The influences of fuel dilution, inlet velocity, and gravity on the shape and structure of laminar coflow CH4–air diffusion flames were investigated computationally and experimentally. A series of nitrogen-diluted flames measured in the Structure and Liftoff in Combustion Experiment (SLICE) on board the International Space Station was assessed numerically under microgravity ( μ g) and normal gravity (1 g) conditions with CH4 mole fraction ranging from 0.4 to 1.0 and average inlet velocity ranging from 23 to 90 cm/s. Computationally, the MC-Smooth vorticity–velocity formulation was employed to describe the reactive gaseous mixture, and soot evolution was modeled by sectional aerosol equations. The governing equations and boundary conditions were discretized on a two-dimensional computational domain by finite differences, and the resulting set of fully coupled, strongly nonlinear equations was solved simultaneously at all points using a damped, modified Newton’s method. Experimentally, flame shape and soot temperature were determined by flame emission images recorded by a digital color camera. Very good agreement between computation and measurement was obtained, and the conclusions were as follows. (1) Buoyant and nonbuoyant luminous flame lengths are proportional to the mass flow rate of the fuel mixture; computed and measured nonbuoyant flames are noticeably longer than their 1 g counterparts; the effect of fuel dilution on flame shape (i.e., flame length and flame radius) is negligible when the flame shape is normalized by the methane flow rate. (2) Buoyancy-induced reduction of the flame radius through radially inward convection near the flame front is demonstrated. (3) Buoyant and nonbuoyant flame structure is mainly controlled by the fuel mass flow rate, and the effects from fuel dilution and inlet velocity are secondary.
Liquid foams are omnipresent in everyday life, but little is understood about their properties. On Earth, the liquid rapidly drains out of the foam because of gravity, leading to rupture of the thin liquid films between bubbles. Several questions arise: are liquid foams more stable in microgravity environments? Can pure liquids, such as water, form stable foams in microgravity whereas they do not on Earth? In order to answer these questions, we performed experiments both in parabolic flights and in the International Space Station.
Foams made of gas bubbles dispersed in a liquid have limited stability and disappear rapidly unless surface active species are used. Foams can be a nuisance or very much sought after, however the control over the foaming and stability is still hampered because of the limited understanding of foam properties. On Earth, liquid rapidly drains out of the foam because of gravity, the liquid films formed between bubbles thin and break. In microgravity conditions, gravity drainage is suppressed and stability is expected to be greatly enhanced. We describe investigations of foams that are very unstable on Earth, including foams made with liquids containing antifoaming agents. Experiments performed in the International Space Station (ISS) show that foam generation can still be limited, however once created these foams are very stable.
Cosmic ray investigations during the marco polo and eneide missions with the sileye-3/alteino experiment
The Sileye-3/Alteino experiment is devoted to the measurement of the radiation environment and the cosmic ray nuclear abundance inside the International Space Station. Other goals include the investigation of the Light Flash phenomenon and the measurement of the shielding effectiveness of different materials. The detectors used are a silicon strip detector capable to detect cosmic rays up to Iron in the energy range above 60Mev/n and an electroencephalograph to monitor astronaut’s brain activity. The experiment has been used during the Marco Polo (2002) and Eneide (2005) missions. Currently Sileye-3 is being employed in the framework of the ESA ALTCRISS project to perform a long term survey of the radiation environment on board the ISS.
The Altcriss project aims to perform a long term survey of the radiation environment on board the International Space Station. Measurements are being performed with active and passive devices in different locations and orientations of the Russian segment of the station. The goal is to perform a detailed evaluation of the differences in particle fluence and nuclear composition due to different shielding material and attitude of the station. The Sileye-3/Alteino detector is used to identify nuclei up to Iron in the energy range above ≃60 MeV/n. Several passive dosimeters (TLDs, CR39) are also placed in the same location of Sileye-3 detector. Polyethylene shielding is periodically interposed in front of the detectors to evaluate the effectiveness of shielding on the nuclear component of the cosmic radiation. The project was submitted to ESA in reply to the AO in the Life and Physical Science of 2004 and data taking began in December 2005. Dosimeters and data cards are rotated every 6 months: up to now three launches of dosimeters and data cards have been performed and have been returned with the end of expedition 12 and 13.
The experiment Sileye-3/Alteino was first operational on board the International Space Station between 27/4 and 1/5/2002. It is constituted of a cosmic ray silicon detector and an electroencephalograph and is used to monitor radiation environment and study the light flash phenomenon in space. As a stand-alone device, Sileye-3/Alteino can monitor in real time cosmic ray nuclei. In this work, we report on relative nuclear abundance measurements in different regions of the orbit for nuclei from B to Fe in the energy range above ≃60 MeV/n. Abundances of nuclei such as O and Ne relative to C are found to be increased in respect to particle composition outside of the station, whereas the Fe group is reduced. This effect could be ascribed to nuclear interactions with the hull of the station.
The ability to predict the atomic oxygen erosion yield of polymers based on their chemistry and physical properties has been only partially successful because of a lack of reliable low-Earth-orbit erosion yield data. The retrieval of the polymer erosion and contamination experiment after 3.95 years in low Earth orbit as part of the Materials International Space Station Experiment 2 provided accurate measurements of the erosion yields of 38 polymers and pyrolytic graphite. The resulting erosion yield data was used to develop a predictive tool with a correlation coefficient of 0.895 and uncertainty of ±6.3×10-25 cm3/atom. The predictive tool uses the chemical structures and physical properties of polymers to predict in-space atomic oxygen erosion yield. A technique which uses the erosion yields of two materials is presented to allow prediction of the erosion yield of a composite material.
The constrained vapor bubble experiment schedule to fly aboard the International Space Station in the near future promised to give us new insight into the fundamental science of interfacial thermophysics. The evaporating meniscus formed at the corner of the vapor bubble is expected to behave in a significantly different manner in the microgravity environment as compared with the Earth’s gravity environment. Since the constrained vapor bubble can also behave as a micro heat pipe, it will additionally help in gaining a technical understanding of the performance of a micro heart pip in a space environment. Earth-based experiments have been conducted for the past two decades to gain a better knowledge of the rich phenomenon observed in the relatively simple constrained vapor bubble setup. Here, some recent Earth’s-gravity-environment-based data obtained on a 30-mm-long constrained vapor bubble have been presented. The data were fitted to a model, and a self-consistent value of the inside heat transfer coefficient was obtained. The external convective and radiative hear transfer coefficients were also determined. These ground-based experiment forma calibration against which the future data from space-based experiments will be compared.
The concept of using low gravity experimental data together with fluid dynamical numerical simulations for measuring the viscosity of highly viscous liquids was recently validated on the International Space Station (ISS). After testing the proof of concept for this method with parabolic flight experiments, an ISS experiment was proposed and later conducted onboard the ISS in July, 2004 and subsequently in May of 2005. In that experiment a series of two liquid drops were brought manually together until they touched and then were allowed to merge under the action of capillary forces alone. The merging process was recorded visually in order to measure the contact radius speed as the merging proceeded. Several liquids were tested and for each liquid several drop diameters were used. It has been shown that when the coefficient of surface tension for the liquid is known, the contact radius speed can then determine the coefficient of viscosity for that liquid. The viscosity is determined by fitting the experimental speed to theoretically calculated contact radius speed for the same experimental parameters. Experimental and numerical results will be presented in which the viscosity of different highly viscous liquids were determined, to a high degree of accuracy, using this technique.
A constrained vapor bubble heat pipe experiment was run in the microgravity environment of the International Space Station. Here we present the initial results that demonstrate significant differences in the operation of the constrained vapor bubble heat pipe in the microgravity environment as compared to the Earth’s gravity. The temperature profile data along the heat pipe indicate that the heat pipe behavior is affected favorably by increased capillary flow and adversely by the absence of outside convective heat transfer as a heat loss mechanism. The reflectivity pattern viewed through the transparent quartz wall documented complex microflow patterns. Image data of the liquid profile in the grooves of the heat pipe indicate that the curvature gradient giving capillary flow is considerably different from that on Earth. Using experimental data for the temperature and meniscus profiles, a one-dimensional model gives the inside heat transfer coefficient, which was significantly higher in microgravity. An initial discussion of some of the data collected is presented.