This thesis compares air/water two-phase flow regime transition models in zero gravity with data and makes recommendations for zero gravity models to incorporate into the RELAP5-3D thermal hydraulic computer code. Data from numerous researchers and experiments are compiled into a large database. A RELAP5-3D model is built to replicate the zero gravity experiments, and flow regime results from the RELAP5-3D code are compared with data. The comparison demonstrates that the current flow regime maps used in the computer code do not scale to zero gravity. A new flow regime map is needed for zero gravity conditions. Three bubbly-to-slug transition models and four slug-to-annular transition models are analyzed and compared with the data. A mathematical method is developed using least squares to objectively compare the accuracy of the models with the data. The models are graded by how well each represents the data. Agreement with data validates the recommendations made for changes to the RELAP5-3D computer code models. For smaller diameter tubes, Dukler’s bubbly-to-slug model best fits the data. For the larger tubes, the Drift Flux model is a better fit. The slug-to-annular transition is modeled best by Creare for small tubes and Reinarts for larger tubes. A major finding of this thesis work is that more air/water data is needed at equally distributed flow velocities and a greater variety of tube diameters. More data is specifically needed in the predicted transition regions made in this study.

Fully understanding soot formation in flames is critical to the development of practical combustion devices, which typically operate at high pressures, and fire suppression systems in space. Flames display significant changes under microgravity and high-pressure conditions as compared to normal-gravity flames at atmospheric pressure, but the exact causes of these changes are not well-characterized. As such, the effects of gravity and pressure on the stability characteristics and sooting behavior of laminar coflow diffusion flames were investigated. To study these effects, a new highly-scalable combustion modelling tool was developed specifically for use on large multi-processor computer architectures. The tool is capable of capturing complex processes such as detailed chemistry, molecular transport, radiation, and soot formation/destruction in laminar diffusion flames. The proposed algorithm represents the current state of the art in combustion modelling, making use of a second-order accurate finite-volume scheme and a parallel adaptive mesh refinement algorithm on body-fitted, multi-block meshes. An acetylene-based, semi-empirical model was used to predict the nucleation, growth, and oxidation of soot particles. Reasonable agreement with experimental measurements for different fuels and pressures was obtained for predictions of flame height, temperature and soot volume fraction. Overall, the algorithm displayed excellent strong scaling performance by achieving a parallel efficiency of 70% on 384 processors. The effects of pressure and gravity were studied for flames of two different fuels: ethylene-air flames between pressures of 0.5–5 atm and methane-air flames between 1–60 atm. Based on the numerical predictions, zero-gravity flames had lower temperatures, broader soot-containing zones, and higher soot concentrations than normal-gravity flames at the same pressure. Buoyant forces caused the normal-gravity flames to narrow with increasing pressure while the increased soot concentrations and radiation at high pressures lengthened the zero-gravity flames. Low-pressure flames at both gravity levels exhibited a similar power-law dependence of the maximum carbon conversion on pressure which weakened as pressure was increased. This dependence decayed at a faster rate in zero gravity when pressure was increased beyond 1–10 atm.

Fully understanding soot formation in flames is critical to the development of practical combustion devices, which typically operate at high pressures, and fire suppression systems in space. Flames display significant changes under microgravity and high-pressure conditions as compared to normal-gravity flames at atmospheric pressure, but the exact causes of these changes are not well-characterized. As such, the effects of gravity and pressure on the stability characteristics and sooting behavior of laminar coflow diffusion flames were investigated. To study these effects, a new highly-scalable combustion modelling tool was developed specifically for use on large multi-processor computer architectures. The tool is capable of capturing complex processes such as detailed chemistry, molecular transport, radiation, and soot formation/destruction in laminar diffusion flames. The proposed algorithm represents the current state of the art in combustion modelling, making use of a second-order accurate finite-volume scheme and a parallel adaptive mesh refinement algorithm on body-fitted, multi-block meshes. An acetylene-based, semi-empirical model was used to predict the nucleation, growth, and oxidation of soot particles. Reasonable agreement with experimental measurements for different fuels and pressures was obtained for predictions of flame height, temperature and soot volume fraction. Overall, the algorithm displayed excellent strong scaling performance by achieving a parallel efficiency of 70% on 384 processors. The effects of pressure and gravity were studied for flames of two different fuels: ethylene-air flames between pressures of 0.5–5 atm and methane-air flames between 1–60 atm. Based on the numerical predictions, zero-gravity flames had lower temperatures, broader soot-containing zones, and higher soot concentrations than normal-gravity flames at the same pressure. Buoyant forces caused the normal-gravity flames to narrow with increasing pressure while the increased soot concentrations and radiation at high pressures lengthened the zero-gravity flames. Low-pressure flames at both gravity levels exhibited a similar power-law dependence of the maximum carbon conversion on pressure which weakened as pressure was increased. This dependence decayed at a faster rate in zero gravity when pressure was increased beyond 1–10 atm.

<div>As space exploration continues to accelerate, various cooling applications follow suit. Refrigeration and freezing of biological samples, astronaut food as well as electronics cooling and air-conditioning are necessary and demand increased capacity. In the past, these demands have been met by thermoelectric cooling or cryogenic cycles, which are easily adapted to a microgravity environment but have a relatively low efficiency in the refrigeration and freezing temperature range. A number of studies have investigated the development of higher efficiency vapor compression cycles for spacecraft, which would have the benefit of a smaller mass penalty due to the reduced power consumption. Despite notable research efforts during the 1990s, the number of vapor compression coolers that have operated in microgravity until today is small and their performance was insufficient to provide confidence into the technology for microgravity applications. Related experimental research has decreased since the 2000s.<br></div><div><br></div><div>For this dissertation, all vapor compression cycles (VCC) that have operated in microgravity according to the open literature were reviewed with their applications, compressor types and reported issues. Suggested design tools were summarized with a focus on gravity independence criteria for two-phase flow. For the most effective increase of the technology readiness level, simple but systematic experiments regarding the stability of VCCs against orientation and gravity changes were prioritized in this dissertation. An important goal of the research was the continuous operation and start-up of vapor compression cycles on parabolic flights, experiments that have not been reported in the open literature. Two separate test stands were built and flown on four parabolic flights, totaling 122 parabolas for each experiment.<br></div><div><br></div><div>The parabolic flight experiments were prepared with extensive ground-based testing. Multiple anomalies were encountered during the pursuit of continuous vapor compression cycle operation through a rotation of 360 degrees, including liquid flooding of the compressor. Systematic inclination testing was conducted with two different cycle configurations and a wide range of operating conditions. A strong correlation was found between the relative stability of the heat source heat transfer rate and the refrigerant mass flux for an inclination procedure with angle changes once every 2 minutes.<br></div><div><br></div><div>The parabolic flights exposed the test stand to quickly alternating hyper and microgravity. The evaporation temperature reacted to the different gravity levels with fluctuations that stretched on average 2.2 K from the maximum to minimum temperature measured during one set of parabolas. Changes of the evaporator inlet flow regime as a function of gravity were observed visually and the low-side pressure and mass flow rate sometimes oscillated in microgravity. The cycle responses induced by ground-based inclination testing were typically stronger than changes caused by the parabolic flight maneuvers for relatively low mass flow rates. Overall, the parabolic flight maneuvers were not detrimental to the cycle operation. <br></div><div><br></div><div>The second test stand was dedicated to liquid flooding observations at cycle start-up. Different flow regimes were observed in microgravity during testing with a transparent evaporator but the absence of gravity did not significantly alter the general time-based flooding quantifiers.<br></div><div><br></div><div>Design recommendations are drawn from the research where possible and summarized at the end of the dissertation. Selected data, code, pictures and videos were released together with this dissertation(Brendel, 2021)<br></div>

Regardless of new mining technologies and environmental regulations, the minerals we extract from the earth’s crust will eventually run out. Likewise, our society demands a constant increase of technology to improve our quality of life. Mining in Zero Gravity is a speculative design project that offers a vision of our first attempt at mining platinum group metals from asteroids by the year 2040. Kolibri is designed within the boundaries of the future challenges facing the mining industry and the development of our space industry.

<p dir="ltr"> As part of humanity's constant effort to explore and expand, the race to establish a cislunar economy is afoot. The Cryobubbles experiment seeks to advance the state of the art in long-term cryogenic propellant management, a field that is an integral part of exploring the next great frontier. The Cryobubbles experiment was created to understand an unexpected bubble formation phenomenon during a tank-pressure control strategy test of NASA's Zero Boil-off Tank (ZBOT) on the International Space Station. A few hypotheses about the causes of bubble formation were developed, and thanks to a NASA flight opportunities grant, the Cryobubbles experiment was designed and manufactured with a \$95,000 budget to test these hypotheses on a parabolic flight.</p><p dir="ltr"> This master's thesis explains the importance of understanding the causes of bubble formation and the thermodynamic operating point chosen to replicate ZBOT conditions. The operation of the experiment and the design of technologies developed to make these operations work are also discussed. Some notable technologies include an insulation sizing algorithm created to maintain the experiment operating point, cryogenically rated viewports that allow for high-quality video recording of the experiment, and copper coils sized to allow for the safe use of noncryogenic equipment in a cryogenic test setup. All of these designs were constrained by a budget, a fast-approaching flight test deadline, and safety considerations.</p><p dir="ltr"> At the time of this writing, the experiment has been fully designed, manufactured, and assembled. The next step is to conduct testing.</p>