Impact of jetImpulse- Momentum Principle

Introduction

• The study of forces resulting from the impact of fluid jets involves the application of newtons second law in the form of

F = m.a.

• The forces are determined by calculating the change of momentum of the flowing fluids.   

• Newtons Second Law : The force acting on a body in a fixed direction is equal to rate of increase of momentum of the body in that direction.  

• A fluid is essentially a collection of particles and the net force, in a fixed direction, on a defined quantity of fluid equals the total rate of momentum of that fluid quantity in that direction.

Consider a mass m with initial velocity u and is brought to rest. Its loss of momentum is m.u and if it stopped in a time interval t then

the rate of change of momentum is m.u /t.    The force F required to stop the moving mass F = m.u / t .  Now jet of fluid with a mass flow rate ( m / t ) which equals to

the volumetric flow rate x the density ( Q.ρ )

The equivalent force on a flowing fluid is F = Q.ρ u.  

In its simplest form, the force on a fluid flow in a set direction is equal to its mass flow rate times by the change in velocity in the set direction. The fluid flow also exerts an equal and opposite reaction force as a result of this change in momentum.

F = Qρ (u 1 - u 2). ..( F and u are vector quantities)

The resultant force on a fluid in a particular direction is equal to the rate of increase of momentum in that direction.

Expt. Set-up

Impact for various plate potions

Expt. Set-up

Fa

Vs

QAs the discharge increases the actual force increases