Microgravity Science and Technology最新文献

This study investigates the feasibility of replacing computational fluid dynamics (CFD) techniques with machine learning (ML) models for heat transfer modeling, focusing on forced convection processes. The research leverages artificial intelligence algorithms, specifically random forests (RF), super-gradient boosting (SGBoost), and artificial neural networks (ANN), to predict key heat transfer metrics such as Reynolds number, nanoparticle size, volume percentage, and Nusselt number. Using a dataset of 210 data points, the ML models are systematically applied to forecast heat transfer outcomes. Model performance is evaluated using Root Mean Squared Error (RMSE), Pearson’s correlation coefficient (r), and Mean Absolute Error (MAE). Results indicate that SGBoost achieves an accuracy of 91%, RF 90%, and ANN 86%, with corresponding RMSE values of 1.07, 1.65, and 16.1, respectively. These findings demonstrate that ML models not only deliver high accuracy and predictive power but also outperform traditional CFD methods in computational efficiency and adaptability to new data. Unlike conventional techniques that rely on predefined physical models and require extensive computational resources, ML approaches streamline the modeling process and enhance accessibility for diverse engineering applications. This study underscores the transformative potential of ML in advancing thermal analysis and optimizing forced convection heat transfer simulations.

In this paper, using propagating Lamb waves along the inclined curved surfaces, we present a technique to reduce the impact of rainy days on-camera performance. Our experimental results show that Lamb waves, generated at a location distant from a point of droplet impact, can suppress the formation of satellite droplets during partial rebound. Additionally, a high-fidelity numerical simulation model was developed, revealing that the liquid’s surface tension significantly affects the occurrence of satellite droplets during partial rebound. Moreover, by applying Lamb waves, the droplet on the curved surface can be propelled at different speeds. Combining numerical simulations, we can clearly observe the deformation of the gas-liquid interface after the droplets impact the substrate. Afterward, we systematically investigated the effects of droplet impact height, inclination angle, and applied input power on the Lamb Waves on droplet removal.

In this study, fluid flow during condensation in a tube under different gravity conditions is simulated by utilizing centrifugal force to offset gravitational effects. The role of fins, tube diameter, and steam quality on the two-phase flow pattern, temperature distribution, and pressure drop is investigated. The results show that gravity, tube diameter, and steam quality have a significant effect on the flow pattern. The flow characteristics were also significantly affected by the operating parameters, with undulating and laminar flow dominating, while bubbling flow emerges under specific conditions. In microgravity environments, as steam quality decreases, the temperature drop diminishes progressively compared to normal gravity conditions. Under normal gravity and low flow conditions, the average temperature of finned tubes increased by 7 °C to 16.4 °C relative to bare tube temperatures, and the pressure drop escalated by up to 56%. The introduction of fins notably enhanced heat transfer efficiency and facilitated a more uniform temperature distribution. However, this enhancement in heat transfer was accompanied by an increase in pressure drop due to the heightened resistance to fluid flow caused by the presence of fins. These experimental insights offer a deeper comprehension of fluid behavior under diverse gravity conditions and lay a scientific foundation for designing future thermal management systems.

Exposure to acute and prolonged microgravity triggers numerous physiological adaptations. To date, the underlying molecular mechanisms are not well understood, and several pathways have been proposed. Among other candidates, specific ion channels are hypothesized to be gravity dependent, but it has not been possible to conclusively demonstrate gravity dependency of specific protein entities. Therefore, we developed a miniaturized two-electrode voltage clamp (TEVC) that allowed electrophysiological experiments on Xenopus laevis oocytes using the GraviTower Bremen Prototype (GTB-Pro). The GTB-Pro is capable of flying experiments on a vertical parabolic trajectory, providing microgravity for a few seconds. As an interesting first candidate, we examined whether the nonselective mechanosensitive ion channel PIEZO1 is gravity dependent. The results showed no difference between PIEZO1-overexpressing and control oocytes under acute microgravity conditions.

This paper experimentally investigated the impact of the electric field strength (E), electrode installation heights (H), and the electrode shape on enhanced pool boiling heat transfer performance under a downward heating surface with an electric field. It is observed that the critical heat flux (CHF) generally increases with increasing electric field strength. For instance, for the mesh electrode, the CHF is increased by 100.0%, 240.0%, 340.0%, and 440.0% at E = 0.35 × 10⁶ V/m, 0.70 × 10⁶ V/m, 1.05 × 10⁶ V/m, and 1.40 × 10⁶ V/m, respectively, compared to E = 0 V/m. Furthermore, the electrodes hinder the detachment of vapor bubbles, which becomes more pronounced when the electrode installation height is low. At the same time, the more micro-ribs of the electrodes and the denser the distribution, the more uniform the electric field generated. Under this condition, the “pinch-off effect” caused by the non-uniform electric field is reduced, which is more conducive to enhancing boiling heat transfer performance. Ultimately, at H = 5.0 mm and E = 1.40 × 10⁶ V/m, the CHF with grid electrodes improved by 101.1% compared with the horizontally upward without the electric field, which is a superior combination of working conditions and suggests that a more optimistic boiling heat transfer performance can be obtained in microgravity. This work provides guidance for enhancing boiling heat transfer in microgravity by an electric field.

This study employed a lumped vapor model to investigate the depressurization dynamics during the thermodynamic venting process in a cryogenic liquid hydrogen storage tank under microgravity conditions. The effects of different control strategies-such as flow distribution, circulation flow rate, spray angle, and throttle valve switching time-on the performance of the thermodynamic venting system (TVS) were studied. Building on this foundation, the control strategies are refined across various filling rates and heat loads. The findings indicate that directing the flow towards the upper nozzle proximate to the vapor enhances the depressurization rate and augments the utilization of cooling capacity. The optimal circulation flow rate matches the heat entering the air pillow, and increases with higher heat load and lower filling rate. When the injection angle is 60°, the TVS achieves optimal performance with the fastest depressurization rate and no thermal stratification. The throttle valve opens during the early depressurization stage and closes when the pressure drops to the critical pressure P_cr, resulting in better performance. A lower filling rate and higher heat load lead to an increase in P_cr. This study provides a solid foundation for optimizing TVS control under various conditions, ultimately extending the storage duration of propellants in orbit.

Particle separation holds great significance as it has the potential to enhance product quality, efficiency, and safety across various industries by selectively sorting particles based on their specific characteristics. This, in turn, contributes to the improvement of processes in areas such as product manufacturing, environmental protection, and resource extraction. This paper proposes a novel microfluidic platform employing dielectrophoresis (DEP) principles to achieve the sorting of particles based on their size. This methodology leverages the dielectric characteristics of polystyrene particles. By manipulating various control parameters, such as electrode shapes (planar, V-shaped, and sinusoidal), the alteration of angles within the same electrode shape, adjustments in electrode widths, and electrode quantity. The study utilizes numerical simulation to compute the spatial distribution of the electric field within the microfluidic chip and predict the trajectories of particles within the microfluidic channel. Through quantitative comparison and analysis, a more optimized microfluidic chip with smaller size and shorter time, capable of effectively separating particles, is ultimately presented.

Continuous-flow devices used in microfluidics and flow chemistry often have a channel width large enough to make simple diffusion mixing ineffective but small enough to use mechanical mixing. Therefore, one must supplement these devices with a specific unit that enhances their mixing performance. In this work, we experimentally and numerically study the self-oscillatory process near an air bubble implanted into an outlet channel of a T-shaped device at some distance from the branching point. If one supplies a non-uniform surfactant solution at the inlet, the solutal Marangoni instability at the liquid–air interface can occur. The excitation of soluto-capillary convection leads to a relatively prompt homogenization of the solution downstream. A feature of the process is that it proceeds in a pulsed manner due to the rapid activation of convection, which mixes the solution near the bubble. This leads to damping of instability, followed by subsequent restoration of the concentration gradient by throughflow. We show that the relaxation process depends on the channel geometry, the flow rate, and the properties of the surfactant, but not gravity. Therefore, one can use this method to enhance mixing in any continuous-flow device that operates in microgravity conditions. The scheme’s crucial advantage is the possibility of easy external mixing control, which is essential for applications. In this work, we study the nonlinear properties of relaxation oscillation and the mixing enhancement by the Marangoni convection. The experimental findings are in good agreement with the numerical results.

In order to explore the dynamic properties and heat transfer mechanism of droplet impact on the heated wall, this study employs numerical simulation to analyze the Leidenfrost phenomenon caused by droplet impact. The occurrence mechanism of Leidenfrost phenomenon is analyzed from various perspectives, including droplet morphology, gas film formation, and interaction with the heated wall. The study reveals that the droplet, gas film, and heated surface mutually influence each other. As the droplet evaporates, water vapor is produced, and the gas film prevents direct contact between the droplet and the heated wall, resulting in the Leidenfrost phenomenon. The effects of droplet impact velocity, droplet size, and wall temperature on the Leidenfrost phenomenon were further investigated. The results indicate that a higher droplet impact velocity results in increased kinetic energy and a higher spreading coefficient, leading to enhanced heat exchange ability. However, the time taken to reach the maximum spreading coefficient differs from that of non-phase-change droplets. Additionally, smaller droplet sizes exhibit a more significant effect of surface tension on maintaining droplet shape. This results in a shorter spreading time for the droplet, but also higher kinetic energy consumption and a relatively smaller spreading coefficient. For the heat flow density, the larger impact velocity and size of droplet can increase the heat flow density and improve heat transfer. An increase in wall temperature significantly increases the heat flow density and is a crucial factor in sustaining the droplet Leidenfrost phenomenon.

This paper is devoted to the investigation of the stability of plane-parallel flow in a vertical fluid layer with uniformly distributed heat sources in modulated gravity field. The layer boundaries are rigid and maintained at equal constant temperatures. Gravity is assumed to be vertical and consisting of both mean and sinusoidal modulation (‘jitter’). Specific feature of this problem is that in the absence of modulation, at zero Prandtl number, the decrements of normal-mode perturbations of the base state are complex-valued and hydrodynamic instability mode is caused by travelling perturbations (travelling vortices at the boundaries of counter flows). With the increase in Prandtl number the instability mode changes from hydrodynamic instability of the counter flows to growing thermal waves. In the presence of gravity modulation, the base flow is the superposition of the same stationary flow as in the absence of modulation and time-periodic flow. The linear stability of this base state is studied by the numerical solution of the linearized equations of small perturbations. Numerical data on temporal evolution of perturbations are used to determine the decrements of perturbations and instability boundaries at different values of the Prandtl number. The calculations confirm that all perturbations are quasi-periodic. Parameter ranges where modulation makes stabilizing or destabilizing effect are defined. Sharp stabilization of the base flow in low-frequency range is discovered and explained by transformation of the neutral curves with the decrease of frequency which incleds formation of a bottleneck, break into two instability regions (the isolated region of hydrodynamic instability at lower Grashof number values and bag-shaped region of thermal wave instability at higher Gr), decrease in the size of the hydrodynamic instability region and shift upward of the thermal wave instability region and vanishing the isolated region of hydrodynamic instability.