The Effect of Nanoparticle Coating on the Thermal Conductivity of Nanofluids

2009 ◽  
Vol 1207 ◽  
Author(s):  
Michael John Fornasiero ◽  
Diana-Andra Borca-Tasciuc
Keyword(s):  
Thermal Conductivity ◽  
Iron Oxide ◽  
Effective Thermal Conductivity ◽  
Colloidal Suspensions ◽  
Maxwell Model ◽  
Carrier Fluid ◽  
Coated Nanoparticles ◽  
Transient Hot Wire Technique ◽  
Potential Applications ◽  
Iron Oxide Core

AbstractNanofluids are engineered colloidal suspensions of nanometer-sized particles in a carrier fluid and are receiving significant attention because of their potential applications in heat transfer area. Theoretical investigations have shown that the enhanced thermal conductivity observed in nanofluids is due to nanoparticle clustering and networking. This provides a low resistance path to the heat flowing through the fluid. However, the surface coating of the nanoparticles, which is often used to provide stable dispersion over the long term, may act as a thermal barrier, reducing the effective thermal conductivity of the nanofluid. Moreover, nanofluids with the same type of nanoparticles may exhibit different effective thermal conductivities, depending upon the thermal properties and thickness of the coating. In this context, thermal conductivity characterization of well dispersed iron oxide nanoparticles with two different surface coatings was carried out employing the transient hot wire technique. The diameter of the iron oxide core was 35 nm and the coatings used were aminosilane and carboxymethyl-dextran (CMX) of 7nm in thickness. Preliminary results suggest that effective thermal conductivity of CMX coated nanoparticle suspensions is slightly higher than that of aminosilane coated nanoparticles. In both cases, the effective thermal conductivity is higher than that predicted by the Maxwell model for composite media.

scholarly journals Ground-Source Heat Pump Systems: The Effects of Variable Trench Separations and Pipe Configurations in Horizontal Ground Heat Exchangers

Energies ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3919
Author(s):  
Yu Zhou ◽  
Asal Bidarmaghz ◽  
Nikolas Makasis ◽  
Guillermo Narsilio
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Heat Pump ◽  
Heat Exchangers ◽  
Element Model ◽  
Fluid Temperature ◽  
Ground Source Heat Pump ◽  
Carrier Fluid ◽  
Ground Heat Exchangers ◽  
Ground Source

Ground-source heat pump systems are renewable and highly efficient HVAC systems that utilise the ground to exchange heat via ground heat exchangers (GHEs). This study developed a detailed 3D finite element model for horizontal GHEs by using COMSOL Multiphysics and validated it against a fully instrumented system under the loading conditions of rural industries in NSW, Australia. First, the yearly performance evaluation of the horizontal straight GHEs showed an adequate initial design under the unique loads. This study then evaluated the effects of variable trench separations, GHE configurations, and effective thermal conductivity. Different trench separations that varied between 1.2 and 3.5 m were selected and analysed while considering three different horizontal loop configurations, i.e., the horizontal straight, slinky, and dense slinky loop configurations. These configurations had the same length of pipe in one trench, and the first two had the same trench length as well. The results revealed that when the trench separation became smaller, there was a minor increasing trend (0.5 °C) in the carrier fluid temperature. As for the configuration, the dense slinky loop showed an average that was 1.5 °C lower than those of the horizontal straight and slinky loop (which were about the same). This indicates that, when land is limited, compromises on the trench separation should be made first in lieu of changes in the loop configuration. Lastly, the results showed that although the effective thermal conductivity had an impact on the carrier fluid temperature, this impact was much lower compared to that for the GHE configurations and trench separations.

Investigation on Thermal Conductivity of Low Concentration AlN/EG Nanofluids

2013 ◽  
Vol 546 ◽  
pp. 112-116
Author(s):  
Yan Jiao Li ◽  
Chang Jiang Liu ◽  
Zhi Qing Guo ◽  
Qiu Juan Lv ◽  
Fang Xie
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Volume Fraction ◽  
Maxwell Model ◽  
Experimental Results ◽  
Effect Of Temperature ◽  
Transient Hot Wire ◽  
Hot Wire ◽  
Wire Method ◽  
Nanoparticles Volume Fraction

The thermal conductivity of AlN/EG nanofluids was investigated by transient hot-wire method. Experimental results indicated that the thermal conductivity of AlN/EG nanofluids increase nearly linear with the increase of nanoparticles volume fraction, and the results can’t be predicted by conditional Maxwell model. The effect of temperature on effective thermal conductivity of AlN/EG nanofluids was investigated. Result indicated that the thermal conductivity of AlN/EG nanofluids increased with the increase of temperature.

Formulation of Percolating Thermal Underfill by Sequential Convective Gap Filling

2011 ◽  
Vol 2011 (DPC) ◽  
pp. 001621-001648 ◽  
Author(s):  
T. Brunschwiler ◽  
J. Goicochea ◽  
H. Wolf ◽  
C. Kuemin ◽  
B. Michel
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Heat Dissipation ◽  
High Viscosity ◽  
Thermal Impedance ◽  
Gap Filling ◽  
Carrier Fluid ◽  
Filling Time ◽  
Small Pore ◽  
The Matrix

In 3D chip stacks, heat dissipation through wiring layers and the bonding interface contributes to the total temperature gradient. The effective thermal impedance of micro solder-ball arrays filled with a poorly-conducting silica underfill can be as high as 30 K*mm2/W, three times the value of a thermal grease interface. Efforts to improve the underfill conductivity to 5 W/(m*K) are underway, which would translate into in a significant interface-resistance reduction. To achieve thermal conductivities >1 W/(m*K), alumina particles were introduced in capillary underfills at particle loadings above the percolation threshold, but at these loading levels the high viscosity of the resulting underfill no longer permits capillary filling. We propose a novel sequential gap-filling method. Particles are suspended in a carrier fluid at a low concentration (0.1 vol%). Using forced convection, the suspension is injected into the cavity formed between the IC dies by the C4 array. A filter element at the cavity outlet triggers particle accumulation in the cavity. The particles form a percolation network with an effective thermal conductivity of >1 W/(m*K). Next an evaporation step removes the carrier fluid, and the exposed pores between the particles are refilled with a particle-free adhesive using capillary forces. Finally, the matrix is cured at 65 °C. 10x10 mm2 standard and micro-C4 cavities (>30 μm) can be completely filled in 2 min at 0.2 bar, resulting in a homogeneous volumetric fill of 36%. Percolation was identified by SEM inspection. For the micro-C4 arrays filler particles of < 10 μm were used. Uniform particle filling is precluded because of the longer filling time due to the small pore sizes. Particle trapping sites are introduced to form local stacks that provide an additional drainage network to guarantee acceptable filling times. Effective thermal-conductivity values of the percolating thermal underfill method proposed here are reported.

Prediction of effective thermal conductivity of nanofluids by modifying renovated Maxwell model

2016 ◽  
Vol 30 (3) ◽  
pp. 289-301 ◽  
Author(s):  
Deepti Chauhan ◽  
Nilima Singhvi
Keyword(s):  
Neural Network ◽  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Base Fluid ◽  
Volume Fraction ◽  
Maxwell Model ◽  
Theoretical Models ◽  
Solid Particles ◽  
Nanoparticle Volume Fraction ◽  
Suspended Nanoparticles

Nanofluids, which are formed by suspending nanoparticles into conventional fluids, exhibit anomalously high thermal conductivity. Renovated Maxwell model was developed by Choi in which the presence of very thin nanolayer surrounding the solid particles was considered, which can measurably increase the effective thermal conductivity of nanofluids. A new model is proposed by introducing a fitting parameter χ in the renovated Maxwell model, which accounts for nanolayer, nonuniform sizes of filler nanoparticles together with aggregation. The model shows that the effective thermal conductivity of nanofluids is a function of the thickness of the nanolayer, the nanoparticle size, the nanoparticle volume fraction and the thermal conductivities of suspended nanoparticles, nanolayer and base fluid. The validation of the model is done by applying the results obtained by the experiments on nanofluids, other theoretical models, and artificial neural network technique. The uncertainty of the present measurements is estimated to be within 5% for the effective thermal conductivity.

Prediction of effective thermal conductivity of two-phase porous media by nomogram

1974 ◽  
Vol 24 (8) ◽  
pp. 437-445 ◽  
Author(s):  
P. B. Lal Chaurasia ◽  
D. R. Chaudhary ◽  
R. C. Bhandari
Keyword(s):  
Thermal Conductivity ◽  
Porous Media ◽  
Effective Thermal Conductivity ◽  
Two Phase
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