Life Test Results for Water Heat Pipes Operating at 200 °C to 300 °C

Abstract

For lunar or planetary bases to be viable, a robust electric generating system will be required for powering the habitat. Water heat pipes offer an attractive solution for lunar base heat rejection, and would serve as a qualification for them on other long duration missions. Successful operation near the upper end of water operating range is a requirement for the application. Results are reported for life tests on water heat pipes that were operated at various temperatures between 200 °C and 300 °C. Tests were conducted on twenty three gravity‐assisted water heat pipes. Eleven titanium/water heat pipes and ten Monel/water heat pipes were tested at temperatures above 200 °C. Two cupronickel heat pipes were also assembled and tested. Titanium alloys tested included CP‐2 titanium, as well as two beta‐titanium alloys, namely 15‐3 and Nitinol alloys. Some of the titanium alloy life tests used wicks fabricated from CP‐2 titanium screen or porous felt. Monel alloys tested included 400 and K‐500 alloys. Some of the Monel heat pipes contained copper/nickel wicks that were fabricated by brazing nickel‐plated copper felt metal wicks. Although most of the envelope/material combinations exhibit favorable results at 200 °C, some of the combinations failed at higher temperatures. Causes of failure included stress‐creep of envelopes and corrosion at axial or end cap welds. This information represents a significant advance in selection of materials for 200 °C to 300 °C water heat pipes. Life testing work is being continued.