Heat Transfer in Fluidized Beds

CFD-DEM investigation of flow and heat transfer characteristics in a directly irradiated fluidized bed

Mass transfer in fluidized beds is an important operation for separation processes. Two effects can be achieved by using fluidized beds in mass transfer processes increasing interface area and relative movement between the phases. These effects are both desirable because they lead to greater process rates. This paper presents an experimental investigation regarding mass transfer from the wall of a column to the fluid in a fluidized bed of inert spherical particles. The experiments were conducted in column 40 mm in diameter with spherical particles 0,8-3 mm in diameter and water as one fluidizing fluid. The method of dissolution of benzoic acid was used to provide very low mass flux. The average wall-to-fluid mass transfer coefficients were determined for two systems: single-phase fluid flow and a fluidized bed of inert particles The measurements encompassed a Reynolds number range from 100-4000 for single-phase flow and 600-4000 in fluidized beds. The mass transfer coefficients for both systems were calculated from weight loss of benzoic acid. The effects of superficial liquid velocity and particle diameter on the mass transfer coefficient were investigated. It was found that mass transfer was more intensive in the fluidized bed in comparison with single phase flow. The best conditions for mass transfer were reached at a minimum fluidization velocity, when the mass transfer coefficient had the greatest value. The experimental data were correlated in the form: jd = f(Re), where jd is the dimensionless mass transfer factor and Re the Reynolds number.

Fundamental particle fluidization behavior and handling of nano-particles in a rotating fluidized bed

To find the optimal structure of the converging–diverging tube and develop a high-efficiency falling-film evaporator, the heat and mass transfer performances of falling-film evaporation with converging–diverging tubes of different dimensions were studied. The optimal converging–diverging tube was used in falling-film evaporation desorption of the basic aluminum sulfate desulphurization–regeneration solution, and different influential factors on the desorption effect were analyzed. It was found that converging–diverging tubes with large falling-film flow rate performed well in the heat and mass transfer of falling-film evaporation, and their rib height largely affected the heat and mass transfer performances. At the same rib height and rib pitch, the longer the converging segment of the converging–diverging tube was, the better the heat transfer performance was. The evaporation heat transfer coefficient and evaporation mass transfer rate in the optimal converging–diverging tube were 1.6 and 1.38 times larger than the smooth tube, respectively. The optimal converging–diverging tube was used in falling-film evaporation desorption of basic aluminum sulfate desulphurization–regeneration solution, at a perimeter flow rate of 0.114–0.222 kg m−1 s−1, the desorption efficiency inside the tube was up to 94.2%, which was 10.3–10.5% higher than that of the smooth tube. At the inlet sulfur concentration of 0.02–0.1 kmol m−3, the desorption efficiency was up to 94.1%, which was 12.0–16.3% larger than that of the smooth tube. At the heating temperature of 371.15–386.15 K, the desorption efficiency was up to 93.4%, which was 6.7–11.5% larger than that of the smooth tube. Smaller falling-film flow rate, higher sulfur concentration, or higher heating temperature was more constructive to SO2 desorption. Correlations were obtained to predict the mass transfer coefficient and SO2 desorption efficiency. This study develops a new type of falling-film evaporator for SO2 desorption from basic aluminum sulfate desulphurization–regeneration solution and provides a basis for process design and industrial application.

DEM numerical investigation of wet particle flow behaviors in multiple-spout fluidized beds

Heat transfer from an immersed tube in a pulsating fluidized bed

Experimental mass and heat transfer at a serpentine tube heat exchanger located at the wall of a square stirred tank reactor

Gas solid fluidized bed application has gained popularity as an excellent contacting device that is been widely used in thermo-chemical processes, drying application in food processing industries etc. due to its favorable heat transfer characteristics. Most of the outmoded fluidization activities reported is confined with columnar/cylindrical shaped bed reactors. Conventionally, tapered/conical reactors are used for energy conversion which has substantial dynamic characteristics over the columnar reactors in terms of smooth, steady operation with marginal pressure variation. This work focuses on the computational modelling and simulation on the effect of various parameters like par, Stagnant bed height, Superficial velocity, Minimum fluidization velocity and Heat transfer characteristics upon variation in the taper angle of Tapered Fluidized Bed Reactor (TFBR) using Computational Fluid Dynamics (CFD) solver FLUENT. Two Fluid Model (TFM) is adopted for the simulation studies where both the phases (Solid, Gas) are treated as fluids. The results obtained are compared with simulation conducted for columnar reactor having same axial length. 2D domain has the axial length of 1.2 m and bottom diameter of 0.15 m. Simulation results shows that the finer the particle size becomes, greater is the heat transfer by conduction from bed to wall compared to larger particles. The interphase heat transfer from Solid-Air is maximum in the reactor core section. Although the particle volume fraction is observed to be more in columnar reactor, better fluidization characteristics is observed in reactor with taper angle 4.52°.

Numerical investigation of the effects of variable fluid properties on cilia-driven flow of tangent hyperbolic fluid in a channel with heat and mass transfer: A new approach to microfluidic pumps

Advancements of the Fluidized Bed Fenton (FBF) Technology for wastewater treatment: Mechanism, mass and heat transfer

The article contains sections titled:1.Introduction1.1.The Fluidization Principle1.2.Forms of Fluidized Beds1.3.Advantages and Disadvantages of the Fluidized‐Bed Reactor2.Fluid‐Mechanical Principles2.1.Minimum Fluidization Velocity2.2.Expansion of Liquid–Solid Fluidized Beds2.3.Fluidization Properties of Typical Bed Solids2.4.State Diagram of Fluidized Bed2.5.Gas Distribution2.6.Gas Jets in Fluidized Beds2.7.Bubble Development2.8.Elutriation2.9.Circulating Fluidized Beds2.9.1.Hydrodynamic Principles2.9.2.Local Flow Structure in Circulating Fluidized Beds2.9.3.Design of Solids Recycle System2.10.Cocurrent Downflow Circulating Fluidized Beds (Downers)2.11.Attrition of Solids3.Solids Mixing in Fluidized‐Bed Reactors3.1.Mechanisms of Solids Mixing3.2.Vertical Mixing of Solids3.3.Horizontal Mixing of Solids3.4.Solids Residence‐Time Properties3.5.Solids Mixing in Circulating Fluidized Beds4.Gas Mixing in Fluidized‐Bed Reactors4.1.Gas Mixing in Bubbling Fluidized Beds4.2.Gas Mixing in Circulating Fluidized Beds5.Heat and Mass Transfer in Fluidized‐Bed Reactors6.Gas–Solid Separation7.Injection of Liquid Reactants into Fluidized Beds8.Industrial Applications8.1.Heterogeneous Catalytic Gas‐Phase Reactions8.2.Polymerization of Olefins8.3.Homogeneous Gas‐Phase Reactions8.4.Gas–Solid Reactions8.5.Applications in Biotechnology9.Modeling of Fluidized‐Bed Reactors9.1.Modeling of Liquid–Solid Fluidized‐Bed Reactors9.2.Modeling of Gas–Solid Fluidized‐Bed Reactors9.2.1.Bubbling Fluidized‐Bed Reactors9.2.2.Circulating Fluidized‐Bed Reactors9.3.Newer Developments in Modeling Fluidized‐Bed Reactors9.3.1Computational Fluid Dynamics9.3.2Modeling of Fluidized‐Bed Systems10.Scale‐upThe article gives an overview on fundamentals and applications of fluidized‐bed technology. Some basic fluid‐mechanical principles—minimum fluidization velocity, status diagram, gas distribution, bubble development, and solids entrainment and elutriation—are presented at the beginning, followed by a detailed discussion of circulating fluidized beds, downers, and attrition effects in fluidized‐bed systems. Sections on solids mixing, gas mixing, and heat and mass transfer in fluidized beds complete the fundamentals section, which is followed by an overview on industrial applications. Fluidized‐bed processes for heterogeneous catalytic gas‐phase reactions, for the polymerization of olefins, for homogenous gas‐phase reactions, gas–solid reactions and applications in biotechnology are described in detail. A final chapter is devoted to the modeling of fluidized‐bed reactors.

This paper investigates the effects of activation energy and nonlinear thermal radiation on the flow, heat, and mass transfer of magneto-bioconvective Eyring–Powell nanofluid due to a stretching sheet. It analyzes the influences of magnetohydrodynamic forces, nonlinear thermal radiation, chemical reactions, and the activation energy of species within the Powell–Eyring nanofluid. Motile microorganisms are introduced alongside nanoparticles to prevent agglomeration and stabilize the suspension. The governing nonlinear partial differential equations (PDEs) are transformed into ordinary differential equations (ODEs) using similarity transformations and solved numerically with the RKF45 algorithm in MATLAB. Results indicate that increasing the Powell–Eyring fluid parameter and Grashof number enhances the velocity profile, while the Hartmann number and buoyancy ratio reduce it. Temperature distribution increases with higher thermal radiation, Hartmann, Eckert, Brownian motion, and thermophoresis parameters, but decreases with greater Grashof and Prandtl numbers. The nanoparticle concentration profile declines with increasing Lewis number, chemical reaction, and Brownian motion parameters but rises with thermophoresis and activation energy. The density of gyrotactic microorganisms decreases with higher bioconvection Lewis and Peclet number, concentration deference of motile microorganism parameter, while it increases with the Hartmann number. In table, we are observed that as the ε and Gr values are increases, then skin friction coefficient value are decreases. As the M , Rb , δ , Nr values are increases, then skin friction coefficient value are increases. In table, we are observed that Gr , R , θ w values are increases, then local Nusslet number increases. As the M , Pr , Ec , Nb , Nt values are increases, then local Nusslet number decreases. In table, we are observed that as the values of Le , Nb , Nt , σ , E , ω upsurges, then Sherwood number decreases. In table, we observed that as M values increases, then Local density number decreases. As the Lb , Ω , Pe increases, then Local density number increases. Main objective of the present study is observed from tables and the amount of heat transmission increases by increasing the values of M , R , θ w , Ec , Nb , Nt whereas it declines by increasing the values of Gr , Pr . It is noticed that the rate of mass transmission increases by increasing the values of Nt , E , ω whereas it declines by increasing the values of Le , Nb , σ . Shows an overview of the θ η ( 0 ) observations for different values of Nb & Nt . The activation energy significantly impacts the flow and heat transfer characteristics of Magneto-Bioconvective Eyring–Powell Nanofluid, affecting its velocity and temperature profiles. Higher activation energy reduces nanoparticle diffusion, slowing mass transfer, and concentration gradients, which is essential in applications requiring controlled diffusion, such as targeted drug delivery and biochemical processing. Nonlinear thermal radiation enhances the heat transfer rate near a stretching sheet and decreases thermal boundary layer thickness, particularly under high-temperature gradients, making it valuable for high thermal load applications, microfluidic cooling, and industrial heating. Magnetic fields influence bioconvection patterns of gyrotactic microorganisms, either enhancing or hindering heat and mass transfer based on magnetic field strength. The Hartmann number increases flow velocity and reduces temperature gradients, offering control over flow profiles in applications like magnetic-assisted manufacturing and microfluidic devices. The nanoparticle volume fraction notably affects the thermophysical properties and heat and mass transfer behavior of the nanofluid. The findings have critical applications in fields such as biomedical engineering, biomedical applications, and energy conversion devices, where controlled diffusion is essential, and in industrial microfluidics, where efficient heat and mass transfer are required. Simulation results provide insight into optimizing heat and mass transfer processes in practical engineering systems, thermal management systems.

Surface-to-bed heat transfer in fluidised beds: Effect of surface shape

Simultaneous heat and mass transfer characteristics for wavy fin-and-tube heat exchangers under dehumidifying conditions

Convective drying of particulate solids – Packed vs. fluid bed operation