Porous Panels Research Articles

Experimental investigation on the cooling performance of a solid hybrid gel with self-transpiration cooling at high temperature

Transpiration cooling technology represents a viable cooling method for ultra-high temperature or high heat flux environments, offering high cooling efficiency. In previous studies, coolants were primarily in the form of gases and liquids. Therefore, the exploration of solid coolants remains a promising avenue for further research. This paper utilizes a compound with a substantial heat absorption capacity upon decomposition to prepare a solid hybrid gel as a coolant, and constructs a transpiration cooling structure with a high porosity zirconia foam as the coolant carrier and a stainless-steel wire mesh panel as the outer porous panel. Subsequently, the cooling structure was subjected to a thermal load experiment at a high temperature of 1654 K for a period of 1600 s. The present study offers novel and valuable insights by comparing the results with those of previous studies on hydrogel and ammonium carbonate, which have been extensively investigated with strong applicability: Hybrid gel stored at room temperature demonstrate superior long-term stability compared to hydrogel and ammonium carbonate. Hybrid gel, ammonium carbonate, and hydrogel demonstrated the capacity to cool the underside of the structure with a level of efficiency exceeding 30 % for a duration exceeding 1000 s under the experiment conditions. Among the hybrid gel, ammonium carbonate, and hydrogel, the hybrid gel exhibited the most efficient cooling of the surface of the specimen, achieving a rate of 10.6 %. Following an increase in the porosity of the porous panel from 20 μm to 120 μm, the hybrid gel has been observed to enhance the cooling efficiency of the specimen surface by 1.6 %, whereas ammonium carbonate and hydrogel do not possess this capability.

Two-dimensional visualisation of a travelling sound wave over porous medium

Prior research has demonstrated a variation in sound speed and a wave bending in the air when an acoustic wavefront approaches a porous medium at a grazing angle. The impact is found to be explicitly dependent on the frequency of the sound and the nature of the adjacent absorber. The current study expands the investigations by using a distributed array of eight microphones mounted on a single-axis motorised mover. The measurement setup allowed for an extensive collection of impulse responses within a confined area near a horizontally placed porous panel. The sensors captured a frequency sweep every 10 millimetres on multiple horizontal planes above the air-material boundary. Moreover, the array configuration allowed for simultaneous capture of wave propagation both above and outside the projection area of the absorbing material. The progression of a travelling wavefront is reconstructed as an image-sequence-based 2D animation on four discrete vertical planes, 60 cm by 50 cm each, traversing or passing outside the porous material.

Failure modes of laminated porous panel with different connection methods

This paper discussed the problem of porous structural panel, which compared the bending and compression performance of three different layered porous structure panels with single-layer integration, multi-layer SolidWorks software coordination and multi-layer bolted connection. And through experimental and finite element simulation results, it showed that the third group of bolted specimens could prevent the occurrence of cracks and maintain the integrity of the structure effectively. The second group of software had the best bending and compression performance, and its bearing capacity, strength and deformation ability increased with the number of member layers, while the third group of bolted specimens was the opposite.

Experimental investigation on transpiration cooling of ammonium carbonate in porous composite structure at high-temperature

This paper presents and experimental investigation of a novel transpiration cooling concept using ammonium carbonate as the solid coolant. Ammonium carbonate is a promising solid transpiration coolant with stable physicochemical properties at room temperature, high heat absorption by decomposition, and no solid residual after decomposition. In order to enhance the load-bearing properties of the thermal protection structure, alumina and zirconia ceramic foams with high porosity and large pore size were used as the coolant carrier, and the foam layer could still provide thermal insulation capacity after the coolant was exhausted. The transpiration cooling experiment were conducted with a stainless-steel wire mesh porous panel as the heated surface of the cooling structure within the high-temperature radiant apparatus, and the cooling performance was compared with that of hydrogel and a passive thermal protection structure. The results indicated that the thermal protection effect using the transpiration cooling technique has a significant advantage over the passive thermal protection method. The maximum cooling efficiencies of the ammonium carbonate cooling structure were up to 6.5 % and 33.7 % for the surface and bottom, respectively. In the transpiration cooling system without coolant injection force, the addition of a thin foam layer can extend the cooling time of ammonium carbonate from 981 s to 1800 s. However, this approach is detrimental to the cooling performance of the hydrogel. Influenced by the huge heat absorption of ammonium carbonate, the difference in heat transfer between alumina and zirconia foams within the cooling structure can be negligible.

Nonlinear bending characteristics of multidirectional functionally graded porous panels using higher-order finite element solution with parametric optimization

The current study aims to investigate the nonlinear bending behavior of unidirectional (1D) and multidirectional (2D/3D) functionally graded porous shell panels. Here, the material properties of the multidirectional functionally graded (FG)-panels are estimated by employing the representative volume element method and Voigt’s micromechanical homogenization scheme. The nonlinear mathematical model of the FG-panel is developed by incorporating Green-Lagrange type nonlinear strains in higher-order-midplane kinematics. The minimum potential energy principle is used to obtain the final form of the equilibrium equation for the multidirectional FG shell panel and further solved by using Picard’s iterative-based 2D-isoparametric finite element method via quadrilateral Lagrangian elements. The efficacy and robustness of the present model are checked by comparing its results with previously reported literature. Numerous examples are solved to analyze the impact of material parameters, such as volume fraction index and porosity index, and geometrical parameters, such as aspect ratio and support conditions, on the nonlinear deformation behavior of multidirectional FG shell panels. In addition, parametric optimization is carried out to minimize the flexural response by using the response surface methodology and, hence, determining the optimal values of multidirectional porous FG-panel. The results demonstrate that, within the defined ranges of FG-panel, lower values of porosity index and volume fraction index yield lesser deflection.

Optimization and comprehensive evaluation of liquid cooling tank for single-phase immersion cooling data center

Single-phase immersion cooling has emerged as a highly promising solution for addressing energy challenges and the substantial heat dissipation demands in data centers (DCs). The liquid cooling tank is a curial component in such system where numerous servers are immersed and the coolant are evenly flowed to each server. However, its performance and the comprehensive evaluation for the tank have not received much attention. In this study, by using the validated numerical model, the different tank structures, with or without consideration of baffle and porous panel, were firstly discussed. Then, four key parameters of tank, including inlet flowrate (Parameter A), the ratio of separation chamber height to server height (Parameter B), the ratio of pressure chamber height to server height (Parameter C), and the porosity of the porous panel (Parameter D) were explored in detail. Finally, the tank performance is evaluated and optimized by the orthogonal analysis and the entropy weight method (EWM). Results showed that, flow uniformity within the tank can be enhanced by incorporating a porous panel, and it was advisable to minimize the gaps between servers, despite the potential increase in pressure loss. Parameter A significantly impacted both the maximum temperature and pressure loss. Parameters B and C demonstrated effects on coolant weight and pressure loss, while Parameter D influenced pressure loss. By using orthogonal analysis and the EWM, maximum temperature carried the highest weight (0.362), followed by temperature difference (0.245), coolant weight (0.216), and pressure loss (0.177). The recommended values for Parameters A-D were 4 m3/h, 1.35 %, 4.05 %, and 11.33 %, respectively, which could be also considered as universality, since the comprehensive evaluation index only changed by 8 % when the server number increased from 10 to 40.

Study on the effect of humidity on formaldehyde emission parameters of wood-based panels

Wood-based panels are a significant source of indoor volatile organic compounds (VOCs), crucial for managing indoor pollution. The emissions from wood-based panels are influenced by both intrinsic factors, including their composition and manufacturing process, and extrinsic environmental conditions, such as temperature and humidity. In this paper, the emission of formaldehyde in plywood was studied under different temperature conditions (15°C, 23°C, 32°C and 37°C) and different humidity conditions (40%, 60% and 80%) by environmental chamber method. To understand the influence of relative humidity on the key parameters of panels from a mechanism perspective, this paper investigates the influence of relative humidity on the initial emittable concentration of formaldehyde, based on the hydrolysis reaction of urea-formaldehyde resin. Concurrently, the molecular dynamics and porous panels model were amalgamated to assess the influence of relative humidity on both the partition and diffusion coefficient. To simulate the emission process in a real environment, a control equation that allows for variations in both temperature and humidity is needed. This paper employs the method of variable separation to derive a simplified control equation. Subsequently, experimental data was utilized to validate the derived equation’s effectiveness within the practical indoor environmental range.

Vibration analysis of porous orthotropic cylindrical panels resting on elastic foundations based on shear deformation theory

Cylindrical panels are one of the most essential structural members of engineering structures, with mechanical, civil, aeronautical, and marine engineering applications. They are subjected to a wide range of vibrational loads. This article presents a novel higher-order porosity distribution and a free vibration analysis for porous orthotropic cylindrical panels resting on elastic foundations under higher-order shear deformation theory. It is assumed that cylindrical panels are composed of porous materials with uniformly and non-uniformly distributed pores. The porous panels' material properties are distributed in the thickness direction using specific functions. The equations of motion are derived using Hamilton's principle based on trigonometrical shear deformation theory and solved by performing the Galerkin solution procedure with simply supported edge conditions. The accuracy of the obtained natural frequency equation is confirmed by comparing the results to those of previously published in literature. Under comprehensive parametric studies, the influence of porosity coefficient, porosity distribution patterns, radius-to-curve length ratio, orthotropy, and stiffness of elastic foundation parameters on the free vibration response of porous orthotropic cylindrical panels are discussed in detail.

Acoustic wave propagation through eco-friendly porous panels at normal incidence

Human and non-human subjects are exposed to micro plastics through drink, food, and air. Micro-plastics propagating through atmosphere are breathable particles during inhalation and exhalation leading to deposition of them in the deep lung via the alveoli of the lungs. Teabags are made of plastics that are not recyclable and biodegradable. Therefore, we intend to remove used teabags from the natural environment by repurposing them to make sound attenuating panels for building and architectural industries, contributing in this way to a sustainable circular economy. The panels were designed and developed from consumed teabags as porous material by filling a frame to investigate acoustics wave propagation through them at normal incidence. Experimental testing was carried out on circular teabag panels in an impedance tube using a transfer function method to determine their sound absorption coefficient and transmission loss. Furthermore, the impedance gun method was used to determine the absorption properties of square panels. Results show that 75 mm thick circular panels give an absorption coefficient higher than 0.8 between 400 and 1600 Hz. Up-to 9.8 dB sound transmission loss of circular panels is obtained at higher frequencies. Absorption coefficients for square teabag panels are very good despite a coincidence-dip seen at 800 Hz. The satisfactory sound absorption and sound transmission characteristics of acoustic panels made of consumed tea bags can make this recycled material a cost-effective solution in the production of sustainable acoustic treatment in indoor spaces. The results suggest that recycling of consumed teabag as the panel could be applied as alternative sound absorbing materials.

Improvement of Environmental Uniformity in a Seedling Plant Factory with Porous Panels Using Computational Fluid Dynamics

A seedling plant factory requires precise environmental control to ensure uniform growth within a limited cultivation period. A porous panel exhaust system was installed to maintain a stable and uniform internal environment. To provide optimal temperature, humidity, and airflow, it is necessary to interpret the internal aerodynamics. However, field monitoring has limitations in analyzing the invisible flow patterns. To overcome this limitation, CFD simulations can be utilized to understand internal environmental conditions and uniformity. The objective of this paper is to develop and validate a CFD model of a seedling plant factory with a porous panel for improving the uniformity of the internal environment. Multiple data loggers were evenly installed at various locations inside the seedling plant factory, and 24 h field monitoring was conducted. The average temperature and humidity during the 16 h light period and 8 h dark period were maintained within 1% of the set values, while the regional temperature deviation had an average of 1.65 °C and a maximum of 2.63 °C. The regional humidity deviation had an average of 14.1% and a maximum of 23.8%. The CFD model was designed to analyze the internal environmental uniformity after validation by comparing it with the field monitoring data. The Realizable k-ε turbulence model, which exhibited an error of 4.0% in comparison with the field data, was selected through a validation test among four different turbulence models with the same configuration of the seedling plant factory. The CFD simulation results were interpreted quantitatively and qualitatively, focusing on the airflow, temperature, and humidity distributions caused by the air conditioner and humidifier. Variations in the average temperature of up to 0.5 degrees and velocity differences of 0.28 m/s were observed depending on the location of the cultivation shelves. The locations and causes of stagnant regions resulting from the airflow patterns were identified through the simulations.

SOFTWARE FOR SIZING PAD-FAN EVAPORATIVE COOLING SYSTEMS OF GREENHOUSES

The calculations for sizing pad-fan evaporative cooling systems depend on the psychrometric properties of the air inside and outside of the greenhouse, appearing as a constant need for professionals in the agricultural sector. A software capable of performing these calculations is important to speed up this procedure. In this study a free software was developed to estimate the maximum efficiency of the porous panel, the ventilation rate of the exhaust fan and the climatic conditions of pad-fan evaporative cooling systems in greenhouses. The software, called Theoretical Evaporative (TE), was written in Java programming language, using the NetBeans platform. All equations and algorithms used in this development are presented, and were based on the mechanical ventilation and cooling principles. The software was tested by means of comparisons with real system sizing calculations performed manually and in electronic spreadsheet. The TE was efficient in sizing different evaporative cooling systems for greenhouses and can be used for performing consultations in the academic and commercial areas of agricultural sciences, being also advantageous for didactic purposes. Although this software is applied to greenhouse conditions, the methodology presented can be adapted for other environments, such as poultry, cattle and swine facilities.

Theoretical thermoelastic frequency prediction of multi (uni/bi) directional graded porous panels and experimental verification

A novel finite element algorithm has been developed to analyse the eigenvalue characteristics of porous functionally graded (FG) curved panel under a thermal environment, considering the material gradings along the length and thickness, i.e. unidirectional (1D) and bidirectional (2D). In this research, exponential (EN), sigmoid (SM) and power-law (PL) gradings and porosity variations, i.e. even (POT-I) and uneven (POT-II), are adopted. The finite element (FE) computational algorithm has been prepared using a mathematical model of the FG panel based on the higher-order theory (HSDT). The structural governing equation is derived via Hamilton’s principle and solved numerically (FE solutions) to predict the eigenvalues. The obtained solution’s convergence is verified to establish the necessary stability. The difference between the present and published results is below 3.7%, and that between the present and experimental results is under 9.1%, which shows the accuracy of the developed model. A few natural fibre-reinforced (linearly varying through the thickness) polymeric layered FG plates are prepared for experimental validation. Finally, regarding the applicability of the proposed computational FE algorithm, a few parametric studies have been conducted to examine the effect of input variables on the thermal frequencies of the graded panel.

Scattering of Mack modes by solid-porous junctions in hypersonic boundary layers

Porous coating is regarded as an effective control strategy to delay the laminar-turbulent transition in hypersonic boundary layers, whose effects include not only the successive distortion of the Mack-mode growth rate but also the scattering effect appearing at the junctions between the solid and porous walls. The present paper focuses particularly on the latter mechanism by employing the harmonic linearized Navier–Stokes approach, which is confirmed to be sufficiently accurate as compared to the results obtained by direct numerical simulations. A transmission coefficient is introduced to quantitatively characterize the scattering effect, which is define as the ratio of the Mack-instability amplitude downstream of the junction to that upstream. For a solid-to-porous junction, the scattering effect leads to a stabilization of the majority of the second mode but destabilizes slightly the first mode. In contrast, the porous-to-solid junction plays the opposite role. The overall effect of a finite-length porous panel requires a combined consideration of the Mack-mode-growth-rate distortion and the scattering effect of the two junctions at both boundaries of the panel, which shows a critical frequency separating the destabilizing and stabilizing frequency bands. Additionally, a decrease in the wall temperature leads to an enhanced scattering effect on the Mack modes.

On the stochastic natural frequency of graphene reinforced functionally graded porous panels with unconventional boundary conditions

The present study explores the stochastic natural frequency of graphene reinforced functionally graded porous panels with unconventional boundary conditions. The material uncertainty is considered in the parameters associated with constituents that is, metal and graphene nanoplatelets (GPLs) individually and simultaneously. The metal matrix is reinforced with ultra-lightweight and high stiffness carbonaceous nanofiller, that is, GPLs. Halpin-Tsai micromechanics model is adopted to estimate effective Young’s modulus of the metal-GPLs composite whereas effective mass density and Poisson’s ratio are calculated using the Voigt model. The micro-structural gradation by creating pores is accomplished along the thickness direction of the panel employing certain continuous functions. These functions describe symmetric and asymmetric porosity distributions and associated patterns of GPLs. The equation of motion is developed using Euler-Lagrange’s equation which is based on C 0-continuous structural kinematics with 7 degrees of freedom. Finite element modeling in conjunction with the first-order perturbation technique has been applied to quantify the stochastic natural frequency in terms of the mean and standard deviation of the natural frequency. Various results have been examined to highlight the influence of parameters especially related to porosity, and graphene nanoplatelets on the stochastic natural frequency of FG-GPLs porous panel constrained with conventional and unconventional boundary conditions.

Pattern transformation induced waisted post-buckling of perforated cylindrical shells

A comprehensive investigation on the extremely large post-buckling deformation of perforated cylindrical shells is conducted using experiments and verified with an analytical shell model and nonlinear finite element simulations. A “waisted” post-buckling configuration, which is characterized by uniform shrinking in the middle section of the perforated cylindrical shell, is identified. The waisted behavior is attributed to the triggering of a pattern transformation under compressive load that shows special hyperelastic metamaterial characteristics. The load-carrying capacity of waisted post-buckling suffers a sudden drop and then recovers when the holes are completely collapsed and closed. Plenty of design parameters can be utilized to enrich variations of the waisted post-buckling responses. The negative Poisson's ratio induced by pattern transformation plays a key role in forming the waisted post-buckling modes. This special hyperelastic metamaterial behavior can be easily achieved by fixing the boundaries and adjusting the geometric parameters of the shell. By comparing the characteristics of a porous cylindrical shell with those appeared for an equivalent porous panel, it is highlighted that pattern transformation can occur in a thinner porous cylindrical shell without lateral support. The waisted post-buckling modes of a perforated cylindrical shell are stable, and the shell is invulnerable to the progressively increasing applied loads. In comparison, an ordinary cylindrical shell may snap from one mode to another in the post-buckling process. Moreover, we find that some non-closed cylindrical panels can also buckle into the waisted-like modes. These findings can be applied to the construction of functional devices for soft robotics, actuators, and structural protection for facilities, etc.

On the wave propagation in a higher-order multi-phase curved porous system

The porosity affecting the vibrational characteristics of structures should be considered due to the fact that these porosities can happen during the manufacturing process. The solid body and the liquid or gas compose the porous materials. In this regard, for the first time, wave propagation corresponding to the curved panel made of reinforced porous composites is investigated. Higher-order shear deformable theory (HSDT) is employed in order to extract the formulation. The effective material is attained by employing the rule of the mixture as well as the modified Halpin–Tsai model. Also, equations of motions that are solved analytically are extracted via Hamilton’s principle. The impacts of radius-to-total thickness ratio, the weight fraction of carbon nanotubes (CNTs), porosity factor, that different composite patterns, the pattern of porosity, as well as carbon fibers on phase velocity behavior corresponded with a reinforced curved porous panel are studied. The presented results can be employed in ultrasonic inspection techniques as well as structural health monitoring.

In situ acoustic characterization of a locally reacting porous material by means of PU measurement and model fitting

Reliable data on acoustical properties of materials are crucial for the design of a desired acoustic environment as well as to obtain accurate results from acoustic simulations. Although the acoustical properties of materials can be obtained via laboratory measurements, situations where in situ measurements are needed are often encountered. However, in situ measurement methods presented so far are limited by their poor portability or inaccuracies in the low-frequency range. In this work, we propose a characterization method that combines an in situ pressure-velocity (PU) measurement with a model fitting procedure using the Delany-Bazley-Miki impedance model for porous materials. The method uses an optimization routine to find the best match of measured and modelled reflection coefficient values within a given frequency range for the optimization parameters: flow resistivity, panel thickness, and probe-sample distance. The optimal parameter values allow, in turn, calculating the porous panel’s reflection coefficients for a broad frequency range including frequencies below the lower bounds of the optimization frequency range. The sensitivity of the method to panel width, lower bound of fitting frequency range, and to excluding parasitic reflections by time windowing is studied. The study shows that the proposed method provides characterization results in good agreement with reference data for panels of dimensions larger than 1800 mm and that the method is robust for reduction of one dimension of the panel down to 300 mm. It also shows that the model fitting accuracy is best when the frequency range of analysis is restricted to 1000–5000 Hz.

Nonlinear eigenfrequency characteristics of multi-directional functionally graded porous panels

The eigenfrequency characteristics of the doubly-curved FG panel are examined in the present article considering multi-directional grading influence and geometrical large deformation. In this study, different kinds of material grading patterns and porosity distributions are used for the modelling of the FG structure. Initially, a mathematical model has been established by utilizing HSDT mid-plane kinematics along with Green Lagrange kind of nonlinear strain terms. The finite element technique is utilized for the discretization of the structure. And Hamilton’s principle is adopted to obtain the governing equation of the FG structure and solved by utilizing a direct iterative method. Based on the mathematical model, a computer code in MATLAB is established for the calculation of the nonlinear frequencies. The suitability of the code has been checked by performing the validation and convergence tests. Lastly, the influence of several design parameters i.e., multi-directional grading, porosity distribution, grading patterns, amplitude ratio, curvature ratio, geometrical shapes, support conditions, thickness ratio and aspect ratio on the nonlinear eigenfrequency parameters is shown by presenting different numerical examples.

Acoustic Attenuation of Hybrid Sonic Crystal Made with Periodic Cylindrical Scatterers and Porous Panels

Acoustic Attenuation of Hybrid Sonic Crystal Made with Periodic Cylindrical Scatterers and Porous Panels

Improvement of noise reduction performance in bellows using multilayer perforated panels

When the speed of a railway vehicle increases, the level of noise inside the vehicle inevitably increases as well, which is a major cause of discomfort to passengers. The most effective method is to improve the overall noise reduction performance of a vehicle. In particular, the gangway of the railway vehicle is made of silicone rubber; therefore, its noise reduction performance is inferior to that of other components of the vehicle. Thus, it is essential to improve the interior noise performance of railway vehicles. This study aims to reduce the noise in the low-frequency region of a railway vehicle gangway. It examines the applicability of the multi-layered resonance type panel, which has not been previously applied to the bellows in railway vehicles. In particular, the transmission loss was improved by changing the structure without filling the bellows with sound-absorbing material. First, a theoretical review of the noise reduction performance of a perforated multilayer structure was performed. Based on this, the major design parameters of the perforated multilayer structure that are effective in reducing noise in the low-frequency region of the bellows were derived. Through this, it was confirmed that in the multilayered structure, the hole diameter of 1 mm was effective in increasing the transmission loss in the low-frequency region, and the transmission loss was improved at 1% of the porosity. In addition, through a simple two-dimensional analysis model, it was confirmed that the transmission loss of the porous panel was improved at low frequencies of 100 to 400 Hz. Based on this result, a gangway with perforated multilayer structures was developed and tested. Through this verification test, it was confirmed that the noise performance of 9.2 dB was an improvement in the low frequency range of 100 Hz.