Patent Grant
7059341
The invention relates to discharge ducts for pumping water from a supply reservoir to a delivery reservoir.
In particular this invention relates to a method to minimize head loss in discharge ducts between a supply and a delivery reservoir.
The overall head acting on a pump is the sum of static water level difference in suction and delivery reservoirs of a pumping system, the dynamic head difference at suction and delivery and the losses in the ducting.
In the case of very large flow pumping system, the losses are of prime importance as any increase in pumping head due to friction, obstructions like valves including non return valve and the like could cause a sizeable power loss.
Typical parameters are provided in the below shown tables:
For a single discharge duct in the conventional system
Similar parameter for multiple discharge ducts
The method and apparatus of this invention seeks to obviate the problems that might be faced at the start of the pumping system and in the event of a sudden stoppage of the pumping system such as from a power failure.
Another object of this invention is to devise a system and a discharge duct which does not need non return valves and butterfly valves.
Still another object of this invention is to provide a system which has a reduced head and therefore reduces energy losses during operation.
Though the system of this invention looks very simple it is associated with complex flow phenomenon like, entrapment of air during starting of the system and flow reversal in case of power failure due to siphon action which have to be obviated.
According to this invention there is provided a discharge duct for discharging pumped water from a supply reservoir defined by a first minimum water level and a supply reservoir floor to an operatively higher located delivery reservoir defined by a second minimum water level and the delivery reservoir floor, the said discharge duct being defined by:
an inlet at one end of the discharge duct in communication with the outlet orifice of a conventional pumping device fitted at the supply reservoir,
an outlet at the other end of the discharge duct, said outlet, in the operative configuration of the discharge duct, being below the second minimum water level;
a peak at a location relatively closer to the delivery reservoir and at a height between h+2d+0.5 meters and h+2d+8 meters where h represents the height difference between the floor levels of the supply reservoir and the delivery reservoir and 2d represents the diameter of the cross section of the discharge duct;
inclined sections leading from the peak towards the said inlet and the said outlet, the angle of inclination of the inclined sections leading to the said outlet and the said inlet being at an angle lying between 45 and 60 degrees to a virtual central axis [B—B] passing through the said peak;
a siphon breaking orifice provided at the peak or within five degrees of the peak towards the delivery reservoir; and
an evacuator orifice provided at a location on the inclined section leading from the peak towards the said outlet at a position 10 to 17 degrees off the peak towards the delivery reservoir.
Typically, the discharge duct is arcuate at the peak.
Typically, a pneumatic controlled valve with a separate power back up is fitted to the siphon breaking orifice.
In accordance with a preferred embodiment of the invention a vacuum pump is provided at the evacuator orifice.
In accordance with another aspect of this invention, there is provided a method of delivering water through a discharge duct from a supply reservoir to a delivery reservoir located at a level operationally higher than supply reservoir, said method comprising the steps of:
The discharge duct in accordance with this invention is a unique configuration involving two phase flows during start up of the pumping unit and during sudden stopping of the unit due to power failure. The evolution of the discharge duct is based on a combination of the principles of Froude Similarity, Reynolds Similarity and the computational approach.
The discharge duct in accordance with this invention is devised after careful experiments and application of concepts to correlate the results to prototypes.
The practical embodiment of the discharge duct of this invention is devised using model studies and calculations based partly on Froude Similarity and partly computational tools to arrive at sizing of equipment to establish the siphon and breaking of siphon for saving of valuable energy during pumping and saving of work already done after the sudden failure of power.
The two parameters i.e. the pressure levels at the interface and the volume contained in the cavity are used to finalize the sizing of the evacuator orifice nozzle and the siphon breaker valve orifice. In case of model tests the air is sucked using a vacuum pump. The vacuum pump is essential so as to suck air to still lower pressure than prevailing in the cavity. The evacuator system is designed using compressible flow analysis to arrive at nozzle size for the prototype.
This way the problem of air entrapment during starting of the pumping is resolved. In the absence of this device, the discharge duct would have had to be provided water supply to the line without establishing siphon action advantage for the discharge duct and wasting energy over the extra static head provided.
The invention also addresses the issue of the flow situation after sudden power failure. A significant feature of the system of this invention is that it dispenses with the use of a Non Return Valve or any device in the system to close down flow reversal. Siphon action gets established after power failure and flow direction is reversed. If this is allowed, huge amount of work already done in pumping water to higher elevation is lost.
To avoid this phenomenon, in accordance with this invention the siphon action is broken by injecting air. There is an advantage in this situation. The pressure in the duct is sub-atmospheric. Air can be injected by using a simple controlled vent at the peak which is opened immediately after power failure so that the siphon is not established. This results in breaking the siphon. However it is essential to ensure that sufficient air enters to break the siphon action. It is observed experimentally that if the air injected is not sufficient, water flowing with high velocity in reverse flow condition carries the air bubbles away without breaking siphon.
Air valves are chosen to supply sufficient quantity of air to achieve siphon breaking. The period of reverse flow operation should be limited to two to four seconds.
In embodiment envisaged in accordance with this invention NRV/butterfly valves are totally eliminated. This arrangement is required to overcome the serious problems during start up and unscheduled power failure.
It is impossible to conduct the experiment in the prototype because of the huge size of the pumping system. Instead a model is made out in proportion, to study the behaviour of flow in the duct.
The uniqueness lies in the fact that model study cannot be carried out based on Froude's similarity alone because it is not a free surface flow phenomenon. Reynolds similarity also will not be applicable in isolation because of two-phase flow. It is also difficult to use computation tools alone to resolve the matter as it involves transient flow studies with two-phase flow. It is possible to devise the sizes using a combination of all the above three methods using CFD.
A model study is conducted using Froude's similarity principle. A geometrical similar model can be used with appropriate flows to capture the phenomena of air entrapment during starting of the pump and reverse siphon action during abrupt power failure. A computational model representing the prototype is generated using a solid modeler. The air trapped in the prototype is estimated using the geometrical scaling in the computational model. For instance, the amount of the air to be removed from the discharge duct is found to be approximately 15 m3 in a particular case. The compressible flow parameters are used to estimate the sizing of the air orifice in the evacuator orifice using appropriate coefficient of discharge.
Similarly, the sizing of siphon breaking arrangement is estimated from the quantum of air to be pushed in to effectively break the siphon in a relatively shorter time period. The volume of air to be injected in a particular experimental work to break the siphon was approximately 45.97 m3.
The invention will now be described with reference to the accompanying drawings, in which
Referring to
In the prior system 100 there is shown Components of a pumping system using conventional method are seen in
1. Concrete volute pump assembly [CVPA] having a pump unit PU
2. At least two controlling valves over the discharge pipe (Non-return valve NRV and hydraulic/pneumatically control butterfly valve. BV)
3. Discharge duct, DD connecting pump CVPA from the supply reservoir RES1 having a minimum water level MWL1 to a delivery reservoir RES 2 having a minimum water level MWL2. The discharge duct is made up of two horizontal portions HP1 and HP2 connected to each other via an inclined portion IP.
Advantages of the prior art system shown in
The Control for the over flow/reverse flow is provided by the butterfly valve BV and the non ensures control of the reversal of flow when power fails/pump trips. The presence of the obstruction to the flow in terms of Non-Return Valve/Butterfly valve NRV is the source of head loss.
As seen in
The peak level P should be in the range of 0.5 M to 8 M from the water level MWL2 in the delivery reservoir RES2. The limit of 0.5 M come from the fact that below this there will not be any siphon action. The highest value of 8 M comes from the fact that the static pressure at the peak location will approach vapor pressure of liquid causing column separation and breaking of the siphon action.
From the peak inclined sections IS1 and IS2 lead towards the discharge inlet DI and discharge outlet DO respectively. The peak P lies on the imaginary axis BB and the inclined sections are inclined at angles θ1 and θ2 which are respectively 45 to 60 degrees with respect to the axis BB. A siphon breaker valve orifice SBV is provided as seen in the enlarged
The discharge duct DD1 has a flow in two phase (air plus water) at the start of pumping. The two phase flow features are derived from experimental studies and the single-phase flow features of CFD tools are used to estimate pressure levels, velocities etc.
The invention will now be described with reference to
Static head (difference in water level at delivery to supply reservoir RES2 and RES Dynamic head Friction losses in the discharge duct.
During pump first start condition, the discharged water starts to flow towards down stream reservoir RES2 with discharge duct partially filled. The remaining portion of the discharge duct will be filled with air. As the water level in the discharge duct increases above the opening of the discharge duct, the air in the discharge duct gets trapped. This air gets compressed and stays as a pocket near the peak position P of the discharge duct DD1. The presence of this bubble will not give the benefits of siphoning action and the pump will have much higher head than expected causing loss of power. One of the features of this invention is to remove this air pocket BF1. During start of the operations, as seen in
The height of the air bubble from peak of the discharge duct is measured for various flow conditions. The volume of air trapped is estimated using a solid modeling software. The solid modeler has a capacity to bring out volume of the cavity formed by curved surfaces. The solid models are prepared for the geometrical models as well as prototypes. Knowing the shape of the duct and the height of interface between air and water from the peak position, the volume of the cavity is brought out from solid model. Using the same scale ratio the air trapped in prototype is estimated from the solid model. The angles of inclination 01 and 02 are optimized to collect the air bubble BF1 at the peak so as to ease the evacuation of entrapped air at the evacuator EJ and also to ensure a smooth flow during pump operation. During experimental studies it has been observed that the collection of air is at the peak more towards the exit of discharge duct in the inclined section IS2. Due to this reason the evacuator is positioned at an angle of 10 to 17 from the peak of the discharge duct.
To remove the compressed air bubble/air pocket BF1, the evacuator valve EJ is actuated by means of the Lever VL1. This causes the compressed air to be evacuated. A vacuum pump VP may be fitted advantageously to the evacuator valve EJ to assist in the evacuation of air from the air pocket BF1. Once all air is evacuated a single water column W as seen in
A siphon breaking valve SBV is provided at the peak P or within five degrees off the peak towards the discharge reservoir RES2 in the inclined section IS2. Siphon breaker valve SBV is typically a pneumatic controlled valve with a separate power back up of direct current solenoid valve. And can be controlled by actuating lever VL1 from the pump station at the Reservoir RES1. This will operate in preset time when the power goes off in the pumping station. Also it has advantageously a fail proof opening mechanism if it fails to open in preset time. When valve SBV is actuated air is introduced into the peak area P and forms a bubble BF2 between the water columns WC1 and WC2. This bubble BF2 enlarges as more air is sucked in as seen in
Preferred velocity in pipes ranges from 2–3 m/s. This means for a flow of 4 m3/s to 6 m3/s the diameter will range from 1.3 m to 1.95 m respectively. Therefore advantageously the discharge duct is practically designed to have a velocity of 2 m/s.
Experiments were carried out to compute the different values for selected discharge ducts in accordance with this invention which are shown in the table below where cases refer to actual examples of ducts which were fitted between a supply reservoir and a discharge reservoir.
It is impossible to conduct the experiment in the prototype because of the huge size of the pumping system. Instead a model is made out in proportion, to study the behaviour of flow in the duct.
The uniqueness lies in the fact that model study cannot be carried out based on Froude's similarity alone because it is not a free surface flow phenomenon. Reynolds similarity also will not be applicable in isolation because of two-phase flow. It is also difficult to use computation tools alone to resolve the matter as it involves transient flow studies with two-phase flow. It is possible to devise the sizes using a combination of all the above three methods using CFD.
A model study is conducted using Froude's similarity principle. A geometrical similar model can be used with appropriate flows to capture the phenomena of air entrapment during starting of the pump and reverse siphon action during abrupt power failure. A computational model representing the prototype is generated using a solid modeler. The air trapped in the prototype is estimated using the geometrical scaling in the computational model. For instance, the amount of the air to be removed from the discharge duct in the aforesaid cases was found to be approximately 15 m3. The compressible flow parameters are used to estimate the sizing of the air orifice in the evacuator orifice using appropriate coefficient of discharge. The diameter of the evacuator orifice was 300 mm. By placing suitable reducer means the bore of the orifice can be reduced.
Similarly, the sizing of siphon breaking arrangement is estimated from the quantum of air to be pushed in to effectively break the siphon in a relatively shorter time period i.e. 2 to 4 seconds. The volume of air to be injected in the particular experimental work to break the siphon was approximately 45.5 to 46 m3. The diameter of the siphon breaking orifice was 600 mm. By placing suitable reducer means the bore of the orifice can be reduced.
The inventors of the present invention worked on investigating these flow features by conducting a model experiment combined with latest computational tools and correlated the results to large scale prototypes handling 72000 M^3/Hr flow.
In the method of making the discharge duct of this invention a transparent model was constructed using Froude Similarity principal. The model ratio is chosen to make the experiments practical. The model is constructed typically with a geometrically similar discharge duct with 150-mm diameter/duct width.
The operating flow for the ducts was estimated from Froude Similarity. The cases of Concrete Volute pump and Vertical Pump were modeled separately as the geometry and flow conditions are different for both these units.
While considerable emphasis has been placed herein on the structures and structural interrelationships between the component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the invention. These and other changes in the preferred embodiment as well as other embodiments of the invention will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.
| Number | Date | Country | Kind |
|---|---|---|---|
| 953/MUM/2003 | Sep 2003 | IN | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 967512 | Gregory et al. | Aug 1910 | A |
| 3763887 | MacVey et al. | Oct 1973 | A |
| 5123438 | Henderson | Jun 1992 | A |
| 5199455 | Dlouhy | Apr 1993 | A |
| Number | Date | Country | |
|---|---|---|---|
| 20050058511 A1 | Mar 2005 | US |
