What happens if a gas flow passes through a resistance?

When gas flow passes through a resistance, a pressure drop occurs due to the energy loss as the gas encounters friction and turbulence while moving through the constricted area. This resistance can be caused by several factors, including narrowing passages, bends in pipes, or filters. As the gas is forced through these areas, it loses some of its pressure because work must be done to overcome the frictional forces, thereby converting some of its potential energy into heat. This phenomenon is governed by principles of fluid dynamics, particularly Bernoulli's principle and the concept of pressure loss in fluid systems.

The other outcomes mentioned involve different aspects of gas flow dynamics. While flow reduction can occur, it is a secondary effect of the pressure drop rather than a direct consequence of passing through a resistance. Similarly, while gas may experience cooling as it expands after passing through a restriction, this is not a direct result of the resistance itself but rather a characteristic of gas behavior under certain conditions. Thus, the most direct and accurate consequence of gas flow encountering resistance is a pressure drop.