393 publications from this institution
Natural convection heat transfer of a nanofluid in the presence of an electric field is investigated. The control volume finite element method (CVFEM) is utilized to simulate this problem. A Fe3O4–ethylene glycol nanofluid is used as the working fluid. The effect of the electric field on nanofluid viscosity is taken into account. Numerical investigation is conducted for several values of Rayleigh number, nanoparticle volume fraction, and the voltage supplied. The numerical results show that the voltage used can change the flow shape. The Coulomb force causes the isotherms to become denser near the bottom wall. Heat transfer rises with increase in the voltage supplied and Rayleigh number. The effect of electric field on heat transfer is more pronounced at low Rayleigh numbers due to the predomination of the conduction mechanism.
Recently, new-nanometer sized particles have been dispersed in the base fluid in heat transfer fluids. The fluids containing the solid nanometer-sized particle dispersion are called “nanofluids.” Two main categories were discussed in detail. Single-phase modeling is the combination of a nanoparticle and a base fluid and is considered as a single-phase mixture with steady properties. Two-phase modeling is that in which the nanoparticle properties and behaviors are considered separately from the base fluid properties and behaviors. Moreover, nanofluid flow and heat transfer can be studied in the presence of thermal radiation, electric field, magnetic field, and porous media. In this chapter, definition of nanofluid and its application have been presented.
This research presents an innovative alteration to the solar collector's design by integrating a 4-lobed tube with helical tape. The choice of a working fluid, a combination of water and alumina nanoparticles, is purposeful, aiming to reduce irreversibility. Extensive numerical simulations, along with thorough benchmark verification, meticulously assess the system's performance, demonstrating strong alignment with established benchmarks.This study delves into the interaction among pivotal parameters—D* (diameter ratio), Re (Reynolds number), and N (revolution number)—and their impact on essential performance metrics, encompassing ηII (second law performance), Xd (exergy drop), and Φx (exergy drop ratio). With the elevation of all three parameters, the intensified swirl flow facilitates improved heat absorption by the nanofluid, resulting in reduced entropy generation and subsequently, a decrease in exergy drop. More precisely, the increments in Re, N, and D* lead to significant reductions in the value of Xd, with approximately 52.1 %, 4.02 %, and 5.03 %, respectively. When N = 4, D*=0.02, the amount of ηII for Re = 2e4 is 8.38 times greater than that of Re = 4e3. Increasing D* and N leads to substantial improvements in ηII, with approximately 50.02 % and 30.15 % enhancements, respectively. The highest ηII, reaching 0.582, is attained when D*=0.048, N = 7, and Re = 2e4.
Recognizing the pivotal role of the cooling method in enhancing Photovoltaic-Thermal (PVT) efficiency, this study delves into the combined application of two innovative techniques: a finned tube and a confined jet. Additionally, the integration of a TEG (Thermoelectric Generator) is introduced to amplify output power. The improvement in cooling efficiency is achieved through infusing a composite of Carbon Nanotubes (CNT) and Fe3O4 into the coolant. The investigation encompasses three distinct cooling system configurations: 1) the base case employing a conventional pipe, 2) a system with a finned-tube cooling unit, and 3) a setup combining a confined jet with a finned tube. The introduction of hybrid nanoparticles results in an overall performance boost of around 2.64% compared to the base case. Furthermore, the efficacy of the nanofluid concentration (ϕ) in the base case surpasses that of the Finned Jet case by a factor of 3.86. Notably, an increase in irradiance magnitude and jet inlet velocity contributes to a commendable enhancement in thermal performance, registering approximately 8.66% and 3.48%, respectively. The incorporation of fins and confined jets yields substantial improvements, resulting in an 86.13% enhancement in TEG performance and a commendable 26.42% rise in thermal performance.
No abstract is provided for this article.
New configuration of concentrated photovoltaic thermal (CPVT) with the implementation of parabolic concentrator and heat sink combined with the vortex generator (VG) were presented in current work. The testing fluid is water and temperature-dependent features were utilized. The regime of water flow in absence and presence of VG are laminar and turbulent, respectively. Numerical simulations were done for different values of angle of VG (θ = 30°, and 60°), pitch ratio (S = 0.025, 0.0375, and 0.05), and volumetric flow rate (Q = 0.5, to 2 Lit/min). Four values for width of reflector have been applied and radiation model was utilized to derive the absorbed heat flux. The accuracy of modeling has been examined for three cases and good accommodations have been reported. The maximum values of thermal (ηth) and electrical (ηel) performance are 63.75 % and 13.96 % which happens when θ = 30°, S = 0.025, Q = 2 Lit/min. Installing VG leads to increments of ηth and ηel about 1.42 % and 2.74 %. Increase of S and θ cause performance to decrease while this function increases with rise of Q. Increase of Q causes ηth and ηel to increase about 1.17 % and 2.55 % for the best case.
Current numerical simulation investigates the turbulent flow of nanomaterial and forced convection behavior within a solar system equipped with twisted tape. The top side of unit is under the impact of solar flux and the bottom side is isolated. Entropy generation (S gen ) of the tubular flows at Reynolds numbers ranging from 4000 to 20000 have examined for various cases with two geometric parameters namely; diameter ratio and number of revolution. Component of S gen , Bejan number and entropy ratio are reported in outputs. Utilizing greater pumping power generates more disturbances in flow and Bejan number reduces. S gen,f is directly proportional to diameter ratio because of more interaction of nanofluid
Recently, various ways are investigated to augment heat transfer in different applications such as porous ceramic domain. Adding nanoparticles to fluid is the best operational way to increase the conduction of fluids. In this paper, migration of nanofluid inside a porous duct under the impact of magnetic force is scrutinized. LBM is applied to present comprehensive parametric analysis for various concentrations of nanofluid, Hartmann, Reynolds, and Darcy numbers. Outputs illustrate that Nu augments with improve of Lorentz forces. Augmenting Da significantly enhances the convective flow in our model.
The three-dimensional problem of steady fluid deposition on an inclined rotating disk is illustrated in this study. The governing non-linear partial differential equations are reduced to the nonlinearordinarydifferentialequationssystembysimilaritytransform.Theanalyticalsolutionapplied tosolvethissystemistheHomotopyPerturbationMethod(HPM).Thevelocityandtemperatureprofiles areshownandtheinfluenceofPrandtlnumberandrotationratioontheflowfieldandtheNusseltnumber arediscussedindetail.Thevalidityofoursolutionsisverifiedbythenumericalresults. '2012SharifUniversityofTechnology.ProductionandhostingbyElsevierB.V.Allrightsreserved.
No abstract is provided for this article.
In this paper, the unsteady flow of a nanofluid squeezing between two parallel plates is investigated. The Adomian Decomposition Method (ADM) is used to solve this problem. The base fluid is water containing different kinds of nanoparticles namely copper, silver, alumina and titanium oxide. The effective thermal conductivity and viscosity of the nanofluid are calculated using the Maxwell–Garnetts (MG) and Brinkman models, respectively. The analytical investigation is carried out for various governing parameters such as the squeeze number, nanoparticle volume fraction and Eckert number. The results show that for the case in which two plates are moving together, the Nusselt number increases with increase of nanoparticle volume fraction and Eckert number while it decreases with growth of the squeeze number.
The core aim of this investigation is to simulate the melting of paraffin within a solar heat pipe unit combined with thermal storage unit, while taking into account the presence of metallic fins. To enhance system performance, Multi-Walled Carbon Nanotube (MWCNT) nanoparticles were blended into the paraffin material (RT82) using a homogeneous mixture approximation. The temperatures of the heat pipe and inner walls were derived from previous experimental research. Three distinct fin arrangements were utilized, and simulations were carried out employing numerical method. Validation procedures were undertaken to verify the accuracy of the modeling and the applied approximations, relying on both prior experimental data and numerical publications. The investigation presents data on the liquid fraction (LF), temperature (T), and stream function for diverse configurations. This holistic approach seeks to deepen comprehension of the interactions among these elements within a solar collector system, offering vital insights for performance optimization. The outcomes demonstrated a notable improvement in LF, increasing by roughly 15.15% at t = 1200s with the integration of MWCNT. Furthermore, with the passage of time from 400 s to 1200s, the incorporation of additives results in a notable rise in LF and T, demonstrating enhancements of approximately 97.74% and 130.8% correspondingly. Notably, the utilization of fins positioned at a 90o angle expedites the melting process, yielding a 38.24% LF increase compared to the base case at t = 1200s. Moreover, the impact of fins demonstrates a 3.32% increase over time. In essence, these results emphasize the effectiveness of incorporating MWCNTs and fine-tuning fin configurations to accelerate the melting process, offering valuable insights for the progress of solar thermal systems.
In this article, Lattice Boltzmann method (LBM) has been applied to investigate the influences of magnetic field and heat sources on water based nanofluid natural convection inside a porous cavity with three square heat sources. Koo–Kleinstreuer–Li (KKL) model is applied to study Brownian motion impact on nanofluid flow. Effects of Rayleigh number (Ra), Darcy number (Da), nanofluid volume fraction (ϕ), and Hartmann number (Ha) on heat transfer characteristics are analyzed. From the obtained results we observe a decrease in the temperature gradient with increasing Ha; while quite the opposite effect is true with increasing Da and Ra. In the absence of magnetic field, for higher values of Darcy and Rayleigh numbers, thermal plumes are generated and the temperature gradient is enhanced. Moreover, small eddies are generated near the vertical centerline. However, in the presence of magnetic field, the number of thermal plumes decreases.
No abstract is provided for this article.
Studies of fluid flow and heat transfer in a porous medium have been the subject of continuous interest for the past several decades because of the wide range of applications, such as geothermal systems, drying technologies, production of thermal isolators, control of pollutant spread in groundwater, insulation of buildings, solar power collectors, design of nuclear reactors, and compact heat exchangers, etc. There are several models for simulating porous media such as the Darcy model, Non-Darcy model, and non-equilibrium model. In porous media applications, such as the environmental impact of buried nuclear heat-generating waste, chemical reactors, thermal energy transport/storage systems, the cooling of electronic devices, etc., a temperature discrepancy between the solid matrix and the saturating fluid has been observed and recognized.
The differential transformation method (DTM) is an alternative procedure for obtaining an analytic Taylor series solution of differential equations. The main advantage of this method is that it can be applied directly to nonlinear differential equations without requiring linearization and discretization, and therefore, it is not affected by errors associated with discretization. The concept of DTM was first introduced to solve linear and nonlinear problems in electrical circuits. This chapter introduces DTM generally and contains the following: 1.1 Introduction 1.2 Principle of Differential Transformation Method 1.3 Multistep Differential Transformation Method 1.4 Hybrid Differential Transformation Method and Finite Difference Method 1.5 Differential Transformation Method Applying on Initial-Value Problems and Ordinary Differential Equations 1.6 Two-Dimensional Differential Transformation Method for Partial Differential Equations 1.7 Differential Transformation Method–Padé Approximation 1.8 DTM-Padé Approximation on Singular Two-Point Boundary Value Problem
