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Effect of Viscosity on Wall-to-Bed Mass
Transfer Coefficient in a Three-Phase Fluidized Bed
-- G N Ravi Shankar, G M J Raju, M S N Murty and K V Ramesh
Investigations have been carried out experimentally to study the effect of viscosity on wall-to-bed
mass transfer coefficient in a three-phase fluidized bed. The system chosen was an electrolyte as liquid
phase, glass spheres of different diameters as solid phase and inert nitrogen as gaseous phase. The electrolyte
was an equimolar solution of 0.01 N potassium ferricyanide and potassium ferrocyanide with 0.4 N
NaHCO3/Na2CO3 as indifferent electrolyte. To vary the viscosity, Carboxy Methyl Cellulose (CMC) sodium salt in
0.1, 0.2 and 0.4 wt% was added to the electrolyte. The reaction considered was the reduction of ferricyanide
ion. The experiment was conducted at a constant temperature of 25 oC at which the physical property values
of the electrolyte were obtained from literature. The mass transfer coefficient was computed from the
measured limiting current. It was found that the mass transfer coefficient was relatively independent of liquid
velocity within the range covered in the present experiment. The kL increased with increasing gas velocity
and approached a constant value. kL was also observed to increase with increasing particle size and
decreased with increasing CMC concentration. The entire experimental data was correlated in terms of
modified Coulburn j-factor and modified Reynolds number.
© 2010 IUP. All Rights Reserved.
Cfd Simulation of Subcooled Vertical Nucleate
Flow Boiling of Water
-- K Navas Mohamed and P Sivashanmugam
This investigation was carried out at an elevated pressure to study the volume fractions, velocities
and temperature distributions. GAMBIT 2.3.16 was used for geometry creation and meshing, while solver
and post-processing were done with FLUENT 6.3.26. A 2D geometry of 8872 nodes was generated in
GAMBIT and exported to FLUENT. Pressure-based solver with unsteady state specification, RNG k-e Turbulent model and Eulerian multiphase model were selected in FLUENT to study the boiling process. The
RPI model of heat partitioning and user-defined functions were applied to the subcooled boiling
process. Simulation was carried out at elevated pressures, varying heat flux and varying degree of subcooling.
Axial and radial distributions of volume fraction, velocity and temperature were done, and the initiation
of boiling for various conditions was also observed. The simulated result was compared with the
experimentally reported value and was found to be satisfactory.
© 2010 IUP. All Rights Reserved.
Studies on Momentum Transfer Aspects
of Semifluidized Beds in Annular Sections
-- A B Soni, H Kumar and Pooja V Shrivastava
Semifluidization (SF) is a novel fluid-solid contact technique. An SF bed overcomes the
inherent disadvantages of a packed bed as well as that of a fluidized bed. It is a combination of fluidized bed at
the bottom and packed bed at the top in series within a single contacting vessel. Various aspects of
semifluidized beds in cylindrical columns and conical vessels have been reported in literature (Fan and Wen, 1959;
Roy and Sharma, 1972; Govindrajan and Sengupta, 1976; Murthy and Roy, 1986; Murthy et al., 1987; Briens et al., 1997; and Jing et al., 2000). This paper presents studies on momentum transfer aspects of semifluidized
beds in annular sections, which are likely to be useful in the design and operation of SF bed reactors.
Data was collected using the variables: liquid mass velocity, particle size and particle density.
Correlations were developed based on dimensional analysis approach for the prediction of semifluidized bed
pressure drop and of minimum and maximum semifluidized velocity. A fairly good agreement was obtained
between the calculated and experimental data.
© 2010 IUP. All Rights Reserved.
Plasma Gasification:
A Waste Treatment Technology
-- Mehali J Mehta, Robin A Christian,
Narendra J Mistry and Mausumi Mukhopadhyay
Plasma gasification is an upcoming and environment friendly waste treatment technology with useful
by-products like syngas and slag. The objective of the study is to review the plasma gasification system
which has the potential to replace the existing methods of waste management. In addition to its applicability
to municipal wastes, plasma gasification is also effective for treatment of hazardous wastes which are otherwise difficult to be treated. This paper focuses on plasma gasification technology, its environmental
application and its by-products. It also focuses on advantages, various revenue sources and future applications
of plasma gasification.
© 2010 IUP. All Rights Reserved.
Pervaporation Reactor: Principles
and Applications
-- Ajit P Rathod, Kailas L Wasewar and Shriram S Sonawane
Various separation processes are used in the chemical industry along with their corresponding
separating agents. The separation processes play a critical role in various chemical process industries. This
paper discusses the need of membrane technology along with membrane separation process. Pervaporation is
one of the important membrane processes. When it is coupled with reaction, especially equilibrium
controlled reactions, the equilibrium shifts towards a higher reaction rate and hence higher conversion. In the
present paper, pervaporation reactor, i.e., reaction with separation using pervaporation has been discussed.
© 2010 IUP. All Rights Reserved.
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