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Typical sample whole milk powder products obtained using the MDDSD operated at 140 C based at Xiamen University (China).
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Mono-disperse droplet generation and subsequent drying in a spray-drying chamber, i.e., mono-disperse droplet spray dryer (MDDSD), provides a better-defined “flight experience” for liquid droplets. The related particle formation can be investigated more easily than that in the usual poly-disperse droplet spray dryer (PDDSD). Previously, skim milk,...
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... each feed, the nozzle pulsing frequency was ensured to produce a mono-disperse droplet regime. Typical powder samples obtained are shown in Fig. 5. It can be seen that the particles are fairly uniform in size and in shape, similar in quality and size deviations to those obtained for skim milk. [15,16] Bulk particle size information was obtained from microscope image recognition using the public domain soft- ware package ImageJ. [32] The droplets were non-spherical. To explore a broader range of solids contents, whole milk solutions were prepared at several initial solids concen- trations. Trials were either carried out with an air inlet tem- perature of 140 C and=or 180 C. All feeds were adequately dried at this temperature to produce easy-to-handle pow- der, though some had high final moisture contents. In each case, the total solids content of the feed exiting the nozzle was assessed by oven drying to carefully monitor the poss- ible solids content reduction due to the filtration step, as mentioned earlier. The experimental conditions that gener- ated the shrinkage data are given in Table ...
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... However, the dry particles obtained by MDSD from milk samples with different fat content (0.3-33 w/w %) usually exhibit significantly wrinkled and irregular surface (You et al., 2014). Only a minor fraction of the whole powder population displays a spherical morphology and a vacuole in the core, as well as a quite larger size compared to the average of the sample. ...
In order to guarantee the properties of infant formulas, perfect control of drying is necessary. It requires understanding the drop-to-particletransition, which is still difficult given the closed feature of drying chambers and the fast-drying kinetics. This thesis aims to study the skinformation on the surface of drops of mixture of whey proteins (WPI) and casein micelles (NPC), which effect the morphology and properties ofthe particles. The impact of the WPI / NPC (WPI%R) ratio on skin formation, particle morphology and drying kinetics has been explored on single drop.Beyond a critical WPI%R ratio, WPI control the interfacial characteristics, from the sol-gel transition to solidification, since WPI prefers to accumulate at outer layer of the skin. In addition, 4 characteristic morphologies were observed according to a phase diagram as a function of the overall concentration (Cp) and of the WPI%R ratio validated in monodisperse drying. Regardless of WPI%R, the increase in Cp induces an early sol-gel transition, with reduced shrinkage and delamination of the particles. Besides, replacing NPC with sodium caseinates (SC) in the mixes showed an intermediate behavior induced by their physico-chemical properties and their smaller size. Finally, a preliminary model was established to predict thedroplet phase transition in spray drying chambers. This work provides a better understanding of the phenomenology of the drying of dairy colloids,and more generally of the physics of the structuring of the interface of polydispersed systems. The perspectives of this study concern the formation of particles from more complex formulations representative of nutritional products.
... There are many types of lumped drying models available and readers interested in this area are referred to the cited sources. [7,17,[29][30][31][32][33][34][35][36][37][38][39] While the diameter of the chamber is not explicitly included in the equations above, it manifests itself in the calculation of the velocity of the drying air (converting volumetric flow rate to velocity). In some cases, an effective 'plug-flow' diameter may be used in place of the diameter of the chamber and this will be discussed later on in this section of the review paper. ...
... If for simplicity, a single initial droplet size is chosen to represent the spray, only a single discretized time scale will be required to be computed at each discretized dryer length scale. [7,17,[30][31][32][33][34][35][36][37][38][39] It will be explained later on in detail that this poses to be the key source of numerical instability whilst capturing different droplet sizes within the theoretical framework and in adopting the one-dimensional framework for countercurrent spray drying. ...
... Results from that pilot scale experiment (measurements only undertaken in the spray zone) were in good agreement with the proposed model by Zbici nski. [37] Comparing these earlier works cited above, it is interesting to note that more recent one-dimensional simulation works [7,8,10,36] also reported reasonable agreement for comparison with experimental data, despite not capturing the spray dispersion phenomenon (uniform distribution as shown in Figure 1a). It is noteworthy that all of these validation works, apart from that reported by Pearce, [9] rely mainly on comparison at the outlet. ...
Recent initiatives covered in this review can be divided into three broad categories. The first category concerns mathematically describing the spray drying process using a plug-flow model which allows quick what-if evaluations of the process. Intricacies associated with capturing the drying of a range of droplet sizes are discussed. Challenges in adapting the plug-flow simulation approach to counter-current spray drying, which is common in the production of non-heat sensitive detergent powder, was further elaborated. The second broad category features modeling the spray drying process using the Computational Fluid Dynamics technique. A critical review was provided to guide readers on a common dilemma plaguing this area of spray drying modeling. Recent developments in agglomeration modeling in spray dryers are discussed as well. The final part of this review touches on modeling techniques which can be used to predict the development of specific powder qualities. This includes modeling the degree of protein denaturation during spray drying, predicting the characteristics of crystalline type spray dried powder, and determining the properties of the powder surface at the molecular scale.
... [40] It has been widely applied in the food and pharmaceutical industries for various applications. [32,37,39,[41][42][43] It gives higher encapsulation efficiency in comparison with the other encapsulation techniques. [12,16,19,37,44] Namely, hot-air drying is the basis of encapsulation, which is remarkably affected by the spraying process and feed emulsion properties. ...
There are various bioactive components exist in plants, fruits, and vegetable origins that have many beneficial health effects (mainly antioxidant). However, they suffer from low-stability against the environmental condition. Thus, the encapsulation approach emerged to decrease their sensitivity and present a target delivery system. Generally, native carrier agents (polysaccharides and proteins) are being applied to embed the core materials. Accordingly, many encapsulation methods have been developed to protect vulnerable components by these carriers. Spray and freeze-drying are common encapsulation methods with the ability of powder production. Both feed emulsion production and drying process factors substantially influence the core embedded within the carrier agents. Spray-drying is well-known to higher applicable and scalable encapsulation procedure in the food and pharmaceutical industries. It is predominantly related to its lower process costs. Nevertheless, its application is limited for more sensitive bioactive compounds due to hot-air drying exertion. In contrast, freeze-drying has been mostly used for thermo-sensitive ingredients. Its application is restricted by economic drawbacks for which long process time (24-48 h) is required. However, freeze-drying is adequately taken into an advantage in the encapsulation of therapeutic compounds since high-added value products will be produced so that bioactive compounds with higher biological activity are needed. ARTICLE HISTORY
... Spray drying is a conventional technology for converting large quantities of liquid into powder products in short time with many industrial applications such as foods, pharmaceuticals, and chemical industries, etc. (Liu et al., 2011;Rogers et al., 2012;Vicente et al., 2013;You et al., 2014). From merely producing huge capacity of powders it is traditionally known for, spray drying has advanced to the present stage of controlling the functionalities of the particles (Ré, 2006;Baldwin and Truong, 2007;Sagadin and Hriberšek, 2017). ...
... This constitutes a huge problem in particle quality control. These challenges led to the development of a simple and robust set-up that provides precise control of the spray drying operation, known as mono-disperse droplet spray dryer (MDSD) (Woo et al., 2012;You et al., 2014;Yang et al., 2015;Foerster et al., 2016). ...
The discrete phase model (DPM) has been widely used in CFD simulations to track discrete particles or droplets in a continuum fluid filed. This powerful technique, however, may face tremendous difficulty in tracking droplets flying through chambers with significantly different sizes. In such cases, it becomes very challenging to develop effective mesh for the big and small chambers together with the transition zone that can ensure solution convergence within reasonable computational time. In this work, a systematic method is introduced to tackle this problem. This method allows simulation of different sized chambers separately to avoid the meshing difficulty. A unique coupling approach offers smooth transition of droplets from one chamber to the other with rigorous conservation of their mass, energy and momentum. The effectiveness of the method is demonstrated through the simulation of skim milk droplet drying in a mono-disperse droplet spray dryer (MDSD), where droplets must pass through a small dispersion chamber before entering the main big drying chamber. For the first time, droplet drying process from exiting nozzle to the arrival at the dryer outlet can be simulated. The new model can be used in the future to optimize the spray drying process.
... An Nomenclature A p Droplet/particle surface area (m 2 ) C p Specific heat under constant pressure (J/(kg K)) d inefficient water removal process can be necessary in the absence of droplet pre-dispersion. In a similar manner, tuning the operating settings that control droplet distribution has been found to significantly affect the conditions of the resulting powder (You et al., 2014). However, key factors that could influence droplet dispersion remain unclear and unexplored, due to experimental limitations in visualizing the dispersion dynamics. ...
... To explore the droplet dispersion in a real dispersion chamber, numerical simulations have been conducted using typical experimental conditions. The base case conditions in Table 1 are typical inlet experimental values (You et al., 2014). Other scenarios listed in Table 2 have been included to demonstrate the effects of different operating settings on droplet dispersion. ...
Monodisperse droplet spray dryers have great advantages in particle formation through spray drying because of their ability to produce uniform sized particles. Experimental analyses of this system have shown that droplets atomized through the piezoceramic nozzle need to be sufficiently well dispersed before entering the drying chamber to achieve sufficiently dried particles. However, the dispersion dynamics cannot be readily observed because of experimental limitations, and key factors influencing the dispersion state currently remain unclear. This study carried out numerical simulations for droplet dispersions in the dispersion chamber, which allow this important process to be visualized. The systematic and quantitative analyses on the dispersion states provide valuable data for improving the design of the dispersion chamber, and optimizing the spray drying operation.
In den letzten Jahren wird die akustische Levitation zunehmend zur Untersuchung einzelner Partikel während des Trocknungsprozesses eingesetzt. Dabei wird ein Tropfen in einem stehenden Ultraschallfeld so positioniert, dass eine kontaktlose Beobachtung stattfinden kann. Im Rahmen dieser Arbeit wurde ein Messstand bzw. Versuchsaufbau für einen Levitator gestaltet und das Trocknungs- und Levitationsverhalten von verschiedenen Stoffsystemen untersucht.
Active pharmaceutical ingredient (API)-embedded dry powder for inhalation (AeDPI) is highly desirable for pulmonary delivery of high-dose drug. Herein, a series of spray freeze-dried (SFD) ciprofloxacin hydrochloride (CH)-embedded dry powders were fabricated via a self-designed micro-fluidic spray freeze tower (MFSFT) capable of tuning freezing temperature of cooling air as the refrigerant medium. The effects of total solid content (TSC), mass ratio of CH to L-leucine (Leu) as the aerosol dispersion enhancer, and the freezing temperature on particle morphology, size, density, moisture content, crystal properties, flowability, and aerodynamic performance were investigated. It was found that the Leu content and freezing temperature had considerable influence on the fine particle fraction (FPF) of the SFD microparticles. The optimal formulation (CH/Leu = 7:3, TSC = 2%w/w) prepared at - 40°C exhibited remarkable effective drug deposition (~ 33.38%), good aerodynamic performance (~ 47.69% FPF), and excellent storage stability with ultralow hygroscopicity (~ 1.93%). This work demonstrated the promising feasibility of using the MFSFT instead of conventional liquid nitrogen assisted method in the research and development of high-dose AeDPI.
In this article, sodium alginate/polyvinyl alcohol/polyethylene oxide/ZSM-5 zeolite (SA/PVA/PEO/ZSM-5) nanohybrid adsorbent was produced with the casting technique and adsorption of uranium ions from aqueous solutions was scrutinized with it. The effects of several batches adsorption parameters such as zeolite content, acidity, adsorbent content, contact time, initial concentration, and temperature were investigated. The kinetic data were analyzed with various kinetic models. The results demonstrated that experimental data were fitted well by the double-exponential kinetic model. The equilibrium data were described thanks to the Freundlich, Langmuir, and Dubinin-Radushkevich isotherm models. The maximum adsorption capacity of uranium ions was found to be 92.76 mg g⁻¹ at a pH of 5.0 and a temperature of 45 °C. The obtained thermodynamic and Dubinin-Radushkevich parameters indicated that the physical sorption of uranium onto the SA/PVA/PEO/ZSM-5 adsorbent was dominant. Furthermore, the SA/PVA/PEO/ZSM-5 nanohybrid adsorbent was regenerated by HCl/HNO3, and then after five steps of adsorption-desorption cycles, the adsorption capacity was changed less than 20%.
The evaporation of liquid solution droplets and solute crystallization can be highly complex and is an important problem, particularly in spray drying where powdered products are produced from sprayed liquid droplets, such as in the food or pharmaceutical industries. In this work, we study the relationship between the evaporation rates of single levitated NaNO3 droplets under varying environmental conditions and the propensity for nucleation of NaNO3 crystals. We use a combination of an electrodynamic balance to study single-droplet evaporation kinetics, SEM imaging of dried particles and modelling of the internal solute distribution inside a drying droplet. We show that the aqueous NaNO3 droplets exhibit broad distributions in the time that crystal nucleation is observed, droplet-to-droplet. The distribution of nucleation time is dependent upon environmental conditions such as the drying temperature, relative humidity (RH) and solute concentration. Even when evaporating in 0 % RH, some droplets do not nucleate crystals in the time taken for all water to evaporate and dry to form an amorphous particle. We believe that this interplay between crystalline or amorphous particle formation is a result of the viscosity of aqueous NaNO3 solutions, which rises by several orders of magnitude as the concentration increases. We show that for droplets with an initial radius of ~ 25 µm the propensity for aqueous NaNO3 droplets to nucleate crystals upon drying increases with a decreasing RH, and increases with an increasing temperature in the range of 278 – 306 K. This work demonstrates the importance of the drying kinetics on the propensity of evaporating droplets to nucleate crystals.
