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Wednesday, April 28, 2010

How to calculate the diameter and number of nozzles for Pelton turbine

By Ahmad Suhendra

Example :
A Pelton turbine is planned to be working on the head netto 80 m and a flow 20 liters / s , what is the number of nozzles installed on these turbines?

Pelton turbine requirements are :
  • ns (specific speed , rpm) = 8 – 72 rpm
  • Nominal speed = 500 – 1500 rpm
1.Specific speed of turbine
  • Taken 1500 rpm as nominal turbine speed (N_turbine)
  • Flow (Q) = 0.020 m3/s
  • H_netto = 80 m
ns = 3.65 *N_turbine (rpm) * Q(m^3/s) 0.5 / H_netto(m)^ 0.75
= 3.65 * 1500 rpm * (0.020 m3/s)^0.5 / (80 m)^0.75
= 774.28 / 26.75 = 28.95 rpm

Based on the practical calculation,
  • If ns >= (8) and < (29.5) then 1 nozzles
  • If ns >= (29.5) and < (42) then 2 nozzles
  • If ns >= (42) and < (54) then 3 nozzles
  • If ns >= (54) and < (58) then 4 nozzles
  • If ns >= (58) and <=(72) then 6 nozzles
ns = 28.95 rpm -------> Ok, Pelton turbine with one nozzles

2. Absolute velocity of water
kc ( nozzles coef.) = 0.96 to 0.98, Taken kc = 0.98
C = kc (2 * 9.8 m/s^2 * H_netto(m) )^ 0.5
= 0.98 (2 x 9.8 x 80 ) 0.5 = 38.81 m/s

3. Diameter of nozzles
Dn = [ (4 x Q/(number of nozzles)) / (phi x C) ] ^0.5
= [ 4 x (0.020/1) / (3.14 x 38.81)] ^0.5
= [ 0.08 / 121.86 ] 0.5 = 0.0256 m or 26 mm

Ref : Edy Sunarto dan Markus Einsering”,Turbin Pelton Mikro”, MHPG Andi Offset Yogyakarta 1992

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