Fluids Mechanics Question It is relatively easy to design an

It is relatively easy to design an efficient nozzle to accelerate a fluid. Conversely, it is very difficult to build an efficient diffuser to decelerate a fluid without boundary layer separation and its subsequent inefficient flow behavior. Use the ideas of favorable and adverse pressure gradients to explain these facts.

Solution

It is relatively easy to design an efficient nozzle to accelerate a fluid because the the pressure difference creates a favourable pressure gradient along the flow which helps to accelerate the fluid without boundary layer separation but in case of a diffuser the same pressure gradient is now a adverse pressure gradient because the flow has to slowed down in the direction of the pressure gradient. Due to this adverse pressure gradient the boundary layer thickens rapidly and becomes unstable reducing the efficiency of the diffuser.