The aim of this study is to determine the flow characteristics of inline and staggered cylinders in deep water by using Particle Image Velocimetry (PIV) technique. Experiments were undertaken in a water channel in Fluid Mechanics Laboratory, Mechanical Engineering Department of Cukurova University. Due to importance of heat exchangers usage, flow structure in the flow passage of the fin-tube type heat exchanger were studied experimentally using particle image velocimetry technique. Besides the important parameters of flow characteristics around cylinders and slot-cylinders were investigated by dye visualization for different reynolds numbers.