Raman Spectroscopic Analysis of Cupriavidus metallidurans LMG 1195 (CH34) Cultured in Low-shear Microgravity Conditions

In this study, the effect of low-shear microgravity on the metabolism of Cupriavidus metallidurans LMG 1195 was studied with Raman spectroscopy. Therefore, the strain was cultured for 24 or 48 h in a rotating wall vessel to simulate microgravity (SMG) and in a control setup. The differences in Raman spectra recorded from both setups after 24 h of culturing were small. The most prominent features in a difference spectrum, calculated between the mean spectra from the microgravity and the control setup separately, could be assigned to the presence of poly-β-hydroxybutyrate (PHB). SMG seems to yield a higher PHB production after 24 h of culturing. Additional processing of the spectra suggested that SMG induced also other changes in the carbon-metabolism. After 48 h, similar results were found for the carbon metabolism, while PHB concentrations were reduced in SMG compared to the control. However, these differences could also be caused by interfering effects that may occur in the bioreactors after a prolonged incubation time.     

Characteristics of turbulent nonpremixed jet flames under normal- and low-gravity conditions

An experimental study was performed with the aim of investigating the structure of transitional and turbulent nonpremixed jet flames under different gravity conditions. Experiments were conducted under three gravity levels, viz., 1 g, 20 mg, and 100 μg. The milligravity and microgravity conditions were achieved by dropping a jet-flame rig in the University of Texas at Austin 1.25-s and NASA-Glenn Research Center 2.2-s drop towers, respectively. The flames studied were piloted nonpremixed propane, ethylene, and methane jet flames at source Reynolds numbers ranging from 2000 to 10,500. The principal diagnostic employed was time-resolved cinematographic imaging of the visible soot luminosity. Mean and root-mean-square (RMS) images were computed, and volume rendering of the image sequences was used to investigate the large-scale structure evolution and flame tip dynamics. The relative importance of buoyancy was quantified with the parameter, ξL, as defined by Becker and Yamazaki (Combust. Flame 33 (1978) 123-149). The results showed, in contrast to some previous microgravity studies, that the high-Reynolds-number flames have the same flame length irrespective of the gravity level. The mean and RMS luminosity images and the volume renderings indicate that the large-scale structure and flame tip dynamics are essentially identical to those of purely momentum-driven flames provided ξL is less than approximately 2-3. The volume renderings show that the luminous structure velocities (i.e., celerities) normalized by the jet exit velocity are approximately constant for ξL<6, but scale as for ξL>8. The flame length fluctuation measurements and volume renderings also indicate that the luminous structures are more organized in low gravity than in normal gravity. Finally, taken as a whole, this study shows that ξL is a sufficient parameter for quantifying the effects of buoyancy on the fluctuating and mean characteristics of turbulent jet flames.     

A DIFFERENTIAL APPROACH TO HEAT PIPE PRIMING IN MICROGRAVITY

Presented here is a study of the forces governing the liquid and vapor flow, in an external artery heat pipe. A differential analysis was performed on the heat pipe based upon the continuity and momentum equations.

Using these fundamental equations, a computer model was developed, capable of predicting the fluid motion resulting from the surface tension and viscous frictional forces in a microgravity environment. The model used a nested iterative technique to first establish the pressure distribution along the longitudinal axis of the heat pipe for a known displacement. Then the time necessary, for a given fluid to initially assume or return to the configuration required for proper operation was calculated.

In addition to providing an estimate of the required priming time, the model predicted that priming could be prematurely terminated. Comparisons of the predicted priming time and priming limitations were made with the results of an experimental test package flown on the NASA KC-135 Zero-g aircraft. The results of this comparison helped to establish the accuracy of the modeling techniques.     

Chemical oven technology and its application in AlN composites fabricated under microgravity condition

The microgravity experiments of fabrication materials by using TiC chemical ovens have been performed on the parabolic flight plane. The gravity behaviors in the combustion reactions of chemical ovens themselves during the aircraft parabolic flight were investigated. The results show that, the combustion temperatures and reactions vary with different gravity levels. These influences are related with the function of gravity on the molten titanium. As an example of the application of chemical ovens, the first and preliminary investigation of AlN-borosilicate glass composites fabricated in the chemical ovens during aircraft parabolic flights is conducted. The results indicate that, microgravity condition allows the synthesis of AlN-borosilicate glass composite with improved microstructure as compared with that on the ground.     

Sooting characteristics of isolated droplet burning in heated ambients under microgravity

This paper presents an investigation into the sooting characteristics of isolated droplets (for fuel n-decane) burning in heated ambients in microgravity. A backlit video view of the droplet was taken to determine the soot shell size and to judge the transient soot generation according to qualitative amount of soot. The independent experiment variables were the ambient temperature and initial droplet diameter. Soot generation was higher for initially larger droplets when compared at the same burning time normalized with the initial droplet diameter squared (called normalized burning time). At the same absolute burning time there existed an obvious initial transient period after ignition in which the stated relationship was not satisfied. This transient time increased with increasing the ambient temperature. There was a peak in the soot generation at about 1000 K throughout the lifetime of the droplet. The soot shell size was generally larger for an initially bigger droplet at the same instantaneous droplet diameter or normalized burning time. At the same absolute burning time, however, an initially smaller droplet exhibited larger relative soot shell sizes (the soot shell size normalized with the initial droplet diameter). The soot shell size increased monotonically with increasing ambient temperature. This is due to the increase in the Stefan flow drag with the larger burning rate at the higher temperature. The consequent result is that the soot shell sizes are much larger for droplets burning in heated ambients than for droplets burning in room-temperature ambients.     

Radiative extinction of gaseous spherical diffusion flames in microgravity

Radiative extinction of spherical diffusion flames was investigated experimentally and numerically. The experiments involved microgravity spherical diffusion flames burning ethylene and propane at 0.98 bar. Both normal (fuel flowing into oxidizer) and inverse (oxidizer flowing into fuel) flames were studied, with nitrogen supplied to either the fuel or the oxygen. Flame conditions were chosen to ensure that the flames extinguished within the 2.2 s of available test time; thus extinction occurred during unsteady flame conditions. Diagnostics included color video and thin-filament pyrometry. The computations, which simulated flow from a porous sphere into a quiescent environment, included detailed chemistry, transport, and radiation and yielded transient results. Radiative extinction was observed experimentally and simulated numerically. Extinction time, peak temperature, and radiative loss fraction were found to be independent of flow rate except at very low flow rates. Radiative heat loss was dominated by the combustion products downstream of the flame and was found to scale with flame surface area, not volume. For large transient flames the heat release rate also scaled with surface area and thus the radiative loss fraction was largely independent of flow rate. Peak temperatures at extinction onset were about 1100 K, which is significantly lower than for kinetic extinction. An important observation of this work is that while radiative heat losses can drive transient extinction, this is not only because radiative losses are increasing with time but also because the heat release rate is falling off as the flame expands away from the burner and the reactant supply to the flame decreases.     

Thermovibrational Convection in Microgravity: Preparation of a Parabolic Flight Experiment

This work describes the preparation of the future experiments on thermovibrational convection in microgravity during parabolic flights. The experimental setup for observing thermovibrational flows is designed. It consists of a cubic cell with liquid, which is subjected to controlled vibration, and equipment for registering velocity and temperature fields with a help of optical digital interferometry. The question of choosing working liquid and control parameters of the experiment is addressed. A 3D numerical simulation of thermovibrational convection in a cubic cavity is performed for real parabolic flight conditions. The study is aimed at estimating the values of physical quantities that manifest the presence of thermovibrational flows and can be experimentally measured during short microgravity time (20 s).     

Titanosilicate ETS-10 as a Lewis acid catalyst in the Meerwein–Ponndorf–Verley (MPV) reaction

The potential of ETS-10 as a Lewis acid catalyst was investigated using the MPV reaction at one atmosphere total pressure and 273 K. ETS-10 was hypothesized to be a potential Lewis acid catalyst as it has titanium in octahedral symmetry, which is the symmetry shown in zeolite Beta to be the most active site for the Lewis acid catalyzed Meerwein–Ponndorf–Verley (MPV) reaction. The MPV reaction is a hydrogen transfer reaction that can be used for obtaining information about the structure and performance of catalysts by comparing the product selectivities and catalytic activities. Due to their similar structures, the catalytic activity of ETS-10 was compared to zeolite Beta samples that were space-grown (flight, fewer defects) and to their earth-grown terrestrial controls. The higher tr-alcohol selectivity (i.e., trans-4-tert-butylcyclohexanol, ∼80% vs. 40%) observed over ETS-10 was attributed to a larger volume being available in the pores of ETS-10 compared to the zeolite Beta samples. By-product formation (i.e., 4-tert-butylcyclohexene) was significantly less over ETS-10 (∼5%) in comparison with the zeolite Beta samples (flight and control; ∼35%). These results reaffirm the octahedral symmetry as the Lewis active site for the MPV reaction, and illustrate that ETS-10 is a good catalyst for MPV type reactions.