Use Of Porous Material Research Articles

Utilising Polyester and Steel Slag‐Derived Metal/Carbon Composites as Catalysts in Biodiesel Production

Synthetic textiles such as polyesters are essential for daily life. However, large‐scale production generates large amounts of waste. This study introduces a new approach for valorising polyester textile waste (PTW) by transforming it into a catalyst for biodiesel production via pyrolysis. Specifically, a metal/carbon composite (PTW + steel slag [SS] composite—PSC) with enhanced catalytic properties was prepared by pyrolysing PTW with SS. The alkaline metals in SS facilitate the carbonisation of PTW via decarboxylation, resulting in a PSC rich in carbon, iron, and alkaline compounds. This composite featured mesopores that were larger than the micropores (MPs) typically found in PTW char. The use of porous material (silica) in thermally induced transesterification has been proven to be an efficient method for biodiesel production, achieving a yield of 97.20 wt.% in 1 min (faster than the 93.82 wt.% yields in 60 min observed from conventional alkali‐catalysed transesterification). However, the high reaction temperature (≥ 360°C) poses economic/technical challenges. To overcome this, PSC has been employed as a catalyst in thermally induced transesterification, leveraging its mesoporous structure and high alkaline content, particularly calcium oxide. The PSC achieved a biodiesel yield of 98.10 wt.% at a markedly lower reaction temperature of 120°C within 1 min. This performance was not attainable using silica or PTW char under similar conversion conditions. These findings highlight the potential of PSC produced through the pyrolysis of PTW and SS as effective catalysts for biodiesel production. This process is a promising strategy for converting waste into valuable resources and mitigating the environmental impacts associated with polyester waste.

Porous Material for Gas Thermal Compression in Space Conditions: Thermal Design Aspects

Abstract It is almost impossible to name a field of human activity where porous materials are not used. Filters, membranes, thermal insulators, fuel cells, catalysts, wicks of heat transfer devices, sorbents, textiles, and other examples of porous materials explain such an increased interest in the study of their properties, design of new materials, and development of technologies for their manufacture. The recent need for in-orbit spacecraft refuelling has led to the development of gas thermal compression technology based on the use of porous material as both a fuel retention mechanism and thermal interface. The present paper reveals the thermal aspects of porous material design for a device intended for pumping xenon, fuel for ion thrusters, in zero-gravity conditions – Xenon Refuelling Compressor.

Investigating Heating Transfer and Turbulent Flow in a Channel for Different Cross Sections Full-Filled of Glass Spheres as a Porous Media

 In recent years various modern improvements have been used to raise the performance of heat systems in various engineering and industrial applications. One of these improvements is the use of porous material. This research focuses on conducting a theoretical study (numerical simulation) via forced convection heat transfer of three channels of various cross-sections (square, rectangular, and triangular) with an equal hydraulic diameter of (0.15 m) with glass spheres filled of a diameter (0.012 m) as a porous martial. The lower surface of the test section is subjected to a uniform heat flux along the fluid flow of (5000 W/m2), while the upper surface is thermally insulated. The type of model used in this study (k- epsilon turbulent model) to simulate and analyze fluid flow inside three channels. This study aims to enhance the thermal properties of the fluid (water) and study its effect on the distribution of temperature, velocity, and pressure, respectively. The results showed that the channel with a triangular cross-section gives the highest distribution of temperature and pressure compared to the rest, and therefore it is considered the optimal design for the channels.

Effect of geometrical parameters and use of porous material in a Helmholtz resonator on suppression of thermo-acoustic instabilities

Thermo-acoustic instabilities are mainly formed due to in-phase superposition of non-uniform heat release and pressure variation in the combustors of gas turbines, rocket engines and other acoustically confined spaces. These instabilities not only damage the structural system but also reduce its combustion efficiency and heat transfer rate. Hence suppression of thermo-acoustic instabilities is a prominent requirement for stable and safe heat generation in the combustors. In this work, the Helmholtz resonator has been used to suppress the instability. The efficacy of the resonator has been further increased by the addition of absorptive material to it. This work concentrates on inspecting the influence of cavity volume, neck length and neck diameter of the Helmholtz Resonator and the thickness of the absorptive material in the damping process of thermo-acoustic instabilities. The experimentation was carried out for various combinations of resonator cavity volume, neck diameter and neck length, and the best combination was found to be 6 mm neck diameter with 20 mm neck length at 60% volume which provided an acoustic damping of around 30 dB. Further, it was noticed that the addition of absorptive material is effective at lower volumes of Helmholtz resonator, and with an increase in thickness of absorptive material beyond a certain limit, the damping ability of the resonator reduces.

Characteristic parameter to predict the lubricant outflow from porous polyimide retainer material

The lubrication performance of oil-impregnated porous polyimide retainer depends on the release of lubricant from the pores. The centrifugal effect induced by rotation is one of the important inducements of lubricant outflow. In this paper, molecular dynamics simulations and experiments are conducted to investigate the lubricant outflow process in the porous polyimide material. The results show that the lubricant outflow can be controlled by five features: pore sizes, rotation speeds, radii of rotation, lubricant viscosities, and surface tensions. Inspired by molecular dynamics simulation results and experimental observations, a characteristic parameter is proposed to evaluate the lubricant outflow state. This new understanding may help expand the use of porous material to improve lubrication in space bearing.

A review on heat transfer enhancement techniques during natural convection in vertical annular geometry

Heat transfer enhancement caught the attention of researchers owing to the need for compact size heat exchangers. This is because of the development of micro-devices due to advancements in electronics. The heat transfer through natural convection in vertical annular geometry has many benefits and, if designed efficiently, will result in energy saving due to no/less moving parts. This paper reports the review of techniques used by researchers for heat transfer enhancement during natural convection flow in vertical annular geometry. Several techniques that have a significant impact on the design and performance are discussed here in detail viz. use of nanofluids, use of the magnetic field, use of cylinder wall rotation, use of discrete wall heating, use of porous material, use of boiling, use of rings, etc. The implementation of each technique along with its advantages and drawbacks are also discussed. The authors also suggested their recommendation of techniques to be used for heat transfer enhancement. The study highlights research gaps and weak points that have not received the researchers' attention so far. This article outlines areas that needed the most attention in the future.

Performance enhancement of a split air conditioner using porous material inside the evaporator pipes

AbstractIn this experimental study, a porous material is used inside the pipes of the evaporator as the main heat exchanging device in the air conditioning cycle. The used porous material consists of stainless steel balls of different diameters. As a case study, refrigerant R454B, which is a drop‐in replacement to refrigerant R410A, is used as a working fluid in the air conditioner thermodynamic cycle. Four different porosities were used during the experimental tests; 100% (empty tube), 46%, 40%, and 33%. This study investigated the influence of variation of porosity as well as outside air temperature and refrigerant evaporation temperature on the cycle coefficient of performance, evaporation capacity, pressure drop, and power consumption during the compression process. Measured evaporation temperatures and indoor temperatures during tests were in the range of 1.5–12°C and 18–25°C, respectively. The use of porous material in the evaporation heat exchanger resulted in a considerable increase in the cycle evaporation capacity and coefficient of performance. Varying porosity from 100% to 33% resulted in an average percent increase of cycle evaporation capacity and coefficient of performance by 48.8% and 84.3%, respectively. Also, decreasing porosity from 100% to 33% resulted in an average percent increase in power consumption during the compression process by about 27%. An average percent increase of power consumption of compressor by about 25.9% is also reported, when evaporation temperature increased from 1.5°C to 12°C. Increasing outside air temperature from 27.1°C to 39.5°C resulted in decreasing evaporation capacity and coefficient of performance by 35.2% and 34.5%, respectively, and in increasing compressor power consumption by about 14.3%. A considerable pressure drop was recorded during the evaporation process when using porous material. The volumetric evaporation capacity, as well as compressor discharge temperature, are increased by increasing evaporating temperature and by decreasing evaporator porosity. The increase in air ambient temperature resulted in a considerable increase in refrigerant mass flow rate.

Effect of PCM and porous media/nanofluid on the thermal efficiency of microchannel heat sinks

The present study is a genuine attempt to improve the thermal behavior and hydraulic performance of a conventional microchannel heat sink (MCHS) using porous material, phase change material (PCM) and nanofluid. Three-dimensional microchannels with square, circular and flattened circular geometries are examined numerically by considering the thermal conduction in solid parts. Various factors are examined, including the effect of the number of channels, fluid velocity passing through channels, porous substrate thickness, PCM layer thickness, Darcy number, porosity coefficient, thermal conductivity ratio in the porous material, volume fraction and nanoparticle diameter. According to the findings, for a critical thickness of the porous substrate, the thermal performance is at its minimum. With increasing values of Darcy number, porosity coefficient, nanoparticle diameter and PCM thickness, the thermal performance of MCHS decreases. An MCHS with square geometry displays a better thermal performance compared to the other two geometries. Furthermore, the use of porous material, nanofluid and PCM improves the thermal behavior compared with a conventional microchannel. The thermal performance of MCHS with PCM is approximately 47% and 17% higher than that of a microchannel with the porous substrate and a microchannel incorporating a combination of the porous layer and nanofluid.

Heat Transfer Enhancement using Porous Materials as Receiver in Solar Parabolic Trough Collector

Research and new innovative technologies have started a new revolution in the area of energy development with storage capacity. One or other issues is that researchers are lacking with the conservation or storage of this energy. Porous Materials could be the concept which can be used to conserve energy in the solar sector. Metal foam or porous material which results in an increase in surface area can be taken as a source for energy conservation or storage received from the energy source. Solar Parabolic Trough Collector which is solar operated device can be an approach of the energy conversion. In this research article, performance and working of solar parabolic trough collector is been observed utilization of porous material as receiver of solar energy. The temperature of water flowing through the system was increased with the use of porous material in the solar parabolic trough collector. Finally, the efficiency of the system is improved.

G EXPERIMENTAL AND THEORETICAL STUDY OF FORCED CONVECTION AROUND A CYLINDER EMBEDDED IN POROUS MEDIA

An experimental and theoretical study of air forced convection heat transfer at Reynoldsnumber (1091.5 to 1560) around a circular cylinder placed in an iron test section (0.2x0.2x0.4m3) filled with saturated porous material glass balls of 5mm in diameter. A copper circularcylinder heater of diameter 0.015m and length 0.2m is heated electrically; it is located indifferent positions in X and Y direction within the test section. The forced convection heattransfer is simulated using the ANSYS program (Fluent). The results showed that the surfacetemperature distribution of the cylinder has the same trends for the different locations withinthe test section. The average Nusselt number increases with Reynolds number and heat flux.Also, the results show that the use of porous material improves heat transfer by 67.4%. Themaximum percentage deviation between the experimental and theoretical results is 1.622%.Moreover, experimental correlations were introduced and comparison was performedbetween the present results with the previous studies and it gives a good agreement.

Free Convection Heat Transfer Around a Cylinder Embedded in an Enclosure Filled with Porous Media

An experimental and theoretical study of free convection heat transfer for a cylinder placed in an iron test section of dimensions (0.2x0.2x0.2 m3), the test section filled with saturated porous material glass balls (5 mm), and the air is the working fluid with Raleigh number (7692.6 ≤ Ra ≤ 17654). The circular cylinder heater (D = 0.015 m, L = 0.2 m) is heated electrically, made of Copper and located in different positions (in X & Y direction). The theoretical part includes solving the free convection heat transfer using the ANSYS program (fluent). The experimental and theoretical results showed that the surface temperature values around the cylinder perimeter when changing its position within the test section are changing as moving up and down where the effect of buoyancy force appears. The maximum difference between the upper and lower position at the experimental result is 7.22%, and the average Nusselt number increases with Raleigh number and heat flux. Also, the experimental results showed that the use of porous material significantly improves the heat transfer by 48.6%. The maximum percentage change between the experimental and theoretical results is 5.46%. Moreover, experimental correlations were achieved, and a comparison was performed between the present results with the previous studies and it gives a good agreement.

Optimization of packed bed solar air heaters—A thermo‐hydraulic approach

AbstractThe present work deals with the thermo‐hydraulic optimization of solar heater with packed bed duct. Heat transfer and fluid flow characteristics of solar air heater have been analyzed to obtain optimal performance. The use of porous material in packed bed duct of solar air heater shows as an efficient method to enhance the thermal efficiency of solar air heaters. However, the use of packed bed results in higher friction factor requiring more pumping power, due to which, there is a need of optimization of the system to obtain maximum benefit from the packed bed. The present investigation has been emphasized on heat transfer and friction characteristics of solar air heater, provided with packed bed duct. Under thermo‐hydraulic consideration, relationship between system and operating parameters resulting in optimum performance has been developed, that can be utilized for the design of such thermo‐hydraulic optimized system. It is concluded that the enhancement factor slightly decreases with the increase in values of temperature rise parameter for every set of bed depth to packing element size ratios. For every set of bed depth to packing element size ratios, the maximum values of enhancement factors attains at (X1 = 0.009, X3 = 0.6), gives the optimal condition.

Mixed convection of non-Newtonian nanofluid in an H-shaped cavity with cooler and heater cylinders filled by a porous material: Two phase approach

In the present problem, two-phase mixed convection of a non-Newtonian nanofluid in a porous H-shaped cavity is studied. Inside the enclosure there are four rotating cylinders, using the Boussinesq approximation, mixed convection is created. Nanofluid includes H2O + 0.5% CMC and copper oxide nanoparticles. The mixture model was used to model physical phenomena. Different aspect ratios were used in order to achieve the best heat transfer rate. The Darcy and Richardson numbers ranges are 10−4 ≤ Da ≤ 10−2 and 1 ≤ Ri ≤ 100 respectively. Also, the aspect ratio and dimensionless angular velocities of cylinders ranges are 1.4 ≤ AR ≤ 1.6 and −10 ≤ Ω ≤ 10 respectively. Streamlines and isotherm-lines contours have been obtained for the variation of Darcy and Richardson numbers, aspect ratio and angular velocity. The heat transfer rates have been obtained for various aspect ratios, Darcy and Richardson numbers, and the direction of the cylinder's rotation, and are compared with each other. The results show that the direction of cylinders rotation influences the strength and extent of the generation vortices. Also, the use of porous material in high permeability can be a good alternative to lowering the angular velocity of the cylinders and ultimately reducing the need for less energy.

Numerical Investigation of Two-Phase Flow Over Unglazed Plate Collector Covered With Porous Material of Wire Screen for Solar Water Heater Application

This paper presents three-dimensional numerical simulation results of the effect of surface tension on two-phase flow over unglazed collector covered with a wire screen. The homogenous model is used to simulate the flow with and without the effect of porous material of wire screen and surface tension. The Eulerian-Eulerian multiphase flow approach was used in this study. The phases are completely stratified, the interphase is well defined (free surface flow), and interphase transfer rate is very large. The liquid–solid interface, gas–liquid interface, and the volume fraction for both phases were considered as boundaries for this model. The results show that the use of porous material of wire screen will reduce the velocity of water flow and help the water flow to distribute evenly over unglazed plate collector. The possibility of forming any hot spot region on the surface was reduced. The water velocity with the effect of surface tension was found higher than the one without this effect, due to the extra momentum source added by surface tension in longitudinal direction. The use of porous material of wires assures an evenly distribution flow velocity over the inclined plate, therefore helps a net enhancement of heat transfer mechanism for unglazed solar water collector application.

Modelling of Thermal and Gas-Dynamic Processes in the Porous Structures

In this article is considered the use of porous material in heat exchangers. The programming model with a porous regenerator heat exchanger was compiled in the program ANSYS Fluent complex. The paper does comparative analysis of influence of different material porosity on flow parameters.

I Using Porous Material for Heat Transfer Enhancement in Heat Exchangers: Review

The increase in energy cost and energy consumption has required more effective use of energy. The problem of dissipating high heat fluxes has received much attention due to its importance in applications such as heat exchanger. The heat transfer duty of heat exchangers can be improved by heat transfer enhancement techniques. In recent years, Considerable efforts have been made to increase heat transfer rates in heat exchangers by implementing passive enhancement methods that require no direct consumption of external power. On the basis of a theoretical and experimental analysis the conclusion derived was that the best heat transfer enhancement can be reached by the use of porous material as an inexpensive technique to extend the heat transfer area, improve effective thermal conductivity, and mix fluid flow. This paper presents a brief discussion on the application of using porous media to heat exchangers by means of heat transfer enhancement.

Laminar flow with combustion in inert porous media

This work presents one-dimensional numerical results for combustion of an air/methane mixture in inert porous media using laminar and radiation models. Comparisons with experimental data are reported. The burner is composed by a preheating section followed by a combustion region. Macroscopic equations for mass, momentum and energy are obtained based on the volume average concept. Distinct energy equations are considered for the porous burner and the flowing gas. The numerical technique employed for discretizing the governing equations was the control volume method with a boundary-fitted non-orthogonal coordinate system. The SIMPLE algorithm was used to relax the entire equation set. Inlet velocity, excess air, porosity and solid-to-fluid thermal conductivity ratio were varied in order to investigate their effect on temperature profiles. Results indicate that higher inlet velocities result in higher gas temperatures, following a similar trend observed in the experimental data used for comparisons. Burning of mixtures close to the stoichiometric conditions also increased temperatures, as expected. Increasing the thermal conductivity of the preheating section reduced peak temperature in the combustion region. The use of porous material with very high thermal conductivity on the combustion region did not affect significantly temperature levels in the combustion section.

Aerodynamic Noise Reduction in Pantographs by Shape-smoothing of the Panhead and Its Support and by Use of Porous Material in Surface Coverings

To reduce the aerodynamic noise generated by a pantograph, which is one of the dominant noise sources in high speed trains, the authors have proposed a set of noise reduction techniques, namely, shape-optimization of the panhead, relaxation of aerodynamic interference between the panhead and the articulated frame, and the use of porous material for surface covering. To evaluate the total noise reduction effect of these techniques, they were applied to a prototype pantograph which was tested in a wind tunnel. Test results showed that the prototype pantograph lowered the noise level from the current low-noise pantograph by about 4dB. Furthermore, they also confirmed that the prototype pantograph had sufficient aerodynamic stability against change of attack angle.

Materials and design development for bipolar/end plates in fuel cells

Abstract Bipolar/end plate is one of the most important and costliest components of the fuel cell stack and accounts to more than 80% of the total weight of the stack. In the present work, we focus on the development of alternative materials and design concepts for these plates. A prototype one-cell polymer electrolyte membrane (PEM) fuel cell stack made out of SS-316 bipolar/end plate was fabricated and assembled. The use of porous material in the gas flow-field of bipolar/end plates was proposed, and the performance of these was compared to the conventional channel type of design. Three different porous materials were investigated, viz. Ni–Cr metal foam (50 PPI), SS-316 metal foam (20 PPI), and the carbon cloth. It was seen that the performance of fuel cell with Ni–Cr metal foam was highest, and decreased in the order SS-316 metal foam, conventional multi-parallel flow-field channel design and carbon cloth. This trend was explained based on the effective permeability of the gas flow-field in the bipolar/end plates. The use of metal foams with low permeability values resulted in an increased pressure drop across the flow-field which enhanced the cell performance.

A simple concentric heat exchanger

An investigation was made into the effective application of porous heat exchangers of cylindrical shape through which fluid passes axially. On the basis of a theoretical analysis the conclusion derived was that the best thermal efficiency can be reached by the use of porous material with a large heat-exchanger surface, a high radial and low axial thermal conductivity (ie with a marked anisotropy of thermal conductivity), and a small radius of the heat exchanger operating at lower flows of cooling agent. The results of experiments carried out at helium and nitrogen temperatures are presented. These results have confirmed the high effectiveness of porous heat exchangers, even in comparison with chamber-type heat exchangers. For the temperature range from 1.5 to 300 K the heat exchangers composed of highly conductive metal nets (mesh gauge of the order of magnitude of 10−1 mm) stacked perpendicularly to the direction of flow of the cooling fluid, appear to be the most promising ones.