• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.16 no.1
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• pp.9-16
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• 2020

In this study, a numerical study was conducted to evaluate the performance improvement when CuO nanofluid was used in the plate heat exchanger. As a result, the heat transfer amount is increased by 5.45% when 2 vol% CuO nanofluid is used. The influence on the CuO nanofluid on the performance of heat exchanger is decreased by increasing the flow rate of working fluid. In addition, the overall heat transfer coefficient using 2 vol% CuO nanofluid decreased compared to the base fluid. However, the pressure drop and the consumption of the pump power is increased as the concentration of CuO nanofluid increased because the increase of the viscosity. These are increased up to 15.4% compared to those of the base fluid. Moreover, the performance index of CuO nanofluid is decreased by 12.6% compared to that of the base fluid.

• International Journal of Fluid Machinery and Systems
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• v.9 no.4
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• pp.382-393
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• 2016

Flow over a bluff body is an attractive research field in thermal engineering. In the present study, laminar flow over a confined heated square cylinder using CuO-Water nanofluid is considered. Unsteady two-dimensional Navier-Stokes and energy equations are solved numerically using finite volume method (FVM). Recent correlations for the thermal conductivity and viscosity of nanofluids, which are function of nanoparticle volume fraction, temperature and nanoparticle diameter, have been employed. The results of numerical solution are obtained for Richardson number, nanoparticle volume fractions and nanoparticle diameters ranges of 0-1, 1-5% and 30-100 nm respectively for a fixed Reynolds number of Re = 150. At a given volume concentration, the investigations reveal that the decreasing in size of nanoparticles produces an increase in heat transfer rates from the square cylinder and a decrease in amplitude of the lift coefficient. Also, the increment of Nusselt number is more pronounced at higher concentrations and higher Richardson numbers.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.7
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• pp.647-653
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• 2013

The evaporation characteristics of nanofluid droplets on a heated solid surface were experimentally investigated. The experiments were conducted using pure water and a nanofluid of water mixed with CuO nanoparticles, and the solid surface was made of a copper block heated by a nine cartridge heater. The experimental results showed that the evaporation rate of the nanofluid droplet was higher than that of the pure water droplet on the heated solid surface because nanoparticles increased the thermal conductivity of the nanofluid. Furthermore, it was found that the evaporation rate of the nanofluid droplet increased with the solid surface roughness. This may be because the actual area of the liquid-solid interface increased with the solid surface roughness.

• Journal of Advanced Marine Engineering and Technology
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• v.34 no.1
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• pp.53-61
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• 2010

In the present study, a laminar natural convection flow of $H_2O$-Cu nanofluid in a two dimensional enclosure has been investigated using a thermal lattice Boltzmann approach with the Bhatnagar-Gross-Krook (BGK) model. The effect of suspended nanoparticles on the fluid flow and heat transfer process have been studied for different controlling parameters such as particle volume fraction ($\Phi$), Rayleigh number (Ra). For this investigation the Rayleigh number changes from 104 to 106 and volume fraction varied from 0 to 10% with three different particle diameters (dp), say 10 nm, 20 nm and 40 nm. It is shown that increasing the Rayleigh number (Ra) and the volume fraction of nanofluid causes an increase of the effective heat transfer rate in terms of average Nusselt number (Nu) as well as the thermal conductivity of nanofluid. On the other hand, increasing the particle diameter causes the decrease of the heat transfer rate and thermal conductivity. The result of the analysis are compared with experimental and numerical data both for pure and nanofluids and it is seen a relatively good agreement.

• Korea-Australia Rheology Journal
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• v.17 no.2
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• pp.35-40
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• 2005

Nanofluid is a novel heat transfer fluid prepared by dispersing nanometer-sized solid particles in traditional heat transfer fluid to increase thermal conductivity and heat transfer performance. In this research we have considered the rheological properties of nanofluids made of CuO particles of 10-30nm in length and ethylene glycol in conjunction with the thermal conductivity enhancement. When examined using TEM, individual CuO particles have the shape of prolate spheroid of the aspect ratio of 3 and most of the particles are under aggregated states even after sonication for a prolonged period. From the rheological property it has been found that the volume fraction at the dilute limit is 0.002, which is much smaller than the value based on the shape and size of individual particles due to aggregation of particles. At the semi-dilute regime, the zero shear viscosity follows the Doi-Edwards theory on rodlike particles. The thermal conductivity measurement shows that substantial enhancement in thermal conductivity with respect to particle concentration is attainable only when particle concentration is below the dilute limit.

• Structural Engineering and Mechanics
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• v.58 no.1
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• pp.93-102
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• 2016

This article presents an experimental study on the effect of temperature and solid volume fraction of nanoparticles on the dynamic viscosity for the CuO/EG-water nanofluid. Nanoparticles with diameter of 40 nm are used in the present study to prepare nanofluid by two-step method. A "Brookfield viscometer" has been used to measure the dynamic viscosity of nanofluid with solid volume fraction up to 2% at the temperature range between 20 to $60^{\circ}C$. The findings have shown that dynamic viscosity of nanofluid increases with increasing particle volume fraction and decreasing temperature. Nine different correlations are developed on experimental data point to predict the relative dynamic viscosity of nanofluid at different temperatures. To make sure of accuracy of the proposed correlations, margin of deviation is presented at the end of this study. The results show excellent agreement between experimental data and those obtained through the correlations.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.6
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• pp.559-566
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• 2013

The effects of solid surface roughness on the contact angle of a nanofluid droplet were experimentally investigated. The experiments were conducted using the solid surface of a 10 mm cubic copper block and the nanofluid of water mixed with CuO nanoparticles. The experimental results showed that the contact angles of nanofluid droplets were lower than those of water droplets and that the contact angle of the nanofluid droplet increased with the solid surface roughness. Furthermore, it was found that the contact angles of water droplets on the solid surface quenched by both water and the nanofluid were lower than those of water droplets on the pure solid surface. However, significant differences were not observed between the contact angles on the solid surfaces quenched by water and the nanofluid.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.474-478
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• 2008

It has been shown that a nanofluid consisting of nanoparticles dispersed in base fluid has much higher effective thermal conductivity than pure fluid. In this study, four kinds of nanofluids such as multiwalled carbon nanotube (MWCNT) in water, CuO in water, SiO2in water, and CuO in ethylene glycol, are produced. Their thermal conductivities are measured by a transient hot-wire method. The thermal conductivity of water-based MWCNT nanofluid is shown to be increased by up to 11.3% at a volume fraction of 0.01. The measured thermal conductivities of MWCNT nanofluids are higher than those calculated with Hamilton-Crosser's model due to neglecting solid-liquid interaction at the interface. The results show that the thermal conductivity enhancement of nanofluids depends on the thermal conductivities of both particles and the base fluid. Stability of nanofluids is estimated by UV-vis spectrum analysis. Stability of nanofluid depends on the type of base fluid and the suspended particles. Also it can be improved in addition of a surfactant.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.7
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• pp.599-607
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• 2015

In this study, we theoretically investigate the thermal performances of heat pipes that have different nano-fluid properties. Two different types of nano-particles have been used: $Al_2O_3$ and CuO. The thermal performances of the heat pipes are observed for varying nano-particle aggregations and volume fractions. Both the viscosity and the conductivity increase as the volume fraction and the aggregation increase, respectively. Increasing the volume fraction helps increase the capillary limit in the well-dispersed condition. Whereas, the capillary limit is decreased under the aggregate condition, when the volume fraction increases. The dependence of the heat pipe thermal resistance on the volume fraction, aggregation, and conductivity of the nano-particles is analyzed. The maximum thermal transfer of the heat pipe is highly dependent on the volume fraction because of the high permeability of the heat pipe. For the proposed heat pipe, the optimum volume fraction of the nano-particle can be seen through 3D graphics.

• Journal of computational fluids engineering
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• v.18 no.4
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• pp.25-34
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• 2013

A numerical study of a laminar natural convection of the CuO-water nanofluid in a square cavity using the Buongiorno's nonhomogeneous model is presented. All the governing equations including the volume fraction equation are discretized on a cell-centered, non-uniform grid employing the finite-volume method with a primitive variable formulation. Calculations are performed over a range of Rayleigh numbers and volume fractions of the nanopartile. From the computed results, it is shown that both the homogeneous and nonhomogeneous models predict the deterioration of the natural convection heat transfer well with an increase of the volume fraction of nanoparticle at the same Rayleigh number, which was observed in the previous experimental studies. It is also shown that the differences in the computed results of the average Nusselt number at the wall between the homogeneous and nonhomogeneous models are very small, and this indicates that the slip mechanism of the Brown diffusion and thermophoresis effects are negligible in the laminar natural convection of the nanofluid. The degradation of the heat transfer with an increase of the volume fraction of the nanoparticle in the natural convection of nanofluid is due to the increase of the viscosity and the decrease of the thermal expansion coefficient and the specific heat. It is clarified in the present study that the previous controversies between the numerical and experimental studies are owing to the different definitions of the Nusselt number.