US3174719A

US3174719A - Francis turbines and centrifugal pumps

Info

Publication number: US3174719A
Application number: US201881A
Authority: US
Inventors: Robert S Sproule; Lawrence M Boyd
Original assignee: Dominion Engineering Works Ltd
Current assignee: Dominion Engineering Works Ltd
Priority date: 1962-06-12
Filing date: 1962-06-12
Publication date: 1965-03-23
Anticipated expiration: 1982-03-23
Also published as: LU43868A1; CH435163A; ES281495A1; ES288946A1

Description

March 1965 R. s. SPROULE ETAL 3,174,719

FRANCIS TURBINES AND CENTRIFUGAL PUMPS Filed June 12, 1962 2 Sheets-Sheet l INVENTORS ROBERT 5. PE'OLJLE LAM/BEING. M. BOYD March 23, 1965 R. s. SPROULE ETAL 3,174,719

FRANCIS TURBINES AND CENTRIFUGAL PUMPS Filed June 12, 1962 2 Sheets-Sheet 2 F'EOM CASING xal 7 g 22 31 I3 36 o g 35 FEOM CASNG INVENTORS. ROBERT S. SPEOU LE LAM/$1}: NCE M. BOYD United States Patent 3,174,719 FRANCIS TURBINES AND (IENTRIFUGAL PUMPS Robert S. Sproule, Montreal, Quebec, and Lawrence M.

Boyd, Senneville, Quebec, Canada, assignors to Dominion Engineering Works Limited Filed June 12, 1962, Ser. No. 201,881 3 Claims. (Cl. 25326) This application is a continuation-in-part of our application Serial No. 120,301 filed June 28, 1961, now abandoned.

This invention relates to new and useful improvements in rotary fluid machines, whereby losses due to fluid friction are reduced. This is accomplished by the introduction of an additional fluid of less density and absolute viscosity than the working fluid, into the spaces surrounding the runner or impeller shrouds.

In hydraulic turbines, significantly improved efliciencies may be derived from reduction of fluid friction, the extent of such improvements being dependent on the operating hydraulic head and being progressively greater with increasing head. An improvement of 1% efiiciency, capitalized, could amount to as much as the price of the turbine.

The factors which atfect fluid friction are: The hydraulic characteristics of the working fluid, wetted area and velocity.

The general equation for friction loss is of the form F =K.n.d F friction horsepower K=a parameter n=the revolutions per minute of the machine d=the diameter of contact between the rotating parts and the working fluid.

Numerous attempts have been made to increase the efliciency of rotating fluid machines by reduction of fluid friction. These attempts have been based on the concept of reducing either K or d, or a combination of both of these factors, but the maximum possible benefits obtain able have never been realized.

The present invention relates to increasing the efliciency of rotary fluid machines by the optimum combination of the lowest value of eifective parameter (K), for specified design conditions, and minimum diameter of contact between the rotating parts and the working fluid.

The value of K decreases directly with decrease of absolute viscosity of the fluid between the relatively rotating parts. Therefore, by replacing the working fluid which is normally in contact with the outer surface of the rotating parts, by a fluid of less absolute viscosity, considerable improvements in efficiency can be realized.

Although this invention is applicable to turbines, pumps and pump-turbines, the following disclosure will, for the sake of clarity, be referred specifically to hydraulic turbines of the Francis type.

As an example, air is a fluid of less absolute viscosity than water, hence, within the field of hydraulic turbines, attempts have been made to increase the efiiciency of Francis turbines by replacing with air the water which is ordinarily between the stationary and rotating parts. A well known method has been to seal the runner band and crown at their peripheries, leaving the inner portions of the spaces between the crown and the stationary turbine parts, and between the band and the stationary turbine parts, open to the draft tube. Air is then introduced to these spaces so that leakage water can pass to the draft tube without accumulating in the spaces mentioned above.

In the case of Francis turbines designed for high head operation, the diameter of the runner at the inflow is ice considerably greater than the diameter at the out-flow. Since the fluid friction losses at a runner seal vary as the 4th power of the diameter, it is desirable to keep the seal diameter to the minimum practicable value. This is to say that the seal for the lower shroud of such a vertical Francis turbine according to this invention, is located at the lower extremity of the shroud, Where the diameter is minimum. The crown seal could actually be atfected on the runner shaft diameter, but this, although giving the minimum possible seal diameter would give rise to very high downward hydraulic thrust on the runner, with an increment of thrust bearing load which would in most cases be undesirable, if not intolerable. It is evident that the thrust increment due to employment of the minimum crown seal diameter would result in greater friction losses in the thrust bearing; this increase of thrust bearing losses could otiset the reduction of friction losses in the crown seal.

In the preferred execution of this invention, the crown seal diameter is intermediate between the outside diameter of the upper shroud and the diameter of the runner shaft, whereby the optimum compromise is affected and the minimum aggregate thrust bearing and seal losses is achieved.

Referring to the drawings:

FIG. 1 is a fragmentary sectional view embodying one execution of the present invention, as applied to a high head Francis turbine;

FIG. 2 is an enlarged partial sectional view taken on line 22 of FIG. 1, looking in the direction of the arrows;

FIG. 3 is a fragmentary sectional view showing the preferred execution of the present invention, as applied to a high head Francis turbine, shown opposite hand from FIG. 1.

In the drawings the invention has been shown by way of illustration as applied to a high head Francis turbine, but it is understood that it could be equally well applied to other types of rotary fluid machines.

Referring to the drawings wherein similar reference characters designate corresponding parts throughout, and more particularly to FIG. 3, the Francis turbine shown embodying the invention includes upper runner shroud 1 and lower shroud 2, connecting the runner blades 3 to each other and to shaft 4. Water under pressure is supplied to the runner at distributor 5 containing the conventional Wicket gates and is discharged, at much lower pressure, to the draft tube at 6. Seals, shown generally at 7 and 8, are of the type described in our co-pending application Serial No. 808,546 dated March 26, 1959, now Patent No. 3,081,975, suitably modified as described in the following, although they may be any type of conventional space seal embodying the aforementioned modifications.

Pipes

30 and 31 supply a relatively small flow of air to spaces 11 and 10 respectively.

To fully describe the operation of this invention, consider the turbine as starting from rest and running up to normal operational speed.

With the turbine at rest, spaces 10 and 11 are filled with water. As the runner commences to rotate, it imparts rotary motion to this water thereby subjecting it to centrifugal force. Introduction of air, which is a fluid of less density than water, to space 11 creates a void in the water by centrifugal action and, as the ratio by volume of air to water increases, the void extends progressively from the lower end 32, to the upper end 33, of the outside of the lower shroud 2. The water which has been displaced by the air escapes through clearance 14, whereupon it joins the main stream of water entering the runner. This is not to say that all water is expelled from space 11. Such water as remains has rotary motion imparted to it by the rotating body of air, acted upon by the lower shroud 2, and tends to climb the sloping wall 34. I

In the same way, introduction of air to space creates a void in the water by centrifugal action and, as the ratio by volume of air to water increases, the void extends progressively from the inner zone 35, to the outer zone 36, of the outside of the upper runner shroud 1. The water which has been displaced by the air escapes through clearance 13, whereupon it joins the main stream of water entering the runner. Again, not all water is expelled from space 10, and the remaining water has rotary motion imparted to it by the rotating body of air, acted upon by the upper runner shroud 1, and tends to run down the sloping wall 37, also any water which makes contact with the outside of upper shroud 1 between inner zone 35 and outer zone 36, will be expelled centrifugally through clearance 13.

In the event that air is supplied to spaces 18 and 11 in excess of that necessary to maintain a balanced condition, the excess air will escape through

clearances

13 and 14 and so automatically maintain a balanced condition. Any excess air which escapes will be of such a small amount that it will have no adverse affects on the operation of the turbine.

Conventional space seals are not effective enough to retain the air in spaces 10 and '11; water is therefore fed to

space seals

7 and 8 at a pressure higher than the air pressure. This water can normally be taken from any convenient source, for example, the penstock, by way of pipes 17 and 18 to

seals

8 and 7 respectively. Leakage across

sections

19 and 20 of

seals

7 and 8 respectively is small, due to the small pressure diiferential across these sections.

Sections

21 and 22 of

seals

8 and 7 respectively are subjected to substantially the full pressure drop across the turbine between the distributor and draft tube and the amount of this leakage is approximately the same as that through a conventional turbine.

The small amount of leakage water from seal sections 19 and 25) passes into spaces 10 and 11 respectively, and is subjected to the same actions as those imparted to the water originally in these spaces, as described above. This is a continuous and stable operation.

Leakage from

seal sections

21 and 22 passes through the turbine into the draft tube in a conventional manner.

From the foregoing it will be seen that we have provided new and improved means for obtaining all of the objectives and advantages of the invention.

We claim:

1. In a hydraulic turbine, a runner and a housing, said runner comprising an upper shroud provided with a sealing shoulder on its upper face, a plurality of blades and a lower shroud, a radial runner inlet bounded by said shrouds in the region of their similar maximum diameters, an axial runner discharge through said lower shroud in the region of its minimum diameter, the peripheral edges of said shrouds being positioned in cooperating relationship to corresponding bores in said housing dimensioned so as to provide running clearances between said peripheral edges and said bores, a lower seal cooperating with said lower shroud near to said minimum diameter, a stationary element of said lower seal associated with said housing, an upper seal cooperating with said sealing shoulder, a stationary element of said upper seal associated with said housing, said upper seal diameter being substantially less than the diameter of said peripheral edges, a lower annular space bounded by said lower seal, said housing, and said lower shroud, an upper annular space bounded by said upper seal, said housing, and said upper shroud outside of said sealing shoulder, means for introducing sealing water into each of said seals intermediate of its axial extremities, and means for introducing air into each of said annular spaces whereby centrifugal separation of air and water is effective in expulsion of water from said annular spaces by way of said running clearances.

2. A hydraulic turbine as claimed in claim 1 in which the upper seal diameter and the lower seal diameter are substantially the same. 3. .In a hydraulic turbine having a runner with axially spaced upper and lower shrouds to define a radial flow duct therebetween, each of said shrouds having a large diameter intake edge and a small diameter discharge edge, a housing about said runner having a distributor for discharging pressure liquid directly into the radial flow duct of the runner, said distributor having a close running clearance with the large diameter intake edges of the shrouds, said housing having upper and lower walls extending radially inwardly toward the axis of the runner but spaced therefrom so as to define therebetween annular chambers having smoothly continuous wall portions, labyrinthseal means interposed between the small diameter discharge edges of the shrouds and the adjacent upper and lower walls of said housing for preventing the escape of high pressure air into the low pressure end of the flow duct, conduit means providing communication between the supply of pressure liquid to the runner and the labyrinth seal means whereby the pressure liquid lubricates the labyrinth seal means, and means for supplying pressurized air to said annular chambers at a higher pressure than that of the pressure liquid in the distributor whereby, upon rotation of said runner, liquid is expelled from said annular chambers and is prevented from re-entering said annular chambers, the sole means for escape of the pressurized air being through the clearance spaces between the large diameter intake edges of the shroud and the distributor.

References Cited by the Examiner UNITED STATES PATENTS 1,823,702 9/31 Ring 253-117 1,934,628 ll/33 Powell 253-417 1,962,380 6/34 Briggs 253-117 3,051,441 8/62 Sproule 253-117 FOREIGN PATENTS 179,275 8/54 Austria. 184,880 3/56 Austria. 714,290 11/41 Germany.

KARL I. ALBRECHT, Primary Examiner.

WALTER BERLOWITZ, JOSEPH H. BRANSON, 112.,

Examiners.

Claims

1. IN A HYDRAULIC TURBINE, A RUNNER AND A HOUSING, SAID RUNNER COMPRISING AN UPPER SHROUD PROVIDED WITH A SEALING SHOULDER ON ITS UPPER FACE, A PLURALITY OF BLADES AND A LOWER SHROUD, A RADIAL RUNNER INLET BOUNDED BY SAID SHROUDS IN THE REGIONS OF THEIR SIMILAR MAXIMUM DIAMETERS, AN AXIAL RUNNER DISCHARGE THROUGH SAID LOWER SHROUD IN THE REGION OF ITS MINIMUM DIAMETER, THE PERIPHERAL EDGES OF SAID SHROUDS BEING POSITIONED IN COOPERATING RELATIONSHIP TO CORRESPONDING BORES IN SAID HOUSING DIMENSIONED SO AS TO PROVIDE RUNNING CLEARANCES BETWEN SAID PERIPHERAL EDGES AND SAID BORES, A LOWER SEAL COOPERATING WITH SAID LOWER SHROUD NEAR TO SAID MINIMUM DIAMETER, A STATIONARY ELEMENT OF SAID LOWER SEAL ASSOCIATED WITH SAID HOUSING, AN UPPER SEAL COOPERATING WITH SAID SEALING SHOULDER, A STATIONARY ELEMENT OF SAID UPPER SEAL ASSOCIATED WITH SAID HOUSING, SAID UPPER SEAL DIAMETER BEING SUBSTANTIALLY LESS THAN THE DIAMETER OF SAID PERIPERHAL EDGES, A LOWER ANNULAR SPACE BOUNDED BY SAID LOWER SEAL, SAID HOUSING, AND SAID LOWER SHROUD, AN UPPER ANNULAR SPACE BOUNDED BY SAID UPPER SEAL, SAID HOUSING AND SAID UPPER SHROUD OUTSIDE OF SAID SEALING SHOULDER, MEANS FOR INTRODUCING SEALING WATER INTO EACH OF SAID SEALS INTERMEDIATE OF ITS AXIAL EXTREMITIES, AND MEANS FOR INTRODUCING AIR INTO EACH OF SAID ANNULAR SPACES WHEREBY CENTRIFUGAL SEPARATION OF AIR AND WATER IS EFFECTIVE IN EXPULSION OF WATER FROM SAID ANNULAR SPACES BY WAY OF SAID RUNNING CLEARANCES.