A study of the effect of flow maldistribution on heat transfer performance in evaporators

摘要

The performance of a heat exchanger with parallel channels can be seriously affected by flow maldistribution. In two-phase flow applications, such as evaporators, this situation may lead to local dryout and off-specification products. However, due to the complexity of describing this effect, it is normally not considered in the design process. Two models are proposed in this work for predicting the effect of maldistribution on performance. The first model neglects the interaction between channels, while the second one incorporates an equal pressure drop constraint. Both models analyze the geometry (shell-and-tube) in terms of radial layers. Here, the number of layers considered is irrelevant for the first model, while it affects the results of the second one. All results were compared to a homogeneous reference case, and reduction of performance was noticed in all cases. The first model predicts unrealistic pressure differences at the outlet. This situation is controlled by the second model, which predicts a secondary maldistribution to fit the constraint that further reduces the performance. When both models are compared, the first one underestimates the reduction in performance roughly by half.