cocurrent

Co-current, also written cocurrent, is a term used in fluid dynamics and process engineering to describe a flow arrangement in which two fluid streams move in the same axial direction. The streams may differ in temperature, composition, or phase, and they interact through a contact surface as they flow.

In heat exchange, cocurrent flow contrasts with countercurrent flow. In a cocurrent heat exchanger, both fluids enter at the same end and travel together, exchanging heat along the length. The temperature driving force is largest at the inlet but diminishes toward the outlet, which can limit the maximum heat transfer for a given length and may require a larger unit than a countercurrent design for the same duty. Nevertheless, cocurrent configurations are often simpler to fabricate and operate, offering straightforward control and startup.

In mass transfer operations such as absorption, desorption, or liquid–liquid extraction, cocurrent contact can be used when a simple, compact, or low-maintenance unit is desired. The trade-off is that the driving force for mass transfer decreases along the column, potentially reducing separation efficiency relative to countercurrent arrangements. Design decisions depend on process objectives, thermodynamics, and economic constraints, including factors such as pressure drop, phase stability, and equipment scale.