EP0359794A1

EP0359794A1 - Gas-operated appliance for personal use

Info

Publication number: EP0359794A1
Application number: EP19890902741
Authority: EP
Inventors: Wilhelm Schneider
Original assignee: Braun GmbH
Current assignee: Braun GmbH
Priority date: 1988-02-29
Filing date: 1989-02-27
Publication date: 1990-03-28
Also published as: JPH02503349A; WO1989007898A1

Abstract

Appareil à gaz pour usage personnel, comportant un réservoir de gaz, une tuyère de mesure de gaz (21, 29), une zone de mélange (111) et un brûleur. Le jet de gaz sortant de la tuyère (21, 29) est entouré par l'air ambiant (25). La tuyère (21, 29) comporte au moins deux canaux (35, 36) dont l'axe médian forme avec l'axe médian de la tuyère un angle alpha de telle manière que les jets de gaz s'interpénètrent au moins partiellement dans une zone (24) située à peu près au niveau de la surface de la sortie de la tuyère (26) ou en aval de celle-ci.Gas appliance for personal use, comprising a gas tank, a gas measuring nozzle (21, 29), a mixing zone (111) and a burner. The gas jet leaving the nozzle (21, 29) is surrounded by the ambient air (25). The nozzle (21, 29) has at least two channels (35, 36), the median axis of which forms with the median axis of the nozzle an angle alpha so that the gas jets interpenetrate at least partially in a zone (24) located approximately at the level of the surface of the outlet of the nozzle (26) or downstream thereof.

Description

Gas powered device for personal use

The invention relates to a gas-powered device for personal use according to the preamble of the main claim. Such a device is already known from US Pat. No. 4,539,974. The known curling iron has a catalytically active heating device in which the gas emerging from a tank or a cartridge is oxidized. The resulting heat is used to heat a tube on which the hair to be curled is wound. Before entering the catalyst, the gas flows through a nozzle with a single nozzle bore and into a zone adjoining the nozzle upstream, in which the gaseous fuel is mixed with oxygen.

However, the invention is not limited to a catalytically heated curling iron, but can be used for all gas-operated devices for personal use, for example also for a gas-operated hair care device with heating by open flames. The invention can also be used advantageously in the case of gas-operated soldering irons, irons, hair dryers, warm air brushes or other devices having a jet pump or injector. Basically, it is an improvement of a jet pump for gaseous media in particular, which is also operated at low flow rates.

To ensure an optimal combustion process for all gas-operated devices, it must be required that the ratio of the gas and air fractions in the air-gas mixture is approximately a stoichiometric ratio. If, for example, isobutane is used as fuel, there is a stoichiometric ratio between air fractions and gas fractions when about 31 volume fractions of air are added to a volume fraction of gaseous isobutane. By means of a suitable dimensioning, in particular of the diameter of a bore in the gas metering nozzle and the adaptation of the mixing zone adjoining the gas metering nozzle - for example in the form of a diameter of a suitable Venturi tube - a certain mixing ratio can be set for fixed gas flow rates. As a rule, however, these devices for personal use are not operated with a constant, fixed gas flow rate, this varies depending on a setting controlled, for example, by a temperature control, depending on whether the user gives the device a small or a large amount of heat deprives. In order to keep the temperature of the device constant, the gas flow rate through the metering nozzle must of course also be varied.

On the whole, the gas-operated devices of personal need described at the outset have proven themselves quite well in practice. However, it has been shown that the mixing ratio of the gas-air mixture in the conventional jet pumps described in gas-operated devices has a strong dependence on the absolute gas flow rate through the nozzle. It could be shown by theoretical as well as experimental investigations that this dependency of the mixing ratio on the absolute gas flow rate is due to a change in the flow dynamic properties of the gas jet emerging from the metering nozzle. An undesired change in the mixing ratio occurs in particular when the gas flow decreases to small values in the order of 20-50 mg / min and less (nozzle diameter approx. 50 / tm-100 m).

One solution to this problem, namely to ensure an approximately constant, almost stoichiometric, adjustable gas / air mixture over the entire variation range of the gas flow rates, that is to say even with very small gas flow rates not to be found in the known state of the art with regard to gas-operated devices for personal use. All devices described there work, as far as can be seen, with conventional single-jet nozzles.

As far as can be seen, there is no experience in the field of the invention that is described in the publicly available literature. The experiences with jet pumps relate without exception to mass flow rates, and thus Reynolds numbers, which are orders of magnitude above the range of interest here. Also in the monograph "Injection and Mixing in Turbulent Flow". from J. A. Schetz there is no information about the pumping effect at such low Reynolds numbers.

However, the more distant prior art relating to jet pumps and the like also does not disclose any useful solutions. FR-PS 14 10 801 deals with the problem of improving the effectiveness of water jet pumps of considerable dimensions. The basic idea is to increase the jet surface of the pump jet by using several pump jets with a smaller diameter instead of one pump jet. For example, instead of one jet of 20 mm in diameter, 10 jets of 6 mm in diameter are used, as a result of which a threefold surface of the pump jets and a corresponding increase in output should be achieved with approximately the same amount of water. In addition, the different beams can be aligned at correspondingly defined angles, so that a rotational movement is forced on the overall beam consisting of the individual beams. However, the individual do not influence the rays of this arrangement, the through bores of the nozzle are designed so that the individual jets do not interact with one another. Experimental investigations have shown that this arrangement is unsuitable especially at very low flow rates.

The subject of GB-PS 875610 is based on similar considerations, which discloses a multi-channel nozzle, the individual jets of which are arranged in such a way that they come to lie approximately on a single-shell hyperboloid. It is expressly pointed out in this document that any interference or interaction of the individual beams is to be avoided by such an arrangement of the individual beams.

DE-PS 496 640 discloses an annular nozzle for blowing gas into the conveyed material of a conveyor, in which the individual gas holes in the individual parts of the nozzle have different inclinations to the nozzle axis. This document does not indicate that the individual partial beams influence each other in any way. DE-PS 916 748 relates to a feed pump for delivering liquids which are mixed with solids. A plurality of driving nozzles are provided, which likewise have an inclination with respect to the central axis of the catching nozzle. This is intended to avoid frictional losses which the driving jet otherwise experiences on the wall of the collecting nozzle, since the driving jet surrounds the medium to be conveyed in a ring. An interaction of the rays of the individual driving nozzles with one another is not apparent from this document.

From GB-PS 15 69 736 a device for cutting or cleaning by means of a water jet is known, for which purpose an abrasive is added to the water jet. The abrasive is preferably provided by three above the water jet nozzles Inlet metered. In one embodiment, the water jet is generated by three nozzles offset by 60 ° with respect to the abrasive agent inlets. The channel axes are aligned such that they intersect the axes of the abrasive inlets. As a result, the water jet receives a twist or rotation component, so that separate means for preventing rotary movements of the nozzle carrier are to be provided. This

Device works at very large Reynolds numbers in the range

5 RE ^ IO, in which there is definitely a turbulent flow.

The feed pumps of German patent applications M 19576 Ia / 59c and DE-OS 24 24 054 also have driving nozzles, the nozzle axes of which form an acute angle with the axis of the collecting nozzle. These pumps also serve to convey solids and are designed to minimize the impact losses on the walls of the edge nozzle primarily because the medium to be conveyed is in turn surrounded by the propellant jet in a ring. In particular, the driving nozzles open into pocket-shaped bulges of the driving nozzle carrier, as a result of which the requirements for a sufficient width of the nozzle carrier and a sufficient forward speed of the conveyed material are to be met. Mutual influencing of the individual nozzle jets of the driving nozzles is not addressed in these documents.

Finally, US Pat. No. 3,694,107 discloses a feed pump with a first drive jet and a first mixing chamber, at the end of which additional drive jet nozzles are arranged in order to reduce turbulence. These propulsion jet nozzles are subjected to a higher pressure than the first nozzle. This is intended to ensure that the first nozzle sucks in the fluid to be conveyed and the additional nozzles, which are subjected to higher pressure, ensure compression. As a result, the parameters of each individual nozzle can be set independently of those of other nozzles according to the specific requirements, and each of the individual nozzles under different operating conditions than the others

Nozzles are operated. All developments of the type specified above either serve to minimize friction losses or to increase the effectiveness of the jet pumps. It is not important to maintain a certain mixing ratio between the jet and the fluid.

In contrast, the invention is based on the object of developing a device of the type mentioned at the outset or the jet pumps used in these devices in such a way that an over wide, in practice required variation ranges of the gas flow rate at least approximately constant mixture ratio between the gas and the air, in particular even with low gas flow rates, guaranteed and adjustable in the range of the stoichiometric mixture ratio.

This object is achieved by a gas-operated device according to the features of the main claim. As the studies have shown, with an arrangement according to the invention, even with very low gas flow rates through the two- or multi-channel nozzle, a mixture ratio of gas to air in the required range can be achieved due to the interaction of the individual jets the range of variation of the gas flow rate required in practice is approximately constant. However, the invention is generally applicable to any jet pump operating under similar conditions, i.e. especially at low flow rates or Reynolds numbers.

This surprising effect can be explained as follows: In the range of low gas flow rates, the flow characteristics of the gas jet change from a turbulent flow form (at high gas flow rates) to a laminar flow form. A measure of this transition point is the Reynolds number, that for the In the present case, circular outlet openings are determined by the product of the mean outflow velocity and the diameter (or hydraulic diameter for non-circular outlet openings) of the outlet opening, divided by the kinetic viscosity of the medium. In the case of very low gas flow rates, values of the Reynolds number in the range of 400 and less are obtained, which characterize the presence of a laminar free jet under the conditions examined here. For values of the Reynolds number of approximately greater than 1000 or 1500 there is practically always a turbulent free jet. Although for smaller Reynolds numbers in the range down to Re r-50-100 the free jet can in principle also become turbulent, the accumulation of the disturbances of the laminar free jet which is always present is so weak that within the technically usable dimensions of the device, which in the are essentially determined by the length of the diffuser and the distance between the diffuser and nozzle, there is no change in the turbulent flow form. To achieve a practical size, it is necessary to ensure a turbulent free jet with small Reynolds numbers even in the immediate vicinity of the nozzle opening.

A laminar flow is essentially characterized in that practically no path movement of individual fluid particles perpendicular to the beam direction occurs in the fluid flow. In contrast to this, in the case of a turbulent flow, the fluid particles have quite considerable velocity components perpendicular to the direction of beam propagation, which on the one hand cause the individual fluid particles to be mixed within the fluid flow and on the other hand to mix this fluid jet with the surrounding second medium is guaranteed. Because, instead of a single gas jet, two gas jets are generated, which are oriented in such a way that the individual gas jets intersect at least partially in the area of the nozzle exit plane or after exiting the nozzle, each of the individual gas jets experiences an interference from the other jet tion that turns the laminar flow of the individual gas jets into a turbulent flow after the jets have been cut. At least from this point of intersection there is then a free jet which reliably entrains the fluid surrounding the gas jet, namely air. Thus, regardless of the gas flow rate of the nozzle, even with Reynolds numbers in the range of 200, which result in a laminar free jet for conventional single-channel nozzles, the arrangement according to the invention ensures a turbulent flow.

Further advantages of the invention emerge from the subclaims in connection with the description and graphic representation of the exemplary embodiments.

Show it:

1 is a gas powered hair curling iron,

2a shows a conventional single-channel nozzle,

2b shows a first embodiment of a two anal nozzle according to the invention in longitudinal section and plan view,

2c shows a second embodiment of a two-channel nozzle according to the invention in longitudinal section,

3 a, b free jets generated in an experiment with the nozzles of FIGS. 2a, b and Fig. 4 a, b, c, d experimentally generated free rays with the

Nozzle of Fig. 2b, in which the Para enter b (normal distance) was varied.

1 consists of a tube 1, a handle part 2 connected to the tube 1, which has a fuel tank and is filled with fuel gas 3. Reference number 4 denotes an ignition device for initiating the combustion process in a combustion chamber 5. A burner is held within the tube 1 by spring windings 7, 8 of a spiral spring 45. A burner tube 42 is arranged in the combustion chamber 5. The burner consists of a catalyst 43 located between the spiral spring 45 and held by an inner spring 44. The gas-air mixture to be burned enters the burner tube 42 via a mixing tube 111, into which the gas emerging from a valve member 13 enters and mixes with the ambient air. The valve member 13 is acted upon by a temperature controller, not shown in the drawing, in such a way that the amount of gas emerging from the valve member 13 is metered accordingly in order to maintain a predetermined temperature setpoint. Further details of this hair waving device can be found, for example, in EP-Bl 0030257.

The previously known, gas-operated devices for personal use have a metering nozzle, as is shown in principle in FIG. 2a. It is a single-channel nozzle 21, the outlet opening 22 of which is arranged centrally to the central axis of the nozzle. As already mentioned at the beginning, such nozzles (diameter about 50-70 / on), especially at low gas flow rates (50 mg / min and less), have the property that the mixing ratio between gas and air, as is the case with the Passing through the mixing tube 111 in the combustion chamber 5, from which the optimum value set for high gas flow rates in the vicinity of 1 - 1 (the stoichiometric ratio) deviates considerably in the direction of a low-oxygen mixing ratio. 2b shows a first solution according to the invention. The gas stream 23 exits through two nozzle openings 27, 28 of the channels 35, 36 of the multi-channel nozzle 29, the axes of which form an angle ZQC with one another, so that these intersect at point 24. This point 24 is located downstream of the nozzle exit plane 26 in the free jet region, at least from this point 24 a free jet is created which reliably entrains the air surrounding the gas jet indicated by arrow 25 into the mixing tube 111. Unter¬ investigations have shown that the angle of intersection of the channel axes 2o {preferably to values of 10 ° 2θ = = ^'should be set 50 °. Successful tests were carried out in particular with values of 2o = 20 °, 40 °. The distance a between the channel axes, measured in the nozzle exit plane 26, is preferably set to values in the order of a channel diameter d. limited, as experimental studies show. The preferred range is determined by the condition d. = a - 5d. fixed.

A further embodiment for illustrating the invention is shown in FIG. 2c. The nozzle according to FIG. 2c again has two channels 35, 36, the axes of which form an angle 2. However, the axes of the channels 35, 36 do not intersect only downstream of the nozzle exit plane 26, but in the nozzle exit plane 26. In this way, a multichannel nozzle with only a single nozzle opening 37 is formed, the diameter of which is d. corresponds approximately to the diameter of the channels 35, 36. Surprisingly, the experimental investigations on this multi-channel single-hole nozzle show results which are similar to the results obtained for the nozzle arrangement of a multi-channel two-hole nozzle shown in FIG. 2b. With the arrangement of the channels 35, 36 shown in FIG. 2c, the range of variation for the parameter a can thus be extended to the value a = 0 while maintaining a turbulent free jet even with small Reynolds numbers. Of course, the intersection 24 of the axes of the channels 35, 36 can also be a certain amount in the order of approximately a channel diameter d. upstream (a takes on negative values) or downstream (a takes on positive values) of the nozzle outlet plane 26. Such small, among other things also production-related variations in the position of the intersection 24 of the channel axes do not impair the advantageous behavior of this two-channel single-hole nozzle. Ultimately, the shape of the nozzle opening 37 changes, which instead of a circular shape can also have the shape of an ellipse or two circles intersecting in the edge regions.

It is essential for all of the exemplary embodiments that the nozzle has at least two channels, the axes of which intersect in the region of the nozzle exit plane, in such a way that only one nozzle outlet opening is present or that the diameter is a few channels apart. Cut downstream of the nozzle exit plane so that there are at least two nozzle outlet openings. The variations of other parameters of the nozzle described below, namely the parameter h, b, are valid for every embodiment of the multi-channel nozzle, regardless of whether it is a multi-channel single-hole nozzle or multi-channel two-hole nozzle.

The length of the nozzle bores marked with h or the thickness of the nozzle plate preferably takes on values between 2d ^ ^ r h 4 6d .. In particular, it has proven advantageous to set values of h approximately equal to 4d., In which there is a good compromise between sufficient impulse channeling of the fluid jet and the avoidance of excessive frictional resistance within the nozzle bores.

The normal distance between the axes designated b is on the other hand limited by the condition that b is less than or approximately equal to that The sum of the radii of the two nozzle openings 27, 28 or channel diameter should be. For the case of the same nozzle diameter, the condition b = d applies. A maximum disturbance of both nozzle jets at the intersection 24 naturally occurs when b assumes the value 0. However, if one assumes in practice nozzle opening diameters d ^ about 50J H, the last-mentioned condition for b may become important with regard to the specification of manufacturing tolerances. As the experimental investigations show, a deviation of the value b from 0 by d./2 is entirely tolerable. If b takes on values not equal to zero, in addition to the turbulence introduction downstream of the intersection point 24, the flow in the mixing tube 111 also swirls. For the effect of the nozzle according to FIG. 2b according to the invention, however, this turbulence at values b 40 is not critical. It is essential that the jets emerging from the nozzle intersect at least in partial areas of their jet cross sections and thus interfere with one another, that is to say they interact with one another. This interaction of the individual nozzle jets with one another is apparently responsible for the good results that could be obtained with such designed nozzles. In this respect, values b = 0 should be aimed for in practice, although this cannot always be achieved ideally for design or manufacturing reasons.

The invention is not limited to the exemplary embodiments of FIGS. 2b, c, but can be modified in various ways. So it is possible and possibly useful to provide more than two channels, for example to improve the axial symmetry of the jet or to vary the normal distance between the axes of the nozzle bores in small areas. In the event that, for example, three nozzle openings offset by 120 ° in the nozzle exit plane 26 are provided, the angle o is defined by the central axis of the nozzle 29 and in each case one channel axis. Finally, the channels can also have different diameters and thereby influence the course of the free jet. Then in the above given relations instead of the diameter d. to use the mean nozzle diameter d or hydraulic diameter of the individual diameters d ^, d, ... d _R.

3a, b are experimentally generated free jets with the nozzles of F1g. 2a, b shown. The Reynolds numbers are in the range of Re • * - 300, the nozzle diameter of the jet nozzle is d. = 1.4 mm, the nozzle diameter of each nozzle bore of the two-jet nozzle is d. = 0.75 mm, 40 °, a = 1.25 mm and b = 0. The free rays are made visible by means of very small particles which were generated by pneumatic atomization of a water-glycerol mixture. With the help of a cylindrical lens, the beam of an argon laser for illuminating the free beam was converted into a flat fan of light and the free beam was photographed. Figures 3 and 4 are graphic representations of these photographic recordings. The experiments with single jet nozzles of FIG. 2a show in FIG. 3a that the jet remains essentially laminar even for Reynolds numbers up to about 1000-1500. Under the same dynamic flow conditions, that is to say with the same Reynolds number, the two-jet nozzle of FIG. 2b according to FIG. 3b clearly produces a turbulent free jet immediately after the two jets meet at the intersection 24.

In the representations of FIGS. 4a, b, c and d the parameter b, that is to say the normal distance between the axes of the bores, was varied between b = 0 mm, 0.4 mm, 0.8 mm and 1.5 under otherwise essentially identical conditions mm. It is clearly visible that for values b = 0 mm and 0.4 mm the desired mutual interference of the rays with the accompanying turbulence formation occurs. However, the value b comes in areas that correspond to a single beam diameter d. correspond, the individual beams no longer experience mutual interference and maintain their laminar flow dynamics. In summary, it can be stated that the arrangement according to the invention is suitable for reliably guaranteeing a turbulent free jet with good conveying action even with Reynolds numbers down to values of approximately 200. Characteristic of the nozzles used are two or more channels, the axes of which enclose a certain angle 2oC with one another or respectively form the angle with the center axis of the nozzle. It was possible to show by speed measurements and by determining the flow rate that favorable angles are in the range of 2 <approximately 20 ° -40 °. Inaccuracies in the manufacture of the nozzle bores can lead to a crossing of the jet axes instead of the desired cutting. Smaller deviations result in a slight decrease in the output. Larger dislocations of the jet axes, which are in the order of magnitude of the channel diameter, lead to a drop in the delivery capacity to approximately the values which result in the case of a laminar jet from a single-jet nozzle, since the individual jets no longer interact with one another.

Claims

1. Gas-operated device of personal need with a gas container, a gas metering nozzle (21, 29), a mixing zone (111) and a burner, in which the gas jet emerging from the gas metering nozzle (21, 29) is surrounded by the ambient air (25), characterized in that the gas metering nozzle (21, 29) has at least two channels (35, 36), the central axes of which form an angle θC with the central axis of the nozzle, such that the gas jets are approximately at the level of a nozzle exit plane (26) or downstream at least partially penetrate the nozzle in an area (24).

2. Gas-powered device according to claim 1, characterized in that the channel center axes with the nozzle center axis a Win¬ kel oC with 5 ^β Include 25 °.

3. Gas-operated device according to claim 1, characterized in that a distance a of the channel center axes, measured in the nozzle exit plane (26), assumes values in the range 0 = a = 5d, with d the mean diameter of the channels (35, 36) is designated.

4. Gas-operated device according to claim 1, characterized in that the channel center axes with the nozzle center axis include a angle θ £ with 5 ° = c { ^~ 25 ° and that a distance a of the channel center axes, measured in the nozzle exit plane (26), values assumes in the range 0 = a = ^~ 5d, with d being the mean diameter of the channels (35, 36).

5. Gas-operated device according to claim 1, characterized in that a normal distance b of the axes of the channels (35, 36) assumes values b d, with d being the mean diameter of the channels (35, 36).

6. Gas-powered device according to claim 1, characterized in that the channel center axes include an angle o with 5 ° ^ i = 25 ° and that a normal distance b of the axes of the channels (35, 36) assumes values bd, with d being the average diameter of the channels (35, 36) is designated.

7. Gas-operated device according to claim 1, characterized in that the channel center axes with the nozzle center axis enclose an angle σ with 5 ° = ~ <τ = ^~ 25 °, that a distance a of the channel center axes, measured in the nozzle exit plane (26), Assumes values in the range 0 = ~ a = 5d and that a normal distance b between the axes of the channels (35, 36) assumes values b <d, d being the mean diameter of the channels (35, 36).

8. Gas-operated device according to claim 1, characterized in that a height h, which characterizes the thickness of the nozzle plate or length of the channels (35, 36), assumes values in the range 2d C h -C.6d, preferably h ~ 4d, wherein with d the average diameter of the channels (35, 36) is designated.

9. Gas operating device according to claim 7, characterized in that a height h, which characterizes the thickness of the nozzle plate or length of the channels (35, 36), assumes values in the range 2d ^ h ^ 6d, preferably h *** 4d.

10. Gas-powered device according to claims 1- S, gekenn¬ characterized by the use in hair care devices such as curling irons, hair dryers, hot air brushes.