Partition Gap Research Articles

Fluidization regimes for alginate aerogel particles in a laboratory scale Wurster fluidized bed

Fluidization regimes for alginate aerogel particles with two different particle sizes were characterized in a laboratory scale Wurster fluidized bed both in the annular zone and the tube zone. For both particle sizes, minimum fluidization and bubbling regimes were observed in both of the zones whereas pneumatic regimes existed only in the tube zone. Moreover, a new regime which was horizontal circular motion was identified for large particles in the tube zone. There existed two other regimes in the bed which were turbulent and circulatory particle motion regimes. All fluidization regimes were mapped on Kunii and Levenspiel diagrams. Circulatory particle motion regime was given on these diagrams for the first time. Furthermore, effects of particle size, batch volume, Wurster tube size, perforated plate geometry and partition gap height on the boundaries of each fluidization regime were investigated by measuring superficial air velocities at the onset and the end of each regime.

Measuring the dynamic response of the thylakoid architecture in plant leaves by electron microscopy.

The performance of the photosynthesis machinery in plants, including light harvesting, electron transport, and protein repair, is controlled by structural changes in the thylakoid membrane system inside the chloroplasts. In particular, the structure of the stacked grana area of thylakoid membranes is highly dynamic, changing in response to different environmental cues such as light intensity. For example, the aqueous thylakoid lumen enclosed by thylakoid membranes in grana has been documented to swell in the presence of light. However, light‐induced alteration of the stromal gap in the stacked grana (partition gap) and of the unstacked stroma lamellae has not been well characterized. Light‐induced changes in the entire thylakoid membrane system, including the lumen in both stacked and unstacked domains as well as the partition gap, are presented here, and the functional implications are discussed. This structural analysis was made possible by development of a robust semi‐automated image analysis method combined with optimized plant tissue fixation techniques for transmission electron microscopy generating quantitative structural results for the analysis of thylakoid ultrastructure.Significance StatementA methodical pipeline ranging from optimized leaf tissue preparation for electron microscopy to quantitative image analysis was established. This methodical development was employed to study details of light‐induced changes in the plant thylakoid ultrastructure. It was found that the lumen of the entire thylakoid system (stacked and unstacked domains) undergoes light‐induced swelling, whereas adjacent membranes on the stroma side in stacked grana thylakoid approach each other.

Simulation of pellet coating in Wurster coaters.

A combination of computational fluid dynamics (CFD), discrete element method (DEM), and discrete droplet method (DDM), i.e., a CFD-DEM-DDM model, was developed to simulate coating of pellets in a Wurster coater. The model equations were implemented in parallel using an approach that uses the computational resources of both CPU and GPU. Effects of the gas flow pattern, inlet gas temperature, partition gap, and spray characteristics were studied on the process. Decreasing the peripheral gas velocity, increasing the central jet velocity, and reducing the partition gap caused more uniform distributions of the circulation time and draft tube time, while the inlet gas temperature had negligible effect on them. Very high jet velocity caused a wider distribution of the circulation time. The dynamics of the spray and its interaction with pellets had significant effects on the coating mass distribution. Widening the spray angle while maintaining the droplet size constant caused the most uniform coating mass distribution and the highest deposition rate. Heat and mass transfer conditions as well as the deposition pattern changed the distributions of the solvent content and temperature of the pellets.

Investigation of Hydrodynamic Behavior of Alginate Aerogel Particles in a Laboratory Scale Wurster Fluidized Bed.

The effects of design and operating parameters on the superficial velocity at the onset of circulatory motion and the residence time of alginate aerogel particles in a laboratory scale Wurster fluidized bed were investigated. Several sets of experiments were conducted by varying Wurster tube diameter, Wurster tube length, batch volume and partition gap height. The superficial velocities for Wurster tube with 10 cm diameter were lower than the tube with 8 cm diameter. Superficial velocities increased with increasing batch volume and partition gap height. Moreover, increasing batch volume and partition gap height led to a decrease in the particle residence time in the Wurster tube. The results showed that there is an upper limit for each parameter in order to obtain a circulatory motion of the particles. It was found that the partition gap height should be 2 cm for proper particle circulation. Maximum batch volume for the tube with 10 cm diameter was found as 500 mL whereas maximum batch volume was 250 mL for the tube with 8 cm diameter. The fluidization behavior of the aerogel particles investigated in this study could be described by the general fluidization diagrams in the literature.

EFDC simulation of fishway in the Diversion Dahaerteng River to Danghe Reservoir, China

In order to mitigate the threat that hydraulic engineering will have on the fish’s living environment, fish migration can be accomplished by building fishway. This paper takes the Diversion Dahaerteng River to Danghe Reservoir project in Gansu, China as an example. Through field investigation and data analysis, it was found that the main fish in the study area was Triplophysa. Through the comparison of the advantages and disadvantages of the fishways, it is determined that the fishway and the nature-like fishway are suitable. By constructing the evaluation method, the 19 indicators of the fishway were scored from the aspects of ability to lure fish, ability to pass fish, fish adaptability, engineering quantity, operation and maintenance, and the nature-like fishway was determined to be the best choice. The surface runoff from March to August is calculated by the P-III curve to simulate the flow field of the Dahaerteng River under the conditions of maximum, minimum and average runoff. The flow velocity of the simulation results is suitable for the Triplophysa migration, and the right bank is suitable for building nature-like fishway. The fishway section is rectangular, with a slope of 1%, a width of 2 m, and a total length of 520 m. It is arranged with a staggered baffle, and the revetment is rough masonry stones. The inside of the fishway is inlaid with pebbles so that the roughness of the fishway is more than 0.03. Then, numerical simulation calculations were carried out for the fishways composed of the partitions of 10 m and 5 m apart. The comparison shows that the fishway with the partition gap 5 m is closer to the right bank of the river, which is suitable for Triplophysa migration and survival. For later evaluation and adjustment, an observation room and a fish collection pool are provided near the entrance of the fishway, and an observation room is provided near the exit. This paper can provide reference for the planning, construction and post evaluation of fishways.

Development and experimental study of an improved basin type vertical single distillation cell solar still

This paper presents an experimental study on basin type solar still having tilted double glass cover and having single vertical distillation cell consisting of two closely spaced vertical parallel plates, at the backwall. The feed water side of plate was covered with partitioned wick structure and individual feed water channels were used for each of the partitioned wick structure areas to ensure uniform wetting of wick. In order to increase the productivity of proposed improved still, the temperature drop across the distillation cell was maintained low by controlling the cooling of second plate by placing a third external vertical plate at a gap of 25mm from second plate of distillation cell. The cumulative efficiency of the proposed improved still with 10mm partition gap was found to be 10–15% (magnitude) higher than that of the conventional basin type still of same basin area and glass cover area.

Cluster Formation and Drag Reduction—Proposed Mechanism of Particle Recirculation within the Partition Column of the Bottom Spray Fluid-Bed Coater

Bottom spray fluid-bed coating is a common technique for coating multiparticulates. Under the quality-by-design framework, particle recirculation within the partition column is one of the main variability sources affecting particle coating and coat uniformity. However, the occurrence and mechanism of particle recirculation within the partition column of the coater are not well understood. The purpose of this study was to visualize and define particle recirculation within the partition column. Based on different combinations of partition gap setting, air accelerator insert diameter, and particle size fraction, particle movements within the partition column were captured using a high-speed video camera. The particle recirculation probability and voidage information were mapped using a visiometric process analyzer. High-speed images showed that particles contributing to the recirculation phenomenon were behaving as clustered colonies. Fluid dynamics analysis indicated that particle recirculation within the partition column may be attributed to the combined effect of cluster formation and drag reduction. Both visiometric process analysis and particle coating experiments showed that smaller particles had greater propensity toward cluster formation than larger particles. The influence of cluster formation on coating performance and possible solutions to cluster formation were further discussed.

An Efficient Data Collection Model Using Phantom Partitioning to Reconnect Traffic Partitioned Node in Wireless Sensor Network Structure

Abstract Although traffic partitioned node on wireless sensor network has been under way for many years and many energy optimization model have been investigated, it is still unclear whether integer linear programming problem is consistently effective on overlapping time over multiple mobile elements. With the objective of measuring the energy consumption on partitioning multi-hop wireless communications, a Traffic Reconnect Set-up Partitioning (TRSP) method is proposed in this paper. TRSP finds the affected location on varying range of mobile elements and reconstruct the network structure accordingly. A framework for traffic reconnect set-up partitioning based on inter partition gaps using the phantom partitioning concept is designed that identifies the network partitioning for most practical conditions using the NS2 simulator. With this, the TRSP with phantom partitioning balances the constraints with double cut method. The double cut based partitioning leads to safe route path by minimizing the energy consumption of sensor nodes in sensor network structure. The reestablishment of connectivity using the TRSP method provides improved data collection using the centroid mean point collection. The centroid mean point collection works with reconnect partition free sensor network system for varying range of mobile elements by achieving higher performance rate. The most affected location (i.e.,) partitioned nodes is identified and connectivity is reestablished during data aggregation. Simulation results demonstrate that the proposed TRSP method achieves better performance than the state-of-the-art methods in terms of energy consumption, data collection efficiency, and bandwidth rate.

Quality control of photosystem II: direct imaging of the changes in the thylakoid structure and distribution of FtsH proteases in spinach chloroplasts under light stress.

Under light stress, the reaction center-binding protein D1 of PSII is photo-oxidatively damaged and removed from PSII complexes by proteases located in the chloroplast. A protease considered to be responsible for degradation of the damaged D1 protein is the metalloprotease FtsH. We showed previously that the active hexameric FtsH protease is abundant at the grana margin and the grana end membranes, and this homo-complex removes the photodamaged D1 protein in the grana. Here, we showed a change in the distribution of FtsH in spinach thylakoids during excessive illumination by transmission electron microscopy (TEM) and immunogold labeling of FtsH. The change in distribution of the protease was accompanied by structural changes to the thylakoids, which we detected using spinach leaves by TEM after chemical fixation of the samples. Quantitative analyses showed several characteristic changes in the structure of the thylakoids, including shrinkage of the grana, outward bending of the marginal portions of the thylakoids and an increase in the height of the grana stacks under excessive illumination. The increase in the height of the grana stacks may include swelling of the thylakoids and an increase in the partition gaps between the thylakoids. These data strongly suggest that excessive illumination induces partial unstacking of the thylakoids, which enables FtsH to access easily the photodamaged D1 protein. Finally three-dimensional tomography of the grana was recorded to observe the effect of light stress on the overall structure of the thylakoids.

Separation of Dry Particulate Mixtures by Controlled Vertical Vibration

Physicists at the University of Nottingham, UK, have identified that through careful control of frequency and acceleration during the course of vertical vibration different types of particles can be positioned and/or segregated in a small rectangular cell. Based on this work the work presented in this paper focuses on the operation of a novel, dry-based, semi-continuous, and scaled-up version of the prototype scaled particle separator. The newly designed separator was driven by a pneumatically powered vertical vibration bench. Dry, noncohesive mixtures of sand and bronze particles (<500 µm) were vertically vibrated under different operating conditions to assess their separation behaviors. The work reported in this article led to the identification of significant particle separation parameters such as: particle bed height, partition gap distance, and initial mixture concentration. Experiments on a new semi-continuous particle separator confirmed what was identified previously in that good separation could be achieved through careful control of the frequency and acceleration. This information lays the foundations for a new breed of low cost, dry separator for fine particle mixtures.

Online monitoring of particle mass flow rate in bottom spray fluid bed coating—Development and application

The primary purpose of this study is to develop a visiometric process analyzer for online monitoring of particle mass flow rate in the bottom spray fluid bed coating process. The secondary purpose is to investigate the influences of partition gap and air accelerator insert size on particle mass flow rate using the developed visiometric process analyzer. Particle movement in the region between the product chamber and partition column was captured using a high speed camera. Mean particle velocity and number of particles in the images were determined by particle image velocimetry and morphological image processing method respectively. Mass flow rate was calculated using particle velocity, number of particles in the images, particle density and size information. Particle velocity and number findings were validated using image tracking and manual particle counting techniques respectively. Validation experiments showed that the proposed method was accurate. Partition gap was found to influence particle mass flow rate by limiting the rate of solids flux into the partition column; the air accelerator insert was found to influence particle mass flow rate by a Venturi effect. Partition gap and air accelerator insert diameter needed to be adjusted accordingly in relation to the other variability sources and diameter of coating cores respectively. The potential, challenges and possible solutions of the proposed visiometric process analyzer were further discussed.

Air-dictated bottom spray process: impact of fluid dynamics on granule growth and morphology

Background: Growing interest in the use of the less-explored bottom spray technique for fluidized bed granulation provided impetus for this study. Aim: The impact of fluid dynamics (air accelerator insert diameter; partition gap) and wetting (binder spray rate) on granule properties were investigated. Method: In this 33 full factorial study, the results were fitted to a quadratic model using response surface methodology. The air velocity at the spray granulation zone for the investigated conditions was measured using a pitot tube. Results: Air accelerator insert diameter correlated to measured air velocity at the spray granulation zone and was found to not only dictate growth but also influence granule morphology. The partition gap was found to play important roles in regulating particle movement into the spray granulation zone and optimizing process yields, whereas binder spray rate significantly affected granule morphology but not granule size. Conclusions: Unlike conventional fluidized bed granulation, ease of modulation of fluid dynamics and insensitivity of the bottom spray process to wetting allow flexible control of granule size, shape, and flow. Its good drying ability also indicated potential use in granulating moisture-sensitive materials.

Dynamic flexibility in the structure and function of photosystem II in higher plant thylakoid membranes: the grana enigma

Grana are not essential for photosynthesis, yet they are ubiquitous in higher plants and in the recently evolved Charaphyta algae; hence grana role and its need is still an intriguing enigma. This article discusses how the grana provide integrated and multifaceted functional advantages, by facilitating mechanisms that fine-tune the dynamics of the photosynthetic apparatus, with particular implications for photosystem II (PSII). This dynamic flexibility of photosynthetic membranes is advantageous in plants responding to ever-changing environmental conditions, from darkness or limiting light to saturating light and sustained or intermittent high light. The thylakoid dynamics are brought about by structural and organizational changes at the level of the overall height and number of granal stacks per chloroplast, molecular dynamics within the membrane itself, the partition gap between appressed membranes within stacks, the aqueous lumen encased by the continuous thylakoid membrane network, and even the stroma bathing the thylakoids. The structural and organizational changes of grana stacks in turn are driven by physicochemical forces, including entropy, at work in the chloroplast. In response to light, attractive van der Waals interactions and screening of electrostatic repulsion between appressed grana thylakoids across the partition gap and most probably direct protein interactions across the granal lumen (PSII extrinsic proteins OEEp-OEEp, particularly PsbQ-PsbQ) contribute to the integrity of grana stacks. We propose that both the light-induced contraction of the partition gap and the granal lumen elicit maximisation of entropy in the chloroplast stroma, thereby enhancing carbon fixation and chloroplast protein synthesizing capacity. This spatiotemporal dynamic flexibility in the structure and function of active and inactive PSIIs within grana stacks in higher plant chloroplasts is vital for the optimization of photosynthesis under a wide range of environmental and developmental conditions.

Recovery of photoinactivated photosystem II in leaves: retardation due to restricted mobility of photosystem II in the thylakoid membrane

The functionality of photosystem II (PS II) following high-light pre-treatment of leaf segments at a chilling temperature was monitored as F(v)/F(m), the ratio of variable to maximum chlorophyll fluorescence in the dark-adapted state and a measure of the optimal photochemical efficiency in PS II. Recovery of PS II functionality in low light (LL) and at a favourable temperature was retarded by (1) water stress and (2) growth in LL, in both spinach and Alocasia macrorrhiza L. In spinach leaf segments, water stress per se affected neither F(v)/F(m) nor the ability of the adenosine triphosphate (ATP) synthase to be activated by far-red light for ATP synthesis, but it induced chloroplast shrinkage as observed in frozen and fractured samples by scanning electron microscopy. A common feature of water stress and growth of plants in LL is the enhanced anchoring of PS II complexes, either across the shrunken lumen in water-stress conditions or across the partition gap in larger grana due to growth in LL. We suggest that such enhanced anchoring restricts the mobility of PS II complexes in the thylakoid membrane system, and hence hinders the lateral migration of photoinactivated PS II reaction centres to the stroma-located ribosomes for repair.

Drying efficiency and particle movement in coating—Impact on particle agglomeration and yield

The purpose of this study was to determine the influences of drying efficiency and particle movement on the degree of agglomeration and yield of pellets coated under different conditions. Thermodynamic conditions were varied using different inlet air temperatures and airflow rates, fluid dynamics were varied using different airflow patterns and air velocities, and two sizes of pellets were coated at different airflow rates and partition gaps. Agglomeration was minimized when all the moisture introduced into the system was removed by the drying air. Excessively dry conditions led to increased loss of yield due to spray-drying effect and attrition. Fluid dynamics were still important even with adequate drying, as the degree of agglomeration was relatively higher in the non-swirling airflow of Wurster coating than in the swirling airflow of precision coating. Increasing air velocities increased pellet velocities, resulting in lower degrees of agglomeration. Hence, agglomeration due to fluid dynamics was attributed to differences in pellet velocities, pellet proximity and pellet trajectories within the partition column. Smaller pellets agglomerated primarily from inadequate drying and not due to inadequate opportunities for particle movement. Larger pellets were more affected by the partition gap due to restriction of their movement through the partition gap. Hence, both thermodynamics and fluid dynamics were found to be important in minimizing agglomeration and ensuring quality coated products.

Use of swirling airflow to enhance coating performance of bottom spray fluid bed coaters

As there is strong interest in coating increasingly smaller particles or pellets for use in compacted dosage forms, there is a need for better small particle coating systems. This study explored the use of swirling airflow to enhance the performance of the bottom spray coating system. Firstly, pellet coating in the non-swirling airflow of conventional Wurster coating was compared with that of swirling airflow in precision coating under standardized conditions. Secondly, precision coating was studied in greater details at different airflow rates (60–100 m 3/h) and partition gaps (6–22 mm). Precision coating was found to have higher Reynolds numbers ( Re) than Wurster coating, indicating higher turbulence. It produced coated pellets of better properties than Wurster coating, having less agglomeration and gross surface defects, more uniform coats, increased flow and tapped density, and slower drug release. Higher surface roughness did not affect the yield. In precision coating, increasing airflow rates decreased the degree of agglomeration but had minimal effect on pellet quality attributes (colour intensity, colour uniformity and surface roughness) and yields. Increasing partition gaps increased the degree of agglomeration proportionally, but this effect was small. However, greater changes in yield, surface roughness, colour intensity and colour uniformity were detected. This study showed that precision coating, while having a higher drying ability, was able to maintain the same yield and produce coated pellets with superior quality compared to Wurster coating. In precision coating, airflow rate had greater influence on the drying of pellets while partition gap had greater influence on pellet quality attributes.

Comparative study of the fluid dynamics of bottom spray fluid bed coaters

Fluid dynamics of pellets processed in bottom spray traditional Wurster coating and swirl accelerated air (precision) coating were compared with the intent to understand and facilitate improvements in the coating processes. Fluid dynamics was described by pellet mass flow rate (MFR) obtained using a pellet collection system and images captured using high speed photography. Pellet flow within the partition column was found to be denser and slower in Wurster coating than in precision coating, suggesting a higher tendency of agglomeration during the coating process. The influence of partition gap and load on the MFR indicated that the mechanism of transport of pellets into the coating zone in precision coating depended on a strong suction, whereas in Wurster coating, pellets were transported by a combination of peripheral fluidization, gravity, and weak suction pressure. In precision coating, MFR was found to increase uniformly with air flow rate and atomizing pressure, whereas MFR in Wurster coating did not correlate as well with air flow rate and atomizing pressure. This demonstration showed that transport in precision coating was air dominated. In conclusion, fluid dynamics in precision coating was found to be air dominated and dependent on pressure differential, thus it is more responsive to changes in operational variables than Wurster coating.

Identification and characterization of factors controlling tablet coating uniformity in a Wurster coating process

The product coating uniformity in the Wurster column coating process is primarily determined by two factors — the coating-per-pass distribution and the circulation-time distribution. Experimental techniques were developed for a tablet-coating system to quantify these two factors. A magnetic-tracing technique was used to measure the circulation time, circulation-time distribution, and the number of passes made by the tablets during the coating process. The coating-per-pass and total-coating distributions were measured by a dye tracing technique. The circulation time decreased and the circulation-time distribution became narrower as the inlet air flow rate and the partition gap increased. A tail on the circulation-time distribution at low air flow rates and low partition gaps indicated the formation of dead/slow zones, which could result in non-uniform coating. Modifications to the distributor plate resulted in a narrow circulation-time distribution. The coating-per-pass distribution contributed significantly (>75%) to the total-coating uniformity. This was due to the broad coating-per-pass distribution, measured by coating the tablets for one pass only. The contribution due to the coating per pass increased with increase in the partition gap. The broad coating-per-pass distribution was due to differences in the proximity of the tablets to the spray zone, pulsing flow of the tablets, and tablet-to-tablet sheltering. High-speed video imaging in the spray zone confirmed the cause of the broad coating-per-pass distribution. Optimal total-coating uniformity requires process conditions that give narrow coating-per-pass and circulation-time distributions. Thus, the quantitative techniques developed serve as powerful tools to characterize and optimize the coating process.

The Prediction of Variability Occurring in Fluidized Bed Coating Equipment. I. The Measurement of Particle Circulation Rates in a Bottom-Spray Fluidized Bed Coater

The purpose of this work was to investigate the effect that changes in design and process variables had on the movement of particles around a fluidized bed coating apparatus. To measure the mean and variance of the particle cycle time distribution (CTD), the number of passages taken by a magnetic tracer particle through the spray zone was measured by a detector coil wound around the partition. The reproducibility of the measurement technique was tested by taking repeated measurements of the tracer particle movement, using similar bed operating conditions, and the method was found to give reproducible results. A series of experiments was carried out by varying operating conditions such as the partition gap, fluidizing air rate, and partition diameter and length, and measuring the change in the rate at which the tracer particle circulated in the coating device. The results of the experiments showed that, over the range of parameters tested in this work, the partition gap had the strongest influence on the rate of particle circulation. Moreover, for the 6-in.-diameter Wurster process used in the current work, the mean circulation time for the 1.1-mm-diameter Nu-Pareil particles was found to vary over the range of 2.2–10.4 sec. In addition, the mean and standard deviation of the CTD could be linearly correlated over a wide range of operating conditions, with a correlation coefficient of 0.80. Finally, an estimate of the variability in mass coating uniformity was made based on the results from the cycle time distributions. It was concluded that the effect of variability in the CTD could account for only a small fraction of the variability in the observed mass coating distribution.

Ultrastructure of spinach chloroplasts as revealed by freeze-substitution

Unfixed and glutaraldehyde-fixed spinach chloroplasts were frozen on a copper block cooled by liquid helium and subsequently substituted in acetone at −87°C. Fixed chloroplasts were substituted in pure acetone, unfixed ones also in acetone containing 2% osmium tetroxide. Unfixed and aldehyde-fixed specimens were infiltrated with Low-icryl HM23 at −85°C. The resin was polymerized at −80°C. Osmium-fixed specimens were infiltrated with Epon 812 at room temperature, followed by polymerization at 65°C. The thylakoids of intact chloroplasts appeared similar in all embeddings, consisting of three, approximately equally wide layers: two peripheral, light ones and a central, darker one. A thin, very dark stratum, the partition gap, separated the grana thylakoids from one another. The grana were surrounded by an unevenly stained stroma. The chloroplast envelope could not be discerned. In lysed chloroplasts no stroma could be observed. In unfixed and aldehyde-fixed specimens the three-layered pattern seen in thylakoids of intact chloroplasts was replaced by a lightly stained band. In osmium-fixed specimens the thylakoids exhibited both structural types or resembled the thylakoids of conventionally fixed and embedded chloroplasts.