Flow In Horizontal Channel Research Articles

Supercritical heat transfer of Novec 649 refrigerant in a minichannel with various inclination angles: Horizontal to vertically downward flows

The study of organic fluids under supercritical conditions has been less extensive than that of supercritical carbon dioxide and water. In addition, most studies on supercritical heat transfer have focused on horizontal or vertical channels, with limited research on inclination angles. Therefore, the focus of this study was to investigate the supercritical heat transfer of organic fluid (Novec 649) in a miniaturized channel across various inclination angles. The experimental findings reveal that the heat transfer coefficient (HTC) increases with an increase in the fluid's bulk temperature at a given mass flux and with an increase in the mass flux at a given bulk temperature. Notably, the HTC in horizontal flow channels marginally surpasses that in non-horizontal channels. The buoyancy effect, found to be non-dominant in a studied channel, does not lead to heat transfer deterioration. In vertical flow channels, under the experimental conditions, the acceleration parameters exceeded the threshold values, suggesting a potential significance of the acceleration effect. Particularly at higher mass fluxes, the acceleration parameter peaked as the film temperature approached the fluid's pseudocritical value. We further developed the supercritical heat transfer correlation by introducing an inclination angle parameter, achieving a mean absolute error of 12.7 %.

Numerical simulations of bubbly flows in a vertical periodic channel

In this study, numerical simulations of bubbly flows in an infinitely long vertical channel were performed. Generally, the upper and lower boundaries of such channels are simplified as periodic boundary conditions. Unlike horizontal channel flows, the presence of gravity in the streamwise direction complicates the establishment of periodic boundary conditions. Therefore, a specialized treatment is required to prevent fluid acceleration. Here, we developed a novel treatment for the imposition of periodic boundaries and proposed a new microbubble model to consider the surface tension effect of microbubbles. To detect each bubble in the flow field, we implemented a bubble identification algorithm, which facilitates a thorough statistical analysis of bubble number, size, and spatial distribution. Validation tests were conducted, and good agreement was achieved between our results and reference data. We also confirmed that the results obtained with periodic boundaries are consistent with those achieved without them. Finally, we simulated the evolution of rising bubble swarms in a quiescent liquid. The method presented here contributes to the numerical simulations of bubbly flows in industrial systems, including oil-gas transportation, bubble columns, and nuclear reactors.

COMSOL Multiphysics simulation of hydromagnetic flow in horizontal channels with diverse media: Insights into momentum and heat diffusion limitations

AbstractThe Darcy–Forchheimer model for a two‐dimensional hydromagnetic flow in a horizontal channel, including the dynamic interaction of porous and nonporous media, is investigated in this study due to the importance of the consequences of heat exchange in porous materials. The novelty of the current investigation is to study the hydrodynamics of fluid flowing through a channel with free and non‐Darcy porous media linked next to one another influenced by the potent Lorentz force. The prime objective of this investigation is to analyze the influence of critical nondimensional parameters on the rate of heat transfer and shear forces exerted on the walls of the channel. Numerical simulations are carried out using the finite element method within the COMSOL Multiphysics program, which offers a versatile framework to explore the behavior of velocity and isothermal contours. The essential optimal stability of this adopted model is achieved for specific scenarios employing a finely meshed grid and grid‐independent analysis. It is noteworthy that larger Prandtl numbers enhance heat transmission rates from surfaces at high temperatures, whereas greater Eckert numbers are correlated with lower Nusselt numbers. On the lower surface, the Forchheimer and magnetic drag forces reduce skin friction, whereas the top surface displays a different pattern. The aforesaid findings have a variety of engineering applications by improving the flow dynamics in porous and nonporous materials. This study can be beneficial in designing heat exchanger devices.

Experimental Investigation on Two-Phase Flow in Horizontal Channel with Vortex Generator

Vortex generator can be used to enhance heat transfer as it is capable of providing better mixing. Vortex generator is easy to manufacture and install in heat transfer units without much additional cost. Present work is planned to investigate the effect of vortex generators on local heat transfer coefficient, critical heat flux (CHF) and pressure drop to ensure design and safety of heat transfer units with vortex generators. Experiments are carried out for three values of pitch 22, 32 and 41 mm and an angle of attack of 45° of vortex generators with horizontal configuration in a smooth tube of diameter 11.9 mm, length 1,000 mm and 0.4 mm wall thickness with R-123 as the working fluid. The effect of mass flux (175–681 kg/m2s) and heat flux (7.9 − 221.7 kW/m2) are studied. Both horizontal and vertical-oriented configurations of the vortex generator are tested. Local wall temperature measurement is carried out with Infrared thermography. Comparing results with plain tube shows the heat transfer coefficient and CHF enhancement. Horizontal orientation (HO) of the vortex generator gives better results than the vertical orientation (VO). Heat transfer coefficient, CHF and pressure drop penalty increase with a decrease in the pitch of the vortex generator.

Rayleigh–Bénard type PCM melting and solid drops

In this paper we document both theoretically and numerically the melting of PCM in an enclosure heated from the bottom, in the presence of vertical metallic fins. We start with the analysis of the PCM melting in the absence of fins to discover the main scales of the problem, stressing the occurrence of Rayleigh-Bénard cells generated during the convection regime of melting. We continue with predicting the impact of fins on the development of the melting interface. The numerical experiments allow to understand the impact of the aspect ratio between the height of the enclosure and the distance between fins on the melting dynamics. They highlight the existence of solid drops for a certain range of aspect ratios when the horizontal flow channels in the convective loops along the fins become in contact, and they show how the solid drop is dragged downward to finish melting on the heated bottom of the enclosure.

Numerical analysis of the effects of interconnector design and operating parameters on solid oxide fuel cell performance

Fuel cells can provide higher electrical conversion efficiency than traditional coal-fired power plants and electric generators based on internal combustion engines. In addition, high-efficiency solid oxide fuel cells (SOFC) have two specific advantages compared with other fuel cells as a result of their high-temperature operation. First, SOFCs are compatible with various fuels, ranging from hydrogen to CO and hydrocarbons. Second, SOFCs generate significant amounts of exhaust heat that can be used in combined heat and power systems. Furthermore, SOFCs have quiet and vibration-free operation, eliminating the noise typically associated with power generation systems. These fuel cells also produce no or very low levels of SO2 and NO emissions. In this study, we numerically investigated the performance of a planar SOFC with different interconnector designs at various operating temperatures. Multiple parameters were considered, such as interconnection geometries, anode and cathode materials, operating temperatures, and flow rates. As a result, the horizontal sinusoidal flow channel geometry, operating temperature of 600 °C, hydrogen gas flow rate of 86.5 SCCM/min, and oxygen gas flow rate of 28.75 SCCM/min, NiO anode material, and LSCF cathode material provided the greatest performance in terms of energy and current density.

Role of slip in the stability of viscoelastic liquid flow through a channel

For a horizontal channel flow of a weakly viscoelastic liquid that follows the constitutive model of Walters’ liquid B′′, a linear stability analysis is performed when the channel walls are slippery. In this case, the viscoelastic channel flow is driven by the streamwise pressure gradient. We explore the primary instability for a symmetric slip flow with the same slip length of the channel walls, an asymmetric slip flow with different slip lengths of the channel walls, and an analogy to the Poiseuille–Couette flow of a viscoelastic liquid with a slip effect on the lower wall but no slip effect on the upper wall. We observe that the viscoelastic parameter shows a destabilizing impact, but the slip length shows a stabilizing impact on the most unstable shear mode in all three flow configurations. Moreover, the Poiseuille and Poiseuille–Couette flows for the viscoelastic liquid are linearly more unstable to infinitesimal disturbances than those of the Newtonian liquid. As a result, wall velocity needs to be higher than in the Newtonian liquid to stabilize the viscoelastic Poiseuille–Couette flow. Using the asymptotic analysis, we have determined the critical value of the slip length, or equivalently, the critical value of the lower wall velocity, above which the asymmetric slip flow and the Poiseuille–Couette flow of the viscoelastic liquid are permanently stable to infinitesimal disturbances.

Research on internal flow characteristics of the labyrinth disc regulating valve

As a new type of multi-stage high-performance regulating valve, the labyrinth disc regulating valve takes advantage of the labyrinth channel on the sleeve disc to dissipate the high-pressure differential energy into the multi-stage throttling flow resistance. It can effectively prevent the failure problems such as erosion, cavitation, and noise caused by extreme working conditions such as the high-pressure differential, high-speed flow, and high temperature. In order to study the flow characteristics of the fluid inside a new type of labyrinth disc-type regulating valve in the thermal power process, an experiment on the pressure reduction characteristics of a double-entrance labyrinth flow channel was carried out. Firstly, an experimental device was designed and built, and then the pressure drop values of each horizontal flow channel were measured and compared with the numerical simulation results to verify the accuracy of the numerical model. Aiming at the actual working conditions of the labyrinth disc regulating valve in thermal power generation applications, the Realizable k-- turbulence model and the mixture multiphase flow model are combined with the Zwart-Gerber-Belamri cavitation model to clarify the flow characteristics and cavitation of the incompressible medium water in the labyrinth flow channel inside the labyrinth disc regulating valve and the flow characteristics of a double-entrance labyrinth flow channel under different opening degrees.

Experimental Study on Heat Transfer Characteristics of Two-Phase Flow in Square and Rectangular Channels

Two-phase flow in non-circular cross-section flow channels such as micro-heat sinks and micro-channel heat exchangers has received extensive attention due to its heat-enhancing properties. In this paper, under the boundary of constant heat flux, an experimental investigation of the heat transfer properties of gas–liquid two-phase flow in horizontal channels with cross-sections of 4 × 4 mm and 8 × 3 mm is carried out using air and water as working fluids. The effects of different inlet gas and liquid inlet Reynolds numbers on the wall temperature and Nusselt number are discussed. The results show that the effects of the liquid Reynolds number and the gas phase Reynolds number on the heat transfer coefficient of the square tube and the rectangular tube are different. Under the same gas–liquid Reynolds number, the Nusselt number of the gas–liquid two-phase flow in the square-section tube can be increased by 3.2 times compared with that in the single-phase flow, while the Nusselt number of the gas–liquid two-phase flow in the rectangular tubes can be increased by 1.87 times. The results of this paper provide a reference for the design of microchannel heat exchangers and the establishment of mathematical models for Taylor flow heat transfer in rectangular and square tubes.

Slugging in horizontal channel flow

Abstract The stratified flow of gas–liquid mixtures is important in many industries, in particular oil and gas, where the formation of liquid slugs is usually undesirable. In this paper, we analyse the hydraulic model for turbulent, two-layer, gas–liquid flow in a horizontal channel developed by Needham et al. (2008, The development of slugging in two-layer hydraulic flows, IMA J. Appl. Math., 73, 274–322) who considered only the thin layer limit, for liquid layers of arbitrary thickness. This allows us to consider the effect of the prescribed inlet velocity ratio and the interaction of the gas layer with the upper wall of the channel on the formation of slug formation. We show that there is a critical Froude number above which small-amplitude disturbances to the uniform flow are unstable and grow to form non-linear roll waves. We investigate the existence of periodic travelling wave solutions and find that these are strongly influenced by the existence of two equilibrium solutions that are not present when the liquid layer is thin. The system of ordinary differential equations that describe travelling wave solutions has a complicated phase portrait which we study in some typical cases. We find that periodic solutions that have the channel close to filled with liquid can exist, and we identify them as slugs. We also study an initial value problem driven by noise at the inlet of the channel and find that structures locally similar to these periodic travelling waves are generated. We provide numerical evidence for the formation of slugs in cases where the initial liquid to homogeneous velocity ratio is greater than 0.5.

Shear induced lift and rotation on MicroFiber deposition in low Reynolds number flows

Lateral migration is of significant importance to fiber deposition in wall-bounded flows, especially when other active external physical transport mechanisms are absent. Due to great technical difficulty, investigation on this phenomenon is limited to fundamental derivations, and the implication to particle deposition has not been fully explored. To fill the gap, this study investigated the shear-induced lift and rotation on microfiber transport and deposition in low Reynolds number flows. Transport and deposition of non-neutrally buoyant ellipsoidal fibers in Poiseuille flow in horizontal and vertical channels is systematically examined, and various lateral migration scenarios are carefully investigated. It was found out that, in absence of the sideway gravity, shear-induced lift and rotation cause the fibers to drift across main streamlines in the vertical channel. This lateral movement is either the driving force for fiber deposition in a downward flow or pushes the particles toward channel center in an upward flow configuration. Lateral migration velocity in the vertical channel is found to correlate positively with fiber length and shear rate. Lateral migration is negligible in a horizontal channel where the sideway gravity is dominant. Current study clearly identified the presence of fiber transport scenarios where lateral migration driven by the shear-induced lift and rotation is the major contributor for fiber deposition in wall-bounded flows. The finding is of particular significance to practical applications, as frequently, they involve a combination of these transport scenarios either actively or passively. The study also provided additional insights to examine the equivalency of spheres to fiber dynamics.

Numerical Investigation of Convective Heat Transfer and Fluid Flow Past a Three Square Cylinders Controlled by a Partition in Channel

This document presents a research article on the control of fluid flow around three heated square cylinders placed side by side in a 2D horizontal channel using a flat plate. The objective of this research is to examine the effect of the position, length and height of a flat plate on fluid flow and heat transfer. For this purpose, numerical simulations are performed by using the Boltzmann double relaxation time multiple network method (DMRT-LBM). The MRT-D2Q9 and MRT-D2Q5 models are used to treat the flow and temperature fields respectively. In contrast to several existing investigations in the literature in this domain which study the passive control of the flow using a horizontal or vertical plate around a single cylinder, this work presents a numerical study on the effect of the position, length and height of a flat plate (horizontal and vertical) on three heated square cylinders on the flow and temperature fields. First, the effect of the position and length of the horizontal flat plate is examined. This study shows that the implementation of a flat plate of length Lp = 4D at a position g=3 behind the central cylinder reduces the amplitude of the Von Karman Street and allows large and regular heat exchange. Thus, in the second part, the effect of the position and height of the vertical flat plate is studied. The results obtained show that the implementation of a flat plate of height h=2D at a position g=3 behind the central cylinder improves the thermal exchange between the incoming fluid and the heated cylinders. This numerical work could lead to the prediction of the cooling of the electronic components: The cooling of the obstacles is all the better when the control plate is arranged at g = 3 and its height h = 2D in the case of the vertical plate or its length Lp equal to 4D in the case where the plate is implemented horizontally

Dynamics of suspended sediment transport: A Direct Numerical Simulation study

The dynamics of suspended sediment transport in horizontal open channel flow is analysed using point-particle one-way coupling Direct Numerical Simulations (DNS), with a virtual wall as a simple particle resuspension model. In sediment transport, the bed-load is dominated by the inter-particle interactions, but the suspended sediments are transported essentially in a one-way coupling situation. The validity of one-way coupling DNS with point-particle approach for the transport of suspended sediment is analysed, by comparing the simulations with existing well-designed experiments performed under very similar conditions. The range of the relevant non-dimensional parameters of the simulations is roughly the same as in actual sediment transport, except for the flow Reynolds number. Good agreement is observed between the simulations and the experiments; furthermore, the simulation results of the motion of the suspended sediment are insensitive to the position of the virtual wall, provided this wall is placed in a region where the fluid velocity fluctuation in the wall-normal direction is comparable to the particle settling velocity. Using the simulation results, the interplay between the different fluid–particle interaction forces is analysed, with and without gravity. In the absence of gravity, the dynamics is dominated by the balance between the stress-gradient force and the turbophoretic effects; as the particle-to-fluid density ratio for the sediment particles is on the order of one, the situation is quite different when compared to the dynamics with a density ratio on the order of 1000. When gravity is included, the dynamics is dominated by the interplay between the drag and gravitational forces, and they balance each other. Both with and without gravity, the lift and added-mass forces have only secondary effects and do not play an important role.

Experimental study on length, liquid film thickness and pressure drop of slug flow in horizontal narrow rectangular channel

In this paper, a visualization investigation for the characteristic parameter (velocity, length, liquid film thickness, etc.) and pressure drop of slug flow in a narrow rectangular channel with a cross-sectional area of 68 mm × 1.9 mm was carried out under horizontal condition. The slug bubble velocity is linearly related to the two-phase mixture velocity. The slug bubble velocity of laminar flow zone (Relo<2500) and turbulent flow zone (Relo≥2500) was fitted, respectively. The slug bubble liquid film thickness was measured based on PCB (Printed Circuit Board) liquid film sensor. The experiment results show that the liquid film thickness increased with increasing Ca under Reb<3100, while liquid film thickness approximately a constant under Reb≥3100. A new correlation for predicting liquid film thickness was proposed and validated with 210 available data. Moreover, based on the present and published data, a new slug bubble length correlation was also developed. The slug frequency increases significantly with the increasing liquid flow rate and decreases slightly with the increasing gas flow rate. But the flow condition has little influence on the slug length. Existing correlations for pressure drop based on separated flow model were summarized and evaluated with the current data. Lee’s correlation perform well for the region dominated by surface tension(Reb<3100) while Chisholm’s correlation perform well for the region dominated by inertia force (Reb≥3100).

The investigation of the efficiency of oil displacing from the pore in the rock formation depending on the width and height of the pore using nanosuspension as a displacing agent

The numerical investigation of the two-phase fluid flow in a microchannel was carried out. The effect of the pore width and height on the oil displacing efficiency by nanofluids for various Reynolds numbers was studied. The computational domain was a T-shaped microchannel with a horizontal main flow channel and a vertical channel that imitated the pore in the rock formation, called a pore channel. The main channel width and height were 200 µm, and the pore channel width and height were varied in the range from 100 µm to 800 µm. The Reynolds number was varied from 0.1 to 100. The main studied characteristic was the oil recovery coefficient, defined as the ratio of the volume of oil remaining in the pore to the volume of the pore. That characteristic, obtained for a case, when the nanofluid was used as a displacing agent, was compared to the similar one obtained for a case, when pure water was used as a displacing agent. A single-phase fluid with properties, determined experimentally, was considered the nanofluid. The mass concentrations of SiO2 nanoparticles were 0.25% and 0.5%. The average diameter of nanoparticles was equal to 5 nm. It was found, that the oil recovery coefficient increased with an increase in width of the pore channel and a decrease in its height. It was obtained that the nanofluid can enhance the oil recovery in several times as compared to pure water. It was also found that the main factor affecting the efficiency of oil recovery is the contact angle of wetting.

Stability analysis of pedestrian traffic flow in horizontal channels: A numerical simulation method

The operational state of the pedestrian flow through the horizontal passage has a direct bearing on the operational efficiency of the entire urban railway transit hub. This study aimed to build a lattice hydrodynamic model considering the overtaking effect of pedestrian traffic and the proportion of the pedestrian flow in two opposite directions. Based on the linear stability analysis, the stability condition of the model was obtained. The results showed that reducing the difference in the proportion of the pedestrian flow in two opposite directions could expand the stable region. Further, the mKdV equation describing the density wave propagation behavior near the critical point was derived based on nonlinear analysis. The kink–anti-kink wave solution was found for the mKdV equation. The results showed that when the overtaking effect was less than the threshold of 0.16, the jamming transition occurred between the uniform pedestrian flow and the kink density waves. When the overtaking constant was more than the threshold, a chaotic region appeared on the phase diagram. The anti-interference capability of the pedestrian flow decreased, and the entire system was in an unstable state. The numerical simulation verified the accuracy of the linear and nonlinear analyzes.

Spatial development of single void pulse in a horizontal turbulent bubbly channel flow investigated by a time-resolved two-laser measurement

The presence of void waves, alternative dense and sparse distribution of bubbles, can promote frictional drag reduction in horizontal turbulent boundary layers compared with the uniform passage of bubbles. This paper aims to determine how long a void pulse (i.e. simplest waveform in void waves) can persist downstream. First, we explored the internal structure of the void pulse and its spatial development by establishing a time-resolved two-laser measurement system. Then, advection and distortion of the pulse were analyzed and modeled by a one-dimensional Korteweg de Vries–Burgers (KdV–B) equation for water including and excluding surfactant, leading to the following conclusions; (i) the KdV–B equation well approximates the measured void pulse behavior and can be used as a mathematical predictor for the downstream propagation, (ii) advection velocity and diffusion of the pulses are explained by the velocity variation of bubbles and the depth of the bubbly layer, (iii) the pulse contains significant nonlinear advection velocity associated to local void fraction, and it causes the pulse to lean backward to retain a sharp streamwise gradient in each rear part of the pulse, and (iv) the pulse finally disappears in the channel flow because it does not include the solitary wave appearing in the KdV equation, judged by a combination of the nonlinear advection velocity and the dispersion coefficient.

Repetitive bubble injection promoting frictional drag reduction in high-speed horizontal turbulent channel flows

Air lubrication adopting repetitive bubble injection was examined in a facility of high-speed turbulent channel flow. The bulk water velocity in the channel was controlled from 5.0 to 7.0 m/s, resulting in a channel Reynolds number Rem > 105 and friction Reynolds number Reτ > 103. Bubbles were injected with gas flow rates periodically fluctuating at frequencies of 1.0–6.0 Hz in the upstream section of the channel. In the downstream of the channel, a periodic pattern of bubble distributions and a periodic fluctuation of wall shear stress were observed at a frequency coinciding to the frequency of bubble injection. Measurements of the wall shear stress show that the ratio of the time-averaged drag reduction was improved by the repetitive bubble injection relative to the conventional method of continuous bubble injection. The largest ratio was obtained at a frequency of 2.0 Hz. Under this condition, the ratio of the drag reduction per unit volume of injected gas was almost twice that for continuous bubble injection, demonstrating the superiority of repetitive bubble injection in terms of the efficiency of drag reduction.

Direct numerical simulation of frictional drag modulation in horizontal channel flow subjected to single large-sized bubble injection

Bubble drag reduction (BDR) is desirable for achieving better propulsion performance in underwater applications. Large-sized bubbles have significant potential for application in BDR, as they provide excellent drag reduction. In this study, we analyzed the drag modulation effects of large-sized bubbles, especially high-Weber number bubbles, on the horizontal turbulent channel flow using direct numerical simulation. The Weber number (We) was varied from 130 to 337 based on the equivalent diameter and bubble velocity. The two-phase model based on the volume-of-fluid approach and IsoAdvector method for sharpening the bubble interface was used. To study the drag modulation mechanism of large-sized bubble, the skin friction profile along the centerline of the bubble and local mean ratio of skin friction were analyzed at different Weber numbers. The bubble length was found to have a significant effect on drag reduction toward the rear region of the bubble. Based on this observation, we analyzed the influence of the bubble regions on drag modulation by confining each region. The numerical results indicated that the skin friction was sensitive to the bubble size and bubble regions, the changes in the skin friction profile, contour, and local averaged values with the variation in the Weber number were analyzed. Considering the relationship between the bubble regions and skin friction, most bubbles exhibited an increase in drag on the liquid film until We = 337. Meanwhile, the area of drag reduction in the secondary flow increased and broadened with an increasing Weber number. Owing to this tendency, the effect of drag reduction is expected from sufficiently larger bubbles around We = 337. These results afford new insights into bubble-induced drag modulation in different regions of horizontal flow, and important parameters of large-sized bubbly flow for the investigation of overall drag reduction performance.

Characterization of the Pressure Drop during Condensation in Channels of Multi-Channel Cylinder Dryer Using Homogeneous and Separated Flow Models

The condensation resistance characteristics of steam flow in horizontal rectangular channels of multi-channel cylinder dryer (MCD) is a very important factor that affects the heat transfer, while it is not very clear due to the limited studies. In this paper, the frictional resistance characteristics of the two-phase flow (steam and water) in the rectangular small channels of MCD were investigated with deionized water as the working fluid, and the calculation models, homogeneous and separated flow models, of the two-phase flow pressure drop in the channel were verified and evaluated. It showed that the main part of the total pressure drop was the frictional pressure drop, which means that the calculation of frictional pressure drop was the key to the calculation of the pressure drop of the two-phase flow in the channel. Meanwhile, it was found that the homogeneous model was not suitable for the calculation of the frictional pressure drop and the separated flow model was completely in line with the experimental data. In this study, the converted coefficient of complete steam/liquid phase were concerned to calculate the frictional resistance using five separated flow models. It was found that the Chisholm B model showed better accuracy than prior correlations, which was greatly consistent with experimental data, and the average absolute percentage deviation (MAPE) was 24.9%.