Void fraction measurements by quick acting valves and capacitance measurements

Abstract

Two-phase flow systems are widely estimated to have superior capability in comparison with single-phase thermal management systems for spacecraft. However, microgravity two-phase flow technology is insufficiently advanced to allow development with acceptable risk levels. A capacitance effect, void fraction measurement sensor has been developed by Creare Inc. to begin to satisfy microgravity technology needs. Under a NASA Johnson Space Center grant, microgravity tests of the capacitance void fraction sensors were performed aboard the NASA KC-135. Twelve KC-135 flights were conducted in three series. Test points were collected over a wide range of void fractions (0%–90%). Data were collected from stratified, slug, and annular flow regimes. Void fraction measurements from the capacitance sensors were compared with the void fractions from a trapped volume in the test section between two quick acting valves. Under the annular flow regime, void fractions measured by the capacitance sensors compared well with values from the trapped volume. In slug flow regime, some discrepancies between the sensors and trapped volumes were found. However, when the working fluid (Suva) mass flow rate increased from 0.00314 kg/s to 0.007756 kg/s, the void fraction measurements between the capacitance sensors and the trapped volume had better agreement. Overall, the FRIM experimental package produced satisfactory test conditions in the microgravity conditions of the KC-135 aircraft, to validate and calibrate the Creare capacitance void fraction sensors.