Study on growth characteristics of TBAB clathrate hydrate from flowing TBAB solution in a rectangular channel

Tetra-n‑butyl ammonium bromide (TBAB) is a quaternary ammonium salt, and its hydrate has been identified as a potential phase-change material possessing an appropriate phase-change temperature for air-conditioning systems. Moreover, depending on the hydrate formation conditions, TBAB hydrate can form a slurry that is promising as a secondary refrigerant. In a harvest-type TBAB hydrate slurry generation system, the hydrate crystals formed on the cooling surface are scraped with a scraper. The amount of the TBAB hydrate formed on the surface then needs to be predicted. In this study, the growth of TBAB clathrate hydrate in a flowing TBAB solution in a rectangular acrylic channel was experimentally investigated. The dependence of the thickness of the layered hydrate on the flow rate, concentration of the solution, and temperature difference between the TBAB solution and brine was investigated. Moreover, numerical analysis of the layered hydrate formation was performed using the measured values, such as the inlet-solution temperature and cooling-plate temperature. A comparison between the experimental and numerical results was performed. It was found that the growth rate of the hydrate layer was lower than that of the ice layer regardless of the concentration of the solution. Moreover, the experimental thickness of the TBAB hydrate layer was smaller than that obtained by numerical analysis regardless of the temperature difference, although good agreement was obtained in the case of ice.