FR2635169A1 - HOT GAS AIR GENERATOR - Google Patents

Abstract

This heater comprises means (14, 16) for producing a mixture of air and fuel gas in movement, a flame catching grille (35) arranged transversely in the path of the mixture, and a guide tube (41) for channelling a current of hot mixture of air and of burnt gas which results from the combustion of the fuel gas, the downstream end (46) of the tube opening into the open air, and a flame flattening grille (36) arranged transversely in the path of the mixture, downstream of the catching grille, the flattening grille having aperture dimensions and/or an aperture ratio greater than those of the catching grille. A short flame is thus obtained, which does not reach the outlet of the guide tube.

Description

The invention relates to a current generator

  hot air, that is to say a device projecting a hot air flow beyond the free end of a tube

who directs it.

  Such devices are known, for example

  hair, in which a draft is produced

  by a fan and heated by an electrical resistance

  than. Hot air current generators are also known-or more exactly a current of a hot mixture of air and flue gas-in which this current

  is heated by burning a combustible gas.

  Such devices are used for example for the

forming of plastics.

  In gas hot air current generators, it is necessary to prevent the flame produced by the combustion of the gas from extending beyond the free end of the steering tube. This condition is difficult to fulfill because the flame tends to extend until it meets an influx of fresh air sufficient to allow

complete combustion of the gas.

  To solve this problem, it has been proposed to adopt a relatively long head tube. In addition to its adverse impact on the size and weight of the device,

  this measure is not very effective because, for the indi-

  above, the length of the flame increases with

that of the tube.

  Another known technique is to adopt a large diameter tube to allow the outside air to enter through the downstream end at the same time that the stream of hot air comes out. But this results in a decrease in the speed and efficiency of the hot air stream. The object of the invention is to provide a gas hot air current generator whose flame does not protrude beyond the steering tube and which does not have the drawbacks mentioned above of the known solutions. The subject of the invention is a hot air current generator comprising means for producing a mixture of air and moving fuel gas, a flame attachment grid arranged transversely in the path of the mixture, and a steering tube. to channel

  a hot mixture of air and flue gas resulting from

  both of the combustion of the combustible gas, the downstream end of the tube opening to the open air, characterized in that it further comprises at least one transversely arranged flame crushing grid. in the path of the mixture, downstream of the gripping grid, the crushing grid having opening dimensions and / or an opening rate higher than

those of the grid of attachment.

  Preferably, the gripping and crushing grids define between them a limited combustion chamber

  laterally by a substantially continuous side wall

  naked. Advantageously, the three minimum, maximum and preferential values of each of the geometrical parameters are approximately as follows, for a burner with a flow rate of the order of 40 g / h LPG at 1.5 bar. Of course

  these values would be different for a different flow rate.

  - longitudinal distance between the two grids: 6mm, 12m and 9mm. diameter of the openings of the grid of attachment:

2mm, 4mm and 3mm.

  - Opening rate of the shackle:

%, 25% and 20%.

  - diameter of the openings of the crushing grid:

2,5mm, 4,5mm and 3,5mm.

  - opening rate of the crushing grid:

22%, 34% and 27%.

  - distance between the crushing grid and the end

  free of the steering tube: 40mm, 60mm and 45mm.

  - internal diameter of the steering tube:

mm, 40mm and 30mmn.

  According to one embodiment of the invention, the apparatus

  includes a body forming a hollow handle in which

  the can be inserted an interchangeable cartridge as a source of gas, the handle forming an obtuse angle with the steering tube. It is then advantageous that the free end of the hollow handle defines an oblique plane relative to the longitudinal direction of the handle so that the generator can be placed in stable equilibrium by said end on a

horizontal receiving surface.

  According to a second aspect, the purpose of the invention is to facilitate

  switch off the appliance without the need for

  intended to temporarily change the characteristics of

air-gas mixture.

  In this second aspect, the invention applies not only

  to a hot air current generator as defined above, but to any combustion apparatus

  of gas comprising means for mixing a combustion gas

  and at least one of the air in predetermined proportions and to form a stream of the resulting mixture, and ignition means comprising an ignition chamber filled with said mixture and from which an ignition flame can propagate to form a

main flame of combustion.

  According to the invention, the ignition chamber is away from the path of said current and communicates with a space interposed on said path, space in which the speed of the current is relatively reduced and / or the proportion of the fuel gas in the mixture before ignition is higher than the proportion in which this gas

  is introduced by the mixing means.

  According to one embodiment, the apparatus comprises means forming an obstacle to the current downstream of said space, these means possibly comprising a grid provided with

  openings that must cross the current of the mixture.

  According to a third aspect, the invention relates to a gas combustion apparatus, in particular, but not exclusively, a hot air current generator as defined above, able to operate in different orientations, comprising a injector provided with a hole. small diameter for forming a jet of pressurized combustible gas from a liquefied gas tank and mixing it with air, and means for transmitting heat to the injector

produced by the combustion of gas.

  When such an apparatus operates in a position where the liquefied gas tank is located higher than the injector, liquefied gas may flow through

  gravity towards the injector. The warm-up of this one

  it makes it possible to vaporize the liquefied gas and to prevent it from crossing the injection hole, which

  would result in excessive flow.

  However, it has been found that the heat flow rate transmitted to the injector is not always sufficient to ensure the evaporation of the quantities of liquefied gas.

coming to this one.

  To solve this problem, the invention provides means located upstream of the injection hole to limit

  gravity influx of liquefied gas to the injector.

  According to one embodiment of the invention, these limiting means comprise a diaphragm interposed on the path of the gas under pressure and provided with a small diameter through hole, preferably between

O, lmm and 0.3mm approximately.

  Other features and advantages of the invention

  from the following detailed description and the following

  attached drawings in which: - Figure 1 is a sectional view along the line I-I of Figure 3, a first embodiment of a hot air generator according to the invention; FIGS. 2 and 3 are front views of two constituent parts of the hot air generator of FIG. 1; and

  FIGS. 4a and 4b are incomplete partial views.

  in section representing a second mode of

  production of a hot air generator according to the invention

tion.

  In the description that follows, the terms "before" and

  "backward" refer respectively to the downstream and upstream directions with respect to the gas flow in the apparatus,

  corresponding to the left and right sides of the figures.

1 and 4a.

  The hot air generator shown in FIG. 1 comprises a molded zamak body 1 having an outside contour of revolution with the exception of a boss 2 which protrudes outwards over a small part of the circumference and ventilation apertures not shown. The body 1 has the general shape of a cup having a bottom 3 pierced with a circular central opening 4 and a side wall 5, in which the aforementioned openings are formed, widening in a truncated cone from the bottom 3 and extending by a cylindrical portion 6 opposite the bottom. From the latter, an annular flange 7

  surrounding the opening 4 extends to the outside.

  of the body forming a cylindrical housing 8.

  The frustoconical wall 5 carries an inner boss 9 at a location on the circumference. The outer boss 2 extends inwardly of the body by two curved wings towards each other 10 which in cooperation with the boss 2 define a housing 11 for a piezoelectric igniter 12. FIG. front view of the body 1, also shows two axial cylindrical studs 13 depending from the bottom inwards

of the body 1.

  A brass mixing tube 14 extends coaxially with the body 1 and has a front end slightly set back from the open end of the body

  1 and a rear end located beyond the bottom 3.

  Openings 15 are formed through the wall of the tube 14 between the outside thereof and its axial bore 16. These openings are located at the bottom 3 of the body. At its front end, the mixing tube 14 has an outer diameter portion

  reduced 18 externally threaded, limited by a shoulder-

Annular 17.

  An injector 19, provided at its front end with a gas injection hole 20, is threaded into the bore 16

  at the rear of the tube 14 and abuts against it

  ci by an annular flange 60. Across the inner cavity of the injector, there is arranged a filter 21 in the form of a porous mass and, at the rear end of the injector, a diaphragm 22 in the form of a disc pierced with a hole 23, the edge of the diaphragm 22 being trapped axially between a shoulder

  internal and a crimping lip 24 of the injector.

  The rear end of the mixing tube 14 is surrounded by a ring nut 25 having at its rear part an internal thread intended to cooperate with an outlet fitting 26, shown in broken line, making

  part of a fuel gas supply valve

  tible. The ring-nut 25 has at its front end an annular flange 27 directed towards the axis, which cooperates with a shoulder of the tube 14 to prevent the latter from moving forward. This front end of the ring-nut penetrates with a radial clearance in the

housing 8 of the body 1.

  The mixing tube 14 is screwed by its front part into a spun brass spider 28, shown in FIG. 2 in axial view from the rear, and whose rear end abuts against the shoulder 17 of the tube 14. The spider 28 comprises a central portion 29 forming a sleeve, from which four radial arms are directed opposite the axis 58 of the tube 14 and arranged at right angles to each other. Three of these referenced arms 30 have the same reduced circumferential width and extend continuously from front to back, while the fourth arm 31 has a larger circumferential width and has an internal recess 32 communicating with the axial bore 33 the sleeve 29. The wall of the arm 31 located behind the recess 32 is traversed axially by a frustoconical opening 34 whose small base

is adjacent to the recess 32.

  A flame catching grid 35 is disposed across the bore 33. It is supported rearwardly against a shoulder of the latter, in which it

  is immobilized for example by adjustment with clamping.

  A flame crushing grid 36 blocks the front end of the bore 33 and is immobilized axially between a shoulder of the latter and a lip of

annular crimping of the sleeve 29.

  The arms 30 and 31 have front faces 38 located in the same radial plane, beyond which extend axial flanges 39 defining internal surfaces belonging to a cylindrical surface of axis 58 and in which a guide tube fits 41 for the hot air, whose rear end abuts against the faces 38. The outer ends 42 of the

  arm 30 and 31 also form cylindrical bearing surfaces

  Convex convexes on which adjusts an outer tube 43. At its rear end, the tube 43 is crimped into crimping zones 44 located circumferentially facing the arms 30. At right arm 31 the tube is not deformed. The front end of the outer tube 43 is pushed inward to serve as a forward support at the end 46 of the

steering tube 41.

  The spider 28 and the tubes 41 and 43 form a set

  rigid thanks to the mutual cooperation of the ends 45 and 46 of the tubes, the cooperation thereof with the bearing surfaces 40 and 42 and partial crimping 44. The grids 35 and 36 and the mixing tube 14 screwed to the bottom

  in the cross are integral with this set.

  Two axial rods in stainless steel, not shown

  The pins are pressed tightly by blind bores on the pins 13 of the body 1 and bear forwards by shoulders against the sleeve 29 of the spider 28. Beyond these shoulders, the tie rods have cylindrical centering projections

  cooperating with notches 47 on the periphery

  sleeve 29 to ensure centering and immobilization

  rotation of the spider relative to the body.

  Finally, an elastic corrugated washer 48 is interposed

  between the ring-nut 25 and the bottom 3 of the body, to the

  This washer tends to push the body and with it the tie rods relative to the nut-ring 25 and, consequently, to the mixing tube 14 and the cross-member 28. All the parts described so far are thus assembled and centered relative to each other. The piezoelectric igniter 12 is, for its part, trapped longitudinally between the rear end of the outer tube 43 and the bottom 3 of the body 1, its actuating pushbutton 49 protruding from the rear of this bottom to through a

opening in it.

  The boss 9 of the body 1 serves as a rear support for a spark plug 50 oriented axially, which has a frustoconical portion 51 cooperating with the frustoconical opening 34 of the arm 31 of the spider under the thrust of a spring. helical 52, housed in a recess 53 of the boss 9 and compressed between the shoulders of this boss and the candle. The front end of this

  last penetrates, beyond the opening 34, into the

  32 of the arm 31, protrudes the end of its electrode 54. A -cable 55 connects the electrode to

the igniter 12.

  The centering tie rods pass in two opposite quadrants defined by the arms 30 and 31 of the spider, while the igniter 12 passes into a third quadrant

between two arms 30.

  We now describe the operation of the generator

hot air.

  A fuel gas, for example butane, propane or a mixture of these two compounds, from a liquefied gas tank, is injected under pressure

  through the injection hole 20 of the injector 19 into the

  Wise 16 of the mixing tube 14, where it drives air that enters through the radial openings 15. The gas and air mix homogeneously in the front portion of the bore 16, whose diameter is reduced by relative to the portion o open the openings 15. The mixture enters the bore 33 of the cross and passes through the flame holder grid 35 to reach the combustion chamber 56 constituted by the portion of the bore 33 between the grilles and 36. This combustion chamber is closed over its entire axial length and over most of its perimeter and communicates by a single passage with an ignition chamber constituted by the recess 32 of the arm 31 of the spider, this chamber 'ignition

  being located away from the axial path of the gas stream.

  The passage between the combustion chamber 56 and the ignition chamber 32 is practically the only access way of the latter, the frustoconical opening 34 being sealed substantially sealed by the frustoconical portion 51 of the spark plug urged by the spring 52 and the outer end of the recess 32 by the adjustment of the tube 43 on the scope 42 of the arm 31. No gas flow circulates therefore in

  the chamber 32, which contains a stationary mixture.

  In addition, the presence of the flame crushing grid 36 causes a pressure drop resulting in a fuel gas richness of the mixture contained in the chambers 56 and 32 greater than that corresponding to the flow rates of gas and penetrating air in the mixing tube 14, with a flow velocity of the mixture

  relatively small in the combustion chamber 56.

  These conditions are favorable for the birth of a flame in the ignition chamber 32 and its propagation

in room 56.

  When the button 49 of the igniter 12 is pressed, a spark is established between the end of the electrode 54 of the spark plug 50 and the front wall of the arm 31 of the spider, which faces it and is spaced from it. About 4mm. This spark causes the ignition of the gas contained in the chamber 32 and the propagation of

the flame in the room 56.

  In the example described, relating to a burner delivering approximately 40g / h of LPG at 1.5bar, the grids 35 and 36 are spaced from each other 9mm. The grid 35 has a central hole with a diameter of 1.2 mm and four holes of diameter 3 mm arranged in a quaternary symmetry about the axis 58 of the chamber 56 and the tubes 14, 41 and 43. These five holes represent a section of passage 29.4mm2 for an outer diameter of 13.8mn, a section of the combustion chamber 56 at its rear end of 150mm2. The opening rate is about 20%. The gate 36 has five 3.5mm diameter holes, one in the axis and the other four distributed in a quaternary symmetry around it. The corresponding passage section is 48.1mn2 for a section of the chamber at its front end of 177mm2, an opening rate of about 27%. With these geometrical arrangements, the flame is split by the first grid 35, then tends to regroup in the chamber 56 when it meets

  the second grid 36 which splits it again.

  But splitting the flame is like favoring

  its oxygenation. By multiplying the fractional stages

  by setting up several consecutive grids whose opening rate is increasing, oxygenation is further promoted and therefore

its shortening.

  It will be noted moreover that the oxygenation is favored by the induction of fresh air created by the dynamic flow of the flue gases through the spider 28 from

  opening ears of the body 1 (not shown).

  The sleeve 29 of the spider 28, adjacent to the combustion chamber 56, heats up strongly. The mixing tube 14 is in good thermal contact with the sleeve and has a substantial fraction of its length, between the shoulder 17 and the rear extension of

  the bore 16, an important wall cross-section

  aunt allowing it to provide a high heat output to the rear. Injector 19 is in turn

  in good thermal contact with the tube 14 by its adhesive-

  30 which is pressed against a shoulder of the tube

  by the end of the threaded connection 26, a seal of

  Chest 57 being interposed between the end of the connector 26 on the one hand, the tube 14 and the flange 30 on the other hand. The injector is thus raised to a sufficiently high temperature so that liquefied gas arriving in the filter 21 vaporizes therein and is not likely to cross the injection hole 20. The diaphragm 22 makes it possible to limit the influx of liquefied gas to the filters 21 when the apparatus is oriented so that the

  Liquefied gas tank is above the injector.

  The steering tube 41, in contact with the flow of

  burned gas, is also brought to a high temperature.

  But this high temperature is not communicated to the outer tube 43 which is in contact with the tube 41 only by an extremely small area. The tube 43 is also in contact with reduced surfaces with the ends of the arms 31 and 40 of the spider, whose small section still limits the supply of heat to the tube 43. The appearance of the latter is not affected. by warming up. As for the body 1, it is not in direct contact with the spider or with the mixing tube 14. It is only in relation to the spider by means of the centering tie rods, and with the tube 14 that by means of the nut-ring 25 - which itself has a reduced contact surface with the tube- and the corrugated washer 48. The piezoelectric igniter 12, mounted loosely in the

  body 1, in turn undergoes only a rise in temperature

  less than 50 K, which is not likely to deteriorate

  rer. The hot air generator shown in FIGS. 4a and 4b

  comprises a mixing tube 14, an injector 19 with-

  its filter 21, a nut-ring 25, a seal 57, a spider 28, grids 35 and 36, a guide tube 41, an outer tube 43 and a spark plug 50 identical to the elements bearing the same references to the Figure 1, arranged and assembled together in the same way. These elements will not be described again in detail. However, the spider 28 may not include the notches 47 shown in Figure 2, the latter being useless in the embodiment

Figures 4a and 4b.

  The rigid assembly formed by the elements 14, 28, 36, 41 and 43 is secured to a valve 101 for adjusting the flow rate of a pressurized liquefied gas by screwing the nut ring 25 onto a threaded outlet connection. 102 of the taps. The latter is of conventional construction and is not shown in detail. It comprises in particular a rotary control knob 103, as well as a threaded housing 104 for the outlet nozzle 105 of an interchangeable gas cartridge 106, equipped with a sealing gasket 107, and a pusher providing the opening an outlet valve of the cartridge when it is screwed

in dwelling 104.

  The apparatus further comprises a body 108 made of plastic material filled with glass fibers, formed of two half-shells assembled together in the plane of FIGS. 4a and 4b, by means of screws 109 oriented perpendicularly to this plane and passing through bosses. two half-cups. The body 108 has the general shape of a bent tube whose end portion 110, surrounding the tube 14 and a portion of the spider 28 and the tube 43, is oriented along the axis 58 of the tubes 14, 41 and 43, and of which another handle portion 111 surrounds the cartridge 106 and is oriented along the axis 112 thereof. The two parts 110 and 111 make an obtuse angle of about 120 between them, which

  corresponds to the angle between the axes 58 and 112.

  The handle portion 111 is flared near its open free end 113 to permit screwing and unscrewing of the cartridge 106. This end 113 is located in a plane slightly inclined with respect to the axis 112, so that the device can be placed by this end on a horizontal bearing surface with the axis 112 deviating somewhat from a vertical orientation so that the center of gravity of the device, outside this axis, is above of the lift surface defined by the end 113. In addition to the opening of the end 113, the handle 111 has a notch 114 which reveals a portion of the lateral surface of the cartridge 106. An opening is also provided in the vicinity of the front end of the handle for passing a drum 125 of the valve 101 in which

  is mounted the axis of the operating knob 103.

  Finally, an opening is formed on the ccncave side of the junction between the body parts 110 and 111 to accommodate an ignition trigger 115. This trigger, made of plastic, is slidably mounted on a spindle 116 of brass extending in parallel. to the axis 58 and held at its ends by an outer portion 117 and an inner portion 118 of the body. A piezo igniter 12 'similar to the igniter 12 of Figure 1 is held in a housing being directed parallel to the axis 58, its operating knob 49' being oriented forward. The housing of the igniter 12 'is limited upward (in the normal use position of the hot air generator), that is to say towards the axis 58, by an inner wall 119 of the body 108 downwards by another internal wall 120 of the body and by the trigger 115, and forwards by a projection 121 of the latter directed towards

  the top. The igniter is also retained towards the rear.

  The trigger 115 can be operated by the index finger of the hand holding the handle 111. When the trigger is pushed backwards, the

  projection 121 pushes the button 49 'and causes the production

  tion of a voltage pulse which is sent to the spark plug 50 via a cable 55 'passing through the wall 119. The spark plug 50 is applied in the frustoconical opening 34 of the spider 28 by a spring 52' acting from the same way as the spring 52 of Figure 1 and supported at the rear on a projection depending on the wall 119. The trigger 115 is brought forward in its rest position by the return spring of the button 49 ' the igniter and another coil spring 122 oriented parallel to the axis 58, compressed between the trigger and an inner wall 123 of the body 108. The button 49 'and the spring 122 are located respectively above and below pin 116 so as to ensure a balance of forces and a

  good sliding guide of the trigger.

  The ring-nut 25 is centered in an annular inner wall 124 of the body 108. This centering contributes, with that of the cartridge 106 in the handle 111

  and that of the barrel 125 in the opening 126, to the solidari-

  body with the rigid set it contains.

  This mode of connection further reduces the heat input to the body 108 relative to that received the body 1 of Figure 1, and therefore the igniter 12 '. For the remainder, the operation of the apparatus of Figures 4a and 4b is similar to that described about

of Figure 1.

  In this apparatus, the cartridge 106 may be replaced by a connection accessory to a reservoir of

larger gas.

  This accessory consists of a tube having at its downstream end a shape similar to that of the valve of the cartridge 106, and upstream a form of nipple for receiving a hose connected tightly

and tight by necklace.

  The other end of the flexible hose is tightly connected with a hose clamp to a fitting

for LPG tank.

Claims (18)

claims   1. - Hot air current generator comprising   means to produce a mixture of air and heating gas.   in motion, a flame latch (35) disposed transversely in the path of the mixture, and a steering tube (41) for channeling a hot mixture stream of air and flue gas resulting from combustion of the fuel gas , the downstream end (46) of the tube opening to the open air, characterized in that it further comprises at least one flame crushing grid (36) arranged transversely in the path of the mixture, downstream of the latching grid, the crushing grating having opening dimensions and / or an opening rate   superior to those of the grid of attachment.   2. - Hot air current generator according to the   cation 1, characterized in that the gripping and crushing grids define between them a combustion chamber (56) limited laterally by a wall   lateral (33) substantially continuous.   3. - Hot air current generator according to one   Claims 1 and 2, characterized what the   longitudinal distance between the two grids is   is between 6 minutes and 12 mm, and preferably close to 9 mm, for a burner with a flow rate of the order of 40 g / h LPG at about 1.5 bar.   4. - Generator of hot air stream according to one   previous claims, characterized by what   the diameter of the openings of the latching grid is between 2mm and 4mn approximately, and preferably neighbor of 3mm.   5. - Hot air current generator according to one   of the preceding claims, characterized what   the opening rate of the latching grid is between about 15% and 25% and preferably about 20%. 6. - Hot air draft generator according to one   of the preceding claims, characterized in that   the diameter of the openings of the crushing gate is between approximately 2.5mm and 4.5mnt and preferably neighbor of 3,5mm.   7. - Hot air current generator according to one   of the preceding claims, characterized in that   the opening rate of the crush gate is between about 22% and 34% and preferably about 27%. 8. - Hot air current generator according to one   of the preceding claims, characterized in that   the distance between the crush gate and the free end of the steering tube is between 40 nm and   About 6cm and preferably about 45mm.   9. - Generator of hot air stream according to one   of the preceding claims, characterized in that   the inside diameter of the steering tube is between approximately 25 mm and 4 cm and preferably close from 30mut.   10. - Generator of hot air stream according to one   of the preceding claims, characterized in that   the steering tube is surrounded radially by a tube outside (43).   11. - Generator of hot air stream according to one   of the preceding claims, characterized what he   comprises a spider (28) having a sleeve (29) provided with an axial bore defining the combustion chamber, and radial arms (30,31) at least one (31) of which has an internal recess (32) with said bore, and in which protrudes, through an opening (34), the end of a spark plug.   12. - hot air current generator according to claim 11, characterized in that it comprises a mixing tube (14) of large section screwed to the front of the sleeve (29) of the spider and bearing on that by a bearing surface (17), and leaning back against a collar (60) of an injector (19) so as to   to achieve a good thermal contact between these elements.   13. - Generator of hot air stream according to one of   preceding claims, characterized in that; it   comprises a body (108) forming a hollow handle (111) into which a cartridge can be inserted   interchangeable (106) as a source of gas.   14. - Generator of hot air current according to the   cation 13, characterized in that the free end (113) of the hollow handle defines a plane oblique to the longitudinal direction (112) of the handle so that the generator can be placed in stable equilibrium by said end on a area horizontal receiver.   15. - Generator of hot air stream according to one   of the preceding claims, characterized in that   comprises an ignition chamber (34) communicating with the combustion chamber (56) and means (12.50) for producing in the ignition chamber an ignition flame that can propagate in the combustion chamber. 16. - Generator of hot air stream according to one   of the preceding claims, characterized in that   the means for producing a mixture of air and fuel gas comprises an injector (19) having a small diameter injection hole (20) for forming a jet of pressurized gas from a reservoir   liquefied gas (106), means (29, 14) for transmitting   be injected with the heat produced by the combustion   of the gas, and means (22) located upstream of the injection hole to limit gravity influx of liquefied gas to the injector.   17. - hot air current generator according to claim 16, characterized er. said limiting means comprise a diaphragm (22) interposed on the path of the gas under pressure and provided with a hole passage (23) of small diameter.   18. - Hot air current generator according to claim 17, characterized in that the diameter of the through hole is between 0.1 mm and 0.3 mm, approximately.