Phase Separation in Porous Media Integrated Capillary ChannelsBisht, Kamal S.; Dreyer, Michael E.
doi: 10.1007/s12217-020-09828-6pmid: N/A
Phase separation in space is critical for gas-free propellant supply, life support systems, refueling of spacecraft in low earth orbit (LEO), and for deep space exploration missions. In the absence of gravity, the stability of the liquid-gas interface depends on capillary forces. High liquid flow rates, sudden accelerations, and vibrational disturbances can cause the free surface of the liquid to collapse, which results in the ingestion of gas. Propellant tanks may have screen channel liquid acquisition devices (SCLADs) to position and maintain a gas-free propellant supply to the outlet. A saturated porous screen permits liquid to pass through but acts as a barrier to the gas. We investigated phase separation in porous media integrated capillary channels during parabolic flights (33rd DLR parabolic flight campaign in March 2019). An open side of a rectangular channel was covered with a dutch twill weave 200×1400. The liquid was ingested into the channel from its surroundings by establishing a differential pressure across the screen section. The gas-phase was blocked during the liquid withdrawal. We could show that the gas breakthrough occurs when the pressure difference across the screen exceeds the bubble point pressure. The experimental results showed good agreement with correlations from literature.
Cross Diffusion and Internal Heat Generation Effects on Mixed Convection of Non-Newtonian Fluids Flow Adjacent to a Vertical VHF/VMF Wedge in Porous Media: the Entire RegimeYih, Kuo-Ann; Huang, Chuo-Jeng
doi: 10.1007/s12217-020-09826-8pmid: N/A
The problem of cross diffusion (Soret/Dufour) and internal heat generation effects on combined convection flow of non-Newtonian fluids flow over the vertical wedge in a saturated porous medium with the entire regime is solved numerically. The internal heat generation is assumed to be an exponential decaying form. The power law model of Ostwald-de-Waele for non-Newtonian fluids is considered here. The entire regime of the combined convection is included, as the combined convection parameter varies from 0 (pure free convection) to 1 (pure forced convection). The transformed equations are obtained by using a suitable coordinate transformation and then Keller box method (KBM) is utilized to solve the non-similar equations for the variable heat flux and variable mass flux (VHF/VMF) conditions. Comparisons with the previously published article are performed and the good agreement is achieved. The main numerical results for the dimensionless temperature and concentration distributions, the local Nusselt and Sherwood numbers are obtained.
A Similarity Solution for Natural Convection Flow near a Vertical Plate with Thermal RadiationJha, Basant K.; Samaila, Gabriel
doi: 10.1007/s12217-020-09830-ypmid: N/A
This paper examined the fluid transport on boundary layer near a vertical wall with thermal radiation effect. The coupled nonlinear partial differential equations are reduced to a system of ordinary differential equations through similarity transformation. The resultant system of ordinary differential equations is integrated with maple software using RKF45 method. The effect of the active parameters such as Grashof number, thermal radiation parameter, temperature difference, Prandtl number, and local convective heat transfer parameter on the velocity profile, skin friction, temperature profile and Nusselt number are presented using graphs and tables. The outcome of the study revealed that the Prandtl number has a decreasing effect on thermal boundary layer thickness. It also revealed that the thermal radiation has an increasing effect on the Nusselt number, temperature distribution, temperature gradient and skin friction. The temperature distribution increases with increasing values of the temperature difference and local convective heat transfer parameter whereas decreases with Grashof number.
Dynamic Behavior in a Storage Tank in Reduced Gravity Using Dynamic Contact Angle MethodLi, Ji-Cheng; Lin, Hai; Li, Kai; Zhao, Jian-Fu; Hu, Wen-Rui
doi: 10.1007/s12217-020-09831-xpmid: N/A
The oscillation of liquid/gas free surface in a partially filled storage tank caused by an abrupt drop of gravity level is of critical importance for the fluid management in space. In the present study, the dynamic behavior of free surfaces in a model tank (tube) is numerically investigated using volume of fluid (VOF) method in the context of dynamic contact angle (DCA) model. It is concluded that the dynamic behavior of free surface could be captured pretty well using the selected DCA model, as shown by comparison with the results of Drop Tower Beijing experiment. The temporal evolution of free surface reproduces exactly the characteristics of damping oscillations. The detailed dynamic deflections of meniscus reveal crucial dependency between the oscillation frequency of free surface and the boundary condition in the contact line. The oscillation frequency increases when the range of the moving contact line transfers from the spherical-shaped part to the cylindrical part of the tank and maintains constant when the moving contact line remains always at the cylindrical part of the tank. Meanwhile, the oscillation amplitude decreases in line with the increase of oscillation frequency.
Surface Properties of Liquid Al-Ni Alloys: Experiments Vs TheoryNovakovic, R.; Mohr, M.; Giuranno, D.; Ricci, E.; Brillo, J.; Wunderlich, R.; Egry, I.; Plevachuk, Yu; Fecht, H.-J.
doi: 10.1007/s12217-020-09832-wpmid: N/A
The present study is an overview of the surface properties of liquid Al-Ni alloys, which are of great importance for the design and development of new Al-Ni and Ni-based industrial alloys, widely used as functional and structural materials. The solidification and thus, the microstructural evolution are directly dependent on the interface/surface properties of metallic melts. Therefore, numerical simulation of microstructure evolution requires reliable property data as input to such models. Taking into account the experimental difficulties related to a high reactivity of liquid Al-Ni alloys and the effects of impurities on their surface properties, the surface tension over the whole concentration range has been determined in the frameworks of three international research projects. Namely, the surface tension measurements have been carried out by both traditional container-based and as an alternative, containerless methods within the ESA-MAP ThermoProp and ESA-MAP Thermolab Projects and also under the EU FP6-IMPRESS Project. The obtained datasets were analysed and subsequently compared with the model predicted values as well as with the literature data. A strong exothermic mixing characterises the Al-Ni system and the presence of a few intermetallic compounds in the solid state leads to the formation of short range ordered elements or complexes in the liquid phase, at least near the melting temperature, which significantly affects the surface properties of alloy melts. Aiming to estimate the effects of short range ordering on these properties, the Compound Formation Model (CFM) and the Quasi Chemical Approximation (QCA) for regular solution were applied.
Flame Extinction of Spherical PMMA in Microgravity: Effect of Fuel Diameter and ConductionWu, Chuanjia; Sun, Peiyi; Wang, Xiuzhen; Huang, Xinyan; Wang, Shuangfeng
doi: 10.1007/s12217-020-09829-5pmid: N/A
A series of experiments were conducted in the 3.6-s microgravity drop tower and normal gravity to investigate the effect of solid fuel curvature, conduction, and reradiation on the flame extinction of spherical polymethyl methacrylate (PMMA). In the semi-quiescent microgravity environment, flame extinction was observed if the PMMA diameter was larger than 40 mm, because of a smaller flame conductive heating in larger diameter (i.e., the curvature effect). Compared to the droplet combustion with a low evaporation point and fast heat convection in the liquid phase, the solid fuel has a high pyrolysis point and large transient heat conduction. Thus, the large surface reradiation effectively cools down the fuel surface to promote extinction. Also, as the initial burning duration increases, the conductive cooling into the solid fuel decreases, which delays or prevents the flame extinction in microgravity. The extinction criterion for microgravity flame is explained by the critical mass flux and mass-transfer number. This work helps to understand the curvature effect of solid fuel on flame extinction and the material fire safety in the microgravity spacecraft environment.
Gravity-Independent Experimental Study on a High-Speed Rotor Supported by Aerostatic BearingsRong, Chengjun; Wu, Hong; Li, Yulong; Lian, Huaqi; Xu, Xianghua; Yu, Xingang
doi: 10.1007/s12217-020-09834-8pmid: N/A
Vapor compression heat pump technology has great potential in future space thermal management application. Considering microgravity in space, this paper proposes using aerostatic bearings for the lubrication of the heat pump compressor. An experimental apparatus was built to study the performance of a rotor supported by aerostatic bearings subjected to microgravity. The gravity-independent experiment was conducted by changing the angle between the rotor axis and the direction of gravity on the ground. The gas consumption and rotor stability at different rotor orientations were investigated and compared. Results showed that the largest difference in gas consumption due to the change in rotor orientation was 3% for the journal bearing and 5.56% for thrust bearings. The difference in rotation speed at the second peak amplitude under different rotor orientations was smaller than 4.2%. The experimental results imply that the aerostatic bearing-rotor system is independent of gravity. Aerostatic gas lubrication technology is thus a viable option for the vapor compression heat pump used in a space thermal management system.
Drop Tower Experiment to Study the Effect of Microgravity on Friction Behavior: Experimental Set-up and Preliminary ResultsDuan, Yong; Qu, Shengguan; Yang, Chao; Li, Xiaoqiang; Liu, Fucai
doi: 10.1007/s12217-020-09838-4pmid: N/A
This paper refers to studying the effect of microgravity on the friction behavior of friction units and to further analyzing the influencing mechanism. The potential factors affecting the friction behavior of the moving joints of space mechanisms in microgravity environment were analyzed. A friction apparatus was designed and manufactured by reducing the complexity and costs. A microgravity test program was designed and performed using the Beijing Drop Tower platform with designing three positioning styles for the friction apparatus by changing the relationship between the normal load and gravity. For each positioning style of the friction apparatus, the friction behavior of friction unit in gravity and microgravity environment was compared. It was found that microgravity can not only change the value of friction, but also affect its dynamic characteristics. For different positioning styles of the friction apparatus, the influencing mechanism of microgravity on friction behavior was different. The normal load or the relative position between the connected bodies of the friction unit could be changed by microgravity, resulting in that the friction behavior was different from that in gravity environment.