METHOD AND APPARATUS FOR ATOMIZING LIQUIDS

Abstract: In a method of atomizing liquids, a first gaseous medium is caused by ejector action to be sucked along with, and mixed up with, a second flowing gaseous medium, the first gaseous medium being caused to entrain liquid medium, which is caused by said ejector action to be sucked into the flow path of the first gaseous medium, so that the liquid medium is mixed with, and atomized in, the first and second gaseous media. An apparatus for this purpose comprises a nozzle element (1), means (14, 15) for supplying the second gaseous drive medium to the nozzle element (1) and means (4, 10) for supplying liquid which is to be atomized. Inlet means (2, 18) for the first gaseous medium are arranged for sucking it into the nozzle element (1) by means of said ejector action, and the liquid supply means comprise container means (4, 9) with an at least partially open upper part opening out in connection with the incoming flow path of the first gaseous medium, so that liquid in the container means (4, 9) can be caused by said ejector action successively to rise above the container upper part and into said flow path, and to be continuously entrained by the first gaseous medium flowing into the nozzle for being atomized in the mixture of the gaseous media.

Description: METHOD AND APPARATUS FOR ATOMIZING LIQUIDS The present invention relates to a method and apparatus for atomizing liquids for different purposes, e.g. forming a cooling, humidifying or spraying mist. In the steel industry, long rows of jets are customarily used for cooling steel plates, the jets spraying water in an atomized form onto the plate. It is desirable that the water droplets are as small as possible in order to achieve the most effective cooling possible. The jets or nozzles cus¬ tomarily used have fine orifices, through which water is forced with the aid of compressed air at high pressure (usu¬ ally about 600 kPa). This requires the use of water purified to a high degree. In spite thereof there are often still problems with the nozzles clogging, which is partly caused by the hot environment. In most cases the water is not suffi¬ ciently finely divided either. Providing the required high air pressure is also expensive in this connection. For examples of different cooling arrangements in the prior art it may be referrred to DE-A1-2804982, DE-A1- 3523829, SE-B-355 507, US-A-3,533,261, and US-A-4,226,108. The present invention has the object of providing an improved method and apparatus for atomizing liquid, which in a simpler, more effective and operationally reliable way than previously atomizes cooling water to the desired extent without using extreme air pressures, but which can also be used for other purposes where atomizing a liquid is required, e.g. for humidifying in green houses, or spreading artificial fertilizer mists in them, moistening timber stocks etc. Such a method and apparatus has the distinguishing features dis¬ closed in the following claims. The method and apparatus in accordance with the inven¬ tion are partially based on the so-called ejector or jet pump principle (e.g. as described in "Svensk Pumpmarknad" pub- lished by EuroContact AB, 1977, pp 212-215). According to a basic concept of the invention, a drive gas (e.g. air) flo¬ wing into a nozzle is allowed to suck with it, in per εe known manner by ejector action, an extraneous, gaseous medium (e.g. ambient air), the sucked-up medium being caused to entrain liquid which is sucked or forced by said ejector action into the flow path of the medium. In this way, excel- lent atomizing of the continuously entrained liquid in the mixed gas flow can be obtained, so that an effective liquid mist can leave the nozzle outlet. In the following the invention will be described in more detail with regard to some special embodiments. Reference will be made to the accompanying drawings, where Figure 1 is a cross-sectional view of an embodiment of a liquid atomizing apparatus in accordance with the invention, intended for spraying substantially downwards; Figure 2 is a side view of the apparatus in Figure 1; Figure 3 is a cross-sectional view of an apparatus corresponding to the one in Figures 1 and 2, and intended for spraying substantially upwards; Figure 4 is a side view of the apparatus in Figure 3, and Figure 5 is a side view of a pair of apparatuses similar to the ones in Figures 1 and 2, and 3 and 4, respectively, where they have been adapted for cooling a steel plate. The liquid atomizing apparatus illustrated in Figures 1 and 2 comprises a substantially cylindrical nozzle element 1 having an inlet opening 2 and an outlet opening 3. At its inlet part, the nozzle element 2 is surrounded by an annular container 4 for a liquid, e.g. cooling water, which is to be atomized and sprayed out through the nozzle element 1. The liquid container 4 is here implemented integrally with the nozzle element 1 and is formed by a flange portion 5, from the outer edge of which a side wall 6 extends up¬ wards, so that an annular space is defined between the upper part of the nozzle element 1 and the container wall 6. A concentric partition wall 7, extending downwards form a container partial upper part 8 towards , but not up to, the bottom of the container 4, i.e. the flange 5, divides the container 4 into two annular chambers in mutual communi¬ cation in the lower part thereof. By a thickening of the nozzle element wall, the inner wall of the inner chamber, i.e. the outer wall of the nozzle element 1, has its upper portion projecting radially somewhat outwards, so that a relatively narrow, annular gap 9 is defined between the partition wall 7 and the upper part of the nozzle element. A liquid supply pipe 10 connects to the annular container 4 in its lower part. The upper part 8 of the container, this part only covering the outer annular chamber, is provided with one or more unillustrated openings to enable the outer chamber to communicate with the surrounding air pressure. By suitable means, not described in any detail here, a predetermined constant liquid level 11 is maintained in the outer chamber, and also in the inner chamber when the apparatus is in an inactive state, as will be described in more detail below. The interior of the nozzle element 1 has a converging inlet portion 12, a tubular mixing portion 13 and a weakly converging diffuser portion 13a, which is terminated at the nozzle opening 3. A jet 14 fixed in the end of a gas supply pipe 15 thrusts somewhat into the nozzle opening 2. Through the gas supply pipe 15, a gas or gas mixture such as air, nitrogen or hydrogen, desired for the purpose, can be blown in by an unillustrated apparatus such as a fan, gas container etc. The tubular part of the jet 14 projecting out from the gas supply pipe 15 is provided with threads and is threaded into the upper part of a yoke-like holder 16, the lower part of which is fixed to the outer wall of the liquid container 4. A regulating collar 17, the bottom part of which extends radially outwards somewhat further than the partition wall 7, is threaded onto the lower, tubular part of the jet 14, so that a gap 18 is defined between the regulating collar 17 and the upper surface of the nozzle element 1. This gap will be the inlet opening for gas, e.g. ambient air, which is to be sucked into the nozzle element 1 when the apparatus is func- tioning, as will be described below. By virtue of the regula¬ ting collar 17 being threadedly connected to the jet 14 the gap height may be adjusted. The liquid atomizing apparatus described above operates in the following manner. When e.g. air is blown through the tube 15 with the aid of a fan means, for example, a subpres- sure caused by ejector action will occur in the gap 18 between the outer edge of the regulating collar and the opposing inner liquid chamber for a suitable adjustment of the distance between the regulating collar 17 and the nozzle opening 2. When the liquid level 11 in the liquid container 4 is suitably adjusted to this subpressure, the liquid level in the inner liquid chamber will be raised by suction into the gap space 9 and up over its upper edge, simultaneously as extraneous gas is sucked into the gap, as illustrated by the arrows 19, which gas can be the same gas as the gas. supplied via the tube 15, or another gas/gas mixture, e.g. ambient air in the case illustrated. The air being sucked in will thus continuously "slice off" the protruding liquid column in the annular gap 9. The entrained liquid is mixed in the nozzle element 1 with the air blown in via the jet 14 and leaves the nozzle opening 3 in an atomized state. By suitable adjustment of the different parameters, excellent atomization of the water is achieved, so that a very homogeneous liquid mist is obtained, as indicated by the chain dotted lines D. It will be understood that the apparatus described above has great operational reliability, due to its relative sim¬ plicity. For such as cooling purposes, no high purification of the cooling water is required either, and ordinary mecha¬ nically purified water conventionally used in industry can be used. For the supply of e.g. air, no air compressing equip¬ ment is necessary and an ordinary blower apparatus giving 11- 12 kPa, for example, can be used. Since the risk of clogging has been substantially eliminated, the apparatus can further operate reliably in a hot environment, which is of importance for different cooling applications. As indicated above, the atomizing apparatus in accor¬ dance with the invention is, of course, not restricted to cooling purposes, e.g. cooling in plate rolling mills, grooved rolls, etc, but it is also excellently suited for such as humidifying or moistening purposes, e.g. binding heavy dust (such as metal oxides) in steel works, etc, for heat recovery via humidified air, for humidifying green houses, or for spreading artificial fertilizer mists in them ( which is done today with the aid of conventional nozzles). Another field of use is moistening stored timber. An apparatus corresponding to the one in Figures 1 and 2 is illustrated in Figure 3, but this apparatus is intended for spraying substantially upwards, e.g. for cooling rolled plate from below. Corresponding parts are provided with the same reference numerals supplemented by a prime sign. The main difference in relation to the apparatus in Figures 1 and 2 is that the apparatus according to Figures 3 and 4 has the liquid container 4' integrated with the gas supply jet 14'. instead of the nozzle element 1. The regulating collar 17 is thus not needed, and the suction gap 18' between the upper part of the container and the nozzle opening 2' can be ad¬ justed by the nozzle element 1' being threaded into the holder 16'. Further, the inner and outer chambers in the liquid container defined in conjunction with Figure 1 have changed places. Numeral 26 denotes a pair of flats for a spanner. In Figure 5 there are illustrated similar cooling appa¬ ratuses as those illustrated in Figures 1 and 2, and 3 and 4, respectively, for cooling steel plate, e.g. in a heavy plate rolling mill, corresponding parts being denoted with the same reference numerals as in Figures 1-4. Here, several rows of atomizing apparatuses are envisaged as being arranged trans¬ verse the plate travel direction, the figure illustrating a cross section taken between a pair of atomizing apparatuses in a row of such apparatuses. Thus, several rows, e.g. two, of atomizing apparatuses for spraying from above are arranged on the upper side of, and suitably spaced from, a steel plate 20 which is to be cooled, these apparatuses here being represented by one like the one according to the Figures 1 and 2, and generally denoted by the reference numeral 21. In a corresponding way, apparatuses for spraying from below are arranged on the underside of the plate 20, these apparatuses being represen¬ ted by one like the one according to Figures 3 and 4, and generally denoted by the reference numeral 21'. The upper spray apparatuses 21 are connected to a ςommon air duct 22, and in a similar way the lower spray apparatuses 21" are connected to a common air duct 22' . In the embodiment illu- strated here, the outer chamber in Figures 1-4 is, however, not concentric with the partition wall 7, 7', but this cham¬ ber is formed by a common duct 23 for the upper apparatuses, which duct extends on the upper side of a similarly common cooling box 24, the apparatuses 21, without an outer chamber and with appropriately modified partition walls, being in¬ serted in corresponding recesses made in the duct 23 and cooling box 24. In a corresponding way, the lower apparatuses 21' without their liquid chambers are arranged in a common liquid duct 23' and a common cooling box 24' spaced there- from. The cooling boxes 24, 24', which are intended to pro¬ tect the apparatuses 21, 21', from the heat of the steel plate 20, are provided with cooling water via inlets 25 and 25' in the box ends. There is achieved in accordance with the arrangement outlined in Figure 5 excellent cooling of the rolled plate due to the extremely effective cooling mist obtained by the atomizing apparatuses in accordance with the invention. In the embodiments described above, atomizing apparatus has been illustrated which is intended for spraying εubstan- tially upwards and downwards, respectively. For angled spraying, e.g. with 30°-40° inclination of the nozzles, the apparatuses must be modified, e.g. by suitable oblique imple¬ mentation of the liquid containers/suction parts of the apparatuses. Alternatively, a suitable guide plate could be sufficient. Necessary modifications for different applica¬ tions can readily be accomplished by one skilled in the art. The invention is, of course, not restricted to the embodiments described above and especially illustrated, and many variations and modifications are possible within the scope of the inventive concept and the following claims.

Claims: CLAIMS 1. A method of atomizing liquid, characterized in that a first gaseous medium is caused to be sucked along with, and mixed with, a second flowing gaseous medium by means of ejector action, the first gaseous medium being caused to entrain liquid medium which is caused by said ejector action to be sucked into the flow path of the first gaseous medium, so that the liquid medium is mixed with, and atomized in, the first and second gaseous media. 2. The method as claimed in claim 1, characterized in that the first and second gaseous media are the same gas or gas mixture. 3. The method as claimed in claim 2, characterized in that the gaseous media are air. 4. The method as claimed in claim 1, 2 or 3, characterized in that the liquid medium at least substantially is water, possibly containing one or more dissolved substances. 5. The use of the method according to any one of claims 1- 4. for cooling, humidifying or moistening purposes. 6. An apparatus for atomizing liquid, comprising a nozzle element 1, means (14, 15) for supplying gaseous drive medium to the nozzle element (1), and means (4, 10) for supplying liquid which is to be atomized, characterized in that it further includes inlet means (2, 18) for another gaseous medium to be sucked in by the drive medium by means of ejec¬ tor action, and that the liquid supply means comprise con¬ tainer means (4, 9) with an at least partially open upper part opening out in connection with the flow path of said other gaseous medium, so that liquid in the container means ( 4, 9) can be caused by said ejector action successively to rise above the container upper part and into said flow path. and to be continuously entrained by said other gaseous medium flowing into the nozzle for being atomized in the mixture of the gaseous media. 7. The apparatus as claimed in claim 6, characterized in that said container means (4) comprise two mutually communi¬ cating chambers, the space above the liquid surface in one chamber communicating with the incoming flow path of said other gaseous medium, and the space above the liquid surface in the other chamber communicating with the surroundings. 8. The apparatus as claimed in claim 7, characterized in that it comprises means for maintaining a constant liquid level in the chamber communicating with the surroundings. 9. The apparatus as claimed in claim 7 or 8, characterized in that the chamber communicating with said other gaseous medium extends εubεtantially concentric to the flow path of the drive medium, and in that inlet means (18) for said other gaseous medium are arranged for substantially radial inflow over said chamber and into the nozzle element (1). 10. The apparatus as claimed in claim 9, characterized in that said both chambers are defined by a common, preferably annular partition wall (7).

Inventors: ERICSSON C G FOLKE, ERICSSON, C., G., FOLKE
Applicants: MITAB PRODUCTS AB, AB MITAB PRODUCTS
Application year: 1989
Main classification: F24F6
IPC codes: B05B7