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The purpose of this study is to determine the optimum design parameters of the heat exchanger with circular ring inserts and Al2O3/water nanofluid using Taguchi experimental design method. The basic principle of using nanofluid and circular ring inserts is to enhance the heat transfer characteristics of a heat exchanger, thus reducing the size and cost of it. The effects of the three design parameters, such as Reynolds number (Re), pitch to diameter ratio (p/d) of circular ring inserts, and volume concentration (ϕ) of nanofluid on heat transfer characteristics are investigated. In the Taguchi experimental design method, Nusselt number and friction factor are considered as performance parameters. An L9 orthogonal array is chosen as an experimental plan for the design parameters. The results are then analyzed by using ANOVA statistical tools. The optimum configurations of control factors for Nusselt number and friction factor are A3B3C3 and A3B1C2, respectively. The results also proved that the Taguchi experimental design method has been successfully applied in the study. Numerical and experimental results are in very good agreement with each other. [ABSTRACT FROM AUTHOR]

Abstract: Experimental investigations on thermophysical properties and forced convective heat transfer characteristics of various nanofluids are reviewed and the mechanisms proposed for the alteration in their values or characteristics due to the addition of nanoparticles are summarized in this review. A comprehensive review on the experimental works on specific application of nanofluids is also presented. As the literature in this area is spread over a span of two decades, this review could be useful for researchers to have an accurate screening of wide range of experimental investigations on thermophysical properties, forced convective heat transfer characteristics, the mechanisms involved and applications of various nanofluids. [Copyright &y& Elsevier]

Abstract: An experimental investigation on the convective heat transfer and friction factor characteristics in circular tube with spiraled rod inserts (pitch=15mm, 30mm) under turbulent flow with constant heat flux is carried out with distilled water and Al2O3/water nanofluids. For this purpose, Al2O3 nanoparticles were synthesized by using chemical precipitation method. The average size of particle is found to be 40.3nm. The nanoparticles are then dispersed in distilled water to form stable suspension of Al2O3/water nanofluids with 0.3, 0.4 and 0.5% volume concentration of nanoparticles. It is found that (i) heat transfer enhancement is caused by suspending nanoparticles and becomes more pronounced with the increase of the particle volume concentration (ii) the Nusselt number for spiraled rod inserts under turbulent flow showed an increase of about 10–48% compared to the Nusselt numbers obtained with plain tube (iii) the isothermal pressure drop for turbulent flow with spiraled rod inserts were found to be between 2 and 8% higher than the plain tube. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

Abstract: An experimental investigation on the convective heat transfer and friction factor characteristics in the plain and helically dimpled tube under turbulent flow with constant heat flux is presented in this work using CuO/water nanofluid as working fluid. The effects of the dimples and nanofluid on the Nusselt number and the friction factor are determined in a circular tube with a fully developed turbulent flow for the Reynolds number in the range between 2500 and 6000. The height of the dimple/protrusion was 0.6mm. The effect of the inclusion of nanoparticles on heat transfer enhancement, thermal conductivity, viscosity, and pressure loss in the turbulent flow region were investigated. The experiments were performed using helically dimpled tube with CuO/water nanofluid having 0.1%, 0.2% and 0.3% volume concentrations of nanoparticles as working fluid. The experimental results reveal that the use of nanofluids in a helically dimpled tube increases the heat transfer rate with negligible increase in friction factor compared to plain tube. The experimental results showed that the Nusselt number with dimpled tube and nanofluids under turbulent flow is about 19%, 27% and 39% (for 0.1%, 0.2% and 0.3% volume concentrations respectively) higher than the Nusselt number obtained with plain tube and water. The experimental results of isothermal pressure drop for turbulent flow showed that the dimpled tube friction factors were about 2–10% higher than the plain tube. The empirical correlations developed for Nusselt number and friction factor in terms of Reynolds number, pitch ratio and volume concentration fits with the experimental data within ±15%. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, fully developed laminar flow convective heat transfer and friction factor characteristics of Al2O3/water nanofluid flowing through a uniformly heated horizontal tube with and without wire coil inserts is presented. For this purpose, Al2O3 nanoparticles of 43nm size were synthesized, characterized and dispersed in distilled water to form stable suspension containing 0.1% volume concentration of nanoparticles. The Nusselt number in the fully developed region were measured and found to increase by 12.24% at Re=2275 for plain tube with nanofluid compared to distilled water. Two wire coil inserts made of stainless steel with pitch ratios 2 and 3 were used which increased the Nusselt numbers by 15.91% and 21.53% respectively at Re=2275 with nanofluid compared to distilled water. The better heat transfer performance of nanofluid with wire coil insert is attributed to the effects of dispersion or back-mixing which flattens the temperature distribution and make the temperature gradient between the fluid and wall steeper. The measured pressure loss with the use of nanofluids is almost equal to that of the distilled water. The empirical correlations developed for Nusselt number and friction factor in terms of Reynolds/Peclet number, pitch ratio and volume concentration fits with the experimental data within ±15%. [Copyright &y& Elsevier]

The present work analyzes the thermal performance of a cylindrical copper mesh wick heat pipe using water based CuO nanofluids. The studies are extended further by varying the heat pipe inclination angle and heat input. Thermophysical properties of CuO/DI water nanofluids are also effectively analyzed. The reduction in thermal resistance ratio is about 23.83% and 10.43% respectively for 1.0 and 1.5 wt.% of CuO nanofluid compared with low concentration. Evaporation and condensation heat transfer coefficient ratios are improved by the use of CuO nanofluid and the maximum enhancement obtained is 30.50% and 23.54% respectively for an optimum tilt angle of 60°. Thermal efficiency of heat pipe tends to increase with the heat load and inclination angle and an improvement of 33.34% is observed for 120 W heat load at 60° inclination angle compared with the horizontal heat pipe. After the experimentation, characterizations of mesh wick structures are carried out. It is found that the deposition of CuO nanoparticles creates a thin coating layer on the wick surfaces in evaporator section. This increases the surface wettability and enhances the thermal performance of heat pipe. [ABSTRACT FROM AUTHOR]

Abstract This paper reports the design and construction of a modified active solar distillation system (MSDS) and comparison of its performance parameters with that of a conventional solar still (CSS). MSDS consists of a solar still, a Fresnel lens concentrator with an evacuated receiver tube and a serpentine loop type heat exchanger. Al 2 O 3 –Therminol-55 nanofluid (nHTF) is used as the heat transfer fluid in the solar collector loop. Various performance parameters of MSDS and CSS such as saline water temperature, hourly yield and total yield have been compared under the ambient and solar conditions prevailing at Trichy. The experimental results indicate the hourly yield of MSDS with 0.1% nHTF is 45–250.27% more than CSS, and the total yield of MSDS with 0.1% nHTF is 12.190 L/m2 day compared to 3.48 L/m2 day for CSS. The daily efficiency of MSDS is found to vary with volumetric concentration of nanofluid, and maximum efficiency of 53.55% is obtained for 0.1% nHTF. Estimated cost for production of one litre-distilled water is approximately 1.54 INR for CSS and 1.41 INR for MSDS. MSDS developed in this study is found to be a better alternative to the CSS still due to its high productivity and cost-effectiveness. Highlights • Performance of the modified solar distillation system (MSDS) is evaluated experimentally. • Total freshwater yield enhanced by 250.27% for MSDS compared to conventional solar still. • The daily average efficiency of MSDS is found varying with the concentration of nano fluid. • MSDS can lead to better alternatives to replace the conventional solar still. [ABSTRACT FROM AUTHOR]

Nanofluids that directly absorb solar radiation have been proposed as an alternative to selectively coated metallic receivers in solar thermal collectors. Given the expense of characterising a potential nanofluid experimentally methods for comparing nanofluids virtually are needed. This paper develops a computational wave optics model using COMSOL to simulate the absorption of nanoparticles suspended in a fluid for solar radiation (380–800 nm) and compares it to experimental results using reflectance and transmission spectrometry. It was concluded that while both yielded data with matching trends, the exact absorption of some fluids differed by up to 1 AU. Optical characteristics of nanofluids comprising ethylene glycol (melting point −12.99 °C and boiling point range 195–198 °C at 1013 h Pa) and graphene oxide (sheets size 5 nm × 19 nm × 19 nm, volume fraction 0.004–0.016%) have been experimentally measured. An optimum volume fraction of 0.012% of graphene oxide has been identified achieving a minimum reflectance and highest absorbance over the visible spectral range. [ABSTRACT FROM AUTHOR]