Thursday, April 28, 2011

cross flow turbine

CROSS FLOW TURBINE





This impulse turbine, also known as Banki-Michell in remembrance of its inventors and Ossberger after a company which has been making it for more than 50 years, is used for a wide range of heads overlapping those of Kaplan, Francis and Pelton. It can operate with discharges between 20 litres/sec and 10 m3/sec and heads between 1 and 200 m. Water (figure 6.7) enters the turbine, directed by one or more guide-vanes located in a transition piece upstream of the runner, and through the first stage of the runner which runs full with a small degree of reaction. Flow leaving the first stage attempt to crosses the open centre of the turbine. As the flow enters the second stage, a compromise direction is achieved which causes significant shock losses. The runner is built from two or more parallel disks connected near their rims by a series of curved blades). Their efficiency is lower than conventional turbines, but remains at practically the same level for a wide range of flows and heads (typically about 80%).




 Site Data

According to the head, schemes can be classified in three categories:
. High head:                100-m and above
. Medium head:           30 - 100 m
. Low head:                 2 - 30 m
The site under consideration in the present work for installing a turbine is located in hyber Pakhtunkhwa with a head of 13.6m and can thus be categorized as a low head site. The volumetric flow rate available is 0.206m3/s.

 Theoretical Power Output

The theoretical power output is an assumption of the energy potential of the site with alue of the micro-hydro scheme. It can be calculated using the site head and volumetric flow rate. Following formula is true for the calculation of theoretical power output:
Pt = γηHQ
With an assumption of 80% efficiency, the theoretical power output comes out to be:
Pt = 21.94kW

 Runner Outer Diameter

The following steps are involved in the calculation of the runner outer diameter:
·         Selection of Generator rpm (Usually taken as 1500)
·         Selection of Speed Ratio (6:1 in our case)
·         Calculation of Runner rpm
The runner rpm is calculated using the generator rpm and the speed ratio, in our case the runner rpm is:
            Runner rpm = 1500/6
                            ω  = 250

Construction