Floating and Sinking Behaviour of a Heat Transfer Sphere Submerged in a Gas-Solid Fluidised Bed

One of the most important features of a fluidised bed is its good heat-transfer characteristics. The role of various parameters and the mechanism of heat-transfer in fluidised beds have been a subject of extensive investigations in the recent past [1,2]. Oshitani et al. [3] reported that under certain conditions, a sphere can sink or float depending on the relative density. This phenomenon has been attributed to a local fluidization around the sinking sphere. Assuming this is correct, the heat transfer on such a sphere is therefore affected too. In this study a metallic sphere is used to monitor the heat transfer coefficient in such conditions involving as it does a few inter-dependent variables. The position of the sphere has been also monitored giving further information about the hydrodynamics of the system. This study has industrial relevance as it affects dry separators, catalytic cracking or thermochemical energy conversion processes.

1. García-Triñanes, J.P.K. Seville, R. Ansart, H. Benoit, T.W. Leadbeater, D.J. Parker, Particle motion and heat transfer in an upward-flowing dense particle suspension: Application in solar receivers, Chemical Engineering Science, Volume 177, 2018, 313-322, htps://doi.org/10.1016/j.ces.2017.11.041.
2. Mayumi Tsukada and Masayuki Horio, Maximum heat-transfer coefficient for an immersed body in a bubbling fluidized bed, Industrial & Engineering Chemistry Research 1992 31 (4), 1147-1156 htps://doi.org/10.1021/ie00004a025.
3. Jun Oshitani, Toshiki Sasaki, Takuya Tsuji, Shusaku Harada, Hirokazu Kajiwara, Kei Matsuoka, Unstable sinking of spheres at higher air velocity in a gas-solid fluidized bed, Advanced Powder Technology, Volume 32, Issue 4, 2021, 1300-1304,https://doi.org/10.1016/j.apt.2021.02.021.