Flow In Tube Research Articles

Thermal analysis of electroosmotic flow in a vertical ciliated tube with viscous dissipation and heat source effects: implications for endoscopic applications

Thermal analysis of electroosmotic flow in a vertical ciliated tube with viscous dissipation and heat source effects: implications for endoscopic applications

Numerical investigation on mixed convection for laminar molten salt in horizontal square tubes

Molten salts are the key working media in nuclear and new energy fields. However, the mixed convection of molten salt is rarely investigated. The mixed convection of laminar flow in horizontal square tubes with constant heat flux is analyzed using Fluent software for the first time. The effects of heat flux, inlet temperature and Reynolds number on the flow and heat transfer performances are evaluated. It is found that as the buoyancy force increases, the friction factor, flow entropy generation rate, Nusselt number, and exergy efficiency increase, while the heat transfer entropy generation rate and exergy loss decrease. Compared to the forced convection, the maximum local friction factor, flow entropy generation rate, mean Nusselt number and mean exergy efficiency for mixed convection increase by 25.8%, 50.5%, 109.0% and 7.6%, respectively. Moreover, the maximum mean heat transfer entropy generation rate and exergy loss decrease by 56.1% and 57.3%, respectively. In addition, approximately 42% of the friction factor predicted by Fluent and 30% of the heat transfer predicted by Fluent exceed 20.0% uncertainties of conventional correlations. Therefore, an accurate friction factor correlation with 12.9% uncertainty and an accurate heat transfer correlation with 9.1% uncertainty are proposed.

Investigation of the Newtonian fluids flow in circular horizontal tubes at low inlet pressures

The issues of increasing hydrodynamic efficiency, improving the operational and technical characteristics of various apparatus and devices used in the fi eld of heat and mass transfer, as well as ensuring the required regime and flowow conditions of liquids of different viscosities do not lose their relevance. To solve these issues, in addition to studying the nature of the flowow of various liquids in round horizontal tubes (capillaries), it is necessary to determine the conditions when the flowow of liquid in capillaries and round tubes of small diameter is laminar and can be described by the Poiseuille equation. Experimental data on determining water flow ow through horizontal round tubes of various diameters are presented. Determining the patterns and features of such flow ows is mostly aimed at increasing hydrodynamic efficiency, improving the operational and technical characteristics of various apparatus and devices, as well as ensuring the required flow ow regime and conditions. Experimental data on determining the flow ow rate of water through horizontal tubes of circular cross-section with different diameters are presented in the article. The dependence of the volumetric flow ow rate on the pressure drop has been determined; it has been shown that the main parameters that determine the nature of the flow ow of liquids in horizontal tubes are the tube radius and the dynamic viscosity of the liquid. The flow ow of distilled water in tubes with diameters of 0.95, 1.6 and 2.0 mm at an overpressure of 0.266 kPa to 4 kPa is considered. It is shown that the dependence of the volumetric flow ow rate on the excess pressure remains linear at 0.95 mm in the entire considered pressure range. An increase in the tube radius increases the likelihood of velocity flow uctuations and the appearance of a radial velocity component, i.e. the occurrence of elements of a turbulent structure. In this regard, with tube diameters of 1.6 and 2.0 mm, a deviation of the water flow ow regime from the laminar character was established at pressures of more than 1.3 kPa and 1 kPa, respectively. The dependence of the volumetric flow ow rate on pressure for a 40 % aqueous solution of CaCl2, transformer, transmission and engine oils with dynamic viscosity coefficients from 0.002 Pa·s to 0.182 Pa·s remains linear up to pipe diameters of 5–6 mm. The experimental results are shown in the form of a nomogram of the dependence of the coefficient K* on the tube radius at different values of the viscosity coefficient. The results of studies of liquids of various viscosities are presented in the form of a nomogram of the dependence of the ratio of the radius of the tube to the fourth power to the viscosity of the liquid on the radius of the tube. The analysis of which makes it possible to predict the nature of the flow ow of the investigated liquid at the given values of the tube radius and the dynamic viscosity coefficient. Heat exchange devices for the design of which the presented results can be used include a variety of radiators that include tubes through which coolant circulates.

Numerical Investigation of Turbulent Airflow in Heat Exchanger Tube Equipped with Perforated Conical Rings (NOZZLES)

Numerical investigation of turbulent air flow in heat exchanger tube equipped with perforated conical rings (nozzles). The main aim of this project to conduct thermal analysis on heat exchanger tubes to find the Reynolds number and rate of heat transfer and overall heat transfer coefficient by equipping it with perforated conical rings (nozzles). Nozzles, conical rings are popular heat transfer enhancement tools due to their simple installation, low cost and efficient performance. They can simply improve the thermal efficiency of the system and also used to investigate thermal characteristics of heat exchanger tube. This can be achieved by sending the air with turbulence into the heat exchanger tube equipped with nozzles and 3d simulation is conducted to analyses and compare with the standard values. Key Words: Heat exchanger, Perforated rings, Reynolds number, Overall heat transfer coefficient.

A Comparative Study of the Mode-Decomposed Characteristics of the Asymmetricity of a Vortex Rope with Flow Rate Variation

In hydro turbines, the draft tube vortex rope is one of the most crucial impact factors causing pressure pulsation and vibration. It is affected by operating conditions due to differences in the flow rate and state and can be symmetric or asymmetric along the rotational direction. It may influence the stability of draft tube flow. To achieve a better understanding, in this work, dynamic mode decomposition is used in a draft tube case study of a simplification of a vortex rope. As the flow rate increases, the shape of the vortex rope becomes clear, and the flow rotation becomes more significant as the inlet flow rate increases. Dynamic mode decomposition was used to determine the relative frequencies, which were 0 (averaged), 0.7 times, and 1.4 times the features of the reference frequency. As the inlet flow rate increases, the order of high-energy modes and their influence on the vortex rope gradually increase, and this characteristic is exhibited further downstream of the draft tube. When the inlet flow rate is low, the impact of mode noise is greater. As the flow velocity increases, the noise weakens and the rotation mode becomes more apparent. Identifying the mode of the vortex flow helps extract characteristics of the vortex rope flow under different operating conditions, providing a richer data-driven basis for an in-depth analysis of the impact of operating conditions on the flow stability of a draft tube.

Development of a new criterion for predicting critical heat flux in rod bundles with supercritical water flowing upward

Investigations of heat transfer characteristics in channels with supercritical fluids are crucial for power cycle applications, such as supercritical water-cooled reactors. To ensure the safety of the system, heat transfer deterioration (HTD) should be avoided. The criteria to identify the onset of HTD in heated rod bundles are still not determined. This study summarizes indicators for the onset of HTD in a rod bundle with supercritical water flowing upward based on observations from experimental data. Existing criteria for the tube flow are assessed by comparing predicted critical heat flux (CHF) values with experimentally identified values. Considering effects of different operating parameters, a new criterion for predicting HTD behavior in rod bundles is developed. The results indicate that the new criterion has a better performance than all existing criteria, with a mean average relative deviation of 0.26 %. Predicted CHF values are within ± 20 % of the respective experimentally identified CHF values.

Effects of Darcy and Viscous Dissipation on Natural Convection Flow in a Vertical Tube Partially Filled with Porous Material under Convective Boundary Condition

In this paper, a study is presented considering the effects of Darcy and Viscous dissipation in a steady natural convection incompressible fluid through a vertical composite tube partially filled with a porous material. The fluid motion in the vertical composite tube is caused by a temperature gradient due to heat applied to the wall of the tube. The Brinkman Darcy extended model was used to stimulate the fluid flow under the working fluids of water and air. The Homotopy pertubation method was used to solve the temperature and velocity equations in both the clear and porous fluids. An increase in the Brinkman number increases the temperature and velocity profiles of both working fluids. An increase in the thickness of the porous material can be used to increase the velocity of the fluid in the composite vertical tube. An increase in the internal conductive resistance leads to a decrease in the buoyancy force and, as a result, the fluid thickness, which leads to a decrease in the velocity of the fluid.

An explicit approximation of the central angle for the curved interface in double-circle model for horizontal two-phase stratified flow

Stratified flow in horizontal tubes is frequently observed in gas-liquid two-phase flow system. In the two-fluid modeling, it is important to define the interface shape in solving the balance equations to determine the key parameters such as the interfacial transfer terms, void fraction, and pressure drop. A double-circle model is usually introduced to depict the concave-down interface in a horizontal circular tube under the stratified-wavy flow condition. However, calculation of the central angle in the double-circle model, which represents the interfacial curvature, requires an appropriate iterative numerical root-finding scheme to solve the implicit transcendental equation. In this study, an explicit approximate equation has been proposed without requirement of the iterative scheme and numerical instability, which is expected to improve the coding process and computation efficiency in the analysis code with the two-fluid model.

Does Number Changes of Open Manometers Filled with Pure Water Impact Wind Speeds in Venturi Tube Systems?

Fluid flow in a venturi tube (VT) is a dynamic fluid phenomenon that plays an important role in human life. Flow safety control is necessary by installing several manometers of open (MoO) containing static fluid. The study's purpose was to know the change impacts of the number of installed MoOs against flow speed characters within VTs from conditions of 1 to 2 MoOs. The research uses experimental methods. The main research equipment includes 1 blower-rheostat system, 1 VT with 8 different diameters, and 2 MoOs containing pure water. Data analysis was done using SPSS. Within measurement intervals of 4 Ω ≤ R ≤ 281 Ω and 4.58 cm ≤ d ≤ 9.45 cm, the study showed the comparison of the mean of wind speed, wind speed gradient to R (d fixed), convergent wind speed gradient to d (R fixed), and divergent wind speed gradient to d (R fixed) between 1-MoO and 2-MoO type, respectively, were1. 21E+01 ms-1 vs 1.55E+01 ms-1, -2.73E-02 ms-1Ω-1 vs -4.11E-02 ms-1Ω-1, -3.13E+02 s-1 vs -4.25E+02 s-1, and -4.31E+02 s-1 vs -4.84E+02 s-1. While its impact differences are insignificant, insignificant, significant, and insignificant, respectively.

Numerical investigation of solute dispersion in a non-Newtonian fluid flow through a catheterized artery with mild stenosis

The phenomenon of Casson fluid flow and solute dispersion through a catheterized artery with constriction is studied. An analytical solution to the flow equations is obtained for low Womersley number. The finite element method is utilized to numerically solve the governing equation for solute dispersion and obtain the local and mean concentrations. The combined influence of pulsatile flow nature, catheter insertion, non-Newtonian rheology, and mild stenosis on dispersion within the artery are analysed by considering axial and temporal variations of the local concentration and mean concentration. The study shows that the Womersley frequency parameter and amplitude of the pressure gradient have no qualitative effect on the dispersion in the case of mild stenosis artery; this is in agreement with the case of tube flow with rigid walls. However, the fluid yield stress and height of the stenotic region have a marked impact on the dispersion phenomenon. These results have applications to oxygen or drug transport processes in catheterized and stenosed arteries.

Complex cilia-generated flow of hybrid nanofluid with electroosmosis, viscous dissipation and slippage

In this study, we investigated how electroosmsis, viscous dissipation, and slippage affect the peristaltic flow of complex cilia-generated flow of hybrid nanofluid in a ciliated tube. The complex cilia-generated flow is characterized by a complex sinusoidal wave that transmits along the wall of the tube with a uniform speed having distinct amplitudes. The main objective of this work is to examine how this complex cilia on the wall drives the hybrid nanofluid flow under electroosmosis. The Helmholtz–Smoluchowski equation is used to model the electroosmosis, and the Poisson equation is solved analytically using the Debye-Huckel approximation. The lubrication approach is utilized to simplify the governing equations. The governing non-dimensional equations for hybrid nanofluid are solved exactly using the DSolve command of Mathematica. The results are presented graphically to accomplish the theoretical results from the complex-cilia wave evolution from the necessary flow parameters in an asymmetric tube. The study shows that increasing the electroosmotic parameter leads to an increase in the velocity profile at the boundary and a decrease in the middle of the tube. Conversely, the Helmholtz–Smoluchowski velocity parameter has the opposite effect. The Brinkman parameter increases the temperature of the hybrid nanofluid. The study also presents a graphical analysis of pressure rise and pressure gradient for various values of the parameters. The pressure rise against volumetric flow is rate and pressure gradient increases by increasing the electroosmotic parameter and Helmholtz-Smoluchowski parameter, while it decreases for increasing the velocity slip parameter. The streamlines are drawn to study the trapping phenomena of blood in the hybrid nanofluid flow in an asymmetric tube by the formation of bolus and the division of streamlines. It is observed that the size and number of bolus close to the artery walls increases for electroosmotic parameter while reverse behavior is observed for Helmholtz-Smoluchowski parameter. The tabular presentation of the heat transfer coefficient at the wall is presented. The current results can be used in bio mathematical models to control fluid flow through micro-channels and to investigate ways to cure artery blockages and cancer tumors in biomedicine. The study can also be used to design and optimize microfluidic devices for drug delivery, lab-on-a-chip devices, and other biomedical applications.

About the Current Flow in a Discharge Tube with a Metal Section. Analysis of the Thermal Balance

About the Current Flow in a Discharge Tube with a Metal Section. Analysis of the Thermal Balance

Heat Transfer in Gas-Liquid Taylor Flow in Mini-Scale Coiled Tubes

This paper focuses on heat transfer in gas-liquid Taylor flows in mini-scale coiled tubes. An experimental study is conducted to investigate the effects of liquid slug ratio, radius of curvature, and Prandtl number. Previously, the conducted studies on Taylor flows in straight tubes revealed that heat transfer rates are related to the flow segmentation ratio. Single-phase flows show a higher heat transfer rate in the coiled tubes. In the present study, an experimental setup is assembled using open loop of mini-scale coiled tubes subjected to a constant wall temperature. The Taylor flow data are carefully collected using 0.65, 1 and 3 cSt silicone oils and segmented by gas phase at 0.5 liquid fraction. Three coils of radii, 10, 20, and 40 mm are formed to demonstrate the effect of the secondary flows on the heat transfer rates. The results are presented in the dimensionless forms of the Nusselt number. A new model is proposed to predict Nusselt number of the gas-liquid Taylor flow in coiled tubes. This achievement presents a significant insight on the heat transfer in mini/micro scale channels.

Flow and Heat Transfer Characteristics of Superheater Tube of a Pulverized Coal-Fired Boiler Using Conjugate Heat Transfer Modeling

This study is a numerical study to predict the temperature of the heat exchange tubes inside the pulverized coal-fired boiler through the conjugate heat transfer analysis. Due to the aspect ratio and number of tubes inside the pulverized coal-fired boiler, actual tube modeling analysis has rarely been conducted. Most of the research has been conducted through the porous media method, resulting in limited information on the temperature distribution of each tube. However, for the development of a digital twin model for improving the performance of the boiler and reducing maintenance costs, information on the local temperature of the tubes is required. In this study, all the tubes inside the boiler were modeled, and conjugate heat transfer analysis was performed to confirm the local temperature distribution. For this purpose, the analysis was conducted using Fluent 2020 r2, and the analysis model was constructed using more than 300 million structured grids. The calculation was performed considering conjugate heat transfer in the pulverized coal-fired boiler, heat exchange by steam inside the tubes, and conductive heat transfer of the tubes. As a result, it was confirmed that there is a significant deviation in the local temperature for each tube position. Furthermore, the maximum temperature of the PrSH tube ranges widely, between 492 and 532 degrees, depending on the tube’s position. It was observed that the point of the highest temperature inside the tubes also varies for each tube due to the flow of external combustion gas. Based on these results, it is expected that strategic approaches to boiler design and maintenance can be achieved. Furthermore, it is anticipated to contribute to the high efficiency of power facilities by being utilized as basic data for the development of a digital twin model for the boiler.

Ammonia single-phase and two-phase frictional pressure losses in horizontal smooth and straight inner-grooved tubes

The experimental study of single-phase and two-phase frictional pressure losses has been performed with ammonia flow in stainless steel smooth tubes (internal diameter of 5.5 mm and 8.5 mm) and six straight inner-grooved aluminium tubes with different nominal diameters (7.15 to 13.3 mm), length (0.45 to 2.0 mm) and thickness (0.35 to 0.8) of fins. Single-phase test boundary conditions correspond to Reynolds numbers of 1000 to 20,000. Two-phase tests have been carried out at saturation temperature of 45 to 65 °C, mass velocity of 50 to 210 kg·m−2s−1 and vapour quality of 0.1 to 0.9. Comparison of obtained test data with the existing frictional losses approaches shows that the Blasius model is appropriate to single-phase flows in smooth tubes, and Müller-Steinhagen and Heck's (1986) model is most accurate in predictions of two-phase frictional losses in smooth tubes. Existing approaches of single-phase frictional pressure loss predictions in the pipes and channels with longitudinal fins (Carnavos, 1980; Edwards and Jensen, 1994) are not adequately suited to the ammonia test points obtained in the considered straight inner-grooved tubes. A new semi-empirical model has been proposed, based on generalisation around the revealed geometric dimensionless factor, which accurately describes friction pressure losses in the considered inner-finned profiles. The simplest homogeneous model for defining two-phase friction pressure losses, using McAdams et al.'s (1942) recommendation for mixture dynamic viscosity definition and a new model of single-phase friction factor, best fit both quantitatively and qualitatively to ammonia two-phase test points in most of the considered straight inner-grooved tubes.

Reactive transport in open-channel flows with bed adsorption and desorption

Researches on the solute dispersion with boundary adsorption and desorption are common in various fields, such as chemistry, biology, and hydraulics. However, the Laplace transform, as a method available for the transient transport with coupled processes of adsorption–desorption at boundaries, is complicated to apply. Recently, Jiang et al. (2022) proposed a much simpler analytical method by extending the classic framework of separation of variables to derive solutions of concentration moments for tube flows, which is valid for the entire range of the reactive transport process. Here we apply this simple approach to solute transport in open-channel flows with bed adsorption and desorption. We obtain analytical solutions capturing exactly the transient statistics for the solute cloud as compared to the numerical simulations, regarding the variation of the cloud mass, the motions of the centroid of the cloud, and the scattering of the cloud, respectively. We further investigate the effect of adsorption–desorption on the dispersion process and the influence of initial conditions on the non-uniformity of dispersion characteristics over the cross-section before the Taylor dispersion regime. Through comparisons with that of tube flows, we find that the distribution of solute mass, the drift, and the dispersivity for open channel flows change more slowly with time and the response time is longer.

Streamwise dispersion of soluble matter in solvent flowing through a tube

For the dispersion of soluble matter in solvent flowing through a tube as investigated originally by G.I. Taylor, a streamwise dispersion theory is developed from a Lagrangian perspective for the whole process with multi-scale effects. By means of a convected coordinate system to decouple convection from diffusion, a diffusion-type governing equation is presented to reflect superposable diffusion processes with a multi-scale time-dependent anisotropic diffusivity tensor. A short-time benchmark, complementing the existing Taylor–Aris solution, is obtained to reveal novel statistical and physical features of mean concentration for an initial phase with isotropic molecular diffusion. For long times, effective streamwise diffusion prevails asymptotically corresponding to the overall enhanced diffusion in Taylor's classical theory. By inverse integral expansions of local concentration moments, a general streamwise dispersion model is devised to match the short- and long-time asymptotic solutions. Analytical solutions are provided for most typical cases of point and area sources in a Poiseuille tube flow, predicting persistent long tails and skewed platforms. The theoretical findings are substantiated through Monte Carlo simulations, from the initial release to the Taylor dispersion regime. Asymmetries of concentration distribution in a circular tube are certified as originated from (a) initial non-uniformity, (b) unidirectional flow convection, and (c) non-penetration boundary effect. Peculiar peaks in the concentration cloud, enhanced streamwise dispersivity and asymmetric collective phenomena of concentration distributions are illustrated heuristically and characterised to depict the non-equilibrium dispersion. The streamwise perspective could advance our understanding of macro-transport processes of both passive solutes and active suspensions.

Numerical analysis and an approach for optimization of the Ranque–Hilsch vortex tube for a compressible flow

The Ranque–Hilsch vortex tube is a fluidic device well-known for its energy separation capability. In the present study, the swirling flow inside the vortex tube are computational predicted and analyzed for the optimization purpose. The numerical analysis was conducted on a previously available vortex tube design and the results are well validated. After a thorough comparison, the Re-Normalization Group K-epsilon turbulence model is choose for a reliable computation of the vortex tube flow field. Effects of the inlet compressed gas properties shows a vital increment in the energy separation until the critical condition occurs in vortex tube. At the critical condition, the increase in the inlet pressure ratio result in the loss of swirl momentum through the hot exit rather than increasing the thermal separation. Analyzing the results, the optimal vortex tube dimensions such as radius and length are predicted to reduce the loss in kinetic energy. The graphical optimization method proposed by the parametric study has to be validated by reliable experimental studies.

Numerical analysis of flow instability with vortex cavitation in venturi tube

The swirling flow with cavitation can cause pressure pulsations in a draft tube of a hydro turbine at off-design operating conditions. Especially at the full load condition, the cavitation volume may fluctuate greatly, causing pressure pulsations with flow rate fluctuations known as cavitation surge throughout the hydraulic system. The cases that predicted the phenomenon qualitatively using the CFD analysis have been reported previously, whereas the methods to predict the cavitation volume and the fluctuation frequency in the cavitation surge condition quantitatively have not yet been established. Therefore, in this study, unsteady CFD analysis was conducted for the experimental apparatus that simulates the flow in the draft tube downstream of a runner using the stationary guide vane and the venturi tube. In CFD analysis, the influence of the turbulence models by using LES and SST and the influence of the number of meshes in LES simulation were investigated. It was founded that LES simulation captured the vortex generation finely and improved the prediction accuracy of the cavitation volume than SST simulation. On the other hand, it was founded that too fine mesh has a small effect on the prediction accuracy of the cavitation volume, although the resolution of the vortex is improved.

Investigation of the inlet useful temperature difference effect on the distribution of hydrodynamic characteristics of the vapor-liquid flow inside the falling-film evaporator heating tube designed for a nitric acid solutions evaporation

We present the results of mathematical modeling of effect of inlet useful temperature difference on the vapor- liquid flow in the heat exchange tube of a vertical evaporating film apparatus, which is designed for evaporation of nitric acid solutions. Distributions obtained along the heat exchange tube length of local values of the: mass flow rate of the fluid and secondary steam, the velocity of the fluid film, the velocity of the secondary steam, the Reynolds criterion of the liquid and vapor phases, the absolute pressure depending on the values of this useful temperature difference. The study was carried out using numerical simulation. To study the effect of the initial useful temperature difference on the hydrodynamics of the vapor-liquid flow, the vertical evaporator equipped with the tube ø38x3 mm and length of L = 4 m was adopted. The linear nature of the distribution of hydrodynamic parameters along the length of the heat exchange tube is established. The absolute pressure in the tube space decreases along the heating tube due to pressure drop. The limiting factor in reducing the absolute pressure is the friction losses of the secondary vapor on the solution film surface. A decrease in the pressure in the tube space leads to decrease in the boiling point of the solution. This leads to increase useful temperature. This has a positive effect on the evaporation efficiency The obtained data should be used in the design of evaporation plants, which are designed for evaporation of nitric acid solutions.