Development of an Oxygen Heat Exchanger and Flow Meter for the Exploration Portable Life Support System

The ventilation loop in NASA�s Exploration Portable Life Support System (xPLSS) includes a compact heat exchanger that cools the ventilation gas before it enters the suit helmet. In addition to cooling the ventilation gas, the heat exchanger also serves as a pressure drop element for measuring the flow rate of ventilation gas. We have developed an innovative heat exchanger that meets the challenging requirements for service in the xPLSS. The miniature shell-and-tube heat exchanger is built from all oxygen-safe materials around a core comprising an array of Inconel microtubes. The microtubes provide a very high surface area and high heat transfer coefficients for efficient gas cooling with minimal pressure losses. The microtube design also provides a highly linear flow vs pressure drop characteristic that enables accurate measurement of gas flow. The first design validation test (DVT) heat exchanger is installed and undergoing integrated system testing in the first xPLSS prototype.

This paper reports on the status of the heat exchanger development program and reviews some of the key lessons learned from the development and testing effort: (1) Maintaining stability of test conditions for a small heat exchanger across wide range of pressures and flow rates; (2) Measurement of pressure losses in a component designed for a compact, highly integrated system; (3) Challenges obtaining flight-qualified electronics for the flow sensor. The techniques that were developed to measure performance and qualify the current set of DVT heat exchangers will be used to support flight qualification tests for future units.