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THERMAL FLUID ASSIGNMENT

NOZZLES AND DIFFUSERS:

NAME:__________ROLL#:___________YEAR:____________DEPT.:____________

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Nozzles and diffusersIntroduction:NOZZLE:Nozzle is the mechanical device which is used for accelerating steam or gas or a device that

increases the velocity of a fluid at the expense of pressure. In it net work done, net heat supplied

and the net potential energy of the system remains zero. .The chief use of nozzle is to produce a

jet of steam (or gas) of high velocity to produce thrust for the propulsion of rocket motors and jet

engines and to drive steam or gas turbines.

Nozzle Representatio

DIFFUSER:Diffuser is the mechanical device which is used for the decelerating the steam or gas or a device

that increases the pressure of a fluid by slowing it down. In it net work done, net heat supplied

and the net potential energy of the system remains zero. Diffusers are used in compressors,

combustion chambers etc.

Diffuser Representation

Nozzle and diffuser are usually same in geometrical shape as shown above

but perform different function because of their direction

TYPES OF DIFFUSER & NOZZELS

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There are three types of nozzles and diffusers

Converging Diverging Convergingdiverging

Diagram:

FIG: 1 (converging and diverging nozzle and diffuser)

FLOW OF STEAM THROUGH NOZZLES:1. The flow of steam through nozzles may be regarded as adiabatic expansion.2. The steam has a very high velocity at the end of the expansion, and the enthalpy

decreases as expansion takes place.

3. Friction exists between the steam and the sides of the nozzle; heat is produced as theresult of the resistance to the flow.

4. The phenomenon of super saturation occurs in the flow of steam through nozzles. This isdue to the time lag in the condensation of the steam during the expansion .

FLOW OF STEAM THROUGH DIFFUSERS:1. The flow of steam through diffuser may be regarded as adiabatic compression.2. The steam has a very high velocity at the end of the compression, and the enthalpy

decreases as compression takes place.

3. Friction exists between the steam and the sides of the diffuser; heat is produced as theresult of the resistance to the flow.

STEADY FLOW EQUATION FOR NOZZLES

AND DIFFUSERS:

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Since no shaft work is involved in a nozzle or a diffuser, and since the potential energy differ-

rence across a nozzle or a diffuser is usually negligible, the steady flow energy for the flow,

Through a nozzle or a diffuser becomes

DIAGRAM:

Diagram showing flow of steam through nozzle and diffuser

Schematics of a nozzle and a diffuser

The flow through nozzles and diffusers are often considered adiabatic, so that the rate of heat

Transfer is neglected; therefore the above expression reduces to

For adiabatic nozzles and diffusers. It can be clearly seen in 2nd

expression that an increase in

the speed of the flow is accompanied by a decrease in its enthalpy, as in the case of flow thr-

ough an adiabatic nozzle. And, a decrease in the speed of the flow is accompanied by an incr-

ease in its enthalpy, as in the case of flow through an adiabatic diffuser.

NOZZLES & DIFFUSERS EFFICIENCY:

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In ideal case, flow through nozzle and diffuser is isentropic. But in actual case, friction exists and

affects in following ways:

1. Reduces the enthalpy drop2. Reduces the final velocity of steam3.

Increases the final dryness fraction4. Increases specific volume of the fluid.

5. Decreases the mass flow rateEquation for efficiency for nozzle and diffusers:

= (h1h

2a) / (h

1h

2s) = (C

2a

2

- C1

2

) / ( C2s

2

- C1

2

)

EFFICIENCY FACTOR:

The efficiency of nozzle and diffusers depends on the following factors:

1. Material from which they are made up of2. Smoothness of surface3. Size and Shape4. Angle of nozzle divergence and diffuser convergence5. Nature of fluid flowing and its State6. Fluid Velocity

APPLICATIONS OF DIFFUSERS AND NOZZLES:

1. They are ideal for firefighting applications of all kinds and countless industrial uses.2. They are used to maintain required flow rate and pressure3. They are widely use in rockets and jet fighter4. Nozzles for feeding hot blast into a blast furnace or forge are called TUYERS5. A gas jet, fluid jet, or hydro jet is a nozzle intended to eject gas or fluid in a coherent

stream into a surrounding medium. Gas jets are commonly found in gas stoves or ovens.6. Spray nozzles are the most common type of nozzle, used for surface coating, washing,

humidification, chemical reactions, combustion and various other uses

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