Heat Transfer Characteristics Of Nanofluids Research Articles

Lattice Boltzmann simulation on thermal management of electronic components with nonuniform temperature based on nanofluids

In order to conduct thermal management of electronic components with nonuniform temperature, the flow and heat transfer characteristics of nanofluids in four kinds of cavities with inclined nonuniform heating surfaces were simulated by the lattice Boltzmann model. Classified from the two-dimensional geometry, the influence of parallelogram cavity, inverted parallelogram cavity, trapezoid cavity, and inverted trapezoid cavity was researched. Considering the complex thermal environment in reality, effects of four kinds of heating wall boundary conditions (constant temperature, gradient temperature, piecewise temperature, and normal temperature) are discussed. Results showed that the flow velocity of nanofluid in the inverted trapezoid cavity is the highest. The highest average Nusselt number near the heating wall of the inverted parallelogram cavity can reach 3.97. Among all kinds of wall heating conditions, cavities with constant temperature have the best heat transfer effect, whose Nu number is 33.4% higher than that of cavities with piecewise temperature in average. The average total entropy change of inverted parallelogram cavity is 16.83. According to the simulation results, the best arrangement of natural convection cooling can be determined.

Experimental study of heat transfer characteristics of nanofluids nucleate and film boiling on horizontal flat plate

In this paper, the heat transfer characteristics of nanofluids nucleate and film boiling is studied experimentally. For this purpose, Al2O3 and SiO2 deionized water-based nanofluids prepared with three volumetric concentrations of 0.1%, 0.3% and 0.5%. The boiling experiments were conducted on a circular and polished copper surface with a diameter of 25 mm. The results showed that the addition of nanoparticles to the base fluid reduced the heat transfer coefficient of nucleate boiling. The boiling of nanofluids increased the surface wettability and the critical heat flux was significantly higher than that of pure deionized water. The Al2O3 deionized water-based nanofluid with a volumetric concentration of 0.5% had the best performance, with a critical heat flux of 44.56% higher than that of pure deionized water. The presence of nanoparticles in the deionized water-based nanofluid improved the heat transfer coefficient of film boiling. The results showed that the stable film boiling for nanofluids starts at higher wall superheat temperature difference than pure deionized water. Among the investigated concentrations, volumetric concentration of 0.5% had best performance for both nanofluids, so that the minimum heat flux of Al2O3 and SiO2 deionized water-based nanofluids were increased 35.01% and 34.40% compared to pure deionized water, respectively.

Convective heat transfer characteristics of nanofluids including the magnetic effect on heat transfer enhancement - a review

• Experimental and numerical investigations on the convective heat transfer of various nanofluids are summarized and discussed. • Convective heat transfer can be improved when small-sized nanoparticles was used. • Magnetic field in magnetic nanoparticles improves the convective heat transfer performance. The scope of this review enlightens the experimental and numerical investigations conducted on the convective heat transfer of various nanofluids, particularly hybrid nanofluids. Essential studies on the improvement of the convective heat transfer using suspensions of nanoparticles in traditional working fluids have recently appeared in the literature. Optimized heat and mass transfer of nanofluid are significantly affected by inherent nanofluid characteristics, synthesizing method for the nanofluid, the effect of magnetic force, concentration and size of nanoparticles, and Re (Reynolds number). Besides, a critical factor regarding the material properties, thermal properties, and performance of the magnetic nanofluids is highly sensitive to the small variation in the magnetic force and magnetic field gradient. Several studies have concluded that the magnetic field in magnetic nanoparticles improves the convective heat transfer performance of a nanofluid by approximately 13%–75%. Furthermore, some applications of a hybrid nanofluid in thermal systems have also been introduced.

Research on convective heat transfer characteristics of Fe3O4 magnetic nanofluids under vertical magnetic field

This paper focuses on the convective heat transfer characteristics of Fe3O4-water magnetic nanofluids under laminar and turbulent conditions. After verifying the accuracy of the experimental apparatus, the effects of magnetic field strength, concentration, Reynolds number and temperature on the convective heat transfer coefficient have been studied. The convective heat transfer characteristics of nanofluids under laminar and turbulent flow conditions were studied in depth, and the influence of each factor on the heat transfer coefficient was analyzed by orthogonal experimental design method. Under the laminar flow conditions, the convective heat transfer of magnetic nanofluids performed best when the Reynolds number was 2000, the magnetic field strength was 600, the temperature was 30?C, and the concentration was 2%. The convective heat transfer coefficient, h, increased by 3.96% than the distilled water in the same conditions. In turbulent state, the convective heat transfer of magnetic nanofluids performed the best when the Reynolds number was 6000, the magnetic field strength was 600, the temperature was 40?C, and the concentration was 2%. The h increased by 11.31% than the distilled water in the same Reynolds number and the magnetic field strength conditions.

Thermophysical Properties for ZnO-Water Nanofluid: Experimental Study

This paper presents the thermophysical properties of zinc oxide nanofluid that have been measured for experimental investigation. The main contribution of this study is to define the heat transfer characteristics of nanofluids. The measuring of these properties was carried out within a range of temperatures from 25 °C to 45 °C, volume fraction from 1 to 2 %, and the average nanoparticle diameter size is 25 nm, and the base fluid is water. The thermophysical properties, including viscosity and thermal conductivity, were measured by using Brookfield rotational Viscometer and Thermal Properties Analyzer, respectively. The result indicates that the thermophysical properties of zinc oxide nanofluid increasing with nanoparticle volume fraction increasing, as well as the thermophysical properties of zinc oxide nanofluid affected by the change in temperature.

Nucleate and Film Boiling Performance of Ethanol-Based Nanofluids on Horizontal Flat Plate: An Experimental Investigation

In this paper, the heat transfer characteristics of nanofluid nucleate and film boiling are studied experimentally. For this purpose, Al2O3 and SiO2 ethanol-based nanofluids prepared with three volumetric concentrations of 0.1 %, 0.3 %, and 0.5 %. The boiling experiments were conducted on a circular and polished copper surface with a diameter of 25 mm. The results showed that the addition of nanoparticles to the base fluid reduced the heat transfer coefficient of nucleate boiling. The critical heat flux of ethanol-based nanofluids was significantly higher than that of pure ethanol. The Al2O3 ethanol-based nanofluid with a volumetric concentration of 0.5 % had the best performance, with a critical heat flux of 42.36 % higher than that of pure ethanol. The presence of nanoparticles in the ethanol-based nanofluid improved the heat transfer coefficient of film boiling. The results showed that the stable film boiling for nanofluids starts at higher wall superheat temperature difference than pure ethanol. Among the investigated concentrations, volumetric concentration of 0.5 % had the best performance for both nanofluids, so that the minimum heat flux of Al2O3 and SiO2 ethanol-based nanofluids were increased by 45.96 % and 45.67 % compared to pure ethanol, respectively.

Numerical and experimental investigation on heat transfer characteristics of nanofluids in a circular tube with CDTE

This paper reported numerical simulation investigations on heat transfer performance of ZrO2-water and Cu-water nanofluids in the tube with concentric double twisted element(CDTE)(Re = 6000-12000). Furthermore, experiments verified that the two-phase flow model method was more suitable for the numerical simulation of nanofluids in the tube with CDTE. The Nusselt numbers with CDTE and nanofluids obviously increased and also showed a positive correlation with the nanofluid concentration. The Nusselt numbers of Cu-water nanofluid were better than ZrO2-water nanofluid. While the friction factor(f ) of CDTE tube between the nanofluids increased little, the maximum difference was only 3.23%. The heat transfer performance was evaluated by performance evaluation criteria (PEC), cross-section entransy efficiency(ψc) and radial-flow(RF) number. The heat transfer performance of Cu-water nanofluids was all superior to ZrO2-water nanofluids. The PEC values in nanofluids increased with increasing concentration. The maximum PEC value was 1.96 in 1% Cu-water nanofluid. Subsequently, the ψc of CDTE tube increased with the increase of cross-section position and nanofluid concentration. The maximum ψc was 91.22% in 1% Cu-water nanofluid at Re= 6000. When an appropriate concentration of nanofluids was used and the nanofluid was passed through the CDTE, the RF numbers increased obviously. The maximum RF number was 0.1028 with 0.5% Cu-water nanofluid at Re= 6000.

INVESTIGATION OF THERMAL CONDUCTIVITY OF SILVER NANOPARTICLES IN BASEFULID OF WATER ETHYLENE GLYCOL

Nanotechnology is interface technologies that span many different science and applications area. When engineering, science and technology are conducted at the nanoscale is called as nanotechnology. It is about 1 to 100 nm (nano-meter) where nano denotes the scale range of one billionth of meter. Nanotechnology refers the properties of atoms and molecules measuring 0.1 to 1000 nm. Nanofluids are nothing but suspension of nanometer sized particles in the base of fluid. The base fluid can be water based or non water based depending on the application. Common nano particles are oxides, carbides, metals, carbon nano particles or nitrides. These fluids act as Newtonian fluids but in some cases these fluids do not work accurately hence non-Newtonian fluids are considered. Recent investigations on nanofluids, suggest that the suspended nanoparticles alter the transport properties and heat transfer characteristics of the suspension. This research summarizes recent trends on nanofluid heat transfer characteristics of Ag/H2O-EG nanofluids in free convection flows and identifies opportunities for future research.

Application of Superhydrophobic Surface on Boiling Heat Transfer Characteristics of Nanofluids

Boiling heat transfer is a mode using the phase change of working medium to strengthen the heat exchange due to its good heat exchange capability, and it is widely used in heat exchange engineering. Nanofluids have been used in the direction of enhanced heat transfer for their superior thermophysical property. The wetting, spreading and ripple phenomena of superhydrophobic surfaces widely exist in nature and daily life. It has great application value for engineering technology. In this article, the boiling heat exchange characteristics of nanofluids on superhydrophobic surface are numerically studied. It was found that with the increase of superheating degree, the steam volume ratio of unmodified heated surface increases to saturation, while the steam volume and evaporation ratio of modified superhydrophobic surface increase firstly and then decrease. At the same time, bubbles are generated and accumulated more fully on superhydrophobic surface. It was also found that nanofluids with low viscosity are more affected by superhydrophobic surface characteristics, and the increase is more significant with high superheating degree, and the superhydrophobic surface is beneficial to enhancing boiling heat exchange. Compared with the simulation results, it could be concluded that the boiling heat exchange performance of CuO-water nanofluids on the modified superhydrophobic surface is better than that of CuO-ethylene glycol nanofluids under high superheating degree.

Numerical study on fly ash–Cu hybrid nanofluid heat transfer characteristics

The current numerical study is aimed to examine the forced convection heat transfer of fly ash-Copper (80:20% by volume) water-based hybrid nanofluids flowing in a horizontal circular copper tube under a constant heat flux of 7962W/m2 using STAR CCM+ software. The volume concentrations of 0.5% and 1% are considered for the analysis within the Reynolds number range of 6900-26500. The findings show that the heat transfer coefficient and the Nusselt number of hybrid nanofluid at a concentration of 1 vol.% are increased by about 66.0% and 36.67% compared to that of water.

가열된 금속구에 집중 용량 방법을 적용하여 해석한 나노 유체의 열전달 특성

본 연구는 순수 유체와 나노 유체의 대류 열전달 성능을 평가하는 새로운 장치에 대하여 설명한 것이다. 가열된 금속구가 유체 속에서 냉각되는 경우 측정된 시간-온도 그래프로부터 시간 상수를 계산할 수 있다. 시간 상수는 대류 열전달 계수의 정보를 가지고 있고 시간 상수가 작으면 대류 열전달 계수가 큰 것이다. 따라서 두 유체의 경우 실험을 통하여 각각의 시간 상수를 측정하면 유체들의 대류 열전달 성능 비교가 가능할 것이다. 본 논문의 전반부에서는 장치의 관련 이론과 실험 장치 제작을 설명하였고 열전달 물성이 잘 알려진 글리세린과 엔진오일에 대한 실험 결과를 비교하였다. 논문의 후반부에는 순수 및 나노 엔진오일에 대한 대류 열전달 실험 결과를 비교하여 예시하였다.

A review on nanofluid: preparation, stability, thermophysical properties, heat transfer characteristics and application

Nanofluid is a suspension of nanoparticles which is promising heat transfer fluid in the heat transfer enhancement having a plethora of applications because of its superior thermal conductivity and rheological properties. This paper points out the previous studies and recent progress in the improvement of heat transfer using nanofluid. The recent progresses on preparation and enhancement of stability were reviewed. Thermophysical, heat transfer characteristics of nanofluid and different factors such as particle size, shape, surfactant, temperature, etc. on thermal conductivity were presented. The present study reveals potential applications by utilizing nanofluid such as heat exchanger, transportation cooling, refrigeration, electronic equipment cooling, transformer oil, industrial cooling, nuclear system, machining operation, solar energy and desalination, defense, etc. Few barriers and challenges were also addressed. Finally, the challenges and further research opportunities were presented.

Impact of magnetohydrodynamic and buoyancy‐driven forces on carbon nanotube‐water nanofluid

Present analysis brings out the study of an electrically conducting carbon nanotube (CNT) water‐based nanofluid flow occurrences with the existence of buoyant forces. Inclusion of the impact of thermal radiation in the energy balance also enhances the heat transfer characteristics of nanofluid. Due to considerable interest in the conductivity of CNT's and practical applications in industries, its study plays an important role. Closed form solution does not hold good for the nonlinear coupled system into nonlinear ODE. For the solutions, we have employed a semianalytical technique baptized Adomian Decomposition Method (ADM) with suitable guess solutions using initial conditions. The influence of physical restrictions describing the flow behavior is presented through figures. The outcomes of numerical validation for the rate of heat, shear stress, and mass transfer coefficients are also presented in tabular form. The physical phenomena of these parameters are also discussed in the discussion section for stretching surfaces. It is observed that the CNT nanoparticle volume fraction is favorable to enhance the fluid temperature, and more importantly, in comparison to pure fluid, CNT‐water nanofluid retards the velocity greatly which is an important phenomenon for the production of materials in industries.

An investigation on the heat transfer characteristics of nanofluids in flow boiling by molecular dynamics simulations

Molecular dynamics simulation is employed to investigate the heat transfer characteristics of nanofluids in flow boiling. A nanofluids model consisting of both suspended and deposited nanoparticles is established to investigate the mechanisms of nanoparticles in improving the heat transfer of flow boiling. The effects of driving force (i.e. flow velocity) and heating temperature on the heat transfer of flow boiling are analyzed. Results show that both flow velocity and heating temperature have an effect on the heat transfer of flow boiling at lower heating temperature. While with an increase in the heating temperature, the heat flux depends on the higher heating temperature extensively. Furthermore, compared with the base fluid, the heat transfer is enhanced by nanofluids, and the enhancement ratio in flow boiling (F≠0) is higher than that in pool boiling (F=0). A higher frequency of bubble nucleation in nanofluids enhances the thermal convection at the near-surface region. Moreover, the surface wettability is improved by the deposited nanoparticles to increase the efficiency of heat transfer between the surface and the liquid. For suspended nanoparticles, their translational and rotational motions in flow boiling are much stronger than those in pool boiling, which can further enhance the heat transfer of nanofluids.

Turbulent thermal convection of nanofluids in cubical enclosure using two-phase mixture model

In this paper, numerical simulation is performed to investigate the turbulent thermal convection flow and heat transfer characteristics of nanofluids inside a cubical enclosure with partially mounted heat and cold source. A transient, three-dimensional, two-phase mixture model with LamBremhorst k−ϵ turbulence model is developed, validated and solved using finite difference method. The heat transfer performance of different water based nanofluids such as aluminum oxide (Al2O3), copper (Cu) and silver (Ag) are investigated for a wide range of Grashof numbers (Gr) varying between 106 ≤ Gr ≤ 1010. The nanoparticle diameter (dp) and volume fractions (ϕ) are varied between 20nm ≤ dp ≤ 80nm and 2% ≤ ϕ ≤ 4%. The results indicate that the random Brownian motion of nanoparticles increases the thermal convection and enhances the rate of energy exchange between the fluid and particle phase. The average heat transfer rate increases with increase in Grashof number and volume fraction. It is found that the effect of volume fraction on average heat transfer rate is more effective in transitional flows than fully turbulent flows. The average heat transfer rate increases with decrease in particle size and the influence of nanoparticle size on heat transfer enhancement are significant in turbulent flows than transitional flows.

Thermal Conductivity of Nanofluids-A Comprehensive Review

The present study deals with a comprehensive review on the enhancement of effective thermal conductivity of nanofluids. The present article summarizes the recent research developments regarding the theoretical and experimental investigations about thermal conductivity of different nanofluids. The current study analyzes several factors those strongly affecting thermal conductivity of nanofluids include solid volume fraction, temperature, particle size, particle type, particle shape, different base fluids, magnetic field, pH, surfactant and ultrasonic time. In addition, different reasonably attractive models contributing augmentation of thermal conductivity of nanofluids are invoked. Finally, important heat transfer mechanisms namely Brownian motion, nanoclustering, thermophoresis, osmophoresis and interfacial nano-layer responsible for significant role in ameliorating the thermal conductivity and therefore the heat transfer characteristics of nanofluids are discussed.

Investigation on heat transfer characteristics of nano titania added transformer oil with hotspot temperature

The heat transfer characteristics of nanofluid produced by mixing nano titania with transformer oil, facilitated by addition of surfactants are analyzed. A 2D model is used to analyze the heat transfer and fluid flow characteristics of nano fluid for understanding the formation of hot spots in the chamber filled with nanofluid. Governing equations for conservation of mass, momentum and energy for capturing the above characteristics are described. The temperature along the vertical mid line from the hot spot are measured experimentally and compared with simulation results. Temperature distribution obtained for nanofluid and transformer oil under both steady and transient state has revealed high rate of heat dissipation in nanofluid. Streamlines have shown the presence of press board affects flow in the bulk of the cavity. Nusselt number estimated across the edges of the hot spot has shown higher convective heat transfer in nanofluid.

Experimental investigation on the heat transfer performance of MHTHS using ethylene glycol-based nanofluids

Experimental investigation on the heat transfer characteristics of the nanofluids passing through mini hexagonal tube heat sink (MHTHS) was accomplished. Al2O3–EG, CuO–EG, and SiO2–EG nanofluids with volume fraction ranging from 0.01 to 0.04% were chosen in the present study. The dispersion of nanoparticles in ethylene glycol (EG) was used as the working fluids. The volume flow rate of nanofluids flow through the hexagonal tube side was varied from 15 to 50 L h−1, and the hot deionized water in mini passage side was kept constant at a volume flow rate of 30 L h−1. The heat transfer characteristics of nanofluids were studied with the concentration of nanoparticles in base fluid and effect of Reynolds number. The heat transfer coefficient of MHTHS was measured under fully developed laminar and turbulent flow conditions. Based on the experimental data, it was observed that thermal conductivity, heat transfer coefficient, and Nusselt number of CuO–EG nanofluid were found to be higher when compared to other two nanofluids. The thermal conductivity of nanofluids was enhanced with an increase in concentration of nanoparticles in EG. The enhancement in heat transfer coefficient of nanofluid was achieved at higher turbulence in turbulent flow. It was due to stable dispersion of nanoparticles in EG. Therefore, the enhancement in heat transfer coefficient was found to be 36%, 32%, and 22% for CuO–EG, Al2O3–EG, and SiO2–EG nanofluid, respectively, at the concentration of 0.04 vol%. At higher Reynolds number, the agglomeration of nanoparticles decreases. Hence, it caused a decrease in boundary layer thickness which leads to an increase in the heat transfer-enhanced Nusselt number. The friction factor of SiO2–EG nanofluid was found to be lower in turbulent flow regime, and furthermore, it had no substantial effect in laminar flow regime.

Single-phase fluid flow and heat transfer characteristics of nanofluid in a circular microchannel: Development of flow and heat transfer correlations

The convective heat transfer in microchannels with the use of nanofluids has proved to be a potential candidate for cooling of micro-electromechanical system devices. The current research article presents the experimental study on fluid flow and heat transfer characteristics of [Formula: see text]/water nanofluid in a microchannel under thermally developing laminar flow at Reynolds number ranging from 300 to 1000. The experimental set-up of a circular microchannel test section with an inner diameter of [Formula: see text] and length of [Formula: see text] is fabricated to conduct the experimental study. The effect of nanoparticle concentration ([Formula: see text]), Reynolds number ([Formula: see text]) on fluid flow and heat transfer characteristics of [Formula: see text]/water nanofluid have been measured and compared with that of distilled water (DW). The results indicate that the maximum enhancement in local heat transfer coefficient is achieved up to [Formula: see text], while friction factor is achieved up to [Formula: see text] for [Formula: see text]/water nanofluid with nanoparticle concentration of [Formula: see text] as compared to DW. The results showed that the performance evaluation criterion of [Formula: see text]/water nanofluid is greater than unity ([Formula: see text]), implying the benefits of nanofluids as compared to DW. Moreover, the predicted data obtained by the present proposed correlations for friction factor and local Nusselt number using [Formula: see text]/water nanofluid show reasonably good agreement with the deviations of [Formula: see text] and [Formula: see text], respectively, with the numerical data as compared to the predicted data obtained by the existing correlations available in the literature.

Natural Convection of Nanofluid in a Triangle Cavity with Different Angular Positions

The effects of the angular position on the flow and heat transfer of the nanofluid in a triangular cavity is investigated numerically. A triangular cavity is chosen with the same boundary conditions as the published results are available. The comparison between the current numerical results with the available data is made to show the accuracy of the numerical simulation. The current structure of triangular cavity is rotated to investigate the effects of various angular positions on the flow and heat transfer characteristics of nanofluid. For this purpose, the equations of continuity, momentum and energy are solved numerically. The results show that the hot fluid is more freely penetrated into the domain by increasing of the angular position. The velocity of fluid in the flow field becomes maximum for the angle of 120 . Also, the creation of vortices in the flow field depends on the value of angular position.