Design and Development of Lightweight Air-Liquid Composite Heat Exchangers for Space Exploration Applications

Abstract

An Engineering Development Unit (EDU) of a lightweight composite Air/Liquid (A/L) heat exchanger (HX) was successfully designed and manufactured for potential space exploration thermal management applications including Orion CEV, Altair, and Lunar Surface Systems. The EDU was a full-scale HX comparable to the existing metallic HX demonstrator, but only required to meet the thermal specifications, especially targeting 3.5kW heat removal. This composite EDU was 37% lighter than the corresponding metallic unit weighted total about 47.5 lbs (or 21.6 Kg). Design concepts, material variables, fabrication methods, and their effects on heat exchanger performance were systematically evaluated in an earlier coupon-level experimental study. The EDU, designed as a modular system, utilized a low density, open cell, but thermally conductive carbon foam which was embedded with multiple stainless steel cooling tubes as a HX core. The stainless steel tube was selected for its compatibility to the chosen coolant, de-ionized water. Lightweight but strong carbon fiber reinforced epoxy matrix composite material was used for air inlet and outlet plenums, and housed the entire HX core with air-tight sealing. The EDU cooling system was pressure proof tested up to 75 psi. A special test rig was developed for thermal performance evaluation of the full-scale HXs based on actual space hardware specifications. Thermal performance of the EDU and the metallic HX demonstrator from NASA-JSC was evaluated with the newly developed test system. The EDU showed ~ 85-87% of metal HX in Qh at most comparable test conditions. However, in terms of specific heat transfer (i.e., Qh/wt of HX), the EDU outperformed the metal HX by 34 – 37%. Details of the EDU design, material-selections, step-by-step fabrication procedures, weight analysis and thermal performance are discussed in this paper. Findings from the composite EDU will be implemented in design and manufacturing of a full-scale composite A/L HX Prototype which is required to meet both thermal and structural specifications. Nomenclature