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This research investigates the effects of employing nanofluids in a tubular heat exchanger on the heat transfer process. The performance of employing water as a base fluid and multi-wall carbon nanotubes (MWCNTs) with a varying concentration nanofluid as operational fluids was investigated in an experimental investigation. The current study makes use of an Armfield Heat Exchanger (HT31) and an Armfield heat exchange service unit (HT30X). Five volumetric concentrations of nanomaterials were used to make nanofluids (0.22%, 0.33%, 0.66%, 1.1%, 1.53%). The Reynolds number of the flow inside the tube ranged from 1598 to 8000. By measuring the variables, the overall heat transfer coefficient, pressure drop, friction factor, and mean Nusselt number are computed. The overall heat transfer coefficient increases as the concentration of MWCNTS and the mass of flow increase, according to the experimental data. In comparison to distilled water, the Nusselt number value has increased by 68%, this increase is due to the nanoparticles' volume concentration. Pressure drop values increase significantly when nanofluids are used. The friction factor increases as the volume concentration of nanoparticles increases. A relationship between Reynolds number and MWCNT volume concentration is proposed for computing the Nusselt number. An acceptable agreement may be found by comparing the results of the current investigation to the literature. [ABSTRACT FROM AUTHOR]

Global warming is increasing as CO 2 emissions from the use of conventional fossil fuels continue to rise. The development of geothermal energy is gradually becoming the key to the sustainable development of human society in the future. Enhancing the heat transfer performance of circulating heat transfer fluids is one of the effective means to efficiently exploit deep geothermal resources. In this study, a self-developed circulating heat exchange experimental setup was established. The convection heat transfer characteristics of nanofluids in high-temperature rocks were experimentally investigated. Al 2 O 3 nanofluid and CuO nanofluid were used as the working medium for heat transfer in high temperature granite samples. The effects of the Reynolds number (1000–6000) and parameters such as nanoparticle type (CuO & Al 2 O 3), size (20 nm & 40 nm) and mass fraction (0 wt%-2wt%) on the heat transfer intensity were analyzed. The effect of nanoparticle accumulation on the rock surface on the local heat transfer strength was also investigated. The results indicate that the increase of Reynolds number enhances the heat transfer strength of nanofluids in rocks. Nanofluid containing 20 nm Al 2 O 3 nanoparticles has better heat transfer performance in rock than nanofluid containing 20 nm CuO nanoparticles. Meanwhile, the heat transfer performance of nanofluid containing 20 nm Al 2 O 3 nanoparticles in rock is better than that of nanofluid containing 40 nm Al 2 O 3 nanoparticles. The heat transfer intensity increases and then decreases as the nanoparticle mass fraction increases. The heat transfer coefficient at Reynolds number 6000 is 52.2 % higher than that of water. For nanofluids and water, the local heat transfer intensity decreases with increasing distance from the inlet. Meanwhile, accumulation of nanoparticles on rock surfaces during convective heat transfer enhances heat transfer intensity. The results show that nanofluids have the potential to be applied to deep geothermal resource extraction. This paper provides data and technical support for the application of nanomaterials in medium and deep geothermal systems to enhance heat transfer efficiency. [ABSTRACT FROM AUTHOR]

A numerical attempt of the two-phase (non-homogeneous) nanofluid approach towards the convection heat transfer within a 3D wavy direct absorber solar collector is reported. The solar collector is permeated by a water- Al 2 O 3 nanofluid and contains a wavy glass top surface that is exposed to the ambient atmosphere and a flat steel bottom surface. The left and right surfaces are maintained adiabatic. The governing equations of the Navier–Stokes and energy equations for the nanofluid are transformed into a dimensionless pattern and then solved numerically using the Galerkin weighted residual finite-element technique. Validations with experimental and numerical data are performed to check the validity of the current code. Impacts of various parameters such as the number of oscillations, wave amplitude, Rayleigh number and the nanoparticles volume fraction on the streamlines, isotherms, nanoparticle distribution, and heat transfer are described. It is found that an augmentation of the wave amplitude enhances the thermophoresis and Brownian influences which force the nanoparticles concentration to display a nonuniform trend within the examined region. Furthermore, the heat transfer rate rises midst the growing wave amplitude and number of oscillations. More importantly, such enhancement is observed more significantly with the variation of the wave amplitude. [ABSTRACT FROM AUTHOR]

In this study, thermal and rheological behavior of non-Newtonian nanofluids in a tube is studied using a new power-law relation. The tube is under a constant heat flux and the viscosity of power-law non-Newtonian nanofluids is assumed to be a function of shear rate and temperature simultaneously. Fully developed velocity and uniform velocity profiles are considered as inlet boundary condition. It is demonstrated that the viscosity along the tube is affected by temperature and shear rate for fully developed and uniform flow profiles. Local heat transfer coefficient along the tube increases with the volume fraction, however volume fraction less than 3% does not affect local heat transfer. It is demonstrated that local heat transfer and average Nusselt number are decreasing functions of Reynolds number. Contrary to the previous studies, average Nusselt number is a decreasing function of the volume fraction of nanoparticles. The Nusselt number is suggested to be a function of Peclet number when the temperature effects are considered in the power-law relation. [ABSTRACT FROM AUTHOR]

In the present study, the effects of a constant magnetic field on convective heat transfer and friction factor of pseudo-plastic copper oxide nanofluid through a horizontal annular tube are investigated experimentally. The nanofluid is a solution of distilled water, carboxymethyl cellulose powder and copper oxide nanoparticles. The nanofluid with 0.25%, 0.5% and 1% volume fractions is used. The Reynolds number between 115 and 800 is applied. Based on the results, at the presence of magnetic field, application of nanofluid with 1% volume fraction causes a maximum improvement of 30.4% in the mean Nusselt number compared to the base fluid. The presence of the magnetic field increases friction factor along the tube. The empirical correlations to predict the Nusselt number and friction factor are presented. [ABSTRACT FROM AUTHOR]

The aim of the present study is to experimentally investigate the thermal performance and the pressure drop in copper tubes partially filled with open-cell metal foams using MgO nanofluid. The tubes are produced by casting liquid metal around space holder material with the porosity of 70% and bounded by constant heat flux. MgO nanoparticles are added to the base fluid (water and ethylene glycol) to make the working fluid at the volumetric concentrations of 0.0625%, 0.25%, and 0.5%. The experiments are performed in a pipe with steady-state laminar flow. The obtained experimental results are compared with the correlation outputs, where a proper agreement between the results was observed. It is perceived that both pressure drop and Nusselt number are highly dependent on the Reynolds number. The data further shows that using nanofluid and porous media inside the tubes increases the pressure drop and convection heat transfer coefficient, significantly. Unlabelled Image • Experiments of MgO/water-EG flow through tubes containing metal foam were conducted. • Effects of MgO concentration and porous medium on heat transfer were analyzed. • Convection heat transfer and pressure loss were directly dependent on Re number. • Copper foams affected pressure drop and thermal performance substantially. [ABSTRACT FROM AUTHOR]

The present paper is a numerical study on heat transfer and pressure drop of a nanofluid including water as base fluid with Al2O3 nanoparticles inside a square channel having an inner cylinder, with and without fin under constant heat flux condition using two-phase Euler-Lagrange approach. Numerical investigation has been carried out for various combinations of base fluid, nanoparticle size and concentration through a straight cylinder. Simulation has been performed in a laminar flow regime using finite volume method. Besides, the thermal boundary condition of constant uniform heat flux on the channel wall was applied. The results show that the increase in Reynolds number and nanoparticle volume concentration have considerable effects on heat transfer coefficient enhancement. The heat transfer coefficient decreases when nanoparticles diameter increases. The passive way used in this study, leads to higher pressure drops. For all fluids under consideration, pressure drop escalates with Reynolds number. Adding nanoparticles to the base fluid leads to rise in pressure drop, and this effect is more intensive for higher concentrations. [ABSTRACT FROM AUTHOR]

Existence of magnetic field causes heat transfer to reduce in free convection but in several engineering uses for example: electronic application; enhancing heat transfer is a purpose. Thus, nanofluid should be selected as working fluid. Nanofluid is dispersion of very small metal particles in the base fluid. Two phase and single phase are two ways for estimating the behavior of nanofluid. At first model, nanofluid suppose as homogenous fluid without any slip mechanism. But in second method, slip velocities are included. Brownian motion and Thermophoresis impacts are taken into consideration in second approach. In this paper, previous publications about nanofluid hydrothermal treatment in existence of magnetic field are reviewed. Rely of variable and constant magnetic fields, Ferrohydrodynamic (FHD) and Magnetohydrodynamic (MHD) can take role in simulations. Numerical and analytical methods are considered by authors. Results proved that temperature gradient augments with augment of solid particle concentration and buoyancy forces, while it decreases with augment of magnetic field. [ABSTRACT FROM AUTHOR]

Heat sink has been widely used as a cooling device for electronic systems in recent years. Because of the considerable heat generated by electronic devices and low efficiency of conventional heat sinks, a large number of researches have been focused on the performance enhancement of these systems. Innovative heat sink in the presence of Al 2 O 3 -water nanofluid is experimentally investigated in this study. The effects of adding various volume fractions of nanoparticles on the convective heat transfer coefficient, pressure drop, thermal resistance and heat sink base temperature are investigated in different flow rates from 6.14 to 32.2 (cm 3 /s). The obtained results reveal that the convective heat transfer enhances 16% and thermal resistance reduces more than 15%. The innovative thermal energy absorption system in present research is a tangential heat sink with impinging liquid jet and elliptical cross section which is expected to be able to achieve significant enhancement in thermal energy removal as a cooling device, which is proposed as the novelty here. Also comparison between cylindrical and elliptical cross sections in this type of heat sink is carried out. The results disclose that using tangential heat sink with liquid jet impingement achieves convective heat transfer coefficient 2.26 times greater than conventional heat sink in the presence of pure water. [ABSTRACT FROM AUTHOR]

This paper presents a state of the art review on the research and development of conduction (thermal conductivity) and convection heat transfer characteristics of ethylene glycol-based nanofluids. Nanofluids preparation and stabilization methods are summarized and discussed. The effects of nanoparticles type, size and concentration as well as temperature on the thermal conductivity of available ethylene glycol and ethylene glycol/water mixture-based nanofluids have been critically and individually analyzed and discussed. Studies on convective heat transfer of these nanofluids have also been reviewed and results from different studies are compared. The review clearly demonstrates that these nanofluids possess considerably higher thermal conductivity and convective heat transfer characteristics compared to their base fluids i.e., ethylene glycol and its aqueous mixture. These thermal features of nanofluids are key factors for their performance in thermal management and energy applications. With the enhanced thermal conductivity and convective heat transfer coefficient nanofluids offer immense potential in energy harvesting and storage as well as to advanced cooling applications. [ABSTRACT FROM AUTHOR]

In this paper, the effect of hybrid Nanofluids on heat transfer of flow around a vertical rod with cosine heat flux is investigated. TiO 2 and Al 2 O 3 Nanoparticles are added to deionized water to produce hybrid Nanofluids. Experiments are conducted for both turbulence and laminar flow regimes. The test rig is an annulus in which a pitch-variable helical element applies a cosine heat flux to its inner tube. Results reveal that the increase in concentrations would reduce maximum rod temperature significantly. This is near l20% for 1.5%Al 2 O 3 compared to water. The effect of pressure was also studied. The data obtained at pressures of 1, 2, 5, and 10 bar shows that pressure does not affect heat transfer performance. The thermal enhancement of Nanofluid decreases as the Reynolds number increases. [ABSTRACT FROM AUTHOR]

The fluid flow and heat transfer characteristics of ZnO-Ethylene glycol (EG) nanofluid through rectangular microchannels having different aspect ratios (a is 1 to 2) are numerically investigated. The different nanoparticle volume percentages (f is 1% to 4%) of ZnO-EG nanofluid are used. The flow is considered under single-phase, three-dimensional, steady-state, incompressible, thermally developing, laminar flow conditions. As a result, the microchannel with an aspect ratio value of 1 has the highest convection heat transfer coefficient and the lowest pressure drop. It is also observed that the convection heat transfer coefficient and pressure drop increases with an increase in nanoparticle volume fraction value of nanofluid. However, the Nusselt number decreases with increasing nanoparticle volume fraction, while the Darcy friction factor is not affected. [ABSTRACT FROM AUTHOR]

The present study aims to provide an overall analysis about nanofluids flowing through microchannel heat sinks. Al 2 O 3 and TiO 2 nanofluids based on deionized water with particle volume fractions of 0%, 0.1%, 0.5%, 1.0% were prepared by the two-step dispersion method. Nonionic surfactant polyvinylpyrrolidone (PVP) was added into the nanofluids to avoid particle aggregation and enhance stability. An ImageIR 3350 was used to get the temperature distribution on the substrate of microchannel heat sinks. The results reveal that the thermal conductivity and dynamic viscosity of Al 2 O 3 and TiO 2 nanofluids are both improved with the increase of particle volume fraction. Compared with a rectangular microchannel heat sink, the performance of heat transfer in fan-shaped microchannel heat sink is more strengthened using Al 2 O 3 nanofluids. The thermal motion of nanoparticles could promote the interruption of laminar flow and intensify the heat transfer between fluids and channel walls. The cyclical change with a fixed period on equivalent diameter could also help destroy the boundary layers. [ABSTRACT FROM AUTHOR]

In this work, effective thermal conductivity and convective heat transfer at different Reynolds number of nanofluid containing nanometer-size particles in N -methyldiethanolamine solution is measured. Thermal conductivity and stability of nanostructures in water-based nanofluid, as well as their dependence to temperature and time variation, are of a great concern. These nanofluids consists of 0.1 mass fraction of spherical silica nanoparticles (SiO 2 ), carbon nanofiber (CNF), UiO-66-NH 2 MOF, carbon nanotube functionalized with carboxylic acid as ligand (CNT-COOH), MgO nanoparticles, and colloidal silica. These nanofluids mixed with of N -methyldiethanolamine solution and thermal conductivity coefficients were measured. The appropriate result demonstrated the thermal conductivity is highly related to the optimum concentration of nanoparticle in base fluid, velocity, flow rate, and heat flux. It was found that a combination of CNF and SiO 2 nanoparticles in a 1:1 ratio with 0.1 wt.% could enhanced thermal conductivity which will induces greater enhancement by combined nanoparticle base amine fluid in heat transfer application. It has been shown increase of Reynolds number at the mass concentration 0.1 wt.% an increase in convective heat transfer coefficient of nanofluid about 13%. These results improve the thermal conductivity properties of solution in amine plants. [ABSTRACT FROM AUTHOR]

Nanofluid has great potentials in heat transfer enhancement and entropy generation decrease as an effective cooling medium. Effects of Al2O3-water nanofluid flow on entropy generation and heat transfer performance in a rectangular conventional channel are numerically investigated in this study. Four different volume fractions are considered and the boundary condition with a constant heat flux is adopted. The flow Reynolds number covers laminar flow, transitional flow and turbulent flow. The influences of the flow regime and nanofluid volume fraction are examined. Furthermore, dimples and protrusions are employed, and the impacts on heat transfer characteristic and entropy generation are acquired. It is found that the average heat transfer entropy generation rate descends and the average friction entropy generation rate rises with an increasing nanofluid volume fraction. The effect of nanofluid on average heat transfer entropy generation rate declines when Reynolds number ascends, which is inverse for average friction entropy generation rate. The average wall temperature and temperature uniformity both drop accompanied with increasing pumping power with the growth in nanofluid volume fraction. The employment of dimples and protrusions significantly decreases the average entropy generation rate and improve the heat transfer performance. The effect of dimple-case shows great difference with that of protrusion-case. [ABSTRACT FROM AUTHOR]

New cooling techniques are being explored for the dissipation of heat fluxes. Many recent studies on heat transfer in micro/minichannels (M/MCs) with nanofluids have focused on combining the advantages of both, for the purpose of obtaining higher single-phase enhancement of heat transfer. Developing of many applications such as cooling electronic device, solar cell, and automotive technology is highly demanded now a day to obtain high efficiency and reduce the operating cost. This review article summarizes recent studies, with a focus on two main topics: The first part contains the main concepts such as scaling effects of M/MCs, physical properties and convective heat transfer. The second part displays the main recent applications of M/MCs with nanofluids with the challenges to be widely used. The purpose of this article to provide exhaustive and comprehensive review of updated works published in this new area, with general conclusions. [ABSTRACT FROM AUTHOR]

In current research about nanofluid convection heat transfer, random motion of nanoparticles in the liquid distribution problem mostly was not considered. In order to study on the distribution of nanoparticles in liquid, nanofluid transport model in pipe is established by using the continuity equation, momentum equation and Fokker-Planck equation. The velocity distribution and the nanoparticles distribution in liquid are obtained by numerical calculation, and the effect of particle size and particle volume fraction on convection heat transfer coefficient of nanofluids is analyzed. The result shows that in high volume fraction (φ = 0.8% ), the velocity distribution of nanofluids characterizes as a “cork-shaped” structure, which is significantly different from viscous fluid with a parabolic distribution. The convection heat transfer coefficient increases while the particle size of nanoparticle in nanofluids decreases. And the convection heat transfer coefficient of nanofluids is in good agreement with the experimental result both in low (φ ⩽0.1% ) and high (φ=0.6% ) volume fractions. In presented model, Brown motion, the effect of interactions between nanoparticles and fluid coupling, is also considered, but any phenomenological parameter is not introduced. Nanoparticles in liquid transport distribution can be quantitatively calculated by this model. [ABSTRACT FROM AUTHOR]

Abstract: We consider a theoretical model of a two-phase flow consisting of a nanofluid adjacent to a clear fluid. A method of obtaining the exact solution to the two-fluid vertical channel flow and convective heat transfer model is presented. The results constitute a rare case in which completely exact solutions are possible for a nonlinear flow problem involving nanofluids, as the governing equations are often highly nonlinear. We show rigorously that the nanofluid can modify the fluid velocity at the interface of the two fluids, and can be used to reduce shear at both the surface of the clear fluid and the interface of the two fluids. Upon exploring the existence of the exact solutions, we discover that in some situations there exist two mathematical solution branches, one of which is the physically relevant solution. We then discuss the behavior of the velocity and thermal profiles with the important parameters dictated by the nanoparticles. [Copyright &y& Elsevier]

The fluid flow and heat transfer in a three-dimensional microchannel filled with Al2O3- water nanofluid is numerically investigated. The hybrid scheme is used to discretize the convection terms and SIMPLER algorithm is adopted to couple the velocity and pressure field in the momentum equations. The thermal and flow fields were analyzed using different volume fractions of nanoparticles and different Reynolds numbers. The temperature fields, the average Nusselt number on the bottom surface, the thermal resistance and the pressure drop were obtained from the simulations. Results indicated enhanced performance with the usage of nanofluids, and slight penalty in pressure drop. The increase in Reynolds number caused increase in the heat transfer rate as well as pressure drop and decrease in the thermal resistance. [ABSTRACT FROM AUTHOR]

Abstract: In this research, the convective heat transfer coefficients of water-based FMWNT nanofluid have been measured under both laminar and turbulent regimes flowing through a uniformly heated horizontal tube in entrance region. For the first time, we have compared effective parameters to measure the convective heat transfer coefficients for functionalized MWNT suspensions such as Re, mass fraction and temperature, altogether in entrance region. The experimental results indicate that the convective heat transfer coefficient of these nanofluids increases by up to 33–40% at a concentration of 0.25wt.% compared with that of pure water in laminar and turbulent flows respectively and 20°C. [Copyright &y& Elsevier]

In current report, hybrid nanomaterial free convection through a permeable region was scrutinized involving magnetic force. Porosity effect is studied using non-Darcy porosity model. Hybrid nanoparticles, multiwall carbon nanotubes (MWCNT) and Ferrous Ferric Oxide (Fe 3 O 4), are merged into pure water (H 2 O) to compose working nanofluid. Moreover, effects of radiation and various shapes nanoparticles has also been reported. The corresponding mathematical model consists of set of nonlinear partial differential equations (PDEs) including conservation of mass, momentum and energy along with specified boundary conditions. The numerical modeling is carried out via Control Volume Finite Element Method (CVFEM). The space discretization is performed using non-uniform finite number of triangular elements. Impacts of Darcy number, magnetic force, radiative and buoyancy forces on nanomaterial behavior have been displayed. Result revealed augment in Nusselt number due to augment in radiation, while converse trend is seen due to rise in Hartmann and porosity effect. [ABSTRACT FROM AUTHOR]

Due to their superior thermophysical properties, there is a growing body of work on nanofluids in the field of thermal systems. However, there is no specific review of the role of the nanoparticle shape, which has been found crucial to their performance adjustment. A comprehensive literature review of the effect of nanoparticle shape on the hydrothermal performance of thermal systems utilizing nanofluids was compiled. The review covered the forced, mixed, and natural convection regimes and included heat exchangers, boundary layer flows, channel flows, peristaltic flows, impinging jets, cavity flows, and flows of hybrid nanofluids. It indicated that the control of nanoparticle shape is a promising technique for the optimization of heat exchange and the required pumping power. However, no uniform conclusion was reached for the role of nanoparticle shape on the hydrothermal performance of thermal systems. In most of the previous studies in the natural and forced convection regimes, the platelet–like nanoparticle acquired the highest heat transfer rate. However, most of the works in the mixed convection regime reported the best heat transfer performance for the blade–like nanoparticle. More research studies are required in future to determine the role of nanoparticle shape for thermal management of energy systems. • Nanoparticle shape is crucial to the performance control of various nanofluids. • The effects of nanoparticle shape on thermal system performance were reviewed. • Nanoparticle shape control is a promising technique for heat transfer optimization. • More research is required for the role of nanoparticle shape in thermal systems. [ABSTRACT FROM AUTHOR]