Fluid flow :
Fluid flow Prepared by: Mr. Jitendra L. Patel Fluid flow :
Fluid flow Fluids (liquids and gases) are a form of matter that cannot achieve equilibrium under an applied shear stress but deform continuously, or flow, as long as shear stress is applied.
The fluid flow means the movement of materials through certain bounded regions (pipe).
The study of fluid flow can be divided in to :
Fluid Static : it deals with fluid at rest in equilibrium.
Fluid dynamic : it deals with fluid in motion. Fluid at rest-Hydrostatics :
Fluid at rest-Hydrostatics The study of fluids at rest is based on two principles:
1. Pressure intensity at a point, expressed as force per unit area, is the same in all directions.
2. Pressure is the same at all points in a given horizontal line in a continuous fluid.
The pressure, P, varies with depth, h, in a manner expressed by the hydrostatic equation: dP = ρg dh
where ρ is the density of the fluid and g is the gravitational constant. Since water and most other liquids can be regarded as incompressible, the density is independent of the pressure, and integration between the limits P1 and P2, h1 and h2, gives P1 - P2 = ρg (h1 - h2) PROPERTIES OF FLUIDS :
PROPERTIES OF FLUIDS 1.Viscosity. Viscosity is a property that characterizes the flow behavior of a fluid, reflecting the resistance to the development of velocity gradients within the fluid. A fluid is contained between two parallel planes each of area A m2 and distance h m apart. The upper plane is subjected to a shear force of F N and acquires a velocity of u m/sec relative to the lower plane. The shear stress, t, is F/A, N /m2. The velocity gradient or rate of shear is given by u/h or, more generally, by the differential coefficient du/dy, where y is a distance measured in a direction perpendicular to the direction of shear.. For gases, simple liquids, true solutions, and dilute disperse systems, the rate of shear is proportional to the shear stress. 2.Compressibility. :
2.Compressibility. Compressibility is the measure of the change in volume a substance undergoes when a pressure is exerted on the substance.
Liquids are generally considered to be incompressible. For instance, a pressure of 16,400 psi will cause a given volume of water to decrease by only 5% from its volume at atmospheric pressure.
Gases on the other hand, are very compressible. The volume of a gas can be readily changed by exerting an external pressure on the gas 3.Surface Tension. :
3.Surface Tension. Surface tension, a property confined to a free surface and, therefore, not applicable to gases, is derived from unbalanced intermolecular forces near the surface of a liquid.
This may be expressed as the work necessary to increase the surface by unit area. Although not normally important, it can become so if the free surface is present in a passage of small diameter orifice of tube. Type of pressure :
Type of pressure 1. Fluid Head : if a vertical tube, open to the atmosphere at one end, is attached to pipe containing a fluid under any pressure greater than atmospheric, the fluid will rise in the tube. The fluid will continue to rise until its weight in the tube produce enough pressure at the bottom to balance the diff between the pressure in the pipe and the atmospheric pressure. P2 > P1, P2 – P1 = ΔP = h.ρ1.
This height of fluid (h) is termed as fluid head. Slide 8:
The actual pressure in the pipe obtained by multiplying the fluid head (h) by the fluid density and adding this value to atmospheric pressure
2. STATIC PRESSURE:
If the fluid is flowing in the pipe. The pressure exerted on a plane parallel to the direction of flow of moving fluid is called the static pressure.
It is measured at the inner surface of the pipe wall where the velocity is negligible, and it is called as the “pressure”. Slide 9:
3. IMPACT PRESSURE : If the fluid is flowing in the pipe. The pressure exerted on a plane perpendicular to the direction of flow of moving fluid is called the impact pressure.
4.VELOCITY PRESSURE : The diff between the impact pressure and the static pressure when both are measured at the same point is known as the velocity pressure.
For a stationary fluid, the pressure is same in all the direction therefore static pressure = impact pressure and velocity pressure is zero Measurement of pressure :
Measurement of pressure Manometer is devices to measure differential pressure ΔP.
3 type of manometers
Simple
Differential
Inclined Simple Manometer :
Simple Manometer Most commonly used
Made up of glass
U-tube filled with a liq. A (Mercury) having a density ρA.
Above liq. A the arms are filled with liq.B. (water) having density ρB.
The liq A and B are immiscible.
Two diff pressure P1 and P2 are applied on two arms.
Let at point 1 pressure P1 and at point 5 the pressure is P2. P1>P2. Simple Manometer :
Simple Manometer Pressure at point 1= P1
At point 2 = P1+ ρB (m+R) (g/gc)
“ “ 3 = P1+ ρB (m+R) (g/gc)
“ “ 3 = P2 + ρBm (g/gc) + ρAR(g/gc)
“ “ 4 = P1+ ρB (m+R) (g/gc)- RρA (g/gc)
“ “ 4 = P2 + ρBm (g/gc)
“ “ 5 = P1+ CB (m+R) (g/gc) – RρA (g/gc)- mρB (g/gc).
“ “ 5 = P2
P1-P2 = ∆P = R (ρA – ρB) (g/gc). Simple Manometer :
Simple Manometer If the pressure diff are large use liq. A having high density (mercury). If the pressure diff. are small use lighter liq. (Carbon tetrachloride).
Applications:
Consumption of gas can be measured
Manometers in conjugation with flow meters for measurement of flow of fluids
Pitot tube measures the velocity head using a manometer U – tube Manometer :
U – tube Manometer Inclined Manometer :
Inclined Manometer It is used to measure a small diff in pressure.
One arm of manometer is inclined in such a manner that for a small value of reading R the meniscus must move a considerable distance (Ri) along the inclined tube.
Ri = R/ sine α
By making α small we can increase the reading Ri Inclined Manometer :
Inclined Manometer As (ρC – ρA) smaller the larger will be the reading R. for a given value of pressure diff.
It is used to measure minute gas pressure diff and for calibration of low range of gauges.
They are free from errors due to capillarity and require no calibration. Inclined Manometer :
Inclined Manometer Differential Manometer :
Differential Manometer It is also known as two fluid U tube manometer.
It contains two immiscible liq A and C having nearly same density.
The u tube consist of enlarged chamber on both side.
The meniscus of the liq in the enlarged chambers does not change with change in reading R.
The changes in pressure in Passing through the series of points 1 to 7 are as follows Differential Manometer :
Differential Manometer 1= P1
2= P1 +a .ρB . g/gc.
3= P1 +a .ρB . g/gc + b. ρA.g/gc.
4= P1 +a .ρB . g/gc + b. ρA.g/gc.
5= P1 +a .ρB . g/gc + b. ρA.g/gc. – R . ρC. g/gc.
6= P1 +a .ρB . g/gc + b. ρA.g/gc. – R . ρC. g/gc.- d ρA.g/gc.
7= P1 +a .ρB . g/gc + b. ρA.g/gc. – R . ρC. g/gc.- d ρA.g/gc.- a .ρB . g/gc .
∆P = P1-P2 = R (ρC – ρA) . g/gc. Fluid is in Motion :
Fluid is in Motion Mechanism of fluid flow when fluids move through a closed channel of any cross section, either of two type of flow occur. :
Mechanism of fluid flow when fluids move through a closed channel of any cross section, either of two type of flow occur. Steady or Unsteady Fluid Flow :
Steady or Unsteady Fluid Flow In steady flow the velocity of the fluid particles at any point is constant as time passes.
Unsteady flow exists whenever the velocity at a point in the fluid changes as time passes. Turbulent Flow :
Turbulent Flow Turbulent flow is an extreme kind of unsteady flow and occurs when there are sharp obstacles or bends in the path of a fast-moving fluid.
In turbulent flow, the velocity at a point changes erratically from moment to moment, both in magnitude and direction. Turbulent Flow :
Turbulent Flow Turbulent flow is characterized by the irregular movement of particles of the fluid.
There is no definite frequency as there is in wave motion.
The particles travel in irregular paths with no observable pattern and no definite layers.
The flow becomes irregular
exceeds a certain velocity
any condition that causes abrupt changes in velocity
Eddy currents are a characteristic of turbulent flow Streamline Flow :
Streamline Flow When the flow is steady, streamlines are often used to represent the trajectories of the fluid particles.
A streamline is a line drawn in the fluid such that a tangent to the streamline at any point is parallel to the fluid velocity at that point.
Steady flow is often called streamline flow. Streamline Flow :
Streamline Flow Laminar flow= streamline =viscous flow.
layers of water flowing over one another at different speeds with virtually no mixing between layers,
fluid particles move in definite and observable paths or streamlines, and
the flow is characteristic of viscous (thick) fluid or is one in which viscosity of the fluid plays a significant part. Streamline flow :
Streamline flow different streamlines cannot cross each other
the streamline at any point coincides with the direction of fluid velocity at that point STREAMLINE FLOW :
STREAMLINE FLOW In the steady flow of a liquid, a colored dye reveals the streamlines.
A smoke streamer reveals a streamline pattern for the air flowing around this pursuit cyclist, as he tests his bike for wind resistance in a wind tunnel. Critical region :
Critical region It is the region when the value of Reynolds no. is 2100 to 4000.
Reynolds no < 2100, Streamline Flow
Reynolds no > 4000, Turbulent Flow.
In the region of 2100 to 4000 the flow may be Viscous or Turbulent.
Critical Velocity is defined as average velocity of any fluid at which viscous flow changes into Turbulent. Characteristics of an Ideal Fluid :
Characteristics of an Ideal Fluid The fluid is non viscous
– There is no internal friction between adjacent layers
The fluid is incompressible
– Its density is constant
The fluid is steady
–Its velocity, density and pressure do not change in time
The fluid moves without turbulence
– No eddy currents are present Diif. between Streamline & Turbulent :
Diif. between Streamline & Turbulent Laminar Flow
Layers of water flow over one another at different speeds with virtually no mixing between layers.
The flow velocity profile for laminar flow in circular pipes is parabolic in shape, with a maximum flow in the center of the pipe and a minimum flow at the pipe walls.
The average flow velocity is approximately one half of the maximum velocity.
Reynolds no < 2100 Turbulent Flow
The flow is characterized by the irregular movement of particles of the fluid.
The flow velocity profile for turbulent flow is fairly flat across the center section of a pipe and drops rapidly extremely close to the walls.
The average flow velocity is approximately equal to the velocity at the center of the pipe.
Reynolds no > 4000, Reynold’s Experiment :
Reynold’s Experiment The existence of streamline flow and transition to turbulent flow may be demonstrated by Reynold’s experiment.
A glass tube is connected to constant over head water tank.
The rate of flow of water controlled by the coke.
Dye solution is fed from a hypodermic needle forming a fine jet on the pipe axis.
At low flow rates a continuous, straight and steady line of dye may be caused to flow down the whole length of the centre of the pipe. Reynold’s Experiment :
Reynold’s Experiment The color stream are seen as parallel lines.
The flow of water is considered to be streamline.
When the velocity of water increased, the colored line begins to waver and the entire mass of water gets uniformly colored.
Such type of flow is known as a turbulent flow.
On reducing the flow of water again this turbulence is damped out and the continuous dye line reestablished itself. Reynolds Number :
Reynolds Number The flow regime (either laminar or turbulent) is determined by evaluating the Reynolds number of the flow
The Reynolds number, based on studies of Osborn Reynolds, is a dimensionless number comprised of the physical characteristics of the flow.
NR = r v D / μ gc Reynolds Number :
Reynolds Number where:
NR = Reynolds number (unit less)
v = average velocity (ft/sec)
D = diameter of pipe (ft)
μ = absolute viscosity of fluid (lbf-sec/ft2)
r = fluid mass density (lbm/ft3)
gc = gravitational constant (32.2 ft-lbm/lbf-sec2)
For practical purposes, if the Reynolds number is less than 2100, the flow is laminar. If it is greater than 4000, the flow is turbulent. Flows with Reynolds numbers between 2100 and 4000 are sometimes referred to as transitional flows. Most fluid systems in nuclear facilities operate with turbulent flow. THE SIGNIFICANCE OF REYNOLDS’ No, RE :
THE SIGNIFICANCE OF REYNOLDS’ No, RE if the Reynolds number is less than 2100, the flow is laminar. If it is greater than 4000, the flow is turbulent. Flows with Reynolds numbers between 2100 and 4000 are sometimes referred to as transitional flows.
The fluid in the middle of the pipe will be moving faster than the fluid next to the walls.
At constant velocity fluid can change from laminar to turbulent if pipe diameters increased. Decrease in viscosity due to temperature change may also show similar effects. Velocity distribution :
Velocity distribution The velocity increases from zero at wall to max at the axis of the tube.
For Streamline flow
The graph of velocity Vs Distance from the wall is parabola, sharply pointed at middle.
Ave. V = ½ Vmax
For turbulent flow
The graph is some what flattened in the middle and
Ave. V =0.8 Vmax Velocity profile
for turbulent flow Velocity profile
if flow were laminar
everywhere Velocity distribution :
Velocity distribution Viscosity :
Viscosity Viscosity is force required to cause two parallel liquid planes in the fluid, one cm. apart and having unit area to slide past one another with a relative viscosity 1cm/sec. Ab. Viscosity is difficult to measure, hence relative viscosity is measured with reference to water.
Kinematic Viscosity = Absolute viscosity of fluid/ density of water Type of Fluids as per Viscosity behavior :
Type of Fluids as per Viscosity behavior Two type
1. Newtonian Flow
2. Non-Newtonian Flow
A) Plastic Flow
B) Pseudo Plastic
C) Dilatant
D) Thixotropic flow Type of Fluids as per Viscosity behavior :
Type of Fluids as per Viscosity behavior 1. Newtonian Flow : :
1. Newtonian Flow : When the shear stress is proportional to the rate of shear and if we plot shear stress vs. rate of shear, a straight line passing through origin will be obtained for a Newtonian liq. And tan Ф gives the viscosity of the liq. E.g. Water, Benzene, Alcohol, Glycerin, Chloroform. ή = tan Ф Shear stress, T Rate of Shear v 2. Non-Newtonian Flow :
2. Non-Newtonian Flow Rheology properties of heterogeneous dispersion such as emulsion, suspension and semisolid are more complex and do not obey Newton’s equation of flow
(ή=F/A / dv/dx ) and fail to show the proportionality. A) Plastic Flow :
A) Plastic Flow The curve does not pass through the origin.
The substance fails to flow when less amt of stress is applied further increase in stress lead to non-linear increase in shear rates which later get linearised.
The linear portion when extrapolated the intercepts the x-axis at a point called yield value. This plastic flow behave like a Newtonian flow above the yield value.
E.g. concentrated flocculated suspension, Butter, Ointment.
Material that show plastic flow are called as a Bingham. Shear stress, T Rate of Shear v B) Pseudo plastic Flow :
B) Pseudo plastic Flow The curve begins at the origin.
As the shear stress increases, the shear rate also increases but non-linearly.
E.g. Polymer
Tragacanth, M.C, Na. CMC, Na. Alginate, Rubber
Up on withdrawal of shear stress, System revert to its original state and hence viscosity increases. It is called as sol — gel — sol phenomenon. Rate of Shear v Shear stress, T Shear stress, T Shear rate thinning C)Dilatant :
C)Dilatant The rheogram exhibiting dilatant flow is shown in figure. It exhibit shear thickening.
The system gets thickened upon increasing rate of shearing.
Up on shearing volume expanded so called dilatant.
When the stress is removed, the system returns to its initial state of fluidity.
E.g. suspension of starch in water, Kaolin (12%) in water, ZnO (30%) in water. Rate of Shear v Shear stress, T D) Thixotropic flow :
D) Thixotropic flow Newtonian
When rate of shear is reduced, the down curve is identical and super imposable on the up curve.
Non Newtonian ( Shear Thinning)
When agitated and kept aside, it returns to its original fluidity, but it takes longer time to recover. This behavior is known as Thixotropic.
Gel to Sol to Gel
E.g. gels of Aluminum Hydroxide
gels of Magnesium Hydroxide
Bentonite Suspension Rate of Shear v Rate of Shear v Shear stress, T Shear stress, T Newtonian Pseudo
plastic plastic Non Newtonian Bernoulli’s Theorem :
Bernoulli’s Theorem By considering diff type of energy, which a fluid may possess, and
by equating total energy at all points in the flow path,
making allowance for work done on the fluid and work done by the fluid on surrounding Bernoulli’s equation may be obtained.
It is known as the eq. for steady flow
Three principles can be applied to the system.
Conservation of matter
“ “ energy
Rules of fluid friction. Slide 49:
Statement : In a steady state ideal flow of an incompressible fluid, the total energy per unit mass, at any point of the fluid is constant.
The total energy of a fluid in motion is made up of number of components.
Assuming unit mass of fluid and neglect changes in magnetic and electrical energy and considering no accumulation of energy Energy of fluid :
Energy of fluid Internal energy (E)
Pressure energy (P.V)
Mechanical work (Wo)
Potential Energy (PE)
Kinetic energy (KE)
Friction (F) Internal energy (E) :
Internal energy (E) It is due to physical state of fluid.
Taken as zero at some reference state. E.g. Ab. 0 tepm.at atm pressure.
As it depends on temp and state of matter, change in I.E is equal to the diff between the net amt of heat (Q) added and net amt of work done (ws) by the system on its surrounding.
ΔE = ΔQ – Δ Ws
ΔQ/T = ΔS (change in Entropy)
ΔQ = T ΔS
ΔWs =P.dv it is work done resulting from change in vol.
ΔE = T ΔS – P.dv
If there is no volume change
ΔE = ΔQ = Cv. ΔT where cv = Sp heat at constant vol. Pressure energy :
Pressure energy It represents the work which must be done in order to introduce the fluid at point 1 and expressed as p1v1, where p1 is static pressure and v1 is Sp vol of fluid.
Fluid leaving the system does an amt of work on the surrounding p2v2.
Net work done on the fluid system
= p1v1 – p2v2. Mechanical work (wo) :
Mechanical work (wo) It is the work imparted to the system from outside mechanical sources such as a pump or turbine.
Net external work done on system is equal to
W = Wo + (p1v1-p2v2) – ft Lb. force/Lb.Mass
Mechanical Net pressure energy Potential energy :
Potential energy It is due to its position relative to a reference plane.
Let, Z represents the vertical diff from the reference plane.
P.E = Z. (g/gc)- ft Lb. force/Lb.Mass Kinetic energy (K.E) :
Kinetic energy (K.E) It is due to its motion
K.E = V2 /2g - ft Lb. force/Lb.Mass Friction (F) :
Friction (F) It is always between the fluid and pipe wall.
Friction is energy loss.
Considering a fluid flowing at a steady rate with no accumulation or depletion of energy or material, the fluid entering and leaving the system contains 3 fundamental forms of energy. (P.E, K.E, E).
External work done (w) and heat (Q) only at entering and considering frictional energy loss is zero.
Designate entrance condition by 1 and exit by 2 Slide 57:
Z1. g/gc +V12/2gc +E1 +Q +W = Z2. g/gc +V22/2gc +E2
W = Wo + (p1v1-p2v2)
V is the point velocity which is varies over cross sectional area of pipe.
If the flow is turbulent, velocity distribution is uniform across the pipe and point velocity becomes average linear velocity.
If the flow is stream line, velocity distribution is parabolic so K. E = V2/2gc = V2/2αgc
Where α =1 if the flow is turbulent
= 0.5 if the flow is streamline Total energy balance :
Total energy balance Z1. g/gc +V12/2 α1gc +E1 +Q +Wo + p1v1-p2v2 = Z2. g/gc +V22/2 α 2gc +E2
Enthalpy = I.E + pressure work
At entry = E1 + p1v1 = H1
At exit = E2 + p2v2 = H2
For a perfect gases ΔH
=mean heat capacity (cp) . ΔT –at constant p
Enthalpy change H2-H1 = E2-E1 + (p2v2-p1v1)
Δ E = mean heat capacity (cv) . ΔT –at constant V Total mechanical energy balance :
Total mechanical energy balance Total energy balance is described by
Z1. g/gc +V12/2 α1gc +E1 +Q +Wo + p1v1-p2v2 = Z2. g/gc +V22/2 α 2gc +E2 can be written in a form involving only mechanical energies.
a fluid flowing normally not undergo a chemical change, making this assumption a mechanical energy balance can be set-up.
Mechanical energy comprises of P.E., K.E., compression energy, any external mechanical work done on the fluid by pump (Wo) and pressure volume work. Total mechanical energy balance :
Total mechanical energy balance Non of the system is frictionless, so consider the loss of mechanical energy in friction.
Energy input at entry = energy output at exit
Input – output = ∑f (friction losses)
Input = output + ∑f
Z1. g/gc +V12/2 α1gc +1∫2p.dv +Wo + p1v1 = Z2. g/gc +V22/2 α 2gc +p2v2 +∑f
Compression ( work of expansion and contraction between point 1 and 2 ) energy is only applicable to compressible fluids. For non-compressible fluids this term become zero. Total mechanical energy balance :
Total mechanical energy balance The compression energy is due to volume change due to change in temp and pressure.
Z1. g/gc +V12/2 α1gc + Wo + p1v1 = Z2. g/gc +V22/2 α 2gc +p2v2 +
∑f = Z1. g/gc - Z2. g/gc + V12/2 α1gc - V22/2 α 2gc + p1v1 – p2v2 + Wo
For water v1=v2=v = specific volume Energy losses :
Energy losses Fluids experience loss of energy in several ways, such as
Friction losses
End effects
Enlargement losses
Contraction losses
Losses in fittings Friction losses :
Friction losses It causes a loss in pressure.
In general pressure drop is
Directly proportional to the velocity of fluid
Directly proportional to the density of fluids
Directly proportional to the length of pipe
Inversely proportional to the diameter of pipe
It depends on conditions or flow and physical properties of the fluid. Slide 64:
For stream line flow
Hagen Poiseuille equation is used to calculate pressure drop due to friction in viscous flow
Δ P = 32. L.V.ή /gc.D2.ρ
Where Δ P = pressure drop due to friction
L = length of pipe
V = Velocity of flowing fluid
ή = Viscosity of fluid
ρ = density of fluid
D = diameter of pipe
Limitation : only for streamline flow, only for circular pipe of uniform diameter. ρ Slide 65:
For turbulent flow :
Fanning equation is used to calculate pressure drop due to friction in viscous flow or turbulent flow.
ΔPf = 2 f V2 L / gc.D
ΔPf = pressure drop due to friction
f = friction factor
V = Velocity of fluid
L = length of pipe
D = inside diameter of pipe
For stream line flow f = 16 ή / D V ρ Variables affecting friction losses :
Variables affecting friction losses Velocity of flow
Density of fluid
Viscosity of fluid
Inside diameter of pipe
Length of pipe
Roughness of pipe €
The friction factor is based on exp. Data and it is a function of Reynolds's no and relative roughness of the pipe (€/D). Slide 67:
The relative roughness of pipe is d Fined as dimensionless ratio of the equivalent pipe roughness to the pipe diameter.
Relative roughness = equivalent pipe roughness / pipe diameter
Limitation of Fanning and Poiseille’s law:
Limited to point condition
Limited to steady flow of fluid
Limited to long straight pipes
Velocity, density and viscosity of the fluid should remain constant
For non compressible fluid Friction losses due to sudden Enlargement :
Friction losses due to sudden Enlargement The loss of mechanical energy as friction due to the sudden enlargement of the cross sectional area of the duct can be calculated by the eqn.
Fe = (V1-V2)2 / 2 α.gc
Where V1 = AV. Velocity at smaller diameter
V2 = Av. Velocity at larger diameter
α = 1 for turbulent velocity, 0.5 for stream line. Friction losses due to sudden contraction :
Friction losses due to sudden contraction The loss of mechanical energy as friction due to the sudden contraction of the cross sectional area of the duct can be calculated by the eqn.
Fc = Kc. V22 / 2 α.gc
Where v2 = down stream velocity
Kc = constant, depends on the ratio of the cross sectional areas involved. If sudden contraction occur the ratio of S2/S1 is zero and Kc is 0.5 Friction losses due to pipe fittings :
Friction losses due to pipe fittings When fittings are introduced in to a straight pipe, they cause disturbance in pipe.
Loss in fittings is due to change in direction.
We can consider losses by assigning a fictitious length (Le) to various fittings.
This length is equivalent to the length of pipe which would cause the same frictional loss as that caused by a fitting it self.
The actual length Le can be substituted for L in eqn to give the total frictional loss due to pipe plus fitting. Friction losses due to pipe fittings :
Friction losses due to pipe fittings Values of Le for various pipe fittings
Fittings Le / D
90 o elbow 32
45 o elbow 15
Gate valve 07
Globe valve 300
For 2 “, 45 o elbow
Le = 15 .2 = 32 inch End effect :
End effect Bcz of the friction caused by contraction and expansion, it is very imp to indicate the points between which the energy balance is to be made.
E.g. for a water pumped to overhead tank, if the end point is just outside the exit from the pipe in tank. Here, The velocity of water is zero.
There is a frictional effect due to sudden enlargement.
If the end point is just inside the pipe exit , there would be no enlargement effect and at that point the water have finite velocity Orifice meter (Orifice Plate) :
Orifice meter (Orifice Plate) Principle : it works on the principle of the diff pressure drop created across orifice plate in flow line.
Orifice plate is circular plate with a central hole, smaller in diameter than up stream and down stream in which it is mounted.
When a fluid stream is suddenly allowed to pass through the narrow constriction, the velocity of the fluid at the orifice increases compared to the velocity of the fluid in the upstream at the cost of pressure drop.
Bernoulli's theorem correlates the increases in velocity with decrease in pressure head between two points. Orifice meter :
Orifice meter Construction: orifice meter consist a pipe and orifice plate.
Orifice plate consist an orifice with a sharp edged aperture in the centre of the orifice plate.
Three type of orifice plates
Concentric : here, the opening through which the fluid flows is round and concentric to the centre line of the pipe. Its edge is at 90 o to the up stream flat of the orifice.
Ecentric :
Segmental : Why Pipe fittings ? :
Why Pipe fittings ? To join two pipe
To change the direction of flow
To change diameter of pipe
To connect branch line
To make branch line
To stop or close the end of line Parts used for pipe fittings :
Parts used for pipe fittings Coupling
Reducers
Elbows
Tees
Crosses
Y- Bends
Regular Bends
Nipple
Plugs or Caps what is Friction Losses? :
what is Friction Losses? When fluid passes through a pipe, a loss take place in its velocity it is known as Friction loss.
It leads to loss of energy Factors responsible for friction losses :
Factors responsible for friction losses Material of pipe construction
Age of pipe
Methods of enlargement and contraction in pipelines
Losses due to fittings
Direction of flow Valves :
Valves Valves are used to regulate the flow of pipe and to isolate piping or equipment for maintenance, without interrupting other connected units.
Valves design should meet the pressure Temp change and Strain from connected piping.
Valves bodies may be of cast, iron, steel, Bronze, Brass, P.V.C or Stainless Steel.
On steam boiler mounting brass or bronze valves are preferred.
Iron will be subjected to rust formation
In some area of Pharma plant valves of stainless steel , neoprene and Teflon material are used. Globe valve :
Globe valve These valve have a globular body with horizontal internal partition, having a circular passage way in which a ring called as a seat is inserted.
With variation in seat and disk diff models available.
They are used in pipe sizes not larger than 50 mm.
In most design the discs rotate freely on the vertical stem.
Angle valves are similar to globe valves. Gate valve :
Gate valve Two types
1) Rising stem gate valve
The gates are edge shaped.
The stem rises or lowers along with the gate in the rising type.
2) Non- Rising stem gate valve
Here, the thread of the valve stem engages the gate and the gate rises or falls with out rising stem.
Gate valves are preferred for larger sizes.
They are used to minimize the differential pressure in the open position and to stop the flow of fluid in Butterfly Valve :
Butterfly Valve They occupy less space, light weight, compact with easy quarter turn operation.
They are relatively tight sealing, more reliable and long life operation.
These valves can handle gases and liquids, including slurries. Ball valve :
Ball valve They offer quarter turn operation, longer life period and low maintenance efforts.
Used in small sizes extensively in formulation plants made out of ss 3o4 and ss 316 grades and in fermentation plants Diaphram valve :
Diaphram valve It is made up of natural rubber or synthetic rubber.
This goes up and down on operating the stem and allows the liq. To flow.
They are linear motion valve.
They are excellent for fluid congaing suspended solids.
Most common problem is frequent rupturing.
For sterile air and sterile process lines in fermentation industry some form of diaphram valves are used as it is easily sterilizable. Check valves :
Check valves They are used when unidirectional flow is desired and to prevent reversal of flow.
They are automatically operated and allow the in only one direction.
Diff type
Swing check
Ball check
Tilting Disk check Slide 89:
Swing check valves
Used to prevent the reversal of flow.
Normally designed to use in horizontal line.
Lift check valves
3 type
Vertical lift check
Used in vertical lines where the flow is normally upward
Globe check valves used in horizontal lines
Angular lift check valves used where a vertical line with upward flow turns horizontal.
Tilting Disk check valves used in lines in which the flow is vertically upward. Cocks :
Cocks Cocks are simplest method of regulating the flow of fluids.
They consist of a body casting, in which fits a conical plug with a passage through it.
Liq. Passes through this passage or opening.
They are used in small pipe for compressed air.
They are used when either complete opening or complete closing is desirable. Slide 92:
In positive displacement pumps, the fluid is drawn in to the chamber and the definite quantity of fluid is forced out through the outlet with a pressure for each stroke.
Centrifugal pump deliver the volume of fluid depending up on the discharge pressure.
The reciprocating pump has an enlargement which moves to and fro in a stationary cylinder. Reciprocating pump :
Reciprocating pump Diaphram pump :
Diaphram pump Rotary pump :
Rotary pump Gear pump
Lobe pump
Vane pump Gear pump :
Gear pump Van pump :
Van pump