Pipe Flow Fundamentals Rev 0
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Transcript of Pipe Flow Fundamentals Rev 0
PIPE FLOW FUNDAMENTALS COURSEPIPE FLOW FUNDAMENTALS COURSE
Gayungsari Timur 5 Blok MGH No. 9Gayungsari Timur 5 Blok MGH No. 9 23 23 –– 24 Nopember 201324 Nopember 2013
by Wendi Junaediby Wendi Junaedi
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What You Should KnowWhat You Should Know
Course only for two days !!Course only for two days !!
You may not You may not become a become a superman nor superman nor even goku in 2 even goku in 2 days....days....
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IntroductionIntroduction
What is piping system ?What is piping system ?
A Piping system consist of tanks, pumps, A Piping system consist of tanks, pumps, valves, and components connected together valves, and components connected together by pipelines to deliver a fluid at a spesific by pipelines to deliver a fluid at a spesific flow rate and/or pressure in order to flow rate and/or pressure in order to perform work or make a product. The piping perform work or make a product. The piping system may also contain a variety of system may also contain a variety of instrumentation and controls to regulate the instrumentation and controls to regulate the processes that are occuring within the processes that are occuring within the boundaries of the piping systemboundaries of the piping system
What is piping system ?What is piping system ?
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IntroductionIntroduction
Value of a Clear Picture of a Piping SystemValue of a Clear Picture of a Piping System
To see the piping system clearly, the system boundaries must be To see the piping system clearly, the system boundaries must be defined, including where the system begins and ends, what device are defined, including where the system begins and ends, what device are installed in the system, and how all the devices in the system are installed in the system, and how all the devices in the system are configured.configured.
IntroductionIntroduction
Value of a Clear Picture of a Piping SystemValue of a Clear Picture of a Piping System
A clear picture of system operationA clear picture of system operation
Understanding normal operation (flow, pressure, level, Understanding normal operation (flow, pressure, level, temperature, etc)temperature, etc)
Understanding why and how they changed at different operating Understanding why and how they changed at different operating conditioncondition
Understanding the function and expected of hydraulic performanceUnderstanding the function and expected of hydraulic performance Understanding the processes are occuring inside the piping, and Understanding the processes are occuring inside the piping, and
how the processes measured and controlled.how the processes measured and controlled.
IntroductionIntroduction
Value of a Clear Picture of a Piping SystemValue of a Clear Picture of a Piping System
A clear picture for troubleshootingA clear picture for troubleshooting
Not only provides a better understanding of normal conditionNot only provides a better understanding of normal condition Helps to identify abnormal conditionHelps to identify abnormal condition
A clear picture for energy consumption and costA clear picture for energy consumption and cost
Transporting fluid requires energyTransporting fluid requires energy Energy loss occurs due to friction, noise, vibration, inefficient in the Energy loss occurs due to friction, noise, vibration, inefficient in the
motor and pump, head loss in the components such as piping, motor and pump, head loss in the components such as piping, valves, fitting, etcvalves, fitting, etc
Surely, energy costs moneySurely, energy costs money
IntroductionIntroduction
Understanding Total SystemUnderstanding Total System
Understand type of piping systemUnderstand type of piping system
Single path open systemSingle path open system Branching systemBranching system Single path closed loop systemSingle path closed loop system Multi loop closed systemMulti loop closed system
Understand hydraulic performanceUnderstand hydraulic performance
Understand piping system curve vs pump curveUnderstand piping system curve vs pump curve
Understand total energy graphUnderstand total energy graph
Understand abnormal conditionUnderstand abnormal condition
Terminology, Unit, and Physical LawsTerminology, Unit, and Physical Laws
Fluid PropertiesFluid Properties Any characteristic of a system is called a property. Familiar: pressure P, temperature T, volume V, and mass m.
Less familiar: viscosity, thermal conductivity, modulus of elasticity, thermal expansion coefficient, vapor pressure, surface tension.
Intensive properties are independent of the mass of the system. Examples: temperature, pressure, and density.
Extensive properties are those whose value depends on the size of the system. Examples: Total mass, total volume, and total momentum.
Extensive properties per unit mass are called specific properties. Examples include specific volume v = V/m and specific total energy e=E/m.
Terminology, Unit, and Physical LawsTerminology, Unit, and Physical Laws
Fluid PropertiesFluid Properties The properties relevant to fluid flow are summarized below:
Density:
This is the mass per unit volume of the fluid and is generally measured in kg/m3. Another commonly used term is specific gravity. This is in fact a relative density, comparing the density of a fluid at a given temperature to that of water at the same temperature.
Terminology, Unit, and Physical LawsTerminology, Unit, and Physical Laws
Fluid PropertiesFluid Properties Viscosity: This describes the ease with which a fluid flows. A substance like treacle has a high viscosity, while water has a much lower value. Gases, such as air, have a still lower viscosity. The viscosity of a fluid can be described in two ways.
• Absolute (or dynamic) viscosity: This is a measure of a fluid's resistance to internal deformation. It is expressed in Pascal seconds (Pa s) or Newton seconds per square meter (Ns/m2). [1Pas = 1 Ns/m2]
• Kinematic viscosity: This is the ratio of the absolute viscosity to the density and is measured in metres squared per second (m2/s).
Terminology, Unit, and Physical LawsTerminology, Unit, and Physical Laws
Fluid PropertiesFluid Properties Reynolds Number:
• Critical Reynolds number (Recr) for flow in a round pipe
Re < 2300 laminar
2300 ≤ Re ≤ 4000 transitional
Re > 4000 turbulent
• Note that these values are approximate.
• For a given application, Recr depends upon
– Pipe roughness
– Vibrations
– Upstream fluctuations, disturbances (valves, elbows, etc. that may disturb the flow)
Terminology, Unit, and Physical LawsTerminology, Unit, and Physical Laws
Fluid PropertiesFluid Properties Laminar vs Turbulent
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Terminology, Unit, and Physical LawsTerminology, Unit, and Physical Laws
Pressure Loss in PipePressure Loss in Pipe Whenever fluid flows in a pipe there will be some loss of pressure due to several factors:
a) Friction: This is affected by the roughness of the inside surface of the pipe, the pipe diameter, and the physical properties of the fluid.
b) Changes in size and shape or direction of flow
c) Obstructions: For normal, cylindrical straight pipes the major cause of pressure loss will be friction. Pressure loss in a fitting or valve is greater than in a straight pipe. When fluid flows in a straight pipe the flow pattern will be the same through out the pipe. In a valve or fitting changes in the flow pattern due to factors (b) and (c) will cause extra pressure drops.
Terminology, Unit, and Physical LawsTerminology, Unit, and Physical Laws
Pressure Loss in PipePressure Loss in Pipe
Pressure drops can be measured in a number of ways. The SI unit of pressure is the Pascal. However pressure is often measured in bar.
This is illustrated by the D’Arcy equation:
Terminology, Unit, and Physical LawsTerminology, Unit, and Physical Laws
Pressure Loss in PipePressure Loss in Pipe
Before the pipe losses can be established, the friction factor must be calculated. The friction factor will be dependant on the pipe size, inner roughness of the pipe, flow velocity and fluid viscosity. The flow condition, whether ‘Turbulent’ or not, will determine the method used to calculate the friction factor.
Moody Chart can be used to estimate friction factor. Roughness of pipe is required for friction factor estimation. The chart shows the relationship between Reynolds number and pipe friction. Calculation of friction factors is dependant on the type of flow that will be encountered. For Re numbers <2320 the fluid flow is laminar, when Re number is >= 2320 the fluid flow is turbulent.
Terminology, Unit, and Physical LawsTerminology, Unit, and Physical Laws
Pressure Loss in PipePressure Loss in Pipe
The following table gives typical values of absolute roughness of pipes, k. The relative roughness k/d can be calculated from k and inside diameter of pipe.
Terminology, Unit, and Physical LawsTerminology, Unit, and Physical Laws
Pressure Loss in PipePressure Loss in Pipe
Calculate pressure drop for a pipe of 4” diameter. carrying water flow of 50 m3/h through a distance of 100 meters. The pipe material is Cast Iron
Terminology, Unit, and Physical LawsTerminology, Unit, and Physical Laws
Pressure Loss in Components in Piping SystemPressure Loss in Components in Piping System
Minor head loss in pipe systems can be expressed as:
ValvesValves
Valves isolate, switch and control fluid flow in a piping system. Valves can be operated manually with levers and gear operators or remotely with electric, pneumatic, electro-pneumatic, and electro-hydraulic powered actuators. Manually operated valves are typically used where operation is infrequent and/or a power source is not available. Powered actuators allow valves to be operated automatically by a control system and remotely with push button stations. Valve automation brings significant advantages to a plant in the areas of process quality, efficiency, safety, and productivity.
ValvesValves Gate ValvesGate Valves
Best Suited Control: Quick Opening Recommended Uses:
Fully open/closed, non-throttling Infrequent operation Minimal fluid trapping in line
Advantages: High capacity Tight shut off, Low cost, Little resistance to flow
Disadvantages: Poor control Cavitate at low pressure drops Cannot be used for throttling
Applications: Oil, Gas, Air, Slurries, Heavy liquids, Steam, Non-condensing gases, and Corrosive liquids
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ValvesValves Globe ValvesGlobe Valves
Best Suited Control: Linear and Equal percentage Recommended use-
Throtteling services/flow regulation Frequent operation
Advantages: Efficient throttling Accurate flow control valves Available in multiple ports
Disadvantages: High pressure drop More expensive than other
Applications: Liquids, vapors, gases, corrosive substances, slurries
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ValvesValves Ball ValvesBall Valves
Best suited control – Quick opening linear.
Recommended uses –
Fully open/closed limited throttling
Higher temperature fluids
Advantages –
Low cost
High capacity
Low leakage & maintenance
Tight sealing with low torque
Disadvantages –
Poor throttling characteristics
Prone to cavitation
Applications – Most Liquids, high temperatures, slurries
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ValvesValves Butterfly ValvesButterfly Valves
Best Suited Control: Linear, Equal percentage
Recommended Uses: Fully open/closed or throttling services
Frequent operation
Minimal fluid trapping in line
Advantages:
Low cost and maint.
High capacity
Good flow control
Low pressure drop
Disadvantages –
High torque required to control
Prone to cavitation at lower flows
Applications: Liquids, gases, slurries, liquids with suspended solids
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ValvesValves Cavitation on ValvesCavitation on Valves
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Pump & Pumping SystemPump & Pumping System
• 20% of world’s electrical energy demand
• 25-50% of energy usage in some industries
• Used for
• Domestic, commercial, industrial and agricultural
services
• Municipal water and wastewater services
What are Pumping Systems
Pump & Pumping SystemPump & Pumping System
What are Pumping Systems
Objective of pumping system
(US DOE, 2001)
• Transfer liquid from
source to destination
• Circulate liquid around a
system
Pump & Pumping SystemPump & Pumping System
What are Pumping Systems
• Main pump components
• Pumps
• Prime movers: electric motors, diesel engines, air
system
• Piping to carry fluid
• Valves to control flow in system
• Other fittings, control, instrumentation
• End-use equipment
• Heat exchangers, tanks, hydraulic machines
Pump & Pumping SystemPump & Pumping System
33
©© UNEP 2006UNEP 2006
• Head
• Resistance of the system
• Two types: static and friction
• Static head
• Difference in height between
source and destination
• Independent of flow
Pumping System Characteristics
destination
source
Static head
Static
head
Flow
Pump & Pumping SystemPump & Pumping System
Pumping System Characteristics
• Static head consists of
• Static suction head (hS): lifting liquid relative to
pump center line
• Static discharge head (hD) vertical distance between
centerline and liquid surface in destination tank
Pump & Pumping SystemPump & Pumping System
Pumping System Characteristics
• Friction head
• Resistance to flow in pipe and fittings
• Depends on size, pipes, pipe fittings, flow
rate, nature of liquid
• Proportional to square of flow rate
• Closed loop system
only has friction head
(no static head) Friction head
Flow
Pump & Pumping SystemPump & Pumping System
Pumping System Characteristics
In most cases:
Total head = Static head + friction head
System
head
Flow
Static head
Friction
head
System curve
System head
Flow
Static head
Friction head
System
curve
Pump & Pumping SystemPump & Pumping System
Pumping System Characteristics
Pump performance curve
• Relationship between head and flow
• Flow increase
• System resistance increases
• Head increases
• Flow decreases to zero
• Zero flow rate: risk of
pump burnout
Head
Flow
Performance curve for
centrifugal pump
Pump & Pumping SystemPump & Pumping System
Pumping System Characteristics
Pump operating point
• Duty point: rate of
flow at certain head
• Pump operating
point: intersection
of pump curve and
system curve
Flow
Head
Static head
Pump performance curve
System
curve
Pump
operating point
Pump & Pumping SystemPump & Pumping System
Pumping System Characteristics
Pump suction performance (NPSH)
• Cavitation or vaporization: bubbles inside pump
• If vapor bubbles collapse
• Erosion of vane surfaces
• Increased noise and vibration
• Choking of impeller passages
• Net Positive Suction Head
• NPSH Available: how much pump suction exceeds
liquid vapor pressure
• NPSH Required: pump suction needed to avoid
cavitation
Pump & Pumping SystemPump & Pumping System
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Pump & Pumping SystemPump & Pumping System
Pumping System Characteristics
Pump & Pumping SystemPump & Pumping System
Pumping System Characteristics
Pump & Pumping SystemPump & Pumping System
Pumping System Characteristics
Pump & Pumping SystemPump & Pumping System
Pumping System Characteristics
Type of PumpsType of Pumps
Centrifugal PumpCentrifugal Pump
Are classified as nonpositive displacement pumps because they do not pump a definite amount of water with each
revolution. Rather, they impart velocity to the water and
convert it to pressure within the pump itself.
Centrifugal PumpCentrifugal Pump
Centrifugal PumpCentrifugal Pump
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Centrifugal PumpCentrifugal Pump
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Centrifugal PumpCentrifugal Pump
• Pump shaft power (Ps) is actual horsepower delivered
to the pump shaft
• Pump output/Hydraulic/Water horsepower (Hp) is the
liquid horsepower delivered by the pump
How to Calculate Pump Performance
Hydraulic power (Hp):
Hp = Q (m3/s) x Total head, hd - hs (m) x ρ (kg/m3) x g (m/s2) / 1000
Pump shaft power (Ps):
Ps = Hydraulic power Hp / pump efficiency ηPump
Pump Efficiency (ηPump):
ηPump = Hydraulic Power / Pump Shaft Power
hd - discharge head hs – suction head,
ρ - density of the fluid g – acceleration due to gravity
Centrifugal PumpCentrifugal Pump
Energy Efficiency Opportunities
1. Selecting the right pump
2. Controlling the flow rate by speed variation
3. Pumps in parallel to meet varying demand
4. Eliminating flow control valve
5. Eliminating by-pass control
6. Start/stop control of pump
7. Impeller trimming
Centrifugal PumpCentrifugal Pump
Energy Efficiency Opportunities
1. Selecting the Right Pump
• Pump performance curve for centrifugal pump
• Oversized pump
• Requires flow control (throttle valve or by-pass line)
• Provides additional head
• System curve shifts to left
• Pump efficiency is reduced
• Solutions if pump already purchased
• VSDs or two-speed drives
• Lower RPM
• Smaller or trimmed impeller
Centrifugal PumpCentrifugal Pump
Energy Efficiency Opportunities
2. Controlling Flow: speed variation
Explaining the effect of speed
• Affinity laws: relation speed N and
• Small speed reduction (e.g. ½) = large power
reduction (e.g. 1/8)
Centrifugal PumpCentrifugal Pump
Energy Efficiency Opportunities
3. Parallel Pumps for Varying Demand
• Multiple pumps: some turned off during low demand
• Used when static head is >50% of total head
• System curve
does not change
• Flow rate lower
than sum of
individual
flow rates
Centrifugal PumpCentrifugal Pump
Energy Efficiency Opportunities
4. Eliminating Flow Control Valve
• Closing/opening discharge valve (“throttling”) to
reduce flow
• Head increases:
does not reduce
power use
• Vibration and
corrosion: high
maintenance costs
and reduced pump
lifetime
Centrifugal PumpCentrifugal Pump
Energy Efficiency Opportunities
5. Eliminating By-pass Control
• Pump discharge divided into two
flows
• One pipeline delivers fluid to
destination
• Second pipeline returns fluid
to the source
• Energy wastage because part of
fluid pumped around for no
reason
Centrifugal PumpCentrifugal Pump
Energy Efficiency Opportunities
6. Start / Stop Control of Pump
• Stop the pump when not needed
• Example:
• Filling of storage tank
• Controllers in tank to start/stop
• Suitable if not done too frequently
• Method to lower the maximum demand (pumping at
non-peak hours)
Centrifugal PumpCentrifugal Pump
Energy Efficiency Opportunities
7. Impeller Trimming
• Changing diameter: change in velocity
• Considerations
• Cannot be used with varying flows
• No trimming >25% of impeller size
• Impeller trimming same on all sides
• Changing impeller is better option
but more expensive and not always
possible
Centrifugal PumpCentrifugal Pump
Energy Efficiency Opportunities
Comparing Energy Efficiency Options
Parameter Change
control valve
Trim impeller VFD
Impeller
diameter
430 mm 375 mm 430 mm
Pump head 71.7 m 42 m 34.5 m
Pump efficiency 75.1% 72.1% 77%
Rate of flow 80 m3/hr 80 m3/hr 80 m3/hr
Power
consumed
23.1 kW 14 kW 11.6 kW
Centrifugal PumpCentrifugal Pump
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PipelinePipeline
Generally need to deliver oil or gas at a specified flow rate and pressure
Hydraulic design required for preliminary selection of pipeline diameter
Fluid must be kept above a minimum velocity
• Minimise surging
• Prevent build up of solids
Fluid flow must be below a maximum velocity
• Prevent erosion
• Optimise pumping requirements
Hydraulic Design
PipelinePipeline
Hydraulic Design
Hydrocarbons for transport may be
Liquid (incompressible: straightforward to analyse)
Gas (compressible & properties vary along pipe: more challenging to analyse)
Multi-phase (e.g. gas & condensate)
(highly complex)
PipelinePipeline
For liquid lines:
Max velocity 4 m/sec
Min velocity 1 m/sec
For gas lines:
Max velocity 18-25 m/sec
Min velocity 4-5 m/sec
Trade off between
- CAPEX (Large pipe diameter) and
- OPEX (Lower pumping costs)
Fluid Velocities
PipelinePipeline
Pressure drop in liquid pipelines is principally due to
• Change in elevation (described by change in hydraulic head, or Pressure = gh )
• Friction loss
Pressure Drop
The remainder of the section on hydraulic design will be concerned with liquid pipelines
PipelinePipeline
There are two equations that may be used for calculating the friction loss
Darcy-Weisbach
Fanning
Friction Loss Calculation
2
2L DARCY
L Vh f
D g
æ öæ ö= ç ÷ç ÷
è øè ø
2
2L FANNING
L Vh f
D g
æ öæ ö= ç ÷ç ÷
è øè ø
Oil pipelines
Gas pipelines
So, fDARCY = 4fFANNING
PipelinePipeline
Friction Loss Calculation
For Laminar Flow
For Turbulent Flow use the Moody Chart Depends on pipe relative roughness
64
ReDARCYf = For Re < 2300
For Re > 4000
Best PracticeBest Practice Compressed Air System
Best PracticeBest Practice Compressed Air Leakage
Leaks can be a significant source of wasted energy in an industrial compressed air system and may be costing you much more than you think. Audits typically find that leaks can be responsible for between 20-50% of a compressor’s output making them the largest single waste of energy. In addition to being a source of wasted energy, leaks can also contribute to other operating losses:
• Leaks cause a drop in system pressure. This can decrease the efficiency of air tools and adversely affect production
• Leaks can force the equipment to cycle more frequently, shortening the life of almost all system equipment (including the compressor package itself)
• Leaks can increase running time that can lead to additional maintenance requirements and increased unscheduled downtime
• Leaks can lead to adding unnecessary compressor capacity
Best PracticeBest Practice Compressed Air Leakage
Best PracticeBest Practice Steam Distribution
There are numerous graphs, tables and slide rules available for relating steam pipe sizes to flow rates and pressure drops. To begin the process of determining required pipe size, it is usual to assume a velocity of flow. For saturated steam from a boiler, 20 - 30 m/s is accepted general practice for short pipe runs. For major lengths of distribution pipe work, pressure drop becomes the major consideration and velocities may be slightly less. With dry steam, velocities of 40 metres/sec can be contemplated -but remember that many steam meters suffer wear and tear under such conditions. There is also a risk of noise from pipes.
Pipe Selection
Best PracticeBest Practice Steam Distribution
Best PracticeBest Practice Steam Distribution
Recommended Thickness of Insulation (inches) for Mineral Wool
Best PracticeBest Practice Water Distribution
As a rule of thumb, the following velocities are used in design of piping and pumping systems for water transport:
Best PracticeBest Practice
Water Distribution
If you want to pump 14.5 m3/h of water for a cooling application where pipe length is 100 metres, the following table shows why you should be choosing a 3” pipe instead of a 2” pipe.
If a 2” pipe were used, the power consumption would have been more than double compared to the 3” pipe. It should be noted that for smaller pipelines, lower design velocities are recommended. For a 12” pipe, the velocity can be 2.6 m/s without any or notable energy penalty, but for a 2” to 6” line this can be very lossy.
Best PracticeBest Practice
Water Distribution
Recommended water flow velocity on suction side of pump
Capacity problems, cavitation and high power consumption in a pump, is often the result of the conditions on the suction side. In general - a rule of thumb - is to keep the suction fluid flow speed below the following values:
ReferencesReferences
1.1. Piping System Fundamental, The Complete Guide to Gaining a Clear Piping System Fundamental, The Complete Guide to Gaining a Clear Picture of Your Piping System, 2012 Engineered Software, incPicture of Your Piping System, 2012 Engineered Software, inc
2.2. Best Practice Manual, Fluid Piping System, 2006, Best Practice Manual, Fluid Piping System, 2006, Devki Energy Consultancy Pvt. Ltd.
3. Pump Handbook, 2004 Grundfos Industry 4. Valve Sizing & Selection, Ranjeet Kumar 5. Pumps & Pumping System, 2006, www.energyefficiencyasia.org 6. Pumps for Process Industry, Ranjeet Kumar 7. Critical Pump Selection, Webinar 8. Repair Engineering
Simulation & ModellingSimulation & Modelling