What type of flow occurs when fluids travel at a right angle to each other?

Cross flow is the correct term used to describe the situation where fluids move at right angles to each other. This type of flow is significant in many engineering applications, such as heat exchangers, where one fluid flows horizontally while another flows vertically. The interaction between the two fluids at this perpendicular angle enhances mixing and heat transfer, making cross flow an efficient configuration for various systems.

In contrast, counterflow involves two fluids moving in opposite directions, which is prevalent in heat exchangers but does not align with the definition of fluids traveling at right angles. Parallel flow refers to fluids moving alongside each other in the same direction, thereby not intersecting at right angles. Multi-stream flow involves more than two fluid streams but does not specifically indicate that they are at right angles to one another. Thus, cross flow stands out as the accurate description of fluids traveling perpendicularly.