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[en] Highlights: • Prepared samples showed excellent stability after 14 days of preparation. • Thermal conductivity has been enhanced and the maximum enhancement was 40%. • A new correlation to predict the thermal conductivity has been proposed. • The nanofluid showed great potential to be used as a coolant fluid. • The convective heat transfer coefficient enhanced by increasing solid concentration. - Abstract: The present research aims to suggest a three-step guideline towards selecting a proper Nanofluid regarding the heat transfer effectiveness. To do so, employing two-step technique, the nanofluid’s samples were prepared in various nanoparticles’ concentrations (0.125, 0.25, 0.5, 0.75, and 1%) of MWCNT-ZnO hybrid nanoparticle in a thermal oil. The samples’ stability has been examined employing the Zeta potential analysis. The samples’ thermal conductivity has been experimentally measured at various temperatures (15, 25, 35, 45, and 55 °C) and solid concentrations. After that, a three-step guideline to select a proper nanofluid as a heat transfer fluid has been proposed. Then, for both the internal laminar and turbulent regimes, variations of pumping power due to adding hybrid nanoparticle has been theoretically studied. Furthermore, the possible effects of adding nanoparticles on the convective heat transfer coefficient in a microchannel heat sink have been investigated. The results declared that the convective heat transfer coefficient had been enhanced by 42%. It is concluded that the produced nanofluid, as coolant fluid, would bring a certain benefit in heat transfer applications. These pre-assessment process would ease the decision-making process in selecting a new coolant which possesses superior heat transfer properties in comparison to the conventional coolants (i.e., water and oil).
[en] This article studies the effect of suction/blowing, inclined magnetic field, and chemical reaction on heat-absorbing unsteady radiative Casson fluid past a semi-infinite flat plate in porous medium incorporating the oscillatory plate movement as a linear combination of ‘cosine’ and ‘sine’ functions in time. Further, the mass and heat transfer characteristics are examined under the influence of conjugate mass and heat transfer phenomena at the boundary. The governing equations of the model, viz. the energy, mass transfer, and momentum, are transformed into the non-dimensional form adopting suitable non-dimensional variables and parameters. The exact analytic solutions of the model for species concentration and fluid temperature are obtained using Laplace transform technique whilst, the solution for the fluid velocity has been obtained numerically with the help of the INVLAP routine of MATLAB. The expressions for fluid temperature, species concentration, and velocity are obtained and studied graphically for various physical parameters influencing the fluid flow model taking into account the case of both suction and blowing. Further, the solutions when the Casson fluid parameter α→∞ are also obtained as special cases. Results for the skin friction coefficient, Sherwood number, and Nusselt number are numerically calculated and put in tabular form. An increment for the inclination angle of the magnetic field enhances the fluid velocity while it has a reverse effect on skin friction. Increasing the Schmidt number Sc leads to a reduction in fluid concentration and increasing the value of thermal radiation accelerates fluid temperature. This fluid flow model has several industrial applications in the field of chemical, polymer, medical sciences, etc. (author)
[en] Highlights: • Stretching cylinder. • Steady 2D flow of Maxwell nanofluid is modeled. • The effects of magnetic field and heat sink/source are considered. • Convective boundary conditions is considered here. • Analytical solutions are established through HAM technique. - Abstract: Nanofluids are forthcoming new generation heat transfer fluids, which have been scrutinized precisely, in current years. Thermophysical assets of these fluids have noteworthy impact on their heat transfer features. In this current investigation a mathematical relation for two dimensional (2D) flow of magnetite Maxwell nanofluid influenced by a stretched cylinder is established. To visualize the stimulus of Brownian moment and thermophoresis phenomena on Maxwell fluid Buongiorno's relation has been considered. Moreover, heat sink/source and convective condition are also presented for heat transport mechanism. The homotopic scheme has been developed for the solutions of nonlinear ordinary differential equations (ODEs). The achieved outcomes are planned and consulted in aspects for somatic parameters. It is noteworthy that the velocity of Maxwell fluid display conflicting performance for curvature parameter and Deborah number. It is also reported that the liquid velocity decays for magnetic parameter, whereas the nanoliquid temperature and concentration field enhance for magnetic parameter. Furthermore, the liquid temperature intensifies for the progressive values of thermophoresis parameter and Brownian motion. Additionally, endorsement of current significances is organized via benchmarking with earlier famous limiting situations and we pledge a marvelous communication with these outcomes.
[en] A novel methodology to analyze non-Gaussian probability distribution functions (PDFs) of intermittent turbulent transport in global full-f gyrokinetic simulations is presented. In this work, the auto-regressive integrated moving average (ARIMA) model is applied to time series data of intermittent turbulent heat transport to separate noise and oscillatory trends, allowing for the extraction of non-Gaussian features of the PDFs. It was shown that non-Gaussian tails of the PDFs from first principles based gyrokinetic simulations agree with an analytical estimation based on a two fluid model. (paper)
[en] In this paper, different heat sinks are investigated to improve CPU cooling experimentally. Different types of copper heat sinks including a novel “porous heat sink” are proposed and compared to obtain the optimum heat transfer rate. Water and Al2O3/water nanofluids (40 nm) in two different volume fractions (0.1 and 0.2 vol.% from 40-nm nanoparticles) are used as heat transfer fluid to cool the CPU. Different flow rates are also examined in the experimental study. The Nusselt number, wall temperature, thermal resistance and LMTD temperature have been analyzed for a wide range of parameters of the heat sinks. Also, the effect of geometry, heat transfer fluid, input power and flow rate on the heat transfer rate is reported. The result shows that the geometry of the heat sink has an important effect on the thermal performance of the system. The rate of heat transfer in the proposed novel porous heat sink is larger than the other cases. The Nusselt number in the porous heat sink by using nanofluids is 2.2 times larger than the heat sink with an inline pattern.
[en] Highlights: • Cu-nanofluids show enhanced thermal properties. • The heat transfer coefficient is improved for Cu-nanofluids. • Molecular dynamics calculations show the metal-fluid interactions. • The Cu-fluid interaction is the responsible of the enhanced thermal properties. • Thermal conductivity and isobaric specific heat is increased for Cu-nanofluids. This study presents the preparation of nanofluids based on a heat transfer fluid commonly used in concentrating solar power (CSP) plants. They are comprised of a eutectic mixture of diphenyl oxide and biphenyl with Cu and Ni nanoparticles. The nanofluids based on Cu nanoparticles were shown to dramatically improve thermal properties, the heat transfer coefficient being up to 11% higher for the Cu nanofluid compared with the base fluid. Thus, their use in CSP plants could lead to enhancements in their overall efficiency. Accordingly, nanofluids were prepared with varying nanoparticle concentrations and their properties were characterised, including their radiation absorption capacity, viscosity, isobaric specific heat and thermal conductivity. In addition, a molecular dynamics analysis was performed of the experimental systems prepared from a theoretical perspective. This analysis revealed the same tendencies as those found experimentally. That is, adding Cu nanoparticles to the base fluid led to an increase in both the isobaric specific heat and thermal conductivity. In turn, the results of both the experimental and theoretical study showed that nanofluids based on Ni nanoparticles did not have the same effect, the values for isobaric specific heat showing little variation and there was a decrease in thermal conductivity. The theoretical analysis revealed that both of these behaviours can be related to the different internal structures of the nanofluids, which depend on the metal added. These structures are generated by the different interactions between the metal and the molecules of the base fluid. This study improves the understanding of heat transfer mechanisms in this kind of fluids.
[en] In some industrial heating processes, fuel represents only a very small fraction of the total cost of manufacturing. But in most industrial heating processes, fuel is a considerable expense. Since the last decade of the twentieth century, embargoes, wars, regulations, and deregulation have caused the costs of oil and gas to go through unsettling fluctuations. Costs of electric energy also have also risen, because of the increasing cost of fuels, wages, and equipment. The difference between fuel saving and fuel wasting often determines the difference between profit and loss; thus, heat saving is a must. The words “economy” and “efficiency,” when used in their true sense in connection with industrial furnaces refer to the heating cost per unit mass of finished, sellable product. Analytical, experimental and computational approaches represent three distinct methods to solve a given problem in heat transfer, fluid flow or energy efficiency. However, in actual practice, combinations of these three methods are used to obtain an approach that is best suited to a given problem.Keywords: analytical, numerical, heating equipment, heat transfer, energy efficiency
[en] Nanofluid that made up of fluid and solid nanoparticles has gained attention from diverse fields due to its superior thermophysical properties to enhance the performance of different systems which require flowing medium with excellent heat transfer behavior. Many past researchers have proven that conventional heat transfer fluid can be replaced by the rising nanotechnology–nanofluid which showed astonishing performance under different circumstances. In this paper, we attempt to present a recent review on the consequences of implantation of nanofluid, especially in vehicle engine cooling system and other heat transfer applications such as solar collector, electronics cooling system, flow boiling and thermal energy storage system. Thermophysical properties and heat transfer performance of nanofluids obtained in simulation, test rigs and even real vehicle engine experiments are discussed thoroughly. Models and correlations used by past researchers to compute thermophysical properties are also included. In the last part, various advantages from using nanofluid are summarized, and suggestions for research gap between past studies are discussed to further improve the investigation work in the future.