Closed Cycle Gas Turbine

Closed cycle gas turbine is divided into two types, namely gas turbine with direct closed cycle and gas turbines with   indirect closed cycle. In direct closed cycle gas turbine, cooler gas is heated in the reactor and expands through turbine, cooled in heat exchanger and it is compressed back into reactor. This cycle can also use other gas. There is not radioactive gas be discharged into atmosphere in normal operation. The most suitable fluid for this cycle is helium.

Figure 1: Direct Closed Cycle Gas Turbine

While on indirect closed cycle gas turbine, gas turbine with this cycle is combination of indirect open-cycle turbines and direct closed-cycle turbine, because reactor separate from working fluid by heat exchanger. While working gas was throwing heat into the atmosphere through heat exchanger. Primary coolant material that is usually used is water or helium gas.

Figure 2: Indirect Closed Cycle Gas Turbine

In this closed cycle, working fluid is not connected to surrounding atmosphere; thereby its purity can be maintained. This is very advantageous in terms of prevention of damage caused by erosion and corrosion. In this system can also be used with high pressure air up to 40 atm as the installation of steam, but the works did not experience phase change.

The advantages in closed cycle gas turbine are:

1. For the same power turbine has a smaller size
2. Can be used on high-pressure system
3. The use of fuel can be more efficient 

Reaction Water Turbine

The blades of reaction water turbine have special profile that results in decreased water pressure during flow through the blade. This different pressure exerts force on the blade so that the runner (turbine part that rotates) can rotate. Turbine generator that works based on this principle is grouped as reaction water turbine. Runner reaction water turbine is fully immersed in water and in the turbine house.

Reaction water turbine can be classified as two types:

1. Francis water turbine

2. Kaplan and propeller water turbine

Kaplan-Propeller Water Turbine

Kaplan and Propeller turbines are included in reaction turbine type with axial flow. Kaplan and Propeller turbines is composed of the propeller as the boat. The propeller usually has three to six blades.

Figure 1: Kaplan and Propeller Water Turbine
(source: http://en.wikipedia.org/wiki/Kaplan_turbine)

Francis Water Turbine

Francis water turbine is one of reaction turbine type. A Francis water turbine is installed between the source of high pressure water at the entrance side and low water pressure at the exit side. Francis water turbine uses the blade steering. Steering blades directs incoming water tangentially. The steering blades of Francis water turbine may be fixed steering blade or adjustable steering blade which can adjust angle of blade. For use on various conditions of water flow using an adjustable steering blade is the right choice.

Figure 1: Francis Water Turbine
(Source: http://en.wikipedia.org/wiki/francis_turbine)

Figure 2: Skecth of Francis Water Turbine

(Source: http://lingolex.com/bilc/engine.html)

Crossflow Water Turbine

Crossflow water turbine is one of impulse water turbine type and can be also known as the Michell-Banki turbine. Michell-Banki is discoverer of this turbine type. Crossflow water turbine can be also called as Osberger turbine because of Osberger is company that manufactures Crossflow water turbine. Crossflow water turbine can be operated at discharge 20 liters/sec up to 10 m³/sec and head between 1 m up to 200 m.

Crossflow water turbines use rectangular nozzle which has width suitable the width of runner. Jets of water enter turbine and hit blades resulting in conversion of kinetic energy into mechanical energy. Water flows out hit the blade and provide energy (lower than at admission) and then leave the turbine. Runner turbine is made of several blades that are attached on a pair of parallel plate.

Figure 1: Crossflow Water Turbine
(source: http://europa.eu.int/en/comm/dg17/hydro/layman2.pdf)

Turgo Water Turbines

Turgo water turbines can operate on the head 30 m up to 300 m. As Pelton water turbine, Turgo water turbine is categorized in impulse water turbine type, but its blades is different. Jets of water from the nozzle hit the blades at angle 20^o.

Rotational speed of turgo water turbine is greater than the pelton water turbine. As a result, the transmission can be ​​possible distributed directly from the turbine to the generator thereby increasing total efficiency and lowering cost of maintenance.

Figure 1: The Blades and Nozzles of Turgo Water Turbine

Pelton Water Turbines

Pelton water turbines are grouped in water turbine impulse. Pelton water turbine consists of a set of running blades that are rotated by jets of water which is sprayed from one or more device called as nozzle. Pelton water turbine is one of water turbine type that has highest efficiency. Pelton water turbine is suitable for high head.

Figure 1: Pelton Water Turbine
(Source: http://en.wikipedia.org/wiki/pelton_wheel)

Form of turbine blade consists of two symmetrical parts. Blade is formed so that the jets of water will hit the middle of blades and jets of water will be turned in both directions so that it can reverse the jets of water well and release the blade from side forces. For turbines with high power, water spray system is divided by multiple nozzles. Thus the diameter of water jet can be reduced and bucket blade will be smaller. Pelton water turbines for large-scale plant require approximately 150 meters head but for the micro-scale 20 meters head is adequate.

Figure 2: Pelton Water Turbine Blade

Figure 3: Pelton Water Turbine Nozzle
(Source: http://europa.eu.int/en/comm/dg17/hydro/layman2.pdf)