FLUID MACHINE - Universiti Teknologi Malaysiasyahruls/3-teaching/2-fluid-II/fluid-II-enote/31... ·...
Transcript of FLUID MACHINE - Universiti Teknologi Malaysiasyahruls/3-teaching/2-fluid-II/fluid-II-enote/31... ·...
FLUID MACHINES
FLUID MACHINE A fluid machine is a device either for converting the energy held by a fluid into mechanical energy or vice versa. Fluid machine may be divided into two groups;
1. Positive displacement group * Reciprocating pump, etc
Part one : Introduction of Pump 1
FLUID MACHINES
2. Rotodynamic group * Pelton wheel, etc
Depend on energy movement; fluid machine could be divided into three categories
1. Pump 2. Turbine 3. Jack
Part one : Introduction of Pump 2
FLUID MACHINES
PUMP INTRODUCTION Rotodynamic pump is essentially a turbine ‘in reverse’; which mean that mechanical energy is transferred from the rotor to the fluid. It is classified according to the direction of the fluid path through them.
1. Radial / centrifugal flow
Part one : Introduction of Pump 3
FLUID MACHINES
2. Axial flow 3. Mixed-flow type
In general usage, the word ‘PUMP’ is applied to a machine dealing with a liquid. A machine in which the working fluid is a gas is more usually termed as fan, blower or compressor.
Part one : Introduction of Pump 4
FLUID MACHINES
HEAD OF PUMP
Part one : Introduction of Pump 5
FLUID MACHINES
CENTRIFUGAL PUMP
This type of pumps is the converse of the
radial-flow (Francis) turbine. Whereas the flow
in the turbine in inwards, the flow in the pumps
is outwards.
The rotor (impeller) rotates inside a spiral
casing. The inlet pipe is axial, and fluid enters
the ‘eye’, that is the center of the impeller with
little, if any, whirl component of velocity.
Part two : Centrifugal Pump 1
FLUID MACHINES
From there it flows outwards in the direction
of the blades, and having received energy from
the impeller, is discharged with increased
pressure and velocity into the casing.
It then has a considerable tangential (whirl)
component of velocity which is normally much
greater than that required in the discharge pipe.
The kinetic energy of the fluid leaving the
impeller is largely dissipated in shock losses
unless arrangements are made to reduce the
velocity gradually.
Part two : Centrifugal Pump 2
FLUID MACHINES
Velocity triangle
Inlet ;
Tangential velocity of impeller
11 rU ω=
Absolute velocity vector at 1α to tangent
1V
Relative velocity to impeller blades
111 UVVr −=
Components velocity of 1V
: whirl velocity 1wV
: radial flow velocity 1fV
Inlet blade angle
1β
Part two : Centrifugal Pump 3
FLUID MACHINES
Outlet ;
Tangential velocity of impeller
22 rU ω=
Absolute velocity vector at 2α to tangent
2V
Relative velocity to impeller blades
222 UVVr −=
Components velocity of 2V
: whirl velocity 2wV
: radial flow velocity 2fV
Inlet blade angle
2β
Part two : Centrifugal Pump 4
FLUID MACHINES
Velocity triangle for centrifugal pump:
Part two : Centrifugal Pump 5
FLUID MACHINES
Calculation is done base on “Euler’s Turbine
Equation”. The one-dimensional theory
simplifies the problem very considerably by
making the following assumptions:
1. The blades are infinitely thin and the
pressure difference across them is replaced
by imaginary body forces acting on the fluid
and producing torque.
2. The number of blades in infinitely large.
Thus, 0=∂∂θv
3. No variation of velocity in the meridional
plane (z-axis). Thus,
In reality, ),,( zrfv θ=
Part two : Centrifugal Pump 6
FLUID MACHINES
Torque = Rate of change of angular momentum
Angular momentum = (Mass) x (Tangential
velocity) x (Radius)
Specific energy, mPgEY&
== (unit : J/kg)
Euler’s Head ;
( )11221 uvuvg
H wwE ⋅−⋅= (unit : m)
Part two : Centrifugal Pump 7
FLUID MACHINES
Relation of u2, vw2 and HE
( )111222 coscos1 αα uvuvg
HE −=
o901 =α 01 =wv and fvv =1
guvH w
E22 ⋅=
Part two : Centrifugal Pump 8
FLUID MACHINES
relation of β2 and HE
from ;
221
22
tan1β
⋅+=⋅
= QCCg
uvH wE
Euler’s head is depends on the value of 2β
Part two : Centrifugal Pump 9
FLUID MACHINES
velocity triangle and the position of blades
Blade condition with has the highest Euler’s head value.
o902 =β
Part two : Centrifugal Pump 10
FLUID MACHINES
Relation of 2β and with Bernoulli equation.
EH
Euler’s head :
gVHHHH w
PVPE 2
22+=+=
Reaction degree of pump =
⎥⎦
⎤⎢⎣
⎡⋅
+=+=22
22
2
tan1
21
21
βUV
gHV
HH f
E
w
P
E
Part two : Centrifugal Pump 11
FLUID MACHINES
LOSSES IN PUMP
3 major types of losses
1. Losses of hydraulic power
a. Circulatory flow
b. Friction
c. Shocking in impeller
2. Loss of volume
3. Loss of mechanical energy
Part three : Losses and Efficiency of Pump 1
FLUID MACHINES
a. Circulatory Flow
SF : Slip Factor
Eideal
actual
w
w
HHH
VVSF
==
′=
2
2
Part three : Losses and Efficiency of Pump 2
FLUID MACHINES
b. Friction losses
2
1 Qkhf ⋅=
: Friction losses fh
: Constant 1k
: Flow rate Q
c. Shock losses
( )22 osh QQkh −=
: Shock losses 2k
: Designed flow rate Q
: Actual flow rate oQ
Part three : Losses and Efficiency of Pump 3
FLUID MACHINES
EFFICIENCY OF PUMP
Overall Efficiency :
i
mo P
gQHρη =
Mechanical Efficiency : [ ]( )i
wwgmech P
UVUVQQg 11221)( −∆+
=ρ
η
Manometric Efficiency :
1122 UVUVgH
ww
mmano −
=η
Volumetric Efficiency :
QQQ
v ∆+=η
Part three : Losses and Efficiency of Pump 4
FLUID MACHINES
Part four : Reaction Turbine – Francis Turbine 6