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EN
In this paper a numerical study of natural convection of stationary laminar heat transfers in a horizontal ring between a heated square inner cylinder and a cold elliptical outer cylinder is presented. A Cu-water nanofluid flows through this annular space. Different values of the Rayleigh number and volume fraction of nanoparticles are studied. The system of equations governing the problem was solved numerically by the fluent calculation code based on the finite volume method and on the Boussinesq approximation. The interior and exterior surfaces are kept at constant temperature. The study is carried out for Rayleigh numbers ranging from 310 to 510. We have studied the effects of different Rayleigh numbers and volume fraction of nanoparticles on natural convection. The results are presented as isotherms, isocurrents, and local and mean Nusselt numbers. The aim of this study is to study the influence of the thermal Rayleigh number and volume fraction of nanoparticles on the heat transfer rate.
EN
The onset of stationary convection in thermal instability of porous layer saturating a Jeffrey nanofluid is studied. The behaviour of nanofluid is described by a Jeffrey fluid model and the porous layer is assumed to follow Darcy’s law. Due to the presence of the Jeffrey parameter and nanoparticles, the momentum-balance equation of fluid is modified. The linear stability analysis and normal modes analysis method are utilised to derive the dispersion relation for the Rayleigh number in terms of various parameters for free-free boundaries. The effects of the Jeffrey parameter, Lewis number, modified diffusivity ratio, nanoparticles’ Rayleigh number and medium porosity on the physical system are discussed analytically and graphically.
EN
Enhancing the Convective heat transfer in the carrier fluids, by augmenting the thermal conductivity in fluids, with nano particles is one of the passive techniques. Enhancement in the thermal conductivity in the carrier fluids can be achieved by suspending particles of nano-size into the base fluids, such colloidal suspensions are called as nanofluids. Nanofluids are proven fluids which improve the convective transfer of heat in the base fluids in the heat exchangers. But still, there are lot of challenges that are existing in understanding the mechanisms of enhancement of convective heat transfer for large scale applications. In this work, an attempt is made to summarize recent advancements on augmentation of convective heat transfer in heat exchangers in turbulent flows using various nanofluids and present various setbacks for the development of nanofluids for critical applications.
EN
With its superior thermo-physical characteristics to the carrier fluid, nanofluid is the most impactful heat transfer fluid. Thermal conductivity, density, viscosity, specific heat, coefficient of volumetric expansion, and other thermo-physical parameters play an important part in the thermal management of any heat transfer application. This thermal management governs the service life of an equipment or apparatus, which dissipates heat during its operation. If the equipment is well-managed thermally, then its service life will be extended. Otherwise the equipment stops functioning due to excess heat. Thermo-physical properties of nanofluid vary with the change in the concentration of nanoparticles. Estimation of the properties with the varying concentrations of the nanoparticles is time consuming and is economically not viable. There were many empirical models available in the literature for determining the thermo-physical properties of nanofluids. However, each model provides different values of thermo-physical properties and choosing the best model among the models available is a complex task. In this regard, to avoid the complication in choosing the best model, and in order to envisage the thermo-physical properties of the nanofluid, the Artificial Neural Network (ANN) technique was used. This technique is widely used among the researchers for various applications. The ANN approach was utilized in this work to estimate viscosity and thermal conductivity of water-based Al2O3 nanofluid for volume fractions between 0.01% and 0.1%. For thermal conductivity, mean square error (MSE) was observed as 4.504e-09 and for viscosity, it was observed as 6.4742e-09. Training times were 5 seconds and 4 seconds for thermal conductivity and viscosity datasets, respectively.
EN
In this paper the laminar unsteady natural convection heat transfer of (Al2O3-water) nanofluid inside 3D triangular cross section cavity was investigated. The cavity was heated differentially, the vertical walls were kept at different constant temperatures. The left hot and the right cold. The effect of the solid volume fraction was examined for two values and compared with the pure water results. The (Ra) range studied was (103≤Ra≤106). Inserting cylindrical body inside the cavity also investigated in three cases. One concentric cylinder has radius (15%) of the cavity side length. The other cases were of two cylinders having radius (7.5%) of the cavity side length, aligned vertically or nonaligned. The results show that the higher solid volume fraction gives the maximum enhancement of the average (Nu) and this enhancement increases with (Ra) increase. For the cases with inner cylinders, the average (Nu) enhanced for the case of double cylinders over single cylinder. On other hand, the nonaligned position of the cylinders giving more enhancement than other position. As like as, the location of maximum horizontal or vertical velocities were varied with the cylinders position while (Ra) has no effect.
EN
Thermal augmentation in flat tube of car radiator using different nanofluids has been performed more often, but use of artificial roughness has been seldom done. Artificial roughness in the form of dimple is used in the present research work. Present study shows the impact of dimple shaped roughness and nanofluid (Al2O3/pure water) on the performance of car radiator. The pitch of dimples is kept at 15 mm (constant) for all the studies performed. The Reynolds number of the flow is selected in the turbulent regime ranging from 9350 to 23 000 and the concentration of the nanofluid is taken in the range of 0.1–1%. It has been found that the heat transfer rate has improved significantly in dimpled radiator tube on the expense of pumping power. Furthermore, the heat transfer rate also increases with increase in nanoparticle concentration from 0.1% to 1.0%. The highest heat transfer enhancement of 79% is observed at Reynolds number 9350, while least enhancement of 18% is observed for Reynolds number of 23 000.
EN
A special group of hybrid assisted processes termed media-assisted processes which apply liquid media with special additives in the form of nanoparticles supplied to the cutting zone is overviewed. Special attention is paid to minimum quantity lubrication (MQL) technique with the use of nanofluids. In this review paper some important thermal and tribological effects resulting from the applications of various nanoparticles are outlined and compared. The MQL-nano cutting fluid mechanisms (rolling and ploughing) are described. In particular, some important quantitative effects concerning thermal and tribological behaviour of the cutting process as well as surface quality are presented.
EN
In this paper, the effects of rotation on a Jeffery nanofluid flow in a porous medium which is heated from below is studied. Darcy model is employed for porous medium and the Jeffrey fluid model is used as a base fluid. The Navier-Stokes equations of motion of fluid are modified under the influence of the Jeffrey parameter, naoparticles and rotation. The basic perturbation technique based on normal modes is applied to derive the dispersion relation for a Rayleigh number. The effects of the Taylor number, Jeffrey parameter, Lewis number, modified diffusivity ratio, nanoparticles Rayleigh number and medium porosity on the stationary convection of the physical system have been analyzed analytically and graphically. It is observed that the rotation parameter has a stabilising influence for both bottom/top-heavy configurations.
EN
An analysis into the transient natural convective flow of a nanofluid in a vertical tube is made. The governing equations of momentum, heat transfer and nanoparticle volume fraction are deduced, and the influence of the thermophoresis parameter and Brownian motion is incorporated. By direct integration and variation of the parameter, analytical solutions are obtained for flow formation and heat/mass transfer at steady-state. On the other hand, due to the complexity of same problem at transient state, a numerical solution is used to solve the discretized equations of motion using the implicit finite difference technique. The influence of the thermophoresis parameter and Brownian motion is noted and well discussed. For accuracy check, a numerical comparison is made between the steady state and transient state solution at large time; this comparison gives an excellent agreement. The role of various principal parameters on velocity profile, temperature, concentration of nanoparticles, Sherwood and Nusselt numbers are presented graphically and well discussed. It is noted that the buoyancy ratio decreases the fluid velocity significantly.
EN
A revised model of the nanoparticle mass flux is introduced and used to study the thermal instability of the Rayleigh-Benard problem for a horizontal layer of nanofluid heated from below. The motion of nanoparticles is characterized by the effects of thermophoresis and Brownian diffusion. The nanofluid layer is confined between two rigid boundaries. Both boundaries are assumed to be impenetrable to nanoparticles with their distribution being determined from a conservation condition. The material properties of the nanofluid are allowed to depend on the local volume fraction of nanoparticles and are modelled by non-constant constitutive expressions developed by Kanafer and Vafai based on experimental data. The results show that the profile of the nanoparticle volume fraction is of exponential type in the steady-state solution. The resulting equations of the problem constitute an eigenvalue problem which is solved using the Chebyshev tau method. The critical values of the thermal Rayleigh number are calculated for several values of the parameters of the problem. Moreover, the critical eigenvalues obtained were real-valued, which indicates that the mode of instability is via a stationary mode.
EN
This paper studies hydrodynamic and heat transfer performance of Al2O3/H2O nanofluid flowing through a Bessel-like converging pipe in laminar flow regime using the computational fluid dynamic approach. A parametric study was carried out on the effect of Reynolds number (300– 1200), convergence index (0-3) and nanoparticle concentration (0–3%) on the both hydrodynamic and thermal fields. The results showed the pressure drop profile along the axial length of the converging pipes is parabolic compared to the downward straight profile obtained in a straight pipe. Furthermore, an increase in convergence index, Reynolds number and nanoparticle concentration were found to enhance convective heat transfer performance. Also, a new empirical model was developed to estimates the average Nusselt number as a function of aforementioned variables. Finally, the result of the thermohydraulic performance evaluation criterion showed that the usage of Bessel-like converging pipes is advantageous at a low Reynolds number.
EN
This study presents the behavior of a single wall carbon nanotube (SWCNT)/water nanofluid for convective laminar flow inside a straight circular pipe heated by a constant heat flux. Five volume fractions of SWCNT were used to investigate their effect on the heat transfer coefficient, Nusselt number, temperature distribution and velocity field in comparison with pure water flow. One model for each property was tested to calculate the effective thermal conductivity, effective dynamic viscosity, and effective specific heat of the SWCNT/water mixture. The models were extracted from experimental data of a previous work. The outcomes indicate that the rheological behavior of SWCNT introduces a special effect on the SWCNT/water properties, which vary with SWCNT volume fraction. The results show an improvement in the heat transfer coefficient with increasing volume fraction of nanoparticles. The velocity of SWCNT/water nanofluid increased by adding SWCNT nanoparticles, and the maximum increase was registered at 0.05% SWCNT volume fraction. The mixture temperature is increased with the axial distance of the pipe but a reduction in temperature distribution is observed with the increasing SWCNT volume fraction, which reflects the effect of thermophysical properties of the mixture.
EN
The work presents a numerical investigation for the convective heat transfer of nanofluids under a laminar flow inside a straight tube. Different models applied to investigate the improvement in convective heat transfer, and Nusselt number in comparison with the experimental data. The impact of temperature dependence, temperature independence, and Brownian motion, was studied through the used models. In addition, temperature distribution and velocity field discussed through the presented models. Various concentrations of nanoparticles are used to explore the results of each equation with more precision. It was shown that achieving the solution through specific models could provide better consistency between obtained results and experimental data than the others.
EN
The paper is a thermodynamics analysis of the removal of any inert gas from the tank using the vapors of any liquefied petroleum gas cargo (called cargo tank gassing-up operation). For this purpose, a thermodynamic model was created which considers two boundary cases of this process. The first is a ‘piston pushing’ of inert gas using liquefied petroleum gas vapour. The second case is complete mixing of both gases and removal the mixture from the tank to the atmosphere until desired concentration or amount of liquefied petroleum gas cargo in the tank is reached. Calculations make it possible to determine the amount of a gas used to complete the operation and its loss incurred as a result of total mixing of both gases.
EN
The current research demonstrates the revolving flow of water-based Fe3O4 nanofluid due to the uniform rotation of the disc. This flow of nanofluid is investigated using CFD Module in COMSOL Multiphysics. However, the similarity solution for this flow is also ob-tained after transforming the given equation into a non-dimensional form. In the CFD Module, streamlines and surface plots are compared with the similarity solution for the magnitude of the velocity, radial velocity, tangential velocity, and axial velocity. The results from the direct simulation in the CFD Module and the solution of dimensionless equations represent a similar solution of velocity distribution. The derived results show that increasing the volume concentration of nanoparticles and effective magnetic parameters decrease the velocity distribu-tion in the flow. Results in the CFD Module are important for monitoring the real-time particle tracing in the flow and, on the other hand, the dimensionless solution is also significant for the physical interpretation of the problem. Both methods of solution empower each other and present the physical model without sacrificing the relevant physical phenomena.
EN
The main objective of this work is to efficiency prediction and parameter optimisation of an electrocaloric refrigeration system based on ceramic materials (BaTiO3) and nanofluids (Al2O3, CuO). For this purpose, an electrocaloric device is used and studied. The principle consists in the heating and cooling of the ceramic material under the application and removal of electrical field respectively. The nanoparticles suspended in water increase the heat thermal between solid electrocaloric material and carried fluid, so we have much faster heat exchanges that cause an increase in coefficient of performance (COP) and temperature span; the temperature difference between the cold heat exchanger (CHEX) and the hot heat exchanger (HHEX). Indeed, the performances of these systems are strongly dependent on the interactions between the thermal, the fluidic and the electricity in order to be able to evaluate and optimize these systems in terms of cooling power, and the observation is that there are very few current studies in this area. Finally, a parametric study effected by using the COMSOL Multiphysics identified the characteristic quantities that have a significant influence on thermal behavior in electrocaloric refrigeration systems based nanofluids and ceramic material.
PL
Tematem artykułu jest analiza i optymalizacja systemu chłodzenia bazującego na materiale ceramicznym BaTiO3 i nanocieczy Al2O3, CuO. W tym celu analizowano element elektrokaloryczny I współczynnik wymiany ciepła CCP. Przedstawiono wyniki badań elementu jak I całego systemu chłodzenia.
EN
This contemporary work explores the theoretical analysis of energy transfer performance of distinct nanoparticles (silver, copper, aluminium oxide and titanium oxide) adjacent to a moving surface under the influence of a porous medium which is driven by the buoyancy force. A mathematical model is presented which is converted to similarity equations by employing similarity transformation. The condensed nonlinear equations were approximated by the iterative method called RKF 45th-order. The flow and energy transference characteristics are explained through graphs and tabulated values. The notable findings are: silver- water is an appropriate nanofluid for enhancing the thermal conductivity of the base fluid. Titanium oxide – water shows a lower fluid flow movement due to porosity.
EN
In this work we have discussed the impact of thermal radiation on heat transfer to nanofluid flow over an unsteady permeable stretching sheet using various types of arbitrary shape nanoparticles of Copper (Cu), Silver (Ag), Alumina [...], and Titania Oxide [...] in the base fluid. Suitable transformations have been employed to build ODEs from the partial differential equations. Numerical results are therefore obtained particularly for cylindrical shape and spherical shape nanoparticles. Our analysis substantiates that the velocity and temperature profiles increases with enhanced thermal radiation parameter. Further, Nusselt number is more advanced for the nanofluid that contains cylindrical shape nanoparticles as compared to spherical shape nanoparticles.
EN
In the current study, a three dimensional incompressible magnetohydrodynamic (MHD) nanofluid flow over a shrinking surface with associated thermal buoyancy, thermal radiation, and heating absorption effects, as well as viscous dissipation have been investigated. The model has been represented in a set of partial differential equations and is transformed using suitable similarity transformations which are then solved by using the finite element method through COMSOL. The results for velocity and temperature profiles are provided for various values of the shrinking parameter, Biot’s number, heat generation/absorption parameter, thermal Grashof number, nanoparticle volume fraction, permeability parameter, magnetic parameter and radiation parameter.
EN
The objective of the present work is to investigate the influence of nanoparticles of copper within the base fluid (water) on magneto-hydrodynamic mixed-convection flow in a square cavity with internal generation. A control finite volume method and SIMPLER algorithm are used in the numerical calculations. The geometry is a lid-driven square cavity with four interior square adiabatic obstacles. A uniform heat source is located in a part of the left wall and a part of the right wall of the enclosure is maintained at cooler temperature while the remaining parts of the two walls are thermally insulated. Both the upper and bottom walls of the cavity are considered to be adiabatic. A comparison with previously published works shows a very good agreement. It is observed that the Richardson number, Ri, significantly alters the behavior of streamlines when increased from 0.1 to 100.0. Also, the heat source position parameter, D, significantly changes the pattern of isotherms and its strength shifted when D moves from 0.3 to 0.7.
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