  Flow across heated parallel channel systems exists in many applications. The
performance of such systems experiencing multiphase flow could suffer from the
deleterious effects of flow non-uniformity or maldistribution. Modeling the
behavior of such systems is challenging due to the inherent non-linearity
associated with the multiphase flow and the difficulty in determining the
actual flow among several possible flow distributions. This study addresses the
challenge by analyzing the entropy production in such systems. Using
experiments on two thermally isolated, nominally identical, and externally
heated parallel channels, we quantify irreversibility in the resulting
multiphase flow by evaluating the entropy generation rate. Our experiments
reveal that certain flow conditions result in severe maldistribution (flow
ratio > 10) in the channels, associated with a sharp rise in entropy
production. Such an increase is not predicted for uniform flow distribution
across parallel channels, making maldistributed flow a thermodynamically
favored state over equally distributed flow. We extend this understanding to
non-identical parallel channels as well. With entropy analysis providing
additional insight besides the fundamental equations governing mass, momentum,
and energy conservation, this approach is valuable in predicting and
controlling flow distribution in parallel channel systems.
