Work Done by an Impulse Turbine

Work Done by an Impulse Turbine Points : Work Done by an Impulse Turbine, Power Produced by an Impulse Turbine, Efficiencies of an Impulse Turbine, Hydraulic efficiency, Mechanical efficiency, Overall efficiency also. The jet of water, issuing from the nozzle, strikes the bucket at its splitter. The splitter then splits up the jet in two parts. One part of the jet glides over the inside surface of one portion of the vane and leaves it at its e:treme edge. The other part of the jet glides over the inside surface of the other portion of the vane and leaves it at its extreme edge. A little consideration will show, that the mid-point of the bucket, where the jet strikes the splitter and gets divided, forms the inlet tip, and the two extreme edges, where the divided jet leaves the bucket, from the two outlet tips. First of all, draw the velocity triangles at the splitter (which will be a straight line only) and any one of the outer tips of the hemispherical bucket. All the notations and theory of jet impinging on series of vanes is applicable in the case Power Produced by an Impulse Turbine: We have seen in the previous articles, that some work is done per kg of water, when the jet strikes the buckets of an impulse turbine. If we know the quantity of water in kg, flowing through the jets per second, and the amount of work done per second, then the power produced by the turbine maybe found out by the relation,
P = Work done / kg of water x Weight of water flowing / sec in kg/75
= wQH/75 In S.I. Units, the power produced,
P = 9.81 QHkW Efficiencies of an Impulse Turbine: In general, the term efficiency may be defined as the ratio of work done to the energy supplied. An impulse turbine has the following three types of efficiencies:
1. Hydraulic efficiency,
2. Mechanical efficiency, and
3. Overall efficiency Hydraulic Efficiency: It is the ratio of work done on the wheel, to the energy of the jet. We know that the hydraulic efficiency of a turbine,
=2v(V - v)(1 + cos ?) and maximum hydraulic efficiency,
max (1+ cos)/2 Mechanical Efficiency: It has been observed that all the energy supplied to the wheel does not come out as useful work. But a part of it is dissipated in overcoming friction of bearings and other moving parts. Thus the mechanical efficiency is the ratio of the actual work available at the turbine to the energy imparted to the wheel. Overall Efficiency: It is measure of the performance of a turbine, and is the ratio of actual power produced by the turbine to the energy actually supplied by the turbine, i.e.
= P/wQh/75