scholarly journals Heat Transfer and Rheological Behavior of Fumed Silica Nanofluids

Processes ◽  
2020 ◽  
Vol 8 (12) ◽  
pp. 1535 ◽  
Author(s):  
A.I. Gómez-Merino ◽  
J.J. Jiménez-Galea ◽  
F.J. Rubio-Hernández ◽  
J.L. Arjona-Escudero ◽  
I.M. Santos-Ráez
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Rheological Behavior ◽  
Fumed Silica ◽  
Shear Thickening ◽  
Good Control ◽  
Thermomechanical Properties ◽  
Polypropylene Glycol ◽  
Conductivity Measurements ◽  
Liquid Phases

The addition of nanoparticles to liquid media can improve thermomechanical properties of dispersants. This ability gives rise to the development of multiple applications of nanofluids (NF) in branches so different as electronic and photonic devices or cosmetic industry. Logically, these applications require a good control of heat transfer and flow properties. Moreover, if we consider the necessity to optimize industrial processes in which NF take part, it is necessary to obtain possible relationships between both physical mechanisms. Specifically, in this work, a study about thermal conductivity and rheological behavior of fumed silica suspensions in polypropylene glycol (PPG400) and polyethylene glycol (PEG200) was performed. The study of these two suspensions is interesting because the flow behaviors are very dissimilar (while the fumed silica in PEG200 suspension is viscoplastic, the fumed silica in PPG400 suspension shows shear-thickening behavior between two shear-thinning regions), despite the addition of fumed silica producing similar enhancement of the relative thermal conductivity in both liquid phases. The more outstanding contribution of this work lies in the combination of rheological and conductivity measurements to deepen in the understanding of the heat transfer phenomenon in NF. The combination of rheological together with thermal conductivity measurements have permitted establishing the mechanisms of liquid layering and aggregate formation as the more relevant in the heat transfer of these silica fumed suspensions.

A Self-Heated Thermistor Technique to Measure Effective Thermal Properties From the Tissue Surface

1987 ◽  
Vol 109 (4) ◽  
pp. 330-335 ◽  
Author(s):  
P. A. Patel ◽  
J. W. Valvano ◽  
J. A. Pearce ◽  
S. A. Prahl ◽  
C. R. Denham
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Thermal Properties ◽  
Tissue Blood Flow ◽  
Conductivity Measurements ◽  
Bioheat Equation ◽  
Tissue Conductivity ◽  
Diffusivity Measurements ◽  
Tissue Surface ◽  
Effective Thermal Properties

A microcomputer based instrument to measure effective thermal conductivity and diffusivity at the surface of a tissue has been developed. Self-heated spherical thermistors, partially embedded in an insulator, are used to simultaneously heat tissue and measure the resulting temperature rise. The temperature increase of the thermistor for a given applied power is a function of the combined thermal properties of the insulator, the thermistor, and the tissue. Once the probe is calibrated, the instrument accurately measures the thermal properties of tissue. Conductivity measurements are accurate to 2 percent and diffusivity measurements are accurate to 4 percent. A simplified bioheat equation is used which assumes the effective tissue thermal conductivity is a linear function of perfusion. Since tissue blood flow strongly affects heat transfer, the surface thermistor probe is quite sensitive to perfusion.

The Thermal Conductivity and Viscosity of Non-Polar Hybrid CuO Nanofluid (CuO+ DEA + Cyclohexane) (CuO + DEA + 1-4 Dioxane)

2019 ◽  
Vol 17 (12) ◽  
pp. 965-967
Author(s):  
B. Rohini ◽  
A. Kingson Solomon Jeevaraj
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Copper Oxide ◽  
Viscosity Measurement ◽  
Nano Particles ◽  
Conductivity Measurements ◽  
Transfer Enhancement ◽  
Binary Fluid ◽  
New Class ◽  
Nano Fluid

Nano fluid is the new class of engineering fluid for the heat transfer applications. Copper Oxide (CuO) nano particles were dispersed in the binary fluid (Cyclohexane + DEA) and (1-4 dioxane + DEA) then prepared non-polar hybrid CuO nano fluid. Thermal conductivity (K ) and viscosity (η) of non-polar hybrid CuO nanofluid measured for very low concentration from 0.01 M to 0.06 M and various temperatures ranging from 298 K to 318 K. The transient hotwire method is used for the thermal conductivity measurements and viscometer is used for the viscosity measurement. As the concentration increases K decreases but it increases with the increase of temperature. η increases with the increase of concentration as well as with temperature. From the results the spectacular heat transfer enhancement occurred in the hybrid CuO nanofluid compared to the binary mixtures. The percentage increment of thermal conductivity of non-polar hybrid CuO nano fluid is of 15% to 20% and the viscosity increment is of from 18% to 25%.

Transient Study on the Shear Thickening Behaviour of Surface Modified Fumed Silica Suspensions in Polypropylene Glycol

2008 ◽  
Author(s):  
F. J. Galindo-Rosales ◽  
F. J. Rubio-Hernández ◽  
Albert Co ◽  
Gary L. Leal ◽  
Ralph H. Colby ◽  
...  
Keyword(s):  
Fumed Silica ◽  
Shear Thickening ◽  
Polypropylene Glycol ◽  
Transient Study ◽  
Surface Modified ◽  
Silica Suspensions

PROCESSED STRAW AS EFFECTIVE THERMAL INSULATION FOR BUILDING ENVELOPE CONSTRUCTIONS

2012 ◽  
Vol 4 (3) ◽  
pp. 96-103 ◽  
Author(s):  
Jolanta Vėjelienė
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Thermal Insulation ◽  
Building Envelope ◽  
Gas Content ◽  
Barley Straw ◽  
Conductivity Measurements ◽  
Insulation Materials ◽  
Thermal Transfer ◽  
The Impact

The efficiency of thermal insulation materials obtained from renewable resources depends on the possibilities of reducing thermal transfer via solid and gaseous conduction, thermal radiation and, in some cases, convection. The heat transfer mechanism for thermal insulation materials mostly depends on the structure and density of the material used. Efficient thermal insulation materials consist of a gaseous phase and a solid skeleton. Gas content in such materials can take more than 99% of material by volume. In this case, thermal transfer via solid conductivity is negligible. The current work analyses the possibilities of reducing heat transfer in the straw of a varying structure. For conducting experiments, barley straw was used. To evaluate the impact of straw stalk orientation in a specimen on thermal conductivity, strongly horizontally and vertically oriented specimens of straw stalks were prepared. To reduce heat transfer via gaseous conduction and convection in large cavities in straw stalks and between stalks, barley straw were chopped and defibered. In order to decrease heat transfer via radiation after thermal conductivity measurements, mechanically processed straw were coated with infrared absorbers. Due to thermal conductivity measurements of chopped and defibered straw, an optimal amount of infrared absorbers were determined.

scholarly journals Thermal conductivity measurements of thin films by non-contact scanning thermal microscopy under ambient conditions

2021 ◽  
Author(s):  
Yun Zhang ◽  
Wenkai Zhu ◽  
Theodorian Borca-Tasciuc
Keyword(s):  
Heat Transfer ◽  
Thin Films ◽  
Thermal Conductivity ◽  
Finite Element ◽  
Transition Regime ◽  
Conductivity Measurements ◽  
Scanning Thermal Microscopy ◽  
Ambient Conditions ◽  
Fast Analysis ◽  
Heat Transfer Modeling

Accurate thermal conductivity measurements of nanoscale thin-films on substrate samples by non-contact SThM with finite element heat transfer modeling in transition regime and with fitting functions and analytical heat transfer modeling for fast analysis.

scholarly journals Impact of the Carbon Nanofillers Addition on Rheology and Absorption Ability of Composite Shear Thickening Fluids

Materials ◽  
2020 ◽  
Vol 13 (17) ◽  
pp. 3870
Author(s):  
Paulina Nakonieczna-Dąbrowska ◽  
Rafał Wróblewski ◽  
Magdalena Płocińska ◽  
Marcin Leonowicz
Keyword(s):  
Carbon Nanotubes ◽  
Graphene Oxide ◽  
Rheological Behavior ◽  
Shear Thickening ◽  
High Energy ◽  
Polypropylene Glycol ◽  
Shear Thickening Fluids ◽  
Carbon Nanofillers ◽  
Energy Absorbing ◽  
Composite Shear

Synthesis and characterization of composite shear thickening fluids (STFs) containing carbon nanofillers are presented. Shear thickening fluids have attracted particular scientific and technological interest due to their unique ability to abruptly increase viscosity in the case of a sudden impact. The fluids have been developed as a potential component of products with high energy absorbing efficiency. This study reports on the rheological behavior, stability, and microstructure of the STFs modified with the following carbon nanofillers: multi-walled carbon nanotubes, reduced graphene oxide, graphene oxide, and carbon black. In the current experiment, the basic STF was made as a suspension of silica particles with a diameter of 500 nm in polypropylene glycol and with a molar mass of 2000 g/mol. The STF was modified with carbon nanofillers in the following proportions: 0.05, 0.15, and 0.25 vol.%. The addition of the carbon nanofillers modified the rheological behavior and impact absorption ability; for the STF containing 0.25 vol.% of carbon nanotubes, an increase of force absorption up to 12% was observed.

scholarly journals RESEARCH ON THE EFFECT OF PROTECTING COATING ON THE FIRE RESISTANCE OF ALUMINUM ALLOY STRUCTURES

Fire Safety ◽  
2019 ◽  
pp. 16-20
Author(s):  
S. Y. Vovk ◽  
N. O. Ferents ◽  
D. V. Kharyshyn
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Aluminum Alloy ◽  
Fire Resistance ◽  
Protective Coating ◽  
Fire Protection ◽  
Protective Coatings ◽  
Component Composition ◽  
Thermomechanical Properties ◽  
Heat Transfer Process

Polyfunctional protective coatings based on filled polysiloxane compositions are technological and can be used to increase the fire resistance of metal structural materials due to high thermomechanical properties, which are determined by stable structural and phase composition. The influence of protective coatings on the basis of polysiloxane-filled oxide components on fire resistance of aluminum alloys is investigated in the work. The choice of the initial compositions for fire protection coatings was carried out with the aim of obtaining of expanded heat-insulating heatresistant layer on the surface of an aluminum alloy at temperatures of 473 K and higher. The methods of physico-chemical analysis have established that when heated more than 473 K as a result of thermo oxidative degradation of polysiloxane with the release of gaseous products, there is an expanding coating with the formation of a fire-proof porous heat-insulating layer on the surface of an aluminum alloy. The coefficient of expanding the coating is within the range of 9.8 ... 12.4. The reliability of the use of physicochemical criteria when choosing the component composition of the coating and the effectiveness of the fire protection function is estimated from the results of the test on the aluminum alloy AMG6 and on the model of its thermal conductivity. 20 Пожежна безпека, №34, 2019 A model of thermal conductivity of a protective coating is proposed, which consists of a layer that limits heat transfer through a two-layer wall. When exposed to the aluminum plate of the heat flow, it is heated to the depth of the coating, which leads to its expanding and the formation of a thermal barrier. The dynamics of temperature distribution during a fire on the protective coating of an aluminum alloy is predicted by simulating the heat transfer process in a homogeneous solid by a mathematical model. The theoretical and practical researches have established the dependence of the parameter of heating the protected aluminum alloy to the critical temperature, depending on the thickness of the coating. The presence on the surface of a protected alloy coating, based on the filled polysiloxane, changes the process of heat transfer to its surface, which increases the fire resistance of the structure by 3 ...4 times.

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