Field of the Invention
This invention relates to transport of fluids by an apparatus described in the introductory part of claim 1. More specifically the invention relates to an apparatus which employs pressure transients to transport fluids. Moreover, the invention describes exemplary applications where the energy needed to generate said pressure transients are captured from ocean waves. Hence, in these applications the described apparatus operates as an apparatus for capturing the energy in ocean waves.
Brief Description of the Related Art
There is one type of device for transporting fluids that has almost been forgotten, or overlooked for practical reasons which employs a physical phenomenon commonly known as “Water Hammer”. The first device of this type was built in 1772 by J. Whitehurst for use in a brewery and is classified as “Hydraulic ram pumps” or just “Ram pumps”.
“Water Hammer” is a phenomenon that occurs when a fluid flowing in a pipeline experience a sudden halt by e.g. closing a valve, thereby causing the fluid motion to generate a pressure transients. However, the “Ram pumps” also employ the reversed process, i.e. where pressure transients produces a fluid flow. The reversed process is not part of the “Water Hammer” phenomena, and it has mostly been ignored resulting in a close to non-existing theoretical knowledge about this process.
The “Water Hammer” phenomenon also occurs if a body, which is in contact with a fluid at rest, experiences a sufficiently sudden movement, since this is, due to symmetry of relative motion, essentially the same as a sudden halt of a flowing fluid by closing of a valve. An equation relating the pressure transients to the fluid flow speed was formulated by the Russian scientists Nikolai Joukowsky. This equation states that Γ=ρcu, where Γ is the pressure transient, ρ is the density of the fluid, c is the sound speed in the fluid and u is the fluid flow velocity. N. Joukowsky published this equation in 1898 after extensive experiments of the “Water Hammer” phenomena in long steel pipes, and is hence commonly known as the Joukowsky equation. However, the same equation was introduced by the German scientist Johannes von Kries in 1883 based on his studies of blood flow in the arteries.
In industrial pumping application mostly three kinds of pressures are observed: static pressure, pressure waves and pressure transients.
Static pressure is employed in all fluid transporting devices today with only one exception, namely applications where “Ram pumps” are used. Fluids are transported by the gradient of static pressure along the pipelines which the pumping device has established in the system. The static pressure is constant in time during the normal steady state operation of the pumping device, but the pressure is time dependent during the start up of the pump until a steady state is reached. Hence, in the initial phase a pumping device can produce pressure waves. A purely static pressure is not possible to obtain in any industrial pumping application since there will always be some disturbances in the steady state operation. However, various means are applied in order to maintain a close to static situation.
A pressure wave is not capable of generating a net transport of fluids since pressure waves only generate oscillations in a fluid but no net transport. An example of pressure waves are sound waves in air. Notice that the disturbances mention above are mostly pressure waves, and hence one employ different procedures to minimize the generation of these useless pressure waves.
If a pumping device makes a sudden stop due to some failure of the operation of the pump, a pressure transient can be generated in the same way as in the case of a sudden closing of a valve.
In many industrial applications “Water Hammer” is regarded as a dangerous phenomenon that should be avoided due to the plausible occurrence of disruptive cavitations generated by the pressure transients. The pressure transient Γ, which is positive in the beginning, can change sign to become negative due to interactions with some solid surfaces in the system. If the sum of the local pressure and the pressure transient is less than the vapor pressure, cavities containing vapor are formed. After some time the cavity will collapse (implode), i.e. when the pressure in the neighborhood again rises above the vapor pressure. The cavity walls thus rush towards one another thereby generating hard impulse on the system owing to the low degree of compressibility of liquids. The impulses spreading out from each collapsed cavity is an important, and usually undesirable, feature, often heard as disturbingly loud noises in applications such as water supply systems and hydraulic pumps. Most seriously, the continual collapse of cavities leads rapidly to deterioration and erosion of nearby solid surfaces. To summarize one can state that during the “Water Hammer” phenomena all of the positive pressure transients become negative pressure transients, and all of the negative pressure transients are generating disruptive cavitations. Hence, to actively generate the “Water Hammer” phenomena for industrial applications have not been considered feasible among experts in the field.
Pressure transients are avoided in industrial applications, mainly since they would normally lead to disruptive cavitations in the system as in the case of the “Water Hammer” phenomena. One of many reasons to actively produce pressure transients is that pressure transients can be both positive and negative as mention above, and thus pressure transients in a partly enclosed space with one or more openings can produce a flow in the direction out of and into the partly enclosed space. This effect is apparent from the Joukowsky equation Γ=ρcu, thus when Γ is positive u is positive (flow in the direction out of a partly enclosed space), and when Γ is negative u is negative (flow in the direction into a partly enclosed space). In this way both positive and negative pressure transients generate flows, thereby suppressing disruptive cavitations due to negative pressure transients. Notice that only one fraction of the positive pressure transients produces a flow, whereas the other fraction become negative pressure transients due to the abovementioned interactions at some solid surfaces in the system. Since the pressure transients cannot be simultaneously negative and positive, such inflows and outflows may in principle occur through the same opening. The possibility of applying only one opening is an important uniqueness of the described apparatus compared with all fluid transporting devices today that employs one opening for the inflow and one for the outflow. The only exception is the “Ram pump” that has one more opening for the “Waste valve”, thus a “Ram pump” has three openings.
How does the “Ram pump” avoid the disruptive cavitations that normally occur during the “Water Hammer” phenomena? Looking at
What is a pressure transient? There are many ways of generating a static pressure or a pressure wave, but there are only a few known situations where pressure transients occur. The most known case where pressure transients appear is during the “Water Hammer” phenomenon. Pressure transients are a time dependent propagating phenomenon like pressure waves, but unlike pressure waves fluids can be transported by pressure transients in accordance with the Joukowsky equation.
To find out what pressure transients are one need to know more about the concept of pressure in fluids. On a microscopic level pressure is the results of the thermal motion of the particles in the fluid, and one can interpret pressure as energy density in the fluid. However, on a macroscopic level pressure is more commonly regarded as the ability of the fluid to exert a force on a body. The force F that the pressure p inside a hydraulic cylinder can push the piston (body) with is given by F=Ap, where A is the size of the surface of the piston which is in contact with the fluid in the hydraulic cylinder. Hence, a general method of producing a pressure p inside a hydraulic cylinder is to act on the piston (body) with a force F obtaining a pressure given by p=F/A. In this way a static pressure can be generated by a constant force, and a pressure wave is obtained by employing a time dependent oscillating force.
To our knowledge, pressure transients can only be generated by a collision process. The momentum of a fluid flowing in a pipeline (with cross section σ) disappears during a time interval Δt after a valve is suddenly closed, and due to the conservation of momentum something must be created during this time interval Δt. To find out what is happening one can follow the work by N. Joukowsky. Newton second law can be written in the momentum form FΔt=Δ(mu), where F is the force, Δt is a time interval and Δ(mu) is the change in momentum of a body with mass m and velocity u. Applying that a pressure transient can be expressed as Γ=F/σ one can write that ΓσΔt=ρuV=ρuσL=ρuσcΔt, where σ is the cross section of the pipeline, Δt is the time interval during which the momentum ρu disappears, V=σL is the volume V of the part of the fluid (with density ρ) where the momentum has disappeared, and L is the length that the pressure transient Γ has propagated with the sound speed c during the time interval Δt. Hence, the Joukowsky equation Γ=ρcu is obtained.
One could argue that the pressure transient Γ is generated by a force F as in the case of an ordinary static pressure p, since the relation Γ=F/σ is employed. This is, however, a force that appears in a collision process and the only way to produce such a force is to perform a collision. As mentioned above, pressure transients can be produced by a body (which is in contact with a fluid at rest) which experiences a sufficiently sudden movement. It is now possible to specify more precisely what kind of movement that is needed in order to obtain pressure transients. The movement of said body must be generated by a collision process. The collision process can be obtained with an object (having a nonzero momentum) colliding with said body. More precisely, a collision process is an event where said object is set in motion at time τ and gains a nonzero momentum (during a time interval T) before it collides with said body at a later time τ+T.
The pressure loss p along a pipeline with length L during laminar constant flow is given by the Hagen-Poiseuille equation p=32 μLu/d2, where μ is the coefficient of viscosity and u is the fluid flow velocity. Introducing the cross section σ=πd2/4 of the pipeline, the Hagen-Poiseuille equation can be written as p=8 πμLu/σ. Hence, an ordinary pumping device must produce a static pressure that is equal to the pressure loss p in order to maintain the fluid flow velocity u in the pipeline. In the case of turbulent flow the pressure loss can be estimated with the Darcy-Weisbach equation p=2 fLρu2/d if an empirical friction factor f is introduced, and the dependence of the friction factor f with the Reynolds number is often illustrated in Moody diagrams. It is important to notice that the relation between the flow velocity u and pressure p in both the Hagen-Poiseuille and Darcy-Weisbach equations are different from the relation obtained with the Joukowsky equation Γ=ρcu, hence there is a fundamental difference in how a pressure p and a pressure transient Γ can produce a fluid flow velocity u.
A prior art piston pump is also shown in
All the prior arts pumps illustrated in the
Based on the state of the known art the objective with the invention is to provide a robust and efficient apparatus for transporting fluids by employing pressure transients, and where the need of a “Waste valve” and a “Drive pipe” (
One objective with the invention is to provide an apparatus for transporting fluids that is new in many fundamental aspects. The apparatus produces a pulsating fluid flow that is different from the flow obtained with ordinary pumps, but to some extent similar to that of the “Ram pump”. The “Ram pump” and the described apparatus both employ pressure transients to transport fluids. However, the “Ram pump” generates these transients by opening and closing a “Waste valve”, whereas the described inventive apparatus generates such pressure transients utilizing a sudden movement of at least one body (piston). Said movement must be sufficiently sudden, and in the described apparatus this is obtained by at least one object (a hammer) colliding with said body (piston).
According to the invention said objectives are achieved by an apparatus for transport of fluids as stated in the introduction, and having the characteristic features stated in the independent claim 1. Advantageous embodiments of the invention are stated in the remaining dependent claims.
More specifically, the invention relates to an apparatus employing pressure transients for transporting fluids comprising at least one partly enclosed space, at least one body in said at least one partly enclosed space, where said at least one body is movable relatively to the interior of said at least one partly enclosed space, at least one opening in said at least one enclosed space which allows a fluid to flow alternately in the direction into and out of said at least one partly enclosed space, at least one first conduit and at least one second conduit in fluid communication with at least one of said at least one opening, at least one first reservoir and at least one second reservoir connected to said at least one first conduit and at least one second conduit respectively, at least one first mechanical unit and at least one second mechanical unit in said at least one first conduit and at least one second conduit respectively, where said at least one first mechanical unit only allows flow in said at least one first conduits from said at least one first reservoir and towards said at least one partly enclosed space, and said at least one second mechanical unit only allows flow in said at least one second conduit in the direction from said at least one partly enclosed space and towards said at least one second reservoir.
The invention is further characterized in that at least one positive pressure transient is generated in at least one of said at least one partly enclosed space by at least one object, with nonzero momentum, colliding with said at least one body, where at least part of said at least one positive pressure transient produces flow of fluid out of said at least one partly enclosed space through said at least one second mechanical unit and into said at least one second reservoir, and at least one negative pressure transient is generated in said at least one partly enclosed space, where said at least one negative pressure transient, together with the resulting at least one hydrostatic head between at least one of said at least one first reservoirs and at least one of said at least one partly enclosed space, produce flow of fluid out of said at least one first reservoir through said at least one first mechanical unit and into said at least one partly enclosed space.
An advantageous embodiment of the invention is to terminate any disruptive cavitations occurring in said partly enclosed space by assuring a sufficient flow of fluid into said partly enclosed space(s). Preferably this is obtained by arranging at least one of said first reservoir(s) with a sufficiently hydrostatic head between at least one of said partly enclosed space(s) and at least one of said first reservoir(s), so that said sufficient flow of fluid comes from at least one of said first reservoir(s).
Preferably at least one of said partly enclosed space(s) and at least one of said body or bodies are a hydraulic cylinder and a piston, respectively.
Another advantageous embodiment is to arrange at least one chamber that is filled with a mixture of liquid and gas, wherein one or more third conduits are connected to the liquid filled parts of the chamber(s). Said third conduit(s) is/are in fluid communication with said partly enclosed space(s) through said second mechanical unit(s). Preferably at least one membrane suitable for separating gas and liquid is arranged within at least one of said chamber(s). Said chamber(s) may e.g. be any kind of pressure tanks and/or hydraulic accumulators.
Said first and second mechanical units are with advantage valves of specific types such as one-way valves, check valves, restrictor check valves, throttle check valves, restrictor one-way valves or/and throttle one-way valves.
Furthermore, said conduits consist preferably of pipelines, e.g. pipelines made of stainless steel and/or plastic.
As an alternative to the above-described embodiments the inventive apparatus may be employed in one or more heat exchanging systems such as heating or cooling systems. This may be achieved by merging at least one of said first reservoir(s) with at least one of said second reservoir(s), thereby obtaining at least one common reservoir into which both an inflow and an outflow of fluid are present.
Another possible application using one or more of the above-mentioned embodiments is to employ at least one of said at least one second reservoir as a hydropower reservoir. Moreover, in some other applications at least one of said reservoir(s) might be replaced by a pressure tank, and at least one of said pressure tank(s) could be connected to hydropower turbine(s).
Another possible application is to use the apparatus as described above and claim 1-8 as an energy converting system, wherein at least one of said object(s) is/are connected to at least one wave motion capturing system.
One apparatus having connected said wave motion capturing system, and thus suitable for capturing energy in wave motions, has one or more objects connected to one or more floating buoys which may be set in motion by waves. Said motions are then generating movements of said object(s), thereby causing a non-zero momentum of said object(s) prior to the collision(s) with at least one of said body or bodies.
Said object(s) is/are preferably connected to one or more buoy(s) by one or more cord(s) running through pulleys, wherein at least one pulley is/are anchored to at least one sinker, and at least one of the other pulleys is/are connected to a fixed construction.
In another, alternative apparatus with said wave motion capturing system, and thus suitable for capturing energy in wave motions, said object(s) is/are connected to at least one wall which can be set in motion by waves, and that the motion of said at least one wall induces movement of said object(s), and thereby obtaining a nonzero momentum of said object(s) prior to collision with at least one of said body or bodies
Said object(s) in the latter described apparatus is/are preferably connected to said wall with at least one cord running through one or more pulleys that are linked to a fixed construction and where said wall(s) is/are anchored to at least one sinker with one or more joints.
The inventive apparatus may be produced employing known components, and the invention is not by any means limited to neither choice of material during the manufacturing of components such as said object(s), nor how said object(s) are moved towards and away from said piston(s). However, one possible method of achieving such movement of the object(s) is to apply ocean waves as mentioned above. Ocean waves are in nature a periodic or quasi-periodic phenomenon, which may contain large amount of energy. Hence the described apparatus may constitute an ocean wave energy converting system as described above when at least one of said at least one second reservoir is a hydropower reservoir. More specifically, the inventive apparatus may be applied as said ocean wave energy converting system(s) in which said object(s) constitute a part of an ocean wave motion capturing system(s). Such an apparatus allows the construction of an ocean wave power concept where said ocean wave motion capturing system(s) and said ocean wave energy converting system(s) are fully disconnected. This ocean wave power concept would most probably lead to a more robust solution compared to prior art solutions. For ocean wave motion capturing systems either prior art systems or new innovative solutions may be employed to assure a movement of the object(s) due to the ocean waves.
The invention will be disclosed with reference to the drawings wherein:
The total head, i.e. the sum of the hydrostatic head and the friction head, between second reservoir 232 and hydraulic cylinder 201 is larger than the total head, i.e. the hydrostatic head plus the friction head, between first reservoir 231 and hydraulic cylinder 201. Notice that the hydrostatic head between first reservoir 231 and hydraulic cylinder 201 might be larger than the hydrostatic head between second reservoir 232 and hydraulic cylinder 201 even if the difference in the total head is reversed. This would be the case when the friction head is largest between second reservoir 232 and hydraulic cylinder 201.
Object 208 collides with the end of a piston 202, and the sudden movement of piston 202 caused by the collision generates positive pressure transients in hydraulic cylinder 201 which again generate a fluid flow in the direction from the hydraulic cylinder 201 through second check valve 222 and towards second reservoir 232. First and second check valves 221,222 ensure that the positive pressures transient only produce a flow in the above described direction due to their one-way directional properties.
A fraction of the positive pressure transients is likely not to be converted into a fluid flow. Instead this fraction will interact with the solid surfaces within the apparatus, thereby transforming the fraction of positive pressure transients into negative pressure transients within hydraulic cylinder 201. The negative pressure transients generate a fluid flow in the direction from first reservoir 231 through first check valve 221 and towards hydraulic cylinder 201. First and second check valves 221,222 ensure that the negative pressure transients only produce a flow in the above described direction due to the one-way directional properties of valves 221,222. Notice that the hydrostatic head between first reservoir 231 and hydraulic cylinder 201 also contributes to the generation of the described fluid flow.
In this embodiment the hydraulic cylinder has only one opening 304 which is connected to a third conduit 310. First and second conduits 311, 312 are connected at one of their ends to the third conduit 310 and at their opposite ends to first and second reservoirs 331,332, respectively. In the embodiment show in
This embodiment has only one common reservoir 430 in which both first and second conduits 411,412 are connected. Such embodiment is advantageous when applied as heat exchange systems such as heating or cooling systems. One example of the latter application is storage of hot or cold fluid in reservoir 430, using first and second conduits 411,412 as climate distributors to the surrounding environment.
One of said first check valves 521 only allows the fluid to flow in the direction from first reservoir 531 and towards the hydraulic cylinder 501, while one of said second check valves 522 only allows fluid to flow in the direction from hydraulic cylinder 501 and towards second reservoir 532. Another of said additional first check valves 523 only allows the fluid to flow in the direction from said additional first reservoir 533 and towards hydraulic cylinder 501, while said additional second check valves 524 only allows fluid to flow in the direction from hydraulic cylinder 501 and towards said additional second reservoir 534.
The embodiment shown in
This embodiment applies two hydraulic cylinders 601,606 to perform one fluid transport application. The inventive apparatus is hence not limited to only one hydraulic cylinder for each fluid transport application. Furthermore, one hydraulic cylinder is not limited to perform only one fluid transport application, as described above.
Chamber 740 may be a pressure tank or a hydraulic accumulator, and thus a fraction of or all fluids flowing through second check valve 722 can flow into chamber 740. Chamber 740 is preferably filled with both liquid and gas and only the liquid filled part is connected to third conduit 713. The liquid and gas may be separated by a boundary such as a membrane as in the case of a hydraulic accumulator. Such embodiment decreases the resistance of the fluid flow in second conduit 712 since the gas in chamber 740 compresses during the inflow of the fluid from third conduit 713 and thus fluid can flow more easily into chamber 740 than into second reservoir 732. The gas starts to decompress when the fluid flow through second check valve 722 stops and the flow into chamber 740 halts. As a result of the gas decompression fluid begins to flow out of chamber 740 through third conduit 713, where one-way directional second check valve 722 ensures that the fluid flows from chamber 740 into second reservoir 732.
The effect of such arrangement causes more fluid to be transferred to second reservoir 732 per collision. This again serves two purposes:
1. The efficiency of the inventive apparatus increases
2. The flow of fluid into second reservoir 732 becomes more continuous.
The method of connecting a chamber 740 as illustrated in
The prior art piston pump shown in
Piston 902 has one end that is inside hydraulic cylinder 901 and the other end is inside chamber 903. Piston 902 is moved by a fluid which can expand inside chamber 903 and thus move piston 902. The movement of piston 902 by the expanding fluid inside the chamber 903 shown in
Membrane 1002 is moved by a fluid which can expand inside chamber 1003 and thus move membrane 1002. Movement by membrane 1001 is not able to generate pressure transients inside hydraulic cylinder 1002. The reason for this is that the movement is not obtained by a collision process as described in the introductory part.
Floating buoy 1150 is floating in the ocean and can be set in motion by the ocean waves, and thus producing a movement of object 1108. Hence, object 1108 gains a nonzero momentum before it collides with body 1102.
Wall 1250 is partly submerged into the ocean and can be set in motion by the ocean waves, and thus producing a movement of object 1208. Hence, object 1208 gains a nonzero momentum before it collides with body 1202.
Number | Date | Country | Kind |
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2009 2071 | May 2009 | NO | national |
This application is a Continuation of co-pending application Ser. No. 13/322,358, filed on Jan. 27, 2012, which is a U.S. National Stage of International Application No. PCT/NO2010/000190 filed on May 26, 2010, for which priority is claimed under 35 U.S.C. §120; and this application claims priority of Application No. 2009 2071 filed in Norway on May 27, 2009 under 35 U.S.C. §119; the entire contents of all of which are hereby incorporated by reference.
Number | Date | Country | |
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Parent | 13322358 | Jan 2012 | US |
Child | 15425829 | US |