Horizontal Channel Research Articles

Numerical investigation of supercritical flow and heat transfer mechanism in printed circuit heat exchanger (PCHE) channels

A numerical study is conducted to investigate supercritical hydrogen flow and heat transfer mechanisms and characteristics in printed circuit heat exchanger (PCHE) channels. The impact of large variations of the thermal-physical properties due to a wide range of operating temperatures have been studied and analyzed in detail. The heat transfer mechanisms of supercritical hydrgen under horizontal and vertical flow conditions are studied numerically. In addition, the influence of different cross-section shapes of the channel is also analyzed. The results show that asymmetrical fluid temperature distributions near the top wall and bottom wall due to the buoyancy effect result in heat transfer deterioration. Spiral flow occurs in the heat transfer deterioration region, which further confirms that the heat transfer deterioration is related to the spiral flow effect caused by the buoyancy effect. The heat transfer coefficient without gravity is lower than that with gravity, indicating that the buoyancy effect enhances the overall heat transfer in the horizontal circular channel. Furthermore, the fluid temperature in the vertical upflow channel decreases slowly from the near wall to the core area, while the fluid temperature in the vertical downflow channel changes sharply, which directly leads to the difference in the temperature gradient near the wall. Compared with the square cross-section channel and semicircular cross-section channel, the supercritical hydrogen can achieve greater heat transfer performance in the circular cross-section channel.

Exergy and entropy analysis of metal foams based on 2nd law of thermodynamics

The available (exergy) and effective use (entropy generation) of energy at the end of thermodynamic processes are significantly important parameters in the design of optimum thermal system. Entropy analysis based on 2nd law of thermodynamics through various pore density metal foams placed in an asymmetrical heated horizontal channel is presented in the current work. Water flows through the channel at different flow rates (inlet velocity varies from 0.02 to 0.3 m/s). Highly porous and different pore density aluminum metal foams such as 10 (0.95), 20 (0.90), 30 (0.92) and 45 (0.90) are inserted into the channel to boost the heat transfer. Darcy Extended Forchheimer (DEF) and local thermal equilibrium (LTE) models are used for the calculation of flow and thermal variables respectively. The numerical outcomes of the examination are first confirmed by comparing with existing experimental literature results. The mean exergy Nusselt number results presented shows that the 10PPI metal foam stretches 35.41 % and 12.20 % higher thermal presentation with respect to 20PPI and 30PPI metal foam. The entropy examination showed that the 20PPI metal foam produces minimum entropy generation at a Reynolds number of 3464.32 and 10PPI metal foam shows highest presentation based on Bejan and entropy generation number.

Buoyancy influences on local heat transfer characteristic of supercritical LNG across the pseudo-phase transition in variable cross-section horizontal channels

The regasification process within the printed circuit heat exchanger (PCHE) channel for supercritical liquefied natural gas (S-LNG) will produce a large temperature difference. This process is considered a pseudo-phase transition process, and the resulting density difference driving buoyancy has a crucial action in influencing the heat transfer and flow of S-LNG. Three horizontal variable cross-section channels are established to examine the buoyancy impact on the local heat transfer and flow of S-LNG within the pseudo-phase transition process in the PCHE channel. It comprehensively analyzes the buoyancy impact on local heat transfer and flow under different channel shapes and mass flow rates. The findings demonstrated that the eddy blockage caused by buoyancy mainly acts on the top of the channel and mainly occurs in the liquid-like and pseudo-critical regions, resulting in the deterioration of local heat transfer on the upper and lower walls of the channel. The hybrid channel achieves the intended design goal, and the diverging channel is almost unaffected by buoyancy. The overall performance evaluation criterion (PEC) is used to evaluate the thermal and hydraulic performance of each channel under different mass flow rates. The data show that the diverging channel has the best thermal and hydraulic performance, and its PEC can reach 1.28. The hybrid channel also achieves the expected effect, and its PEC can reach 1.09.

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.

High-speed noncoherent underwater acoustic communication using permutation alphabets and sliding hypothesis-tree decoding.

A framework for joint synchronization and decoding is presented, named sliding hypothesis-tree decoding (SHDT), which targets communication applications in adverse underwater acoustic channels. The framework is exemplified by constructing a robust noncoherent link with spectral efficiency 0.149-0.222 bit/s/Hz using Polar coding and super permutation frequency shift keying. The link method is evaluated with randomized time-Doppler shifts through replay simulation of recorded UWA channels, where the five benchmark channels of the public benchmark Watermark and two channels from the Baltic Sea are used; these simulations show that a low frame error rate is achievable in all seven channels. The constructed link method is further evaluated in an adverse acoustic horizontal shallow-water channel using a high-mobility setup; the link method is able to perform synchronization, and a decoder performance similar to the replay simulations is observed. SHDT allows the construction of link methods with a performance limited by the information decoding rather than the time-Doppler synchronization, making it applicable to communication with lower-rate methods in non-line-of-sight scenarios.

Simulation Analysis of Metallic Particles Movement in Typical Structure of Oil-immersed Power Transformer

The insulation performance of oil-immersed power transformers is closely involved with the movement of metal particle impurities, and the movement characteristics of metal particles are not only influenced by the electric field, but also by the oil flow. In this paper, a solid-liquid two-phase flow simulation model was constructed, and the effect of electric field on the motion of metal particles was considered. Firstly, the validity of the simulation model was verified by using the experimentally observed motion of metal particles in the horizontal oil channel between parallel flat plate electrodes, based on which the motion of metal particles in the typical oil channels of a 500kV power transformer was studied. It was found that when the metal particles passed through the oil flow inlet, the number of metal particles settling increased with the increase of particle size. All the metal particles with 1mm particle size sank in the oil flow inlet during the oil migration process, it was almost impossible to enter the low, medium and high voltage winding parts. Through the middle or upper end of the high voltage winding, the smaller particles (50μm, 150μm) would easily migrate with the oil flow and move faster; the larger particles (500μm) would move slower or be more easily deposited. This research holds significant practical implications in the engineering study of metal particle motion distribution within transformers.

A heat transfer correlation of Poiseuille-Rayleigh-Bénard convection in the thermal entrance region of a horizontal rectangular channel

In order to understand heat transfer characteristics and obtain a heat transfer correlation of Poiseuille-Rayleigh-Bénard (P-R-B) convection in the thermal entrance region of a horizontal rectangular channel, we performed a series of the direct numerical simulations. The working fluid is water, and the spanwise aspect ratio of the rectangular channel ranges from 2 to 10. The results show that the thermal entrance length for the onset of buoyancy-driven convection extends with the decreasing Rayleigh number and the increasing Reynolds number. The average Nusselt number in the thermal entrance region increases with the increase of Rayleigh number and Reynolds number. Furthermore, a smaller aspect ratio and a shorter length of the channel contributes to enhanced heat transfer in the thermal entrance region. Based on the simulation results, the heat transfer correlation in the thermal entrance region is established, which can be used as a reference for the engineering design on P-R-B convection.

Deep learning model for rapid temperature map prediction in transient convection process using conditional generative adversarial networks

This article presents a deep learning model for three-dimensional (3D) transient mixed convection in a horizontal channel with a heated bottom surface. Using Conditional Generative Adversarial Networks (cGAN), we successfully approximate temperature maps at arbitrary channel locations and time steps. The model is specifically designed for mixed convection at Reynolds number 100, Rayleigh number 3.9 × 106, and Richardson number 88.8. To investigate the impact of the discriminator network architecture on model accuracy, we compare Convolutional Neural Network (CNN) based classifiers with PatchGAN classifiers, both with and without strided convolutions. Remarkably, the cGAN with PatchGAN based classifier (without strided convolutions) yields the highest clarity and accuracy in inferring temperature maps. Additionally, other factors such as image contrast, spatiotemporal variation rate of temperature, and the number of channels in the temperature image significantly influence cGAN accuracy. This work highlights the potential of deep learning in efficiently modeling complex transport processes.

The influence of flow electrode channel design on flow capacitive deionization performance: Experimental and CFD modelling insights

Flow capacitive deionization (FCDI) is an emerging desalination technology at which flow electrodes (shear-thinning flowable carbon slurries) are used to remove ions from saline water. The geometry of flow electrode channels, which provide the path and ensure the distribution and mixing of the flow electrodes, is one of the most important aspects to be optimized. This work presents experimental and computational fluid dynamics (CFD) modelling analysis of the influence of the geometry of flow electrode channels on FCDI performance. Flow electrode gaskets (with open, serpentine (short) horizontal and serpentine (long) vertical channels) were 3D printed using a polyethylene terephthalate glycol (PET-G) filament. The FCDI cell with a vertical serpentine flow electrode channel exhibited the poorest performance due to channel blockage by carbon particles, while the best results were achieved with a horizontal serpentine flow electrode channel. CFD simulations aided in understanding this behaviour by showing that the channel geometry strongly affects the local shear rate, and thus the local viscosity of flow electrodes. Thus, it is recommended to design channels that induce flow disturbance aiming for increasing the shear rate and hence reducing flow electrode viscosity, therefore promoting their flowability and reducing clogging chances.

Electron density measurement by the three boundary channels of HCOOH laser interferometer on the HL-3 tokamak

Far-infrared (FIR) interferometer is widely used to measure the electron density in the magnetically confined fusion plasma devices. A new FIR laser interferometer with a total of 13 channels (8 horizontal channels and 5 oblique channels) is under development on the HL-3 tokamak by using the formic-acid laser (HCOOH, f = 694 GHz). In order to investigate the boundary electron density activity during the divertor discharge, three horizontal interferometry channels located at Z = −97, −76, 76.5 cm have been successfully developed on HL-3 in 2023, and put into operation in recent experimental campaign, with a time resolution of < 1.0 μs and line-integrated electron density resolution of ~ 7.0 × 1016 m−2. This paper mainly focuses on the optical design of the three-channel interferometry system, as well as optical elements and recent experimental result on HL-3.

Entropy generation for exact irreversibility analysis in the MHD channel flow of Williamson fluid with combined convective-radiative boundary conditions

The scrutinization of entropy optimization in the various flow mechanisms of non-Newtonian fluids with heat transfer has been incredibly enhanced. Through the investigation of irreversibility sources in the steady flow of a non-Newtonian Willaimson fluid, an analysis of entropy generation is carried out in this current work. The current study has an essential aspect of investigating the heat transfer mechanism with flow phenomenon by considering convective-radiative boundary conditions. A horizontal MHD channel is assumed with two parallel plates to develop a mathematical model for the flow phenomenon by considering the variable viscosity of the fluid. The contribution of physical impacts of thermal radiation, Joule heating, and viscous dissipation is interpolated in the constitutive energy equation. The complete flow of the current analysis is established in the form of ordinary differential equations which further take the form of the dimensionless system through the contribution of the similarity variables. A graphical scrutinization of the physical features of the flow phenomenon in relation to the pertinent parameters is proposed. This study reveals that the higher magnitude of radiation parameter and Brinkman number dominates the system's entropy. Moreover, the temperature distribution experiences an increasing mechanism with improved conduction-radiation parameter at the lower plate.

On Electronics Cooling Using an Electrohydrodynamic Gas Pump with Aligned Electrodes

Previous studies have shown that electrohydrodynamic (EHD) gas pumps are a viable alternative for traditional fans. In this study, it is further demonstrated that an EHD gas pump is ideal for cooling electronic components. To this end, four electronic components, which are individually mounted on each wall of a horizontal channel, are cooled by a two-stage EHD gas pump with aligned electrodes. Three heat dissipation rates are evaluated: 100, 200, and 500 W/m2. To evaluate the performance of the EHD gas pump, the results are compared with those obtained without using the EHD pump. The present results show that an EHD gas pump can generally produce desirable cooling effects if used properly. The average surface temperature and maximum temperature on the electronic components cooled by the EHD gas pump with electrodes mounted on the horizontal walls are lower than those obtained with electrodes mounted on the vertical walls. Thus, it is important to consider the effect of electrode orientation in selecting an appropriate EHD gas pump for application in electronics cooling.

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.

Fractal patterns in fluid flows: A radial basis pseudospectral analysis of CuO-EG water nano, Saffman dusty, and plain Newtonian fluids in immiscible layers of a horizontal channel

Nano and dusty fluids provide new possibilities to improve energy transfer efficiencies. Motivated by immiscible fluids duct flow framework in the filtration of hydrocarbon materials, the objective of this manuscript is to present the numerical study of three immiscible fluids namely, copper oxide-ethylene glycol (CuO-EG) water nano, Saffman dusty, and plain Newtonian fluids in the horizontal channel. For the formulation of the mathematical model, the dusty fluid is positioned between the immiscible layers of the nanofluid and Newtonian fluid. The interface between the immiscible fluids is continuous and non-deformable in nature. The flow is driven by an externally time-dependent pressure gradient. The novel radial basis function pseudospectral (RBFPS) method is employed to solve the governed partial differential equations, and the resulting outcomes are compared with cubic B-spline differential quadrature and finite difference method. The impact of several crucial fluid parameters, comprising the volume percentage of CuO nanoparticles, the dust particle concentration parameter, and various others on velocity profiles, are presented graphically. It is observed that despite being present only in the lower zone, the CuO nanoparticles have an impact on the flow velocities in other zones also. The fluid and particle velocities decrease as the volume fraction of CuO increases.

Methodology for the Synthesis of a Multicopter Controller Acting as a Swarm Agent using the Thermal Motion Equivalent Method

The paper is dedicated to the development of a method for the synthesis of the control system of a swarm multicopter. The motion of the agents in the swarm is organised by the thermal motion equivalent method. The idea of the method is the behavioral similarity of the thermal motion of the atoms by the agents. In the practical implementation of the thermal motion equivalent method, it is important to ensure constancy of velocity and isotropy of agent dynamics. Violating these properties will cause the swarm to fail a mission, such as an area exploration, by reducing the RMS speed of the agents to zero. The proposed solution to these problems is to synthesize a modal controller for the agent-boundaries test system for the slowest control channel, thereby ensuring RMS velocity constancy of the agent. The synthesized controller is used as a filter in the fast-acting channels, the second horizontal channel and the vertical channel. In the fast-acting channels, an additional filter is proposed to bring their dynamics to the slowest channel, thereby ensuring isotropy. The inclusion of a limit on the maximum length of the equivalent field vector ensures isotropy. The synthesis was carried out using a simplified multicopter dynamics mathematical model, obtained with small UAV deviations from the vertical and without considering the Coriolis force. The methodology for the synthesis of a multicopter control system for functioning as part of a swarm is developed using the obtained results. Numerical simulation results of both a single vehicle in closed space and a swarm using a more complete nonlinear dynamic quadcopter model are presented. The proposed method has the advantage of simple synthesis using a linear model. Numerical simulation results confirm the operability of the developed methodology.

Apron and macro roughness as scour countermeasures downstream of block ramps

ABSTRACT A block ramp is a grade-control structure commonly used to stabilize the river bed with a high efficiency of energy dissipation. This study investigates the effects of using macro roughness and a downstream apron as scour countermeasures on the maximum scour depth downstream of block ramps in straight rivers. All the experiments have been carried out in a horizontal channel and in clear water conditions (no sediment transport). A wide range of hydraulic conditions including densimetric Froude numbers, water drop heights, and tailwater depths for three different rough ramp slopes (1 V:3 H, 1 V:5 H, and 1 V:7 H) was tested. The results have been compared with the results from a smooth ramp (no roughness), which has been considered as a reference. Results show that both macro roughness on the ramp and downstream aprons work well as scour countermeasures while as a comparison, using macro roughness (big-size stones) on the ramp is more effective than downstream aprons to reduce the scour depth. The other finding of this study shows that increasing the downstream apron decreases the length of the scour hole, consequently decreasing the volume of eroded material.

Analysis of mixed convection and surface radiation in a horizontal channel containing different finned heat-generating blocks

In this work, mixed convection coupled with surface radiation in a ventilated horizontal channel is studied numerically. The channel containing three circular heat sources is ventilated by three openings; an inlet and two outlets. All the walls of the channel are adiabatic, and the flow enters the inlet at a cold temperature. To improve the performance of the cooling system, straight or curved fins are mounted on the surface of the hottest cylinder. The governing equations are discretized and solved using the Galerkin finite element method. The key parameters are the Reynolds number, the surface emissivity, the heat ratio and the geometric parameters of fins (size, number, and form). The numerical results show that the system's thermal performance improves by increasing the Reynolds number and the emissivity. In the absence of surface radiation (ε=0), the results indicate that adding fins leads to a decrease in the maximum temperature of the cylinder by about 6.6 °C for both straight and curved fins. However, the outcomes revealed that for ε=1, straight fins should be chosen instead of curved ones. Finally, for engineering purposes and based on the numerical data, correlations between the maximum temperature and the key parameters have been developed.

Failure Process of High-Loess-Filled-Slopes (HLFSs) during Precipitation under Different Mitigation Measures

The problems of gully and soil erosion caused by large-scale urban construction and agricultural development in China have become more and more serious in recent years. In an effort to solve this problem, a series of gully stabilization and highland protection projects have been carried out on the Loess Plateau, and this has resulted in a large number of high-loess-filled-slopes (HLFSs). Although these filled slopes uses several different mitigation measures, the HLFSs have been eroded and destroyed under the action of water. In order to study the influence of different mitigation measures on the stability of HLFSs and their failure process, this paper uses a flume test of the effects of various mitigation measures on this failure process. The results show that: (1) the failure processes of slopes with different mitigation measures are obviously different. Slope deformation u with a declining gradient mitigation mainly occurs on the surface of the slope body, and although slope erosion is quite serious, the slope does not fail as a whole. Slopes with a stepwise drainage channel mitigation show little erosion, but material can easily slide along the horizontal drainage channels. (2) The slope deformation process is correlated with changes in pore-water pressure. When local instability occurs, there is always a pre-process of continuously rising pore-water pressure. When a failure occurs, the pore-water pressure of the soil at each position of the slope body suddenly fluctuates under instantaneous excitation. (3) The response of soil pore pressure and the development characteristics of tension cracks affect the deformation of the slopes, which is also the cause of the differences slope instability caused by different mitigation measures. These research results provide reference for the protection of HLFS engineering projects from heavy rains.

Binary mixture convection in a horizontal channel under the Soret effect action

The mathematical model describing stationary flow of binary liquid mixture is under consideration. The exact solution of the equations of convective heat and mass transfer is constructed for the special form of the functions of temperature and concentration. All possible statements of boundary value problems are studied in order to analyse thermal diffusion separation of binary mixture in a long horizontal channel with rigid walls. It is discovered that only one of the statements (at inhomogeneous heating of both rigid walls) leads to feasible results. With the help of the constructed solution for the mentioned boundary value problem the effect of layer thickness, given flow rate and action of gravity force on the separation process, is analysed.

Simulation of the effect of horizontal airflow channel on natural ventilation in apartments

Natural ventilation has an important impact on people's work and life. Reasonable use of natural ventilation can effectively improve indoor air quality and thermal comfort, reduce the use of air conditioning and reduce energy consumption. With the continuous development of urbanization, many apartments cannot effectively use natural ventilation. This paper uses CFD simulation to analyze the improvement effect of indoor ventilation after the installation of airflow channel in residential public transportation. The results show that the horizontal airflow channel can improve the indoor air environment and effectively reduce the dissatisfaction rate of indoor thermal comfort and indoor air age.