GB2354043A

GB2354043A - Cooling radial flow turbine

Info

Publication number: GB2354043A
Application number: GB9919886A
Authority: GB
Inventors: Fred Starr
Original assignee: Individual
Current assignee: Individual
Priority date: 1999-08-24
Filing date: 1999-08-24
Publication date: 2001-03-14
Also published as: GB9919886D0

Abstract

A coolant, such as hydrogen, helium, or a mixture of the two, is admitted to the disc 1, of a radial flow turbine by means of channels 14, in a shaft 13, and passes via heat transfer passages 7 to heat rejection channels 12, which are etched into the shaft 13. A hollow plate 3, is provided, which may be evacuated, or may contain material of low conductivity. The internal surfaces of the disc 1 and the surfaces of the plate 3, may be etched to provide a network of heat transfer passages. Heat may be removed from the coolant, as it passes along the shaft, by means of cooling water pumped into a passage 15. Alternatively, heat may be removed by oil or rejected to the environment by other means. The coolant may be circulated by an external pump or by a combination of centrifugal forces and temperature-induced coolant density changes.

Description

1 2354043 Radial Inflow Gas Turbine Improvement 1. This invention relates

to the improvement in efficiency and output of radial flow gas turbines by permitting a substantial increase in turbine inlet temperature without the use of new or unusual materials.

2. Radial inflow flow turbines, sometimes referred to as centrifugal gas turbines have many advantages over axial flow machines. They are compact, do not suffer from Reynolds number and scale effects to anything like the same effect, so that for localised and automotive type power production or energy conversion, up to 5 MW they would be the preferred choice of prime mover.

3. The principal shortcoming of radial flow machines is that of low thermal efficiency, which is determined basically by the turbine inlet temperature and the polytropic efficiency of the compressor and radial inflow turbine components. Furthermore, turbine outlet temperature basically determines the work output of the machine, hence it is a vital feature influencing the performance.

4. Unfortunately due to the lack of progress in developing high temperature materials suitable for use in radial inflow turbines, the increase in turbine inlet temperature has stagnated in this type of machine. This is not so for axial flow gas turbines, where it has proved possible to utilise more and more sophisticated means of internally cooling vanes and blades. Hence there is now a wide disparity between the turbine inlet temperatures of radial inflow and axial gas turbines.

5. This disparity has been accentuated even more by the development of thermal barrier or insulating coatings that are applied to the external surfaces of axial flow turbine stator and rotor blades. Such coatings are only beneficial when the blades themselves are cooled. Since the constructors of conventional radial inflow machines consider it to be impractical to cool this type of gas turbine, there has been very little interest in the use of thermal barriers in this respect.

6. The most common approach to turbine blade cooling in axial flow machines is to utilise a portion of the high pressure air from the compressor and to pass this through hollowed out axial flow turbine blades. Coolant flow is turbulent rather than laminar. After producing the cooling effect this air is discharged through holes or slots in the blade surfaces, more or less parallel to the combustion gas flow. This loss of air from the compressor can be deemed to be a parasitic loss and will be referred to as such, subsequently. More recently systems utilising steam or high pressure water have been envisaged to give improved cooling.

7. None of these techniques are suitable for radial inflow machines. If parasitic type air cooling was attempted it would be difficult to arrange a suitable path from the outlet compressor flow through to the radial inflow turbine section of the machine. Furthermore it would be difficult to arrange the discharge of cooling air through the vanes and disc of the turbine without disrupting the natural inward flow of combustion gases. Steam or water cooling would create the same problems, and here it would be necessary to provide a source of high purity water to prevent fouling of the cooling passages.

8. It should be noted that both air and water cooling of axial flow turbines rely on an external pressure source or pump to force the cooling fluid through the turbine blades.

2- hollowed out turbine disc. In another form, which may be more convenient, the respective channels may be etched or otherwise formed into outer surface of the sandwich.

18. The sandwich plate 3, in the proposed example will be of complex construction, and will itself be hollow 10 so as to impede the flow of heat from the outward flowing to the inward flowing helium. To reduce the through conductivity of the sandwich plate this will be evacuated, or will contain material of low conductivity. Webs and stiffeners may be incorporated so as to maintain rigidity under the effect of external pressure.

19. The size of the heat transfer passages 7 within the hot surface of the disc or in the vanes, from which heat is to be abstracted, will be principally of the type intended to give laminar flow, without undue pressure drop, although portions of the disc may have differently arranged passages.

20. It should be noted that because of the " forced vortex effect " the flow of helium would not take place without the aforesaid density differences. However, providing there is a density induced flow in the first place, angling the flow passages may be used to assist the flow.

21. After the inward flowing helium reaches the shaft region I I it moves along a series of longitudinal internal heat rejection channels 12 which are cut or etched into the shaft 13. The flow of helium then returns along another set of longitudinal channels 14 which are off-set from these so as to bring the cooled helium back to the hub region. In the example shown, the shaft 13 and the hub region of the disc contain a lengthways central hollow passage 15 into which cooling water is pumped, so as to remove the heat from the helium as it passes along the shaft heat rejection channels. Figures 2, 3 and 4 show the form of the flow passages within the shaft proper and at points 6 and 9 and the direction of flow of helium at these points.

22. In the proposed example, the internal surface of the hollowed out radial turbine, from which the heat must be removed is etched so as to give a net work of heat transfer passages radiatmig from the entry point of the cool helium into the disc area and then outwards toward the rim. Over this area the disc like sandwich plate 3 is brazed or diffusion welded into place so as to produce true fully enclosed heat transfer passages.

23. Similar passages 16 are etched or cut into the cool side of the sandwich plate that direct the return or 'inward flowing helium. Heat transfer is not important at this point, so that the channel width is set to minimise pressure drop on the cool side of the sandwich plate, rather than on the hot side where there must be a balance between heat transfer and pressure drop.

24. Upon leaving the hollowed out disc, the helium is made to pass along the cooling channels, which are machined into shaft. Figure 2 shows that in the proposed embodiment to reduce manufacturing costs, the channels are first machined on the outer diameter of a primary shaft 13. An outer sleeve 17 is then shrunk fit, brazed, or diffusion welded over the inner shaft, so as to give true heat transfer passages and to provide a convenient bearing surface. Figures 3 and 4 show suitably disposed holes or slats in the outer sleeve to provide a convenient way of directing the outward and inward flowing flows of helium to and from the hot and cold surfaces of the disc. Arrows 18 and 19 show the direction of flow inward and out ward flows.

3 9. According the present invention the cooling process is provided by the continuous recirculation of a cooling fluid within the rotor disc and, if appropriate, vane surfaces. Heat is abstracted by the cooling fluid from these regions, and carried off by the cooling fluid, preferentially to the shaft region or other suitable surface, where the heat is then removed by an external coolant such as lubricating oil or cooling water. The cooling fluid, now at a low temperature, returns to the disc region where it begins the process of abstracting heat from the disc and vanes again.

10. The circulation of coolant relies on the surprising fact that the high centrifugal force on the rotor, which is transmitted to the cooling fluid, plus the difference in temperature between the fluid entering the rotor proper and that exiting the rotor proper provides the driving force for the circulation. Essentially the normal density differences between hot and cold fluids are greatly accentuated under the effects of the very high centrifugal forces. This difference, which can be translated into a pressure differential, provides the pumping action necessary for the recirculation process.

11. In principle any fluid which will exhibit a density difference due to a change in temperature would be a suitable coolant. However the ideal fluid should be non-corrosive, should not degrade or lose performance during use, and not induce undue energy losses when being circulated in the manner outlined.

12. It can be shown that helium or hydrogen, or mixtures of the two, particularly when used in a pressurised form have unique qualities for the proposed application, exhibiting high rates of heat transfer, high density changes, minimal corrosivity, and high stability.

13. A further feature of the invention is the use of passages of an appropriate type to maximise heat transfer at strategic_points utilising laminar flow techniques.

14. A specific embodiment of the invention will now be described by way of an example with reference to the accompanying drawings.

15. Figure I shows that so as to arrange the recirculation of fluid, the disc 1 of a radial inflow turbine is hollowed out, so as to make an enclosed space 2. Another disc or "sandwich plate"3 is inserted into the enclosed space so as to direct the flow of cooling fluid to the combustion surface of the disc 4, and to return it to the shaft where it is cooled 5. Through this technique a density difference is created between each side of the sandwich plate.

16. In the example shown pressurised helium enters the hub region 6 of the turbine on the hot or combustion side of the sandwich plate 3. Since it of high density at this point the helium is flung outward under the effect of centrifugal force towards the rim of the disc, through the coolant passages 7 which are etched into the face of the heated or "hot" side of the disc. Since the rim region 8 of the turbine is substantially hotter than the hub region 6, as the helium begins to move towards the rim it heats up, thereby suffering a density drop. The true density will therefore be at minimum as the helium reaches the rim. In the example cited the hot helium returns towards the shaft region radially inwards along the opposite side of the sandwich plate 9.

17. The sandwich plate 3 itself is an important feature of the design, and consists of a disc like plate or plates, which separates the outward going and inward going flows of helium. In the proposed example it provides a surface to contain the heat transfer and flow passages, which in this case are etched or otherwise formed into the surface of the

Claims

1. A radial inflow gas turbine of hollow form utilising self contained recirculation coolmig provided by an external pump or that motivated by natural forces so as to reduce disc surface and vane temperature and in which the abstracted heat in the recirculated cooling fluid is rejected to the environment via a secondary cooling system utilising water, lubricating oil, air or other convenient means of disposing of the heat.

2. A radial inflow turbine of hollow form utilising primarily self contained recirculation cooling so as to reduce disc surface and vane temperature in which the pumping action to maintain the flow of coolant is provided by a combination of centrifugal forces and temperature induced density changes in the coolant and in which the abstracted heat in the recirculated cooling fluid is rejected to the environment via a secondary cooling system utilising water, lubricating oil, air or other convenient means of disposing of the heat.

3. A radial inflow turbine of hollow form utilising primarily self contained recirculation cooling so as to reduce disc surface and vane temperature in which the pumping action to maintain the flow of coolant is provided by a combination of centrifugal forces and temperature induced density changes in the coolant, and in which the flow of coolant is controlled by suitable design of the coolant passages and flow passages, in conjuction with a sandwich plate to direct the flow, and in which the abstracted heat in the recirculated cooling fluid is rejected to the environment via a secondary cooling system utilising water, lubricating oil, air or other convenient means of disposing of the heat.

4. A radial flow turbine as in Claims 1,2 and 3 in which the heat which is taken from the disc or vane surfaces and is then rejected into a turbine shaft or other convenient assembly, cooled by the secondary coolant referred to Claim I through which the primary cooling fluid circulates continuously through internal cooling channels which are directly connected to the channels within the disc and or vanes referred to in Claim 3.

5. A radial flow turbine substantially as in Claims 1, 2, 3, and 4 in which the coolant consists of gases which will not induce corrosion of the internally surfaces of the hollow radial flow turbine nor decompose to produce deposits to any significant extent.

6. A radial flow turbine substantially as in Claims 1, 2, 3, and 4 in which the coolant consists of helium or hydrogen or a mixture of the two gases.

7. A radial flow turbine substantially as in Claims 1, 2, 3, and 4 'in which the coolant consists of helium or hydrogen at elevated pressure or a mixture of the two gases, also at elevated pressure.