POSITIVE DISPLACEMENT PUMP HAVING FLOW-PROMOTING SURFACES

Abstract

The present invention relates to a positive displacement pump having a delivery chamber, which is connected to a discharge connection and a suction connection, characterized in that the surface of the delivery chamber is configured in the form of an at least partially microstructured surface. The at least partially microstructured surface has a multiplicity of ribs and channels located therebetween, these running in a direction along the direction of flow of the delivery medium. As a result of the surface being structured, the situation where gas bubbles stick is reliably prevented and the harmful gas volume is considerably reduced.

Claims

1. Positive displacement pump having a delivery chamber, which is connected to a discharge connection and a suction connection, characterized in that the surface of at least one positive-displacement-pump element which is in contact with fluid is configured in the form of an at least partially microstructured surface.

2. Positive displacement pump according to claim 1, characterized in that the surface of the delivery chamber, of the working chamber, of lines and/or bores in the pump, of the displacing piston, of the diaphragm, of the valves and/or of all other positive-displacement-pump elements which are in contact with fluid is or are configured in the form of an at least partially microstructured surface.

3. Positive displacement pump according to claim 1, characterized in that the surface or the surfaces have or has a multiplicity of ribs and channels located therebetween.

4. Positive displacement pump according to claim 1, characterized in that ribs and channels run at least partially, in particular fully, in a direction along the direction of flow of the delivery medium.

5. Positive displacement pump according to claim 1, characterized in that the ribs and channels are arranged at least partially, in particular fully, in segmented form, wherein the individual segments are offset in relation to one another, and wherein it is possible for the respective segments to be of identical length or of different lengths.

6. Positive displacement pump according to claim 1, characterized in that the ribs and channels are arranged at least partially, in particular fully, in segmented form, wherein it is possible for the individual segments to have ribs and channels of different heights and widths.

7. Positive displacement pump according to claim 1, characterized in that the ribs are designed at least partially, in particular fully, in honeycomb form, wherein the honeycomb boundary interrupts the ribs and channels.

8. Positive displacement pump according to claim 1, characterized in that at least one of the ribs, preferably all the ribs, in a single segment, in particular all the ribs, are pointed and at least one of the channels, preferably all the channels, in a single segment, in particular all the channels, are round.

9. Positive displacement pump according to claim 1, characterized in that at least one of the ribs, preferably all the ribs, in a single segment, in particular all the ribs, and at least one of the channels, preferably all the channels, in a single segment, in particular all the channels, are triangular and/or trapezoidal.

10. Positive displacement pump according to claim 1, characterized in that the ribs have a height from 0.3 to 1000 m, preferably between 30 and 300 m.

11. Positive displacement pump according to claim 4, characterized in that the ribs have a height between 30% and 120%, preferably between 50% and 100%, of the distance from an adjacent rib.

12. Positive displacement pump according to claim 3, characterized in that the ribs have a width from 0.3 m to 1000 m, preferably 25 m to 300 m, in particular 35 m to 200 m.

13. Positive displacement pump according to claim 3, characterized in that the channels have a width from 0.3 m to 1000 m, preferably 25 m to 300 m, in particular 35 m to 200 m, wherein the channels are preferably rounded and/or taper in relation to the ribs in particular at an acute angle of smaller than, or equal to, 75, in particular smaller than, or equal to, 60.

14. Method for producing an at least partially microstructured surface of an element of a positive displacement pump, in particular of a delivery chamber, working chamber, of lines and/or bores in the pump, of a displacing piston, of a valve, of a line and/or a seal, preferably of a positive displacement pump according to claim 1, characterized in that a microstructured film is adhesively bonded to the surface and/or the microstructured surface is produced by casting or injection moulding and/or by imprinting and/or by machining, in particular milling, and/or a lacquer applied to the surface is structured and/or the structure is produced using a pulsed laser beam or using fine jet plasma.

15. Use of microstructured surfaces for optimizing the harmful volume of pumps and/or for reducing noise or vibration in pumps, in particular by coating the delivery chamber, the working chamber, lines and/or bores in the pump, the displacing piston, the diaphragm and/or seals of the pump, preferably in a positive displacement pump according to claim 3.

Description

[0015] This object is achieved according to the invention in that the surface of at least one positive-displacement-pump element which is in contact with fluid is configured in the form of an at least partially microstructured surface. As a result, the situation where gas bubbles stick is reliably prevented and the harmful volume is considerably reduced.

[0016] It can, in particular, be advantageous here if the surface of the delivery chamber, of the working chamber, of the lines, of the displacing piston, of the diaphragm, of the valves and/or of all the other positive-displacement-pump elements which are in contact with fluid is or are configured in the form of an at least partially microstructured surface. Lines and/or bores are also intended here to denote, in general terms, fluid-guiding channels and generally represent the (through-) passage and guidance of fluids.

[0017] Further advantageous exemplary embodiments of the present invention form the subject matter of the dependent claims.

[0018] Scales of fast-swimming sharks have, for example, microscopically small ribs or riblets in the longitudinal direction. As a result of the riblets, during turbulent flow, the components of the vortices which run transversely to the direction of flow are impeded. Surface structures which are particularly beneficial for large components can be derived therefrom. An appropriate flow-promoting coating can be used to reduce, for example, the fuel consumption of aircraft and ships by up to three percent:

http://www.ifam.fraunhofer.de/content/dam/ifam/de/documents/Kl ebtechnik_Oberflaechen/Lacktechnik/riblets_fraunhofer_ifam.pdf
http://www.uni-saarland.de/fak8/bi13wn/projekte/umsetzung/fischhaut.html
http://rwscharf.homepage.t-online.de/faz06/faz0308.html

[0019] Microstructured surfaces such as the previously cited flow-promoting riblet surfaces, or those with the lotus-leaf structure, are required more and more for special functions. Products which can be optimized in terms of speed and energy consumption as a result of flow-promoting surfaces are basically, on the one hand, objects which are self-propelling, for example aircraft, rail vehicles, automotive vehicles, ships or also rotor blades of wind turbines, and, on the other hand, objects around which, or through which, movement is to take place, e.g. pipelines. In addition, microstructured surfaces serve to reduce fouling or growth of vegetation (in particular in respect of ships).

[0020] A riblet structure usually has ribs and channels located therebetween. The channels are depressions in the surface of the component. The ribs are arranged such that recessed channels or grooves run between adjacent ribs. It is usually the case that the ribs and channels here run in a direction along the direction of flow of the delivery medium over the corresponding surface.

[0021] Provision can be made here, according to one embodiment, for the ribs and channels to be arranged at least partially, in particular fully, in segmented form, wherein the individual segments are offset in relation to one another, and wherein it is possible for the respective segments to be of identical length or of different lengths.

[0022] It can also be advantageous here for the ribs and channels to be of different heights and widths.

[0023] As an alternative, or in addition, provision can also be made for the ribs to be designed at least partially, in particular fully, in honeycomb form, wherein the honeycomb boundary interrupts the ribs and channels.

[0024] As a result of a riblet structure being applied, during turbulent flow, the components of the vortices which run transversely to the direction of flow are impeded. This results in a reduction in the frictional resistance and an increase in the flow speed in the wall vicinity. The latter gives rise here, surprisingly, to increased entrainment of gas bubbles adhering to critical locations of the surface of the delivery chamber. In addition, the structure according to the invention reduces vibration and noise.

[0025] The at least partially microstructured surface of the delivery chamber can be produced in the form of films, for example by extrusion or imprinting methods, the films then being adhesively bonded to the respective workpiece.

[0026] For the purpose of structuring films, imprinting methods which imprint films, or film-like materials, in stationary machines are known. EP 0 205 289 A1 discloses, for example, a method in which a microstructure is applied to a film using a roller. It is also the case that WO 2013/050018 A1 describes a riblet foil and a method for producing the same.

[0027] The material of which the surface is to be microstructured must nevertheless be basically flexible, so that it can be guided over a pressure-exerting roller. For the purpose of structuring a non-flexible, rigid object such as, for example, the inner surface of a delivery chamber of a pump, therefore, methods which do not use film are more suitable. For example, a lacquer which is applied to the inner surface of a delivery chamber of a pump can be structured directly. Such a method for microstructuring surfaces by selective application of a curable coating material is known, for example, from WO 2005/030472 A1.

[0028] The depressions of a riblet structure can also be produced using a pulsed laser beam or using fine jet plasma, wherein the structures are introduced either directly into the surface of the delivery chamber or into film or lacquer applied to the surface. The channels and/or ribs are formed by individual laser pulses, which preferably follow one another and form a continuous structure. Use is preferably made of a femto laser for the purpose of forming the riblet structure.

[0029] If a riblet structure is introduced into film or lacquer applied to a surface, particular importance is attached to the materials which are to be selected as the film or lacquer. On the one hand they have to be resistant to the medium which is to be delivered; on the other hand they have to adhere well to the surface and to be capable of being structured by suitable methods. A person skilled in the art will select the material which is suitable for the respective pump and is resistant to the delivery medium. This is usually a polymer-based material. The adhesion thereof to the surface can be optimized by suitable adhesives and/or adhesion promoters and/or sizes. Furthermore, the inclusion of polar functional groups in the polymer can improve the adhesion to polar surfaces even without use being made of adhesion promoters or sizes.

[0030] The riblet ribs are only a few m high and preferably have a height from 0.3 to 1000 m, in particular between 30 and 300 m, wherein the ribs have a height between 30% and 120%, preferably between 50% and 100%, of the distance from an adjacent rib.

[0031] The ribs have a width ranging from approximately 0.3 m to 1000 m, preferably 25 m to 300 m, in particular 35 m to 200 m.

[0032] The channels have a width ranging from approximately 0.3 m to 1000 m, preferably 25 m to 300 m, in particular 35 m to 200 m, wherein the channels are preferably rounded and/or tapered in relation to the ribs in particular at an acute angle of smaller than, or equal to, 75, in particular smaller than, or equal to, 60.

[0033] It has been found that channels which are rounded in particular in relation to the ribs have achieved particularly good effects. This applies, as it were, to channels which taper virtually to a point and preferably to a combination of channels which taper to a point and form a rounded transition in relation to the ribs. The latter combination has proven particularly advantageous for a number of applications.

[0034] Channels and ribs are arranged preferably parallel and in the direction of flow. However, other arrangements are also possible.

[0035] Oscillating positive displacement pumps modified by microstructured surfaces are distinguished by high, stable metering accuracy, improved hydraulic/energy efficiency and good intake behaviour. The microstructured-surface modification according to the invention is advantageously used in particular in the case of pumps which are designed for metering small quantities. However, the technology according to the invention is also suitable for use with other delivery-pump systems, for example centrifugal pumps.

[0036] A function test was carried out in order to demonstrate the functioning of the invention. The function test involved comparing two identical pumps, one equipped with a standard PLEXIGLAS metering head and the other equipped with an identical standard PLEXIGLAS head with additionally microstructured surfaces (riblet structure) in the delivery chamber.

[0037] Then, start-up was simulated for both pumps, the metering head typically being filled with air and, at the start of the delivery operation, always some residual air/gas having to be taken in as well from the suction pipe.

[0038] It is usually the case that the air from the metering head and suction line is delivered out within 20 to 60 seconds (oscillating positive displacement pumps are self-priming) and normal operation with fluid takes over.

[0039] On a PLEXIGLAS head, this operation can be observed to good effect and any bubbles of air and gas which may also remain in the delivery chamber can be easily identified.

[0040] On the standard metering head, the function test identified gas bubbles which remain in the delivery chamber following the start-up cycle and are also still present after a relatively long period of operation.

[0041] On the riblet metering head, the metering head is free of bubbles of air and gas following the start-up phase.

[0042] It was therefore possible to show that no formation of air bubbles is identified when use is made of the microstructured surfaces according to the invention.