Particle Formation

The project ″Modeling Porosity Development during Drying of Liquids and Slurries″ aims to build a mechanistic, three-dimensional model that predicts how internal morphology (e.g., porosity) evolves as gas-saturated slurries dry. Started in September 2023 and updated as of May 2025, the project combines pore-scale simulations and microfluidic experiments to elucidate bubble formation, transport, and interaction in slurries containing dissolved gas in the course of drying.

The model, at its core, captures the dominant physical mechanisms driving drying kinetics: bubble nucleation, growth, coalescence, collapse, gas diffusion, surface evaporation, and capillary effects. These processes were formulated as discrete rules and implemented within a three-dimensional pore-network model. To verify these rules, preliminary two-dimensional microfluidic experiments were performed to monitor bubble dynamics and interface evolution. The observations confirmed key model behaviors, including the transition from concave to convex interfaces and characteristic nucleation and coalescence patterns.

Simulation results showed that the presence of bubbles significantly accelerates drying. Compared to bubble-free systems, bubble networks experienced reduced total drying time, driven primarily by an extended constant rate period. Bubble growth induced internal liquid transport toward the drying surface, maintaining surface wetness and delaying the onset of the falling-rate period.

Spatially, simulations accounting for bubbles exhibited more uniform saturation profiles, whereas in simulations without bubbles pronounced gradients from the surface downward. These findings underscore the role of internal bubble dynamics in redistributing liquid and promoting homogeneous drying. Consistent results across cubic and spherical pore network geometries further demonstrate the robustness and generality of the model.

In the remaining time of the first funding period, the model will be extended to account for solid-particle displacement driven by capillary pressure, enabling full simulation of morphology evolution during drying of a single slurry droplet. Systematic simulations will then be performed across a range of material properties and process conditions. Once this extension is completed, the model will be able to generate the high-resolution datasets required to parameterize a continuum-scale single-droplet model. After model reduction, this continuum model will be integrated into a CFD framework to simulate foaming spray-drying behavior at the tower scale during the second funding period of the project.

This report summarizes three years of IFPRI-supported research on cohesive powder flows and deagglomeration processes. The project’s primary objective was to investigate the drying of cohesive granular materials, specifically focusing on strategies to minimize salt deposits on dried powders. Over this period, we developed several lab-scale experimental approaches for both testing agglomerate fragmentation and characterizing cohesive powders. We detail insights ranging from the development of drying and fragmentation processes to the fundamental mechanics of bulk- and capillary-scale cohesion, alongside quantitative results from specialized techniques used to analyze these flows.

Experimental and Theoretical Study on Atomization Process

We present the results of an experimental and theoretical study on the atomization process of high viscosity and polymeric fluids. We have developed a model for the atomization process in swirl and fan nozzles. The primary atomization in such nozzles results in the formation of filaments and long ligaments, which breakup into droplets.

Primary Atomization Model

We propose a primary atomization model based on the interaction of two breakup mechanisms: the growth of surface wave and the formation of perforations. At the nozzle orifice, small scale surface waves are formed due to a high relative velocity between the liquid sheet and ambient gas. As the surface waves grow, the liquid sheet forms alternating thick and thin regions due to the nonlinearity of the surface wave. The thin region becomes thinner as the sheet expands and perforations appear.

As these perforations expand, streamwise filaments form as the boundaries of these perforations approach each other. Close to the breakup position, the growth of these perforations will eventually be stopped by the thick regions on the liquid sheet. As these streamwise filaments detach from the liquid sheet, the liquid sheet breaks up and forms filaments.

Types of Filaments

As a result, there are two types of filaments formed:

• The thin streamwise filaments formed from the breakup of thin regions due to perforations.
• The thick spanwise filaments formed from the thick regions due to the surface wave.

These filaments become thinner due to the lateral velocity and eventually these two types of filaments break up into droplets due to surface waves and form the spray with a wide range of droplet sizes. Theoretical models are developed to predict the droplet size distribution for this breakup for both Newtonian and Viscoelastic fluids.

The objective of this research project is to assess and enhance the ability of a recently-advanced high-fidelity modeling framework for spray formation to model complex liquid break-up and predict drop size distributions in high viscosity and non-Newtonian liquid atomization systems, such as found in spray drying applications. This framework, dubbed enhanced Volume of Fluid (eVOF), was developed by the PI’s research group and hinges on two key components:

1. a fully conservative Eulerian interface capturing technique with the ability to capture sub-grid scale liquid features such as thin films and thin ligaments, known to be of critical importance in the break-up of viscous and non-Newtonian fluids, and
2. simple physics-based break-up models to convert these thin liquid features into spray droplets that can be tracked in a Lagrangian fashion.

In this project, non-Newtonian constitutive models were implemented and tested in the PI’s research flow solver, and shown to influence spray formation in simple flow configurations. Moreover, a simple pressure-swirl configuration was explored to demonstrate the ability of eVOF to preserve thin liquid films and virtually eliminate numerical break-up. Following this, the non-Newtonian constitutive models were further refined and validated against bubble rise experiments and deployed in complex simulations. A realistic pressure-swirl nozzle was selected for study based on availability of nozzle geometry and drop size measurements. Despite the complexity of the resulting flow, eVOF was again shown to preserve sub-grid scale liquid films successfully. Advances were made on sub-grid scale modeling of film and ligament break-up, allowing preliminary comparisons of drop sizes against experiments to be shown. Finally, a cylindrical reconstruction method was demonstrated for capturing ligaments at the sub-grid scale, which offers avenues for increased simulation accuracy for non-Newtonian and high-viscosity cases.

Going forward, the sub-grid scale modeling of film and ligament break-up will be further improved, in particular in the limit of high-viscosity liquids, and a more comprehensive comparison of drop sizes will be made against experiments.

The main objective of this project was to apply an innovative pneumatic nozzle design, the Air-Core-Liquid-Ring (ALCR)-nozzle, for spray-drying of highly viscous liquids and pastes. The project is divided into three main working packages (WP). WP 1 aimed to validate the ACLR atomizer technology to enable spraying of highly viscous liquids, using both experimental measurements and CFD simulations. WP 2 aimed to evaluate the impact of the composition and morphology of the atomized droplets on the drying kinetics, for highly concentrated feeds. WP 3 aimed to join the results of both packages to investigate the applicability of the ACLR nozzle for spray-drying of highly viscous liquids. The project schedule is shown in Fehler! Verweisquelle konnte nicht gefunden werden.. This is a short overview of the main findings of the project:

WP 1: Atomization with the ACLR nozzle

• The ACLR can achieve stable atomization with feed viscosities as high as 3 Pa·s, at relatively low pressures (7 bar) and low air-to-liquid ratios (0.8).
• The internal flow and the external spray instabilities are directly correlated.
• A CFD model was successfully adapted in STAR-CCM+ v.2206 to predict the internal flow of non-Newtonian maltodextrin solutions being atomized with an ACLR nozzle. In general, the predicted ALRs from the simulations agree with experimental results. Additionally, the liquid lamella thickness inside the nozzle follows the same trend in simulations and experiments: A smaller internal lamella variation is observed as the ALR increases.
• The possibility of using simulations to evaluate operating conditions outside of experimental capabilities was evidenced. The lamella variation can be severely reduced by increasing the operating pressure to 15 bar, which is still far below the 50-250 bar that is common in pressure swirl nozzles.

WP 2: Evaluation of the impact of the composition and morphology on the drying kinetics and model development by single droplet drying

• A method for the analysis of the mass data and calculation of the drying kinetics was developed in a single droplet drying (SDD) setup.
• The impact of the drying temperature was evaluated. While the impact of the drying temperature on the drying time agrees well with expectation, its influence on the drying kinetics showed no apparent trend.
• Experiments were conducted to evaluate the impact of initial solids concentrations up to 53 wt%. The results for the particle size, mass and drying kinetics showed good agreement with theoretical considerations. Looking at the drying time, it was revealed that the impact of lower water contents and lower water flux seem to level out at constant droplet size for higher solids concentrations.
• The results showed a significantly shorter time to the locking point for higher dry matter concentrations, reducing the risk of powder stickiness.

WP 3: Proof-of-concept of industrial applicability of the ACLR nozzle for spraydrying of highly viscous liquids

• The numerical investigation for an optimized nozzle design identified that a shorter outlet length, a larger mixing chamber inclination, and rounded internal edges lead to thinner and more stable liquid lamellas.
• Two improved nozzle designs were proposed, and the one with the shortest outlet length (0.8 mm) was shown to consistently produce the thinnest and most stable lamellas.
• The optimized nozzle demonstrated consistent performance improvements, leading to thinner lamellas and smaller droplets compared to the original design in both simulations and experimental tests.
• The improved design highlights significant potential for energy consumption and operating cost reductions, as it outperformed the original nozzle even when operating at lower pressures and air-to-liquid ratios.
• Optimized ACLR nozzle design leads to 33 % smaller spray droplets (x90,3) compared to the initial (basic) design.
• has been elucidated in WP 2.

The focus of this project is to understand the physical mechanisms that lead to defect formation – pitting, cracking, and delamination – during pharmaceutical tableting. A leading hypothesis among IFPRI members is that trapped interstitial air leads to high pore pressures that tend to fracture adhered particle interfaces after removal of the confining pressure. The project objective is to explore this problem through coupled numerical methods including:

• (i) continuum mixture models
• (ii) the discrete element method (DEM) coupled with a fluid solver.

The primary barrier to using these methods is that fact that the behavior of cohesive powders is not well understood, with neither a generally accepted constitutive relation nor contact model in existence.

To address this, the project has emphasized developing a reliable cohesive powder contact model for usage in DEM. This is the natural progression, since a powder DEM model will be indispensable in determining a constitutive relation for continuum simulations. In particular, we have concentrated on creating a mechanically-derived contact model for adhesive elastic-perfectly plastic particles.

In year one of the project, the majority of the theoretical framework for the contact model (i.e., the MDR contact model) was developed, but a number of issues remained. The JKR-type adhesion of the contact model needed to be validated once significant plastic deformation had occurred and the scheme to respect plastic incompressibility required an overhaul. The contact model was limited to simple symmetric loadings of a single particle, necessitating adaptation to manyparticle interactions. Additionally, the model, initially coded in Matlab, needed implementation in an established software like LIGGGHTS or LAMMPS, with a reliable fluid-solid coupling strategy.

In year two, the theoretical framework was completed by validating the adhesive model within the fully-plastic regime and correcting the plastic incompressibility scheme. The completed contact model was published in the premier solid mechanics journal, Journal of Mechanics and Physics of Solids, as a two part series. E↵orts to extend the contact model to the many-interacting particle case were started, as this was a necessary step to allow simulation of full-scale industrial applications. An initial implementation into LIGGGHTS was carried out and preliminary simulations showed promise in replicating compaction simulator data. Although progress was made, there were problems that remained both from a modeling and computational perspective when attempting to extend to the the many-interacting particles case. On the modeling side, the rigid-flat placement scheme used to extend the MDR contact model formulation to the many-interacting particle case was realized to be inaccurate with increasing polydispersity. On the computational side, a switch from LIGGGHTS to LAMMPS was desirable for three primary reasons:

• (i) LAMMPS is and will remain fully open-source with continual upkeep from Sandia National Laboratories (SNL),
• (ii) Joel Clemmer and Dan Bolintineanu, two SNL research scientists and primary contributors to LAMMPS, volunteered to assist with the implementation of the MDR contact model into LAMMPS, and
• (iii) LAMMPS provides the advantage of allowing immediate coupling with a multi-particle collision dynamics fluid solver, capable of simulating a compressible gas phase.

In the third year, a fully-parallelized implementation of the many-interacting MDR contact model was integrated into LAMMPS. The implementation was tested using both simple configurations involving a small number of particles and large-scale tableting simulations with tens of thousands of particles. This rigorous testing process prompted an overhaul of the rigid flat placement scheme and the development of a new topological algorithm to prevent contact through material during large deformation DEM. The unique ability of the MDR contact model to reconstruct deformed particle shapes was validated by comparisons with FEM predictions. The industrially relevant problem of pharmaceutical tableting was simulated, with experimental data provided by Vertex Pharmaceuticals for the compaction of Avicel PH102 (microcrystalline cellulose) serving as a benchmark. Good agreement was observed between experiments and numerical simulations for axial and radial stress measurements as functions of axial strain. Notably, the simulation also accurately predicted residual radial stresses after the release of axial confining pressure and the ejection force, aligning with experimental results. Preliminary coupled simulations involving the new DEM implementation and a compressible gas phase were also conducted. These simulations demonstrated that fracture caused by entrapped air could occur under specific loading conditions, though these were outside typical operating ranges.

In summary, a robust and reliable powder DEM model has been developed, which is opensource and accessible to all IFPRI members and is currently being used by some such as Amir Esteghamatian from Merck. Its utility in understanding defect formation in pharmaceutical tableting has been qualitatively demonstrated, and we are now positioned to conduct a comprehensive numerical investigation into air-induced defects. The mechanically-derived nature of the contact model o↵ers two significant advantages:

• (i) it provides a solid foundation for the future development of a continuum constitutive relation, and
• (ii) it enables the simulation of a wide range of industrial powder compaction problems beyond tableting, provided the material properties are known.

The following report is split into four chapters. Chapter 1 gives a high level update of the project and details on progress made that is not included in the attached papers. Chapter 2 is the soon to be submitted to Powder Technology paper covering the major advances and results from extending the MDR contact model to the many-interacting particle case. Chapter 3 and 4 are both papers of the two part series published in the Journal of Mechanics and Physics of Solids. These papers contain detailed explanations regarding the theoretical background of the contact model in addition to validations made against finite element simulations.

Over the past year we have built on a previously developed mechanistic model of granuleswelling and disintegration behaviour, with the aim to create a practical, fast tool for predicting and designing wet-granulated product performance. This work integrates physics with machine learning so that routine formulation inputs can be turned into reliable performance curves in seconds.

Core Models

• Mechanistic Performance Models (Single-granule Swelling → PBM Disintegration). Coupled single-granule swelling with population balance disintegration model to predict: Rp(t)  (granule radius) and F(t) (released-mass/ particles-released fraction).
• Physics-Informed Neural Network (PINN). A neural network implementation of the same physics that preserves mechanistic meaning while enabling efficient learning across formulations.
• ANN-Based Parameter Mapper. A supervised neural network that ingests standard formulation descriptors (e.g., L/S ratio, %SSG, filler type, %HPMC, initial porosity, skeletal density) and predicts the mechanistic parameters required by the Mechanistic model.

The workflow (Figure A) has been implemented and delivers rapid, physics-based forward prediction by converting formulation descriptors into mechanistic parameters, then full disintegration performance curves. Following further experimental validation, it will be ready to incorporate inverse modelling. Once incorporated, this inverse model will optimize formulation inputs and granulation conditions to give a desired released fraction at specific times.

modelling. Once incorporated, this inverse model will optimize formulation inputs and granulation conditions to give a desired released fraction at specific times.

Executive Summary

The focus of this project is to understand the physical mechanisms that lead to defect formation – pitting, cracking, and delamination – during pharmaceutical tableting. A leading hypothesis among IFPRI members is that trapped interstitial air leads to high pore pressures that tend to fracture adhered particle interfaces after removal of the confining pressure. The project objective is to explore this problem through coupled numerical methods including:

• (i) continuum mixture models
• (ii) the discrete element method (DEM) coupled with a fluid solver.

The primary barrier to using these methods is that fact that the behavior of cohesive powders is not well understood, with neither a generally accepted constitutive relation nor contact model in existence.

To address this, the project has emphasized developing a reliable cohesive powder contact model for usage in DEM. This is the natural progression, since a powder DEM model will be indispensable in determining a constitutive relation for continuum simulations. In particular, we have concentrated on creating a mechanically-derived contact model for adhesive elastic-perfectly plastic particles.

In year one of the project, the majority of the theoretical framework for the contact model (i.e., the MDR contact model) was developed, but a number of issues remained. The JKR-type adhesion of the contact model needed to be validated once significant plastic deformation had occurred and the scheme to respect plastic incompressibility required an overhaul. The contact model was limited to simple symmetric loadings of a single particle, necessitating adaptation to many-particle interactions. Additionally, the model, initially coded in Matlab, needed implementation in an established software like LIGGGHTS or LAMMPS, with a reliable fluid-solid coupling strategy.

In year two, the theoretical framework was completed by validating the adhesive model within the fully-plastic regime and correcting the plastic incompressibility scheme. The completed contact model was published in the premier solid mechanics journal, Journal of Mechanics and Physics of Solids, as a two part series. Efforts to extend the contact model to the many-interacting particle case were started, as this was a necessary step to allow simulation of full-scale industrial applications. An initial implementation into LIGGGHTS was carried out and preliminary simulations showed promise in replicating compaction simulator data. Although progress was made, there were problems that remained both from a modeling and computational perspective when attempting to extend to the many-interacting particles case. On the modeling side, the rigid-flat placement scheme used to extend the MDR contact model formulation to the many-interacting particle case was realized to be inaccurate with increasing polydispersity. On the computational side, a switch from LIGGGHTS to LAMMPS was desirable for three primary reasons:

1. (i) LAMMPS is and will remain fully open-source with continual upkeep from Sandia National Laboratories (SNL),
2. (ii) Joel Clemmer and Dan Bolintineanu, two SNL research scientists and primary contributors to LAMMPS, volunteered to assist with the implementation of the MDR contact model into LAMMPS, and
3. (iii) LAMMPS provides the advantage of allowing immediate coupling with a multi-particle collision dynamics fluid solver, capable of simulating a compressible gas phase.

In the third year, a fully-parallelized implementation of the many-interacting MDR contact model was integrated into LAMMPS. The implementation was tested using both simple configurations involving a small number of particles and large-scale tableting simulations with tens of thousands of particles. This rigorous testing process prompted an overhaul of the rigid flat placement scheme and the development of a new topological algorithm to prevent contact through material during large deformation DEM. The unique ability of the MDR contact model to reconstruct deformed particle shapes was validated by comparisons with FEM predictions. The industrially relevant problem of pharmaceutical tableting was simulated, with experimental data provided by Vertex Pharmaceuticals for the compaction of Avicel PH102 (microcrystalline cellulose) serving as a benchmark. Good agreement was observed between experiments and numerical simulations for axial and radial stress measurements as functions of axial strain. Notably, the simulation also accurately predicted residual radial stresses after the release of axial confining pressure and the ejection force, aligning with experimental results. Preliminary coupled simulations involving the new DEM implementation and a compressible gas phase were also conducted. These simulations demonstrated that fracture caused by entrapped air could occur under specific loading conditions, though these were outside typical operating ranges.

In summary, a robust and reliable powder DEM model has been developed, which is open-source and accessible to all IFPRI members and is currently being used by some such as Amir Esteghamatian from Merck. Its utility in understanding defect formation in pharmaceutical tableting has been qualitatively demonstrated, and we are now positioned to conduct a comprehensive numerical investigation into air-induced defects. The mechanically-derived nature of the contact model offers two significant advantages:

• (i) it provides a solid foundation for the future development of a continuum constitutive relation, and
• (ii) it enables the simulation of a wide range of industrial powder compaction problems beyond tableting, provided the material properties are known.

The following report is split into four chapters. Chapter 1 gives a high level update of the project and details on progress made that is not included in the attached papers. Chapter 2 is the soon to be submitted to Powder Technology paper covering the major advances and results from extending the MDR contact model to the many-interacting particle case. Chapter 3 and 4 are both papers of the two part series published in the Journal of Mechanics and Physics of Solids. These papers contain detailed explanations regarding the theoretical background of the contact model in addition to validations made against finite element simulations.

Spray drying is a widely used and well-established process across many industries, including food, pharmaceuticals, cosmetics, and chemicals. The process offers numerous benefits, such as reducing microbial growth, minimizing enzymatic degradation reactions, and significantly reducing the final volume of the product. This makes spray drying an important tool for production of high-quality, stable powders suitable for storage, application, and transportation (Dantas et al., 2023).

In the spray drying process, a solution, suspension, or emulsion is atomized into fine droplets, which are then exposed to a heated carrier, such as air or superheated steam, in the drying chamber (Dantas et al., 2023; Sobulska et al., 2022; Walton & Mumford, 1999). As a result of this interaction, the droplets rapidly lose moisture, which leads to the conversion of the liquid into solid. The fundamental criterion of spray drying processes classification is the method by which the atomized material comes into contact with the drying medium. This can take form of a co-current, counter-current, or mixed flow mode. Drying systems that operate in co-current flow are often preferred in the industry due to simple construction setup and easy control of the process. Unlike counter-current dryers, co-current systems enhance safety for thermosensitive materials by preventing contact of the dry material with hot inlet air (Zbicinski & Piatkowski, 2009a).

Most spray-dried products can be divided into three main categories, according to the morphology of their particles: skin-forming materials, porous materials, and materials with crystalline structure. Porous materials, also known as agglomerates, form particles bound by submicron dust or a binder, typically with a regular, highly spherical shape and with minimal surface irregularities. The drying process involves gradual solvent evaporation from within the particles, facilitated by the highly porous structure. This prevents significant pressure build-up inside the particle and thus avoids deformation or expansion, so blowholes and cratering are not commonly observed features. Porous materials include silica, colloidal carbon, cocoa, and detergents (Zbiciński & Kwapińska, 2003).

Materials with crystalline structure exhibit highly ordered arrangements of atoms or molecules, forming solid structures composed of large individual crystal nuclei bound together in a microcrystalline phase. The morphology, shape, and size of particles depend on the type of substance and drying conditions. Both solid and hollow particles occur. In some cases, significant internal pressure can develop from the evaporation of solvents within a particle. This can lead to disruptions, resulting in the formation of craters and secondary nucleation centers. Examples of materials with crystalline structures include sodium chloride, sodium carbonate, zinc sulfate, sodium pyrophosphate, sodium benzoate, and sodium formate (Walton & Mumford, 1999).

In skin-forming materials, drying initially occurs on the droplet's surface, increasing local viscosity and leading to the formation of a thin, hard outer layer known as a 'skin' or 'shell.' This layer is composed of a continuous, non-liquid phase, either polymeric or sub-microcrystalline. These materials typically form spherical particles with smooth surfaces and may be either hollow or solid. Hollow particles, are susceptible to collapse after drying, unlike solid particles, which retain their structural integrity. Surface-active molecules facilitate skin development by accumulating at the phase interface. An increase in temperature, which leads to a higher evaporation rate, also accelerates this process. Rapid skin formation can cause the trapped gas within the particle to expand and potentially rupture, leading to disintegration of the particle. Additionally, residual moisture in the particles may lead to the formation of secondary bubbles. The drying kinetics can lead also to other phenomena, such as particle inflation, shrinkage, crater formation, agglomeration, cracks and gaps, as well as particle vacuolation. This stands in stark contrast to the relatively narrow spectrum of morphological features typically observed in agglomerate and crystalline structures, which generally exhibit cracks, occasional crater formation, blowholes, and hollow particles. According to Walton et al. (Walton & Mumford, 1999), the ability to modify structural morphology of skin-forming particles during the drying process is instrumental in achieving extensive diversity and applicability, mainly in food industry. Skin-forming materials include: sodium silicate, sodium dodecyl sulfate (SDS), potassium nitrate, gelatin, skim milk, chicken eggs and maltodextrin (Walton & Mumford, 1999; Zbiciński & Kwapińska, 2003).

Maltodextrin, a water-soluble carbohydrate, plays a prominent role in the food and pharmaceutical industries, offering diverse functionalities, serving as a carrier for flavors and active agents (Sultana et al., 2018), functioning as an emulsifier (Bae & Lee, 2008; Rowe et al., 2006), filler, or substitute for lactose (Hofman et al., 2016). Thanks to its morphological properties, it offers a solution to the degradation challenges frequently faced by powdered products susceptible to caking or stickiness, primarily caused by the presence of low-molecular weight sugars with a low glass transition temperature (Koç & Kaymak‐Ertekin, 2014). Maltodextrin is used as a surface material in microencapsulation of sensitive components, including β-carotene (Loksuwan, 2007), avocado oil (Bae & Lee, 2008) and nutraceutical extracts (Sansone et al., 2011), and serves as an additive to increase the glass transition temperature of products such as honey (Samborska et al., 2015), sumac extract (Caliskan & Nur Dirim, 2013), or strawberry juice (Gong et al., 2018).

An inappropriately carried out drying process can deteriorate the final product’s quality, which is why precise process control is critical for obtaining high quality product. The nutritional and physical properties of food powders, comprising those containing maltodextrin, include aspects such as taste, aroma, color, and particle: agglomeration, density, porosity, dissolution rate, surface properties and size (Anandharamakrishnan & Ishwarya, 2015; Dantas et al., 2023; Hofman et al., 2016; Koç & Kaymak‐Ertekin, 2014). These properties can be altered by manipulating drying parameters, including temperature and flow rate of the drying medium, atomization method, and overall apparatus design, as shown by numerous published studies (Anandharamakrishnan & Ishwarya, 2015; Caliskan & Nur Dirim, 2013; Dantas et al., 2023; Koç & Kaymak‐Ertekin, 2014; Sobulska et al., 2022; Walton & Mumford, 1999; Zbicinski & Piatkowski, 2009a). In addition, it has been demonstrated (Takeiti et al., 2010) that a significant determinant influencing the particle properties of maltodextrin is the source of the starch hydrolyzed to obtain maltodextrin, along with its dextrose equivalent (DE) value. Recent works on mixtures of maltodextrin with other ingredients, such as proteins or oils, has emphasized the role of maltodextrin concentration in droplet dispersion, which is one of the factors that determine the specification of the resulting powders (Bae & Lee, 2008; Both et al., 2020). Nevertheless, the influence of these parameters is still complex and not sufficiently understood. This research is promising not only for optimizing powder quality but also for improving the energy efficiency of spray drying and encapsulation as well as for exploring potential applications.

Research work performed on a spray drying tower constructed at the Technical University of Lodz has been conducted for an extended period. A substantial body of literature exists that describes the impact of process parameters on the characteristics of the resulting powders in co- and counter-current systems (Zbiciński & Piątkowski, 2004) (Zbicinski et al., 2002), (Kwapińska & Zbiciński, 2005). Additionally, publications described experiments conducted using spray drying, which investigated the quality of products obtained by modifying the process itself. These modifications included the introduction of new parameters, such as foaming the sprayed solution (Rabaeva & Zbiciński, 2010),(Lewandowski et al., 2019), introducing a swirl of drying air (Wawrzyniak et al., 2020), using two levels of spray nozzles (Wawrzyniak et al., 2024), flame drying (Piatkowski et al., 2014) or conducting a microencapsulation process of oily substances (Lewandowski et al., 2020), (Adamiec & Marciniak, 2006). However, these studies did not fully analyse the level of significance of individual process parameters on the quality of the obtained product, nor did they focus on determining the significance of the effect of the state of the atomised solution on powder formation. What effect does a sudden change in the physical properties of the atomised solution, occurring, for example, as a result of an accident, have on the quality of the obtained product and the course of the drying process?

The research program presented for IFPRI assumes finding the relationship between the rheological properties of the solution and the drying speed on the morphology of the particles obtained by the spray drying method. Therefore, the following tasks were set during the project:

• Selection of suitable experimental media and determination of quality criteria.
• Measurements of rheological properties of aqueous solutions of selected materials.
• Adaptation of the existing equipment to the project requirements.
• Design of particle-free fall SDD measurement system.
• Carrying out spray drying experiments on the semi-industrial scale.
• Analysis of the physicochemical properties of the obtained powder samples.
• Preparation of a monodisperse droplet generator to construct devices to measure drying kinetics.
• Analysis of the influence of the rheological properties and conditions of the spray drying process on the morphology of the melts obtained in the experiments.
• Experiments to determine the temperature of particles during free fall using the IRTUC (InfraRed Temperature for Unknown Coefficients) method.