1 Turbomachinery Turbomachinery Turbo : latin prefix, means spin Energy is extracted or supplied by...

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Transcript of 1 Turbomachinery Turbomachinery Turbo : latin prefix, means spin Energy is extracted or supplied by...

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1 Turbomachinery Turbomachinery Turbo : latin prefix, means spin Energy is extracted or supplied by a rotating shaft Not all pumps use rotating shaft so we can call them fluid machine ( nowadays turbomachine is used for all ) Slide 2 2 Pump: adds energy to a fluid, resulting in an increase in pressure ( not necessarily increase in velocity) across the pump. ( not necessarily increase in velocity) across the pump. Turbine: extracts energy from the fluid, resulting in a decrease in pressure (not necessarily decrease in velocity) across the turbine. (not necessarily decrease in velocity) across the turbine. Slide 3 3 General comments on the pipeline design ease and cost of pumping=f(Design of pipeline ) -Design piping to minimize energy requirement of pumping ( especially energy losses due to friction and shock losses) -Keep the total length of pipeline as short as possible -Keep the total length of pipeline as short as possible Slide 4 4 maintain same pipe diameter, if changes are unavoidable use reducing or expanding unions rather than abrupt changes in diameter Use the correct type and minimum number of fittings. avoid using gate valve ( on-off valve) to regulate flow rate Then select a suitable pump Slide 5 5 Factors influencing the choice of the pump 1- The quantity of liquid to be handled: affects the size and type of the pump, determines if parallel pumps needed. 2- The head against which the liquid is to be pumped. determined by the difference in pressure and velocity, the vertical height of the downstream and upstream reservoirs and by the frictional losses which occur in the delivery line. The suitability of a centrifugal pump and the number of stages required will largely be determined by this factor The suitability of a centrifugal pump and the number of stages required will largely be determined by this factor ( as D decreases, v increases, energy loss increases in turn expensive pumping.so optimum pipe diameter must be selected) ( as D decreases, v increases, energy loss increases in turn expensive pumping.so optimum pipe diameter must be selected) Slide 6 6 3- The nature of the liquid to be pumped. a) consistency ( viscosity) the viscosity largely determines the frictional losses and hence the power required b) density b) density c) temperature ( effects viscosity, pump material, cavitation ) c) temperature ( effects viscosity, pump material, cavitation ) d) corrosive and/or erosive nature of fluid (The corrosive nature will determine the material of construction.With suspensions, the clearance in the pump must be large compared with the size of the particles.) d) corrosive and/or erosive nature of fluid (The corrosive nature will determine the material of construction.With suspensions, the clearance in the pump must be large compared with the size of the particles.) e)shear deformation( fluid flow characteristic and crystal habbit may change under high shear) e)shear deformation( fluid flow characteristic and crystal habbit may change under high shear) e) lubricating properties of fluid ( for all metal rotary pumps requires fluid to be lubricant) e) lubricating properties of fluid ( for all metal rotary pumps requires fluid to be lubricant) Slide 7 7 4- The nature of power supply. ( though most pumps are coupled to electric motors either directly or via pulleys and v-belts reciprocating pumps can be also actuated by steam or compressed air) 5- hygenic requirements. In the food industry contamination must be quarded against all times Slide 8 8 Categories Fans, Blowers, and Compressors Fans: Low pressure gradient, High volume flow rate. Examples include ceiling fans and propellers. Blower: Medium pressure gradient, Medium volume flow rate. (ie centrifugal blowers found in furnaces, leaf blowers, and hair dryers.) Compressor: High pressure gradient, Low volume flow rate. (ie air compressors for air tools, refrigerant compressors for refrigerators) Slide 9 9 Fans: P = from 2 or 3 of water up to about 0.5 psi. classified into three types: The propeller type : electric fan Plate fan : 8 to 12 plate steel blades inside a casing. (P from 0 to 5 water) If blades curved : P up to 27 water. The multi-blade fans P from 0 to 5 water. ( much higher efficiencies and deliver much larger volumes for a given size of drum than steel-plate fans.) Slide 10 10Blowers: Any pump of the rotary type can be used as a blower ( two or three lobes) P from 0.5 to 10 psi. The appearance of centrifugal blower resembles a centrifugal pump, except that the casing is narrower and larger impeller diameter. The operating speed 3000 rpm. The operating speed 3000 rpm. Slide 11 11Compressors: process gas - up to 100 m 3 /sec at the inlet - to an outlet pressure of 20 atm. ( smaller capacity up to several hundred atms. ) cooling is needed on the high pressure units. Axial flow machines :up to 300 m 3 /sec, press of 2 to 10 atm. Rotary positive displacement compressors: press to 6 atm. Most compressors operating at discharge press above 3 atm are reciprocating positive displacement machines. If required compression ratio is greater than that can be achieved in one cylinder, multistage compressors are used. The maximum pressure ratio normally obtained in a single cylinder is 10 atm but values above 6 are unusual Slide 12 12 Airflow through a centrifugal air compressor Slide 13 13 PUMPS PUMPS -piston -diaphram Centrifugal, dynamic, kinetic -Helical screw -gear -lobe -peristaltic RotaryReciprocating Positive displacement Slide 14 14 Categories Positive-displacement machines Closed volume is used to squeeze or suck fluid. Pump: human heart Turbine: home water meter Turbine: home water meter Slide 15 15 All PD pumps not be allowed to pump against a closed delivery line since over pressure can develop. A pressure relief valve should be incorporated in the discharge line to allow controlled release of any excessive pressure through mal operation. Slide 16 16 Reciprocating PD pumps PISTON pumps -single cylinder( pulsating flow) -multi cylinder( smoother flow) -can handle high -develop high P -dont use with abrasive fluids -delivers accurately known volumes so known volumes so used as metering pump Slide 17 17 Slide 18 18 Diaphragm pump Simple Limited P development Check valves had to be used Inexpensive Able to handle corrosive and abrasive fluids Fluid is not in contact with most of the with most of the moving parts moving parts Slide 19 19 Rotary PD pumps Slide 20 20 HELICAL SCREW pump Can handle very high pressure Abrasive liquids can be run Should not be run dry Ie. Extruders in food production food production Slide 21 21 Gear pumps External gear pump As # of teeth inreases flow gets smoother develop high P (up to 200 bar ) dont use with abrasive fluids High shear Slide 22 22 Internal gear PD pumps -develop high P (up to 200 bar ) -Gentler than external gear PD -More expensive and complicated Slide 23 23 lobe pump - can transfer fluid at flowrates up to 500 m 3 /hr - can deliver total heads of 20 bar. - easy to clean - can handle shear sensitive products - Most widely used PD pump for food aplications Slide 24 24 Peristaltic Pump -most hygenic pump available) -can generate heads of up to 5m at flows of up to 10 m 3 /hr. - -most gentle : Fragile blood cells are not damaged by this pump. Orange segments, wallnut pieces can be transferred. (another application: The EnTire Self-Inflating Tire system)EnTire Self-Inflating Tire Slide 25 25 Jet pumps: Bernoullis principle no moving parts h in + v in 2 /2 = h out + v out 2 /2 High velocity creates vacuum Slide 26 26 Air lift pump Air lift pump Air is injected to the bottom of the vertical pipe. Air is injected to the bottom of the vertical pipe. The specific gravity of the water inside the pipe becomes less than that outside the pipe. The specific gravity of the water inside the pipe becomes less than that outside the pipe. This difference transfers the liquid upward in the pipe. This difference transfers the liquid upward in the pipe. simple simple used for petroleum, handling of hazardous fluids, the design of bioreactors, recycle aeration in sludge digesters. used for petroleum, handling of hazardous fluids, the design of bioreactors, recycle aeration in sludge digesters. Slide 27 27 Geyser pump Geyser Pump was invented in 1999 Geyser Pump was developed to overcome weak points of airlift pump. Slide 28 28 Following weekneses of airlift pump is prevented Slide 29 29 Slide 30 30 Dynamic machines (centrifugal, kinetic) No closed volume. Instead, rotating blades supply or extract energy. Enclosed/Ducted Pumps: torpedo propulsor Open Pumps: propeller or helicopter rotor Slide 31 31 Enclosed Turbines: hydroturbine Open Turbines: wind turbine Slide 32 32 The faster you spin, the more water comes out the small hole, the water is pressurized inside the cup using centrifugal force in a similar fashion to a centrifugal pump. Slide 33 33 How to select a centrifugal pump expected to deliver exactly the flow rate you require. The flow rate =f( physical characteristics of your system such:length,size of the pipes, elevation difference ) The pump manufacturer has no means of knowing what these constraints will be. This is why buying a centrifugal pump is more complicated than buying a positive displacement pump which will provide its rated flow no matter what system you install it in. Slide 34 34 Dynamic Pumps include centrifugal pumps: fluid enters axially, and is discharged radially. mixed--flow pumps: fluid enters axially, and leaves at an angle between radially and axially. axial pumps: fluid enters and leaves axially. Slide 35 35 Centrifugal Pumps Snail--shaped scroll Most common type of pump: homes, autos, industry. Slide 36 36 Centrifugal Pumps Slide 37 37 Centrifugal Pumps: Blade Design Slide 38 38 Pump Head Net Head Water horsepower( useful energy actually delivered to fluid) Brake horsepower ( energy supplied to pump) Pump efficiency