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Research Papers

Effect of Dispersion Homogeneity on Specific Heat Capacity Enhancement of Molten Salt Nanomaterials Using Carbon Nanotubes

[+] Author and Article Information
Byeongnam Jo

Nuclear Professional School,
The University of Tokyo,
Shirakata 2-22, Tokai-mura, Naka-gun,
Ibaraki 319-1188, Japan;
Department of Mechanical Engineering,
Texas A&M University,
3123 TAMU,
College Station, TX 77843
e-mail: jo@vis.t.u-tokyo.ac.jp

Debjyoti Banerjee

Department of Mechanical Engineering,
Texas A&M University,
3123 TAMU,
College Station, TX 77843

Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING. Manuscript received January 3, 2014; final manuscript received July 13, 2014; published online August 25, 2014. Editor: Gilles Flamant.

J. Sol. Energy Eng 137(1), 011011 (Aug 25, 2014) (9 pages) Paper No: SOL-14-1006; doi: 10.1115/1.4028144 History: Received January 03, 2014; Revised July 13, 2014

The specific heat capacity of a carbonate salt eutectic-based carbon nanotube nanomaterial was measured in present study. Differential scanning calorimeter (DSC) was used to measure the specific heat capacity of the nanomaterials. The specific heat capacity value in liquid phase was compared with that of a pure eutectic. A carbonate salt eutectic was used as a base material, which consists of lithium carbonate and potassium carbonate by 62:38 molar ratio. Multiwalled carbon nanotubes (CNT) at 1% mass concentration were dispersed in the molten salt eutectic. In order to find an appropriate surfactant for synthesizing molten salt nanomaterials, three surfactants, sodium dodecyl benzene sulfonate (SDBS), sodium dodecyl sulfate (SDS), and gum arabic (GA), at 1% mass concentration with respect to the salt eutectic were added. In preparation of dehydrated nanomaterials, water was evaporated by heating vials on a hot plate. Three different temperature conditions (120, 140, and 160 °C) were employed to investigate the effect of dispersion homogeneity of the nanotubes in the base material on the specific heat capacity of the nanomaterials. It is expected that the amount of agglomerated nanotubes decreases with increase of evaporation temperature (shorter elapsed time for evaporation). The results showed that the specific heat capacity of the nanomaterials was enhanced up to 21% in liquid phase. Additionally, it was found that the specific heat capacity enhancement of the nanomaterials, which contained SDS, was more sensitive to the evaporation time. Also, it can be decided that GA is the most appropriate to disperse CNT into the aqueous salt solution. Finally, CNT dispersion was confirmed with scanning electron microscope (SEM) images for pre-DSC and post-DSC samples. Furthermore, theoretical predictions of the specific heat capacity were compared with the experimental results obtained in present study.

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Figures

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Fig. 5

Specific heat capacity of nanomaterials in liquid phase (525 °C–555 °C) for various evaporation temperatures using: (a) SDBS, (b) SDS, and (c) GA. ∗Error bar indicates 95% confidence interval.

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Fig. 4

Heat flow curves obtained from DSC experiments for a pure eutectic sample and a nanomaterial sample with SDS [29]

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Fig. 3

Durations for water evaporation for nanomaterial samples with different surfactants

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Fig. 2

Schematic for the synthesis procedure for nanomaterials

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Fig. 1

TEM images of multiwalled CNT [29]

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Fig. 6

Specific heat capacity of nanocomposites in solid phase for various evaporation temperature using: SDBS (a) and (b), SDS (c) and (d), and GA (e) and (f)

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Fig. 7

Specific heat capacity of nanomaterials in liquid phase once using SDS of 5% mass concentration

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Fig. 8

Average enhancements in specific heat capacity of nanomaterials in liquid phase for each evaporation temperature

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Fig. 9

Schematics of water evaporation process: (a) using SDS or SDBS and (b) using GA

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Fig. 10

SEM images of pre-DSC and post-DSC samples: using SDBS (a) and (b), using SDS (c) and (d), and using GA (e) and (f)

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