Microgravity Science and Technology最新文献

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.

In the present study, opposed flow flame spread over several fuel configurations of thin cellulosic fuels are investigated experimentally in normal gravity and microgravity environments. The fuel is configured in different shapes, namely, planar, hollow cylindrical (circular duct), C channel, and L channel, with the help of specifically designed fuel sample holders. The flame spread phenomena are examined for each configuration in both normal gravity and microgravity environments under ambient conditions of 21% oxygen and 1 atm. pressure. The microgravity experiments are conducted using a 2.5 s drop tower facility. The flame spread rates are measured at various opposed flow speeds. The effective flow speed accounts for the induced reference buoyant flow speed and externally imposed flow. The flame spread rates for each configuration are plotted against the effective flow speed ranging from 10 cm/s to 40 cm/s. While there is a nonmonotonic increasing-decreasing flame spread rate trend with respect to the effective opposed flow speed for all configurations, the flame spread rate can vary significantly with changes in the configuration. The C-channel configuration shows the highest flame spread rate compared with the other configurations of the same scale and identical experimental conditions. The effect of fuel size on the flame spread rate is also investigated for the duct configuration. The flame spread rate is noted to increase with the increase in fuel diameter.

This work summarizes the first results from a cloud seeding in microgravity experiment built by the Saudi Space Agency (SSA) and conducted on the International Space Station (ISS). The microgravity conditions provided in the ISS enable examining the interaction between the seeding agent, silver iodide, and the water droplets. Silver iodide particles dynamics of radius of 0.6, 0.3, 0.2, and 0.1 μm are examined in the ground and at the ISS at room temperature and atmospheric pressure in four 5cm³ chambers. Meanwhile, computer simulations are employed to examine the dynamics of seeding agent falling under the effect of gravity. It is found that microgravity conditions along with reducing seeding particles’ size enhance the interaction between seeding particles and the water droplets by increasing the period at which particles staying in the air before dropping down to the floor of the experiment. Humidity level in the experiment is observed to decrease onboard of the ISS because of the interaction between seeding agent and the water droplets.

The research on granular column collapse under various gravity levels is of great significance for the study of granular rheology and its applications in reduced-gravity space engineering. We firstly reviewed a rare experimental investigation that observed a gravity-related run-out distance of the granular column collapse in this paper. To identify the origin of the gravity-related run-out distance, a unified constitutive model was used to simulate the behavior of granular materials in these experiments based on a large deformation numerical method, the smoothed particle hydrodynamics (SPH). The parameters of this constitutive model were also discussed. Numerical simulations can reproduce the run-out distances that positively correlate with the gravity level, above 0.03 g in particular. Based on the numerical and constitutive analysis, this gravity-related runout distance is attributed to the combined influence of gravity-induced pressure and shear strain rate levels on granular flow.

This work investigates the capillary rise dynamics of highly wetting liquids in a divergent U-tube in the microgravity conditions provided by 78th European Space Agency (ESA) parabolic flight. This configuration produces a capillary-driven channel flow. We use image recording in backlight illumination to characterize the interface dynamics and dynamic contact angle of HFE7200 and Di-Propylene Glycol (DPG). For the case of HF7200, we complement the interface measurements with Particle Tracking Velocimetry (PTV) to characterize the velocity fields underneath the moving meniscus. In the DPG experiments, varying liquid column heights are observed, with a notable decrease in meniscus curvature when the contact line transitions from a pre-wetted to a dry substrate. In contrast, for HFE7200, the interface consistently advances over a pre-wetted surface. Despite this, a reduction in meniscus curvature is detected, attributed to inertial effects within the underlying accelerating flow. PTV measurements reveal that the region where the velocity profile adapts to the meniscus velocity decreases as interface acceleration increases, suggesting a direct relationship between acceleration and the velocity adaptation length scale.

According to the existing scenarios of interplanetary missions, the Moon is considered as an intermediate base on the way to deep space. In order to prepare for landing and work on the Moon, it is important to study the applicability of countermeasures in such missions. The paper presents the results of a pilot study performed during a short-term spaceflight (12 days). A new experience of using countermeasure impacts of lower body negative pressure (LBNP) at the early stages of adaptation to microgravity conditions has been gained. To assess the effectiveness of LBNP and changes in human physical performance after the spaceflight, we conducted tests on a treadmill, a bicycle ergometer, and testing with model tasks of on-planetary activity "express test". Regulatory mechanisms of the cardiovascular system proved to be quite effective when creating decompression up to -20 mm Hg, which is less than in preparation for returning to Earth. In the treadmill test, a lower speed was achieved after the spaceflight than before (13 km/h and 15 km/h, respectively) and cardiovascular system response to the change in load was slower. At the same time changes in such physiological parameters as oxygen consumption, respiratory rate and pulmonary ventilation were minimal. In the bicycle ergometer test, peak heart rate values were higher after the spaceflight than before, the physiological value of the standard exercise increased. «Express test» showed the positive dynamics from the first day to the third after returning to Earth: the performance of a dual task, the task of controlling the movement of the non-leading hand, and getting up from the supine position improved. Thus, assessment of the state of gravity-dependent physiological systems after short-term flight indicates the decrease of functional reserves of the organism and the necessity to develop appropriate countermeasures. The study was one of the first steps in the development of new medical control operations at the stage of paradigm shift from orbital flights to deep space exploration.