Steady Flow Behavior Research Articles

Entropy generation analysis and thermal synergy efficiency in the T-shaped micro-kenics

In this work, three different twist angles of a micro helical insert in a T-shaped are studied numerically in order to evaluate the laminar steady flow behavior of Newtonian fluid in chaotic geometry. In the geometries under consideration, thermal mixing behavior is carried out using fluids having two distinct input temperatures. Under the influence of chaotic advection and low rates of Reynolds number, the second law of thermodynamics is controlled in terms of the entropy generation caused by hydrodynamic and thermal processes. The governing equations are numerically solved using the CFD Fluent code. Thus, the micromixer's configuration demonstrated a very significant improvement in mixing degree while minimizing friction and thermal irreversibilities. The synergy coefficient, which depicts the link between velocity and heat transfer in angle form, is analyzed and the results are provided.

Rapid electrical impedance detection of sickle cell vaso-occlusion in microfluidic device.

Sickle cell disease is characterized by painful vaso-occlusive crises, in which poorly deformable sickle cells play an important role in the complex vascular obstruction process. Existing techniques are mainly based on optical microscopy and video processing of sickle blood flow under normoxic condition, for measuring vaso-occlusion by a small fraction of dense sickle cells of intrinsic rigidity but not the vaso-occlusion by the rigid, sickled cells due to deoxygenation. Thus, these techniques are not suitable for rapid, point-of-care testing. Here, we integrate electrical impedance sensing and Polydimethylsiloxane-microvascular mimics with controlled oxygen level into a single microfluidic chip, for quantification of vaso-occlusion by rigid, sickled cells within 1min. Electrical impedance measurements provided a label-free, real-time detection of different sickle cell flow behaviors, including steady flow, vaso-occlusion, and flow recovery in response to the deoxygenation-reoxygenation process that are validated by microscopic videos. Sensitivity of the real part and imaginary part of the impedance signals to the blood flow conditions in both natural sickle cell blood and simulants at four electrical frequencies (10, 50, 100, and 500kHz) are compared. The results show that the sensitivity of the sensor in detection of vaso-occlusion decreases as electrical frequency increases, while the higher frequencies are preferable in measurement of steady flow behavior. Additional testing using sickle cell simulants, chemically crosslinked normal red blood cells, shows same high sensitivity in detection of vaso-occlusion as sickle cell vaso-occlusion under deoxygenation. This work enables point-of-care testing potentials in rapid, accurate detection of steady flow and sickle cell vaso-occlusion from microliter volume blood specimens. Quantification of sickle cell rheology in response to hypoxia, may provide useful indications for not only the kinetics of cell sickling, but also the altered hemodynamics as obseved at the microcirculatory level.

Steady Magnetohydrodynamic Casson Nanofluid Flow Between Two Infinit Parallel Plates Using Akbari Ganji’s Method (AGM)

This paper presents an investigation for steady Casson nanofluid flow behavior between parallel plates in the presence of uniform magnetic field. The governing equations are solved via Semi-analytical method, The Akbari Ganji’s Method (AGM). The validity of this method was verified by comparison with results given by using Runge-Kutta. The analysis is carried out for different parameters namely: Viscosity parameter, Magnetic parameter, casson parameter. Results reveal that skin friction coefficient enhances with rise of viscosity, Magnetic parameters and volume fraction. The results of this study can help engineers improve, and researchers can conduct research faster and easier on this type of problem. Also This work helps researchers to master the theoretical calculation of this type of problem.

Estimation of entropy generation and heat transfer of magnetohydrodynamic quadratic radiative Darcy–Forchheimer cross hybrid nanofluid (GO + Ag/kerosene oil) over a stretching sheet

The steady two-dimensional magnetohydrodynamic flow and heat transfer behavior of Darcy–Forchheimer non-Newtonian (Cross) hybrid nanofluid consisting of Go/Kerosene oil and Go + Ag/Kerosene oil through the porous medium past astretched sheet are analyzed here. The heat energy is augmented with quadratic thermal radiation, Ohmic heating, and convective boundary conditions. There is a huge market for nanotechnology, and the development of these materials can be predicted to be very light. Non-Newtonian hybrid nanofluids have several uses in the biomedical, culinary, industrial, and polymer industries. The governing set of nonlinear partial differential equations is converted to ordinary differential equations before being solved numerically. Numerical simulation is completed through MATLAB solver bvp4c by setting the default tolerance. The solver is applied recursively to achieve the desired accuracy in picking the best blend of the assorted parameters we entrenched in the system. The influence of different fluid flow parameters on the velocity, temperature, skin friction, and local Nusselt number are analyzed tabularly and graphically. It is observed that velocity and temperature profile upsurges for the higher values of Weissenberg number. It is also found that quadratic thermal radiation has a significant impact on fluid temperature and heat transfer rate. Forchheimer number and magnetic field resistance make the flow slower and cause enhancement in liquid temperature. Further, adding a volume fraction of silver with Graphene oxide becomes responsible for stabilizing the flow and enhancing heat transportation. The entropy generation becomes more significant with quadratic thermal radiation and Eckert number.

A Simple Line-Element Model for Three-Dimensional Analysis of Steady Free Surface Flow through Porous Media

Considering the fact that only pores can transport water, pores in the homogeneous control volume are conceptualized as a three-dimensional orthogonal network of line elements, which is in contrast to the continuum hypothesis in traditional numerical approaches. The related flow velocity, hydraulic conductivity and continuity equation equivalent to the continuum model are formulated based on the principle of flow balance. Subsequently, the unified form for flow velocity and continuity equation is established based on the local coordinate system, and a finite line-element method is developed, in which three-dimensional steady free surface flow is reduced to one-dimensional form, and the numerical difficulty is greatly decreased. The proposed line-element model is validated by the good agreements of free surface locations with other methods through steady flow in a rectangular dam and a right trapezoidal dam, respectively. It is found that the proposed line-element model is not heavily dependent on the mesh size and penalty parameter. Steady free surface flow on the left bank abutment slope of the Kajiwa Dam in Southwestern China is further evaluated, and a parabolic variational inequality algorithm based on the continuum model is also employed for comparison. The consistent results indicate that the proposed line-element model can capture the steady free surface flow behavior as well as the continuum-based method. Moreover, the proposed line-element model can rapidly achieve accurate solutions whether for simple examples or for complicated engineering applications.

A comparative study on phenomenological and artificial neural network models for high temperature flow behavior prediction in Ti6Al4V alloy

Due to its critical use in lightweight components requiring elevated temperature operation, it is very important to determine and model the high temperature thermomechanical flow behavior of Ti6Al4V. In this study, uniaxial tensile tests were performed at quasi-static strain rates and at temperatures ranging from 500°C to 800°C. The ductile behavior provided at a temperature of 800°C and at a strain rate of 0.001 s -1 can be preferred for forming operations due to the steady state flow behavior. However, stress peaks during deformation at the strain rates of 0.1 s -1 and 0.01 s -1 are indicative of an unsafe zone. For modeling the flow stress behavior, three models including the Artificial Neural Network, Modified Hensel-Spittel and Arrhenius are employed with varying prediction performance as shown by the correlation coefficient (R) and average absolute relative error (AARE) values. Accordingly, the Artificial Neural Network model is claimed to be a more suitable approach for capturing the mechanical behavior of Ti6Al4V within the forming temperature range utilized in this study. • Determination of hot deformation mechanisms and prediction of the high temperature mechanical behavior are vital for hot forming processes. • Modified Hensel-Spittel, Arrhenius and Artificial Neural Network models were used to predict the flow behavior. • The Arrhenius model including the activation energy is more accurate than the modified Hansel-Spittel model. • Neural Network model provides higher accuracy than the other empirical models evaluated in this study.

Numerical Simulation Study of the Effect of Liquid Depth on the Stability of Thermal Marangoni Convection in a Shallow Cavity

The effect of liquid depth on thermal Marangoni convection stability in a shallow cavity was investigated via three-dimensional (3D) numerical simulations. The liquid film in the cavity is silicone oil with a Prandtl number of 6.7. The cavity is subjected to perpendicular temperature gradients. The simulation results show that, for thinner films, a primary instability appears when the flow transits from a steady state to a 3D oscillatory pattern. In thicker films, a secondary instability appears when the flow changes from oscillatory to chaotic. The critical thermal Marangoni numbers (at which transitions occur) of thin films are higher than those of thicker films. The simulation results imply that the uniform steady flow behavior in thinner films can be utilized to a benefit in coating and thin film applications, while the chaotic flow behavior predicted in thicker films can be utilized to obtain better mixing in applications such as lubrication and mixing.

Multiple hysteresis effects and their destabilization mechanism in the enclosed mixed convection enclosure with three representative aspect ratios

Mixed convection in the lid-driven cavity model widely represented real engineering applications, especially electronic cooling and wind across buildings. In past decades, avalanche experiments and numerical calculations have been done on the lid-driven cavity model. Unfortunately, one unusual flow behavior in the cavity mixed convections—multiple steady solutions, i.e., identical boundary conditions and governing parameters whereas different initial conditions or loading perturbations may lead to two or more flow states, and it was hardly investigated. Multiple steady enclosure flow behaviors essentially complicate the convective transport of heat and air, which has been vividly analyzed by streamlines, heatlines and isotherms. In the present work, the flow mechanisms and evolution driven by mixed convections in lid-driven cavities for multiple aspect ratios will be investigated through the numerical methodology of computational fluid dynamics. The effects of dimensionless parameter (Grashof number, Reynolds number, and Richardson number) on multiple flow motions have been disclosed, regarding of hysteresis effect and their destabilization mechanism. Investigations on these complicated flow motions essentially facilitate the optimization of engineering flows similar to lid driven enclosures, whatever mechanical cooling of electronics, or wind across street canyons.

Effects of fluid shear-thinning and yield stress on free convection in concentric and eccentric cylindrical annuli

Laminar free convection in yield-pseudoplastic fluids (the Herschel-Bulkley model) for concentric and eccentric cylindrical annuli has been studied numerically. The combined effects of shear-thinning viscosity and yield stress on the heat transfer characteristics have been examined for the following ranges of parameters: Rayleigh number, Ra (103 to 106), Oldroyd number, Od (0 to Odmax), power-law index, n (0.2–1), Prandtl number, Pr (10–100), eccentricity, ε (0–1.18) and angular position of the inner cylinder, ϕ (0° to 180°). The results are interpreted in terms of the yield surfaces, fraction of yielded fluid, streamlines, isotherms, local Nusselt number and average Nusselt number. Overall, the eccentric positioning of the heated cylinder along the vertical centreline fosters convective transport with reference to that for the case of the concentric annulus. It is possible to achieve augmentation of up to 30% in heat transfer for the case of ε = 1.18, ϕ = 0° with respect to the concentric case at Ra = 105, Pr = 10. This is ascribed to the greater fraction of the annular area occupied by the yielded fluid-like regions. Conversely, horizontal shifting of the inner cylinder to an off-centre position has an adverse effect on heat transfer. Limited transient simulations have also been run to identify the conditions for the loss of steady flow behaviour. A predictive correlation has been developed for the average Nusselt number for its estimation in new applications.

Parallel-Disk Viscometry of a Viscoplastic Hydrogel: Yield Stress and Other Parameters of Shear Viscosity and Wall Slip.

The rheology, i.e., the flow and deformation properties, of hydrogels is generally a very important consideration for their functionality. However, the accurate characterization of their rheological material functions is handicapped by their ubiquitous viscoplasticity and associated wall slip behavior. Here a parallel-disk viscometer was used to characterize the shear viscosity and wall slip behavior of a crosslinked poly(acrylic acid) (PAA) carbomer hydrogel (specifically Carbopol® at 0.12% by weight in water). It was demonstrated that parallel-disk viscometry, i.e., the steady torsional flow in between two parallel disks, can be used to unambiguously determine the yield stress and other parameters of viscoplastic constitutive equations and wall slip behavior. It was specifically shown that torque versus rotational speed information, obtained from parallel-disk viscometry, was sufficient to determine the yield stress of a viscoplastic hydrogel. Additional gap-dependent data from parallel-disk viscometry could then be used to characterize the other parameters of the shear viscosity and wall slip behavior of the hydrogel. To investigate the accuracy of the parameters of shear viscosity and apparent wall slip that were determined, the data were used to calculate the torque values and the velocity distributions (using the lubrication assumption and parallel plate analogy) under different flow conditions. The calculated torques and velocity distributions of the hydrogel agreed very well with experimental data collected by Medina-Bañuelos et al., 2021, suggesting that the methodologies demonstrated here provide the means necessary to understand in detail the steady flow and deformation behavior of hydrogels. Such a detailed understanding of the viscoplastic nature and wall slip behavior of hydrogels can then be used to design and develop novel hydrogels with a wider range of applications in the medical and other industrial areas, and for finding optimum conditions for their processing and manufacturing.

Hydromagnetic flow and thermal interpretations of Cross hybrid nanofluid influenced by linear, nonlinear and quadratic thermal radiations for any Prandtl number

The steady hydromagnetic flow and heat transfer behavior of non-Newtonian (Cross) hybrid nanofluid with water as base fluid and SWCNT, and MWCNT as nanoparticles past a stretched cylinder has been analyzed. Dissipative medium characterized by fluid friction and Ohmic heating is considered. The linear, non linear and quadratic radiations of non Newtonian hybrid nanofluid in line association with Cross fluid model are modeled in the energy equation. The transformed non linear equations are solved numerically by 4th order RK method along with shooting technique. The contributory outcomes of the present investigation include upgraded Weissenberg and curvature parameters intensify the fluid motion and rate of heat transportation while that of magnetic field strength controls the motion. Heat transfer characteristics for any Prandtl number (10−10 ≤ Pr ≤ 104) subject to linear, quadratic and non linear radiations have been narrated efficaciously in the present research.

A branched galactoglucan with flexible chains from the basidioma of Macrolepiota albuminosa (Berk.) Pegler

A homogeneous galactoglucan was purified from the alkali-extracted polysaccharides from the basidioma of Macrolepiota albuminosa by gradient ethanol precipitation, whose proposed structure was given for the first time. Results showed it had a molecular weight of 210 kDa, and mainly consisted of glucose and galactose. There were abundant filaments, randomly distributed sheet-like and flaky appearance in its surface by SEM observation. Its backbone comprised β-(1 → 6)-Glcp, α-(1 → 6)-Galp and β-(1 → 3,6)-Glcp residues at 4:1:1, terminated by β-(1 → 3)-Glcp and T-Glcp residues. Rheological measurements suggested its steady flow behavior was highly dependent on concentrations. Newtonian behavior was evident at low concentrations, whereas pseudoplastic behavior was observed at high concentrations. Besides, the X-ray diffraction patterns proved the presence of amorphous structure. The conformational parameters were detected by HPSEC-MALLS-RI, revealing a random coil conformation in NaNO3 aqueous solution. This work provides a theoretical basis for the application of polysaccharides from M. albuminosa in food- and drug-based therapies.

Evaluation of bend curvature of superheater tube using CFD analysis

PurposeThe heat transfer within a heat exchanger is highly influenced by geometry of the components especially those with hollow structures like tubes. This paper aims to intend toward the study of efficient and optimized heat transfer in the bends of superheater tubes, with different curvature ratio at constant Reynolds Number.Design/methodology/approachThe effect of changing curvature ratio on enthalpy of the fluid passing through the superheater tubes for multi-pass system has been studied with the aid of computational fluid dynamics (CFD) using ANSYS 14.0. Initially a superheater tube with two pass system has been examined with different curvature ratios of 1.425, 1.56, 1.71, 1.85 and 1.99. An industry specified curvature ratio of 1.71 with two pass is investigated, and a comparative assessment has been carried out. This is intended toward obtaining an optimized radius of curvature of the bend for enhancement of heat transfer.FindingsThe results obtained from software simulation revealed that the curvature ratio of 1.85 provides maximum heat transfer to the fluid flowing through the tube with two pass. This result has been found to be consistent with higher number of passes as well. The effect of secondary flow in bends of curvature has also been illustrated in the present work.Research limitations/implicationsThe study of heat transfer in thermodynamic systems is a never-ending process and has to be continued for the upliftment of power plant performances. This study has been conducted on steady flow behavior of the fluid which may be upgraded by carrying out the same in transient mode. The impact of different curvature ratios on some important parameters such as heat transfer coefficients will certainly upgrade the value of research.Originality/valueThis computational study provided comprehensive information on fluid flow behavior and its effect on heat transfer in bends of curvature of superheater tubes inside the boiler. It also provides information on optimized bend of curvature for efficient heat transfer process.

Thermal mixing performances of shear-thinning non-Newtonian fluids inside Two-Layer Crossing Channels Micromixer using entropy generation method: Comparative study

In this work, a numerical comparative study is carried out to investigate a laminar steady flow behavior of shear-thinning non-Newtonian fluids in three chaotic geometries: Two-Layer Crossing Channel Micromixer, C-shaped channel and serpentine channel. The process is validated for non-Newtonian flow in a complex geometry which heated by a constant flux. Secondary flow structures are formed in the chosen geometries enhance significantly the fluid dynamic performances. To characterize this performance Poincaré map method is presented for different geometries with various cases of fluid power-law index. Thermal mixing behavior with two different inlet temperatures of shear-thinning fluids in the considered geometries is performed. For various cases of fluid power-law indexes, the TLCCM displayed thermal mixing degree enhancement of 42–84% relative to the thermal mixing degree in both C-shaped and serpentine channels. The second law of thermodynamics is controlled in terms of entropy generation due to the thermal and hydrodynamic process, as a function of low rates of generalized Reynolds number and power-law index, under the effects chaotic advection. Thereby, the TLCCM configuration exhibited very important enhancement of mixing degree than that obtained in other considered geometries, with minimization of friction and thermal irreversibilities.

Rheological Characteristics and Methodology of Ice Cream: A Review

The rheological analysis is important analytical tools used to obtain fundamental information about food structure. For instance, the properties of flow of liquid and semi-solidity are characterized by the consistency and flow behavior experiments as two important rheological parameters. The rheological parameters of foods are applied in quality control of the products and processing of food products such as energy input calculations, process design, equipment selection, and especially for deciding on heat exchangers and pumps. Steady flow behavior, oscillatory, and penetration tests are among commonly used parameters for evaluating rheological characteristics of ice cream. The purpose of this paper is to provide an overview of recent experiments and methods for measuring the rheological and texture properties of ice cream.

PH mediated rheological modulation of chitosan hydrogels

Chitosan (CS) hydrogels are used widely for multifarious applications in diverse fields due to the property of pH responsiveness. This study aims to explain the sensitivity of CS hydrogels to alteration in pH due to change in the concentration of acetic acid, which is a solvent for CS. Studies on changes in rheological properties in this regard are still scarce. The present study evaluated the change in rheological properties of the CS hydrogels by studying the flow behaviour, creep recovery and thixotropic property. The obtained data were used to fit mathematical models, like power law model and Herschel-Bulkley model to gain a vivid understanding of the rheological properties of CS hydrogel. Overall analyses revealed that the CS hydrogels, irrespective of the pH, were highly elastic in nature and exhibited significant creep recovery. However, the steady flow behaviour and thixotropy varied substantially with variation in pH.

G-jitter fully developed heat transfer by mixed convection flow in a vertical channel with constant heat flux

A theoretical study of mixed convection heat transfer was carried out in an infinite length of vertical channel with both open ends. One of the vertical plates was prescribed with constant heat flux. The effect of g-jitter was also taken into consideration. The Fourier method was utilized to solve the resulting governing equations. The behavior of the fluid temperature and velocity of the flow were studied and presented graphically in this paper. The graphical results were later on analyzed and discussed. The behavior of steady state flow was also investigated. Results confirmed that as wall temperature increased, the fluid temperature increased. The velocity increased due to increments in mixed convection and oscillation parameter, on the other hand, it decreased as a frequency of g-jitter increased.

Understanding the rheology of novel guar-gellan gum composite hydrogels

Hydrogels are hydrophilic polymeric materials, prepared from either synthetic or natural macromolecules. However, synthetic hydrogels are now gradually being replaced with natural hydrogels owing to their non-toxicity, biocompatibility and biodegradability. The present work focused on synthesizing novel composite hydrogels of guar gum and gellan. The synthesized guar-gellan composite hydrogels were further characterized rheologically to understand their functional properties. Arrhenius and power law models were fitted for elucidation of their steady flow behavior. Interestingly the guar-gellan composite hydrogels showed remarkable stability and maintained elasticity at high temperatures and angular frequency. The comprehensive analysis of rheological data of novel guar-gellan gum composite hydrogels suggested their potential advantages over gellan gum and its applicability in diverse industrial sectors.

Stress-fractional soil model with reduced elastic region

The original stress-fractional plasticity approach was developed for the axisymmetric stress state. However, it cannot accurately capture the stress-strain behaviour, e.g., quasi-steady state flow, temporary stress peak and state-dependent dilatancy of soils under different loading conditions. In this study, a modified fractional-order plasticity model for soils under the general stress state is developed using an alternative yielding surface with a reduced elastic region at the dry side of the critical state line. The proposed model is then validated against the results of a series of drained and undrained tests conducted on different soils, including sand, rockfill, ballast and clay, subjected to different loading paths. It is observed that the proposed model can reasonably simulate the key features, such as the hardening/softening, contraction/dilation, liquefaction, quasi-steady state flow and steady state flow behaviour, of different soils.

Pore-Scale Flow Characterization of Polymer Solutions in Microfluidic Porous Media.

Polymer solutions are frequently used in enhanced oil recovery and groundwater remediation to improve the recovery of trapped nonaqueous fluids. However, applications are limited by an incomplete understanding of the flow in porous media. The tortuous pore structure imposes both shear and extension, which elongates polymers; moreover, the flow is often at large Weissenberg numbers, Wi, at which polymer elasticity in turn strongly alters the flow. This dynamic elongation can even produce flow instabilities with strong spatial and temporal fluctuations despite the low Reynolds number, Re. Unfortunately, macroscopic approaches are limited in their ability to characterize the pore-scale flow. Thus, understanding how polymer conformations, flow dynamics, and pore geometry together determine these nontrivial flow patterns and impact macroscopic transport remains an outstanding challenge. This review describes how microfluidic tools can shed light on the physics underlying the flow of polymer solutions in porous media at high Wi and low Re. Specifically, microfluidic studies elucidate how steady and unsteady flow behavior depends on pore geometry and solution properties, and how polymer-induced effects impact nonaqueous fluid recovery. This work thus provides new insights for polymer dynamics, non-Newtonian fluid mechanics, and applications such as enhanced oil recovery and groundwater remediation.