Modeling Effective Thermal Conductivity of Al2O3 Nanoparticles in Water and Ethylene Glycol Based on Shape Factor

This study was undertaken to gain a better understanding of the countercurrent heat exchange of thermally significant blood vessels in skeletal muscle by measuring the vascular structure and flow in an exteriorized rat spinotrapezius muscle and estimating the enhancement in the effective thermal conductivity of the muscle. Detailed anatomic measurements of the number density and length of countercurrent vessel pairs between 45 and 165 μm diameter were obtained. Moreover, diameter and blood flow in the 1A to 3A vessels were measured for muscles in which pharmacological vasoactive agents were introduced, allowing one to vary the local blood flow Peclet number from 1 to 18 in the major feeding arteries. These combined measurements have been used to estimate the range of possible enhancement in the effective thermal conductivity of the tissue. The newly derived conduction shape factor in Zhu et al. [23] for countercurrent vessels in two-dimensional tissue preparations was used in this analysis. Our experimental data indicated that the value of this conduction shape factor was about one-third to two-thirds the value for two countercurrent vessels of the same size and spacing in an infinite medium. The experiment also revealed that the Weinbaum–Jiji expression for keff was valid for the spinotrapezius muscle when the largest vessels were less than 195 μm diameter. A fivefold increase in keff was predicted for 195 μm diameter vessels. Vasoregulation was also shown to have a dramatic effect on keff. A tissue that exhibits only small increases in keff due to countercurrent convection in its vasoconstricted state can exhibit a more than fivefold increase in Keff in its vasodilated state.

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Thermal Conductivity Affected by Temperature and Particle Size in Al2O3-Water Nanofluids

ASME/JSME 2011 8th Thermal Engineering Joint Conference ◽

10.1115/ajtec2011-44649 ◽

2011 ◽

Author(s):

D. Kwek ◽

A. Crivoi ◽

Fei Duan

Keyword(s):

Thermal Conductivity ◽

Particle Size ◽

Effective Thermal Conductivity ◽

Experimental Results ◽

Al2o3 Nanoparticles ◽

Particle Sizes ◽

Transient Hot Wire ◽

Hot Wire ◽

Nanoparticle Concentration ◽

Wire Method

The effective thermal conductivity of Al2O3-water nanofluids has been measured using a transient hot wire method. Experimental results demonstrate that the thermal conductivity of Al2O3 nanofluids increases linearly with increasing nanoparticle concentration. Adding 5 vol % of Al2O3 nanoparticles in water increases the effective thermal conductivity of the nanofluids by 20%. Thermal conductivity of Al2O3 nanofluids increases with an increase of temperature. The enhancement is around 1.7% at 15 °C in comparison with around 16% at 55 °C in a 1 vol % nanofluid. The particle size is another important parameter for the effective thermal conductivity. The increase of thermal conductivity reduces from 30% to 10% as the particle sizes increase from 10 nm to 35 nm. The increase of the effective thermal conductivity starts as the particle size increases above 35 nm, reaching about 27.5% in the nanofluid with the particle size at 150 nm.

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Physical-Statistical Model of Thermal Conductivity of Nanofluids

Journal of Nanomaterials ◽

10.1155/2014/756765 ◽

2014 ◽

Vol 2014 ◽

pp. 1-6 ◽

Cited By ~ 3

Author(s):

B. Usowicz ◽

J. B. Usowicz ◽

L. B. Usowicz

Keyword(s):

Thermal Conductivity ◽

Ethylene Glycol ◽

Statistical Model ◽

Effective Thermal Conductivity ◽

Multinomial Distribution ◽

Water Based ◽

Classical Models ◽

Parallel Connections ◽

Solid Liquid ◽

Thermal Resistors

A physical-statistical model for predicting the effective thermal conductivity of nanofluids is proposed. The volumetric unit of nanofluids in the model consists of solid, liquid, and gas particles and is treated as a system made up of regular geometric figures, spheres, filling the volumetric unit by layers. The model assumes that connections between layers of the spheres and between neighbouring spheres in the layer are represented by serial and parallel connections of thermal resistors, respectively. This model is expressed in terms of thermal resistance of nanoparticles and fluids and the multinomial distribution of particles in the nanofluids. The results for predicted and measured effective thermal conductivity of several nanofluids (Al2O3/ethylene glycol-based and Al2O3/water-based; CuO/ethylene glycol-based and CuO/water-based; and TiO2/ethylene glycol-based) are presented. The physical-statistical model shows a reasonably good agreement with the experimental results and gives more accurate predictions for the effective thermal conductivity of nanofluids compared to existing classical models.

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AL2O3 Nanofluids as Heat Transfer Liquids in Automotives

International Journal of Mechanical and Industrial Engineering ◽

10.47893/ijmie.2014.1156 ◽

2014 ◽

pp. 206-212

Author(s):

M. YASASWI ◽

R.V. PRASAD ◽

T.JAYANDA KUMAR

Keyword(s):

Heat Transfer ◽

Thermal Conductivity ◽

Ethylene Glycol ◽

Energy Efficient ◽

Solid Particles ◽

Al2o3 Nanoparticles ◽

Particle Volume ◽

Heat Transfer Fluids ◽

Potential Impact ◽

Efficient Heat Transfer

The thermal conductivity of heating or cooling fluids is a very important property in the development of energy efficient heat transfer systems, which is one of the important needs of many industries. However, low thermal conductivity is a primary limitation in developing energy-efficient heat transfer fluids that are required for cooling purposes. Nanofluids are nanotechnology-based heat transfer fluids that are engineered by stably dispersing nanometer-sized (below 100nm) solid particles (such as ceramics, metals, alloys, semiconductors, nanotubes, and composite particles) in conventional heat transfer fluids (such as water, oil, diesel, ethylene glycol and mixtures) at relatively low particle volume concentrations. These suspended nanoparticles can change the transport and thermal properties of the base fluid. Adding to ethylene glycol, it has been observed that an enhancement of nearly 36 % with al2o3 nanoparticles and 40% enhancement with copper nanoparticles in the thermal conductivity. This paper focuses on some of the automotive applications such as coolant for automobiles, showcases a few of them that are believed to have the highest probability of success in this highly competitive industry and to raise the awareness on the promise of nanotechnology, its potential impact on the future of the automotive industry.

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