Al2O3-water Nanofluid Research Articles

Optimization of corrugated-receiver solar collector's geometry using LBM analysis based on curved boundary scheme

BackgroundDue to growing demand of renewable energy for reducing the air pollution and costs, the optimization of the thermal systems using the renewable energy are attractive for the researchers. At this end, a parabolic trough solar collector, which converts the solar radiation to consumable heat energy for the daily use, is studied by numerical approach. This solar collector is consisted by a reflector gathering the solar radiation, corrugated solar receiver and inner tubes. MethodsThe lattice Boltzmann method (LBM) is utilized to solve the governing equations, and the curved boundary approach is taken into account to treat with the curved boundaries. With this combination, the accuracy and reliability of the results may be guaranteed. Using Koo-Kleinstreuer-Li (KKL) correlations, the Al2O3-water nanofluid's thermal/physical parameters, such as thermal conductivity and dynamic viscosity, are predicted before being inserted into the collector. Significant FindingsRayleigh number (103<Ra<106), nanoparticle concentration (0<φ<0.04), and receiver geometry were all examined variables. In addition, the main goal of the present work is to find an optimized geometry for the receiver of a solar collector. The hydrothermal efficiency and the second law analysis are the basis of the optimization.

Effect of Buoyancy Force on an Unsteady Thin Film Flow of Al2O3/Water Nanofluid over an Inclined Stretching Sheet

The present study looks at the heat transfer and the unsteady thin film flow of Al2O3 water nanofluid past an inclined stretching sheet having a buoyancy force effect. The boundary value problem solver (bvp4c) package in Matlab is utilized in solving the converted set of ordinary differential equations (ODEs). The multi-shape Al2O3 nanoparticles’ impact with respect to the flow as well as heat transfer characteristics are studied and visually displayed for certain governing parameter values, which include the mixed convection, inclination angle, magnetic, slip, and Biot number. Thus, the skin friction coefficient and the local Nusselt number are also determined. Here, the platelet shape of Al2O3 nanoparticles possesses a high heat transfer and flow rate based on the outcomes. In addition, increasing the slip and magnetic parameters improves the temperature, whereas increasing the buoyancy and inclination angle parameters has reverse effects. The results also show that increasing the unsteadiness parameter and the magnetic parameter reduces the film thickness.

Numerical Forced Convection Heat Transfer, Fluid Flow and Entropy Generation Analyses of Al2O3- Water Nanofluid in Elliptical Channels

This study investigates a three-dimensional elliptical microchannel heat sink for heat dissipation in laminar forced convection. The study seeks to improve thermal performance and overcome overheating associated with excessive temperature commonly experienced in heat-generating equipment, which is beyond the temperature usually specified by the manufacturer. The objective of the study is to evaluate the heat transfer, fluid flow, and entropy generation characteristics of Al2O3-water nanofluid in an elliptical cooling channel. The numerical analysis is investigated on the structure experiencing constant volumetric heat generation. The parameters considered are Reynolds number of 100 ≤ Re ≤ 500, nanoparticle concentration ϕ, from 0% to 4% with channel aspect ratio Ar from 1 to 3. The impacts of these parameters on the maximum temperature, heat transfer coefficient, friction factor, and volumetric entropy generation are reported. The study demonstrates that heat transfer is enhanced in the elliptical cooling channel at different aspect ratios, nanoparticle concentrations, and Reynold numbers. The results showed that as the nanoparticle concentration, channel aspect ratio, and Reynolds number (Re) increase, the maximum temperature, and total entropy generation decrease. As the channel aspect ratio increases at a specified Re = 200 and nanofluid concentration, ɸ = 3%, the maximum temperature, and total entropy generation decrease by up to 62% while the heat transfer coefficient increases by up to 78% and the friction factor increase by less than 2% with aspect ratio. However, the friction factor is not sensitive to the nanofluid concentration as a coolant.

A three stages transition into chaos for mixed convection nanofluid inside a differentially-heated square ventilated cavity

In this paper, we present a numerical study of an unsteady Al2O3 water nanofluid mixed convection in a differentially-heated square ventilated cavity. The routes from steady state to chaotic mixed convection state have been also studied for a constant Reynolds Number (Re), Re = 50 and Richardson number (Ri) ranging from Ri = 40 to Ri = 150. The governing equations are solved using an implicit finite-volume scheme and TDMA algorithm. Results are presented through streamlines, isotherms, mean temperature, average Nusselt number, pressure drop, etc. It is observed that the average Nusselt number and the mean cavity temperature values are all the higher as the Ri number is great. The pressure drop slightly decreases as Ri number increases. The fully chaotic flow regime is reached after three stages. The first stage is similar to the Ruelle-Takens-Newhouse scenario. At the end of this stage, apparition of periodicity interrupted the development of a full chaos initiating the second stage of the route to chaos where another series of three supercritical Hopf type bifurcations and a period doubling bifurcation takes place. The third stage starts by the emergence of intermittencies which interrupts the apparition of a full chaotic flow. A complete chaos is achieved at the end of this third stage.

Experimental Investigation of Al2O3 Nanofluid for Thermal Energy Management of Microchannel Heat Sink

Energy is one of the primary foundations supporting evolutionary changes. Heat transfer is improved by increasing the surface area density and/or changing the base fluid characteristics. Because of its small size and improved heat transfer properties, nanofluid cooled microchannel heat sinks (MCHS) have lately become a popular choice for electronics and thermal applications. The influence of employing nanofluids for cooling a chip was investigated experimentally in this work to evaluate the heat transfer characteristics. The investigations were carried out in order to confirm the influence of nanofluid concentration and wall temperature upon thermal-hydraulic properties of the microchannel heat sink. In present study, Al2O3 water nanofluid was employed, with 0.1, 0.2, 0.3, 0.4, and 0.5% nanoparticle volume fractions, mass flow rate (MFL) 2, 5, and 8 m/s at 25, 30 and 35oC inlet tempreture. The resulting experimental findings was verified from results obtained by other researchers, which showed important correlation. The heat transfer efficacy of electronics cooling systems has been enhanced by the nanofluid technology and the configuration of the rectangular heat sink.

Entropy Generation and Mixed Convection of a Nanofluid in a 3D Wave Tank with Rotating Inner Cylinder

The generation of entropy and mixed convection in a nanofluid-filled 3D wavy tank containing a rotating cylinder is investigated. The top wavy surface of the tank is heated and all vertical surfaces are assumed to be adiabatic, while the bottom horizontal surface remains isothermally cold. The tank contains a solid cylinder and is saturated with an Al2O3–water nanofluid. The numerical simulations using the FEM are performed for the Richardson number (0.01≤Ri≤100), nanoparticle volume fraction (0≤ϕ≤0.04) and number of oscillations (0≤N≤4). The numerical results of the present work are given in terms of 3D streamlines, isotherms and local entropy generation, as well as average heat transfer and Bejan number. The results show that for low values of the Richardson number and oscillation, heat transfer enhancement can be achieved by increasing the nanoparticle volume fraction.

Mixed convection in an open T-shaped cavity utilizing the effect of different inflow conditions with Al2O3-water nanofluid flow

Mixed convection in an open cavity has been growing into one of the most attractive topics of investigation for years, owing to its importance in many engineering applications. In this study, the effect of different inflow conditions on mixed convective flow inside an open cavity of T shape is investigated thoroughly to find the optimum condition for efficient heat transfer. Three different inlet conditions (uniform, Poiseuille, and Couette) have been considered, and a comparative study has been conducted to assess their performance of mixed convection heat transfer enhancement. Moreover, the presence of water-Al2O3 nanofluid over conventional fluid (water) to improve thermal performance is examined by varying solid volume fractions from 0 to 0.04. The Galerkin Weighted Residual based finite element analysis is used to resolve the current problem. Numerical solutions are obtained by varying Grashof number (Gr) from 0.1 to 104 and Reynolds number (Re) from 0 to 1000. Pure mixed convective heat transfer is also emphasized by keeping Richardson number (Ri) at unity while varying Gr and Re simultaneously. A profound effect for the uniform inflow condition has been observed on the rate of heat transfer inside the cavity with the variation of Gr and Re. In addition, the nanofluid increases the heat transfer performance, particularly at higher values of Grashof number (Gr > 103) at Ri = 1.

Magneto laminar mixed convection and entropy generation analyses of an impinging slot jet of Al2O3-water and Novec-649

In this study, the cooling capability and heat transfer characteristics in the mixed convective regime of a hot surface by a confined impinging slot jet in the presence of a uniform magnetic field have been investigated numerically. Besides, the second law of thermodynamics is applied to analyze the entropy generation inside the simulation medium. The simulations are for a two-dimensional slot jet that is directed vertically downward and impinges on a hot isothermal surface at the bottom. The set of non-dimensional governing equations is solved using ANSYS Fluent, which employs a finite volume approach in combination with a non-dimensionalization scheme. Flow patterns, isotherms, and entropy generation rates were calculated for various fluids (Air, Water, Novec-649, Al2O3-Water (3 %) nanofluid), that cover a wide range of Prandtl number values (Pr = 0.71–12.64), in the presence of a uniform magnetic field with Hartmann number values ranging from 0 (no magnetic field) to 100 (strong magnetic field). We prove that the Prandtl number plays a key role in determining heat transfer efficiency and entropy generation. Fluids with a high Pr number are more efficient for surface cooling, although they generate more entropy than low Pr fluids. Nanofluid with a high-volume fraction can be a better choice rather than air and water. On the other hand, we show that applying the magnetic field result in a very efficient method to reduce entropy generation although they degrade heat transfer efficiency. It is interesting that at a higher magnetic field, a high Prandtl number plays a better role. The percentage of reduction of Nuave by applying magnetic field is 28.5 % for air (Pr = 0.71), 45.2 % for water (Pr = 6.2), 43.4 % for Al2O3-water nanofluid (Pr = 4.91) and 48.3 % for Novec-649 (Pr = 12.64).We postulate that applying magnetic fields combined with high Pr number fluids, could provide an excellent balance between heat transfer efficiency and exergy destruction, thus providing efficient control options for thermal management and heat transfer.

IRREVERSIBILITY ANALYSIS IN Al2O3-WATER NANOFLUID FLOW WITH VARIABLE PROPERTY

The present numerical work deals with the optimization of the micro-channel heat sink using irreversibility analysis. The nanofluid of Al2O3-water with the different nanoparticles concentration and the temperature-dependent property is chosen as a coolant. The flow is considered as fully developed, steady, and laminar in the constant cross-section of circular channels. Navier-Stokes and energy equations are solved for a single-phase flow with total mass flow rate and heat flow rate as constant. The objective functions related to the frictional and heat transfer irreversibilities are framed to assess the performance of the micro-channel heat sink. The optimum channel diameter corresponding to the optimum number of channels is determined at the lowest total irreversibility for both constant property solution and variable property solution. Designed optimum diameter is observed maximum for 2.5% Al2O3-water nanofluid with μ(T) variation followed by 1% Al2O3-water nanofluid with μ(T) variation, 2.5% Al2O3-water nanofluid with constant property solution, and 1% Al2O3-water nanofluid with constant property solution.

Multi-Phase Nano Fluid Natural Convection in A Partially Divided Cavity for Cooling of Radioactive Waste Containers

The innovation of this investigation is fins arrangement effects on Al2O3-water Nano fluid natural convection in a partially divided cavity for energy storage systems and cooling of radioactive waste containers. Simulation of fluid velocity and temperature fields done based on the Lattice Boltzmann Model using the D2Q9 and D2Q5 methods, respectively. Streamline, isotherm, Nusselt number, velocity and temperature fields have been studied for different shapes of fins. In this investigation, we surveyed 4 shape of fins that arranged in three cases; case 1: yL=0.25 L, yR=0.75 L, case 2: yL=0.5 L, yR=0.5 L and Case 3: yL=0.75 L, yR=0.25 L. The results illustrated, assuming case 2: yL=0.5 L, yR=0.5 L is base case, so with changing arrangement of fins for case 1: yL=0.25 L, yR=0.75 L, rate percentage of average Nusselt number for cavities arranged with rectangular, circle, vertical and horizontal Ellipse fins were %26, %8, %4 and %8, respectively. Furthermore, with changing arrangement of fins to case 3: yL=0.75 L, yR=0.25 L, these percentages were %62, %24, %14 and %22.

A Review on Experimental and Numerical Investigations of Jet Impingement Cooling Performance with Nanofluids.

Nanofluids offer great potential heat transfer enhancement and provide better thermophysical properties than conventional heat transfer fluids. Application of nanofluids in jet impingement cooling is used for many industrial and scientific purposes as it manages to effectively remove high localized heat. Owing to its tremendous improvement of the heat transfer field, the use of nanofluids in jet impingement cooling has caught the attention of many researchers. This paper reviews previous research and recent advancements of nanofluid jet impingement via both experimental and numerical studies. In experimental approaches, Al2O3-water nanofluids are the most used working fluids by researchers, and most experiments were conducted with conventional impinging jets. As for the numerical approach, the single-phase model was the preferred model over the two-phase model in obtaining numerical solutions, due to the lower computational time required. A deep insight is provided into nanofluid preparation and methods for stabilization. Parameters affecting the performance of the jet impinging system are also investigated with comparison to numerous publications. The main parameters for jet impinging include the jet-to-plate distance (H/D), the shape of the impinged plate (curved, flat or concave), nozzle configurations and the twisted tape ratio. Studies on conventional impinging jets (CIJs), as well as swirling impinging jets (SIJs), are presented in this paper.

Turbulent convective heat transfer enhancement modeling of water-Al2O3 nanofluid using CFD mixture model and adaptive neural fuzzy inference system

ANFIS and multiphase Mixture model, two different methods from two very distinct engineering domains: Machine Intelligence and Computational Mechanics, have been put into a good amount of use over the past few years for modeling of nanofluids heat transfer enhancement. However, not only the previous investigations using both of these approaches suffer from the use of narrow range of nanofluid and flow properties, but also never have these two particular approaches been juxtaposed to point at a superior approach for specific flow regimes for predicting nanofluids heat transfer enhancement. In this study, water-Al2O3 nanofluid has been simulated using CFD multiphase Mixture model and ANFIS in order to assess the precision of both approaches to predict heat transfer enhancement of water-Al2O3 nanofluid for a very wide range of nanofluid configurations and flow properties, and to suggest the better approach for prediction of heat transfer enhancement for each specific flow regime. The results suggest that almost in every single case ANFIS is able to predict the heat transfer enhancement of nanofluids very efficiently with a maximum error of 0.35%, but the Mixture models’ predictions deviate significantly from the experimental correlation in some cases, though for intermediate nanofluid configurations, yielded results by Mixture model could be reliable with error around 1%.

The use of staggered grid in numerical solution of nanofluid convection within a rectangular chamber with semicircular fins and the use of artificial neural networks in optimizing dimensionless numbers

The present study investigates the mixed convection of the Al2O3-water nanofluid in a rectangular cavity using artificial intelligence (AI). The top wall of the cavity was cold and lid-driven, while the bottom wall and its five semicircular fins were at a high temperature. The two lateral walls were insulated. The cavity was under a magnetic field. The entropy production (ENP), Nusselt (Nu) number, and Bejan (Be) number were studied at Hartmann (Ha) numbers of 0–100, Richardson (Ri) numbers of 0.01–100, and Rayleigh (Ra) numbers of 103-106. Also, optimization was carried out to maximize the Nu and minimize the ENP and Be in the aforementioned ranges. The simulations were performed using the SIMPLE algorithm and finite volume method (FVM). Moreover, a staggered grid was employed for the simulation. It was found that a rise in the Ha increased the Nu and reduced the ENP. An increase in the Ri diminished the ENP and Nu and raised the Be. The Nu and ENP increased as the Ra increased, while the Be declined. A maximum Nu of 3.69 was obtained, while the minimum ENP and Be were 10.94 and 0.25, respectively, predicted with 89% desirability.

Structure optimization and cooling performance of a heat sink with discontinuous arc protrusions impacted by nanofluid confined slot jet impingement

PurposeThe purpose of this paper is to improve the overall heat transfer performance and the temperature uniformity of the heat sink and to explore the effects of the jet Reynolds number and the nanoparticle volume fraction of the nanofluids on the flow and heat transfer performance.Design/methodology/approachA heat sink with discontinuous arc protrusions in the wall jet region is proposed for confined slot jet impingement. A sloping upper cover plate is added to improve the heat transfer effect in this area. An Al2O3–water nanofluid is selected as the working fluid of the jet for better heat transfer. The Standard k-e turbulence model is used for numerical calculation. The key structural parameters of the heat sink are optimized by the response surface method and a genetic algorithm. The effects of the jet Reynolds number (Re) and the nanofluid concentration (ϕ) on the flow and heat transfer performance of the optimized heat sink are investigated.FindingsThe average Nusselt number of the optimal heat sink is 8.2% higher and the friction resistance is 5.9% lower than that of the initial flat plate heat sink when ϕ = 0.02 and Re = 8,000. The discontinuous arc protrusions and the sloping upper cover plate substantially enhance the heat transfer in the later stage of jet development, improving the temperature uniformity of the heat sink. The maximum temperature difference of the optimal heat sink is 28.1% lower than that of the flat plate heat sink at the same nozzle height. As the jet Reynolds number and the nanofluid particle concentration increase, the Nusselt number of the optimized heat sink and the friction coefficients increase, resulting in a decrease in the evaluation coefficient. However, the overall temperature uniformity of the heat sink is improved under all conditions.Originality/valueThe novel heat sink structure provides a new way to enhance the heat transfer and temperature uniformity of confined slot jet impingement. The flow and heat transfer performance of the heat sink impinged by confined slot jet of nanofluids are obtained. The combination of response surface method and genetic algorithm can be applied to the multi-objective optimization of heat resistance and flow resistance of heat sink.

BORU YÜZEYİNDEKİ KAPSÜL TİPİ KABARTMANIN VE AL2O3 SU NANOAKIŞKANIN ISI TRANSFERİNE ETKİSİNİN SAYISAL ANALİZİ

This study aims to numerically investigate and evaluate the enhancement of heat transfer by new capsule dimples on tube surfaces for flow of water and Al2O3-water nanofluid with different concentrations, under uniform surface heat flux. The originality of this work lies in combining two passive heat transfer enhancement methods such as geometrical improvements and nanofluids together. Capsule dimples with different depths were considered. Al2O3-water nanofluid was modeled as a single-phase flow based on the mixture properties. The effects of dimple depth and nanoparticle concentrations on Nusselt number, friction factor and performance evaluation criteria (PEC) were studied. Numerical computations were performed using ANSYS Fluent commercial software for 2000 14000 Reynolds number range. It was found that when laminar, transient and fully developed turbulent flow cases are considered, increase in the dimple depth increases the Nusselt number and friction factor for both pure water and Al2O3-water nanofluids cases. Also, the friction factor increases as dimple depth increases. Results show that increase in PEC is more pronounced in the laminar region than in the transition region, it starts to decrease for turbulent flows. For nanofluid, PEC values are considerably higher than pure water cases. The variation of PEC for capsule dimpled tubes are dependent on flow regimes and dimple depths. Increasing the nano particle volume concentration and dimple depth in laminar flows increase the PEC significantly.

The Thermal Performance Analysis of an Al2O3-Water Nanofluid Flow in a Composite Microchannel

Partial filling of porous medium insert in a channel alleviates the tremendous pressure drop associated with a porous medium saturated channel, and enhances heat transfer at an optimum fraction of porous medium filling. This study pioneered an investigation into the viscous dissipative forced convective heat transfer in a parallel-plate channel, partially occupied with a porous medium at the core, under local thermal non-equilibrium condition. Solving the thermal energy equation along the Darcy-Brinkman equation, new exact temperature fields and Nusselt number are presented under symmetrical isoflux thermal boundary condition. Noteworthy is the heat flux bifurcation at the interface between the clear fluid and porous medium driven by viscous dissipation, in cases where the combined hydrodynamic resistance to fluid flow and thermal resistance to fluid conduction is considerable in low Darcy number porous medium insert. However, viscous dissipation does not affect the qualitative variation of the Nusselt number with the fraction of porous medium filling. By using Al2O3-Water nanofluid as the working fluid in a uniformly heated microchannel, partially filled with an optimum volume fraction of porous medium, the heat transfer coefficient improves as compared to utilizing water. The accompanied viscous dissipation however has a more adverse impact on the heat transfer coefficient of nanofluids with an increasing Reynolds number.

Investigation of thermal performance and entropy generation in a helical heat exchanger with multiple rib profiles using Al2O3-water nanofluid

This research aims to assess the in detail thermal performance and entropy generation of a helical heat exchanger with multiple rib profiles and coil revolutions using water-based Al2O3 nanofluid with 5% concentration. A steady-state computational fluid dynamic model was used in determining the thermal and hydraulic parameters. The numerical model was validated with a numerical study and an experimental study. Three multiple rib profiles (2 rib, 3 rib and 4 rib) and three different coil revolutions (10, 20 and 30) were considered to design nine cases of heat helical exchangers. The geometrical effect was assessed and further represented as the streamlines, isotherms, overall Nusselt number, friction factor, thermal enhancement factor, and entropy generation. It is found that with the growth of coil revolutions the overall heat transfer rate and friction factor rise. The most efficient heat exchanger found in terms of thermal enhancement factor is 3 rib 10 revolutions with the value of 1.34. The entropy generation increases with the rise of the coil revolution. The maximum entropy generation increased by 19.5% for varying the coil revolution with a constant rib profile. Finally, this study is a guide of choosing an efficient heat transfer in terms of thermo-hydraulic performance.

Determination of the performance improvement of a PV/T hybrid system with a novel inner plate-finned collective cooling with Al2O3 nanofluid

ABSTRACT In order to increase module efficiency in photovoltaic systems, research on passive fin cooling or active fluid cooling applications continues. It was thought that a collective cooling, which is a combination of both applications, could be more effective on the increasing electrical efficiency and so the increase of the total efficiency of the PV/T system by increasing the thermal gain. In this study, the effects of the amounts of nanoparticles on the electrical and thermal performance of the Al2O3 nanofluid in a newly designed, manufactured system which is named collective cooling system with internal direct fins were investigated in detail. Nanofluid coolants were prepared with the use of Al2O3 nanoparticles at a mass ratio of 0.2%, 0.4% and 0.6% and they were used in the system at constant mass flow rates. The highest panel temperature drop was observed as 17.3 °C and corresponding power increase rate was observed as 6.11% in the panel with 0.4% Al2O3-water nanofluid at 12:00. The averages of daily power increase rates for 0.2%, 0.4%, 0.6% of Al2O3-water nanofluid cooling compared to the uncooled panel were 3.862%, 3.286%, 3.238% and 2.693% for the water-cooled panel, respectively. Compared to the water-cooled panel, the Al2O3-water nanofluid panel has average thermal efficiency increases of 39.77%, 28.92% and 15.92%, respectively, for 0.2%, 0.4%, and 0.6%.

Impact of Temperature and Nanoparticle Concentration on Turbulent Forced Convective Heat Transfer of Nanofluids

Theoretical analysis of the influence of nanoparticles and temperature on the average Nusselt (Nu) number and the average heat transfer coefficient (HTC) during the turbulent flow of nanofluid in a horizontal, round tube was carried out. The Nu number is a function of the Reynolds (Re) number and the Prandtl (Pr) number, which in turn are functions of the thermophysical properties of the liquid and the flow conditions. On the other hand, the thermophysical properties of nanoliquids are primarily a function of nanoparticle concentration (NPC) and temperature. Hence, the correct determination of the value of the Nu number, and then the HTC, which is needed for engineering calculations, depends on the accuracy of determining the thermophysical properties of nanofluids. In most cases, the thermophysical properties of the nanofluids are calculated as functions of the corresponding thermophysical properties of the base liquid. Therefore, the accuracy of the calculations of the thermophysical properties of nanofluids is equally determined by the reliable correlations for the base liquids. Therefore, new correlations for the calculation of the thermophysical properties of water have been developed. The results of calculations of the thermophysical properties of the base liquid (water) and the water-Al2O3 nanofluids by use of carefully selected correlations is presented. It was established that even for small concentrations of nanoparticles, a significant intensification of heat transfer using nanofluids as compared to the base liquid is obtained for the tested temperature range.

Heat transfer enhancement of nanofluid flow at the entry region of microtubes

A numerical investigation on laminar nanofluid flow and convective heat transfer at the entry region of microtubes subjected to constant wall temperature and constant heat flux boundary conditions has been carried out employing a multiphase Eulerian–Lagrangian method. The impacts of the Peclet number (175 ≤ Pe ≤ 3500), nanoparticle volume fraction (0.1 ≤ φ ≤ 1.0%), and nanoparticle diameter (40 ≤ dp ≤ 130 nm) on thermal characteristics of Al2O3-water nanofluid flow through a microtube are analyzed in detail. The results indicate that the influence of the Reynolds number on apparent friction factor and the impact of the axial heat conduction on the Nusselt number for the nanofluids have to take into account in the entry region. Compared with the influences of particle concentration and particle size, the entrance effect dominates pressure drop and thermal performance of the nanofluids near the entrance of the channel. As the dimensionless axial distance increases, the entrance effect is weakened, and the influences of particle concentration and particle size are gradually reflected in flow and heat transfer results. Besides, the particle effects on thermal performance of the nanofluids are earlier and higher than that on flow resistance. Performance evaluation demonstrates that the nanofluids in the entrance region have not only heat transfer enhancement but also a good economy. When Pe = 175, the PEC of Al2O3-water nanofluids with particle concentrations of 0.1, 0.2, 0.5, and 1% increased by 104.0, 103.1, 113.8, and 128.5% under constant heat flux condition, respectively, at the dimensionless axial distance x* = 0.01 compared with deionized water; the PEC improved by 74.6, 77.2, 85.6, and 102.5% under constant wall temperature condition compared with deionized water, respectively.