36
2 Bubbling Properties in Pulsed Fluidised Beds
popular in pulsed fluidisation. One could deliver a gas flow whilst oscillating its
flow rate periodically. In such a way, the inlet gas stream changes, or even fully
stops for a fixed time interval, during each cycle. Such an oscillation is typically
realised by temporal manipulation of valves, such as solenoid valves and butterfly
valves. Besides, the type of oscillation also varies, including square patterns, sawtooth
patterns and sinusoidal waves, which are the most widely used and readily achievable
in common operations [5, 6, 9].
Over the last 30 years, pulsed fluidisation has been studied considerably. As
demonstrated in Sect. 1.4, there are a significant number of studies investigating
pulsed fluidisation with respect to particular interests of the researchers, such as
flow pattern, bubble formation, pressure drop, minimum fluidisation velocity, mixing
effect, heat and mass transfer and so forth [4]. Nevertheless, the potential of pattern
formation in pulsed fluidised beds is yet largely ignored. In the early 2000s, experiments have already demonstrated that pulsating a gas flow periodically, within a
certain range of operating conditions, leads to a unique fluidisation state, in which
gas bubbles rearrange in a tuneable hexagonal array. Overall, such structured hydrodynamics show great potentials to facilitate engineering design, control, and scale-up
practice of fluidised beds. Nevertheless, since its first discovery, there has been very
little reported progress on exploring this structured pattern of bubbles, let alone
understanding the physics underpinning pattern formation. The different bubbling
characteristics between structured and unstructured pulsed beds are still largely
unknown.
In this chapter, experiments are carried out to investigate the bubbling flows in a
quasi-2D, pulsed, gas-solid bubbling fluidised bed under oscillatory flows of varying
pulse amplitude, frequency and offset. The results show that, independent of structuring, it is possible to manipulate size, number, separation and rising velocity of
bubbles via a modulated periodic flow. Under certain pulsations, structured flows
emerge and bring in extra precision on the control of populations, tightening the
size, separation and rising velocity distributions of bubbles, which highlights the
potential to facilitate engineering solid operations and develop new applications.
2.2 Experimental Implementation and Analysis
Methodology
2.2.1 Design of Quasi-2D Fluidised Bed Setup
The experiments are conducted using a quasi-2D cell constructed of Plexiglas with
a width of 45 cm, a thickness of 1 cm, and a length of 80 cm. The cell is connected
with a 20 cm long plenum chamber. Two domains are separated by a 3 mm thick
porous bronze metal plate (Grade 07, BK 10.30.07, Sintertech). A schematic of the
experimental setup is shown in Fig. 2.1.
2 Bubbling Properties in Pulsed Fluidised Beds
popular in pulsed fluidisation. One could deliver a gas flow whilst oscillating its
flow rate periodically. In such a way, the inlet gas stream changes, or even fully
stops for a fixed time interval, during each cycle. Such an oscillation is typically
realised by temporal manipulation of valves, such as solenoid valves and butterfly
valves. Besides, the type of oscillation also varies, including square patterns, sawtooth
patterns and sinusoidal waves, which are the most widely used and readily achievable
in common operations [5, 6, 9].
Over the last 30 years, pulsed fluidisation has been studied considerably. As
demonstrated in Sect. 1.4, there are a significant number of studies investigating
pulsed fluidisation with respect to particular interests of the researchers, such as
flow pattern, bubble formation, pressure drop, minimum fluidisation velocity, mixing
effect, heat and mass transfer and so forth [4]. Nevertheless, the potential of pattern
formation in pulsed fluidised beds is yet largely ignored. In the early 2000s, experiments have already demonstrated that pulsating a gas flow periodically, within a
certain range of operating conditions, leads to a unique fluidisation state, in which
gas bubbles rearrange in a tuneable hexagonal array. Overall, such structured hydrodynamics show great potentials to facilitate engineering design, control, and scale-up
practice of fluidised beds. Nevertheless, since its first discovery, there has been very
little reported progress on exploring this structured pattern of bubbles, let alone
understanding the physics underpinning pattern formation. The different bubbling
characteristics between structured and unstructured pulsed beds are still largely
unknown.
In this chapter, experiments are carried out to investigate the bubbling flows in a
quasi-2D, pulsed, gas-solid bubbling fluidised bed under oscillatory flows of varying
pulse amplitude, frequency and offset. The results show that, independent of structuring, it is possible to manipulate size, number, separation and rising velocity of
bubbles via a modulated periodic flow. Under certain pulsations, structured flows
emerge and bring in extra precision on the control of populations, tightening the
size, separation and rising velocity distributions of bubbles, which highlights the
potential to facilitate engineering solid operations and develop new applications.
2.2 Experimental Implementation and Analysis
Methodology
2.2.1 Design of Quasi-2D Fluidised Bed Setup
The experiments are conducted using a quasi-2D cell constructed of Plexiglas with
a width of 45 cm, a thickness of 1 cm, and a length of 80 cm. The cell is connected
with a 20 cm long plenum chamber. Two domains are separated by a 3 mm thick
porous bronze metal plate (Grade 07, BK 10.30.07, Sintertech). A schematic of the
experimental setup is shown in Fig. 2.1.