Question

A Francis turbine works under a head of 25 m and produces 11800 kW while running at 120 r.p.m. The turbine has been installed at a station where atmospheric pressure is 10 m of water and vapour pressure is 0.2 m of water. Calculate the maximum height of the straight draft tube for the turbine.

Answer 1

Given data PE_|| 802 kw N - 120 32m -Patra = 10 m of the Head = 25m Volowa pesare= 0.2 m of the TI Thomas cavitation facto. Critical value = - Olcoritical)= 0.0445 Ns 1" 1100 we have_NsENP Ng = 12011187294 - 25)574 2_1204108-62 55.9. Ns = 233.173 8pm Critical = 0.044233-173 100 20:044X5.4369 A Crit 0.23922) Cavitation factor o Harm - Hrop) -Hs (10-0.2) - Hs. 25 _ We know that 5 Zo crot bavoid cavitation it = critical 0.23922 - (10-0.2)-ts = 9.8-ts. Height of draft tube Hs = 9.8-5.98 1 Hg = 3.82m7