REACTION TURBINE

 

REACTION TURBINE

IMPULSE REACTION TURBINE: - Available Inlet Energy is both pressure and Kinetic Energy.

Examples: - Francis Turbine

PURE REACTION TURBINE: -Available Inlet Energy is only pressure Energy.

RADIAL FLOW TURBINE: -Direction of flow is radially inward or outward.

Examples: - Old Francis Turbine

AXIAL FLOW TURBINE: -Direction of flow is parallel to the axis of shaft.

Examples: - Kaplan, Propeller

MIXED FLOW TURBINE: -Direction of flow is radially at inlet and axially at outlet.

Examples: - Modern Francis Turbine

 

RADIAL FLOW REACTION TURBINE: -

Fig.1 | Radial (Inward) Flow reaction turbine

MAIN COMPONENTS OF RADIAL FLOW TURBINE: -

1.   Casing –

• Shape – Casing’s shape is spiral and reducing cross section area.

2.   Guide vane –

• It is a fixed circular wheel, vanes are mounted on it.
• Allows the water strikes the runner vane without shock.
• It can control the amount of water striking the runner.

3.   Runner -

• It is a moving circular wheel.
• Radial curve vanes are mounted on the wheel.
• Made of –Cast steel, Stainless steel etc.

4.   Draft Tube –

• It is a tube of gradually increasing cross section area.
• It is fitted on the outlet portion of the turbine.
• It is used to increase Pr. Energy of water at exit because pressure energy at exit is less than the atmospheric pressure.
• It is also reduce the negative suction head and possibility of cavitation.

 

TYPES: -1. Inward flow turbine, 2. Outward flow turbine

 

1.   Inward flow Radial turbine: -

FIG. 2  | INWARD FLOW REACTION TURBINE

• In this turbine the flow of water is occurs towards inward direction.
• Guide vane is all around the runner.
• This type of turbine is used maximum.

WORK DONE AND EFFICIENCIES: -

Work done per second = ρAV₁ (V_w1u₁±V_w2u₂)

Work done per second per weight =

= 1/g [V_w1u₁ +V_w2u₂] (Assuming β<90⁰)

 

Hydraulic Efficiency (η_H) = R.P. /W.P.

= [ρAV₁ (V_w1u₁+V_w2u₂)] / (ρAV₁g x H_net)

η_H = (V_w1u₁ +V_w2u₂) / (g x H_net)

If discharge is radial (β=90⁰)

η_H = V_w1u₁ / (g x H_net)

 

2.   Outward flow Radial turbine: -

FIG. 3 | OUTWARD FLOW REACTION TURBINE

• In this turbine the flow of water is occurs towards outward direction.
• Runner is all around the guide vane.

 

FRANCIS TURBINE: -

FIG. 4 | FRANCIS TURBINE

• It is an inward flow re action turbine.
• Old Francis Turbine –Purely Radial turbine
• Modern Francis Turbine – Mixed flow turbine (Water Enter Radially But exit axially).
• It is a medium head and medium sp. Speed turbine.
• No of Blade generally used in Francis turbine is 16 to 24.

 

 WORK DONE AND EFFICIENCIES: -

Work done per second = ρAV₁ (Vw₁u₁)            [∵ β = 90⁰]

Work done per second per weight = 1/g [V_w1u₁]

Hydraulic Efficiency (η_H) = R.P. /W.P.

= (V_w1 u₁) /g x H_net

IMPORTANT RELATION: -

n = B₁ /D₁ [Where, B₁ = Width of runner, D₁ = Dia. Of runner]

Flow Ratio = V_f1 / V₁ = V_f1 / √(2gH_net)

Speed Ratio = u₁ /V₁= u₁ / √(2gH_net)

Discharge (Q) = πD₁B₁V_f1 = πD₂B₂V_f2

 

AXIAL FLOW REACTION TURBINE: -

• In this turbine water is flow parallel to the axis of shaft.
• Energy at the inlet is both pressure and kinetic energy.
• It is a low head and high discharge turbine.
• It is a low specific speed turbine.
• As blade is less in this turbine, friction is less but load on the blade is more.

Discharge (Q) = π/4[D_o² – D_b²] V_f1

Where D_o =Outer Dia.

D_b = Bosh Dia.

1.   KAPLAN TURBINE: -

• In this turbine vanes are adjustable.
• In this turbine no. of blade is 4 to 8.

 

2.   PROPELLER TURBINE: -

• In this turbine vanes are fixed.