Parallel Plate Research Articles

Performance evaluation criteria based on the first and second laws of thermodynamics

Numerical simulations were conducted to investigate the correlation between assessments based on the total entropy generation rate criterion and the thermal resistance criterion in the context of evaluating heat transfer performance. This study focused on a parallel plate channel heat sink with the lower wall subjected to a constant heat flux, under various flow constraints. The flow was assumed to be laminar and fully developed. The energy equation was discretized using the control volume-based power law scheme, and the resulting algebraic equations were solved by the line-by-line method. Optimal channel heights which lead to minimize irreversibility and temperature difference between heated wall and inlet fluid temperatures were determined by both the total entropy generation rate and thermal resistance criteria under four distinct flow constraints: identical mass flow rate, identical inlet velocity, identical pumping power, and identical pressure drop. The investigation revealed a lack of significant correlation between the optimal channel heights derived from assessments based on the total entropy generation rate and thermal resistance. Consequently, the utilization of the total entropy generation rate criterion for evaluating heat transfer performance, based in the second law of thermodynamics, instead of the thermal resistance criterion, based in the first law of thermodynamics, was deemed inappropriate. The total entropy generation rate criterion was based on the minimization of the irreversibility and served as an indicator of heat transfer quality. As a recommendation, it is suggested that results obtained from both the total entropy generation rate and thermal resistance criteria for assessing heat transfer performance be presented separately for each specific application.

New Analytical and Numerical Solutions for Squeezing Flow between Parallel Plates under Slip

In this article, the effects of physical flow parameters on squeezed fluid between parallel plates are explored through the Darcy porous channel when fluid is moving as a result of the upper plate being squeezed towards the stretchable lower plate, such as velocity slip, thermal slip, solutal slip, thermal stratification parameter, solutal stratification parameter, squeezing number, Darcy number, Prandtl number, and Schmidt number. The governing equations are transformed into a nonlinear ordinary differential equation using the appropriate similarity transformations. The resulting equations are solved by using the perturbation iteration method (PIT) to produce a convergent analytical solution with high accuracy. The phenomena of the squeezing fluid as the plates are moving apart and when they are coming together are illustrated using the resulting analytical solutions. Plots are used to discuss the significant effects of physical parameters on velocity, temperature, and fluid concentration profiles. The skin friction coefficient and Nusselt Sherwood values have graphical interpretations that are listed. For strong velocity slip parameters, the results demonstrate the existence of a minimum velocity profile close to the plate and a growing velocity profile distant from the plate. Additionally, as the slip effects rise, the fluid temperature and concentration both considerably drop. The results of the fourth-order Runge-Kutta method (RK4M) and the presented analytical solutions provided are in excellent agreement.

A fast response time gas ionization chamber detector with a grid structure.

The time response characteristic of the detector is crucial in radiation imaging systems. Unfortunately, existing parallel plate ionization chamber detectors have a slow response time, which leads to blurry radiation images. To enhance imaging quality, the electrode structure of the detector must be modified to reduce the response time. This paper proposes a gas detector with a grid structure that has a fast response time. In this study, the detector electrostatic field was calculated using COMSOL, while Garfield++ was utilized to simulate the detector's output signal. To validate the accuracy of simulation results, the experimental ionization chamber was tested on the experimental platform. The results revealed that the average electric field intensity in the induced region of the grid detector was increased by at least 33%. The detector response time was reduced to 27% -38% of that of the parallel plate detector, while the sensitivity of the detector was only reduced by 10%. Therefore, incorporating a grid structure within the parallel plate detector can significantly improve the time response characteristics of the gas detector, providing an insight for future detector enhancements.

Assessing the effect of test parameters on the determination of the rheological behavior of calcium sulfoaluminate cement pastes

Calcium sulfoaluminate cement (CSA) is renowned for its application in technologies that require rapid setting and high initial strengths, such as 3D concrete printing and repairs. However, their rheological behavior needs to be more adequately explored. This study assesses the impact of rotational rheometer test conditions on CSA pastes with different water-to-cement ratios. For the determination of static yield stress (τ0s), stress growth test with shear rates between 0.01 and 0.05 s−1 were employed. The results revealed that higher shear rates anticipated the occurrence of the material's peak destructuring and resulted in lower values of τ0s. In addition, the effects of geometry and testing routine on the flow curve were analyzed. The results showed that the use of vane geometry provides more consistent results of the measured dynamic yield stress, viscosity, and hysteresis area of CSA pastes than parallel plate geometry.

Operational and structural parametric analysis of a photovoltaic/thermal system integrated with phase change material

Applying PCM to the photovoltaic/thermal (PV/T) system can adjust the operating temperature of the photovoltaic cell and further enhance system efficiency. Hence, in the present study, a novel PV/T-PCM collector by connecting the PCM with the heat-absorbing plate in parallel is first proposed. Then, the dynamic model of the PV/T-PCM system is established and verified. Finally, the sensitivity analysis is performed on key parameters, including the water mass flow rate, water tank volume, PCM thickness, and phase transition temperature. The results show that raising the water mass flow rate improves electrical gain, total heat gain, and total system efficiency; however, their change gradient is all inconspicuous as the water mass flow rate is greater than 0.02 L/s. As the water tank volume expands from 75 L to 105 L, electrical gain, total heat gain, and total system efficiency are improved. Thickening the PCM can promote the electrical gain, while the total system efficiency and total heat gain will increase slightly at first and then decrease. The best thickness is 0.015 m. When the phase transition temperature increases from 40 ℃ to 50 ℃, the total system efficiency and total heat gain decline, but the electrical gain decreases insignificantly. The changes of the above four parameters all affect the complete melting ratio of PCM as well as the phase transition start time on the entrance side and exit side of the collector.

Dynamics of a bubble-pair between two parallel rigid walls

The dynamics of two gas bubbles placed side-by-side in liquid between parallel rigid plates is studied numerically using the multiphase volume of fluid (VOF) model in OpenFOAM. This model solves a single set of Navier–Stokes equations for both the gas in the bubbles and the surrounding liquid. Being initially stationary, the bubbles first expand to their maximum volume due to the high gas pressure inside them and then collapse. Both phases are treated as viscous and immiscible without any phase change. The model is validated against available experimental data of a single bubble oscillation between parallel plates and a bubble-pair oscillation near a single rigid wall. Parametric studies are then performed, with the main variables being the initial sizes of the bubbles and their standoff distances from the rigid plates. The bubbles exhibit symmetric or asymmetric behavior depending on these two variables. Three distinct scenarios are identified in the symmetric case based on the relative influence of bubble-bubble and bubble-wall interactions. The jet strength and direction, bubble oscillation period, coalescence, and early asymmetric bubble collapse are characterized by initial distances and radii. This study provides valuable insights into intricate hydrodynamic interactions and behaviors of bubble pairs bounded by rigid surfaces.

MHD Squeezed Radiative Flow of Casson Hybrid Nanofluid Between Parallel Plates with Joule Heating

MHD Squeezed Radiative Flow of Casson Hybrid Nanofluid Between Parallel Plates with Joule Heating

Role of suction/injection on free convective flow in a vertical porous channel with non‐Fourier effects in the presence of periodic boundary

AbstractThe key attention of this work is on the impact of suction/injection on the free convective flow of a viscous fluid passing between two infinite, parallel, vertical and porous plates with non‐Fourier effects. The analysis focuses on a porous channel with boundaries featuring a steady–periodic temperature regime. The governing equations, representing velocity(momentum) and temperature(energy) fields, are well‐stated in dimensional form. Employing a separation technique, the momentum and energy equations are separated into steady and periodic components. On solving, the resulting second‐order ordinary differential equations derived, revealed the expressions for velocity and temperature in dimensionless form. However, the study investigates the influence of various flow parameters used in this work, including suction/injection , heat source/sink , Strouhal number , Prandtl number , and dimensionless relaxation time , on the velocity and temperature distributions. Also not left out is the rate of heat transfer on the flow performance and the skin‐friction coefficient on the plates. The findings are visualized using MATLAB‐generated graphs. An interesting observation found during the course of investigation in that the introduction of suction/injection enhances the flow velocity and fluid temperature within the channel, and they are both seen as declining functions of the Strouhal number, which measures the frequency of periodic heating on the plates. Furthermore, when the suction/injection parameter(s) is being relaxed, this study demonstrates a strong agreement with the findings of Ajibade and Mukhtar.

Instability of Jeffrey Fluid Throughflow in a Porous Layer Induced by Heat Source and Soret Effect

Abstract In this study, we investigated the instability of thermosolutal convection of Jeffrey fluid in a porous layer with internal heating and the Soret effect. The layer is bounded by two fixed permeable parallel plates which are assumed to be isothermal and isosolutal. An existing initial flow in the vertical direction is passing the layer at a constant speed. The flow fields are adequately presented by PDEs and transformed into dimensionless forms. A small perturbation to the basic flow profiles with linear stability analysis results the problem in an eigenvalue problem. The Runge-Kutta method is used to derive the numerical value of the critical thermal Rayleigh number. The convective instability for asymptotic cases for Le = 1 and Pe = 0 are also examined as special cases. The analysis reveals that for a non-positive Soret parameter, the flow is stable for all Lewis numbers and independent of the heat source. But with a positive Soret parameter in the absence of a heat source, the fluid flow is stable for Le = 3 while the influence of a heat source destabilizes the flow for Le > 2. In high and low shear flows with increasing solutal gradient, the solutal Rayleigh number shows a highly destabilizing nature for all Le. Moreover, smaller relaxation and higher retardation time are the most unstable characteristics of the heat source system. In convective longitudinal rolls, the uni-cellular streamline patterns tend to become bi-cellular by the influence of positive Soret parameters and energy sources.

Multiobjective optimization of Vortex Generators for heat transfer enhancement in turbulent flows

Convective heat transfer can be enhanced by streamwise vortices and coherent flow structures produced downstream Vortex Generators (VGs). The thermal performance depends on the VG shape which controls the intensity and topology of the vortices. Thus, VG shape optimization is a major challenge in designing sustainable and efficient heat exchangers. In the present study, a multi-objective optimization is performed through large space exploration design to find optimal VG shapes that adapt to different flow regimes. Simulations are carried out in parallel plate turbulent flow for three different Reynolds numbers; Re1=4600,Re2=9920, and Re3=30050. The present numerical results are first validated against numerical and experimental data from the open literature. Then, and for the first time, seven design parameters are investigated, based on VG shape dimensions. The new optimized VG show a thermal enhancement factor between 11 and 35%, relative to a smooth channel case, and between 3 and 14%, relative to different VG shapes from the recent open literature. The present results are analyzed in details by focusing on the physics of the flow structure and its correlation to the convective heat transfer enhancement using local criteria for flow visualization and vortex intensity quantification.

High spatial resolution diffuse optical tomography based on cross-correlation of chaotic light.

A diffuse optical tomography system with chaotic laser is proposed for the three-dimensional optical phantom. The high signal-to-noise ratio is beneficial to improve the spatial resolution of diffuse optical tomography. It is essential to drive the chaotic laser as the incident light into the optical phantom. The transmitted light emitted from phantom as the detection light and a part of the incident light as the reference light to carry out cross-correlation analysis. The high-density source-detector configuration in parallel plate structure is designed for detecting targets in the phantom. The propagation of chaotic laser in the phantom is studied theoretically and experimentally based on the diffusion equation. Image reconstruction is achieved by the cross-correlation analysis of chaotic laser and the Newton-Raphson nonlinear algorithm. The performance of the proposed system has been assessed by reconstruction localization accuracy and contrast-noise-ratio. The results show that the spatial resolution of the proposed system can reach 1.5 mm and the localization error is less than 1 mm.

Еdgе fiеld of dеflеctorplаtes with expanding screens

Deflector plates consist of two parallel conductive plates that create a deflecting electric field. They can be used to control the flow of charged particles ― electrons or ions. The effect of the еdgе fiеld of deflector plates leads to a change in the velocity of charged particles in the longitudinal and transverse directions, consequently of which their real trajectories change, deviating from ideal ones, which violates the space-time resolution of corpuscular optical devices in which they are used. Apart from that, the electric field at the input to the plates of deflector can vary over time, which must also be taken into account when the deflector diverts the beam of charged particles. Thus, in many cases, the use of deflector plates with open ends is inappropriate, since uncontrolled scattering fields are formed. In this article, we can consider the field of deflector plates with expanded screens at the output, so that deflecting beams of charged particles can be used at the output of deflector plates. Using the methods of the theory of complex variable functions, analytical expressions for the edge field of deflector plates with grounded screens were obtained. Firstly, by grounding the screens and shielding the plates from the deflection field, we can localize the edge electric field and reduce the uncontrolled scattering fields, and secondly, such a field can be accurately calculated analytically.

Vortex-plate interaction in wake-induced vibration: A study of single and parallel flat plates behind a cylinder

This numerical study investigates the wake-induced vibration of single or parallel flat plates mounted in the wake of a circular cylinder in laminar flow. The results highlight the critical role of flat plate positioning, as it influences their ability to act as control mechanisms or experience significant vibrations. For a single plate, mounting outside the critical position initiates large amplitude vibrations, gradually decreasing as the plate moves away from the horizontal axis. Additionally, vibrations with moderate amplitudes are observed at specific short horizontal positions due to variations in the near-wake structure. In the case of parallel plates constrained to vibrate independently, vibrations only occur when there is sufficient space for shear-layer interaction. Different vortex suppression and plate vibration mechanisms are identified by adjusting the vertical gap, where increasing the gap reduces the non-vibrating zone. The study also examines a range of reduced velocities, revealing that although the plate(s) follow the upstream cylinder's shedding frequency in all configurations, this frequency may be affected and altered in short gaps. Comparing single and parallel plates demonstrates their potential for designing energy harvesting systems. However, parallel plates offer a slight advantage due to using independent objects within a relatively identical area.

Concentrated aqueous solutions of multivalent macroions enhance the electrical double layer capacitance and differential capacitance of a planar supercapacitor

The electrostatic properties of the ionic cloud, or electrical double layer, neutralizing a charged electrode are relevant to improve the storage of electrical energy and the efficiency of supercapacitors and/or batteries using coulombic fluids. In this work, we study the microscopic profiles of charged particles, integrated surface charge density, and the mean electrostatic potential associated to a pair of infinite parallel plates uncharged or, else, with opposite charge, in the presence of a salt-free aqueous solution constituted by big positive macroions and small anions, which interact via an explicit electrostatic coulombic potential and are dissolved in an implicit solvent. The particle profiles and the integrated surface charge density associated to Monte Carlo simulations and integral equations theory display an oscillatory or non-monotonic behaviour producing the phenomena of charge inversion and charge reversal. These phenomena are not predicted by the non-linear Poisson-Boltzmann equation, which highlights the importance of ion correlations and ionic volume excluded effects. The phenomenon of surface charge amplification is observed near the point of zero charge, which is yielded by the particle size-asymmetry. For a fixed concentration of macroions, a monotonic increase of the mean electrostatic potential difference between the charged parallel plates is predicted by simulations and theories as a function of the electrodes' charge. For a fixed surface charge density, the capacitance of the parallel plates capacitor increases when the ionic strength of the macroion's solution increases. A concavity inversion and an augment of the differential capacitance is also observed for an electrode near the point of zero charge as function of the macroion's concentration.

Time-dependent model of temperature distribution in continuous flow pulsed electric field treatment chambers

A key component of a continuous flow pulsed electric field (PEF) system is the treatment chamber, where the product is exposed to electric pulses. Determination of the temperature distribution in the chamber during PEF treatment is important since high local increases in temperatures can affect the quality of the product. Coupled simulations of electric field, fluid flow, and heating in the existing literature do not model each individual electric pulse, but rather employ a “duty cycle” approach, which does not account for transient variations in treatment intensity and temperature changes in the medium. We present a time-dependent approach to modelling PEF treatment in continuous flow treatment chambers, which can model each pulse separately, and thus enables a more accurate study of temporal and spatial distributions of electric field and temperature. The model has been validated on laboratory scale treatment chambers of parallel plate or colinear design and using realistic protocols. Industrial relevance textThe paper is relevant to all pulsed electric field (PEF) applications either on laboratory or industrial scale that implement a continuous flow treatment chamber. It presents an improved modelling approach which allows for an analysis of the electrical current, electric field, and temperature distribution in the chamber during, at the end, and in between application of electrical pulses. The model can be used to predict the peak temperature at the end of each pulse in the hot spots, which if large enough could potentially lead to thermal damage of the product or in extreme cases even potential local boiling of the medium, resulting not only in degradation of the treated product, but also in accelerated electrode fouling, oxidation, and dissolution (etching), as well as arcing. This would not only affect the quality of the treated product but would also affect the wear and lifetime of electrodes/chambers, and of the pulse generator. The model can also be used to avoid expensive trial-and-error optimization of the PEF protocols and chamber geometries in situ.

Electromagnetic near-field mutual coupling suppression with active Janus sources

Electric dipoles and magnetic dipoles are the most fundamental particles in electromagnetic theory. Huygens and Janus sources, formed by the orthogonal combination of electric and magnetic dipoles, both show good directionality in the near field. Although the Huygens source has been widely used in antennas and metasurfaces, the applications of Janus source are heretofore limited. In this paper we report the physical construction of an active Janus source. Through full-wave simulations within the parallel plate waveguide (PPW) environment, we show that our source achieves the directional electromagnetic near-field and quasi-isotropic far-field requisite of the Janus source. Using this fact, we demonstrate that two active Janus and Huygens sources in close proximity (about 0.10 to 0.25 wavelengths) achieve a near 1000-fold reduced mutual coupling compared to electric dipole sources. Particularly, the simultaneous achievement of strong mutual coupling suppression and quasi-isotropic radiation make the Janus source an ideal candidate for consideration in future compact multi-input multi-output (MIMO) communication systems.

Electrolubrication in liquid mixtures between two parallel plates

We describe theoretically ‘electrolubrication’ in liquid mixtures: the phenomenon whereby an electric field applied transverse to the confining surfaces leads to concentration gradients that alter the flow profile significantly. When the more polar liquid is the less viscous one, the stress in the liquid falls on two electric-field-induced thin lubrication layers. The thickness of the lubrication layer depends on the Debye length and the mixture correlation length. For the simple case of two parallel and infinite plates, we calculate explicitly the liquid velocity profile and integrated flux. The maximum liquid velocity and flux can be increased by a factor $\alpha$ , of order 10–100 or even more. For a binary mixture of water and a cosolvent, with viscosities $\eta _w$ and $\eta _{cs}$ , respectively, $\alpha$ increases monotonically with inter-plate potential $V$ and average ion content, and is large if the ratio $\eta _{cs}/\eta _w$ is large.

Lorentz boosted parallel plate Casimir cavity

Lorentz boosted parallel plate Casimir cavity

Study on the change rule of low-temperature properties of asphalt binder with aging time

ABSTRACT Low-temperature cracking is common distress in asphalt pavements. Understanding the change rule of its low-temperature properties is helpful in investigating the optimal maintenance timing of asphalt pavement. In this paper, the change rule of low-temperature properties of asphalt binders with aging time is investigated by various indexes. Four asphalt binders and four anti-aging modified asphalt binders were subjected to the rolling thin film oven (RTFO) test and pressure aging vessel (PAV) test. Dynamic Shear Rheometer (DSR) with the 4 mm parallel plates was used to determine the low-temperature properties of asphalt binders. The results show that aging and low temperature have a negative impact on the low-temperature properties of asphalt binders. The anti-aging agent improves the low-temperature properties and aging resistance of asphalt binders. Compared with other indexes, the critical cracking temperature Tc and the critical temperature difference ΔTc are more suitable for analysing the effect of aging on the low-temperature properties of asphalt binders. Also, the ΔTc shows the three-stage decreasing rule of ‘fast-slow-fast’, with the inflection points. It meant that the low-temperature properties of asphalt binders had been altered at the inflection points, which provided a favourable reference to research on the optimal maintenance timing of asphalt pavement.

Effect of Induced Magnetic Field on MHD Flow Between Two Parallel Porous Plates at Constant Temperature Gradient in Presence of Inclined Magnetic Field

Effect of Induced Magnetic Field on MHD Flow Between Two Parallel Porous Plates at Constant Temperature Gradient in Presence of Inclined Magnetic Field