Heat Transfer from Wires to Gases - Maximum Flow Rates in Thermal Conductivity Measurements

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.

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

Sensor Letters ◽

10.1166/sl.2019.4181 ◽

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%.

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PROCESSED STRAW AS EFFECTIVE THERMAL INSULATION FOR BUILDING ENVELOPE CONSTRUCTIONS

Engineering Structures and Technologies ◽

10.3846/2029882x.2012.730286 ◽

2012 ◽

Vol 4 (3) ◽

pp. 96-103 ◽

Cited By ~ 4

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.

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

Nanoscale Advances ◽

10.1039/d0na00657b ◽

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.

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Heat Transfer and Rheological Behavior of Fumed Silica Nanofluids

Processes ◽

10.3390/pr8121535 ◽

2020 ◽

Vol 8 (12) ◽

pp. 1535 ◽

Cited By ~ 1

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.

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Nongrey radiant heat transfer corrections to thermal conductivity measurements

Wärme- und Stoffübertragung ◽

10.1007/bf01108032 ◽

1970 ◽

Vol 3 (2) ◽

pp. 114-119 ◽

Cited By ~ 5

Author(s):

W. Leidenfrost ◽

R. J. Latko

Keyword(s):

Heat Transfer ◽

Thermal Conductivity ◽

Radiant Heat ◽

Radiant Heat Transfer ◽

Conductivity Measurements

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Improved Flow Rate in Electro-Osmotic Micropumps for Combinations of Substrates and Different Liquids With and Without Nanoparticles

Journal of Electronic Packaging ◽

10.1115/1.4028746 ◽

2015 ◽

Vol 137 (2) ◽

Cited By ~ 3

Author(s):

Marwan F. Al-Rjoub ◽

Ajit K. Roy ◽

Sabyasachi Ganguli ◽

Rupak K. Banerjee

Keyword(s):

Heat Transfer ◽

Zeta Potential ◽

Thermal Management ◽

Flow Rate ◽

Maximum Flow ◽

Enhanced Heat Transfer ◽

Flow Rates ◽

Current Leakage ◽

Different Types ◽

Electro Osmotic Flow

A new design for an electro-osmotic flow (EOF) driven micropump was fabricated. Considering thermal management applications, three different types of micropumps were tested using multiple liquids. The micropumps were fabricated from a combination of materials, which included: silicon-polydimethylsiloxane (Si-PDMS), Glass-PDMS, or PDMS-PDMS. The flow rates of the micropumps were experimentally and numerically assessed. Different combinations of materials and liquids resulted in variable values of zeta-potential. The ranges of zeta-potential for Si-PDMS, Glass-PDMS, and PDMS-PDMS were −42.5–−50.7 mV, −76.0–−88.2 mV, and −76.0–−103.0 mV, respectively. The flow rates of the micropumps were proportional to their zeta-potential values. In particular, flow rate values were found to be linearly proportional to the applied voltages below 500 V. A maximum flow rate of 75.9 μL/min was achieved for the Glass-PDMS micropump at 1 kV. At higher voltages nonlinearity and reduction in flow rate occurred due to Joule heating and the axial electro-osmotic current leakage through the silicon substrate. The fabricated micropumps could deliver flow rates, which were orders of magnitude higher compared to the previously reported values for similar size micropumps. It is expected that such an increase in flow rate, particularly in the case of the Si-PDMS micropump, would lead to enhanced heat transfer for microchip cooling applications as well as for applications involving micrototal analysis systems (μTAS).

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Sensitivity and Spatial Resolution for Thermal Conductivity Measurements using Non-contact Scanning Thermal Microscopy with Thermoresistive Probes under Ambient Conditions

Oxford Open Materials Science ◽

10.1093/oxfmat/itab011 ◽

2021 ◽

Author(s):

Yun Zhang ◽

Wenkai Zhu ◽

Theodorian Borca-Tasciuc

Keyword(s):

Heat Transfer ◽

Thermal Conductivity ◽

Spatial Resolution ◽

Conductivity Measurement ◽

Thermal Conductivity Measurement ◽

Conductivity Measurements ◽

Scanning Thermal Microscopy ◽

Ambient Conditions ◽

Measurement Sensitivity ◽

Sample Heat

Abstract Thermoresistive probes are increasingly popular in thermal conductivity characterization using Scanning Thermal Microscopy (SThM). A systematic analysis of the thermal conductivity measurement performance (sensitivity and spatial resolution) of thermoresistive SThM probe configurations that are available commercially is of interest to practitioners. In this work, the authors developed and validated 3-Dimensional Finite Element Models (3DFEM) of non-contact SThM with self-heated thermoresistive probes under ambient conditions with the probe-sample heat transfer in transition heat conduction regime for the four types of SThM probe configurations resembling commercially available products: Wollaston wire (WW) type probe, Kelvin Nanotechnology (KNT) type probe, Doped Silicon (DS) type probe, and Nanowire (NW) type probe. These models were then used to investigate the sensitivity and spatial resolution of the WW, KNT, DS and NW type probes for thermal conductivity measurements in non-contact mode in ambient conditions. The comparison of the SThM probes performance for measuring sample thermal conductivity and for the specific operating conditions investigated here show that the NW type probe has the best spatial resolution while the DS type probe has the best thermal conductivity measurement sensitivity in the range between 2-10 W·m−1·K−1. The spatial resolution is negatively affected by large probe diameters or by the presence of the cantilever in close proximity to the sample surface which strongly affects the probe-sample heat transfer in ambient conditions. An example of probe geometry configuration optimization was illustrated for the WW probe by investigating the effect of probe wire diameter on the thermal conductivity measurement sensitivity, showing ∼20% improvement in spatial resolution at the diameter with maximum thermal conductivity measurement sensitivity.

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