EP2761240A1

EP2761240A1 - Device for transferring heat or mass, comprising hexagonal jet nozzles, and method for treating surface layers

Info

Publication number: EP2761240A1
Application number: EP12756377.3A
Authority: EP
Inventors: Philipp CAVADINI; Wilhelm SCHABEL; Philip SCHARFER; Lukas WENGELER
Original assignee: Karlsruher Institut fuer Technologie KIT
Current assignee: Karlsruher Institut fuer Technologie KIT
Priority date: 2011-09-29
Filing date: 2012-09-07
Publication date: 2014-08-06
Anticipated expiration: 2032-09-07
Also published as: WO2013045026A1; DE102011115257A1; EP2761240B1

Abstract

The invention relates to a device for transferring heat and mass, in particular for drying thin layers or coatings. The main focus of the invention is a jet array (3) with hexagonal jet nozzles (5) and the effusion openings (4) arranged around said nozzles. A particularly advantageous heat/mass transfer coefficient with excellent homogeneity is produced by the geometry of the spray and intake nozzles. Said device is therefore advantageous for drying sensitive components. The invention is additionally well-suited for deposition processes on surfaces. A drying hood that uses said device is also proposed. The invention further relates to a method for treating surface layers, in particular for gently drying organic (opto-)electronic components.

Description

Device for heat or mass transfer with hexagonal impingement jet nozzles and method for the treatment of surface layers

The present invention relates to a device for the heat and mass transfer, in particular for drying thin layers or coatings. In the foreground here is the hexagonal geometry of the impact jet nozzles and the effusion openings arranged around it, because in this arrangement a particularly favorable heat transfer coefficient can be achieved with excellent homogeneity. Furthermore, the invention relates to a method for the treatment of surface layers, in particular a method for gentle drying of organic (opto) electronic components.

Impact jets are widely used in industrial production processes where workpieces must be cooled, heated or dried. However, although impact blasting is able to force convective-driven processes, they produce a highly inhomogeneous distribution of heat and mass transfer coefficients.

In the drying of thin coatings of organic electronics, the homogeneity of the heat transfer is of great importance, because the demands on the surface quality of multifunctional, liquid phase-applied polymer films increase drastically with decreasing layer thickness. Inhomogeneities in the distribution of the mass transfer coefficient thus potentially lead to surface tension driven convection currents, the effect of which in the solidified film is detected by inhomogeneity in the surface topology leaves. The possibilities, area homogeneous and defined Mass transfer conditions are limited. Both the limiting case of drying in a static environment (limited by convection in the gas phase) and drying in parallel overflow (influenced by concentration boundary layer) lead to a local distribution of the mass transfer coefficient. A system that allows for homogeneous and defined mass transfer conditions must minimize both effects.

There are currently two competing solutions in the field of drying coatings by means of impact blasting. Slot and round nozzle systems are used. In both systems, inhomogeneities inevitably occur in the field of heat and mass transfer coefficients. The use of round dies in dry-belt drying processes leads to inhomogeneity in ribbon and transverse to the ribbon direction. For this reason, the market dominating systems are slot die systems, e.g. in DE 196 19 547 AI described. These have a well thought-out design only at the edges and in the belt direction on a gradient in the field of heat and material coefficients. The gradient in the ribbon direction is tolerable in low-sensitive products (in DE 196 19 547 A1: paper), which permit high belt speeds, since each region, despite inhomogeneity, ultimately experiences identical conditions.

Applicability limitations come to the fore when systems are to be processed that allow only low tape speeds. Here it can no longer be argued that identical conditions in ribbon direction also lead to uniform product properties. Another point to consider is the inhomogeneity in momentum exchange. At high flow velocities, the product may experience surface deformation due to the impinging fluid jets. This can lead to a reduction in performance. One way to increase the homogeneity of the drying process and to minimize the influence of the impact rays among each other, provides the local extraction of the injected fluid via effusion openings, by the fluid is discharged directly after the impact. Potentially, two designs are possible for the placement of the effusion openings - in the baffle plate in the nozzle plate. The design depends on the application and the geometric constraints derived from it.

Huber and Viskanta (AM Huber, R Viskanta (1994) Int J. Heat Mass Transfer, 37 (18), 2859-69) are concerned with circular effusion openings in the nozzle plate. The arrangement chosen by them corresponds to an equidistant nozzle array with staggered nozzles. They investigate the heat transfer in the vicinity of the central and thus theoretically not influenced by cross-flow nozzle. Their studies show that suction provides a higher degree of homogeneity compared to systems influenced by transverse flow. However, the hole spacing chosen by them with six times the nozzle diameter are relatively large. Despite extraction, this leads to strongly pronounced wall jet areas and thus to extended areas with relatively low heat transfer, which is detrimental to homogeneity.

Onstad et al. (AJ Ondstad, CJ Elkins, RJ Moffat, JK Eaton, (2009) J. Heat Transfer, 131 (8), 082201) investigated an equidistant nozzle array with a circular nozzle staggered array. In their study, they surround each impinging jet with six regularly arranged effusion openings (A _{ef f} usion / A _St ra _h i = 2.23). The field of the heat transfer coefficient is not displayed locally resolved, but only averaged values are given. However, speed measurements by means of magnetic resonance showed that the interaction of the radiation can be minimized with their neighbors and thus create a homogenous flow unit cells, ie it can succeed by local extraction that the rays behave in a field like single rays.

A drying device that meets the requirements for coatings in organic electronics must perform a more homogeneous drying work than the drying technologies known in the prior art. At present, large-area electronic components having bumps in peripheral zones due to inhomogeneous drying must be cut at these zones, or when the bumps in the film occur and are critical, then these regions can not be used. Large-area optical films are thus expensive. Furthermore, there is a need for a rapid or efficient drying process with good heat and mass transfer coefficients, which at the same time is gentle on the surfaces to be dried.

Proceeding from this, it is the object of the invention to overcome the stated problems in the drying of sensitive laminar coatings. In particular, a device is to be provided which is suitable for drying flat substrates and has good heat and mass transfer coefficients with at the same time homogeneous distribution. This device must be particularly suitable for uniformly and efficiently drying sensitive thin layers of organic electronics, so that as little as possible or as little as possible unevenness forms in the layer.

The present invention achieves the object by the apparatus claimed in claim 1 and the dry hood claimed in claim 5 and the method claimed in claim 7. Preferred embodiments of the devices or of the method are described in the dependent claims.

The subject of the present invention is a device for the heat and mass transfer to surfaces in impact blast systems with simultaneous extraction via effusion openings embedded in the impact blast field. The impact jet nozzles have a hexagonal shape and are distributed regularly and equidistantly over the impact radiation field, so that a lattice-like structure is formed. The impact jet nozzles serve to radiate a fluid for the heat and mass transfer to the substrate surface. Between the impact jet nozzles or around the impingement jet nozzles around the effusion openings are arranged, through which the radiated fluid is sucked.

In a preferred embodiment of the device, the effu sion openings are hexagonal arranged around the impingement jet nozzles, so that there is a honeycomb structure of impingement jet nozzles and effusion openings.

In a further preferred embodiment of the device, the effusion openings around the impingement jet nozzles are arranged in slot or gap form, which surround the impingement jet nozzles as completely as possible so that the individual impingement jet nozzles are separated from one another by the effusion slots or gaps. Optionally, the individual impingement jet nozzles can be held in position against one another via webs.

It has surprisingly been shown that due to the hexagonal geometry of the impact jet nozzles and targeted suction through directly adjacent effusion openings, the interaction effects between adjacent beams are reduced and the wall jet region is minimized. Through these densely grouped fields of hexagonal impact jet nozzles and the directly adjacent effusion openings the possibility is created to produce a nearly flat impact region. The effects resulting from this geometry are a very homogeneous distribution of the heat and mass transfer coefficients over the entire impact blast field and a good distribution of the fluid flow, which also unevenness on the substrates to be dried can be prevented.

Preferably, the device for the heat and mass transfer is a drying device. This drying device can be used in all processes in which an efficient and homogeneous drying of flat substrates must take place. This drying device is ideal for drying organic (polymer) electronics.

The device according to the invention can likewise be a sublimation, condensation or deposition device in which a substance can be deposited on a substrate from the gas phase or in which a substance sublimes into the gas phase. The device according to the invention is also advantageous for these applications since, because of the high heat and mass transfer coefficients and their homogeneous distribution over the impact radiation field, longer residence times of the substrate are achieved

Can achieve impact beam field.

The invention further relates to a drying hood equipped with a device for the heat and mass transfer according to the above description. The hood includes an airtight outer housing, wherein the heat and mass transfer device is disposed at the distal end of this housing. The housing also includes ports for exhausting process gas from within this housing. Furthermore, at least one connection for pressurizing process gas is arranged under pressure on the housing, which presses the impact jet nozzles of the device at the distal end via a process gas distributor. supplied with process gas. The entirety of the process gas connection, process gas distributor and impingement jet nozzles is hermetically separated from the areas of reduced pressure inside the housing. The housing interior, so the area of reduced pressure is connected to the effusion openings at the distal end. This ensures that the extracted process gas takes place via the interior of the housing and the connections for suction. With the aid of this construction of the drying hood, the process gas can be emitted to the outside in the distal direction and the emitted process gas can be sucked from the distal direction into the infusion openings.

The drying hood according to the invention is advantageous, since thus a movable device, which includes all the advantages of the device for the heat and mass transfer can also be moved in the direction of the components to be dried, in contrast to the assembly line system, in which the component is transported past a drying device. Batch drying with a resting substrate is not possible with other systems.

In a preferred embodiment of the drying hood, the connection of the effusion openings with the connections for sucking off process gas via the inner cavity of the outer housing is directly ensured, thus no further distributor structure is necessary.

In a further preferred embodiment, the connection of the impingement jet nozzles with the connections for the process gas is ensured via an inner housing, which is hermetically closed in the outer housing. By means of this distributor structure, the individual impingement jet nozzles, fed by a plenum, are supplied with identical inflow conditions.

The invention also includes a method of treating surface layers on workpieces using one of Devices described above. A sheet workpiece (substrate) provided with a surface layer to be treated is brought into contact with the device. The bringing into contact does not mean touching the two objects, but that the substrate remains at a certain distance from the device, or is transported past during the continuous assembly line process.

In the following steps, a volume flow is applied to the surface of the workpiece, at a distance such that the impact jets from the impact jet nozzles reach the surface of the workpiece to be treated and the exhausted fluid, preferably a process gas, is sucked out again by the effusion nozzles.

In a preferred embodiment, this method is a method of drying wet surface layers on workpieces.

In a further preferred embodiment, this method is a deposition method for applying substances from the gas phase to a surface layer of a workpiece. For example, these deposition methods may also be sublimation or condensation processes.

This distance is individually defined as required and depends on the size of the nozzle, the configuration of the impingement jet field, the distance between the nozzles, the shape of the nozzles, the fluid flow rate, the substrate to be dried (gentle or rapid drying), the belt speed, temperature, etc The person skilled in the art does not have to be inventive in order to adapt the parameters for a drying process of the process conditions. Basically, however, the distance should be chosen so that the core jet of the collision jet (region in the free jet which is still unaffected by the Environment is) when hitting the surface of the substrate is still preserved.

This procedure leaves open, whether the workpiece on a

Conveyor belt is transported past the drying device or the drying device is approached in the form of a drying hood the stationary workpiece (batch-wise

Dry) .

In a preferred embodiment of the method, the volume flow can oscillate in such a way that the fluid flows alternately out of the impact jet nozzles and the effusion nozzles and the suction is taken over by the respective other nozzles. This means that there is no longer any fixed allocation between injection and exhaustion. This is because areas under the exhaust have low transition coefficients. The oscillation now allows to be homogeneous here on average. If the method is used for deposition processes or condensation or sublimation processes, the oscillation increases the residence time of the mass flow on the substrate.

The invention will be explained below with exemplary embodiments and the following figures.

Fig. 1 collision beam fields and their resulting distribution of the heat transfer coefficient at the baffle.

Fig. 2 Relative frequency of the heat transfer coefficient at the baffle in a round nozzle field and a honeycomb field.

Fig. 3 Schematic representation of a drying hood with honeycomb panel.

Example 1: Distribution of the heat transfer coefficients In the following, investigations on systems of impact radiation fields are compared. In Fig. 1, upper row, the investigated impact beam fields are shown. In black color the impact jet nozzles are shown, while the effusion openings are highlighted in light gray color. The lower row in Fig. 1 represents the corresponding ones

Impact beam fields resulting heat transfer coefficients, as they are distributed over the area.

Fig. 1 a) - c) corresponds to systems of the prior art. Fig. 1 a) is a round nozzle field without additional suction, Fig. 1 b) a round nozzle field with additional suction and

Fig. 1 c) corresponds to a slot nozzle field with additional suction. The system according to the invention with hexagonal impact jet and effusion nozzles with additional extraction is depicted in FIG. 1 d). The existing investigations were carried out by means of CFD simulations and serve the qualitative evaluation of the distributions of the heat transfer coefficient at the impact surface.

The system in Fig. 1 a) does not allow any additional removal of the fluid. Here, the fluid can only escape to the sides. Clearly visible are the interaction effects of the individual impact rays. The rays are deflected and no longer form defined stagnation points. Shown is a system with a very low number of beams. If you increase the expansion for a similar system, the outer beams are completely deflected and a channel flow will form. It follows that this system creates a very inhomogeneous boundary condition for drying systems.

The systems acc. Fig. 1 b) and c) take into account an additional discharge of the injected fluid. The configuration in Figure 1 (b) is similar to that just described, but here each jet is surrounded by exhaust ports. The system in FIG. 1 c) corresponds to a slot nozzle arrangement. It can be clearly seen that in the round nozzle system due to the local discharge

Cross flow reduced and thus the homogeneity could be increased.

It can be seen that in systems with round nozzles as well as with slot dies inevitably comes to inhomogeneities in the field of heat and mass transfer coefficients. The use of round nozzles leads to inhomogeneity in band and transverse to the band direction. For this reason, the systems dominating the market are slot die systems. These have a well thought-out design only at the edges and in the belt direction on a gradient in the field of heat and material coefficients. The gradient in the ribbon direction is tolerable in low-sensitive products that allow high belt speeds, since each area eventually experiences identical conditions despite inhomogeneity. Applicability limitations come to the fore when systems are to be processed that allow only low tape speeds. Here it can no longer be argued that identical conditions in ribbon direction also lead to uniform product properties. Another point to consider is the inhomogeneity in momentum exchange. At high flow velocities, the product may experience surface deformation due to the impacting jets. This can lead to a reduction in performance.

The representation in FIG. 1 d) represents the field of the heat and mass transfer coefficient at the baffle plate in the hexagonal nozzle field according to the invention. It can clearly be seen that, although under the chosen conditions, a certain gradient occurs transversely to the belt direction, this is a lot lower gradient in the tape direction brings with it. Of Furthermore, the distribution of the heat transfer coefficient is much more homogeneous than in round or slot nozzle systems.

FIG. 2 illustrates the homogenization of the distribution on the basis of the representation of the relative frequencies of the heat transfer coefficients over the flowed-on area. It becomes clear that the distribution of the heat transfer coefficients occurring in the honeycomb structure presented here is significantly narrower in comparison to a round nozzle field (see FIG. 1 a) corresponding to the current state of the art. This is, from the point of view of a uniform energy input, an essential criterion in the selection of a nozzle array. Here, narrow distributions are preferable. The expected heat input and / or mass transfer to a flat surface is primarily much more uniform, at the same time it should be at least equal to or even higher for a given mass flow and a fixed number of nozzles.

Example 2: Drying hood

In Fig. 3 a) is shown schematically a technical realization of a drying hood using a hexagonal nozzle geometry according to the invention. The hood comprises an outer housing 1, on which a device for extracting process gas (suction tube) 2 from the interior of this housing 1 is arranged. At the distal end of the outer housing 1 there is an impact radiation field 3 with hexagonal impact jet nozzles 5 and the effusion openings 4, which in this embodiment surround the respective impact jet nozzles 5 in slot form. In Fig. 3 b) the collision beam field 3 is shown from a distal point of view. Here, the hexagonal impact jet openings and the slot-shaped interspaces of the effusion openings 4 are visualized. In the outer casing 1, there is disposed an airtight inner casing 8 serving as a distributor for the process gas from the ports for the process gas 6 to the respective impingement jet nozzles 5. This type of feeding of the process gas to the impact jet nozzles 5 through a plenum ensures identical flow conditions for the individual nozzles. The process gas can only escape via the impact jet nozzles 5 in the distal direction. The impact jet nozzles 5 themselves have an elongated shape and are arranged parallel to each other at a certain distance, so that a gap is created between the individual nozzles. In its extension to the distal end, this intermediate space has the function of the effusion openings 4. The effusion openings 4 or the intermediate spaces are in direct contact with the area of reduced pressure in the inner cavity 7. Thus, in the area of the effusion openings 4, the greatest possible homogeneity in the pressure - or vacuum distribution over the entire impact radiation field 3 achieved.

In order to ensure that in this embodiment of the drying hood, the pressure loss of the individual effusion openings 4 is kept low on the impact radiation field 3, the length of the impact jet nozzles 5 can be varied via the impact radiation field 3, in such a way that arranged in the middle of the field As a result, it can be ensured that the suction effect on the effusion openings 4, triggered by the reduced pressure in the inner cavity 7, in the central area of the impact radiation field 3 lead to the same mass flows as in the peripheral areas. This particular embodiment has the effect that the static pressure in the area of the impact radiation field 3 is the same everywhere. The same effect can also be achieved if the impact jet nozzles 5 are sufficiently long.

Claims

Patent claims:

1) Device for heat and mass transfer to surfaces, comprising a regular grid-shaped arrangement of

i) hexagonal impact jet nozzles (5) in an equidistant arrangement, with which a fluid can be jetted onto the surface to be dried, and

ii) Effusion openings (4) which surround the impact jet nozzles (5) and through which the extruded fluid can be sucked off.

2) Device according to claim 1, wherein the effusion openings

(4) are arranged hexagonally around the impact jet nozzles (5), so that there is a honeycomb-shaped structure of impact jet nozzles

(5) and effusion openings (4).

3) Device according to claim 1, wherein the effusion openings

(4) are arranged around the impact jet nozzles (5) in a slot or gap shape, which surround the impact jet nozzles (5) as completely as possible, so that the individual impact jet nozzles

(5) are separated from each other by the effusion slots or gaps.

4) Device according to one of claims 1 to 3, wherein the

Device for heat and mass transfer is a drying device, a condensation device, a sublimation device or a separation device.

5) Drying hood comprising an airtight outer housing (1) with connections for suction (2) of process gas from the interior of this housing (1) and a device for heat and material transfer (3) according to one of claims 1 to 4, which on Distal end of the housing is arranged, wherein the effusion openings (4) of the device (3) are connected to the suction connections (2), and wherein the WO 2013/045026 - 15 - PCT/EP2012/0037S1

Impact jet nozzles (5) of the device (3) are connected to connections for introducing process gas (6), so that the process gas can be emitted outwards in the distal direction and the emitted process gas can be introduced into the effusion openings (4) from the distal direction.

Drying hood according to claim 5, wherein the connection of the effusion openings (4) to the connections for suction (2) of process gas is ensured via the inner cavity of the outer housing (7) and the connection of the impingement jet nozzles (5) to the connections for the process gas ( 6) is ensured via an inner housing (8), which is hermetically sealed in the outer housing (1).

Method for treating surface layers on workpieces comprising the following steps: i. Providing a device according to one of claims 1 to 6,

ii. Providing a flat workpiece to be treated,

iii. bringing the surface layer of the workpiece into contact with the device and applying a volume flow to the surface of the workpiece, at such a distance that the impact jets from the impact jet nozzles (5) reach the surface of the workpiece to be treated and the ejected process gas through the effusion nozzles (4) is sucked off again,

wherein the workpiece is either transported past the device on a conveyor belt or the device is approached to the workpiece in the form of a hood.

8) Method according to claim 7, wherein the method is a drying method of wet surface layers. 9) Method according to claim 7, wherein the method is a deposition method for applying substances from the gas phase to a surface layer.

Method according to one of claims 7 to 9, wherein the volume flow oscillates in such a way that the process gas flows alternately from the impingement jet nozzles (5) and the effusion openings (4) and the suction is taken over by the other nozzles.