A passage-to-passage model is introduced to the
study, which simplifies the indication of flow in the
cross-section from many channels to 13 passages along
the y direction of header by means of a macro analyzing
method. To discuss the performance of the flow maldistribution
in 13 passages, the flow nonuniformity for
individual passage and the sum of flow nonuniformity
for the cross-section are introduced as follows: