Layer Of Porous Medium Research Articles

Experimental study on temperature distribution of double-layer solid cylinder under local heating source

Abstract Heating equipment is widely used in production and life, the transient temperature of the heated object reflects the effect of heating equipment, but also an important basis for the design of heating equipment. In the internal temperature measurement of micro heating equipment, some of the temperature measurement instruments are large in size, which makes it difficult to realize precision measurement, and the use of infrared measurement, laser temperature measurement and other methods cannot be used to accurately measure the temperature of the internal points of the material without destroying the material and equipment at the same time. In this study, based on the thermocouple temperature measurement technology and considering the problem of fragility and breakage caused by the small diameter of very fine thermocouple wires, a multi-point temperature synchronization measurement platform is constructed to realize the precise measurement of the temperature at multiple points inside the micro-heating element. Transient temperatures were measured at different locations of a water-containing porous medium inside a 15 mm long heating element under static heating and dynamic suction conditions in the case study. The results show that moisture and suction have a significant effect on the temperature inside the porous media layer. During the suction process, the temperature drop near the suction opening was larger, and the temperature drop near the wall was about 47% of the temperature drop inside. This study is a guide to the design of heating structures for vacuum drying equipment, electrically heated atomization systems and other micro-miniature heating equipment.

Analytical and numerical examinations on the stability investigation of Casson nanofluid flow in a permeable layer controlled by vertical throughflow

Purpose The purpose of the study is to analytically as well as numerically investigate the weight of throughflow on the onset of Casson nanofluid layer in a permeable matrix. This study examines both the marginal and over stable kind of convective movement in the system. Design/methodology/approach A double-phase model is used for Casson nanofluid, which integrates the impacts of thermophoresis and Brownian wave, whereas for flow in the porous matrix the altered Darcy model is occupied under the statement that nanoparticle flux is disappear on the boundaries. The resultant eigenvalue problem is resolved analytically as well as numerically with the help of Galerkin process with the Casson nanofluid Rayleigh–Darcy number as the eigenvalue. Findings The findings revealed that the throughflow factor postpones the arrival of convective flow and reduces the extent of convective cells, whereas the Casson factor, the Casson nanoparticle Rayleigh–Darcy number and the reformed diffusivity ratio promote convective motion and also decrease the extent of convective cells. Originality/value Controlling the convective movement in heat transfer systems that generate high heat flux is a real mechanical challenge. The proposed framework proved that the use of throughflow is one of the most important ways to control the convective movement in Casson nanofluid. To the best of the authors’ knowledge, no inspection has been established in the literature that studies the outcome of throughflow on the Casson nanofluid convective flow in a porous medium layer. However, the convective flow of Casson nanofluid finds many applications in improving heat transmission and energy efficiency in a range of thermal systems, such as the cooling of heat-generating elements in electronic devices, heat exchangers, pharmaceutical practices and hybrid-powered engines, where throughflow can play a significant role in controlling the convective motion.

Numerical Study on the Cooling Method of Phase Change Heat Exchange Unit with Layered Porous Media

The implementation of heat sinks in high-power pulse electronic devices within hypersonic aircraft cabins has been facilitated by the emergence of innovative phase change materials (PCMs) characterized by excellent thermal conductivity and high latent heat. In this study, a representative material, layered porous media filled with paraffin wax, was utilized, and a three-dimensional numerical model based on the enthalpy-porosity approach was employed. A thermal response research was conducted on the Phase Change Heat Exchange Unit with Layered Porous Media (PCHEU-LPM) with different cooling methods. The results indicate that water cooling proved to be suitable for the PCHEU-LPM with a heat flux of 50,000 W/m2. Additionally, parametric studies were performed to determine the optimal cooling conditions, considering the inlet temperature and velocity of the cooling flow. The results revealed that the most suitable conditions were strongly influenced by the coolant inlet parameters, along with the position of the PCM interface. Finally, the identification of the parameter combination that minimizes temperature fluctuations was achieved through the Response Surface Analysis method (RSA). Subsequent verification through simulation further reinforced the reliability of the proposed optimal parameters.

Numerical Simulation of Underwater Supersonic Gaseous Jets of Underwater Vehicle with Porous Media Layer

Numerical Simulation of Underwater Supersonic Gaseous Jets of Underwater Vehicle with Porous Media Layer

The Impact of In-Flight Acceleration Environments on the Performance of a Phase-Change Heat Exchanger Unit with Layered Porous Media

The Phase-Change Heat Exchanger Unit in Layered Porous Media (PCEU-LPM) is obtained through frozen pouring processing, and exhibits characteristics such as high thermal conductivity, high latent heat, and high permeability, making it suitable for dissipating heat in airborne electronic devices. This study numerically investigates the impact of aircraft speed acceleration conditions, which lead to weightlessness or overload, on the performance of the PCHEU-LPM, with a particular focus on the influence of natural convection in the liquid-phase region. Initially, a microscale thermal analysis model is established based on the Navier–Stokes equation scanning electron micrograph to calculate the effective thermal conductivity and permeability of the PCHEU-LPM under different porosities. Subsequently, these parameters are incorporated into a macroscale thermal analysis model based on Darcy’s law, employing an average parameter approach. Using the macroscale thermal analysis model, temperature and velocity fields are computed under various porosities, acceleration magnitudes, and directions. The calculation results indicate that as the acceleration increases from α = 0 to α = 10 g, the interface temperature of the PCHTU-LPM decreases by approximately 5.2 K, and the temperature fluctuation decreases by 2.4 K. If the porosity of the PCHTU-LPM is increased from ε = 70% to ε = 85%, the influence of acceleration change on natural convection will be further amplified, resulting in a decrease in the interface temperature of the PCHTU-LPM by approximately 10.2 K and a decrease in temperature fluctuation by 5.8 K. When the acceleration direction is +z, the interface temperature of the PCHTU-LPM is at its lowest, while it is highest when the acceleration direction is −z, with a maximum difference of 15.4 K between the two. When the acceleration direction is ±x and ±y, the interface temperature lies between the former two cases, with the interface temperature slightly higher for ±y compared to ±x, with a maximum difference of 3.9 K between them.

MHD natural convection in a wavy nanofluid enclosure with an internally corrugated porous cylinder

The present work focuses on investigating magnetohydrodynamic (MHD) natural convection in a complex I-shaped enclosure with corrugated walls, filled with nanofluid and porous media layers. This study analyzes various parameters' effects on heat transfer and fluid flow. The enclosure's left and right walls maintain low temperatures, while the other walls are insulated. The inner corrugated cylinder experiences high temperatures. The study examines the impact of Rayleigh number (Ra), Hartman number (Ha), nanofluid volume fraction (ϕ), Darcy number (Da), MHD inclination angle (γ), position of the corrugated cylinder (δ) and number of undulations (N) on isotherms, streamlines, velocity profiles and average Nusselt number variations. The results show that higher Ra values increase the average Nusselt number while increasing Da enhances it by 65%. Magnetic source inclination greatly affects heat transfer, with Nusselt at γ = 90° being 15.34 compared to 10.234 at γ = 0°. The study concludes that optimal heat transfer occurs at γ = 90°, Ra = 106, Da = 10−3, Ha = 30 and N = 2.

Effect of gravity settling on the onset of thermal convection in a nanofluid-saturated porous medium layer

The onset of convection in a horizontal porous medium layer saturated with a nanofluid and heated from below is investigated via linear stability analysis and numerical simulation. The Darcy–Buongiorno model is used to describe the convective transport behaviour of the nanofluid and the settling effect of nanoparticles due to gravity is considered in addition to thermophoresis and Brownian diffusion. The linear stability analysis shows that the gravity settling is a substantial stabilizing mechanism restraining the destabilizing factors such as thermal buoyancy and thermophoresis. The stability threshold is determined by the relative strength of thermophoresis to gravity settling. It is found that the system is destabilized when the thermophoretic mobility prevails. As the nanoparticle size increases, the gravity settling effect is promoted and makes the system more stable. In particular, the onset of instability is dominated by the oscillatory mode once the nanoparticle concentration is in a stably stratified profile across the porous layer. When the Rayleigh–Darcy number $Ra_D$ exceeds the critical value, the spectrum of the growth rates of the unstable modes rises with increasing $Ra_D$ and $Rn$ (i.e. the concentration Rayleigh number), and eventually the unstable modes in the high-wavenumber region exhibit the same instability. The evolution of the convection is further examined by numerical simulation. The results verify the stability characteristics predicted by linear stability analysis. Moreover, the pattern of fingering convection of the nanofluid concentration is observed once the nanofluid concentration is unstably stratified and the density difference across the porous layer is large enough.

The Effect of Throughflow and Gravitational Modulation on Weakly Nonlinear Bio-Thermal Convection in a Porous Medium Layer

We investigate the impact of periodically varying gravitational fields and a throughflow on the bio-thermal Darcy–Brinkman convection within a porous medium layer saturated with a Newtonian fluid containing gyrotactic microorganisms. The study includes an examination of two types of a throughflow: one directed against the gravity field and another one along it. We assume that the gravitational modulation has a small amplitude, quantified as a second-order smallness in the dimensionless parameter ϵ, which represents the supercritical parameter of the Rayleigh number. For weakly nonlinear convection, a Ginzburg–Landau (GL) equation with a periodic coefficient is derived in the third order in ϵ. To analyze the heat and mass transfer, we numerically solve the GL equation. The numerical results reveal that the vertical throughflow in the bio-thermal convection exhibits a dual nature, allowing for both augmentation and a reduction of the heat and mass transfers. We investigate the influence of variations in the Vadasz number, Peclet number, bioconvective Peclet number, frequency, and amplitude of modulation on the heat and mass transfer. The effects of these parameters are depicted graphically, illustrating that higher values of the Vadasz and Peclet numbers, as well as increased modulation amplitude, positively impact the heat and mass transfer. In addition, a comparative analysis of modulated and non-modulated systems shows a significant effect of the modulation on the stability of systems.

Weakly Nonlinear Bio-Thermal Convection in a Porous Media Layer Under Rotation, Gravity Modulation, and Heat Source

Weakly Nonlinear Bio-Thermal Convection in a Porous Media Layer Under Rotation, Gravity Modulation, and Heat Source

The lie group analysis method for heat transfer in steady boundary layer flow field of nanofluid

In order to reveal the mechanism of the abnormal movement (Brownian motion enhances thermal scattering) of nanoparticles on the fluid enhanced heat transfer, the two-phase model was used to study the abnormal convection and diffusion of viscous nanofluids in the flat boundary layer of porous medium. Firstly, for the two-dimensional steady boundary layer stagnation point flow of incompressible Newtonian-nanofluids, the nonlinear governing equations of the flow field and temperature field of nanofluids are established from the Oberbeck-Boussinesq approximate equations. Secondly, the modern Lie group analysis method is introduced, we give the Lie symmetry determining equation of the flow field partial differential equations and the characteristics of the solutions. Further, using the relationship between the Lie symmetries and the conserved quantities, the conservation vector form of the flow field and the group invariant solution are derived in detail, and the reduced order model of the nanofluid flat boundary layer is obtained. Finally, the correctness of the analytical results obtained by the Lie group method was verified for different values of the flow parameter Prandtl. Research has shown that the Lie group method can be used to analytically solve the velocity and temperature distribution functions of abnormal motion of nanoparticles. The fluid temperature increases with the increase of the volume fraction parameter of nanoparticles, but decreases with the increase of the Prandtl value of the base fluid, and decreases with the increase of the plate stretching speed. The Lie group analysis method in this paper provides reference value for numerical simulation solutions of various heat and mass transfer in nanofluids.

Effects of porous structures on point source dispersion across the sediment–water interface

Abstract Understanding the transport of point source solutes across the sediment–water interface (SWI) is important for the protection of river environments. Conventional coupled models assume the porous media layer as Darcy's laminar flow and therefore cannot accurately capture the transport processes within the porous media. Furthermore, the effect of the porous structure of the riverbed on the transport process is largely unknown. In this study, we performed pore-scale numerical simulations of point source solutes transport across the SWI to investigate the effects of different porous structures in the riverbed on flow and point source dispersion. By solving the Reynolds-averaged Navier–Stokes equations with the k–ω shear stress transport turbulence closure model, we determine the complex flow field information and the spatial distribution of point source solutes for the coupled model. The results indicate that the presence of porous structures creates recirculation zones in the coupled model, which prevents turbulent structures reaching deeper layers. Random porous structures induce more preferential flow, inhibit the formation of recirculation zones, and exhibit higher solute dispersion, which is directly related to turbulent solute fluxes. Furthermore, our study reveals that the release position of point sources significantly influences the distribution of solute concentrations within the porous bed.

GRAVITY MODULATION AND ITS IMPACT ON WEAKLY NONLINEAR BIOTHERMAL CONVECTION IN A POROUS LAYER UNDER ROTATION: A GINZBURG-LANDAU MODEL APPROACH

The effect of gravity modulation on weakly nonlinear biothermal convection in a porous rotating layer has been investigated in this study. The system under consideration is a porous medium layer saturated with a Newtonian fluid containing gyrotactic microorganisms, and it is subjected to both gravity modulation and rotation. Through a weakly nonlinear analysis, the behavior of the system at finite amplitudes is studied. The Ginzburg-Landau equation, obtained from perturbation analysis, provides insights into the system's behavior in the presence of gravity modulation. The amplitude of convection in the unmodulated case is determined analytically, serving as a reference for comparison. The research explores the influence of various parameters on the system, including the Vadasz number, modified Rayleigh-Darcy number, Taylor number, cell eccentricity, and modulation parameters such as amplitude and frequency. By varying these parameters, the heat transfer, quantified by the Nusselt number, is analyzed and compared in different cases. The modulation amplitude is found to have a significant effect on enhancing heat transfer, while the modulation frequency has a diminishing effect.

Transmission probability of gas molecules through porous layers at Knudsen diffusion

Gas flow through layers of porous materials plays a crucial role in technical applications, geology, petrochemistry, and space sciences (e.g., fuel cells, catalysis, shale gas production, and outgassing of volatiles from comets). In many applications the Knudsen regime is predominant, where the pore size is small compared to the mean free path between intermolecular collisions. In this context common parameters to describe the gas percolation through layers of porous media are the probability of gas molecule transmission and the Knudsen diffusion coefficient of the medium. We show how probabilistic considerations on layer partitions lead to the analytical description of the permeability of a porous medium to gas flow as a function of layer thickness. The derivations are made on the preconditions that the molecule reflection at pore surfaces is diffuse and that the pore structure is homogenous on a scale much larger than the pore size. By applying a bi-hemispherical Maxwell distribution, relations between the layer transmission probability, the half-transmission thickness, and the Knudsen diffusion coefficient are obtained. For packings of spheres, expressions of these parameters in terms of porosity and grain size are derived and compared with former standard models. A verification of the derived equations is given by means of numerical simulations, also providing evidence that our analytical model for sphere packing is more accurate than the former classical models.

Effect of Three Types of Gravity Modulation on Rivlin Ericksen Nanofluid Saturated in Porous Medium with Internal Heating

In this paper, authors have studied the Rivlin-Ericksen elastico-viscous nanofluid thermal instability with internal heating under three types of gravity modulation in a horizontal layer of porous medium using both linear and nonlinear ways. Linear stability analysis is done using normal mode approach, whereas nonlinear stability analysis is done using truncated Fourier series method. The results demonstrate that the internal heating, modified diffusivity ratio, and concentration Rayleigh number advance the initiation of convective motion in the system. On the other hand, Darcy number stabilize the system. To understand the behaviour of mass/heat transfer in the system two different approaches viz Mathematica NDSolve and Runge-Kutta-Fehlberg method (RKF-45) are used, and it is found that the rate of heat/mass transfer is exactly the same in both cases. In comparison to other gravity modulation profiles, day-night gravity modulation profile accelerates mass/heat transfer more quickly than the other two types of gravity modulation profiles. Steady state graph has demonstrated, convection occurs earlier when internal heating and amplitude values are increased. Moreover, it is also observed that heat/mass transport is very much affected by the variation of kinematic viscoelasticity parameter.

Study on suppression of violent sloshing in a multiple tuned liquid column damper by porous media layers

Multiple tuned liquid multi-column damper (MTLCD) is a passive damping device that is used to suppress the motion of semisubmersible floating offshore wind turbine (FOWT). However, the violent sloshing within the MTLCD under extreme sea environments reduces the anti-pitch motion effect. Thus, this study employed an innovative MTLCD with porous media layers, which can increase the flow energy dissipation, suppress the violent sloshing and enhance the damping moment (Mdamping). The OpenFOAM is used to simulate the hydrodynamic force in MTLCD, where the numerical method is validated by the decay test of a scaled model. The numerical natural period of the MTLCD shows good agreement with the experimental and analytical results. The sloshing characteristics, including pressure, damping moment impulse and work of the MTLCD without porous media, are analyzed firstly under simple harmonic rotation amplitudes (θ0) of 2°–20°. Subsequently, porous media layers are installed in the MTLCD with different heights (hp), including immersion and suspension, in order to improve the MTLCD's damping moment. Wavelet transform and wavelet-based bicoherence are utilized to analyze the nonlinear behaviors of the damping moment under violent sloshing. The breaking, surging and converging in the MTLCD are captured by the numerical method. The analyses show that the porous layers can suppress the violent sloshing by dissipating the fluid kinetic energy, and the damping moment work can be significantly improved when θ0 >6°. The liquid surging with bubbles leads to the nonlinear behaviors in the MTLCD, the sloshing energy transfer to the frequency doubling by three-wave interaction.

A Revised Work on the Rayleigh-Bénard Instability of Nanofluid in a Porous Medium Layer

To reveal the mechanism of the enhanced heat transfer in nanofluids, Buongiorno (ASME J. Heat Transfer, vol. 128, 2006, pp. 240–250) developed a convective transport model by considering the slip mechanisms of nanoparticles migration. By now, many extended researches are based on his model. Among them, the study on porous medium flow pioneered by Nield & Kuznetsov (Int. J. Heat & Mass Transfer, vol. 52, 2009, pp.5796–5801) has received much attention. Their work employed the Darcy model and Buongiorno’s model to investigate the thermal instability in a horizontal porous medium layer saturated by a nanofluid. Through a sophisticated analysis, they obtained an approximate formula capable of predicting the stability threshold. However, a potential contradiction exists in their analysis owing to an improper assumption about the thermophoretic coefficient, which may lead to an unphysical result. To date, much of current works still adopted this improper assumption in various extended problems. To resolve this contradiction, the present study revises their work by considering the dependence of thermophoretic coefficient on the volume fraction of nanoparticles. A nonlinear basic-state solution of concentration is obtained and then used to implement the linear stability analysis. In comparison with Nield’s formula, the present result shows that the threshold of instability shifts to a lower concentration by more than one order of magnitude. The mechanism causing the shift is discussed and the novelty of the present study is stressed.

Effect of gravity modulation on weakly nonlinear bio-thermal convection in a porous medium layer

Investigating thermal convection within porous media permeated by fluids and micro-organisms stands as a significant inquiry with broad relevance across geophysical and engineering domains. Studying convection within porous media can aid in controlling temperature and nutrient distribution for cell growth and tissue regeneration, as well as the efficiency of biofuel fermentation and production processes. Hence, the primary objective of this study is to investigate the influence of time-periodic gravitational forces on Darcy–Brinkman bio-thermal convection within a porous medium layer. This medium is saturated with a Newtonian fluid that encompasses gyrotactic micro-organisms. The gravity modulation amplitude is assumed to be very small. A weak nonlinear stability analysis is performed to analyze the stationary mode of bioconvection. The heat transport, measured by the Nusselt number, is governed by a non-autonomous Ginzburg–Landau equation. The research explores the influence of several parameters on heat transport, including the Vadaszs number, the modified bioconvective Rayleigh–Darcy number, cell eccentricity, modulation frequency, and modulation amplitude. The results are presented graphically, illustrating the impact of these parameters on heat transfer. The findings reveal that both the Vadaszs number and the modulation amplitude have a positive effect on heat transfer, enhancing the process. On the other hand, an increase in the modified bioconvection Rayleigh–Darcy number and cell eccentricity leads to a decrease in heat transfer. Furthermore, a comparison between the modulated and unmodulated systems indicates that the modulated systems have a more significant influence on the stability problem compared to the unmodulated systems. This highlights the effectiveness of external modulation in controlling heat transport within the system.

Throughflow effect on bi-disperse convection

The aim of this paper is to investigate the effect of a vertical constant throughflow on convective instabilities in a horizontal layer of fluid-saturated bi-disperse porous medium heated from below. Via linear instability and nonlinear stability analyses of the throughflow solution, the linear and nonlinear critical Rayleigh numbers for convective instabilities have been determined and studied as functions of the strength of the throughflow.

Optimization of Flow Channel Design with Porous Medium Layers in a Proton Exchange Membrane Electrolyzer Cell

This study aims to optimize the flow channel design for a proton exchange membrane electrolyzer cell (PEMEC) to minimize the pressure drop across the cell. The pattern of parallel flow channels is considered with a dual-porous layer structure sandwiched between the flow channel plate and the catalyst layer. Four geometric factors are considered in the optimization analysis, including the width of the flow channel, the depth of the flow channel, the particle diameter of the large-pore porous layer, and the particle diameter of the small-pore porous layer. Computational fluid dynamics (CFD) is used to simulate the flow field, and based on the results of the CFD simulation, the Taguchi method is employed to analyze the optimal flow channel design. The importance of the factors is further analyzed by the analysis of variance (ANOVA) method. Three inlet velocities are assigned in the Taguchi analysis, which are 0.01, 0.1332, and 0.532 m/s, and then an orthogonal array is constructed and analyzed for each inlet flow condition. It is found that the optimal combination of the factors is the depth of the flow channel 1 mm, the width of the flow channel 3 mm, the particle diameter of the large-pore porous layer 0.212 mm, and the particle diameter of the small-pore porous layer 0.002 mm. The pressure drop across the PEMEC is minimized at the condition with the optimal combination of the factors. The ANOVA analysis shows that the depth of the flow channel exhibits the most significant impact on the pressure drop, while the other factors play minor roles only.

Uncovering asymmetrical mass transfer in layered porous media: Insights from pore-scale analysis

Natural sediments or aquifers frequently exhibit layering and structural contrasts, which give rise to anomalous mass transfer behavior. Moreover, the effects of the interface on mass transfer and mixing in layered porous media (LPM) may be different when the flow direction is reversed, resulting in asymmetrical dispersive transport and a significant disparity between predictions and actual observations. Despite its importance, the underlying mechanism remains an open question. To address this gap, laboratory experiments and numerical simulations were conducted. The results demonstrated that the effective dispersion coefficient is larger when the solute migrates from the coarse grain layer to the fine grain layer (C-F direction) compared to the F-C direction. The history of the solute across the interface and the flow adjacent to the interface affect this deviation. Pore-scale simulations revealed a more tortuous flow field with a higher proportion of low and high velocities in the fine grain layer, although the velocity characteristics of the entire LPM were insensitive to flow direction. Measuring the velocity characteristics of LPM alone is insufficient to predict the asymmetrical dispersive transport behavior. To quantitatively evaluate mass transfer between layers and residual contaminants in LPM, a mass transfer index ε was introduced. The results of ε, along with the pore-scale concentration, directly indicated that the interface limited the mass transfer. The effect was more pronounced in the C-F direction and particularly evident in the heterogeneous LPM, which ultimately enhanced the solute mixing. In the heterogenous LPM, the maximum dilution index for the C-F direction is 1.31 times larger than that for the F-C direction. The findings contribute to a better understanding of anomalous solute transport and develop models for contaminant transport in layered sediments.