Flow and heat transfer analyses of a plate-fin heat exchanger in an HTGR

The effects of different plate-fin heat exchanger structures in high temperature gas-cooled reactors (HTGR) were studied numerically. Four fin structures and four working conditions were analyzed to scrutinize the plate-fin heat exchanger performance with detailed analyses of the velocity distributions, pressure distributions, temperature distributions and heat transfer. The results show that the velocity curves around staggered fins have two peaks with high velocity fluid near the fins. For the same average inlet velocity, the fluid temperature is more uniform with the staggered fins. The fluid temperatures are more stratified with the plain fins unlike the staggered fins periodically disrupt the boundary layer and mix the flow, so the boundary layer along the staggered fins is thinner than along the plain fin and the heat exchange rates are higher. However, the pressure drop with the staggered fins structure is also increased. The total heat transfer rates for Model 2 were 1.3-1.4 than for Model 1, with those for Model 3 1.4-1.5 and those for Model 4 1.5-1.6 times higher than those for Model 1 for all conditions. The total pressure drop with Model 2 was 1.5-1.8 times higher, Model 3 was 2.1-2.6 times higher and Model 4 was 2.8-3.7 times higher than for Model 1. The complete thermal-hydraulic evaluation indicates that the staggered fin structure with a modest fin length, approximately 3.5 mm, is the best choice.