• Journal of Advanced Marine Engineering and Technology
• /
• v.38 no.10
• /
• pp.1200-1205
• /
• 2014

The effect of nanofluids on the heat transfer performance of a pulsating heat pipe has been experimentally investigated. Water-based diamond nanofluid and aluminium oxide ($Al_2O_3$) nanofluid were tested in the concentration range of 0.5-5%. The pulsating heat pipe was constructed using clear Pyrex tubes of 1.85 mm in inner diameter in order to visualize the pulsating action. The total number of turns was eight each for heated and cooled parts. The supply temperatures of heating water and cooling water were fixed at $80^{\circ}C$ and $25^{\circ}C$ respectively. The liquid charging ratio of the nanofluid was 50-70%. The test results showed that the case of 5% concentration of diamond nanofluid showed 18% increase in heat transfer rate compared to pure water. The case of 0.5% concentration of $Al_2O_3$ nanofluid showed 24% increase in heat transfer rate compared to pure water. But the increase of $Al_2O_3$ nanofluid concentration up to 3% did not show further enhancement in heat transfer. It is also observed that the deposited nanoparticles on the tube wall played a major role in enhanced evaporation of working fluid and this could be the reason for the enhancement of heat transfer by a nanofluid, not the enhanced thermal conductivity of the nanofluid.

• Journal of ILASS-Korea
• /
• v.21 no.4
• /
• pp.177-183
• /
• 2016

In this study, the evaporation characteristics of water or nanofluid droplets on a heated surface was investigated by visualization of the evaporation process and evaluation of the heat transfer coefficient using the droplet temperature measured. The evaporation characteristics was compared between water and nanofluid droplets and the effects of the mass ratio of nanofluid and the inclination of heated surface were analyzed. The heat transfer rate of nanofluid droplet was higher than that of water droplet. The heat transfer coefficient was increased with the increase of the mass ratio of nanofluid. The effect of the inclination of heated surface was much higher than that of fluid type used, which indicates that the inclination of heated surface should be considered as one of influential parameters in the spray cooling process.

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

• Journal of ILASS-Korea
• /
• v.20 no.1
• /
• pp.7-13
• /
• 2015

In this study, the behavior of water or nanofluid droplets impacting upon a hot surface was investigated by visualization of impacting phenomena with time-delayed photographic technique. Changing the mass ratio of nanofluid and the temperature of the heated surface, the characteristics of the spreading behavior and the diameter of spreading liquid film was compared between water and nanofluid droplets. The impacting droplet spreaded as a liquid film after impact and nanofluid droplets spreaded more widely than water droplets. After reaching the maximum diameter, water droplets shrinked more than nanofluid droplets. Based on this, the heat transfer area from a hot surface to impacting nanofluid droplets would be wider than that of impacting water droplets. Considering individual impacting droplet only, spray cooling using nanofluid would be better than using water.

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

• Journal of Advanced Marine Engineering and Technology
• /
• v.32 no.6
• /
• pp.862-868
• /
• 2008

Many studies have been conducted to increase heat transfer in fluid. One of the various heat transfer enhancement techniques is suspending fine metallic or nonmetallic solid powder in traditional fluid. Nanofluid is defined as a new kind of heat transfer fluid containing a very small quantity of nanometer particles that are uniformly and stably suspended in a liquid. This study investigates the effect of nanofluid containing diamond, CuNi and CuAg nanometer particles, and proposes the heat transport mechanism of nanofluid. The test result shows that the thermal conductivity of nanofluid is much higher than that of traditional fluid, and the increasing rate of the conductivity is dependent on the conductivity of the solid metal.

• 한국태양에너지학회:학술대회논문집
• /
• 2012.03a
• /
• pp.188-193
• /
• 2012

Recently, the nanofluid which is stably dispersing or suspending of nanoparticles in the conventional heat transfer fluids (HTF) such as water and ethylene glycol has attracted significant interests as a solar thermal energy absorbing medium because they have excellent absorption and thermophysical properties compared to the typical HTF. In the present study, the efficiency of nanofluid-based flat-plate solar collector is analytically evaluated using the theoretical model of energy balance equation. The theoretical model considers the incoming solar radiation as a volumetric heat generation and the water-based single wall carbon nanohorn(SWCNH) nanofluid is used as a solar energy absorbing medium. Finally, the efficiency of nanofluid-based collector is calculated according to the volume fraction of SWCNH using the analytical solution.

• Journal of ILASS-Korea
• /
• v.20 no.4
• /
• pp.236-240
• /
• 2015

This study aims to experimentally investigate the evaporation characteristics of nanofluid droplet on heated surface at boiling temperature of DI-water. In particular, textured surface was used to examine the effect of wettability on evaporation. At the initial stage of evaporation process, dynamic contact angle (DCA) of nanofluid droplet with 0.01 vol.% concentration on textured surface rapidly increased over its equilibrium contact angle by generated large bubble inside the droplet due to lower wettability. However, contact angle of nanofluid droplet with higher concentration on textured surface decreased with surface tension. In addition, total evaporation time of droplet on textured surface was considerably delayed due to reduction of contact area between droplet and solid surface. Thus, evaporation characteristics were highly affected by the nanofluid concentration and surface wettability.

• Advances in Energy Research
• /
• v.8 no.3
• /
• pp.125-136
• /
• 2022

Entropy generation along with exergetic analysis is carried out using turbulent nanofluid flow in the heat exchanger. To obtain the optimized percentage constituent of nanofluid, the nanofluid volume concentrations is varied for the given input conditions. For different Reynolds number of the fluid and heat capacity rate ratio between the streams, the heat transfer improvements are studied in terms of nano particles diameter. Parametric analysis is carried out for a counterflow heat exchanger using turbulent nanofluid flow with exergetic efficiency along with entropy generation number as performance parameters. The exergetic efficiency provides realistic approach in the design of nanofluid applications in heat exchanger leading to conservation of energy.

• Korea-Australia Rheology Journal
• /
• v.19 no.3
• /
• pp.99-107
• /
• 2007

A nanofluid is a mixture of solid nanoparticles and a common base fluid. Nanofluids have shown great potential in improving the heat transfer properties of liquids. However, previous studies on the characteristics of nanofluids did not adequately explain the enhancement of heat transfer. This study examined the distribution of particles in a fluid and compared the mechanism for the enhancement of heat transfer in a nanofluid with that in a general microparticle suspension. A theoretical model was formulated with shear-induced particle migration, viscosity-induced particle migration, particle migration by Brownian motion, as well as the inertial migration of particles. The results of the simulation showed that there was no significant particle migration, with no change in particle concentration in the radial direction. A uniform particle concentration is very important in the heat transfer of a nanofluid. As the particle concentration and effective thermal conductivity at the wall region is lower than that of the bulk fluid, due to particle migration to the center of a microfluid, the addition of microparticles in a fluid does not affect the heat transfer properties of that fluid. However, in a nanofluid, particle migration to the center occurs quite slowly, and the particle migration flux is very small. Therefore, the effective thermal conductivity at the wall region increases with increasing addition of nanoparticles. This may be one reason why a nanofluid shows a good convective heat transfer performance.