The slurries-containing tetra-n-butyl ammonium bromide (TBAB) solution and its semiclathrate hydrate have attracted a lot of interest as latent heat transport media. These hydrate slurries contain some microparticles of crystal, and the size and shape of these hydrate particles could affect the mobility of slurries. Hence, it is essential to investigate the efficient hydrate-slurry preparation methods and the effect of hydrate particles on the fluid property of slurries for the application to latent heat transport media. In the present study, the effect of agitation on particle size distribution and aggregation of particles was studied to prepare easily flowing TBAB hydrate slurries that were suitable for fluid transport. First of all, the effects of impeller rotational speed and impeller type on the particle size and frequency of aggregation were investigated. The results suggested that the particle size distribution and the frequency of particle aggregation are strongly affected by the intensity of shear rate and its uniformity, which was controllable with impeller type and its rotation speed. 1. Introduction Recently, a large-scale district (regional) cooling system has attracted attention of many researchers because it works on saving energy and global sustainability due to its high performance of utilization of exhausted heat from large plants or factories [1]. In such system, the pumping energy loss due to the transportation of heat media is not small. To solve this problem, a high-density heat transportation system involving slurries with phase change materials (hereafter, PCM) having latent heat has been developed, for example, ice/water slurries [2]. The utilization of such PCM slurries can reduce flow rate of heat media, since latent heat of some materials is much larger than sensible heat. Fukushima et al. [3] reported the ability of slurries-containing tetra-n-butyl ammonium bromide (hereafter, TBAB) semiclathrate hydrate and its solution as latent-heat transport media, which was more favorable than ice/water system because they can be operated at relatively high temperature (ca. 285？K) and atmospheric pressure. Unlike ordinary gas hydrates, in these semiclathrate hydrates, the quaternary ammonium cation and anion are incorporated with the hydrogen bonds of water molecules to construct the hydrate cage [4]. In addition, four butyl groups are one-by-one encaged with a large cage separately in this semiclathrate system. There are various reports about the crystal structure and the role of bromine for the TBAB hydrates [4, 5]. The hydration
References
[1]
S. Kilkis and B. Kilkis, “An analytical, multi-objective an optimization algorithm for energy efficiency in district cooling systems and green buildings,” ASHRAE Transactions, vol. 117, pp. a13/1–a13/8, 2011.
[2]
S. Fukusako, Y. Kozawa, M. Yamada, and M. Tanino, “Fundamental researches and developments on fine crystallineice slurries,” Transactions of the Japan Society of Refrigerating and Air Conditioning Engineers, vol. 17, no. 4, pp. 413–437, 2000.
[3]
S. Fukushima, S. Takao, H. Ogoshi et al., “Development of High-density Cold Latent Heat with Clathrate Hydrate,” NKK Technical Report, vol. 166, pp. 65–70, 1999 (Japanese).
[4]
L. S. Aladko, Y. A. Dyadin, T. V. Rodionova, and I. S. Terekhova, “Clathrate hydrates of tetrabutylammonium and tetraisoamylammonium halides,” Journal of Structural Chemistry, vol. 43, no. 6, pp. 990–994, 2002.
[5]
W. Shimada, T. Ebinuma, H. Oyama et al., “Separation of gas molecule using tetra-n-butyl ammonium bromide semi-clathrate hydrate crystals,” Japanese Journal of Applied Physics, vol. 42, no. 2A, pp. L129–L131, 2003.
[6]
W. Shimada, M. Shiro, H. Kondo et al., “Tetra-n-butylammonium bromide-water (1/38),” Acta Crystallographica Section C, vol. 61, no. 2, pp. o65–o66, 2005.
[7]
S. Hashimoto, S. Murayama, T. Sugahara, H. Sato, and K. Ohgaki, “Thermodynamic and Raman spectroscopic studies on H2+ tetrahydrofuran+water and H2+tetra-n-butyl ammonium bromide+ water mixtures containing gas hydrates,” Chemical Engineering Science, vol. 61, no. 24, pp. 7884–7888, 2006.
[8]
S. Hashimoto, T. Sugahara, M. Moritoki, H. Sato, and K. Ohgaki, “Thermodynamic stability of hydrogen + tetra-n-butyl ammonium bromide mixed gas hydrate in nonstoichiometric aqueous solutions,” Chemical Engineering Science, vol. 63, no. 4, pp. 1092–1097, 2008.
[9]
S. Hashimoto, T. Tsuda, K. Ogata, T. Sugahara, Y. Inoue, and K. Ohgaki, “Thermodynamic properties of hydrogen + tetra-n-butyl ammonium bromide semi-clathrate hydrate,” Journal of Thermodynamics, vol. 2010, Article ID 170819, 5 pages, 2010.
[10]
H. Oyama, W. Shimada, T. Ebinuma et al., “Phase diagram, latent heat, and specific heat of TBAB semiclathrate hydrate crystals,” Fluid Phase Equilibria, vol. 234, no. 1-2, pp. 131–135, 2005.
[11]
M. Darbouret, M. Cournil, and J. M. Herri, “Rheological study of TBAB hydrate slurries as secondary two-phase refrigerants,” International Journal of Refrigeration, vol. 28, no. 5, pp. 663–671, 2005.
[12]
S. I. Kondo, M. Motoda, K. Takahashi, and H. Horiguchi, “The influence of the bottom shape of an agitated vessel stirred by dual impellers on the distribution of solid concentration,” Journal of Chemical Engineering of Japan, vol. 40, no. 8, pp. 617–621, 2007.
[13]
K. Shimizua, K. Takahashi, E. Suzukia, and T. Nomura, “Effect of baffle geometries on crystal size distribution of aluminum potassium sulfate in a seeded batch crystallizer,” Journal of Crystal Growth, vol. 197, no. 4, pp. 921–926, 1999.
[14]
A. Barresi and G. Baldi, “Solid dispersion in an agitated vessel,” Chemical Engineering Science, vol. 42, no. 12, pp. 2949–2956, 1987.
[15]
A. B. Metzner and R. E. Otto, “Agitation of non-Newtonian fluids,” AIChE Journal, vol. 3, no. 1, pp. 3–10, 1957.
[16]
N. Kamei, S. Hiraoka, Y. Kato, et al., “Development of power correlations for various impellers in an agitated vessel in laminar region based on a numerical analysis of 2-D flow,” Kagaku-kogaku Ronbunshu, vol. 20, no. 5, pp. 595–603, 1994 (Japanese).
[17]
T. N. Zwietering, “Suspending of solid particles in liquid by agitators,” Chemical Engineering Science, vol. 8, no. 3-4, pp. 244–253, 1958.
