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Flat plate solar collectors are extensively used in buildings, however due to excessive heat losses, these collectors are not efficient. Metal foams can enhance the thermal efficiency in expense of higher pumping power. A numerical simulation is carried out to investigate the influence of geometrical characteristics of porous medium on the pressure drop and heat transfer. An innovative design with gradually increasing or decreasing height is proposed. Porous block consists of three smaller blocks, two rectangular blocks at the inlet and outlet connected with a trapezoidal block. Non-dimensional height and length of the rectangular blocks vary between 0.2–0.6 and 0.1–0.9 respectively, and the optimum geometry of the porous block is proposed. Central composite design is conducted to find an optimum geometrical design and 25 design points have been investigated. The main target of this optimization is the simultaneous increment of Nusselt and decrement of pressure drop. Results demonstrate that porous block with non-dimensional inlet and outlet height of 0.9 and 0.5 and inlet and outlet length of 0.4 and 0.4 respectively, result in the highest Nu (= 15.2). Comparing the optimal results with those of a conventional rectangular porous block with constant height of 0.9 represents that in the optimum design Nu is only 7.23% less than that of the conventional design, while, pressure drop is improved up to 38.46% in the proposed geometrical design. Additionally, response surface methodology has been carried out and results have been reported in response surface plots. [ABSTRACT FROM AUTHOR]

Hydrothermal performance through multiple shapes of microchannels (MCHS) using nanofluids is summarized as the previous studies in the present work. The enhancement of heat transfer dissipation in electronic equipment becomes more necessary where high heat can damage it and cause more problems, so the Microchannel heat sinks can be a solution fore these problems. The heat transfer enhancement through Microchannels can be acheived by a passive technique which includes using corrugated channels such as wavy, zigzag, and converge-diverge MCHS. Also, flow disruptions such as using MCHS with cavities, ribs, grooves, dimples, and offset strip pin fins. In otherside the fluid additives included using nanofluid with different MCHS shapes, and Secondary flow as an MCHS with oblique fins is another method fore passive techniques. Wavy microchannels with secondary channels have higher hydrothermal performance compared to other types. Zigzag MCHS could provide good heat transfer enhancement but with high pressure drops. Regarding flow disruptions, the hydrothermal performance of MCHS with ribs is better than pin fin. The results showed that using a hybrid nanofluid gives more enhancement heat transfer as well as higher pressure drops. Concerning single-phase fluid, the review results showed that using metal oxide nanofluid has higher thermal conductivity compared to carbon-based and dielectric nanofluids; therefore, the single phase of nanofluids can be arranged descending from the best to worst, according to its use as the cooling liquid in microchannels and their efficiency in heat transfer enhancement, metals (Ag, Cu), metal oxides (TiO2–H2O, CuO–H2O, ZnO–H2O, and Al2O3–H2O), and dielectric nanofluid (SiO2–H2O). The specific application requirements and design considerations will guide the selection of the appropriate microchannel type for optimal heat transfer performance, so MCHS with mixing flow, higher thermal conductivity nanofluids, and low pressure drop are the most important factors that achieve hydrothermal efficiency. [ABSTRACT FROM AUTHOR]

Porous structures, owning a high specific surface area, are widely employed in the industry. Microporous metal foams have high thermal performance, and their combination with nanoparticles is a genuine solution to increase heat transfer. This numerical study aims to inspect laminar flow characteristics and heat transfer of water-based nanofluids through a horizontal circular tube filled with metal foam under constant heat flux. Four nanoparticles, including NiO, Ag, SiO2 and TiO2, have been studied, and the effect of the volume fraction, Reynolds number, porosity and pores per inch on the heat transfer coefficient and pressure drop has been investigated. The highest Nusselt numbers, at 0.8% porosity, 1% concentration of nanofluid and a Reynolds number of 1000, are 16.27, 16.03, 16.47 and 16.39 for NiO, Ag, SiO22 and TiO2, respectively. The results show that, in all cases, the highest Nusselt number corresponds to the SiO2, TiO, NiO and Ag nanofluids, respectively. The pore per inch has the greatest effect on the pressure drop, and its change from 5 to 60 increases the pressure drop by about 125 times. [ABSTRACT FROM AUTHOR]

This study aims to comprehensively investigate the thermal properties of steel–steel composite metal foams (S–S CMFs) compared to traditional bulk steel across a wide temperature range. To achieve this, a combination of computational modeling and laser flash (LF) experimental methods was employed to characterize the thermal behavior of S–S CMF. Initially, the thermal conductivities of S–S CMF were analyzed using computational fluid dynamics software ANSYS Fluent within the temperature range of 300–600 °C. These computational results were then compared to experimental data obtained from the high-temperature guarded-comparative longitudinal heat flow (GCH) technique used in a previous study, ensuring their accuracy. The comparison indicated an average deviation of only 6% across the investigated temperature range. Subsequently, the computational model was extended to predict the thermal conductivity of S–S CMF up to 1000 °C. Thermal conductivity measurements were taken using the LF experimental technique to validate these predictions at elevated temperatures, covering the temperature range from room temperature to 1000 °C. The experimental findings revealed that the thermal conductivity of S–S CMF was six times lower than that of bulk 316L stainless steel, while its thermal diffusivity was half that of bulk steel. Finally, an uncertainty analysis was performed to assess the reliability and accuracy of both the computational model and the LF experimental data. The results showed uncertainties of 3.6% and 5.5% at a 95% confidence level for the computational and LF approaches. Notably, these values were lower than the reported uncertainty in thermal conductivity obtained through the GCH technique in the earlier study (7–7.5%). Additionally, the comparison between the computational and experimental results from the LF technique demonstrated a mere 2% deviation throughout the investigated temperature range, highlighting the superior accuracy of the LF technique for evaluating thermal conductivity in porous materials. Given the outstanding thermal insulation properties, low mass nature, and high energy absorption capacity of S–S CMFs, one potential application for these materials could be in tank cars designed to transport hazardous materials. [ABSTRACT FROM AUTHOR]

In this study, an experimental forced convection through three metallic foam samples embedded in a plate heat exchanger is presented. The metallic foam samples are made from Copper, NiFeAlCr and Inconel with different effective thermal conductivity and closed morphological parameters. The mass velocity ranging was from 38 to 77 kg m-2 s-1. The heat transfer is represented by the local and mean heat transfer and also in terms of the Nusselt number. A new correlation was developed as a function of Reynolds and Prandtl numbers and the effective thermal conductivity ratio, which was neglected by the authors in the previous studies. This one gives a good agreement compared to the experimental results in the cases of copper and Inconnel samples, but it overestimates a bit the Nusselt number in the case of the NiFeAlCr sample. [ABSTRACT FROM AUTHOR]

The present study analyzed the behavior of a hybrid nanofluid with the aim of improving its heat transfer in tubes filled with a porous medium, which is a metal foam in this case. To this end, the impact of changes in influential factors, namely the Reynolds number, nanofluid concentration, porosity, number of pores per inch and Prandtl number on the heat transfer performance of an Al2O3–Cu/water hybrid nanofluid in tubes containing a porous medium, was investigated via numerical simulation. According to the results, increases in Reynolds number (in the laminar flow range), nanofluid concentration, pores per inch, and Prandtl number improved the Nusselt number and, hence, the thermal performance of the nanofluid. In contrast, an increase in porosity in the studied range reduced Nusselt number, resulting in a drop in the thermal efficiency of the nanofluid. Subsequently, the thermal behavior of the Al2O3–Cu/water hybrid nanofluid was studied under the presence and absence of the porous medium. The results indicated the positive effect of the porous medium on the Nusselt number and, as a result, the thermal efficiency of the nanofluid. Ultimately, the data obtained from the numerical simulation were used to obtain a general Nusselt correlation for the Al2O3–Cu/water hybrid nanofluid under constant- and variable-porosity media. The accuracy of the Nusselt correlation produced for examining the thermal performance of the hybrid nanofluid was 98% for the constant-porosity medium and 96% for the variable-porosity medium. [ABSTRACT FROM AUTHOR]

Thermal resistance of ice slows down the charging/discharging process of ice storage systems which results in long operating cycles and thus high energy consumption. To overcome this drawback, various heat transfer enhancement methods have been investigated in the literature. In this paper, a systematic review of the studies dealing with heat transfer enhancement methods is presented. The enhancement methods covered in this review paper include adding fins, embedding metal foam, dispersing nano-additives as well as hybrid methods combining at least two of the mentioned techniques. The literature review shows the significant potential of each enhancement method in reducing the charging/discharging time. Hybrid enhancement methods showed higher impact for reducing the time of operating cycles. Fins combined with metal foam are shown to achieve the highest enhancement with heat transfer rate increase of 200.9% but a trade-off is often required to keep the storage capacity. On the other hand, the review shed light on limitations of the literature, research gaps, and future challenges. The future of heat transfer enhancement methods is headed toward optimization approaches that can play a significant role in improving the performance of ice storage units. [ABSTRACT FROM AUTHOR]

The purpose of this study is a presentation of the thermal management of a flat plate solar collector via employing entropy generation analysis. The collector channel is completely saturated by porous metal foam locating in thermal non-equilibrium conditions. Al2O3–Cu/water hybrid nanofluid has been chosen in the role of working fluid, and considered flow has been assumed fully developed, hydrodynamically and thermally. The model of Darcy–Brinkman has been utilized to describe the hybrid nanofluid flow through the porous metal foam. Existing a magnetic field in the uniform state, its force affects the momentum equation. In addition, to characterize the temperature field of either phases of solid and fluid of the high porosity medium, two-equation model is utilized. Finally, the effect of key factors including porous media, volume fraction of hybrid nanofluid, and magnetic field on the total entropy generation and its components has been investigated. These results demonstrate that for weak magnetic field, when the base fluid's Reynolds number is less than 613, adding more nanoparticle to the base fluid would decrease the dimensionless average total irreversibility and a reverse trend is observed for the base fluid's Reynolds number. But, when the magnetic field is strong, for the Reynolds lower than 369.6, the dimensionless average total irreversibility is a decreasing function of nanofluid volume fraction and for Reynolds higher than 369.5, the trend would be reverse. In addition, due to the high-temperature gradient on the adsorption plate, a maximum local heat transfer irreversibility occurs on the adsorption plate. Also, due to the high velocity gradient on the solid walls of the collector channel, the maximum local fluid's friction irreversibility value is placed on the solid walls. [ABSTRACT FROM AUTHOR]

As the energy demand is increasing and conventional energy sources are declining, renewable energy sources are becoming increasingly popular. It is very important to store this energy efficiently. The use of phase change materials (PCMs) as latent heat thermal energy storage (LHTES) technology has utmost importance to researchers due to its high storage density and stable thermal characteristics. During charging and discharging of PCM, correspondingly occurring phase change processes (i.e. melting and solidification/ freezing) have been the crux of discussions in most of the subject-related articles in the recent literature. The objectives of those articles are to analyse and understand the phase change properties of PCM in its natural form, with nano-additives, and with or without metal foams. This manuscript provides a detailed review of energy storage, heat transfer, and melting process characteristics of coconut oil, which is an organic phase change material in its nature. Melting features like the progression of solid–liquid interface, time to complete the melting process, rate of melting, and augmentation in the rate of heat transfer owing to a colloidal suspension of nano-material inside PCM are reviewed and presented. [ABSTRACT FROM AUTHOR]

In this paper, a mathematical model for heat transfer in a heat sink covered by an open-cell metal foam under impinging jet flow is presented. Hydrogen and air were considered as the cooling fluids. The Darcy–Brinkman–Forchheimer relationship for the momentum equation was employed, while the two-equation energy model under the local thermal non-equilibrium (LTNE) condition for the energy equation was used. The mathematical model of similarity solution was first validated with analytical and experimental data from literature, and numerical data from Ansys-Fluent®. Then, the differences between numerical predictions under the local thermal equilibrium (LTE) and LTNE on flow and temperature distributions were presented and analyzed. It was shown that when the effective thermal conductivity of solid is very low, the difference of temperature of solid and gas cannot be neglected and LTNE should be considered. In other words, when effective thermal conductivity ratio, β, declines, the deviation between the LTNE and LTE models increases considerably. Finally, the effects of critical dimensionless parameters on the flow and heat transfer characteristics were investigated. The results indicate that cooling performance of the metal foam can be improved by increasing the Reynolds and Darcy numbers while decreasing the aspect ratio of the heat sink. Besides, the properties of metal foam and gas were studied. Hydrogen, as a cooling gas, has better thermal performance than air. [ABSTRACT FROM AUTHOR]

In this paper, nanofluid forced convective heat transfer through an open-cell metal foam heatsink under a uniform heat flux, numerically has been investigated. A uniform magnetic field has been applied to the nanofluid flow. For the momentum equation, Darcy–Brinkman model and, for the energy equation, two-equation model under the condition of fully developed from the thermal and hydrodynamical standpoints have been used. In recent study, by utilizing a numerical method, an attempt was made to avoid a complete and complex CFD approach. To validate the results, the dimensionless parameters such as non-dimensional velocity and temperature, pressure gradient and Nusselt number have been compared with previous researches and a good agreement appeared. Eventually, the effects of different dimensionless parameters such as porosity, Hartman number, nanofluid volume fraction, Reynolds number, thermal conductivity ratio and pore density on the hydrodynamical and thermal characteristics of heatsink have been investigated. The outcomes show that the rise of pore density and Hartman number and the decline of the porosity will enhance the thermal performance; however, it also will reinforce the resistance to the flow through the porous media. Focusing on results illustrates that Nusselt number variation for increasing porosity from 0.85 to 0.95 at the minimum and maximum of the pore density are Δ Nu ε ω = 10 = - 331.7 and Δ Nu ε ω = 60 = - 367.8 , and these values for friction factor are equal to Δ f ε ω = 10 = - 22.3 and Δ f ε ω = 60 = - 793 , respectively. On the other hand, increasing Hartman number from 0 to 100 would change the Nusselt number and friction factor as Δ Nu Ha ω = 10 = 9.4 , Δ Nu Ha ω = 60 = 0.2 , Δ f Ha ω = 10 = 213 , and Δ f Ha ω = 60 = 211 , respectively. The amount of Hartman and Reynolds numbers effects on the heat transfer rate depends on the pore density. In other words, when the pore density becomes saturated, the effects of these parameters decrease. In addition, the use of nanofluid will improve the heatsink thermal performance. [ABSTRACT FROM AUTHOR]

Numerical simulations are performed to analyze the thermal characteristics of a latent heat thermal energy storage system with phase change material embedded in highly conductive porous media. A network of finned heat pipes is also employed to enhance the heat transfer within the system. ANSYS-FLUENT 19.0 is used to create a transient multiphase computational model to simulate the thermal behavior of the storage unit. Copper foam is the porous medium used to enhance the heat transfer and is impregnated with the phase change material, potassium nitrate (KNO3). The effects of the porosity of the metal foam and the quantity of heat pipes on the thermal characteristics of storage unit have been investigated. The results indicated that increasing the quantity of the embedded heat pipes leads to drastic acceleration of both charging and discharging process. Impregnating the copper foam with potassium nitrate phase change material significantly affects the total charging and discharging times of the storage unit. It was shown that the porosity of the metal foam plays a key role in the thermal behavior of the system during the charging and discharging processes. [ABSTRACT FROM AUTHOR]

Safety issues of Li-ion batteries imposed by unfavorable thermal behavior accentuate the need for efficient thermal management systems to prevent the runaway conditions. To that end, a hybrid thermal management system is designed and further investigated numerically and experimentally in the present study. The passive cooling system is fabricated by saturating copper foam with paraffin as the phase change material (PCM) and integrated with an active cooling system with alumina nanofluid as the coolant fluid. Results for various Reynolds numbers and different heating powers indicate that the hybrid nanofluid cooling system can successfully fulfill safe operation of the battery during stressful operating conditions. The maximum time in which all PCM field is changed to the liquid phase is defined as the onset of the stressful conditions. Therefore, the start time of stressful conditions at 41 W and Re 420 is increased from 3700 s with nanofluid composed of 1% volume fraction nanoparticles (VF-1%) to 4600 s with nanofluid VF-2% during high current discharge rates. Nanofluid cooling extends the operating time of the battery in comparison with the water-based cooling system with 200-s (nanofluid with volume fraction of 1%) and 900-s (nanofluid with volume fraction of 2%) increases in operating time at Reynolds of 420. Using nanofluid, instead of water, postpones the onset of paraffin phase transition effectively and prolongs its melting time which consequently leads to a decrease in the rate of temperature rise. [ABSTRACT FROM AUTHOR]

In this study, thermal performance of an impingement jet with the presence of porous block is numerically investigated. The study is comprised of two main parts. At first, a parametric study is conducted on the steady impingement jet with porous block. Later, the effect of porous block is assessed on the pulsative impingement jet. The effect of different pulsation frequencies and amplitudes is analyzed on the heat transfer between the jet and porous block. In order to model the thermal performance, the local thermal non-equilibrium model is applied to the system. An entropy generation study was also conducted in order to investigate the system's performance from second law of thermodynamics point of view. In addition to the mentioned studies, by utilizing the energy density flux vector, different regimes of heat transfer in various cases are demonstrated and some of the trends obtained in parametric study are justified. The results suggest that porous block can change the Nusselt number distribution on the target plate. A more flattened Nusselt number distribution is observed with the presence of porous blocks. While lower frequencies and amplitudes of pulsation do not affect the thermal performance of the jet, higher ones have a moderate effect on the heat transfer rate of the impinging jet. [ABSTRACT FROM AUTHOR]

Batteries, especially lithium-ion ones, are the main energy sources of electric vehicles. In order to remove the generated heat in these batteries, passive cooling systems such as those employing phase change materials (PCMs) can be used, without any energy consumption. The main drawback of conventional PCMs is their low thermal conductivity, which can be solved by adding conductive additives to pure PCM. In this study, nine passive battery thermal management systems (BTMSs) based on paraffin wax as pure PCM, and copper foam as conductive additive, but with nine different amounts (from 1 to 9 vol%), are numerically simulated to reveal the role of additive content. The results show that the addition of metal foam greatly influences the time evolution of PCM liquid fraction. It is turned out that the addition of 6 vol% copper foam can create the best cooling effect and preserves the cell in the desired temperature range. In fact, adding more than this value can significantly reduce the heat absorption capacity of BTMS and makes the BTMS unreliable. [ABSTRACT FROM AUTHOR]

This is a numerical study of heat transfer and flow in a counter-flow sinusoidal parallel-plate heat exchanger using metal foam in the channels' divergent sections. The cold water fluid with Reynolds number of 100 and hot oil fluid with Reynolds number of 2 enter the downer and upper channels of the heat exchanger, respectively. The sinusoidal heat exchanger is investigated with two-wave amplitudes (0.3 and 0.6 cm), two wavelengths (6 and 12 cm) inserting the porous media with three particle diameters (0.1, 0.05 and 0.01 mm) and three thicknesses (A/3, 2A/3, and A). Darcy–Brinkman–Forchheimer and local thermal non-equilibrium models are used. To evaluate the increased heat transfer versus the increased pumping power, a dimensionless number called performance evaluation criteria (PEC) has been defined in the current study. The obtained results showed that the heat transfer rate, effectiveness and overall heat transfer coefficient of the heat exchanger are increased up to 19.2%, and the PEC number is enhanced to 1.171 in the optimum case with wave amplitude, wavelength, metal foam particle diameter and thickness equal to 0.6 cm, 6 cm, 0.01 mm and 2A/3, respectively. Moreover, since the metal foam is embedded in the wake region of the heat exchanger or channels' divergent sections, its effect on pumping power is subtle, which is an advantage of using the porous medium at these regions. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this paper, TiO2–H2O nanofluids are used instead of traditional mediums such as water and oil as the heat transfer medium. For the purpose of research on the natural convection heat transfer characteristics of TiO2–H2O nanofluids in a cavity filled with metal foam, a natural convection experiment system filled with different pore density (PPI) copper foam was established. The experimental results showed that the filling of the metal foam greatly improves the heat transfer effect in the cavity. When the PPI of the metal foam copper is 5 and 25, the Nusselt numbers are similar and larger than that of PPI = 15. The heat transfer effect of water in a cavity with the PPI = 5, PPI = 15 and PPI = 25 metal foam can be enhanced by 58.8%, 31.4% and 63.3% compared with that without metal foam, respectively. The heat transfer effect increases with the concentration of nanofluids. TiO2–H2O nanofluids with 0.1%, 0.3% and 0.5% mass fraction can enhance heat exchange by 6.3%, 22.9% and 32.1% compared with water, respectively. In addition, as the heating power increases, the heat transfer is improved while the heat transfer enhancement efficiency deteriorates. [ABSTRACT FROM AUTHOR]

This paper presents an investigation of the boiling heat transfer of R141b in a mini-channel with a 2.42-mm inner diameter filled with metal foam. Investigations are performed at velocity of 0.01 m s−1 and temperature of 450 K. The coupled level set and volume-of-fluid method is applied to simulate flow boiling in metal foam. It considers that the bubble number and the average bubble area have influence on the heat transfer coefficient. The simulation model is verified by experimental data with an emphasis on the effect of boiling bubbles and turbulent kinetic energy on heat transfer. The simulation results show that even though the bubble motion range and vortices area is smaller, more vortices appear in the channel filled with foam metal, which increase the mixing frequency and improve the heat transfer performance. Meanwhile, the heat transfer coefficient is inversely proportional to the average bubble area but proportional to the bubble number. The relationship between turbulent kinetic energy and heat transfer coefficient is also compared. Results indicate that the differentiation of turbulent kinetic energy to time appears consistent with the heat transfer coefficient in the mini-channel filled with metal foam. [ABSTRACT FROM AUTHOR]

The following study aimed to determine the effect of nanofluid concentration and the inclusion of porously filled channels on the thermal performance of highly porous open-cell foam metals. The study considered variable heat flux, nanofluid concentration and considered porously filled channels and bulk porous media. The nanofluid used in the experimental and numerical work was γ-Al2O3 nanoparticles suspended in water. The foam metal used was composed of 6061-T6 aluminum with a porosity of 0.91 and a permeability of 3.36e − 8 m2. The nanofluid concentrations used for the study were 0.1%, 0.3%, and 0.6% by volume. The experimental and numerical work showed good agreement with a maximum relative error between numerical and experimental temperature of 4.8% and an average error of 3.0%. The thermal performance of the system was evaluated based on Nusselt number and an index of performance including pressure effects. The results indicate that the optimal conditions for system operation are 0.6% with porously filled channels when pumping power is not considered of importance. However, should the pumping power be considered as an essential operating parameter then the optimal system conditions are 0.3% with bulk porous media. [ABSTRACT FROM AUTHOR]

Present experimental investigation focuses on the performance analysis of metallic foam and phase change material (PCM)-based heat sink at variable heat loads. High porosity (97%) copper and nickel foams are used with PCM (RT-54HC) to enhance the surface area for the heat transfer. Experimental results reveal that metallic foam-based heat sink embedded with PCM can reduce the base temperature of the heat sink efficiently. Copper foam is recognized to be more promising when compared to nickel foam in lowering base temperature for all heat loads (8 W, 16 W and 24 W). It was found that copper foam embedded with 0.8 volume fraction of PCM reduced the base temperature by 26% as compared to that of nickel foam without PCM at 24 W. Furthermore, when the PCM fraction is increased, final temperature of the heat sink gets lessened at the end of charging process while discharging process remains almost intact. So, in this study, copper foam with 0.8 volume fraction is determined to be an optimized configuration. [ABSTRACT FROM AUTHOR]

The present study aims to enhance the hydrothermal performance of a porous sinusoidal double-layered heat sink using nanofluid. The optimum thickness of metal foam (nickel) for different Reynolds numbers ranging from 10 to 100 for the laminar regime and Darcy numbers ranging from 10−4 to 10−2 is obtained. At the optimum porous thicknesses, nanofluid (silver–water) with three volume fractions of nanoparticles equal to 2, 3, and 4% is employed to enhance the heat sink thermal performance. Darcy–Brinkman–Forchheimer model and the local thermal non-equilibrium model or two equations method are employed to model the momentum equation and energy equations in the porous region, respectively. It was found that in the cases of Darcy numbers 10−4, 10−3, and 10−2 the dimensionless optimum porous thicknesses are 0.8, 0.8, and 0.2, respectively. It was also obtained that the maximum PEC number is 2.12 and it corresponds to the case with Darcy number 10−2, Reynolds number 40, and volume fraction of nanoparticles 0.04. The validity of local thermal equilibrium (LTE) assumption was investigated, and it was found that increasing the Darcy number which results in an enhancement in porous particle diameter leads to some errors in results, under LTE condition. [ABSTRACT FROM AUTHOR]

Although many studies have addressed the urge of exploring the porous media partially embedded in a channel due to its wide engineering applications, the heat transfer and fluid flow of a channel consisting of multilayered metal foam are relatively untouched. To tackle this research gap, a numerical study is conducted to analyze a channel partially filled with a three-layered porous medium—occupying sixty percent of a heat sink—over the Reynolds numbers ranging from 50 to 150 and water base fluid. To this aim, two configuration models of porous media are evaluated here: metal foam with (A) similar particle diameters (2 mm) and different porosities (0.75, 0.85, 0.95) and (B) similar porosities (0.88) and different particle diameters (1, 2, 3 mm). Darcy–Brinkman–Forchheimer and local thermal non-equilibrium methods are used to solve the momentum and energy equations in the porous region, respectively. The validity assessment of the local thermal equilibrium method elucidates that its accuracy is questionable at higher porosities and particle diameters of the metal foam—highlighting the necessity of incorporating the LTNE method under the mentioned circumstances. Among the considered geometries, the optimal arrangements of metal foam at both models are selected according to the performance evaluation criteria value. [ABSTRACT FROM AUTHOR]

Two sets of aluminum foam cylinders, 5 and 15 mm thick, are being tested in two-row and three-row bundles for their thermo-hydraulic performance. The bundles are formed using fixed transversal and longitudinal pitch distances and subject to airflow between 0.5 and 5.0 at 0.5 m s−1 interval under cross-flow. The effects of foam layer thickness and the number of row under staggered configuration are investigated. Thermo-hydraulic results are benchmarking against those of a conventional finned tube bundle of similar dimensions with pre-determined number of fins and assembled using the same pitch distances. [ABSTRACT FROM AUTHOR]

flexible polyurethane (PU) foam prepared from a polyol and an isocyanate prepolymer was stabilized against thermooxidation with two types of compounds: 2,6-di- t-butyl-4-methyl-phenol (non-reactive) and, respectively, 3,5-di- t-butyl-4-hidroxy-benzyl alcohol (reactive). The TG were obtained at different heating rates: β = 5, 7, 10, and 12 °C min and the TG/DTG were processed with the following methods: Freidman, Flynn-Wall-Ozawa, Budrugeac-Segal, and, respectively, Non-Parametric Kinetics. By Freidman and Flynn-Wall-Ozawa methods it was observed a significant (more that 10%) variation of the activation energy, E, versus the conversion degree, this being an indication of a complex process. Therefore, the more sophisticated Budrugeac-Segal and NPK methods were used. The Budrugeac-Segal method presents a very good descriptive ability, so it is useful for simulations of the thermal behavior. The NPK method is the less speculative one and in the majority of cases the obtained values of the activation energy were in a rather good agreement with both Friedman and Flynn-Wall-Ozawa kinetic data. The value of the activation energy seems to be an appropriate parameter for the estimation of the thermal stability. In comparison with the unstabilized PU, the one stabilized with the reactive compound presented the best thermal stability [ABSTRACT FROM AUTHOR]