Understanding Nozzles and Diffusers in Thermodynamics

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1. Abstract
This paper presents the meaning of diffusers and nozzles in details as used in thermodynamics.
Various application of nozzles such as water turbines, jet engines, steam turbines, flow
measurement and those of diffusers such as in axial compressors, centrifugal compressors, and
ramming of air are discussed in this paper.
2. Introduction
2.1. Background
In the year 1960, a bed load sampler was developed by the California District and these samples
were the pressure differential type and they consisted of the nozzle having a larger cross-
section opening at the rear of the nozzle than at the entrance. This enabled the acceleration of
the flow as it passes into the nozzle.
2.2. Objective
This research discusses the nozzles and the diffusers into detail with various types of nozzles
and diffusers. The calculations involving the fluid flow are also included in the paper and lastly
the various applications of nozzles and diffusers.
2.3. Scope
The scope of the research project entails the applications of diffusers for example in axial and
centrifugal compressors and also the applications of nozzles in various industrial application s
and other sectors which they are helpful.

3. Project Outline
A nozzle is a device intended to help in governing the characteristic or direction of a fluid flow
particularly for velocity increment as it move in an enclosed pipe or chamber. A nozzle is simply
a tube used in governing the flow shape, mass, velocity, path and stream pressure that emerges
from them. The nozzle has a changing area of the cross-section thus allowing it to be applied to
directly or modifying the fluid flow (Ahn, 2011, p. 432).
A fluid jet, is a nozzle envisioned to insert fluid or gas in a comprehensible stream into an
adjacent medium. The equipment such as the ovens, gas stoves and barbecues consist of the
gas jets and in the past, they were developed to be used in lightning before the electric light
came into use (Bain, 2011, p. 45). The carburetors make use of fluid jets such that attuned
orifices which are smooth are applied to assist in controlling the flow of fuel into an engine, and
in spas or Jacuzzis (Bejan, 2009, p. 548).
The tuyeres is a type of nozzle which is used in feeding the hot blast into a blast forge or
furnace. And in large rooms where it is not practical or possible to distribute the air via ceiling
diffusers then the jet air is preferred (Ahn, 2011, p. 432). The jet diffusers are those type of
diffusers which uses jet nozzles whereby deflection of air takes place on the upper direction to
stream air which is warm or downwards to supply cold air. This takes place as a result of the
difference in temperature between the room air and the air supplied (Bollinger, p. 78).

The nozzle aims at increasing the kinetic energy of the flowing medium at the expense of its
internal energy and pressure. The convergent and divergent are the best terms which can be
used in describing the nozzles. And convergent simply means lessening down from a wide
diameter to a smaller diameter in the flow direction while divergent involves expanding from a
smaller diameter to a larger one (Demirel, 2013, p. 219).
The subsonic fluids are accelerated by the by divergent nozzles but the fluid is slowed if the
flow is subsonic. The gases direction of escape is directly backward since thrust would not be
contributed to by the sideways component. This achieved by the shape of the divergent section
(Duncan, 2010, p. 65).
The needed energy from the combusting fuel which is supplemented to the initiated air allows
the jet exhaust to produce a net thrust. The passing of warm air through a high-speed nozzle, a
thrusting nozzle which immensely upsurges its kinetic energy. A thrust of a certain mass flow is
increased by an increase in drain velocity but paramount energy proficiency is achieved by
matching the drain velocity to the speed of air (El-Sayed, 2008, p. 185).
The use of CD nozzle enables the engines of supersonic jet aircraft to attain high exhaust speed
notwithstanding cost consequences and weight. The using of convergent-divergent nozzles with
large pressure and area ratio enables the rocket motors to maximize thrust and exhaust
velocity. The use of magnetic nozzles has also been recommended for some kinds of driving
force, for example, plasma flow is controlled by magnetic fields as a substitute of walls
prepared with solid substance (Flack, 2009, p. 129).

The nozzle also assists in increasing the velocity and decreases the pressure. And there is no
heat transfer in nozzle while considering it as insulated. The nozzle major application is to
create a jet of gas or steam of high velocity to create thrust for the driving force of jet engines
and rocket motors and t.c drive steam or gas turbine (Hall, 2013, p. 97).
Diffusers
A diffuser is a device used for reducing the velocity and increasing the static pressure of a fluid
passing through a system. The velocity of the fluid is slowed down by the diffusers as its static
pressure is increased (Hall, 2013, p. 675).
Pressure recovery is noticed when there is an increase in static pressure as it passes through a
duct. In disparity, a nozzle is always planned for increasing the discharge velocity and reducing
pressure while guiding the flow in a single specific route.
Bernoulli’s principle can be used in analyzing the duct containing fluids rolling at greater
velocities with Mach numbers in exceeding 0.3 normally require compressible flow dealings
(Demirel, 2013, p. 467). A diffuser known as subsonic is a duct that upsurges in size in the
direction of flow. A rise in static pressure, a decrease in velocity of the fluid is noticed when
there is an increase in the size of the duct. The changes in pressure and velocity is a caused by

Bernoulli’s principle and mass flow rate (Johnson, 2015, p. 142). The Mach number is merely
the ratio of the speed of an object to the speed of sound
The calculation of mass flow rate can be done by
M= p. V = p.v.A
Where
V is the volume flow rate
P is the mass density of the fluid
V is the flow velocity of the mass elements
A is the cross-sectional vector area
Supersonic diffusers are a type of duct whose size declines in the flow route. As the size duct
reduces, there is increment in the fluid density, pressure and temperature of the fluid as the
velocity decreases (Klapp, 2016, p. 318). These changes in temperature, density, velocity, and
pressure are caused by compressible flow. There are certain devices that should not place near
diffusers inlet for example extractors and dampers since they increase noise production and in
case of compiled performance of the diffuser, a duct straight section requires a diffuser.