Draft tube is used to increase the pressure from the low turbine exit pressure to the pressure of the surrounding to which the fluid is rejected.Only reaction turbines require a draft tube as there is low pressure at the exit of the turbine,where as in an impulse turbine the pressure at the inlet and the exit is essentially the same, which is above the pressure to which the fluid is rejected and thus it require no draft tube.
turbine will trip
in the case of impule turbine total energy at inlet is kinetic energy and in case reaction turbine energy at inlet is kinetic and pressure......
The comparison kaplan and francis hydro power turbine is as under: 1. Efficiency of Kaplan hydro power turbine is higher. 2. Kaplan turbine is more compact in cross-section and has higher rotational speed to that of francis hydro power turbine. 3. In Kaplan turbine, the water flow is axia and in francis trubine it is radial. 4. The runner blades in the kaplan turbine is less in number. 5. Specific speed of Kaplan turbine is 2 to 3 times that of Fancis turbine. 6. Friction loss in Kaplan turbine is less. 7. Francis turbine requires medium head while Kaplan trubines are low head hydro power turbines.
only moving blades
pelton turbine is used for high head low flow but the turgo turbine is used for low head high flow, in pelton turbine number of jet can increased but in turgo it can't be done, in pelton the water hits the bucket once at a time but in tugo it hits more than one
pelton turbines are suited to high head,low flow application but kaplan turbine are used for low head and a large amount of discharge needed. kaplan turbines are expensive to design,manufacture and install as compared to pelton turbine but operate for decades.
Draft tube is used to increase the pressure from the low turbine exit pressure to the pressure of the surrounding to which the fluid is rejected.Only reaction turbines require a draft tube as there is low pressure at the exit of the turbine,where as in an impulse turbine the pressure at the inlet and the exit is essentially the same, which is above the pressure to which the fluid is rejected and thus it require no draft tube.
HP Turbine is High Performance Turbine LP Turbine is Low Performance Turbine
1) Impulse turbine 2) reaction turbine
impulsive turbine reaction turbine
1. To reduce velocity/ kinetic energy of water making exit thereby converting kinetic energy to pressure head allowing turbine to be installed above tail pool level. 2. To create negative suction head. 3. Provide added head.
turbine will trip
The inward flow reaction turbine having radial discharge at outlet is called Francis turbine
in reaction turbine pressure compounding is employed as every stage has a set of nozzle ring nozzle control is not feasible.
Due to high KE at the exit of reaction turbine, there would be a loss of overall reduction in KE. So to prevent this loss, the draft tube is provided which produces nett effect of increasing the pressure head at the expense of KE. So this helps the effective pressure head to increase between the inlet and exit of reaction turbine.
in the case of impule turbine total energy at inlet is kinetic energy and in case reaction turbine energy at inlet is kinetic and pressure......