EP3446787B1 - Method and device for generating a sequence of beam sections of a discontinuous, modified liquid jet - Google Patents

Description

The invention relates to a method and a device for generating a sequence of jet sections of a discontinuous, modified liquid jet, a single jet section of the liquid jet being modified such that it has a shorter length in the direction of movement before hitting a target surface than after it emerged the nozzle. The invention further relates to uses of the liquid jet. A beam modified in this way has increased mechanical effectiveness, which can be used, for example, for separating or removing. This improves 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 industry there is a demand across all industries for shorter cleaning times to reduce cycle times. This applies, for example, to industrial component cleaning in the automotive industry. An increase in machine availability is also required, for example through automated self-cleaning of processing machines, particularly in the food sector. The two aforementioned areas are also key applications in which cleaning is an important process step in the creation of value. In the entire area of mechanical engineering, the semi-finished products, raw and component parts as well as assemblies generally have to be cleaned before each further processing step. Here, a modified liquid jet can be used in a cleaning robot chamber for the flexible cleaning of industrial components. The second particularly interesting area of application relates to the production of hygiene-critical consumer goods, with the cleaning of food tanks being an advantageous area of application.

The basic effectiveness of pulsating spray cleaning systems is recognized in specialist circles and industry, although opinions on previously used pulsation methods based on beam breakage due to interference contours are divided or rather rejecting. The known pulsation methods, generated by pump or valve circuits, have disadvantages in the pressure profile generated on the target surface. They do not generate hard pulsation, which is why the cleaning effect is limited, albeit better than with non-pulsating liquid jets.

A number of such systems can also be found in the printed prior art. So describes the document DE 10 2011 080 852 A1 an apparatus and a method for generating a pulsating fluid jet from pressurized fluid with a line system having at least one nozzle. It has a nozzle mouth from which the fluid jet can emerge from the pressurized fluid. The device also has a chamber in which a pressure wave generating device for generating fluid pressure waves is formed. The chamber communicates with the pipe system through an outlet opening for the generated fluid pressure waves. The device includes an adjustment device for controlling the amplitude of the fluid pressure waves in the line system in front of the nozzle mouth. The setting 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 outlet 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 is used to remove material, 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 coupling vibration 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 vibrational energy is converted into kinetic energy. The kinetic energy that can be transmitted to the fluid by generating pressure waves can be maximized by ensuring that the reflections of pressure waves in a line system for supplying pressurized fluid to a nozzle do not cancel out the generated pressure waves, but amplify them due to interference. In the proposed device, therefore, the ratio of the effective path length which the pressure waves travel in the line system from the outlet opening of the chamber to the nozzle mouth of a nozzle, and the wavelength of the fluid pressure waves, i. H. a Helmholtz number characterizing the fluid pressure waves in the line system can be set.

Furthermore, paragraph [0060] states that the pressure pump is designed such that it generates a fluid pressure in the range between 40 bar and 150 bar, preferably a fluid pressure in the order of 100 bar, in the chamber can be adjusted. By adjusting the fluid pressure in the chamber, the frequency v and the amplitude of the pressure waves, the size and the mutual distance of liquid droplets in fluid jets emerging from 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 clumps or drops that hit 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 pulsed under high frequency, pulsating. A high-frequency signal generator is used to transmit the high frequency to an oscillator with a microtip. The vibrating microtip creates a vibrating water jet that emerges from a nozzle opening. The pulsating water jet with the contained mini water balls has an improved erosion ability, e.g. B. for cutting or cleaning.

From the publication US 3,687,147 A. a method is known in which two jets of an incompressible fluid are at an acute angle to one another and interact in such a way that, in addition to an increase in speed, individual lumps of liquid of finite length and duration form.

The document describes another method for liquid jet shaping and a device suitable therefor DE 600 28 949 T2 . The device for producing a high-pressure fluid jet for treating a selected surface comprises a nozzle and a feed line with a first line opening that is in fluid communication with the nozzle opening, the feed line further comprising a second line opening that is spaced apart from the first line opening for aligning the Fluid jet is used. The nozzle and / or the feed line has at least one opening upstream of the second line opening, the opening being equipped such that it can be connected to the source of the second fluid. The opening is a first opening, the nozzle and / or the feed line further comprising a second opening spaced apart 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 conduit between the first and second openings is at least about ten times greater than the average diameter of the second conduit.

The controlled introduction of a second fluid comprises the periodic interruption of a flow of the second fluid in the direction of the fluid jet in order to pulsate the fluid jet. Furthermore, selecting at least the length of the line and / or the pressure of the second fluid and / or the flow rate of the second fluid includes such that the high pressure fluid jet is resonated when the high pressure fluid jet passes through the line.

From the publication DE 215 20 05 A1 a hydraulic chamber with an outlet nozzle is known. A hydraulic chamber containing a nozzle capable of providing a very high instantaneous pulsed dynamic jet in a device that generates a shock wave in a relatively incompressible liquid is obtained when the effective location of the shock wave is such that the pressure wave generated thereby is applied quickly and evenly in one direction along the center line of the nozzle for the purpose of building. 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 part of such a chamber, thereby converting the resulting spherical waves into additive plane waves towards the center line of the nozzle. The shock wave used in the device can be produced by mechanical or electrical energy or a combination thereof.

The publication DE 334 35 55 C1 describes a method and a device for accelerating amounts of liquid. Individual specific amounts of liquid are accelerated to high speeds subject to the energy stored by compressing the liquid. The liquid is pressed into a pressure vessel which is already filled with liquid in order to carry out the compression. Due to the energy stored in the compressed liquid, a certain amount of liquid is expelled from the pressure vessel into a collecting nozzle when a valve is opened quickly. The valve is opened when an opening force generated by the compressed liquid exceeds a closing bias. By repeatedly introducing high pressure fluid into the pressure vessel, the valve takes off working cycles automatically to generate a sequence of pulsating liquid jets. The rapid opening of the valve is assisted by an extension on the valve element that slides sealingly within the passage of the collection nozzle to block the release of the liquid until the valve element accelerates sufficiently to achieve the required opening speed when the extension reaches the Releases nozzle passage.

Paragraph [0005] specifies that pulsating jet devices preferably use a "collection" nozzle, such as that in the patent US 33 43 794 Device described, 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 brief liquid jet that emerges from the nozzle has a peak back pressure that is several times greater than the static pressure that occurs somewhere within the nozzle. The liquid jet also includes discrete volumes or lumps of liquid (cf. US 4,863,101 , which belongs to the same patent family as DE 334 35 55 C1 ).

The description in paragraph [0033] provides further clarification. According to this, for example in the case of a device which is used to machine rocks, concrete and other hard materials instead of a conventional rotary hammer, pressurized water at approximately 1379 bar can be supplied to a chamber which has an inner diameter of approximately 20 cm. This pressure could lead to a compression of about 5% and would eject water volumes with a volume of about 213 cm ³ each with a pulse energy of about 13 560 J into the nozzle.

The document also describes a method and a device for generating pulsed liquid jets DE 215 20 03 A . The proposed solution generates the water jets pulsed at high frequency by the discharge of electrical energy and is based on the knowledge that, when electrical energy is discharged from, for example, a capacitor in a closed container filled with a liquid, electrodes form a tubular space between the electrodes arises. The temperature here is very high in front. Discharges of this kind have three effects. On the one hand, a high-pressure sound wave front runs from the discharge tube to the outside. Secondly, a very hot and expanding gas bubble is created in the area of the hose, which contains superheated steam and a considerable amount of ionized and neutral molecules. Thirdly, a high-intensity continuum of light is created simultaneously with the discharge. The pressure surge takes place by heating at least part of a liquid volume closed with the exception of an outlet nozzle by means of an electrical discharge within the liquid with a discharge duration and intensity such that a shock wave is generated in the liquid.

From the publication DE 372 48 64 C1 the specialist can gain knowledge of a high-pressure water jet device with a 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 feed line and is connected to a main vibration generator via a pipeline. On the outlet side, a second vibration generator is connected to the main vibration generator via a pipeline with a built-in check valve, in the housing of which a valve piston connects the inlet nozzle to an outlet nozzle or separates it from the latter. A second gas-loaded pressure accumulator is connected to the inlet port of the second vibration generator, in which, in cooperation with the check valve, the peak pressures of the pressure waves arriving from the main vibration generator are stored and so a step-by-step charging takes place until the trigger pressure on the valve piston is reached and the stored energy accumulates discharged with a powerful jet of water.

The check valve arranged in the pipeline connecting the main vibrator to the second vibrator allows the second pressure accumulator to be gradually charged by allowing only the peak pressures of the pressure waves generated by the main vibrator in the natural vibration state to pass. The energy of these high pressure pulses is stored in the second pressure accumulator and discharged in a single powerful water jet pulse when the trigger pressure adjustable at the source is reached.

The other publications that are devoted to the generation of percussive liquid jets include US 3,924,805 A . This procedure creates the percussive liquid jet from a continuous jet discharge, consisting of the generation of a relatively small cyclic variation in the discharge speed around its time average, the free jet being given a longitudinal change in the forward speed. This forces the free jet, in order to become a bundled jet, to change the lateral diameter, which occurs periodically along the length of the jet. The cyclical variation of the discharge speed is obtained by generating a cyclical change in the liquid pressure at the inlet to an ejection nozzle.

The resulting movement can be regarded as a forward movement of the jet section at the average speed u, while the part of the liquid in question tends to flow to the center of this part due to the change in speed. So as the portion of the beam moves forward, it also tends to decrease or increase in diameter. That is, it tends to "cluster". The process can also be viewed in such a way that the part of the faster fluid overtakes and combines with the slower within the cycle. The process is necessarily accompanied by a separation of each slow-fast (thereby bundled) beam part from the previous and subsequent ones. Thus, the cyclical change in ejection speed has the effect of converting the continuous jet from a uniform stream to a sequence of liquid plugs.

However, the effect previously described in different variants takes place randomly and uncontrolled, at least without special effects that would go beyond the effects of pulsating liquid jets already known from the prior art.

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, the drop forming device being 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 with a varying electrical potential between the charge electrode and the liquid jet. The source of the varying electrical potential provides a waveform that includes a period that is equal to the drop pair period. The waveform includes a first and a second different voltage state, the charging device being synchronized with the drop formation device in order to generate a first charge state on the first drop and to generate a second charge state on the second drop. The drop speed modulation device changes the relative speed of the first and second drops to control the connection of the drops to a combined drop with a third charge state. A deflection device is provided which causes the first drop with the first charge state to move along a first path, the second drop with the second charge state to move along a second path, and the combined drop with the third charge state move along a third path emotional.

Since slight changes in the amplitude affect the waveform of the energy pulses which are transmitted to the liquid jet for drop formation, the speed of the drops formed, the speed of one or both drops in a drop pair can be modulated. 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. A cylinder bore surface is prepared using a pulsed water jet. The following method steps are provided: generating a signal with a frequency using a signal generator; Applying the signal to generate a pulsed water jet through an outlet opening of a nozzle with an outlet opening and with a cylindrical section of the outlet opening; Allow the pulsed water jet to hit 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 that include distance, nozzle crosshead speed, water pressure, water flow rate, orifice length to diameter ratio, frequency and 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 generating high-frequency pulsating liquid jets. These high-frequency liquid jets can be generated with internal mechanical flow modulators, Helmholtz oscillators, self-resonating nozzles and / or ultrasound nozzles. In addition, the pulsed water jet can be generated using acoustic waves, for example an acoustic wave, which acts on the liquid by means of an acoustic transducer. The desired effect is based on the fact that the water jet impact on a material target is increased by ultrasound modulation. Namely, if a drop or a drop of liquid hits the same surface, the initial impact pressure will be much higher.

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

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

In practice, the speed of the water exiting the cannon valve changes continuously, but a pulse of about 0.5 m in length is generated at a speed of over 500 m / s. The kinetic energy of the pulse increases linearly up to about 0.5 m and then increases further at a lower rate. The speed is slow when the valve opens, peaks after opening the valve, and then drops when the pressure also drops (decompressed). A straight nozzle section accumulates the water at the leading edge of the pulse and allows the fluid to catch up at the higher speed, thereby forming a plug of liquid at a uniform speed.

Numerical analysis shows that a compressed water cannon tool can produce compressed water pulses that are 300 mm long and move at a speed of about 520 m / s. The leading edge accelerates to over 2000 m / s while the trailing edge brakes.

In addition to the state of the art in print, further publications are known which relate to the field of modulation of liquid jets. However, the modulation of liquid jets has so far been considered almost exclusively to increase the efficiency of water-jet cutting of rock and hard materials, as is also shown by the state of the art previously recognized. The high pressure range p ≥ 1000 bar is used. Publications on this include the conference volumes of the Water Jet Conferences and the Jet Cutting Symposia ( Cooley, WC: Rock Breakage by Pulsed High Pressure Water Jets, First International Symposium on Jet Cutting Technology, Paper B7, 1972 ; Nebeker, EB; Rodriguez, SE: Percussive Water Jets for Rock Cutting, Third International Symposi-um on Jet Cutting Technology, BHRA Fluid Engineering, Paper B-1, 1976 ; Nebeker, EB: Development of Large-Diameter Percussive Jets, 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 examined 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 it in a targeted manner. This chopping mainly occurs in the relatively low-frequency range up to approx. 100 Hz for this high pressure. Other publications use resonators in the nozzle to modulate the beam ( 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. Only recently ultrasound-modulated beams have been used by the group around Foldyna 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 Highspeed 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 area can only be found from 2010 ( Augustin W .; Fuchs T .; Föste H .; Schöler, M .; Majschak, 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 cleaning efficiency by pulsating spray cleaning, Chem. Ing. Tech., 86, No. 5, pp. 707-713, 2014 ).

A fundamental disadvantage of the prior art is that spray cleaning cannot reduce the cleaning time by significantly increasing the cleaning mechanics. In addition to time and mechanics, temperature and chemistry are the other important factors influencing cleaning. However, the increase in temperature and the use of chemicals is not a socially acceptable alternative to minimizing environmental and cost considerations Target value is cleaning time. Furthermore, the maximum adjustable operating pressure of the cleaning system, which serves as a possible manipulated variable for increasing the mechanics, is generally limited in terms of system or process technology. The economically interesting and most frequently used range for spray cleaning is between 2 and 6 bar. The reasons for this are that the costs for the pumps as well as the work and noise protection 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 promoted by the cleaning system is also impractical from the point of view of resource efficiency and because of the wastewater treatment that is subsequently required. As a result, new approaches are required 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 deliver individual sections of a liquid jet or to apply a more or less controlled pulsation to the liquid jet, so that, compared to a continuous liquid jet, a higher energy input into the target surface and a better result when editing the target surface, e.g. B. a desired abrasion can be achieved. For this purpose, various types of devices have been proposed, which are complex, expensive and prone to failure due to additional devices, such as an additional beam generation or an oscillation device, for the actual beam generation. In addition, there is currently no pulsation method in spray cleaning which has a suitable beam modulation in order to generate a maximum hard pulsation in accordance with 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 a device for producing a modified liquid jet with increased mechanical effectiveness, which is simple in construction and has a further improved effect, in particular an improved abrasion effect, with a reduced liquid requirement.

The object is achieved by a method for producing a sequence of sections of a liquid jet, wherein a single jet section of the discontinuous, modified liquid jet before striking one Target surface has a shorter length in the direction of movement than after exiting from a nozzle. According to the invention, the modification is brought about by different speeds within the individual jet section of the discontinuous, modified liquid jet in such a way that, as a result of a constant increase in the jet speed as it emerges from the nozzle, a jet area which is in the rear in the direction of movement catches up with a front jet area of the jet section by the individual jet section also increasing speed emerges from the nozzle, the later it exits the nozzle, and wherein a breakup of the liquid previously combined to form the jet section is prevented by not exceeding a critical ratio of inertial force to surface force.

The mechanism of a modified liquid jet with increased mechanical effectiveness, with the help of which sniper fish hunt insects in nature, has been scientifically elucidated. A very defined modulation of both the mouth opening acting as the nozzle surface and the pressure in the oral cavity of the fish provides a constant increase in both the water jet speed and the water jet impulse over time. This particular form of water acceleration causes a build-up of water to build up at the tip of the jet with the collected impulse that was released from the mouth of the fish over the duration of the ejection. This "clump of water" is therefore able to exert a force in the short collision with the insect that corresponds to a multiple of the force of the simple water jet, because force is the time derivative of the impulse. The invention therefore has set itself the goal of collecting a pulse over the entire jet length, which corresponds to the distance between the nozzle and the target surface, in order then to convert it into a strong force in a very short stroke. This physical principle is used in other ways, e.g. B. already used in impact drills in mechanics.

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

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

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

The force F that a beam exerts on impact with a substrate is equal to the change in momentum of the beam. In the case of an undisturbed beam, the speed is constant and thus the impact force. This is equal to the product of mass flow times jet speed before impact: $$F_u=\frac{\mathit{\delta m}}{\mathit{\delta t}}\cdot u=\frac{\pi }{\mathrm{4th}}\cdot \rho \cdot d_u^{\mathrm{2nd}}\cdot u^{\mathrm{2nd}}=0.13N$$

With the values for the undisturbed case, a force of 0.13 Newton results. For the unsteady case, the pulse of the lump is calculated and the time Δt in which this pulse is delivered to the substrate is estimated. This is possible using the thickness of the lump. Its thickness 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 is 2.76 Newtons according to the following calculation: $$F_k=\frac{\mathrm{\Delta }\mathrm{I.}}{\mathrm{\Delta }t}=\frac{\mathrm{I.}-0}{\mathrm{\Delta }t}=\frac{m_k\cdot u}{\mathrm{\Delta }t}=2.76N$$

This value is 21 times higher than with the undisturbed beam. The experiments on which the calculation was based were not carried out with the aim of maximizing the pulse collection.

Different approaches are suitable for practical technical implementation. The implementation of the modulation of the nozzle surface is technically feasible, but significantly more complex than the more practical modulation of the pressure. B. can be achieved via a camshaft that 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 print modification are also contemplated.

The main aim of the practical application of the modified liquid jet is to remove contamination from a substrate against the adhesive force. With small pressures, but a very defined, temporal development of the speed from the nozzle, the aim is to collect momentum in the liquid, in particular in water, which in this way exerts a much higher, jerk-like force on impacting the impurity than a continuous jet is able to apply the same speed.

The technical implementation must be carried out periodically. The period will preferably be chosen so long that the subsequent impact of a beam section hits the target surface or the contamination present there directly and not directly, but not the water of the previous impact that is still running off. A longer period also allows a stronger collection of impulses and thus increases the effectiveness of the single impact.

Surprisingly, it has been shown that it is possible to collect a jet pulse over a given spray duration Δt. In order to achieve this, there must be a constant increase in the jet speed, so that fluid elements that are subsequently discharged from the nozzle can catch up with the previously dispensed fluid elements.

The time t _k and location x _k , when and where this happens, can be seen schematically on the basis of a path-time diagram (cf. Fig. 1 ). Place-time lines are shown for three different fluid elements that left the nozzle at times t ₀ , t ₁ , t ₂ . It can be seen that these lines intersect at one point, at x _k at time t _k . Taking into account the knowledge that the slope of this straight line corresponds to the speed of the fluid elements, it becomes clear that the speed has to increase with a later start time in order to ensure an intersection, ie a union of the fluid elements. A time-varying speed is nothing more than an acceleration. Accelerations of the order of 300-400 m / s ² at the start of the spraying process have proven to be particularly advantageous. This acceleration may seem very high, but it is only a momentary value. The typical global Accelerations are of the order of 150 m / s ² . Another reason for the high values is the small time scale that is available for the processes. These take place in hundreds 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 met a previous, slower fluid element, this would result in the fluid collected up to this point being broken up and continuing to fly in the form of small drops. The small drops lose momentum to the surrounding air and are distributed over a much larger volume. An excessive acceleration is therefore not desirable. Experience shows that a global acceleration of 200 m / s ² still makes sense. This global acceleration a is defined as the difference between the maximum speed during the spraying process minus the speed at the start of the spraying process, divided by the time of the speed increase.

It has therefore proven to be important that the previously collected fluid must be prevented from being broken up. 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 it is no longer possible to unite the fluid elements and the accumulated fluid breaks apart and bursts. Since there is currently no scientific knowledge to answer this question for jets (fluid elements), the results can be used for a very similar but reverse phenomenon. In the collision of drops of diameter d with a relative speed u _rel , according to Nobari and Tryggvason, the critical Weber number is 24 for a union of the drops. $$\mathrm{We}=\mathrm{\rho }{{\mathrm{u}}_{\mathrm{rel}}}^{\mathrm{2nd}}\mathrm{d}/\mathrm{\sigma }$$

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

If the critical weaver number We is exceeded, the drops are only coalesced for a short time. The combined liquid disintegrates into smaller fragments. The reason for this is the excessive kinetic energy of the collision. With collision energies that are smaller than the critical Weber number, the surface tension as a restoring force with the inertial 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-on collision of drops-A numerical investigation, Physics of Fluids 8 (1), pp. 29-42, 1996 .

Fig. 3 shows results on 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. 5, No. 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 $${\mathrm{v}}_{\mathrm{tip}}={\mathrm{v}}_{\max }-\mathrm{\Delta }\mathrm{v}\mathrm{f}\left(\mathrm{t}\right)$$

lautet.Over time, the excess energy of the union is dissipated or destroyed due to the toughness, the vibrations subside. Furthermore, the toughness means that the fluid elements always come together when the Reynolds number is small. If the maximum relative speed that can occur between fluid elements, the drops, before the jet breaks open, the influence of the Weber number will predominate for water. For a beam with a diameter of 1 mm, the maximum relative speed would be approx. 0.8 m / s due to the Reynolds number <800, ie through dissipation of the interaction energy. On the other hand, according to the condition of Saroka Ashgriz We <34, ie the effect of surface tension with a water jet with a diameter of 1 mm, a maximum relative speed Δv of approx. 1.6 m / s would result. However, these numbers are based on drop impact results. Are the results for measurements on Sagittarius [ P. Gerullis and St. Schuster, Archerfish Actively Control the Hydrodynamics of Their Jets, Current Biology 24, pp. 2156-2160, 2014 ] considered for the speed of the beam _tip , v _tip : $${\mathrm{v}}_{\mathrm{tip}}={\mathrm{v}}_{\mathrm{Max}}-\mathrm{\Delta }\mathrm{v}\exp \left(-\mathrm{t}/\mathrm{\tau }\right)$$

the value for the relative speed is higher by a factor of 1.7 to 2.7 (2.7 - 3.8 m / s). The specified exponential function is an example, other functions are possible (e.g. quadratic). Basically, every monotonically falling function comes into consideration, so the general formula $${\mathrm{v}}_{\mathrm{tip}}={\mathrm{v}}_{\mathrm{Max}}-\mathrm{\Delta }\mathrm{v}\mathrm{f}\left(\mathrm{t}\right)$$

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 union processes take place, is based on the model of the Sagittarius in the range of 6 to 20 ms and the maximum speed v _max is approx. 20 - 25 m / s. The maximum relative speed Δv is 3 m / s, because from this relative speed the atomization of the accumulated liquid begins. These two values provide a relative speed modulation ε according to the formula $$\mathrm{\epsilon }=\mathrm{\Delta }\mathrm{v}/{\mathrm{v}}_{\mathrm{Max}}$$

where the relative speed modulation ε is at most 0.66. This roughly corresponds to a doubling of the initial speed.

Based on these considerations, it was possible to estimate the parameter ranges for cleaning according to the principle according to 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 speed increases during this time by 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 if the maximum speed is exceeded, not a single continuous liquid volume hits the target and instead hits several drops in a small, narrow area within a short time on the surface to be cleaned. However, it has been found that an effect similar to that obtained with a single drop is achieved. Decisive for the principle of action is the concentration of the liquid on a small volume and therefore also for a short-term, ie impulsive force effect on the target.

There is a further limitation of the fluid velocity, namely the aerodynamic weaver number for drop opening: $${\mathrm{We}}_{\mathrm{aero}}={\mathrm{\rho }}_{\mathrm{gas}}{{\mathrm{u}}_{\mathrm{relg}}}^{\mathrm{2nd}}\mathrm{d}/\mathrm{\sigma },$$

The aerodynamic forces on the liquid play a role here. The main difference to the normal Weber number is that the density of the surrounding gas and the relative velocity to the gas are effective here. With increasing relative speed to the gas, the drop loses its spherical shape and is flattened. From an aerodynamic weaver number of approx. 20, a flattened pocket is created, which inflates and breaks open. An estimate of this relative speed for water drops in air gives a value of 35 m / s for drops of 1 mm in diameter, for drops with 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. It was therefore shown that the beams should not exceed speeds of approx. 25 m / s. This would correspond to a driving loss-free differential pressure of approx. 3 bar.

It has proven to be advantageous if the liquid jet is generated by means of a piston pump and the steady increase in the jet speed when it emerges from the nozzle is brought about by at least time-dependent control of the piston pump and the piston movement. As an alternative to this or as a supplementary measure, the steady increase in the jet speed when exiting the nozzle is brought about by appropriate control of a nozzle cross section and / or a nozzle opening.

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

The method according to the invention enables the collection of beam impulses during the phase of the beam formation and propagation. In the subsequent short interaction of the beam with the target surface, e.g. B. a substrate or pollution, significantly higher forces arise, which are available for cleaning in the jet impact and damage the pollution much more. The approach thus differs fundamentally from previously known active principles of pulsating rays. This difference can be easily explained by comparing the hammer drill and hammer drill: in both, pulse-like impacts are exerted on the workpiece. However, the firing pin on the rotary hammer is accelerated for a considerably longer time before it hits the chisel. This means that correspondingly more momentum is collected in the firing pin, as a result of which the hammer drill achieves significantly greater force peaks - comparable to the modified liquid jet according to the invention. On the other hand, the pulsating jets known to date in research show closely intermittent interruptions in the jet - comparable to the less effective impact drill.

Another aspect relates to a device for generating a sequence of sections of a liquid jet, wherein a single jet section of the discontinuous, modified liquid jet has a shorter length in the direction of movement before hitting a target surface than after exiting from a nozzle. The device comprises the nozzle and a device for generating pressure in the liquid that is fluidly connected to the nozzle. According to the invention, it is provided that the device for generating pressure of a liquid comprises a controlled piston pump, designed for at least time-dependent control of a piston movement, and / or the nozzle has a controllable nozzle cross-section or a controllable nozzle opening, a controller being configured to do so is to control the piston movement and / or the nozzle cross-section or the nozzle opening in such a way that the modification is caused by different speeds within the individual jet section of the discontinuous, modified liquid jet in such a way that as a result of a steady increase in the jet speed as it emerges from the nozzle in the direction of movement of the rear jet area, catches up with a front jet area of the jet section, in that the individual jet section emerges from the nozzle with increasing speed, the later it emerges from the nozzle, and a widening The liquid previously combined to form the jet section is prevented by not exceeding a critical ratio of inertial force to surface force.

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

Another aspect of the present invention relates to the use of the device according to the invention as a cleaning device. It is intended to be used for spray cleaning industrial components. It is also provided that Modified liquid jet can be used as a cleaning jet for container cleaning or tank cleaning with a jet cleaner. Spray cleaning of open surfaces of industrial devices and systems or of surfaces of industrial floors, walkways and driveways, terrace floors or facades is also provided. In addition to cleaning applications, surface processing or cutting are also planned. Applications in the areas of stone processing, such as tunneling, mining, fire extinguishing technology or police technology, are also envisaged.

The method according to the invention promises an unprecedented mechanical cleaning effect even with large nozzle distances and low operating pressure. The objects are cleaned gently, because the high force peaks only work 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 saved to a great extent compared to known systems.

The need for relevant spray cleaning systems in the area of industrial parts cleaning is enormous, since almost all components must be cleaned before each further processing step or upon final delivery in accordance with the process-related cleanliness requirements. Wet chemical processes have a market share of 60%, with spray cleaning being used by more than half of the companies. The reduction of cycle times is directly associated with a higher output and thus the increase in the productivity of a system or an entire production line if the required component cleanliness is observed. A large number of companies monitor throughput times as an optimization criterion. Furthermore, many companies estimate the share of cleaning costs on average to be about 10% of the overall manufacturing process of components, which shows the great savings potential in the cleaning area.

The processes of both industrial applications can usually be assigned to mass production, which means that the reduction in cycle times for parts cleaning or downtimes in the cleaning of processing plants, particularly in the food and pharmaceutical industries, is directly linked to the higher output and thus increased productivity of a plant is. In order to the desired decoupling of economic growth from resource consumption, which will be essential for the future viability of entire economies, is also 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 also results in commercial applicability. The social relevance of this innovation lies primarily in the contribution to resource conservation (reduction of time, water, chemical additives and energy), the improvement of competitiveness and the increase of consumer safety through thoroughly cleaned food plants.

• 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 an example of three discrete sections of the beam section flowing up to time t _k and 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.

The invention is explained in more detail below on the basis of the description of exemplary embodiments and their representation in the associated drawings. Show it:

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

Fig. 11 shows schematically a representation of the nozzle and target surface and the jet sections formed between them, as generated by a pulsation according to the present invention. In the use shown here for a cleaning jet, this goes hand in hand with a considerable escalation of the cleaning action. 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, pulse-collecting shocks, the spray pauses on the surface increase compared to conventional pulsation (see FIG. 4), as a result of which the damping liquid film can run off completely and the jet force acts directly on the contamination on the target surface. Due to the effects mentioned, the pollution is destroyed many times more 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 impact pressure p _impact is a multiple of the _dynamic pressure p _dynamic . Both Figures 11 to 14 the time course of the jet pressure applied to the surface to be cleaned by the spray jet is shown, which, when integrated, corresponds to the force course over the jet cross section.

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

Fig. 13 _{Figure 3} shows schematically a representation of a conventional cleaning _{jet with jet interrupters} according to the prior art, including an explanatory diagram 32, which shows matching levels of _dynamic pressure p _dynamic and _surge pressure p _dynamic . Except for the interruptions in the pressure curve, a similar jet pressure curve occurs with nozzles with jet interrupters to the continuous case.

Cleaning benefits can be expected from two effects. On the one hand, the contamination is more severely impaired if, due to the jet interruptions, the liquid film which dampens the spray jet does not completely clean the one to be cleaned Can form surface. On the other hand, the cleaning fluid will generally flow around the component in a much more turbulent manner. Since the beam interruption is also associated with a loss of momentum on the surface over time, it can be expected that there will be no significantly improved cleaning effect.

Fig. 14 shows schematically a representation of a nozzle in pulsating operation according to the prior art, including an explanatory diagram 33 on the ratio of the levels of the _dynamic pressure p _jam and the _shock pressure p _jerk . Here, when switching on the nozzle in pulsating operation, for. B. realized by valve circuits, no constant, the back pressure corresponding jet pressure reached on the surface. Rather, shock waves hit the surface in a short succession, which in turn generate higher pressure peaks than the dynamic pressure. In addition, only the positive ones of the beam interrupters (cf. Fig. 3 ) existing side effects of the not fully developing damping liquid film with high turbulence, since in the case shown there is no loss of momentum over time.

Fig. 15 shows how the exit velocity of the jet has to increase steadily in order to achieve an abrupt liquid accumulation at the tip of the jet. In the embodiment shown, this could be achieved with a linear motor. The accumulation was achieved by a shaker, which was used to drive a porous piston at 60 Hz. The relative excitation amplitude in figures a) to g) (from left to right) is 0.5; 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 part of the figure. The figures show the formation of water lumps and the jet that is significantly thinner between these lumps. This is evident from the thickness d and length L of the beam between the collections (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 individual clumps of water that strike one after the other are formed, so that the water has already run out before a new clump of water hits. As a result, the surface, the target surface, is always hit directly, which further improves the effectiveness.

This form of pulse collection from the right figure g) is already completed at 120 mm. Longer integration times can be achieved by increasing the distance from the nozzle. It has proven beneficial, more Allow time for the further away the target is (up to 70 ms at a distance of 600 mm). This would correspond to a frequency of 14 Hertz. The momentum collection and the resulting force are once again up to four times greater.

The illustration on the right shows that the lumps can also have the shape of a wide, flat cylinder. This shape may be very interesting for cleaning because it covers a larger area at the same time. In this case the diameter of the lump is approximately ten times the undisturbed beam diameter. However, since the jet pressure (impact) applied to the soiled surface is reduced when the diameter is increased, an optimal lump shape for cleaning must be determined and generated.

Fig. 16 shows schematically 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 target surface 26 by a corresponding position of a nozzle lance 112 with the nozzle 110. The adjustment of the nozzle lance 112 in the direction of the arrow is made possible by a swivel drive 114, which also includes a joint.

The device 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 to a piston drive 120, which in the preferred embodiment shown here is designed as a linear drive.

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. There is also such a control connection to the swivel drive 114 and to a metering valve 126. The metering valve 126 doses an intended amount of liquid from a liquid reservoir 124 for each period in order to be able to generate a modified liquid jet with the desired properties.

Instead of a single nozzle 110, alternative configurations of the proposed solution also provide several exit locations on the nozzle lance 112. These further nozzles 110 can also be configured to be individually controllable, so that too without moving the nozzle lance 112 different locations can be treated simultaneously or in succession.

In its preferred embodiment, the process sequence according to the invention starts with the metering of the amount of liquid into the piston pump 116. The nozzle 110 is then brought into the desired orientation relative to the target surface 26 by means of the swivel drive 114. The piston drive 120 is then controlled such that the modified liquid jet with the desired properties emerges from the nozzle 110 and strikes the target surface 26 as a lump.

Reference list

10, 110

jet

12th

Beam (continuous)

14

Beam (interrupted)

16

Beam (conventional pulsation)

20

Beam (hammer pulsation)

21st

Beam section

22

Lump of water

26

Target area

28

Direction of movement

30-33

Diagrams

41

Area of permanent 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

Swivel drive

116

Piston pump

118

piston

120

Piston drive

122

control

124

Liquid reservoir

126

Dosing valve

Claims (13)

1. A method for generating a sequence of jet sections (21) of a discontinuous, modified liquid jet (20), wherein an individual jet section (21) of the liquid jet (20) undergoes a modification such that it has a shorter length (L_f) in the direction of movement (28) before impinging on a target surface (26) than after exiting a nozzle (10), characterized in that the modification is caused by different velocities within the individual jet section (21) of the discontinuous, modified liquid jet (20) in such a manner that, as a result of a continuous increase of the jet velocity during exit from the nozzle (10), a jet region at the rear in the direction of movement (28) catches up with a front jet region of the jet section (21) due to the individual jet section (21) exiting the nozzle (10) with increasing velocity the later it exits the nozzle (10), and wherein a break-up of the liquid previously combined to form the jet section (21) is prevented by not exceeding a critical ratio of inertial force to surface force.
2. The method according to claim 1, wherein n jet regions of a jet section (21) exit the nozzle (10) at the times t₀ to t_n and impinge at a location x_k at a time t_k, wherein a velocity of a jet tip v_tip is obtained from a time scale τ within which a unification process takes place at the location x_k, a maximum velocity v_max, and a relative velocity Δv according to the formula $${\mathrm{v}}_{\mathrm{tip}}={\mathrm{v}}_{\max }-\mathrm{\Delta }\mathrm{v}\mathrm{f}\left(\mathrm{t}\right);$$

   

   wherein
   a relative velocity modulation ε is obtained according to the formula $$\mathrm{\epsilon }=\mathrm{\Delta }\mathrm{v}/{\mathrm{v}}_{\max };$$

   

   wherein
   a Weber number We is obtained from a density p, a droplet diameter d, a relative velocity u_rel, and a surface tension σ according to the formula $$\mathrm{We}=\mathrm{\rho }{{\mathrm{u}}_{\mathrm{rel}}}^2\mathrm{d}/\mathrm{\sigma }.$$

   
3. The method according to claim 2, wherein the individual jet section (21) exiting the nozzle (10) with increasing velocity undergoes a global acceleration a, wherein the difference of the maximum velocity during the ejection process minus the velocity at the beginning divided by the time scale τ of the increase in velocity reaches an order of magnitude of up to 300 - 400 m/s², wherein the typical time scale τ within which the unification processes take place is in the range from 6 to 20 ms, wherein the maximum velocity vmax is 20 m/s, wherein the maximum relative velocity Δv is 3 m/s, and wherein the maximum relative velocity modulation ε is 0.66.
4. The method according to claim 3, wherein the global acceleration a is around 200 m/s², wherein the increase in velocity during this time is by a factor of up to 3 - 4, wherein the maximum velocity reaches up to 20 m/s, wherein the individual jet section does not exceed a velocity of about 25 m/s, which corresponds to a driving loss-free differential pressure of about 3 bar.
5. The method according to any one of the preceding claims, wherein the sequence of jet sections (21) is generated periodically, wherein the period is long enough for the subsequent jet section (21) to alone and directly impinge on the target surface (26) but not on still draining liquid of the previous jet section (21).
6. The method according to any one of the preceding claims, wherein the liquid jet (20) is generated using a piston pump and the continuous increase of the jet velocity during exit from the nozzle (10) is caused by an at least time-dependent control of the piston pump and the piston stroke.
7. The method according to any of the preceding claims, wherein the continuous increase of the jet velocity during exit from the nozzle (10) is caused by a corresponding control of a nozzle cross-section and/or a nozzle opening.
8. An apparatus for generating a sequence of sections of a liquid jet (20), comprising a nozzle (10) and a device for generating pressure in the fluid which is in fluid communication with the nozzle (10), wherein an individual jet section (21) of the discontinuous, modified liquid jet (20) has a shorter length (L_f) in the direction of movement (28) before impinging on a target surface (26) than after exiting the nozzle (10), characterized in that the device for generating pressure of a fluid comprises a controlled piston pump designed for at least time-dependent activation of a piston stroke and/or the nozzle (10) has a controllable nozzle cross-section or a controllable nozzle opening, wherein a control (122) is provided which is configured to control the piston stroke and/or the nozzle cross-section or the nozzle opening of the nozzle (10) such that the modification is caused by different velocities within the individual jet section (21) of the discontinuous, modified liquid jet (20) in such a manner that, as a result of a continuous increase of the jet velocity during exit from the nozzle (10), a jet region at the rear in the direction of movement (28) catches up with a front jet region of the jet section (21) due to the individual jet section (21) exiting the nozzle (10) with increasing velocity the later it exits the nozzle (10), and wherein a break-up of the liquid previously combined to form the jet section (21) is prevented by not exceeding a critical ratio of inertial force to surface force.
9. The apparatus according to claim 8, wherein the nozzle (10) is provided with variable orientation for manual or robot-based cleaning.
10. Use of the apparatus according to claim 8 or claim 9 as a cleaning apparatus.
11. Use according to claim 10, wherein a spray cleaning of industrial components is provided.
12. Use according to claim 10, wherein a container cleaning or tank cleaning with a target jet cleaner or a spray cleaning of open surfaces of industrial devices and installations or of surfaces of industrial floors, pavements and driveways, terrace floors or facades is provided.
13. Use according to claim 10, wherein a surface treatment or a cutting operation is provided.

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