WO2011023344A1

WO2011023344A1 - Microstructure evaporator

Info

Publication number: WO2011023344A1
Application number: PCT/EP2010/005142
Authority: WO
Inventors: Jürgen Brandner; Ulrich Schygulla; Eugen Anurjew; Edgar Hansjosten
Original assignee: Karlsruher Institut für Technologie
Priority date: 2009-08-31
Filing date: 2010-08-21
Publication date: 2011-03-03
Also published as: DE102009039397A1; DE102009039397A8

Abstract

The aim of the invention is to provide a microstructure evaporator with increased efficiency. To this end, a microstructure evaporator is provided with a fluid inlet (10, 15), a vapour outlet (16) and at least one evaporation stage heated by heating means and comprising at least one nozzle opening (2) respectively having at least two fluid admissions (3) oriented in relation to each other.

Description

Microstructured evaporator

The invention relates to a microstructure evaporator preferably for the continuous evaporation of liquids or aerosols according to the first claim.

Evaporators are procedural devices for the transfer of liquids or aerosols in a vapor state, the supply of preferably thermal energy is absolutely necessary. An evaporation of a liquid or a liquid fraction occurs when the temperature dependent on the temperature and the ambient medium vapor pressure exceeds the ambient pressure. Consequently, thermally operated evaporators for continuous evaporation have a heat transfer surface through which thermal energy is transferred into the medium to be evaporated.

Microstructured evaporators are characterized by a microstructuring of the heat transfer surface, for example by a parallel arrangement of a plurality of microchannels or by heat transfer structures, which are impinged by the substance or substance mixture to be vaporized. The microstructuring increases in particular the specific surface and thus improves the heat transfer to the substances to be evaporated. Microstructured evaporators come in particular as micro-evaporator for execution, which are characterized not only by small dimensions, but often by the production with microstructure techniques.

DE 101 32 370 A1 discloses a known micro-evaporator type having a multiplicity of long, preferably straight microchannels with a constant flow cross-section. In this case, a first evaporation process is carried out by heating in at least one first heater channel and, after homogenization of the heated medium in an intermediate volume, further heating up to the desired evaporation in at least one second heater channel. The microstructure evaporator has a layered structure. DE 103 35 451 A1 also describes a method with a micro-evaporator with channels for the guidance and evaporation of a substance mixture to be evaporated. The microevaporator has hydraulic channel diameters of 5 to 100 μm and a specific evaporator area of at least 10 ³ m ² / m ³ .

Furthermore, DE 10 2005 017 452 A1 shows a micro-evaporator with channels for the evaporation of a liquid with cross-sectional dimensions in the sub-millimeter range, which are arranged next to one another on a plane. Starting from an entry volume, the channels serving as a heat transfer surface radiate a flat, trapezoidal region in a radiating manner and terminate in a common vapor collection chamber spanning all the channel outlets. The homogenizing in the Dampfsammeikammer vapor is then discharged via a common outlet.

However, laminar fluid flow fractions in microchannels create distinct boundary layers relative to the flow cross-section which, in turn, limit flow velocity and / or significantly increase flow resistance with flow velocity.

Also results for the evaporation in microchannels, a limiting speed as a function of the enthalpy of evaporation of the medium to be evaporated. If the flow velocity of the medium in a microchannel corresponds to this limit velocity, complete vaporization of the medium to a wet vapor takes place. The limit velocity thus dictates the residence time of the medium in the channel required for complete evaporation. Overheating of the steam takes place only at flow velocities below the limiting speed, ie at longer residence times. If, on the other hand, the flow rate of the medium in a microchannel exceeds this limiting speed, only incomplete evaporation takes place. Both of the aforementioned limitations result in limiting the efficiency of microstructure evaporators.

Based on this, the object of the invention is to propose a microstructured evaporator for the evaporation of fluids with increased efficiency. In particular, it is intended to achieve a very homogeneous vapor quality, i. the liquid content and / or droplet content in the steam should be as low as possible even before overheating. Furthermore, the microstructure evaporator should not only allow overheating of the steam, but also a good controllability.

The object is achieved with a microstructured evaporator with the features of claim 1. Advantageous embodiments are given in the subclaims.

The solution of the problem provides a heat exchanger, preferably a microstructured evaporator with at least one evaporation stage, comprising a nozzle opening with at least two mutually aligned fluid feeds. The fluid feeds are preferably fluid channels with heat transfer surfaces as walls.

An evaporation stage can also have a plurality of said nozzle openings, which are connected in parallel to one another and have identical operating parameters such as pressure drop, flow rate, mixing behavior and temperatures and preferably also dimensions. It is advantageous that the vapor composition of all parallel-connected nozzle orifices of an evaporation stage is identical or almost identical and in a stationary operation is constant and thus a subsequent use or further evaporation such. is supplied in subsequent evaporation stages.

One goal is continuous evaporation with or without overheating with consistent and homogeneous steam quality. To ensure a continuous as complete as possible Overheating of the steam, ie from the wet steam area into the

In the area of the superheated steam, it is preferable to provide evaporation stages for the evaporation (at boiling temperature) of liquid constituents and for the subsequent overheating of vapor constituents to temperatures above the boiling temperature. For this purpose, at least two of the aforementioned evaporation stages are to be provided in series, which are passed through by the medium to be evaporated in succession. Preferably, at least a first stage of said evaporation of liquid components, while at least one second stage is predominantly used for overheating.

An increasing number of evaporation stages with expansion nozzles (expansion stages) is advantageous for continuous evaporation progress. By subdividing into a plurality of smaller expansion and evaporation steps, preferably combined with each additional mixing or homogenization, in particular the likelihood that uncontrolled vapor bubbles form in the fluid channels, which accelerate in the direction of the steam outlet or against it and with these vapor bubbles unvaporized liquid portions be carried away. Furthermore, an increasing number of expansion stages allow a higher pressure differential between fluid inlet and vapor outlet of the evaporator. In addition, the pressure gradient is divided into several expansion steps, which at the respective expansion nozzles lower pressure drops and thus generally lower maximum flow velocities occur in the nozzles. The speed of sound as the upper limit for the flow velocity in a nozzle is reached much later with small pressure gradients, which advantageously additionally causes an increase in capacity and an increase in efficiency. Preferably, the Mikrosturkturverdampfer on at least three, more preferably at least six, more preferably nine evaporator or expansion stages between fluid inlet and steam outlet.

The alignment of at least two channels against each other means that the channels or the imaginary extensions of these after occurs from the channels downstream directed merge or overlap in any other way. Preferably, the channels or the lines of symmetry of the channels intersect. This results in a collision of at least two streams from different flow directions and thus to a turbulent mixing of these streams.

The mixing area, i. the region in which this mixing takes place preferably discharges directly into a nozzle, via which the mixed material streams still present in the turbulent state are expanded together. In front of the nozzle in the mixing zone, there is initially a congestion of the mixed material flows and thus an increased dynamic pressure in the mixing zone, which on the one hand leads to a delayed evaporation and thus to an increase in the liquid content and on the other hand promotes turbulence in the mixing. After mixing, the mixed stream expands on leaving the nozzle in an expansion region, wherein it comes despite adiabatic expansion by spontaneous pressure reduction to an accelerated excess of the vapor pressure and in particular to a simultaneous evaporation in the mixed Stoffström. Preferably, the expansion region is heated to counteract cooling by said adiabatic expansion.

In a further embodiment, the steam is deflected immediately in the expansion region by a steam deflection and derived in subsequent FIU idführungen, while opposite the nozzle in the expansion region, a preferably heated baffle is provided. The liquid or recondensed vapor constituents of the expanded material stream that are not or only insufficiently diverted into the subsequent fluid guides because of their inertia impinge on this baffle surface and evaporate again.

Preferably, the entire microstructure evaporator with all evaporation stages as a channel structure on a substrate is preferably made of a good heat conductor such as metal. This is done preferentially by incorporating grooves for the guide (for fluids and

Vapors) such as said fluid guides, nozzles, mixing areas and expansion areas in the substrate.

A particularly advantageous embodiment comprises a concentric arrangement of the evaporation stages on a heated substrate about a central fluid inlet. In particular, in contrast to unidirectionally oriented evaporator designs with constant fluid cross sections of basically radially increasing expansion, there is an increasing space available for receiving the expanding vapor.

The invention will be explained in more detail below with reference to advantageous embodiments with the following figures. Show it

1a and b show a first embodiment with fluid channels with annular walls arranged around the fluid inlet,

A second embodiment with fluid channels with elliptical arranged around the fluid inlet walls and

3a to c possible application examples for the aforementioned embodiments.

The dargestellen embodiments each have a plurality of evaporation stages, exemplified in Fig. Ib as an enlarged detail of a marked in Fig. Ia section 1 (schematically in detail). The enlarged detail shows a nozzle opening with two mutually aligned fluid feeds 3. The two fluid feeds open into a mixing region 4 in front of the nozzle opening. The fluid streams supplied by the fluid feeds 3 during an evaporation operation are mixed in the mixing zone 4 and thus homogenized, wherein a turbulent flow is preferably established there by the mutually oriented fluid streams. The resulting merged common fluid flow leaves the mixing area through the nozzle opening 2 in an expansion region 6, wherein it passes through the nozzle opening to an expansion and thus spontaneous evaporations in the fluid flow. The evaporation stages with the respective fluid feeds 3 and nozzle openings 2, preferably also with respective mixing areas 4 and / or expansion areas 6, are heated by heating means, preferably solid-state, electrically-ohmic heaters.

1 a shows an embodiment of an evaporator insert 7 of a first embodiment of the microstructured evaporator in a schematic plan view. The evaporator insert comprises a disc-shaped substrate 8 and microstructures 9 placed thereon, which form the walls (webs) for the fluid guides, such as the aforementioned fluid feeds 3, nozzle openings 2, mixing areas 4 and expansion areas 6. The evaporator stages are arranged concentrically around a central fluid inlet 10, wherein each evaporation stage in the exemplary embodiment in each case has two opposite nozzle openings 2, each with two fluid feeds 3. Starting from a central fluid inlet 10, the fluid to be evaporated flows through a first nozzle arrangement 11 into the fluid feeds 3 of the first evaporation stage and from there via the respective nozzle openings into the following evaporation stages arranged concentrically in a circle around the fluid inlet. In each case, two opposite nozzle openings 2 (at 180 ° to each other) are provided per evaporation stage, which are each offset by 90 ° to the fluid inlet openings to the nozzle openings of the adjacent evaporation stages and thus a constant length of fluid feeds between two nozzle openings in an evaporation stage to ensure. There are also three, four or more nozzle openings per evaporation stage possible, but which are preferably arranged uniformly and at an equal angle to each other on the circumference of the concentric evaporation stage. Essential for the same length of fluid supply per evaporation stage is that the nozzle openings 2 of adjacent evaporation stages each because in the bisector to the said angle between two

Nozzle openings is arranged offset from each other.

In the expansion region, in the exemplary embodiment illustrated in FIGS. 1a and b, a direct flow towards a preferably heated baffle 12 on the wall of the opposite microstructure (FIG. 1b) takes place. While already vaporized or gaseous components are already deflected immediately after leaving the nozzle opening 2 in subsequent fluid supplies, meet mass-carrier liquid components on the baffle and are evaporated there.

FIG. 2 shows a further embodiment which corresponds in its basic construction to the embodiment shown in FIGS. 1a and b, but differs in that the structures 9 are arranged concentrically around the fluid inlet 10 in a non-circular, elliptical manner. The nozzle openings are located on the shortest ellipse axis. In this case, tapered fluid cross-sections are also realized in the fluid feeds 3 to the nozzle openings 2, whereby the flow velocity increases in the tapered fluid feeds to the nozzle openings or to the mixing areas 4 and thus promotes in particular a turbulent mixing in front of the nozzle openings. However, this embodiment has a greater distance between the nozzle opening 2 and baffle 12 and thus worsens in this area the separation of liquid and already vaporized phases.

In an exemplary evaporation of water, for example, it is assumed that the wet steam expands through the nozzle openings and divides into two partial streams. These partial streams are passed on via the fluid feeds and collide against each other at the next two downstream nozzle openings, so that at these positions a mixing of the liquid with the steam, which supports the evaporation process. In the illustrated embodiment with the microstructured blanks with many len rings exist an increasing number of evaporation stages, so it can be assumed that the evaporation process is quasi-continuous and thus more effective overall feasible than in a geometry with few rings (evaporation stages). If microchannels with a non-constant flow cross-section (see FIG. 2) are used, as is the case with the concentrically arranged ellipses, the wet steam is additionally accelerated by reducing the flow cross-section and the mixing effect is enhanced.

3a to c represent exemplary applications for the aforementioned embodiments of the evaporator cartridge.

One or more microstructured evaporator inserts 7 are used in the embodiments shown in Figure 3a or b in a cylindrical recess of the adapter shell 5 and placed together on a heating surface 13. Heating surface and adapter part are mutually sealed by sealing rings 14. In this case, the adapter upper part comprises a fluid connection 15 for the fluid inlet 10 as well as one or more steam outlets 16. The steam flows radially outwardly into an annular channel 17 and from there into the steam outlet 16 as shown in the arrows through the nozzle openings from the evaporator insert.

3 a shows the embodiment with an evaporator insert 7, FIG. 3 b shows an embodiment with a plurality of stacked evaporator inserts 7 one above the other. In a stacked arrangement, the fluid inlets 10 pierce the substrates and allow access of the fluid to be evaporated also to subsequent evaporator cartridges. In principle, both sides of the evaporator inserts arranged heating surfaces and in the case of the embodiment according to. Fig.3b heating surfaces between two evaporator cartridges within the scope of the invention is not excluded.

FIG. 3 c, on the other hand, shows an embodiment in which an evaporator insert is structured on both sides with the abovementioned evaporation stages and also has openings for electrical or fluidic operation. ne heating cartridges 18 are provided in the substrate. A separate heating surface as described in the aforementioned embodiments is not absolutely necessary and can be replaced by a lower housing part 19.

List of reference numbers:

1 marked section

2 nozzle opening

3 fluid supply

4 mixing area

5 adapter shell

6 expansion area

7 evaporator use

8 disc-shaped substrate

9 microstructure

10 fluid inlet

11 first nozzle arrangement

12 baffle

13 heating surface

14 sealing ring

15 fluid connection

16 steam outlets

17 ring channel

18 heating cartridge

19 housing base

Claims

Claims:

1. microstructured evaporator comprising a fluid inlet (10, 15), a steam outlet (16) and at least one heated by heating evaporation stage with at least one nozzle opening (2) each with at least two mutually aligned fluid supply lines (3).

2. microstructure evaporator according to claim 1, characterized in that between each nozzle opening (2) and the respective fluid supply lines (3) each have a mixing region (4) is arranged.

3. microstructure evaporator according to claim 1 or 2, characterized in that the fluid supply lines (3) to the nozzle opening (2) taper in the flow cross-section.

4. Microstructure evaporator according to one of the preceding claims, characterized in that the nozzle opens into a heated expansion region (6).

5. microstructure evaporator according to claim 4, characterized in that the expansion region (6) has a steam deflection and relative to the nozzle opening (2) heated by a heating means baffle surface (12) for liquid vapor components

6. microstructure evaporator according to one of the preceding claims, characterized in that at least one evaporation stage has at least two parallel nozzle openings (2) each with fluid feeds (3) having identical dimensions.

7. microstructure evaporator according to one of the preceding claims, characterized in that the heating means are formed by at least one planar heating surface on which the evaporation stages is arranged.

8. Microstructure evaporator according to one of the preceding claims, characterized in that the evaporation stages are incorporated as channel structures on or in a substrate (8).

9. microstructure evaporator according to claim 8, characterized in that the substrate has heating means.

10. microstructure evaporator according to one of the preceding claims, characterized in that the evaporation stages are arranged concentrically around the fluid inlet.

11. microstructure evaporator according to claim 10, characterized in that the fluid channels have annularly arranged around the fluid inlet walls.

12. microstructure evaporator according to claim 10, characterized in that the fluid channels have elliptical arranged around the fluid inlet walls.