SPECIFIC SPEED

CREATED BY : RITU GOSWAMI

ROLL NO : 18545

DEPARTMENT : APPLIED SCIENCE (IT)

WHAT IS SPECIFIC SPEED ?

– Specific speed of a turbine is defined as the speed of a geometrically similar turbine which produce a unit power when working under a unit head.

– By geometrically similar means that turbine is identical in shape, dimensions, blade angles and gate opening etc. it is denoted by the symbol Ns. The specific speed is used in comparing the different type of turbines as every of turbine has different specific speed.

SPECIFIC SPEEDSR. NO. TYPES OF TURBINE SPECIFIC SPEED

1. Pelton wheel with single jet(nozzle) 80-30

2. Pelton wheel with multiple jet(nozzle) 30-50

3. Francis turbine 50-250

4. Kaplan turbine 250-850

SELECTION OF TURBINE

– 1. HEAD

– 2. SPECIFIC SPEED

– 3. PART LOAD OPERATIONS

– 4. NUMBER OF UNITS

– 5. CAVITATION

– 6. POSITION OF TURBINE SHAFT

– 7. COST

SELECTION OF TURBINE ON THE BASIS OF SPECIFIC SPEED– The specific speed of a pump is defined as the speed of geometrically similar

pump that delivers units discharge under units head.

– Thus the specific speed , Ns is given as Ns = N√Q/H3/4

– Where N is the speed of the pump in r.p.m

– Q is discharge in m3/s and H is head in meters.

CLASSIFICATION OF HYDRAULIC TURBINES.ACCORDING TO THE SPECIFIC SPEED

– According to the specific speed, turbines may be classified as:

– (a) high specific speed turbine

– (b) medium specific speed turbine

– (c) low specific speed of a turbine

HIGH SPECIFIC SPEED TURBINE.

– Specific speed of these turbines are 250 to 850. so these are called as high specific speed turbines. Kaplan and propeller turbine are the examples of high specific speed turbines.

MEDIUM SPECIFIC SPEED TURBINE.

– Specific speed of these turbines are 50 to 250 . So these are called medium specific speed turbine. Francis turbine turbine is the example of medium specific speed turbine.

Francis turbine

LOW SPECIFIC SPEED TURBINE

– Specific speed of these turbines are 8 to 30 with single nozzle and up to 50 with nozzles. So these are called low specific speed turbines. Pelton turbine is the example of low specific speed.

Pelton turbine

Table gives the values of specific speed of different types of pump.

Specific speed of centrifugal pump

SR. NO. PUMP SPEED SPECIFIC SPEED

1. Radial flow SlowMediumHigh

10-30 30-50 50-80

2. Mixed flow 80-160

3. Axial flow 160-425

THANK YOU

REFERENCES

– https://en.wikipedia.org/wiki/Specific_speed

– www.engineeringtoolbox.com/specific-speed-pump-fan-d_637.html

– Basics of mechanical engineering by vineet jain