Experimental observations on directly irradiated fluidized beds: even and uneven fluidization

Abstract This paper presents the experimental results obtained in a directly irradiated fluidized bed. A bed with a diameter of 314.76 mm was filled with SiC particles and directly irradiated from the top with a beam-down reflector with a 2 kW Xe-lamp. The study examines the influence of the bed height and airflow rate on the temperature distribution over the top surface of the bed (where the concentrated irradiation impinged), measured with an infrared camera. In addition, two fluidization patterns were compared: even and uneven fluidization. In the first case, the air is uniformly distributed through the cross-sectional area of the bed, while in the second case, a higher flow is deliberately introduced through the center of the bed, with minimum fluidization conditions being maintained in the rest of the bed. The heat exchange of the concentrated radiative flux over the fluidized particles in motion under the action of bubble bursting was assessed by characterizing the temperature of the particles (Probability Density Function, mean value and standard deviation). The results of this work show how the uneven fluidization can reduce the maximum temperature of the particles, especially in the case of shallow beds. In any event, uneven fluidization exhibits a similar behavior to even fluidization but with lower pumping costs, as the airflow rate is reduced by up to 26.4%, compared to even fluidization. The effects of the uneven fluidization are more important for shallow beds especially at high air velocities, although under the experimental conditions of this work, no clear heat diffusion improvements were found in the uneven fluidization tests when the air velocity in the center of the bed exceeded two times the minimum fluidization velocity.