Isothermal Flow Research Articles

APPLICATION RESERCH OF CHAIRS WITH COOLING AND HEATING FUCTIONS

In this study, the evaluation results using a prototype machine of the chair with cooling and heating functions were described. Isothermal air flow was used for the cooling function, and seat heating was used for the heating function. The results showed that the SET* was reduced by 1.4K by improving the convective heat transfer. The seat surface temperature did not exceed the threshold of low temperature burns during heating. From the subjects’ experiments, it was shown that the thermal sensation votes of the seven levels were reduced by 0.7 points during cooling and increased by 0.8 points during heating.

Mixed Convective Heat Transfer Analysis by Heatlines on a Lid‐Driven Cavity Having Heated Wavy Wall Containing Tilted Square Obstacle

The current problem studies the mixed convective heat transport by heatlines in lid‐driven cavity having wavy heated walls with two diamond‐shaped obstacles. The left and right vertical walls are both cold, whereas the top wall is adiabatic, and the bottom wavy wall is heated. The relevant governing equation has been calculated through using the finite element method as well as the Galerkin weighted residual approach. The implications of the Reynolds number (10 ≤ Re ≤ 500), Richardson number (0.01 ≤ Ri ≤ 10), Hartman number (0 ≤ Ha ≤ 100), Prandtl number (0.015 ≤ Pr ≤ 10), Undulations number (1 ≤ N ≤ 4), and inner diamond shape obstacle are depicted by the streamlines, isotherms, and the heatlines. The convection heat transfer is observed to be fully developed at a high Prandtl number, whereas heat conduction happens at poor Pr. In particular, the undulations number has the greatest effect on the streamlines and isotherm contrast to a flat area. The Nusselt numbers increase as the Reynolds and Prandtl numbers rise as well. The isotherm, streamlines, heatlines, Nusselt number, and fluid flow are shown graphically for several relevant dimensionless parameters. The result demonstrates that a single oscillation of a heated wall with such a poor Richardson number is optimal heat transport in the cavity. The presence of undulations minimizes the cavity area; the case N = 3 makes quicker fluid motions and better heat transfer in the present research. Additionally, the interior obstacle size reduces the amount of space it takes up within the wavy cavity, and it was observed that the obstacle with diamond size D = 0.15 is better than that with any other size.

Experimental and numerical studies of the effects of the contraction ratios on the swirling flow characteristics of the model combustor outlet in lean gas turbines

Large Eddy Simulation (LES) is utilized in this work to study isothermal turbulent swirling flow characteristics for a lean partially premixed gas turbine model combustor. The goal is to investigate the influence of contraction ratio (CR) variation on the vortex breakdown phenomena features and the turbulence structure in these combustors. Particle image velocimetry (2D-PIV) measurements were carried out on a single-case model combustor using (air-air) phase to perform the mean flow behavior and the validation process under atmospheric conditions with CR equal to 0 (largest diameter, Dinlet = Doutlet), the equivalence ratio (φ) of 0.3, swirl number of (Sn) = 0.66 and Reynolds number of (Re) = 42,000. While five test cases with various CRs were applied in LES under the same conditions using (air-CH4) phase to predict the vortical structure and the precession vortex core (PVC). The CRs ranged as follows: 0, 50 %, 60 %, 70 % and 80 % (smallest diameter). Experimental and LES results show that there was a reasonable agreement between the PIV and LES results with maximum deviations of 2.8 % and 4.65 % for the normalized mean axial and radial velocities, respectively. As the CR was increased, the pressure drop and the mean axial velocity increased linearly at the contraction part. In addition, the downstream stagnation point and the size of the central toroidal recirculation zone (CTRZ) stabilized when CR = 60 %, 70 %, and 80 %. The swirl level was further enhanced by 40 % when CR = 60 % and 80 %. The presence of CR successfully suppressed the pressure and axial velocity fluctuations generated in the shear layer zones by 35 %. LES data was analyzed by Fast Fourier Transformation (FFT) and Proper Orthogonal Decomposition (POD) to investigate the PVC dynamics. The FFT showed four dominant frequencies as a result of the appearance of the PVC and vortex breakdown oscillation. The frequency of PVC (fpvc) decreased linearly with an increase in the CR where the fpvc was 20.8 Hz when CR = 0 and became 12.5 Hz at CR = 80 %. In contrast, the other frequencies were still constant even with increased CR at 187 Hz, 562 Hz, and 979 Hz. The POD analysis showed the first mode was more energetic and had 40 % of the total pressure fluctuations.

Explicit implicit domain splitting for two phase flows with phase transition

Two phase flows that include phase transition, especially phase creation, with a sharp interface remain a challenging task for numerics. We consider the isothermal Euler equations with phase transition between a liquid and a vapor phase. The phase interface is modeled as a sharp interface and the mass transfer across the phase boundary is modeled by a kinetic relation. Existence and uniqueness results were proven in the work by Hantke and Thein [“A general existence result for isothermal two-phase flows with phase transition,” J. Hyperbolic Differ. Equations 16, 595–637 (2019)]. Using sharp interfaces for simulating nucleation and cavitation results in the grid containing tiny cells that are several orders of magnitude smaller than the remaining grid cells. This forces explicit time stepping schemes to take tiny time steps on these cells. As a remedy, we suggest an explicit implicit domain splitting where the majority of the grid cells is treated explicitly and only the neighborhood of the tiny cells is treated implicitly. We use dual time stepping to solve the resulting small implicit systems. Our numerical results indicate that the new scheme is robust and provides significant speed-up compared to a fully explicit treatment.

Влияние компонентного состава нефтей на их структурно-механические свойства

In this work, various oils were studied, for which the group chemical composition, viscosity-temperature and structural-mechanical properties were determined. It has been established that these oils are paraffinic, resinous and highly resinous, as well as low paraffinic, highly resinous. For these crude oils, isothermal flow curves of the forward and reverse strokes were obtainedat temperatures of 10, 0 and -10°C. The values of the internal energy of destruction of the supramolecular structure (ΔW)of oils were calculated. It has been established that for all crude oils with decreasing temperature, an increase in ΔW is observed.This is due to the formation of a spatial crystal lattice of paraffinic hydrocarbons in the volume of crude oil. It is shown that with an increase in the value of the total content of solid paraffinic hydrocarbons and asphaltenes (P+A) and a decreasein the proportion of resins (S), the degree of structuring of the crude oil system increases. It has been established that at low temperatures for the studied crude oils, the value of the index (Р+А)/ S, equal to 0,4, is the threshold value abovewhich the crude oil exhibits thixotropic properties due to the structuring of the system.

РАСПРОСТРАНЕНИЕ ПУЛЬСАЦИЙ ПО ПОТОКУ ЖИДКОГО МЕТАЛЛА

This work develops a method for measuring the speed of an isothermal flow of liquid metal in a cylindrical channel. The method does not require calibration, is non-contact and is based on a correlation technique. The generation of pulses is carried out using rotating magnetic field inductors. Pulses of the axial velocity component are recorded by recording the electromagnetic response of local velocity meters. It is shown that with a small number of pulses, the value of the correlation function is small, which does not allow the velocity to be reliably measured, even with increasing pulse intensity. Conversely, a high degree of correlation for this technique is achieved with a significant increase in the number of pulses, which entails an increase in the duration of measurements.

Establishment of regularities of isothermal flow and mixture formation in microjet burners with three-row jet fuel supply

The object of this research is the aerodynamics and mixture formation of fuel and oxidizer in stabilizer-type burners with a three-row system of fuel jets, focused on operation at coefficients of excess air 1.1...1.5. The study was conducted on the basis of CFD modeling using the RANS (Reynolds Averaged Navier-Stokes) approach. The analysis of the basic regularities of the course of these processes in the proposed microjet burners was carried out. In this case, special attention was paid to the consideration of the characteristics of flow and mixture formation in the aft region of the flame stabilizer, where vortex structures are formed that are responsible for stabilizing the torch. The regularities of influence on the flow and mixture formation in the proposed burner devices of such factors as the row number NR of the jet fuel supply, the relative pitch, S/d, of the location of gas supply holes and the coefficient of excess air, α, have been investigated. The presence of noticeable differences in the structure of flow and mixture formation in burners during fuel supply to different rows of gas supply holes has been established. It is shown that aerodynamics and the pattern of mixing fuel and oxidizer undergo significant changes when varying the value of S/d. For the considered burner devices, rational design parameters of the fuel supply system have been determined, at which favorable conditions for mixture formation in the field of flame stabilization are ensured. In particular, it is shown that the rational S/d values are 5.4; 5.6; and 5.8, respectively, for the first, second, and third sections of the fuel supply. The results can be widely used in energy practice for objects operated under conditions of variable values of the coefficient of excess air

Lattice Boltzmann modeling and simulation of velocity and concentration slip effects on the catalytic reaction rate of strongly nonequimolar reactions in microflows.

A lattice Boltzmann (LB) interfacial gas-solid three-dimensional model is developed for isothermal multicomponent flows with strongly nonequimolar catalytic reactions, further accounting for the presence of velocity slips and concentration jumps. The model includes diffusion coefficients of all reactive species in the calculation of the catalytic reaction rates as well as an updated velocity at the reactive boundary node. Lattice Boltzmann simulations are performed in a catalytic channel-flow geometry under a wide range of Knudsen (Kn) and surface Damköhler (Da_{s}) numbers. Comparisons with simulations from a computational fluid dynamics (CFD) Navier-Stokes solver show good agreement in the continuum regime (Kn<0.01) in terms of flow velocity and reactive species distributions, while comparisons with direct simulation Monte Carlo results from the literature attest to the model's applicability in capturing the correct slip velocity at Kn as high as 0.1, even with a significantly reduced number of grid points (N=10) in the cross-flow direction. Theoretical and numerical results demonstrate that the term Da_{s}×Kn×A_{2} (where A_{2} is a function of the mass accommodation coefficient) determines the significance of the concentration jump on the catalytic reaction rate. The developed model is applicable for many catalytic microflow systems with complex geometries (such as reactors with porous networks) and large velocity/concentration slips (such as catalytic microthrusters for space applications).

Self-directed molecular diagnostics (SdMDx) system for COVID-19 via one-pot processing

Rapid, sensitive, and specific detection of the severe acute respiratory syndrome coronavirus (SARS-CoV)− 2 during early infection is pivotal in controlling the spread and pathological progression of Coronavirus Disease 2019 (COVID-19). Thus, highly accurate, affordable, and scalable point-of-care (POC) diagnostic technologies are necessary. Herein, we developed a rapid and efficient self-directed molecular diagnostic (SdMDx) system for SARS-CoV-2. This system combines the sample preparation step, including virus enrichment and extraction processes, which involve dimethyl suberimidate dihydrochloride and diatomaceous earth functionalized with 3-aminopropyl(diethoxy)methylsilane, and the detection step using loop-mediated isothermal amplification-lateral flow assay (LAMP-LFA). Using the SdMDx system, SARS-CoV-2 could be detected within 47 min by hand without the need for any larger instruments. The SdMDx system enabled detection as low as 0.05 PFU in the culture fluid of SARS-CoV-2-infected VeroE6 cells. We validated the accuracy of the SdMDx system on 38 clinical nasopharyngeal specimens. The clinical utility of the SdMDx system for targeting the S gene of SARS-CoV-2 showed 94.4% sensitivity and 100% specificity. This system is more sensitive than antigen and antibody assays, and it minimizes the use of complicated processes and reduces contamination risks. Accordingly, we demonstrated that the SdMDx system enables a rapid, accurate, simple, efficient, and inexpensive detection of SARS-CoV-2 at home, in emergency facilities, and in low-resource sites as a pre-screening platform and POC testing through self-operation and self-diagnosis.

New formulation of the Navier–Stokes equations for liquid flows

Abstract For isothermal liquid flows, the condition of incompressibility provides a useful simplification for describing their mechanical properties. Nevertheless, it overlooks acoustic effects, and it provides the unpleasant shortcoming of infinite propagation speed of velocity perturbations, no matter the type of constitutive equation for the shear stresses is adopted. In this paper, we provide a derivation of a new formulation of the Navier–Stokes equations for liquid flows that overcomes the above issues. The pressure looses its ancillary status of mere gauge variable (or equivalently Lagrange multiplier of the incompressibility condition) enforcing the solenoidal nature of the velocity field, and attains the proper physical meaning of hydrodynamic field variable characterized by its own spatiotemporal evolution. From the experimental evidence of sound attenuation, related to the occurrence of a non-vanishing bulk viscosity, the evolution equation for pressure in out-of-equilibrium conditions is derived without introducing any adjustable parameters. The connection between compressibility and memory effects in the propagation of internal stresses is established. Normal mode analysis and some preliminary simulations are also discussed.

Enhanced alite dissolution by CAH10 addition

The influence of varying Al addition in the form of CAH10 on the hydration of alite was studied to gain further insights into the alite hydration mechanisms in the presence of increased Al concentration in pore solution. Therefore, pure alite and mixtures of alite and CAH10 were investigated by means of isothermal heat flow calorimetry, XRD and pore solution chemistry analysis. The two occurring hydration events can be attributed to the precipitation of two different silicate-bearing hydrate phases, C2ASH8 and C-(A)-S-H. In this case, the consumption and removal of Al in pore solution initiated the change to C-(A)-S-H-forming hydration. Furthermore, the formation of C2ASH8 and the alite reaction rate and reaction were directly influenced by the amount of Al provided by CAH10 addition, leading to an alite reaction turnover of up to 68–86 % within 48 h.

The effect of Cu2+ doping in β-tricalcium phosphate on the hydration mechanism of a brushite cement

Brushite cements show excellent biocompatibility and are therefore an often-used material for bone repair. However, methods to prevent inflammations after surgery are needed. As Cu2+ was proven to provide antibacterial properties, as well as other application relevant features, it is a promising additive. Concerning these factors, a brushite cement containing Cu2+-doped β-tricalcium phosphate, monocalcium phosphate monohydrate, and phytic acid as setting retarder was investigated with powder and in situ X-ray diffraction, isothermal heat flow calorimetry, in situ 1H-time domain – nuclear magnet resonance, and pore solution analysis. The influence of Cu2+ ions on the hydration kinetics of the brushite cement and the locations of the Cu2+ ions after completion of the hydration were the main questions of interest. Heat flow calorimetry showed a significant retardation and deceleration of the hydration with increasing Cu2+ content in β-tricalcium phosphate. This effect can be directly correlated to the Cu2+ ions, as it was also shown for cements without phytic acid. X-ray diffraction showed brushite as main hydrate phase. Additionally, Cu2+-doped cements formed a hydrate phase not assignable by X-ray diffraction, which is assumed to be Cu2+ containing. Furthermore, Cu2+ was detected in the pore solution after the hydration, and no signs of Cu2+ incorporation in the crystal structure of brushite were found.

Towards a consistent lattice Boltzmann model for two-phase fluids

We revisit the construction of discrete kinetic models for single-component isothermal two-phase flows. Starting from a kinetic model for a non-ideal fluid, we show that, under conventional scaling, the Navier–Stokes equations with a non-ideal equation of state are recovered in the hydrodynamic limit. A scaling based on the smallness of velocity increments is then introduced, which recovers the full Navier–Stokes–Korteweg equations. The proposed model is realized on a standard lattice and validated on a variety of benchmarks. Through a detailed study of thermodynamic properties including co-existence densities, surface tension, Tolman length and sound speed, we show thermodynamic consistency, well-posedness and convergence of the proposed model. Furthermore, hydrodynamic consistency is demonstrated by verification of Galilean invariance of the dissipation rate of shear and normal modes and the study of visco-capillary coupling effects. Finally, the model is validated on dynamic test cases in three dimensions with complex geometries and large density ratios such as drop impact on textured surfaces and mercury drops coalescence.

A gas kinetic Lax–Wendroff scheme for low-speed isothermal rarefied gas flows

Previously, a gas kinetic Bhatnagar–Gross–Krook (BGK) scheme was proposed by us for incompressible flows in the continuum limits. [W. Li and W. Li, “A gas-kinetic BGK scheme for the finite volume lattice Boltzmann method for nearly incompressible flows,” Comput. Fluids 162, 126–138 (2018).] In the present work, we extend the gas kinetic BGK scheme to simulate low-speed isothermal rarefied nonequilibrium gas flows. This scheme is a gas kinetic Lax–Wendroff scheme (GKLWS) for the discrete velocity Boltzmann equation in the finite volume discretization framework with second-order accuracy in both time and space. As collision and transport of the molecular particles are coupled in the present GKLWS, the time step of the present method is not limited by the relaxation time, for which the present scheme is efficient for multiscale gas flows. Moreover, the present GKLWS holds the asymptotic preserving (AP) property, which ensures that both the Navier–Stokes solutions in the continuum limits and free-molecular flow solutions in the rarefied limits can be reliably obtained. To validate the accuracy and AP property of the GKLWS, several numerical benchmarks of isothermal low-speed rarefied gas flows are simulated by the present scheme. The numerical results show that the present scheme can be a reliable multiscale method for all Knudsen number low-speed isothermal gas flows.

Simple and field amenable loop-mediated isothermal amplification-lateral flow dipstick assay for detection of west Nile virus in human clinical samples.

West Nile encephalitis caused by infection with the West Nile virus (WNV) is endemic in many regions of the world and is a global public health threat. The aim of this report was to develop a method using colorimetry-based reverse-transcription loop-mediated isothermal amplification (cRT-LAMP) and RT-LAMP combined with lateral-flow dipstick (LFD) for rapidly detecting WNV in low-infrastructure settings. The primers for the cRT-LAMP and RT-LAMP-LFD assays were designed based on env gene of the WNV. Primers concentration, temperature and time were optimized for cRT-LAMP and RT-LAMP-LFD. The diagnostic performance of the cRT-LAMP and RT-LAMP-LFD assays was evaluated using human serum samples from 110 patients who were clinically suspected to be infected with WNV. The RT-LAMP was performed in a heating block at 63°C for 40 min. The LAMP amplicons were visible in the lateral-flow dipstick within 5min. The detection limit of the developed cRT-LAMP and RT-LAMP-LFD assays was 10 copies and this assay showed a high degree of specificity for WNV. Compared with quantitative real-time RT-PCR assay, the kappa value of cRT-LAMP and RT-LAMP-LFD were 0.970. These results showed that the newly developed WNV-specific cRT-LAMP and RT-LAMP-LFD assays can be employed as an alternative method for screening of WN-suspected human samples. The results revealed that the assay could potentially identify the virus without interference from human serum samples. Collectively, all results revealed that cRT-LAMP and RT-LAMP-LFD assays offer a suitable field-based diagnosis of WNV. The cRT-LAMP and LAMP-LFD platform for the detection of WNV is rapid, accurate and simple-to-perform. Our present method has not only a short turnaround time but also avoided cross-contamination problem. Moreover, the use of simple lateral flow dipsticks broadens its application potential for the point-of-care use in resource-limited settings during outbreak situations. To the best of our knowledge, this is the first report for the development of cRT-LAMP and LAMP-LFD assays for rapid, simple, specific and sensitive detection of WNV using human clinical samples and EvaGreen dye.

Steady isothermal flow of a Carreau–Yasuda model fluid in a straight circular tube

The five-parameter version of the Carreau–Yasuda model has sufficient flexibility to fit various experimental viscosity vs. shear rate curves. Here, analytical solutions are derived for the velocity distribution and the average flow velocity for the steady isothermal flow of a Carreau–Yasuda model fluid in a straight, circular tube. The solution procedure can be applied to other incompressible generalized Newtonian fluids. The analytical expressions herein derived can be useful in validating numerical solutions. • Analytical solutions are derived for the velocity distribution and flow rate—pressure drop relation for the steady Hagen–Poiseuille flow of a Carreau-Yasuda model fluid in a pipe and between parallel plates. • The solution procedure can be applied to many other incompressible generalized Newtonian fluids. • The analytical expressions herein derived can be useful in validating numerical solutions.

On the structure of isothermal acoustic shocks under classical and artificial viscosity laws: selected case studies*

Assuming Newton’s law of cooling, the propagation and structure of isothermal acoustic shocks are studied under four different viscosity laws. Employing both analytical and numerical methods, 1D traveling wave solutions for the velocity and density fields are derived and analyzed. For each viscosity law considered, expressions for both the shock thickness and the asymmetry metric are determined. And, to ensure that isothermal flow is achievable, upper bounds on the associated Mach number values are derived/computed using the isothermal version of the energy equation.

Dispersion Mechanism of Styrene–Butadiene Rubber Powder Modified by Itaconic Acid and Its Toughening Effect on Oil Well Cement

Styrene-butadiene rubber (SBR) has been extensively applied to enhance the toughness of hardened cement. The instability of existing liquid latex leads to difficulties in storage and transportation, and even performance regression. Thus, the well-dispersed carboxylated butylbenzene (SISBR) latex powders were fabricated through the seed emulsion polymerization of liquid polybutadiene (LPB), styrene (St), itaconic acid (IA), and sodium p-styrenesulfonate (SSS) to overcome the difficulties. The dispersion performance of latex powders with various IA amounts was quantitatively evaluated using particle size distribution, zeta potential, and ultraviolet-visible spectrophotometry. Results showed that the carboxylic ionic (COO-) from IA enhanced the dispersing abilities of SISBR latex powders, which ensured the uniform distribution in water. Based on this, the influence of latex powder on cement was assessed mainly by fluidity, isothermal heat flow calorimetry, X-ray diffraction (XRD), and triaxial mechanical testing. Results showed the fluidity and dispersion performance of cement were improved with more IA in latex, while the hydration of cement was retarded due to excessive adsorption of carboxyl (-COOH) groups in IA. Triaxial mechanical testing showed that cement with SISBR-3 (latex containing 3% IA) exhibited the minimal elastic modulus of 3.16 GPa, which was lower than that of plain cement (8.34 GPa).

OpenFOAM-Hybrid: A Morphology Adaptive Multifield Two-Fluid Model

Industrial multiphase flows are typically characterized by coexisting morphologies. Modern simulation methods are well established for dispersed [e.g., Euler-Euler (E-E)] or resolved [e.g., volume-of-fluid (VOF)] interfacial structures. Hence, a morphology adaptive multifield two-fluid model is proposed that is able to handle dispersed and resolved interfacial structures coexisting in the computational domain with the same set of equations. An interfacial drag formulation for large interfacial structures is used to describe them in a VOF-like manner. For the dispersed structures, the baseline model developed at Helmholtz-Zentrum Dresden-Rossendorf is applied. The functionality of the framework is demonstrated by investigating a single rising gas bubble in a stagnant water column, a two-dimensional stagnant stratification of water and oil sharing a large-scale interface that is penetrated by micro gas bubbles, and an isothermal countercurrent stratified flow case. Recent developments focus on the transition region, where bubbles are overresolved or underresolved either for E-E or for VOF. Furthermore, a concept is presented for the transition of oversized dispersed bubbles into the resolved phase.

Numerical analysis of the influence of wall roughness on the turbulent boundary layer separation

Passive control of turbulent boundary layer (TBL) separation in a channel with adverse pressure gradient (APG) condition towards the outlet is investigated using Reynolds-averaged Navier-Stokes (RANS) methods and Large Eddy simulations (LES) with the help of commercial ANSYS software. Isothermal and incompressible flow in the near-wall area of the flat plate as well as various configurations of wavy wall is studied. It is shown that the amplitude and period of the waviness significantly influence the near wall region and point of separation.