Investigation of Hydrodynamics, Heat Transfer and Drying Characteristics Along the Variable Cross-Sectional Riser of BFBs

Along with my supervisor, I would like to express my deepest gratitude and respect to the members of the doctoral committee, Prof. I would also like to thank all the faculty members and staff of the Department of Mechanical Engineering for their continuous support in my research in various subjects such as procurement of materials and others.

Abstract

The action of a spiral reduces the drying time by 16.67% in a conical dryer of 10° cone angle. The EU and EUR are found to increase with the addition of a spiral and an increase in cone angle.

INTRODUCTION

MOTIVATION
IMPORTANCE OF DRYING

Constant rate period
Falling rate period

DIFFERENT TYPES OF DRYERS AND DRYING METHODS

Solar drying
Mechanical dryers

OUTLINE OF THE THESIS

In the first stage, moisture is removed from the surface of the particles, and. It is the average moisture content of the material at which the drying rate begins to decline.

2 Literature review

LITERATURE REVIEW

INTRODUCTION

NUMERICAL SIMULATION OF FLUIDIZED BEDS

Heat transfer study on fluidized beds

It was found that the heat transfer coefficient is the highest when installing a spherical immersion heater. Nevertheless, the heat transfer coefficient was found to decrease with increasing specularity coefficient.

EXPERIMENTAL STUDY OF FLUIDIZED BEDS

Peng and Fan studied the hydrodynamic behavior of Geldart-B type particles in a conical liquid-solid fluidized bed. investigated the minimum fluidization velocity (Umf), the minimum full fluidization velocity (Umff) and the maximum pressure drop (ΔPmax) in a conical fluidized bed.

PARAMETRIC STUDY ON HYDRODYNAMICS AND HEAT TRANSFER

Effect of cone angle
Effect of static bed height
Effect of particle size
Effect of superficial air velocity
Effect of particle density

Their study revealed that with the increase in the cone angle, both the minimum fluidization velocity and the minimum velocity for full fluidization increase. The maximum rate of full fluidization was found to increase with the increase in particle density [73,122] .

DRYING PHENOMENA IN DIFFERENT TYPES OF DRYERS

dried soybeans in a fluid bed dryer (FBD) and microwave assisted fluid bed dryer (MFBD). The drying rate was found to be higher in the fluid bed drying than in the hot air drying method.

ENERGY AND EXERGY ANALYSIS OF DRYING

The maximum exergy efficiency was observed to evaluate the energy and exergy analysis in a vertical fluid bed paddy dryer. Luthra and Sadaka performed energy and exergy analysis in a fluidized bed drying of rough rice by dry air temperature (40°C, 45°C, 50°C), drying bed condition (fluidized and fixed), drying time (30 min. , 45 min, 60 min), and dehumidification (yes, no) as parameters. performed energy and exergy analyzes for deep bed drying of paddy in a convective dryer.

RESEARCH GAP AND SCOPE FOR THE PRESENT INVESTIGATION

Literature discussing the effect of a coil or, for that matter, an internal one on the performance of drying properties in the context of conical bubbling fluid bed dryers is limited. Therefore, there is scope for studying the drying properties in fluidized bed dryers by incorporating a spiral as an interior. Literature related to investigating the effect of operating parameters such as spiral and cone angles on energy and exergy analysis in conical bubbling fluidized bed paddy dryers is limited.

CHAPTER CONCLUSION

The investigation of the second and third objectives will be discussed in Chapter 6, and the detailed investigation of the fourth objective will be discussed in Chapter 7.

Numerical simulation and procedure

NUMERICAL SIMULATION AND PROCEDURE

INTRODUCTION

NUMERICAL SIMULATION OF DRYERS

For the mesh analysis of the 2D model, a quadrilateral mesh with a bias factor of 10 towards the wall was used. Inflation function was used for all dryers with first layer thickness 0.0001 - maximum layers 18 - growth size 1.2. Multizone as hexahedral cells was used both in the core area and near the wall.

GOVERNING EQUATIONS AND THEIR CONSTITUTIVE RELATIONS

Previous studies show that the numerical results agree with the experimental results for the value of Ka= 0.7, so in the present study, Ka= 0.7 is considered. For solving problems, the value Kc was assumed to be a constant value of 1 in the present study. In the simulation, the following equation was used to calculate the interphase heat transfer coefficient, which is strongly dependent on the Nusselt number of solid particles.

CFD MODEL AND FORMULATION

Since the density of the secondary phase is much higher than that of the primary phase, the Schaeffer equation was therefore used. The fixed pressure consists of two terms: the primary term is the kinetic term and the next term comes from particle collisions. In fluidized bed simulation, solid pressure was determined from an equation of state similar to the equation of state for gases in the Van der Waals equation, as Pidduck et al.

NUMERICAL SOLUTION PROCEDURE

In this regard, the 3-D simulations were performed on a conical dryer with a cone angle of 10° for the operating parameter air velocities as 1.1 and 1.6 m/s. The other parts of the fluidized bed were considered as the wall, where there was a no-slip condition for the gas phase and a partial slip condition for the solid phase. The numerical formulation and probabilistic models used for this study were also explained in detail.

Table 3.2 Parameters used in the simulations

INTRODUCTION

EXPERIMENTAL SETUP

DETERMINATION OF MINIMUM FLUIDIZATION AND TERMINAL VELOCITY

If the cone angle is α, from the geometry of the figure it can be written as-. Equating equations (4.8) and (4.11), the minimum fluidization velocity can be calculated using the following equation. The equation was solved for three dryers, and minimum fluidization velocity was determined for sand and paddy particles.

EXPERIMENTAL PROCEDURE

Energy consumption
Energy analysis
Exergy analysis

Depending on the drying temperature, the following is the equation used to determine the specific heat of the drying air [156]:. Exergy analysis is the total exergy of the input, output and losses due to the irreversibility of the processes. The following expression is used to determine the exergy of the drying air at the inlet and outlet of the dryers.

Table 4.3 Input variable matrix considered for sand in the dryers

MILLING AND DRYING QUALITY

The steady-state exergy at any location of the dryer is the maximum potential work that can be achieved by drying the air relative to the surroundings and is evaluated from the second law of thermodynamics. In exergy analysis, thermodynamic properties include mass flow, specific heat, velocity, and temperature of the drying air, which is a combination of dry air and water vapor. When the drying air exergy at the inlet and outlet of the dryers was calculated using the above relationship, the exergy destruction was determined by the difference between the inlet and outlet exergy as described in Equation 4.26.

CHAPTER CONCLUSION

The drying quality of paddy rice was determined in terms of fiber, protein, fat and carbohydrate percentage. Different measurement methods are required to determine this dietary amount of rice grains, and a list of them is included in Table 4.5.

Performance evaluation of BFB dryers with sand as bed inventory

CHAPTER – 5

PERFORMANCE EVALUATION OF BFB DRYERS WITH SAND AS BED INVENTORY

INTRODUCTION

INTERDEPENDENCE OF GRID FOR 2-D MODEL

The bed pressure drop and pressure drop along the height of the three dryers from the 2-D simulation were compared with the experimental results. The pressure drop along the height of the three dryers is also demonstrated in Fig. It was observed that the 2-D simulation results of bed pressure drop and pressure drop along the height of three dryers differed significantly from the experimental results.

Figure 5.3: Contours of time-averaged solid volume fraction, (a) α = 0°, (b) α = 5°, and (c) α

GRID AND TIME INDEPENDENCE FOR 3-D MODEL

INCORPORATION OF DRAG MODEL

As a result, 1×10-3 s was used for further simulation to ensure accuracy and reduce physical simulation time. As a result, the Syamlal-O'Brien drag was used to describe the interphase exchange coefficient of the drag force equation during the entire simulation [ 36 ].

HYDRODYNAMIC BEHAVIOUR OF THREE DRYERS

Pressure analysis in three fluidized bed dryers
Bed expansion ratio for three dryers
Radial solid volume fraction for three dryers
Solid velocity in the radial direction for three dryers
Granular temperature with solid volume fraction for three dryers

It was observed from the figure that the pressure drop decreased along the height of the three dryers. From the contour of the solid volume fraction, it is observed that the uniform distribution of solid particles prevails in the conical riser of the highest degree of the cone angle. In this investigation, the numerical simulation of the radial profile of the solid volume fraction is shown.

Figure 5.12: Effect of cone angle on pressure drop along the height of three dryers

HEAT TRANSFER CHARACTERISTICS OF THREE DRYERS

Temperature distribution of three dryers

Since the grain temperature is determined by the square of the solid velocity fluctuation, the grain temperature increases as the solid velocity fluctuation increases. An increase in the velocity of the solid causes the formation of bubbles, which represent greater air permeability. Therefore, there is room for a detailed analysis of the hydrodynamic behavior and heat transfer characteristics of an efficient dryer with different operating parameters.

Figure 5.23: Comparison of temperature distribution between 3-D simulation and experiment 5.7.2 Interphase heat transfer for three dryers

HYDRODYNAMICS IN A CONICAL DRYER OF 10° CONE ANGLE

Bed expansion ratio of the conical dryer
Variation of pressure drop on the conical dryer

Therefore, the pressure drop is seen to decrease with the increase in intake air velocity. It was observed that the pressure drop height increases with the increase in air velocity. As a result, the pressure drop height is more for the higher value of air velocity.

Figure 5.25: Effect of bed height on bed expansion ratio

HEAT TRANSFER CHARACTERISTICS IN A CONICAL DRYER OF 10° CONE ANGLE

Experimental result of temperature distribution
Validation of 3-D simulation temperature distribution with the experimental temperature distribution
Interphase heat transfer coefficient

As a result, the convective heat transfer between air and solid particles and particle to particle increases. More solid particles move upwards as the airspeed increases, and they appear to be distributed in a radial direction. Therefore, the interphase heat transfer increases with the intake air velocity for the constant intake air temperature.

Figure 5.41: Bed temperature with bed height Figure 5.42: Bed temperature with particle size

CHAPTER CONCLUSION

It has been observed that the interphase heat transfer coefficient increases from 296 to 320 W/m2K with an increase in air velocity from 1 to 2 m/s. It was found that the interphase heat transfer coefficient increases from 288 to 306 W/m2K with increasing cone angle. It was also observed that the interphase heat transfer coefficient increases from 296 to 320 W/m2K when the air velocity increases from 1 to 2 m/s.

Performance evaluation of drying characteristics in BFB dryers

PERFORMANCE EVALUATION OF DRYING CHARACTERISTICS IN BFB DRYERS

INTRODUCTION

HYDRODYNAMIC BEHAVIOUR

At a given height of the dryer, the pressure drop was lower for a higher surface velocity. In addition, the effect of mixing sand particles with paddy dust on the pressure drop along the height of a conical dryer with a cone angle of 10° is investigated. Therefore, the effective height of the pressure drop was lower in the conical dryer with a larger cone angle.

Figure 6.1 shows the variation of experimental and numerical pressure drops between two consecutive pressure taps along the height of the conical dryer (α = 10°) at different superficial air velocities (1.1, 1.6 and 2.1 m/s) and a constant be

DRYING CHARACTERISTICS

As a result, drying time was reduced when sand particles were mixed with paddy particles. 6.14 (a) and (b) that a higher cone angle reduces drying time for the same amount of bed stock. A higher cone angle dryer with a coil was observed to have a drying time of 25 minutes.

ENERGY CONSUMPTION .1 Thermal energy consumption

Energy consumption of blower (ECB)

Similarly, the effect of the cone angle on the thermal energy consumption for the heater with a coil was also studied and shown in Fig. The thermal energy consumption was lower in case of the 10 cone angle of the conical dryer. The energy consumption of the blower has been reduced by 18% due to the installation of a spiral.

Figure 6.16: Thermal energy consumption at different inlet air temperatures

DRYING AND MILLING QUALITY

However, the difference in fan energy consumption between spiral and non-spiral was more prominent when the air speed increased. reaction whereby the protein and carbohydrate content of the paddy decreases. It was suggested by Cho et al. that due to oxidation, the percentage of protein content is reduced due to drying. Similarly, the milling quality for the same dryer was compared in table 6.3 with and without spiral.

THERMODYNAMIC (ENERGY AND EXERGY) ANALYSIS

Variation in energy utilization (EU)
Variation in energy utilization ratio (EUR)
Variation in exergy utilization
Variation in exergetic efficiency

The variation in EU was observed to increase over time with an increase in intake air velocity [158]. The effect of paddy rice mass and inlet air temperature on the variation of EU is also examined in Fig. The exergetic efficiencies were found to increase with the increase in intake air velocity, paddy mass and intake air temperature.

Figure 6.29: Variation in EU with inlet air velocity

CHAPTER CONCLUSION

The maximum exergy efficiency was found to be at an air velocity of 2.1 m/s and an inlet air temperature of 65°C for a mass of 3 kg. Therefore, it can be said that the conical dryer of a cone angle of higher degree has a higher exergetic efficiency with a coil. It was also observed that the cone dryer having a cone angle of 10° has higher single-coil energy efficiency than other non-coil dryers.

Economic Analysis of Dryers

CHAPTER – 7

ECONOMIC ANALYSIS OF DRYERS

INTRODUCTION
COST OF DRYING

Fixed cost
Variable cost

COST ANALYSIS OF THREE DRYERS

Cost analysis of conical dryer with cone angle 10°
Cost analysis of conical dryer with cone angle 5°
Cost analysis of cylindrical dryer (α = 0°)

SENSITIVITY ANALYSIS
CHAPTER CONCLUSION

CInstrumentation = Instrumentation cost (Rs./kg) Cdepreciation = Depreciation cost (Rs./kg) Cothers = Other cost (Rs./kg). Correspondingly, changes in sales price/kg and variable costs/kg have an impact on production results. Only the effect of selling price/kg and variable price/kg on output results for the three dryers was investigated.

Table 7.1 Different costs for the three dryers Calculation

Conclusions and scope for future work

CHAPTER – 8

CONCLUSIONS AND SCOPE FOR FUTURE WORK

CONCLUSIONS

Numerical and experimental investigation of hydrodynamic behaviour and heat transfer characteristics of sand particles in atmospheric bubbling fluidized bed dryers
Performance evaluation of drying characteristics of paddy particles in bubbling fluidized bed dryers with different operating parameters
Effect of spiral and cone angles on hydrodynamics and drying characteristics of paddy granules in bubbling fluidized bed dryers

The energy consumption of the blower was also found to decrease with a larger cone angle. The break-even period turned out to be shorter for a conical dryer with a cone angle of 10°. However, the profit per year turned out to be higher for the conical dryer at a cone angle of 10°.

APPLICATION POTENTIAL

Above this selling price, the BEP increased with the variable cost price/kg. After a critical analysis of the current research, it is recommended that a significant amount of exergy is lost at the end of a drying process. This loss of exergy can thus be reused as drying air by dehumidifying the exhaust air.

SCOPE FOR FUTURE WORK

Tsutsumi, Heat transfer in a conical fluidized bed of biomass particles with a pulsed gas flow, Particulology. Im, Numerical study of wall-to-bed heat transfer in a fluidized bed conical combustor, Int. Im, Numerical study of heat transfer in a fluidized bed conical combustor considering particle elasticity, Int.