Heat Transfer Characteristics of Lithium Titanate Particles in Gas-Solid Packed Fluidized Beds

Lithium titanate (Li₂TiO₃) is a potential ceramic material for generation of tritium, which is exploited as a fuel in fusion reactor. However, Li₂TiO₃ has poor thermal conductivity, due to which thermal management of this material during nuclear reaction is a bottleneck. If this material is used in the form of pebble packed in a column or vessel, namely Test Blanket Module (TBM), the effective thermal conductivity is further brought down due to interstitial voids in the packed bed and also due to point to point contact between spherical pebbles. It is therefore essential to develop a suitable technique to enhance heat transfer properties of a packed pebble bed of Li₂TiO₃. In the present studies, an attempt has been made to develop a packed fluidized bed wherein particulate Li₂TiO₃ will be allowed to fluidize in the interstitial void of large stationary pebbles, called packing. Experiments have been carried out on heat transfer from wall to bed in a 162.74-mm-diameter column. Stationary pebbles of Li₂TiO₃ of size 1 mm to 10 mm and fluidized Li₂TiO₃ particulate solids of size 231 m to 780 m in the interstitial voids were used. Bed wall temperature in the range of 200°C to 600°C and operating fluidizing gas velocity corresponding to 1-4 times minimum fluidization velocity of fluidized particulate solids in the voids, were used for 20 to 60 volume percent of fluidized particulate solid of Li₂TiO_3. It has been found that the effective thermal conductivity of packed fluidized bed increased close to the value of thermal conductivity of pure Li₂TiO₃ at an optimum fluidization velocity corresponding to 2-3 times minimum fluidization velocity depending on fluidized particle, size, its volume fraction and wall temperature.