Lecture # 8 Transportation & Metering of Fluids
Fluid Transportation Fluids are transported through pipes or tubes: Pipes Tubes Heavy walled, large diameter, and Thin walled and coils comes several moderate length 20 ft to 40 ft hundred feet long Pipes can be threaded Tubing cannot Rough surface Smooth surface Pipes are joined by: Tubes are joined by: Screwed Compression joints Flanged Flare fittings Welded fittings Soldered fittings Pipes are made by: These are extruded or cold drawn. Welding Casting Piercing a billet in a billet mil
Sizing of pipes and tubes Pipe sizes: Pipes are specified by their “diameter” and “wall thickness”. Steel pipes nominal diameter ranges from 1/8 to 30 in. For pipes, more than 12 in diameter, nominal diameter is outside diameter. Nominal value close to actual inside diameter for 3 to 12” pipe. Appendix ‘5’ is for steel pipe sizes. (IPS = Iron Pipe Size, NPS = Normal Pipe Size) Thus, “ 2 in. nickel IPS pipe ” means 2 in. nickel pipe having same dimensions as 2 in. steel pipe. Wall thickness is represented by “Schedule #” . 10 schedule # are given as 10, 20, 30, 40, 60, 80, 100, 120, 140, 160. For pipe, less than 8 in. diameter, only 40, 80, 120, & 160 are common. Tube Sizes: Tubes are sized by outside diameter. Wall thickness is given by BWG (Birmingham Wire Gauge) number, ranges from 24 (very light) to 7 (very heavy).
Selection of Pipe sizes For specific situation: the optimum size of of pipe depends on Relative cost of investment Power Maintenance Stocking pipe and fittings In small installations rule of Thumb are sufficient. • Low velocities should ordinarily favored for gravity flow from overhead tanks • For large complex systems the cost of piping may be substantial and also computer programs of optimizing pipe sizes are justified
Joints and Fittings Method to join the tubes and pipes depends not only on the properties of fluid but also on the thickness of wall. Thick Walled tubular structures are joined by : Screwed Fitting (higher schedule # pipe is required for threading……….because of difficulty of threading and handling of large pipes they are rarely used in the field with pipe larger than 3in.) Flanges Welding Thin-walled tubing get attached by: Soldering Flare or Compression fittings Pipes made of brittle material ( like glass, carbon or cast iron) are joined by: Flanges (Flanges are matching disks or rings of metal bolted together and compressing a gasket between their faces. A flange with no opening used to close a pipe is called a blind flange or blank flange ) Bell and Spigot Joints
Comparison of Joints and Fittings For Larger steel pipe in process piping and high pressure services welding has become the standard method. Welding makes the stronger joint than screwed or flanges. Welded joints are leak-proof whereas other types of joints are not. Environmental protection Legislation considers flanges and screwed joints to be the source of leakage and emission of Volatile matter. The only drawback of welded joint is that it cannot be opened without destroying it.
Allowance for Expansion Pipes has to face varying temperature and pressure and such changes cause the pipe to expand or contract. If the pipe is rigidly fixed to its support, it may tear loose, bend or even break. In large lines, fixed supports are not used instead the pipes rests loosely on rollers or is hung from above by chains or roads. For high temperature lines (for taking up expansion and to avoid the strain on the valves and fitting) the bends, bellows, packed Expansion joints, and flexible metal hose are employed.
Leakage Prevention around Moving Parts In Process Machinery sometimes one part has to move on another part without leakage like; Packed Expansion Joints Valve where the stem should be free to turn without allowing the fluid in the valve to escape. Shaft of Pump or Compressor Agitator Shaft passes through the wall of pressure vessel Common devices for minimizing the leakage while permitting relative motion are Stuffing Box and Mecahnical seals .
Stuffing Box
Stuffing Box (Cont..)
Stuffing Box (Cont..)
Stuffing Box (Cont..)
Stuffing Box (Cont..)
Mechanical Seal
Mechanical Seal (Cont..)
Mechanical Seal (Cont..)
VALVES “A small obstruction can be placed in the path of the fluid that can be moved about as desired inside the pipe with little or no leakage of the fluid from the pipe to outside. That obstruction including its movement mechanism are boxed in one unit which is called Valve” . Valves are used in the piping networks to meet the following purposes; To regulate the flow (i.e. to stop or slow down the flow) Control the temperature, pressure, liquid level or other properties of fluid at points remote from the valve itself Unidirectional Flow under certain conditions of temperature and pressure
Terminology for Valve body Parts
CLASSIFICATION OF VALVES • CLASSIFICATION BASED ON MECHANICAL MOTION Linear motion valve Rotary motion valve Quarter turn valve • CLASSIFICATION BASED ON VALUE SIZE Small valves (NPS 2 and smaller) Large valves (NPS 2 1/2 and larger) • CLASSIFICATION BASED ON FUNCTION Isolation Gate valve, Ball valve, Butterfly valve, Diaphragm valve Control (flow/pressure) Globe valve, Ball valve, Butterfly valve, Diaphragm valve Prevention of flow reversal Check valve (swing, lift, piston, etc.) Flow diversion Ball valve, Plug valve, Angle valve (Three way, Four way, etc.)
ADVANTAGES & DISADVANTAGES OF GATE VALVE • ADVANTAGES Pressure drop through the valve is minimal. Good shutoff characteristics. Operation torque is smaller than those of globe valves. • DISADVANTAGES Cannot be throttled. Not suitable for frequent switch-on/off operation. Requires large space envelope for installation, operation and maintenance. Repair or machining of valve seats in place is difficult.
Typical Usage of Gate Valve Block valve for control valve Pump suction valve Pump discharge valve Block valve for level controller & level gauge Drain valve of equipment Drain valve of process & utility line First block valve of sampling nozzle Block valve for safety valve Block valve for equipment Block valve for steam trap By-pass valve for emergency shut-down valve Flow control valve for large size gas & city water line
Valve symbols for PID (Piping and Instrumentation Diagram)
Turbo machine A turbo machine is a device in which energy is transferred either to or from a continuously flowing fluid by the dynamic action of one or more moving blade rows The word turbo is a Latin origin and implies that which spins or whirls around
Classification of Turbo-machinery Major subdivisions A. Power classifications (power is added or extracted from the fluid) • Pumps are power addition machines and include liquid pumps, fans, blowers and compressors. Fluids are water, fuels, air, steam, refrigerants. • Turbines are power extraction devices and include windmills, water wheels, hydroelectric turbines, automotive engine turbochargers, gas turbines. Fluids; gases, liquids, mixtures.
Classification of Turbo-machinery (Cont..) B. The manner in which the fluid moves through and around a machine • Open flow No casing or enclosure for the rotating devices Examples: propeller is an open flow pumping device. Windmill is an open flow turbine • Enclosed or encased flow devices
Classification of Turbo-machinery (Cont..) C. Turbo-machines are further categorized according to the nature of the flow path through the passages of the rotor. When the path of the through-flow is wholly or mainly parallel to the axis of rotation, the device is termed an axial flow turbo-machine. When the path of the through-flow is wholly or mainly in a plane perpendicular to the rotation axis, the device is termed a radial flow turbo-machine. Mixed flow turbo-machines are widely used. The term mixed flow refers to the direction of the through-flow at rotor outlet when both radial and axial velocity components are present in significant amounts.
Classification : Flow Path
Classification of Turbo-machinery (Cont..) D. Compressibility of the fluid • Incompressible The density is constant through the entire flow process; liquid pumps. • Compressible; Gas flows: compressors, Fan and Blower E. Impulse or reaction machines • Impulse: pressure changes are absent in the flow through the rotor. In an impulse machine, all the pressure change take place in nozzles Example: Pelton wheel • Reaction: pressure changes in rotor are absent
Terminology (Mechanical) of Fluid Moving Machinery
Terminology (Cont.)
Flow Dynamics in Fluid Moving Machine
Sectional view of Impeller
Sectional view of Impeller (cont.)
Sectional view of Impeller (cont.)
Pump Classification
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