Microgravity Science and Technology最新文献

Formation of highly viscous droplets and liquid bridges under the influence of electric fields is widely used in material preparation, food processing, inkjet printing and 3D (three-dimensional) printing. To investigate the formation of droplets and liquid bridges, a visual experimental platform is designed and constructed. A non-uniform electric field is constructed using a metal capillary and a copper pole plate. By varying the voltage, capillary diameter and liquid volume flow rate, the formation of silicone oil droplets and liquid bridges is investigated. The influence of electric forces to the coiling effect of viscous fluids is researched, which has not been thoroughly investigated in previous research. The results verify that at low volume flow rates and small pipe diameters, the silicone oil formation pattern is in the droplet state. As the voltage increases, the droplet formation period decreases. When the voltage is gradually increased at higher volume flow rates, the silicone oil changes from the initial liquid bridge to the droplet. This experimental phenomenon demonstrates that the electric field can alter the instability of the jet. In the case of small volume flow rates and large pipe diameter, the droplet formation state changes from droplet mode to multi-strand jet mode after the voltage is increased to a certain level. At large pipe diameters and large volume flows rates, the liquid bridge mode with a rope coiling effect occurs due to the highly viscous nature of the silicone oil, but the rope coiling effect disappears after a certain voltage is applied.

Experimental and numerical simulation methods were employed to investigate the effect of gravity orientation on the dynamics of premixed conical flames. The study focused on a typical propane-air flame established on a Bunsen burner, under normal gravity (+ g), reverse gravity (-g), and transverse gravity (⊥g). In the initial phase of the research, flame shapes were examined using flame chemiluminescence imaging. Result shows that gravity orientation has a slight impact on the flame height, and buoyancy caused flame asymmetry in ⊥g case is first discovered. In addition, flame flickering frequencies were collected through heat release signal experiments, and a wide range of data is acquired. Though being affected by the same pattern by equivalence ratio and Reynolds number, the frequencies in ⊥g case are generally lower than those in + g case. Based on this, the research also obtained the new empirical correlation for ⊥g case. For clearer explanations of the flame behavior under different gravity orientations, velocity fields were visualization using Particle Image Velocimetry (PIV) experiments and Direct Numerical Simulation (DNS). Results indicated that the gravity orientation mainly influences the flame through effects on shear layer between ambient air and burnt gas, which cause different forms of K-H instability and vortex shedding motions.

The mechanisms controlling the dependence on low-velocity flow of the piloted ignition of a solid material under external radiant heating is investigated through a numerical modeling. The poly (methyl methacrylate) (PMMA) was used as the fuel. The objective of the present study is to gain insight into the intrinsic ignition mechanisms of a solid fuel, as well as to gain a more comprehensive understanding of the dynamical characteristics of the ignition process near the extinction limit. For this purpose, a two-dimensional numerical model has been developed using the Fire Dynamic Simulator (FDS5) code, in which both solid-phase and gas-phase reactions are calculated. Two radiant heat flux, which are 16 and 25 kW/m² were studied, and an external air flow was varied from 3 to 40 cm/s. The simulation results showed that transient gas reaction flashed before a continuous flame was attached to the sample surface for gas flow velocities lower than a critical value. As the flow velocity is reduced, the flashing time, which is defined as the time when any flame is seen above the sample surface, decreases, while the duration of flashing increases. The solid surface temperature and mass flow rate increase rapidly during flashing. The ignition time, which is defined as the time when a continuous flame is attached to the fuel surface, decreases, reaches a minimum, and then increases until ignition cannot occur. Mechanisms were considered to explain the ‘‘V-shaped” dependence of ignition time on flow-velocity, and two regimes were identified each having a different controlling mechanism: the mass transport regime where the ignition delay is controlled by the mixing of oxygen and pyrolyzate; and the heat transfer regime where the ignition delay is controlled by changes in convection heat losses and critical mass flux for ignition. With the decrease of the airflow velocity, the critical mass flux shows a trend of decreasing and then increasing, which is dominated by the mixing of the pyrolyzate and the oxidizer, while the critical temperature monotonically decreases, which is dominated by a reduction of the net heat flux at the fuel surface. The results provide further insight into the ignition behavior of solid fuel under low-velocity flow environment, and guidance about fire safety in microgravity environments.

Unprecedented experimental conditions were provided for research in space biology following the completion of the Chinese Space Station. The next decade is predicted to witness considerable developments in this subject. Space cell culture is a crucial experimental technique in space biology. The Cell Tissue Culture Experiment Module (CTCEM) aboard the space station's Biotechnology Experiment Rack is customized equipment designed for the microgravity environment in space. It provides suitable culture conditions for cell growth, including temperature and CO₂ concentration control, automatic liquid exchange, and automated observation via visible light microscopy, fluorescence microscopy, and laser confocal microscopy. The Tianzhou-5 Launch Cell Life Support Module (LCLSM) was developed to meet the requirements for transporting samples for space station cell experiments. This device can provide the required temperature, CO₂ concentration, and nutrient solution replacement for cell experiment sample transportation. It also stores cells during ground transportation, launches, and in-orbit flights to ensure that they arrive at a space station with good physiological conditions. This article describes space cell bioreactors, the detailed functions and usage methods of CTCEM and LCLSM, and discusses the entire process of transporting cells to the space station and conducting space cell culture experiments through the TZ5 mission.

The experimental investigation of the critical heat flux (CHF) of saturated nucleate pool boiling of pure water and water-based Al₂O₃ nanofluids on the platinum wire with a diameter of 50 μm was conducted under earth gravity and hypergravity. The gravity level ranges from 1 to 3 g, the saturation pressures range from 0.1 to 0.6 MPa, and the Al₂O₃ concentration in the nanofluids ranges from 0.001wt% to 0.015wt%. The experimental results show that both pressure and gravity are vital factors enhancing the CHF, with the effect of pressure more pronounced. For nanofluids with concentration C > 0.005wt %, CHF initially increased with the increase in gravity. When the gravity is greater than 2 g, CHF does not increase further with the increase in gravity. Increasing nanoparticle concentration significantly enhances the CHF for low nanoparticle concentrations less than 0.005 wt%, and the CHFs change little for further increasing the concentration. Nanofluid has a stronger enhancement to the pool boiling CHF than the combination of the heating surface coated with the same kind of nanoparticles and the base fluid. With the increase of particles concentration, Surface modification gradually becomes dominant mechanism for CHF enhancement.

In a microgravity environment, the flow pattern, flow characteristics, and heat transfer characteristics of gas–liquid two-phase flow are different from those in a normal gravity environment. To study the influence of microgravity on the flow and heat-transfer characteristics in an evaporator, this study develops a flow and heat-transfer model in an evaporator based on a previously proposed microgravity solution where the refrigerant and lubricating oil are mixed. This work also examines the flow and heat-transfer characteristics of gas–liquid two-phase flow in an evaporator with gravity of 10^–6-10⁻³ g and studies the influence of lubricating-oil content on the flow and heat-transfer characteristics of mixed two-phase flow in the evaporator. The results show that when gravity is equal to 10⁻³ g, the gas volume fraction at the outlet is between 0.6 and 0.7, and when gravity is decreased to 10^–6 g, the gas volume fraction at the outlet of the evaporator, after gradually decreasing, comes close to a zero gravity-state. In addition, the gas volume fraction remains between 0.3 and 0.6. It can also be seen that when gravity increases, the heat-transfer coefficient increases nearly linearly and reaches a maximum value of 14.013 W/(m²·K) and 16.066 W/(m²·K) when the lubricating oil content is 2% for normal gravity, and 4.443 W/(m²·K) and 5.519 W/(m²·K) when the lubricating oil content is 2.5% for microgravity.

Traversing granular regolith, especially in reduced gravity environments, remains a potential challenge for wheeled rovers. Mitigating hazards for planetary exploration rovers requires testing in representative environments, but direct Earth-based testing fails to account for the effect of reduced gravity on the soil itself. Granular scaling laws (GSL) have been proposed in the literature to predict performance of a larger wheel based on tests with a smaller wheel, or to predict performance in one gravity level based on tests in another gravity level. However, this is the first work to experimentally validate GSL in reduced gravity. Here, an expanded version of existing GSL was evaluated experimentally by measuring performance of a single wheel driving through cohesionless lunar soil simulant GRC-1 aboard parabolic flights that reproduce the effects of lunar gravity, and comparing those results to scaled tests performed on the ground. This scaled-wheel testing achieved less than 10% prediction error on three measured output metrics: drawbar pull (i.e. net traction), sinkage, and power draw. Predictions also erred on the conservative side. Subsurface soil imaging revealed similar soil behavior between scaled tests. GSL thus offers an accurate and conservative method for predicting wheel performance in reduced gravity based on 1-g experiments, at least in cohesionless soil.

In this study, a gravity unloading method based on electrostatic adsorption is proposed to address the issue of large flexibility in membrane phased-array antennas. Through considering the gravity distribution of the antenna and the edge effect of the electrode system, the unloading efficiency and system robustness are improved using a grouping strategy and size optimization. The deformation equilibrium equation under both gravity and electrostatic fields is established, and the voltage optimization model of the electrode system is also formulated with the goal of complete compensation for gravity deformation. The advantages and effectiveness of the proposed method are demonstrated by comparing simulation and unloading experiment results with those obtained using the suspension method. Both results indicate that the electrostatic unloading method can achieve the same unloading effect as the suspension method. Moreover, without introducing in-plane deformations during unloading, this method enhances accuracy and provides valuable insights for optimizing the assembly and testing processes.

An experimental investigation was conducted to prepare and study the thermal conductivity performance of copper and diamond composite materials. Copper powder and diamond particles were used as fillers, epoxy resin was used as matrix, and composite materials were prepared by vacuum-assisted mechanical stirring. The thermal expansion coefficient of different composite materials was measured by a laser flash method, which can be used to calculate the thermal conductivity. The effect of the filling rate of copper powder, the morphology of copper powder, the filling rate of diamond, and the thermal conductivity of the particles on the thermal conductivity of composite materials was studied. The results showed that thermal conductivity of copper powder and diamond particles composite materials were 874% and 535% higher than that of the epoxy resin when their filling rates were 50.3 vol.% and 40.0 vol.%, respectively. For two-dimensional flake copper powder materials, the thermal conductivity could be effectively improved at a lower filling rate. However, the flake particles were easy to aggregate at a high filling rate, which maybe cause the composite materials to pulverize.

During the lunar surface activities of the manned lunar landing project, the design verification and driving training of the manned lunar rover system should be carried out according to the requirements of space mission verification and astronaut comprehensive operation training. In this case, it is difficult to conduct somatosensory simulation of human rover driving training in the lunar surface environment. To solve the above problems, first, the characteristics of astronaut motion sensing information reception were analyzed, the lunar surface environment was created in the virtual environment, the lunar gravity conditions were established, and the dynamics model of the man-vehicle-moon system was established for motion sensing simulation. Then, the parameters of the somatosensory model are provided by dynamics calculation, and the astronaut's attitude adjustment is considered to simulate and verify the somatosensory model. Finally, the motion characteristics of astronauts driving on the Moon are analyzed, which provides support for the design verification and driving operation training of manned lunar rovers.