with a rising rotating Mach number, while the flowing Reynolds number demonstrated a minor influence.

Sedimentation of short-lived fluid-solid suspensions

In this study, we propose a particle sedimentation/aggradation law for homogeneous concentrated suspensions. This law, valid in the Stokes flow regime, can be used to describe the sedimentation process observed in short-lived rapid flows, developed at high Reynolds numbers, that can be described as low-viscosity quasi-parallel flows traveling at constant velocity and that progressively sediment during the dominant phase of transport to leave a triangular or trapezoidal deposit of constant slope. The particle aggradation velocity can thus be predicted from the product of the mean flow velocity and the deposit slope and turns out to be roughly similar to that measured from static suspensions of the same concentration, provided that the flow Reynolds number, based on the mean flow velocity, the fluid properties, and the particle size, remains inferior to a few hundred, such as the mixture agitation cannot disturb the sedimentation process. These important results provide the possibility of describing the depositional dynamics during the final stage of extreme events, as well as to infer the mixture rheology, from physical parameters that can be easily measured in the field.

Spatiotemporal structure of flow field by a dielectric-barrier-discharge plasma actuator using phase-resolved particle image velocimetry

A typical dielectric-barrier-discharge plasma actuator (DBD-PA) operating in continuous mode generates a self-similar starting vortex followed by a quasi-steady wall jet. In the burst mode, it generates periodic vortices, leading to a spatially wider mean flow field. The characteristics of periodic vortices can be controlled by adjusting the duty cycle α and burst frequency fb of the actuation signal. In the present study, the flow field generated by the actuator in burst mode is studied for 50%≥α≤90%, and 10 Hz ≥fb≤90 Hz. The Reynolds number of mean flow based on the maximum induced velocity and jet half-width ranges from 171 to 524. High-speed laser-sheet visualization and time-resolved particle image velocimetry are used for flow field measurements. The flow field generated during burst mode operation shows the strong influence of the burst frequency. Periodic vortices with comparable size and convection speed of starting vortex are generated at low fb. Dipoles and small-scale vortices are formed at moderate fb similar to the behavior of a transitional wall jet. Kelvin–Helmholtz instability is observed at higher burst frequency. An ornamental vortex consisting of several small periodic vortices is formed at high values of fb during the starting period. Based on the temporal evolution of momentum, the flow field generated by the DBD-PA can be classified into (i) starting flow regime, (ii) transitional flow regime, and (iii) periodic flow regime. The self-similarity of the mean flow field generated by the DBD-PA is verified by comparing the mean velocity profile at multiple downstream locations with the self-similar solutions of laminar and turbulent wall jets. The entrainment coefficient of the mean flow field is similar to that of an axisymmetric turbulent wall jet. The bi-orthogonal analysis shows that both coherent mode energy content and the entropy are minimum (about 5% only) for the continuous mode actuation. For the burst mode actuation, both the coherent mode energy content and the entropy are higher in magnitude compared to that of continuous mode and decrease with increasing burst frequency. The vortices in the periodic flow regime are locked in with fb. The distance between subsequent vortices, λx and flow frequency, f follow a power-law relationship, λx=cf−n, where c is a constant and n can be approximated as 2/3.

Experimental and machine learning study on the influence of nanoparticle size and pulsating flow on heat transfer performance in nanofluid-jet impingement cooling

Maximizing heat transfer efficiency is crucial for enhancing performance and durability in diverse engineering applications, including fuel cells, EV batteries, and solar PV/T systems, thereby advancing sustainable energy innovation. This study investigates thermal dissipation from a simulated heat sink aligned with a PV cell’s back plate via jet impingement cooling. Specifically, it examines the impacts of pulsatile cooling and nanoparticle size in hybrid nanofluids, comprising combinations of Al2O3 and MWCNT in water, with varied nanofluid volume fraction (0.05 vol% ≤ ɸ ≤ 0.3 vol%) and flow Reynolds number (15000 < Re < 40000). Key findings reveal significant influences of nanoparticle size, nanofluid concentration, and pulsating flow on heat transfer performance. Notably, sample D demonstrated the highest heat transfer enhancement, achieving approximately 52.94 % and 79.06 % improvement in continuous and pulsating jet cooling compared to de-ionized water under continuous jet cooling. Machine learning classifiers were employed to identify critical thermal performance parameters, with Reynolds number identified as the most significant factor influencing heat transfer. Random Forest and Gradient Boosting classifiers showed notable accuracy in predicting Nu, emphasizing the role of machine learning techniques in optimizing thermal management strategies for improved heat dissipation from solar PV cell backplates.

Design, experimental optimization, and flow analysis of a novel bioreactor for dynamic mammalian cell culture at laboratory scale using Box-Behnken design

Improving the quality of dynamic cell culture in laboratories is an important field in bioengineering. In this study, a novel lab-scale bioreactor using a vibrating agitator and a modified flask has been introduced to create a strong mixing at low shear stress. This bioreactor has been optimized using Box-Behnken design based on three dimensionless important structural factors including disc diameter, vibration amplitude, and the height of the disc placement. Three growth indicators including the specific growth rate, the natural logarithm of the maximum cell density, and productivity have been considered as biological responses. The results show that the disc diameter has the most important role in these indicators. If the disc diameter, vibration amplitude, and the height of disc placement are set to 0.24, 0.02, and 0.4 of the flask diameter, respectively, the values of the specific growth rate, the maximum cell density, and productivity at this optimum settings are 0.033 (h−1), 13.11, and 5133 (cells/(mL.h)), respectively. These values of the indicators are high and indicate the better performance of this bioreactor than other lab-scale bioreactors. In addition, investigating Reynolds number in the fluid flow indicates that in the range of 780 up to 1150, growth indices are high.

EXPERIMENTAL INVESTIGATION AND CFD SIMULATION OF THE ORIFICE FLOW METER TO MEASURE TWO-PHASE FLOW

In this study, an investigation is conducted to examine various methods for measuring the two-phase flow of water and air. The two-phase flow loop and its equipment, including the orifice flow meter, were designed and manufactured in accordance with relevant standards. By employing the orifice flow meter in the two-phase flow loop and determining the total mass flow rate of the two-phase flow passing through it, the pressure drop of the orifice flow meter was determined for different values of the flow rate and volume fractions of the water and air phases in the two-phase flow. The Reynolds number of the two-phase flow ranged from 700 to 11000, while the air volume fraction ranged from 10% to 45%. We observed that, for the orifice flow meter, the slope of the discharge coefficient variation in relation to the two-phase flow Reynolds number was higher at low Reynolds numbers, where a laminar flow pattern was established. As the two-phase flow Reynolds number increased, the flow pattern transitioned from laminar to plug flow, resulting in a decrease in the slope. The orifice flow meter under two-phase flow conditions was simulated using computational fluid dynamics (CFD) with different turbulence models. The results indicated that the k-epsilon RNG turbulence model yielded more accurate results compared to other turbulence models. This study provides a foundation for the measurement of two-phase flows in the oil and gas industries.

Drag reduction utilizing a wall-attached ferrofluid film in turbulent channel flow

This study explores the application of a wall-attached ferrofluid film to decrease skin-friction drag in turbulent channel flow. We conduct experiments using water as a working fluid in a turbulent channel flow set-up, where one wall is coated with a ferrofluid layer held in place by external permanent magnets. Depending on the flow conditions, the interface between the two fluids is observed to form unstable travelling waves. While ferrofluid coating has been previously employed in laminar and moderately turbulent flows (Reynolds number $Re&lt;4000$ ) to reduce drag by creating a slip condition at the fluid interface, its effectiveness in fully developed turbulent conditions, particularly when the interface exhibits instability, remains uncertain. Our primary objective is to assess the effectiveness of ferrofluid coating in reducing turbulent drag with particular focus on scenarios when the ferrofluid layer forms unstable waves. To achieve this, we measure flow velocity using two-dimensional particle tracking velocimetry (2D-PTV), and the interface contour between the fluids is determined using an interface tracking algorithm. Our results reveal the significant potential of ferrofluid coating for drag reduction, even in scenarios where the interface between the surrounding fluid and ferrofluid exhibits instability, with observed drag reduction rates up to 95 %. In particular, waves with an amplitude significantly smaller than a viscous length scale positively contribute to drag reduction, while larger waves are detrimental, because of induced turbulent fluctuations. However, for the latter case, slip outcompetes the extra turbulence so that drag is still reduced.

Study on the motion characteristics of Janus based on the squirmer model in the flow

The motion characteristics of Janus in the flow are studied numerically using the lattice Boltzmann method based on the squirmer model. The effects of velocity ratio J on the right and left hemisphere surface of Janus, particle Reynolds number Rep, flow Reynolds number Rec, initial orientation angle φ0 on Janus trajectory, and lateral equilibrium position yeq/H are analyzed. The results showed that, for the motion of Janus in stationary power-law fluids in a channel, Janus moves randomly in a small space in shear-thickening fluids when Rep is low and exhibits three motion modes at Rep = 5. The larger the J value, the easier it is for Janus to reach yeq/H. The higher the Rep, the closer the yeq/H is to the lower wall. In shear-thinning fluids, the motion of Janus exhibits significant randomness at Rep = 0.5 and 1, reaches the same yeq/H at Rep = 2 and 3, and tends toward yeq/H near the centerline and along the upper wall, respectively, at Rep = 4 and 5. For the motion of Janus particles in a channel flow of power-law fluids, in shear-thinning fluids, no matter what value J is, Janus reaches yeq/H on the centerline. The lower the Rep, the closer the yeq/H is to the wall. Two particles move toward yeq/H when Rep ≥ 1. The higher the Rep, the closer the yeq/H is to the centerline. The two particles will exhibit the upstream mode at Rep = 2. Two particles eventually reach yeq/H at different Rec. When φ0 &amp;gt; 0°, the two particles first eventually tend toward yeq/H = 0.2 and 0.8. When the value of φ0 is negative, the larger the absolute value of φ0 and higher the Rep, the more likely particles are to exhibit upstream mode.

Effects of a spoiler attachment on the wake flow of a bed-mounted horizontal pipe

This research investigated the spatial flow field of a pipe with a spoiler attachment and the modifications in the wake flow field of a bed-mounted horizontal pipe due to the attachment of a spoiler to the pipe for two different approach flow conditions. To attain the above-mentioned objective, the spatial evolution of the mean and turbulence flow properties in the flow field of the cylinder with an attached spoiler was determined. In addition, the mean flow and turbulence properties of a pipe without a spoiler attachment were compared with the properties of a pipe with an attached spoiler of height 0.2 D. For this purpose, two approach flow Reynolds numbers based on the pipe's diameter (D) and the free-stream velocity (U∞), Re∞ = 8850 and 11650, were considered. Three-dimensional (3D) velocity measurements were recorded with an acoustic Doppler velocimetry (ADV) between locations 4 D upstream (u/s) and 12 D downstream (d/s) of the pipe. It is observed that the length of the recirculation region is increased extensively due to the spoiler on the pipe from 6 D and 6.4 D to 10.7 D. The peak streamwise velocities for both Reynolds numbers are located near the free-water surface, as separated flows are deflected upward and result in enhanced free-stream velocities, which are higher than their approach flow free-stream velocities. In addition to that, the strength of the backflow is enhanced by 23% due to the attachment of the spoiler as compared to that of the pipe without the spoiler. The streamwise and vertical turbulence intensities are increased by 24% and 36%, respectively, and the wake flow field is found to be highly anisotropic. The streamwise turbulence intensities, Reynolds shear stress (RSS), turbulent kinetic energy (TKE), and turbulence indicator are attaining their peaks near the top level of the spoiler in the wake region. The triple velocity correlations indicate that the switching of sweeps and ejection events takes place near the top level of the spoiler. Therefore, it can be concluded that the spoiler attachment has increased the turbulence level in the wake region, and their highest magnitudes are located near the top level of the spoiler.

Nusselt Number and Friction Factor Characteristics of Two Pass Solar Air Collector Provided with Double Sided Roughened Absorber Plate

Thermal efficiency of flat collector surface solar air heater (SAH) is relatively poor due to poor heat transfer coefficient. This article’s primary objective is to evaluate the heat transfer and pressure loss characteristics of counter flow SAH (CFSAH) by adopting novel discrete multi-V-shaped and staggered rib geometry. The experimentations are performed for various flow Reynolds number (Re) ranging from 3000- 21000 and rib parameters including relative gap distance (Gd /Lv) from 0.24 -0.69 and relative gap width (g/e) from 0.5-1.5 while other parameters are kept as constant. The study revealed that the maximum increment in heat transfer as 4.52 times and friction factor as 3.13 times as compared to non-roughened duct has been obtained. Further, the thermohydraulic performance parameter (TPP) has also been investigated to obtain the optimum parameters. The minimum and maximum value of TPP has been achieved as 1.94 and 3.88 corresponding to Re=2000 and Re=16000 respectively. Therefore, the present work can be fruitful for heating and drying application

Numerical Investigation of the Effects of Air Flow Geometry and Reynolds Number in Cooling Systems of Lithium-Ion Batteries

In this study, two factors affecting the cooling performance of lithium-ion batteries have been selected and investigated using numerical methods. They have been determined as airflow geometry design and different Reynolds numbers. First, the differences between a classical flow path design (Z channel) with air inlets and outlets in the same direction and an alternative design (U channel) with air inlets and outlets in different directions have been evaluated. To understand the effect of the turbulent properties of the fluid in both designs, the results of the analyses performed using different Reynolds numbers (Re=4000, 6000, 8000, 10000, 15000) have been compared with each other. As a result, it has been observed that the U-channel design provided more homogeneous cooling on the battery surfaces and that the heat transfer is at higher values. In addition, it was observed that the Nusselt number increased with the increase in the Reynolds numbers used in the analyses. This study provides important data to understand the effects of airflow geometry and Reynolds number on the design of lithium-ion battery cooling systems and contributes to the development of optimized cooling solutions.

Numerical investigation of fluid flow and heat transfer of a nanofluid around two circular cylinders arranged in tandem in horizontal duct

In this study, two-dimensional unsteady laminar convective heat transfer from two isothermal cylinders arranged in tandem in horizontal duct has been numerically investigated. The numerical study is performed by solving the governing equations (continuity and momentum) and energy equations using a finite volume-based code ANSYS Fluent. The present study was conducted using nano sized copper particles suspended in water. The Prandtl number Pr of the resulting suspension being equal to 7. The range of solid volume fractions studied is and the flow Reynolds number is equal to 100.The spacing ratio of the two cylinders was varied from 2 to 5 while the blockage ratio was kept constant β=0.25. A detailed discussion has been provided regarding the variation of flow structure and the characteristics of flow, including total drag and lift coefficients, as a function of the dimensionless parametersIn order to visualize the flow and heat transport, streamlines, vorticity contours and isotherms were generated. In addition, the local and average Nusselt numbers for the upstream and downstream cylinders are calculated. The results demonstrate that the force coefficients, the wake structure behind the cylinders, and the Nusselt number are significantly influenced by the value of the spacing ratio and the volume fractions of nanoparticles. The results demonstrate a significant enhancement in heat transfer efficiency relative to the base fluid. The aforementioned improvement is more pronounced in the case of higher gap ratios and higher nanoparticle volume fractions.

Effect of fluid flow behavior on sustainability and exergy efficiency of solar heat collectors having multiple V‐ribs with gaps

AbstractIn the current numerical study, the viability and sustainability of a solar heat collector (SHC) have been rigorously analyzed through the lens of exergy analysis. The SHC with roughness in the form of symmetrical V‐rib gaps has been selected for detailed numerical investigation. The study focuses on deriving the dominant parameters affecting the performance of the SHC, including the relative gap width (), number of gaps () in the limbs of ribs, and fluid flow Reynolds number, which varied from 4000 to 18,000. The absorber plate with roughness was thoroughly examined to evaluate the losses and irreversibility that persist in the thermal system. The results of the numerical analysis revealed the maximum exergy efficiency to be 3.87%. Furthermore, the study examined the long‐term feasibility of the system, evaluating its sustainability index at a remarkable 1.0319 value, while the magnitude of the waste–energy ratio fetched an impressive score of 0.991. Additionally, the study found that the system has a significant improvement potential of 10.04. Overall, these findings provide critical insights into the performance and sustainability of SHCs, paving the way for future research and development in this crucial field.

Computational investigation of both geometric and fluidic compressible turbulent thrust vectoring, using a Coanda based nozzle

This study addresses the challenge of enhancing aircraft maneuverability, particularly for vertical landing and takeoff, focusing on the fluidic aerial Coanda high efficiency orienting jet nozzle that employs the Coanda effect to achieve thrust vectoring. This research advances understanding of the interplay between geometric and fluidic factors in thrust vectoring. Stationary, turbulent, and compressible flow conditions are assumed, employing Favre-averaged Reynolds-averaged Navier–Stokes approach with the standard k-ε model. Computational solutions were obtained using a pressure-based finite volume method and a structured computational grid. The key findings include thrust vectoring enhancement due to an increase in the total mass flow rate, septum position (at no shock wave-related issues), and Reynolds number. In addition, shock wave formation (at specific mass flow rates and septum positions) considerably affects thrust vectoring. These insights are crucial for optimizing Coanda-based nozzle design in advanced propulsion systems, including in unmanned aircraft vehicles.

Extensive computational fluid dynamics analysis of microchannel flow topology and friction factor in arrays of conical pin-fins

The design of integrated circuits presents an increasing challenge for engineers, who seek to identify effective methods for cooling the miniature electronic components that are becoming increasingly complex. One potential solution is the use of micro pin-fin heat sinks, which have the potential to be an effective thermal management technique. This study compares the potential thermo-hydraulic efficiency of micro heat exchangers with conical pin-fins, arranged in two alternative patterns. The flow topology was investigated using the critical points theory and Ω-criteria to gain a deeper understanding of vortical structures and flow separation. 75 variations of pin-fin arrays were simulated and analyzed. It is noteworthy that no pattern similar to bidirectional pin-fins has been studied previously. The input datasets for the simulations included pitch/height ratios ranging from 0.823 to 1.235, cone angles from 0° to 13.48°, and flow Reynolds numbers of 40–117. The numerical results show that Ω and kinetic energies can predict the onset of instabilities. The degree of conicity and the pattern affect the friction factor, typically reducing it. The conical shape and arrangement of pin-fins can also aid in stabilizing the flow. Furthermore, the dependence of the friction factor on pitch/height and Reynolds was quantified with the calculated mean relative error of 1.7%. Moreover, turbulence parameters and friction factors were used to evaluate the thermohydraulic properties, deliberately excluding heat transfer simulations. This approach allows a much wider range of geometric modifications to be investigated for the preliminary optimization of the thermal and hydraulic performance of microchannels.

Enhancing thermal field prediction in a jet in cross flow through turbulent heat flux model optimization by using large eddy simulation

High fidelity big data obtained from highly accurate large eddy simulation (LES) was utilized to enhance current models for turbulent heat transfer, boosting the precision of the realizable Reynolds averaged Navier Stokes (RANS) k-ε model in forecasting film cooling thermal field. The LES analysis was conducted on a flat plate with a jet in crossflow, at a primary flow Reynolds number (Re) of around 17382. Post-validation of the LES outcomes, a data analysis, and a numerical optimization (gradient descent algorithm) technique were employed to fine-tune three chosen models for turbulent Prandtl number using data near the coolant wall. In order to demonstrate the effectiveness of these refined models for RANS simulations of various film cooling setups with distinct shapes and flow situations, a series of simulations were executed, encompassing two curved surfaces to simulate flow around leading-edge and over the blade suction side. The optimized models exhibited marked enhancement in forecasting film cooling effectiveness in both averaged lateral and longitudinal directions (achieving reductions in numerical errors of up to 68.0 % and 43.67 % respectively). These fine-tuned models were proven suitable for use across different geometries and flow conditions according to their performance in three analyzed problems.

Investigation of two-phase flow distribution in the vertical annular distribution header of a variable refrigerant flow heat pump system

The characteristics of two-phase flow distribution from a vertically installed annular refrigerant distribution header to multiple branch ports are investigated, with a specific focus on simulating a real variable refrigerant flow heat pump (VRF HP) system. A test section is fabricated to replicate an actual distribution header for empirical investigation, utilizing an air–water mixture as the working fluid. A series of experiments are conducted to examine distribution characteristics, involving variations in the location of the main inlet port, operational mode, total mass flow rate, and void fraction. The experimental results indicate that the two-phase mixture exhibits a relatively uniform liquid phase distribution to the branch ports when the main inlet port is positioned at the bottom side. However, maldistribution to branch ports is intensified as the inlet void fraction increases and the flow rate of the two-phase mixture decreases. Furthermore, a series of computational fluid dynamics analyses is performed to investigate the distribution characteristics of R410A, the actual working fluid utilized in VRF HP systems. These analyses are conducted under the operational conditions typical of VRF HP systems. Despite identical Reynolds numbers for the two-phase R410A flow and air–water mixture flow, the former exhibits a notably uneven distribution to branch ports owing to the distinct thermophysical properties, particularly density and viscosity. The findings from this investigation enhance the comprehension of two-phase flow distribution characteristics in a vertically installed refrigerant distribution header under real VRF HP system conditions, offering valuable insights into mitigating the maldistribution of refrigerant flow to branch ports.

Effects of different momentum ratios and Reynolds number in a T-junction with an upstream elbow

This study focuses on analysing thermal mixing in T-junctions with varying momentum and Reynolds number ratios, utilizing computational fluid dynamics (CFD) simulations. The T-junction is a critical component of the primary nuclear thermal–hydraulic circuit within a pressurized water-cooled reactor (PWR). The T-junction connects the pressurizer (PRZ) with the steam generator (SG) and the reactor pressure vessel (RPV). Water from the PRZ and the SG are at different temperatures and incomplete thermal mixing occurs when these two fluid streams meet at the T-junction. This incomplete thermal mixing can induce thermal stratification of the water within the T-junction as well as thermal striping phenomena. Thermal striping phenomena can lead to fluctuations of the temperature at the inner pipe wall of the T-junction. Thermal stratification and thermal striping phenomena can induce thermo-mechanical fatigue and eventual pipe failure which can affect the safety of the reactor. Therefore, a high-fidelity, mechanistic understanding of the turbulent thermo-fluid mixing within T-junctions of PWRs might lead to improvements in component reliability and safety within nuclear power plants (NPPs).The primary aim of the research, presented in this paper, is to understand and quantify the effect of variations in the momentum ratio on the turbulent fluid flow within T-junctions. This is achieved by either varying the branch pipe diameter while keeping the inlet velocity constant (part one) or by adjusting the branch pipe inlet velocity while maintaining a constant diameter (part two). Despite the different variations in momentum ratios, the specific momentum ratios under consideration in both parts of the study remain consistent (namely 98 and 66.4). It is also noteworthy that the momentum ratios considered in the paper can be classified as wall-jet and impinging-jet, according to the definition in (Hosseini, Yuki, & Hashizume, 2008). It should be noted that the momentum ratio is manipulated by adjusting the flow parameters, leading to variations in the Reynolds number ratio between the main pipe inlet and the upstream branch pipe at the T-junction. The turbulent flows in the cases that are considered are simulated using the Improved delayed detached eddy simulation (IDDES-SST) model. The numerical results from these simulations indicate, for the considered momentum ratios, that maintaining the same momentum ratio does not produce similar mean flow behaviour and turbulent quantities of interest (QoI). For instance, the size of the flow recirculation zone is more likely linked to the diameter of the branch pipe. Moreover, the turbulent QoI and temperature fluctuations at the determined locations are likely affected by the changed flow recirculation zone as well as the Reynolds number of the branch pipe flow.

Heat transfer analysis of nanofluid flow with entropy generation in a corrugated heat exchanger channel partially filled with porous medium

AbstractHeat exchanger research is mainly exploited to develop and optimize new engineering systems with high thermal efficiency. Passive methods based on nanofluids, fins, wavy walls, and the porous medium are the most attractive ways to achieve this goal. This investigation focuses on heat transfer and entropy production in a nanofluid laminar flow inside a plate corrugated channel (PCC). The channel geometry comprises three sections, partially filled with a porous layer located at the intermediate corrugate channel section. The physical modeling is based on the laminar, two‐dimensional Darcy–Brinkman–Forchheimer formulation for nanofluid flow and the local thermal equilibrium model for the heat equation, including the viscous dissipation term. Numerical solutions were obtained using ANSYS Fluent software based on the finite volume technique and the appropriate meshed geometries. The numerical results are validated with theoretical, numerical, and experimental studies. The simulations are performed for CuO–water nanofluid and AISI 304 porous medium. The coupled effects of porous layer thickness (δ), Reynolds number (Re), and nanoparticle fraction (φ) on velocity, streamlines, isotherm contours, Nusselt number (Nu), and entropy generation (S) are analyzed and illustrated. The simulation results demonstrate that heat transfer enhancement in clear PCC can be achieved using a porous layer insert. For the porous thickness range of [0.1–0.6], the corresponding range of average Nusselt number increase is [35.7%–176.9%], and the average entropy generation is [105.4%–771.9%]. The effect of the Reynolds number is more important in a porous duct than in a clear one. For δ = 0.4 and φ = 5%, the increase of Re in the range of [200–500] induces an increase in average Nusselt number in the range of [80.9%–108.4%] and average entropy in [222.9%–309.1%] comparatively to clear PCC. The effect of φ is practically the same for porous and clear channels. For φ = 5%, the increase on average Nu is about 9%, and entropy generation is 5%. Accordingly, important improvements in heat transfer in PCC can be achieved through the combined effect of flow Reynolds number and porous layer thickness.

Experimental and numerical investigation of water flow in different media models at multiple scales

ABSTRACT The study of the flow behavior in pores, fractures, and pore-fracture dual media plays a crucial role in understanding the mechanisms of sudden water inrush and sand flow. In this study, laboratory experiments were conducted using a custom-made transparent porous model to investigate the flow characteristics of fluids in complex media. Additionally, finite element simulations were employed to explore the flow features at multiple scales. A detailed analysis at the micrometer scale was conducted to examine the variations in the water velocity, volumetric flow rate, Reynolds number, flow field, and permeability under different porosity and pressure drop conditions. The results indicate that within the studied range of flow velocities and pressures, the fluid flow in all the media models adhered to Darcy’s law. The improvement in structural connectivity in the random pore model has made the flow channels of fluids in the random pore network more diverse, resulting in an increase in the peak water flow velocity from 4.89E–5 m/s to 4.19E–4 m/s. The fluid accelerated while bypassing the protruding solid particles, resulting in the formation of high-velocity zones in the vicinity. As the pressure drop increases, the volume flow rate of the random dual-medium model with a porosity of 0.6 can increase to 1.01E–9 m3/s, with the highest growth rate. We also simulate the fluid flow of a regular dual-medium model at different porosities and find that the permeability rapidly increases from 5.65E–13 m2 to 1.01E–11 m2, demonstrating that the presence of fractures can significantly improve the permeability performance of the medium. The research findings deepen our understanding of the migration behavior of water in complex geological environments and provide theoretical guidance for groundwater resource protection and underground engineering.