This study seeks to analyze the effect of manufacturing defects and inlet header design on the effectiveness of heat exchangers. A commercial computational fluid dynamics code, FLUENT 5.4, was used to numerically simulate individual and pairs of passages as well as sections of an inlet header and heat-exchanger core. The one- and two passage models show that the four representative manufacturing defects do not have a large impact on overall effectiveness, even when the defects are quite large relative to the passage dimensions. The core and header sections showed that the basic header contour and the angle of the incoming flow as well as the pressure drop through the core have a significant impact on the flow distribution. Small variations in the header dimensions and the core/header aspect ratio have little effect on the effectiveness. Decreasing the angle the incoming flow turns through and increasing the pressure drop through the core both create a more even flow distribution through the heat exchanger, hence increasing its effectiveness.
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