Role of Particle Size to Channel Thickness Ratio on Performance of Nanofluids in Micro-Channels

2016 ◽  
Author(s):  
Sonya T. Smith ◽  
Mohsen Mosleh ◽  
Khosro A. Shirvani
Keyword(s):  
Thermal Conductivity ◽  
Particle Size ◽  
Reynold Number ◽  
Channel Height ◽  
Hydraulic Pressure ◽  
Conductivity Enhancement ◽  
Numerical Predictions ◽  
Design Variables ◽  
Micro Channels ◽  
Channel Thickness

Experimental and numerical investigations were conducted to explore the viability of single-phase nanofluids for microchannel cooling. The experiments were conducted with water/ethylene glycol-based nanofluids to investigate the thermal conductivity enhancement. In the numerical analysis, micro-channels ranged in width from 40 μm to 90 μm with the fixed channel height were considered. Thermal conductivity enhancements of nearly 14% at particle concentration of 0.1% by weight was observed in the experiments. Numerical predictions suggest that design variables (particle size and channel aspect ratio) and thermo-physical properties of the nanofluid have a significant effect on the thermal performance of micro-channel heat sinks. It was shown that at fixed Reynold number, reduction of channel width reduces the hydraulic pressure loss and the heat transfer coefficient, and utilizing nanofluids increases these parameters.

Experimental Studies of Adiabatic Flow Boiling in Fractal-Like Branching Micro-Channels

2008 ◽  
Author(s):  
Brian J. Daniels ◽  
James A. Liburdy ◽  
Deborah V. Pence
Keyword(s):  
Pressure Drop ◽  
Void Fraction ◽  
Flow Boiling ◽  
Experimental Studies ◽  
Channel Length ◽  
Channel Height ◽  
Channel Network ◽  
Adiabatic Flow ◽  
Numerical Predictions ◽  
Micro Channels

Experimental results of adiabatic boiling of water flowing through a fractal-like branching microchannel network are presented and compared to numerical simulations for identical flow conditions. The fractal-like branching channel network had channel length and width ratios between adjacent branching levels of 0.7071, a total flow length of 18 mm, a channel height of 150 μm and a terminal channel width of 100 μm. The channels were DRIE etched into a silicon disk and pyrex was anodically bonded to the silicon to form the channel top and allowed visualization of the flow within the channels. The water flowed from the center of the disk where the inlet was laser cut through the silicon to the periphery of the disc. The flow rates ranged from 100 to 225 g/min and the inlet subcooling levels varied from 0.5 to 6 °C. Pressure drop across the channel as well as void fraction in each branching level were measured for each of the test conditions. The measured pressure drop ranged from 20 to 90 kPa, and the measured void fraction ranged from 0.3 to 0.9. The pressure drop results agree well with the numerical predictions. The measured void fraction results followed the same trends as the numerical results.

Thermal Conductivity of Metal-Oxide Nanofluids: Particle Size Dependence and Effect of Laser Irradiation

2006 ◽  
Vol 129 (3) ◽  
pp. 298-307 ◽  
Author(s):  
Sang Hyun Kim ◽  
Sun Rock Choi ◽  
Dongsik Kim
Keyword(s):  
Thermal Conductivity ◽  
Particle Size ◽  
Effective Thermal Conductivity ◽  
Laser Irradiation ◽  
Volume Fraction ◽  
Suspended Particle ◽  
Titanium Dioxide Nanoparticles ◽  
Size Change ◽  
Conductivity Enhancement ◽  
Wide Range

The thermal conductivity of water- and ethylene glycol-based nanofluids containing alumina, zinc-oxide, and titanium-dioxide nanoparticles is measured using the transient hot-wire method. Measurements are performed by varying the particle size and volume fraction, providing a set of consistent experimental data over a wide range of colloidal conditions. Emphasis is placed on the effect of the suspended particle size on the effective thermal conductivity. Also, the effect of laser-pulse irradiation, i.e., the particle size change by laser ablation, is examined for ZnO nanofluids. The results show that the thermal-conductivity enhancement ratio relative to the base fluid increases linearly with decreasing the particle size but no existing empirical or theoretical correlation can explain the behavior. It is also demonstrated that high-power laser irradiation can lead to substantial enhancement in the effective thermal conductivity although only a small fraction of the particles are fragmented.

Characterizing the Stability of Carbon Nanotube Enhanced Water as a Heat Transfer Nanofluid

2010 ◽  
Author(s):  
Brian K. Ryglowski ◽  
Randall D. Pollak ◽  
Young W. Kwon
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Electrical Conductivity ◽  
Phase Change ◽  
Heat Dissipation ◽  
Coolant Fluid ◽  
Conductivity Enhancement ◽  
Design Variables ◽  
The Stability ◽  
The Many

Heat dissipation is a major challenge for many technologies. Possible solutions include thermal energy transfer via coolant fluid to a phase change material (PCM), with higher thermal conductivity a design goal. In recent years, heat transfer nanofluids (fluids with suspended nanoparticles) have received attention based on their potential for improving thermal conductivity. Carbon nanotubes (CNTs) are an attractive additive due to their enhanced thermal conductivity and ability to remain suspended over long times. However, characterizing their potential is difficult due to the many design variables and the need for repeated thermal conductivity tests for comparison. Since thermal conductivity enhancement is dependent on a dispersed nanotube network, the electrical conductivity of CNTs can be exploited to monitor the stability of such nanofluids, as such testing is quick and simple. The aim of this research was to evaluate electrical conductivity testing as a means to monitor stability of CNT-enhanced distilled water as a PCM, with varying CNT size, type, and concentration; and various other processing variables. The prepared nanofluids were tested after repeated phase change cycles. Results indicate that electrical conductivity testing is a practical means of monitoring the nanofluid stability, and CNT-based nanofluids show both promise and limitations as a PCM.

A Model of Nanofluids Thermal Conductivity

2005 ◽  
Author(s):  
Jinbo Wang ◽  
Gang Chen ◽  
Zongqin Zhang
Keyword(s):  
Thermal Conductivity ◽  
Particle Size ◽  
Zeta Potential ◽  
Volume Fraction ◽  
Ion Concentration ◽  
Research Groups ◽  
New Model ◽  
Conductivity Enhancement ◽  
Temperature Surface ◽  
Suspension Electrolyte

Since the experimental observations were reported that nanofluids exhibit unusually high thermal conductivity, different candidate models have been proposed by several research groups in order to reveal the underlying physics. Despite the efforts, mechanisms of the thermal conductivity enhancement are still being hotly debated. In this paper, we report a new model that correlates nanofluids thermal conductivity to particle size, volume fraction, temperature, surface zeta potential, and suspension electrolyte ion concentration. Our model provides new insights on the mechanisms and guidelines for future experimental exploration.

scholarly journals Particle size effects in the thermal conductivity enhancement of copper-based nanofluids

2011 ◽  
Vol 6 (1) ◽  
pp. 217 ◽  
Author(s):  
Michael Saterlie ◽  
Huseyin Sahin ◽  
Barkan Kavlicoglu ◽  
Yanming Liu ◽  
Olivia Graeve
Keyword(s):  
Thermal Conductivity ◽  
Particle Size ◽  
Size Effects ◽  
Thermal Conductivity Enhancement ◽  
Particle Size Effects ◽  
Conductivity Enhancement

Contradictory Evidence for the Role of Temperature and Particle Size in Nanofluid Thermal Conductivity

2011 ◽  
Vol 1347 ◽  
Author(s):  
Rebecca J. Christianson ◽  
Jessica Townsend
Keyword(s):  
Thermal Conductivity ◽  
Particle Size ◽  
Cooling Capacity ◽  
Conductivity Enhancement ◽  
The Past ◽  
Nanoparticle Suspensions ◽  
Significant Step ◽  
Tremendous Amount ◽  
Contradictory Evidence

ABSTRACTThe prospects for increased cooling capacity from the use of nanofluid coolants has created a tremendous amount of interest. However, in the years since the initial thermal conductivity measurements of nanoparticle suspensions were reported, there has been much inconsistency in data published in the literature. The International Nanofluids Benchmarking Exercise was a significant step towards creating a reliable set of data on the thermal conductivity enhancement of stable nanofluids, however there remain many unanswered questions. Most significant, perhaps, is the contradictory results on the effects of particle size and temperature. In the past year alone it is possible to find published reports on nominally identical samples claiming precisely opposing trends in thermal conductivity with decreasing particle size at room temperature. Some studies also claim an increasing enhancement at higher temperatures, sometimes linking this to small particle sizes. In this work we review the literature claims for particle size and temperature results, the theories used to support those claims, as well as presenting new data with the aim of resolving the dispute and identifying the origins of the evidence for contradictory claims.

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