Maximum Heat Transfer Performance Research Articles

The flow and heat transfer behavior of synthetic jets with star shaped orifice of different lobes

In the present experimental investigation, the flow and heat transfer characteristics of synthetic jet (SJ) issuing from different lobed (3–10) star-shaped orifices are studied. Tests are performed by actuating the SJ actuator at constant input power of 4Vrms, with varied range of orifice to surface spacings (1–16) and numerous values of Reynolds number (8692–10746). The synthetic jet's flow characteristics are studied using hot-wire anemometry, while the thermal characteristics are analyzed using an IR camera. Distinct peaks in turbulence intensity are observed in major and minor planes for different lobed (3–6) star orifices; this may be due to the development of two shear layers in such orifices, which consequently merges into a single shear layer for higher lobed (8–10) star orifice. The 6-lobed star orifice is found to exhibit maximum heat transfer performance at z/d varying between 2 and 14. At z/d = 2, the 6-lobed star orifice exhibit 7.6% and 10.1% improvement in average Nusselt number compared to circular and 10-lobed star orifice respectively, which may be due to formation of vortical structures along the lobed edges and subsequent switching of axes between the major and minor planes. To comprehend the energy associated with the issuing vortices, the power spectral density of the velocity signal at the orifice exit is examined. A unified correlation for the average Nusselt number is also derived for various star-shaped orifices.

Numerical study on heat transfer characteristics of molten salt in a flat tube with circular helical wire

The combination of a new type of irregular-shaped helical wire and flat tube is used to further enhance heat transfer of molten salt for the first time due to the demands of efficient utilization of molten salt. The thermo-hydraulic performance of turbulent flow in a flat tube with irregular-shaped helical wire under constant wall temperature condition is investigated using Fluent software. The effects of helical pitch, wire diameter, gap width between the tube wall and helical wire, different fluids and inlet Reynolds number ranging from 1500 to 8500 are evaluated. It is found that adding irregular-shaped helical wire insert in flat tube can reduce greatly the lengths of flow and thermal entrance regions. The maximum heat transfer performance of flat tube with irregular-shaped helical wire is 400% that of smooth flat tube. The heat transfer performance increases with the wire diameter and decreases with the gap width and helical pitch. The maximum thermal performance factor with a value of 1.72 is observed based on a constant pumping power. Besides, the heat transfer performance of flat tube with irregular-shaped helical wire is 24.0%-40.2% larger than that of circular pipe with helical wire at low Reynolds number.

A study on thermal resistance evaluation of carbon nanotube buckypaper with cellulose material for thermal interface material

Multi-walled carbon nanotubes (MWCNTs), which has been studied as a heat conduction material, has excellent thermal properties, with thermal conductivity value of 3000 W/m·K. This study aims to reduce the thermal resistance of MWCNTs–buckypaper (BP) as a thermal interface material (TIM). Three methods are used in this experiment: ultrasonication, oxidation, and the addition of cellulose nanocrystal (CNC). The oxidation process is to remove impurities, which when prepared as a suspension, disturb the particle dispersion, and reveal a tendency to agglomerate. Therefore, a strong acid treatment removes impurities, and improves the dispersibility of nanofluids. The third method, the addition of CNC, which has been in the limelight recently, can affect structural stability, is eco-friendly, and is used for composite material synthesis with high tensile strength. These preeminent effects of CNC help improve the thermal resistance of CNC/treated CNT (C–tCNTs) mixed buckypaper. The thermal performances of TIMs used an ASTM D5470 standard tester, and various ratios of BP were tested using thermal resistance test. BP manufactured by adding MWCNTs and CNC had a resistance value of 0.776. This provided a 33.1 % decrease, compared to the oxidized MWCNTs BP. As a result, it was confirmed that CNC–CNTs BP has the possibility of being applied as TIM. • Cellulose nanocrystals, an eco-friendly material, are applied to carbon nanotubes. • It is made of paper-type buckypaper for use as a thermal interface material. • ASTM D5470 standard instrument is used for thermal resistance comparison. • It achieves maximum heat transfer performance at the optimum ratio.

Heat Transfer Performance Optimization of Rectangular Channel with Truncated-root Ribs

Cooling designs inside the gas turbine blades of aircraft engines are aimed to solve a problem that has existed since the very beginning of the aerospace industry. Since the working environment of turbine blades is extremely harsh when the temperature can rise to 2000K, which is considered a huge challenge for any materials. Therefore, cooling designs such as rib turbulators have always been researched and optimized for better heat transfer enhancement in the cooling mechanism of turbine blades. In this study, a geometric optimization of the rib turbulators inside a rectangular channel was performed with the aim to maximize heat transfer performance. This study investigated the effect of four rib configurations on the heat transfer efficiency of the channel, which include square, truncated-root, convergent truncated-root, and divergent truncated-root rib. Thereby, a module of coupling Python and OpenFOAM was developed to automatically perform the optimization of truncated-root rib design at Reynolds number of 37,000 with design variables are the upstream and downstream height with Powell optimization method. The aim is to figure out the point where the maximum heat transfer performance of the channel is achieved. The study presented in a specific, productive, and accurate way the factors that directly and indirectly affect the heat transfer performance of the channel, thereby giving the optimal results that the channel has the highest heat transfer performance of the presented designs. The results show that the highest heat transfer performance of the optimized design is 12.45% higher than the standard square ribs case.

Numerical Investigation of Heat Transfer Performance of Microchannel with Wall-Mounted Obstacles Using Hybrid Nanofluids

In the present study, the thermal performance of a microchannel with rectangular, triangular and circular shaped wall-mounted blocks on the top and bottom walls are studied numerically using hybrid nanofluids (Cu+Al/water, Cu+Al2O3/water, Ag+CuO/water, Ag+Al2O3/water) and ionic Nanofluid (Al2O3/[C4mim] [NTf2]). A constant Reynolds number equal to 10, volume fraction for first and second nanoparticle as 0.1 and 0.05 respectively, wall temperature of 27°C and coolant inlet temperature of 20°C are considered. The microchannel with triangular block showed maximum heat transfer performance. The Nusselt number of the microchannel with triangular blocks and nozzle at the inlet was enhanced by 145.76%. The maximum Nusselt number has been found for (Ag+Al2O3)/water hybrid nanofluid which is 13.8 %, 30 %, 37.12 % and 640 % greater as compared to (Ag+CuO)/water, (Cu+ Al2O3)/water, (Cu+ Al)/water and base fluid respectively. The microchannel with ionic nanofluid enhanced by 208 % as compared to water.

On the effect of elliptical pin Fins, distribution pin Fins, and tip clearance on the performance of heat sinks in flow boiling

Flow boiling in heat sinks has been rigorously exploited in the heat transfer community to achieve high heat removal rates for a variety of applications. In this regard, a higher cooling performance could be possible with surface modifications including the use of micro pin fins and tip clearance. The aim of this study is to reveal the effects of pin fins and tip clearance as well as distribution pin fins, which served for more uniform flow distribution, on flow boiling. For this, experiments were conducted on five different heat sinks including a reference configuration (plain channel) and different elliptical pin fin and tip clearance configurations at mass fluxes of 125kg/m2s, 225kg/m2s, and 325kg/m2s within the heat flux range of 18-175W/cm2 using de-ionized water as the working fluid. Experimental flow boiling heat transfer results and performances of each heat sink were presented with the help of flow visualization. Accordingly, the maximum heat transfer performance was achieved with a pin fin heat sink with distribution pin fins and no tip clearance on the heating area. It was also proven that streamlined pin fin configurations with uniform flow distribution are helpful in enhancing the heat transfer performance in flow boiling.

Guidelines for Designing Micropillar Structures for Enhanced Evaporative Heat Transfer

Abstract Over the last several decades, cooling technologies have been developed to address the growing thermal challenges associated with high-powered electronics. However, within the next several years, the heat generated by these devices is predicted to exceed 1 kW/cm2, and traditional methods, such as air cooling, are limited in their capacities to dissipate such high heat fluxes. In contrast, two-phase cooling methods, such as microdroplet evaporation, are very promising due to the large latent heat of vaporization associated with the phase change process. Previous studies have shown that nonaxisymmetric droplets have different evaporation characteristics than spherical droplets. The solid–liquid and liquid–vapor interfacial areas, volume, contact angle, and thickness of a droplet confined atop a micropillar are the primary parameters that influence evaporative heat transport. These parameters have a strong influence on both the conduction and diffusion resistance during the evaporation process. For example, a droplet with a higher liquid–vapor interfacial area will favorably increase heat transfer. Increased droplet thickness, on the other hand, has a detrimental influence on the evaporation rate. The dimensions of these droplets will vary in response to changes in each of the aforementioned parameters. Lowering the droplet thickness can be achieved by decreasing the liquid volume while maintaining a constant solid–liquid area. However, if the solid–liquid area and volume vary simultaneously, the average droplet thickness may increase, decrease, or remain constant. Furthermore, changes in the shape of the droplet modify the local equilibrium contact angle of the droplet for different azimuthal angles. As a result, the optimal combination of these parameters must be identified to maximize the heat transfer performance of an evaporating microdroplet. These droplet parameters can be manipulated by selecting different micropillar cross sections. In this work, we develop a shape optimization tool using the particle swarm optimization algorithm to maximize evaporation from a droplet confined atop a micropillar. The tool is used to optimize the shape of a nonaxisymmetric droplet. Compared to droplets atop circular and regular equilateral triangular micropillar structures, we find that droplets confined on pseudo-triangular micropillar structures have 23.7% and 5.7% higher heat transfer coefficients, respectively. The results of this work will advance the design of microstructures that support droplets with maximum heat transfer performance.

Experimental investigation of heat transfer performance of novel bio-extract doped mono and hybrid nanofluids in a radiator

The paper investigates the heat transfer performance of distilled water (DW) and ethylene glycol-DW mixture (EG-DW) based aluminum and magnesium sulfate nanofluids and their hybrid nanofluids in a radiator. Mono and hybrid nanofluids at 0.05% and 1% volume fractions with Malay Apple (Syzygium Malaccense) extract were formulated and run in the experimental set up at 0.4 kg/s. The heat transfer performances of DW, EG-DW, mono, and hybrid nanofluids were determined using Nusselt number (Nu), heat transfer rate (Q˙) and coefficient (h), effectiveness (ε), heat transfer (Q), Prandtl number (Pr). An increment in the volume fraction was found to enhance Q˙, h, Nu, Q, Pr, and ε. The maximum heat transfer performance was obtained using mono (Mg/DW (Q = 2.26 kW and Nu = 175), Al/EG-DW (Q = 6.57 kW and Nu = 462)) and hybrid (Mg–Al/DW (Q = 10.06 kW and Nu = 348)) nanofluids. In comparison with the corresponding base fluid, maximum heat transfer enhancements of 13.9%, 306.7%, and 493.9% were obtained for Mg/DW, Mg–Al/DW, and Al/EG-DW nanofluids, respectively. This remarkable heat transfer enhancement obtained can be related to the presence of the Malay Apple (Syzygium Malaccense) extract. These novel nanofluids appeared to be suitable candidates for radiator cooling.

Optimization of heat transfer and pressure drop of the channel flow with baffle

Abstract In this article, the numerical analysis has been carried out to optimize heat transfer and pressure drop in the horizontal channel in the presence of a rectangular baffle and constant temperature in two-dimension. For this aim, the governing differential equation has been solved by computational fluid dynamics software. The Reynolds numbers are in the range of 2,000 < Re < 10,000 and the working fluid is water. While the periodic boundary condition has been applied at the inlet, outlet, and the channel wall, axisymmetric boundary condition has been used for channel axis. For modeling and optimizing the turbulence, k–ω SST model and genetic algorithm have been applied, respectively. The results illustrate that adding a rectangular baffle to the channel enhances heat transfer and pressure drop. Hence, the heat transfer performance factor along with maximum heat transfer and minimum pressure drop has been investigated and the effective geometrical parameters have been introduced. As can be seen, there is an inverse relationship between baffle step and both heat transfer and pressure drop so that for p/d equal to 0.5, 1, and 1.25, the percentage of increase in Nusselt number is 141, 124, and 120% comparing to a simple channel and the increase in friction factor is 5.5, 5, and 4.25 times, respectively. The results of modeling confirm the increase in heat transfer performance and friction factor in the baffle with more height. For instance, when the Reynolds number and height are 5,000 and 3 mm, the Nusselt number and friction factor have been increased by 35% and 2.5 times, respectively. However, for baffle with 4 mm height, the increase in the Nusselt number and friction factor is 68% and 5.57 times, respectively. It is also demonstrated that by increasing Reynolds number, the maximum heat transfer performance has been decreased which is proportional to the increase in p/d and h/d. Moreover, the maximum heat transfer performance in 2,000 Reynolds number is 1.5 proportional to p/d of 0.61 and h/d of 0.36, while for 10,000 Reynolds number, its value is 1.19 in high p/d of 0.93 and h/d of 0.15. The approaches of the present study can be used for optimizing heat transfer performance where geometrical dimensions are not accessible or the rectangular baffle has been applied for heat transfer enhancement.

Enhancement of the critical heat flux of saturated pool boiling by the breathing phenomenon induced by lotus copper in combination with a grooved heat transfer surface

In this study, to improve the heat transfer performance of two-phase immersion cooling with saturated pool boiling using the “breathing phenomenon”, we evaluate the heat transfer performance of boiling surfaces composed of a lotus copper joined to a grooved surface of various groove sizes in water and FC-72. The critical heat flux is the highest 534 W/cm2 in the case of water using a 1.0-mm-square groove. The visualization experiments demonstrated that the breathing phenomenon is expected to be mode G, in which the vapor is mainly discharged through the grooves and the liquid is supplied from the top of the lotus copper. These experimental results verify that there is an optimal groove size to enhance the critical heat flux. In water, the maximum heat transfer coefficient is 126 kW/(m2•K). The maximum heat transfer performance of FC-72 is 104 W/cm2 for the 1.5-mm-square groove. The breathing phenomenon is considered to be mode L, in which the vapor is mainly discharged from the top of the lotus copper accompanied by the liquid supply through the grooves. These saturated pool boiling experiments and the visualizations verify that the present two-phase immersion cooling can enhance both the boiling heat transfer and the critical heat flux of water and FC-72.

Natural convection from a bottom heated of an asymmetrical U-shaped enclosure with nano-encapsulated phase change material

In the current study, free convection of a hybrid nanofluid in asymmetrical U-shaped enclosure is studied numerically. The bottom plate is heated and the top U-shaped walls is cooled, while the other walls are insulated. The cold basin moves along the horizontal centerline that measure the asymmetrically shape. The hybrid nanofluid is formed of a phase-change material (PCM) suspended in the water. The PCM utilize polyurethane as the protective case and nonadecane inside. The core absorb or release thermal energy in the shape of latent heat. The nanoparticle concentration, asymmetrical parameter, aspect ratio, fusion temperature and Rayleigh number have been investigated in detail. The results shows that the global heat transfer performance can be enhanced more than 9% by adding 1% nano-capsules volume fraction. Symmetry U-shaped does not give the maximum heat transfer performance and changing the basin location has small effect the heat transfer enhancement at moderate aspect ratio and fusion temperature.

An experimentation on gravity influence in concentric tube heat pipe heat exchanger using various working fluids

In present work the experimentation is carried out in the heat pipe introduce inside concentric-tube heat exchanger. Methanol, Acetone as working fluids, and water as heat transport fluid. The investigation is done by different mass flow rates and temperatures of the fluids. The effect of gravitational angles for 0° and 90° are experimented. The maximum heat transfer performance is obtained at angle is 0°. In this investigation for acetone as working fluid there is an increment of 30.42% for effectiveness, 2.5% for Reynolds number and 21.57% decrease in thermal resistance than with methanol. This experimentation clearly shows that heat pipe heat exchanger with acetone exhibits enhanced performance when related with methanol.

MHD convection flow of Ag–water nanofluid in inclined enclosure with center heater

ABSTRACT Simulations are performed to examine magnetohydrodynamic convection of an Ag–water nanofluid within an inclined enclosure containing a center heater oriented in different directions. In performing the analysis, the left and right vertical walls are assumed to be isothermally cooled, while the bottom wall is isothermally heated and the top wall is adiabatic. The governing equations are solved numerically using the finite-volume method. The simulations focus on the effects of the Rayleigh number (Ra = 104, 105 and 106), Hartmann number (Ha = 0, 25 and 50), inclination angle (γ = 0°, 45°, 90° and 135°), orientation of heater (horizontal or vertical) and internal heat generation (S = 0, 10 and 20) on the convective heat transfer performance within the enclosure. The results show that the heat transfer performance is dominated by the inclination angle of the enclosure and the Hartmann number. In particular, the heat transfer rate reduces as inclination angle and Hartmann number increase. The maximum heat transfer performance is obtained with a vertical center heater, an inclination angle of γ = 45° and a Rayleigh number of Ra = 106. It is additionally shown that the heat transfer performance improves with an increasing volume fraction of nanoparticles.

Fluid flow and heat transfer characteristics of microchannel heat sinks with different groove shapes

Microchannels are effective heat sinks for integrated electronic circuits. However, it remains unclear what form of channels will be most effective in improving the overall performance of microchannel heat sinks. The effect of channel geometry on overall performance was studied to understand the fluid flow and heat transfer characteristics of microchannel heat sinks having groove sidewalls. Five types of silicon-based microchannel heat sinks were designed, and the periodic grooves arranged on channel sidewalls were rectangular, triangular, trapezoidal, water-droplet, and semicircular in shape. A three-dimensional computational fluid dynamics model was developed, validated, and used to optimize the geometric structure. Comparisons were made between different groove shapes in order to determine the optimum structure. The results indicated that the overall performance can be greatly improved by arranging grooves on channel sidewalls. The significant improvement of overall performance can be achieved with all the groove shapes except rectangles. When the Reynolds number falls within the range from 194 to 610, triangles are the optimum groove structure in terms of the level of the maximum heat transfer performance improvement, but with a significant increase in pressure drop. Water-droplet shaped grooves offer many advantages and improvements that make them the preferred choice for the development of microchannel heat sinks. They offer significant advantages as an effective heat transfer enhancement structure at higher Reynolds numbers, and allow for the lowest pressure drop at lower Reynolds numbers due to the vortexes formed inside the grooves.

Impact of heat source on combined convection flow inside wavy-walled cavity filled with nanofluids via heatline concept

The appearance of a heat source at the bottom of a cavity against the cold part at the top wavy surface is examined in this work. The heat transportation, velocity of the fluid, and the temperature behaviour toward the mixed convection of nanofluids are obtained from the simulation of the Galerkin finite element technique and the Navier-Stokes equations. The other surfaces are considered adiabatic as well as both sides of the lid-driven cavity. It should be noted that the Grashof number, the volume fraction of alumina-nanoparticles, and the differentially-moving vertical walls are fixed at 105,0.02, the upward (right) and downward (left), respectively. To verify the computational code of derivation, the experimental and theoretical data from other researchers are compared. The results of the non-primitive variables, including the Richardson number, Reynolds number, number of undulations, dimensionless length, and the location of the heat source are compared. The numerical results indicate that larger values of the Richardson number and the Reynolds number enhance the rate of heat transfer. Not only two waves appear at the upper surface, but the heat source located at the centre with optimum height causes the entire cavity to have maximum heat transfer performance. The current problem is solved to benefit the installation of microelectronic cooling of a water-to-air heat exchanger or a pin-fin MHS heat transfer media.

Numerical prediction of dropwise condensation performances on hybrid hydrophobic-hydrophilic surfaces

The use of hybrid surfaces, alternating hydrophobic and hydrophilic (or less-hydrophobic) areas, has been recently proposed as a valuable tool for dropwise condensation performances enhancement. The hydrophilic region, in particular, is designed in order to promote the removal of the droplet from the hydrophobic region, reducing their average size and thus increasing the heat transfer performance. Here, dropwise condensation on heterogeneous surfaces composed by a texture of alternating hydrophobic and hydrophilic (or less-hydrophobic) vertical strips is numerically investigated through a Lagrangian-based phenomenological model, originally developed to study droplet evolution in the framework of in-flight icing phenomenon. The effects of droplet nucleation, growth, coalescence and motion are implemented. The model is extended to the case of curved surface. In order to properly assess the hybrid surface, however, a better knowledge of the interaction between the droplet and the film is required. Thus, additional numerical simulations are carried out using an in-house Eulerian full solver of the liquid film layer, in order to understand the migration mechanism of a drop between two different wettability regions. This will give useful information for a proper implementation of the effect of hydrophilic strips in the phenomenological Lagrangian model. A parametric analysis allows to find the optimal geometric configuration of the hybrid pattern, leading to maximum heat transfer performance, for a given set of wettability properties, nucleation density and condensation rate per unit area. Comparison with experimental data from the available literature ensures the capability of the current Lagrangian model to properly catch the physics behind dropwise condensation process on both planar and curved hybrid surfaces. The uncertainty of the estimate of some model input parameter and their influence on the computed solution are be also discussed.

Investigation of the thermal performance of a novel thermosyphon combined with fluidized bed heat transfer technology

In this paper, a novel method for enhancing the heat transfer performance of TPCT is proposed. And this novel method is to build a novel thermosyphon by introducing fluidized bed heat transfer technology into TPCT. The heat transfer performance of the novel thermosyphon is experimentally investigated. Results show that the heat transfer performance of the novel thermosyphon is significantly improved compared with the TPCT with pure water. In the domain of the filling volumes considered in the experimental work, the maximum heat transfer performance is obtained with filling volume ϕ = 40%, the amount of added particles εs = 10% and heating power QH = 1000 W, and the overall thermal resistance is reduced by 8.3%. The evaporation and condensation heat transfer coefficients are improved by up to 8.9% and 50.9%, and the corresponding optimal filling volume is 40% and 60% at εs = 10%, QH = 1000 W and εs = 5%, QH = 500 W, respectively.

MHD Heat Transfer in W-Shaped Inclined Cavity Containing a Porous Medium Saturated with Ag/Al2O3 Hybrid Nanofluid in the Presence of Uniform Heat Generation/Absorption

In this paper, a 2D numerical study of natural convection heat transfer in a W-shaped inclined enclosure with a variable aspect ratio was performed. The enclosure contained a porous medium saturated with Ag/Al2O3 hybrid nanofluid in the presence of uniform heat generation or absorption under the effect of a uniform magnetic field. The vertical walls of the enclosure were heated differentially; however, the top and bottom walls were kept insulated. The governing equations were solved with numerical simulation software COMSOL Multiphysics which is based on the finite element method. The results showed that the convection heat transfer was improved with the increase of the aspect ratio; the average Nusselt number reached a maximum for an aspect ratio (AR) = 0.7 and the effect of the inclination was practically negligible for an aspect ratio of AR = 0.7. The maximum heat transfer performance was obtained for an inclination of ω = 15 and the minimum is obtained for ω = 30 . The addition of composite nanoparticles ameliorated the convection heat transfer performance. This effect was proportional to the increase of Rayleigh and Darcy numbers, the aspect ratio and the fraction of Ag in the volumetric fraction of nanoparticles.

Numerical Study of the Heat Transfer Behavior in Helical Microcoil Tube

This work introduces a numerical study of the convective heat transfer of helical micro coils tube heat exchanger coil. It tested for both circle and elliptical geometry with 18 mm pitch and diameter of copper pipes. It is very difficult and time-consuming if these analyses could be carried out experimentally. Water is used as a working fluid by using 80°C for hot water and 25°C for cold water. The Reynolds number selected in the range of 200 to 1800 for hot water, while specified 5000 for cold water. ANSYS-FLUENT 18.0 has been used to investigate the heat transfer behavior. In computational fluid dynamics (CFD), the partial differential equations was represented by using the finite volume method (FVM) in the form of algebraic equations and the Navier-Stokes equations were solved by using a numerical procedure which is the Semi Implicit Method for Pressure-Linked Equations (SIMPLE) algorithm. The elementary results observed a proportionality relationship between the heat transfer and the Reynolds number raised values. Also, the circular configuration present maximum heat transfer performance and the maximum values are 5.6, 3.42 for Thermal performance factor and Nuselte number respectively at Reynolds number 1800.

Effects of Coil Pitch Spacing on Heat Transfer Performance of Nanofluid Turbulent Flow through Helical Microtube Heat Exchanger

This article provides Numerical simulation on forced convective heat transfer performance of Nanofluid flowing through copper helical microtube of inner diameter of 1.5 mm with different pitch using ANSYS-FLUENT 18.0. The simulation was performed for water, CuO/water, Al2O3/water Nanofluid with 1-2% volume concentration and different pitch of microtube (10, 14 and 18 mm) for turbulent flow regime of Reynolds number varied 5000 to 20000 and governing equations of mass, momentum and heat transfer were solved simultaneously, using the k-e two equations turbulence model. Based on the obtained results, regardless of the concentrations used, the nanofluids exhibited a higher transfer rate than water. This is mainly attributed to the nanoparticles that are in the used nanofluids. The friction factor and the heat transfer rate were enhanced considerably due to the shape and size of the tube, which in this case is a helical microtube. Moreover, the maximum heat transfer performance has been conducted by Al2O3/water Nanofluid with 2% volume concentration and microtube pitch of 18 mm.