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An example related to fluid mechanics utilizes high speed video of a flow boiling system was recorded at different heat flux levels.[i] Nine videos were used in the analysis corresponding to five values of heat flux which are shown below at selected points in time. The larger values of heat flux are shown to have a larger number of bubbles due to the higher amount of energy being transferred to the working fluid. It is apparent that the change in the number of bubbles is not linear.

To demonstrate the result of the method, two videos at heat
fluxes of 80 ^{kW}/m^{2}, 120
^{kW}/m^{2}, 140 ^{kW}/m^{2}, and
160 ^{kW}/m^{2}, were used as the known inputs and
the heat flux was predicted for the 100
^{kW}/m^{2}video. Each image in the 340 frames of
the video corresponds to 141 x 400 pixels resulting in 19,176,000
elements or variables to evaluate per movie. The 19 million
variables are reduced to 64 variables which are embedded into a two
dimensional diffusion space (Shown in the Figure below). These two
element vectors are used to predict the heat flux. Thus, the two
diffusion coordinates of the eight videos corresponding to four
known heat fluxes are used to construct a probability distribution
for the remaining video which is shown in the Figure below.

The resulting mean of the probability density function closely predicts the actual heat flux applied. Thus, one can potentially use video of known operating conditions to predict new states.

[i] C. ESTRADA-PEREZ, E. DOMINGUEZ-ONTIVEROS, H. AHN, N. AMINI, and Y. HASSAN, "PTV Experiments of Subcooled Boiling Flow through a Rectangular Channel," in16thInternational Conference on Nuclear Engineering, Orlando, Florida, 2008.

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This manifold geometry is found in many spacecraft systems including radiators. For single phase flow, determining the mass flow in each leg is straightforward with a simple conservation laws but becomes challenging for two-phase flow due to the uncertainty associated with determining the phase distribution that occurs at the splitting junctions (branches). Furthermore, instabilities can occur leading to significant changes in flow conditions.

A reason for flow maldistribution in each branch is due to the momentum of each phase as it moves along the header. The high density liquid will tend to move along the header whereas the low density gas can turn into the branches. A significant amount of research has been carried out in Earth gravity with a number of different fluids, manifold geometries, and orientations but limited work has been completed for reduced gravity conditions where a lack of buoyancy impacts the phase distribution and thus, the splitting of gas and liquid at the junctions. The ITP performed some tests and modeling outlined here and some test results and model predictions are shown in the accompanying Figure.

The test consisted of a manifold with three parallel branches. The first two branches (1 and 2 in the Figure) consists of T-junctions while the last branch (branch 3) is simply an elbow. The results show that liquid preferentially moves toward the far end of the header whereas gas enters the branches at the T-junctions. A video of the testing performed on NASA's reduced gravity aircraft can be found here. The video shows a number of interesting phenomena including changes in flow regime due to the change in gravity and changes in the mass fraction between the branch and run of the T-junction. The situation becomes more complex when one considers phase change (condensation or boiling) or other effects that upset the balance of forces. In addition, the flow velocity will differ which is further exasperated by the differences in viscosity between the phases.

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A demonstration of a variable heat rejection radiator technology was carried out at the Interphase Transport Phenomena Laboratory (ITP) at Texas A&M University (TAMU). The technology utilizes a vortex type separator and a passive educator/jet pump to exchange working fluid in the radiator segments/lines with a non-condensable gas located in the phase separator. The Figure below is an illustration of the proposed system that is based on variable heat rejection studies in the literature and includes a phase separator and eductor. The system shown here illustrates the warm liquid (in red) entering the radiator and being cooled (cool liquid shown in blue) returning to the pump and phase separator. Non-condensable gas shown in green can be used to displace liquid in the radiator based on the orientation of 3-way latch valves located at the entrance and exit of either a single radiator line or a manifold of lines. By actuating the valves, gas and liquid can be exchanged between the separator and radiator which can control the area of radiator available for thermal energy rejection.

Component and system level experiments were carried out and modeling was completed for use in the sizing of separator and eductor components for a given radiator line volume to be evacuated. Tests were carried out to show the integration of a passive eductor pump with a phase separator could be used to clear lines and vary heat rejection. A bath type heat exchanger was used rather than a radiator. A review of various instrumentation methods was also performed and is mentioned in the report. Results show that the technology can successfully perform variable heat rejection by repeated evacuation and filling of selected pipe sections used to simulate single phase radiator line segments.

]]>As mentioned in Dr. Carron's blog, the GoDec solver performs a low rank decomposition added with a sparse and noisy component. The video on the accompanying page (link can be found on the sidebar of this page) is the result 800 frames at 1 minutes into video 2. The accompanying .mat file can be downloaded here. ]]>