Atomizer nozzle assembly

An atomizer nozzle assembly for producing an extrafine mist of liquid includes a nozzle assembly, with a liquid passage hole of each nozzle tip of the assembly extending along a longitudinal axis of the nozzle tip. A front end opening of each liquid passage hole is centrally formed in the front end face of each nozzle tip. The angle of taper of a front tapered portion of each nozzle tip is 16.degree.-24.degree.. With the above arrangement, it is possible to produce a substantially ultrafine mist when the atomizing operation is started and it is also to produce an ultrafine mist having a constant particle diameter during a rise in the initial pressure of compressed air immediately following the start of atomization.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention generally relates to a nozzle for an atomizer which 
produces a jet of liquid in the form of a mist and, more particularly, to 
a nozzle assembly applicable to an ultrafine particle atomizer of a type 
which produces an extrafine mist of liquid, such as water, fuel oil, or 
medical solution, having a mean particle diameter (a Sauter mean particle 
diameter as referred to hereinafter) ranging from a submicron to some ten 
microns as most, or in other words, a dry mist which does not feel wet if 
touched (referred to hereinafter as an "ultrafine mist"). 
2. Description of the Related Art 
Atomizers are employed in various fields for various purposes, such as 
humidifying, cooling, dust controlling, disinfectant solution spraying, 
and fuel oil atomizing. Generally, it is desirable that any mist produced 
by means of such a device should be an ultrafine mist. The reason is that 
of component particles of the mist are coarse, the surfaces of 
circumjacent objects will get wet in a given period of time when, for 
example, the atomizer is employed for humidifying purposes; and if the 
atomizer is employed for the purpose of disinfectant solution spraying, 
the circumjacent objects will get wet resulting in stains being left 
thereon. 
The present inventor, after his series of studies on such a problem, found 
that for an ultrafine mist to be realized its component liquid particles 
must not have a maximum particle diameter greater than 50 microns and not 
have a Sauter mean diameter greater than 10 microns. On the basis of such 
a finding, the present inventor has already proposed various ultrafine 
mist producing atomizers (Japanese Published Unexamined Patent Application 
Nos. 54-111117, 55-49162, and 57-42362). 
There are two types of nozzle assemblies, one or the other of which is 
employed in the ultrafine mist producing atomizers proposed by the present 
inventor. One type involves passing compressed air through a passage 
outside the nozzle tip, which may be called the outer air-passage type 
(Japanese Published Unexamined Patent Application Nos. 55-49162 and 
57-42362). The other type involves passing compressed air through a 
passage defined within the nozzle tip, which may be called the inner 
air-passage type (Japanese Published Unexamined Patent Application No. 
54-111117). From the standpoint of preventing the diffusion of a jet 
stream of a gas-liquid mixture from the nozzle orifice, it is generally 
believed that nozzles of the outer air-passage type are preferable. 
As an illustration of a nozzle of the outer air-passage type, a general 
arrangement of the nozzle in the ultrafine mist producing atomizer 
disclosed in said patent publication No. 55-49162 is described below by 
way of example. 
The basic arrangement of this nozzle is generally identical with that shown 
in FIGS. 1 and 2, on which one embodiment of the present invention is 
based. That is, a nozzle body has a plurality of nozzle heads arranged in 
an equi-spaced relation around the longitudinal axis thereof, each of the 
nozzle heads having a mounting hole in which a nozzle tip is mounted. Each 
nozzle tip, as can be seen from FIG. 12 (in which a part of a nozzle is 
shown), has a liquid passage hole 5a, while an air jet passage 5e is 
defined in a mounting hole 5b between a nozzle body 5c and the outer 
periphery of a nozzle tip 5d. Individual mounting holes and individual 
nozzle tips are so arranged that the respective longitudinal axes of the 
nozzle tips converge at one point on the longitudinal axis of the nozzle 
body, whereby as currents of compressed air are caused to jet out toward 
said one point on the longitudinal axis of the nozzle body passing, 
through the air jet passages, the currents suck liquid thereinto through 
the respective front end openings 5f of the liquid passage holes to form 
jet streams of a gas-liquid mixture and the jet streams impinge against 
one another at said one point on said longitudinal axis, thereby producing 
an ultrafine mist of liquid. 
With respect to the above-described prior art nozzle arrangement, it must 
be noted that, as FIG. 12 shows, the front end openings 5f of the liquid 
passage hole 5a defined in each nozzle tip 5e are open at sides of the 
front end 5g of the tip and not on the front end 5g itself; that the angle 
of taper of a front end tapered portion 5h of the nozzle tip 5d is about 
7.degree.-22.degree.; and that the front end of the nozzle tip 5d projects 
little, if any, from the nozzle body 5c (the amount of such projection 
being in the order of 0.2 mm at most). 
Now, in the prior art nozzle arrangement, the relationship between 
compressed air pressure and liquid atomization rate is shown in FIG. 4a 
(conditions in FIG. 4 are: liquid pressure=0; liquid suction height=100 
mm). In other words, there is no proportional relationship between 
compressed-air pressure and liquid atomization rate. In FIG. 4a, the mean 
particle diameter in the mist is about 50 microns--about 10 microns in a 
low pressure zone ranging from an initial air pressure at which 
atomization starts to a pressure level of about 3 kg/cm.sup.2 with no 
ultrafine mist being available realized. An ultrafine mist having a mean 
particle diameter of less than about 10 microns is produced only in a high 
pressure zone in which the air pressure is in excess of about 3 
kg/cm.sup.2. However, as air pressure becomes higher, the mean particle 
diameter becomes smaller, and as shown in FIG. 4a, atomization is 
terminated when an air pressure of less than 4 kg/cm.sup.2 is reached. 
With prior art arrangement, therefore, one problem is that at on/off 
control stages for compressed air supply, a mist having a relatively 
coarse particle size is produced, so that the floor and circumjacent 
surfaces get wet. Another problem is that when only a small amount of 
ultrafine mist is required, it is necessary to increase the air pressure, 
which means a disproportionally greater amount of air consumption for the 
liquid atomization is required which is extremely uneconomical. A further 
problem is that the diameter of particles in the mist varies with changes 
in the air pressure, or in other words, a mist having a constant particle 
diameter cannot be produced. 
These problems are considered to be attributable to the front end structure 
of the nozzle and, more particularly, to the fact that a negative pressure 
develops thereat as a compressed air current passes at a supersonic 
velocity through the nozzle orifice. 
SUMMARY OF THE INVENTION 
It is, therefore, an essential object of the present invention is to 
provide an atomizer nozzle assembly having an improved front end structure 
which is likely to cause a negative pressure and a satisfactory pattern of 
compressed air flow which enables a substantially ultrafine mist to be 
produced at a point of time when atomization is initiated under an initial 
pressure of compressed air, and which enables an ultrafine mist to be 
produced when a slightly higher level of air pressure is reached, at a 
flow rate generally proportional to the pressure rise. 
In accomplishing this and other objects, according to the present 
invention, there is provided an atomizer nozzle assembly comprising the 
following arrangement: 
a nozzle assembly generally identical with the above-described prior-art 
arrangement, but in which a liquid passage hole of each nozzle tip 
extending along the longitudinal axis of the nozzle tip has a front end 
opening centrally formed in the front end of the nozzle tip and the angle 
of taper of a front tapered portion of each nozzle tip is 
16.degree.-24.degree.. 
Such an arrangement of the invention is based on findings derived from 
certain experiments which will be described hereinafter. With such an 
arrangement it is possible to produce a substantially ultrafine mist at 
the start of the atomizing operation and also to produce an ultrafine mist 
having a constant particle diameter during rise in the initial pressure of 
compressed air immediately following the start of atomization. 
Therefore, according to the invention, there will be no generation of any 
coarse particle mist at on/off stages for compressed air jetting, and thus 
there is no possibility of the mist causing the floor and other 
circumjacent surfaces to become wet. Furthermore, with a rise in the 
pressure of compressed air, an ultrafine mist having a generally uniform 
particle diameter can be produced at a rate proportional to the pressure 
rise. 
In the foregoing arrangement, it is desirable that the front end of each 
nozzle tip should project forward from the front end of the corresponding 
nozzle tip, and that the length of such projection be set within the range 
of 0.3-0.8 mm. With such an arrangement, it is possible to ensure stable 
atomization. That is, by arranging the front end of each nozzle tip so 
that it projects forward more than 0.3 mm, it is possible to produce a 
steady jet stream of a gas-liquid mixture, because droplets of liquid 
sucked outward from the liquid passage hole become less inclined to be 
attracted toward an enlarged portion defined between the front tapered 
portion of the nozzle tip and the interior of the nozzle head, that is, in 
a back flow direction, while on the other hand by limiting the length of 
the nozzle tip projection to not more than 0.8 mm it is possible to 
control the maximal diameter of liquid particles in a mist to not more 
than 50 microns, the permissible maximum particle diameter for realizing 
an ultrafine mist. 
It is to be noted in this conjunction that if the front end opening of the 
liquid passage hole in the nozzle tip is reverse tapered, it is possible 
to obtain an ultrafine mist having a more uniform particle diameter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
One preferred embodiment of the present invention will now be described in 
further detail in conjunction with experimental examples. 
FIGS. 1 and 2 illustrate general aspects of a nozzle assembly in accordance 
with the invention. The nozzle assembly consists generally of a nozzle 
body (1) and and adapter (2) for air and water supply which is connected 
to the nozzle body 1. The nozzle body 1 has a plurality of nozzle heads 
(10) arranged in equi-spaced relation around its center, that is, the 
longitudinal axis (X--X) thereof. 
The number of nozzle heads (10) is not particularly limited. In the present 
embodiment, the nozzle body (1) has two nozzle heads. That is, the nozzle 
assembly has a two-head nozzle construction. 
FIG. 3b is an enlarged sectional view of the nozzle body (1) shown in FIGS. 
1 and 2. As shown, each nozzle head (10) of the nozzle body 1 has an air 
introduction path (17) for introducing compressed air thereinto, and a 
liquid introduction path 16 for introducing liquid, such as water of 
disinfectant solution, according to the purpose for which the atomizer is 
to be employed. The air introduction path (17) and the liquid introduction 
path (16) are respectively connected at one end to a compressed air 
introduction path and a liquid introduction path, both formed in the 
adapter 2. 
Each nozzle head (10) has a mounting hole (14) in which a a nozzle tip (11) 
is housed or mounted. As shown, the nozzle tip (11) is housed in the 
mounting hole (14) at the front end side thereof, and is fixed by a plug 
(12) housed in the hole (14) at the rear end side thereof. 
Individual nozzle heads (10) and individual nozzle tips (11) housed therein 
are arranged so that the respective longitudinal axes (Y--Y) of the nozzle 
tips (11) converge at one particular point (A) on aforesaid longitudinal 
axis (X--X). Generally, the angle (.beta.) at which a pair of longitudinal 
axes (Y--Y), (Y--Y) intersect each other is preferably set at 
70.degree.-160.degree.. The distance between a pair of nozzle orifices is 
generally preferably set at 3-15 mm. 
The mounting hole (14) in each nozzle head (10) has a generally cylindrical 
configuration, and its front end portion includes a forwardly tapered 
portion (22) and a discharge port (19) having a smaller diameter 
cylindrical configuration and contiguous with the tapered portion (22). 
Each nozzle tip (11) consists generally at a large diameter base portion 
(25) and a small diameter front portion (26). The liquid passage hole (23) 
of the nozzle tip (11) extends along the longitudinal axis (Y--Y) of the 
nozzle tip (11) and has a front end opening (24) which is open centrally 
in the front end (33). This front end opening (24) may have a straight 
configuration as shown in FIG. 3b, or may have a slightly divergent 
configuration as shown in FIG. 3a. The large diameter base portion (25) is 
in contact with the cylindrical interior of nozzle head (10) defining the 
mounting hole (14), while the small diameter front portion (26) projects 
slightly outward passing through the tapered portion (22) of the mounting 
hole (14) and then through the discharge port (19) (the length of 
projection=.delta.). The large diameter base portion (25) of each nozzle 
tip (11) has a circumferential groove or communicating groove (30) formed 
on its outer periphery, and also has a communicating hole (27) which 
extends between the communicating groove (30) and the space in the tapered 
portion (22) of the mounting hole (14). The air introduction hole (17) is 
open to the communicating groove (30) so as to be in communication 
therewith. Accordingly, the compressed air supplied through the air 
introduction hole (17) is allowed to pass along an air discharge path (18) 
defined adjacent the outer periphery of the small diameter front portion 
(26), that is, through the tapered portion (22) and the discharge port, 
via said communicating groove (30) and said communicating hole (27), until 
it is jetted out. The small diameter front portion of the nozzle tip (11) 
extends in the discharge port (19) to form a throat portion (21) relative 
to the tapered portion (22), while the outer periphery of the small 
diameter front portion (26) of the nozzle tip (11) is forwardly tapered at 
the front end thereof so that the front end of the discharge port (19) is 
enlarged to form an enlarged portion (32). Therefore, the velocity of the 
compressed air to be jetted out reaches a sonic velocity level by causing 
the compressed air to pass through the throat portion (21), and when the 
air reaches the enlarged portion (32) of the discharge port (19), negative 
pressure is developed. 
On the outer periphery of the plug (12) are mounted a pair of O-rings 13a, 
13b in spaced apart relation, with a circumferential groove or 
communicating groove (28) formed between the pair of O-rings 13a, 13b. The 
liquid introduction path (16) is open into the communicating groove (28). 
The plug (12) has a center hole (15) in the center thereof at the front 
end side, and a communicating hole (29) extends between the center hole 
(15) and the communicating groove (28). Accordingly, the liquid supplied 
into the liquid introduction path (16) is guided into the liquid passage 
hole (23) of the nozzle tip (11) after passing through the communicating 
groove (28), communicating hole (29), and center hole (15) in that order. 
Now, if the operation of the device is begun by supplying liquid (liquid 
pressure=0) and compressed air to the nozzle assembly of the 
above-described construction, the compressed air sucks liquid droplets 
thereinto from the front end opening (24) of the nozzle tip (11) as it is 
jetted out from the discharge port (19), so that a jet stream of a 
gas-liquid mixture is realized. At this time, droplets of liquid are 
sheared by the compressed air into fine particles. Jet streams of a 
gas-liquid mixture discharged from the individual nozzle heads impinge 
against each other at one point (A) on the longitudinal axis (X--X), 
whereby a process of mutual shearing is repeated and simultaneously a 
supersonic wave of 20,000-40,000 Hz is generated, with the result of the 
droplets being reduced to finer particles. Thus, an ultrafine mist 
composed of microfine particles is released forward. 
(Experimental Example 1) 
With careful attention directed to the fact that in the nozzle assembly 
having the above-described construction, the angle of taper (.alpha.) at 
the front end portion of the nozzle top (11) is a factor having an 
important bearing on the flow pattern of compressed air and the magnitude 
of the resulting negative pressure, the present inventor conducted 
experiments with a variety of changes in the angle of taper (.alpha.) and 
found out several facts of great interest. The experiments are explained 
in detail hereinbelow. 
Experiment Conditions 
Nozzle tips, each having a front end diameter of 1.3 mm and a liquid 
passage hole diameter of 0.4 mm, were mounted to a double head jet nozzle 
body (1) having a pair of discharge ports (an inter-discharge port 
distance: 8 mm, an intersecting angle (.beta.): 120.degree.), in such a 
way that the front end of each nozzle tip (11) projected forward 0.3 mm 
from the corresponding discharge port (19) of the nozzle body (1) and that 
the throat portion (21) between the nozzle body (1) and the nozzle tip 
(11) had a sectional area of 0.5 mm.sup.2 for allowing the passage of 
compressed air. The angle of taper (.alpha.) at the front tapered portion 
of the nozzle tip was varied in order to find out the relationship between 
the angle of taper (.alpha.) and maximal particle diameter (FIG. 5), the 
relationship between air pressure and liquid atomization rate (FIG. 4b), 
the relationship between liquid atomization rate and air consumption (FIG. 
6), and particle diameters in mists produced (FIGS. 7a and 7b). The liquid 
pressure was set at 0, and the height of liquid suction at 100 mm. 
Experimental Results 
As can be seen from FIG. 5, under the air pressure condition of 3 
kg/cm.sup.2, the maximal particle diameter was more than 50 microns (with 
mean particle diameter of more than about 10 microns) if the angle of 
front end taper (.alpha.) was less than 16.degree. or in excess of 
24.degree., and with such conditions (maximal particle diameter of not 
more than 50 microns) an ultrafine mist was accordingly not produced. When 
the angle of taper (.alpha.) was in the vicinity of 20.degree., the 
maximal particle diameter was reduced to a minimum, say, about 30 microns 
(with mean particle diameter of 8 microns). When the angle of taper 
(.alpha.) was within the range of 16.degree.-24.degree., the conditions 
for producing an ultrafine mist was satisfied. This can be explained by 
the fact that, as FIG. 5 shows, when the angle of taper was in the 
vicinity of 20.degree., drops of liquid sucked under a negative pressure 
were first diverged, but were subsequently caused to impinge upon one 
another in a well contracted condition under currents of air discharged at 
a supersonic velocity. This is, if the taper angle (.alpha.) was 
excessively small, currents of air discharged were diverged under the 
influence of the circumjacent air resistance, and accordingly the jet 
streams were also diverged and slowed down, so that drops of liquid became 
coarse. If the taper angle (.alpha.) was excessively large, compressed air 
was separated without being allowed to run along the tapered portion, and 
therefore jet streams were not well contracted. Thus, the density of 
impingement energy was substantially reduced with the result of liquid 
drops becoming coarse. 
On the basis of the above-described results, it can be said that if the 
angle of taper (.alpha.) at the front end of the nozzle tip is set within 
the range of 16.degree.-24.degree., it is possible to obtain an ultrafine 
mist with a maximal particle diameter of not more than 50 microns. The 
provision of a liquid passage hole in the nozzle tip at the front end side 
thereof facilitate an effect in which the higher the pressure of 
compressed air, the larger is the negative pressure in the liquid passage 
hole. Thus, it is possible to increase the liquid atomization rate in 
proportion to the rise in the air pressure. The present invention is based 
on these experimental results. 
FIG. 6 shows, by way of example, the relationship between liquid 
atomization rate and air consumption when the taper angle (.alpha.) is set 
at 18.degree.. In this case, atomization starts under an air pressure (Pa) 
of 1 kg/cm.sup.2, and the liquid atomization rate continues to increase 
notably in relation to the rate of air consumption until an air pressure 
of 2kg/cm.sup.2 is reached. When air pressure is increased to a level of 
more than 2 kg/cm.sup.2, the rate of air consumption tends to increase in 
proportion to the rise in air pressure. Where the air pressure is between 
1 kg/cm.sup.2 and 2 kg/cm.sup.2, there is not sufficient negative pressure 
to provide any sufficient shearing action of sucked liquid droplets; 
therefore, the liquid drops are rather coarse and, even after their 
impingement, the maximal particle diameter is in the vicinity of 60 
microns, a value somewhat larger than the maximal particle size for 
realizing an ultrafine mist. However, when the air pressure is greater 
than 2.5 kg/cm.sup.2, a negative pressure corresponding to the liquid 
atomization rate results, so that the maximal diameter of liquid particles 
after impingement is not more than some 35 microns, a perfect ultrafine 
mist thus being realized. 
FIG. 4b shows the data of FIG. 6 in terms of the relation between air 
pressure and atomization rate. An ultrafine mist is produced when the 
pressure of compressed air is more than 2.5 kg/cm.sup.2, the Sauter mean 
particle diameter being 10 microns. When the pressure is less than 2.5 
kg/cm.sup.2, the mean particle diameter is 12 microns, which is slightly 
coarser. That is, even at on/off stages of nozzle operation, no coarse 
particle mist is produced, and there is little or no possibility of the 
mist creating wetness on a floor and any other circumjacent surface. 
In the above-described experiment, jet streams of a gas-liquid mixture were 
jetted out simultaneously from a pair of discharge ports so that they were 
impinged against each other. In order to further clarify the fact that 
particle diameters of the mist produced in such a case were very fine and 
uniform, the above results were compared with those obtained when one of 
the discharge ports were sealed and jetting was effected from the other 
discharge port only. FIG. 7a shows results of atomizing operation with a 
single head nozzle, and FIG. 7b shows results of operation with a double 
head nozzle. In both cases, examination was made under an air pressure of 
3.0 kg/cm.sup.2. With the single head nozzle, coarse particles having a 
maximum particle diameter of more than 90 microns were produced, whereas 
with the double head nozzle, the maximum particle diameter was in the 
order of 35 microns at most. In the latter case, more than one half of the 
particles produced had a particle diameter of several microns and some 95% 
of the particles produced had a particle size of ten and odd microns, the 
particles as a whole being very fine and uniform. 
(Experiment 2) 
In addition to Experiment 1, the present inventor conducted a second 
experiment. Attention was paid to the fact that the amount of projection 
(.delta.) from the nozzle body (1) of the nozzle tip (11) at the front end 
thereof is another factor which determines the magnitude of a negative 
pressure produced as a result of compressed air passage. In this 
experiment, the amount of such projection was varied. It was found that 
where the amount of projection was within the range of 0.3-0.8 mm, 
atomization could be effected most steadily. 
Experiment Conditions 
The experiment conditions applied were basically the same as those in 
Experiment 1. In this case, however, the angle of taper at the front end 
of the nozzle tip (11) was set at 18.degree., and the amount of projection 
(.delta.) was varied in several increments. 
Experimental Results 
In the above experiment 2, the pressure of compressed air was first set at 
3.0 kg/cm.sup.2, and the amount of projection of the nozzle tip front end 
was increased sequentially from zero to 0.3 mm. FIG. 8a shows the 
condition of gas/liquid flow when the amount of projection was zero, and 
FIG. 8b shows the condition of gas/liquid flow when the amount of 
projection was 0.3 mm. As is apparent from FIG. 8a, when the projection 
amount was zero, a negative pressure is produced as compressed air is 
jetted out from the discharge port (19) at a supersonic velocity, and 
simultaneously upon liquid drops being sucked from the front end opening 
(24) of the liquid passage hole (24), the liquid is first drawn into the 
discharge port (19) and then jetted out in conjunction with compressed 
air. This phenomenon dimishes gradually as the projection amount is 
increased, and almost ceases to exist when the amount of projection is 
increased to about 0.3 mm. If the phenomenon shown in FIG. 8a develops, a 
serious problem arises which may adversely affect the stability of 
atomization. That is, if such phenomenon develops impurities contained in 
the liquid, such as silica, silicon, and magnesium, deposit on the sides 
of the nozzle tip over time, with the result that the desired atomization 
rate relative to the predetermined pressure of compressed air cannot be 
maintained. FIG. 9a shows such unfavorable results. In this instance, 
while the atomization rate is at 2.0 l, it is apparent that actual rate of 
atomization is scattered on both the + side and the -side, with 2.0 l as a 
border line. As deposition of such impurities increases, a problem of 
blinding of the discharge port (19) will develop. 
If the amount of projection is set at about 0.3 mm as shown in FIG. 8b, the 
effect of a negative pressure, if any, is insignificant and drops of 
liquid sucked from the liquid passage hole (23) do not spread except on 
the front end (33) of the nozzle tip; therefore, if such impurity 
deposition does occur at all, it only affects the tip front end (33), and 
it is very easy to remove such deposit. 
Therefore, the flow of liquid drops is stabilized so that a uniform 
atomization rate can be assured. FIG. 9b shows the results obtained where 
the nozzle in FIG. 8b was used. It can be clearly seen that the rate of 
atomization corresponds generally to the atomization rate setting of 2.0 
l/hr. 
Hence, it is desirable that the amount of projection at the front end of 
the nozzle tip be set at more than 0.3 mm, but with the increase in the 
amount of such projection, particle diameters in a mist tend to become 
larger. In order to obtain an ultrafine mist, there is a certain 
limitation on the amount of such projection. 
In view of these facts, the relationship between the quantity of projection 
(.delta.) at the front nozzle tip end and mist particle diameter was 
examined using the pressure of compressed air as a parameter. FIG. 10 
shows the results thereof. 
As FIG. 10 shows when the projection is within the range of 0.3 mm-0.8 mm, 
the maximal particle diameter is 35 microns to less than 50 microns, 
necessary conditions for producing an ultrafine mist being fully met. 
However, if the projection is in excess of 0.8 mm, the maximum particle 
diameter is more than 50 microns, said conditions not being satisfied. 
Therefore, an optimum range of nozzle tip front-end projection lengths is 
from 0.3 to 0.8 mm. 
(Experiment 3) 
The prior art nozzle arrangement shown in FIG. 12 is subject to a problem 
in which a temperature drop may occur as a result of compressed air 
expansion in the discharge port (19), resulting in possibilities of the 
liquid drops freezing at the discharge port. Experiments were made in 
order to find how well this problem could be solved by this invention. The 
results were found satisfactory. 
In this experiment, the prior art nozzle in FIG. 12 and the nozzle employed 
in Experiment 2 (with the nozzle tip projection set at 0.3 mm) were both 
employed, and droplet freeze initiation temperature were compared between 
the two nozzles while varying compressed air temperatures. The results are 
shown in FIG. 11. As can be seen, if the air pressure is more than some 3 
kg/cm.sup.2, freezing starts at some 17.degree. C. with the prior-art 
nozzle, whereas freezing starts at about 8.degree. C. in the present 
invention. In other words, the compressed air freezing temperature 
observed with the nozzle of the invention is about 9.degree. C. lower than 
that observed with the prior art nozzle. Therefore, the nozzle in 
accordance with the invention is advantageous in that no preheating of 
compressed air is required in a normal range of uses. 
Although the present invention has been fully described by way of example 
with reference to the accompanying drawings, it is to be noted here that 
various changes and modifications will become apparent to those skilled in 
the art. Therefore, unless such changes and modifications depart from the 
scope of the present invention, they should be construed as included 
therein.