A technology gap persists in the visualization of optically inaccessible flow fields such as those in integrated systems. Advances in positron emission tomography (PET) technology are enabling its use in the engineering field to address this technology gap. This paper discusses a numerical study performed to characterize a modern PET system’s ability to reconstruct a three-dimensional mapping of the optically inaccessible flow field downstream of an orifice. A method was devised to simulate a ring detector response to a flourine-18 radioisotope/water solution injected into the flow through a standard thickness pipe with orifice. A commercial computational fluid dynamics code and the GEANT4 Applications for the Tomographic Emission Monte Carlo simulation physics package were used to carry out the simulations. Results indicate that geometrical features, such as the pipe internal diameter, can be resolved to within a few millimeters with specific activity levels of 155 Bq/Voxel (91.2 Bq/mm3), and acquisition times as low as 15 s. Results also suggest that flow features, such as the radial extent of the shear layer between the primary and secondary recirculating flow can be resolved to within 5 mm with the same activity level, but with acquisition times of 45 s.
As satellite on-orbit service operations become increasingly aggressive and complex (such as on-orbit refueling, rescuing, repairing, etc.), the need for identifying varied inertial properties of a satellite is becoming a critical task. The importance of this task stems from the dependence of spacecraft’s guidance, navigation and control system on these properties. In order to accurately control a spacecraft, its control system must be capable of fully identifying these properties as they change. Previous techniques use thruster firing or momentum wheels to accomplish this task. However a newly developed robotics based method requires measuring the spacecraft’s velocity changes only, which can be induced by an onboard robotic arm powered by solar energy. This paper gives a brief overview of this method and then focuses on the design of experimental verification of the method. The verification consists of a series of experiments including a simulated microgravity test onboard the NASA JSC Reduced Gravity aircraft in order to accurately simulate an environment similar to a flying satellite in orbit.
The steady state heat transfer characteristics under internal forced convection of liquid methane were experimentally investigated using a rectangular channel with a cross section of 1.8 mm x 4.1 mm and square channels with a cross section of 3.2 mm x 3.2 mm; three square channels had surface finishes typical of milled channels and another three square channels had internal longitudinal fins. A High Heat Flux Test Facility (HHFTF) capable of handling cryogenic temperatures that was developed at the Center for Space Exploration Technology Research (cSETR) for the purpose of simulating the high heat load conditions representative of regeneratively cooled rocket engines was used in this study. For the rectangular channel, Reynolds numbers ranged between 68,000 and 131,000, while the Nusselt numbers were between 40 and 325. For the rough channels, Reynolds numbers ranged from 82,000 to 131,000, and Nusselt numbers were between 65 and 810. The longitudinally finned channels had Reynolds numbers ranging from 50,000 to 128,000, and Nusselt numbers between 70 and 510. Sub-cooled film-boiling phenomena were discovered for all the channels presented in this study. Film-boiling onset at Critical Heat Flux (CHF) was correlated to the Boiling Number, Bo ~0.1. Convective Nusselt number follows predicted trends for Reynolds number with a wall temperature correction for both the boiling and non-boiling regimes. NomenclatureA w = Test section coolant channel wall surface area, m 2 A c = Test section coolant channel cross-sectional area, m 2 Bo = Boiling number C p = Isobaric heat capacity, kJ/kg-K D hyd = Hydraulic diameter, m h = Convection coefficient, kW/m 2 -K i fg = Fluid heat of vaporization, kJ/kg k = Fluid conduction coefficient, W/m-K ̇ = Mass flow rate, kg/s Nu D = Nusselt number based on hydraulic diameter P avg = Fluid test article average pressure, MPa 2 P in = Fluid test article inlet pressure, MPa P out = Fluid test article outlet pressure, MPa Q = Total heat transfer, kW q" = Heat flux, kW/m 2 R a = Arithmetic mean value scale, microns Re = Reynolds number T b = Average fluid bulk temperature, K T in = Fluid test article inlet temperature, K T out = Fluid test article outlet temperature, K T sat = Fluid saturation temperature, K T w = Wall temperature, K v = Fluid bulk velocity, m/s x = Fluid quality, x < 0 for sub-cooling z crit = Critical length of tube to reach critical heat flux, m ΔT = Fluid inlet/outlet temperature difference, K = Fluid viscosity, Pa-s = Fluid density, kg/m 3
The steady-state heat transfer characteristics under internal forced convection of liquid methane were experimentally investigated using a rectangular channel with a cross section of 1.8 × 4.1 mm and square channels with a cross section of 3.2 × 3.2 mm; three square channels had surface finishes typical of milled channels and another three square channels had internal longitudinal fins. A high heat flux test facility capable of handling cryogenic temperatures, which was developed at the Center for Space Exploration Technology Research for the purpose of simulating the high heat load conditions, representative of regeneratively cooled rocket engines, was used in this study. Subcooled film-boiling phenomena were discovered for all the channels presented in this study. Film-boiling onset at critical heat flux was correlated to the boiling number Bo ∼ 0.1. The convective Nusselt number follows predicted trends for Reynolds number with a wall temperature correction for both the boiling and nonboiling regimes.Nomenclature A c = test section coolant channel cross-sectional area, m 2 A w = test section coolant channel wall surface area, m 2 Bo = boiling number C p = isobaric heat capacity, kJ∕kg · K D hyd = hydraulic diameter, m h = convection coefficient, kW∕m 2 · K i fg = fluid heat of vaporization, kJ∕kg k = fluid conduction coefficient, W∕m · K _ m = mass flow rate, kg∕s Nu D = Nusselt number based on hydraulic diameter P av = fluid test article average pressure, MPa P in = fluid test article inlet pressure, MPa P out = fluid test article outlet pressure, MPa Q = total heat transfer, kW q 0 0 = heat flux, kW∕m 2 R a = arithmetic mean value scale, μm Re = Reynolds number T b = average fluid bulk temperature, K T in = fluid test article inlet temperature, K T out = fluid test article outlet temperature, K T sat = fluid saturation temperature, K T w = wall temperature, K v = fluid bulk velocity, m∕s x = fluid quality, where x is less than zero for subcooling z crit = critical length of tube to reach critical heat flux, m ΔT = fluid inlet/outlet temperature difference, K μ = fluid viscosity, Pa · s ρ = luid density, kg∕m 3
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