Coupling effects of bend corners with alternating direction on the heat transfer and hydraulic characteristics of zigzag-type printed circuit heat exchanger for the next generation nuclear systems

Abstract

To deep understanding the heat transfer and flow process in zigzag-type printed circuit heat exchanger (PCHE) for advanced nuclear system, the coupling effects of bend corners are studied numerically. Bend corner, as the fundamental unit of zigzag channel, has great influence on its heat transfer and hydraulic performance of zigzag-type PCHE. In this study, the effects of bend corner and the coupling effects of adjacent bend corners were investigated, with bending angle 10°–40°, and Reynolds number (Re) 2500–20000. Concept of Influence Distance (ID) was proposed to describe the effects of bend corner on the convective heat transfer coefficient (HTC) and Fanning friction factor (f) quantificationally. It is found that the presence of the bend corner leads to secondary flow, recirculation and boundary layer separation. When bending angle is about 17°, ID-f almost keeps as a constant value, about 21 mm, for Re 2500–20000. And each curve of ID-HTC reaches a peak value when bending angle reaches about 30°. What's more, the coupling effects of adjacent bend corners of zigzag channels was demonstrated by comparing the heat transfer and hydraulic characteristics between bend corners arranged alternatingly and non-alternatingly. The shorter of midstream length and the higher Re, the stronger coupling effects of the adjacent bend corners. For the cases with Re = 20000, bending angle 30° and midstream length 10 mm–30 mm, the HTC near the second bend corner is about 9% lower than that of the first bend corner. The coupling effects influences the heat transfer and hydraulic characteristics obviously.