Device and method for generating microcurrents

Abstract

The present invention relates to a device for generating microflows, comprising at least one first fluid supply channel, in which at least a first fluid (4) can be conducted, and at least one second fluid supply channel, in which at least a second fluid (5) can be conducted. The fluids are immiscible. Furthermore, at least one fluid flow channel (1) is formed, into which the fluid supply channels open, wherein a segmented fluid flow can be conducted in the fluid flow channel (1), which has at least a first segment comprising the first fluid (4) and at least one second segment comprising the second fluid (5). The first segment and the second segment are immiscible. Furthermore, the surface of the fluid flow channel (1) facing the segmented fluid flow has at least one first solid surface (2) and at least one second solid surface (3).Here, the first solid surface (2) and the second solid surface (3) alternate periodically at least twice along the longitudinal axis of the fluid flow channel (1), wherein the at least one first solid surface (2) has a wettability different from that of the at least one second solid surface (3).

Description

The present invention relates to an apparatus and a method for generating microflows.The mixing or also contacting of fluids in process engineering apparatuses regularly presents a great challenge. Typical technical tasks include a) contacting gas and liquid, b) contacting two immiscible liquids, c) mixing solid and liquid, and d) creating bubbles, droplets and particles of as uniform a size as possible. These technical tasks have to be solved inter alia in the chemical industry, for example in the realization of gas-liquid reactions such as chlorination, hydrogenation, oxidation or nitration reactions and of liquid-liquid reactions such as aromatic nitrations, Friedel-Crafts alkylations, emulsion polymerizations or esterifications and also further gas-liquid and liquid-liquid reactions with and without solid catalyst, in the process industry, for example in the reaction of dispersion, extraction, crystallization processes, and in the food industry, for example in the production of suspensions. In addition, fluid mixers are an important component of microfluidic analyzers for detecting pollutants and pathogens or for diagnosing diseases.Technical solutions for mixing fluids and solids comprise, inter alia, apparatuses with moving stirring units (stirred tank apparatuses), moving containers (shaker apparatuses), and apparatuses with integrated static mixers, mixing and spray nozzles or pulsation generators. In apparatuses without pulsation generators, the mixed energy is either introduced mainly by the moving stirring element or the moving apparatus or is taken from the flow energy of the fluid or fluids. In small-scale apparatuses, such as microstructured absorbers, emulsifying and dispersing apparatuses and reactors, however, the fluid mixing is made more difficult by the limited use of stirring elements and the predominantly laminar flow conditions owing to the small characteristic dimensions. Microstructured apparatuses usually consist of a multiplicity of parallel-connected channels having dimensions in the range from 10 μm to 5000 μm.To improve the mixing of fluids in small-scale apparatuses, active and passive mixers are used. Active mixers are based on the introduction of additional mixing energy in the form of electrical, magnetic or acoustic fields. Passive or static mixers are essentially based on a special apparatus or channel geometry. In this case, in particular periodic restrictions and widenings of the duct of a wide variety of designs (e.g. screens, fish bones), internals for dividing and remixing and also special duct arrangement are used in order to influence the flow field and thereby bring about intensive mixing of the fluids.The disadvantage of the active mixers is that additional equipment such as electrodes or sound generators including the necessary control unit is required. In addition, the active mixers are difficult to transfer to other apparatus dimensions. The passive mixers, on the other hand, currently require increased manufacturing costs for the additional copolymerization because of the complex geometry. Additional mixing elements integrated in the channel promote the formation of dead zones in which undesired side reactions take place and can lead to a reduction in the yield of the target product. In addition, dead zones promote so-called fouling and the formation of channel blockages and cause an increased pressure loss during operation and thus an increased energy consumption.Currently, some approaches exist to solve these problems. Thus, KR 100 864 880 B1 proposes that a micromixer is to be used in which the inner surface of the flow channel has in particular two different surfaces which differ in terms of their wetting properties. In addition, various patterns are disclosed as to how the various surfaces may be disposed in the flow channel. In this case, particularly periodic changes between the various surfaces are preferred. The object of this disclosure is to create a fully intermixed and turbulent fluid flow.A disadvantage here is that only turbulent fluid flows can be generated and that it is not possible to obtain a segmented fluid flow after passing through the channel. This invention can therefore only be used where the presence of segmented flows is not a prerequisite for a successful process.The object of the present invention is thus to provide a device and a method such that intensive mixing takes place in the segments of a segmented fluid flow without causing the segments to mix with one another.This object is achieved according to the invention by a device for generating microflows according to claim 1 and by a method for generating microflows according to claim 10.A device for generating microflows has at least one first fluid supply channel in which at least one first fluid can be guided, and at least one second fluid supply channel in which at least one second fluid can be guided. In this case, the fluids are designed to be immiscible. In addition, at least one fluid flow channel into which the fluid supply channels open is formed, wherein a segmented fluid flow can be guided in the fluid flow channel, which comprises at least one first segment, which comprises the first fluid, and at least one second segment, which comprises the second fluid. In this case, the first segment and the second segment are designed to be immiscible. In addition, the surface of the fluid flow channel facing the segmented fluid flow has at least one first solid surface and at least one second solid surface, wherein the first solid surface and the second solid surface periodically change at least twice along the longitudinal axis of the fluid flow channel. In this case, the at least one first solid surface has a wettability which is different from the at least one second solid surface.The simple design of the device reduces the formation of dead zones, as a result of which fouling and the formation of duct blockages are minimized, which in turn prevents the pressure loss and thus the energy requirement from increasing during operation. Furthermore, no complex control and regulating systems have to be used, as are used in conventional active mixers. By different arrangement of the different solid surfaces, a large design freedom for adapting the mixing intensity to the respective mixing task results.In addition, these solid surfaces can be manufactured easily and economically using simple technical processes established in the art (coating, etching, laser treatment). This also significantly simplifies potential scaling of the micromixer for adaptation to different mixing tasks.Additionally, the segmented fluid flow may be formed under laminar flow conditions. Due to the associated operation at a low flow rate, it is possible to allow long residence times for mass conversion in reactors and contactors and also to further reduce the pressure loss, so that the energy consumption of the apparatus during operation is significantly reduced. In this context, "low" flow speeds are understood to mean those flow speeds v which, with a constant characteristic length l of the flow channel and the dynamic viscosity η and the density ρ of the flowing fluid, result in a Reynolds number Re krit< 2320 (Re krit=( v*l*p) / η)). This means "laminar flow conditions" when Re is krit< 2320.Furthermore, turbulence-like vortices can be formed in the at least one first segment of the segmented fluid flow and or in the at least one second segment of the segmented fluid flow. As a result of these swirlings within a segment, each segment forms an ideally intermixed fluid on its own. As a result, for example, when used in a reactor, the chemical reactions can be predicted or carried out precisely and reproducibly.In addition, the segmented fluid flow may include at least one gaseous phase and at least one liquid phase. By forming the segments from different phases, a particularly stable segmented fluid flow can be generated. This in turn increases again the prediction accuracy and the reliability of the device. Here, "stable" is understood to mean that the segmentation of the fluid flow cannot be easily canceled, i.e. the different phases are particularly highly immiscible and have uniform phase boundary surfaces. In this context, "immiscible" should in principle be understood to mean that the two fluids do not bond to one another unlimitedly and therefore no homogeneous mixture is formed. In addition, the segmented fluid flow can also have at least two liquid phases different from one another.In addition, an additional phase, in particular a solid phase, can be formed in the first fluid and or the second fluid. By using multi-phase fluid segments, the field of application of the device can be extended to a plurality of areas. The use of catalysts which may be present as a solid can also be realized in this way.In addition, the fluid supply channels can open into at least two fluid flow channels connected in parallel. This parallel connection makes it possible to increase the efficiency of the device, since the number of intermixed segments can thus be increased. Alternatively, a plurality of devices for generating microflows can also be configured in parallel.Furthermore, the at least one first solid surface can have hydrophilic properties and the at least one second solid surface can have hydrophobic properties, in particular superhydrophobic properties. In this context, a "hydrophilic surface" is understood to mean that the contact angle between fluid and surface is <90°. "hydrophobic surfaces", on the other hand, have a contact angle of 90°-150°. Starting from a contact angle > 150°, "superhydrophobic surfaces" should be understood. The choice of suitable surface properties here depends substantially on the degree of intermixing within the respective segments. If extensive mixing is to be achieved, it is advantageous if the difference Δ between the contact angles of the two solid surfaces is as large as possible. In particular |Δ| is at least 10°, but particularly preferably at least 50°. Alternatively, the values for |Δ| are in a range of 20°-30°.In addition, the solid surfaces can periodically change at least twice in the radial direction of the fluid flow channel. A periodic pattern in the radial direction enhances the effect of generating microflows, so that improved mixing within the segments can be achieved.In addition, the fluid flow channel can have a constant diameter, i.e. a diameter which is constant over the length of the fluid flow channel in the direction parallel to the flow direction of the fluid. This makes it possible for the device to be produced in a simple manner and particularly cost-effectively. In this case, the fluid flow channel can have in particular a circular, oval or rectangular cross section perpendicular to the flow direction of the fluid flow. Nevertheless, any other geometry of the fluid flow channel cross section perpendicular to the flow direction of the fluid flow is also conceivable. In addition, the fluid flow channel can also have a diameter that varies over the length of the fluid flow channel in the direction parallel to the flow direction of the fluid.In a method for generating microflows, at least one first fluid flows through a first fluid supply channel and at least one second fluid flows through at least one second fluid supply channel into at least one fluid flow channel, wherein the fluids are designed to be immiscible. A segmented fluid flow is thereby formed in the fluid flow channel, wherein the segmented fluid flow comprises at least one first segment of the first fluid and at least one second segment of the second fluid. In this case, the segments are not mixed. Subsequently, the segmented fluid flow flows through the fluid flow channel along the longitudinal axis of the fluid flow channel, wherein the surface of the fluid flow channel facing the segmented fluid flow has at least one first solid surface and at least one second solid surface, which periodically change at least twice along the longitudinal axis of the fluid flow channel. In this case, the at least one first solid surface has a wettability which is different from the at least one second solid surface.As a result of the solids surfaces periodically changing along the longitudinal axis of the fluid flow channel, microflows are induced in the segments and the fluid films, which lead to improved mixing being achieved within the segments. At the same time, the method achieves the situation where a segmented fluid flow is also present after the fluid flow channel has been flowed through.The method can be carried out with the described apparatus, i.e. the apparatus is suitable for carrying out the described methods.Exemplary embodiments of the device are illustrated in the drawings and are described below with reference to FIGS. 1 to 4. Recurring features are provided with identical reference numerals.The following are shown: FIG. 1 shows a schematic view of the cross section of a fluid flow channel parallel to the fluid flow with solid surfaces alternating in the axial direction; FIG. 2 shows a schematic view of the cross section of a fluid flow channel parallel to the fluid flow with solid surfaces alternating in the axial and radial direction; FIG. 3 shows a schematic view of the cross section of a fluid flow channel parallel to the fluid flow with solid surfaces alternating in the axial and radial direction, with an alternative pattern in comparison to FIG. 2 ; and FIG. 4 shows a schematic view of a transition between a first solid surface and a second solid surface with a segmented fluid flow in a fluid flow channel.FIG. 1 illustrates a fluid flow channel 1 in longitudinal cross section, i.e. in cross section parallel to the flow direction of the segmented fluid flow, having a first solid surface 2 and a second solid surface 3 which are periodically arranged in the axial direction. In this exemplary embodiment, the first solid surface 2 is formed as a hydrophilic surface, here from glass, and the second solid surface 3 is formed as a hydrophobic surface, here from polytetrafluoroethylene (PTFE).In this case, a large number of different materials can also be used (metals, inorganic nonmetals (glasses, ceramics) and organic nonmetals (plastics)). Metals are mechanically stable and are particularly suitable for the production of printing apparatuses and can be structured well by abrasive methods. Ceramics, on the other hand, are particularly inert and therefore of particular interest for reactors. In addition, an active component can be introduced with established methods in order to modify the wetting properties. Glasses are also inert and the surfaces can easily be modified by a coating. Plastics can be used where large length microsystems can be produced relatively easily with commercial hoses (available in various dimensions and materials). Thus, in particular solid surfaces 2, 3 formed from metal, glass or plastic are suitable.In this case, the solid surfaces 2, 3 can be produced, for example, by the incorporation of different materials having different wetting properties (as in the exemplary embodiment shown) and or by the application of coating and or by the use of etching techniques and or laser ablation. It is always decisive that the solid surfaces have a difference Δ with respect to the contact angles between fluid and the respective solid surfaces, which is at least 10°.FIGS. 2 and 3 illustrate two further embodiment variants of the fluid flow channel 1, wherein now, in contrast to FIG. 1, the solid surfaces also change periodically in the radial direction. By forming an additional periodic pattern in the radial direction, the number of transitions between the first solid surface 2 and the second solid surface 3, i.e. in particular the change between hydrophobic and hydrophilic surface, is increased. Thus, better mixing in the segments and the fluid films that may be present can be achieved by increasing or enhancing the induced microflows.In this case, the segmented fluid flow has a multiplicity of first segments comprising a first fluid 4 and a multiplicity of second segments comprising a second fluid 5. The segmented fluid flow arises as a result of the alternating supply of the first fluid 4 and the second fluid 5 into the fluid flow channel 1. In this case, the segmented fluid flow is formed by microfluidic effects. By choosing an additional mixing system, its shape can be further influenced (e.g. smaller or larger bubbles and droplets).The two fluids 4, 5 are immiscible and are also not mixed during the flow through the fluid flow channel 1. This means that even after the flow through the fluid flow channel 1, the fluid flow introduced with regard to the original segmentation is unchanged. Nevertheless, it can also be provided that after the flow through the fluid flow channel 1, the sizes of the respective segments have been changed in a targeted manner. This means that there is still a segmented fluid flow which, however, has changed in size of the respective segments compared to the fluid flow before the fluid flow through the fluid flow channel 1.FIG. 4 illustrates the change in the contact angle of the segmented fluid flow in this embodiment variant of the second fluid 5, depending on the wettability of the first solid surface 2 and of the second solid surface 3. In addition, the segmented fluid flow flows in a fluid flow channel 1 having a circular cross section perpendicular to the flow direction of the segmented fluid flow. The fluid flow channel 1 has a diameter of 1 mm. The contact angle of the water in the glass capillary is at most 30°, whereas the contact angle in the PTFE channel is >100°. The flow velocity in this exemplary embodiment is 0.048 m / s. In principle, low flow velocity, i.e. <1 m / s, is preferably used.By changing the wettability within the fluid guide channel 1, additional microflows are generated in comparison to channels with a uniform wettability, which enable improved mixing within the segments of the two alternating fluids. This is especially clear in the case of segmented fluid flows with gas bubbles and liquid droplets which occur when immiscible fluids flow through the fluid flow channel 1 at low flow speeds, i.e. <1 m / s.FIG. 4 also shows that in the wetting glass capillary, i.e. the first solid surface 2, the gas bubbles, i.e. the first fluid 4, are curved outwards (concave), and the curvature changes from concave to convex on entry into the PTFE channel, i.e. on contact with the second solid surface 3. This change of shape induces additional flows in the gas or liquid phase. These bring about improved mixing within a phase and at the same time also promote mass transfer processes such as mass transfer from the gas phase into the liquid phase, for example in reaction or absorption processes. This does not mean that the segments are intermixed. This also improves the movement of solids suspended in the liquid, for example in the case of heterogeneous catalysis with suspended solids.At the same time, the change in the wetting properties can lead to the change or to the renewal of the stationary liquid films, which advantageously affect the reaction behavior, for example due to an improved mass transfer in otherwise saturated liquid films, or contributes to homogenization of the residence time for the fluid elements.It is important to emphasize that, with wetting mixers, process and process advantages also occur for other flow schemes, e.g. film,rinnal or parallel flow, on account of the additionally induced microflows.The essence of the invention is thus to utilize surfaces with different wettability for inducing additional flow patterns (microflows) in microfluidic flows and thus for improved mixing of fluids or fluid and solid in the segments of segmented fluid flows. Up to now, additional flow patterns have been realized exclusively by passive measures such as differently geometrically designed channel installations and mixing elements or spirally wound channels and active measures such as the introduction of acoustic, electric or magnetic fields.Thus, the advantages of the invention can consist in that deposits or dead zones can be avoided by a constant fluid flow channel diameter and that the construction of the device is simplified by eliminating complex control and regulating systems in comparison with conventional active mixers. The invention can thus be integrated in a simple manner into different existing method or plant concepts.This means that a high design freedom for adapting the mixing intensity to the respective mixing task arises due to the invention: the degree of flow influence can be controlled in various ways, e.g. by the intensity of the contact angle jump, as the height of |Δ|, by the number of axial contact angle jumps per fluid flow channel length or else by additional radial variation of the wettability of the fluid flow channel walls. In addition, the hydrophobic and super hydrophobic surfaces can be produced on various materials in a simple manner by coating, etching or laser surface structuring.In addition, the simple construction enables scaling, i.e. a simple scale transfer or enlargement of the apparatuses to the existing mixing task. Here, the scaling takes place according to the "scale-up by number-up" approach, i.e. the apparatus magnification is based on an increase in the number of channels while maintaining the underlying and just described physical phenomena.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedKR 100 864 880 B1

[0006]

Claims

Device for generating microflows, comprising: at least one first fluid supply channel in which at least one first fluid (4) can be guided and at least one second fluid supply channel in which at least one second fluid (5) can be guided, wherein the fluids are immiscible, and at least one fluid flow channel (1) into which the fluid supply channels open, wherein a segmented fluid flow can be guided in the fluid flow channel (1), which comprises at least one first segment comprising the first fluid (4) and at least one second segment comprising the second fluid (5), wherein the first segment and the second segment are immiscible, and the surface of the fluid flow channel (1) facing the segmented fluid flow has at least one first solid surface (2) and at least one second solid surface (3), wherein the first solid surface (2) and the second solid surface (3) periodically change at least twice along the longitudinal axis of the fluid flow channel (1), wherein the at least one first solid surface (2) has a wettability different from the at least one second solid surface (3).The microflow generation device of claim 1, characterized in that the segmented fluid flow is formed under laminar flow conditions.Device for generating microflows according to one of the preceding claims, characterized in that turbulence-like turbulences are formed in the at least one first segment of the segmented fluid flow and / or the at least one second segment of the segmented fluid flow.Device for generating microflow according to one of the preceding claims, characterized in that the segmented fluid flow has at least one gaseous phase and at least one liquid phase.Device for generating microflows according to one of the preceding claims, characterized in that an additional phase, in particular a solid phase, is formed in the first fluid (4) and / or the second fluid (5).Device for generating microflows according to one of the preceding claims, characterized in that the fluid supply channels open into at least two fluid flow channels connected in parallel.Device for generating microflows according to one of the preceding claims, characterized in that the at least one first solid surface (2) has hydrophilic properties and the at least one second solid surface (3) has hydrophobic properties, in particular superhydrophobic properties.Device for generating microflows according to one of the preceding claims, characterized in that the solid surfaces (2, 3) periodically change at least twice in the radial direction of the fluid flow channel (1).Device for generating microflows according to one of the preceding claims, characterized in that the fluid flow channel (1) has a constant diameter.Method for generating microflows, in which at least one first fluid (4) flows through a first fluid feed channel and at least one second fluid (5) flows through at least one second fluid feed channel into at least one fluid flow channel (1), wherein the fluids (4, 5) are designed to be immiscible, such that a segmented fluid flow is formed in the fluid flow channel (1), wherein the segmented fluid flow has at least one first segment comprising the first fluid (4) and at least one second segment comprising the second fluid (5), wherein the segments are not mixed, and subsequently the segmented fluid flow flows along the longitudinal axis of the fluid flow channel (1) through the fluid flow channel (1), wherein the surface of the fluid flow channel (1) facing the segmented fluid flow has at least one first solid surface (2) and at least one second solid surface (3), which periodically change at least twice along the longitudinal axis of the fluid flow channel (1) and the at least one first solid surface (2) has a wettability different from the at least one second solid surface (3).

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