First Experimental Results on a Silicon-Nitride Recuperator With Six Heat Exchanger Elements

A prototype ceramic recuperator consisting of six heat exchanger elements of Si₃N₄, being arranged side by side in a self-sealing and self-supporting configuration, was investigated experimentally with respect to the heat transfer-, friction- and mechanical-properties as well as to the sealing performance. The heat exchanger elements are developed in collaboration by Kernforschungsanlage Jülich GmbH (KFA) and Rosenthal Technik AG (RTAG). The recuperator arrangement corresponds well to an unique design principle for small automotive “ceramic” gas turbines. The thermodynamic measurements were carried out with air, electrically heated up to temperatures of about 100 C, and at pressures on the HP-side up to about 2 bar. The self-sealing and self-supporting heat exchanger arrangement promises to be satisfying for vehicular application purposes. Partial rupture of heat exchanger walls in the prototype-elements began at a pressure difference of about 3 bar. On the basis of the experimental results, a design of a vehicular gas turbine for 70-Kw shaft power and with heat exchanger elements for advanced fabrication technique is presented. A planned test facility for gas temperatures up to about 1200 C and with a new set of heat exchanger elements from Si₃N₄ or SiC is described briefly.