Field of the Invention The present invention relates to pumps and pumping methods. Background of the Invention

Airlift pumps are known as useful way of raising fluids in particular applications. As with all fluid pumping applications, improving pump efficiency is important. One pumping application where efficiency is particularly important is in relation to pumped storage or recirculation systems that operate to raise fluid against gravity or another bias, and then to recapture energy from the raised fluid using a turbine or other recovery system. The present invention aims to address at least one disadvantage associated with the prior art, whether identified herein, or otherwise.

Summary of the Invention In the first aspect the present invention provides a pump comprising:

a riser with a lower inlet and an upper outlet and a downpipe with a lower outlet and an upper inlet,

wherein the riser is coupled to a buoyant fluid introducing means operable in use to introduce buoyant fluid into working fluid in the riser to thereby cause the working fluid to discharge from the upper outlet of the riser, and then to pass into the upper inlet of the downpipe for delivery to the lower outlet of the downpipe; and characterised in that the lower outlet of the downpipe is in use in contained working fluid connection with the lower inlet of the riser. In this way a relatively high flow rate may be maintained through the riser and downpipe in operation when buoyant fluid is introduced into the riser.

Suitably, the lower outlet of the downpipe is arranged to discharge into an enclosed volume of working fluid. Suitably, the pump comprises a working fluid reservoir operatively coupled to the lower outlet of the downpipe. Suitably, the pump comprises a working fluid reservoir operatively coupled to the lower inlet of the riser. Suitably, the pump comprises a working fluid reservoir arranged such that in use working fluid discharges from the lower outlet of the downpipe into a closed volume completely filled with working fluid. Suitably, the pump is arranged to operate such that working fluid is discharged from the upper end of the riser to atmosphere. Suitably, the pump is arranged to operate such that in use working fluid in the downpipe comprises a free surface open to atmosphere. Suitably, the upper inlet of the downpipe comprises flow shaping means. Suitably, the flow shaping means is arranged such that with the pump in use a shaped flow profile in initiated in the working fluid as it travels from the upper inlet of the downpipe to the lower outlet of the downpipe. Suitably, the flow shaping means comprises a tapered section. Suitably, the flow shaping means comprises a funnel section. Suitably, the flow shaping means comprises a frustoconical section. Suitably the flow shaping means is arranged such that as the pump operates a vortex is introduced or facilitated or supported in working fluid travelling in the downpipe from the upper inlet of the downpipe to the lower outlet of the downpipe.

Suitably, the pump comprises a plurality of risers. Suitably, the pump comprises a plurality of risers comprising an upper outlet, a lower inlet. Suitably, the pump comprises a plurality of risers coupled to buoyant fluid introducing means. Suitably, the risers are arranged around the downpipe. Suitably, the risers are distributed evenly around the downpipe. Suitably, the risers are arranged with reflective and/or circular symmetry around the down pipe. Suitably, two of or more than two of, preferably all of the risers are of substantially identical form. Suitably, two of or more than two of, preferably all of the risers are coupled to a common source for supply of buoyant fluid thereto. Suitably, one of, two of or more than two of the risers are arranged with upper outlets configured to introduce or facilitate or support directed flow of working fluid at the upper outlet thereof when the pump is operative. Suitably, one of, two of or more than two of the risers are arranged with upper outlets configured to introduce or facilitate or support directed flow of working fluid at the upper outlet thereof by providing an angled outlet flow directed around the downpipe, or flow shaping means of the downpipe. Suitably the upper ends of the riser or risers are arranged to introduce or facilitate or support a directed flow of working fluid, preferably a circular, circulatory or vortex-like flow around the downpipe or flow shaping means. Suitably, the cross-sectional area of the riser, or combined cross-sectional areas of the risers is greater than or equal to the cross-sectional area of the downpipe. Suitably, the, or each riser is of circular cross-section. Suitably, the, or each riser is of internal diameter of 5cm to 10cm. Suitably, each individual riser is of relatively smaller cross-sectional area than the downpipe. Suitably, each individual riser has a cross-sectional area less than 10% of the cross-sectional area of the downpipe, preferably less than 5%, more preferably less than 3%.

Suitably, the pump comprises a working fluid. Suitably, in a resting state where buoyant fluid is not being introduced into the riser, the riser and downpipe are both substantially filled with working fluid. Suitably, in a resting state where buoyant fluid is not being introduced into the riser, working fluid approaches but remains below the upper inlet of the downpipe. Suitably, the riser comprises excitation means, arranged to excite working fluid and/or buoyant fluid arranged there. Suitably, the excitation means comprise electromagnetic and/or acoustic excitation means. Suitably, the excitation means is arranged to introduce a time varying and/or spatially varying pressure and/or density and/or flow condition varying effect on the working fluid. Suitably, the excitation means is arranged to introduce a time varying and/or spatially varying pressure and/or density and/or flow condition varying effect on bubbles of buoyant fluid in the working fluid. Suitably, the excitation means is arranged to operate in a time varying, periodic manner. Suitably, the excitation means it provided in, around or adjacent to the riser. Suitably, the excitation means is located at and/or above the buoyant fluid introducing means. Suitably, in use the working fluid substantially fills the riser and the downpipe. Suitably, the downpipe and riser are closed to the atmosphere between the upper and lower inlets thereof. Suitably, the working fluid is a liquid. Suitably, the working fluid is magnetically active. Suitably, the working fluid comprises an electrolyte solution. Suitably, the working fluid comprises an aqueous salt solution. Suitably, the working fluid comprises an aqueous gel. Suitably, the magnetically active liquid comprises magnetically active particles. Suitably, the working fluid comprises magnetically active particles in suspension. Suitably, the working fluid comprises ferromagnetic particles. Suitably, the magnetically active particles comprise iron particles or particles containing an iron compound. Suitably, the magnetically active particles comprise a protective coating. Suitably, the protective coating forms a barrier around the magnetically active particles to render them chemically inert with respect to the working fluid. Suitably, the protective coating forms a barrier around the magnetically active particles to prevent coalescence of the magnetically active particles. Suitably, the working fluid comprises a liquid. Suitably, the working fluid comprises a liquid metal. Suitably the working fluid comprises liquid ferromagnetic metal. Suitably, the working fluid comprises an electrorheological fluid. Suitably, the working fluid comprises a ferrofluid. Suitably, the working fluid comprises a magnetic ionic liquid. Suitably, the buoyant fluid comprises a gas. Suitably, the buoyant fluid comprises air. Suitably, the pump comprises a buoyant fluid introducing means in the form of a compressor arranged in use to force buoyant fluid into the riser. Suitably, the buoyant fluid introducing means is arranged to provide supply the buoyant fluid at a point closer to the lower inlet of the riser than the upper outlet of the riser. Suitably, the buoyant fluid introducing means is arranged in the bottom 50% of the riser, preferably the bottom 60%, more preferably the bottom 75%, preferably toward the bottom 90%, as considered between the lower inlet and the upper outlet of the riser. Suitably the downpipe and riser comprise a substantially equal vertical separation between respective inlets and outlets thereof.

Suitably, the pump further comprises a turbine or other mechanical energy capture device to capture and extract energy from moving working fluid associated with the pump. Suitably, the downpipe comprises a turbine or other mechanical energy capture device operable to extract energy from fluid flowing in the downpipe. Suitably, the pump comprises part of a hydroelectric generation installation. Suitably, the pump comprises part of a re-circulatory system including a fixed volume of working fluid.

In a second aspect the present invention provides a method of operating a pump comprising a riser with a lower inlet and an upper outlet and a downpipe with a lower outlet and an upper inlet, wherein the riser is coupled to a buoyant fluid introducing means operable to introduce buoyant fluid into working fluid in the riser to thereby cause the working fluid to discharge from the upper outlet of the riser, and then to pass into the upper inlet of the downpipe for delivery to the lower outlet of the downpipe; and characterised in that the lower outlet of the downpipe is in contained working fluid connection with the lower inlet of the riser, the method comprising introducing buoyant fluid into the riser such that working fluid discharges from the upper outlet of the riser, passes into the upper inlet of the downpipe and is delivered to the lower outlet of the downpipe to pass there-from through a contained working fluid connection to the lower inlet of the riser.

Suitably, the pump comprises further features as described above in relation to the pump of the first aspect of the invention. Suitably, the method comprises operating the pump in accordance with the operability described above in relation to the pump of the first aspect of the invention.

Introduction to the Drawings For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawing in which:

Figure 1 shows a schematic view of pump according to an example embodiment of the present invention.

Description of Example Embodiments

Referring now to Figure 1 there is shown a schematic view of a pump according to an example embodiment of the present invention. The pump 1 comprises a riser 2 in the form of a conduit connecting a lower working fluid inlet 2 and an upper working fluid outlet 4. The upper working fluid outlet 4 is located above the lower working fluid inlet 2. The pump 1 further comprises a buoyant fluid inlet 8 arranged on the riser 2. The schematic view of Figure 1 shows four riser elements, but it is to be understood the complete pump 1 includes thirty six riser elements that cooperate with one another and are substantially identical in structure and operation to one another. The holes 3, in the complete pump are coupled to the lower inlets of the rest of the riser elements and are distributed evenly around the edge of the pump 1. The pump 1 further comprises a downpipe 10 that includes an upper inlet 12 and a lower outlet 14. The downpipe receives working fluid from the riser 2 and delivers working fluid from its upper inlet 12 to its lower outlet 14. The lower outlet 14 discharges into a working fluid reservoir 16 that is completely filled with working fluid and provides a contained working fluid connection between the lower outlet 14 of the downpipe 10 and with the lower inlet 14 of the riser 2.

By supplying buoyant fluid into the working fluid in the riser 2 the pump 1 operates as an air-lift type pump. A relatively high flow rate may be maintained through the riser 2 and downpipe 10 in operation of the pump 1 when buoyant fluid is introduced into the riser 2, due to the pressure of working fluid in the downpipe acting on the fluid in the riser combined with the large operational distance over which the airlift effect operates. In the example embodiment shown the working fluid comprises a liquid in the form of a water-based fluid, and the buoyant fluid comprises air introduced into the riser 2 by operation of a compressor (not shown). The bubbles of buoyant fluid in the riser 2 are increased in size and/or in efficacy in operation by the effect of excitation and/or suitable choice of working fluid. Excitation may be acoustic, electromagnetic or in other suitable forms, for example provided at or around portions 20 of the riser 2 above the point at which buoyant fluid is introduced. The pump 1 is useful, for example in providing working fluid to a turbine or the like (not shown) mounted in the downpipe 10, for example at a narrowing 18 therein.

Also shown in Figure 1 at the upper inlet 14 of the downpipe 10 is a flow shaping means 22 in the form of a frustoconical section. The flow shaping means 22 helps to guide working fluid down into the downpipe 10. To further aid this process the riser 2 is suitably arranged to discharge around the upper inlet 14 of the downpipe, to cause a vortex effect to be established in the working fluid.

Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.