scholarly journals Modeling the effect of shrinkage on fluidized bed drying of orthodox broken type tea

2019 ◽  
Vol 25 (3) ◽  
pp. 299-307
Author(s):  
K. Raveendran ◽  
W.A.R. Jayarathna ◽  
A.D.U.S. Amarasinghe ◽  
W.S. Botheju
Keyword(s):  
Fluidized Bed ◽  
Ambient Air ◽  
Minimum Fluidization Velocity ◽  
Fluidized Bed Dryer ◽  
Moisture Contents ◽  
Fluidization Velocity ◽  
Minimum Fluidization ◽  
Archimedes Number ◽  
Fluidized Bed Drying ◽  
The Difference

Fermented tea particles (dhool) are a polydisperse system subject to shrinkage during fluidized bed drying, which is an important process in the production of orthodox broken type tea. The effect of shrinkage on the physical properties and the minimum fluidization velocity were studied. Five different moisture contents of dhool particles were chosen in the range of 3-106 mass% (dry basis) and the changes in particle diameters and particle densities were measured. For each of the moisture contents, the minimum fluidization velocity was found for three different bed loadings using ambient air at 25?C in a fluidized bed with an area of 351?345 mm2. Since the conventional industrial type fluidized bed dryers operate at 124?C, the new correlations among the Archimedes number, Reynolds number at minimum fluidization and dimensionless moisture content were developed using air properties at 124?C. The results were validated for orthodox broken type tea, drying at 124?C, in a fluidized bed dryer with bed loadings in the range of 44.5 to 50.5 kg/m2. The predicted fluidization velocity was found to be in good agreement with the experimental data and the difference was below 10% for most cases.

Flow Properties of Moisturized Powders in a Couette Fluidized Bed Rheometer

2012 ◽  
Vol 10 (1) ◽  
Author(s):  
Giovanna Landi ◽  
Diego Barletta ◽  
Paola Lettieri ◽  
Massimo Poletto
Keyword(s):  
Fluidized Bed ◽  
Gas Flow ◽  
Vertical Direction ◽  
Variable Load ◽  
Air Humidity ◽  
Flow Properties ◽  
Minimum Fluidization Velocity ◽  
Fluidization Velocity ◽  
Minimum Fluidization ◽  
The Difference

This work investigates on the effect of air humidity on the flow properties of powders. The moisture of a powder sample (50 µm glass beads) was conditioned by fluidization with humid air. Air humidity was kept between 0 and 70% at ambient temperature. A Schulze shear cell was used to measure the bulk flow properties of the moisturized samples. A Couette fluidized bed rheometer was used to measure the torque necessary for the rotation of the inner cylinder when the fluidized powder had been moisturized with the same procedure. These experiments show a certain continuity of the results below and above the minimum fluidization velocity, suggesting a similar continuity of the role that interparticle interactions play in the fixed and in the fluidized bed. Experiments below the minimum fluidization velocity were interpreted with a rheological model in which the variable load along the vertical direction in the Couette was calculated with a modified Janssen equation. In this approach the apparent weight of the powder is given by the difference between the gravity and the upward body force determined by the rising gas flow. The agreement between the model and the experiments supports the proposed approach.

scholarly journals Prediction of minimum fluidization velocity in pulsed gas–solid fluidized bed

2020 ◽  
pp. 127965
Author(s):  
Yanjiao Li ◽  
Chenyang Zhou ◽  
Guannan Lv ◽  
Yongxin Ren ◽  
Yuemin Zhao ◽  
...  
Keyword(s):  
Fluidized Bed ◽  
Minimum Fluidization Velocity ◽  
Fluidization Velocity ◽  
Minimum Fluidization

Bed Height Effects on Fluidized Bed Hydrodynamics

2010 ◽  
Author(s):  
David R. Escudero ◽  
Theodore J. Heindel
Keyword(s):  
Fluidized Bed ◽  
Experimental Studies ◽  
Gas Holdup ◽  
Minimum Fluidization Velocity ◽  
Non Invasive ◽  
Fluidization Velocity ◽  
Bed Height ◽  
Minimum Fluidization ◽  
Imaging Results ◽  
X Ray Computed

Characterizing the hydrodynamics of a fluidized bed is of vital importance to understand the behavior of these multiphase flow systems. Minimum fluidization velocity and gas holdup are two important factors used to understand the hydrodynamics of a fluidized bed. Experimental studies on the effects of bed height on the minimum fluidization velocity and gas holdup were carried out using a 10.2 cm diameter cylindrical fluidized bed filled with 500–600 μm glass beads. In this study, four different bed height-to-diameter ratios were used: H/D = 0.5, 1, 1.5, and 2. Minimum fluidization velocity was determined for each H/D ratio using pressure drop measurements. Local time-average gas holdup was determined using non-invasive X-ray computed tomography imaging. Results show that minimum fluidization velocity is not affected by the change in bed height, while local gas holdup does appear to be affected by the change in bed height.

scholarly journals SIMULASI PENGARUH KECEPATAN GAS TERHADAP KARAKTERISTIK FLUIDISASI PADA FLUIDIZED BED MENGGUNAKAN METODE CFD

POROS ◽  
2018 ◽  
Vol 16 (1) ◽  
Author(s):  
Asyari Daryus Daryus
Keyword(s):  
Pressure Drop ◽  
Fluidized Bed ◽  
Particle Density ◽  
Gas Velocity ◽  
Experiment Data ◽  
Minimum Fluidization Velocity ◽  
Fluidization Velocity ◽  
Minimum Fluidization ◽  
Gas Fluidization ◽  
Simulation Results

The gas fluidization velocity or superficial gas velocity entering the fluidized bed will affect the fluidization in fluidized bed. If the superficial velocity is below the minimum fluidization velocity then there is no fluidization, and if it is more than it should be then the fluidization characteristic will be different. To obtain the effect of gas fluidization velocity to fluidization characteristics, it had been conducted the research on lab scale fluidized bed using CFD simulation method validated with the experiment data. The simulations used Gidaspow model for drag force and k-ε model for turbulent flow. From the experiments obtained that the minimum fluidization velocity was 0.4 m/s and the pressure drop was around 700 Pa. The simulation results for pressure drop across the bed were close to the experiment data for the gas fluidization velocity equal and bigger than the minimum fluidization velocity. For the velocity below the minimum fluidization velocity, there was the big differences between the simulation results and the experiment, so the simulation results cannot be used. For the fluidization velocity of 0.4 m/s and 0.45 m/s, fluidized bed showed the bubbling phenomena, and the higher velocity showed the bigger bubble. For the fluidization velocity of 0.50 m/s to 0.70 m/s, the fluidized bed showed the turbulent regime. In this regime, the bubble was breaking instead of growing and there was no clear bed surface observed. The simulation result for particle density showed that if the gas velocity was higher, the density of particles at the base of bed was decreasing since many of the particles was moving upwards. The particle density was lower in this regime than that of bubbling regime.

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