We study experimentally and theoretically convective flows, which are induced in a horizontal liquid layer by a concentrated heat source: the split coherent beam of laser radiation. The layer surface is deformable. Depending on controlling factors, laboratory experiments demonstrate a variety of flow structures and surface configurations. The flow primarily has a single vortex pattern, but in a certain range of governing parameters, secondary nonstationary vortices are superimposed. Among the surface configurations there are the concave meniscus, the convex one, and the concavo-convex one. The numerical simulation is performed on a mathematical model, which involves nonlinear partial di¤erential equations for two-dimensional amplitude functions associated with distributions of temperature, vorticity, and surface deformation. In the long-wave approximation, the model describes the contribution of thermocapillary convection to the heat transfer as well as the degree of the interface deformation. The proposed model generalizes the existing one by taking into account the heating inhomogeneity.

The paper presents new results on the study of thermokinetics of gel system based on agarose in the process of transition from solution to gel and opposite. This issue is extremely relevant, since the stability and predictability of thermophysical and rheological properties in such transformations, especially in the presence of components of the nutrient medium and immobilized microorganisms, come to the fore in terms of design and selection of modes of operation of the printing device promising 3-D bioprinters, as well as the system of preparation and storage of the presence of the hysteresis effect, both from the point of view of the kinetics of gel formation and from the point of view of the dependence of rheological properties on temperature, at different concentrations of modifying components, is shown. The obtained results allow to draw a conclusion about the possibility of using the scheme with preliminary preparation of the initial biogel for the implementation of bioprinting technology based on agarose, and to recommend the obtained values for modeling the operating modes of devices of this type.

Unsteady heat transfer in agarose gels of various concentrations was studied in order to make a breakthrough in the technology of 3-D additive bioprinting. Data on the kinetics of the phase transformation was obtained using spectroscopy as a function of temperature during the formation of agarose hydrogel. The dynamics of aging was investigated for gels of different densities. The time dependence of the structural changes was obtained. Particular attention was paid to the changes in the structure of the gel due to the processes of evaporation of the liquid during the gel formation and during long-term storage. Experiments were performed to determine the dynamics of the temperature fields simultaneously with heat flux measurements during the formation of agarose gels from different initial concentrations. A technique based on experimental data for the computations of the thermophysical coefficients of agarose gels was developed.

The same properties of agarose gels containing neutral bioresorbable additives and living microorganisms which are important for use in additive technologies of bioreactors creation were considered. Data on the kinetics of gel formation from the solution during cooling were obtained by spectroscopic measurement by measuring the shift of the maximum spectrum of light passing through the gel, depending on the temperature. The dynamics of aging was investigated for gels of different concentrations of agarose, bioresorbable additives and living cells. The time dependences of the decrease in the optical transparency of such gels during the aging process, characterizing the changes in their structure, were obtained. Special attention was paid to the effect of liquid evaporation from gels in the process of gel formation and during long-term storage on relaxation processes leading to their spontaneous increase in density. Experiments were performed to determine the dynamics of the temperature fields simultaneously with heat flux measurements during the formation of studied gels with different concentrations. On the basis of the obtained experimental data and previously developed method, the thermophysical coefficients of agarose gels containing an admixture of starch and living yeast cells were calculated.

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