Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
24~
The ;nvent;on relates ~o a process and a device
for spray-d;spens;ng electr;cally conduct;ve l;quids
hav;ng a specif;c res;stance ~ 104 -Q-.m, ;n part;
cular aqueous crop protect;on agent solutions.
The spray-dispens;ng of liqu;ds, ;n particular of
solut;ons or d;spers;ons, under the action of electr;c
fields is known from var;ous f;elds of ;ndustry. Exam-
ples ~hich may be ment;oned are the coating w;th pa;nts
;n the automot;ve ;ndustry and the large-area application
of crop protection agents in agriculture. Crop protec-
t;on products are conventionally sprayed over the crops
to be treated ;n the form of suspens;ons or emuls;ons
dispersed ;n water us;ng nozzles or rotary atom;sers and
are depos;ted more or less successfully onto the leaves
of the plants~ ;n the ma;n on the upper s;de of the
protruding leaves.
In order for the crop protect;on agents to
develop the;r optimum act;on, however, ;t is necessary
for the product spray also to h;t the underside of
2û the leaves and the stalks. When spray;ng ;n the open air
some of the m;st ;s frequently deflected by the w;nd and
carried to other plants ~h;ch are not to be treated.
Furthermore, a large proport;on of the mist is lost as
it sinks to the ground or drifts away. This was the
reason for specifying a process where the dissolved pro-
duct is electrostatically atomised at a high-voltage
electrode into very fine aerosol droplets carry;ng a h;gh
un;polar charge. ~his process ;s more effect;ve ;n
depos;t;ng the l;qu;d onto earthed objects, s;nce ~he
plants act as counterelectrode to the atom;sing electrode
and attract the charged droplets. The process has the
disadvantage, however~ that only organ;c liqu;ds having
a spec;f;c electr;c res;stance within a certa;n range
(about 104 IL .m to 107 IL.m) can be electrostat;cally
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atomised and deposited. In particular, the aqueous
solut;ons cannot be processed~ since the;r surface
tens;on ;s too high and the;r spec;f;c res;stance
(S ~ = 5.7 ~m) ;s too low~
It ;s a further d;sadvantage that the h;ghly
charged, very f;ne droplets can only be deposited on the
outs;de parts of the plant, espec;ally if the crops are
densely planted, and do not penetrate ;nto the electr;c-
ally screened ;nner parts of the crop. Furthermore, the
1û amount oF cha~ge of the drops cannot be controlled in fl
s;mple manner, s;nce only a h;gh charge on the l;qu;d at
the edge of the spray electrode ~;ll produce the atom;s-
;ng effect. If the electrode voltage ;s reduced the
l;qu;d ;s no longer atom;sed and merely drips off.
Pract;cal exper;ence ;n the appl;cat;on of crop
protect;on agents d;ctates the follow;ng requ;rements:
1. Aqueous, non-flammable formulations are prefer-
able to organic l;qu;ds.
2. The drop s;ze should be w;th;n the range from
100 to 250 ~m.
3. The penetrat;on depth of the drops of l;qu;d ;nto
the crop stand should be adjustable. For the purposes
of the ;nvent;on "penetrat;on depth" is to be understood
as mean;ng the area ~h;ch, when v;ewed from above, ;.e.
from the t;p of the plant, ;s covered dur;ng spray;ng.
It might be poss;ble, for example, to vary the penetra-
t;on depth by varying the drop s;ze or by vary;ng the
drop charge. Heavy, uncharged drops fall to the ground
along the shortest path. By contrast, l;ght, h;ghly
charged droplets are most h;ghly deflected from the free-
fall fl;ghtpath and are attracted by the most protruding
parts of the plant~ Both these extreme cases are undes;r-
able. On the contrary~ the ;deal ;s a process where the
controlled adjustment of the rat;o of drop charge to drop
mass ;s poss;ble, s;nce ;n th;s way the zones between the
top layers of the stands and the;r bottom Layers can be
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covered.
It is the object of the invention to develop a process
uniformly dispensing aqueous liquids in drop form (plus the device
required for this purpose) which will satisfy the above-mentioned
conditions.
This object is achieved according to the invention which
provides a process for dispensing electrically conductive crop
protection liquids in droplet form having a specific resistance
~ 104-f~m, characterised in that the liquid escapes from a small
exit orifice at a flow velocity so low that, immediately beyond
the exit orifice, the liquid forms a cohesive thread which then
disintegrates into individual droplets, and in that an electric
voltage of at least 500 V relative to ground is applied to the
thread of liquid to stablise the drop size and to produce a cone
of droplets whose apex angle depends on the level of the voltage.
The flow velocity is preferably adjusted with due regard
to the dimensions of the nozzle or capillary via the operating
pressure in such a way that the length of the continuous thread
of liquid behind the exit opening is 2 to 100 mm, preferably 5-20
mm. In practice this lengith is obtained for a capillary a few
millimetres long under a liquid pressure of 0.1 to lO bar, pref-
erably 1 to 3 bar.
It has been found that the penetration depth of the show-
er of droplets in the case of densely planted crops can be control-
led by varying the liquid pressure.
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The device for carrying out the process for drop dis-
pensing liquids is characterised by a large number of nozzle
elements which are connected in parallel from a flow-engineering
point of view and which consist of capillaries of which each is
surrounded by a concentric protective sheath which is at the
same electric potential as the capillaries, as well as by a high-
voltage generator whose high-voltage output is connected, in a
manner permitting conduction, to the liquid flowing through -the
capillaries. This protective sheath is sealed at one end by a
base plate and forms a pot through the bottom of
:~22~9~2
,4
~h;ch the cap;llary appears. The l;qu;d to be d;spensed in
droplec form is suppl;ed by a stock reservo;r vessel
connected to the cap;llary. The po;nt at wh;ch the drop-
iet formation takes place, ;re. the end of the cap;l-
lary, ;s ~;th;n the pot. The backpressure requ;red forma;nta;n;ng the flow ;s generated by means of a pump
wh;ch keeps the stock reservo;r vessel under superatmo~
spher;c pressureO
The ent;re dev;ce can be constructed ;n a space-
sav;ng manner. In part;cular, ;t ;s poss;ble to realisea portable droplet dispenser which works according to this prin-
c;ple. Accord;ngly, a further development of the ;nven-
tion provides for a holder on which the nozzle elements
are arranged and wh;ch ;s attached to a rod shaped mounting
wh;ch conta;ns a battery-operated h;gh-voltage generator,
an a;r pump for generat;ng the backpressure on the
cap;llar;es, and a stock reservoir vessel for the l;qu;d
to be spray-d;spensed.
Spec;f;c embodiments and further developments of
the ;nvent;on are descr;bed ;n the subcla;ms.
The follou;ng advantages are real;sed by the
;nvent;on:
a) It has been found that aqueous solut;ons as well as
salt solut;ons and aqueous suspens;ons and emuls;ons are
dispensedand deposited on tarqet ob~jects using the new
process w;thout problems. As ;s known, l;qu;ds of th;s type
cannot be atom;sed by purely electrostat;c means. b) The
degree of charge on a drop or the charge/mass rat;o of the
drops ;s determ;ned by the level of the appl;ed voltage and
can be var;ed w;th;n wide l;m;ts. This makes ;t possible to
control the dispensinn characteristics via the P1Pctrir voltaqe.
Th;s advantage - ~h;ch ;s of great ;mportance as regards the
appl;cat;on of crop protect;on formulat;ons - can l;kew;se
not be real;sed w;th the known purely electrostat;c processes
of atom;s;ng l;qu;ds.
c) It ;s a further advantage that the requ;red l;qu;d
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pressures are onLy relat7vely Low. The requ;red back-
pressure can be generated by means of pumps of simple
design.
d) The process according to the invention can be real;sed
~;thout much hardware. In particular, the device can be
constructed in such a compact and space-sav;ng form that
portable, eas;ly operated dispensing units are now available for
aqueous crop protection formulat;ons.
e) Since only relat;vely large drops with a narrow drop
s;ze spectrum are formed in the process, this avo;ds
health-damaging aerosols or fine mist (which are a respira-
tory danger to people).
Before the ;nvention is descr;bed in more detail
by reference to ;llustrative embodiments and drawings,
the principle and the underly;ng physics of the new spray-
dispensing process will be explained in more detail below.
In the draw;ngs
F;gure 1 shows the d;s;ntegrat;on ;nto drops of
a liquid thread after ex;t;ng from a caplllary;
Figure 2 shows a cone of spray be;ng produced by
apply;ng an electr;c voltage to the thread of l;qu;d;
F;gures 3a and b show how the penetrat;on depth
of the cone of droplets is controlled when treating crop
stands;
F;gures 4a and b show how the penetrat;on depth
of the cone of droplets is controlled o~y varying the direc-
t;on of spraying;
F;gures 5a and b show how d;rected jets of droplets
can be used to ;ncrease the space charge dens;ty at the
target s;te;
. F;gure 6 schemat;cally shows a complete portable
dispensing unit;
F;gure 7 shows the holder tspray head) w;th nozzle
elements wh;ch ;s used ;n the dev;ce shown ;n F;gure 6;
~5 and
Figure 8 shows an ind;v;dual nozzle element.
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A jet of water emerg;ng at a low velocity from a
s;mple or;fice nozzle or cap;llary ;s kno~n to d;s;nte-
grate ;n a defined manner ;nto drops of a certa;n s;ze~
The smooth part of the jet, or thread of l;quid, ~hich
;s st;ll cohes;ve at the exit point has, after a short
;nit;al sect;on~ period;cally recurr;ng constr;ct;ons
wh;ch become deeper w;th increas;ng d;stance from the
ex;t open;ng unt;l, f;nally, it separates ;nto ;ndividual
drops whose d;ameter is directly related to the diameter
of the cohes;ve part of the jet. This process is depic-
ted in F;gure 1. Capillary 1, which has a d;ameter of
100 ~um, e~ects a jet of l;qu;d 2 (for example ~ater)
wh;ch is at a speed V = 6 m/second and the shape of wh;ch
;nit;ally rema;ns cyl;ndr;cal along a stretch a few cm
long, but thereafter shows surface constr;ct;ons 3 which
recur at equ;d;stant ;ntervals, all the ~h;le deepening
unt;l, f;nally, ;nd;vidual drops 4 become detached from
the jet~
The lower lim;t of the veloc;ty range for the
emerg;ng l;qu;d ;s reached when a cohes;ve thread of
l;qu;d fails to form at the exit open;ng and ;nstead the
l;qu;d comes out ;n dr;ps. The upper l;m;t for the ex;t
veloc;ty of the l;qu;d ;s reached when the lam;nar flow
turns ;nto turbulent flow and the d;s;ntegrat;on ;nto
drops of equal size is replaced by an atomising process
where the drop size spectrum is widely t,roadened.The disin-
tegrat;on of a thread of l;qu;d ;nto drops ~h;ch is
descr;bed here ;s referred to as "natural jet-d;s;ntegra-
t;on".
3û The d;ameter d of drops 4 wh;ch are the product
of natural jet d;s;ntegrat;on can be calculated from the
jet d;ameter D and the spac;ng of the constr;ct;ons or
the d;s;ntegrat;on wavelength ~ by the follow;ng formula:
d = V 1~5 D2 ~ 89 D
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In practice the ~avelength A can be set = 4.5 D. In
addit;on to the drops 4, the diameter d of which can be
calculated, there is also formed a very small proport;on
by volume of secondary satellite droplets 5 ~hose dia-
meter d5 is of the order of, for example, d5 = 0.2 d.
If the drops thus produced are followed on their fl;ght-
path, for example over a fl;ght of 1 m, ;t ;s observed
that a lar~e proport;on of the drops recomb;nes into
larger drops 6 and 7. The result ;s that the drops do
not have the expected drop s;ze d ~ 189 ~m but have a
s;ze ~ith;n the range from 190 to 8ûO ~m, ;.e. far out-
s;de the desired range. The recomb;nat;on process wh;ch
the drops undergo ;n fl;ght can be demonstrated by photo-
graphs.
It has been found, surpr;s;ngly, that the recom-
b;nat;on ;nto larger drops can be prevented by apply;ng
an eLectric voltage aga;nst earth to the cohes;ve
part of the electrically conductive thread of l;qu;d.
The drops are then preserved ;n their or;g;nal size and
arrive at the target unchanged, even if the latter ;s a
long d;stance away~ Moreover, th;s leads to the forma-
t;on of a w;de angled cone which consists of
electr;cally charged droplets ~h;ch can be depos;ted ;n
a controlled manner onto earthed objects. Th;s process
;s dep;cted ;n F;gure 2. The flo~ cond;t;ons are the
same as for the jet d;s;ntegrat;on dep;cted ;n F;gure 1,
except that an electric voltage of 10 kV aga;nst ear~h
;s applied to the cohes;ve thread 2 of l;quid. The
cap;llary 1 ;s made of electr;cally conduct;ve mater;al,
for example metal, and has a rat;o of length to d;ameter
of about 50 : 1O The l;qu;d pressure at the cap;llary
;s adjusted to values of 0.1 to 10 bar, preferably w;th;n
the range from 1 to 3 bar. Under these cond;t;ons the
result;ng thread of l;qu;d at the cap;llary ;s cohes;ve
and has a length of 2 to 100 mm, preferably 5 to 20 mm.
Instead of cap;llar;es ;t ;s also possible to use, for
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produc;ng the jet, simple or;fice nozzles whose or;fire
d;ameter is w;th;n the range from 50 m to 500 m, prefer-
ably between 100 m and 200 m. The rat;o between length
and ~;dth of su~h an or;f;ce no~zle ;s, for example, 3:1.
The h;gh voltage of 10 to 50 kv gsnerated by the
h;gh-voltage apparatus 8 ;s appl;ed to the cohes;ve
l;qu;d thread 2 v;a the cap;llary 1. The voltage and the
resulting electr;c field have the effect of ;nduc;ng a
h;gh-dens;ty electr;c charge at the surface of the con-
duct;ve thread of Liquid, the h;ghest surface charge
dens;ty ar;s;ng at the end of the thread of l;qu;d, at
about locat;on 9. As the drops 4 and 5 become detached
they take w;th them some of th;s surface charge. It ;s
of cons;derable importance that the l;qu;d ;n th;s pro-
cess is conduct;ve ~;th a spec;fic res;stance ~104 ~L.m.No lo~er l;m;t is descr;bed for the res;stance. The
l;qu;d can be ;nf;n;tely h;ghly conduct;ve~
In contrast to the fl;ghtpath of the uncharged
drops ;n the f;rst section of F;gure 1, ~hich d;ffers
only little from the or;g;nal direction of the jet, the
flightpaths of the electrically charged drops in Figure 2
are markedly spread out. The lightwe;ght satell;te drops
5 leave the ma;n fl;ghtpath ;mmediately after format;on
and then move to~ards the nearest earthed body ;n the
environment~ The normal drops formed from the bulk of
the emerging l;qu;d do not step out of line until later,
and the d;stance between them ;ncreases. The result is
the formation of a cone of droplets lO having an apex angle
The droplets retain their orig;nal size even over lengths
of fl;ght of 1 m or more. The action of the electric
field is thus due to two effects, namely prevent;on
of recomb;nation ;nto larger drops and the formatîon
of a cone of droplets as a result of electrostatic repul-
sion. Chang;ng the polarity of the charge does not
affect the effects. The apex angle of the cone of droplets
can be made small or large, depending on the level of the
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cap;Llary eject;on velocity tl;qu;d pressure) poss;ble
w;th;n ~he allowed range, on the th;ckness of the jet,
and on the electric voltage. As a consequence it is
poss;ble to depos;t the droplets in a targeted
manner. For example, adjustment of the dispensing direction
makes ;t poss;ble to treat a s~and;ng crop elther under
a flat angle, so that the charged droplets preferent;ally
reach the upper parts of the plant, or under a steep
angle~ in wh;ch case the droplets are not deposited until
they reach the lower parts of the standr In other words,
the penetration depth of the droplets can be matched to
the particular requirements of any crop stand.
F;gures 3a and b sho~ how the penetration depth of
the droplet shower into dense stands can be controlled by vary-
ing the l;quid pressure ;n the nozzle and the associatedjet exit veloc;ty~ In sub-frame a, ~ater ;s ejected
under a pressure of P1 = 0.6 bar at an average ejection
velocity V1 = 5.6 m/s from a no zle 9 having an internal
diameter d = 100 ~m. The jet ;s under a voltage of -15
kV wh;ch ;s maintained by the h;gh-voltage apparatus 10.
Beneath the nozzle there are two plants 11 and 12 of a
major stand of plants. The he;ght of the plants is 0.5 m.
The d;stance from the plant tip to the nozzle is 0.3 m. The
cone of droplets 13 opens up above the plants 11 and 12.
The drops, becom;ng a liqu;d thread of low kinetic energy,
are qu;ckly braked through air resistance and are quan-
t;tat;vely depos;ted ;n the upper parts of the plants 11
and 1Z under the act;on of Coulomb forcesn In sub-frame b,
the shower comes from nozzle 14 under the same voltage,
but the pressure ;s 3 bar and the ex;t velocity V2 =
16.8 m/s. In this case, the moving drops are not effec
tively braked unt;l the lower part of the plants 15 and
16, uhereafter the forces of electrostat;c attract;on
prevail and deposit the drops in this zonen The cone of drop-
lets 17 ;s less w;de-angled than cone 13. In both cases
(a and b) the drop size and the charge remain virtually
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the same, so that the drops are depos;ted under controlLed
cond;t;ons once the free-fall velocity has been braked.
In Figure 4a the nozzle or capillary 18 is
arranged above the stand 19 in such a way that the
emerg;ng thread of l;qu;d ;nit;ally goes ;n the hor;zon-
tal d;rection. The high-voltage generator has been
om;tted here~ The cone of droplets produced is braked by
the air res;ctance and then deposits at a reduced velo-
city ;n the upper parts of the plants of stand 19, so
that the penetration depth obtained ;s only lo~. In
Figure 4b the dispensing direction has been turned b~ 90
relat;ve to the first position, ;.e. the capillary 21 is
in th;s case vertical. The h;gh-voltage source is not
drawn ;n, as ;n F;gure 4a. The cone of droplets falls out
of the cap;llary 21 and ;nto the stand 22 at a higher
veloc;ty than in the arrangement dep;cted in F;gure 4a,
s;nce grav;ty acts ;n the same d;rect;on. As a result
the penetration depth is higher and the drops are prefer-
ent;ally depos;ted in the lower parts of the ind;v;dual
plants. It will be read;ly understood that the penetra-
tion depth ;s ;nfin;tely var;able by vary;ng the nozzle
pos;t;ons between these two extreme pos;tions 1R and 21.
It ;s thus possible to control the penetrat;on depth of the
cnne of droplets into crop stands by varying the direc-
tion in ~hich the liquid is ejected~ Large-area planta-
tions can be treated by mov;ng a row of such nozzles
across a field parallel to the ground ~drawn arrows)~
S;multaneous use of a large number o~ nozzle
elements makes it possible to concentrate the space charge
generated by the drops ;n the immediate vicinity of ~he
target object. Thus, ;n F;gure 5a, a space charge cloud
23 of high charge density is bu;lt up ;n front of the
target object 24 by means of a large number of parallel-
orientated nozzles 25. F;gure 5b shows another way of
building up a high space charge density by means of a
large number of nozzles 26. In this case the nozzles are
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or;entated ;n such a way that the extens;on of the l;qu;d
threads, i.e. the ;n;t;al direct;ons of the jets~ ;nter-
sect at the s;te of the space charge 27 and form a power-
ful deposit;on f;eld at the target object 28. In this case
the dispensing nozzLes are spaced a cons;derable d;stance
apart and the jet d;rect;ons are concentrated on one
point ;n space.
F;gure 6 shows a complete device which is con-
structed in such a compact and manageable form that ;t
can be operated by one person as a portable appl;ance.
It cons;s~s of the shower head 29, the liquid-filter 30,the
l;qu;d-valve 31, the stock reservo;r vessel 32 for the
l;qu;d to be dispensed, a high-voltage generator 33, a
battery cas;ng 34 and an a;r pump 35~ All the components
are conta;ned ~;th;n a rod-shaped mount;ng 36 made of
;nsulat;ng mater;al. The electr;c system ;s earthed by
means of an earth;ng cable 37 whose free end ;s on the
ground or electr;cally connected to the object to be
treated.
To set the appl;ance ;n opera~;on the a;r pump 35
;s used to pump a;r ;nto the vessel 32 ~hich ;s partially
full of the l;quid to be discharged.A proportion of the
capac;ty, for example 30X, ;s left free for the com-
pressed air to form an a;r cushionO The pressure in th;s
capac;ty is ra;sed to 2 to 3 bar. The valve 38 prevents
the L;quid from flow;ng back. The nozzle head 29 is put
under h;gh voltage, for example a voltage of 50 kV~ by
sw;tch;ng on the h;gh-voltage generator 33 by means of
the sw;tch 39 wh;ch closes the pr;mary c;rcu;t. When
valve 31 ;s opened the l;qu;d flows out through ~he nozzle
head 29 and ;s d;spensed ;n cone form as described above.
The nozz1e or dispensing head 29 is depicted in Fig. 7. In
pr;nc;ple ;t cons;sts of a large number of nozzle e1ements
wh;ch are connected ;n paralLel from a flow-engineer;ng
po;nt of v;ew and are connected to the l;qu;d conta;ner
32 by way of l;ne 44~ ~h;n jets of L;qu;d are very
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effic;ently produced us;ng short cap;llary tubes, wh;ch,
however, are very sens;t;ve to so;ling and damage on
d;rect contact w;th other objects, for example plants.
For th;s reason the capillary ;s here protected by a con-
centr;c shea~h. Although the formation of an electr;cf;eld ;s ;nh;b;ted by the screen;ng act;on of the pro-
tect;ve sheath - the sheath be;ng at the same potent;aL -
the d;spensîng ;s not ;mpaired. The reason for th;s ;s tat
that cohes;ve first section of the thread of liqu;d wh;ch
projects beyond the edge of the protect;ve sheath ;s, by
v;rtue of the fact that the l;qu;d ;s conduct;ve, a sub-
st;tute ~or a tip electrode at wh;ch the requ;red f;eld
for charg;ng up the drops bu;lds up outs;de the cyl;nder.
In F;gure 7, the cap;llary 47 is ;nserted ;nto
the base plate of a pot 48 and thus forms a nozzle element
40 wh;ch ;s pressed ;nto the correspond;ng bores of the dis-
pensino head 29.The project;ng edge 42 (the collar of
pot 48) l;m;ts the penetrat;on depth. The free end of
the cap;llary 47 d;ps ;nto the l;qu;d duct 43 ~h;ch ;n
turn ;s connected to the supply tube 44.
S;nce the cap;llar;es 47 can eas;ly become so;led
on prolonged use ;n the form of encrusted depos;ts ;t ;s
necessary to have a fac;l;ty wh;ch allows the nozzle ele-
ments 40 to be replaced s;mply and qu;ckly. For th;s
purpose,eve~y nozzle element 40 ;s enclosed by a r;ng 45
made of res;l;ent mater;al and hav;ng a c;rcu~ference
greater than the c;rcumference of the holder 41 for the
nozzle elements. The r;ng 4~ has a dr;lled hole at the
top (F;gure 7) and ;s bolted to the holder 41 on the
oppos;te s;de (46). The nozzle element 40 ;s then ;nserted
;nto the holder 41 through the dr;lled hole ;n the
res;l;ent r;ng in such a ~ay that the collar 42 of the
protect;ve sheath 48 projects beyond the dr;lled hole and
thus forms an abutment (see F;gure 8). To replace a
nozzle element 40 the r;ng 45 ;s compressed (arrows ;n
F;gure 8). As a result the ring 45 ;s deformed and
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exerts suff;c;ent force on the nozzle element 40 to d~a~
;t out of the socket in the holder 41. Thereafter a
new eLemen~ can be ;nserted through the drilled hole
;n the r;ng 45 and be plugged ;nto the correspond;ng
orifice of the holder 41. The exchange of nozzle elements
can be done by hand ~ithout the use of tools.
The d;ameter of the res;lient ring 45 ;s S to 50
mm, preferably 10 to 30 mm. The length of the holder 41
and the pack dens;ty of the nozzle elements 40 can be
adapted to demand. The pack density is onLy l;m;ted by
the mutual contact of the components.
The level of the electr;c charge on the drops has
a maximum which ;s reached ~hen the electr;c f;eld
strength in the env;ronment of the starting points of the
jets takes on a value beyond ~hich corona discharg;ng
occurs~ The level of the most su;table operating voltage
depends on the d;mensions of the apparatus. It must
therefore be determ;ned exper;mentally. A s;ngle nozzle
element hav;ng a cap;llary w;dth of 1ûO ~um anc1 a very
remote counter-electrode tat least 0.5 m away) has a
most suitable operat;ng voltage of about 10 kV~ The
upper l;mit for the operat;ng voltage ;s about 50 kVo
Compared ~ith known dev;ces for generat;ng
electr;cally charged mists, the descr;bed device has a
great advantage ;n that no counter-electrode ~;th earth
potent;al ;s requ;red ;n the ;mmed;ate v;c;n;ty of the
nozzle un;t under h;gh voltage. As a result ;t ;s pos-
s;ble to use very long ;nsulat;ng sest;ons between the
voltage-conduct;ng parts of the set-up. In th;s ~ay ;t
;s poss;ble largely to el;m;nate operating problems due
to mo;st a;r or due to so;ling of the ;nsulators. It ;s
furthermore of ;mportance that the currents are very lo~
tof the order of ~A), so that the battery used to supply
the voltage has a long life and the h;gh-voltage generator
can have a h;gh ;nternal res;stance. In th;s ~ay people
are not endangered by h;gh voltage.
Le A 22 441
