Browsing by Author "Ungar, Eugene K."
Now showing 1 - 3 of 3
- Results Per Page
- Sort Options
Item Columbus IFHX Ammonia Leak Analysis(48th International Conference on Environmental Systems, 2018-07-08) de Palo, Savino; Tilloca, Alessio; Ungar, Eugene K.After the Columbus Moderate Temperature Loop Interface Heat Exchanger (MTL-IFHX) Close-Call Investigation, concerning possible freezing of the IFHX water on-orbit on GMT 345-2013, NASA investigated relevant transient scenarios involving IFHX rupture after freezing and consequent thawing. The result was a recommendation to develop a Fault Detection, Isolation and Recovery (FDIR) procedure that would close the Water On Off Valves (WOOVs) to prevent ammonia from the external Active Thermal Control System (ATCS) from spreading into the cabin. NASA performed preliminary simplified analysis for the reference case of IFHX rupture, but for a deeper understanding TAS developed detailed Sinda-Fluint models built and run through the SINAPS GUI of the Columbus ATCS bus. This allowed simulation of the physical variation of the ammonia due to environmental parameter variations, providing more accurate and specific input to the FDIR under development and in particular finalization in terms of IFHX WOOVs closure sequence, pressure profiles and wait times to contain the ammonia propagation to Columbus and properly identify the leaking IFHX. In addition the analyses results provided reference pressure profiles to be used on console and by engineering support in assessing the telemetry data in case of failure. This paper gives an overview on the issue described and focuses on the analytical aspects of the multi-phase fluid dynamics involved.Item Mitigation of Orion Ammonia Boiler Outlet Coolant Thermal Stratification(48th International Conference on Environmental Systems, 2018-07-08) Ungar, Eugene K.; Foley, LaurenPart of NASA’s Orion Multi-Purpose Crew Vehicle (MPCV) active thermal control system is the Ammonia Boiler Heat Exchanger (ABHX). The ABHX is used as a topper when the Orion radiators cannot provide sufficient cooling and is the sole method of cooling the spacecraft after the command module/service module separation prior to reentry. Ammonia and propylene glycol water (PGW) flow through the heat exchanger in a counter-flow fashion, allowing the evaporating ammonia to cool the PGW. After exiting the heat exchanger , the PGW travels through a 0.5-inch diameter tube with three bends and enters temperature sensor block containing two thermistors. Development testing showed that the floe at the sensor block was not well mixed - the two PGW temperature sensors registered temperature differences of up to 5°C. A gravity fed water test stand was constructed of 1 inch clear PVC pipe to investigate the stratification. The test stand contained a long lead in section to allow the flow to fully develop. The bend area was geometrically scaled and the water flow rate was set to match the PGW Reynolds number of approximately 1000. Dye injection was used to visually assess the flow and mixing. Baseline testing clearly showed that the flow was poorly mixed at the thermistor location. Turbulators of different types and lengths were added to mix the flow. In the end, a turbulator configuration was chosen that resulted in well mixed flow while adding minimal pressure drop. In the present work, the Orion stratification issue is described, the test stand configuration and scaling is detailed, and the test is discussed. The chosen turbulator configuration is explained and its effect on the performance of the Orion ABHX is described.Item Pressure Drop Caused by the Neckdown of Cut Tubes(48th International Conference on Environmental Systems, 2018-07-08) Ungar, Eugene K.; Walker, MaryThe on-orbit repair of the International Space Station Alpha Magnetic Spectrometer (AMS) Carbon Dioxide (CO2) Tracker cooling loop will require that multiple flow tubes be cut during a spacewalk (extra vehicular activity or EVA). A module containing new pumps, an accumulator, a CO2 storage tank, and instrumentation will be connected to the cut tubes during the EVA. When the 4 mm OD x 0.7 mm wall stainless steel tubes are cut with an EVA-adapted tubing cutter, the ends will neck down. Reaming the tube end to its full inner diameter is not tenable owing to the possibility of creating debris and the undesirable use of a sharp object on EVA. The pressure drop associated with the connections made to the repair module must be understood to ensure proper operation. If the pressure drop caused by the cut tube neckdown is severe and is not uniform from cut to cut, it could cause unacceptable flow maldistribution in the Tracker cooling loop. A water pressure drop test was performed on test sections with internal dimensions identical to the mated repair configuration. The test was designed to obtain information that would allow the pressure drop from the repair to be predicted. This document describes the test setup, the test and the results, compares the results to predictions in the literature, provides a recommended pressure drop prediction methodology, and defines an allowable neckdown diameter ratio.