Fluid sprinkling – spraying – and diffusing – Including supplemental gas shaping or shielding jet
Reexamination Certificate
2000-11-14
2002-07-09
Doerrler, William C. (Department: 3752)
Fluid sprinkling, spraying, and diffusing
Including supplemental gas shaping or shielding jet
C239S291000, C239S296000
Reexamination Certificate
active
06415991
ABSTRACT:
FIELD OF INVENTION
The present invention relates to a silenced blowing nozzle for emitting a gas medium, in particular air, under high overpressure.
DESCRIPTION OF THE BACKGROUND ART
For many years within the engineering industry, blowing nozzles of so-called “silent type” have been used, i.e. blowing nozzles which for a given blowing force are considerably quieter than corresponding standard blowing nozzles. Belonging to this group of blowing nozzles are tapered slot nozzles of type Silvent® 511 and 512, cupped hole nozzles of type Silvent® 208 and 209 and blowing nozzles with flat ends, type Silvent ® 701-720. These blowing nozzles are used for low and moderate blowing forces and blowing distances. So-called “large blowers” are used where large blowing forces are required at long distances. Belonging to this group are aggregates consisting of a larger number of co-operating hole nozzles, which belong to the Silvent® 1100- and 1200-series of the same applicant. These tools are used for instance for applications in steel plants, paper mills, and foundries for cleaning, cooling, drying etc.
However in certain cases within the pulp and paper industry, blowing nozzles with even higher air flows are used, which generate extremely high noise levels due to the expansion of the air stream after it has left the nozzle. The operator can be subject to a level of approx. 115 dB(A), and for other personnel in the vicinity of the discharge, it is not unusual with values in the range 100-110 dB(A). As the nozzle 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 personnel for immediate action. Many times one simply does not have time to put on hearing protection, which in unfortunate cases can imply permanent hearing damage after only a few seconds of exposure time.
The powerful air nozzles used within the pulp and paper industry can be said to have two areas of application. In one case the air is used as a bearing surface for the paper web in connection with start-up of the paper machine, “pulls the leading end”. In this case the air must act as a guide, helping to steer the paper web between rollers in the paper machine. In this case it is suitable that the flow be moderately large and that it be distributed over a large area. The other case is when the paper web has broken and a quickly growing amount of paper must be blown immediately away from the machine at the same time as the leading end must be steered into the correct position. For cleaning, a very strong, concentrated air stream is required, which tends to tear apart the web even at large distances from the nozzle itself; the distance can reach up to 10 m! Other devices for managing the said tasks are not available within known technology. Certain limited tasks can be managed by blowing nozzles with fixed installation, but in all essential work the hand-regulated blowing nozzle, which generates extremely high noise levels, is necessary for giving the required flexibility in use.
BRIEF DISCLOSURE OF THE INVENTION
The object of the present invention is to offer an efficient blowing nozzle with which a significantly higher and/or quieter blowing force can be achieved for a given frontal area than with corresponding known nozzles.
The invention has been developed especially to solve the above-mentioned problems and to meet needs within the pulp and paper industry, and hereby aims to offer a blowing nozzle which can generate very large blowing forces at significantly lower noise levels than for comparable conventional nozzles. Other areas where these nozzles can be used are e.g. steel plants, foundries etc. The principles of the invention can, however, also be applied to nozzles for small or moderate blowing forces, where the nozzle according to the invention can replace conventional or silenced blowing nozzles employed within the engineering industry.
To achieve the desired blowing force, the nozzle according to the invention comprises at least one first discharge opening in a central part of the nozzle, where the first discharge opening is diverging, suitably formed as a Laval nozzle, to give the discharging gas, normally air, supersonic velocity at the pressure prevailing most immediately behind the discharge. For a correctly formed Laval nozzle, the pressure of the air/gas is converted completely to kinetic energy, which implies that the gas stream does not expand sideways after it has left the nozzle, as is the case for conventional nozzles, where the expansion creates intense noise. A powerful noise occurs nevertheless when gas flows with supersonic velocity out of a correctly dimensioned Laval nozzle. This is assumed caused by violent turbulence arising in the boundary zone between the gas/air stream which rushes forward with a very high velocity, and the surrounding air. The invention aims to solve this problem. According to the invention, the vortex formation in a gas exiting with supersonic velocity in a core stream near said first discharge opening, and therewith the generation of high frequency sound within the audible region, is suppressed in that the core stream is surrounded by a gas flow aimed in the direction of the core stream, which prevents or significantly reduces vortex formation of the core stream near said discharge opening, by which the initially mainly laminar character of the core stream is preserved to a large degree at least within a critical region near the discharge, where the velocity of the core stream is greatest.
The invention is thus based on the interaction of two principles:
1. The core stream is formed such that the working capacity thereof becomes maximum by said core stream emitted through an expanding (diverging) exit (discharge) opening which is formed such—preferably in the form of a Laval nozzle—that the internal energy of the gas is almost completely transformed into velocity under the influence of the pressure prevailing immediately behind the exit opening. For the dimensional ranges specific to the invention, the velocity in the discharge section of the nozzle lies far above sonic velocity.
2. The formation of turbulence around the rapidly gushing core stream is decreased by said core stream being surrounded by a protective gas flow aimed in the direction of said core stream. The velocity of the surrounding flow shall be lower than that of the core stream. The protective gas flow is released by a larger number of smaller exit (discharge) openings situated around the core stream—this is to suppress vortex formation due to the interaction with surrounding air and therewith also to suppress the generation of sound within the audible region. The most favourable condition is reached if the velocity of the protective gas flow decreases gradually with increased distance from the centre line.
Acoustically, the combination of these principles implies that the sound generation becomes relatively low in that the turbulence of the core stream is suppressed in a region downstream of the discharge orifice within which powerful generation of high frequency sound within the audible region otherwise takes place.
Mechanically, the combination implies a nozzle with a very high degree of efficiency, as the surrounding gas flow causes insignificant slowing down of the velocity of the core stream in the critical region after the orifice by the surrounding stationary air, as most of the mechanical work in accelerating the stationary air in the direction of the core stream is carried out by the surrounding gas flow.
The outstanding feature of the invention is thus that the blowing nozzle in a central part thereof has at least one first exit (discharge) opening formed to generate a core stream of gas with supersonic velocity and that the central part is surrounded by a more peripheral part containing a number of second discharge openings at a distance from each other and from the said first discharge opening(s), which second discharge openings are formed to generate a gas flow with lower velocity than that of
Bednarek Michael D.
Doerrler William C.
Hwu Davis
Shaw Pittman LLP
Silvent Aktiebolag
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