Jeffrey R. Mackey

Experimental Investigation of Flow Condensation in Microgravity

Future manned space missions are expected to greatly increase the space vehicles size, weight, and heat dissipation requirements. An effective means to reducing both size and weight is to replace single-phase thermal management systems with two-phase counterparts that capitalize upon both latent and sensible heat of the coolant rather than sensible heat alone. This shift is expected to yield orders of magnitude enhancements in flow boiling and condensation heat transfer coefficients. A major challenge to this shift is a lack of reliable tools for accurate prediction of two-phase pressure drop and heat transfer coefficient in reduced gravity. Developing such tools will require a sophisticated experimental facility to enable investigators to perform both flow boiling and condensation experiments in microgravity in pursuit of reliable databases. This study will discuss the development of the Flow Boiling and Condensation Experiment (FBCE) for the International Space Station (ISS), which was initiated in 2012 in collaboration between Purdue University and NASA Glenn Research Center. This facility was recently tested in parabolic flight to acquire condensation data for FC-72 in microgravity, aided by high-speed video analysis of interfacial structure of the condensation film. The condensation is achieved by rejecting heat to a counter flow of water, and experiments were performed at different mass velocities of FC-72 and water and different FC-72 inlet qualities. It is shown that the film flow varies from smooth-laminar to wavy-laminar and ultimately turbulent with increasing FC-72 mass velocity. The heat transfer coefficient is highest near the inlet of the condensation tube, where the film is thinnest, and decreases monotonically along the tube, except for high FC-72 mass velocities, where the heat transfer coefficient is enhanced downstream. This enhancement is attributed to both turbulence and increased interfacial waviness. One-ge correlations are shown to predict the average condensation heat transfer coefficient with varying degrees of success, and a recent correlation is identified for its superior predictive capability, evidenced by a mean absolute error of 21.7%.

Testing of Regeneration Filtration Concepts for Future Spacecraft Applications

NASAs future planetary surface and long duration transit missions will require the development of robust and effective filtration systems. Contamination from planetary dust and build up of internally generated particulate matter over long periods will significantly encumber the nominal operation of cabin filtration systems and would involve increased maintenance resources. One option for consideration is a combination of surface prefiltration and inertial/cyclonic particulate separation which can provide critical secondary filtration and regeneration capabilities. To test this concept, an experimental apparatus was devised to demonstrate, using JSC-1af lunar simulant and mono-sized silica particles as challenge aerosols, (a) the performance and loading characteristics of various surface prefilters and (b) regeneration concepts for in-place cleaning of the surface filter. In addition, high-speed reverse flow jets were used behind the pre-filter to break up the accumulated dust cake. The tests consisted of measuring flow velocities, pressure drops across filter elements, and particle counts (filter efficiency). Standard as well as high-speed video imaging was also performed in order to observe particle transport and dust cake breakup. The results from a series of filter loading and regeneration tests, including data from some low gravity tests, are presented in this paper.

Reduced Pressure Cyclone Separation Studies using Synthetic Lunar Regolith

In order to provide a safe and sustainable astronaut crew environment at a lunar or extraterrestrial outpost, dust mitigation techniques appropriate for the crew vehicle or space environment must be developed. Cyclonic separation is an attractive method because of equipment durability and maintainability. Further dust mitigation studies are required to optimize cyclone separator performance under the reduced air pressures anticipated in crew habitat and air-lock environments. In this paper we examine the collection efficiency of several cyclonic separators under ambient and reduced pressures. Performance testing of a commercial cyclone separator is used as a baseline for comparison with a custom-designed cyclone. Details of the experimental test system along with the design, performance, fabrication, and implementation of a custom cyclone separator are examined. We also describe the customization and implementation of specialized optical diagnostic instrumentation providing particle size, count, and flow data. Test results are compared with cyclone computational flow dynamic modeling to evaluate model parameters and optimize collection efficiency under anticipated flow conditions.

Toward Adaptation of fNIRS Instrumentation to Airborne Environments

The paper reviews potential applications of functional Near-Infrared Spectroscopy (fNIRS), a well-known medical diagnostic technique, to monitoring the cognitive state of pilots with a focus on identifying ways to adopt this technique to airborne environments. We also discuss various fNIRS techniques and the direction of technology maturation of associated hardware in view of their potential for miniaturization, maximization of data collection capabilities, and user friendliness.

Competition of linearly polarized modes in fibers with Bragg gratings over a wide temperature range

Fiber Bragg gratings (FBGs) embedded in conventional fibers may serve as temperature sensors over a wide temperature range and withstand temperatures around 1200 K. A variety of linearly polarized (LP) modes for the wavelengths between 400 and 700 nm may be sustained in fibers with and without FBGs. The composition of the LP modes and their competition is instrumental for understanding physics of thermo-optics and thermal expansion effects in silica-based fibers. The first objective of this work was to model mathematically the competition between LP modes and modal distribution using the solutions of Bessel equations for the fibers with and without the gratings. Computer generated modes were constructed and the cut-off V-numbers (and Eigen values W and U) were determined. Theoretical results then were compared with experimental observations of LP modes for two separate ranges of temperatures: 77– 300 K and 300-1200 K. To study the formation of LP modes over the first temperature range, liquid nitrogen was used to cool down the fiber and a thermocouple was used to monitor the temperature of the fiber. Real time recording of the modal structure was performed using digital imaging and data acquisition instrumentation. To study LP modes between 300– 1200 K, the fibers were inserted into a tube furnace with temperature control. The wavelength of the infrared radiation was reflected by a FBG and detected by an optical spectrum analyzer. Radiation at the visible wavelength propagated through the fibers, and transmitted visible light was collected, analyzed and recorded with a CCD camera to monitor distribution of the LP modes in the samples with and without the FBGs.

Optical Thin Film Measurements using a Vapor Phase Catalytic Ammonia Removal System at Elevated Temperatures

A Vapor Phase Catalytic Ammonia Removal (VPCAR) test system was developed for the purpose of purifying water from wastewater products in low gravity environments. The wiped film rotating disk inside of the engineering test apparatus has been outfitted with a heater element on its back side to produce temperatures adequate to increase evaporation rates and even boil water. One of the main characteristic indicators of the VPCAR efficiency is the water film thickness present on the wiped film rotating disk (WFRD). This paper examines two different VPCAR optical film measurement systems and their performance in the VPCAR system during operations near boiling point. The film measurement method is based on trace amounts of an organic tracer dye in solution. The fluorescence emission energy and thus the interpretation of film thickness become more complicated at elevated temperatures. With elevated temperature variance, emission is no longer strictly a function of the excitation energy, dye concentration and optical path length (i.e. film thickness). The temperature of the dye/water solution has a profound effect on the emission amplitude making fluorescence-based film thickness calibration essential for anticipated elevated temperatures to compensate for this temperature dependence.