What is stratification in fluid dynamics?

Stratification in fluid dynamics refers to the phenomenon where a fluid separates into distinct layers, typically due to differences in temperature or density. When fluids are heated, the warmer, less dense fluid tends to rise, while the cooler, denser fluid sinks. This process leads to the formation of layers, which can have significant implications in various HVAC applications, especially in maintaining temperature stability and ensuring efficient thermal distribution in systems.

In contrast, the other options describe different fluid behaviors. The movement of fluid through a duct focuses on how fluids are transported within a system but doesn't address layer formation. The mixing of different fluid densities converses the idea of stratification, as it implies that the layers are being mixed, rather than remaining separate. Lastly, the formation of vortices relates to the swirling or rotational flow of fluid, which is distinct from the concept of stratification, emphasizing organization of fluid in layers rather than their chaotic movement. Thus, stratification is specifically identified by the layering of fluid by temperature or density rather than mixing or movement characteristics.