Pressure Drop Caused by the Neckdown of Cut Tubes

The 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.