The purpose of this paper is to offer the reader some insight into how a bladeless steam turbine can be constructed and used. The use of inexpensive slotted disc turbines in place of much more expensive bladed turbines can fill a void in the need to convert heat energy to electrical energy, and can help to reduce dependence on the electrical grid. Slotted discs may be used in other applications such as gas turbine and hydroelectric applications. It is the goal of the author and inventor of the slotted disc to encourage qualified readers to experiment with this invention and to share the results with others. The following discussion is strictly theoretical and includes only conceptual designs. The reader is encouraged to reduce these concepts to practice. The Holy Grail in this business will be a 5kW to 10kW steam or gas turbine generator, the size of a bread box, at a cost of less than $200.00, that can supply the needs of an average household.
The Slotted Disc.
A slotted disc, illustrated in Fig. 1, is made from a round flat disk of sheet metal. Slits are cut along the radials of the disk and tabs are formed by expanding the metal on one side of the slit in such a manner as to form a tab, and therefore an opening through which steam can pass. The combination of the opening and the tab is referred to as a slot. The length and position of the slots, the angle of the tabs and the number of slots are important to the operation of the disc. In the case of steam turbines, steam properties, mass flow of the steam and the number of discs are critical to the expected power output of the turbine and are beyond the scope of this discussion.
Rotation of the disc is caused by the sum of the reaction forces, created by a change in direction of the mass flow of steam through the slots in the disc. As the steam passes through a slot, it hits the tab and changes direction. As this action occurs, some energy is converted to mechanical energy and is lost from the steam. This loss of energy causes the steam to cool resulting in a reduction of pressure from one side of the disc to the other side. This results in a change in the properties of the steam. In bladed turbines the diameter of each consecutive bladed wheel, or turbine stage, is increased to compensate for the change in the steam properties. In the slotted disc turbine, it is not necessary to vary the diameter of the disc, and therefore the diameter of the casing. The same effect can be achieved by increasing the length of the slots, by changing the angle of the tabs, or a combination of both.
The Steam Turbine.
A steam turbine assembly is illustrated in Figure 3. The operation of a steam turbine relies on the temperature and pressure differences between the intake and the exhaust steam. It is noted that adding nozzles to the intake stream can attain some impulse forces. Increasing the number of discs in the system results in reducing the rotational velocity of the turbine, and this reduces the gearing needed to drive other devices. A set of discs in a turbine is referred to as a disc-stack. There are theoretical limits as to how many discs can be added.
Types of Discs.
There can be two types of discs in a turbine, a rotor disc and a stator disc. The same fabrication method can be used to forms both types. The main difference is that the stator disc is essentially a mirror image of the rotor disc.
The purpose of the stator disc, also known as a guide disc, is to redirect the flow of steam in such a manner that the mass flow tends to maintain an axial direction. The stator disc is attached to the case and does not rotate. The hole in the center of the disc is larger than the shaft to prevent contact with the shaft as it rotates. The disc may be sealed at the boundary with the shaft or a bearing surface may be designed to provide added support to the shaft.
The rotor disc is attached to the shaft and transfers forces to the shaft. These forces are derived from steam passing through the slots. The sum of the forces on the shaft produces torque that causes the shaft to turn.
To avoid use of the term turbine stage, a set of rotor discs mounted on a shaft in a bladeless turbine is referred to as a disc-stack.
The 32-slot disc assembly in Figure 2 illustrates one concept for attaching a single disc to a shaft. The outer ring can be attached to the disc using spot welds, solid rivets or by other means. This ring provides additional stiffness and strength to the disc. It is probably needed only in discs greater than 10″ in diameter. The flange in the illustration is attached to the disc using screws or solid rivets and is pinned or keyed to the shaft. The drawing shows both a key and a pin but only one or the other is needed.
A Turbine Assembly Concept.
Figure 3 shows a conceptual design of a slotted disc turbine assembly. The tabs on both the rotor and stator discs are clearly illustrated. Steam flows from left to right from an input port through the disc stack and out the exhaust ports. The chamber on the left acts as a steam header. Two exhaust ports are shown but more can be added. Exhaust port connections to a condenser are not required in a non-condensing system and steam could be exhausted directly to the atmosphere. The nozzles are shown only to illustrate a method of speeding up intake steam to achieve some impulse action on the first slotted disc. The stators are shown in solid black. Seals are shown around the rotors but may not be required if close tolerances can be held. Adding seals would tend to increase efficiency but would considerably complicate the fabrication requirements. A belt pulley is shown as one way to achieve a mechanical connection to a generator, alternator, pump or other device. A flywheel could be added to smooth out the operation of the turbine if required. Bearing assemblies are shown on both ends of the shaft.
Copyright 2005 Robert D. Saunders
All Rights Reserved
September 14, 2005source: here