SE539913C2 - A silenced blowing nozzle and a method for its manufacture - Google Patents

Abstract

The invention relates to a silenced blowing nozzle for blowing of a gas medium under overpressure, in particular air. The blowing nozzle includes a central part (11) with a primary nozzle means (13) which includes at least one Laval nozzle (14) and has at least one primary discharge opening (15) such that the primary discharge opening (s) (15) will generate a core stream of gas with supersonic velocity. The central part (11) is surrounded by a more peripheral part (12) containing a plurality of secondary nozzles (16a, 16b, 16c) with respective secondary discharge openings (17a, 17b, 17c). These are spaced from another and from said primary discharge opening(s) (15).According to the invention each secondary discharge opening (17a, 17b, 17c) is arranged to generate a gas stream that is divergent from the axis of the core stream.

Description

A SILENCED BLOWING NOZZLE AND A METHOD FOR ITS MANUFACTURE FIELD OF INVENTIONThe present invention relates in a first aspect to a silenced blowing nozzle forblowing of a gas medium under overpressure, in particular air, which blowingnozzle includes a central part with a primary nozzle means which includes at leastone Laval nozzle and has at least one primary discharge opening such that thedischarge opening (s) will generate a core stream of gas with supersonic velocity,which central part is surrounded by a more peripheral part containing a plurality ofsecondary nozzles with respective secondary discharge openings spaced fromanother and from the primary discharge opening(s)ln the present application terms like axial, radial and circle has the axis of thecore stream, i.e. the centre line of the blowing nozzle, as the reference, if notexplicitly defined otherwise.

BACKGROUND OF INVENTION Pressure air is used in many applications within the industry e. g. for cleanblowing, cooling, separation, drying or transporting. Blowing with pressure air isnormally entailed with a high noise level. Environment demands are continuouslyincreasing. With respect to work environment, lower sound level and energysaving are frequently required, or at least desired.

Therefore it has been an endeavour to attain blowing nozzles that generate aslow sound as possible for a given blowing force, so called “silent type nozzles”.Examples of this type of nozzle are tapered slot nozzle of type Silvent ® 511 and512, cupped hole nozzles of type Silvent ® 208 and 209 and blowing nozzles withflat ends, type Silvent ® 701-720. These blowing nozzles are used for low andmoderate blowing forces and blowing distances. So called “large blowers” areused when large blowing forces are required at long distances. Belonging to thisgroup are aggregates consisting of a large number of co-operating hole nozzles,which belong to the Silvent ® 1100- and 1200-series. These tools are used forinstance for application in steel plants, paper mills and foundries for cleaning,cooling drying etc. ln certain cases within the pulp and paper industry, blowing nozzles with evenhigher air flows are used, which generate extremely high noise levels due to the 2 expansion of the air stream after it has left the nozzle. The operator can be subjectto a level of approx.1 15 dB(A), and for other personnel in the vicinity of thedischarge it is not unusual with values in the range of 100-110 dB(A). As thenozzle is often required for sudden interruptions in production at the factory, e.g.when a paper web goes out of line, high requirements are placed on the personnelfor immediate action. Many times one simply does not have time to put on hearingprotection, which in unfortunate cases can imply permanent hearing damage afteronly a few seconds of exposure time.

The need to increase the blowing forces and to reduce the noise level isaddressed in US 6 414 991, the disclosure of which hereby is incorporated in thepresent application by reference. US 6 415 991 discloses a silenced blowingnozzle which has a central part with at least one first discharge opening generatinga core stream of gas with supersonic velocity. The central part is surrounded by amore peripheral part having a number of second discharge openings generating agas flow of lower velocity than the core stream, which gas stream surrounds thecore stream and has the same direction as the core stream. The dischargeopenings may have circular shape or be shaped as slits.

Similar blowing nozzles are disclosed in CN 104069962 and CN 104069966.

Although a silenced blowing nozzle of the kind disclosed in US 6 414 991represents significant improvements with regards to increasing the blowing forceand reducing the noise level, it still remains a need for further improvement inthese respects. There is also a demand for attaining a more concentrated streamfrom the blowing nozzle due to a need for better precision of the gas stream. The object of the present invention is to meet these demands.

SUMMARY OF INVENTION The object of the present invention is achieved in that a silenced blowingnozzle of the kind specified in the preamble of claim 1 includes the specificfeatures specified in the characterizing portion of the claim. Thus, each secondaryeach secondary discharge opening is arranged to generate a gas stream that isdivergent from the centre line of the core stream.

By the divergent direction of the peripheral gas stream it has been shown thatthe concentration of the central beam becomes more accentuated in comparisonwith peripheral gas streams that are parallel to the core steam. The propagation 3 pattern of the core stream has been simulated through computer flow program andanalysed, which indicates such an increased concentration of the core stream.This has also been confirmed by laboratory tests. A more concentrated corestream results in lower energy consumption, since a concentrated stream resultsin a better blowing precision. This leads to shorter blowing time and thus lessenergy consumption. The invented blowing nozzle also decreases the turbulence,which means a lower noise level. Thereby less energy gets wasted in soundgeneration which leads to a higher blowing force. A higher blowing force in relationto the gas consumption means that the efficiency of the nozzle is increased.

According to a preferred embodiment, the divergent gas stream has an anglerelative to the axis of the core stream in the range of 2,5 - 5°.

The simulation and the laboratory tests mentioned next above have shown thatthe concentration of the core stream in relation to the blowing distance is mostsignificant when the deviation is in this range. ln particular a deviation angle withinthe range of 2,5 - 5° has been shown to be optimal in most applications.

According to a further preferred embodiment all secondary nozzles are Lavalnozzles.

This further contributes to attain a core stream that is as concentrated aspossible. The Laval nozzles allow the peripheral streams to have supersonicspeed, although lower than the supersonic speed of the core stream. This furtherdecreases turbulence, and thereby leads to a lower sound level. When all of themare Laval nozzles it provides an optimal effect in this respect.

According to a further preferred embodiment, the secondary nozzles arelocated along at least one circle, which circle is concentric with the axis of the corestream.

A circular arrangement is optimal with regards to the effects achieved with theinvented blowing nozzle regarding concentration, sound level and energyconsumption. Preferably the nozzles are evenly distributed along the circle.

According to a preferred embodiment, when all the secondary nozzles arearranged along one circle, the number of secondary nozzles is 4 - 8.

The advantageous effects discussed above will be more significant the largerthe number of secondary nozzles along the circle is. A large number of nozzles,however adds to the complexity of the blowing nozzle. The specified range is an 4 adequate balance between these considerations. A number of 6 secondarynozzles in most cases is optimal in this respect.

According to a further preferred embodiment, the secondary nozzles aredivided into at least two groups, wherein the nozzles in each group have adifferent |oca|isation from the nozzles in the other group (s) with regards to theaxial position of the discharge opening and/or with regards to the diameter of thecircle along which the nozzles in the group are located.

Arranging the nozzles in e.g. two groups where the axiai positions of thedischarge openings are different between two groups makes it possible to obtainspace for a larger number of secondary nozzles along one and the same circleand increase the concentration of the core stream. Preferably the secondarynozzles along the circle are arranged such that every second secondary nozzlebelongs to one group, and the other secondary nozzles belong to the other group.

There may be applications where it is advantageous for increasing theconcentration of the core stream and decrease the turbulence for a given flow rateto arrange a first group of secondary nozzles along a first circle and a secondgroup along another circle concentric with the first.

According to a further preferred embodiment the number of nozzles in eachgroup is 2 - 32.

The optimal number of nozzles in a group follows similar considerations asmentioned above regarding the number of nozzles where there is only one group.lt has also to be taken into account the constellation of the groups; whether thereare two different groups arranged along different circles, which may give reason tohave a relatively large number for the radially outer group or whether two groupsare located along one and the same circle, which may give reason to have arelatively small number of nozzles in these groups. ln most cases an optimalnumber will be found within the specified range, in particular within the range 4 -16. A number of 6 nozzles in each group is generally found to be optimal.

According to a further preferred embodiment, the numbers of nozzles in twogroups arranged along the same circle are equal.

This further harmonizes the flow pattern with a minimum of turbulence andtherefore leads to a good concentration and low noise level.

According to a further preferred embodiment, a circular front ring with a frontedge surrounds the primary nozzle means, and each discharge opening is located 5 ahead of said front edge as seen in the flow direction through the primary nozzlemeans.

By this front ring it is assured that the discharge openings of the secondarynozzles are not destroyed due to wear. Deterioration of the edges of the outletopenings would give rise to increased turbulence. The ring thus maintains the lowturbulence achieved with the invented blowing nozzle. Since increased turbulencealso decreases the concentration of the core stream, the ring is also important formaintaining a concentrated core stream.

A further advantage with this ring is that it contributes to that the blowing nozzlemeets the requirement of OSHA (Occupational Safety and Health Administration),a US organization enforcing regulations for workers safety. ln its framework ofrules there are rulings regarding maximal pressure in case the discharge openingbecomes closed by obstruction. lf there is a risk that the discharge can becompletely obstructed, the pressure may not exceed 30 psi (210 kPa) according toOSHA 29CFR 1910.242(b). With the front ring, the blowing nozzle will meet therequirements of OSHA. The air velocity pressure has been measured to be farbelow 210 kPa.

According to a further preferred embodiment a relief channel means isarranged within the blowing nozzle, which relief channel means communicateswith the space formed between the front edge and the primary discharge openingand communicates with the surrounding at a location ahead of the front ring asseen in the flow direction through the primary nozzle means.

The channel means in an advantageous way allows the gas to escape in thebackwards direction in case the front ring would be completely obstructed. Thechannel means is a simple and advantageous way to meet the OSHArequirements mentioned above.

The above described preferred embodiments of the invention are set out in thedependent claims. lt is to be understood that further preferred embodiments maybe constituted by any possible combination of features of the described preferredembodiments and by any possible combination of features in these with featuresdescribed in the description of examples below. 6 BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a section along the axis of a blowing nozzle according to a firstexample of the invention.

Fig. 2 is a side view of the blowing nozzle in fig. 1.

Fig. 3 is a side view of the blowing nozzle of fig. 1 as seen from anotherangular position than that of fig. 2.

Fig. 4 is a perspective view of a blowing nozzle according to a second exampleof the invention.

Figs. 5-7 are diagrams illustrating various examples of the positioning of thesecondary nozzles.

Fig. 8 illustrates the shape of the core stream of a blowing nozzle according to the invention.

DESCRIPTION OF EXAMPLES Figs 1 to 3 illustrate a first example of a silenced blowing nozzle according tothe invention, where fig 1 is a longitudinal section through the centre of the blowingnozzle. The blowing nozzle has a main housing 20 with an inlet 21 for pressurizedgas such as air. The main housing 20 has an internal thread 22 adjacent the inlet21 for connection with a pipe connected to a source of pressurized air. Theblowing nozzle is arranged to generate a core stream with a centre axis C.

The blowing nozzle at its outlet portion has a central part 1 in which a primarynozzle means 3 is arranged. The primary nozzle means 3 consists in theillustrated example of one Laval nozzle 4 with a discharge opening 5, whichgenerates the core stream with the axis C. It is to be understood that the corestream alternatively could be generated by a plurality of Laval nozzles.

The central part is surrounded by a peripheral part 2, which has six secondarynozzles 6 with a respective discharge opening 7. Each of the secondary nozzles 6is a Laval nozzle. The direction of each secondary nozzle has an orientation suchthat the air stream generated therethrough has a direction that is divergent fromthe direction of the axis C of the core stream. The direction thus forms an angle oiwith the axis C. ln the illustrated example oi is 4,75°.

The blowing nozzle is designed such that a circular front ring 8 with a frontedge 9 is formed. The front ring 8 projects in the flow direction beyond the primary 7 discharge opening 5 and the secondary discharge openings 7. The front edge 9thereof thus forms the very downstream end of the blowing nozzle.

Fig. 2 is a first side view of the blowing nozzle, and fig. 3 is a second side viewthereof, which second side view is turned 60° in relation to that of fig. 2.

Fig. 4 i||ustrates a second example of the blowing nozzle. ln this example thesecondary nozzles are divided into three groups. Also in this example the primarynozzle means 13 has one single Laval nozzle 14 with a discharge opening. 15. lnthe figure the nozzle and its discharge opening are located behind the ring 18 andthus not visible. The reference numbers for these are within brackets and thebroken reference line points towards the location.

The peripheral part 12 of the blowing nozzle has a number of secondarynozzles 16a, 16b, 16c. The secondary nozzles are divided into three groups,wherein a first group has six nozzles 16a with a respective discharge opening 17a.A second group likewise consists of six nozzles 16b with a respective dischargeopening 17b. A third group also consisting of six nozzles 16c with dischargeopenings are arranged radially innermost around the primary nozzle 14. All thesecondary nozzles in the first and second groups 16a, 16b are arranged atsubstantially the same radius from the centre line of the blowing nozzle, i.e. alonga common circle. This circle has larger diameter than that of the circle along whichthe third group of nozzles 16c is arranged. And each of the secondary nozzles is aLaval nozzle. All the secondary nozzles are oriented such that they generate an airstream that diverges about 5° from the centre line of the blowing nozzle.

The first group of secondary nozzles 16a are axially longer than the secondgroup of secondary nozzles 16b, and the discharge opening 17a of each nozzle16a in the first group are located downstream of the discharge openings 17b ofeach nozzle 16b in the second group.

Also this blowing nozzle is designed such that a circular front ring 18 with afront edge 19 is formed. The front ring 18 projects in the flow direction beyond theprimary discharge opening 15 and the secondary discharge openings 17a, 17b,17c The front edge 19 thereof thus forms the very downstream end of the blowingnozzle.

Fig. 4 also i||ustrates a channel means 10 formed by the space between theinner secondary nozzles 16c. The channel means 10 in this example thus has six channels. Should the ring 19 be completely covered by an object, the gas streams 8 from the primary nozzle and the inner secondary nozzles 16c will reflect againstthe obstacle, return through the intermediate channels and escape to thesurrounding at the rear end 19b of the ring 18. Similar channels 10 are presentalso in the example illustrated in figs 1-3.

Many variations of arranging the secondary nozzles in different groups arepossible within the scope of the claimed blowing nozzle. A few such examples areillustrated in the diagrams in figs 5 to 7. Each diagram shows the positions of thenozzles in a plane perpendicular to the centre axis of the blowing nozzle. ln fig. 5 there are six inner secondary nozzles 16c arranged along a circle andtvvelve outer secondary nozzles arranged along a common circle. Of these everysecond nozzle 16a, indicated with a cross, has its discharge opening in a commonfirst plane perpendicular to the centre axis of the blowing nozzle. The othernozzles 16b have their discharge openings in a second common planeperpendicular to the centre axis. The first plane is located closer to thedownstream end of the blowing nozzle the second plane. This corresponds withthe example depicted in fig. 4. ln fig. 6 there are twenty-four secondary nozzles arranged in three groups.Along an inner circle there are six secondary nozzles 26c, and along an outercircle are twelve secondary nozzles 26b. Along an intermediate circle are sixsecondary nozzles 26a. ln fig 7 there are thirty-six secondary nozzles arranged in four groups. Along aninner circle there are six secondary nozzles 36c. Along an intermediate circle thereare two groups of secondary nozzles 36a, 36b, with six nozzles in each group, andarranged similar to those of fig. 5. Along an outer circle are eighteen secondarynozzles 36d arranged with their discharge openings in a plane common to thedischarge openings of nozzles 36a. lt is, within the scope of the invention further possible to include secondarynozzles that are not Laval nozzles, e. g. shaped as slits. lt is also to be understood that the cross flow areas of all the secondary nozzlesare not necessarily equal.

Fig. 8 in a side view illustrates the shape of the core stream A obtained with ablowing nozzle according to the invention. The core stream of a blowing nozzleaccording to prior art is indicated as B. As can be seen, the core stream is much more concentrated with a blowing nozzle according to the invention.

Claims (1)

1. A silenced blowing nozzle for blowing of a gas medium underoverpressure, in particular air, which blowing nozzle includes a central part(1, 11)with a primary nozzle means (3, 13) which includes at least oneLaval nozzle (4, 14) and has at least one primary discharge opening (5,15) such that the primary discharge opening (s) (5, 15) will generate aconcentrated core stream (A) of gas with supersonic velocity, whichcentral part (1, 11) is surrounded by a more peripheral part (2, 12)containing a plurality of secondary nozzles (6,16a, 16b,16c) withrespective secondary discharge openings (7, 17a, 17b, 17c) spaced fromanother and from said primary discharge opening(s) (5, 15),characterized in that each secondary nozzle (6, 16a, 16b, 16c) has anorientation such that each secondary discharge opening (7,17a, 17b, 17c)generates a gas stream that is divergent from the axis (C) of the corestream, which divergent gas stream has an angle (d) relative to the axis(C) of the core stream in the range of 1,5 - 8°, and wherein at least someof the secondary nozzles (6, 16a, 16b, 16c) are Laval nozzles A silenced blowing nozzle according to claim 1, wherein said divergentgas stream has an angle (d) relative to the axis (C) of the core stream inthe range of 2,5 - 5°. A silenced blowing nozzle according to claim 1 or 2, wherein all saidsecondary nozzles (6, 16a, 16b, 16c) are Laval nozzles. A silenced blowing nozzle according to any one of claims 1-3, whereinsaid secondary nozzles (6, 6c, 16a, 16b, 16c) are located along at leastone circle, which circle is concentric with the axis (C) of the core stream. A silenced blowing nozzle according to claim 4, wherein the number ofsecondary nozzles (6) is 4 - 8, preferably 6. 10. A silenced blowing nozzle according to claim 4 or 5, wherein saidsecondary nozzles (6,16a, 16b, 16c) are divided into at least two groups,wherein the nozzles in each group have a different Iocalisation from thenozzles in the other group(s) with regards to the axiai position of thedischarge opening (7,17a, 17b, 17c) and/or with regards to the diameter ofthe circle along which the nozzles in the group are located. A silenced blowing nozzle according to claim 6, wherein the number ofnozzles in each group is 2 - 32, preferably 4 - 16, most preferably 6. A silenced blowing nozzle according to claim 6 or 7, wherein the numberof nozzles (16a, 16b) in two groups arranged along the same circle is equal A silenced blowing nozzle according to any one of claims 1-8, wherein acircular front ring (8, 18) with a front edge (9, 19) surrounds the primarynozzle means (3, 13), and wherein each discharge opening (5, 15, 7, 17a,17b, 17c) is located ahead of said front edge (9, 19) as seen in the flowdirection through the primary nozzle means (3, 13). A silenced blowing nozzle according to claim 9, wherein a relief channelmeans (10) is arranged within the blowing nozzle, which relief channelmeans (10) communicates with the space formed between the front edge(9,19) and the primary discharge opening (5, 15) and communicates withthe surrounding at a location ahead of the front ring (8, 18) as seen in theflow direction through the primary nozzle means.