Channel Transfer Research Articles

Superconductivity in an Orbital‐Reoriented SnAs Square Lattice: A Case Study of Li0.6Sn2As2 and NaSnAs

AbstractSearching for functional square lattices in layered superconductor systems offers an explicit clue to modify the electron behavior and find exotic properties. The trigonal SnAs3 structural units in SnAs‐based systems are relatively conformable to distortion, which provides the possibility to achieve structurally topological transformation and higher superconducting transition temperatures. In the present work, the functional As square lattice was realized and activated in Li0.6Sn2As2 and NaSnAs through a topotactic structural transformation of trigonal SnAs3 to square SnAs4 under pressure, resulting in a record‐high Tc among all synthesized SnAs‐based compounds. Meanwhile, the conductive channel transfers from the out‐of‐plane pz orbital to the in‐plane px+py orbitals, facilitating electron hopping within the square 2D lattice and boosting the superconductivity. The reorientation of p‐orbital following a directed local structure transformation provides an effective strategy to modify layered superconducting systems.

Superconductivity in an Orbital-Reoriented SnAs Square Lattice: A Case Study of Li0.6 Sn2 As2 and NaSnAs.

Searching for functional square lattices in layered superconductor systems offers an explicit clue to modify the electron behavior and find exotic properties. The trigonal SnAs3 structural units in SnAs-based systems are relatively conformable to distortion, which provides the possibility to achieve structurally topological transformation and higher superconducting transition temperatures. In the present work, the functional As square lattice was realized and activated in Li0.6 Sn2 As2 and NaSnAs through a topotactic structural transformation of trigonal SnAs3 to square SnAs4 under pressure, resulting in a record-high Tc among all synthesized SnAs-based compounds. Meanwhile, the conductive channel transfers from the out-of-plane pz orbital to the in-plane px +py orbitals, facilitating electron hopping within the square 2D lattice and boosting the superconductivity. The reorientation of p-orbital following a directed local structure transformation provides an effective strategy to modify layered superconducting systems.

Viscosity dissipation and mixed convection flow in a vertical double-passage channel with permeable fluid

The method of regular perturbation is used to analyse the fully developed flow and heat transfer in a vertical two-way channel containing a permeable liquid. The Brinkman model is used for flow through porous media. The energy equation contains a viscosity term and a Darcy dissipation term. The fully conductive thin partition is divided into two stages; the wall is uniformly heated; and the effects of the porous parameter σ and the mixed convection parameter λ on the velocity and temperature distribution near the hot and cold walls are investigated. The results show that these effects mainly depend on the position of the baffle. Analytical solutions are first used to resolve the simpler problems of either a negligible Brinkman number or a negligible Grashof number. Then, using a perturbation series method, the combined effects of buoyant forces and viscous dissipation are examined. The velocity field and the temperature field in the cases under study were assessed.

Sensitivity analysis of nonlinear convective heat transport of a hybrid nanoliquid sandwiched by micropolar liquid using RSM

Petroleum and polymer industries utilize a multilayer flow model for efficient heat transfer. In such applications, the linear Boussinesq approximation is not recommended as the devices used in such experiments would work at moderate or extremely high temperatures. Therefore, the flow and heat transfer in a multilayer vertical channel with a magnetic field and the nonlinear (quadratic) Boussinesq approximation are investigated, with the central region filled with a hybrid nanoliquid and the outer regions filled with an oil-based micropolar liquid. The effects of Joule heating and viscous dissipation are taken into account. The effective viscosity and thermal conductivity are modeled using the experimental data based Esfe model. The modeled equations are coupled and nonlinear, they are solved using the Differential Transform Method (DTM). Results are analyzed for various values of the material parameter, quadratic convection parameter, Brinkman number, mixed convection parameter, Hartmann number, nanoparticle volume fraction (NVF) on Nusselt number, skin friction, velocity, microrotation velocity and temperature distributions. Additionally, multi-objective optimization of Nusselt number and friction factor is performed for three different levels of the quadratic convection parameter , material parameter and the NVF using the Response Surface Methodology (RSM). The material parameter diminishes the velocity whereas enhances the microrotation velocity. Also, the quadratic convection parameter increases the flow field. Sensitivity computations reveal that the Nusselt number is more sensitive to material parameter and NVF whereas the skin friction coefficient is more sensitive to quadratic convection parameter.

Advancing thermal performance through vortex generators morphing

The design of rigid vortex generators (RVG) influences the thermal performance of various technologies. We employed Discrete Adjoint-Based Optimization to show the optimal development of vortex generators. Under turbulent flow conditions, different bi-objective functions on the RVG design were examined. Specifically, we aimed at an optimal RVG shape that minimizes the pressure drop and maximizes the local heat transfer in a rectangular channel. We show that an optimal design of an RVG can be obtained using computational fluid dynamics in conjunction with the Pareto Front at a computational cost of the order ~O(10^{-1}). We obtained three essential vortex generator shapes based on the RVG morphing technique. Compared to the baseline geometry of a delta winglet pair DWP, the first morphed design reduced the pressure drop by 39%, however, at the expense of a 21% reduction in the Nusselt number. The second vortex generator design enhanced the heat transfer by 18%, however, at the cost of a significant increase in pressure drop of about 40%. The final morphed design achieved the highest thermal performance factor of 1.28, representing a heat transfer enhancement of 6% with a moderate increase in pressure drop of about 13% compared to DWP vortex generators. Furthermore, we investigated the effect of introducing different size holes on the mass reduction of vortex generators and their thermal performances. The mass of vortex generators can be reduced by 9% and with an increase of 7% in thermal performance factor concerning the DWP baseline. The findings of this study will lead to highly efficient lightweight heat exchangers.

Numerical analysis of heat transfer of hybrid nanofluid in a porous sinusoidal channel with magnetic field and an alternating heat flux

Recently, a great amount of research was done on wavy conduits due to the importance of heat and flow transfer in wavy channels and conduits, and their special use in various industries. The improvement of heat transfer in these ducts attracted the attention of many researchers, and experimental and numerical studies are devoted. The effect of the presence of a porous medium and magnetic field on forced convection heat transfer and a nanofluid flow in a complex wave-shaped channel with a special boundary condition (Non-uniform with respect to location) was studied for the first time. For this purpose, the heat transfer of a nanofluid in a two-dimensional sinusoidal channel containing a porous medium in the attendance of a magnetic field was analyzed. First, the nanoparticles were optimized using the design of the experiment method, and then modeling was performed using selected optimal particles. To improve heat transfer in a sinusoidal channel, the factors like the injection of optimized nanoparticles, porous medium, and magnetic field usage were used. The equations were discretized using the Fluent software with a finite volume method. The validation of problem outcomes was done using experimental and numerical studies. Porous medium in four different Darcys (10−5, 10−4, 10−3, and 10−2), and applying magnetic fields in four different Hartman (0, 4, 7, and 10) were examined. The results show that the channel wave, and magnetic field intensity improved heat transfer. Furthermore, using a porous medium with high Darcy can increase the Nusselt number. Hence, in the same conditions (Re = 500, Ha = 10) with Darcy number increasing from 10−5 to 10−2, Nu becomes equal to 5.011. This proposed system is an industrial-utility system that can increase heat transfer efficiency.

Fluid Flow and Mixed Heat Transfer in a Horizontal Channel with an Open Cavity and Wavy Wall

Heat exchangers are utilized extensively in different industries and technologies. Consequently, optimizing heat exchangers has been a major concern among researchers. Although various studies have been conducted to improve the heat transfer rate, the use of a wavy wall in the presence of different types of heat transfer mechanisms has not been investigated. This study thus investigates the mixed heat transmission behavior of fluid in a horizontal channel with a cavity and a hot, wavy wall. The fluid flow in the channel is considered laminar, and the governing equations including continuity, momentum, and energy are all solved numerically. The numerical solution is stabilized by using a first-order multi-dimensional characteristic-based scheme in combination with a fifth-order Runge-Kutta method. The flow and heat transfer effects of varying Richardson numbers, Reynolds numbers, wave amplitude, wavelength, channel height, and cavity width are examined. The results indicate that the mean Nusselt number increases with an increase in Reynolds number, wave amplitude, and cavity width, while it decreases with an increase in Richardson number, wavelength, and channel height. The minimum Nusselt number is calculated to be 0.7, whereas the maximum Nusselt number is 27.09. The Nusselt number has only increased by 40% in the higher depths of the cavity, despite the Richardson number being 10,000 times larger. But this figure increases to 130% at lower depths. The mean Nusselt number is thus significantly influenced by channel height and cavity width. The influence of wave amplitude on the mean Nusselt number is twice that of wavelength.

Performance prediction of a distributed Joule-Thomson effect cooler with pillars

• Heat transfer and throttling coupling is used to replace the traditional constant enthalpy throttling. • The performance of the J-T cooler is predicted by simulation. • A novel J-T cooler with multi-layer, multi-pillar micro-channels was designed. Hampson type Joule-Thomson (J-T) throttle coolers are widely used for cooling infrared detectors and many electronic components. The conventional J-T throttle coolers are not compact, with low heat transfer efficiency and small cooling capacity. In this paper, a stacked column cluster type microchannel distributed J-T throttle cooler is designed through combining a compact microchannel etched and shaped by photolithography and an atomic diffusion fusion welding process with a J-T throttle cooler. The dimensions of the cooler are 10 mm for the inlet section, 145 mm for the throttling and heat exchange section,10 mm for the expansion chamber, with 6 layers staggered high pressure channels and 6 low pressure channels. The cooling performance of the cooler under various low-temperature and high-pressure operating conditions were studied through simulations, and the results showed that the cold-end temperatures were 158.0, 147.9, 146.1, 144.1, and 141.1 K for an inlet pressure of 5.20 MPa and inlet temperatures of 280.0, 270.0, 260.0, 250.0, and 240.0 K, respectively, with argon as the work gas. The cold-end temperatures were 163.6, 159.4, 156.8, 154.6, and 152.7 K for an inlet pressure of 5.60, 6.00, 6.40, 6.80, and 7.20 MPa respectively in 288.0 K inlet temperature. In the process of working medium flow and heat transfer in the microcolumn group channel of the cooler, the temperature and pressure change significantly. When the working medium in the flow reaches the phase change state, that is, the phase change temperature and pressure reach, due to the gas liquefies and the flow rate drops, the working medium loses the gas throttling refrigeration effect, and the temperature no longer decreases significantly, and the refrigeration temperature is limited by this. In addition, compared with different inlet pressures, when the inlet temperature is 280.0 K, the 5.20 MPa nitrogen throttling refrigeration temperature is close to the argon gas at 2.98 MPa, which are 223.4 K and 234.9 K, respectively. Therefore, high pressure nitrogen can be considered to replace low pressure argon in engineering applications. In view of the problems involved in the research process of traditional micro-channel throttling coolers, the innovative solutions are put forward in this paper, which can bring new innovations and thoughts for the future research and application of such problems.

Retraction: Fluid Flow and Mixed Heat Transfer in a Horizontal Channel with an Open Cavity and Wavy Wall

Retraction: Fluid Flow and Mixed Heat Transfer in a Horizontal Channel with an Open Cavity and Wavy Wall

Heat transfer in a round channel with circulation of a non-azeotropic mixture

Mixtures are widely used as refrigerants and heat carriers in various energy systems. When a non-azeotropic mixture boils, a light-boiling component releases intensively, which leads to a change in its concentration both in the liquid and vapor phases. The studies were carried out using a non-azeotropic alcohol-water mixture with a mass concentration of ethanol of 20% in a round stainless steel channel. The inner diameter of the channel was 7.6 mm; the wall thickness was 0.2 mm. In this series of experiments, the absolute pressure in the vessel was maintained within 0.050.001 MPa. The range of liquid mass flow rates through the channel was 44–46 kg/m2s; the heat flux density was 1260–11981 W/m2. The wall temperature was measured at 10 points on the lower generatrix of the channel and at 3 points on the upper generatrix. It is shown that with a phase transition, the heat transfer coefficient on the upper generatrix of the channel is significantly higher than that on the lower generatrix of the channel. The heat transfer coefficient on the lower generatrix in the single-phase flow is approximately twice as high as in the two-phase flow.

A review on dryout and Post-dryout heat transfer inside tubes and tube bundles

• Detailed review on dryout mechanism and dryout and post-dryout heat transfer. • Summarizing the dryout criterions and models of dryout and post-dryout heat transfer. • Elaborating the methods of dryout and post-dryout heat transfer enhancement. • Proposing further research suggestions of dryout and post-dryout heat transfer. The working medium changes from subcooled liquid through flow boiling to superheated vapor in actual once-through thermal equipment (such as once-through steam generators, once-through boilers). Dryout heat transfer deterioration inevitably occur in this vapor-liquid two-phase flow and heat transfer process. After dryout occurs completely, vapor almost completely covers the wall, resulting in a rapid deteriorating heat transfer performance and a sharp rising wall temperature, which puts forward higher requirements on the design, manufacture, and operation of the equipment. The mechanism of dryout is elaborated, and the dryout criterion is summarized in this paper. The three methods that are used to describe the mathematical model of dryout and post-dryout heat transfer are arranged, and the dryout and post-dryout heat transfer in the straight channel is introduced. Furthermore, the methods of enhancing dryout and post-dryout heat transfer are introduced such as changing the geometric structure (including changing the shape of the flow channel and processing the surface of the flow channel) and injecting liquid droplets, etc.

Quadratic Displacement Operators—Theory and Application to Millimeter-Wave Channel Tracking

First, a family of quadratic displacement operators based on group Fourier Transform has been proposed for joint distribution analysis. Second, considering the quadratic displacement operators, a novel millimeter-wave massive MIMO channel tracking has been proposed in Time-Angle (TA) plane. Due to a poor scattering environment, millimeter-wave communication suffers from an ill-conditioned channel matrix. Computationally effective compressed sensing has been proposed to estimate a few dominant paths. These methods rely on orthogonal pilot signals to estimate the channel reliably. However, applying compressed-sensing solutions to the continuous channel leads to significant pilot overhead. To reduce the pilot overhead, one needs to consider the channel dynamics, particularly the spectral overlap between the channel samples. Considering that channel spectral properties can be represented as a joint time-angle distribution, we propose a novel quadratic displacement operator in TA-plane. Considering group Fourier transform in TA-plane, we show that the subderivative of an angular parameter is the dual group of the original angular signal. For a group transform defined over the finite Abelian group, with respect to the finite-dimensional antenna arrays, the purposed time-angle representation matches the cover space of manifold defined in the virtual channel model recommended by A. Sayeed. In TA-plane, the quadratic displacement operator maps old time-angle coordinate onto a new coordinate by taking to account the local spectral properties of the channel samples. By applying the purposed quadratic displacement operator to the Saleh-Valenzuela channel model, the time evolution operator for directional millimeter-wave channel has been derived. Assuming independently identically distributed multipath contribution, we show that channel Wigner distribution is the direct sum of the cluster-wise Wigner distribution. Accordingly, we have shown that the continuous linear time-variant channel transfer function can be represented as the Hadamard product between Wigner distribution of the channel and Saleh-Valenzuela model. Considering the fact that the density matrix is a Weyl correspondence of Wigner distribution, a union of subspaces method has been employed to construct the density matrix for channels samples with slightly different states. Numerical results have been presented to evaluate the performance of the proposed channel tracking method.

Heat transfer in a non-uniform channel on MHD peristaltic flow of a fractional Jeffrey model via porous medium

Heat transfer in a non-uniform channel on MHD peristaltic flow of a fractional Jeffrey model via porous medium

Математическая модель канала управления стандарта радиосвязи GSM-R

Purpose: To develop a model for the evaluation and analysis of control logical channels (CC) performance quality of GSM-R radiocommunication standard. Methods: Performance process of shared control channel is presented in the form of a stochastic network with further obtaining equivalent function, average time and the function of distributing the time of information transfer in data transmission channel. Results: Mathematical model of shared CC performance process has been developed, corresponding to the algorithm of establishing connection of a mobile user with a network base station. The modeling results allow to conclude on the model adequacy and to assess the degree of various kind interference impact in a given area, including those created by violator’s jammers. The feasibility of reducing analysis time of the parameters of signals, transmitted from a mobile to base station, as well as the need to increase the noise immunity of signals for the control of entry into communication, received signal level and quality are shown. Practical significance: This model can be used to evaluate and analyze performance efficiency of control channels of GSM-R standard mobile radiocommunication real systems.

Melting heat transport in a mixed convective squeeze flow of a hybrid nanofluid with interfacial nanolayer effects

AbstractThe interfacial nanolayer effect on a mixed convection flow of single wall CNT (carbon nanotube) and CuO (cupric oxide) water based hybrid nanofluid inside a squeezed channel is studied. To maintain the flow, hybrid nanofluid under consideration is either squeezed or dilated in the parallel plate channel. Melting heat condition on one side of the channel is taken. Generalized thermophysical models which include the interfacial nanolayer effects are proposed for the hybrid nanofluid. Governing equations for the flow are tackled via similarity mappings and bvp4c technique. Statistical analysis revealed a strong significance of the interfacial ratio parameters with Nusselt numbers and skin friction coefficients at both ends of the channel. In case of squeezing flow, it is interestingly noted that the melting parameter uplifted the heat transfer rate, however reverse trend prevailed for dilating flow regime. Mixed convection parameter declined the rate of heat transfer in the squeezing channel, but elevated the coefficient of skin friction.

Heat Transfer and Pressure Drops in a Helical Flow Channel Liquid/Solid Fluidized Bed

Industrial liquid/solid fluidized bed heat exchangers are commonly used with particle recycling systems to allow an increased superficial velocity and higher heat transfer rates. Here, experimental results are reported on a novel helical flow channel geometry for liquid/solid fluidized beds which allow higher heat transfer rates and reduced complexity by operating below the particle transport fluid velocity. This eliminates the complexity of particle recycle systems whilst still delivering a compact heat exchanger. The qualitative character of the fluidization was studied for a range of particle types and sizes under several inclinations of the helices and various hydraulic diameters. The best fluidization combinations were further studied to obtain heat transfer coefficients and pressure drops. Improvements over the heat exchange from a plain concentric tube in an annulus were obtained to the following degree: vertical fluidized bed, 27%; helical baffles, 34 to 54%; and fluidized bed with helical baffles, 69 to 89%.

Effects of Jet-to-Target Surface Spacing and Pin-Fin Height on Jet Impingement Heat Transfer in a Rectangular Channel

Abstract An experimental study was completed to quantify heat transfer enhancement, pressure loss, and crossflow effect within a channel of inline impinging jets. The jet diameter is 5.08 mm; the jet-to-jet spacings in the streamwise and spanwise directions are fixed at x/d = 11.1 and y/d = 5.9, respectively. The effect of jet-to-target surface spacing was considered with z/d = 3 and 6. For both jet-to-target surface spacings, smooth, short pin-finned, and long pin-finned target surfaces were investigated. Both roughened surfaces have a staggered array of 120 copper pin-fins. The pin-to-jet diameter ratio is fixed at D/d = 0.94. The pin height-to-jet diameter ratio for the short and long pins are H1/d = 1.5 and H2/d = 2.75, respectively. Regionally averaged heat transfer coefficient distributions were measured on the target surface, and these distributions were coupled with pressure measurements through the array. The heat transfer augmentation and pressure penalty were investigated over a range of jet Reynolds numbers (10k–70k). The results show high discharge coefficients for all the cases. The channels with the small jet-to-target surface spacing experience double the crossflow effect of the large spacing channels. The addition of surface roughness showed a negligible effect on the crossflow. The best heat transfer performance was observed in the narrow impingement channel with the long pins.

OFDM LOW COMPLEXITY CHANNEL ESTIMATION USING TIME-FREQUENCY ADJUSTABLE WINDOW FUNCTIONS

In this paper, we introduce a low complexity algorithm for estimation of the channel transfer function in the OFDM communication system that is using a scattered pilot symbol grid. Although, the use of the scattered pilot grid enables implementation of the flexible, and adaptive radio interface, it suffers from a high estimation error at the edges of the symbol sequence. Due to the sampling in time, and frequency, the signal is circularly expanded in both domains, and this has to be taken into account when the signal is processed. The proposed algorithm is shaping the pilot symbol estimates in time, and frequency domain, such that the aliasing in both domains are reduced or eliminated. We achieve a significant reduction of the estimation error, with a linear increase in computational complexity.

Second Law Analysis of MHD Forced Convective Nanoliquid Flow Through a Two-Dimensional Channel

Abstract The present study deals with fluid flow, heat transfer and entropy generation in a two-dimensional channel filled with Cu–water nanoliquid and containing a hot block. The nanoliquid flow is driven along the channel by a constant velocity and a cold temperature at the inlet, and the partially heated horizontal walls. The aim of this work is to study the influence of the most important parameters such as nanoparticle volume fraction (0%≤ϕ≤4%), nanoparticle diameter (5 nm≤dp≤55 nm), Reynolds number (50≤Re≤200), Hartmann number (0≤Ha≤90), magnetic field inclination angle (0≤γ≤π) and Brownian motion on the hydrodynamic and thermal characteristics and entropy generation. We used the lattice Boltzmann method (LBM: SRT-BGK model) to solve the continuity, momentum and energy equations. The obtained results show that the maximum value of the average Nusselt number is found for case (3) when the hot block is placed between the two hot walls. The minimum value is calculated for case (2) when the hot block is placed between the two insulated walls. The increase in Reynolds and Hartmann numbers enhances the heat transfer and the total entropy generation. In addition, the nanoparticle diameter increase reduces the heat transfer and the irreversibility, the impact of the magnetic field inclination angle on the heat transfer and the total entropy generation is investigated, and the Brownian motion enhances the heat transfer and the total entropy generation.

Numerical Study for Enhancement of Heat Transfer Using Discrete Metal Foam with Varying Thickness and Porosity in Solar Air Heater by LTNE Method

A two-dimensional rectangular domain is considered with a discrete arrangement at equal distances from copper metal foam in a solar air heater (SAH). The local thermal non-equilibrium model is used for the analysis of heat transfer in a single-pass rectangular channel of SAH for different mass flow rates ranging from 0.03 to 0.05 kg/s at 850 W/m2 heat flux. Three different pores per inch (PPI) and porosities of copper metal foam with three different discrete thicknesses at equal distances are studied numerically. This paper evaluates the performance of SAH with 10 PPI 0.8769 porosity, 20 PPI 0.8567 porosity, and 30 PPI 0.92 porosity at 22 mm, 44 mm, and 88 mm thicknesses. The Nusselt number for 22 mm, 44 mm, and 88 mm thicknesses is 157.64%, 183.31%, and 218.60%, respectively, higher than the empty channel. The performance factor for 22 mm thick metal foam is 5.02% and 16.61% higher than for 44 mm and 88 mm thick metal foam, respectively. Hence, it is found that metal foam can be an excellent option for heat transfer enhancement in SAH, if it is designed properly.