Low Spray Rate Research Articles

Material characterization and inter/intra-particle validation for DEM simulation of urea coating process

Particle coating is a common operation in the controlled-release fertilizer (CRF) industry, where a coating layer is appliedto the urea cores. A discrete element method (DEM) computer simulation was applied to model the coating process for the urea granules using measured model parameters. The accuracy of DEM input parameters for the coating material properties and the physical and mechanical characterizations of urea granules are crucial to the study of particle coating processes. Thus, to enhance the simulation accuracy, information on the material properties (urea granules) is required. In this study, the elasticity parameters, shear modulus, coefficient of restitution (CoR), and coefficient of rolling and static friction (CoRF) and (CoSF) of urea granules are estimated experimentally in addition to the physical characteristics. The sensitivity of the angle of repose of the urea bed was investigated at different coefficients of friction. According to the obtained experimental value of the angle of repose, values of 0.2 and 0.3 for CoRF and CoSF, respectively, were adjusted to obtain consistent urea granules’ motion for simulation and the experiment. Moreover, the spray droplet sizes and velocity distributions were estimated using the video-imaging process technique. Based on this experimental characterization, elasticity parameters and spray properties were integrated into DEM simulation software as input data to perform numerical analysis of the coating process to compare simulation and experimental results, which show uniformity at three different pan speeds with a maximum deviation of 0.033 at 5 rpm. Also, consistency between DEM and experiment results was achieved in terms of average coating thickness (μm) of the selected samples and average intra-particle thickness variation (CoVintra). These results revealed that the coating film thickness is proportional to the rotation speed for the experiment and simulation. To enhance the inter-particle coating uniformity, the effects of the most significant parameters such as pan speed, filling ratio, particle size, spray rate, and spray angle, were examined. A low spray rate, filling ratio, and high pan speed improved the coating uniformity. The particle size and spray angle show considerable influence on the coating uniformity, where larger particle sizes and spray angles tend to reduce the inter-particle coating uniformity.

Advancing Sustainability in Tree Crop Pest Management: Refining Spray Application Rate with a Laser-guided Variable-rate Sprayer in Apple Orchards

Advanced variable-rate spray technology, which applies pesticides based on real-time scanning laser rangefinder measurements of plant presence, size, and density, was developed and retrofitted to existing sprayers. Experiments were conducted to characterize the application of four programmed spray rates (0.03, 0.05, 0.07, or 0.09 L·m−3 of crop geometric volume) when applied to Malus domestica Borkh. ‘Golden Delicious’ apple trees using this crop sensing technology. Water-sensitive cards (WSCs) were used as samplers to quantify spray coverage, deposits, and deposit density in the target and nontarget areas, and an overspray index based on a threshold of greater than 30% coverage was calculated. The application rate ranged from 262 L·ha−1 at the programmed spray rate of 0.03 L·m−3 to 638 L·ha−1 at the rate of 0.09 L·m−3. For a given WSC position, spray coverage and deposits increased as the spray rate increased. WSC positions 1 and 2 were oversprayed at all rates. The effect of spray rate on deposit density varied with WSC positions, with high densities achieved by low spray rates for WSCs closest to the sprayer but by high spray rates for WSCs positioned either deeper within or under the canopy. When coalescing deposits were accounted for, deposit densities met or exceeded the recommended pesticide application thresholds (insecticides 20–30 droplets/cm2; fungicides 50–70 droplets/cm2) at all WSC positions for each spray rate tested. The lowest spray rate reduced off-target loss to the orchard floor by 81% compared with the highest rate, dramatically reducing potential exposure to nontarget organisms, such as foraging pollinators, to come into contact with pesticide residues. Applying the lowest rate of 0.03 L·m−3 met deposit density efficacy levels while reducing spray volume by 83% compared with the orchard standard application of 1540 L·ha−1 and by 87% compared with the 1950 L·ha−1 application rate recommended when using the tree row volume method. Thus, there is potential for growers to refine pesticide application rates to further achieve significant pesticide cost savings. Producers of other woody crops, such as nursery, citrus, and grapes, who use air-assisted sprayers, may be able to achieve similar savings by refining pesticide applications through the use of laser rangefinder-based spray application technology.

Experimental Investigation on Flash Evaporation Related to Pipe Leakage

Abstract Pipelines such as the surge line and main pipe are easily subjected to thermal stratification and thermal fatigue as a result of the nonuniform temperature distribution in the nuclear power plants. When the surge line or main pipe subjected to thermal stratification and thermal fatigue keeps operating for long time, the pipe leakage may happen due to the existence of pipeline crack. When the fluids with high temperature and pressure leak in the crack, the water will evaporate quickly, which means this process belongs to spray flash evaporation process. The flash evaporation related to pipe leak was experimentally studied in the paper. The experiment was carried out under high temperature and high pressure with low spray rate. The temperature and relative humidity (T&H) variations over time were monitored in the experiment with installing T&H detectors. The T&H variations at different measurement positions and with different spray rates were analyzed, respectively. In addition, the effect of the dimensionless parameters including the Weber number and Jakob number was also investigated. Results indicated that the response speed increased with the increase of the spray flow rate. Higher Weber number and higher Jakob number led to higher evaporation rate. The slight pipe leakage can be predicted by using the (T&H) in the hazardous areas.

Optimization of a semi-batch tablet coating process for a continuous manufacturing line by design of experiments

The aim of the study was to optimize a tablet coating process for a continuous manufacturing line. High throughputs should be achieved while inter-tablet coating variability should be as small as possible. Drug-free cores were coated with a colored suspension. All processes were monitored in-line with Raman spectroscopy. A statistical design of experiment was performed to find optimum process parameters. Tablet loading, spray rate and drum rotation speed were studied. Image analysis was performed using a computer scanner. Tablet hue and saturation were evaluated to obtain information about the inter-tablet color variabilities and the numbers of outliers. Low variabilities could be achieved using low spray rates and high rotation speeds and they were independent from the tablet batch sizes in the studied factor space. For the prediction of the coating thickness, univariate analysis was compared to PLS-regression. Calibration models were built based on the three center points of the statistical design of experiment resulting in RMSEC of 1.07% of sprayed suspension with R2 of 0.9989 and Q2 of 0.9987. Model prediction was possible independent from loading, spray rate and drum rotation speed. The experiment with lowest color variability was conducted with a desired throughput rate of 25 kg/h and with a RMSEP of 2.5%.

New insights on the influence of manufacturing conditions and molecular weight on phase-separated films intended for controlled release

The aim of this work was to investigate how manufacturing conditions influence phase-separated films of ethyl cellulose (EC) and hydroxypropyl cellulose (HPC) with different molecular weights of HPC. Two HPC grades, SSL and M, with weight average molecular weights (Mw) of 30×103g/mol and 365×103g/mol, respectively, were combined with EC 10 cps (70:30w/w EC/HPC) and spray-coated from ethanol solutions onto a rotating drum under well-controlled process conditions. Generally, a low spray rate resulted in a more rapid film drying process and, consequently, in smaller HPC-rich domains in the phase-separated film structure. For EC/HPC films with the low Mw HPC (SSL) the most rapid drying process resulted in a shift from a HPC-discontinuous to a partly bicontinuous structure and an increase in the permeability for water. In contrast, films containing the high Mw HPC (M) all showed bicontinuous structures, which resulted in overall higher water permeabilities and polymer release compared to the low Mw films. Interestingly, a maximum in permeability was observed for the high Mw films at intermediate spray rates. Below this spray rate the permeability decreased due to a lower amount of polymer released and at higher spray rates, the permeability decreased due to a loss of pore connectivity (or increased tortuosity). To conclude, this study shows that different Mw systems of EC/HPC can respond differently to variations in manufacturing conditions.

Deposição de calda em folhas de cafeeiro e perdas para o solo com diferentes taxas de aplicação e pontas de pulverização

O cafeeiro apresenta diversos desafios para a tecnologia de aplicação dos produtos fitossanitários, principalmente no que se refere à penetração da calda no dossel da cultura e à redução da deriva. Objetivou-se analisar a deposição de calda pulverizada na folhagem do cafeeiro e a perda para o solo, proporcionada pela aplicação com diferentes taxas e pontas de pulverização. O experimento foi conduzido no esquema fatorial 2 x 2 e oito repetições, sendo os fatores pontas de pulverização (jato cônico vazio - ATR e jato cônico vazio com indução de ar - TVI) e taxas de aplicação de calda (200 e 500 L ha-1). Em todos os tratamentos as aplicações foram realizadas utilizando-se um pulverizador hidropneaumático e o marcador Azul Brilhante, o qual foi quantificado por espectrofotometria. Para avaliação de depósito foram coletadas folhas das metades superior e inferior das plantas e também lâminas de vidro já posicionadas junto à superfície do solo. O uso de pontas com indução de ar mostrou-se viável quanto à deposição de calda no cafeeiro, principalmente junto ao uso da maior taxa de aplicação. O emprego da menor taxa (200 L ha-1) mostrou-se viável junto ao uso da ponta de jato cônico vazio. A ponta com indução de ar proporcionou maiores perdas para o solo.

Effect of copper concentration and spray rate on the properties Cu2ZnSnS4 thin films deposited using spray pyrolysis

Polycrystalline Cu2ZnSnS4 (CZTS) thin films were prepared using chemical spray pyrolysis. We examined the influence of concentration of copper in spray solution and spray rate on the properties of the films. Choice of copper concentration in the precursor solution was found to have a pivotal role in adjusting composition, band gap and resistivity of sprayed CZTS thin films. Nearly stoichiometric CZTS thin films with desirable band gap were obtained by using copper concentration of 0.015M. Spray rate also has crucial role in adjusting properties like band gap of the films. Higher spray rates resulted in rougher films with secondary phases of copper sulfide. Secondary phases were also observed at low spray rate of 2ml/min. Good films without any secondary phases and having band gap of 1.5eV were obtained at the spray rate of 6ml/min.

Evaluation of critical process parameters for inter-tablet coating uniformity of active-coated GITS using Terahertz Pulsed Imaging

The aim of this study was the evaluation of critical process parameters (CPP) for inter-tablet coating uniformity in an active pan coating process using nondestructive Terahertz Pulsed Imaging (TPI). Coating uniformity was assessed by calculating the coefficient of variation (CV) of coating thickness measured by TPI, and the CV of API content measured by high performance liquid chromatography (HPLC). A design of experiments (DoE) was performed at pilot scale with drum load, drum speed, spray rate, run duration and spray pressure as factors. Good agreement in the CV of both analytical techniques was shown. The DoE models both revealed the same CPP: a low drum load, high drum speed, low spray rate and high run duration were beneficial for coating uniformity. The spray pressure was only significant in one of the DoE models. It was further shown that the negative impact of a high drum load on the CV cannot only be compensated by high drum speed, but also be compensated by a low spray rate and long run duration. It was demonstrated that TPI is a feasible tool for the measurement of inter-tablet coating uniformity and for the evaluation of CPP in an active pan coating process.

Evaluation of a solid stream radial nozzle on fixed-wing aircraft, for penetration of spray within a soybean canopy

Abstract Experiments were conducted to evaluate the Accu-Flo multiple orifice nozzle for penetration of spray into a soybean (Glycine max L.) canopy by comparing results to those from a popular straight stream nozzle and rotary atomizer. A mixture of water + Induce® adjuvant was applied at three different spray release heights in a random sequence, using an Air Tractor 402-B agricultural aircraft. Sampler stands were placed at twenty-four locations in the field. Water sensitive paper (WSP) cards were clipped onto rigid stands just above the canopy and 30 cm off the ground within the canopy. Weather data were recorded using two different stations on-site. Wind was predominantly from the west and parallel to the direction of the spray runs. The spray delivery systems compared were the Accu-Flo nozzles, (64 needle 0.020 opening), CP®-09 straight stream with 5 degree deflection, and Micronair® AU5000 atomisers (14 mesh screen) at a low volume spray rate of 18.7 l/ha. A total of 54 spray runs were made over three days, and heights were varied at 3.7 m, 4.9 m and 6.1 m. Water sensitive papers were scanned and analysed for coverage per unit card area using an image analysis system. Altitude and [Nozzle X Altitude] interaction were significant effects on coverage at the 0.01 and 0.07 significance levels, respectively, for the top cards. Nozzle type was not a significant effect on coverage for the top cards, but was significant at the 0.01 level for the bottom cards. Altitude alone had no obvious effect on coverage for the bottom cards, although it had an effect for the top cards. The highest percentage area of spray coverage was observed from the Accu-Flo nozzles, especially for the bottom cards. Average spray coverage from the Accu-Flo nozzles was 1.7 times higher than coverage from the CP® nozzles or Micronair® atomisers in the lower portion of the canopy.

Optimization of the inter-tablet coating uniformity for an active coating process at lab and pilot scale

The objective of this study was to enhance the inter-tablet coating uniformity in an active coating process at lab and pilot scale by statistical design of experiments. The API candesartan cilexetil was applied onto gastrointestinal therapeutic systems containing the API nifedipine to obtain fixed dose combinations of these two drugs with different release profiles. At lab scale, the parameters pan load, pan speed, spray rate and number of spray nozzles were examined. At pilot scale, the parameters pan load, pan speed, spray rate, spray time, and spray pressure were investigated. A low spray rate and a high pan speed improved the coating uniformity at both scales. The number of spray nozzles was identified as the most influential variable at lab scale. With four spray nozzles, the highest CV value was equal to 6.4%, compared to 13.4% obtained with two spray nozzles. The lowest CV of 4.5% obtained with two spray nozzles was further reduced to 2.3% when using four spray nozzles. At pilot scale, CV values between 2.7% and 11.1% were achieved. Since the test of uniformity of dosage units accepts CV values of up to 6.25%, this active coating process is well suited to comply with the pharmacopoeial requirements.

Process Optimization of a Novel Immediate Release Film Coating System using QbD Principles

This work describes a quality-by-design (QbD) approach to determine the optimal coating process conditions and robust process operating space for an immediate release aqueous film coating system (Opadry® 200). Critical quality attributes (CQAs) or associated performance indicators of the coated tablets were measured while coating process parameters such as percent solids of the coating dispersion, coating spray rate, inlet air temperature, airflow rate and pan speed were varied, using a design of experiment protocol. The optimized process parameters were then confirmed by independent coating trials. Disintegration time of coated tablets was not affected by the coating process conditions used in this study, while tablet appearance, as determined by measurement of tablet color, coating defects and gloss was determined to be a CQA. Tablet gloss increased when low spray rate and low percent solids were used, as well as with increased coating pan speed. The study used QbD principles and experimental design models to provide a basis to identify ranges of coating process conditions which afford acceptable product quality. High productivity, color uniformity, and very low defect levels were obtained with Opadry 200 even when using a broad range of coating process conditions.

Effect of Solution Spray Rate on the Properties of Chemically Sprayed ZnO:In Thin Films

ZnO:In thin films were grown from 100 mL of spray solution on glass substrates by chemical spray at Ts = 400°C using solution spray rates of 0.5–6.7 mL/min. Zinc acetate and indium(III)chloride were used as Zn and In sources, respectively, with [In]/[Zn] = 3 at.%. Independent of solution spray rate, the crystallites in ZnO:In films grow preferentially in the (101) plane parallel to the substrate. The solution spray rate influences the surface morphology, grain size, film thickness, and electrical and optical properties. According to SEM and AFM studies, sharp‐edged pyramidal grains and canvas‐resembling surfaces are characteristic of films grown at spray rates of 0.5 and 3.3 mL/min, respectively. To obtain films with comparable film thickness and grain size, more spray solution should be used at low spray rates. The electrical resistivity of sprayed ZnO:In films is controlled by the solution spray rate. The carrier concentration increases from 2 · 1019 cm−3 to 1 · 1020 cm−3 when spray rate is increased from 0.5 mL/min to 3.3 mL/min independent of the film thickness; the carrier mobilities are always lower in slowly grown films. Sprayed ZnO:In films transmit 75–80% of the visible light while the increase in solution spray rate from 0.5 mL/min to 3.3 mL/min decreases the transmittance in the NIR region and increases the band gap in accordance with the increase in carrier concentration. Lower carrier concentration in slowly sprayed films is likely due to the indium oxidation.

A Feasibility Study on Pellet Coating Using a High-Speed Quasi-continuous Coater

Pellet coating is traditionally carried out using the Wurster coater. This study investigated the feasibility of pellet coating in a newly developed coater built with a unique airflow system, the Supercell™ coater (GEA Pharma Systems, UK). A full factorial design study was carried out to evaluate the influences of the spray rate of the coating dispersion, batch size of the pellet load, pellet size fraction and plenum pressure of the fluidizing air on the color coating of pellets in the Supercell™ coater. Results showed that pellets could be successfully coated using the Supercell™ coater. Higher plenum pressures and lower spray rates were found to minimize pellet agglomeration during coating. Although coating efficiencies were comparable amongst the different pellet size fractions, larger batch sizes of pellets were coated with higher efficiencies. Process optimization was carried out for each pellet size fraction and a large batch size (120g) in combination with a high plenum pressure (1,500mm WC) were deemed optimal. Optimal spray rates differed according to pellet size fraction and a lower spray rate was required for smaller pellets. Pellet flow patterns observed during coating were dependent on the pressure drop across the fluidized load. A 'swirling' pellet flow pattern was generally observed at coating conditions which led to optimal outcomes.

Production of granola breakfast cereal by fluidised bed granulation

In the fluidised bed granulation process the effect of nozzle air pressure and binder spray rate on key aggregate quality attributes were studied. The experimental results show that a decrease in nozzle air pressure leads to larger mean granule size. The combination of lowest nozzle air pressure and lowest binder spray rate results in granules with the highest levels of hardness and crispness. The combination of low nozzle air pressure and low binder spray rate results in the least distribution span. Granola hardness was affected by nozzle air pressure. Nozzle air pressure and binder spray rate did not have significant effect on crispness.

Tablet film-coating with amylose-rich maize starch

The purpose of the present study was to investigate an aqueous-based amylose-rich maize starch (Hylon VII) film-coating process of tablets performed by a side-vented pan coating system. Three formulation or process parameters of potential importance, including the plasticizer concentration ( X 1), the temperature of coating pan ( X 2) and the spray rate of the coating solution ( X 3), were evaluated using a central composite face-centred experimental design. Only a few process-related limitations associated with the aqueous film coating of Hylon VII were observed, and, in general, the coated tablets were of fairly good quality. At low spray rates, the temperature of the coating pan did not affect the roughness of the coated tablets. At higher spray rates, higher temperature gave smoother films. As regards surface quality and smoothness, a plasticizer concentration (i.e., a 1:1 mixture of sorbitol and glycerol) of approximately 65% of the polymer weight, seems to be suitable for the present formulations. The dissolution of all Hylon VII-coated tablets in an acidic medium was rapid, more than 75% of the drug (theophylline) dissolved within 15 min. On the basis of the present results, it can be concluded that amylose-rich maize starch (Hylon VII) may be considered as an aqueous film-coating agent to be used for pharmaceutical purposes and in established film-coating processes.

Agglomeration Tendency during Top-Spray Fluidized Bed Coating with Gelatin and Starch Hydrolysate

Top-spray fluidized bed coating of glass beads with gelatin and starch hydrolysate leads to an `all or nothing' side-effect agglomeration, that is, a drastic collapse of the fluid-bed when a critical spray rate is exceeded. This undesirable side-effect agglomeration is primarily influenced by the type of coating, and more specifically its hygroscopicity, water binding capacity and viscosity. Hydrolyzed gelatin permits a considerable increase in spray rate compared to the unhydrolyzed type, due to more pronounced coating losses and lack of gelling capacity. Starch hydrolysate enables working only at low spray rates, due to its high hygroscopicity. Increasing the atomization pressure decreases the agglomeration tendency of starch hydrolysate but simultaneously decreases the final coating thickness. Coating quality is primarily influenced by coating properties, such as molecular mass and viscosity during processing.

The Effect of Spray Application Rate and Airflow Rate on Foliar Deposition in a Hedgerow Vineyard

Two experiments were performed in a hedgerow vineyard, in June (after end of blossom) and July (full vegetation development) to assess the influence of spray application rate and air output on the spray distribution from an axial-fan sprayer. Measurements were performed by fluorometry, using Brilliant Sulpha Flavine as a tracer. Increasing spray application rate and air output both led to higher losses to the ground and lower deposition on the foliage. However, differences were statistically significant only in the July experiment. Losses to the soil ranged from 34·5 to 36·8% for the lower spray rates (313-391 l/ha), and from 41·3 to 48·9% for the medium spray rate (648-782 l/ha) treatments. Losses due to drift outside the experimental plots and deposition on branches, shoots and poles ranged from 6·5 to 10·5% for the lower air output (7·0 m 3/s), and from 7·8 to 19·8% for the higher air output (8·6m 3/s). The highest deposition on the foliage was recorded for the combination of a low spray rate and a low airflow rate (54·2 to 56·7%). Deposits per unit leaf surface were invariably lower in the middle (1·2 to 1·6m high), denser part of the canopy. However, differences between heights were lower than in a previous experiment.

Aqueous ethylcellulose dispersion of ethylcellulose. I. Evaluation of coating process variables.

Formulation and process variables play an important role in the film-forming properties of coating polymers. Three selected independent coating process variables, namely, percent solids content in the coating polymeric dispersion, inlet-air temperature, and spray rate of the polymeric dispersion, were investigated in this study to determine their effect on the performance characteristics of tablets coated with a plasticized aqueous ethylcellulose dispersion (Sure-lease) in a fluid-bed equipment. Response surface methodology (RSM) was utilized to study the complex relationship between these process variables and selected response variables. Three response variables were considered, namely, rate of drug release from the "untreated" coated tablets and the "thermal-treated" coated tablets and microindentation hardness of the untreated coated tablets. A 12-point factorial experimental design was utilized, and three-dimensional (3-D) response surface plots were generated using a second-order polynomial model. The model provided information needed to predict optimal process conditions. Drug release from the coated tablets followed zero-order kinetics. Inlet-air temperature was found to be the most critical process variable for all the three response variables studied. A correlation was observed between the drug release rate and the microindentation hardness of the applied polymeric coat in the case of untreated coated tablets. The 3-D response surface plots indicated that lower rates of drug release from the coated tablets may be obtained by using high inlet-air temperature and low spray rate of the polymeric dispersion during coating.

Studies on dynamicI-V curves of semiconductor-liquid junction cells formed with Cd0·8Zn0·2S films prepared at various spray rates

Cd0·8Zn0·2S films were prepared by the spray pyrolysis technique on glass and conducting glass (fluorine doped tin oxide) substrates, by spraying aqueous solutions of cadmium chloride, zinc chloride and thiourea. The spray rate was varied from 4 cc/min to 16 cc/min. It is found that film thickness increases with increase in spray rate. The electrical and optical properties of the films namely dark conductivity, thermoelectric power and optical absorption were studied; conductivity and thermoelectric power are higher for the films prepared at lower spray rate (4·3 cc/min).