Conversion of Water Energy

1. The Water Wheel

The ancient Greeks were the first recorded society to successfully develop a form of hydropower (the

water wheel). The Greek water wheel was designed as a work of art rather than science, and was highly

inefficient. However, the torque from the simple water wheel was successfully used to grind wheat into

flour. The original Greek water wheels later become known an undershot water wheel.

By 1700s, water wheels were used extensively for milling. Efficiency became a key issue in the

development if the waterwheel. New types of water wheel designs were invented which include the

overshot water wheel and the breast shot water wheel.

Undershot Breast shot Overshot

Efficiency 22% 50% 63%

Flow rates 0.5 to 0.95 0.35 to 0.65 0.1 to 0.2

Head difference 0.5 to 2.5 1.5 to 4 2.5 to 10

Development of water wheels into turbines

The main shortcoming of the water wheel was size. Introduction of the tangential water wheel which

utilized water from a pipe at a high pressure led to a breakthrough of inventing smaller water wheels.

The design of the blades and the way water hits the blades also was another area to be explored in the

development of turbines. Because of these intelligent designs up to an efficiency of 95% could be got.

This led to the development of new types of turbines like the Francis turbines (mixed flow and airfoil

blade design), Kaplan (axial flow and airfoil blade design)

Turbine Overview

`They are two types of turbines; the impulse turbine and the reaction turbines

Impulse turbines

Reaction turbines

Differences between Impulse and Reaction Turbines:

S.No Impulse Turbine Reaction Turbine 1 In Impulse Turbine all hydraulic energy is

converted into kinetic energy by a nozzle and it is is the jet so produced which strikes the runner blades.

In Reaction Turbine only some amount of the available energy is converted into kinetic energy before the fluid enters the runner.

2 The velocity of jet which changes, the pressure throughout remaining atmosphere.

Both pressure and velocity changes as fluid passes through a runner. Pressure at inlet is much higher than at outlet.

3 Water-tight casing is not necessary. Casing has no hydraulic function to perform. It only serves to prevent splashing and guide water to the tail race.

The runner must be enclosed within a watertight casing.

4 Water is admitted only in the form of jets. There may be one or more jets striking equal number of buckets simultaneously.

Water is admitted over the entire circumference of the runner.

5 The turbine doesn't run full and air has a free access to the bucket.

Water completely fills at the passages between the blades and while flowing between inlet and outlet sections does work on the blades.

6 The turbine is always installed above the tail race and there is no draft tube used.

Reaction turbine are generally connected to the tail race through a draft tube which is a gradually expanding passage. It may be installed below or above the tail race.

7 Flow regulation is done by means of a needle valve fitted into the nozzle.

The flow regulation in reaction turbine is carried out by means of a guide-vane

assembly. Other component parts are scroll casing, stay ring runner and the draft tub.

8 Example of Impulse turbine is Pelton wheel.

Examples of Reaction Turbine are Francis turbine, Kaplan and Propeller Turbine, Deriaz Turbine, Tubuler Turbine, etc.

9 Impulse Turbine have more hydraulic efficiency.

Reaction Turbine have relatively less efficiency.

10 Impulse Turbine operates at high water heads.

Reaction turbine operate at low and medium heads.

11 Water flow is tangential direction to the turbine wheel.

Water flows in radial and axial direction to turbine wheel.

12 Needs low discharge of water. Needs medium and high discharge of water. 13 Degree of reaction is zero. Degree of reaction is more than zero and

less than or equal to one. 14 Impulse turbine involves less

maintenance work. Reaction turbine involves more maintenance work.

Choice of turbines

Depending on the head and capacity

Depending on efficiency and specific speed

Other factors also include

- Cost - Damage to silt

Power utilization

Demand survey

The following data collected during this survey include

- Socio-economic data e.g number of households and public facilities in supply area, availability of local industries, solvency of local people for electricity, acceptability of local people to the electrification scheme

REFERENCES

B.J Lewis, J.M CImbala, and A.M Wouden, (2014), Major historical developments in the design of water

wheels and Francis hydroturbines, The Pennsylvania State University, USA

Y.A Cenge and J.M Cimbala, (2013), Fluid Mechanics: Fundamentals and Applications 3rd edition, McGraw Hill, New York, USA Micro Hydro Power Scout Guide (2010), Germany