1,720,971 research outputs found
Thermal behaviors of latent thermal energy storage system with pcm and aluminum foam
No full textA numerical investigation on LHTESS with PCM is accomplished. The PCM used is paraffin wax. To enhance the heat transfer inside the system a highly conductive material like metal foam and ceramic nanoparticles are used. The latter method of enhancement leads to a new class of material called Nano-PCM. The system under investigation is a typical 70 L water tank filled up with pure PCM or Nano-PCM and a certain number of pipes are located where the Heat Transfer Fluid (HTF) flows. The surfaces of the pipes are assumed at a constant temperature above the melting temperature of the PCM to simulate the heat transfer from the HTF. The enthalpy-porosity theory is employed to simulate the phase change of the PCM while the metal foam is modelled as a porous media that obeys to the Darcy-Forchheimer law. The ceramics nanoparticles are modelled with the single-phase model. The simulations are accomplished for charging-discharging process at different porosities of the metal foam and different concentration of the nanoparticles. The results show that the presence of the metal foam improves the heat transfer in the system respect to the addition of the nanoparticles, reducing the melting time more than one order of magnitude
Experimental Investigation on Fluid Dynamic and Thermal Behavior in Confined Impinging Round Jets in Aluminum Foam
Full text linkIn this paper an experimental investigation is carried out on impinging jets in porous media with the wall heated from below with a uniform heat flux. The fluid is air. The experimental apparatus is made up of a fun systems, a test section, a tube, to reduce the section in a circular section. The tube is long 1.0 m and diameter of 0.012 m. The test section has a diameter of 0.10 m and it has the thickness of 10, 20 and 40 mm. In the test section the lower plate is in aluminum and is heated by an electrical resistances whereas the upper plate is in Plexiglas. The experiments are carried out employing aluminum foams with 5, 10 and 40 PPI and three thickness over the heated circular plate. Results are obtained in a Reynolds number range from 500 to 1500 and wall heat flux from 500 W/m2 to 1400 W/m2. Results are given in terms of wall temperature profiles, local and average Nusselt numbers, pressure drops, friction factor and Richardson number. Moreover, to evaluate the improvement due to the presence of the metal foam, it is necessary a quantitative methodology. In this work an energy performance ratio is employed to compare the performances of surface with and without foams in terms of heat transfer coefficients and pressure drops. Preliminarily experimental results has confirmed that the use of the porous medium improves the heat transfer promoting the heat dissipation of the surface with high efficacy but determines an increase in pressure drops
Thermal cooling behaviors of lithium-ion batteries by metal foam with phase change materials
No full textLithium ion (Li-ion) batteries are an integral part of electric vehicles and hybrid electric vehicles or smartphones because of their high energy and power density. These batteries suffer from a high temperature rise and generate excessive heat during operation. An improvement technique, passive thermal management (e.g. a phase change material), has become an attractive approach in recent years as it is highly efficient, compact and lightweight. Phase Change Materials (PCMs) store thermal heat in the form of sensible and principally latent heat. PCM changes state from solid to liquid or liquid to gas or vice versa at almost constant temperature during latent heat storage. Metal foams have also been proven to be a viable option in enhancing thermal conductivity of PCMs. High porosity, good thermophysical properties and mechanical strength are salient features of metal foams. In this paper, a simple rectangular electronics passive cooling device was implemented for Li-Ion Battery. A PCM material with metal foam was numerically investigated. Numerical simulations were carried out using the Ansys-Fluent code. Results in terms temperatures, melting time and max reached temperature were reported
Numerical investigation on viscous dissipation effect in forced convection in rectangular microchannels with nanofluids
No full textIn this paper a numerical investigation on laminar forced convection flow of a water-Al2O3 nanofluid in a rectangular microchannel, taking into account the viscous dissipation, is accomplished. A constant and uniform heat flux on the external surfaces has been applied and a single-phase model approach has been employed. The analysis has been performed in steady state regime for particle size in nanofluids equal to 38 nm. The CFD commercial code Ansys-Fluent has been employed in order to solve the 3-D numerical model. The geometrical configuration under consideration consists in a duct with a rectangular shaped crossing area. A steady laminar incompressible flow with viscous dissipation and different nanoparticle volume fractions has been considered. The base fluid is water and nanoparticles are made up of alumina (Al2O3). Thermo-physical properties of the nanofluid are considered constant with temperature. The length the edge and height of the duct are 0.030 m, 1.7 x10-7and 1.1 x10-7m, respectively. A constant and uniform heat flux q on the top wall is applied, the others are adiabatic and at the inlet section uniform temperature and velocity profiles are assumed. The results showed the increase of the convective heat transfer coefficients, in particular, for high concentration of nanoparticles and for increasing values of Reynolds number. However, the disadvantages are represented by the growth of the wall shear stress and the required pumping power, observed in particular, at high particle concentrations
Experimental Investigation on Fluid Dynamic and Thermal Behavior in Confined Impinging Round Jets in Aluminum Foam
No full textIn this paper an experimental investigation is carried out on impinging jets in porous media with the wall heated from below with a uniform heat flux. The fluid is air. The experimental apparatus is made up of a fun systems, a test section, a tube, to reduce the section in a circular section. The tube is long 1.0 m and diameter of 0.012 m. The test section has a diameter of 0.10 m and it has the thickness of 10, 20 and 40 mm. In the test section the lower plate is in aluminum and is heated by an electrical resistances whereas the upper plate is in Plexiglas. The experiments are carried out employing aluminum foams with 5, 10 and 40 PPI and three thickness over the heated circular plate. Results are obtained in a Reynolds number range from 500 to 1500 and wall heat flux from 500 W/m2 to 1400 W/m2. Results are given in terms of wall temperature profiles, local and average Nusselt numbers, pressure drops, friction factor and Richardson number. Moreover, to evaluate the improvement due to the presence of the metal foam, it is necessary a quantitative methodology. In this work an energy performance ratio is employed to compare the performances of surface with and without foams in terms of heat transfer coefficients and pressure drops. Preliminarily experimental results has confirmed that the use of the porous medium improves the heat transfer promoting the heat dissipation of the surface with high efficacy but determines an increase in pressure drops
Solar energy latent thermal storage by phase change materials (PCMs) in a honeycomb system
No full textA computational investigation of a honeycomb system with Phase Change Materials (PCM) for solar energy applications is accomplished. The system is a solid honeycomb structure made in checkerboard matrix using parallel squared channels, half of them are filled with PCM and in the other the Heat Transfer Fluid (HTF) passes through. Transient regime numerical simulations are created for different channels per unit of length (CPL). The Solid-liquid PCM is paraffin wax. A comparison between the direct honeycomb model (Model A) and a porous medium model (Model B) is carried out. The model B is modelled with the extended Darcy-Brinkman law using the Local Thermal Equilibrium (LTE) assumption for heat exchange between solid and liquid zones. By the results of the direct honeycomb model, the characteristics such as permeability, effective thermal conductivity and interfacial heat transfer are evaluated and then compared with the porous medium model. Numerical simulations were carried out using the Ansys-Fluent code. Results in terms of melting time and temperature fields as function of time are presented
Phase change materials (PCMs) in a honeycomb system for solar energy applications
No full textThe present work aims to investigate a honeycomb system with PCM for solar energy applications. The solution is to combine the qualities of PCM and the honeycomb structure, in fact it spreads out the heat all over the PCM improving the effective thermal conductivity of the system. Transient regime numerical simulations are created for different pores per unit of length (PPU). The Solid-liquid PCM is paraffin wax. A numerical model with honeycomb structure is compared with a porous medium model. The porous medium is modelled with the extended Darcy-Brinkman law and to evaluate the heat exchange between the solid and the fluid zones a Local-Thermal Equilibrium assumption is used. By the results of the direct honeycomb model the characteristics such as permeability, inertial resistant coefficient, effective thermal conductivity and interfacial heat transfer are evaluated and then compared with the porous medium model. Numerical simulations were carried out using the Ansys-Fluent code. Results in terms of melting time, temperature fields, and stored energy as function of time are presented
Numerical investigation on a latent thermal energy storage with aluminum foam
No full textIn this paper, a numerical investigation on Latent Heat Thermal Energy Storage System (LHTESS) based on a phase change material (PCM) in a metal foam is accomplished. A vertical shell and tube LHTESS made with two concentric aluminum tubes is investigated. The internal surface of the hollow cylinder is at a constant temperature above the PCM melting temperature to simulate the heat transfer from a hot fluid. The other external surfaces are assumed adiabatic. The phase change of the PCM is modeled with the enthalpy porosity theory while the metal foam is considered as a porous media that obeys to the Darcy-Forchheimer law. Local thermal nonequilibrium (LTNE) model is assumed to analyze the metal foam and some comparison are accomplished with the local thermal equilibrium model assumption. The governing equations are solved employing the Ansys-Fluent 15 code. Numerical simulations for PCM, PCM in the porous medium in LTE and in LTNE assumptions are obtained. Results as a function of time for the charging phase are carried out for different porosities and assigned pore per inch (PPI). The results show that at high porosity the LTE and LTNE models have the same melting time while at low porosity the LTNE has a larger melting time. Moreover, the presence of metal foam improves significantly the heat transfer in the LHTESS giving a very faster phase change process with respect to pure PCM, reducing the melting time more than one order of magnitude
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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