Experimental Study of Laminar Convective Heat Transfer and Pressure Drop of Cuprous Oxide/Water Nanofluid Inside a Circular Tube

Laminar convective heat transfer enhancement of cuprous oxide (Cu₂O)/water nanofluid flowing through a circular tube was investigated experimentally in the present work. A continuous closed loop was designed to measure heat transfer coefficients and pressure drop associated with the flow of Cu₂O/water nanofluid over a wide range of laminar flow conditions. Comparison of the nanofluid experimental results with those of pure water have shown significant enhancement for heat transfer coefficients. On average, a 10% increase in heat transfer coefficient was observed with 16% penalty in pressure drop.     

Convective Heat Transfer of a Cu/Water Nanofluid Flowing Through a Circular Tube

Abstract

Fluids in which nanometer-sized solid particles are suspended are called nanofluids. These fluids can be employed to increase the heat transfer rate in various applications. In this study, the convective heat transfer for Cu/water nanofluid through a circular tube was experimentally investigated. The flow was laminar, and constant wall temperature was used as thermal boundary condition. The Nusselt number of nanofluids for different nanoparticle concentrations, as well as various Peclet numbers, was obtained. Also, the rheological properties of the nanofluid for different volume fractions of nanoparticles were measured and compared with theoretical models. The results show that the heat transfer coefficient is enhanced by increasing the nanoparticle concentrations as well as the Peclet number.     

Heat Transfer and Pressure Drop Characteristics in Turbulent Flow Through a Tube

An experimental investigation has been carried out for turbulent flow through a tube with perforated strip inserts. Strips were of mild steels with circular holes of different diameters. Flow varies, with ranging Reynolds numbers from 15,000 to 47,000. Air velocity, tube wall temperatures, and pressure drops were measured for a plain and strip-inserted tube. The heat transfer coefficient and friction factor were found to be 2.80 times and 1.8 times, respectively, that of the plain tube. The heat transfer performance was evaluated and found to be 2.3 times that of the plain tube based on constant blower power.     

Comprehensive Study of the Effect of the Addition of Four Drag Reducing Macromolecules on the Pressure Drop and Heat Transfer Performance of Water in a Finned Tube Heat Exchanger

Abstract

In the present study the effects of the addition of four drag reducing agents (DRA), including carboxy methyl cellulose with high molecular weight (DRA1) and medium molecular weight (DRA2), polyacrylamide (DRA3) and the natural polymer, xanthan gum (DRA4), to water on the pressure drop and heat transfer performance in a finned tube-heat exchanger were compared. Laminar flow (Reynolds number (Re) <1400) was studied to transfer heat between water and air in the finned tube heat exchanger. The results showed that DRA1, with a maximum %DR of 26%, and DRA4, with a maximum %DR of 5%, were the highest and the lowest obtained results, respectively. In the case of heat transfer reduction percentage (%HTR), DRA4, having more than 34.5%, was the highest, and DRA1, with about 13.7%, was the lowest result for the concentration range of 0-100?ppm and temperature range of 40–65?°C.     

Heat Transfer and Pressure Drop of Nanofluid with Rod-like Particles in Turbulent Flows through a Curved Pipe

Pressure drop, heat transfer, and energy performance of ZnO/water nanofluid with rodlike particles flowing through a curved pipe are studied in the range of Reynolds number 5000 ≤ Re ≤ 30,000, particle volume concentration 0.1% ≤ Φ ≤ 5%, Schmidt number 10⁴ ≤ Sc ≤ 3 × 10⁵, particle aspect ratio 2 ≤ λ ≤ 14, and Dean number 5 × 10³ ≤ De ≤ 1.5 × 10⁴. The momentum and energy equations of nanofluid, together with the equation of particle number density for particles, are solved numerically. Some results are validated by comparing with the experimental results. The effect of Re, Φ, Sc, λ, and De on the friction factor f and Nusselt number Nu is analyzed. The results showed that the values of f are increased with increases in Φ, Sc, and De, and with decreases in Re and λ. The heat transfer performance is enhanced with increases in Re, Φ, λ, and De, and with decreases in Sc. The ratio of energy PEC for nanofluid to base fluid is increased with increases in Re, Φ, λ, and De, and with decreases in Sc. Finally, the formula of ratio of energy PEC for nanofluid to base fluid as a function of Re, Φ, Sc, λ, and De is derived based on the numerical data.     

Experimental Study of CuO/Water Nanofluid Turbulent Convective Heat Transfer in Square Cross-section Duct

Ducts with a square cross-section are widely used in many industrial applications because of their high compactness, easy forming, and low pressure drop. But the thermal performance of a duct will be reduced when the circular cross-sectional shape is not used. In this study, the convective heat transfer for a CuO/water nanofluid through a square cross-section duct in the turbulent flow regime has been investigated. The Nusselt number of nanofluids for different nanoparticle concentrations, as well as various Peclet numbers, was obtained. The results show considerable enhancement in the heat transfer coefficient and Nusselt number by increasing the nanoparticle concentrations as well as the Peclet number.     

含不同形状内热源的圆管内纳米流体自然对流及换热数值研究

采用格子玻尔兹曼方法对有三种恒温热源(圆形、三角形、方形)参与的圆管内纳米流体(铜-水)自然对流进行数值研究.主要研究瑞利(Ra)数,纳米颗粒体积分数以及热源几何形状等控制参数对纳米流体的流动与传热的影响.结果发现纳米颗粒体积分数的增加有利于强化传热,且在Ra数较小时,平均努塞尔(Nu)数增加的幅度要优于Ra数较大的情...     

The Effect of Heat Exchanger Type on Two-Phase Heat Transfer Coefficient and Pressure Drop

Three different types of heat exchangers were tested experimentally to investigate two-phase heat transfer coefficient and pressure drop during the condensation process of CO₂ gas. Experimental results revealed that the convection heat transfer coefficient was enhanced by a factor of four due to the existence of porous media and by a factor of seven due to the use of micro-pipes when compared to the normal macro-tubes. The pressure drop was measured and noticed only in porous tubes and micro-pipes, reaching about 17.5 kPa/m and 8.4 kPa/m, respectively. Comparisons between experimental and correlated results were conducted.     

Heat Transfer Characteristics in a Double-Pipe Heat Exchanger Equipped with Coiled Circular Wires

An experimental investigation has been carried out to study the enhancement in heat transfer coefficient by inserting coiled wire around the outer surface of the inner tube of the double-pipe heat exchanger. Insulated wires, with a circular cross-section of 2 mm diameter, forming a coil of different pitches (p = 6, 12, and 20 mm), were used as turbulators. The investigation is performed for turbulent water flow in a double-pipe heat exchanger with cold water in the annulus space for both parallel and counter flows. The experiments were performed for Reynolds numbers ranging from 4,000 to 14,000. The experimental results reveal that the use of coiled circular wires leads to a considerable increase in heat transfer coefficients compared with a smooth wall tube for both parallel and counter water flows. The mean Nusselt number increases with Reynolds number and pitch. The convective heat transfer coefficient for a turbulent water flow increases for all coiled wire pitches, with the highest enhancement of about 450% for counter flow and 400% for the parallel flow. New correlations for mean relative Nusselt numbers at different coiled wire pitches are provided.     

Laminar Heat Transfer Augmentation through A Square Duct and Circular Tube Fitted with Twisted Tapes

Experimental studies on friction factor and heat transfer characteristics for the laminar flow of ethylene glycol in a square duct fitted with twisted tapes of different twist ratios under nearly uniform wall temperature conditions are reported in this article. The Nusselt numbers were found to be 5.44–7.49 and 2.46–4.87 times that of plain square duct forced convection values based on constant flow rate and constant pumping power criteria, respectively, for y = 2.66. The augmented friction factor and Nusselt number for a square duct is about 1.9 and 2.10 times higher than that for an augmented circular tube.     

Experiments to Explore the Mechanisms of Heat Transfer in Nanocrystalline Alumina/Water Nanofluid under Laminar and Turbulent Flow Conditions

Abstract

Heat transfer characteristics of water-based nanocrystalline alumina (Al₂O₃) nanofluids flowing through a uniformly heated tube under a fully developed laminar and turbulent flow regime is investigated experimentally in the present work to explore the heat transfer mechanism in nanofluids. In a laminar flow, the increase in Nusselt number was attributed to the thermophysical properties of the nanofluid. The movement of nanoparticles, along with the turbulent eddies in the turbulent core region and diffusion mechanism, such as thermophoresis, in the laminar sublayer are believed to be the reasons for enhanced heat transfer in turbulent region. The compatibility of Al₂O₃/water nanofluids was also examined by monitoring its color.     

Heat Transfer in a Tube Fitted with Vertical and Horizontal Wing-Cut Twisted Tapes

This article reports an experimental investigation on the heat transfer, friction factor, and thermal enhancement factor of a tube equipped with vertical wing-cut twisted tapes, horizontal wing-cut twisted tapes, and plain twisted tapes with twist ratios of y = 2.0, 4.4, and 6.0. The obtained results reveal that the heat transfer rate, friction factor, and thermal enhancement factor in the tube equipped with horizontal wing-cut twisted tapes are significantly higher than those in the tube fitted with vertical wing-cut twisted tapes, plain twisted tapes, and a plain tube. An empirical correlation is subsequently derived from the experimental results.     

内置螺旋片的强化传热管的数值模拟研究

本文采用数值计算的方法,以水为流动介质,对内置螺旋片的强化传热管进行流动与传热特性的分析.结果表明,在管内插入螺旋片可以有效提高换热与流动的综合性能,雷诺数Re在300O～12000之间时,其PEC值在1.60～2.40之间.     

Experimental Investigation on Heat Transfer Characteristics of a Gas-to-Gas Counterflow Microchannel Heat Exchanger

Heat transfer characteristics of a gas-to-gas counterflow microchannel heat exchanger have been experimentally investigated. Temperatures and pressures at inlets and outlets of the heat exchanger have been measured to obtain heat transfer rates and pressure drops. The heat transfer and the pressure drop characteristics are discussed. Since the partition wall of the heat exchanger is thick compared with the microchannel dimensions, a simple heat exchange model with constant wall temperature is proposed to predict the heat transfer rate. The predicted heat transfer rate using the constant wall temperature model agrees well with the experimental results.     

Heat Transfer Characteristics for Condensation of R134a in a Vertical Smooth Tube

In this study, condensation of pure refrigerant R134a vapor inside a smooth vertical tube was experimentally investigated. The test section was made of a copper tube with inside diameter of 7.52 mm and length of 1 m. Experimental tests were conducted for mass fluxes in the range of 20–175 kg/m²s with saturation pressure ranging between 5.8 and 7 bar. The effects of mass flux, saturation pressure, and temperature difference between the refrigerant and tube inner wall (ΔT) on the heat transfer performance were analyzed through experimental data. Obtained results showed that average condensation heat transfer coefficient decreases with increasing saturation pressure or temperature difference (ΔT). In addition, for the same temperature difference (ΔT), heat can be removed from the refrigerant at a higher rate at relatively low pressure values. Under the same operating conditions, it was shown that average condensation heat transfer coefficient increases as mass flux increases. Finally, the most widely used heat transfer coefficient correlations for condensation inside smooth tubes were analyzed through the experimental data. The best fit was obtained with Akers et al.'s (1959) correlation with an absolute mean deviation of 22.6%.     

Experimental Investigation on Pressure Drop and Heat Transfer Characteristics of Copper Metal Foam Heat Sink

Abstract

The effect of the cooling performance of a copper metal foam heat sink under buoyancy-induced convection is investigated in this work. Experiments are conducted on copper metal foam of 61.3% porosity with 20 pores per inch. The pressure drop experiment is carried out to find the permeability and foam coefficient of the porous media. It is found that the property of porous media changes by changing the angle of inclination of the porous media from a horizontal to a vertical position while keeping the orientation and porosity the same. The Hazen-Dupuit Darcy model is used to curve-fit the longitudinal global pressure drop versus the average fluid speed data from an isothermal steady-flow experiment across the test section of the porous medium. The study concludes that the permeability and foam coefficient for copper foam is found to be 1.11 × 10^?7 m² and 79.9 m^?1, respectively. The heat transfer study shows that the thermal performance of copper metal foam is 35–40% higher than the conventional aluminum metal heat sink under an actual conventional mode.     

Subcooled Flow Boiling Heat Transfer to Water and Ethylene Glycol/Water Mixtures in a Bottom-heated Tube

Subcooled flow boiling heat transfer experiments were performed with water and ethylene glycol/water mixtures at five flow velocities and four fluid inlet temperatures. Both turbulent flow and laminar flow were tested in a special test facility with its experimental test section heated from the bottom surface only. Boiling curves and subcooled flow boiling heat transfer coefficients of the tested fluids were determined from the experimental measurements. Predictive correlations of the subcooled flow boiling heat transfer coefficients were developed based on the experimental data. Comparisons are presented of wall temperatures between the experimental measurements and the correlation predictions.     

超临界R134a水平圆管内冷却换热模拟研究

采用增强壁面函数的标准k-ε模型对超临界R134a水平圆管内冷却换热进行了模拟研究.分析了管内不同截面上流体温度、速度和湍动能的分布情况及对应关系。研究了质量流量和浮升力对换热系数的影响。结果表明,流体速度随着温度的降低而减小,并且最大速度处对应着最高温度和最小湍动能.换热系数随着质量流量的增加而增大,其峰值出现在准临界温度附近。浮升力在似液体区的影响较大,对流体换热起到增强的效果。     

水平圆管内磁性潜热型功能流体对流换热特性的数值模拟

建立磁场作用下水平圆管内磁性潜热型功能流体对流换热的数学物理模型,分析磁场强度、磁性相变微胶囊体积分数、流体质量流量等因素对流体对流换热的影响.磁场对磁性潜热型功能流体的对流换热具有显著的强化作用,磁场强度愈大强化作用愈明显,强化原因是磁性相变微胶囊受到磁力作用产生扰动.     

水蒸气在竖直微细管外凝结传热特性研究

针对不同压力和不同流速下的饱和水蒸气在竖直微细圆管(内外径分别为0.571 mm和0.793 mm)外的凝结传热特性分别进行了实验研究,分析了蒸气压力和蒸气流速对凝结传热特性的影响。实验结果表明,凝结传热表面传热系数随着蒸气流速的增加而增加,在较高的蒸气压力下增加的更明显,且大于相同实验条件下的Nusselt理论分析解。在蒸气流速为2 m·s~(-1)时,凝结传热系数随压力的变化不大;在4 m·s~(-1)和6 m·s~(-1)时,随着蒸气压力的升高,凝结表面传热系数明显增大。