Critical review of heat transfer characteristics of nanofluids

Researches in heat transfer have been carried out over the previous several decades, leading to the development of the currently used heat transfer enhancement techniques. The use of additives is a technique applied to enhance the heat transfer performance of base fluids. Recently, as an innovative material, nanometer-sized particles have been used in suspension in conventional heat transfer fluids. The fluids with these solid-particle suspended in them are called ‘nanofluids’. The suspended metallic or nonmetallic nanoparticles change the transport properties and heat transfer characteristics of the base fluid. The aim of this review is to summarize recent developments in research on the heat transfer characteristics of nanofluids for the purpose of suggesting some possible reasons why the suspended nanoparticles can enhance the heat transfer of conventional fluids and to provide a guide line or perspective for future research.     

Heat transfer enhancement in microchannel heat sinks using nanofluids

Heat transfer enhancement in a 3-D microchannel heat sink (MCHS) using nanofluids is investigated by a numerical study. The addition of nanoparticles to the coolant fluid changes its thermophysical properties in ways that are closely related to the type of nanoparticle, base fluid, particle volume fraction, particle size, and pumping power. The calculations in this work suggest that the best heat transfer enhancement can be obtained by using a system with an Al₂O₃–water nanofluid-cooled MCHS. Moreover, using base fluids with lower dynamic viscosity (such as water) and substrate materials with high thermal conductivity enhance the thermal performance of the MCHS. The results also show that as the particle volume fraction of the nanofluid increases, the thermal resistance first decreases and then increases. The lowest thermal resistance can be obtained by properly adjusting the volume fraction and pumping power under given geometric conditions. For a moderate range of particle sizes, the MCHS yields better performance when nanofluids with smaller nanoparticles are used. Furthermore, the overall thermal resistance of the MCHS is reduced significantly by increasing the pumping power. The heat transfer performance of Al₂O₃–water and diamond–water nanofluids was 21.6% better than that of pure water. The results reported here may facilitate improvements in the thermal performance of MCHSs.     

A review on natural convective heat transfer of nanofluids

Nanofluids are considered to have great potential for heat transfer enhancement and are highly suited to application in practical heat transfer processes. Recently, several important studies were carried out to understand and explain the causes of the enhancement or control of heat transfer using nanofluids. The main aim upon which the present work is based is to give a comprehensive review on the research progress on the natural convective heat transfer characteristics of nanofluids for both single- and two-phase models. Both experimental and theoretical studies are reviewed for natural convection of nanofluids in different types of enclosures.     

Numerical investigation of heat transfer enhancement using carbon nanotube-based non-Newtonian nanofluids

In this study convective heat transfer of multi-wall carbon nanotube (MWCNT)-based nanofluids in a straight tube under constant wall heat flux condition is numerically investigated. To achieve this goal Navier–Stokes equations are solved using the finite volume technique with considering CNT-based nanofluids as non-Newtonian fluids of shear-thinning character using the non-Newtonian power law model. The objectives of this research are to provide detailed information of non-Newtonian behavior of CNT nanofluids, comparison of the numerical simulation predictions to the experimental measurements and investigation of non-Newtonian effects on the local heat transfer of the CNT nanofluid and compare the thermal performance of the CNT nanofluids and conventional fluids. As a result the heat transfer coefficient is dominated by the wall region due to non-Newtonian behavior of CNT nanofluid. The results reported in this paper illustrate that the numerical simulation can be one of the most powerful and beneficial tools for the CNT nanofluids optimization and performance analysis.     

Simulation of heat transfer enhancement in nanofluids using dissipative particle dynamics

The current paper applied dissipative particle dynamics (DPD) approach to investigate heat transfer within nanofluids. The DPD approach was applied to study natural convection in a differential heated enclosure by considering the viscosity and the thermal conductivity of the nanofluid to be dual function of temperature and volume fraction of nanoparticles. Experimental data for viscosity and thermal conductivity are incorporated in the current DPD model to mimic energy transport within nanofluids. This incorporation is done through the modification of the dissipative weighting function that appears in the dissipative force vector and the dissipative heat flux. For the entire range of Rayleigh number considered in this study, it was found that the DPD results show a deterioration in heat transfer in the enclosure due to the presence of nanoparticles for φ > 4%. However, some slight enhancement is shown to take place for small volume fraction of nanoparticles, φ ≤ 4%. The DPD results experienced some degree of compressibility at high values of Rayleigh number Ra ≥ 10⁵.     

Natural convection heat transfer enhancement in horizontal concentric annuli using nanofluids

Heat transfer enhancement in horizontal annuli using nanofluids is investigated. Water-based nanofluid containing various volume fractions of Cu, Ag, Al₂O₃ and TiO₂ nanoparticles is used. The addition of the different types and different volume fractions of nanoparticles were found to have adverse effects on heat transfer characteristics. For high values of Rayleigh number and high L/D ratio, nanoparticles with high thermal conductivity cause significant enhancement of heat transfer characteristics. On the other hand, for intermediate values of Rayleigh number, nanoparticles with low thermal conductivity cause a reduction in heat transfer. For Ra = 10³ and Ra = 10⁵ the addition of Al₂O₃ nanoparticles improves heat transfer. However, for Ra = 10⁴, the addition of nanoparticles has a very minor effect on heat transfer characteristics.     

Heat transfer enhancement using hybrid nanofluids in spiral plate heat exchangers

A possible way to enhance the rate of heat transfer in the spiral plate heat exchanger (SPHE) is by employing hybrid nanofluids as its working medium. Hence, in the present work, effects of hybrid nanofluids on the thermal performance of SPHE has been investigated numerically. First, a countercurrent SPHE is designed and modeled. Later, simulation of SPHE has been carried out by employing conventional fluid , nanofluids , and hybrid nanofluids to investigate the heat transfer rates. Finally, the performance of SPHE using hybrid nanofluid is compared with that of using water and nanofluids. The heat transfer augmentation of approximately 16%‐27% with hybrid nanofluids of overall 4% nanoparticles volume concentration and 10%‐16% with 2% nanoparticles volume concentration is observed when compared with that of pure water. Therefore, it can be inferred that the application of hybrid nanofluids in SPHE seems to be one of the promising solutions for augmentation of its thermal performance.     

Review of convective heat transfer enhancement with nanofluids

Nanofluids are considered to offer important advantages over conventional heat transfer fluids. Over a decade ago, researchers focused on measuring and modeling the effective thermal conductivity and viscosity of nanofluids. Recently important theoretical and experimental research works on convective heat transfer appeared in the open literatures on the enhancement of heat transfer using suspensions of nanometer-sized solid particle materials, metallic or nonmetallic in base heat transfer fluids. The purpose of this review article is to summarize the important published articles on the enhancement of the forced convection heat transfer with nanofluids.     

A critical review of convective heat transfer of nanofluids

A nanofluid is a suspension of ultrafine particles in a conventional base fluid which tremendously enhances the heat transfer characteristics of the original fluid. Furthermore, nanofluids are expected to be ideally suited in practical applications as their use incurs little or no penalty in pressure drop because the nanoparticles are ultrafine, therefore, appearing to behave more like a single-phase fluid than a solid–liquid mixture. About a decade ago, several published articles focused on measuring and determining the effective thermal conductivity of nanofluids, some also evaluated the effective viscosity. There are only a few published articles on deriving the forced convective heat transfer of nanofluids. The purpose of this article is to summarize the published subjects respect to the forced convective heat transfer of the nanofluids both of experimental and numerical investigation.     

Thermal wave effects on heat transfer enhancement in nanofluids suspensions

The heat transfer enhancement revealed experimentally in nanofluids suspensions is being investigated theoretically at the macro-scale level aiming at explaining the possible mechanisms that lead to such impressive experimental results. In particular, while the possibility that thermal wave effects via hyperbolic heat conduction could have explain the excessively improved effective thermal conductivity of the suspension the comparison with experimental results rules-out this explanation.     

Heat transfer characteristics of nanofluids: a review

Research in convective heat transfer using suspensions of nanometer-sized solid particles in base liquids started only over the past decade. Recent investigations on nanofluids, as such suspensions are often called, indicate that the suspended nanoparticles markedly change the transport properties and heat transfer characteristics of the suspension. This review summarizes recent research on fluid flow and heat transfer characteristics of nanofluids in forced and free convection flows and identifies opportunities for future research.     

Heat transfer characteristics in double tube helical heat exchangers using nanofluids

In the present work a three-dimensional analysis is used to study the heat transfer characteristics of a double-tube helical heat exchangers using nanofluids under laminar flow conditions. CuO and TiO₂ nanoparticles with diameters of 24 nm dispersed in water with volume concentrations of 0.5–3 vol.% are used as the working fluid. The mass flow rate of the nanofluid from the inner tube was kept and the mass flow rate of the water from the annulus was set at either half, full, or double the value. The variations of the nanofluids and water temperatures, heat transfer rates and heat transfer coefficients along inner and outer tubes are shown in the paper. Effects of nanoparticles concentration level and of the Dean number on the heat transfer rates and heat transfer coefficients are presented. The results show that for 2% CuO nanoparticles in water and same mass flow rate in inner tube and annulus, the heat transfer rate of the nanofluid was approximately 14% greater than of pure water and the heat transfer rate of water from annulus than through the inner tube flowing nanofluids was approximately 19% greater than for the case which through the inner and outer tubes flow water. The results also show that the convective heat transfer coefficients of the nanofluids and water increased with increasing of the mass flow rate and with the Dean number. The results have been validated by comparison of simulations with the data computed by empirical equations.     

Comparative study on heat transfer enhancement of nanofluids flow in ribs tube using CFD simulation

This study presents, a numerical investigation of two‐dimensional turbulent nanofluids flow in different ribs tube configurations on heat transfer, friction, and thermal performance coefficients using ANSYS‐FLUENT software version‐16. Governing equations of mass, momentum, and energy have been solved by means of a finite volume method (FVM). Four types of nanoparticles namely; Al₂O₃, CuO, SiO₂, and ZnO with volume fraction range (1%‐4%) and different size of nanoparticles (dp = 30 nm, 40 nm, 50 nm, and 60 nm) with various Reynolds number (10 000‐30 000) in a constant heat flux tube with rectangular, triangular, and trapezoidal ribs were conducted for simulation. The results exhibit that Nusselt number for all cases enhanced with Reynolds number and nanofluid volume fraction increases. Likewise, the results also reveal that SiO₂ with volume fractions of 4% and diameters of nanoparticles of 30 nm in triangular ribs offered the highest Nusselt number at Reynolds number of Re = 30 000. In addition, the higher value of thermal performance factor was obtained at Reynolds number of Re = 10 000.     

Comparative review of turbulent heat transfer of nanofluids

Three essential aspects of the turbulent-flow, convective heat transfer of nanofluids relevant to their applications are comparatively reviewed in detail based on both theoretical analyses and experimental data. These aspects are: (a) selection – the comparison criteria of the thermophysical property-related heat transfer performance of nanofluids and their base fluids, (b) design – the predictions of the heat transfer coefficients of nanofluids based on homogeneous fluid models by using nanofluid effective thermophysical properties, and (c) effectiveness – the enhancements of the heat transfer coefficients of nanofluids over their base fluids. This review, including research from the inception of nanofluids to date, quantifies the accuracy of bases for future nanofluid evaluation.     

The role of microchannel geometry selection on heat transfer enhancement in heat sinks: A review

Extensive research has been carried out by researchers for improving the thermal efficiency of the microchannel. There are various types of methodologies that have been proposed by authors for different geometry and fluid flow. The use of microchannel in the miniature heat exchangers and microchannel heat sink (MCHS) have taken the science of heat transfer to an another level for which the field of electronic device cooling, aerospace applications, automobile sectors, biomedical engineering, and chemical engineering sectors are being keen toward further development of the technology. Since 3 decades, the microchannel has been tested numerically, experimentally, and analytically for establishing the theories of hydraulic and thermal efficiency during fluid flow. Improper geometry selection of microchannel may lead to carry various losses such as pressure drop, friction factor, wall shear stress, and temperature jump. Available investigations and results have been reviewed immensely in this paper to give a clear prospective for further research in selecting a proper channel geometry.     

A review of electrohydrodynamic enhancement of heat transfer

The heat transfer duty of heat exchangers can be improved by heat transfer enhancement techniques. In general, these techniques can be divided into two groups: active and passive techniques. The active techniques require external forces, e.g. electric field, acoustic or surface vibration etc. The passive techniques require fluid additives or special surface geometries. Electrohydrodynamic (EHD) techniques have been introduced as one of the types of active heat transfer enhancement techniques. This paper presents a review of research works on electrohydrodynamic heat transfer enhancement. This paper can be used as the first guideline for the researcher in using EHD techniques for heat transfer enhancement.     

Buoyancy-driven heat transfer enhancement in a two-dimensional enclosure utilizing nanofluids

Heat transfer enhancement in a two-dimensional enclosure utilizing nanofluids is investigated for various pertinent parameters. A model is developed to analyze heat transfer performance of nanofluids inside an enclosure taking into account the solid particle dispersion. The transport equations are solved numerically using the finite-volume approach along with the alternating direct implicit procedure. Comparisons with previously published work on the basis of special cases are performed and found to be in excellent agreement. The effect of suspended ultrafine metallic nanoparticles on the fluid flow and heat transfer processes within the enclosure is analyzed and effective thermal conductivity enhancement maps are developed for various controlling parameters. In addition, an analysis of variants based on the thermophysical properties of nanofluid is developed and presented. It is shown that the variances within different models have substantial effects on the results. Finally, a heat transfer correlation of the average Nusselt number for various Grashof numbers and volume fractions is presented.     

潜热储热系统强化传热研究进展

近年来,潜热储热系统在太阳能和工业废能的利用中发挥着极其重要的作用,因此用于潜热储热的相变材料受到普遍关注.文章对国内外潜热储热系统众多强化传热技术进行了综述与讨论.     

Compound passive heat transfer augmentation techniques: A comprehensive review

The function of energy is becoming increasingly vital in meeting the requirements of modern societies and sustaining rapid economic and industrial growth globally. Heat transfer equipment has been employed for heat recovery and conversion in various domestic and industrial applications. Therefore, due to the recent global energy crisis, boosting the thermal efficiency of energy systems has become an essential requirement, which would reduce both their size and rates of energy demand. There are active and passive methods for boosting heat transfer rates. As they have no moving components, passive methods are more affordable and dependable than active ones. Applying two or more passive techniques concurrently will result in a higher heat transmission rate than any approach working independently. The current article comprehensively reviews experimental and computational investigations of passive compound forced convection heat transfer augmentation techniques at laminar, transition, and turbulent flow regimes. This article focuses on compound techniques arrangement in the form of turbulators, typical twisted tapes (TTs), surface roughness, vortex generators, and so on. The pioneering research suggests that using a lower twist ratio, lower pitch, and smaller winglet angles in TTs can result in higher heat transfer rates, albeit with a slightly increased friction factor. The combination of alternate-axes and wings in TTs leads to more effective heat transfer enhancement within the tube.