Technical Field

The present invention relates in a first aspect to a method for cleaning a surface, in particular a surface of a vehicle, by means of atomizing a liquid in a gas stream with a nozzle. In a second aspect, the invention relates to a nozzle for cleaning the surface according to the method and in a third aspect to an apparatus for clean ing the surface with the method.

Background Art

Cleaning of surfaces that are sensitive to scratches is very challenging. The challenge is to find a way to clean the surface without damaging it at the same time. Common methods like scrubbing or wiping of a surface might result in scratches on the surface, generated by means of small particles that are trapped e.g. between a scrubber and the surface or between a wiper and the surface and moved back and forth over the respective surface during the cleaning step. On the other hand, if a method for cleaning a surface is too gentle, residues remain on the surface and are not properly removed by the respective cleaning method.

In particular, cleaning of a surface of a ve hicle is very challenging. A vehicle can get very dirty during its use but at the same time, the car lacquering is very sensitive to scratches.

On the well-known prior art methods for clean ing a sensitive surface is to use a steamer that generates hot steam and directs it towards the sensitive surface.

US 7, 806, 128 B2 discloses a cleaning appa ratus for cleaning a vehicle with steam. The processing temperatures are in the range of above 120°C and 180°C. Such high processing temperatures are very en ergy consuming. In addition, these high processing temper atures might be dangerous for persons that are standing close to the car washing apparatus.

State of the art cleaning methods often cannot fulfil the requirements of cleaning a surface reliably and at the same time preventing the surface from damages.

In addition, if the state-of-the-art cleaning methods might fulfil such requirements, as the steamer cleaning method, the method is very energy consuming.

Disclosure of the Invention

The problem to be solved by the present inven tion is therefore to provide a method for removing dirt from a surface with high reliability from a surface while working with low energy consumption.

This problem is solved by the subjects of the independent claims.

Accordingly, a first aspect of the invention refers to a method for cleaning a surface, in particular a surface of a vehicle, by means of atomizing a liquid in a gas stream with a nozzle.

Atomizing nozzles are well known from prior art. An atomizing nozzle is ideal for producing extremely fine droplets of a liquid that is discharged from the noz zle. Generally speaking, atomizing nozzles work on the principle that a pressurized gas is used to impact upon a fluid being sprayed. The impact of the gas atomizes the fluid, meaning that it breaks the fluid flow into individ ual droplets.

Advantageously, the nozzle comprises a rota tional body with a longitudinal axis.

The nozzle comprises a liquid passage adapted to direct a liquid stream in a downstream direction towards a liquid discharge orifice, wherein the liquid discharge orifice is adapted to discharge the liquid stream into an expansion zone.

Advantageously, the nozzle comprises a liquid passage extending along a longitudinal axis of the nozzle and terminating downstream the liquid passage in the liquid discharge orifice, wherein the orifice has in particular a circular or I-shape form.

In particular, the direction downstream indi cates a direction in which the liquid flows.

In a further embodiment of the invention, the nozzle can comprise more than one liquid passage, wherein each liquid passage terminates in downstream direction in a respective liquid discharge orifice.

In a further embodiment of the invention, the liquid passage might terminate in a downstream direction into more than one liquid discharge orifice.

In a further advantageous embodiment, the di rection downstream indicates the direction of a longitudi nal axis in which direction the liquid is essentially flow ing through the liquid passage. Even if the liquid might not flow exactly along the longitudinal axis, the flow direction indicates the one direction of the longitudinal axis that it is referred to by the term "downstream".

In particular, the term extending along the longitudinal axis of the nozzle does not restrict the liq uid passage to extend along the longitudinal axis to its full extent, neither to extending along the longitudinal axis in a straight line. The term explicitly includes also passages that extend essentially along the longitudinal extension of the longitudinal axis, therefore extend along the longitudinal axis but with kinks in along their exten sion.

In an advantageous embodiment, the liquid pas sage extends centered along the longitudinal axis of the body.

The nozzle further comprises a gas passage adapted to direct a gas stream towards a gas discharge orifice, wherein the gas discharge orifice is adapted to discharge the gas stream into the expansion zone.

In a further embodiment of the invention, the nozzle can comprise more than one gas passage, wherein each gas passage directs the gas stream towards a respective gas discharge orifice.

In a further embodiment of the invention, the gas passage might terminate in a downstream direction into more than one gas discharge orifices.

The gas discharge orifice might have an annular form.

In an advantageous embodiment, the annular gas discharge orifice is arranged at least partially coaxially to the circular liquid discharge orifice.

In particular, in such a nozzle, the gas dis charge orifice and the liquid discharge orifice are ar ranged such that the gas discharged by the gas discharge orifice encircles the liquid discharged by the liquid dis charge orifice.

In an atomizing nozzle, liquid jet discharged by the liquid discharge orifice is atomized in the expan sion zone by the interaction with the gas stream discharged from the gas discharge orifice, such that the bulk liquid jet discharging from the liquid discharge orifice breaks into droplets.

Advantageously, the gas passage is arranged co axial to the liquid passage. Further advantageously, the liquid discharge orifice and the gas discharge orifice are arranged at the same level of the longitudinal axis, mean ing that the liquid discharge orifice and the gas discharge orifice are arranged essentially in one plane.

In an advantageous embodiment of the invention, a first end of the nozzle is arranged at the end of the longitudinal axis of the nozzle in downstream direction. In an advantageous embodiment of the invention, the first end of the nozzle corresponds to the liquid dis charge orifice.

In a further advantageous embodiment of the invention, the first end of the nozzle extends beyond the liquid discharge orifice, beyond the gas discharge orifice and beyond the expansion zone in a downstream direction of the longitudinal axis, and forms a first end discharge orifice to discharge the atomized liquid.

In particular, the gas discharging from the gas discharge orifice strikes the liquid discharging from the liquid discharge orifice in the expansion zone and atomizes the liquid into individual droplets.

The method comprises the steps of discharging a liquid, in particular with a pressure pi of 10 bar ³ pi ³ 0.1 bar, and a gas, in particular with a pressure p _g of 10 bar ³ p _g ³ 0.1 bar, into the expansion zone, for atom izing the liquid in the gas stream.

The atomized liquid is directed to the surface to be cleaned, wherein a shortest distance d between the surface and a first end of the nozzle in downstream direc tion is 1cm < d £ 20cm, in particular 1cm < d £ 10cm, in particular 1cm < d £ 7cm, in particular 1cm < d £ 5cm, in particular 4cm < d £ 7cm.

In a further advantageous embodiment, the dis tance is 3cm < d £ 20cm, in particular 3cm < d £ 7cm, such that the method works also with a distance from the sur face. Thereby, a larger area of the surface might be cleaned at the time.

In particular, the first end refers to the point of the nozzle that is closest to the surface.

An impact temperature Ti of atomized liquid is the is 80°C ³ Ti ³ 40°C, in particular 65°C ³ Ti ³ 40°C, on impact on the surface.

In particular, the impact temperature Ti refers to the temperature of the atomized liquid that is measured if the atomized liquid hits the surface. In particular, the impact temperature might be measured by a attaching a temperature sensor to the surface on the spot where the atomized liquid hits the surface.

In particular, the nozzle is adapted to dis charge the liquid in a way that the impact temperature Ih of the atomized liquid if it hits the surface is in the range of 80°C ³ Ti ³ 40°C, in particular 65°C ³ Ih ³ 40°C.

In particular, the impact temperature might also be defined by the processing temperatures of the gas and liquid (Th and T _a ) as defined below.

A sum s of all areas of all orifices of the nozzle is 100mm ² > s ³ 0.5mm ² . In particular, the sum re fers to the summed up cross sectional areas of all ori fices, including one or more, if there are more than one, liquid discharge orifices, and including one or more, if there are more than one, gas discharge orifices.

In particular, the liquid entering the liquid passage might have a temperature Ti of 95°C ³ Th ³ 50°C.

In particular, the gas entering the gas passage might have a temperature T _g of 120°C > T _g > 50°C.

For the atomizing of the liquid stream, the pressure and the temperature of the discharged liquid and/or gas are critical.

In particular, only if the liquid and/or gas is discharged with the respective pressure and temperature, the liquid forms droplets that have a size with a mean diameter d _p and a mean speed V _d and therefore are acceler ated enough to hit the surface in a distance d hard enough to remove the dirt and residuals on the surface, but at the same time do not damage the surface.

Furthermore, in particular the sum s of all areas of orifices is relevant in terms of the jetting ef fect, which has an influence on the droplet size.

The effect that this interrelation of parame ters refers to is the "jetting effect". In particular, the measured mean particle di ameter d _p of droplets in the atomized liquid is is 200pm ³ d _p ³ 40pm, in particular is lOOpm > d _p ³ 50pm.

In particular, the atomized liquid or the drop lets are sprayed to the surface at the first end of the nozzle with a spray angle of 140° > a ³ 45°, in particular 120° > ³ 65°, very particular 100° > ³ 75°, very particular essentially 90°.

In a further advantageous embodiment of the invention, the atomized liquid is sprayed to the surface at the first end of the nozzle within a spray angle of 85°³ a ³ 5°, in particular 85°³ ³ 15°,.

In particular, for a circular orifice the spray angle is defined as the angle of a cone with a longitudinal axis that is congruent to the longitudinal axis of the nozzle.

Further particular, for an I-shaped orifice, the spray angle is defined as the angle of an I-shape.

In particular, if the first end of the nozzle corresponds to the liquid discharge orifice, the atomized liquid or droplets are sprayed to the surface with a vertex of the spray angle arranged essentially at the level of the liquid discharge orifice.

In particular, if the first end of the nozzle corresponds to an end arranged after the liquid discharge orifice, the atomized liquid or droplets are sprayed to the surface with a vertex of the spray angle arranged essentially at the level of the first end discharge ori fice.

In an advantageous embodiment of the invention, the droplets, in particular the droplets of the atomized liquid at the exit of the nozzle, are accelerated to a mean/max speed V _d of 0.1 < Ma < 1 Ma, in particular 0.1 Ma < Ma < 0.3 Ma, in particular 0.4 < Ma <0.7 Ma, wherein Ma refers to the Mach number, which is a dimensionless quan tity in fluid dynamics representing the ration of flow velocity and speed of sound with formula I Ma = u/c, formula (I) with

Ma : local Mach number u : local flow velocity with respect to the boundaries c : speed of sound in the medium.

In particular, the flow velocity u is deter mined with the mass flow (volume flow/surface area of con tact per second) We can measure the velocity as well with a doppler particle analyser.

Generally speaking, in particular droplets ac celerated to velocities V _d ³ 0.1 Ma with droplet diameters d _p £ 200pm underlay a burst-out effect of splashing the droplet, called "jetting effect". The emerging pressure is bursting out of the main droplet in plane (2n) with 300m/s or more, along the surface at contact and pushes the dirt rapidly away with the resulting shear forces (drag forces).

In particular, the key parameters for an energy efficient cleaning of the surface is the low temperature of the atomized liquid. The cleaning works at the inventive low temperature (low temperature in reference to known washing processes with steam with temperatures of above 100°C) since warm water has a lower surface tension, so it can wet surfaces better than cold water.

In regard of removing residues like waxes and lipids from a surface, it is a fact that the viscosity phase for waxes and lipids changes for most waxes and li pids from solid to smooth at a temperature of above ca. 40°C. Thus, better wetting, lower surface tension at burst and so higher kinetic energy release and changing of vis cosity states supports the overall cleaning process.

In an advantageous embodiment of the invention, the liquid is water.

In a further advantageous embodiment of the invention, the gas is a moisturized gas, in particular moisturized air. In particular, the air comprises a mois ture range h of lg ³ h ³ 0.01 g water per second and per nozzle.

The moisture in the gas, in particular if the gas is air or air, enhances significantly the heat energy transport.

In a further advantageous embodiment of the invention, the gas is air.

In particular, the atomizing of the discharged water by the airstream encircling the water stream leads to the formation of small water droplets that are dis charged by the nozzle.

In a further advantageous embodiment of the invention, the mass flow ni _f of the liquid in the liquid passage is 0.04 kg/s ³ ni _f ³ 0.001 kg/s per nozzle.

In a further advantageous embodiment of the invention, the mass flow m _g of the gas in the gas passage is 0.02 kg/s > m _g > 0.0005 kg/s per nozzle.

In a further advantageous embodiment of the invention, the ratio of liquid stream entering the liquid passage: gas stream entering the gas passage is equal to essentially 2:3.

In a further advantageous embodiment of the invention, an angle b between the longitudinal axis of the nozzle and the surface plane is 90° ³ b ³ 30°, in particular 85° > b > 45°, very particular 80° > b > 70°. In particular, the angle b is essentially 75°.

In a further advantageous embodiment of the invention, the method further comprises the step of moving the first end of the nozzle with velocity v _n of 5.00m/s ³ v _n ³ O.Olm/s, in particular l.OOm/s > v _n > O.Olm/s, in particular 1.00 m/s ³ v _n > 0.01 m/s, in particular 0.6 m/s > v _n ³ 0.01 m/s in a lateral direction relatively to the surface.

In particular, the first end 101 keeps the dis tance d when it is moved over the surface. In a further advantageous embodiment of the invention, the method comprises multiple nozzles, in par ticular two, three, four or five or more nozzles for clean ing a surface. The four or five or more nozzles can be controlled individually. In particular, the individual nozzles can clean the surface independently from each other or can be coordinated with each other.

In particular, the multiple nozzles are coor dinated with each other for cleaning the surface or multi ple surfaces respectively.

Further particular, the multiple nozzles are individually cleaning the surface or multiple surfaces re spectively, independently from each other.

In particular, each of the respective nozzles might clean a respective surface at the same time. There fore, a first nozzle might be cleaning a first surface of e.g. a vehicle, wherein at the same time, a second nozzles is cleaning a second surface of the same vehicle or of a different vehicle.

In a further advantageous embodiment of the invention, the method further comprises the step of blow drying the surface during the cleaning process, either shortly before the nozzle is directed to a spot on the surface and the atomized air is discharged on that spot, or synchronously with the nozzle. By doing so, the surface is always dry and the atomized liquid, respectively the droplets, can hit the surface without being stopped by an already wet surface.

Advantageously, the blow drying of the surface is achieved by means of a blower system, wherein further details to the blower system are described below.

A second aspect of the invention refers to a nozzle for cleaning a surface according to the method of the first aspect.

In an advantageous embodiment of the nozzle, the first end of the nozzle corresponds to the liquid dis charge orifice. In particular, the liquid discharge orifice and the gas discharge orifice might be arranged on the same level along the longitudinal axis of the nozzle.

In a further advantageous embodiment of the invention, the first end of the nozzle that is arranged downstream the longitudinal axis of the nozzle is formed as a discharge orifice for discharging the atomized liquid, in particular, the first end of the nozzle might form mul tiple discharge orifices to discharge the atomized liquid.

In particular, the first end of the nozzle is arranged after the gas discharge orifice and the liquid discharge orifice and the expansion zone in a downstream direction of the longitudinal axis of the nozzle.

In a further advantageous embodiment of the invention, the nozzle comprises more than one liquid pas sage and/or more than one air passage, in particular wherein the more than one liquid passage and the more than one air passages are all arranged essentially along the longitudinal axis of the nozzle.

A third aspect of the invention refers to an apparatus for cleaning the surface by means of a nozzle according to the second aspect of the invention with the method according to the first aspect of the invention.

A further advantageous apparatus comprises more than one nozzle, wherein the nozzles might be arranged together or might be arranged separated from each other. In particular, the nozzles might clean the surface as a bundle of nozzles or as individual nozzles.

In particular, each nozzle might be controlled individually and therefore each nozzle might clean a dif ferent surface of e.g., a vehicles or different surfaces of various vehicles.

A further advantageous apparatus according to the invention comprises a robot arm, wherein more than one nozzle is arranged on that robot arm. The robot arm is adapted to move the nozzle over the surface with a velocity v _n and at the same time keeping the distance d between the first end of the nozzle and the surface.

As mentioned above, in a further advantageous embodiment of the invention, the method further comprises the step of blow drying the surface during the cleaning process, either shortly before the nozzle is directed to a spot on the surface and the atomized air is discharged on that spot, or synchronously with the nozzle.

Advantageously, the blow drying of the surface is achieved by means of an assembly of the nozzle according to the second aspect and a blower system, or by means of a blower system that is part of an apparatus according to a third aspect.

In particular, the blower system improves the cleaning process on the surface, since stains and leftover residues are removed.

The blower system might be a system working with compressed air (compressor blower) or with non-com- pressed air (leaf blower system).

In an advantageous embodiment, the system work ing with compressed air drives the droplets away from the surface with a pressure of 2 bar to 6 bar. The air flow is 5 1/s to 201/s, respectively 18m3/h to 72 m3/h. In par ticular, the blower moves the air with 60 m/s to 90 m/s along the surface to remove the stains and droplets.

In a further advantageous embodiment, the sys tem works with non-compressed air, wherein the air flow is between 50 1/s and 1201/s, respectively 180 m3/h to 432 m3/h. In particular, the blower moves the air with 130 m/s to 500 m/s along the surface.

In an advantageous embodiment of the blower system, a longitudinal axis of the blower is inclined from the vertical of the surface by an angle y, wherein 10° > g > 40°, in particular if a compressor system is used. In a further advantageous embodiment, the angle g is 90° > g > 70°, in particular for a leaf blower system.

In an advantageous embodiment, the blower is coupled to a dirt guidance/direction management in partic ular controlled by the controller of the nozzle assembly.

Other advantageous embodiments are listed in the dependent claims as well as in the description below.

Brief Description of the Drawings

The invention will be better understood and objects other than those set forth above will become ap parent from the following detailed description thereof. Such description makes reference to the annexed drawings, wherein:

Fig. 1 shows a schematic of an exemplary nozzle according to an embodiment of the invention;

Fig. 2 shows a schematic of a further example of a nozzle according to an embodiment of the invention;

Fig. 3 a) and b) show schematics of a cleaning methods according to embodiments of the invention;

Fig. 4 shows a schematic of an apparatus ac cording to an embodiment of the invention;

Fig. 5 shows a schematic of an embodiment of a nozzle or apparatus comprising a blower system;

Fig. 6 shows a photo picture of the result according to experiment 1,

Fig. 7 shows the data sheet of the nozzle that is used for experiments in Table 1 and 2, according to an embodiment of the invention, and

Fig. 8 shows a photo picture of a result ac cording to experiment 3.

Modes for Carrying Out the Invention Fig. 1 and Fig. 2 show each a respective em bodiment of a nozzle according to an embodiment of the invention.

Each of the nozzles shown in Fig. 1 and Fig. 2 show the following features:

The nozzle comprises a liquid passage 11 adapted to direct a liquid stream in a downstream direction towards a liquid discharge orifice 111. In particular, the liquid passage 11 extends along a longitudinal axis 100 of the nozzle 1 and terminates downstream of the liquid pas sage 11 in a in particular circular liquid discharge ori fice 111. The downstream direction in Fig. 1 and Fig. 2 is indicated by the arrow ds, but is also clear from the description.

In addition, the nozzle comprises a gas passage 12 adapted to direct a gas stream towards an in particular annular gas discharge orifice 121, wherein the gas dis charge orifice 121 is adapted to discharge the gas stream into the expansion zone 13. In particular, the gas dis charge orifice 121 is arranged coaxially to the liquid discharge orifice 111.

In the embodiment of Fig. 1, the liquid passage 11 and the air passage 12 end within the nozzle body. Therefore, the liquid discharge orifice 111 and the gas discharge orifice 121 are arranged within the body of the nozzle. The liquid discharge orifice 111 and the gas dis charge orifice 121 are arranged at the same level in a downstream direction of the longitudinal axis 100 of the nozzle.

The expansion zone 13 is therefore also ar ranged within the nozzle 1. The first end 101 of the nozzle 1 encloses the expansion zone 13 and forms a nozzle dis charge orifice for discharging the atomized liquid. In particular, the first end 101 of the nozzle 1 is arranged after the gas discharge orifice 121 and after the liquid discharge orifice 111 and after the expansion zone 13 in a downstream direction of the longitudinal axis 100 of the nozzle 1.

In particular, the nozzle discharge orifice has a diameter d _n0 zzie of 0.5mm < d _n0 zzie£ 2.00mm.

In Fig. 2, the liquid passage 11 and the gas passage 12 end in particular at the same level as the first end 101 of the nozzle 1. The expansion zone 13 is therefore located outside the nozzle 1. In Fig. 2, the liquid dis charge orifice 111 and the gas discharge orifice 121 are arranged on the same level in downstream direction of the longitudinal axis 100.

In particular, the first end 101 of the nozzle corresponds to the liquid discharge orifice 111.

In particular, the first end 101 of the nozzle 1 is arranged at the same level in a downstream direction of the longitudinal axis 100 as the liquid discharge ori fice 111 and the gas discharge orifice 121.

Fig. 3 a) and b) show schematics of methods for cleaning a surface according to embodiments of a first aspect of the invention.

The method in Fig. 3 a) and b) comprises the steps of discharging a liquid, in particular with a pres sure of pi of lObar ³ pi ³ O.lbar, and a moisturized gas, in particular with a pressure p _g of 10 bar > p _g > O.lbar, into the expansion zone 13, for atomizing the liquid in the gas stream.

The atomized liquid is directed to the surface 2, wherein a shortest distance d between the surface 2 and a first end 101 of the nozzle 1 in downstream direction is lcm < d £ 20cm, in particular 1cm < d £ 10cm, in particular lcm < d £ 7cm, in particular lcm < d £ 5cm, in particular 4cm < d £ 7cm.

An impact temperature Ti of the atomized liq uid is 80°C > Ti > 40°C, in particular 65°C ³ Ti ³ 40°C on impact on the surface. The sum s of all areas of all orifices of the nozzle is 100mm ² > s ³ 0.5mm ² .

Advantageously, the gas is air moisturized with water with a moisture range h of lg/s ³ h ³ 0.01 g/s per nozzle. In particular, the term "per nozzle" refers to the discharging of the moisture mass in the gas passage re spectively discharging from the gas discharge orifice of the nozzle. Even if there are multiple gas passages in the nozzle, the air moisture range h is accumulated to result in the above-mentioned range.

In an advantageous embodiment of the invention, the temperature Ti of the liquid entering the liquid passage 11 is 95°C > Ti > 50°C and/or the temperature T _g of the gas entering the gas passage 12 is 120°C > T _g > 50°C.

Advantageously, the method further comprises the step of moving the first end 101 of the nozzle 1 with a velocity v _n of 1.00 m/s > v _n > 0.01 m/s, in particular of 0.5 m/s ³ v _n ³ 0.05 m/s, in particular 1.00 m/s ³ v _n ³ 0.01 m/s, in particular 0.6 m/s > v _n > 0.01 m/s in a lateral direction relative to the surface, as indicated by the arrow v _n . In particular, the first end 101 keeps the dis tance d when it is moved over the surface.

Advantageously, the mass flow ni _f of the liquid in the liquid passage is 0.04 kg/s ³ ni _f ³ 0.001 kg/s, and/or the mass flow m _g of the gas in the gas passage is 0.02 kg/s > m _g > 0.0005 kg/s.

Advantageously, an angle b between the longi tudinal axis 100 of the nozzle 1 and the surface plane is 90° > b > 30°, in particular 85° > b > 45°, very particular 80° > b > 70°, very particular b is essentially 75°.

In Fig. 3a), it is schematically shown how the method would work with a nozzle 1 according to an embodi ment of the nozzle 1 as shown in Fig. 1.

In a further advantageous embodiment of the invention, the method would further comprise the step of blow drying the surface before the atomized liquid is di rected towards the surface, or synchronous with directing the atomized liquid to the surface.

As described above for Fig. 1, the first end 101 of the nozzle 1 in Fig. 3 a) is forming a first end discharge orifice for discharging the atomized liquid. The distance d between the first end 101 and the surface 2 is shorter than the distance between the liquid discharge or ifice 111 and/or the gas discharger orifice 121 and the surface 2. The atomized liquid that discharges from the expansion zone 13 is sprayed to the surface 2 at the first end 101 of the nozzle within a spray angle a.

In particular, the atomized liquid or the drop lets are sprayed to the surface at the first end 101 of the nozzle 1 with a spray angle of 140° > a ³ 45°, in particular 120° > ³ 65°, very particular 100° > ³ 75°, very particular essentially 90°.

In a further advantageous embodiment of the invention, the atomized liquid is sprayed to the surface at the first end 101 of the nozzle 1 within a spray angle of 85°³ a ³ 5°, in particular 85°³ ³ 15°,.

In Fig. 3b), it is schematically shown how the method would work with a nozzle 1 according to an embodi ment of the nozzle 1 as shown in Fig. 2.

As described above for Fig. 2, the first end 101 of the nozzle 1 in Fig. 3 b) corresponds to the liquid discharge orifice 111. The atomized liquid that discharges from the expansion zone 13 is sprayed to the surface 2 at the first end 101 of the nozzle 1 that corresponds essen tially to the liquid discharge orifice 111, within a spray angle a.

In a further advantageous method according to an embodiment of the invention, multiple nozzles 1 accord ing to the embodiment of Fig. 1 or Fig. 2 or a mixture thereof might be used to clean a surface. The individual nozzles might clean one surface at the same time or might clean different surfaces at the same time, e.g. different surfaces of one vehicle.

Fig. 4 shows a schematic of an embodiment of an apparatus 4 for cleaning a surface by means of the nozzle, e.g. with an embodiment of the nozzle as described in Fig. 1 or Fig. 2, with the method according to the invention, e.g. with an embodiment of the method as de scribed in Fig. 3.

The apparatus 4 might comprise a robot arm 41. The nozzle 1 might be attached to the robot arm 41. More than one nozzle 1 might be arranged on the robot arm 41. The nozzles 1 arranged on the robot arm 41 might be bundled or might be arranged separated from each other.

In particular, the apparatus might comprise more than one robot arm 41, wherein each robot arm 41 comprises one or more nozzles 1.

Fig. 5 shows a section of a nozzle assembly of a nozzle 1 and a blower system 5 of an apparatus according to an embodiment of the invention, comprising a blower 5 and the atomizing nozzle 1.

Advantageously, the blow drying of the surface is achieved by means of a blower system 5 that is part of the nozzle assembly according or part of an apparatus ac cording to a third aspect.

In particular, the blower system 5 improves the cleaning process on the surface, since stains and leftover residues are removed.

The blower system 5 might be a system working with compressed air (compressor blower) or with non-com- pressed air (leaf blower system).

In an advantageous embodiment of the blower system, a longitudinal axis of the blower is inclined from the vertical of the surface by an angle y, wherein 10° > g > 40°, in particular if a compressor system is used. In a further advantageous embodiment, the angle g is 90° > g > 70°, in particular for a leaf blower system. Fig. 6 shows a photo picture of a surface that was cleaned with a method according to an embodiment of the invention. The picture shows a good to excellent result that was achieved by cleaning the surface with the parameters:

^■ Mass flow of water ni _f = 0.0067 kg/s, 65°C

^■ Mass flow of air m _g = 0.0033 kg/s, 80°C

^■ Amount of the water additive h to the heated air =

(+ 0.33 g/s water),

^■ The impact temperature Th of the atomized droplets at surface was 50 °C at a distance d of nozzle 1 at (3 cm). (According to Table 1 No 5)

The surface in Fig. 6 comprises brighter lines LI and L2. The lines LI and L2 are areas where the nozzle was moved laterally to the surface with a distance of essentially 3 cm between the end of the nozzle and the surface.

The cleaned line LI has a width of 1.6 cm, wherein the nozzle was arranged in an angle of 45° to the surface. Therefore, the longitudinal axis of the nozzle is arranged in an angle of 45° to the surface.

The cleaned line L2 has a width of 0.8cm, wherein the nozzle was arranged perpendicular to the surface. There fore, the longitudinal axis of the nozzle is arranged perpendicular to the surface while the surface is cleaned.

It is demonstrated that if the nozzle is ar ranged within an angle of 45° to the surface, the clean ing area of the nozzle is larger.

The invention is not limited to the embodiments as shown in the figures.

Experiments For the cleaning experiments, a standard dirt ONORM b 5106:202007 15 has been applied to a surface. A good cleaning result refers to a removing 93% of the dirt in the specific cleaned area. Detailed information about the dirt is given in table 3. The best car wash tunnel achieves a cleaning result of 75%.

Experiment 1: The datasets No. 1 to 5 in Table 1 demonstrate experiments that are performed according to the method for cleaning of the invention.

A vapour internal mixing nozzle is used for the experiments (corresponding to the embodiment of a nozzle as shown in Fig. 1).

No. 1 to 5 refer to experiments with nozzles of type 07LN.

The datasheet of the nozzle 07LN is shown in Fig. 7. The nozzle 07LN corresponds to the type of nozzle according to an embodiment of the invention as shown in Fig. 1.

The liquid in these experiments is water and the gas is air (moisturized with a certain amount of water as specified in the table). The surface for the experiments is a vehicle surface that is arranged within 3 cm distance of the end of the nozzle.

The data according to No. 1 to 5 shows that if the temperature T of the water discharged and/or of the gas discharged is in the inventive range of 80°C > T > 40°C, in particular 65°C > T > 40°C there is a good cleaning result on the surface.

In particular, the impact Temperature Th to achieve a good cleaning result is Th is shown to work well with Th > 47° as demonstrated in dataset No. 3 in table 1.

Dataset No. 6 refers to a comparison experiment with a steamer (Optima Steamer EST 27K; VeeJet flat nozzle - S.S.CO. BSPT H1/4U VEEJET-S 4050). For the cleaning method with the steamer, which is not in accordance with an embodiment of the invention, the water is heated to 174°C (resulting into an impact temperature Ti of 80°C at surface impact) to achieve an excellent cleaning result. The water temperature must therefore be much higher for this method.

The cleaning process according to datasets No. 3 to 5 achieves a good to excellent cleaning result, wherein the power consumption P is within the range of lkW < P < 3 kW. In comparison, the power consumption of the steamer is ca. 19 kW. Therefore, the cleaning method ac cording to the present invention consumes significant lower power. Methods compared at a travel speed of 0.15 m/s. The amount of water was adjusted so that the steamer generator has almost the same mass-flow and the same impact pressure. Calculated from the mass flow volume per second over the spray surface area.

In particular, a very good cleaning result was achieved with a nozzle 07LN with the parameters air pres sure ca. 5.8 bar, water mass flow ca. 23.101/h and water pressure ca. 3 bar air flow ca. 8.9 m ³ /h, where the air was moisturized with ca. 0.33g/s of water.

An example of a good cleaning result is shown in Fig. 6. The surface in Fig. 6 comprises brighter lines LI and L2. The lines LI and L2 are areas where the nozzle was moved laterally to the surface with a distance of es sentially 3 cm between the end of the nozzle and the sur face.

Experiment 2: The dataset No. 8 in Table 2 demonstrates an experiment that is performed according to the method for cleaning of the invention with a nozzle of type 07LN.

The dataset No. 7 in Table 2 shows a comparison experiment with a steamer (Optima Steamer EST 27K; VeeJet flat nozzle - S.S.CO. BSPT H1/4U VEEJET-S 4050). For the results of dataset No. 8, a vapour internal mixing nozzle is used for the experiments (corre sponding to the embodiment of a nozzle as shown in Fig. 1).

The datasheet of the nozzle 07LN is shown in Fig. 7 b). The nozzle 07LN corresponds to the type of nozzle according to an embodiment of the invention as shown in Fig. 1.

The liquid in these experiments is water and the gas is air (moisturized with a certain amount of wa ter). The surface for the experiments is a vehicle surface that is arranged within 3 cm distance of the end of the nozzle.

To achieve an excellent cleaning result with the steamer, an impact temperature of 82°C is required.

The mean droplet diameter of the droplets in the steam from the steamer that hit the surface is measured to be ca. 4pm. The droplet diameter is measured with a Camsizer X2.

It is measured that the cleaning process with this method consumes 19kW of power.

In comparison, as demonstrated in dataset No. 8, if the cleaning method according to the present inven tion is used for cleaning a surface with an excellent re sult, the impact temperature can be reduced to 50°C. The data refers to the cleaning method performed with a nozzle of type Lechler nozzle - 136.134.16.A2 in Fig. 7 a).

The mean droplet diameter of the droplets in the atomized liquid that hit the surface is measured to be ca. 20-50pm. The droplet diameter is measured with a Camsizer X2.

It is measured that the cleaning process with this method consumes 3.0kW of power.

The droplets in the method according to the present invention in No. 8 are much larger in comparison with the droplets that are generated with the steamer in No. 7.

The larger droplets of the atomized liquid that are generated with the method for cleaning a surface ac cording to the invention arrive at the surface with a higher kinetic energy. Therefore, the dirt or residuals on the surface to be cleaned can be removed easier than with the small droplets with lower kinetic energy from the steamer.

The inventive method generates an atomized liq uid with droplet sizes that are larger than the droplets generated with a prior art steamer.

The larger droplets of the atomized liquid move with higher kinetic impact energy to the surface than the droplets generated with the steamer.

Therefore, better cleaning results can be achieved already at low impact temperatures (Ti is 65°C ³ Ti ³ 35°C, in particular 55°C ³ Ti ³ 40°C) with the cleaning method according to the invention that sprays the atomized liquid towards the surface. In comparison, to achieve good cleaning results with prior art steam cleaning, the pro cessing temperatures of steam is 174°C and the impact tem perature of the droplets with the steamer needs to be above 80°C to get a good result.

Therefore, the inventive method is less power consuming than the prior art steamer cleaning methods. In conclusion, when the dry air is moisturized with h ³ 0.1 g/s, the heat transport is improved in the moisture air compared to dry air. Therefore, while the steam discharges from the nozzle and hits the surface, less energy (and temperature) is lost to the environment compared to tradi tional steam processes. Therefore, the atomized air ac cording to the inventive method has more energy to hit the surface and therefore remove residuals compared to tradi tional steam cleaning, even though the traditional steam cleaning is done with higher temperatures. Therefore, the cleaning result is better with the inventive method at lower temperatures and therefore using less energy for the whole cleaning process than tra ditional methods.

Experiment 3: Fig. 8 shows a photo picture of a surface that was cleaned with a method according to an embodiment of the invention. The picture shows a result that was achieved by cleaning the surface with the param eters:

^■ volume flow of water 0.31/h - 0.51/h

^■ The impact temperature Ti of the atomized droplets at surface was 45°C to 50 °C at a distance d of nozzle 1 at (6 cm).

The surface in Fig. 5 comprises brighter lines. The lines L3 and L4 are areas where the nozzle was moved laterally to the surface with a distance of essen tially 6 cm between the end of the nozzle and the sur face. It is very well visible that the cleaning lines have a width clw of ca. 3cm.

In conclusion, the cleaning method works very well, even if the distance between the vehicle surface and the end of the nozzle is d ³ 5. The large distance d results in the fact that a larger area can be cleaned at once and therefore the process to clean the whole vehi cles is accelerated.

Table 1:

able 2: able 3: