One of the crucial phenomena to enhance the heat transfer of microchannel heat sinks is the flow mixing and wall interaction through the secondary flow. In the present study, a combination of the wavy and the oblique grooved microchannel patterns was investigated to improve the performance of the microchannel heat sink. The oblique grooves with a pitch of 375 ?m were combined with the wavy microchannel. The effect of fins with widths of 250 and 125 ?m on thermal performance was investigated (Type-1 and Type-2). The amplitude of 250 ?m and wavelength of 2500 ?m were considered for wavy microchannels. Furthermore, the effect of pitches on the heat transfer was studied; subsequently, pitches of 750 and 1500 ?m were analyzed (Type-3 a

This study utilizes molecular dynamics (MD) simulations to scrutinize the influence of type and volume fraction of nanoparticle on the density of nanofluids, i.e. silver (as a hydrophilic case) and titanium dioxide (as a hydrophobic case) water-based nanofluids. Ionic structure of TiO2 distinguishes the solid-liquid interactions with those in silver-water nanofluid. The thickness of nanolayer is estimated from density profile formed around the nanoparticle and is included in the density calculation. It is found that the type of interatomic potential between the nanoparticle and surrounding water can highly affect the thickness of nanolayer. The hydrophobicity/hydrophilicity of nanoparticle is of great importance in nanolayer density and its

This study utilizes molecular dynamics simulations to scrutinize the influence of type and volume fraction of nanoparticle on the density of nanofluids, ie silver (as a hydrophilic case) and titanium dioxide (as a hydrophobic case) water-based nanofluids. Ionic structure of TiO2 distinguishes the solid-liquid interactions with those in silver-water nanofluid. The thickness of nanolayer is estimated from density profile formed around the nanoparticle and is included in the density calculation. It is found that the type of interatomic potential between the nanoparticle and surrounding water can highly affect the thickness of nanolayer. The hydrophobicity/hydrophilicity of nanoparticle is of great importance in nanolayer density and its thickn

The effects of using copper metal foam as a volumetric absorber as well as heat transfer enhancement technique on the thermal characteristics of a direct absorption parabolic trough solar collector are examined experimentally. The thermal performance, temperature difference and friction factor for PTC in three cases (full porous, semi-porous and without porous) are investigated and compared with each other. The experiments were performed in different flow rates and inlet temperatures. The thermal performance of solar collector is calculated based on ASHRAE Standard 93-2010. Obtained results indicate that using porous foam increase the friction factor dramatically. Moreover, the maximum temperature differences for full-porous, semi-porous an

In the present work, the effects of using nanofluid, metal foam and their combination on the thermal performance of direct absorption parabolic trough solar collector (DAPTSC) were examined experimentally. The use of these volumetric absorbers were introduced because of some of their characteristics such as superior optical properties and better flow mixing which can lead to a lower thermal losses. In order to compare the optical properties of nanofluids and metal foam, the spectrometric experiments were also performed. Obtained results confirm that both nanofluid and metal foam are good solar absorbers. Therefore, CuO/water nanofluids at different volume concentrations (0.01%, 0.05%, and 0.1%) were examined as volumetric solar absorbers. O

In this paper, the thermal and hydrodynamic characteristics of SiO2 / water nanofluids flow through conically coiled tubes are examined experimentally. An experimental rig is constructed and set of experiments were carried out in order to investigate the heat transfer and pressure drop of SiO2-water nanofluids flow under constant wall heat flux condition through various conically coiled tubes. To better understand the fluid flow physics, the thermal conductivity and dynamic viscosity of nanofluids in different temperatures and volume fractions are measured experimentally. The results show that both heat transfer rate and pressure drop increase with increment in nanoparticle concentration. Moreover, the effects of cone angle and coil pitch w

In this study, the heat transfer enhancement due to using Silicon Carbide nanofluid flowing through the tube side in a shell and tube heat exchanger is studied. Nano-fluid concentrations are 0.25, 0.5, 0.75 and 1 Vol.%, respectively. The hot water is passed through the shell side at temperatures of 35, 45 and 55??C. The flow rate of nanofluid is adjusted at 100, 150, 200, 250 and 300?(L/h), while, the hot water flow rate of the outer tube is 180(L/h). The results show that heat transfer and pressure drop increase with increasing volume fraction of nanoparticles and mass flow rate. 19.8% increase in heat transfer is observed due to adding nanoparticles.

Heat exchangers are among the most applied energy systems and increasing their performance can contribute to resolving current energy and environmental issues. Of the active and passive methods of heat transfer enhancement, air bubble injection and using nanofluids, respectively, were selected for this research. Experiments were conducted to study energy, exergy and hydrodynamic performances of a vertical double pipe heat exchanger under the effects of the combined method applied in the annulus side. Finally, multi-objective optimization based on artificial neural network metamodeling and genetic algorithm was carried out to find the best performance on the basis of heat exchanger effectiveness and exergy performance. Results indicate a pro

Ternary mixture formula with consideration of the effect of nanolayer formation is capable of predicting nanofluid density more accurately compared with the traditional mixture rule. The aim of this investigation is to study the effect of particle shape and type of base fluid on density of nanofluid based on the ternary mixture formula using molecular dynamics simulations. In this regard, two types of base fluids, i.e. water and liquid argon, as well as four different particle shapes, i.e. spherical, planar, block and rod-shaped with different aspect ratios are examined. The results showed that different particle shapes show different behaviors in attracting base fluid molecules and forming nanolayer. The thickness of nanolayer is assumed f

This study aims to analyze the thermal performance of the passive thermal management system (TMS) of the 18,650 lithium-ion battery with application of phase change materials (PCM). To improve performance of TMS, nanoparticles, fins and porous metal foam are used beside the PCM, and their effects on the system performance are compared. The local thermal non-equilibrium (LTNE) model and non-Darcy law are considered to simulate the nano-PCM melting inside the porous media. Numerical results are validated through previously published experimental data and results are presented for two, 4.6?W and 9.2?W, heat generation rates. Sole effects of adding nanoparticles to the PCM, utilizing different numbers of fins, and application of the metal foam

Open-cell porous metal foams and nanofluids are among the solar absorbers for radiation absorption in solar collectors. The optical properties of absorbers have an important role in the thermal performance of direct and volumetric absorption solar collectors. In the present work, porous foam and nanofluid are made from the same materials and their optical properties are measured experimentally. The spectrophotometric experiments are performed on the produced porous metal foams and water based nanofluids from two materials namely SiC and CuO. In water-saturated porous foams, the effect of porosity (90% and 95%), pore diameter (10PPI-30PPI) and type of material (CuO and SiC) are survived while the influence of volume fraction and kind of nano

Fluid flow and heat transfer characteristics of nanofluids flowing through helically coiled tubes under uniform heat flux condition are studied experimentally. The turbulent flow of two different kinds of nanofluids, i.e. Ag-water and SiO2-water, are examined. Three different helically coiled tubes along with straight ones are constructed to investigate the effects of geometrical parameters such as pitch circle diameter and helical pitch as well as nanoparticle volume concentration. The viscosity and thermal conductivity of nanofluids are determined experimentally in different volume fractions and temperatures. The range of Reynolds number is from 8900 to 11970. The experimental outcomes show that using nanoparticles in coiled tubes can be

Melting thermal performance of a vertical cylindrical thermal energy storage unit is numerically investigated in presence of a phase change material (PCM) including nanoparticles (nano-PCM) and also horizontal radial copper fins .The results indicate that an increase in the number of fins will improve the heat transfer with subsequent reduction (up to 25.7%) in the melting time. But, use of nano-PCM without fin can only improve the melting time up to 5.5% for the case including 5% of nanoparticles. The best result corresponds to the case with simultaneous use of nano-PCM (5% of Al2O3) and fins (three fins) that could improve the melting time up to 28.3%.

Heat transfer between a silver nanoparticle and surrounding water has been studied using molecular dynamics (MD) simulations. The thermal conductance (Kapitza conductance) at the interface between a nanoparticle and surrounding water has been calculated using four different approaches: transient with/without temperature gradient (internal thermal resistance) in the nanoparticle, steady-state non-equilibrium, and finally equilibrium simulations. The results of steady-state non-equilibrium and equilibrium are in agreement but differ from the transient approach results. MD simulation results also reveal that in the quenching process of a hot silver nanoparticle, heat dissipates into the solvent over a length-scale of ∼2 nm and over a time sc

Application of nanofluid and coiled tubes are two passive methods for increasing the heat transfer. In the present study, the turbulent flows of water and nanofluid in coiled tubes heat exchanger were numerically studied. CuO-water nanofluid containing 1 vol% copper oxide nanoparticles was used and single-phase approach was considered for nanofluid flow. The effect of different geometrical parameters on Nusselt number was also investigated for both helical and conical coiled tubes. Water properties were defined as temperature dependent function, and constant wall temperature was employed as wall boundary condition. Simulation results were validated by available experimental and numerical data of heat transfer coefficient and pressure drop i