Slot Channel Research Articles

Entrance effect of curved endwall on heat transfer and flow structure in a confluent channel with pin fins

In advanced turbine blade internal cooling channels, the majority of the remaining coolant converges into the trailing edge and constitutes a confluent flow before the slot entrance. The entrance effects of curved endwalls (convex, concave) for confluent internal cooling channel are numerically investigated in this paper. The overall heat transfer performances and flow structures are compared in the slot channel with pin fin cooling at the five momentum ratios (M = 0.1–2.1). Among all the cases studied, the higher momentum inflow not only enhance heat transfer but also reduce pressure loss in the slot channel with concave endwalls. In particular, the substantial comprehensive heat transfer factor (η) increase reaches 29.4% higher than the flat endwalls at the given relative curvature height ratio of 1.83. For the models with convex endwalls, the jet-like flow improves the η at the most by 12.1% compared to the flat endwalls. As the curvature height ratio increases, the effects of curved endwalls diminish eventually. In addition, the momentum ratio determines the formation and specified impact of the above flow characteristics in the confluent flow. The curved endwalls exhibit more increase in the η at lower M.

Designing an IoT platform using Wireless Sensor Network

The Internet of Things (IoT) is not only a well-researched topic but also a growing industry. Although the main idea is to connect devices to the internet, there are many ways to do this since IoT systems are application-oriented. This paper presents a wireless sensor network (WSN)based IoT platform designed for wide are aapplications. The platform consists of one or more wireless sensor networks, gateways, web servers, and databases that provide a reliable connection between field sensors and Internet databases. WSN is based on the IEEE 802.15.4e Time Slot Channel Hopping (TSCH) protocol because it has the high performance. Subsequent to the system designed for many subscribers, new synchronization plans and effective transmission functions are also planned to increase network capacity and reduce energy consumption. Therefore, the platform concept can meet the needs of high-end applications and the battery life of low-end applications

Well perforation optimization using an abrasive jet technique to create oriented slotted channels in terrigenous reservoirs

Various casing perforation methods are used to ensure a hydrodynamic reservoir-to-well connection. However, perforated wells often do not perform satisfactorily during production. This is largely due to a decrease in the permeability of the near-wellbore formation as a result of casing perforation work. Studies and analysis of existing casing perforation methods have shown the effectiveness of abrasive jet perforation. The paper presents the results of numerical modeling to optimize the layout of slot channels during the abrasive jet perforation (AJP) of terrigenous productive object. Geomechanics analysis of the influence the formation scheme and orientation of the slotted channels in the productive layer during abrasive jet perforation on the permeability of terrigenous reservoirs of the oil fields in the Perm Krai was performed. The disadvantages of widespread methods of exposing perforation are described and the advantages of abrasive jet perforation based on geomechanical modeling are revealed. The calculations carried out on the placement of slotted channels showed that the distance between the systems of slotted channels is not important, since they weakly interact with each other in height with standard schemes. It was established that the best placement scheme for jet slot channels is a system of four slot channels shifted along the length of the well to the height of the slot channel with a phasing of 90°. Comparative calculations of the reservoir permeability of the near-well zone for various perforation methods have been performed.

A Comprehensive Performance Comparison of IEEE 802.15.4 DSME and TSCH in a Realistic IoT Scenario for Industrial Applications

In the Industrial Internet of Things (i.e., IIoT), the standardization of open technologies and protocols has achieved seamless data exchange between machines and other physical systems from different manufacturers. At the MAC sublayer, the industry-standard protocols IEEE 802.15.4 Time Slot Channel Hopping (TSCH) and Deterministic and Synchronous Multi-channel Extension (DSME) show promising properties for high adaptability and dynamically changing traffic. However, performance comparison between these MAC protocols rarely has gone beyond a simulation phase. This work presents the results of such a comparison on physically deployed networks using the facilities of the FIT-IoTLab. The evaluation includes fully implementing an IIoT protocol stack based on MQTT in Contiki-NG. It comprises the integration of DSME as part of Contiki-NG’s software stack through OpenDSME, the only publicly available implementation of DSME. Results show that both protocols suit IIoT applications, particularly for data collection. The comparison between TSCH and DSME also includes an evaluation of distributed schedulers for both MAC modes and one autonomous scheduler for TSCH within a UDP protocol stack.

Heat Transfer Slot Matrix for Compact Rotary Heat Exchangers with Ultra-High Regeneration Ratio for Microturbines

This paper considers the problem of the influence of distancing elements in slot matrix channels on the thermohydraulic characteristics of the matrix of a rotary heat exchanger having various values of the height of the slot channels. The following tasks were carried out: mathematical modeling of thermohydraulic processes in different slot channels having constant height along them (from 0.3 mm to 0.5 mm); analysis of the influence of the slit channels' height, the number of distancing elements in rows, the distance between rows and the total number of elements on the average value of the Nusselt number and on the pressure drop; analysis of the effect of changes in speed and temperature conditions on thermal and hydraulic characteristics. The most important results are the following facts: the influence of the relative location of the distancing elements on the thermohydraulic characteristics of the flow is negligible; changes in the temperature and speed regime of the laminar flow practically does not affect the intensity of convection in the matrix channels; an increase in the height of the slot channel leads to a relatively small decrease in the average value of the Nusselt number. The significance of the results obtained is that they can be the basis for adjusting the methods of design calculations of rotary heat exchangers taking into account the decrease in thermal efficiency caused by the presence of distancing elements in the channels of their matrices. Recommendations can be made to minimize the number of distancing elements without considering their mutual location.

Experimental investigation of dynamics of large-scale vortex structures of a sweeping jet emitted into a slot channel

Experimental investigation of dynamics of large-scale vortex structures of a sweeping jet emitted into a slot channel

Simulation of the mixing process in a slot channel with jet injection

The article presents the results of modeling in a two-dimensional formulation of the hydrodynamic process of mixing two streams of Newtonian fluids in a channel with jet injection. The mixing process takes place in a turbulent flow mode, without chemical and thermal interaction. The article considers the flow of a mixture in a flat slit channel when mixing two liquids. The first component of the mixture flows through the main wide channel. At a distance of 50 mm from the point of entry into the channel perpendicular to the main channel, there is a radial jet nozzle with a width of 1 mm, through which the second component enters the mixing channel. The article discusses several problems with different initial mixing rates of components. The characteristics corresponding to water and ethyl alcohol were taken as test components for mixing liquids. The simulation was carried out in the ANSYS-Fluent software package. The purpose of this work is to study the process of mixing two liquids in a slit channel. The article presents the results of modelling the mixing process.

Optimization Efficiency of the Aircraft Wing of Cessna 172 Skyhawk by Absorbent Adverse Pressure Using Tangential Suction Slot Without Vacuum Device

Efficiency of a wing is sufficient at stall angle of attack and breakdown by effecting turbulent flow intensity on upper wing surface which is destroyed the airflow pattern and generated adverse pressure, backflow airstream and forward transition separation point movement closely to the leading edge of the wing. To enhancement a wing efficiency factor at high angle of attacks in this research is using partially sucking adverse pressure to delay the separation point to control the backflow rate and expelling it through the wing tips ends using tangential suction slot channel without using any mechanical means depending on differential static pressure between adverse pressure and the static pressure generated on both win tips ends. Numerical CFD analysis has been managed the case study of the effect suction slot channel located on the upper wing surface at (70%) of the wing chord from the leading edge as a proposed modified wing model of the Cessna 172 Skyhawk half wing at angle of attacks (10°, 12°, 14°, 16°, 18°, 20°, 22°, 24°). The analysis study was conducted at stall speed (90 km/hr.) without flaps where it is equal (25 m/sec). The results of the analytical shows at the range of angle of attacks were chosen between (10° to 24°), lift coefficient CL increased (3.757%), drag coefficient CD is decreased (0.530%) and the wing efficiency lift to drag ratio Δ(CL/CD) is increased to (5.712%) while Δ(CD/CL) is decreased to (5.231%) which these parameters reflected to enhancement the wing to reduce required power at the minimum speed, increase angle of climb and decrease angle of descent reduce landing distance with high angle of attacks.

Improved Thermal Modeling and Experimental Validation of Oil-Flooded High-Performance Machines With Slot-Channel Cooling

Thermal management is often considered a bottleneck in the pursuit of the next-generation electrical machines for electrified transportation with a step change in power density. Slot-channel cooling is considered to be an effective cooling technique, either as an independent method or as a secondary heat transfer path, which compliments traditional cooling systems. The slot-channel specific geometry and position effects on the thermal benefits are not thoroughly investigated in the literature, while previous work focuses on passing fluid through the unused space left in between coils forming concentrated windings. In this article, slot-channel cooling is implemented within an oil-flooded cooling system for a high power density motor that is used as a pump. A flexible and detailed lumped parameter thermal network (LPTN) is proposed for the cooling system, with the LPTN used to optimize the slot-channel dimensions and location for obtaining maximum thermal benefits. Finally, a surface-mount permanent magnet (SPM) machine with the optimized slot channel geometry is built and tested to validate the thermal model, experimentally achieving an armature continuous current density in excess of 30 A/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Simulation of the lubricant flow in thin slot channels with a moving wall under slip boundary conditions

The article presents the results of studying the flow of a Newtonian fluid in a narrow wedge-shaped slot with a moving wall. A solution to the problem with slip boundary conditions on the channel walls is obtained. The influence of the slip conditions on the walls on the flow parameters is shown. In diverging and converging sections of the channel, different types of flow take place. In the region of the diverging flow near the stationary wall, a reverse flow zone is formed, the width of which increases with an increase in the Knudsen number, which is due to an increase in the flow velocity on the stationary wall due to the slip condition. Calculations elucidated the effect of slippage on the variation of the hydrostatic lifting force and hydraulic resistance in the slot channel. The dependence of the relative hydrostatic lifting force on the Knudsen number and the opening angle of the channel were revealed. It has been determined that with an increase in the Knudsen number, the magnitude of the hydrostatic lifting force decreases, since in this case the influence of the flow on the wall weakens. With an increase in the opening angle of the channel, slip effect weakens.

Influence of external magnetic field parameters and throttling channels configuration on the sensitivity of the magnetorheological viscoelastic materials

The influence of magnetic field parameters on the sensitivity of working magnetorheological fluids flowing in throttling slot channels of magnetically controlled hydromounts are investigated. The case of stationary motion of an incompressible conducting liquid with constant electrical conductivity, exposed to a uniform magnetic field, is considered. It is found that with an increase in the strength of the external magnetic field, the magnetization of the working fluid decreases. To compensate for this decrease, it is necessary to increase the excitation current of the electromagnet. Keywords: magnetorheological hydromount, throttling slot channel, magnetoreological transformer, magnetorheological fluid, Hartmann number, magnetization. gord349@mail.ru, oxulkovs@mail.ru, acidwolfvx@rambler.ru

Oscillatory dynamics of immiscible liquids with high viscosity contrast in a rectangular Hele–Shaw channel

The dynamics of the interface of liquids with a high viscosity contrast, performing harmonic oscillations with zero mean in a straight slot channel, is experimentally investigated. The boundary is located across the channel and oscillates along the channel with a harmonic change in the flow rate of the fluid pumped through the channel. Owing to the high contrast of viscosities, the motion of the more viscous liquid obeys Darcy's law, while the low-viscosity liquid performs “inviscid” oscillations. The oscillations of the interface occur in the form of an oscillating flat tongue of low-viscosity liquid that periodically penetrates into the more viscous one. The interface oscillations lead to the manifestation of two effects. One of these consists of changes in the averaged shape of the interface and the liquid contact line. The interface in the cell plane takes the form of a “hill,” the dynamical equilibrium of which is maintained by oscillations, while the deformation of the boundary is proportional to the amplitude of the oscillations and vanishes in their absence. The second effect consists of the development of finger instability of the oscillating boundary, which manifests itself in the periodic development of fingers of low-viscosity liquid at part of a period. The instability develops in a threshold manner when the relative amplitude of the interface oscillations reaches a critical value. It is found that the instability has a local character and manifests itself in those regions of the interface where the amplitude of the oscillations reaches a critical value. The stability threshold decreases with the dimensionless frequency.

Multiple Prime Expansion Channel Hopping for Blind Rendezvous in a Wireless Sensor Network

A channel rendezvous is a significant aspect of communication. In this context, blind rendezvous is the process of selecting a common available channel and establishing a communication link for wireless devices in a wireless sensor network. The rendezvous of asymmetric and heterogeneous wireless devices is a challenge. Thus, to improve speeds and stability of rendezvous, we analyze time slot overlap and channel determinism in the rendezvous algorithm and propose a rendezvous algorithm named Multiple Prime Expansion (MPE). In a final simulation study, we compare the performance of the MPE with other existing algorithms in an asymmetric and heterogeneous scenario. Results show that MPE has excellent performance for the ATTR and MTTR.

A critical review on thermal management technologies for motors in electric cars

• Advanced thermal management technologies for motors in electric cars are reviewed. • Air and liquid cooling methods for stator, winding and rotor were critically examined. • Possible methods to enhance the heat conduction in motors are thoroughly evaluated. • Pros and cons of current studies are presented, with suggestions for future work. The development of electric cars has well been regarded as a major solution for tackling the challenges of carbon-neutrality faced by the modern communities. Electric motor is certainly the core and most important components of an electric car, and the thermal management for electric motors has drawn increasing attention from both industry and academic society. This is because electric motors in modern electric cars are required to be more powerful and competitive with higher torque, higher speed and higher power density, therefore the efficient thermal management has become essential to maintain the motors efficiency, durability and safety. The failure of thermal management will result in demagnetization of magnets, aging of the insulation materials, decrease of efficiency, shorter lifetime and even burnout of motors. To enlighten the future research, in this paper, both the theoretical modeling and experimental investigations of the latest thermal management methods are reviewed. The state-of-the-art of various thermal management techniques, including air cooling (natural and forced air cooling, air impingement cooling) and liquid cooling (water/oil jacket cooling, jet impingement cooling, spray cooling, immersion cooling, slot channel forced convection cooling) for the stator, winding and rotor are critically presented. Meanwhile, heat transfer enhancement methods by conduction based on potting materials, thermal paste, heat guides, PCMs and heat pipes are highlighted. Following that, hybrid thermal management technologies to address extreme conditions are also discussed. In the last section, some suggestions are given for future possible research and applications. The paper is expected to be a good reference and inspiration for the development of new thermal management concepts of electric motors.

Experimental study of flow dynamics of a sweeping jet in a slot channel

In recent years, fluidic oscillators have been actively applied as devices for flow control in the field of aero and hydrodynamics. This study aims to investigate the structure of a flow of sweeping jet ejected from a fluidic oscillator into a confined area – slot channel. Dynamics of sweeping jet flow are investigated using the PIV method with high temporal resolution. The effect of the Re number on the sweeping jet oscillation frequency was studied in the range from 1 500 to 8 000. Linear frequency dependence on Re number was obtained. Bounding walls affect the dynamics of sweeping jet flow that leads to a change of average velocity field. For low Re numbers, obtained results are in good agreement with the results of other studies.

3D structure of the flow in a near wake behind a cylinder in the slot channel

3D structure of the flow in a near wake behind a cylinder in the slot channel

Numerical Simulation of Intrachamber Processes in the Power Plant

This paper considers the issues of numerical modeling of nonstationary spatial gas dynamics in the pre-nozzle volume of the combustion chamber of a power plant with a cylindrical slot channel at the power plant of the mass supply surface. The numerical simulation for spatial objects is based on the solution conjugate problem of heat exchange by the control volume method in the open integrated platform for numerical simulation of continuum mechanics problems (openFoam). The calculation results for gas-dynamic and thermal processes in the power plant with a four-nozzle cover are presented. The analysis of gas-dynamic parameters and thermal flows near the nozzle cover, depending on the canal geometry, is given. The topological features of the flow structure and thermophysical parameters near the nozzle cap were studied. For the first time, the transformation of topological features of the flow structure in the pre-nozzle volume at changes in the mass channel’s geometry is revealed, described, and analyzed. The dependence of the Nusselt number in the central point of stagnation on the time of the power plants operation is revealed.

Heat transfer and skin-friction in a turbulent boundary layer under a non-equilibrium longitudinal adverse pressure gradient

The experimental data on the effect of weak and moderate non-equilibrium adverse pressure gradients (APG) on the parameters of dynamic and thermal boundary layers are presented. The Reynolds number based on the momentum thickness at the beginning of the APG region was Re** = 5500. The APG region was a slot channel with upper wall expansion angles from 0 to 14°. The profiles of the mean and fluctuation velocity components were measured using a single-component hot-wire anemometer. The friction coefficients were determined using two methods, namely, the indirect Clauser method and the direct method of weighting the lower wall region on a single-component strain-gage balance. The heat transfer coefficients were determined by a transient method using an IR camera. It is noticed that in the pressure gradient range realized the universal logarithmic region in the boundary layer profile is conserved. The values of the relative (divided by the parameters in zero gradient flow at the same value of Re**) friction and heat transfer coefficients, together with the Reynolds analogy factor, are determined as functions of the longitudinal pressure gradient. The values of the relative friction coefficient reduced to cf/cf0 = 0.7 and those of the heat transfer to St/St0 = 0.9. A maximum value of the Reynolds analogy factor (St/St0)/(cf/cf0) = 1.16 was reached for the pressure gradient parameter β = 2.9.

Oscillatory dynamics of two liquids interface in straight narrow gap

Oscillatory dynamics of the liquid-liquid interface in a straight slot channel is studied experimentally. We use fluids with a large difference in viscosity and similar densities. The experimental conditions are chosen in such a way that the oscillating motion of a low-viscosity liquid is inviscid, and the oscillating motion of viscous liquid obeys Darcy’s law. At the beginning of the experiment, the interface is oriented perpendicular to the channel axis. It is found that the interface takes a shape of a symmetric hill curved towards a viscous liquid under liquid oscillations. The equilibrium interface shape (the hill height) is determined by the amplitude of the interface oscillations.

An a posteriori error estimator based on least-squares finite element solutions for viscoelastic fluid flows

&lt;p style='text-indent:20px;'&gt;We present a posteriori error estimator strategies for the least-squares finite element method (LS) to approximate the exponential Phan-Thien-Tanner (PTT) viscoelastic fluid flows. The error estimator provides adaptive mass weights and mesh refinement criteria for improving LS solutions using lower-order basis functions and a small number of elements. We analyze an a priori error estimate for the first-order linearized LS system and show that the estimate is supported by numerical results. The LS approach is numerically tested for a convergence study and then applied to the flow past a slot channel. Numerical results verify that the proposed approach improves numerical solutions and resolves computational difficulties related to the presence of corner singularities and limitations arising from the exorbitant number of unknowns.&lt;/p&gt;