Numerical study of different gas–solid flow regimes effects on hydrodynamics and heat transfer performance of a fluidized bed reactor

Abstract

In this study, a two-fluid Eulerian-Eulerian model has been carried out applying the kinetic theory of granular flow (KTGF) to study the hydrodynamics and heat transfer behavior of a fluidized bed reactor simultaneously. The effects of different gas-solid flow regimes on the operating conditions and heat transfer rate between the hot air and two types of low and high-density inert particles are investigated in a fluidized bed dryer. Different gas-solid flow regimes for wood and glass particles of groups A, B, and D of Geldart's classification are simulated to introduce the most optimal flow regime in terms of heat transfer rate and operating costs. The compromise between the heating rate, the height required for the reactor, and the ratio of the final mass to the initial mass of solid particles, which specifies the need for a cyclone separator showed that the bubbling regime of Geldart B powder for low-density particles and the turbulent regime of Geldart D powder or bubbling regime of Geldart B powder for high-density particles are the optimal operating conditions and flow regimes. Furthermore, it was concluded that the convective heat transfer is the dominant mechanism, which increases with increasing the air velocity and decreasing the particle diameter in each group. K E Y W O R D Sfluidized bed reactor, gas-solid flow regimes, Geldart classification, heat transfer rate, hydrodynamics behavior, operating costs, two-fluid model 1 | INTRODUCTION Fluidized bed reactors have the advantages of superior solid mixing, uniform temperature distribution, high controllability of the bed temperature, good gas-solid contact, and high heat and mass transfer characteristics. These reactors find widespread applications in chemical reactors, coal combustors, and energy industries, including fluid catalytic cracking, combustion, gasification, coating processes, and solids drying. 1,2 High heat transfer rate in fluidized bed reactors is attributed to complex hydrodynamics and heat transfer mechanisms, which depend on the different gas-solid flow regimes in fluidized beds. 3 According to various studies, fluidization can be divided into some main regimes, namely incipient or minimum fluidization, smooth or homogeneous, bubbling, slugging, turbulent, fast and pneumatic transport, depending on the inlet gas velocity, particles characteristics, and the system configuration. 3,4 The relative importance of gas-particle, particle-particle, and wall interactions, which would generally affect the heat transfer between phases through convection and conduction are different in each flow regime. Therefore, it is necessary to identify an appropriate operating regime in industrial processes and applications. 5,6 Figure 1 shows a schematic diagram of the flow regimes in a gas-solid fluidized bed reactor. This figure depicts the bubble formation, solids entrainments, and the spouted behavior in the bed region by increasing the gas velocity beyond the minimum fluidization velocity (U mf ). 7,8 Geldart classified the fluidization characteristics...

Numerical Study of Water-air Ejector using Mixture and Two-phase Models

“…Co mputational Flu id Dynamic (CFD) is a suitable tool to investigate many engineering problems, e.g. aerodynamic [1], cavitation [2], hydraulic [3,4], energy systems [5,6], heat transfer [7,8], mu ltiphase flow [9][10][11]. Today, two-phase ejectors are highly efficient and widely applied in various industries.…”

Experimental study of convective heat transfer coefficient for pulsed fluidized bed using microcapsule phase change material

“…2,3 The gas carrier's flow rate in a fluidized bed should be high enough to overcome particles' weight for fluidization. [4][5][6][7] Particle diameter in a fluidized bed is usually in the range of 0.3-3 mm and particularly less than 1 mm. [8][9][10] The focus of fluidized bed research is generally on the hydrodynamic and heat transfer originating from parameters like flow rate, bed geometry, particle diameter and type, thermal field, and heat transfer.…”

“…Generally, fluidization means moving particles relative to each other, walls, and fixed surfaces while overcoming drag, gravity, and cohesive forces between particles 2,3 . The gas carrier's flow rate in a fluidized bed should be high enough to overcome particles' weight for fluidization 4–7 . Particle diameter in a fluidized bed is usually in the range of 0.3–3 mm and particularly less than 1 mm 8–10 .…”