The preliminary experimental results on the fluid-flow patterns and pressure drops in channels of the Indirect Evaporative Air Coolers formed by different types of plastic plates with protrusions of cone and semi-sphere were reported. Flow visualization was performed by an improved tracer-injection technique. Cold water was used instead of air as the working fluid. The Critical Reynolds Numbers for fluid between two types plastic plates are 400 to 600 and 800. A set of empirical correlations of Eu-Re were obtained. It is important for the advanced design of the plastic plate heat Exchangers and Causes large Energy Saving.