INTRODUCTION:

When evenly distributed fluid is passed through a finely divided bed of solid particle the particle are undisturbed at low velocity, as air velocity is gradually increased a stage is reached when the individual particle are suspended in the air stream the bed is said to be a fluidized bed and exhibit a fluidic behavior. Fluidization process is very helpful in the industrial application, fluidization process found its application in fluid-solid contacting process and fluidize bed reactor technology. Fluidization process has advantage of providing a high degree mass transfer rate and heat transfer rate, low pressure drop and high temperature therefore fluidization process is widely used in industrial process since last six decade^[1].

The term hydrodynamics is associated with the theoretical or mathematical study of idealized, frictionless fluid behavior and the term hydraulic is used to describe the experimental aspects of real fluid behavior. The important hydrodynamic parameters are minimum fluidization, velocity, pressure drop and bed height. The minimum fluidization velocity and pressure drop is determined by both theoretical and experimental equation while bed height is only determined by experiment ^[2].

BasmaAbdulhadiBadday and A.V.S.S.K.S. Gupta et al (2014)^[1], Investigated the Minimum Fluidization Velocity of Gas-Solid Fluidization under Different Conditions used. Experiments showed that the minimum fluidization velocity increased as the particle size increased, at the same time there was no influence of bed inventory on minimum fluidization velocity.

Anwar Johari et al, (2007) ^[3], investigate the effect of sand size on the fluidization behavior in circular and rectangular column. The results show that, the fluidization quality was affected by the mean sand size being used. The effect of column sizes also contributed to the fluidization behavior in a fluidized bed. Bigger column was required to produce good fluidization behavior and column shape does not have any effect on the fluidization behavior.

1. MATERIAL:

Coal, green pea and sand selected for bed material during experiment because fluidization characteristics of each of three materials fall within the same category. All the material (coal, green pea, sand) should have the uniform shape, for better quality of the fluidization the particle should be provided with uniform shape. Three different size selected are 2mm, 4mm, 6mm, for comparing the fluidization characteristics of each particle table for property of material are given below.

Table 1 for Properties of the selected material selected for the experiment

S. No	Material	Density (kg/m³)	Size	Bed height
1.	Green pea	1428.57	2mm, 4mm, 6mm	4cm, 6cm, 8cm, 10cm
2.	Coal	1538.46	2mm, 4mm, 6mm	4cm, 6cm, 8cm, 10cm
3.	Sand	2666.7	2mm, 4mm, 6mm	4cm, 6cm, 8cm, 10cm

2. EXPERIMENTAL SET UP AND METHODOLOGY:

Fig.1 Schematic view of experimental set up for measurement of apparent viscosity of fluidized bed.

Table 2 Specification of the component for measuring hydrodynamics of fluidization

S. No	Component	Range
1	Air compressor	0-140 Psi
2	Rota Meter	0-700 LPM
3	Manometer	0-25 Cm of H₂O
4	Acrylic Cylinder pipe	Height - 100 cm Internal Diameter - 4 cm

Assumption:

The assumptions made during the experiment are

1. Fluidizing bed behave as Newtonian fluid^[4].

2. Fluidization in dense phase is assumed continuum on macroscopic scale^[5].

3. Air behaves as ideal gas and the flow is steady.

4. There isno bubblingand no slugging occur during fluid flow through fixed bed.

Procedure:

Air from the atmospheric is compressed in the compressor up to a certain pressure and then the compressed air is stored in the air receiver, the flow of compressed is controlled by regulator. This compressed air is used to fluidize the fixed bed of solid material by passing through the Rota- meter, the solid material is fluidizing within inside the acrylic pipe and the pressure drop is measure with the help U tube manometer

Rota meter is used to measure the flow rate of compressed air, the Rota meter is used for the measurement is having the range of 0-750 LPM, the Rota meter is fitted below the fixed bed so that the flow rate which is measured is the flow rate required for fluidizing the fixed bed, the Rota meter used is floating type and made up of acrylic body.

U-tube manometer is also used for the measurement of pressure of fixed bed, the pressure drop which is measured is the total pressure drop of the static bed therefore the manometer pipeline is fitted just below the fixed bed, an U-tube manometer is filled with the water for the measurement of pressure drop of bed.

Fluidization process is done within inside the hollow cylinder, the body of hallow cylinder is made of acrylic material, dimension of the acrylic body is having 100 cm of height and internal diameter of the cylinder is 4 cm.

Static Bed of the material for fluidization process is prepared by simply putting the desired material of desired size at a required bed height inside the acrylic cylinder column.

Initially the static packed bed of required size is prepared and the air is compressed and stored inside the air receiver and then the with the help of the regulator the flow rate is maintained, now the compressed air is passed through the fixed bed height at a certain flow rate with increasing the flow rate there is rise in the bed height at the same time there is increase in the pressure drop, for different flow rate the different bed height obtained as well as the pressure drop is noted down.

The Minimum Fluidization Velocity is identified by plotting the graph of Gas Velocity VS. Pressure drop initially with increase in flow rate there is increase in pressure drop after that increase in flow rate result in slight decreases in pressure drop and after that pressure drop become independent of flow rate and remain constant. The point of maximum pressure drop is the point of minimum fluidization velocity. By repeating the above procedure the minimum fluidization velocity identified for green pea, coal, sand for three different sizes.

With further increasing the flow rate there is rise in the bed height at the same time pressure drop remain constant, for different flow rate the different bed height obtained as well as the pressure drop is noted down

3. RESULT AND DISCUSSION:

Hydrodynamics of Gas-Solid Fluidization is studied by using air as a fluid and Green pea (ρ=1428.57 kg/m³), Coal (ρ=1538.46 kg/m³), and Sand (ρ=2666.7 kg/m³) as solid particle. In hydrodynamics of fluidized bed, the input parameter are static bed height, size of the particle and flow rate, these parameter are varied and the measuring parameters such as pressure drop, minimum fluidization velocity and rise in bed height are obtained experimentally.

Effect of Static bed height on Pressure Drop:

Effect of flow rate on pressure drop is plotted by fixing the static bed height and then the static bed height is varied and the graph is plotted with four different static bed heights (4cm, 6cm, 8cm, and 10cm) and then this procedure is repeated for three different sizes and three different materials. Now we will discuss the result and trend of graph obtained for green pea, coal and sand with different sizes (2mm, 4mm, and 6mm) of each material respectively.

A. For Green Pea as Fluidizing Bed Material

Fig-2 Graph for Effect of static bed height on pressure drop when Green pea (ρ=1428.57kg/m³) having Particle size 2 mm at four different bed height

Fig-3 Graph for Effect of Flow Rate on pressure drop when Green pea (ρ=1428.57 kg/m³) having Particle size 4 mm at four different bed height

Fig-4 Graph for Effect of Flow Rate on pressure drop when Green pea (ρ=1428.57 kg/m³) having Particle size 6 mm at four different bed height

B. For Coal as Fluidizing Bed Material

Fig-5 Graph for Effect of Flow Rate on Rise in Bed Height when Coal (ρ=1538.46 kg/m³) having Particle size 2 mm at four different bed height

Fig-6 Graph for Effect of Flow Rate on Rise in Bed Height when Coal (ρ=1538.46 kg/m³) having Particle size 4 mm at four different bed height

Fig-7 Graph for Effect of Flow Rate on Rise in Bed Height when Coal (ρ=1538.46 kg/m³) having Particle size 6 mm at four different bed height

C. For Sand as Fluidizing Bed Material

Fig-8 Graph for Effect of Flow Rate on Rise in Bed Height when Sand (ρ=2666.7 kg/m³) having Particle size 2 mm at four different bed height

Fig-9 Graph for Effect of Flow Rate on Rise in Bed Height when Sand (ρ=2666.7 kg/m³) having Particle size 4 mm at four different bed height

Fig-10 Graph for Effect of Flow Rate on Rise in Bed Height when Sand (ρ=2666.7 kg/m³) having Particle size 6 mm at four different bed height

Effect of flow rate on pressure drop for green pea, coal and sand as fluidizing bed material is plotted with fixed static bed height and particle size respectively, it is found that increasing the flow rate will increase the pressure drop up to the certain point after that pressure drop remain constant and pressure drop is independent of flow rate this point is known as minimum fluidization velocity therefore with the help of this plot minimum fluidization velocity is determined. Initially this graph is plotted between flow rate and pressure drop and keeping the static bed height and particle constant therefore the minimum fluidization velocity of each particle size at fixed static bed height is obtained and then this procedure is repeated with different static bed height and minimum fluidization is determined.It is found that with increasing static bed height there is increase in the pressure drop because increasing the static bed height will increase the weight of the static bed and there is rise in pressure drop.

Effect of particle size on pressure drop

Fig-11 Graph for Effect of Flow Rate on Pressure Drop when Green pea (ρ=1428.57 kg/m³) having constant static bed height (6 cm) with three different Particle size

Fig-12 Graph for Effect of Flow Rate on Pressure Drop when Coal (ρ=1538.46 kg/m³) having constant static bed height (6 cm) with three different Particle size

Fig 13 Effect of Flow Rate on Pressure Drop when Sand (ρ=2666.67 kg/m³) having constant static bed height (6 cm) with three different Particle size

Effect of particle size on in pressure drop is plotted with increasing flow rate at constant static bed and constant density, it is found that increasing the particle size will increase pressure drop, this is due to the fact that increasing the particle size will decrease the number of particle hence there is less number of particle available to fluidize in the air this tend to increase in voidage in fluidize bed, which cause fluid to pass between the particle hence more power is required to fluidize the bed therefore with increasing the particle size there is increase in pressure drop.

Effect of density on pressure drop

Fig-14 Graph for Effect of Flow Rate Pressure Drop having constant Static bed Height (6cm) with three different Particle Green pea (ρ=1428.57 kg/m³) Coal (ρ=1538.46 kg/m³) Sand (ρ=2666.67 kg/m³) and keeping the particle size (2mm) constant.

Fig-15 Graph for Effect of Flow Rate Pressure Drop having constant Static bed Height (6cm) with three different Particle Green pea (ρ=1428.57 kg/m³) Coal (ρ=1538.46 kg/m³) Sand (ρ=2666.67 kg/m³) and keeping the particle size(4mm) constant.

Fig-16 Graph for Effect of Flow Rate Pressure Drop having constant Static bed Height (6cm) with three different Particle Green pea (ρ=1428.57 kg/m³) Coal (ρ=1538.46 kg/m³) Sand (ρ=2666.67 kg/m³) and keeping the particle size (6mm) constant.

Effect of particle Density on Pressure is plotted Drop is keeping the static bed height and particle size constant, it is found that increasing the density of the particle will the rise increase pressure drop, this is due the fact that increase the density of the particle will increase the weight of the particle therefore at same flow rate and same static bed height higher density particle will have higher bed weight as compare to lower density material therefore due to the higher weight of particle will have the more Pressure Drop as compare to lower weight of the particle, higher density particle will have more Pressure Drop as compare to lower density particle.

2. Minimum fluidization velocity:

Minimum fluidization for material is obtained by plotting the graph of pressure drop and the obtained value of minimum fluidization is obtained is tabulated in the table.

Table 3 Minimum fluidization velocity of three different material Green pea (ρ=1428.57 kg/m³) Coal (ρ=1538.46 kg/m³) Sand (ρ=2666.67 kg/m³)

S. No	Material size	Particle size (cm)	Minimum fluidization velocity (m/s)	Flow rate (LPM)	pressure drop (cm of H₂0)
1	Green pea	2	1.67	192.5	3.1
2		4	1.944	224.5	4.1
3		6	2.33	269.5	4.6
4	Coal	2	1.83	211.4	3.7
5		4	2.083	240.6	4.4
6		6	2.617	301.5	4.8
7	Sand	2	2.03	234.2	6.3
8		4	3	346.5	8
9		6	3.194	368.9	8.8

Fig-17 Graph for minimum fluidization velocity and particle size with three different material Green pea (ρ=1428.57 kg/m³) Coal (ρ=1538.46 kg/m³) Sand (ρ=2666.67 kg/m³)

Minimum fluidization velocity is determined for green pea coal and sand with three different particle size and four different static bed heights and it is found that minimum fluidization is dependent on material density and size of the particle and minimum fluidization is independent of the static bed height.

Minimum fluidization is increases with increasing the size of the particle and density of the particle this is due to the fact that increasing the density of the particle increases the weight of the particle therefore more force is required to fluidize the bed and hence the minimum fluidization velocity increases while increasing the size of the particle will increase the surface area of the particle and hence the more resistance is provided by the particle therefore the minimum fluidizing velocity increases

Effect of Static bed Height on Rise in Bed Height:

Effect of flow rate on rise in bed height is plotted by fixing the static bed height and then the static bed height is varied and the graph is plotted with four different static bed heights (4cm, 6cm, 8cm, and 10cm) and then this procedure is repeated for three different sizes and three different materials. Now we will discuss the result and trend of graph obtained for green pea, coal and sand with different sizes (2mm, 4mm, and 6mm) of each material respectively

A. For Green Pea as a Fluidizing bed material

Fig. 18 Graph for Effect of Flow Rate on Rise in Bed Height when Green pea (ρ=1428.57 kg/m³) having Particle size 2 mm at four different bed height

Fig-4.19 Graph for Effect of Flow Rate on Rise in Bed Height when Green pea (ρ=1428.57 kg/m³) having Particle size 4 mm at four different bed height

Fig-20 Graph for Effect of Flow Rate on Rise in Bed Height when Green pea (ρ=1428.57 kg/m³) having Particle size 6 mm at four different bed height

B. When Coal is used as Fluidizing Bed material

Fig-21 Graph for Effect of Flow Rate on Rise in Bed Height when Coal (ρ=1538.46 kg/m³) having Particle size 2 mm at four different bed height

Fig-22 Graph for Effect of Flow Rate on Rise in Bed Height when Coal (ρ=1538.46 kg/m³) having Particle size 4 mm at four different bed height

Fig-23 Graph for Effect of Flow Rate on Rise in Bed Height when Coal (ρ=1538.46 kg/m³) having Particle size 6 mm at four different bed height.

C. Sand is used as Fluidizing bed material

Fig-24 Graph for Effect of Flow Rate on Rise in Bed Height when Sand (ρ=2666.6 kg/m³) having Particle size 2 mm at four different bed height

Fig.25 Graph forEffect of Flow Rate on Rise in Bed Height when Sand (ρ=2666.6 kg/m³) having Particle size 4 mm at four different bed heights

Fig-26 Graph for Effect of Flow Rate on Rise in Bed Height when Sand (ρ=2666.6 kg/m³) having Particle size 6 mm at four different bed height

Effect of flow rate on bed height is plotted for green pea, coal and sand by keeping the particle size constant, initially we plot flow rate and rise in bed height at constant static bed height, increasing the flow rate will increase the rise in bed height because increase in the flow rate will increase net upward force on the particle which will cause the individual particle to achieve higher height, hence rise in bed height is increasing and then this procedure is repeated for different static bed height and graph is potted and it is found that while keeping flow rate (flow rate should be above the flow rate required for minimum fluidization velocity) constant and increasing the static bed height will increase the rise in bed height because by increasing the net static bed height will increase the more number of particle having same density as compare to less static bed height therefore higher rise in bed height is achieved.

The graph is plotted for three different particle sizes (2mm, 4mm, 6mm) and four different static bed height and the trend is same for each graph, i.e. increasing the static bed height will increase the rise in bed height.

Effect of Particle Size on rise in Bed Height

Fig-27 Graph for effect of Flow Rate on Rise in Bed Height when Green pea (ρ=1428.57 kg/m³) having constant static bed height (6 cm) with three different Particle size

Fig-28 Effect of Flow Rate on Rise in Bed Height when Coal (ρ=1538.46 kg/m³) having constant static bed height (6 cm) with three different Particle size

Fig-29 Effect of Flow Rate on Rise in Bed Height when Sand (ρ=2666.67 kg/m³) having constant static bed height (6 cm) with three different Particle size

Effect of particle size on rise in bed height is plotted with increasing flow rate at constant static bed and constant density, it is found that increasing the particle size will decrease the rise in bed height, this is due to the fact that increasing the particle size will decrease the number of particle hence there is less number of particle available to fluidize in the air and also there is increase in voidage which cause fluid to pass between the particle hence there is less rise in bed height.

Effect of density on rise in Rise in Bed Height

Fig-30 Graph Effect of Flow Rate on Rise in Bed Height having constant Static bed Height (6 cm) with three different Particle Green pea (ρ=1428.57 kg/m³) Coal (ρ=1538.46 kg/m³) Sand (ρ=2666.67 kg/m³) and keeping the particle size constant.

Fig-31 Graph for Effect of Flow Rate on Rise in Bed Height having constant Static bed Height (6 cm) with three different Particle Green pea (ρ=1428.57 kg/m³) Coal (ρ=1538.46 kg/m³) Sand (ρ=2666.67 kg/m³) and keeping the particle size constant.

Fig-32 GraphEffect of Flow Rate on Rise in Bed Height having constant Static bed Height (6 cm) with three different Particle Green pea (ρ=1428.57 kg/m³) Coal (ρ=1538.46 kg/m³) Sand (ρ=2666.67 kg/m³)

Effect of density on rise in bed height is plotted with increasing flow rate at constant static bed and constant density, it is found that increasing the densitywill decrease the rise in bed height, this is due to the fact that increase the density of the particle will increase the weight of the particle therefore at same flow rate and same static bed height higher density particle will have higher bed weight as compare to lower density material therefore due to the higher weight of particle will have the more Pressure Drop as compare to lower weight of the particle, higher density particle will have more Pressure Drop as compare to lower density particle.

4. CONCLUSION:

In hydrodynamics of fluidization we determine the rise in bed height, pressure drop and minimum fluidization velocity by varying the static bed height size of particle for green pea, coal and sand. It is concluded that both pressure drop and minimum fluidization velocity increases with size of the particle and density of the particle while Minimum fluidization velocity is independent of the static bed height and Pressure drop increases with static bed height. Rise in bed height increases with increase in rise in static bed height and decreases with increase in size and density of the particle.

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Received on 21.07.2017 Accepted on 22.10.2017

Int. J. Tech. 2017; 7(2): 96-112.

DOI: 10.5958/2231-3915.2017.00016.5