Performance Expectations of Closed-Brayton-Cycle Heat Exchangers in 100-kWe Nuclear Space Power Systems

Performance expectations of closed -Brayton -cycle heat exchangers to be used in 100 -kWe nuclear space power systems were forecast. Proposed cycle state points for a system supporting a mission to three of Jupiter's moons required effectiveness values for the heat -source exchanger, recuperator and rejection exchanger (gas cooler) of 0.98, 0.95 and 0.9 7, respectively. Performance parameters such as number of thermal units ( Ntu ), equivalent thermal conductance (UA ), and entropy generation number s ( Ns ) varied from 11 to 19, 23 to 39 kW/K, and 0.01 9 to 0.023 for some standard heat exchanger configurations. Pressure -loss contributions to entropy generation were significant ; the largest frictional contribution was 114% of the heat - transfer irreversibility. Using conventional recuperator designs, the 0.9 5 effectiveness proved difficult to achieve without exceeding other performance targets ; a metallic, plate -fin counterflow solution called for 15% more mass and 33% higher pressure -loss than the target values . Two types of gas -cooler s showed promise. Sin gle -pass counterflow and multipass cross - counterflow arrangements both met the 0.97 effectiveness requirement . Potential r eliability -relat ed advantages of the cross -counterflow design were noted . Cycle modifications, enhanced heat transfer techniques and incorporation of advanced materials were suggested options to reduce system development risk . Carbon - carbon sheeting or foam proved an attractive option to improve overall performance.