Axial Velocity Profiles Research Articles

Exploring the Thermal Behavior of Cu-water and CuO-water Power-law Nanofluids on a Rotating Circular Disc: A Computational Analysis

The current theoretical investigation focuses on the thermal behavior of a power-law nanofluid flow on a rotating circular disc. In which nanofluid is made by taking colloidal suspension of copper (Cu) and copper oxide (CuO) nanoparticles in a base fluid like water. A theoretical investigation is conducted by formulating a mathematical model of a power-law fluid (which exhibits shear thickening and thinning effects) along with the Tiwari and Das model. A similarity transformation is employed to transform the nonlinear partial differential equations (PDEs) into ordinary differential equations (ODEs) and these ODEs are then numerically solved using the shooting technique. The study's findings are analyzed graphically by plotting radial, tangential, and axial velocity profiles, temperature profiles, Nusselt number, and skin friction coefficients to show how various factors affect the fluid's flow and heat transfer. It is revealed that drag force reduces in Cu-water nanofluid as compared to CuO-water nanofluid for all types of fluids (Newtonian, pseudoplastic, and dilatant fluids) and Nusselt number becomes high in Cu-water nanofluid for both Newtonian and dilatant fluids as compared to CuO-water nanofluid but in case of pseudoplastic reverse behavior is observed. Heat transfer rate in Cu-water dilatant and pseudoplastic nanofluids increases up to 20.4% and 12.5% with respect to base fluid and in CuO-water dilatant and pseudoplastic water nanofluids, it increases up to 18.6% and 15.2%.

Laminar swirling slender pipe flows

Swirling flows are extensively used to enhance mixing in chemical and physical processes. Although many fundamental studies involve decaying laminar swirls in circular ducts with constant area—for which several theoretical descriptions exist—converging and diverging pipe sections are often employed, demanding the extension of the analysis to swirling laminar flows in pipes with varying areas. This work analytically investigates axial swirl decay in laminar axisymmetric flows in converging and diverging pipes at moderate Reynolds numbers. The theoretical model extends the classical theory for laminar low swirling flows in straight pipes with impermeable walls to pipes with slowly varying areas. Inlet Reynolds number and converging/diverging angle effects are analyzed for incompressible axisymmetric laminar flows in slender pipes (lengths much greater than the radius). Results show that diverging pipes enhance the swirl decay rate, whereas converging systems have a weakening effect for flows with the same inlet Reynolds number. Conversely, increasing the inlet angle in converging flows decreases the decay rate, whereas larger diverging pipe inlet angles promote swirl decay. A simplified eigenvalue analysis shows that the relationship between the swirl decay lengths in diverging (ℓd,div), straight (ℓd,st), and converging (ℓd,conv) pipes is given by ℓd,div<ℓd,st<ℓd,conv for flows with similar inlet Reynolds numbers. Comparisons with numerical simulations show that the model predictions are almost exact for nondimensional pipe lengths up to 5×10−2 times the inlet Reynolds number. Approximating the axial velocity profile through a fully developed function representative of laminar flows with heat transfer through the walls shows that the narrower axial velocity profile in diverging flows increases viscous effects, enhancing the swirl decay rate. On the contrary, the flatter axial velocity profile in converging pipes further extends the decay length.

Analysis of heat and mass transfer rates in conducting Casson fluid flow over an expanding surface considering Ohmic heating and Darcy dissipation effects

In a recent scenario, the flow of Casson fluid via porous media has practical applications in various engineering processes, such, as the design of cooling systems for electronic devices, oil recovery in porous reservoirs, and polymer extrusion processes, etc. The proposed investigation illustrates the thermal and solutal transfer rates in a conducting Casson fluid flow over an expanding surface. However, the emphasis goes to the behavior of the Ohmic heating and Darcy dissipation when considering the transverse magnetic field and porous matrix. The governing flow phenomena with their dimensional form are altered into a non-dimensional set of equations with the help of suitable similarity rules. Further, an adequate numerical simulation is adopted to solve the transformed equations using the in-house bvp4c function in MATLAB. The physical parameters involved in the flow problem and their behavior on the governing flow phenomena are presented graphically and described briefly. Prior to this investigation, the conformity of the current numerical output obtained for the heat transfer rate was validated with the earlier work with a good correlation. Moreover, the major outcomes are; the non-Newtonian Casson parameter retards the axial and transverse velocity profile and the shear rate also decreases significantly. The Eckert number caused by the inclusion of the dissipative heat encourages the fluid temperature throughout.

A four-way coupled numerical investigation of draft tube baffled crystallizer

In the present paper, the liquid–solid two-phase turbulent flow in a Draft Tube Baffled crystallizer has been simulated using Computational Fluid Dynamics. In this respect, multiphase Eulerian model along with population balance equations were applied. To implement four-way coupling, aggregation and breakage were considered. The RNG k-ε and RSM turbulence models were employed to conduct numerical simulation of two phase turbulent flow. Results demonstrated that applying RNG k-ε and RSM turbulence models, a significant difference in axial velocity profiles along the x-axis is observed, while those along the z-axis exhibit less difference. Moreover, a significant difference in volume fraction between the two models was observed which mostly concerns the region within the draft tube and the distance between the baffle and crystallizer wall. Furthermore, changing the propeller speed from 165 to 495 rpm, the speed of 330 rpm showed to be optimal in terms of particles residence time. The results also showed that a rise in impeller speed is one of the major contributors to mass exchange enhancement between the liquid and the solid phases. Accordingly, as the impeller speed rises, the rate of mass exchange increases from 9.92 kg/h for 165 rpm to 29.07 kg/h for 495 rpm.

Computational fluid dynamics simulation of cryogenic vertical upflow boiling under Earth gravity

This study presents numerical simulations and their validation for flow boiling of liquid nitrogen (LN2) in a vertical upflow orientation, with a primary aim to understand the complex two-phase flow and heat transfer phenomena important to space applications. The computational fluid dynamics (CFD) model utilized the coupled level set volume of fluid (CLSVOF) method, incorporating additional source terms for bubble collision dispersion force and shear lift force in the momentum conservation equation to enhance simulation accuracy. The simulations were conducted for two mass velocities (G = 526 and 804 kg/m2s) and three different heat flux levels (approximately 10%, 30%, and 70% of critical heat flux (CHF) under Earth gravity. The model was validated against measured wall temperature data acquired from the authors’ previous experimental studies, demonstrating average deviations of less than 2.8 K across all operating conditions. The simulated two-phase flow contours illustrated various flow patterns, including bubbly, slug, churn, and annular. Both mass velocity and heat flux were observed to impact the onset of nucleate boiling (ONB), bubble nucleation, growth, and coalescence, and overall vapor structure. The simulations also offered insight into axial and radial void fraction and velocity profiles, revealing local flow acceleration trends synchronized with void fraction development. A comparison between predicted and measured bulk fluid temperature profiles showed excellent agreement, further validating the CFD model’s accuracy and practical usefulness for two-phase cryogenic flow boiling simulations in space applications.

ENTROPY-OPTIMIZED FLOW OF COUPLE STRESSES IN AN POROUS INCLINED PIPE WITH UNIFORM MAGNETIC FIELD AND MIXED CONVENTION

Abstract The research aims to investigate the entropy-optimized flow of couple stresses in a porous inclined pipe exposed to a transverse constant magnetic field and mixed convection. It focuses on understanding the thermodynamic efficiency and fluid behaviour under convective boundary conditions, contributing to improved designs in engineering applications where such flows are relevant. The aim is to enhance heat transfer efficiency in industrial processes such as chemical reactors, heat exchangers, and geothermal systems, while also improving filtration systems for applications like water purification and oil recovery. By subjecting the flow to a uniform magnetic field and mixed convection, nonlinear governing equations arise due to mixed convection. We linearize these equations using a quasi-linearization approach and solve them using Chebyshev spectral collocation. Our analysis focuses on thermodynamic phenomena like entropy generation and the Bejan number, which have implications for the efficiency and sustainability of industrial processes. We visualize temperature and axial velocity profiles across various parameter ranges to understand the fluid's behaviour under the influence of magnetic fields and porous materials. As the magnetic parameter increases, there is a decrease in fluid velocity and temperature. However, the opposite tendency is seen for the couple stress viscosity ratio parameter. We also observe irreversibility dominating heat transfer at the pipe wall, while fluid friction irreversibility dominates around the pipe's centre. This research contributes to advancing our understanding of thermodynamic processes in complex fluid systems and has practical implications for optimizing industrial processes and developing more efficient filtration systems.

Experimental research on the flow field and flame geometry of free buoyant diffusion flames with low dimensionless heat release rates

The flame geometry of turbulent diffusion flames is dominated by the turbulent mixing between the gaseous fuel and the entrained air. The significant variations of the power law for the mean flame height regarding the dimensionless heat release rate (Q˙*) in different Q˙* ranges implied that the turbulent mixing characteristics would change greatly among these Q˙* regimes. This paper presents a combined experimental and analytical study to reveal the turbulent transport properties and flame shape of free turbulent buoyant diffusion flames of relatively low Q˙* prevalent in large-scale fires. The instantaneous velocity fields of free buoyant methane diffusion flames (burner diameter: d = 0.30 m, Q˙*= 0.22–0.40) were measured by the stereo particle image velocimetry (SPIV) technique. The results indicate that the radial profiles of the time-averaged axial velocity, axial normal stress, radial normal stress, shear stress, and turbulent kinetic energy exhibited self-similarity at different heights under all the heat release rates. The turbulent flow in the buoyant flame was found to be anisotropic. Based on the gradient transport approximation, the mean turbulent viscosity within the mean flame height (νt=) was scaled by g1/2d3/2, where g is the gravitational acceleration. The semi-physical correlations for the mean flame height and width were derived based on the concepts of turbulent mixing and equal axial convection and radial diffusion times, respectively. The two correlations agreed reasonably with the experimental data of this work.

Swirling flow and heat transfer in a pipe: Decay and transition to axial flow

This paper describes an experimental study of heat transfer, local and total swirl flow parameters in the pipe 80 mm in a diameter and 150 diameters long. The pipe consists of 12 separate pipes of different length, connected to each other using 20 mm ring spacers. These spacers were also used to provide the flow and heat transfer measurements. Overall, eight blade-type swirl generators with central body and profiled according to the power low, are installed at the pipe inlet. The actual swirl intensity S of swirl generators is ranged from 0.38 to 1.29. The profiles of mean axial and tangential velocity, surface heat flux, swirl flow angle, static and total pressure, flow and surface temperature are measured. A few novel scientific results and equations are obtained, including the axial and tangential speed maximum, axial and tangential momentum flux, swirl number decay and energy loss transformation. The common link between the local and total swirl parameters, one-valued correlation between tangential and axial velocity were obtained. The results, presented in the paper led to the conclusion that transition from swirling to axial flow occurs at S ≈ 0.19 in terms of the heat transfer decrease, but at S ≈ 0.10 – in terms of the energy loss reduction.

Laminar flow with temperature-dependent fluid properties between two stretching rectangular surfaces

Abstract The Navier–Stokes equations and the energy equation are used to investigate a fluid flow between two stretching rectangular surfaces subjected to a temperature difference that affects the dynamic viscosity and thermal conductivity of the fluid. The wall stretching process enhances the momentum boundary layer thickness which slows the axial motion of the fluid away from the flow boundaries. When the stretching parameter γ is equal to 1, that is the case corresponding to symmetric stretching, the minimum of the axial velocity is located at the midplane of the channel y = 0.5 if the viscosity variational parameter α equals 0. This minimum moves towards the region 0.5 < y < 1 for α > 0, but migrates towards the region 0 < y < 0.5 for α < 0. Moreover, in the case of symmetric stretching corresponding to γ = 1, the growth in Reynolds number Re tends to increase the axial velocity around the middle of the channel for α ≥ 0 in the attempt to counteract the effects of enhancing the momentum boundary layer thickness leading to the flattening of axial velocity profiles for Re ≥ 100. While the conductivity variational parameter β does not influence enough the fluid dynamics and heat transfer, the Reynolds number Re and the Péclet number Pé can increase or decrease the temperature distribution inside the channel depending on the sign of the parameter α. Practical applications related to the present study include lubrification, food manufacturing, paint industries, extrusion processes in plastic and metal industries.

Significance of variable thermal conductivity and suction/injection in unsteady MHD mixed convection flow of Casson Williamson nanofluid through heat and mass transport with gyrotactic microorganisms

AbstractThe present paper explores a two‐dimensional mixed bio‐convective unsteady viscous hydro‐magnetic Casson Williamson nanofluid flow model with heat and mass transport incorporating motile microorganisms towards a stretchy spinning disc. The flow concept is accomplished by rotating a stretched disc with a time‐varying angular velocity. By applying a magnetic field normal to the axial direction, a magnetic interaction is taken into consideration. The Casson Williamson nanofluid contains nanosized particles suspended with swimming motile microorganisms and the rotation of the disc is exhibited by buoyancy forces, thermophoresis, suction/injection, zero mass flux conditions, variable thermal conductivity, Joule heating and so forth. The obtained flow narrating differential equations of the model are transformed into ordinary differential system. This is accomplished by simulating boundary value problems using the shooting technique using the ‘ND‐Solve’ approach included in the Mathematica software (Mathematica 12). The implications of the engaged parameters such as Williamson fluid parameter, Casson fluid (CF) parameter, thermophoresis parameter, Brownian motion parameter and so forth, on both axial and radial velocities, temperature, concentration of nanoparticles and microorganisms are explained by means of graphical and tabular constructions. This paper's validity has been confirmed and its findings align with those of other previously published papers. Furthermore, it is found that both the axial and radial velocity profiles are seen to be diminishing functions of the CF parameter. The identified observation may have theoretical implications for a number of engineering procedures, solar energy systems, biofuel cells and extrusion system improvement. Moreover, this work finds application in micro‐fabrication techniques and the chemical industry.

Characterising Horizontal Two-Phase Flows Using Structured-Planar Laser-Induced Fluorescence (S-PLIF) Coupled With Simultaneous Two-Phase PIV (S2P-PIV)

Understanding the physics that underpins the behaviors of two-phase flows is immensely useful for a diverse number of industries, including oil and gas, nuclear, and aerospace. Stratified air-liquid two-phase flows are amenable to the application of two-phase PIV, but this is often only possible if PIV processing parameters can be chosen to match the separate gas and liquid phase image sets. Accurate interface location detection is, therefore, extremely important to facilitate appropriate masking during analysis. This paper examines the effectiveness of using the Structured-Planar Laser Induced Fluorescence (S-PLIF) method to aid in the accurate capture and processing of simultaneous two-phase PIV (S2P-PIV) for a gas-sheared liquid flow. Prior S2P-PIV work made use of direct interface detection, using contrast on images from the air-side camera. However, this method proved limiting in higher gas shear cases when the highly wavy nature of the flow prevented the camera from seeing all of the interface. An alternative prior approach using the liquid-side camera and the planar laser-induced fluorescence (PLIF) technique often led to large errors due to reflections from the free surface. Interface detection using the S-PLIF method facilitates a clearer delineation between the two phases through analysis of the change in the structure of the incident light, significantly reducing errors generated by the traditional PLIF. This then facilitates higher quality PIV analysis, both because interface identification is far more accurate and also because frame specific masking of the individual phases can be more automated. This paper presents air/water data from a rectangular channel with a liquid flowrate of 8 litres per minute and superficial gas velocities in the range 1 - 14 m/s. Data capture of the two phases is concurrent with the developed S-PLIF approach used to locate the interface, enabling separate and more accurate PIV analysis of the two phases over a wider parametric range than was previously possible. The data analysis shows that the transition to the disturbance/roll wave regimes is associated with a change in the liquid’s axial velocity profile and a significant increase in normalized axial velocity root-mean-square velocity fluctuation. Data sets from this work can be used to accurately describe high-speed gas-sheared two-phase flows that will be extremely useful for CFD model development and validation.

An Experimental Investigation Of Sweeping Jets Impinging Flow Field: Effects Of Nozzle-To-Plate Distance And Feedback Channel Minimum Cross-Sectional Area

Without requiring any moving part or piezoelectrical elements, fluidic oscillators are actuators able to convert a steady jet into an oscillating one, only due to internal fluid dynamic mechanisms. Since the oscillations of such jets are self-induced and self-sustained, the interest in fluidic oscillators has grown over the last years, especially for film cooling, flow control and heat transfer applications. The oscillation frequency, the sweeping angle and the flow field characteristics of sweeping jets greatly depend on various geometric and fluid dynamic parameters. Therefore, in the current work, through the application of the planar PIV technique, the effects of nozzle-to-plate distance and feedback channel minimum cross-sectional area on the external flow field of impinging sweeping jets are investigated. Non-dimensional nozzle-to-plate distances H/w equal to 2, 4, 6, 8 and 10 are taken into account, being w the exit nozzle throat section width. To analyze the effects of the feedback channel minimum cross-sectional area, a fluidic oscillator having a mixing chamber length Lf/w = 4.5 is provided with threaded holes in correspondence of the feedback channels, in which a micrometric screw is fastened to vary the parameter g/w, being g the feedback channel minimum passage width; values of g/w equal to 0.17, 0.33, 0.50, 0.67 and 1 are considered. Time-averaged and phase-averaged analyses are performed; indeed, the pressure signal measured between the inlet and outlet sections of one feedback channel is used to identify the phase of each velocity snapshot, despite the velocity measurements are not time-resolved. Firstly, the configuration with g/w=1 is taken as reference case, thus analyzing the nozzle-to-plate distance effect. The phase-averaged velocity and fluctuating kinetic energy fields show that the jet sweeps in the external flow field, with a sweeping angle approximately equal to 25° and a frequency of 50 Hz. Due to this behavior, the time-averaged velocity field exhibits a twin-jet pattern, which can also be identified from the time-averaged Phase-correlated Kinetic Energy (PKE) distributions (see Figure 1, left). Indeed, the extreme positions of the oscillating motion are the zones in which the coherent oscillation of the velocity values is greater and, therefore, the PKE values are the greatest. Furthermore, while at H/w=2 the jet sweeps in an almost rigid-like way between the two extreme positions reached during its oscillating motion, at greater nozzle-to-plate distances a phase delay between the motion of the jet near the impinging plate and near the exit nozzle section can be observed. Considering the effects of the feedback channel minimum cross-sectional area, by reducing g/w the sweeping angle of the jet decreases, while the oscillation frequency increases. Still, a twin-jet pattern can be identified for g/w≥0.33, as it can be seen from the crosswise profiles of the dimensionless time-averaged axial velocity (see Figure 1, right), while for g/w=0.17 a single-jet velocity structure can be identified. Nevertheless, as g/w decreases the maximum values of the velocity increase while the oscillation intensity decreases, resulting in a decrease of the PKE values.

High-Speed Schlieren Imaging And PIV Of Unsteady Free Jet Injection With Plume Formation

This work aims to investigate Schlieren image correlation velocimetry for flow field quantification of gaseous jet injection in non-manipulable apparatus like flow chambers. Such flow cases often struggle using tracer-based methods: Seeding particles may locally cause technical problems, or the plant design prevents the principal opportunity of tracer adding, both of which lead to a reduced method repertory. This is specifically the case under flow conditions, where contamination of apparatus internals by seeding particles should be avoided completely. Therefore, in this paper, we explore a seedless, refraction-based method to quantify the velocity field of a jet plume. As an experimental flow case, we examine a transient jet release into a closed compartment under nearly atmospheric conditions. For simplification and greater clarity, the laboratory model geometry is kept essentially two-dimensional, thus we chose a flat-jet nozzle as injection device. The experimental investigations cover high-speed Schlieren imaging and laser sheet visualization, followed by digital image correlation. Combining the traditionally qualitative Schlieren approach for flow visualization with Fast Fourier Transform and cross-correlation algorithms, we calculated the velocity vector field of an unsteady jet plume formation. Furthermore, we determined the axial jet velocity profile at steady-state conditions. Our research findings highlight the applicability of Schlieren image correlation velocimetry to quantify gaseous jet formation at encased flow sections spatially. Concluding, the results coincide with data from particle image velocimetry measurements and point out the potential of expanding flow diagnostics to hitherto hardly explored (industrial) flow cases.

The Impact of Heat Transfer and a Magnetic Field on Peristaltic Transport with Slipping through an Asymmetrically Inclined Channel

This theoretical investigation explores the intricate interplay of slip, heat transfer, and magneto-hydrodynamics (MHD) on peristaltic flow within an asymmetrically inclined channel. The channel walls exhibit sinusoidal undulations to simulate flexibility. The governing equations for continuity, momentum, and energy are utilized to mathematically represent the flow dynamics. Employing the perturbation method, these nonlinear equations are systematically solved, yielding analytical expressions for key parameters such as stream function, temperature distribution, and pressure gradient. This study meticulously examines the influence of various physical parameters on flow characteristics, presenting comprehensive visualizations of flow streamlines, fluid axial velocity profiles, and pressure gradient distributions. Noteworthy findings include the observation that the axial velocity of the fluid increases by 55% when the slip parameter is increased from 0 to 0.1, indicative of enhanced fluid transport. Furthermore, the analysis reveals that the pressure gradient amplifies by 80% with increased magnetic field strength from 0.5 to 4, underscoring the significant role of MHD effects on overall flow behavior. In essence, this investigation elucidates the complex dynamics of peristaltic flow in an asymmetrically inclined channel under the combined influence of slip, heat transfer, and magnetohydrodynamics. It sheds light on fundamental mechanisms that govern fluid dynamics in complex geometries and under diverse physical conditions.

An impact of Richardson number on the inclined MHD mixed convective flow with heat and mass transfer

AbstractThe two‐dimensional mixed convective MHD flow with heat and mass transfer is investigated for its behavior with Dufour and Soret mechanisms over the porous sheet. The copper–alumina (Cu–Al2O3) hybrid nanoparticles are used in the base fluid water. The governing system of partial differential equations is converted into a system of ordinary differential equations via similarity transformations, obtaining the solution for velocity, temperature, and concentration fields in exponential form. The problem is demonstrated in the Darcy–Brinkman model, the impact of included parameters such as Richardson number, magnetic field, and Dufour numbers are studied for the obtained solution with the help of graphs. Increasing the magnetic field decreases both transverse and axial velocity profiles. Increasing the magnetic field and Richardson's number decreases the solution (Al2O3–H2O). Increasing the values magnetic field and Richardson's number decreases both transverse and axial velocity profiles. Increasing the values of the Dufour effect increases the axial and transverse velocity boundary layer. The magnetohydrodynamic hybrid nanofluid flow over porous media works efficiently in liquid cooling and, therefore, has significant applications in industrial heating and cooling systems, solar energy, magnetohydrodynamic flow meters and pumps, manufacturing, regenerative heat exchange, thermal energy storage, solar power collectors, geothermal recovery, and chemical catalytic reactors.

Liquid flow field and residence time distribution in a baffleless oscillatory flow coil reactor

Baffleless coils can operate as continuous oscillatory flow reactors to produce pharmaceutical products where process intensification is intended. A method to evaluate mixing performance and its impact on reaction conversion is residence time distribution (RTD) analysis. Liquid macromixing in a long baffleless coil reactor (L = 24 m, dt = 4.57 mm) at ranges of oscillation amplitude (11.75–58.75 mm), frequency (0–3.68 Hz), and net flow rate (30–120 g⋅min−1) was investigated based on measured RTDs fitted to the skewed normal distribution model. The impact of operating conditions on the RTD was supported by analyzing the liquid flow field derived from CFD simulations. The RTD variance under different oscillation conditions suggests a near plug flow pattern, although deviations from ideality such as skewness and long tailing were always observed. The model parameters, along with the RTD variance, were correlated to the operating conditions lumped in an oscillatory Dean number that used the flow amplitude as characteristic length (Deox). Values of Deox varied between 150 and 11000, and the RTD variance at the different net flow rates was minimized for 300 < Deox < 600, as also evidenced from the minimum cross-sectional variance of the simulated time-averaged axial velocity profile. Normalizing the data allowed comparison to similar coil studies with different geometrical dimensions and operating conditions, leading to generalized correlations for the RTD model parameters. Finally, chemical conversion was assessed for first- and second-order single phase reactions at different Damköhler numbers using the segregation and maximum mixedness micromixing models combined with the fitted RTDs. The performance of the coil remained consistent with a plug flow reactor despite its departures from ideal flow.

Experimental analysis of lifelines in a 15,000 L bioreactor by means of Lagrangian Sensor Particles

This study employs Lagrangian Sensor Particles (LSPs) with a diameter of 40 mm equipped with a pressure sensor to investigate cell lifelines in a 15,000L stirred tank reactor (STR) with three Elephant Ear impellers. The Stokes number of the LSPs is approx. 0.004 on a macro-scale. The vertical probability of presence, axial velocity profiles, circulation time distributions, and residence time distributions are quantified to analyze single-phase mixing heterogeneities, detect hydrodynamic compartments and conduct a Lagrangian regime analysis. Results reveal a similarly distributed probability of presence in the vertical reactor center but emphasize the LSP’s sensitivity to fluctuating densities. Axial velocity distributions illustrate characteristic impeller-induced flow patterns, and circulation time distributions identify three compartments with comparatively shorter times in the axial center. Residence time distributions exhibit a similar compartmentalized profile. Moreover, the study estimates a potential oxygen deprivation zone for CHO cells in the upper compartment and demonstrates the LSP’s efficacy in characterizing impeller systems. Contrary to literature, the ratio of examined global mixing times to circulation times is 1.0, highlighting macro-scale mixing. The research underscores that LSPs offer crucial insights into industrial-scale STRs, specifically for determining hydrodynamic compartments without having optical access.

A study on peristaltic flow and nanofluid in medication delivery systems considering heat transfer

This study uses analytical and numerical approaches to explore nanofluid peristaltic flow and heat transfer in drug delivery systems. Low Reynolds numbers are used to examine the study using long-wavelength approximations. Along the channel, the walls are distributed sinusoidally. The current issue is resolved by using analytical and numerical methods, and solutions are obtained for the temperature profile, axial velocity, volume flow rate, pressure gradient, stream function, and Nusselt number. The influence of several physical factors on the temperature, velocity profile, and trapping phenomena is shown. These parameters include the thermal and basic-density Grashof numbers and the Brownian motion and thermophoresis parameters. Along the channel, streamlines and Nusselt number variations are also displayed. The axial velocity profile is shown to be greatly reduced when the thermal Grashof number rises, but it increases as the species Grashof number rises. Specifically, the axial velocity increased by 50% with the increase of the species Grashof number from 0.1 to 1, but the thermal Grashof decreased by 33% with the same amount of change. Compared to Newtonian fluids, nanofluids tend to reduce backflow and also exhibit a significant rise in pressure differential, indicating that they are a more practical fluid for use in medical pumps for drug delivery systems. With the increase in Brownian motion and thermophoretic parameters, the Nusselt number decreased sharply. Changing these parameters from 0.1 to 4 brought the Nusselt number to about 10% of its initial value. Also, the increase in these parameters leads to an increase in temperature and a decrease in fluid velocity.

A simple analytical model for turbulent kinetic energy dissipation for self-similar round turbulent jets

This work presents a simple analytical model for the streamwise and radial variations of turbulent kinetic energy dissipation in an incompressible round turbulent jet. The key assumptions in the model are: similarity in the axial velocity profile with a Gaussian shape, axisymmetric flow and the dominance of radial derivatives of the mean velocity over axial direction derivatives (similar to boundary layer theory). Initially, a simplified eddy-viscosity relation for turbulent stresses is derived using the algebraic stress model by Gatski &amp; Speziale (J. Fluid Mech., vol. 254, 1993, pp. 59–78). Subsequently, with this eddy-viscosity relation, the relation for variations of turbulent kinetic energy dissipation is formulated using the conservation of turbulent kinetic energy. To extract the necessary constants of the model, experimental velocity statistics for round jets are obtained through particle image velocimetry measurements. The experimental results of the mean entrainment coefficient for turbulent jets are also analysed. When comparing the radial variation of turbulent kinetic energy dissipation from the model with experimental results at Reynolds number $1.4\times 10^5$ and numerical results at Reynolds number $1200$ from the available literature, we observe a maximum error of $10\,\%$ and $15\,\%$ , respectively. Finally, using the validated model, we analyse the impact of mean velocity evolution parameters on the behaviour of turbulent kinetic energy dissipation and discuss its potential significance in future studies.

Subcooled forced convection boiling flow measured using high-resolution techniques at the COSMOS-L facility and accompanying CFD simulation employing an interface-tracking scheme

This paper describes state-of-the-art experimental measurement techniques and computational fluid dynamics methods applied to subcooled forced convection boiling flow at 2-3 bar, both featuring high spatial- and time-resolution measurements. The objectives are: (i) to provide the measured boiling flow data, e.g. average and RMS profiles of axial and radial velocities and bubble size distributions, and (ii) to evaluate the capabilities of state-of-the-art numerical simulation techniques to model the observed phenomena, by comparison between measured data and numerical prediction. In the experiment, the bubble velocities in the axial and radial directions were measured using laser Doppler anemometry, and the bubble size was estimated by a shadowgraphy method. The simulation results, incorporating an interface capturing technique, showed good agreement with measurement in terms of the wall temperature and axial velocity, but underestimation of the radial velocity, and overestimation of bubble sizes. The paper shows that the discrepancies between measurement and simulation may be traced to: (i) the uncertainties in the nucleation site density model; (ii) too coarse a grid being adopted, which is not able to resolve the thermal boundary layer around the bubbles; and (iii) spurious numerical bubble coalescence, a feature not seen in the experiment. The mechanism of bubble lift-off from the hot surface, without any sliding motion, as observed in the experiment, is discussed in detail, based on the simulation results, and the condensation on the bubble cap as the bubble is ‘sucked’ into the bulk flow is also examined.