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Abstract: The capillary rise of the liquid in concentric annuli under microgravity is studied here. The influences of the dynamic contact angle between the liquid and the annulus wall, the pressure loss caused by the convection, the viscous resistances in the annulus and the reservoir, and the meniscus curvature of the liquid in the reservoir on the capillary rise are all considered in this paper. The capillary driven flow equation in concentric annuli is derived. On the other hand, the equation can also be expressed as a combination of external forces on the control body in the annulus. Under different conditions the capillary driven flow can be divided into two or three regions according to the development of external forces. Two flow models of capillary driven flows in concentric annuli are proposed. This study has been verified by numerical simulations with the VOF (Volume of Fluid) method. PubDate: 2022-05-13
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Abstract: The saturated nucleate pool boiling heat transfer of water on two platinum wires with 30 μm and 50 μm in diameter was experimentally investigated under Earth’s gravity and hypergravity up to 3.0 g, with the numerical simulation of bubble morphology. In the experiments, the saturation pressure ranges from 0.1 to 0.6 MPa and the heat flux from 0.2 to 1.8 MW/m2. The experimental results show that the pool boiling heat transfer coefficient (HTC) decreases with increasing gravity at low system pressure within the experimental gravity range. However, at a pressure higher than 0.3 MPa, no further decrease of the HTC with increasing gravity was observed when the gravity greater than certain value. Increasing saturation pressure enhances pool boiling heat transfer primarily due to that it reduces the critical radius of cavities so that more cavities are activated, leading to more nucleation sites. The HTC on the 30-μm diameter platinum wire is greater than that on the 50-μm diameter one, indicating that reduction in heater size slightly enhances pool boiling heat transfer because it leads to the reduction in surface tension force. The results of the numerical study show that the total gravity effect on pool boiling heat transfer is negative under hypergravity, which is caused by the combined effects of the diameter and frequency of bubble departure and vapor generation. The effects of pressure, gravity, heat flux, and heater size on pool boiling HTC are interacted, which makes it harder to understand the mechanisms of pool boiling heat transfer under hypergravity than under Earth’s gravity. Therefore, much more experimental and numerical studies on pool boiling heat transfer under hypergravity should be performed. PubDate: 2022-05-13
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Abstract: This paper designs a novel flat capillary pump to reduce the heat leak from the evaporator to the compensation chamber and to improve start up and run reliability under anti-gravity and microgravity. The flat capillary pump is equipped with (i) a small pore size, low thermal conductivity silicon nitride primary wick, and (ii) a large pore size stainless steel secondary wick. A loop heat pipe with the novel flat capillary pump, ammonia is used as the working fluid filling rate is 60%, was tested under earth gravity. The results show that: 1) In three orientations (horizontal/compensation chamber above evaporator; vertical; inverted/ evaporator above compensation chamber), the loop heat pipe can start up quickly at 5 W, and the heat transfer limit is more than 400 W (26.3 W/cm2); 2) Under the same heat load, in horizontal, the operating temperature of the loop heat pipe is the lowest, the thermal resistance is the smallest, and the minimum value is 0.02 °C/W (400 W); 3) In vertical and inverted, the operating temperature and thermal resistance are close, and the minimum thermal resistance value is 0.03 °C/W (400 W). Another loop heat pipe with the novel flat capillary pump start up at 50 W and operated stably more than 1 h under microgravity on a geostationary orbit satellite in March 2021. PubDate: 2022-05-12
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Abstract: This study aimed to investigate the differences in the effects of spaceflight and ground environment on the metabolites of the tobramycin-resistant mutant strain of Escherichia coli (T1_13). A spaceflight-exposed tobramycin-resistant Escherichia coli strain (T1_13) in outer space for 64 days was labeled as the ST5, and the ground test group (GT5) was cultivated under the same conditions except for spaceflight. The metabolites in culture supernatant and precipitate of the ST5 and GT5 were identified by liquid chromatography-mass spectrometry (LC–MS). Compared with the GT5, a total of 83 different metabolites were identified in the supernatant of the ST5 (p < 0.05, FC ≥ 2 or p ≤ 0.5, VIP > 1), and 80 different metabolites were additionally identified in the precipitate of the ST5 (p < 0.05, FC ≥ 2 or p ≤ 0.5, VIP > 1). The results showed that spaceflight had a significant impact on different metabolic pathways. KEGG enrichment analysis indicated that the significantly enriched in the supernatant (S) were nicotinate and nicotinamide metabolism, aminobenzoate degradation, ABC transporters, metabolic pathways, and microbial metabolism in diverse environments. In addition, in the precipitate (C), toluene degradation, glycine, serine and threonine metabolism, pentose and glucuronate interconversions, cysteine and methionine metabolism, benzoate degradation, aminobenzoate degradation, microbial metabolism in diverse environments, 2-Oxocarboxylic acid metabolism and degradation of aromatic compounds were significantly enriched. Exploring metabolism characters of Escherichia coli would be helpful to further understand the physiological characteristics of tobramycin-resistant mutagenesis of Escherichia coli in outer space. This research will provide a basis for astronaut safety during spaceflight exposed to pathogenic bacteria. PubDate: 2022-05-11
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Abstract: Abstract Cryogenic pressurization discharge involves on complex heat exchange and fluid flow issues, and the related thermal physical performance should be comprehensively investigated. In this study, a two-dimensional axisymmetric numerical model is adopted to research the outflow characteristic from a cylindrical liquid oxygen storage tank with the gas injection. The VOF method is utilized to predict the pressurization discharge with 360 K high-temperature gaseous oxygen as the pressurant gas. Validated against the liquid hydrogen discharge experiments, the numerical model is turned out to be proper and acceptable with the calculation errors limited within 20%. On the basis of the numerical model, effect of the flight acceleration level on the tank pressurization and liquid outflow performance are numerically simulated and analyzed, with the gas injection rate of 0.18 kg/s and the liquid outflow rate of 36.0 kg/s. Some valuable conclusions are obtained finally. The present study is significant to the safety flight of launch vehicle and may supply some technical supports for the design of cryogenic propellant system. PubDate: 2022-04-29
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Abstract: Abstract The flammable thermoplastics are widely used in our daily life and manned space travels in microgravity, posing a potential fire risk. This work studies the flame spread along with the thin polyethylene (PE) film (15–100 µm) in the microgravity drop tower and normal gravity. Microgravity flame spread faster than vertically downward flame spread in normal gravity due to the weak buoyancy flow and greater flame preheating length. For the ultra-thin film, the influence of melting on the opposed flame spread is negligible. The upward flame spread rate reaches a maximum constant (45 ± 10 mm/s for 20 μm film) when the inclination angle is larger than 30°, due to the dripping removal of molten fuel. The upward flame spread rate changes under the competition between the enhanced flame heating by buoyancy and the dripping removal of the molten fuel. The vertically upward spreading flame cannot be maintained due to the dripping removal of the molten fuel, and a critical extinction condition was determined and analyzed. This work provides valuable data on flame dynamics in plastic films and can help develop more sophisticated material flammability tests for fire safety in space travel. PubDate: 2022-04-23
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Abstract: Abstract To study the electric-field-controlled droplet sorting in the microfluidic chip, an unsteady numerical model of droplet sorting controlled by a nonuniform electric field is developed based on the coupled phase-field method and electric current model. The results indicate that both the shape and trajectory of the droplet are dependent on the permittivity ratio (S = εo/εi) and electric conductivity ratio (R = κi/κo) between the fluids when flowing through the electric field. The behaviors of the droplet are summarized in a sorting regime diagram according to the droplet size (r*) and electric Euler number (Eue). In the case of RS < 1, a small droplet (r* ≤ 0.25) flowing through the horizontal channel is observed under the condition of weak electric intensity (Eue ≥ 1 × 10–4). As Eue decreases, the sorting regime of the droplet transits to downward deflection. Pinning on the grounded channel wall occurs when Eue ≤ 7.21 × 10–5. Eventually, droplet breakup is triggered (r* ≥ 0.3, Eue ≤ 1.17 × 10–4). In the case of RS > 1, droplets are observed flowing through the horizontal channel in the sorting process of both small and large droplets at large Eue (r* ≤ 0.25, Eue ≥ 4.9 × 10–4 and r* ≥ 0.3, Eue ≥ 2.44 × 10–4). A strong electric intensity (Eue ≤ 2.44 × 10–4) contributes to the breakup regime of large droplets (r* ≥ 0.3). PubDate: 2022-04-11
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Abstract: Abstract In this study, the effect of thermal Marangoni (MaT) number on the thermal-solutal capillary convection in a liquid bridge of n-decane/n-hexane solution under microgravity has been studied numerically. The Navier–Stokes equations coupled with the concentration diffusion equation are solved using the finite volume method. Unlike existing studies, the Soret effect is considered as well in the present work and a variety of new oscillation structures have been found. Present results indicate the concentration near the lower disk is always higher than that near the upper disk due to the Soret effect. The thermal-solutal capillary convective wave appears when the MaT numbers is high. The wave includes standing wave and traveling wave, and the traveling wave appears first and then the standing wave is formed. The MaT number affects the flow field structure in the oscillating state of thermal-solutal capillary convection in the liquid bridge. As the MaT number increases, the wave number of thermal-solutal capillary convection changes from 4 to 5. PubDate: 2022-03-30
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Abstract: Abstract Thermocapillary convection of moderate Prandtl number nanofluid in rectangular cavity is numerically investigated in this paper, and the effect of nanoparticle volume fraction on flow instability is analyzed. The computational results show that, the critical temperature difference deceases gradually with nanoparticle volume fraction increasing, and nanofluid thermocapillary convection is less stable than the base fluid. With the increase of nanoparticle volume fraction the velocity oscillatory amplitude decreases, but the oscillatory period increases. Nanofluid oscillatory thermocapillary convection has one dominant oscillation frequency, and with nanoparticles volume fraction increasing the second fundamental frequency strengthens gradually. PubDate: 2022-03-30
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Abstract: Abstract The article considers the thermal shock of large elastic elements of a spacecraft leaving the Earth's shadow. The stress–strain state of the element is analyzed to estimate additional microaccelerations from a thermal shock. Beside the most dangerous cases, the possible initial deflection of the elastic element at the time of the thermal shock is also considered. This deflection can be related to the natural vibrations of elastic elements. The obtained results demonstrate a significant decrease in additional microaccelerations from a thermal shock at certain values of the initial deflection. It was also found that an elastic element can lose stability when bending stresses are added to thermal stresses. The results of the investigation can be used in the design and usage of small technological spacecraft. PubDate: 2022-03-24
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Abstract: Abstract This paper sheds light on the impact of vertical oscillations (or gravity modulation) on triple-diffusive convection in a viscoelastic fluid using the Oldroyd-B model, in the presence of cross effects. Cross effects can significantly impact three-component convective systems, despite having small magnitudes. When the cross terms, indicating coupled molecular cross-diffusion of the mixture components, are included in the equations governing heat and species transport, then a deviation from the usual three-component convection process is observed. An analytical solution has been found using linear and nonlinear analysis. The conditions for the onset of convection have been obtained using the linear analysis, which is based on the perturbation technique and the Venezian method. In nonlinear analysis, the expressions for Nusselt and Sherwood numbers, which quantify the rate of heat and mass transport respectively, are obtained by deriving the Lorenz model. It has been found that the onset of convection and heat and mass transport can be controlled by choosing the appropriate values of the parameters. PubDate: 2022-03-18
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Abstract: Abstract Designing effective thermal control modules in spacecraft is one of the prime concerns for space missions. 2D numerical simulations are carried out for investigating the melting process of paraffin wax as a phase change material (PCM) in microgravity conditions. Divided into three categories, a total of twelve different arrangements of heat source-sink pairs in a square cavity are considered to obtain the stored energy, liquid fraction, and as well as heat transfer characteristics. The differences in the arrangements of the heat sinks and sources affect the performance of these thermal storage devices greatly. Moreover, the discrete and continuous arrangements of the heat sources influence the propagation of the melting front in the PCM, and the spacing in between the discrete heat sources should be optimized considering the duration of the charging cycle. The melting fronts, along with Isotherm lines, are depicted to show the symmetric progression of melting of the PCM in the square cavity for the optimized cases. It is also found that the melting rate can be as high as 60% lower than that observed under Earth's gravity due to the lack of natural convection heat transfer. In addition, the Nusselt number decreases rapidly early in the melting process and tends toward a constant value. The simulation results are validated with available literature with good agreement for both the Earth-bound and the microgravity conditions. PubDate: 2022-03-15
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Abstract: Abstract In 2021, the scientific community celebrated the 85th anniversary of the Chinese scientist Academician Wen-Rui Hu. In addition to his innovative contributions to cosmic magnetohydrodynamics (MHD) during his early scientific career, he has initiated microgravity science research in China from the middle of 1980s, and made many pioneering contributions to microgravity fluid physics. He has also promoted researches in China in the fields of space material science, space biotechnology, space fundamental physics, and relevant applications. He is respected as the founder of microgravity science in China because of his eminent pioneering contributions and prominent leadership. This article tries to provide a brief historical perspective of the tireless explorations of Academician Wen-Rui Hu in the field of microgravity science and other relevant disciplines till today based on personal views of his former students and colleagues. PubDate: 2022-03-15
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Abstract: Abstract A visualization system is introduced to experimentally investigate the droplet freezing process under the influence of atmospheric pressure on a cold aluminum surface. The morphology and temperature evolution during droplet freezing process as well as the impact of wall temperature and droplet volume are analyzed and discussed under the low atmospheric pressure based on the current visualization system. The experiment results manifest that the droplet freezing process is significantly affected by the atmospheric pressure. The droplet freezing process undergoes five stages: the pre-cooling stage, the sub-cooling stage, the nucleation stage, the freezing and cooling stage, and the stable stage. The droplet temperature dramatically rises at the nucleation stage due to the release of latent heat and rapidly decreases at the freezing and cooling stage. The droplet freezing time decreases with the reduction of the atmospheric pressure. When the atmospheric pressure decreases to 0.1 bar, the droplet freezing temperature increases significantly. Under the low atmospheric pressure, the droplet freezing time decreases with the decrease of surface temperature and the increase of droplet volume. PubDate: 2022-03-10
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Abstract: Abstract This study investigates numerically the combined buoyancy and thermocapillary convection thermal and solutal transfer of Ag/Mgo-water hybrid nanofluid in a cylindrical porous enclosure with the impacts of Soret and Dufour. A discrete heater of finite size is positioned in the centre of the left interior wall. The cylindrical cavity exterior wall is supposed to be cool. The top and bottom horizontal boundaries including the unheated region of the interior wall are claimed to be adiabatic. The finite difference approach is used to solve the non-dimensional governing equations. Various graphs have been utilized in the current study to describe the nature of the fluid flow, temperature, and concentration behaviours. The analysis reveals that the Marangoni number performs better with lower buoyancy ratio and lower Lewis number values. The Le and \(D_f\) are efficient in mass transport, while the \(\phi\) and \(S_r\) are efficient in energy transfer. PubDate: 2022-03-03 DOI: 10.1007/s12217-022-09926-7
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Abstract: Abstract Wetting and contact-line dynamics, as well as growth (interface creation) and stability of aqueous drops with microorganisms in microgravity is important for understanding and controlling complex fluids in space. The study of biofluid drops in microgravity has applications in biological 3D printing, pharmaceutical production, and bioremediation. Here, liquid cultures of the microorganisms E. coli, S. cerevisiae (baker’s yeast), and D. radiodurans were deployed in centimeter-scale drops using a simple tube during a parabolic flight. Residual gravity and g-jitter inherent in parabolic flights allowed for the study of how these forces affect the growth of biofluid drops in microgravity. The growth of drops with microorganisms was compared to sterile growth media. Quasi-static simulations were used to assess whether each solution produced measurable changes in the growing droplet. Images of growing drops were analyzed in terms of drop aspect-ratio, contact angles, and the differences in contact angles due to variations in gravity. Results demonstrate that the presence of microorganisms has minimal influence on the behavior of centimeter-scale drops. The small impact of microorganisms on growing drops bodes well for the adaptation of existing Earth-based drop technologies for working with biofluids in reduced gravity. PubDate: 2022-02-22 DOI: 10.1007/s12217-022-09933-8
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Abstract: Abstract With advancements in space exploration, operations in low-gravity environments such as the lunar surface are expected to be conducted. Geotechnical engineering problems such as those associated with the foundation bearing capacity considerably influence the feasibility and safety of these operations. In this study, the findings of experiments conducted by Japan Aerospace Exploration Agency (JAXA) scientists on parabolic flight, aimed at measuring the ultimate bearing capacity of shallow foundations under 1/6 g to 2 g of gravity, are analysed. Specifically, the results are analysed to calculate the ultimate friction angle based on the classical Terzaghi limiting equilibrium solution in soil mechanics. The friction angle of foundation sand increases as the gravity level decreases. This finding is verified through advanced arbitrary Lagrangian–Eulerian (ALE) finite element simulations based on a simple Mohr–Coulomb model. Moreover, the underlying mechanism for this phenomenon is examined considering an ALE finite element simulation based on a newly developed rheological model known as the Tsinghua–MiDi sand model. The pressure-sensitive and rate-dependency constitutive behaviour of sand is clarified. Notably, this phenomenon increases the viscous shear stress and ultimate friction angles in low-gravity conditions. The coupled effects of the loading rate and low-gravity level on the bearing capacity of foundation sand are predicted. The findings can provide a novel theoretical prospective for geotechnical studies in space exploration engineering in low-gravity conditions. PubDate: 2022-02-22 DOI: 10.1007/s12217-022-09929-4
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Abstract: Abstract Evaporation in microstructures has been proven to be a heat transfer enhancement compared with evaporation on flat surfaces due to the thin films formed in the porous or grooved surfaces. To investigate the evaporation characteristics in sintered porous wicks for cryogenic loop heat pipes, a more realistic geometric model to characterize the porous skeleton is developed. Then, a mathematical model considering the Marangoni effect and slip velocity effect to predict the liquid–vapor interface is built. The evaporation interface can be divided into the thin-film region and intrinsic meniscus region. A new solution method calculating from the intersection of these two regions is established and validated, and the initial boundary conditions are not dependent on the contact angle whose value is small and ambiguous for cryogenic fluids. Then the evaporation characteristics of the thin-film region are discussed. About 40% of the temperature drop occurs in the thin-film region, and the evaporation thermal resistance should be considered in this region. Finally, the parametric analysis is conducted to study the effects of superheat, pressure difference at the interface, accommodation coefficient and pore radius on the interface profile and evaporation heat transfer process in sintered microporous structures. The liquid–vapor interface recedes with the superheat increasing and the mean heat transfer coefficient of the interface decreases. With the increase of the pressure difference at the interface, the liquid–vapor interface recedes and the mean heat transfer coefficient decreases. The mean heat transfer coefficient increases with the accommodation coefficient despite the coverage of the liquid–vapor interface reducing and small pores would be helpful to enhance heat transfer in porous media. PubDate: 2022-02-19 DOI: 10.1007/s12217-022-09932-9
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Abstract: Abstract Gravity affects colloidal dispersions via sedimentation and convection. We used dynamic light scattering (DLS) to quantify the mobility of nanoparticles on ground and in microgravity. A DLS instrument was adapted to withstand the accelerations in a drop tower, and a liquid handling set-up was connected in order to stabilize the liquid temperature and enable rapid cooling or heating. Light scattering experiments were performed in the drop tower at ZARM (Bremen, Germany) during a microgravity interval of 9.1 s and compared to measurements on ground. Particle dynamics were analyzed at constant temperature and after a rapid temperature drop using a series of DLS measurements with 1 s integration time. We observed nanoparticles with average gold core diameters of 7.8 nm and non-polar oleylamine shells that were dispersed in tetradecane and had an average hydrodynamic diameter of 21 nm. The particles did not change their diameter in the observed temperature range. The particle dynamics inferred from DLS on ground and in microgravity were in good agreement, demonstrating the possibility to perform reliable DLS measurements in a drop tower. PubDate: 2022-02-19 DOI: 10.1007/s12217-022-09928-5
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Abstract: A major challenge of irrigating limited areas by dropping liquid from a high altitude using aviation is to ensure the required droplet size distribution of the aerosol immediately before contact with the surface to be irrigated. Varying the initial liquid volume and the drop height can provide different droplet sizes in an aerosol cloud when it reaches the irrigated surface. However, it is extremely difficult to predict such aerosol characteristics when using local drop systems. This requires reliable experimental data on the size to which liquid droplets can be atomized when free-falling in a gaseous medium with a variable initial volume and length of the flight path. This paper presents the results of the experimental research into the transformation and subsequent disintegration of free-falling droplets, jets, and non-sprayed arrays of liquid in gas. Using the experimental results, we determined the minimum, average and maximum droplet sizes in the forming aerosol cloud after the deformation and subsequent disintegration of the falling liquid array. When generalizing the experimental findings, we obtained the empirical equation coefficients making it possible to reliably predict the average sizes of liquid droplets when they are dropped as non-sprayed arrays, jets and aerosols from different heights. The research findings can be used to develop effective technologies for supplying liquids with different initial volumes from variable drop heights into the required area, for example, when extinguishing fires or irrigating various areas. Graphical abstract PubDate: 2022-02-16 DOI: 10.1007/s12217-022-09927-6
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