Pores Per Inch Research Articles

Performance of a foam copper-based chromium potassium alum salt pill in an adiabatic demagnetization refrigerator

Hydrated paramagnetic salt pills are important components in an adiabatic demagnetization refrigerator (ADR) for temperatures below 500 mK. To improve the heat transfer performance between salt crystals and external thermal links, thermal buses are commonly employed inside the salt pill. Common forms of thermal buses are either thin copper pillars made from electric discharge machining (EDM) or wire bundles, both of which generally involve considerable machining or labor. This paper introduces a novel design and fabrication of a simple foam copper-based paramagnetic salt pill. The foam copper has 30 pores per inch (PPI), a porosity of 98 %, 0.005 m2/g specific surface area, and an estimated pore diameter of 0.82 mm. The complete design, assembling process, and growth of the foam copper-based chromium potassium alum (CPA) salt pill (40 mm in length and 23 mm in diameter) are introduced. A single-stage ADR is built based on this salt pill to test its performance, while another salt pill with the wire thermal bus has also been tested for comparison. A typical cool-down from 4.3 K @ 4 T with a demagnetization rate of 0.0025 T/s led to a no-load temperature of 176.5 mK, slightly better than that using a wire thermal bus. In terms of cooling power per gram of salt, the cooling capacities at 600 mK of both salt pills have also been measured and both have shown similar performance. This preliminary study has shown the potential of the foam copper-based salt pill though more research is required to optimize its performance.

Investigation of thermal performance and entropy generation rate of evacuated tube collector solar air heater with inserted baffles and metal foam: A CFD approach

This study investigates the impact of metal foam embedding into evacuated tube collector solar air heaters with inserted baffle (IBMF-ETC-SAH) on the device thermal performance using a computational fluid dynamics (CFD) approach. A three-dimensional model is employed to analyze the system under steady-state conditions. The key finding of this study is that the utilization of metal foam leads to a substantial increase in thermal performance, with an average improvement of approximately 300 %. The investigation examines the influence of metal foam porosity and pores per inch (PPI) on the performance of the IBMF-ETC-SAH across Reynolds numbers ranging from 6000 to 18,000. The results indicate that increasing the PPI from 20 to 40 at a constant porosity of 0.93 has negligible effects on device performance. However, the pressure drop increases by 48 % for a PPI of 40 compared to a PPI of 20. Furthermore, reducing the porosity from 0.95 to 0.9 leads to a 7 % enhancement in thermal performance. The IBMF-ETC-SAH exhibits a significant decrease in the total global entropy generation rate (EGR) compared to the device without metal foam. The maximum value of total EGR for the IB-ETC-SAH case is 2.32 times higher than the corresponding values for the IBMF-ETC-SAH case.

Metal foam recuperators on micro gas turbines: Multi-objective optimisation of efficiency, power and weight

Small size and high efficiency of micro gas turbines require a higher surface-to-volume ratio of recuperators. Conventional recuperators can achieve a range of 250–3600 m2/m3. Advances in materials and manufacturing, such as metal foams, can increase significantly the exchange surface and improve compactness ranging approximately from 500 to over 10,000 m2/m3, due to their exceptional micro geometry. The main advantage is that the increase of surface area does not impact the cost of the heat exchanger as much as conventional recuperators due to their easy manufacturing. This work addresses the optimisation of the recuperator using multiple objectives satisfying efficiency, power output and weight criteria, offering a holistic approach that takes into account the entire system rather than individual components or channels. A model is developed to represent the performance of a compact heat exchanger in micro gas turbines. The recuperator is an annular heat exchanger with involute profile filled with porous media in a counterflow arrangement on the hot and cold sides. The model allows the evaluation of the effect of the recuperator geometry features on the electrical efficiency, power output and weight savings in a micro gas turbine. Existing models for the global heat transfer coefficient, effective thermal conductivity, surface area and pressure drop of porous media are selected and implemented. The design variables of multi-objective are the pore density, porosity and number of channels, whilst the objectives are the overall electrical efficiency, power output and recuperator weight. The problem is solved using the Non-Dominated Sorting Genetic Algorithm (NSGA-II) to determine an approximation of the Pareto front, whilst the accuracy of the approximation is assessed against the solution obtained by an exhaustive search. The comparison shows that NSGA-II outperforms an exhaustive search by at least 90 % in terms of computational efficiency. These results allow the quantification of the impact of metal foam technology on performance metrics of the recuperator as well as the entire system. This quantitative analysis provides valuable insights into the behaviour of metal foam recuperators in micro gas turbines. An optimal design with 30 % efficiency and 28 kW power output appears in pore densities of approximately 10 and 20 pores per inch (PPI) for the air and gas side respectively, and a porosity of 85 %, which leads to a state-of-the-art recuperator weight of 48 kg. The efficiency improvement over the industry standard is 15 %, with only a 2.5 % reduction in power output.

Investigation of heat transfer and pressure drop characteristics in metal-foam filled channels in a plate heat exchanger: A comparative experimental study

An experiment was conducted on a single-phase system using water as the working fluid in a Gasket Plate Heat Exchanger (GPHE). The copper metal foam was employed on the corrugated profile in this experiment. The experiment was calibrated using iterative multiple linear regression analysis to find the coefficient of heat transfer on the hot water side for the given heat exchanger with a 60° corrugation angle. A comparative study was carried out between channels that were plain and modified with metal foam. The analysis focused on various factors, including the heat transfer coefficient, frictional pressure drop characteristics, pumping power, and volume goodness factor. The experiments were performed within a Reynolds number range of 200 to 1000, with the hot and cold water temperatures set at 60 °C and 30 °C, respectively. The experiments used copper metal foam with 50 pores per inch (PPI). The foam had a porosity ranging from 0.6 to 0.9, with a pore size of 1 mm. The Nusselt number for the modified GPHE was 1.97 times higher than that of the plain GPHE. Additionally, the frictional pressure drop for the modified heat exchanger was 1.89 times higher than that of the plain heat exchangers. The rate of frictional pressure drop increases at higher Reynolds numbers was higher than the heat transfer coefficient increase for both the plain and modified GPHE. The modified plate heat exchanger shows superior thermal performance compared to a plain GPHE at any given friction power conditions. Additionally, using metal foam-filled channels in contrast to plain corrugated plate channels suggests that the modified GPHE can achieve a more compact design for the same heat-duty application.

Microstructure-based modeling to characterize low pore density open-cell foams and its experimental validation.

Microlattices with large pore sizes are involved in many multifunctional applications, so it is essential to understand their acoustic properties. However, for these low pore density microlattice foams, the classical homogenization or "equivalent fluid" methods fail abruptly. This paper proposes and discusses a microstructure-based direct fluid model (DFM) that would help to predict the acoustic performance of low pore density periodic open-cell foams with spherical pores. The DFM is simulated directly, including the microscale geometric features inherent in the unit cell. A comparative study is performed for designed three-dimensional (3D) body-centered-cubic (BCC) porous foams having pores per inch (PPI) ranging from 1 to 12 over the frequency range of 500-4100 Hz with equivalent fluid models and experiments. The study shows the extent of deviation in homogenization-based methods from the experiment for PPI < 5. On the other hand, the acoustic performance parameters predicted with the DFM agree well with experiments on 3D-printed samples fabricated by additive manufacturing of varying PPI starting from 1. This study shows that the DFM is a valid method to predict the acoustics of low PPI microlattices. Furthermore, the gradual transition from dissipative to the reactive regime with a decrease in PPI is also brought out.

Mechanical and energy absorption properties of multilayered ultra-light sandwich panels produced by 3D-printing and electroforming

This investigation aims to assess the mechanical and energy absorption properties of the light sandwich panel portions made of open-cell polymer and metal/polymer foam cores. These multi-layered sandwich panels were produced by additive manufacturing of polymeric resin and electrodeposition of three layers of metals, Ni/Ni−Cu/Ni, with 4,5, and 6 pores per inch (PPI). The yield strength, energy absorption density, complementary energy, and specific energy absorption (SEA)were measured during uniaxial compression deformation. The results indicate that compared with pure Ni and Cu sandwich panel portions with the same thickness, the abovementioned properties of the sandwich panels had a noteworthy improvement. Mechanical and energy absorption properties were improved by increasing the PPI and the presence of metallic layers. In a sandwich panel with 6 PPI, the yield strength (energy absorption density)wasimproved from 0.12 MPa (0.12 MJ/m3) for the polymeric sandwich panel to 1.83 MPa (0.67 MJ/m3)for the metallic sandwich panel. Investigations on normalized energies of these structures show a predictable behavior for these sandwich panels during plastic deformations. The results show that the multi metallic layers improved the mechanical behavior of these novel sandwich panels. Noticeable enhancement of the calculated properties of these advanced materials guarantees their unique application in variable industries.

Pore-scale numerical investigation on comprehensive heat transfer performance of homogeneous and graded metal foam heat sinks

In order to improve the heat dissipation efficiency of heat sinks, heat sinks filled with metal foam were proposed and numerically studied in this work. Different shapes, including the tetrakaidecahedron, triangular prism, and equivalent tetrahedron, were employed to develop geometries for the cells, ligaments, and nodes of the metal foam. Computational simulation was carried out to analyze the hydraulic and thermal performance of the homogeneous metal foam(HMF)-filled heat sinks and graded metal foam (GMF)-filled heat sinks. The study found that well-designed GMF-filled heat sinks can improve both hydraulic and thermal performance. A graded pores per inch (PPI) negative change along the X-axis direction can improve the comprehensive heat transfer performance (CHTP), and the positive change has a similar effect. Graded PPI negative change along the Y-axis direction can effectively improve the CHTP, while the positive change has no effect. Moreover, a greater thickness of the metal foam with a larger PPI leads to better performance. GMF-filled heat sinks can also effectively reduce the surface temperature of the bottom plane and enhance the convection performance.

Thermo-hydraulic Analysis of Fluid Flowing Through Circular Pipe with Wire Mesh Inserts having Varying Mesh Porosity

The experimental investigation was made to analysis the rate of heat transfer of fluid flowing through a heat exchanger with varying wire-mesh porosity inserts. The Nusselt number (Nu), friction factor (f), and overall heat transfer rate (Q) were evaluated using experiments. Three different wire mesh inserts of square, hexagonal and diamond porosity were examined. The SS 316 stainless wire mesh with a porosity of 9 pores per inch (PPI) were inserted normal to the flow field with a pitch distance of 5 cm for each shape of wire mesh. The experiments were conducted on test rig with air as a working fluid for turbulent flow regime having Reynolds number ranging from 6,000 to 16,000. Experiments were performed on computerized test rig with heated air flowed in one direction through inner pipe and counter flow cold water flowing through the outer concentric pipe. The circular inner pipe of 40 cm long having 4 cm inner diameter (Di), and 3 mm thick was used for experimentation. The experimental results showed that Nusselt number (Nu) increases with decrease in friction factor (f) with increase in Reynolds number (Re). Also, it is observed that the hexagonal porosity shape of wire mesh insert provides higher material contact and gain more energy absorption from hot air resulted in improvement in heat transfer coefficient as compared to diagonal and square porosity shapes of wire mesh inserts, under similar operating conditions. The friction factor and pressure drop for square porosity shape of wire mesh insert is higher as compared to hexagonal and diagonal porosity shapes of wire mesh inserts respectively. This is due to the fact that square porosity wire mesh provides more obstruction in the flow field compared with hexagonal and diagonal porosity shapes of wire mesh inserts. The hexagonal porosity shape of wire mesh insert provides better option for heat exchange applications.

Experimental study on enhancement condensation heat transfer in tube by foam metal in presence of non-condensable gas

Condensation heat transfer in tube is widely applied in industrial production, and the heat transfer process is often weakened by non-condensable gas (NCG) in actual production. Enhancing condensation heat transfer is beneficial to improve production efficiency, which has always been a hot topic in current research. Foam metal material with large specific surface area and good thermal conductivity is an ideal material to enhance heat transfer. In order to study enhancement heat transfer effect and optimize structure of foam metal, this paper investigated condensation heat transfer in tube strengthened by foam metal in presence of NCG experimentally. Section shape of foam metal is annular, and the pores per inch (PPI) of foam metals is 10, 15, 20 respectively. The effects of PPI value, steam/air mixture mass flow, and NCG mass fraction on heat transfer coefficient (HTC) and flow resistance are studied. The results reveal the following: (1) Compared with smooth tube, the foam metal enhances heat transfer significantly, and HTC increases by 1.5-2.3 times. (2) At same steam/air mixture mass flow, 10PPI foam metal tube has the highest HTC compared to others. (3) With increase of NCG mass fraction and PPI value, pressure drop increases and the HTC decreases. Based on experimental data, pressure drop and HTC correlations are developed. This paper provides an important technical basis for foam metal material application in enhancement heat transfer area.

Graphene nanoplatelets and copper foams for improving passive cooling performance of PCMs in Singapore's tropical climate

In Singapore's hot tropical climate, phase change materials (PCMs) hold significant promise for year-round passive cooling solutions in buildings. However, the narrow diurnal temperature range of 24–32 °C poses a great challenge for pure PCMs with poor thermal conductivity to undergo complete melting-freezing cycles. Herein, we tested two composite PCMs in a self-designed thermal box: (1) paraffin RT28HC/graphene nanoplatelets (GNP-PCMs) and (2) paraffin RT28HC/copper foam (CF-PCMs). The passive cooling performance of the composite PCMs was evaluated based on their charging power at 32 °C and discharging power at 24 °C. The focus is on convection heat transfer between the composite PCMs and ambient air, with considering various factors, including GNPs content (0.1–0.9 wt%), CF pore density (40 pores per inch (PPI) and 70 PPI), airflow rate (natural convection and forced convection), and orientation (horizontal and vertical). The results indicate that a minimum temperature range of 26.6–30.3 °C is necessary for complete melting-freezing cycles. The effect of GNPs content is more sensitive to orientation, whereas the effect of CF pore density is more affected by airflow rate. In all cases, the CF-PCMs exhibit superior temperature uniformity than the GNP-PCMs. Under forced convection, the charging power and discharging power of pure PCM reached a maximum of 110.8 and 163.5 W/m2, respectively. The addition of GNPs enhanced the charging power and discharging power of pure PCM by up to 14.2 % and 10.2 %, respectively. Moreover, the incorporation of CF boosted the charging power and discharging power of pure PCM by up to 75.1 % and 64.3 %, respectively.

Efficient Industrial Wastewater and Leachate Evaporation Utilizing Heat Localization in Porous Media

In this paper, an efficient industrial wastewater and leachate evaporation method is proposed and tested experimentally. The goal of this study is to investigate whether the addition of a carbon foam (CF) porous layer can lead to energy savings by evaporating more water mass per unit of energy input. The standard boiling evaporator layout was redesigned by placing the heating element in the upper region of the tank and CF underneath the heat source. The CF purposed to localize the energy in an area by the water's surface and minimize conduction heat losses to the rest of the water. A 90.2% reduction in energy lost to regions outside of the CF isolated control volume, specifically during the evaporator preheating process was observed with the addition of 100 Pores Per Inch (PPI) CF. In addition, a reduction in evaporative energy intensity was observed yielding results of 3.344 , 3.441 , and 3.644 for the 100 PPI, 45 PPI, and 10 PPI tests, respectively. This new evaporation design provides a more energy- and cost-efficient method for reducing the volume of various industrial wastewater and leachate concentrations onsite.

Improved flow boiling characteristics in minichannel with open-cell porous ribs

Porous metal has been proven to exhibit significant heat transfer enhancement in minichannel. Focusing on fully utilizing the advantages of porous metal in heat transfer and reducing pressure penalty, a porous ribs minichannel (PRM) heat sink employing open-cell porous copper as rib was designed and fabricated. PRM heat sink has 19 minichannels that are 1 mm in width and 2 mm in depth. Commercial open-cell porous copper with a porosity of 0.85 and 120 PPI (Pore per Inch, PPI) was selected. Flow boiling experiments were carried out with ethanol as the working fluid. The flow patterns of two heat sinks were recorded with a high speed photograph system and comparative analyzed. High-frequency periodic motion of vapor core boundary in width direction of porous ribs minichannel was recorded. This is considered a fluctuation of density wave along the channel width direction. Cooperating with capillary force, movement of vapor core boundary induces mass transfer between adjacent channels, compensating for uneven flow distribution between channels. The results show that PRM heat sink has better heat transfer performances and flow stability with a slight increment in pressure drop compared with solid ribs minichannel (SRM) heat sink. The porous ribs minichannel heat sink provides a new way to relieve flow insatiability for heat exchangers and thermal management systems.

Experimental and numerical investigations of an open-cell copper foam (OCCF)/phase change material (PCM) composite-based module for satellite avionics thermal management in a thermal vacuum chamber (TVC)

Small satellites' thermal control in the space environment is crucial. Phase change materials (PCM) are promising options for satellite thermal management in space thermal conditions. The current work provides an experimental and numerical investigation of a thermal control module (TCM) using an open-cell copper foam (OCCF)/PCM combination. The experimental tests were carried out in a thermal vacuum chamber (TVC), which simulated the vacuum space environment. The PCM thermal conductivity was boosted using OCCF and aluminium fins. The metallic parallel fins divided the heat sink into six cuboid cavities and were filled with PCM. Two samples with different pores per inch (PPI) of OCCF were adopted, one with 10 PPI and the other with 20 PPI. For the experimental work, the adopted PCM was SP 31. Two levels of heating loads were applied to the TCM: 10 W and 7 W. The numerical model was verified using the experimental work findings. The experimental work concluded that the PCM capsulation sealing is a dominant factor for successful capsule design under vacuum operation. The thermal conductivity enhancers (TCEs) remarkably improved the thermal management performance of the PCM. The case with PCM reported a reduction in the maximum temperature by about 43.67 % and 41.4 % at 7 W and 10 W, respectively, relative to the case without PCM. The PCM/fins combination could improve the PCM performance and mitigate the maximum temperature from 41.7 °C to 39.6 °C with a reduction percentage of 5 %. The OCCF reported better thermal performance than the metallic fins. The OCCF with 10 PPI decreased the PCM maximum temperature by 10.3 %. The OCCF with 20 PPI reported a reduction in the PCM maximum temperature by 13.8 % at 10 W heating power.

Thermal-hydraulic performance of a plate heat exchanger with grooved copper foam

This study proposes a plate heat exchanger (PHE) partially filled with metal foam having checkered pattern grooves. The study presents new experimental data obtained from PHE with grooved copper foam that elucidates the effect of mass flux, copper foam groove width, and pore density on the heat transfer coefficient (HTC) and pressure drop (ΔP). The testing is conducted with a water mass flux ranging from 120 to 320 kg/m2s, a groove width ranging from 2 to 6 mm, and a pore density of 30 pores per inch (PPI) and 50 PPI. The results demonstrate that HTC and ΔP increase as the copper foam groove width is reduced. Considering the impact of copper foam groove width on the filling rate, the HTC ratio increases significantly at a filling rate between 50 and 75%. Furthermore, an increase in pore density enhances HTC and ΔP. The plate heat exchanger inserted with copper foam (PHE_CF) provides the optimum thermal-hydraulic performance (TP). However, at a low Reynolds number, the results show that TP of PHE with grooved copper foam with a groove width of 2 mm is similar to PHE_CF. New correlations are also proposed to predict ΔP and HTC in the practical applications.

Effect of the 40-PPI copper foam layer height on the solar cooker performance

Abstract Two box-type solar cooker (BTSC) prototypes were tested to examine thermal performance under identical conditions. The first box solar cooker used an absorber plate fabricated from copper, and the second box solar cooker used 40 pores per inch (PPI) of copper foam sheets. Many experiments on solar cookers were carried out in September 2022 in Baghdad, Iraq, where the solar cookers were directed to the south and situated at latitude 33.3°N and longitude 44.4°E. In the experimental testing, copper metal foam 40 PPI is used as a heat absorber plate at various absorber plate heights (1, 3, 5, and 7 cm). The results showed that the solar cooker with a 40 PPI copper foam absorber experienced a stagnation temperature of roughly 17° higher compared to a BTSC with a standard absorber. A copper foam 40 PPI absorber plate can reduce cooking time in a BTSC by as much as 23% compared to a standard flat absorber plate. The percentage of increase in the solar cooker’s internal temperature with an increase in absorber plate height from 1 to 7 cm for 40 PPI copper foam absorber plate is approximately 16.1%. The acceptable range for the equation of cooking power indicates that the cooker can be relied upon for consistently cooking food and boiling water.

Outlining the impact of discrete filling of metal foams on thermodynamic performance

The desire of this paper is to present the numerical analysis of thermodynamic performance of high porosity metal foams with discrete filling inside the horizontal pipe. The heater is embedded on the pipe’s circumference and is assigned with known heat input. To enhance heat transfer, aluminum metal foam of 10 PPI (pores per inch) with porosity 0.95 is filled into the pipe. In filling, two kinds of arrangements are made. In the first arrangement, the metal foam is filled adjacent to the inner wall of the pipe (Model (1–3)), and in the second arrangement, the metal foam is located at the center of the pipe (Model (4–6)). So, six different models are inspected for different fluid velocities (0.7–7 m/s) under turbulent flow conditions. Darcy Extended Forchheimer (DEF) is combined with local thermal non-equilibrium (LTNE) models for estimating the flow features and heat transfer via metal foams and initially validated with experimental outcomes. The application of the second law of thermodynamics via metal foams is the novelty of current investigation. In the study, the thermal performance is assessed in terms of heat transfer enhancement ratio and heat transfer performance ratio, and the thermodynamic performance is evaluated based on exergy and irreversibility analysis. In the analysis, the parameters like mean exergy based Nusselt number (Nue), heat transfer and flow frictional irreversibility are considered for the evaluation. The overall thermal performance and exergy transfer found higher in Model (1–3) than the Model (4–6) respectively. The flow and heat transfer irreversibility found less in Model (1–3) than the Model (4–6) respectively. The superior thermodynamic performance is obtained from the metal foam filled cases than from the clear pipe. In that, Model-2 suits the best configuration for designing the thermal system.

Experimental investigation of the heat transport and pressure drop in open-cell polyurethane foams

Foam-like materials have a large specific surface area and complex structure that promotes flow turbulence, which makes them useful for heat transfer. In the literature, heat transfer in metal foams (MF) with high thermal conductivity is mainly considered. In the present paper, an experimental study of the hydraulic and heat transfer characteristics of a rectangular channel filled with polyurethane foam (PUF) inserts with a thermal conductivity of 0.2 W⋅m−1⋅K−1 in the air flow was carried out. The open-cell PUF samples had 20 and 80 pores per inch (PPI), 0.97 and 0.98 porosity, 269 µm and 60 µm fiber diameter, respectively. The Reynolds number, based on the fiber diameter ranged from 0.04 to 50. From the results of hydraulic tests, friction coefficients were determined based on the fiber diameter and permeability. The Forchheimer coefficient was 0.198 and 0.318 for 20 and 80 PPI samples, respectively. The permeability was 1.889 10−7 ⋅m2 and 7.535 10−9 ⋅m2 for 20 and 80 PPI samples, respectively. The Nusselt number for both tested PUF samples was correlated with the Reynolds number based on the fiber diameter in a power law with the Reynolds number exponent and constant equal to 0.61 and 0.037 respectively. The intensity of heat transfer in the PUF samples was 7–12 times lower than that in MF. However, a significant heat transfer enhancement is still possible compared to the empty channel up to 7 times. The heat transfer performance of PUF was higher compared to the empty channel, but the thermal performance factor was lower than one. Nevertheless, in practical situations where the mass or cost of the heat exchanger is preferable, PUF can be considered as a heat transfer intensifier.

Solidification/melting enhancement in ice thermal energy storage by synergistic effect of metal foam and carbon nanotube under magnetic field

In this work, water-based magnetic Multi-walled Carbon Nanotube Phase Change Material and Copper Metal Foam (MWCNT PCM-CMF) were combined to improve the performance in ice thermal energy storage. The effect of concentration of magnetic MWCNT, porosity and pore density of CMF and magnetic field intensity on the thermal cycle characteristics including supercooling degree, solidification/melting time, cold storage/release capacity and cold storage/release rate were studied. The results indicated that the optimal magnetic field intensity corresponding to the optimal thermal cycle characteristics decreases with the increased concentration of magnetic MWCNT. Moreover, the addition of magnetic MWCNT-CMF significantly accelerates the solidification process, which is dominated by heat conduction. Although the cold storage capacity of composites was ∼ 94% of pure water, the time required for cold storage was ∼ 52% of pure water as well as the cold storage rate was improved by ∼ 80%. The melting behavior is further improved by arranging gradient CMF. As a result, the combination of 0.04 wt% magnetic MWCNT under 75 mT magnetic field and CMF with 10/5 pore per inch (PPI) gradient pore density at 95% porosity has 86.8% reduction in supercooling degree, 39.8% advance in complete cycle time and the mean rate of energy storage/release is 1.52 times than pure water.

Heat Transfer and Performance Enhancement of Porous Split Elliptical Fins

To augment the heat transfer phenomenon, the infusion of various fin geometry over the heated plate is being investigated by various researchers. Solid fins of the porous medium can enhance the convective heat transfer, providing a higher surface area-to-volume ratio for heat transfer. In this work, the fluid flow pattern and thermodynamic analysis of porous-based split elliptical fins mounted staggered over a heated base plate is numerically studied with the Reynolds numbers in the range of 783 to 1839, which is dependent on the fin dimension. The variable parameters were dimensionless transverse offset ( TO ∗ = transverse offset / diameter ), which varied from 0 to 0.5; dimensionless longitudinal offset ( L O ∗ = longitudinal offset / diameter ), which varied from 0 to 0.25; porosity (ɸ), which varies from 0.8 to 0.92; pores per inch (PPI), which was 10; permeability ( P n ); and inertial parameter ( F ). To count the viscous and inertial effect inside the porous zone, the Forchheimer–Brinkman extended Darcy model was adopted. The associated parameters, the Nusselt number (Nu), frictional coefficient ( C f ), and performance evaluation criteria (PEC), are thoroughly analyzed over the TO ∗ and LO ∗ combination. The results of the investigation revealed that the highest value of Nu and PEC was obtained by TO ∗ = 0.5 and L O ∗ = 0 at ɸ = 0.92 , which were approximately 54% and 79% higher than the solid circular fin at Re = 1839 . Additionally, a response function based on Nu was obtained using the response surface method, and cuckoo optimization was assessed to identify the optimal Nu. The optimal Nu is established at TO ∗ = 0.4141 and L O ∗ = 0 ( ɸ = 0.92 and Re = 1839 ) and was validated with the present investigation with an accuracy of 1.20%.

Entropy Generation Analysis on a Metal Foam in an Automotive Exhaust Line with Thermoelectric Generator

Abstract In the present paper, an entropy generation analysis on a 2-D steady state problem in convective regime of an aluminum foam partially and totally filled channel with an external TEG element is solved in numerical way. The numerical analyses are accomplished with the assumption of the local thermal equilibrium (LTE) hypothesis in order to model the metal foam and heat transfer inside the channel. The working fluid is exhaust gas characterized by the same properties of the air in correspondence to the TEG upper surface temperature. The TEG is considered as a solid component characterized by an internal energy generation. The thermophysical properties are assumed temperature independent. Ansys-Fluent code is employed in order to resolve the governing equations for exhaust gas, metal foam and TEG. Different exhaust gas mass flow rates on the inlet section are assumed. Several thicknesses of aluminum foam values are employed. The porous media are characterized by a porosity from 0.90 to 0.978 and number of pores per inch (PPI) equal to 5, 10, 20, 40. Results are given in terms of global entropy generations related to the thermal and viscous effects. The total global entropy generation increases with increasing of exhaust gas flow rate for all pore density and porosity values. Bejan number decreases with the increment of mass flow rate and thickness. It increases when the porosity value increases whereas at high mass flow rate and for assigned porosity the values present small difference for different pore density values.