Experimental investigation on surface tension of metal oxide-water nanofluids

"Nanofluids", smart fluids with advanced thermal properties, have proved their promising potential in enhancing the heat transfer performance of a thermal system as well as mitigating the energy crisis of the universe. Besides all other's thermo-physical properties, surface tension governs the transport of the liquid and plays a crucial role in the heat transfer. However, the studies on the effect of surface tension on the performance of nanofluids are quite a few and demonstrated debatable results. Therefore, the present experimental study attempts to determine the surface tension of the nanofluids by dispersing Al2O3, TiO2, and SiO2 nanoparticles in Distilled Water (DW). The experiment was conducted by using the most common Du-Hotly ring method in DCAT11EC automatic surface tensiometer. In this study, the authors analyzed all the possible effects on surface tension of nanofluids with the change in concentrations (from 0.05 to 025 vol.) and temperatures (from 30 degrees C to 50 degrees C), as well as the impact of various nanoparticles along with their sizes. The results indicate that the surface tension of the nanofluids increases with concentration, whereas decreases with the increase in temperature. Besides, the smaller nanoparticles exhibit lower surface tension than the larger ones. All in all, the surface tension of the nanofluids augments from 3.1 to 7.8 in compared with the base fluid for concentrations of 0.05 vol. to 0.25 vol. and temperatures of 30 degrees C to 50 degrees C, in all cases. (C) 2015 Elsevier Ltd. All rights reserved

Effect of Hump Configurations of Porous Square Cavity on Free Convection Heat Transfer

Free convection is widely used in engineering applications, including solar energy, electronic devices, nuclear energy, and heat exchangers. A computational simulation utilizing Ansys Fluent-CFD was employed to examine the natural convection heat transfer inside a square cavity filled with pure water and saturated metal foam as a porous medium (porosity ɛ =0.9). The enclosure's lower wavy wall exhibits a high temperature (Th), while the side and upper walls have a low temperature (Tc). For different Rayleigh numbers, the study examines hump configuration and the bottom wall hump number (N). The predominant design of heat transmission was improved using the circular hump design parameters of ɛ=0.9, N=4 and Tc= 25C˚ for different Ra. This resulted in significant improvements in heat transfer enhancement and energy enhancement which were enhanced by 1.13 times, for both. The authenticity research included determining the optimal design for the square enclosure. This involved estimating the effects of hump configure and number of humps for bottom wall of enclosure. These parameters have not been studied yet. The optimum case showed the highest heat transfer coefficient (h) at circular hump, N=4 and Ra = 30´103. While the standard case had N=0 and Ra = 5´103. The CFD simulation results indicate that the primary objective of the study was achieved through the optimal design, which resulted in a significant enhancement of hydrothermal performance for both heat transfer enhancement and energy enhancement 1.13 times compared to standard case

Energy, economic, and environmental analysis of a flat-plate solar collector operated with SiO2 nanofluid

To overcome the environmental impact and declining source of fossil fuels, renewable energy sources need to meet the increasing demand of energy. Solar thermal energy is clean and infinite, suitable to be a good replacement for fossil fuel. However, the current solar technology is still expensive and low in efficiency. One of the effective ways of increasing the efficiency of solar collector is to utilize high thermal conductivity fluid known as nanofluid. This research analyzes the impact on the performance, fluid flow, heat transfer, economic, and environment of a flat-plate solar thermal collector by using silicon dioxide nanofluid as absorbing medium. The analysis is based on different volume flow rates and varying nanoparticles volume fractions. The study has indicated that nanofluids containing small amount of nanoparticles have higher heat transfer coefficient and also higher energy and exergy efficiency than base fluids. The measured viscosity of nanofluids is higher than water but it gives negligible effect on pressure drop and pumping power. Using SiO2 nanofluid in solar collector could also save 280 MJ more embodied energy, offsetting 170 kg less CO2 emissions and having a faster payback period of 0.12 years compared to conventional water-based solar collectors

Heat Transfer and Pressure Drop Characteristics of Al2O3-R141b Nanorefrigerant in Horizontal Smooth Circular Tube

AbstractSince 1995, research has been going on in different aspects of nanofluids. Most of them are related to thermal conductivity and heat transfer properties of nanofluids based on water or ethylene glycol. Nanorefrigerants are one kind of promising nanofluids that based on refrigerants. Hear transfer and pressure drop characteristics of nanorefrigerants must be determined before putting into application. The objectives of this study are to determine the heat transfer and pressure drop characteristics of Al2O3-R141b nanorefrigerants for different volume concentrations. The experimental conditions include: constant mass flux of 100 kgm-2s-1, vapor qualities from 0.2 to 0.7, temperature at 25°C and 0.078535MPa pressure. Based on the analysis it was found that both heat transfer and pressure drop characteristics increased with the enhancement of nanoparticle volume concentrations. Therefore, an optimum concentration of nanoparticles with refrigerants (compromising the heat transfer performance and pressure drop characteristics) can improve the performance of a refrigeration system as to increase the energy efficiency and cooling capacity

Thermal Conductivity, Viscosity and Density of R141b Refrigerant based Nanofluid

AbstractNanofluids attract researchers in many ways for its enhanced heat transfer properties. Nanorefrigerant is one kind of nanofluids. It has better heat transfer performance than traditional refrigerants. Recently, some experiments have been done about nanorefrigerant, which are mostly related to heat transfer performance of these fluids. Thermal conductivity, viscosity and density are the basic thermophysical properties that must be analyzed before performance analysis. In this paper, the volumetric effects of thermal conductivity, viscosity and density of Al2O3/R141b nanorefrigerant have been studied for different temperature ranges. Based on the analysis about nanorefrigerant it is found that, thermal conductivity increases with the increase of volume concentrations and temperatures. However, viscosity and density increases accordingly with the enhancement of volume concentrations and decreases with the increase of temperature. As, heat transfer performances increases with the augmentation of thermal conductivity and pressure drop and pumping power increases with the enhancement of viscosity and density. Therefore, an optimum volume concentration of nanorefrigerant could improve the performance of a refrigeration system

Latest developments on the viscosity of nanofluids

The past decade has seen the rapid development of nanofluids science in many aspects. Number of research is conducted that is mostly focused on the thermal conductivity of these fluids. However, nanofluid viscosity also deserves the same attention as thermal conductivity. In this paper, different characteristics of viscosity of nanofluids including nanofluid preparation methods, temperature, particle size and shape, and volume fraction effects are thoroughly compiled and reviewed. Furthermore, a precise review on theoretical models/correlations of conventional models related to nanofluid viscosity is presented. The existing experimental results about the nanofluids viscosity show clearly that viscosity augmented accordingly with an increase of volume concentration and decreased with the temperature rise. However, there are some contradictory results on the effects of temperature on viscosity. Moreover, it is shown that particle size has some noteworthy effects over viscosity of nanofluids

Investigation of viscosity of R123-TIO 2 nanorefrigerant

Nanorefrigerant is one kind of nanofluids. It is the mixture of nanoparticles with refrigerants. It has better heat transfer performance than traditional refrigerants. Recently, some researches have been done about nanorefrigerants. Most of them are related to thermal conductivity of these fluids. Viscosity also deserves as much consideration as thermal conductivity. Pumping power and pressure drop depends on viscosity. In this paper, the volumetric and temperature effects over viscosity of R123-TiO 2 nanorefrigerants have been studied for 5 to 20°C temperature and up to 2 vol. . The effect of pressure drop with the increase of viscosity has also been investigated. Based on the analysis it is found that viscosity of nanorefrigerant increased accordingly with the increase of nanoparticle volume concentrations and decreases with the increment of temperature. Furthermore, pressure drop augmented significantly with the intensification of volume concentrations and vapor quality. Therefore, low volume concentrations of nanorefrigerant are suggested for better performance of a refrigeration system