NOZZLE

By: Group 8Amirah Binti Mat JamalAsmahani Binti BarjokNorain Binti JanainNurul Fatiha Binti Abd. HadiSiti NorFaridatul Aisyah ShuhaimiNOZZLEdevice designed to control the direction or characteristics of fluid (especially to increase velocity) as it exits (or enters) an enclosed chamber or pipe.It is generally a pipe or tube of varying diameter, that is used to direct or modify the flow of liquid or gas.

What is nozzle? it is frequently use to control the rate of flow, direction and/or the pressure of the steam that emerges from them.Funtions of nozzle Converging nozzleDiverging nozzleConverging-Diverging nozzle (de Laval nozzle)Types of nozzle accelerate fluids, but do not exceed the speed of sound in the fluid due to sonic choking at the narrowest point.CONVERGING NOZZLE

Consider the nozzle is attached to a reservoir with pressure Pr and temperature Tr. Since the reservoir is sufficiently large, thus the velocity of the nozzle inlet is negligible (Vr=0). Therefore, the flow through the nozzle is approximated as isentropic, the stagnation pressure (P0) and stagnation temperature (T0) is equal to the reservoir temperature (Tr) and pressure (Pr).

State 1: Pb= P0, there is flow and pressure is constant State 2 : Pb> P0, pressure along nozzle decreases State 3 : Pb= P*, flow at exit is sonic, creating maximum flow rate, called choked flow.State 4 and 5: Pb< P*, there is no change in flow or pressure distribution just as in situation 3.

Under steady flow conditions, mass flow rate is constant

Substituting T and P

Mass flow rate is a function of stagnation properties, flow area, and Ma

The maximum mass flow rate through a nozzle with a given throat area A* is fixed by theP0 and T0 and occurs at Ma = 1.

This principal is important for chemical processes, medical devices, flow meters, and anywhere the mass flux of a gas must be known and controlled.

Gas flows through the nozzle from a region of high pressure (usually referred to as the chamber) to one of low pressure (referred to as the ambient or tank). The chamber is usually big enough so that any flow velocities here are negligible. The pressure here is denoted by the symbolpc. Gas flows from the chamber into the converging portion of the nozzle, past the throat, through the diverging portion and then exhausts into the ambient as a jet. The pressure of the ambient is referred to as the 'back pressure' and given the symbolpb.

Converging-Diverging Nozzle

1. When P0 > Pb > Pc, the flow remains subsonic throughout the nozzle, and the mass flow is less than that for choked flow. The fluid velocity increases in the first (converging) section and reaches a maximum at the throat (but Ma Pb > PE , the fluid that achieved a sonic velocity at the throat continues accelerating to supersonic velocities in the diverging section as the pressure decreases. This acceleration comes to sudden stop, however, as a normal shock develops at a section between the throat and the exit plane, which causes a sudden drop in velocity to subsonic levels and a sudden increase in pressure. The fluid then continues to decelerate further in the remaining part of the converging-diverging nozzle. Flow through the shock is highly irreversible, and thus it cannot be approximated as isentropic. The normal shock moves downstream away from the throat as Pb is decreased and it approaches the nozzle exit plane as Pb approaches Pb. When Pb = PE , the normal shock forms at the exit plane of the nozzle. The flow is supersonic through the entire diverging section in this case, and it can be approximated as isentropic. However, the fluid velocity drops to subsonic levels just before leaving the nozzle as it crosses the normal shock.4. When PE > Pb > 0, the flow in the diverging section is supersonic, and the fluid expands to PF at the nozzle exit with no normal shock forming within the nozzle. Thus, the flow through the nozzle can be approximated as isentropic. When Pb = PF , no shocks occur within or outside the nozzle. When Pb < PF, irreversible mixing and expansion waves occur downstream of the exit plane of the nozzle. When Pb > PF, however, the pressure of the fluid increases from PF to Pb irreversibly in the wake of the nozzle exit, creating what are called oblique shocksWhen the flow accelerates (subsonic or supersonically) the pressure decreases. The pressure increases instantaneously across a shock.

Summary points:

steam and gas turbines, aircraft and spacecraft propulsion systems, and even industrial blasting nozzles and torch nozzlesAPPLICATION:

Aircraft and spacecraft propulsion

Industrial nozzle