Presentation on

Nozzle and Diffuser

Presented by:

Prof. Prabha Chand

NIT Jamshedpur

Department of Mechanical Engineering

Introduction

• A nozzle is a passage of smoothly varying cross- section by means of which the pressure energy of working fluid is converted into kinetic energy.

Applications

• Steam, water and gas turbines to produce high velocity jet to impinge on curved blades for driving turbine shaft

• Rocket motors and jet engine to produce thrust

• Flow measurements

• Artificial foundations

Types of nozzles

• Converging nozzle

• Diverging nozzle

• Converging -Diverging nozzle

Types of diffusers

(a) Direction of flow

i. axial diffusers

ii. Radial diffusers

(b) Nature of flow

i. Subsonic diffusers

ii. Supersonic diffusers

Equation of continuity.

According to continuity equation

The continuity equation may be expressed in differential form.

Sonic velocity :- the expression for sonic velocity is derived by considering the propagation of a pressure wave is an isentropic flow through a pipe of uniform cross-section which is given by

For an ideal gas,

Mach Number:-

M=1, for sonic flow

M<1, for subsonic flow

M>1, for supersonic flow

Stagnation properties

• Stagnation properties of fluid are those properties reached at a point where the velocity is brought to zero isentropically.

The steady flow energy equation in nozzles

Energy entering into nozzle=energy leaving the nozzle

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Potential energy is negligible z1 = z2 , there is no heat supplied and no mechanical work done by apparatus.

The momentum equation for the flow through steam nozzle

For SFEE

Nozzle Efficiency

• Nozzle efficiency is define as the ratio of actual heat drop to that due to isentropic expansion

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• For gas Nozzles

• Coefficient of discharge may be define as the ratio of actual mass flow rate to that due to isentropic expansion.

Effect of friction on the velocity of steam leaving the nozzle.

• Consider the flow of steam with friction through a nozzle. The actual heat drop will be

Adiabatic flow through diffuser

SFEE to a diffuser under isentropic flow condition

For isentropic flow enthalpy remains constant and there is no change of entropy and loss of stagnation pressure

Diffuser Efficiency

• Is define as the ratio of isentropic enthalpy rise to the actual enthalpy rise in a diffuser

• For incompressible flow and isentropic process

Total Pressure Loss Coefficient

• The total pressure loss coefficient is define as the ratio of decrease in total pressure to initial kinetic energy.

Pressure recovery coefficient • Pressure recovery coefficient is define as the ratio of static pressure rise

to initial kinetic energy.

continuity equation for incompressible flow yield

Mass of discharge through nozzle

p-v diagram for isentropic expansion in nozzle

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The mass of steam in kg per second flowing through a nozzle under a pressure drop from p1 to p2