METHOD FOR CLEANING SURFACES USING STEAM BUBBLES

Abstract

Method for cleaning surfaces using steam bubbles, wherein the steam bubbles are generated by means of at least one MEMS steam generator (1) and conveyed to the surface to be cleaned by means of at least one MEMS pulsation actuator (16).

Description

[0001] The invention relates to a method for cleaning surfaces using steam bubbles.

[0002] MEMS technology is well-known and stands for Micro Electronic Mechanical Systems. MEMS refers to devices, assemblies, or components whose components have dimensions in the range of 1 µm or smaller and interact as a system. MEMS systems can process mechanical and electrical information, thus integrating electrical and non-electrical functions into a single device.

[0003] MEMS technology is known to be used for electronic-based components in microtechnology, such as sensors, oscillators, filters, or actuators. MEMS devices are also used as microheaters.

[0004] Microheating devices are generally divided into two categories: external and internal microheaters. Internal heating systems feature a heating element located inside a microchamber or microchannel. In an external heating system, heating is achieved using discrete heating elements that are either in contact with the fluid to be heated or are contactless heat exchangers. Heating can be achieved using Joule heating. Temperature control using an exothermic or endothermic reaction, photoactivation, or ultrasonic activation is also known.

[0005] Such microheaters can be used in gas sensing, various biological applications such as cell cultivation, DNA amplification, portable medical or sports devices.

[0006] Microheaters can also be used to generate vapor or bubbles in a liquid medium. DK Maurya et al. (2005 J. Micromech. Microeng. 15 966) describe a MEMS vapor generator constructed from two interconnected silicon chips. The silicon chips are n-doped and arranged as a lower and an upper substrate, forming a vapor chamber. The upper substrate comprises two spaced-apart holes located at opposite ends of the chip. The first hole is connected to a capillary through which the liquid to be vaporized can enter the vapor chamber. A microheater, designed as a p-doped silicon resistance heater, is arranged on the lower substrate in the central region of the vapor chamber and serves to heat the liquid.At the end of the chip opposite the first hole, the second hole serves as an outlet for the resulting gas flow. The upper substrate extends between the two holes, so that the microheater is located below the upper substrate, and both holes are positioned to the side of the heater.

[0007] Volumes of media in various states of matter, such as bubbles or droplets, generated using MEMS technology can be used in a variety of technological areas. For example, they can find application in printing technology, particularly inkjet printing.

[0008] One particularly established process, for example, is thermal inkjet printing, which uses a printhead consisting of an array of up to 400 print nozzles. Each print nozzle is equipped with a heating element with a high operating temperature. The ink to be printed is heated, creating a vapor bubble that leads to overpressure in the print nozzle. This causes the ink droplet created by the heating to be propelled through the print nozzle onto the surface to be printed.

[0009] US Pat. No. 8,815,626 B2 discloses a thermal printhead configured like a MEMS device and comprising an SOI (silicon on insulator) structure. The thermal printhead has a die comprising a printing surface, a substrate, and an oxide layer disposed between the printing surface and the substrate. Several ink outlet openings are provided on the printing surface, which is located on top of the SOI structure. A reservoir containing the liquid ink is located below the ink outlet openings. Resistive heaters are arranged adjacent to the ink outlet openings. Due to capillary forces, the liquid ink rises through the ink outlet openings to the printing surface of the die.The ink is heated by the adjacent resistance heaters, causing the liquid components of the ink to immediately transition into the gas phase, while the solid components remain in the ink outlets. In the second step, the solid components of the ink are heated above their sublimation temperature, causing them to evaporate near the surface to be printed. The subsequent condensation leads to the deposition of a layer of ink on the surface to be printed.

[0010] A MEMS vaporizer can also be used in electronic cigarettes. US Pat. No. 9,801,415 B2 discloses a MEMS vaporizer that is installed in an e-cigarette and comprises a silicon substrate, a microchannel array, a membrane arranged on the microchannel array, a resistance heater, and a resistance temperature sensor. The resistance heater is arranged on top of the membrane so that it is in contact with a side portion of the membrane and an end portion of the top of the microchannel array. At one end, the microchannel array is connected to a liquid reservoir containing the liquid to be vaporized. At the opposite end of the microchannel array is at least one outlet opening. The liquid contained in the reservoir is transported into the microchannels by capillary force, where it vaporizes, and exits the microchannel array through the at least one outlet opening.

[0011] US 11,245,064 B2 discloses a photoacoustic gas sensor device that includes a built-in MEMS heater. The MEMS heater comprises a substrate made of a metal or silicon, germanium, or gallium arsenide, and may be p- or n-doped. Furthermore, the MEMS heater comprises an electrically conductive heating element and a cavity arranged between the substrate and the heating element, which has an insulating function. The cavity may also be covered with a membrane and / or a tensile layer and / or an insulating layer, so that the cavity is separated from the heating element by the aforementioned layers. The insulating layer may have uneven elevations, for example in the form of thorn-like tips, to reduce sticking.

[0012] The MEMS heater can be movably mounted within a photoacoustic gas sensor device and can be activated electrically via resistance heating or photovoltaically via light irradiation. The heating power of the MEMS heater is used to generate acoustic pressure waves in a gas to be analyzed, which can be detected by a pressure sensor built into the photoacoustic gas sensor device.

[0013] US 2015 / 0158720 A1 discloses a MEMS device with an integrated heater, which comprises two hermetically sealed cavities, wherein the cavities have different pressures, such that the first cavity is configured as a getter element and the second cavity as an outgassing element. Each of the plurality of hermetically sealed cavities is defined by a first substrate, a second substrate, and a sealing ring material, wherein the first cavity further comprises at least one getter element for reducing the cavity pressure in the first cavity type and an outgassing element for increasing the cavity pressure in the first cavity type, and wherein the first cavity type further comprises at least one heating element integrated into the first substrate adjacent to the getter element and the outgassing element.The integrated heating element is designed like a resistance heater and is activated to adjust the temperature of the getter element or the outgassing element.

[0014] WO 2022 129 545 A1 discloses a method for cleaning surfaces, in particular teeth, interdental spaces, and gums, using at least one arrangement comprising at least one nozzle. A pulsed fluid stream is generated by the nozzle and directed onto the surface to be cleaned. At least a portion of the used fluid is recirculated. US Pat. No. 9,555,199 B2 discloses a laminar flow vaporizer comprising a laminar electrical resistance heating element. The resistance heating element is used for pulsed heating and vaporization of an inhalable material distributed on the heating element surface. The resistance heating element is arranged in a capillary opening and is made of a porous, preferably metallic, material. It is electrically contacted from two sides to generate a current flow in the porous structure. The current flow lines can run perpendicular to the electrical contacts and extend across the entire surface of the porous material. The current flow lines can be narrowed by slot-shaped recesses introduced laterally in the porous material, creating regions with higher and lower current densities.In conjunction with the porous structure of the material, this creates a temperature gradient in the direction of the surface and in the narrowest areas of the heating element, so that the individual substances contained in the liquid to be evaporated are released as synchronously as possible.

[0015] The liquid to be evaporated is contained in a reservoir that is in communication with the capillary opening, which is arranged laterally to the reservoir and extends longitudinally away from the reservoir.

[0016] Furthermore, it is known to generate mechanical reciprocating movements using MEMS systems. When such microactuators are used in a fluid, they can generate targeted flows, such as those found in an inkjet printer.

[0017] A pulsed microactuator is known from "Study of a vaporizing water micro-thruster" (ZY Zhou et al., Sens. and Actuat. A 89 (2001) 159-165). The microactuator consists of a resistance heater, a vapor chamber, a nozzle, an inlet opening, and a microchannel. The vapor chamber is formed from two silicon wafers and has an inlet opening arranged laterally in the lower substrate, a nozzle arranged in the upper substrate, and a heating wire opening provided in the upper substrate. The nozzle can be converging or diverging, or of the Laval type. Within the vapor chamber, in the lower region, a resistance heater is arranged, which is connected to an electrically conductive heating wire extending through the heating wire opening.

[0018] The microactuator is designed for operation in pulsed mode. Pulsed electrical currents are passed through the heating wire, generating heat pulses in the resistance heater. Normally, the liquid to be vaporized enters the vapor chamber through the inlet opening, is vaporized, and the resulting vapor can exit the vapor chamber at high speed through the nozzle. This creates a thrust force or pressure in the opposite direction to the vapor.

[0019] In general, the performance of steam generators is determined by the parameters pulsation frequency f a , achieved stroke or displacement volume per actuator area h a and surmountable counterpressure p a where A is the actuator area. The output mechanical power (P a ) of a steam generator per actuator area is thus obtained from the following equation: Pa=fa⋅pa⋅ha

[0020] In the practical implementation of steam generators, the parameters are so interdependent that it has not yet been possible to find a physical operating principle in which each of the three parameters can be optimized without restrictions.

[0021] In the piezo actuator segment, for example, high pressures are achieved at high frequencies but with a very low stroke. Electromagnetic actuators, on the other hand, achieve high strokes but low frequencies and low pressures, while simultaneously requiring high energy. Conventional evaporative actuators, for example, can achieve high frequencies and high strokes, but the counterpressures that can be overcome remain low.

[0022] In addition, the required heating power is a relevant factor for MEMS actuators. While known steam generators have heating powers of 20 W / mm 2 up to 300 W / mm 2and high strokes but low pressures are achieved, the heating power in the area of ​​inkjet printers is 500 W / mm 2 up to 2 kW / mm 2 large, which means that precision, dynamics and achieved acceleration forces are high despite low displacement volumes.

[0023] Thus, the disadvantage of known microheaters and microactuators is that they cannot achieve high displacement at a relevant backpressure at moderate heating power. This leads to inefficiency of the known actuators and a gap, especially in evaporation actuators, which are designed to achieve both high displacement with high dynamics and a relevant backpressure of > 2 bar at low heating power.

[0024] Another challenge that has not been solved, especially in the micro range, is to ensure pulsed evaporation of specific amounts of liquid, i.e. the time-controlled provision of defined amounts of vapor.

[0025] Such pulsed steam generation is required, for example, for cleaning technology using pulsed, collapsing steam bubbles. The heater is implemented as a current-carrying heating electrode. The heating power is determined from the following equation: P=U2R

[0026] Where U is the supply voltage and R is the resistance of the heating electrode.

[0027] The object of the invention is to provide a method for cleaning surfaces by means of steam bubbles, which has an improved efficiency and ensures a high displacement of a working medium at relevant back pressure and at moderate heating power.

[0028] The problem is solved with the features of claim 1.

[0029] Advantageous further training is indicated in the dependent subclaims.

[0030] The inventors have recognized that the combination of a MEMS steam generator as a component of an automated movable shuttle of a cleaning device allows the effective cleaning of hard-to-reach surfaces, whereby the micronized size allows the creation of a device that can be used in particular in the oral cavity without causing interference.

[0031] It was discovered that the use of very small steam bubbles, which are generated and emitted in a directed manner, is very gentle yet effective for cleaning, especially of teeth. The steam bubbles collapse on the tooth surface. The pressure change during collapse creates a so-called microstreaming effect, in which small cross-currents arise due to the collapse and refilling of the previous steam volume within a preferably enclosed liquid volume.

[0032] In this case, it is generally advisable to use MEMS steam generators with a specific specification. In particular, it has been recognized that displacements above 10 µm are advantageous.

[0033] The inventors have recognized that the formation of the vapor layer generated during evaporation prevents the achievement of displacements greater than 10 µm. The vapor generated acts as a highly thermally insulating layer and prevents the formation of technically feasible displacements, which are preferably greater than 10 µm.

[0034] The problem of poor evaporation performance and heater burnout in the presence of a vapor bubble can be solved by a microcavity approach. The decoupling of the evaporation site from the location where the lift is generated by the vaporized liquid is particularly advantageous. This decoupling is advantageously achieved through improved vapor removal.

[0035] According to the invention, steam generation takes place in microcavities. There, the liquid to be evaporated is locally stabilized and kept close to at least one heater. After generation, the generated steam is diverted in a controlled manner to an area where it can spread. In this way, the effectiveness of the evaporation is not impaired by the insulating and displacing effect of the steam.

[0036] The invention is advantageous in that a performance-optimizing geometric design of the vapor chamber is achieved by providing microcavities of a specific configuration. This serves, in particular, to remove the generated vapor from the microcavity as efficiently as possible. A poorly designed evaporation cavity results in the vapor generation inside the evaporation chamber being accompanied by a very strong pressure increase, which can disrupt uniform filling of the evaporation cavities and destroy the actuator.

[0037] Furthermore, the inventors recognized that to bridge the gap between piezo actuators and electromechanical drives described above, two parameters in particular must be optimized. First, the overall efficiency of mechanical power to input electrical power must be optimized, which is defined as the ratio between the two power outputs: Eff=PaPin

[0038] Furthermore, the resulting power density, measured in watts per gram of weight, which results from the following ratio, should be optimized: Prho=Pam, where P rho the power density, P a is the mechanical power and m is the mass of the heater.

[0039] Thus, the following aspects are advantageous for the functionality and the resulting highly dynamic and efficient performance: on the one hand, a low thermal mass of the pulsed heater, and on the other hand, the geometric design of the evaporation chamber of the MEMS steam generator.

[0040] The advantageous geometric design of the evaporation chamber is realized through its design in microtechnology or in microcavities that enable efficient evaporation.

[0041] The thermal mass of the heater is minimized by implementing the heater using MEMS thin-film technology and using a substrate with the lowest possible thermal conductivity. The thermal conductivity can be, for example, 1,200 W / m·K, particularly 1,143 W / m·K.

[0042] The invention thus relates to a MEMS steam generator whose central element or core element is at least one microcavity and / or an array of microcavities. The at least one microcavity can achieve highly efficient pulsed vaporization.

[0043] The MEMS steam generator is designed in an open form as a highly dynamic steam generator. Such a MEMS steam generator can generate steam in a highly dynamic, pulsed, and precise manner within a small installation space. In the context of the invention, "dynamic" does not mean static, but pulsed. Pulsation is carried out at defined time intervals and at a defined speed. For example, the pulsation frequency can be 10–10,000 Hz, preferably 50–300 Hz, and particularly preferably 100 Hz. Thus, the pulsation frequency can, in particular, have values ​​in the range of 50 Hz, 60 Hz, 70 Hz, 80 Hz, 90 Hz, 100 Hz, 110 Hz, 120 Hz, 130 Hz, 140 Hz, and 150 Hz.

[0044] Precise means that the vapor volume is defined and can be varied as needed. The vapor volume per vaporization pulse can range from 0.2 µl to 20 µl. A vapor volume of 1 µl / pulse to 10 µl / pulse is preferred. In particular, it can be, for example, 1 µl / pulse, 2 µl / pulse, 3 µl / pulse, 4 µl / pulse, or 5 µl / pulse.

[0045] The vapor volume per vaporization pulse can be variably controlled by changing the heater geometry, vaporization power, and / or backpressure.

[0046] Possible applications include the localized vapor deposition of surfaces. For example, vapor bubbles generated in liquids using MEMS vapor generators can be used to clean surfaces using collapsing vapor bubbles.

[0047] One possible application could be surface cleaning, for example, where the surface to be cleaned is directly vaporized. In particular, the MEMS steam generator can be used for cleaning teeth, for example, inside the mouth or outside the mouth, such as dentures. Teeth and dentures are used synonymously here.

[0048] The use of the MEMS steam generator is particularly advantageous for cleaning small surfaces when a high local resolution of the cleaning level on the object is required. The use of the MEMS steam generator is particularly advantageous when space is limited and steam and / or pulsation generation is required with minimal installation space and high power density. The MEMS steam generator is particularly preferred for dental cleaning.

[0049] Thus, the invention relates to a method for cleaning surfaces by means of steam bubbles, wherein the steam bubbles are generated by means of at least one MEMS steam generator and are conveyed to the surface to be cleaned by means of at least one MEMS pulsation actuator.

[0050] An advantageous development provides that the at least one MEMS steam generator and the at least one MEMS pulsation actuator are provided in a shuttle device, wherein the shuttle device accommodates the at least one MEMS steam generator and the at least one MEMS pulsation actuator and wherein a movement device is provided which is mechanically coupled to the shuttle device in order to move the shuttle device along a surface to be cleaned.

[0051] An advantageous further development provides for a plurality of MEMS steam generators and MEMS pulsation actuators arranged in line on the shuttle.

[0052] An advantageous further development provides that a plurality of MEMS steam generators and MEMS pulsation actuators arranged in a two-dimensional pattern are distributed over a predetermined area of ​​the shuttle.

[0053] An advantageous further development provides that the at least one MEMS steam generator and the at least one MEMS pulsation actuator are formed in one piece, so that they are arranged in one piece in a line or in one piece over a surface.

[0054] An advantageous further development provides that the at least one MEMS steam generator and / or the at least one MEMS pulsation actuator are moved over the work surface with a second movement device.

[0055] An advantageous further development provides that the at least one detection device and the at least one control device are connected to one another, so that sensor data are recorded by the detection device, evaluated and transmitted to the control device.

[0056] An advantageous development provides that the MEMS steam generator comprises at least one heater substrate on which a heater structure is arranged, wherein the heater substrate and the heater structure together form a heater, wherein at least one microcavity is provided on the side of the heater structure facing away from the heater substrate, wherein the heater substrate has at least one opening which connects the microcavity to a space located beneath the heater substrate and containing a working medium, wherein the microcavity is closed off from the heater structure by a perforated cover having at least one outlet opening, wherein the working medium is conveyed from a reservoir into the microcavity through the at least one opening provided in the heater substrate, wherein the working medium is heated by means of the heater at least to the boiling temperature of the working medium,so that at least one gas bubble is generated in the microcavity, wherein the at least one gas bubble is discharged from the microcavity through the at least one outlet opening for spreading on the side of the perforated lid facing away from the microcavity.

[0057] An advantageous development provides that the MEMS pulsation actuator comprises at least one MEMS steam generator, wherein the MEMS steam generator comprises a heater substrate on which a heater structure is arranged, wherein the heater substrate and the heater structure together form a heater and extend continuously over the entire length of the pulsation actuator, wherein at least one microcavity is provided on the side of the heater structure facing away from the heater substrate, wherein the microcavity is closed off by a perforated cover with at least one outlet opening, wherein the heating power of the heater is concentrated directly below the at least one outlet opening, and wherein the at least one outlet opening in the perforated cover has a diameter of 5-500 µm, wherein the MEMS steam generator has a pulsation membrane arranged above the cover,which forms a vapor space above the lid and hermetically seals the MEMS pulsation actuator.

[0058] An advantageous further development provides that the at least one gas bubble is generated directly below the outlet opening by arranging the heater directly below the outlet opening.

[0059] An advantageous further development provides that the working medium in the microcavity is stabilized by means of at least one structure arranged on at least one inner edge of the microcavity and pointing into the interior of the microcavity.

[0060] An advantageous further development provides that the working medium is stabilized by means of at least one structure, wherein the structure has a height in the range of 10-95%, preferably 30-80% of the height of the microcavity.

[0061] An advantageous further development provides that a MEMS steam generator and a MEMS pulsation actuator are used, whose at least one outlet opening A d and an effective evaporation area A k of the heater in a ratio A d / A k to each other, which has values ​​of 0.01-1, preferably 0.1-0.3.

[0062] An advantageous further development provides that the at least one gas bubble is discharged through at least one outlet opening in the perforated lid, which has a diameter of 15-50 µm.

[0063] An advantageous further development provides that the at least one gas bubble is discharged through at least two outlet openings in the perforated lid, which have a hole spacing of 5-1000 µm, preferably 10-100 µm.

[0064] An advantageous further development provides that a stroke of 0.01-1.50 mm, preferably 50-500 µm, is generated.

[0065] An advantageous further development provides that the heater with a heating power of 10-300 W / mm 2 preferably 15-50 W / mm 2 is operated.

[0066] An advantageous further development provides that a back pressure of 0.02-15.00 bar, preferably 0.50-7.00 bar, is generated.

[0067] An advantageous further development provides that an actuation frequency of 10-10000 Hz, preferably 50-300 Hz, particularly preferably 100 Hz is set.

[0068] An advantageous further development provides that the maximum heating temperature of the heater is set to a temperature of 50-800 °C, preferably 80-600 °C, particularly preferably 120-380 °C.

[0069] An advantageous further development provides that at least one heater with at least two heater zones, which have at least two heater stages, is used, wherein the at least one gas bubble is generated and heated with the first heater stage and expelled with the second heater stage.

[0070] An advantageous further development provides that one or more compounds from the following group are used as the working medium in the MEMS pulsation actuator: deionized water, mixtures of deionized water and one or more alcohols, for example methanol, ethanol, isopropanol, special functional evaporation liquids, for example hydrocarbon liquid.

[0071] An advantageous further development provides that the working temperature of the working medium in the MEMS pulsation actuator is set to ≤ 100 °C.

[0072] An advantageous further development provides that one or more compounds from the following group are used as the working medium in the MEMS steam generator: deionized water, mixtures of deionized water and one or more alcohols, for example methanol, ethanol, isopropanol, special functional evaporation liquids, for example hydrocarbon liquid, stabilizers, solid particles.

[0073] An advantageous further development provides that the working temperature of the working medium in the MEMS steam generator is set to ≥ 100 °C.

[0074] An advantageous further development provides that a pulsation membrane comprising PDMS is used in the MEMS pulsation actuator.

[0075] An advantageous further development provides that a pulsation membrane comprising a metallic coating is used in the MEMS pulsation actuator.

[0076] An advantageous further development provides that a pulsation membrane is used in the MEMS pulsation actuator, which is corrugated and comprises at least one metal.

[0077] The invention is explained by way of example with reference to a drawing. It shows: Fig. 1: a MEMS steam generator; Fig. 2: a MEMS pulsation actuator; Fig. 3: a vapor bubble formation; Fig. 4: steam bubble formation at back pressure; Fig. 5: steam bubble formation in the MEMS steam generator according to the invention; Fig. 6: steam management using a perforated cavity cover; Fig. 7: controlled evaporation; Fig. 8: stabilization of the working fluid; Fig. 9: Multi-stage heater designs; Fig. 10: a technology variant with an SOI wafer; Fig. 11: a technology variant with a glass wafer and a PDMS cavity; Fig. 12: a technology variant with a glass wafer and a silicon cover; Fig. 13: a heating curve adjustment.

[0078] The MEMS steam generator 1 comprises a heater substrate 2, which may have a heater structure 3. The heater substrate 2 or the heater structure 3 is contacted by means of a contact 8 ( Fig. 1). The heater substrate 2 and the heater structure 3 form a heater 9. The heater 9 is connected to an electrical circuit via the contact 8 and can thus be heated by Joule heating.

[0079] Openings 4 for supplying the working medium 12 are provided in the heater substrate 2. A cover 6 is arranged above the heater substrate 2. The cover 6 is connected to the heater structure 3 and the heater substrate 2 by means of support webs 7, which rest on the heater substrate 2. The cover 6 is perforated. At least one microcavity 5 is provided between the perforated cover 6 and the heater substrate 2.

[0080] The MEMS steam generator is designed in an open configuration, ensuring highly dynamic, pulsed steam generation. This type of MEMS steam generator can be used, for example, to generate steam bubbles, which can be used for cleaning surfaces.

[0081] The microcavities 5 are covered by the perforated lid 6, allowing the steam 10 generated by heating the working medium to escape directly. The heater 9 can be operated in pulsed mode, allowing steam generation to occur dynamically 11, at defined time intervals and at a defined speed.

[0082] The fluidic pipe resistance is proportional to the length of the inlet opening and inversely proportional to the fifth power of the diameter of the inlet opening. It is advantageous if, if possible, no pressure loss occurs in the direction of the fluidic supply lines, i.e., the inlet openings. The pressure preferably arises in the direction of the perforated cover 6. This is achieved by ensuring that the diameter of the rear side of at least one inlet opening is larger than the diameter of at least one outlet opening 18.

[0083] In general, the MEMS steam generator according to the invention can have a total installation height of 0.3 mm to 2 mm in the open design. While the height of the actuator is determined by the sandwich design of the technology used and is kept to a minimum for efficiency reasons by minimizing the installation space, materials used, and the duration of the technological process steps, the area of ​​the MEMS steam generator is freely scalable within the framework of the basic conditions applicable to the technology. This means that the actuator area can be adapted as required to the application and installation space, or even to the amount of required pulsation volume or steam volume.

[0084] Thus, an effective area within the meaning of the invention is between 1 mm 2 and 2000 mm 2 advantageous. In particular, it is advantageous if the effective area is between 10 mm 2 and 30 mm 2An effective area of, for example, 14 mm 2 , 15 mm 2 , 16 mm 2 , 17 mm 2 , 18 mm 2 , 19 mm 2 or 20 mm 2 .

[0085] An effective surface is a surface which is in contact with the working medium to be evaporated and on which the evaporation of the working medium takes place.

[0086] The specified area does not include the electrical contact and hermetic sealing components. When calculating the total area, the specified area must be expanded to include the contact and sealing components.

[0087] Thus, the multilayer structure of the MEMS steam generator 1 comprises a bottom of the microcavities 5 or the heater substrate 2, the heater structure 3 and the perforated cover 6.

[0088] The MEMS pulsation actuator 1 ( Fig. 2) comprises a heater substrate 2, which may have a heater structure 3. The heater substrate 2 or the heater structure 3 is contacted by means of a contact 8. The heater substrate 2 and the heater structure 3 form a heater 9. The heater 9 is connected to an electrical circuit via the contact 8 and can thus be heated by Joule heating.

[0089] The heater 9, the at least one microcavity 5, the cover 6 with at least one outlet opening 18 and the support webs 7 form a MEMS steam generator 1.

[0090] In the MEMS pulsation actuator 16, the MEMS steam generator 1 is sealed with a pulsation membrane 13 or, alternatively, with a pulsation cover. Sealing with the pulsation membrane 13 generates strong volumetric pulsations or a strong periodic stroke 14. Strong pulsation, in the context of the invention, means strokes with a deflection of 50-300 µm, preferably 100-200 µm, particularly preferably 130-160 µm, and further particularly preferably 150 µm.

[0091] The housing of the MEMS pulsation actuator, i.e. the area between the heater and a pulsation membrane, is hermetically sealed so that neither steam nor liquid can escape from the pulsation actuator.

[0092] A lateral seal is provided so that the working medium 12 and the generated steam 10 remain sealed in the evaporation chamber.

[0093] Through evaporation, the working medium is periodically converted into a gas phase. These evaporation strokes lead to the deflection of the pulsation membrane, generating a periodic pulsation of the MEMS pulsation actuator. The evaporated gaseous working medium then condenses inside the MEMS pulsation actuator, and the microcavity is refilled. In this way, the working medium is circulated.

[0094] The pulsation membrane 13 must ensure appropriate tightness against liquids and gases, while also allowing for a possible connection process with the actuator base. Furthermore, the pulsation membrane 13 must ensure mechanical stability and durability, while also having low rigidity, thus ensuring the elasticity required for pulsation operation. This means that the pressure loss across the pulsation membrane 13 at a nominal maximum deflection should be negligible compared to the deflection pressure.

[0095] These requirements are met, for example, by a membrane comprising PDMS (polydimethylsiloxane). A PDMS-comprising membrane can have a metal coating. Such a membrane is stretched over the cover 6 with the aid of an additional spacer element and laterally connected to the substrate. The connection can be realized by soldering, bonding, or, for example, gluing.

[0096] Furthermore, it is advantageous to use a corrugated membrane, which exhibits high mechanical stability at moderate deflection pressures and can be connected to the base using special welding and / or bonding techniques. In this case, it is advantageous to use a metallic membrane with high long-term stability.

[0097] Advantageously, a polymer membrane with a metal coating can be used.

[0098] Since this is a closed system, no openings are provided in the heater substrate 2 for supplying the working medium 12. The working medium to be evaporated is circulated inside the MEMS pulsation actuator. A cover 6 is arranged above the heater substrate 2. The cover 6 is connected to the heater structure 3 and the heater substrate 2 by means of support webs 7, which rest on the heater substrate 2. The cover 6 is perforated. At least one microcavity 5 is provided between the perforated cover 6 and the heater substrate 2.

[0099] The MEMS pulsation actuator is designed in a closed configuration, ensuring highly dynamic steam generation and pulsation. The MEMS pulsation actuator in such a configuration can be used, for example, to generate periodic pulsations. The pulsations can be used, for example, to accelerate a fluid located behind the membrane. This accelerated fluid can be used, for example, for cleaning.

[0100] The microcavities 5 are covered by the perforated lid 6. The heater 9 can be operated in pulsed mode, so that steam generation can occur dynamically 11, at defined time intervals and at a defined speed.

[0101] In general, the MEMS pulsation actuator according to the invention can have a total installation height of 0.5 mm to 4 mm. While the height of the actuator is determined by the sandwich design of the technology used and is kept to a minimum for efficiency reasons by minimizing the installation space, materials used, and the duration of the technological process steps, the area of ​​the MEMS pulsation actuator is freely scalable within the framework of the basic conditions applicable to the technology. This means that the actuator area can be adapted as required to the application and installation space, or even to the amount of required pulsation volume or steam volume.

[0102] Thus, an effective area within the meaning of the invention is between 1 mm 2 and 2000 mm 2 advantageous. In particular, it is advantageous if the effective area is between 10 mm 2 and 30 mm 2An effective area of, for example, 14 mm 2 , 15 mm 2 , 16 mm 2 , 17 mm 2 , 18 mm 2 , 19 mm 2 or 20 mm 2 .

[0103] An effective surface is a surface which is in contact with the working medium to be evaporated and on which the evaporation of the working medium takes place.

[0104] The specified area does not include the electrical contact and hermetic sealing components. When calculating the total area, the specified area must be expanded to include the contact and sealing components.

[0105] A steam bubble is formed when the working medium 12 heated by heater 9 reaches at least the boiling temperature ( Fig. 3). The amount of energy to be used for effective evaporation corresponds to the energy P v. P v is the energy that can be transferred from the vapor layer created during evaporation to the next liquid layer. The energy transfer is described by Fourier's law of thermal conductivity, which in the 1-dimensional formulation q=λd×dTdx Here q is the heat flow in the x-direction, λ d is the thermal conductivity and dT / dx is the temperature gradient and x is the distance from the heater surface.

[0106] Conventional steam generation has several known problems. On the one hand, the generated steam has a strong thermal insulating effect, and on the other, it generates strong backpressure in the actuator.

[0107] The two main problems of classical evaporation actuators are evident from a qualitatively exemplary temperature and pressure curve, which are shown as a function of the duration of the heating pulse at two different heating powers ( Fig. 4). The configuration of the evaporation element behind a nozzle shows the increasing internal pressure as evaporation begins. It is evident that with increasing thickness of the vapor layer H d or increasing stroke 14, the transmitted power is continuously reduced. This occurs due to the poor thermal conductivity of the steam λ d , and the decreasing temperature gradient. This reduces the heat dissipated by the heater. This leads to disproportionate overheating and the heater's burnout.

[0108] Second, during the displacement or stroke pulse, the pressure in the actuator increases. This leads to an increase in the boiling temperature, which is necessary for evaporation during the stroke pulse at relevant counterpressures. This increased boiling temperature reduces the energy P that can effectively be used for evaporation. v . At a low heating power, the boiling temperature T, which increases with the pressure, stops s the evaporation after a short time t2-t1, since the boiling temperature is the temperature T present at the liquid boundary layer f If the heating power is increased, the evaporation pulse is extended, since the temperature at the interface between steam and working medium T f can be adjusted accordingly quickly in order not to fall below the rising boiling temperature T s to fall.

[0109] Consequently, a disadvantage of conventional MEMS evaporation systems is that if evaporation is to be achieved at rapidly increasing back pressures, it is necessary that the heating temperature follows the rising boiling temperature during the evaporation pulse ( Fig. 4, below). In order to achieve vapor heights of 50 µm to 100 µm, heating capacities of 1.3 kW / mm 2 needed.

[0110] The MEMS steam generator 1 according to the invention can, for example, at heating powers of 5 W / mm 2 - 300 W / mm 2 , preferably at 15 W / mm 2 - 50 W / mm 2 work and achieve strokes in the range of up to 1 mm at pressures up to 10 bar.

[0111] The problem of poor evaporation performance and burnout of the heater 9 with an existing vapor bubble 10 can be solved by the microcavity approach. The process parameters used are Fig. 5. In the evaporator according to the invention, the location of the evaporation is decoupled from the location at which the lift is generated by the evaporated working medium. It is advantageous if the heater 9 is arranged within the microcavity 5. In particular, it is advantageous if the heater 9 is arranged below the outlet opening 18. The height of the microcavity is defined by the height of the space delimited by the heater 9 arranged below and the perforated cover 6 arranged above, and is referred to as H k It is advantageous if Hk is in the range of 0.5 µm - 50 µm, preferably 1 µm - 10 µm.

[0112] The heater 9 can be designed as a thin-film heater. It is advantageous if the thickness of the thin-film heater is in the range of 50 nm to 1500 nm, preferably 100 nm to 400 nm.

[0113] The vapor bubble 10 is generated on the surface of the heater 9. After its creation, it is diverted in a controlled manner to an area where it can spread freely. This can, for example, be a liquid pool 17 located above the perforated cover 6. Since the spread of the vapor bubble is decoupled from the location of its formation, the effectiveness of the evaporation is not impaired by the insulating and displacing effect of the vapor.

[0114] The following parameter ranges can be realized with the MEMS steam generator according to the invention: Heating power: 10 W / mm 2 - 300 W / mm 2 , preferably 15 W / mm 2 - 50 W / mm 2 ; Back pressure: 0.02-15.00 bar, preferably 0.50-7.00 bar; Stroke: 0.01-1.50 mm, preferably 50-500 µm; Actuation frequency: 10-10000 Hz, preferably 50-300 Hz, particularly preferably 100 Hz; Maximum heating temperature: 50-800 °C, preferably 80-600 °C, particularly preferably 100-380 °C.

[0115] The vapor 10 generated in the microcavity 5 is removed in a controlled manner. It is important that the vapor 10 be removed from the microcavity 5 as efficiently as possible. The design of the microcavity 5 is crucial here. A poorly designed microcavity 5 results in the vapor generation inside the microcavity 5 being accompanied by a very strong pressure increase. This disrupts the uniform filling of the microcavities 5 and can lead to the destruction of the actuator.

[0116] In order to ensure that the removal of the steam 10 from the microcavity 5 is as controlled as possible and that the pressure increase inside the microcavity 5 is low, the cover 6 is perforated as finely as possible, preferably as a finely perforated membrane ( Fig. 6). In the context of the invention, a fine perforation means a diameter of the corresponding outlet openings 18 of 5-500 µm, preferably 15-50 µm. The cover 6 has a thickness of 10-1500 µm, preferably 20-200 µm. The distance between the outlet openings 18 is referred to here as the hole distance 19 and is as small as possible. The effective hole distance 19 between the edges of two outlet openings 18 can be, for example, 5-1000 µm, preferably 10-100 µm. Such a design of the cover 6 keeps the pressure loss, i.e. the resulting overpressure in the microcavity 5 upon outflow from the microcavity 5, low.

[0117] The arrangement of the outlet openings 18 can be uniform. It is advantageous if the arrangement of the outlet openings 18 is not uniform, but rather individually adapted to the surface or object to be cleaned. This increases cleaning performance.

[0118] It is advantageous if, for a sensible dimensioning of the cover 6, in order to ensure sufficient steam removal with a high effective evaporation area, a balanced ratio between effective evaporation area A k and total area of ​​all outlet openings 18 A d The effective evaporation area A k is a surface of the heater 9 which is in contact with the working medium 12 to be evaporated and on which the evaporation of the working medium 12 takes place. Thus, it is advantageous if the ratio of A d / A k in the range of 0.01 to 1, preferably 0.1 to 0.3.

[0119] In order to achieve an orderly outflow of the steam 10 from the microcavity 5 with a low pressure loss and to avoid a disorderly outflow and adverse flow conditions, it is advantageous if the discharge of the steam 10 begins as controlled as possible under the outlet openings 18 of the perforated cover 6 and then spreads radially ( Fig. 7). This ensures that the newly generated vapor 10 can flow out of the microcavity 5 without the not yet vaporized working medium 12 preventing its path and unhindered outflow.

[0120] Evaporation beginning centrally below the outlet openings 18 can be achieved by concentrating the heating power below the outlet openings 18. Thus, it is advantageous if the heater 9 is arranged directly below the outlet openings 18.

[0121] It is advantageous if the working medium 12 is stabilized during evaporation ( Fig. 8). This ensures a defined duration of the evaporation process and the filling of the microcavities 5. In addition, this enables a controlled vapor flow between the microcavity 5 and the outlet opening 18 of the perforated lid 6. The stabilization of the working medium 12 is achieved by at least one structure 20 provided in the perforated lid 6. It preferably extends along at least one edge of the outlet opening 18 into the interior of the microcavity 5. At least one inner edge 27 of the outlet opening 18 is extended by the structure 20. The at least one structure 20 is connected to the lid 6 and projects into the interior of the microcavity 5 from the underside 21 of the perforated lid 6, so that it forms an L-shape with the underside 21. The at least one structure 20 can have a height H swhich are in the range of 10-95%, preferably 30-80% of the height of the microcavity 5 H K The structure 20 can be implemented in any number. If multiple structures 20 are provided, they can be provided on one or both inner edges 27 of the at least one outlet opening 18. They can be provided on one or more outlet openings 18.

[0122] In some embodiments, it may be advantageous to eject a specially superheated steam in a highly dynamic manner. This can be achieved, for example, by locally dividing the heating surfaces ( Fig. 9). In an advantageous embodiment, special heater zones 22 are provided to generate steam and subsequently heat it (Heater Design 1). Other separate heater zones 22 are used to expel the already heated steam in a highly dynamic manner (Heater Design 2).

[0123] Pulsation frequencies of 100 Hz or more can be described as highly dynamic.

[0124] According to the invention, different heating stages can be realized. They can, for example, be controlled by a separate electrical control of the heating electrodes ( Fig. 9 in the middle).

[0125] In addition, individually adjusted control of individual microcavities is possible, allowing heaters of different microcavities to provide different heating outputs. For this purpose, individual supply and control of each heater is provided. Each microcavity can be heated independently with a different heating output. This enables selective and sequential vapor deposition of individual areas of the surface to be cleaned.

[0126] In an advantageous embodiment, the MEMS vapor generator may comprise an SOI (silicon insulator) wafer ( Fig. 10). The SOI wafer can be used, for example, for the design of the heater substrate 2, microcavities 5, and / or a membrane heater. This is particularly advantageous because the very small cavity thickness is ensured by the insulating intermediate layer of the wafer-based actuator. Furthermore, this enables the production of the base substrate, microcavity 5, and perforated cover 6 from a single material, thus eliminating the bonding step in which the heater substrate 2 is connected to the perforated cover 6. An SOI wafer can be used here, the useful layer of which has high electrical conductivity and can directly serve as a current-carrying heater. The thickness of the insulating silicon oxide layer is determined by the thickness of the microcavity 5. It is advantageous if the thickness of the silicon oxide layer has the following ratio to the thickness of the microcavity 5: 1:1.It is therefore advantageous if the thickness of the silicon oxide layer is equal to the thickness or height of the microcavity.

[0127] The openings 4, which serve as fluid inlets, can be realized using a DRIE (deep reactive ion etching) step. It is advantageous if the openings 4 have a diameter of 20–1000 µm, preferably 30–200 µm.

[0128] The lid 6 can be perforated using a DRIE etching process. The microcavities 5 can be created using HF etching.

[0129] In another embodiment, the high pulsability can be achieved by a low thermal mass using a heater deposited on glass, for example Borofloat ( Fig. 11). It is advantageous to use gold and / or platinum as the heater material. The thickness of the metal can be 50–1500 nm, preferably 100–400 nm. Chromium and / or titanium can be used as an intermediate layer. This increases adhesion and thus the mechanical stability of the heater. The thickness of the chromium and / or titanium intermediate layer can be in the range of 5–300 nm, preferably 30–80 nm.

[0130] The perforated lid 6 can be made of silicon. It is advantageous if the perforation is realized by DRIE etching. It is advantageous if the glass base and the silicon lid are connected by a PDMS layer. The PDMS can have a structure and a height that corresponds to the thickness of the microcavity 5. In this embodiment, the side seals of the evaporation chamber can comprise PDMS. The PDMS can also be used to create support structures in the evaporation chamber, i.e., in the microcavity 5, which increase the mechanical stability of the microcavity 5.

[0131] In a further advantageous embodiment, high pulsability can be achieved by a low thermal mass of the heater, which is achieved, for example, by vapor deposition of the heater material onto a glass substrate, for example Borofloat. Gold and / or platinum can be used as the heater material, with the layer thickness being 50-1500 nm, preferably 100-400 nm. An intermediate layer can be provided which comprises chromium and / or titanium and has a thickness of 5-300 nm, preferably 30-80 nm. The intermediate layer can be vapor deposited onto the substrate. The perforated cover 6 can be made of silicon, with the perforation being created by DRIE etching. The microcavities can also be etched by DRIE.

[0132] After the etching processes have been completed, the glass base, heater and silicon cover can be connected using an anodic bonding process, so that an anodic bond 26 is created ( Fig. 12). The anodic connection, ie the anodic bond 26, is particularly advantageous because it ensures high mechanical stability and, at the same time, hermetic sealing of the system.

[0133] In this embodiment, the cavity thickness is determined by a separate etching step in which the microcavities 5 are etched out of the cover 6.

[0134] This embodiment can be freely combined with other embodiments. It supports all embodiments of the invention and ensures high mechanical stability of the system.

[0135] The evaporation performance of the MEMS steam generator can be controlled by the selected working medium 12. The working medium 12 can comprise one or more compounds from the following group: deionized water, mixtures of deionized water and one or more alcohols, for example, methanol, ethanol, isopropanol, special functional evaporation liquids, for example, hydrocarbon liquids, stabilizers, and solid particles.

[0136] The particles are small solids with a specifically selected hardness, size distribution, and shape. They perform an abrasive function. Particles with a defined size of, for example, 0.5 - 5 µm, preferably 1.0 - 4.5 µm, and particularly preferably 1.5 - 4.0 µm, should be finely dispersed in the working medium. The particle size should not exceed 5 µm. The particle proportion should be between 2-10%.

[0137] The particles are granular and / or fibrous structures with irregular surfaces. They can be of organic and / or inorganic origin.

[0138] The materials used are preferably of plant origin (cellulose). However, the alternative or additional use of mineral particles is of course possible according to the invention.

[0139] For a uniform distribution of the particles, dispersants such as microcrystalline cellulose, starch, proteins, or other surfactants are used in an advantageous further development. This is preferably achieved by utilizing the so-called Pickering effect.

[0140] The properties of the working medium 12 influence the boiling temperature to be reached by the heater, the nucleation behavior at the beginning of the evaporation pulse, the temporal course of the evaporation and the necessary heating temperature and thus the energy required for the evaporation.

[0141] It is advantageous if the working temperature or boiling point of the working medium in the MEMS steam generator has values ​​of ≥ 100 °C. For example, the working medium used can have a boiling point of 100 °C, 105 °C, 110 °C, 115 °C, 120 °C, 125 °C, 130 °C, 135 °C, or 140 °C. This enables the generation of hot steam bubbles, which are particularly effective for cleaning.

[0142] It is advantageous if the working temperature or boiling point of the working medium in the MEMS pulsation actuator has values ​​of ≤ 100 °C. For example, the working medium used can have a boiling point of 100 °C, 95 °C, 90 °C, 85 °C, 120 °C, 80 °C, 75 °C, 70 °C, 65 °C, or 60 °C.

[0143] It is advantageous not to supply the heater with a constant voltage, but to supply the heating curve adaptively, variably over time ( Fig. 13). The time-variable control can be used to control and adjust steam ejection. Furthermore, the desired steam ejection can be adjusted to a variable, load-dependent backpressure via the time course of the pulse.

[0144] For example, the heating curve adjustment can be used to control the rise time of steam generation and the final temperature of the heater in the last part of the heating pulse.

Claims

[1] Method for cleaning surfaces by means of steam bubbles, wherein the steam bubbles are generated by means of at least one MEMS steam generator (1) and are conveyed to the surface to be cleaned by means of at least one MEMS pulsation actuator (16). [2] Method according to claim 1, wherein the at least one MEMS steam generator (1) and the at least one MEMS pulsation actuator (16) are provided in a shuttle device, wherein the shuttle device accommodates the at least one MEMS steam generator (1) and the at least one MEMS pulsation actuator (16), and wherein a movement device is provided which is mechanically coupled to the shuttle device in order to move the shuttle device along a surface to be cleaned. [3] Method according to claim 2, wherein a plurality of MEMS steam generators (1) and MEMS pulsation actuators (16) arranged in line are provided on the shuttle. [4] Method according to claim 2 or 3, wherein a plurality of MEMS steam generators (1) and MEMS pulsation actuators (16) arranged in a two-dimensional pattern are provided distributed over a predetermined area of ​​the shuttle. [5] Method according to one of the preceding claims, wherein the at least one MEMS steam generator (1) and the at least one MEMS pulsation actuator (16) are formed in one piece, so that they are arranged in one piece in line or in one piece over a surface. [6] Method according to one of the preceding claims, wherein the at least one MEMS steam generator and / or the at least one MEMS pulsation actuator (16) are moved over a work surface by a second movement device. [7] Method according to one of the preceding claims, wherein a control device converts the sensor data of a detection unit into electronic signals and thereby controls the spatial and temporal sequence of the pulses. [8] Method according to one of the preceding claims, wherein the MEMS steam generator (1) comprises at least one heater substrate (2) on which a heater structure (3) is arranged, wherein the heater substrate (2) and the heater structure (3) together form a heater (9), wherein at least one microcavity (5) is provided on the side of the heater structure (3) facing away from the heater substrate (2), wherein the heater substrate (2) has at least one opening (4) which connects the microcavity (5) to a space located below the heater substrate (2) and receiving a working medium (12), wherein the microcavity (5) is closed off from the heater structure (3) by a perforated cover (6) with at least one outlet opening (18), wherein the working medium (12) is fed from a reservoir into the microcavity through the at least one opening (4) provided in the heater substrate (2). (5) is promoted,wherein the working medium (12) is heated by means of the heater (9) at least to the boiling temperature of the working medium (12), so that at least one gas bubble is generated in the microcavity (5), wherein the at least one gas bubble is discharged from the microcavity (5) through the at least one outlet opening (18) for spreading on the side of the perforated cover (6) facing away from the microcavity (5). [9] Method according to one of the preceding claims, wherein the MEMS pulsation actuator (16) comprises at least one MEMS steam generator (1), wherein the MEMS steam generator (1) comprises a heater substrate (2) on which a heater structure (3) is arranged, wherein the heater substrate (2) and the heater structure together form a heater (9) and extend continuously over the entire length of the pulsation actuator, wherein at least one microcavity (5) is provided on the side of the heater structure (3) facing away from the heater substrate (2), wherein the microcavity (5) is closed off by a perforated cover (6) with at least one outlet opening (18), wherein the heating power of the heater (9) is concentrated directly below the at least one outlet opening (18), and wherein the at least one outlet opening (18) in the perforated cover (6) has a diameter of 5-500 µm has,wherein the MEMS steam generator (1) has a pulsation membrane (13) arranged above the cover (6), which forms a steam space above the cover (6) and hermetically seals the MEMS pulsation actuator (16). [10] Method according to claim 9, wherein the at least one gas bubble is generated directly below the outlet opening (18) by arranging the heater (9) directly below the outlet opening (18). [11] Method according to claim 8 or 9, wherein the working medium (12) is stabilized in the microcavity (5) by means of at least one structure (20) arranged on at least one inner edge of the microcavity (5) and pointing into the interior of the microcavity (5). [12] Method according to claim 8 or 9, wherein the working medium (12) is stabilized by means of at least one structure (20), wherein the structure (20) has a height in the range of 10-95%, preferably 30-80% of the height of the microcavity (5). [13] Method according to one of claims 8 to 10, wherein a MEMS steam generator (1) and a MEMS pulsation actuator (16) are used, whose at least one outlet opening (18) A d and an effective evaporation area A k of the heater (9) in a ratio A d / A k to each other, which has values ​​of 0.01-1, preferably 0.1-0.

3. [14] Method according to claim 8, wherein the at least one gas bubble is discharged through at least one outlet opening (18) in the perforated lid (6) which has a diameter of 15-50 µm. [15] Method according to claim 8, wherein the at least one gas bubble is discharged through at least two outlet openings (18) in the perforated lid (6), which have a hole spacing (19) of 5-1000 µm, preferably 10-100 µm. [16] Method according to one of the preceding claims, wherein the MEMS vapor generator (1) generates a stroke of 0.01-1.50 mm, preferably 50-500 µm. [17] Method according to one of claims 8 to 10, wherein the heater (9) has a heating power of 10-300 W / mm 2 preferably 15-50 W / mm 2 is operated. [18] Method according to one of the preceding claims, wherein a back pressure of 0.02-15.00 bar, preferably 0.50-7.00 bar is generated. [19] Method according to one of the preceding claims, wherein the MEMS steam generator (1) is set to an actuation frequency of 10-10000 Hz, preferably 50-300 Hz, particularly preferably 100 Hz. [20] Method according to one of claims 8 to 10, wherein the maximum heating temperature of the heater (9) is set to a temperature of 50-800 °C, preferably 80-600 °C, particularly preferably 120-380 °C. [21] Method according to one of claims 8 to 10, wherein at least one heater (9) with at least two heater zones having at least two heater stages is used, wherein the at least one gas bubble is generated and heated with the first heater stage and expelled with the second heater stage. [22] Method according to one of the preceding claims, wherein one or more compounds from the following group are used as the working medium (12) in the MEMS pulsation actuator (16): deionized water, mixtures of deionized water and one or more alcohols, for example methanol, ethanol, isopropanol, special functional evaporation liquids, for example hydrocarbon liquid. [23] Method according to claim 8, wherein the working temperature of the working medium (12) in the MEMS pulsation actuator (16) is set to ≤ 100 °C. [24] Method according to claim 8, wherein one or more compounds from the following group are used as the working medium (12) in the MEMS steam generator (1): deionized water, mixtures of deionized water and one or more alcohols, for example methanol, ethanol, isopropanol, special functional evaporation liquids, for example hydrocarbon liquid, stabilizers, solid particles. [25] Method according to claim 8, wherein the working temperature of the working medium (12) in the MEMS steam generator (1) is set to ≥ 100 °C. [26] Method according to one of the preceding claims, wherein a pulsation membrane (13) comprising PDMS is used in the MEMS pulsation actuator (16). [27] Method according to one of the preceding claims, wherein a pulsation membrane (13) comprising a metallic coating is used in the MEMS pulsation actuator (16). [28] Method according to one of the preceding claims, wherein a pulsation membrane (13) is used in the MEMS pulsation actuator (16), which is corrugated and comprises at least one metal.

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