• Title, Summary, Keyword: nanofluid

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Heat transfer enhancement of nanofluids in a pulsating heat pipe for heat dissipation of LED lighting

  • Kim, Hyoung-Tak;Bang, Kwang-Hyun
    • Journal of the Korean Society of Marine Engineering
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    • v.38 no.10
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    • pp.1200-1205
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    • 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.

A Study on the Behavior of Nano-fluid Droplet Impacting Upon a Hot Surface (고온벽과 충돌하는 나노유체 액적 거동에 관한 연구)

  • Kim, E.DD.;Park, I.H.;Bae, N.H.;Kang, B.S.
    • Journal of ILASS-Korea
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    • v.20 no.1
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    • pp.7-13
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    • 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.

A Study on the Evaporation Characteristics of Water or Nanofluid Droplets on a Heated Surface (물과 나노유체 액적의 고온 벽면에서의 증발 특성에 관한 연구)

  • Kim, J.H.;Lee, K.J.;Jung, S.W.;Kang, B.S.
    • Journal of ILASS-Korea
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    • v.21 no.4
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    • pp.177-183
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    • 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.

An experimental study and new correlations of viscosity of ethylene glycol-water based nanofluid at various temperatures and different solid concentrations

  • Bidgoli, Mahmood Rabani;Kolahchi, Reza;Karimi, Mohammad Saeed
    • 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.

Numerical Analysis on the Performance Improvement of Plate Heat Exchanger by Applying to CuO Nanofluid (CuO 나노유체를 적용한 판형열교환기 성능에 대한 수치해석적 연구)

  • Ham, Jeonggyun;Cho, Honghyun
    • Transactions of the Korea Society of Geothermal Energy Engineers
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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.

Heat Conductivity Test and Conduction Mechanism of Nanofluid (나노유체의 열전도율 실험과 열전달 메커니즘의 제시)

  • Park, Kweon-Ha;Lee, Jin-A;Kim, Hye-Min
    • Journal of the Korean Society of Marine Engineering
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    • v.32 no.6
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    • pp.862-868
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    • 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.

Characteristics for Nanofluid Droplet Evaporation on Heated Surface at Boiling Temperature of Base Liquid (비등점의 가열 표면에서 나노유체 액적의 증발 특성)

  • Kim, Dae Yun;Jung, Jung-Yeul;Lee, Seong Hyuk
    • Journal of ILASS-Korea
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    • v.20 no.4
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    • pp.236-240
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    • 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.

One-step Physical Method for Synthesis of Cu Nanofluid in Ethylene Glycol

  • Bac, L.H.;Yun, K.S.;Kim, J.S.;Kim, J.C.;Rhee, C.K.
    • Journal of Korean Powder Metallurgy Institute
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    • v.17 no.6
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    • pp.464-469
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    • 2010
  • The Cu nanofluid in ethylene glycol was prepared by electrical explosion of wire, a novel one-step method. The X-ray diffraction, field emission scanning electron microscope and transmission electron microscope were used to study the properties of Cu nanoparticles. The results showed that the nanoparticles were consisted of pure face-centered cubic structure and near spherical shape with average grain size of 65 nm. Ultraviolet-visible spectroscopy (UV-Vis) confirmed Cu nanoparticles with a single absorbance peak of Cu surface plasmon resonance band at 600 nm. The nanofluid was found to be stable due to high positive zeta potential value, +51 mV. The backscattering level of nanofluid in static stationary was decreased about 2% for 5 days. The thermal conductivity measurement showed that Cu-ethylene glycol nanofluid with low concentration of nanoparticles had higher thermal conductivity than based fluid. The enhancement of thermal conductivity of nanofluid at a volume fraction of 0.1% was approximately 5.2%.

Effect of particle migration on the heat transfer of nanofluid

  • Kang, Hyun-Uk;Kim, Wun-Gwi;Kim, Sung-Hyun
    • Korea-Australia Rheology Journal
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    • v.19 no.3
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    • pp.99-107
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    • 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.

Single Bubble Dynamic Behavior in AL2O3/H2O Nanofluid on Downward-Facing Heating Surface

  • Wang, Yun;Wu, Junmei
    • Nuclear Engineering and Technology
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    • v.48 no.4
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    • pp.915-924
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    • 2016
  • After a severe accident to the nuclear reactor, the in-vessel retention strategy is a key way to prevent the leakage of radioactive material. Nanofluid is a steady suspension used to improve heat-transfer characteristics of working fluids, formed by adding solid particles with diameters below 100nm to the base fluids, and its thermal physical properties and heat-transfer characteristics are much different from the conventional working fluids. Thus, nanofluids with appropriate nanoparticle type and volume concentration can enhance the heat-transfer process. In this study, the moving particle semi-implicit method-meshless advection using flow-directional local grid method is used to simulate the bubble growth, departure, and sliding on the downward-facing heating surface in pure water and nanofluid (1.0 vol.% $Al_2O_3/H_2O$) flow boiling processes; additionally, the bubble critical departure angle and sliding characteristics and their influence are also investigated. The results indicate that the bubble in nanofluid departs from the heating surface more easily and the critical departure inclined angle of nanofluid is greater than that of pure water. In addition, the influence of nanofluid on bubble sliding is not significant compared with pure water.