Dissertation
EXPERIMENTAL MEASUREMENTS OF THERMAL CONDUCTIVITY OF NANOPARTICLE PACKED BEDS
Doctor of Philosophy (PhD), Washington State University
01/2017
Handle:
https://hdl.handle.net/2376/111866
Abstract
This thesis presents thermal conductivity measurements of nanoparticle packed beds, and a theoretical model for calculating thermal conductivity for the packed beds. A mathematical model for computing thermal conductivity of moist nanoparticle packed beds is developed based on a combination of ballistic phonon transport through particle interfaces and liquid resistance. Comparison between the experimental and analytical results for dry and moist packed beds are presented.
The thermal conductivities were measured for three sets of nanoparticle packed beds under vacuum (0.1 Torr). The thermal conductivity measurements for the 200 nm silica and 20 nm silica nanoparticle beds under vacuum (0.1 Torr) were found to be as low as 0.018 W/m°C ± 0.007 W/m°C and 0.013 W/m°C ± 0.006 W/m°C respectively, among the lowest thermal conductivities of solid materials ever measured. Additionally, the thermal conductivity measurements for the 300 nm copper nanoparticle beds under vacuum was found to be 0.059 W/m°C ± 0.006 W/m°C.
The thermal conductivities were also measured of the nanoparticle packed beds at ambient pressure under controlled humidity. Experimental measurements of the thermal conductivity of the presented nanoparticle beds over a range of humidity from 0 to 50% demonstrate that exposing the nanoparticle beds to even very low relative humidity air caused large jumps in thermal conductivity. The results are shown, even very small amounts of moisture can noticeably increase the conductivity of the packed beds.
An analytical model, based on the nanoscale constriction resistance developed by Prasher, the JKR model for estimating the contact radius between spheres with significant surface forces, and the packing geometry model for conduction through packed spheres by Tien and coworkers is developed to predict the thermal conductivity of a dry nanoparticle packed bed. The model is extended to predict the thermal conductivity of nanoparticle beds exposed to humid air by assuming that liquid water condenses in the narrow annulus surrounding the contact points between spherical nanoparticles.
The model is in good agreement with the measurements for the 200 and 20 nm silica nanoparticles for dry and moist nanoparticle packed beds.
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Details
- Title
- EXPERIMENTAL MEASUREMENTS OF THERMAL CONDUCTIVITY OF NANOPARTICLE PACKED BEDS
- Creators
- Muftah Omran Elsahati
- Contributors
- Rebort F Richards (Advisor)Cecilia D Richards (Committee Member)Jin Liu (Committee Member)Konstantin Matveev (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- School of Mechanical and Materials Engineering
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Number of pages
- 127
- Identifiers
- 99900581630801842
- Language
- English
- Resource Type
- Dissertation