Use Of Porous Media Research Articles

Effect of Reynolds asymmetry and use of porous media in the counterflow double-pipe heat exchanger for passive heat transfer enhancement

In order to enhance the heat transfer in a double-pipe counterflow heat exchanger, the use of porous media and nanofluid is analyzed. The effect of complete filling of one or both channels of the heat exchanger with porous metal foams on the heat transfer and pumping power has been studied, considering laminar flow with various Reynolds numbers (Re = 100 to 2000) and porous media (Da = 0.1 to 10−4). As a novelty, in order to select proper porous media with an appropriate Reynolds number in each channel, this study focused on the coupling of Re asymmetry and porous medium properties used in the inner and outer channels of the heat exchanger. Flow through porous media is simulated by the non-Darcy law and two-phase mixture model used for the nanofluid flow. Results are presented and investigated in terms of the effectiveness (e-NTU method) and the performance evaluation criterion (PEC). It is shown that the effectiveness could only depict the thermal performance, while the PEC reflects the influences of the porous media on both the pumping power and the heat transfer. Use of porous media in both channels (case D) has led to the highest effectiveness (between 0.6 and 1). In addition, PEC study reveals that the optimal Re values exist for flow in each one of the channels and that case D has the highest PEC (more than 4). To maximize the PEC, for the cases with only one porous channel (B and C), the channel which does not include porous media should have the highest Re, while a low or moderate Re should be selected for the porous channel. However, for case D, Rei should have its highest value, while Reo has an optimal value in the range of 500 to 1000.

Numerical analysis of transport in porous media to reduce aerodynamic noise past a circular cylinder by application of porous foam

Metal foams as porous media have very high porosity and good strength. These materials could easily be applied to exterior surfaces of metals used in different industries. Porous media have been used less in the external flows to control the wake region or reduce the generated sound in high-speed flows. In this study, a numerical investigation is done to explore the effect of different characteristics of a porous medium—such as PPI and porosity or porous coating thickness—on the sound generated by a porous-coated cylinder. The governing transport equations in the clear and porous regions are solved using 3D Navier–Stokes and non-Darcy equations, respectively, and employing the large eddy simulation turbulence model. The generated noise is estimated using the Ffowcs-Williams and Hawkings model at the observer location. The results show that use of porous media could considerably reduce the aerodynamic noise provided that its characteristics are selected precisely. For example, results show that a porous-coated cylinder with PPI = 40 has about 30 dB higher overall sound pressure level (OASPL) than one with PPI = 10 with the same porosity and thickness. Same conditions are also observed about the thickness of the coating. The results indicate that an optimal thickness exists for which the OASPL is minimal. For example, porous-coated cylinders with coating thickness of 5 and 15 mm have about 25 dB higher OASPL compared to a cylinder with the coating thickness of 10 mm.

Experimental evaluation of the performance and exhaust emissions of porous medium diesel and Otto engines

Nowadays, the porous medium engine as a new combustion concept is proposed to achieve high combustion efficiency and low emissions because of providing homogeneous combustion conditions. Rare experimental results have been reported about the effect of using porous media on the performance and exhaust emissions of internal combustion engines, in the previous researches. Therefore, in this paper the effect of using porous Otto and diesel engines on pollution emission, brake-specific fuel consumption (BSFC) and brake torque brake power is investigated. The results show a 70% reduction in CO and HC emission, 27% decrease in fuel consumption and negligible increase in NOx emission due to using porous media in the air manifold of Otto engine, while using porous media in combustion chamber of diesel engine reduces NOx emission by 35% and increases HC emissions by 35%. According to the results, the best place for use of porous media in internal combustion engines with the largest advantages is in the air manifold of Otto engine.

Thermodynamic simulation of porous-medium combustion chamber under diesel engine-like conditions

Currently, one of the most important issue of the diesel engines is the non-homogeneity of the in-cylinder fuel-air mixture. Non-homogeneous mixture causes the non-uniform heat release and high-temperature gradient in the combustion chamber that followed by the production of unburnt hydrocarbons, carbon monoxide, nitrogen oxides and soot. Homogenous combustion decreases the production of the emissions. One novel method for achieving homogenous combustion is the use of porous medium (PM) within the combustion chamber of engine so as to separate the mixture formation process from combustion process. The present article thermodynamically investigates the effect of utilizing PM in a constant-volume combustion chamber via solving the energy equations for both the solid and fluid phases considering the chemical reaction of the fuel combustion. At first, numerical result is validated according to the experimental result of diesel fuel injection in a constant-volume combustion chamber with PM. Then, effects of the initial mixture and PM temperature, the porosity of the PM, the mean pores diameter as well as the use of fuels such as decane, isooctane, methanol, ethanol, propane and hydrogen on combustion initiation, and also pressure and temperature of the combustion chamber studied.

Enhanced Solar Thermal Evaporation of Ethanol-Water Mixtures, through the Use of Porous Media.

A significant enhancement of solar irradiation induced evaporation of water, and ethanol-water mixtures, through the use of carbon foam based porous media, is demonstrated. A relationship between the consequent rate of mass loss, with respect to the equilibrium vapor pressure, dynamic viscosity, surface tension, and density, was developed to explain experimental observations. The evaporative heat loss was parametrized through two convective heat transfer coefficients-one related to the surface and another related to the vapor external to the surface. The work promotes a better understanding of thermal processes in binary liquid mixtures with applications ranging from phase separation to distillation and desalination.

LATTICE BOLTZMANN SIMULATION OF FREE CONVECTION IN AN INCLINED OPEN-ENDED CAVITY PARTIALLY FILLED WITH FIBROUS POROUS MEDIA

The present study deals with natural convection flow in an open-ended cavity partially filled with fibrous porous media. The numerical investigations are performed using the lattice Boltzmann method. The considered porous media are formed of random arrangements of square obstacles and simulated in pore scale. The effects of some dominant variables, such as the Rayleigh number, angle of inclination, porosity, and eccentricity of the porous media on the flow field and the cavity heat transfer, are investigated. Results are reported in terms of isotherms, streamlines, and average Nusselt numbers. The numerical results obtained indicate that appropriate use of porous media can enhance the rate of heat transfer. Also, increasing the inclination angle at high Rayleigh number or decreasing the porosity at low Rayleigh number increases the average Nusselt number. Comprehensive discussions on the effectiveness of the porous cavity compared to a nonporous one, in different situations, are also provided.

Enhanced solar thermal evaporation of Ethanol-water mixtures, through the use of porous media

Enhanced solar thermal evaporation of Ethanol-water mixtures, through the use of porous media

Local Thermal Non-Equilibrium Investigation on Natural Convection in Horizontal Channel Heated from Above and Partially Filled with Aluminum Foam

The configuration of two horizontal parallel walls, with heated upper plate and open cavities, gets considerable attention in many thermal engineering applications. In this work, a numerical investigation on steady state natural convection in a horizontal channel partially filled with a porous medium and heated at uniform heat flux from above is carried out. The local thermal non-equilibrium (LTNE) hypothesis is invoked. A three-dimensional model is realized and solved by means of the ANSYS-FLUENT code. Results are presented in terms of velocity and temperature fields and profiles, and they show that the use of porous medium improves the heat transfer in the channel due to the aluminum foam high conductivity.

Influence of porous media on the performance of hybrid PV/Thermal collector

Porous media play an important role in the process of storage energy. In this paper, the influence of porous media on the performance of a double pass hybrid PV/thermal air collector was achieved by building an experimental set-up for this purpose. The study showed that using porous media expanded the area of heat transfer and thus increased the thermal efficiency and temperature of the exit air from the hybrid solar collector. The compound efficiency was increased (3%) after using the porous medium in the lower ducts of the double-pass hybrid collector. At the same time, the pressure drop was increased after using the porous media.In this analysis, it was concluded that the hybrid solar collector with porous media and glass cover is more thermally efficient than the other design form. The results showed a rise in the electrical efficiency with the increase of the fluid flow rate. This increase in the value of the electrical efficiency was due to the higher volumetric air flow which enhanced the PV panel cooling. Also, the results displayed that fixing a glass layer on the hybrid collector caused the rise in thermal efficiency and reduction in the electrical efficiency of the hybrid collector. The highest value for the daily thermal efficiency was 80.23% in the collector that used porous media and glass cover, while the higher value for the thermal efficiency was 51.25% without porous media and glass cover. Also, the highest value for the daily electrical efficiency was 8.7% in the collector that used porous media and the higher value for the daily electrical efficiency was 10.91% without porous media and without glass cover. The use of porous media and glass cover in the hybrid system is a desirable option when using the hybrid system for electrical generation only.

Mesoporous Silica as a Carrier for Amorphous Solid Dispersion

In the past decade, the discovery of active pharmaceutical substances with high therapeutic value but poor aqueous solubility has increased, thus making it challenging to formulate these compounds as oral dosage forms. The bioavailability of these drugs can be increased by formulating these drugs as an amorphous drug delivery system. Use of porous media like mesoporous silica has been investigated as a potential means to increase the solubility of poorly soluble drugs and to stabilize the amorphous drug delivery system. These materials have nanosized capillaries and the large surface area which enable the materials to accommodate high drug loading and promote the controlled and fast release. Therefore, mesoporous silica has been used as a carrier in the solid dispersion to form an amorphous solid dispersion (ASD). Mesoporous silica is also being used as an adsorbent in a conventional solid dispersion, which has many useful aspects. This review focuses on the use of mesoporous silica in ASD as potential means to increase the dissolution rate and to provide or increase the stability of the ASD. First, an overview of mesoporous silica and the classification is discussed. Subsequently, methods of drug incorporation, the stability of dispersion and, much more are discussed.

Two-Phase Flow Field Simulation of Horizontal Steam Generators

Abstract The analysis of steam generators as an interface between primary and secondary circuits in light water nuclear power plants is crucial in terms of safety and design issues. VVER-1000 nuclear power plants use horizontal steam generators which demand a detailed thermal hydraulics investigation in order to predict their behavior during normal and transient operational conditions. Two phase flow field simulation on adjacent tube bundles is important in obtaining logical numerical results. However, the complexity of the tube bundles, due to geometry and arrangement, makes it complicated. Employment of porous media is suggested to simplify numerical modeling. This study presents the use of porous media to simulate the tube bundles within a general-purpose computational fluid dynamics code. Solved governing equations are generalized phase continuity, momentum, and energy equations. Boundary conditions, as one of the main challenges in this numerical analysis, are optimized. The model has been verified and tuned by simple two-dimensional geometry. It is shown that the obtained vapor volume fraction near the cold and hot collectors predict the experimental results more accurately than in previous studies.

Analytical capillary isotachophoresis after 50 years of development: Recent progress 2014-2016.

This review brings a survey of papers on analytical ITP published since 2014 until the first quarter of 2016. The 50th anniversary of ITP as a modern analytical method offers the opportunity to present a brief view on its beginnings and to discuss the present state of the art from the viewpoint of the history of its development. Reviewed papers from the field of theory and principles confirm the continuing importance of computer simulations in the discovery of new and unexpected phenomena. The strongly developing field of instrumentation and techniques shows novel channel methodologies including use of porous media and new on-chip assays, where ITP is often included in a preseparative or even preparative function. A number of new analytical applications are reported, with ITP appearing almost exclusively in combination with other principles and methods.

LID시설에 적용된 식물의 염분 저항성 및 효과 평가

LID 시설에는 물순환 회복과 오염물질 저감을 위해 다양한 종류의 식물이 적용되고 있다. 그러나 겨울철 제설제 살포와 식물의 성장둔화로 인한 급격한 토양 함수량 변화는 식물의 고사 등 문제를 야기시킨다. 따라서 본 연구는 LID 시설에 적용 가능한 8가지 주요 식물을 선정하여 염분에 대한 저항성과 식물의 성장능력, 오염물질 저감능력 및 물순환 회복 등을 평가하기 위하여 수행되었다. 실험에 적용된 식물은 목본류인 조팝나무(S.P), 연산홍(R.I), 메타세콰이어(M.G)와 초본류인 창포(A.C), 하늘매발톱(A.F), 메리골드(T.L), 패랭이(D.C)와 애기별꽃(P.B)이 선정되었다. 식물의 성장은 조팝나무(S.P), 연산홍(R.I), 메타세콰이어(M.G)와 같은 목본류가 초본류에 비하여 성장률이 높은 것으로 나타났다. 염분에 의한 내성은 목본류에서는 메타세콰이어(M.G)>조팝나무(S.P)>연산홍(R.I) 순으로 나타났으며, 초본류에서는 메리골드(T.L)=패랭이(D.C)>창포(A.C)>애기별꽃(P.B)>하늘매발톱(A.F) 순으로 조사되었다. 대부분의 식물에서 염분에 의한 영향과는 상관없이 TN과 TP 저감효율이 60% 이상으로 높게 나타났으며, 메타세콰이어(M.G)가 높은 성장에 기인한 활발한 광합성과 호흡의 영향으로 높은 오염물질 제거능력과 물순환 능력을 보였다. In LID facilities treating stormwater runoff, various kinds of plants are applied for water circulation recovery and pollutant reduction. However, rapid changes of soil moisture due to the use of porous media and spread of deicing material during winter season cause slow plant growth that detrimentally leads to many problems including death of plants. Therefore, this study was performed to evaluate the salt resistance of plants, its effects on pollutants removal, and water circulation recovery. Eight different kinds of plants applicable to an LID facility were selected for the experiment, which were Bridal wreath (Spiraea japonica, S.J), Azalea (Rhododendron indicum, R.I), Dawn Redwood (Metasequoia glyptostroboides, M.G), Sweet flag (Acorus calamus A.C), Dwarf fan-shape columbine(Aquilegia flabellata, A.F), Pink (Dianthus chinensis, D.C), Pratia pedunculata (Pratia pedunculata, P.B) and Marigold (Tagetes patula, T.P). Woody plants such as S.P, R.I, and M.G appear to have less salt resistance compared to the other herbaceous plants. Specifically, M.G achieved the highest salt resistance among the other woody plants being followed by S.P, and R.I, respectively. For herbaceous plants, T.L and D.C have the higher salt resistances than that of A.C, P.B, and A.F, respectively. Regardless of the influence of salt to most of the plants, TN and TP were reduced more than 60% and the study suggests the M.G showed high pollutant removal efficiency and provided better water circulation by means of active photosynthesis and respiration due to higher growth.

Analyzing the process of gas production for natural gas hydrate using depressurization

Natural gas hydrate is a vast energy resource with global distribution in permafrost regions and in the oceans; its sheer volume demands that it be evaluated as a potential energy source. Understanding the mechanisms of natural gas extraction from hydrate-bearing sediments is critical for the utilization of hydrate accumulations. In this work, methane hydrate dissociation was performed in three kinds of porous media at production pressures of 2.2MPa, 2.6MPa, and 3.0MPa. Results show that the methane gas production process can be divided into three main stages: free gas liberation, hydrate dissociation sustained by the sensible heat of the reservoir, and hydrate dissociation driven by ambient heat transfer. In the process of gas production, hydrate dissociation occurs simultaneously throughout the hydrate zone along the phase equilibrium curve, and then spreads radially from the outside as a result of ambient heat transfer. Hydrate reformation and ice generation always occur in the reservoir interior due to insufficient heat transfer. The use of porous media with increased thermal conductivity accelerates the gas production rate; however, it has little influence on the final percentage of gas production. Furthermore, the Stefan (Ste) number and dissociation rate constant were employed to evaluate the impact of the sensible heat of the reservoir and ambient heat transfer. Results indicate that the sensible heat of the reservoir and ambient heat transfer play a dominant role in hydrate dissociation, and that both are dependent on production pressures.

Viscous dissipative forced convection in thermal non-equilibrium nanofluid-saturated porous media embedded in microchannels

Under local thermal non-equilibrium and isoflux boundary conditions, the two-energy-equation model is employed to investigate the effect of viscous dissipation on the thermal characteristics of nanofluid flow through a porous medium embedded in a microchannel. Analytical closed-form solutions of the two-dimensional temperature distributions are obtained for the models with and without the viscous dissipation terms in the energy equation. The analysis emphasizes on the disparities induced by the viscous dissipation between the two models. The use of porous medium is capable to enhance the thermal performance up to 53%. When the viscous dissipation effect is neglected, the thermal performance of nanofluid is overrated as much as 60%, sufficiently serious to trigger an attention in the performance analysis. The heat transfer coefficient of nanofluid is found to be enhanced in the low-Reynolds-number flow regime but it declines in the high-Reynolds-number flow regime. By reducing the size of nanoparticle, the thermal performance can be enhanced as much as 70%. Furthermore, the thermal performance can be further augmented by increasing the channel aspect ratio as well as by increasing the thermal conductivity of the porous material. This study serves as a useful analytical tool for the design and performance characterization of an integrated system incorporating the use of nanofluid and porous medium into a microchannel.

Pathlength determination for gas in scattering media absorption spectroscopy.

Gas in scattering media absorption spectroscopy (GASMAS) has been extensively studied and applied during recent years in, e.g., food packaging, human sinus monitoring, gas diffusion studies, and pharmaceutical tablet characterization. The focus has been on the evaluation of the gas absorption pathlength in porous media, which a priori is unknown due to heavy light scattering. In this paper, three different approaches are summarized. One possibility is to simultaneously monitor another gas with known concentration (e.g., water vapor), the pathlength of which can then be obtained and used for the target gas (e.g., oxygen) to retrieve its concentration. The second approach is to measure the mean optical pathlength or physical pathlength with other methods, including time-of-flight spectroscopy, frequency-modulated light scattering interferometry and the frequency domain photon migration method. By utilizing these methods, an average concentration can be obtained and the porosities of the material are studied. The last method retrieves the gas concentration without knowing its pathlength by analyzing the gas absorption line shape, which depends upon the concentration of buffer gases due to intermolecular collisions. The pathlength enhancement effect due to multiple scattering enables also the use of porous media as multipass gas cells for trace gas monitoring. All these efforts open up a multitude of different applications for the GASMAS technique.

The Role of Porous Media in Homogenization of High Pressure Diesel Fuel Spray Combustion

Interest is growing in the benefits of homogeneous charge compression ignition engines. In this paper, we investigate a novel approach to the development of a homogenous charge-like environment through the use of porous media. The primary purpose of the media is to enhance the spread as well as the evaporation process of the high pressure fuel spray to achieve charge homogenization. In this paper, we show through high speed visualizations of both cold and hot spray events, how porous media interactions can give rise to greater fuel air mixing and what role system pressure and temperature plays in further enhancing this process.

Experimental study of the low-pressure-vaporization of water in different porous media

The present study aims to evaluate the benefits of using porous media (PM) to enhance the rate of the low-pressure-vaporization (LPV) of water. An experimental characterization of the process of low-pressure-vaporization (LPV) of water is presented considering four different types of porous media and different initial conditions. This characterization involves the measurement of the time evolution of the porous media temperature and of the total and the vapor pressure inside the vaporization chamber, as well as the indirect determination of the saturation pressure, the mass of water vaporized, its specific rate of vaporization and of the energy removed by this phenomenon. A direct comparison between the evolution of the LPV of water in porous media and the LPV of free water was also made for two selected situations. The results show that the evolution of the LPV parameters, namely the temperature decrease and the rate of energy removal, are strongly dependent on the volume of the water initially contained in the porous medium which in turn, depends essentially of the medium microstructure. The significant differences found between the evolution of the LPV parameters in free water and in porous media are related to different boiling onset mechanisms, which is strongly dependent on the surface tension of the liquid water in the whole LPV process in PM. The practical result of these effects is an increased vaporization rate and an enhanced surface heat transfer capability that justify the use of porous media in a wide variety of applications.

Enhancement of methane purification by the use of porous media in hydrate formation process

Methane separation and purification was studied utilizing hydrate formation from a ternary CH4/C2H6/C3H8 gas mixture. The effect of the presence of porous media and the composition of the feed stream was investigated with respect to the enhancement of methane split fractionation and purification. Nanostructure silica-based porous material (SIPM) and a chemically modified (CHMPM1 and CHMPM2) version of this material were used at a weight ratio of 5% with three different gas compositions of the feed stream. The composition of the gas phase in equilibrium with the hydrate was determined by gas chromatography to distinguish how the components split into the two phases of gas and hydrate. The results showed that the CHMPM1 increases the gas storage capacity in the hydrate phase. Providing selective hydrate formation results in the highest methane purification in the presence of SIPM compared with that obtained using the chemically modified material and pure water. The initial feed composition affects both the final gas composition and the purification factor. The continuous stepwise hydrate formation showed good efficiency in selective gas separation when the gas in equilibrium with the hydrate phase was used as a feed for the next step. An increase in methane purification was observed when the amount of methane in the feed gas was lowered. The obtained results can provide the basis for methane separation from natural gas.

Fundamental Experiment and Numerical Analysis of a Modular Microcombustor with Silicon Carbide Porous Medium

The use of porous media in combustion processes has been widely researched and investigated. In this paper, the effect of employing porous media on microcombustion was studied using numerical simulation. Simulated results demonstrated good agreement with the experimental results, and thus validated the model. Analysis has been carried out with dimensional analysis and basic theorem which incorporates the Biot number in an attempt to fundamentally understand the effects brought about by equivalence ratio, thermal conductivity of the solid matrix and mass flow rate on microthermophotovoltaic (TPV) performance. One of the key results has demonstrated that the higher the equivalence ratio of the fuel/air mixture, the higher will be the mean wall temperature. A peak-shift phenomenon has been observed, where the position of maximum flame temperature shifts downstream away from the inlet at lower equivalence ratio. Results from the Biot number analysis has indicated that the higher the thermal conductivity of the wall is, the more uniform the wall temperature distribution will be. A lower mean wall temperature is obtained when the thermal conductivity of the solid matrix is installed at 50 W/mK, whereas higher mean wall temperatures can be achieved for either small (5 W/mK) or very large (500 W/mK) thermal conductivity. It is clearly evidenced that the performance of microcombustors can be markedly enhanced by incorporating a thermally effective porous medium. The theoretical understanding gained from the present research will facilitate the design of more energy efficient, stable and better controllable portable TPV on-field power systems.