Maksims Marinaki’s research while affiliated with University of Latvia and other places

In this research, we extend our studies of the extraction process from diverse plant materials, introducing advancements to our previous models. Our framework considers dynamic elements by taking into account the motion of the particles, departing from the statical particle assumption in prior articles. Several methods such as moving geometries or modified equations for a system with moving particles in Lagrangian coordinates are introduced to boost the precision of our simulations, taking into account the complex dynamics of the solvent and its interaction with the plant material. Expanding beyond our focus on supercritical carbon dioxide (scCO2), our research is addressing some different applications. Besides the traditional solvent-based extractions, we consider potential applications in filtration, wood industry processes, etc. This allows our model to adapt to diverse industrial contexts with varied extraction mediums. Our coupled system of equations contains fluid dynamics equations for solvent flow, reaction-advection-diffusion equations for solute, and equations governing remaining solute concentration in biomass. The exchange of active material between solid and fluid is modelled by the Langmuir law. Applying finite volume techniques and implemented in the Octave/Matlab environment, our model captures the temporal evolution of two and three dimensional solute distribution and solvent velocity field. This modular framework facilitates the integration of tailor-made laws to represent diverse plant materials, ensuring versatility across applications. Through our simulations, we present the analysis of our modified model’s performance and discuss its advantages and limitations. This research is a slight step forward in understanding and optimising extraction processes, offering valuable insights for industries involved in functional foods, nutraceuticals, pharmaceuticals, cosmetics, filtration, and wood processing.

The authors consider the process of extraction from heterogeneous plant material; a novel model offering 3D spatial resolution is proposed and simulation possibilities by applying several modern numerical methods for three dimensional problems are discussed. These types of problems naturally arise when one wishes to mathematically describe the processes of the extraction with solvents such as supercritical carbon dioxide (scCO2). The results of this process meet the demand of the functional foods, nutraceutical, pharmaceutical and cosmetic industries on bioactive compounds. The models used in typical simulations by the industry offer no spatial resolution of the extraction process, however, when novel designs of extractors are developed, the three dimensional flow of the solvent and its interaction with the plant material should be considered. We propose a coupled system of equations consisting of fluid dynamics equations describing the flow of the solvent and reaction-advection-diffusion equations for the solute, plus equations describing the remaining concentration of solute in the biomass. The exchange of the active material between the solid and fluid is modelled by the Langmuir law. The initial distribution of solute in the plant material is not assumed to be homogeneous, nor are the extraction parameters, i.e. heterogeneous mixture of plant materials can be covered by this model. The equations are discretized by using finite volume techniques and currently implemented in Octave/Matlab environment. As a result, the temporal evolution of the three dimensional distribution of the solute is obtained along with the velocity field of the solvent, allowing detailed studies of the extraction process in a virtual design. The model is modular, allowing integrating tailor-made laws to describe various plant materials. The authors present simulation results and analyse the advantages and disadvantages of the proposed methods and approaches.

The main goal of the present study is to promote a more effective use of agriculture residues (straw) as an alternative renewable fuel for cleaner energy production with reduced greenhouse gas emissions. With the aim to improve the main combustion characteristics at thermo-chemical conversion of wheat straw, complex experimental study and mathematical modelling of the processes developing when co-firing wheat straw pellets with a gaseous fuel were carried out. The effect of co-firing on the main gasification and combustion characteristics was studied experimentally by varying the propane supply and additional heat input into the pilot device, along with the estimation of the effect of co-firing on the thermal decomposition of wheat straw pellets, on the formation, ignition and combustion of volatiles . A mathematical model has been developed using the environment of the Matlab (2D modelling) and MATLAB package ”pdepe”(1D modelling) considering the variations in supplying heat energy and combustible volatiles into the bottom of the combustor. Dominant exothermal chemical reactions were used to evaluate the effect of co-firing on the main combustion characteristics and composition of the productsand. The results prove that the additional heat from the propane flame makes it possible to control the thermal decomposition of straw pellets, the formation, ignition and combustion of volatiles and the development of combustion dynamics, thus completing the combustion of biomass and leading to cleaner heat energy production.

This paper deals with a simplified model taking into account the interplay of compressible, laminar, axisymmetric flow and the electrodynamical effects due to Lorentz force’s action on the combustion process in a cylindrical pipe. The combustion process with Arrhenius kinetics is modelled by a single step exothermic chemical reaction of fuel and oxidant. We analyze non-stationary PDEs with 6 unknown functions: the 3 components of velocity, density, concentration of fuel and temperature. For pressure the ideal gas law is used. For the inviscid flow approximation ADI method is used. Some numerical results are presented.