Microgravity Science and Technology最新文献

This study deals with the thermal performance of a flat copper heat pipe with a capillary structure composed of orthogonal grooves filled with water, so-called flat orthogonally grooved heat pipe. The orthogonal grooves are created using a CNC machine and filled using an automated filling apparatus. Under optimal operating conditions (thermosyphon position and cold source temperature of 40 °C), experimental results show that flat orthogonally grooved heat pipes effective thermal conductivity is approximately three times that of copper. Similarly, it is found that the flat orthogonally grooved heat pipe has lower thermal resistance than the flat axially grooved heat pipe studied in a previous work. Furthermore, a heat transfer analysis demonstrates that flat axially grooved heat pipe outperforms the flat orthogonally grooved heat pipe by up to 50% in evaporation, whereas the flat orthogonally grooved heat pipe performs up to 35% better than the flat axially grooved heat pipe in condensation. Based on a dimensionless analysis, heat transfer correlations for evaporation and condensation are proposed. The gap between evaporation and condensation heat transfer coefficients calculated by the correlations and those determined experimentally varies between ± 10% and ± 20%. Finally, a model based on energy conservation equations is proposed to predict the temperature distribution along the flat orthogonally grooved heat pipe. The distributions in wall temperature obtained from the model are consistent with experimental measurements.

Accurate prediction of liquid-vapor interface configurations is mission-critical for autonomous on-orbit propellant management, particularly during microgravity refueling operations where precise fluid control dictates mission success. In such environments, the systematic and rigorous evaluation of hydrostatic interfaces plays a vital role in ensuring optimal performance during liquid management and spacecraft attitude control. These fluid interfaces are primarily governed by residual gravitational effects, contact angles, and the geometric configurations of the containers. This paper investigates the characteristics of liquid-vapor interfaces within axisymmetric containers through a combination of theoretical analysis and numerical simulations. The dimensionless governing equations for hydrostatic surfaces in spherical coordinates are derived theoretically, based on the variational principle and the virtual work principle. A novel algorithm has been developed to compute liquid-vapor interface configurations in axisymmetric containers including ellipsoidal and Cassini tanks. The algorithm is validated by theoretical analysis and comparisons of numerical simulations and experimental data. Meanwhile, the impacts of various parameters on the liquid-vapor interface configurations are further analyzed in detail. Notably, the proposed method demonstrates significantly enhanced computational efficiency compared to conventional approaches. Furthermore, the algorithm can adaptively adjust its input parameters to predict hydrostatic interfaces under varying conditions. This methodology establishes a reliable foundation for real-time analysis of sloshing dynamics and liquid reorientation, thereby enabling autonomous decision-making during critical on-orbit refueling servicing phases.

Electrothermal convection in a horizontal capacitor of a low conducting liquid heated from above is theoretically studied using multi-mode Galerkin expansions. Under the alternating electric field the model exhibits oscillatory convection patterns. The synchronous oscillations appear at the electroconvection threshold. They transform into quasiperiodic oscillations at higher electric driving force. Further growth of the electric Rayleigh number leads to chaotic oscillations. The region of coexistence of chaotic and synchronous oscillations is found.

On Earth, electronic circuits dissipate heat through convective flows driven by gravity, transferring energy from devices to the environment. In microgravity, the absence of buoyancy disrupts this mechanism, causing heat accumulation and potential damage. Here, we present an experimental study on enhancing heat transfer in air in microgravity via acoustic actuation. The setup consists of a test cell and subsystems for heat generation, acoustic actuation, and data acquisition. Experiments were conducted in five drops at the ZARM Drop Tower in Bremen (Germany), each providing 9.3 seconds of microgravity. Thermocouple data and high-speed videos were recorded per drop. We analyzed temperature evolution at different positions from the heat source and heat distribution inside the test cell using the Background Oriented Schlieren technique. Qualitative and quantitative results show that acoustic actuation distributes heat over larger regions, strengthening with increased pressure amplitude. Temperature increased when actuated at resonance frequency, with heat transfer along the actuation direction increasing at a rate of 0.44 K/s. Results confirm that acoustic actuation improves heat transfer in microgravity, likely due to convection-like flows induced by acoustic streaming. This study provides a foundation for new cooling techniques applicable to satellites and spacecraft.

Colour vision, particularly in modern so-called glass cockpits, plays a crucial role in ensuring flight safety. In this study, we investigated how exposure to high G-forces affects visual perception and performance in colour-coded number recognition tasks among pilots. Ten men fast-jet pilots (ages 28–45 years) were tested in a human centrifuge while reading digitalised plates from an Ishihara test displayed on a screen. Generated accelerations ranged from + 3 to + 7 G_z, increasing in nine intervals of 0.5 G with a rapid onset rate of 1 G·s⁻¹. During each 15-s acceleration plateau, three colour plates were displayed. Colour vision in the blue-yellow and red-green axes was tested in two separate sessions. The accuracy of predicting the correct reading of the colour plates based on the + G_z level was 81% for the blue-yellow axis and 76% for the red-green axis. The first impairment in colour perception occurred at + 5.5 Gz and affected both colour axes. The reading time is slightly affected by increasing G levels, with no apparent relationship to colour processing. Sequential changes in colour perception were observed. A high sensitivity threshold of the Ishihara test likely hindered the detection of subtle changes in colour vision among pilots under high G-forces. Despite its limitations, our study provides useful insights for future research on colour vision under high-G conditions.

The intervention of an ultrasonic field can effectively control the kinematic behavior of bubbles, leading to an increase in the efficiency of mass and heat transfer between liquid and gas phases. Since bubbles rarely appear individually in liquid, the mechanism of multiple bubble motion affected by the ultrasonic standing wave must be thoroughly understood. The authors numerically investigated the motion process of centroid of double quasi-spherical bubbles in ultrasonic standing wave fields and the corresponding alteration of the velocity field. The effects of sound pressure amplitude, acoustic frequency and bubble radius on double quasi-spherical bubble motion were fully analyzed. It was found that the above three variables have an important effect on the double bubble motion and the surrounding flow field. When the secondary Bjerknes force is the attractive force between two bubbles, three types of motion pattern are recognized: two bubbles approaching towards each other and then coalescing into one bubble, two bubbles travelling along the same direction and then coalescing into one bubble, and two bubbles remaining in levitation respectively without coalescence. When two bubbles move together in ultrasonic standing wave fields, the appearance of the secondary Bjerknes force breaks the equilibrium relationship between the time-averaged primary Bjerknes force and buoyancy force acting on each bubble, the centroid motion of bubbles changes from levitation to rising or from rising to sinking. When two bubbles coalesce into a single bubble, its motion follows the motion law of a single bubble.

The high-efficiency vapor chamber (VC) is an effective solution for the thermal management of high-heat-flux electronic devices. To further improve the VC performance, this work proposes a gradient wick VC. A systematic experimental investigation of gradient wick VCs is conducted to evaluate their thermal performance enhancement compared to conventional wickless designs. Through comprehensive testing, the gradient wick VC demonstrates superior thermal characteristics, including 33% faster stabilization rates and significant reductions in steady-state temperature (32.5% on evaporator, 7% on condenser surfaces) under identical operating conditions. The research reveals three key operational dependencies: (1) thermal resistance increases with heat source eccentricity, though this effect diminishes at higher heat fluxes; (2) resistance grows with smaller heat source areas but stabilizes above 8 W/cm²; and (3) gravity-assisted orientation achieves up to 56% lower resistance than anti-gravity operation within 2 ~ 10 W/cm² range. The chamber reaches its heat transfer limit at 400 W (120 W/cm²), beyond which performance degrades substantially. These findings provide critical design guidelines for implementing gradient wick VCs in practical thermal management systems, particularly highlighting their improved temperature response, gravity adaptability, and area-dependent performance characteristics.

Microgravity causes disuse osteoporosis in astronauts, lacking effective treatments. The mass transfer within the lacunar-canalicular system (LCS), essential for maintaining bone balance, makes studying molecular Weight solute transfer in LCS under microgravity vital for clinical solutions. In this study, a tail-suspended rat model was used to simulate microgravity on Earth. Rats were injected with fluorescent tracers of three molecular weights as the transport Mass, and the gray values of osteocytes at lacunae were detected in LCS by laser scanning confocal microscopy to represent the concentration of fluorescent tracers. Under microgravity, the gray values in lacunae farther from the Haversian canal were lower, with this trend observed in all molecular Weight fluorescent tracers. As gravity decreased, gray values in the lacunae also declined, with the most significant reductions seen in lacunae farther from the Haversian canal. For fluorescent tracers of 479 Da, 20 kDa and 150 kDa, gray values in deep lacunae decreased by 16.532%, 18.181% and 34.688%, respectively. The larger the molecular weight of the fluorescent tracers, the greater the decrease in gray values of osteocytes in all layers surrounding the Haversian canal, especially in deeper lacunae. Larger molecules face more difficulty penetrating the LCS and reaching deeper lacunae, with microgravity having a more significant effect on these molecules. Microgravity impairs mass transfer within the LCS, particularly reducing the delivery of essential components to deeper lacunae, which may lead to bone loss and induce osteoporosis. This study offers new insights for the clinical treatment of microgravity-induced osteoporosis.

We investigate the linear stability of an incompressible, viscous liquid thin film placed on a solid substrate subjected to vertical harmonic vibrations in the presence of gravity and a negative temperature gradient. The substrate oscillates with a finite frequency, compared to the viscous time and large amplitude, compared to the film thickness. By separating the governing equations into oscillatory (fast) and time-averaged (slow) components, we obtain an analytical solution for the oscillatory fields and represent their velocity structure through isolines of stream function. Averaging over the fast time scale yields a set of amplitude equations that describe the slow evolution of the free deformable surface. The stability analysis reveals that gravity and surface tension stabilise the interface, while van der Waals attraction and the imposed thermal gradient destabilise. Vertical vibrations may stabilise the surface: at low frequencies even large amplitudes fail to suppress the long-wave instability for moderate and high Marangoni numbers, whereas at moderate to high frequencies sufficiently strong vibrations stabilise the film across the entire wavenumber spectrum. For a huge values of Marangoni number small vibrations are ineffective, but when Marangoni number is small complete stabilisation is achieved at moderate frequencies for all amplitudes considered. Results obtained in limiting cases are consistent with the previous studies for isothermal and non-vibrated cases.

The study numerically investigates the mass transfer in an inclined two-layer porous channel in the gravitational field. The lower region of the channel is occupied by a porous medium, while the upper region consists of a pure fluid. The initial concentration distribution is such that the impurity is localized in the central part of the porous domain. The upper and lower walls of the channel are solid and no-flux boundary condition for the concentration is applied. Periodic boundary conditions are applied for the velocity field on the side walls, and the flow is driven by the longitudinal component of the velocity induced by the gravitational field and channel inclination. For the concentration field two boundary condition types are examined on the side walls: periodic boundary conditions, and a non-periodic characterized by a vanishing concentration at the left wall and a constant flux condition at the right wall. The problem is solved for constant porosity and permeability coefficients, with the Schmidt number fixed at (varvec{Sc = 10^3 }). The study focuses on the diffusion of an impurity into a viscous pure fluid for various Darcy numbers (varvec{Da}). The simulations are conducted using the Lattice Boltzmann Method (LBM) on a D2Q9 lattice. A modified multiple relaxation-time (MRT) LBM scheme was introduced for the mass transfer simulation in porous media. The effectiveness and applicability of the proposed scheme for such classes of problems are substantiated through the presented results. For the periodic boundary conditions, it is shown that the integral concentration within the domain is conserved, and the concentration profiles both inside and outside the porous layer converge toward the average value. In contrast, under non-periodic boundary conditions, the impurity is gradually washed out of the domain. The obtained numerical results also demonstrate that the type of boundary condition imposed on the concentration field at the side walls has a negligible effect on the velocity field. At a higher Darcy number (varvec{Da = 10^{-2} }), the evolution of the impurity is more pronounced, and the system reaches a steady state more rapidly. For lower Darcy numbers ((varvec{ Da = 10^{-3} }) and (varvec{Da = 10^{-4}})), the impurity evolution rate outside the porous matrix is approximately the same, whereas within the porous matrix, the evolution is more intense for larger Darcy numbers.