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(2021)ThesisPolymer brushes are arrays of densely surface-tethered polymer chains, and are of interest for two reasons. Firstly, they possess interfacial characteristics, such as antifouling and lubrication, that are desirable in many applications. Secondly, they are model systems that can provide additional insight into polymer behaviour due to their unique geometry. Observing the interfacial structure of these brush layers is critically important for understanding both their properties and the mechanisms driving the polymer behaviour. To date, neutron reflectometry (NR) is the only technique that can demonstrably resolve the nanoscale structure of polymer brushes. However, these diffuse interfaces produce subtle features in the reflectometry data that challenge interpretation, with typical analyses failing to quantify the derived structure's uncertainty. Furthermore, the experimental potential of this technique for the study of brushes is only just being realised. This Thesis advances NR as a tool for studying polymer brush systems by establishing a robust analysis methodology that overcomes previous hurdles and demonstrating novel experimental techniques. In both cases, poly(N-isopropylacrylamide) (PNIPAM) brushes are used as model systems. First, the polymer system is characterised through the novel observation of surface-initiated ARGET ATRP using time-resolved NR, and a study of the dry brush as a function of humidity and temperature. Second, methodologies are developed that allow for robust determination of both solvated and confined brush structures. Lastly, NR is used to elucidate the behaviour of PNIPAM brushes in complex environments. A novel confinement apparatus is used to investigate the structure of a PNIPAM brush under mechanical confinement and contrast-variation provides unparalleled insight into PNIPAM–surfactant systems. In each case, complementary techniques are essential in guiding reflectometry experiments and fully understanding the polymer system. This work develops and demonstrates techniques that enhance the study of diffuse interfaces with the NR technique. Moreover, the holistic structural examination of PNIPAM undertaken sheds new light on the phase behaviour of this ostensibly well-understood polymer and highlights its rich interaction with surfactants.
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(2021)ThesisThis thesis investigated the ecology and metabolism of microorganisms, especially yeasts, during the wet fermentation of Australian coffee beans, and their contribution to coffee quality. Pulped coffee beans were fermented underwater for 36 h where yeast growth was suppressed by the addition of Natamycin at 300 mg/L. Spontaneous fermentation without the addition of Natamycin was conducted as control. The growth and diversity of microorganisms during fermentation were monitored by both culture dependent and independent methods. Major non-volatile metabolites during fermentation were monitored by high performance liquid chromatography (HPLC) and volatiles in the green and roasted beans were measured by solid phase microextraction coupled with gas chromatography tandem mass spectrometry (SPME GC-MS). Both bacteria and yeasts grew significantly during spontaneous fermentation while yeast growth was restricted in the Natamycin treated fermentation without significant impact on bacterial growth. The bacterial community was dominated by Citrobacter sp., Gluconobacter cerinus, Leuconostoc mesenteroides and Lactococcus lactis with maximum populations between 4-7.2 log CFU/g, while Hanseniaspora uvarum and Pichia kudriavzevii were the predominant yeasts at 4.5-5 CFU/g. During fermentation, the microflora utilized sugars in the mucilage and produced mannitol, glycerol and essential volatiles, mainly alcohols, esters, aldehydes and organic acids, with their concentrations generally lower in beans fermented with yeast suppression. Coffee produced from yeast suppressed fermentation received lower sensory scores in flavour and aroma and overall quality by 3 Q-Grade coffee masters. When H. uvarum and P. kudriavzevii were inoculated individually and in combination, they dominated the fermentation by growing to 9-10 log CFU/ml, and produced greater amounts of glycerol and flavour volatiles in the green beans which remained in higher levels after roasting compared with the control. Coffee brewed from these beans received significantly high scores of flavour, aroma, acidity and overall quality. Mucilage degradation seems to be initiated by endogenous enzymes and microbial contributions to the process occurred subsequently either enzymatically or by acidification. These findings demonstrated the crucial contribution of yeasts to successful coffee fermentation and high-quality coffee, and the potential of developing the two yeasts into starter cultures for coffee fermentation.
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(2021)ThesisCO2 hydrogenation represents one of the most practical solutions for mitigating anthropogenic carbon into chemicals/fuels. The overall reactivity in these reactions is often linked to the nature of kinetics relevant surface intermediary steps. Herein, light-induced photoactivation and materials engineering strategies were employed to particularly tailor the sluggish reaction steps and improve the catalytic performance of two CO2 hydrogenation reactions, namely CO2 methanation and methanol synthesis. The light-assisted CO2 methanation over NiOx/La2O3@TiO2 (NLT) was studied using isotopic-assisted in-situ diffuse reflectance infrared transform spectroscopic (DRIFTS) technique. It was shown that one of the important surface reactions – formate (HCO2*) conversion - can be promoted under visible light illumination. The La2O3 promoter and the broad-band localised surface plasma resonance (LSPR) property of Ni nanostructure, which acts as a vital adsorption site for CO2 activation and enables the generation of high-energy electrons, respectively, could play a primary role in this promotion. Next, the effect of photoexcitation on light-assisted methanol production from CO2 hydrogenation over a Cu/ZnO/Al2O3 (CZA) catalyst, where HCO2* conversion also plays an important role, was studied. Interestingly, significant methanol enhancement was only observed under the photoexcitation of both Cu and ZnO, whilst CO production was improved irrespective of the spectral range. This was revealed to be governed by the photo-generated electrons and their subsequent interfacial transfer which were responsible for the simultaneous transformations in surface chemistry and catalytic reactions. Further, CeO2 was studied as a promoter for Cu/ZnO based catalyst where enhanced methanol production was observed at dark condition. Lastly, a dopant strategy (Mg/La doping in ZnO) was adopted to electronically promote the Cu-ZnO interaction to testify its role in light-assisted methanol production. The photothermal catalytic methanol production over promoted CZA was improved benefiting from the enriched interfacial oxygen vacancies which could help channel the photo-generated electrons to the adsorbed HCO2* species. Overall, the study demonstrated the potential of photoexcitation and materials engineering strategy in improving CO2 hydrogenation reaction over oxide supported Ni and Cu catalysts. Significantly, the mechanistic understanding at the molecular level is critical for the design of catalysts that can better harness the potential of photoexcitation.
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(2021)ThesisEmerging membrane technologies such as forward osmosis (FO) and membrane distillation (MD) can provide alternative engineering approaches to current water-treatment membrane technologies, but without the high-pressure requirements. Currently, greater industrial implementation of these technologies is hindered by limitations with low flux, flow polarisation issues, design optimisation and issues with membrane deformation. An experimental and numerical assessment of a plate-and-frame (PF) FO module, revealed significant occlusion of the draw-channel under applied transmembrane-pressure (TMP), at points up to 70% while under an applied TMP of 1.45bar. Subsequently, 3D computational fluid dynamics (CFD) simulations were performed and validated against pressure loss data under TMP, to reveal the impact of flow indicators known to affect concentration polarisation (CP), such as Reynolds number, velocity profiles and shear strain. The pressure-loss method was then applied to a range of commercially available modules, found to occlude a cross-sectional area from 12-16% for the spiral would (SW) types and 49% 1.45bar for the PF module. CP models were then developed in conjunction with flux data to establish the degree of CP occurring in the modules. The CP data was then related to a CFD characterisation to establish detailed relationships on the impact of TMP on CP effects. Finally, a solar vacuum-membrane distillation (solar-VMD) system was developed and assessed experimentally to apply the lessons learned from the FO investigation in another emerging membrane technology. Lab-scale experiments were used to develop and validate a CFD model, using predictive hydrodynamic factors such as Reynolds number and shear strain, to mitigate temperature polarisation (TP) using turbulence promoters. A parametric analysis of the CFD data revealed the flux improvements and TP mitigation available through the addition of a baffle, combined with an economic analysis for real world use (demonstrating a viable decentralised drinking and hot-water supply). Flux performance of the MD system was found at >8LMH in solar conditions of ~800W/m2, with a payback period of 2.06 years. Overall, this thesis provides a detailed assessment of the impacts of applied TMP in FO processes, as well as potential design optimisation pathways by furthering the knowledge of CFD analysis in emerging membrane technologies.
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(2021)ThesisCirculating fluidized bed (CFB) has been widely applied to many chemical engineering processes. Although significant developments have been made in understanding the performance using the complex CFB technology during the last decades, the detailed inner information cannot be obtained by experiments because of complicated flow pattern in the system and backward measuring equipment. Numerical simulation has become the primary method to accelerate the development of complex CFB technology, reduce the cost of design and operating time, as well as reduce the technical risks. This thesis aims to provide more detailed in-furnace phenomena of complex CFB systems, including the hydrodynamic behaviours and chemical reactions based on the numerical simulation method. The promising chemical looping combustion (CLC) technology, as an example of complex CFB systems, will be focused on in this thesis. Meanwhile, the non-uniformity phenomenon in complex CFB units is comprehensively investigated in two symmetrical CFB configurations connected in parallel and series. Sequentially, an integrated method to dynamically combine CFD modelling and the process simulation is developed as a solution to improve the CFB performance. Specifically, it covers the following five aspects: 1. The hydrodynamic characteristics in a full-loop dual CFB CLC unit are comprehensively investigated based on the Eulerian multi-fluid model to give more detailed information about the flow behaviours. 2. The hydrodynamic characteristics in a unique counter-current moving bed full-loop CLC unit are comprehensively investigated based on the Eulerian multi-fluid model to study the unique configuration and in-furnace fluidization. 3. The reaction characteristics in the unique counter-current moving bed full-loop CLC unit are firstly attempt based on the hybrid Eulerian- Eulerian-Lagrangian model to study the in-furnace reaction details. 4. The non-uniformity characteristics of the multiphase flow in two complex CFB units connected in parallel and series, respectively, are studied based on the Eulerian multi-fluid model. 5. A novel direct integrated method to dynamically combine CFD modelling and the process simulation is developed. A case study of real-time regulation of boundary and operating conditions of reactors in complex CFBs is realized. These studies contribute to the deep understanding and further optimization of complex CFB systems.
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(2021)ThesisCells are considered to be the basic function and building units of life, which are able to conduct necessarily life-related activities. Inspired by the natural cells, researchers have endeavoured to construct synthetic cells and made them possible to become surrogates of real cells in different fields. Synthetic cells are generally composed of a semi-permeable membrane enclosing active contents inside, sharing similar structures with real cells. A variety of cellular activities have been realized in these synthetic cells, such as enzyme catalysis, gene expression and cellular movement. Nevertheless, the limitations of the existing synthetic cells should be resolved for further development, for example, instability under harsh conditions, programmable cell events (gene expression). Besides, most of the synthetic cells are unable to replicate specific functionalities of specific types of real cells. More efforts should be made to solve the challenges of synthetic cells and expand their potential in practical applications. The research projects included in this thesis aim to overcome the above issues. To solve the instability issue, metal-organic frameworks (MOFs) are exploited in these studies, whose protection performance on biomacromolecules is validated first on a therapeutic polypeptide. Inspired by the enhanced stability, MOFs-biomacromolecules composite is then engineered as pseudo-organelles for constructing synthetic cells. Metal-phenolic networks (MPNs) are chosen as pseudo-plasma membrane owing to their high physical and chemical stability, facile synthesising procedures and tunable permeability. A MOFs-MPNs based synthetic cell is then constructed, which presents excellent activities across a wide range of operational conditions. On the other hand, since MOFs can be engineered to selectively degrade under mildly acidic conditions, gene expression machinery can be regulated inside of the synthetic cells through encapsulating gene and in-vitro transcription and translation machinery (IVTT) into MOF separately and turned on by facile pH switches. This pH-gated gene expression is relevant to physiological conditions, which proposes a facile strategy to control subcellular events in artificial cells closely mimicking the complex biochemical events in real cells. Inspired by the above results, we further constructed artificial β-cells, which can sense high-level glucose and secrete insulin as a response through insulin gene expression, replicating the biological functionality of islet β-cells. In summary, the results presented in this thesis bring the synthetic cells one-step closer to real cells, expanding their potential in practical applications.
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(2021)ThesisNatural biopolymers, such as DNA, RNA, and proteins, are discrete macromolecules possessing inherent biological functions attributed to their highly organized chemical structures. Their precision structures, in nature, are determined by the unique microstructures (or primary structures), including two major factors throughout the polymer chain: monomer sequence and stereoregularity. For a long time, polymer chemists have dedicated themselves to achieve such dual control during the synthesis of synthetic polymers in order to emulate such structurally perfect biopolymers. Despite the success of directly utilizing natural monomers (nucleotides and amino acids) to create such macromolecules, researchers are now ambitious to employ other non-natural monomers since their broad chemical diversity would excavate even more possibilities to sophisticate functions and applications in both biological and nonbiological niches. Unfortunately, limited methods have achieved the dual control including a newly disclosed method of iterative exponential growth, leaving a gap in terms of any radical addition methods utilizing the most diverse olefins as monomers. This thesis aims to address this gap, by synthesizing discrete and stereoregulated peptide mimics through successive and iterative radical addition of olefin monomers. With significant improvements to the previously disclosed photoinduced-RAFT single unit monomer insertion (Photo-RAFT SUMI) technique, the initial study has achieved perfect monomer sequence control by sequential and alternating insertions of two families of monomers, namely indene and maleimide. In which, two pentamers were successfully synthesized as examples by five iterative insertion reactions. Subsequent chain extension has demonstrated the “livingness” of the pentamers, illustrating the feasibility of further SUMI reactions to form longer discrete polymers. Subsequently, this promising synthetic method was successfully transformed to a flow reaction system. Facilitated by automated column chromatography, gram scale of discrete oligomers with diverse monomer sequences were produced with exceptional isolated yields, short reaction time, and easy purification. Notably, subsequent investigation revealed that the utilization of these cyclic monomers has spontaneously resulted in a trans- stereospecificity within the 5-member ring during each step of insertion. This exciting finding has ultimately led to the final success of controlling both monomer sequence and stereochemistry by Photo-RAFT SUMI with further improvements. A library of enantiopure trimers with the same monomer sequence but different stereochemistry was thus obtained. These enantiopure trimers were comprehensively characterized by NMR, ESI-MS, XRD and 2D NOESY to confirm their unique stereo-structures which were then correlated to their properties including thermal transition, crystallization, and optical activity.
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(2021)ThesisEmerging pollutants generated from pharmaceuticals and personal care products and their potential effect on public health have become a growing concern in recent years. In contrast to conventional treatment techniques, catalytic ozonation is an effective method for removing these pollutants from wastewater. The main aim of this thesis is to investigate the capacity of oxygen vacancies and their electron density to boost the generation of hydroxyl radicals and reactive oxygen species (ROSs) from ozone and consequently improve the mineralisation of organic pollutants. This study chose Cerium oxide as the primary catalyst due to its redox properties and surface oxygen vacancy capacity. Three different approaches are employed in this thesis to regulate the surface oxygen vacancies and explore their effect on catalytic ozonation performance. As the first approach, UV light pre-treatment was used to boost surface oxygen vacancies. Spectroscopic analysis showed that UV light pre-treatment could promote the surface oxygen vacancies and consequently enhance the catalyst performance. A mechanistic study revealed that molecular ozone plays the main role in the initial degradation of aromatic organics and breaking of the benzene ring, while hydroxyl radicals are essential in the mineralisation of later intermediates to CO2 and H2O. To understand the influence of different types of oxygen vacancies (based on their charge state) on catalyst performance, CeO2-SiO2 binary oxide composites (CexSi1-xO2-) were fabricated as the second approach. Experimental and theoretical analyses revealed that oxygen vacancies with two electrons (OV0), existing as peroxide species, are more effective than other types of oxygen vacancies for activating oxygen and ozone to form ROSs. The results also demonstrated that OV0 clusters were more favourable than single OV0 sites for mineralising organics. Key active species were explored in the presence of several radical scavengers, showing that the contribution of •OH for catalytic ozonation is greater than •O2 and surface OH groups. Accordingly, the generation of H2O2 from O2 via peroxide species is proposed as the primary source of •OH generation through ozone molecules. To gain further insight into the role of oxygen vacancies and electron flow on the surface of the catalyst, CeO2 was dispersed on the surface of carbon fibres (CFs). In this approach, the surface chemistry of the CFs was modified using K2S2O8 and H2O2 to promote the electron flow and localised electrons on oxygen vacancies. CF was selected as a support due to its potential for exposing more active sites and providing more localised -electrons. It was found that modifying the surface of CFs to obtain structurally ordered support with surface oxygen functional groups offered better electron transfer capabilities and generated more OV0. Overall, this study demonstrated that high dispersity and greater free-electron availability (in the form of two electron-containing oxygen vacancies) can promote the capability of CeO2 as a catalyst for the catalytic ozonation reaction. The new knowledge enables the development of efficient and low-cost catalysts for catalytic ozonation and other oxidation reactions.
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(2021)ThesisThis thesis presents the development and application of a multi-fluid blast furnace (BF) model, with special reference to the layered burden structure and novel operations. The multi-fluid BF model involves gas-solid-liquid flow and main thermochemical behaviours in the BF. The model is evaluated by applying it to an industrial BF for which top gas information was measured. The predictions and measurements demonstrate a satisfactory agreement. When the layered burden effects are properly accounted for, the fluctuation trends or zig-zag pattern of flow, temperature and chemical can be found. An attempt has been made to develop a BF gas residence time distribution (RTD) model, aiming at improving the understanding of gas flow pattern and the formation of gas RTD in the BF. The results demonstrate that BF gas flow is primarily of piston-type while some flow inside the stagnant region forms the RTD tail. Furthermore, a series of novel operations are systematically studied using the BF model coupling with the respective sub-model. They are briefly introduced here: a sub-model for central coke charging (CCC) operation, a sub-model for nut coke charging, a sub-model for carbon composite briquette (CCB) charging, a sub-model for burden batch weight selection, a sub-model for oxygen enrichment operation and a sub-model for hydrogen shaft injection. The BF model is demonstrated as a useful tool to deepen the understanding of the novel operations. Finally, the effect of shaft angle on BF performance is examined using the BF model. The underlying mechanisms of how the shaft angle could affect in-furnace behaviours are obtained. These studies contribute to the body of knowledge associated with BF inner phenomena, particularly related to the layered burden structure and the abovementioned novel operations.
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(2021)ThesisThe spouted bed is a reactor designed for the gas-solid contacting purpose and can deal with particles of a wide range of particle density, complex shape, and different sizes. Thus, it has been widely applied to a variety of processes, such as drying, mixing, granulation, coating, gasification, pyrolysis, and combustion. Its superior gas-solid mixing performance can be mainly attributed to the symmetrical particle circulation movement brought by the strong vertical spouting. Particles experience the dilute region (i.e., spout region and fountain region) and dense region (i.e., annulus region around the spout region) in a routine process, thereby ensuring the homogeneity and efficiency of the gas-solid contacting. However, the spout deflection phenomenon keeps disturbing the normal spouting, in which spout channel deflects to the annulus region in the lateral direction, rather than keeping vertically upward. This phenomenon is easily triggered by hydrodynamics disturbance and small operating parameter changes, and thus has been reported in both spouted bed and spout fluidised bed. The spout deflection phenomenon is usually regarded as a challenge to the normal spouting because it destroys the symmetrical particle circulation movement and narrows the operation range for stable spouting. Thus, many studies have been conducted aiming to eliminate the spout deflection and enlarge the operating range for stable operation. However, these interventions on the gas-solid hydrodynamics bring new problems and are not satisfying. This can be owed to the lack of fundamental understanding of the spout deflection. On the other side, no valid proof shows that vertical spouting is necessary for high gas-solid mixing efficiency in spouted beds. The gas-solid mixing performance under the spout deflection flow pattern remains unknown. Thus, either the elimination or application of spout deflection all requires an in-depth understanding of the spouted deflection phenomenon. This thesis focuses on the understanding of the spout deflection phenomenon in terms of its quantification, mechanism, and possible application by means of the Computer Fluid Dynamic-Discrete Element Method (CFD-DEM) coupling approach as well as PIV experiments. It is noted that the rectangular spout fluidised bed, as a kind of spouted bed, is widely used in this study because the spout deflection phenomenon in it is most obvious. In the past, the understanding of the spout deflection remains on qualitative description because there lacks a tool to study this mesoscale spout movement. Therefore, the first task of this thesis is to develop a tool to quantify the spout deflection movement. Therefore, spout deflection angle was defined to characterise the spout horizontal movement in the reactor. At first, the CFD-DEM simulation was conducted to obtain detailed information of both the solid and gas phase in the spout deflection process. As the spout channel often shows the polyline shape, and the bottom part (termed as the original spout) is chosen as the indicator of the spout deflection. It is noted that the spout channel has two biggest features, high porosity and large gas velocity. But the former feature is sensitive to background gas. Therefore, the angles of the gas velocity vectors in the original spout core are averaged to represent the spout deflection degree. The amplitude, regularity, and speed of the alternating spout deflection movement are quantified for the first time. The spout deflection angle makes it possible to compare the intensity of alternating spout deflection under different operating conditions. Then, the spout deflection angle is applied to systematically investigate how the operating conditions, including static bed height (H0), background velocity (Ubg), and reactor column width (W), affect the alternating spout deflection in a spout fluidised bed. Some interesting results were found. For example, there is an upper limit for the deflection amplitude because of the self-locking phenomenon in the bottom corner. Large W promotes the regularity of the alternating spout deflection while the effects of H0 on its regularity in the investigated range is neglectable. In addition, the main frequency of the alternating spout deflection reduces with increasing H0 and increasing Ubg, and finally stabilises at around 1.7 Hz in the investigated cases. It is noted that the previous hydrodynamics study about spout deflection is all based on the simulation method. To further validates the findings about the spout deflection, experimental work is conducted. In this experiment, a flat-bottomed rectangular spouted bed is built. The spout deflection angle definition is extended to the experimental data obtained by Particle Image Velocimetry (PIV). The results show that the amplitude of the alternating spout deflection is stable with increasing spouting velocity, which can be owed to the self-locking phenomenon. The regularity of the alternating spout deflection keeps good at first and then becomes chaotic with increasing H0. These findings are similar to the previous result in numerical simulation. After that, the mechanism of the spout deflection is explored in order to control or eliminate the spout deflection better. In this part, two hypotheses are proposed for the spout deflection mechanisms in spout fluidised beds, and two virtual experiments are designed to verify the corresponding hypotheses using the CFD-DEM. To verify Hypothesis I that the unsymmetrical particle fountaining, including particle spurting and particle falling, is one main reason for the spout deflection, the virtual experiment I is designed where the particles are manually collected from the spurting surface and then symmetrically released and fall to the free space above the two annulus regions. Three symmetrical release cases are compared, and the results confirm that the spout deflection disappears when the symmetrical particle fountaining is deployed. Moreover, two univariate tests are conducted to check the role of an unsymmetrical particle falling and unsymmetrical particle spurting, respectively, confirming the Hypothesis I again. To verify Hypothesis II that the rheological properties of the annulus region also play a key role in determining whether the spout deflection happens, virtual experiment II is designed where the rheological properties of the annulus region are changed in terms of particle restitution coefficient, particle friction coefficient, background gas velocity, and particle diameter. The simulation results show that spout deflection tends to happen when the annulus regions have better rheological properties (i.e., larger particle restitution coefficient, smaller particle friction coefficient, larger particle diameter, and larger background velocity of the gas phase). This work unveils the mechanism of spout deflection in spout fluidised beds. The last work is to explore the application possibility of the alternating spout deflection, that is, to get the alternating spout deflection under control and get it independent on the operating conditions. Thus, an umbrella-like baffle is added on the route of the spout channel to obtain the spout deflection. As a result, the spout channel is divided into two parts by the baffle, the first spout and the second spout, respectively. Both first spout and second spout keep deflecting alternatively with time, and their deflection is always in opposite directions. This dynamic balance of the two spouts enables the multistage spouting higher robustness. The efficiency of gas-solid interactions also improves because of two reasons. The first one is that the horizontal spout movement enhance the gas-solid momentum transformation, and the second reason is that the four extra particle circulations occur on both sides of the first spout and second spout due to the obstruction of the baffle. In addition, the control of the alternating spout deflection below and above the baffle can be achieved by adjustments of baffle opening angle. In summary, the alternating spout deflection shows significant advantages in terms of robustness and gas-solid interaction efficiency and is of fascinating engineering and industrial implications.