Superficial Air Velocity Research Articles

Chaos and recurrence analyses of pressure signals from bubbling fluidized beds

Results from chaos and recurrence analyses of pressure signals from bubbling fluidized beds are presented in this study. The experiments were performed in cylindrical columns having internal diameters of 2.5 inches, 4 inches and 6 inches while operating conditions, material properties and static bed height were held constant. Superficial velocity of air at the inlet was varied from 2.97 to 5.35 times minimum fluidization velocity in each column. The test procedure involved randomization and replicates to estimate measurement uncertainty and identify bias if present. The columns were split into regions based on dominant physical mechanisms occurring within. Fractal measures were evaluated from differential pressure data which confirm deterministic chaos. They represent a broad range of spatial and temporal scales and were used to elucidate multiphase dynamics in different sections of these columns. Non-linear analysis is hence shown to provide more intuition particularly when a true scale-up study based on non-dimensional groups becomes prohibitive.

Determination of Heat Transfer Coefficients in Air-Solid Fluidized Bed

The heat transfer of gas-solid fluidized bed has been investigated using pre-heating system. A Perspex column of 7cm inner diameter and 1.5 m height is used as a fluidizing column filling with three different sizes of sand with a height of 21 cm as packing.The experimental work is carried out under superficial air velocities ranged of (0.029-0.365) m/s. The effect of opening area air distributors, particle diameter of sand packing, and different heat fluxes as powers have been investigated. The results show that the minimum fluidizing velocity increases with increasing the particle diameter and opening area of distributor. The gas-particle heat transfer coefficient is found to be increased by increasing superficial velocity, heat flux and opening area of distributor and decreased by particle diameter.A mathematical correlation of dimensionless groups based on experimental data has been suggested. A comparison between results of present correlation and the speculations of previous ones has been made.

An investigation of performance of a conventional U type loop-seal for CFB reactors with side and bottom aerations

Experiments were carried out in a circulating fluidized bed (CFB) system. The riser has a cross sectional area of 100×100mm2, while the supply and recycle chambers of the loop-seal have the same cross-sectional areas. Sand having a Sauter mean diameter of 310μm was used as bed material. Throughout the experiment, the superficial air velocity of the riser and the height of the solid particles in the storage column were kept constant. Four types of loop-seal categorized by their aeration scheme were investigated: aeration at the bottoms of supply and recycle chambers with side aeration at the supply chamber wall (USRQS), aeration at the recycle chamber bottom with side aeration at the supply chamber wall (URQS), aeration at the supply chamber bottom with side aeration at the recycle chamber wall (USQR), and aeration at the bottoms of supply and recycle chambers with side aeration at the recycle chamber wall (USRQR). The relation between the solid circulating rate and the side aeration flow rate was modeled as a saturated function. The results show that the URQS and the USQR types provide the same initial solid circulation rate, which is higher than for the conventional U type loop-seal. For a certain fluidization number, the loop-seals with side aeration provide higher solid circulation rate and require lower total aeration flow rate. The loop-seal with side aeration at the supply chamber wall tends to provide higher solid circulation rate and sensitivity of the circulation rate. For a certain solid particles height in the storage column, the maximum solid circulation rate was restricted by the flow through the horizontal passage.

Heat recovery from the Downcomer of a pressurized circulating fluidized bed during various transient conditions

An enormous amount of heat energy is available in the cyclone and downcomer of a circulating fluidized bed (CFB). The downcomer section can thus be a major source of heat recovery. There is scope for investigation on prospects of recovering heat along the downcomer. In the present work, an attempt is made to utilize the heat from the downcomer of a laboratory-scale Pressurized circulating fluidized bed (PCFB) set up by incorporating a spiral type of heat exchanger inside it. Transient behaviour of the heat recovery for various transient operating conditions such as superficial air velocity and power input which are operated under either step and ramp increase or decrease are reported. The PCFB unit in the present study consists of a riser of 2000 mm height and 54 mm inner diameter. The length of the downcomer is 1465 mm with an inner diameter of 54 mm. The results indicated that a maximum amount of around 350 W of heat could be recovered in the downcomer. It is also observed in some cases that this heat recovery fluctuates in phase with the transients in various operating conditions while it fluctuates with delays and phase shifts in others.

Performance Evaluation of drying Ccharacteristics in conical bubbling fluidized bed dryer

Paddy drying is an important task which is vital to the quality and storability of rice. Hence, evaluation of the drying process has to be performed for achieving a good quality of dried paddy in shorter duration. In this present work, performance evaluation of the drying process of paddy was experimentally investigated in two conical bubbling fluidized bed dryers with cone angles of 5° and 10° and results were compared with a conventional fluidized bed dryer having cone angle 0°. The experiments were conducted at three different superficial air velocities of 1.1, 1.6 and 2.1 m/s with bed inventories between 1 and 3 kg. Three different inlet air temperatures of 55, 60 and 65 °C were maintained for the evaluation of the drying process. Both hydrodynamic behaviour and drying characteristics have been investigated at these operating conditions. It has been evident from the experimental investigations that the conical fluidized bed dryer with 10° cone angle shows better performance than the other two dryers. The quality of the dried product has been tested for three different drying times and results were found to be in good agreement with the previously published literature. The milling quality was also tested for conical dryer and the use of a conical dryer recovered 77% of the milling rice.

A void fraction of high-viscosity air-water flow in capillary pipes with a slope of 30 degrees to the horizontal positio

Two-phase flow is a flow that is composed of several combined substances, namely liquid and gas. Two-phase flow is found in industrial processes, such as in boiler systems, reactors, heat exchangers, geothermal and others. The phenomenon of two-phase flow is also often found in nature, such as fog, snow, clouds, and rain. The purpose of this study was to obtain the characteristics, length, and frequency of flow patterns in two phases based on the experimental value of the fraction in a two-phase flow of a mixture of water-glycerin and air in a capillary tube with a slope of 30˚. The study used a 1.6 mm diameter capillary tube with a working fluid which mixed air and water mixed with glycerin with glycerin concentrations of 40%, 50%, 60%, and 70%. Void fraction values were analyzed using digital image processing methods with the MATLAB R2014a application program. The results showed that the void fraction value was determined by the surface velocity of the liquid and air. The greater the superficial air velocity, the value of the vacuum fraction will develop, while the greater the superficial velocity of the liquid, the vacuum fraction will decrease. The flow pattern of bubbles and plugs is strongly influenced by fluid viscosity. Therefore the higher the viscosity, the velocity of the bubble and plug flow patterns will decrease, conversely if the viscosity of the fluid decreases, the velocity of the bubble and plug flow patterns will increase. The length and flow of the bubble pattern are strongly influenced by homogeneous values (β). If the homogeneous value (β) is higher then the length of the flow pattern will increase. In the stopper flow pattern obtained a high enough frequency, it will produce a high enough void fraction value. Keywords: Two-phase, fluid, void fraction, viscosity, flow pattern.

Drying of stingless bees pot-pollen using swirling fluidized bed dryer

High moisture content in stingless bees pot-pollen makes preservation difficult. Since pot-pollen is heat sensitive, using conventional drying techniques below 40 °C is time consuming. A fluidized bed dryer (FBD) with swirling distributor is proposed for rapid drying of the pot-pollen while conserving the nutrients. The objectives of this study are to investigate the possibility of using swirling FBD to dry pot-pollen, and to investigate the effect of distributor type and superficial air velocity on pot-pollen drying. Stingless bees pot-pollen from the state of Pahang, Malaysia was dried at different conditions. Three distributor types: perforated, 45° inclination angle, and 67° inclination angle were tested at three superficial air velocities of 1.0 m/s, 1.5 m/s, and 2.0 m/s. Then, moisture content before and after drying were studied. To ensure swirling FBD would preserve the nutrition content of pot-pollen, nuclear magnetic resonance (NMR) analysis on the pot-pollen before and after drying was also carried out. It was found that at higher velocity, the drying rate increased. The 67° swirling distributor has the best drying performance, followed by the 45° swirling and perforated distributor. The highest reduction in moisture content, 13.5% in this study was found when using 67° distributor at 2.0 m/s. This translates to a drying rate of 0.450%/min, about 6.2 times faster than conventional FBD, 5.6 times faster drying rate compared to hot air dryer (HAD) at 45 °C, 44.5 times higher than oven drying at 30 °C, and also a staggering 225 times quicker than cyclic convective dryer (CCD). It is also comparable to lower power levels of microwave assisted vacuum dryer (MW-VD), without damaging pot-pollen nutrients. The NMR analysis showed no adverse effect due to drying. Hence, it is possible to dry pot-pollen rapidly using swirling FBD without damaging its nutrition content, and using the 67° swirling distributor is preferred.

Effect of superficial air velocity on the fluidized bed drying performance of stingless bee pot-pollen

Stingless bees or “kelulut” also produce pot-pollen apart from honey. The pot-pollen is mixed with honey and bee secretion before stored in cerumen pots. It has high nutritive value and medicinal benefits. Pot-pollens are often neglected by the beekeepers due to difficulty in storing and preserving them due to high moisture content. Hence, fluidized bed dryer is proposed as a suitable method to dry and enable convenient storage and preservation of the pot-pollen. Pot-pollen sample of initial moisture content 30.5% is dried at three superficial air velocities, 1.0 m/s, 1.5 m/s, and 2.0 m/s for 30 minutes. Fluidized bed drying has managed to decrease the moisture content down to 23%, 20.5%, and 18.5%, respectively. Higher superficial air velocity lead to higher drying rate in of pot-pollen. Hence, using a fluidized bed dryer to dry stingless bee pot-pollen is a promising method for preserving them. Subsequently, the dried pot-pollen can be easily commercialized in the future.

Fluidized bed drying of stingless bee pot-pollen: Performance of swirling distributor

Pot-pollen is pollen collected by stingless bee, mixed with honey and bee secretion, and then stored in cerumen pots. Raw pot-pollen contains high moisture content which can lead to excessive fermentation and spoilage. Drying of pot-pollen is needed to preserve them. Typically, elevated temperature can increase the drying performance. However as pot-pollen is heat sensitive, heating above 40 °C is not preferable. Hence, the objective of this study is to explore drying performance of fluidized bed dryer with swirling distributor. The experiment was conducted using three different distributors, a perforated distributor, 45° and 67° swirling distributor, at 1.0 m/s and 1.5 m/s superficial air velocities. The weight of pot-pollen used in this experiment is 50 grams. The drying experiment was conducted at ambient conditions, with no heating being applied to the pot-pollen samples. It was found that 67° swirling distributor at 1.5 m/s superficial air velocity has the highest improvement in terms of drying performance, able to reduce the moisture content from 30.5 % to 18 % for 30 minutes drying time. Hence, using swirling distributor is a suitable enhancement to fluidized bed drying especially for heat sensitive food materials.

Investigation of the Effect of Fluids Superficial Velocity on Initiation and Development of Slug Flow in a Horizontal Hydraulics Pipe

The aim of this study is to investigate the effect of fluids superficial velocity on the characteristics of two-phase slug flow in a horizontal hydraulics pipe covering slug flow initiation and development. Air and water were employed as the working fluids. Slug flow characteristics were visually observed at 25D and 200D in a 19 mm internal diameter of acrylic pipe for the initiation and fully developed slug flow conditions, respectively. Flow visualization was taken using high speed video cameras at 400 fps and then analyzed using image processing method. Based on the flow pattern characteristics, several slug flow initiation mechanisms were obtained. Under the investigated conditions, at low to medium air superficial velocity (JG) with low to high water superficial velocity (JL), slug flow initiation mechanisms consisted of wave growth, hydraulic jump, blockage, and slug decaying. While wave initiation, wave formation, disturbance, wave coalescence, and incompletely developed slug mechanisms were observed at medium to high JG with low to high JL. After slug flow was fully developed, it was found that the higher the water superficial velocity resulted in lower void fraction and higher slug frequency. In the meantime, pressure drop and liquid slug velocity increased considerably with the increase of both JG and JL. Maximum pressure drop of 8.35 kPa/m occurred at JL of 2.00 m/s and JG of 3.76 m/s. The highest slug frequency of 6.67 1/s was observed at JL of 2.00 m/s and JG of 2.12 m/s. This information is important for designing fluid flow in horizontal hydraulics pipes and for consideration in predicting the development of the slug flow in order to avoid the negative impact of slug flow in industrial applications.

Study of intermittent flow characteristics experimentally and numerically in a horizontal pipeline

The gas-liquid intermittent flow regime is the dominant flow pattern, which significantly occurs in the oil and gas industries. The intermittent flow is challenging in the hydrocarbon transportation systems and separators operation. The present investigation aims to comprehend the behavior of intermittent flow characteristics using experimental and numerical methods simultaneously. Superficial velocities of water and air were set in ranges of (0.18–0.84 m/s) and (1.22–4.9 m/s), respectively. The research was conducted in a horizontal pipe with a diameter of 44 mm and 147D long to study slug frequency, slug length, translational slug velocity, pressure drops, as well as slug's initiation location using static pressure data and high-speed camera tools. In this regard, the volume of fluid (VoF) method and SST k-ω model were also applied to specify film thickness, maximum Taylor bubble velocity, and to grasp behaviors of the flow field in more detail. The results revealed that liquid superficial velocity has more effects on slug frequencies than gas superficial velocity. On the other hand, slug initiation location, as well as slug fully developed length, is affected by the gas superficial velocity more than liquid superficial velocity. Moreover, both the gas and liquid superficial velocities have the same effects on translational slug velocities. The obtained experimental results were also employed to define a distinctive inlet boundary condition in the numerical simulation, which leads to a 65 percent reduction in the computational domain.

Velocimetry and response surface regression analysis of a swirling bed tested with mesh-coupled axial blade distributor.

Fluidized bed technology is being used in several industrial processes. The well-controlled fluidization of a bed material is a prerequisite for successful implementation of this technology. Several variants of distributors are being tested for fluidized beds; however, scant information is available on their working regimes. In this study, an annular distributor was constructed by fixing blades between two concentric rings and covering the assembly with a wire mesh. This new distributor design was tested for fluidization of batches of a spherical bed material at different blade angles and superficial air velocities (SAVs). High-speed imaging and MATLAB supported velocimetry techniques were used to generate velocity vector fields of fluidized beds. These fields were analyzed further for bed velocity measurements at different bed zones. A response surface regression model was applied on the data to predict the response of the bed parameters. Statistically, the bed velocity was predicted to be about 0.497 m/s with the confidence interval in the range of 0.4948-0.4999. The experimental bed velocity remained between 0.531 m/s and 0.538 m/s under an optimized blade angle of 60°, SAV of 2.3 m/s, and bed weight of 500 g.

Prospects of utilization of waste dumped low-grade limestone for iron making: A case study

Low grade dumped limestone sample having high silica of 8.1%, 36.8% CaO, and 3% Al2O3 has been studied with the aim to reduce the silica level to below 3% for its utilization in iron making. Beneficiation study of the sample was initiated with desliming of the feed sample of −100 µm to remove the siliceous ultrafine particles and to improve the feed quality. Flotation study was carried out by column flotation technique varying the collector dosage, superficial air flow velocity and froth depth to assess their effect on silica reduction and CaO recovery. It was observed that increased collector dosage and superficial air velocity increases the recovery of CaO, and increase in the froth depth reduces the mass flow and silica content in the concentrate. The best result was found at 1.25 cm/sec superficial air velocity, 25 cm froth depth, 1.25 kgpt collector dosage and concentrate assayed 47.3% CaO, 2.8% silica with 72% CaO recovery.

Experimental and Numerical Studies of Two-Phase Flow in Ribbed Periodic Vertical Channel

Pressure drop in a ribbed vertical channel was studied for a two-phase (air and water) flow, different shapes of ribs (triangle, semi-circular, and rectangle) were used in this investigation. An experimental rig was constructed with a test channel having the dimensions (10×3×70 cm) that enabled the flow patterns visual observation. An experimental setup of a two-phase was done for the present investigation, as well as a sum of (150) two-phase data with various flow patterns was determined. The used water superficial inlet velocities were in the range (0.0333 - 0.0888 m/s), and the air superficial inlet velocities were in the range (0.0555 - 0.1666 m/s). The experimental pressure drop according to a smooth plate was (41%, 38%, and 35%) for a channel fitted with semi-circle, rectangular and triangular ribs, respectively. The less pressure drop recorded was in the triangular ribbed channel, which indicates that the triangular shaped ribbed channel is the finest shape among the studied ones to lower the pressure drop. As future work, the numbers and dimensions of ribs can be changed to investigate its effect on the two-phase flow and the pressure drop, another suggestion for the future investigations is to include other fluid to have a three-phase flow, also the inclination angle of the duct can be changed to study its effect.

Gradual contraction of pipe cross-section effects on transient behavior of air–water slug flow

The current experimental investigation was aimed at understanding the influence of reducing sections on the transient behavior of slug flow. Experiments were carried out using two concentric area cross-section reducers with 160 mm lengths; the first one was shaped as a conical frustum with a 44 mm inlet diameter reducing to a 30 mm outlet diameter and the second one as a frustum with the same inlet diameter converting to a rectangular cross-section (34 mm × 21 mm). Four different water superficial velocities (0.43, 0.55, 0.72 & 0.84 m s−1) and three different air superficial velocities (2.5, 3.6 & 4.9 m s−1) were applied in the course of the experiments. Visualization studies, as well as frequency distribution analyses, were used to observe flow field changes. The visualization study showed that the gas slug tail, liquid slug, and gas slug subsequent to passing through the reducers converted to non-homogeneous bubbly flow, several small slugs, and pseudo-slugs, respectively. The obtained frequency distributions, which were calculated using a Fourier transform tool, showed that unlike that of the dominant frequency, the power of other frequencies was amplified in the low-frequency range owing to the high formation rate of pseudo-slugs and small slugs. This change indicates that intermittent air–water slug flow with a specified dominant frequency subsequent to passing reducers varies to an uncertain flow with semi-uniform distribution in the low-frequency range. Estimation of Shannon entropy also showed that entropy increased by almost five times downstream of the reducers, which confirms that energy is distributed uniformly in a broad frequency bandwidth. Analyses of the essential bandwidth showed that the reducing section acted as a frequency distribution modifier whose performance decreased with liquid flow rate increments. Based on this achievement, it was found that both the circular and the rectangular reducers were able to generate the named conditions.

Experimental analysis of the humidification of air in bubble columns for thermal water treatment systems

The humidification-dehumidification process (HDH) for desalination is a promising technology to address water scarcity issues in rural regions. However, a low humidifier efficiency is a weakness of the process. Bubble column humidifiers (BCH) are promising for HDH, as they provide enhanced heat and mass transfer and have low maintenance requirements. Previous studies of HDH-systems with BCHs draw different conclusions regarding the impact of superficial air velocity and liquid height on the humidification. Furthermore, the impact of flow characteristics has never been investigated systematically at all. In this study, an optimized BCH test setup that allows for optical analysis of the humidifier is used and evaluated. Our test setup is validated, since the influence of water temperature on the humidification, which is exponential, is reproduced. Measurements with seawater show that the normalised system productivity is increased by about 56% with an increase in superficial air velocity from 0.5cm/s to 5cm/s. Furthermore, the system productivity is increased by around 29% with an increase in liquid height from 60mm to 378mm. While the impact of superficial air velocity can be traced back to temperature changes at the humidifier and dehumidifier outlets, the impact of liquid height is shown to be caused by a smaller heat loss surface in the humidifier with an increase in liquid height. For the impact of sieve plate orifice diameter, a clear influence on the humidification is not apparent, this parameter needs to be investigated further. Finally, our new test setup allows for analysing the humidification of air (1) in a systematic way, (2) in relevant measurement ranges and (3) in comparison with optical analyses of the flow characteristics.

Single- and two-phase pressure drop through vertical Venturis

An experimental investigation of the pressure drops measurements in a Venturi placed in a vertical pipe is achieved. Venturis with diameter ratios equal to 0.4, 0.55, and 0.75 were employed. Differential pressure transducers were used to measure the pressure drop between the Venturi inlet and the throat sections. The void fraction was measured upstream the Venturi using a conductance probe technique. Air and water superficial velocities ranges were chosen to cover single-phase flow and bubbly, slug, and churn flow regimes. The single-phase pressure drop increases with the liquid superficial velocity. The Venturi pressure drop coefficient increases with decreasing the Venturi area ratio. The discharge coefficient increases slightly with this ratio and approaches a value of unity at high Reynolds number. The two-phase flow pressure drop and the multiplier coefficient increase with the gas superficial velocity and with decreasing the area ratio. Dimensionless pressure drop decreases with increasing the liquid to gas superficial velocity ratio and approaches an asymptotic value at high ratio (greater than 10). This value matches the single-phase flow dimensionless pressure drop value at high Reynolds number. The Venturi with area ratio equal to 0.55 was shown to correlate well the two-phase multiplier and the liquid holdup.

Effect of superficial air and water velocities on the erosion of horizontal elbow in slug flow

During the development of oil and gas fields, it is common for elbow suffering from sand wear. In this study, the erosion performance of 316 L stainless steel at the elbow was analyzed using the slug flow erosion experiment loop. The experiment was conducted under slug flow with different superficial air and water velocities using a detachable elbow. After weighing the mass loss and analyzing the sample surface, the erosion rates in different parts of the elbow were quantified and the erosion regularity was analyzed. The results indicate that the increase in superficial air velocity has a greater impact on the erosion rate than that in the superficial water velocity. The maximum erosion damage occurs at the outer wall in the 67.5° position. With the increase in superficial air and water velocity, the number of scratches on the maximum erosion position reduces.

Nutrient (sulphate) removal from wastewater in inverse fluidized bed biofilm reactor

Sulphate is one of the inorganic nutrient pollutants present in wastewater which needs to be treated due to present day global stringent emission norms. Among the several available biological means to treat industrial wastewaters, the use of inverse fluidized bed biofilm reactors (IFBBRs) has gained much attention in recent years over other fluidized bed reactors. In this work, the feasibility of removal of sulphate from synthetic wastewater having initial concentrations of 13.096, 32.74, and 65.48 mg/l was studied using mixed bacterial culture. Spherical polypropylene balls were taken as biomass support particles having density of 920 kg/m3 and diameter of 5.63 mm. Three different bed-volume to reactor-volume (Vb/Vr) ratios i.e., 0.304, 0.380, & 0.445 and three different superficial air velocities i.e., 0.0065, 0.0085, & 0.0106 m/s were considered for experimental runs. The reactor inoculum was prepared from the sludge collected from local steel industry’s wastewater treatment plant. The effects of different input parameters such as Vb/Vr ratio, superficial air velocities, and initial concentration of sulphate in synthetic wastewater on the output sulphate concentration were studied. Temperature of 30–32 °C and pH of 8.3–8.8 were maintained throughout the degradation studies. The reactor was operated in semi-batch recirculation mode with superficial water velocity of 0.0021 m/s. Sulphate concentration was measured by turbidity method using UV spectrophotometer at 420 nm which is as per APHA standards. The maximum removal efficiency of sulphate was found to be 72–75% which was achieved at a Vb/Vr ratio of 0.380 and the superficial gas velocity of 0.0085 m/s observed at a time of 40 h. Higher sulphate reduction was not achieved due to presence of more inorganic salts in the synthetic wastewater. At higher initial sulphate concentration, reactor operational difficulties were observed.

Experimental investigation of two-phase separation in a horizontal T-junction with vertical branch arm

T-junctions are commonly used in offshore platforms and process industry. When two-phase flow passes through T-junction, separation of two-phases takes place. This separation of two-phase flow through T-junction produces high liquid carry-over in the branch arm, causing breakdown of downstream equipment. In this experimental study, phase separation data have been obtained for air-water mixture flow through dividing T-junction with a pipe diameter of 74 mm and the branch arm is positioned vertically upward. T-junctions with diameter ratios of 1, 0.67, 0.5, and 0.27 were tested in the slug flow regime. The superficial velocities of air (JG1) were varied 0.20 - 1.16 m/s and inlet water superficial velocities (JL1) were varied 0.40-0.53 m/s. The extraction ratio between branch arm and main arm (W3/W1) was varied between 0 to 1. It was observed that the phase separation efficiency of T-junction depends upon the diameter ratio, upstream superficial velocities of both phases - air and water. Finally, the experimental data have been compared against the predicted results obtained from the numerical correlations.