EP3446787A1 - Method and device for generating a sequence of beam sections of a discontinuous, modified liquid jet - Google Patents

Abstract

The invention relates to a method and a device for producing a sequence of sections of a liquid jet (20), wherein a single jet section (21) of the discontinuous, modified liquid jet (20), before impinging on a target surface (26), moves in the direction of movement (28). smaller length (L _f ) than after exiting a nozzle (10). According to the invention, the modification is caused by different velocities within the individual jet section (21) of the discontinuous, modified liquid jet (20) in such a way that due to a steady increase in the jet velocity on exit from the nozzle (10) a jet region behind in the direction of movement (28) catching up a front beam area of the jet section (21) in that the individual jet section (21) exits the nozzle (10) with increasing speed the later it exits the nozzle (10), and a break-up of the jet section (21 ) is prevented by not exceeding a critical ratio of inertial force to surface force. Another aspect of the invention relates to the use of the method according to the invention for cleaning, surface treatment or cutting.

Description

The invention relates to a method and a device for generating a sequence of beam portions of a discontinuous, modified liquid jet, wherein a single beam portion of the liquid jet undergoes a modification such that it has a shorter length in the direction of movement before it hits a target surface than after it exits the nozzle. The invention further relates to uses of the liquid jet. Such a modified beam has an increased mechanical effectiveness, which can be used, for example, for cutting or ablation. Thus, there is an improvement in the erosion effect of the liquid jet. For this purpose, the prior art often provides for the generation of a pulsating fluid jet from a pressurized fluid.

In the industry there is a demand for shorter cleaning times across industries to reduce cycle times. This concerns, for example, industrial component cleaning in the automotive industry. Likewise, an increase in machine availability, for example by automated self-cleaning of processing machines, especially in the food sector, is required. The two areas mentioned above are also key applications in which cleaning represents a significant process step in value creation. In the entire field of mechanical engineering, the semi-finished products, raw materials and components as well as assemblies must generally be cleaned before each further processing step. Here, a modified liquid jet can be used in a robot cleaning chamber for the format-flexible cleaning of industrial components. The second particularly interesting field of application relates to the production of hygiene-critical consumer goods, wherein the cleaning of food tanks represents an advantageous field of application.

The principle effectiveness of pulsating spray-cleaning systems is recognized in the art and industry, with opinions on previously applied, based on a beam break by interfering contours pulsation divided or rather reject. The known pulsation methods, generated by pump or valve circuits, have disadvantages in the pressure profile generated on the target surface. They do not produce a hard pulsation, which is why the cleaning effect is limited, albeit better than non-pulsating liquid jets.

A number of such systems are also found in the printed prior art. This is how the document describes DE 10 2011 080 852 A1 an apparatus and method for generating a pulsating fluid jet of pressurized fluid with a conduit system having at least one nozzle. The has a nozzle mouth from which the fluid jet can escape from the pressurized fluid. The apparatus further has a chamber in which a pressure wave generating means for generating fluid pressure waves is formed. The chamber communicates with the conduit system through an exit opening for the generated fluid pressure waves. The apparatus includes adjustment means for controlling the amplitude of the fluid pressure waves in the conduit system in front of the nozzle mouth. The adjustment device can be used to set a Helmholtz number, which is determined from the quotient of the path length for the fluid pressure waves between the exit opening of the chamber and the nozzle mouth of the nozzle in the line system and the wavelength of the fluid pressure waves in the line system. The fluid jet formed serves to remove material, wherein the erosion effect of a treated surface is to be improved. This includes cleaning, cutting and drilling.

According to paragraph [0007], the proposed solution is based on the idea that by injecting vibrational energy in the form of pressure waves into a fluid jet, in particular into a fluid jet with a pressure of 20 bar, 30 bar or more, fluid pulses can be generated in which the vibration energy is converted into kinetic energy. In doing so, the momentum transferable to the fluid by generating pressure waves can be maximized by ensuring that the reflections of pressure waves in a conduit system for delivering pressurized fluid to a nozzle do not cancel the generated pressure waves but amplify them due to interference. In the proposed device, therefore, the ratio of the effective path length, which cover the pressure waves in the conduit system from the outlet opening of the chamber to the nozzle mouth of a nozzle, and the wavelength of the fluid pressure waves, d. H. a Helmholtz number characterizing the fluid pressure waves in the conduit system can be adjusted.

Furthermore, it is stated in paragraph [0060] that the pressure pump is designed so that in chamber a fluid pressure in the range between 40 bar and 150 bar, preferably a fluid pressure in the order of 100 bar, generated and can be adjusted. By adjusting the fluid pressure in the chamber, the frequency v, and the amplitude of the pressure waves, the size and spacing of liquid droplets in fluid jets exiting the nozzle can be varied.

According to paragraph [0065], by adjusting the pressure and the amplitude of the pressure waves in the chamber, the flow rate and the shape of the pulsating fluid jet generated with the nozzles can be adjusted. The formation of a series of lumps or drops impinging on a solid surface is also shown.

The publication EP 2 145 689 A1 deals with a method and a device for the preparation of surfaces with a water jet, which is forced pulsating under high frequency. In this case, a high-frequency signal generator is used, which transmits the high frequency to a vibrator with a microtip. The vibrating microtip creates a vibrating jet of water that emanates from a nozzle orifice. The pulsating jet of water with the included mini-water balls has an improved erosion, z. B. for cutting or cleaning.

From the publication US Pat. No. 3,687,147 A method is known in which two jets of an incompressible fluid are at an acute angle to each other and interact in such a way that, in addition to an increase in the speed, individual lumps of liquid of finite length and duration form.

Another method for liquid jet shaping and a device suitable for this purpose describes the document DE 600 28 949 T2 , The apparatus for producing a high-pressure fluid jet for treating a selected surface comprises a nozzle and a supply line having a first conduit opening in fluid communication with the nozzle opening, the supply conduit further comprising a second conduit opening spaced from the first conduit opening for aligning Fluid jet serves. The nozzle and / or the supply line has at least one opening upstream of the second line opening, wherein the opening is provided so that it can be connected to the source of the second fluid. The opening is a first opening, wherein the nozzle and / or the supply line further comprises a second opening, spaced from the first opening. The first and second openings are positioned at different locations along the axis extending between the first conduit opening and the second. A length of the duct between the first and second openings is at least about ten times greater than the average diameter of the second duct opening.

The controlled introduction of a second fluid comprises periodically interrupting a flow of the second fluid in the direction of the fluid jet to pulsate the fluid jet. Further, selecting at least the length of the conduit and / or the pressure of the second fluid and / or the flow rate of the second fluid comprises causing the high pressure fluid jet to resonate as the high pressure fluid jet passes through the conduit.

From the publication DE 215 20 05 A1 is a hydraulic chamber with outlet nozzle known. A hydraulic chamber containing a nozzle capable of providing a very high instantaneous pulsed dynamic beam in a device which generates a shock wave in a relatively incompressible fluid is obtained when the effective location of the shock wave is such that the shock wave The pressure wave generated thereby is applied to build up quickly and uniformly in a direction along the center line of the nozzle. A suitable configuration for such a chamber is a parabolic cissoid in which the location of the shock wave is effectively at the focal point of the parabolic portion of such a chamber, thereby converting the resulting spherical waves into additive planar waves toward the centerline of the nozzle. The shock wave used in the device can be made by mechanical or electrical energy or a combination thereof.

The publication DE 334 35 55 C1 describes a method and apparatus for accelerating fluid volumes. Individual quantities of fluid are accelerated to high speeds by exposure to the energy stored by compressing the fluid. The liquid is pressed to make the compression in a pressure vessel already filled with liquid. Due to the energy stored in the compressed liquid, a certain amount of liquid is expelled from the pressure vessel into a collection nozzle when a valve is opened rapidly. The valve is opened when an opening force generated by the compressed liquid exceeds a closing bias. Repeatedly introducing high-pressure fluid into the pressure vessel will take the valve automatically work cycles to produce a series of pulsating liquid jets. The rapid opening of the valve is assisted by a lug on the valve element that slides sealingly within the passage of the accumulation nozzle to block the release of the liquid until the valve element accelerates sufficiently to reach the required opening speed when the lug closes Nozzle passage releases.

Paragraph [0005] specifies that pulsating jet devices preferably use a "collection" nozzle, such as those disclosed in the specification US 33 43 794 described device in which an amount of liquid containing energy is supplied to the inlet of a dry nozzle. The foremost portion of the amount of liquid is greatly accelerated as it flows along the narrowing channel of the collection nozzle, which concentrates most of the energy of the amount of liquid as kinetic energy in a small portion of the amount of liquid. The resulting short-term liquid jet exiting the nozzle has a peak back pressure that is several times greater than the static pressure that occurs anywhere within the nozzle. The liquid jet also includes discrete volumes or lumps of liquid (cf. US Pat. No. 4,863,101A which belongs to the same patent family as DE 334 35 55 C1 ).

Another specification provides the description in paragraph [0033]. Hereinafter, for example, in a device used to machine rocks, concrete and other hard materials instead of a conventional rotary hammer, pressurized water at about 1379 bar can be fed to a chamber having an inner diameter of about 20 cm. This pressure could result in a compression of about 5% and would expel into the nozzle amounts of water each having a volume of about 213 cm ³ with a pulse energy of about 13,560 J.

A method and apparatus for generating pulsed liquid jets also describes the document DE 215 20 03 A , The proposed solution generates the high-frequency pulsed water jets by the discharge of electrical energy and is based on the recognition that when discharging electrical energy from, for example, a capacitor in a closed and filled with a liquid container via electrodes between the electrodes, a tubular space arises. In this very high temperatures prevail in front. Discharge of this kind have three effects. On the one hand, a high-pressure sound wave front extends from the discharge hose to the outside. Secondly, in the region of the tube, a very hot and expanding gas bubble is formed, which contains superheated steam and a considerable amount of ionized and neutral molecules. Third, at the same time as discharge, a high-intensity continuum of light is created. The pressure surge occurs by heating at least a portion of a volume of liquid, with the exception of a discharge nozzle, by an electrical discharge within the liquid of such discharge duration and intensity that a shock wave is generated in the liquid.

From the publication DE 372 48 64 C1 the skilled person can learn about a high-pressure water jet device with pulsating water jet. The proposed high-pressure water jet device for generating pulsating water jets has a gas-loaded pressure accumulator which is connected to a supply line and connected via a pipeline to a main vibration generator. On the outlet side, a second vibration generator is connected to the main vibration generator via a pipeline with a built-in non-return valve, in the housing of which a valve piston connects the inlet connection to an outlet nozzle or separates it from this outlet. At the inlet of the second vibrator, a second gas-loaded pressure accumulator is connected, in which in cooperation with the check valve, the peak pressures of the main vibrator incoming pressure waves are stored and so a gradual charge takes place until the release pressure is reached on the valve piston and the stored energy in discharges a powerful jet of water.

The check valve disposed in the pipeline connecting the main vibrator to the second vibrator allows the second accumulator to be gradually charged by passing only the peak pressures of the pressure waves generated by the main vibrator in the natural vibration state. The energy of these high-pressure pulses is stored in the second pressure accumulator and discharged upon reaching the constant pressure at the source trigger pressure in a single powerful water jet pulse.

Other pamphlets devoted to the production of percussive fluid jets include the US 3,924,805 A , This process generates the percussive fluid jet from a continuous jet discharge, consisting of the generation of a relatively small cyclic variation of the discharge speed about its time average value, wherein the free jet is given a longitudinal change of the forward speed. This forces the free jet to become a collimated beam, a change in the lateral diameter which occurs periodically along the length of the beam. The cyclic variation of the discharge rate is thereby obtained by generating a cyclical change of the liquid pressure at the inlet to a discharge nozzle.

The resulting movement can be considered as a forward movement of the jet section at the average speed u, while the relevant part of the liquid tends to flow to the center of that part due to the change in velocity. So, as the section of the beam moves forward, it also tends to decrease or increase the diameter. That is, he tends to "bundle" himself. The process can also be viewed as the part of the faster fluid overriding and connecting to the slower one within the cycle. The process necessarily involves a separation of each slowly-fast (thereby bundled) beam portion from the previous and subsequent ones. Thus, the cyclic change in the ejection velocity has the effect of converting the continuous stream from a uniform stream into a sequence of liquid slugs.

However, the effect described above in different variants is random and uncontrolled, but at least without any special effects that would go beyond the already known from the prior art effects of pulsating liquid jets.

The disclosure of a liquid ejection system with drop velocity modulation can be found in the document EP 2 714 406 A1 , The continuous liquid ejection system includes a liquid chamber in fluid communication with a nozzle, the liquid chamber containing liquid under pressure sufficient to eject a jet of liquid through the nozzle. A drop forming device is connected to the liquid jet, wherein the drop forming device is operable to generate a modulation in the liquid jet. This causes parts of the liquid jet into one Break a series of pairs of drops moving along a path, each pair of drops consisting of a first and a second drop.

A charging device comprises a charge electrode associated with the liquid jet and a source of varying electrical potential between the charge electrode and the liquid jet. The source of varying electrical potential provides a waveform containing a period equal to the drop pair period. The waveform includes a first and a second different voltage state, wherein the charging device is synchronized with the droplet forming device to generate a first state of charge on the first droplet and to generate a second state of charge on the second droplet. The drop velocity modulation device changes the relative velocity of the first and second drops to control the connection of the drops to a combined drop having a third state of charge. A deflector is provided which causes the first droplet of the first charge state to travel along a first path, the second droplet of the second charge state to move along a second path, and the combined droplet of the third charge state to move on a third path emotional.

Since slight changes in amplitude affect the waveform of the energy pulses transmitted to the jet of liquid for droplet formation, they affect the velocity of the droplets formed, the velocity of one or both droplets can be modulated in a droplet pair. This is achieved by changing the properties of the energy transferred to the liquid jet.

The publication EP 2 485 847 A2 teaches a method and apparatus for making cylinder bore surfaces with a pulsed water jet. The preparation of a surface of a cylinder bore is done using a pulsed jet of water. The following method steps are provided: generating a signal with a frequency using a signal generator; Applying the signal for generating a pulsed water jet through an outlet opening of a nozzle with an outlet opening and with a cylindrical portion of the outlet opening; Causing the pulsed water jet to impinge on the surface of the cylinder bore to prepare the surface within a predetermined range of surface roughness. The predetermined range of Surface roughness is selected based on operating parameters including a distance, a nozzle traverse velocity, a water pressure, a water flow rate, an orifice length-to-diameter ratio, the frequency, and an amplitude of the signal.

According to one aspect of the proposed solution described in paragraphs [0015] and [0035], the pulsed water jet can be generated by the generation of high-frequency pulsating liquid jets. These high-frequency liquid jets can be generated with internal mechanical flow modulators, Helmholtz oscillators, self-resident nozzles and / or ultrasonic nozzles. Additionally, the pulsed water jet may be generated using acoustic waves, such as an acoustic wave, which acts on the fluid by means of an acoustic transducer. The intended effect is based on increasing the water jet impact on a material target by ultrasonic modulation. Namely, if a drop or a liquid plug strikes the same surface, the initial impact pressure will be much higher.

In another example, described in paragraph [0039], a pump set at 69 MPa would achieve a hammering water pressure on the target surface of 566 MPa. Since the behavior of the material depends on the impact pressure and time, which in turn are determined by the frequency and nozzle diameter, the use of forced pulsed water jets achieves a significant improvement in material erosion or surface preparation.

From the pamphlets EP 2 877 697 A1 or. WO 2014/018977 A1 is a hyper-pressure pulse excavator known. To generate a fluid pulse, a hyper-pressure water cannon system is provided. This includes a pressure vessel coupled to a source of pressurized fluid, the pressure vessel including a drain valve. A nozzle has a straight portion and a convergent tapered portion, with the nozzle connected to the pressure vessel after a bleed valve. The velocity of the pressurized fluid discharged from the pressure vessel through the bleed valve increases as it flows through the nozzle.

In practice, the velocity of the water leaving the gun valve changes continuously, but a pulse of approximately 0.5 m in length is produced at a speed of over 500 m / s. The kinetic energy of the pulse increases linearly to about 0.5 m and then continues to increase at a lower rate. The speed is low when the valve opens, peaks after the valve opens, and then drops when the pressure drops (decompressed). A straight nozzle section accumulates the water at the leading edge of the pulse and allows the fluid to catch up with the higher velocity, thereby forming a liquid plug at a uniform rate.

A numerical analysis shows that a compressed water gun tool can generate a compressed water pulse that is 300 mm long and moves at a speed of about 520 m / s. The leading edge accelerates to over 2000 m / s while the trailing edge decelerates.

In addition to the prior art, further publications are known which relate to the field of modulation of liquid jets. However, the modulation of liquid jets has heretofore been considered almost exclusively for increasing the efficiency of water-jet cutting of rock and hard materials, as the prior art noted above shows. In this case, p ≥ 1000 bar is used in the high pressure range. Publications include the conference proceedings of the Water Jet Conferences and the Jet Cutting Symposia ( Cooley, WC: Rock Breakage by Pulsed High Pressure Water Jet, First International Symposium on Jet Cutting Technology, Paper B7, 1972 ; Nebeker, EB; Rodriguez, SE: Percussive Water Jets for Rock Cutting, Third International Symposium on Jet Cutting Technology, BHRA Fluid Engineering, Paper B-1, 1976 ; Nebeker, EB: Development of Large-Diameter Percussive Jet, First US Water Jet Symposium, Colorado School of Mines, pp.IV5 .1-11, 1981 ; Nebeker, EB: Standoff Distance Improvement Using Percussive Jets, Proc. 2nd US Water Jet Conference, WJTA, pp. 25-34, 1983 ; Dehkhoda, S .: Experimental Study of Rock Breakage with Pulsed Waterjet, 8th Asian Rock Mechanics Symposium ARMS8, Sapporo, Japan, 2014 ). Methods were investigated to interrupt or chop the water jet ( Metcalfe, RA; Davies, TW: Experimental Study of the Impact of Broken Water Jets, 4th International Symposium on Jet Cutting Technology, 1978 ; Lichtarowicz, A .; Nwachukwu, G .: Erosion by an Interrupted Jet, Proc. 4th International Symposium on Jet Cutting Technology, pp.13-18, 1978 ; Vijay, MM; Remisz, J .; Shen, X .: Fragmentation of Hard Rocks with Discontinuous Water Jets, Proc. 3rd Pacific Rim International Conference on Water Jet Technology, pp.201-224, 1992 ), but not to modulate this purposefully. This chopping is done mainly in the relatively low frequency range for this high pressure to about 100 Hz. Other publications use for modulating the beam resonators in the nozzle ( Chahine, GL; Conn, AF; Johnson, VE; Frederick, GS: Cleaning and Cutting with Self-Resonating Pulsed Water Jets, Proc. 2nd U .S. Water Jet Conference, WJTA, pp.167-173, 1983 ; Conn, AF: Asbestos Removal with Self-Resonating Water Jets, Proc. 5th US Water Jet Symposium, pp.133-139, 1989 ; Bortolussi, A., R .; Ciccu, World Cup; Kim, PP; Manca, P .; Massacci, G .: Jet Power Optimization in Granite Kerfing Using Oscillating Nozzles, Proc. 6th American Water Jet Conference, pp.71-86, 1991 ). These systems deliver pulsations in the range of a few kHz. Recently, ultrasonically modulated beams have been used by the Foldyna group for the processing and cleaning of concrete ( Foldyna, J .; Sitek, L .; Svehla, B .; Svehla, S .: Utilization of ultrasound to enhance high-speed water jet effects, Ultrasonics Sonochemistry, 11, pp. 131-137, 2004 ; Bodnärovä, L .; Sitek, L .; Hela, R .; Foldyna, J .: New Potential Of High Speed Water Jet Technology For Renovating Concrete Structures, Slovac Journal of Civil Engineering, Vol. XIX, no. 2, pp.1-7, 2011 ) or for the removal of asbestos. An application of pulsating or interrupted liquid jets for the purpose of cleaning in the low pressure range can be found only from 2010 ( Augustin W .; Fox T .; Föste H .; Schöler, M .; Majshak, J.-P .; Scholl, S .: Pulsed flow for enhanced cleaning in food processing, Food and Bioproducts Processing 88, pp. 384-391, 2010 ; Weidemann, C .; Vogt, S .; Nirschl, H .: Cleaning of filter media by pulsed flow - Establishment of dimensionless operation numbers describing the cleaning result, Journal of Food Engineering, 132, pp. 29-38, 2014 ; Stoye, H .; Köhler, H .; Mauermann, M .; Majschak, J.-P .: Investigations to increase the cleaning efficiency by pulsed spray cleaning, Chem. Ing. Tech., 86, no. 5, pp. 707-713, 2014 ).

A fundamental disadvantage of the prior art is that for the spray cleaning no reduction of the cleaning time by significantly increasing the cleaning mechanism is possible. In addition to time and mechanics, temperature and chemistry are other important factors influencing cleaning. However, increasing the temperature and the use of chemicals does not provide a socially acceptable alternative for minimizing the environmental and cost aspects Furthermore, the maximum adjustable operating pressure of the cleaning system serving as a possible manipulated variable for increasing the mechanics is generally limited upwards in terms of plant or process technology. Thus, the economically interesting and most used range for spray cleaning is between 2 and 6 bar. The reasons for this are that here the expense for the pumps and the work and noise control measures are in a favorable ratio to the cleaning result and the currently widespread cleaning chemicals are designed for this pressure range. Increasing the volume flow conveyed by the cleaning system is also impracticable from the point of view of resource efficiency and because of the subsequently required wastewater treatment. Consequently, new approaches are needed with which the mechanical cleaning component can be further increased while conserving resources.

With the previously described methods known from the prior art, it is possible to dispense individual sections of a liquid jet or to impart a more or less controlled pulsation to the liquid jet, so that a higher energy input into the target surface and a better result compared to a continuous liquid jet when editing the target surface, z. As a desired abrasion can be achieved. For this purpose, various devices have been proposed, which are complicated, expensive and susceptible to interference by additional facilities, such as an additional beam generation or an oscillation, for the actual beam generation. In addition, there is currently no pulsation method in the spray cleaning which has a suitable beam modulation in order to produce a maximum hard pulsation according to the potential possibilities of the liquid on the surface to be cleaned.

It is therefore an object of the present invention to provide a method and apparatus for producing a modified liquid jet with increased mechanical effectiveness, which is simple in construction and with reduced liquid requirement has a further improved effect, in particular an improved abrasion effect.

The object is achieved by a method for generating a sequence of sections of a liquid jet, wherein a single beam portion of the discontinuous, modified liquid jet before impinging on a Target surface has a shorter length in the direction of movement than after exiting a nozzle. According to the invention, the modification is caused by different velocities within the single jet portion of the discontinuous, modified liquid jet such that due to a steady increase in the jet velocity as it exits the nozzle, a trailing jet region catches a forward jet region of the jet segment by the single jet segment Increasing speed exits the nozzle the later it exits the nozzle, and wherein a disruption of the previously pooled to the beam portion liquid is prevented by a critical ratio of inertial force is not exceeded to the surface force.

The mechanism of a modified fluid jet with increased mechanical effectiveness, which helps to hunt insects in the wild in nature, has been scientifically elucidated. A well-defined modulation of both the mouth opening acting as a nozzle surface and the pressure in the oral cavity of the fish provides a steady increase in both the water jet velocity and the water jet pulse over time. This particular form of acceleration of water causes an accumulation of water at the tip of the jet to build up with the accumulated momentum released from the mouth of the fish over the duration of the ejection. This "water rag" is therefore able, in the short impact with the insect, to apply a force which is a multiple of the force of the simple jet of water, because force is the time derivative of the momentum. The invention has therefore set itself the goal to collect over the entire beam length, which corresponds to the distance between the nozzle and the target surface, a pulse in order then to convert it into a strong force in a very short burst. This physical principle is used in other ways, e.g. B. impact drills in mechanics, already applied.

The mass contained in the undisturbed beam (d _u = 3 mm due to jet contraction at the nozzle) between two impurities is: $$\begin{array}{cc}{m}_u=\rho \cdot V_u=\rho \cdot \frac{\pi }{4}\cdot d_u^2\cdot L& \left(\rho \mathrm{...}\mathit{density}.\mathit{V}\mathrm{...}\mathrm{volume}\right)\end{array}$$

The mass in a lump is the difference between the mass of the undisturbed beam and the mass of the remaining thin beam between the lumps: $$m_k=\rho \cdot V_k=\rho \cdot \frac{\pi }{4}\cdot \left(d_u^2-d_s^2\right)\cdot L$$

If you divide both masses, you get the mass fraction in the lump: $$\frac{m_k}{m_u}=\frac{d_u^2-d_s^2}{d_u^2}=\frac{9-1}{9}=89\%$$

The force F exerted by a beam upon impact with a substrate is equal to the momentum change of the beam. With an undisturbed jet, the speed is constant and thus also the impact force. This is equal to the product of mass flow times jet velocity before impact: $$F_u=\frac{\mathit{.DELTA.M}}{\mathit{.delta.t}}\cdot u=\frac{\pi }{4}\cdot \rho \cdot d_u^2\cdot u^2=0.13N$$

The values for the undisturbed case give a force of 0.13 Newton. For the transient case, the momentum of the clump is calculated and the time Δt at which this pulse is delivered to the substrate is estimated. This is possible with the help of the thickness of the lump. The thickness of which corresponds approximately to the beam diameter (undisturbed), ie, the interaction takes place in a time of Δ t = d _u / u ≈ 0.7 ms. The force of the lump F _k yields 2.76 Newton according to the following calculation: $$F_k=\frac{\mathrm{\Delta }\mathit{I}}{\mathrm{\Delta }\mathit{t}}=\frac{I-0}{\mathrm{\Delta }\mathit{t}}=\frac{m_k\cdot u}{\mathrm{\Delta }\mathit{t}}=2.76N$$

This value is 21 times higher than the undisturbed beam. The calculations underlying the calculation were not conducted with the aim of maximizing the accumulation of impulses.

For practical technical implementation different approaches are suitable. The implementation of the modulation of the nozzle surface is technically feasible, but much more complex than the more practical modulation of the pressure. B. be achieved via a camshaft which moves the compression piston of a pump against a spring. The shape of the camshaft is then decisive for the pressure curve. Other forms of pressure modification are also contemplated.

The aim of the practical application of the modified liquid jet is, above all, to detach contamination from a substrate against the adhesive force. With small pressures, but very well defined, temporal evolution of the velocity from the nozzle, a collection of momentum in the liquid, especially in the water, is to be achieved, which, when impinging on the contaminant, will produce a much higher, jerky force than a continuous stream can apply at the same speed.

The technical implementation must be carried out periodically. The period is preferably chosen so long that the subsequent impact of a jet section alone and directly on the target surface or the impurity encountered there, but not on the still running water of the previous impact. A longer period also allows for more pulse accumulation, thus increasing the effectiveness of the single burst.

It has surprisingly been found that it is possible to collect a beam pulse over a given spray duration Δt. To accomplish this, there must be a steady increase in jet velocity so that fluid elements later discharged from the nozzle can catch up with the previously dispensed fluid elements.

The time t _k and place x _k , when and where this happens, can be seen schematically on the basis of a path-time diagram (cf. Fig. 1 ). Shown are time-place lines for three different fluid elements that have left the nozzle at the times t ₀ , t ₁ , t ₂ . It can be seen that these straight lines intersect at a point, at x _k at time t _k . Considering that the slope of this straight line corresponds to the velocity of the fluid elements, it becomes clear that the velocity must increase with a later start time in order to ensure an intersection point, that is to say a union of the fluid elements. A time-varying speed is nothing more than an acceleration. Accelerations on the order of 300-400 m / s ² at the beginning of the injection process have proven to be particularly advantageous. This acceleration may seem very high but it is only an instantaneous value. The typical global Accelerations are in the order of 150 m / s ² . Another reason for the high values is the small time scale available for the operations. These take place in hundredths of seconds.

At this point another important rule becomes visible. The union of fluid elements must not lead to a collision. Because if a very fast fluid element would hit a previous, slower fluid element, this would cause the fluid collected up to that point to be broken and fly on in the form of small drops. The small drops lose momentum to the surrounding air and spread over a much larger volume. So much acceleration is not wanted. Experience shows that a global acceleration of 200 m / s ² still makes sense. This global acceleration a is defined as the difference in the maximum speed during the injection process minus the speed at the beginning of the injection process, divided by the time of the speed increase.

(Dichte ρ und Oberflächenspannung σ des Fluids). Die Weber-Zahl ist eine dimensionslose Kennzahl der Strömungsmechanik. Sie beschreibt das Verhältnis von Trägheitskraft zur stabilisierenden Oberflächenkraft bei Zweiphasenströmungen, zum Beispiel eines Wassertropfens in Luft.It has therefore been found to be significant that break-up of the previously collected fluid must be prevented. On the one hand, the surface tension σ holds a liquid together, ie there is a critical Weber number, the ratio of inertial force to surface force, from which an unification of the fluid elements is no longer possible and breakup and bursting of the accumulated fluid occurs. Since there is no scientific evidence to answer this question in the case of radiation (fluid elements), the results can be used for a very similar but reversed phenomenon. According to Nobari and Tryggvason, in the collision of drops of diameter d with a relative velocity u _rel , the critical number of weavers is 24 for a union of the drops. $$\mathrm{We}=\mathrm{\rho }{{\mathrm{u}}_{\mathrm{rel}}}^{\mathrm{2}}\mathrm{d}/\mathrm{\sigma }$$

(Density ρ and surface tension σ of the fluid). The Weber number is a dimensionless index of fluid mechanics. It describes the ratio of inertial force to stabilizing surface force in two-phase flows, for example a drop of water in air.

When the critical Weber number We is exceeded, a coalescence of the drops takes place only for a short time. The combined liquid decomposes further into smaller fragments. The reason for this is the too high kinetic energy of the collision. At collision energies smaller than the critical Weber number, the surface tension as the restoring force with the inertia force enables drop vibrations as a result of the collision.

Fig. 2 shows the dividing line between permanent coalescence and only temporary cohesion between colliding drops of the same size MR Nobari and Y.-J. Jan G. Tryggvason, Head of collision of drops-A numerical investigation, Physics of Fluids 8 (1), pp. 29-42, 1996 ,

Fig. 3 shows results of the dividing line between separation and cohesion between colliding drops of the same size MD Saroka, N. Ashgriz and M. Movassat, Numerical Investigation of Head-on Binary Drop Collisions in a Dynamically Inert Environment, Journal of Applied Fluid Mechanics, Vol. 1, pp. 23-37, 2012 ,

so liegt hier der Wert für die Relativgeschwindigkeit um einen Faktor 1,7 bis 2,7 höher (2,7 - 3,8 m/s). Die angegeben exponentielle Funktion stellt ein Beispiel dar, weitere Funktionen kommen in Betracht (z. B. quadratische). Es kommt grundsätzlich jede monoton fallende Funktion in Betracht, so dass die allgemeine Formel $${\mathrm{v}}_{\mathrm{tip}}={\mathrm{v}}_{\max }-\mathrm{\Delta v\; f}\left(\mathrm{t}\right)$$

lautet.Over time, due to the toughness, the surplus energy of the union is dissipated or annihilated, the vibrations fade away. Furthermore, the toughness means that at low Reynolds number always comes to a Zusammenfinden the fluid elements. If the maximum relative velocity is calculated, which can occur between fluid elements, the droplets, before the jet breaks, the influence of the Weber number will predominate for water. For a beam with a diameter of 1 mm, the maximum relative velocity would be about 0.8 m / s due to the Reynolds number <800, ie due to dissipation of the interaction energy. Whereas according to the condition of Saroka Ashgriz We <34, ie effect of the surface tension in a water jet with 1 mm diameter would give a maximum relative velocity Δv of about 1.6 m / s. However, these numbers are based on results for the collision of drops. Will the results for measurements on shooter fish [ P. Gerullis and St. Schuster, Archerfish Actively Control the Hydrodynamics of Their Jets, Current Biology 24, pp. 2156-2160, 2014 ] for the speed of the beam _tip , v _tip : $${\mathrm{v}}_{\mathrm{tip}}={\mathrm{v}}_{\mathrm{Max}}-\mathrm{\Delta v\; exp}\left(-\mathrm{t}/\mathrm{\tau }\right)$$

The relative speed value is thus 1.7 to 2.7 higher (2.7 to 3.8 m / s). The given exponential function is an example, other functions are possible (eg quadratic). In principle, every monotonically decreasing function comes into consideration, so that the general formula $${\mathrm{v}}_{\mathrm{tip}}={\mathrm{v}}_{\mathrm{Max}}-\mathrm{\Delta v\; f}\left(\mathrm{t}\right)$$

reads.

wobei die relative Geschwindigkeitsmodulation ε bei maximal 0,66 liegt. Dies entspricht in etwa einer Verdoppelung der Anfangsgeschwindigkeit.The typical time scale τ, in which the unification processes take place, is in the range of 6 to 20 ms and the maximum velocity v _max at about 20 - 25 m / s. The maximum relative velocity Δv is 3 m / s, because of this relative speed to the atomization of the accumulated liquid begins. These two values provide a relative velocity modulation ε according to the formula $$\mathrm{\epsilon }=\mathrm{.DELTA.v}/{\mathrm{v}}_{\mathrm{Max}}$$

wherein the relative velocity modulation ε is at most 0.66. This corresponds approximately to a doubling of the initial speed.

Based on these considerations, it was possible to estimate the parameter ranges for a purification according to the principle of the invention. Depending on the distance between the nozzle and the surface to be cleaned, the target surface, the duration of the injection is between a few milliseconds and a few tenths of a second. The rate of increase in this time is a factor of up to 3 - 4. The maximum speed of the liquid can reach up to 20 m / s, but it must be expected that in this case or exceeding the maximum speed not a single contiguous volume of liquid the target hits and instead several drops in a small narrow space within a short time hit the surface to be cleaned. However, it has been found that a similar effect is achieved as with a single drop. Decisive for the active principle is the concentration of the liquid on a small volume and therefore also for a short-term, ie impulsive force on the target.

There is another limitation on fluid velocity, namely the aerodynamic Weber number for drop breakup: $${\mathrm{We}}_{\mathrm{aero}}={\mathrm{\rho }}_{\mathrm{gas}}{{\mathrm{u}}_{\mathrm{RELG}}}^{\mathrm{2}}\mathrm{d}/\mathrm{\sigma }.$$

Here the aerodynamic forces on the liquid play a role. The essential difference to the normal Weber number is that here the density of the surrounding gas and the relative velocity to the gas become effective. With increasing relative speed to the gas, the drop loses its spherical shape and is flattened. From an aerodynamic Weber number of about 20 creates a flattened bag that is bloated and breaks up. An estimate of this relative velocity for water droplets in air gives a value of 35 m / s for drops of 1 mm in diameter, for drops of 5 mm the value is 16 m / s. This means that water jets are also destabilized by the air with increasing speed. As the distance between the nozzle and the target increases, this effect becomes effective. Therefore, it was found that the rays should not exceed speeds of about 25 m / s. This would correspond to a driving loss-free differential pressure of approx. 3 bar.

It has proved to be advantageous if the liquid jet is generated by means of a piston pump and the steady increase in the jet velocity on exit from the nozzle is caused by an at least time-dependent control of the piston pump and the piston movement. Alternatively, or as a supplementary measure, the steady increase in the jet velocity on exit from the nozzle is caused by a corresponding control of a nozzle cross-section and / or a nozzle opening.

The particular advantages of the method according to the invention are that with a very hard pulsation through a "water rag" the collected pulse can be achieved. Thus, up to 60 times greater force peaks are generated on the surfaces to be cleaned compared to conventional spray nozzles and thus savings potential of 50% of cleaning time and detergent consumption expected depending on the contamination characteristics. The power gain is also far above that of conventional pulsating liquid jets. This is achieved by the special modulation of the spray jets.

The method according to the invention enables the collection of beam pulses during the phase of beam formation and propagation. In the subsequent brief interaction of the beam with the target surface, z. As a substrate or pollution, significantly higher forces, which are available for the cleaning of the beam during cleaning and damage the pollution much more. The approach thus differs fundamentally from hitherto known principles of action of pulsating rays. This difference can be explained well by comparing the impact drill and the hammer drill: in both, pulsed impacts are exerted on the workpiece. However, the firing pin in the hammer drill is accelerated over a much longer time before he hits the chisel. This means that correspondingly more pulse is collected in the firing pin, whereby the hammer achieves much greater force peaks - comparable to the modified liquid jet according to the invention. On the other hand, the pulsating beams known so far on the research side show narrow successive interruptions of the jet - comparable to the less effective percussion drill.

A further aspect relates to a device for producing a sequence of sections of a liquid jet, wherein a single jet section of the discontinuous, modified liquid jet has a length which is shorter in the direction of movement before it hits a target surface than after exit from a nozzle. The apparatus comprises the nozzle and a device fluidically connected to the nozzle for generating pressure in the liquid. According to the invention, it is provided that the device for generating pressure of a liquid comprises a controlled piston pump, designed for the at least time-dependent control of a piston movement. Alternatively or additionally, the nozzle has a controllable nozzle cross-section and / or a controllable nozzle opening.

It has also proven to be advantageous if a manual or robot-based cleaning by means of a nozzle whose orientation is variable, so that the beam direction can be adjusted. A suitable device may, for. B. be designed as a nozzle lance.

Another aspect of the present invention relates to the use of the modified liquid jet as a cleaning jet. In this case, a use for spray cleaning industrial components is provided. It is also intended that the modified liquid jet used as a cleaning jet for a container cleaning or tank cleaning with a jet cleaner. Also, a spray cleaning of open surfaces of industrial equipment and systems or surfaces of industrial floors, walkways and driveways, terrace floors or facades is provided. In addition to the applications for cleaning, a surface treatment or a cutting process are provided. Similarly, applications in the fields of stone processing, such as tunneling, mining, fire fighting or police technology are provided.

The inventive method promises unprecedented mechanical cleaning effect even at large nozzle distances and low operating pressure. The cleaning of the objects is gentle, because the high force peaks work only for a short time, in contrast to cleaning with a jet under high pressure, in which permanently high forces act. In addition, resources such as time, water, chemical additives and energy are greatly reduced over known systems.

The demand for relevant spray cleaning systems in the field of industrial parts cleaning is enormous, since almost all components have to be cleaned before each further processing step or at the time of final delivery in accordance with the process-related cleanliness requirements. The wet-chemical processes occupy a market share of 60%, whereby spray cleaning is used by more than half of the companies. The reduction of cycle times is directly connected with a higher output and thus the increase in productivity of a plant or an entire production line while maintaining the required component cleanliness. A large number of companies monitor the throughput times as an optimization criterion. In addition, many companies estimate the proportion of cleaning costs as an average of around 10% of the total manufacturing process of components, which shows the great savings potential in the area of cleaning.

The processes of both industrial applications can usually be assigned to mass production, whereby the shortening of cycle times in the parts cleaning or downtime in the cleaning of processing plants, especially in the food and pharmaceutical industries directly associated with the higher output and thus increase the productivity of a plant is. In order to At the same time, the desired decoupling of economic growth from resource consumption, which will be essential for the sustainability of whole economies, will be supported.

The statements made in the context of the present invention on the mode of action and industrial applicability of this technology represent an innovation in the technical field, which at the same time results in industrial applicability. The social relevance of this innovation lies primarily in contributing to the conservation of resources (reducing time, water, chemical additives and energy), improving competitiveness and increasing consumer safety through well-cleaned food facilities.

• Fig. 1: Weg-Zeit-Diagramm, das beispielhaft drei diskrete Abschnitte des bis zum Zeitpunkt t_k und zum Ort x_k strömenden Strahlabschnitts zeigt;
• Fig. 2: die Trennlinie zwischen dauerndem Zusammenhalt (permanent coalescence) und nur temporärem Zusammenhalt zwischen kollidierenden Tropfen gleicher Größe; und
• Fig. 3: Ergebnisse zur Trennlinie zwischen dauerndem Zusammenhalt (permanent coalescence) und nur temporärem Zusammenhalt zwischen kollidierenden Tropfen gleicher Größe.

The following figures have already been mentioned in the above description. They show diagrams.

• Fig. 1 : Path-time diagram showing, by way of example, three discrete sections of the beam section flowing up to time t _k and to location x _k ;
• Fig. 2 : the dividing line between permanent coalescence and only temporary cohesion between colliding drops of the same size; and
• Fig. 3 : Results on the dividing line between permanent coalescence and only temporary cohesion between colliding drops of the same size.

• Fig. 11: schematisch eine Darstellung von Düse und Zielfläche sowie den dazwischen ausgebildeten Strahlabschnitten;
• Fig. 12 bis 14: Düsen nach dem Stand der Technik;
• Fig. 15: schematisch eine Darstellung der Austrittsgeschwindigkeit des Strahls mit Bildung von Wasserklumpen; und
• Fig. 16: schematisch eine Darstellung einer erfindungsgemäßen Vorrichtung zur Erzeugung einer Folge von Strahlabschnitten eines diskontinuierlichen, modifizierten Flüssigkeitsstrahls.

Reference to the description of exemplary embodiments and their representation in the accompanying drawings, the invention will be explained in more detail below. Show it:

• Fig. 11 FIG. 2 is a schematic representation of nozzle and target surface and the beam sections formed therebetween; FIG.
• Fig. 12 to 14 : Nozzles according to the prior art;
• Fig. 15 FIG. 2 is a schematic representation of the exit velocity of the jet with the formation of water rags; FIG. and
• Fig. 16 FIG. 2 is a schematic representation of a device according to the invention for generating a sequence of jet sections of a discontinuous, modified liquid jet. FIG.

Fig. 11 Fig. 12 schematically shows a representation of the nozzle and the target surface as well as the beam portions formed therebetween, as produced by a pulsation according to the present invention. This is accompanied in the case of use shown here for a cleaning jet with a significant escalation of the cleaning effect. In this case, the pulse is collected over the entire beam length and discharged in a very short burst with enormous force directly on the surface to be cleaned.

In addition, due to the very short, impulse accumulating shocks, the splash pauses on the surface increase over the conventional pulsation (see Fig. 4), whereby the damping liquid film can completely drain and the jet force acts directly on the fouling on the target surface. Due to the above effects, the pollution is destroyed many times stronger and in a sustainable manner, whereby the cleaning or cycle times decrease or the cleaning agent concentration and temperature can be reduced with the same cleaning result.

A diagram 30 shows the pressure curve over time. The _shock pressure p _surge is a multiple of the _dynamic pressure p _congestion . Both FIGS. 11 to 14 in each case the time profile of the jet pressure applied by the spray jet to the surface to be cleaned is shown, which corresponds integrated with the force profile over the beam cross section.

Fig. 12 1 schematically shows a representation of a conventional continuous cleaning jet without pulsation according to the prior art, including a diagram 31 which shows the steady _backpressure p _stowage . In continuous operation, after the nozzle is switched on, a constant dynamic pressure occurs.

Fig. 13 _Fig . ₁₂ schematically shows a representation of a conventional cleaning _{jet with prior art jet interrupters} , including an explanatory diagram 32 showing coincident heights of back pressure p and _surge pressure. Except for the interruptions in the pressure curve, jet jet nozzles are subject to a similar jet pressure pattern for continuous operation.

Cleaning advantages are to be expected by two effects. On the one hand, the pollution is more severely impaired if, as a result of the jet interruptions, the liquid jet which damps the spray jet does not completely settle on the surface to be cleaned Can form surface. On the other hand, in general, the cleaning fluid will flow around the component much more turbulent. Since the beam interruption is also associated with a loss of momentum on the surface over time, it can be expected that no significantly improved cleaning effect arises.

Fig. 14 1 schematically shows an illustration of a nozzle in the pulsating operation of the prior art, including an explanatory diagram 33 for the relationship of the heights of the back pressure p _stau and the _shock pressure p _impact . When switching on the nozzle in pulsating operation, eg. B. realized by valve circuits, no constant, the back pressure corresponding jet pressure reached on the surface. Rather, shock waves strike the surface in short succession, which in turn produce higher pressure peaks than the dynamic pressure. In addition, only the positive ones of the beam interrupters (cf. Fig. 3 ) present side effects of the non-fully forming high-turbulence damping liquid film, since in the case shown no pulse loss occurs over time.

Fig. 15 shows how the exit velocity of the jet must steadily increase to achieve an abrupt accumulation of liquid at the tip of the jet. This could be achieved in the illustrated embodiment with a linear motor. The accumulation was achieved by a shaker that powered a 60 Hz porous piston. The relative excitation amplitude is 0.5 in Figures a) to g) (from left to right); 1; 2; 3; 4; 5; 6. The nozzle (nozzle diameter 3.2 mm, basic speed u = 4.29 m / s) is indicated in the upper picture area of each figure. The pictures show the formation of water rags and the jet, which is significantly thinner between these lumps. This is evident in the thickness d and length L of the beam between the accumulations (d _s = 1 mm, L = 71.5 mm, right). In a further embodiment, the modulation is to be driven so far that the jet breaks off completely and form individual, shortly after one another impinging water rags, so that the water has already expired before a new water rag hits. As a result, the surface, the target surface, is always hit immediately, which further improves the effectiveness.

This form of impulse collection from the right figure g) is already completed at 120 mm. By increasing the distance from the nozzle, longer integration times can be achieved. It has proven to be more beneficial Time to plan, the farther away the target is (up to 70 ms at a distance of 600 mm). This would correspond to a frequency of 14 hertz. The impulse collection as well as the resulting force are once again up to four times bigger.

On the right figure g) it becomes clear that the lumps can also have the shape of a broad, flat cylinder. This shape may be very interesting for cleaning as it covers a larger area at the same time. In this case, the diameter of the lump is about ten times the undisturbed beam diameter. As the diameter increases, however, the applied jet pressure (Impact) on the contaminated surface is reduced. Therefore an optimal lump shape for the cleaning should be determined and generated.

Fig. 16 1 schematically shows an illustration of a device 100 according to the invention for generating a sequence of jet sections of a discontinuous, modified liquid jet, which is not shown here but is aligned with the nozzle 110 by a corresponding position of a nozzle lance 112 on the target surface 26. The adjustment of the nozzle lance 112 in the arrow direction is made possible by a pivot drive 114, which also includes a joint.

The apparatus 100 further comprises a piston pump 116 in which a piston 118 moves and causes the pressure of the liquid from which the liquid jet is generated. The piston 118 is connected via its piston rod with a piston drive 120, which is designed in the preferred embodiment shown here as a Linearanrieb.

In order to achieve the pressure curve provided according to the invention, a controller 122 is provided which controls the piston drive 120 and for this purpose is connected to the piston drive 120 in terms of control technology. Such a control connection also consists of the pivoting drive 114 and a metering valve 126. The metering valve 126 meters for each period an intended amount of liquid from a liquid reservoir 124 in order to produce a modified liquid jet with the desired properties can.

Instead of a single nozzle 110, alternative embodiments of the proposed solution also provide multiple exit locations on the nozzle lance 112. These further nozzles 110 can also be individually controllable, so that also Without moving the nozzle lance 112 different locations can be treated simultaneously or sequentially.

In its preferred embodiment, the process sequence according to the invention starts with the metering of the quantity of liquid into the piston pump 116. Thereafter, the nozzle 110 is brought into the desired alignment with respect to the target surface 26 by means of the pivot drive 114. Thereafter, the piston drive 120 is controlled so that the modified liquid jet with the desired properties emerges from the nozzle 110 and impinges on the target surface 26 as lumps.

LIST OF REFERENCE NUMBERS

10, 110

jet

12

Beam (continuous)

14

Beam (interrupted)

16

Ray (conventional pulsation)

20

Ray (hammer pulsation)

21

beam section

22

water Cluster

26

target area

28

movement direction

30 - 33

diagrams

41

Area of continuous cohesion

42

Area of temporary cohesion

43

Area of separation

44

Area of cohesion

100

Device for generating a sequence of beam sections

112

nozzle lance

114

Rotary actuator

116

piston pump

118

piston

120

piston drive

122

control

124

liquid reservoir

126

metering valve

Claims (13)

A method of producing a sequence of beam portions (21) of a discontinuous modified fluid jet (20), wherein a single beam portion (21) of the fluid jet (20) undergoes such modification as to move in a direction of travel prior to impacting a target surface (26) (28) has a smaller length (L _f ) than after exiting a nozzle (10), characterized in that the modification is caused by different velocities within the single jet portion (21) of the discontinuous modified liquid jet (20) in that, as a result of a steady increase in the jet velocity on exiting the nozzle (10), a jet region in the direction of movement (28) catches a forward jet region of the jet segment (21), as the single jet segment (21) moves out of the nozzle (10) with increasing velocity. emerges the later it exits the nozzle (10), and wherein a Aufbr The liquid previously pooled to the jet section (21) is prevented by not exceeding a critical ratio of inertial force to surface force. The method of claim 1, wherein n beam portions of a beam portion (21) at times t ₀ to t _n exit the nozzle (10) and impinge at a time t _k at a location x _k , wherein a speed of a beam _tip v _tip of a time scale τ, in which a unification process takes place at location x _k , a maximum speed v _max and a relative speed Δv according to the formula $${\mathrm{v}}_{\mathrm{tip}}={\mathrm{v}}_{\mathrm{Max}}-\mathrm{\Delta v\; f}\left(\mathrm{t}\right)$$

results; wherein a relative velocity modulation ε according to the formula $$\mathrm{\epsilon }=\mathrm{.DELTA.v}/{\mathrm{v}}_{\mathrm{Max}}$$

results; in which
Weber number We from a density ρ, a drop diameter d, a relative velocity u _rel and a surface tension σ from the formula $$\mathrm{We}=\mathrm{\rho }{{\mathrm{u}}_{\mathrm{rel}}}^{\mathrm{2}}\mathrm{d}/\mathrm{\sigma }$$

results. The method of claim 2, wherein the single beam portion (21) exiting the nozzle (10) at an increasing rate experiences a global acceleration a, the difference in the maximum velocity during the injection process minus the initial velocity divided by the time scale τ of the velocity increase to to an order of magnitude of 300-400 m / s ² , the typical time scale τ in which the merging operations take place being in the range of 6 to 20 ms, the maximum speed v _{max being} 20 m / s, the maximum Relative velocity Δv is 3 m / s, with the relative velocity modulation ε is 0.66 maximum. The method of claim 3, wherein the global acceleration a is about 200 m / s ² , wherein the speed increase in this time by a factor up to 3-4 takes place, the maximum speed reaches up to 20 m / s, wherein the single beam section does not exceed a speed of about 25 m / s, which corresponds to a driving lossless differential pressure of about 3 bar. Method according to one of the preceding claims, wherein the sequence of beam sections (21) is generated periodically, wherein the period is so long that the subsequent beam section (21) alone and directly on the target surface (26), but not on still running liquid the previous beam section (21). Method according to one of the preceding claims, wherein the liquid jet (20) is generated by means of a piston pump and the steady increase of the jet velocity on exit from the nozzle (10) is caused by an at least time-dependent control of the piston pump and the piston movement. Method according to one of the preceding claims, wherein the steady increase of the jet velocity on exit from the nozzle (10) is caused by a corresponding control of a nozzle cross-section and / or a nozzle opening. Apparatus for producing a series of portions of a liquid jet (20) comprising a nozzle (10) and a fluid pressure communication device in the liquid, wherein a single jet portion (21) of the discontinuous modified liquid jet (20 ) before impinging on a target surface (26) has a shorter length (L _f ) in the direction of movement (28) than after exiting the nozzle (10), characterized in that the means for pressurizing a liquid comprises a controlled piston pump designed for at least time-dependent control of a piston movement, and / or the nozzle (10) has a controllable nozzle cross-section or a controllable nozzle opening. Apparatus according to claim 8, wherein a variable orientation nozzle (10) is provided for manual or robotic cleaning. Use of the modified liquid jet (20) obtainable by a process according to claims 1 to 7 as a cleaning jet. Use according to claim 10, wherein a spray cleaning of industrial components is provided. Use according to claim 10, wherein a container cleaning or tank cleaning with a jet cleaner or a spray cleaning of open surfaces of industrial equipment and installations or surfaces of industrial floors, walkways and driveways, terrace floors or facades are provided. Use according to claim 10, wherein a surface treatment or a cutting operation are provided.

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