Experimental Study of a Zigzag Channel for Recuperator Design in a Nitrogen Brayton Cycle Coupled with a Sodium-cooled Fast Reactor

Abstract

This study investigates thermal-hydraulic performances of a zigzag channel for recuperator design in a nitrogen Brayton cycle coupled with a sodium-cooled fast reactor. Because the recuperator dominates system volume, improving channel performance while satisfying design requirements is important for compact and economical systems. With a gas-to-gas experimental loop, a printed-circuit heat exchanger (PCHE) with a zigzag channel with a 40° bending angle, 1.2 mm diameter, 8 mm pitch, and 640 mm core length was tested. Experiments were performed over Reynolds numbers from 1400 to 12000 under Prandtl-number conditions relevant to the target nitrogen cycle. Using measured heat transfer and pressure drop data, Nusselt numbers and Fanning friction factors were obtained after accounting for minor-loss and acceleration effects. The 40° zigzag channel showed heat-transfer performance 1.5–2.3 times higher than the straight channel at the same Reynolds number, whereas pressure-drop performance was 4–6 times higher. Compared with other zigzag channels, the 40° channel showed higher heat transfer and pressure drop than the 15° channel, but lower values than the 52° channel. New correlations were proposed for the 40° zigzag channel, and their mean absolute errors were 3.15% for heat transfer and 2.52% for pressure drop. A performance evaluation criterion indicated that, above Reynolds numbers of 3000, the 40° channel provided the best comprehensive performance among the zigzag configurations and remained within 7% of the straight channel. The proposed correlations were implemented in a validated one-dimensional PCHE design code and applied to recuperator design for a target nitrogen Brayton cycle. Under the same effectiveness and pressure-drop constraints, the 40° zigzag channel yielded a recuperator volume of 50.00 m3, slightly smaller than 51.65 m3 for the straight channel at the same hydraulic diameter. These results show that the 40° zigzag channel is feasible for compact and practical recuperator design in nitrogen Brayton cycles.