The results of an experimental study of the effect of hydrodynamic flow and injection of air bubbles on the spatial distribution and activity of cavitation events in a laboratory model of a flow sonochemical reactor are presented. The relevance of the work is due to the prospects of using acoustic cavitation by ultrasound in microgravity, where the absence of the buoyancy force fundamentally changes the behavior of multiphase media. The experiments were performed using the modified foil test method, which makes it possible to build maps of cavitation activity and monitor the dynamics of aluminum foil fracture that in the absence of a hydrodynamic flow, cavitation manifests itself in the form of horizontal zones spaced vertically, corresponding to the antinodes of a standing wave. A fluid flow leads to the formation of a single domed zone above the transducer and an increase in the fracture area. Aeration also forms a single zone, but sharper and elongated; the final area of destruction is comparable to the regime without aeration, but erosion occurs much earlier.
The effect of the chemical potential difference on the development of diffusion processes in liquid systems with an interfacial boundary was studied experimentally. The study was conducted using the example of mass transfer of a surfactant between a droplet and the surrounding medium. Water and a mixture of benzene and chlorobenzene were selected as the contacting liquids. Acetic acid, which has significantly different solvation energies in water and in the coctacting mixture, was used as the diffusing surfactant. A Fizeau interferometer was used to visualize the flow patterns and concentration fields. It was shown that in liquid systems with an interfacial boundary, the direction and intensity of surfactant diffusion are determined by the difference in chemical potentials between the contacting solutions. A comparison was made of the structures of surfactant concentration fields arising as a result of its diffusion from a droplet or into a droplet, as well as their evolution. Particular attention was paid to the influence of Marangoni convection accompanying the surfactant diffusion process.
Our study employs a percolation approach to describe flame spread and group-combustion excitation in randomly distributed fuel-droplet clouds based on findings obtained from space-based microgravity experiments on the flame-spread limit around interactive droplets. We developed a percolation model in which the flame spreads to droplets existing within the flame-spread-limit distance, which varies depending on the relative positions of two or three flame-spreading droplets. Using 2D- and 3D-percolation models, we investigated the effects of two-droplet and/or three-droplet interaction on the flame spread of randomly distributed droplet clouds and group-combustion excitation. The results show that the critical mean droplet spacing, around which the occurrence probability of group combustion sharply decreases as mean droplet spacing increases, increases with two-droplet interaction both in the 2D- and 3D-percolation models. However, even when three-droplet interaction is taken into account in the 2D-percolation model, the critical mean droplet spacing does not increase to the same extent as it does under two-droplet interaction. The critical mean droplet spacing in the 3D-percolation model is larger than that in the 2D-percolation model. The proportion of droplets ignited solely by droplet interaction relative to the total number of droplets is higher in the 3D-percolation model than in the 2D-percolation model because the increase in dimensionality leads to an increase in the number of droplets ignited solely by droplet interaction.
The Lacunar-Canalicular System (LCS) is a complex micrometer-scale structure that ensures an adequate supply of nutrients and the removal of metabolic waste products. The unique transport characteristics of the LCS may provide insights into the underlying mechanisms of osteoporosis in both astronauts during spaceflight and aged individuals. This study focused on the transport behaviors of three tracers with molecular weights of 376 Da, 20 kDa, and 150 kDa in bone LCS. Fluorescence intensity at osteocyte lacunae was adopted to evaluate the transport performance of three tracers under normogravity and hypergravity. The experimental results demonstrated that the lacunae fluorescence intensity is inversely proportional to the distance from the Haversian canal. When comparing the mass transfer of different molecules, small molecular tracers exhibited higher transfer rates, while large molecular tracers showed lower transfer rates. Under hypergravity conditions, fluorescence intensity within deep-layer lacunae rose significantly for all tracers. The most significant change was observed in the large molecular tracers, with fluorescence intensities in the superficial, shallow, middle, and deep layers elevated by 211.1
To eliminate the influence of centrifuge errors on the calibration accuracy of the platform inertial navigation systems, a high-dimensional system-level calibration method is designed. By combining the error propagation chain of the dual-axis centrifuge with the accelerometer error model, the indicated output of the accelerometer is obtained, and the indicated output-input error model is established, which serves as the basis for high-dimensional filtering. The established model incorporates the accelerometer error model, the accelerometer installation misalignment angles, the centrifuge equipment installation errors, and the platform inertial navigation system installation errors. A 35-dimensional state vector containing these errors is established, with the outputs of three accelerometers taken as observables. Subsequently, the state equation and the observation equation are derived, and a Kalman filter is designed for identifying the state vector. A 20-position rotation scheme through rotating frames of the platform inertial navigation system is designed, which takes advantage of the high-g environment (high-overload environment) provided by the centrifuge to fully excite all error model coefficients of the accelerometer, while eliminating the influence of centrifuge errors on the calibration of the accelerometer assembly. All error model coefficients of the accelerometer converged to the vicinity of the true values with high estimation accuracy.
