Subjects -> AERONAUTICS AND SPACE FLIGHT (Total: 124 journals)
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 Microgravity Science and TechnologyJournal Prestige (SJR): 0.514 Citation Impact (citeScore): 1Number of Followers: 4      Hybrid journal (It can contain Open Access articles) ISSN (Print) 0938-0108 - ISSN (Online) 1875-0494 Published by Springer-Verlag  [2469 journals]
• Effects of Gravity and Surface Morphology on Droplet Contact Angles and
Wetting State

Abstract: Abstract Hydrophobic surfaces have been widely applied for self-cleaning and enhanced heat transfer, and microstructures are closely linked to surface wettability. In this paper, the lattice Boltzmann method (LBM) was adopted to study the contact angle and wetting state variation of single droplets on the surface of an array of microstructures, and to obtain an analysis of the impact of micropillar size, surface wettability and gravity on the contact angle and wetting state of droplets. The results indicate that there is some correlation between microcolumn height and droplet contact angle θw in a small range, and the increase of microcolumn height makes a transformation from the Wenzel to the mixed wetting state for droplets (θw = 105° ~ 125) and from the mixed wetting to the Cassie state for droplets (θw = 125° ~ 140°). The droplet contact angle θw increases and then decreases as the microcolumn gap increases, and there exists an optimum contact area of solid–liquid to maximize droplet contact angle θw. The increase of microcolumn width w causes the droplet contact angle θw to fluctuate lower and both the increase of microcolumn gap s and the decrease of microcolumn width w make the transition from Cassie state droplets to Wenzel. The enhancement of the gravitational field causes a variation of the droplet morphology and droplet contact angle θe, making it easier for droplets to overcome gas–liquid interfacial forces to form Wenzel states, but droplets with a large area of interaction between flow and solid are little affected by the variation of the gravitational field.
PubDate: 2022-06-22

• Throughflow Effect on Local and Large-scale Penetrative Convection in
Superposed Air-porous Layer with Internal Heat Source Depending on Solid
Fraction

Abstract: Abstract The vertical throughflow effect on the onset of penetrative convection in a horizontal air sublayer overlying a porous sublayer is investigated in the gravitational field. The porous sublayer contains an internal heat source with the volumetric strength linearly dependent on the solid fraction. It has been found that the depth ratio and solid fraction are destabilizing at any direction and velocity of the throughflow. The upward and downward throughflows can be both stabilizing and destabilizing in the range of the Peclet number of $$\mathrm{{ - }}6<\mathrm{{Pe}}<6$$ considered. The study has revealed that the non-monotonic dependence of the onset internal Darcy-Rayleigh number versus the Peclet number may get a second minimum in addition to the first dominant one. It is due to an abrupt change in the critical wave number of convection patterns. A special attention is paid to the local and large-scale convective regimes which replace each other with the variation of the Peclet number, solid fraction and depth ratio. One has obtained a regime map which includes a demarcation line between the two regimes and a region of parameters for the bimodal marginal stability curves.
PubDate: 2022-06-20

• Investigation of Space Heat Flow Simulation Methods for Light Entrance of
the Remote Sensor on GEO

Abstract: Abstract The space thermal environment of the remote sensor on the geostationary orbit is exceptionally harsh. It is necessary to carry out a high-precision thermal control design to realize the temperature uniformity and stability of core components such as the central optical and mechanism bodies. Sufficient ground tests must verify the correctness of the thermal control design. Accurate simulation of the space heat flow is the key to ensuring the adequacy and effectiveness of the ground thermal test. Considering the shortcomings of traditional space heat flow simulation methods, this paper proposes two advanced and high-precision space heat flow simulation methods, named combined heat flow simulation method based on a solar simulator and absorption heat flow simulation method based on the electric heater. The two methods have been verified based on the simulations and tests of the different size remote sensors. The results show that the two advanced simulation methods can meet the space heat flow simulation requirements. In addition, the accuracy, economy, and engineering feasibility of heat flow simulation are improved, and the high-precision simulation of the space heat flow for geostationary space remote sensors is realized.
PubDate: 2022-06-09

• Heat Transfer Performance of Novel SiO2 Nanoaerosol: The Numerical
Investigation

Abstract: Abstract Presently nanoaerosol technology has widened its application in the heat transfer area and found to be exhibiting remarkable heat transfer characteristics. This paper focuses on a theoretical investigation on the convective heat transfer characteristics of a SiO2-air nanoaerosol flow inside a tube. Based on the properties of nanoparticles and air, the governing equations and numerical models have been formulated and simulations are carried out. The distribution of temperature in terms of time scale within SiO2 nanoparticles, particle to particle interaction through conduction, and nanoparticles to air by radiation is studied. At particle diameters, 30 nm to 120 nm, the timescale of particle, conduction, and radiation are compared, and it was that the temperature distribution in conduction is more rapid than radiation. Aerosol heat transfer coefficient (AHTC) at different Reynolds number (Re) from 8,000 to 20,000, with different particle volume fractions (PVF) from 0.002 to 0.01 has been investigated. Moreover, the effect of the particle migration factor on AHTC has been analysed. However, PVF has very mild effect on AHTC. A maximum of 51.96% enhancement in AHTC was observed by increasing Re from 8,000 to 20,000. Thus, the nanoaerosol has potential in gaseous cooling applications.
PubDate: 2022-06-09

• Experimental Investigation of the Performance of a 3D Printed Heat Pipe
with Ultra-Small Bending Radius for Space Applications

Abstract: Abstract Highly integrated aerospace products have a small interior space; thus, heat pipes (HPs) with a small bending radius are required for thermal management. An HP sample with an ultra-small bending radius and a capillary channel is fabricated by 3D printing. The cross-sectional area of the sample and its heat transfer capacity are compared with that of a standard aluminum-ammonia channel heat pipe (ACHP). The L-shaped HP samples consist of three sections: two straight parts (L1 and L2) and a curved part with a bending radius of R. A prototype is designed and manufactured for an on-orbit flight test. Statistical methods are used to calculate the filling volume of the working fluid. The maximum heat flow of the HP sample A is 140.0 W at a cold plate temperature of 10.0 ℃, and the thermal resistance is 0.01 ~ 0.07 K/W. The maximum heat-transport capacity of HP sample A is 66.3 ~ 88.4 W•m at different condensation temperatures, which is 4.0% ~ 18.4% lower than that of HP samples B and C. The on-orbit flight data show that the temperature difference between the two ends of the 3D printed HP is 0.001 ~ 0.997 K, and the working condition and performance are excellent.
PubDate: 2022-06-09

• Role of Gravity in Grain and Bubble Morphology Evolution During
Solidification of Al-9.5 Wt.% Zn Alloy

Abstract: Abstract The solidification experiment of Al-9.5 wt.% Zn alloy was conducted under both normal gravity and microgravity conditions by using a 50-m-high drop tube. The solidification microstructure was observed by using optical microscope. The amounts, morphologies together with sizes of the grains in the remelting regions on longitudinal sections of the samples were statistically analyzed with the image analysis software. Moreover, the axial and radial composition distributions were studied by applying SEM–EDX. The results show that the remelted solidification structure morphologies of the samples can be roughly divided into three categories, the small equiaxed grains formed by initial chilling, the elongated columnar crystals and the coarse equiaxed grains at the end, but the amount, size and morphology of the grains are different in the samples solidified under the two gravity conditions. The number of grains obtained in μg sample is larger, and the grain size distribution concentrates in small size intervals. Some pores were observed in the small equiaxed grain regions formed at the early stage of solidification in both samples, and several pores were also observed in the coarse equiaxed grain region formed at the later stage of solidification merely in μg sample. In addition, the distributions of solute element in radial and axial direction are more uniform in μg sample, while solute content in 1g sample fluctuates greatly and tends to converge towards the lower part of the sample. The above results suggest that under normal gravity condition, buoyancy convection could lead to the lower temperature gradient and supercooling, which reduced the nucleation rate. Meanwhile, buoyancy could let nuclei float up and melt rich of Zn flow down, and thus promoted grain growth and downwards segregation of Zn solute as well. Besides, buoyancy could drive bubbles to float up and facilitated them to escape from the melt.
PubDate: 2022-06-08

• Enhanced Boiling Heat Transfer Performance on Mini-pin-finned Copper
Surfaces in FC-72

Abstract: Abstract The uniformly distributed mini-pin-fins on the copper surface were designed and processed, and the enhanced boiling heat transfer performance on mini-pin-finned copper surfaces in FC-72 was investigated. The smooth copper surface was used as the experimental comparison group. The effect of the copper fin height, spacing, and width on the pool boiling heat transfer performance and the fin efficiency were investigated. At the same liquid subcooling, the critical heat flux and heat transfer coefficient of the uniformly distributed mini-pin-finned copper surface increased with the copper fin height, decreased with the rise of the copper fin spacing and fin width. The fin efficiency increases with the rise of the fin height, spacing, and width. The critical heat flux of the mini-pin-finned copper surface (PF0.3–0.2–2) reached 115.4 W·cm−2 at liquid subcooling of 25 K and increased by about 3.62 times compared with the smooth copper surface, and the heat transfer efficiency of mini-pin-finned copper surface (PF0.5–0.2–2) exceeded 95%.
PubDate: 2022-06-06

• On-orbit Test and Analyses of Operating Performances for Mechanically
Pumped Two-phase Loop in Microgravity Environment

Abstract: Abstract As a typically advanced two-phase heat transfer device, the operating performances of mechanically pumped two-phase loop (MPTL) might be affected by microgravity condition. One MPTL setup integrating with a two-phase thermally-controlled accumulator is designed and constructed in present study. Particularly, three capillary structures and self-cooling measure are employed to perform the functions of two-phase fluid management and cooling of accumulator in microgravity environment. The obtained on-orbit test data of MPTL setup aboard the China’s test satellite SY-9 launched in 2021, including the temperatures and pressures, are employed to analyze the operating characteristics during the whole process, thermodynamic behavior of accumulator, and coupling process of heat and mass transfer between accumulator and main loop in μg. Superheat phenomenon takes place during phase changing process and it leads to a higher temperature. During generation and disappearance processes of two-phase fluid in the main loop, phenomenon of fluid exchange between the accumulator and the main loop occurs. The fluid management function and self-cooling ability of accumulator are validated under microgravity condition. The operating characteristics of MPTL system at a high rotation speed are compared with the results at a low speed. The gravity-independence of cross-sectional two-phase distribution in the transport tube of the main loop is discussed in the frame of dominant force analysis. The research would contribute to the theoretical basis of two-phase flow and heat transfer and would promote the development of active two-phase thermal control technology for space.
PubDate: 2022-06-06

• Experimental Study on Flow Condensation Heat Transfer in a Horizontal
Rectangular Channel with Ellipse-shape Pin Fins

Abstract: Abstract In present study, a new type of three-dimensional pin–fin plate with elliptical cross-section was proposed. Experimental study on flow condensation heat transfer in a horizontal rectangular channel with proposed ellipse-shape pin fins was carried out at atmospheric pressure. Droplets on flat plate and elliptical pin fin plate both grew up and coalesced into larger droplets, but never departed or rolled down from the surface, which is visibly different from the condensation on vertical wall. The condensate on elliptical pin–fin surface spread far and wide under the action of pin-fins. All the tested plates were observed to form a stable liquid film. The effects of pin geometry and mass flow rate on condensation heat transfer and pressure drop were investigated. The results showed that all the elliptical pin–fin plates exhibited substantially better performance than the flat plate. Pin geometry had slight influence on condensation heat transfer and pressure drop. However, the effect of mass flow rate was obvious. The highest enhancement ratio of 1.38 was achieved. The results can provide reference for further optimization design of pin–fin enhanced condensation structure.
PubDate: 2022-06-06

• The Effect of Junction Gutters for the Upscaling of Droplet Generation in
a Microfluidic T-Junction

Abstract: Abstract The influence of drop formation due to micro rib-like structures, viz., the Junction Gutters (JGs) within a standard microfluidic T-junction, is numerically investigated. Hydrodynamic conditions that lead to various flow regimes are identified characterized by the Capillary number (Ca) and velocity ratios of the dispersed and continuous phases (q) within a standard T-junction. Subsequently, under such conditions, a range of gutter configurations is introduced in the standard channel. The results predict that the introduction of JGs can favourably alter the formation frequency and morphology of drops and, consequently, promote upscaling significantly for the hydrodynamic conditions associated with low Ca. Detailed flow maps are presented that reveal a plethora of transitions during the formation of droplets with higher Ca and q that would otherwise signify a dripping or a jetting regime in a standard junction. However, specific gutter configurations are identified where JGs are unfavourable for generating monodisperse droplets.
PubDate: 2022-06-04

• Design, Modelling and Implementation of a Foldable Pneumatic Soft
Manipulator

Abstract: Abstract Soft manipulators, which are mainly used to conduct grasping and manipulation tasks, belong to a special category within soft robotics. Their unique characteristics, such as their light weight, foldable volume, and flexible movement, make them ideally suited for a range of spatial manipulation tasks. As such, this study presents the design and development method for a foldable soft manipulator. The soft manipulator comprises three pneumatic actuators and foldable straight arms, and can transfer its shape between the contracted and expanded states, making its volume foldable. According to this design, a relevant kinematic model for the soft manipulator is deduced. The shape deformation and workspace are numerically calculated and analysed. For verifying the prediction accuracy of the aforementioned model with no consideration of gravity effects, a soft manipulator prototype as well as the relevant air-floating devices have been proposed such that it can float on a marble platform. By limiting the motion control of the soft manipulator within the plane, the prediction accuracy of the proposed model is validated through the microgravity experiment. The foldable soft manipulator proposed in this study demonstrates a novel potential application of space manipulators.
PubDate: 2022-06-04

• Experimental Study on Thermal Convection in Annular Pools Heated from
Inner Cylinder

Abstract: Abstract In order to understand the effect of the radius ratio on thermocapillary-buoyancy convection, a series of experimental observations on thermocapillary-buoyancy convection of 0.65cSt and 1cSt silicone oils have been conducted in annular pools with a smaller heating inner cylinder and the radius ratio of 0.25. The results show that the rotating petal-like structure or spoke pattern first appears on the free surface when thermocapillary-buoyancy convection destabilizes. As the Marangoni number increases, the spoke pattern becomes oscillating at the depth of 6–7 mm and the oscillating frequency is decreased compared with the results in the liquid pool with a radius ratio of 0.5. The wavenumber of the flow pattern decreases when the radius ratio decreases from 0.5 to 0.25. Especially at the liquid depth of 7–8 mm, a mode switching of the flow patterns has been observed and the flow pattern becomes more like cellular structures in cylindrical pools instead of the spoke pattern with the increasing Marangoni number. With the increase of the Prandtl number, this flow transition becomes difficult. Besides, the short spokes appear near the inner cylinder at a large Marangoni number and the deep fluid layer. Based on the experimental results, the general relationship of the threshold complex with the dynamic Bond number and the radius ratio is achieved.
PubDate: 2022-06-03

• Numerical Investigation of nano-PCM Melting Enhanced by Thermocapillary
Convection under Microgravity Condition

Abstract: Abstract Natural convection is greatly weakened under microgravity condition, so the nano-PCM (phase change material) melting enhanced by thermocapillary effect is an effective method. This paper reports the numerical investigation of nano-PCM melting under microgravity condition, and the influence of thermocapillary effect and nanoparticles volume fraction on the melting process and heat transfer is studied. The computational results show that, for PCM-CNT, with nanoparticles volume fraction increasing the melting time decreases, however, for PCM-Al2O3 and PCM-Cu, the melting time increases gradually. With temperature difference increasing the molten time of nano-PCM decreases, the melting front of nano-PCM at free surface becomes more convex, and thermocapillary convection instability is more likely to occur in the melting process. For nanoparticles CNT, Cu and Al2O3, the CNT is more suitable for the phase change enhancement of n-octadecane.
PubDate: 2022-06-02

• The Effect of Translational Vibration with Different Direction on
Thermosolutal Convection Onset in a Superposed Fluid and Porous Layers
Under Gravity

Abstract: Abstract A linear stability analysis is carried out to investigate the onset of thermosolutal convection in a fluid layer overlying a fluid-saturated porous layer under the high-frequency small-amplitude translational vibration with different direction in the gravitational field. Distinct temperatures and concentrations are applied at the external boundaries of the two-layered fluid-porous domain in such a way that the buoyancy ratio (the ratio of density drop due to concentration difference to that due to temperature difference) has a positive value. The numerical calculations show that transverse (vertical) vibration suppresses convection by delaying its onset when the domain is heated from below. There is a jump-like transition from local to large-scale convective regimes with intensifying vibration. In the case of longitudinal (horizontal) vibration the convection onset value varies non-monotonically: it increases initially, reaches a maximum, and then decreases. The noticeable enhancement of convection is observed at the vibrational Rayleigh-Darcy number close to its value in weightlessness. The longitudinal vibration in contrast to the transverse one is additionally capable of creating convection when the two-layered domain is heated from above. In such a situation the flow has exclusively thermosolutal vibrational nature. With strengthening longitudinal vibration, the critical flow patterns replace each other in the following order: local flows – large-scale flows – long-wave flows with the system of vertically ordered vortexes – “super-shortwave” flows. If one applies at least a small concentration difference across the layers, all of the mentioned vibration effects manifest themselves at less temperature difference and vibration acceleration than they are in the case of pure thermal convection. The thermal and concentration density gradients reinforce each other at positive buoyancy ratios, so heat and mass transfer become most effective.
PubDate: 2022-06-02

• Design and Validation of Closed Two-phase Thermosyphon Loop in Lunar
Gravity Environment during China Lunar Project CE-4

Abstract: Abstract The structural design, heat transfer capability analysis, ground equivalent validation, and on-orbit flight of the two-phase fluid loop based on flat-plate evaporation module of the Chang’e-4 detector are introduced. Within the temperature range of -30 ℃ ~ -10 ℃, the designed two-phase fluid loop has a heat transfer capacity of greater than 200 W. An equivalent test prototype is designed and manufactured to examine the heat transfer performance of the two-phase fluid loop under the ground condition of 1 g. The driving force of the equivalent test prototype is less than that of the flight prototype, while the flow resistance is equivalent to that of the flight prototype. The test heat transfer capacity is smaller than that of the flight prototype on the lunar surface. According to the equivalent test prototype, the heat transfer capacity is no less than 130 W, which meets the requirements of Chang’e-4. During the 14-moon day-night cycle, the temperature of the two-phase fluid loop gradually decreased to an equilibrium value of -10 °C. During the wake-up process of the detector in moon day, the control valve was closed, and the temperature of the flat-plate evaporation module rose rapidly, indicating that the function of blocking heat transfer is normal.
PubDate: 2022-05-31

• Numerical Simulation of the Reorientation Process Under Different
Conditions in a Vane-type Surface Tension Propellant Tank

Abstract: Abstract The fuel tank, as a significant component for the propellant system in satellites, plays an important role in managing propellant and maintaining stability through its propellant management device (PMD). To analyze the effect of propellant volume fill ratios and acceleration conditions on the fluid flow in vane-type surface tension tanks, this study carried out computational fluid dynamics (CFD) simulation with the Volume of Fluid (VOF) model. The four fill ratios are 5%, 25%, 50%, and 75%; the four acceleration environments are bottom acceleration, lateral acceleration, reverse acceleration, lateral & reverse acceleration, and rotation condition. First, the contour and the interface of gas and liquid were tracked to evaluate the ability of the PMD. Second, the volume flow rate through the initial interface of gas and liquid was monitored to judge the sloshing intensity in the reorientation process. At last, the force in different simulation conditions was analyzed to further research fluid sloshing intensity. The results show reorientation process in the vane-type surface tension tank can be divided into two stages: the mutational stage and the stable stage. The fill ratio and the acceleration condition influence the value and duration of the max flow rate through the initial interface, and further influence the sloshing intensity in the reorientation process. By comparing the results at lateral acceleration, reverse acceleration, and lateral & reverse acceleration with the same fill ratio, it can be found that the acceleration in the Z direction has a stronger influence on the reorientation process.
PubDate: 2022-05-31

• Numerical Study on the Effect of Dynamic Contact Angle on Air Entrapment
and Spreading of a Hollow Droplet Impacting on a Surface

Abstract: Abstract The computational analysis of the importance of dynamic contact angle on the dynamic of air entrapped and spreading factor of hollow droplet impact is presented in this paper. The transient fluid flow of the impacting droplet is considered in this numerical work. The Semi-Implicit Method for Pressure Linked Equations (SIMPLE) method has been used for solving the governing equations numerically. Through the continuum surface force model, the surface tension force of the droplet is represented. The computational model for droplet simulation is well in line with the experimental findings available in the literature. The parameters of dynamic contact angle for the liquid droplet have been found by comparing with experimental data available in the literature. The findings from this paper suggest that modelling the dynamic contact angle accurately is critical in simulating droplet impact behaviour. The numerical simulation quantitatively captures the experimentally observed spreading behaviour when we use a dynamic contact angle model based on experimental findings. It has been numerical found that the splat size of the hollow droplet impact is independent of cavity size at Eu ˂˂ 1. With the systemic simulation of hollow droplets, an empirical relation has been developed for hollow droplet impact splat size.
PubDate: 2022-05-31

• Effect of Adsorption Dynamics on Hydrodynamic Characteristics of a Bubble
Contaminated by Surfactants at Medium Reynolds Numbers

Abstract: Abstract In this paper, the effects of Langmuir number and Peclet number on the hydrodynamic characteristics of a bubble contaminated by surfactants are numerically studied at bubble Reynolds number Re = 100, 150 and 200. It is discovered that the hydrodynamics of a bubble with excessive pollution interface can lose two-dimensional axisymmetric characteristics as Langmuir number increases in the present Reynolds number range. Therefore, it can be concluded that for the numerical study on the influence of adsorption kinetics on the hydrodynamics of a bubble contaminated by different pollutants, it is not accurate to choose a two-dimensional axisymmetric or a three-dimensional model to perform studies only by Reynolds number. Since the magnitude of Peclet number for the present study is small, the effect of Peclet number on the hydrodynamic characteristics of a bubble contaminated by surfactants is not very obvious.
PubDate: 2022-05-30

• Preparation and the Cold Storage Performance of Water/PVA Sponge PCMs for
Aerospace Applications

Abstract: Abstract Phase Change Material has the characteristics of absorbing or releasing large amounts of latent heat during phase change with almost constant temperature, which have competitive advantages in thermal management applications for deep space explorations. Water has large latent heat and thus is among those top PCM candidates. However, the expansion of the water-based PCM during freezing is an application challenge; and the gravity makes it difficult for ground equivalent verification of the heat transfer in liquid state. To overcome the above challenges, we develop a water/PVA sponge composite PCMs by absorbing water with PVA sponge, which overcomes the gravity by capillary force. That makes the water state close to that in microgravity condition, and thus makes the ground equivalent verification possible. In this paper, we introduce the preparation of such water/PVA sponge composite PCMs and its performance. Multiple PVA sponges were used as the matrix to absorb water to form a PCMs block. The PCMs block, together with two hydrophobic sponges on both sides of the block to compensate the volume expansion of water during freezing, was placed inside an aluminum shell to form a Phase Change Regenerator. The effective cold storage density of such prepared PCMs is about 254.8 kJ/kg. Neither gas–solid nor gas–liquid interface is observed during the phase change process, and the capillary force of PVA sponge can counteract the effect of gravity, which can be considered that the on-earth performances of the cold storage/release of the composite PCMs equivalently simulates those in microgravity.
PubDate: 2022-05-23

• Particle Vibration, an Instrument to Study Particle Accumulation
Structures On Board the International Space Station

Abstract: Abstract The scientific and technological aspects of the PARTICLE VIBRATION Project (also known as T-PAOLA i.e. “Thermovibrationally-driven Particle self-Assembly and Ordering mechanisms in Low grAvity”) are described in detail. The project relies on the combined use of the Selectable Optical Diagnostics Instrument (SODI), a Class-2 device developed by ESA for scientific experiments in the field of fluids on board the International Space Station, and the Microgravity Science Glovebox (MSG), a Class-1 general purpose facility under the responsibility of NASA. The related modular architecture has recently been expanded under the umbrella of new scientific research funded by the UK Space Agency to allow for a novel class of experiments dealing with multiphase (solid-liquid) flows. The final aim of this microgravity project is the identification of new dispersed-phase self-organization phenomena driven by the application of vibrations and the ensuing development of new contactless particle manipulations strategies. In the present paper, emphasis is given to the related space hardware and software, the experiment protocol, the ground tests and procedures and all the adaptations that had to be implemented to overcome a number of technological and physical issues, both general and system-specific.
PubDate: 2022-05-17

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