US3027935A

US3027935A - Apparatus for intensive emission of infra-red radiation

Info

Publication number: US3027935A
Application number: US725638A
Authority: US
Inventors: Sobole Yvan
Original assignee: BOURGUIGNONNE MEC SMB
Current assignee: BOURGUIGNONNE DE MECANIQUE Ste; BOURGUIGNONNE MEC SMB
Priority date: 1957-05-07
Filing date: 1958-04-01
Publication date: 1962-04-03
Anticipated expiration: 1979-04-03

Description

April 3, 1962 Y. SOBOLE 3,027,935

APPARATUS FOR INTENSIVE EMISSION OF INFRA-RED RADIATION Filed April 1, 1958 INVENTOR YVAN \SOBOLE rates Unite The present invention relates to an apparatus for intensive emission of infra-red radiation, working vw'th gas.

In the devices of known type for the emission of infrared radiation, the combustible mixture passes through a porous refractory plate or through perforations which are made in this plate, and burns at its exit from the plate, each orifice playing the part of a small elementary burner. A small portion of the gases burns in contact or in the immediate proximity of the surface of the refractory plate, whilst a part of the heat produced is transmitted to the latter, which radiates it into space. Certain improved types are provided with an additional member at a suflicient distance from the refractory plate, this member consisting of a grid or perforated steel sheet which absorbs a fresh quantity of heat.

These devices generally operate with a full quantity of added air, this quantity being even in excess with respect to that strictly necessary to give total combustion. This air is carried into a convergent-divergent air mixer by a jet of gas.

All these apparatuses must comply with the various conditions set out below.

(1) One of the conditions which must essentially be fulfilled by any emission device for heat radiation operating with gas is that whatever else happens, it must not permit any entrance of the flame into the distribution chamber. This entry of flame may be produced in three different ways:

(a) When the speed of flame propagation of the gas is greater than the speed of flow of the gas;

(b) Since the speed is always zero at the point of contact with the wall of the flow conduit or outlet port, there is therefore always a certain thickness of the limit layer for which the speed of flow is less than the speed or flame propagation. Under certain conditions of temperature of the walls, temperature of flame propagation (dependent on the excess of air), thickness of the limit layer (dependent on the speed of flow), there is obtained a progressive entry of flame for which there does not exist any point of stabilization, because the variations of local conditions (temperature of the walls and speeds of flow) act in the unfavourable sense;

(c) By accidental entry of the flame due to the effect of an external action, for example a sharp rush of Wind which slows down the flow of gas and brings it to a speed below the speed of propagation of the flame.

On the other hand, when at a point of the conduit and for the temperature of ignition, the heat absorbed by the wall is greater than the heat diffused by the flamefront, combustion is made impossible. Whatever the speed of flow may be, there is no more propagation.

For each of these causes, there are obviously remedies which are currently used by the makers of this type of apparatus, and which can be summarised as follows:

(a) In order to eliminate this cause of entry of flame, the fuel is given a sufficiently high rate of flow, together with a large excess of air;

(b) In order to avoid this cause, certain manufacturers seek to reduce the temperature of the radiating surface, whilst others avoid it by using an excess of air and a high rate of flow of the gas;

(c) In order to overcome this cause, makers frequently ice use thick refractory plates in order to reduce the temperature of the plate on the side of the distribution chamber, conduits of small diameter and, where this applies, particular protective devices.

(2) A further condition desirable for this type of apparatus is a high efficiency, that is to say a good radiation factor (ratio between the energy consumed and the energy radiated) and a good utilisation of the radiation produced (the useful radiation being that which can be directed towards the object exposed to the radiation, the radiation emitted at a wide angle With respect to the normal being practically lost).

If the extent and the temperature of the radiating surface are assumed to be fixed, the radiation factor is a direct function of the power of emission of this surface; now, the known types of refractory ceramics have rarely a power of emission greater than 4.

The power of emission is given by the equation in which dQ is the quantity of energy radiated into space per unit of time by a radiating surface ds based on wave lengths between A and )\+d)\. The units em ployed are kilocalories per cubic meter per hour. In the equation, dQ is expressed in kilocalories per hour, dx is expressed in meters and ds is expressed in square meters.

(3) Finally, as in this kind of gas apparatus, the air is drawn into a mixer by the fuel gas injected under pressure, a further important condition to be observed resides in the determination of this pressure.

It is well known that the amount of excess air necessary, the diameter and the length of the distribution conduits, are factors of absorption of energy. Now, in the greater part of apparatus of this kind of known types, the injection pressure necessary to obtain a normal power is very often greater than that which is available from public gas-supply mains. It is then necessary either to compress the fuel gas, or to increase the number of apparatus by using them at reduced power, which constitutes a costly solution for the user.

The present invention has for its object to provide an apparatus for the intensive emission of infra-red radiation, in which all the above conditions are surely and economically fulfilled, and which enables a factor of radiation to be obtained which is much higher than that obtained up to the present time with existing apparatus, while the present apparatus has features of use which are much more advantageous.

The said apparatus comprises essentially a distribution chamber in front of which is placed a perforated insulating plate which distributes the gaseous fuel mixture which passes through it on to a mattress formed by a gauze of refractory steel which is held applied against the said insulating plate by thin blades, the apparatus being contained in a casing so as to leave between the said apparatus and said casing a space in which the burnt gases pass upwards along the said distribution chamber and are discharged through an evacuation nozzle in which the said chamber terminates.

All the features of the apparatus are determined in such a manner that the front of ignition is located in the thickness itself of the metallic gauze.

By virtue of these characteristics, the conditions detailed above are respectively satisfied as follows:

(1) Entry of flame into the distribution chamber.-- (a) The speed of propagation of the flame is a direct function of the temperature of the flame front; it is substantially proportional to the difference between the temperature of the flame front and the temperature of the ignition. In the apparatus in accordance with the invention, the combustion takes place in the thickness of a metallic gauze; in this gauze, the free section is on the one hand very small and on the other hand, the developed surface of the gas-metal contact is very large, and the temperature of the flame front is thus considerably lowered.

This arrangement is so efiective that not only has it been possible to reduce the speed of flow (the advantage of which will be clearly shown later) but also that it has been possible to pre-heat the gaseous mixture by recuperation of the heat contained in the burnt gases.

(b) The perforated plate is no longer in direct contact with the very hot gases in combustion, and there is then produced a discontinuity of temperature between the metallic gauze (the radiating surface) and the perforated plate.

(c) The blades forming a Wind-break and the orifices of the conduits being protected by the metallic gauze, the influence of wind is very much reduced. In addition, the mean temperature of the perforated plate is reduced as has been stated above in connection with cause (b).

(2) Factor of radiatin.-In the apparatus forming the object of the invention, the cell-like texture of the gauze and the superposition of the wires at their crossings, which multiply an infinite number of times the reflections between element and element cause the apparent surface of the gauze to have a power of emission very close to that of the black body, or 4.9. Advantage can only be taken of this favourable parameter if the method of absorption of heat will permit. Now, it is clear that the effective surface of the gauze which makes up the mattress is equal to about three times the apparent surface of the latter, and that the contact surface metal to gas is thus greatly increased. To this factor, which is already very favourable, is however added the factor defined below which, whilst being less apparent, is however still greater than that preceding.

If a flame front is considered in an undefined flow, and if there is considered in this front a molecule defined at the moment at which it enters into combination, the molecule is then charged with enormous energy, approaching that of the temperature which would be obtained if the combustion took place in pure oxygen. The energy is diffusedv by shock effect on the adjacent molecules, whilst its level falls. If there is placed in proximity to this particular molecule an absorbing wall, the quantity of energy transmitted will actually be characterised by the difference existing between the'temperature of this wall and the mean temperature of the fluid, or again, by the distance which separates the wall from the molecule considered.

If it is now assumed that in the flow of a mixture of air and gas a piece of iron is placed and brought up to a sufficient temperature, this oxidized iron is coated with atoms of oxygen which can easily be extracted. If a molecule comes into contact with this, it burns and reduces the oxide which is subsequently re-formed. What is important is that the energy of combustion has been set free by the actual contact with the surface of absorption, without the interposition of inert molecules, and the transmission thus takes place at the highest possible degree. The molecule formed leaves the wall practically at a temperature which is roughly equal to that of this wall. The only molecules which are not subject to this privileged state are those placed in the streams of free flow, but the metallic gauze reduces the section of free flow to one quarter, and the distance between the molecule and thewall is reduced at the same time.

It would appear that the reduction in temperature of the flame front may reduce the speed of reaction and extend for this reason the zone of combustion, but the high concentration of oxygen generated by the oxide of iron compensates for the reduction in mobility of the combustible molecules.

To the active method of absorption associated with a high power of emission, which already results in a high factor of radiation, is again added the effect of the thin blades which press the steel gauze against the insulating plate. These blades improve the utilisation of the radiation produced by forming screens which intercept the rays which are too divergent, and they also serve to cool the burnt gases after they have left the metallic gauze.

Finally, the burnt gases are further cooled While supplying the calories for pre-heating the combustible mixture passing along the walls of the distribution chamber, the said walls then playing the part of a heat exchanger.

(3) Pressure of the fuel gas.In the apparatus produced in accordance with the invention all of the above mentioned factors of energy absorption are favourable, and although a part of the useful energy is absorbed in pre-heating, it is possible, because of the useful energy which remains, to reduce substantially the pressure of injection of the combustible gas, and the apparatus can in almost all cases be connected directly to the public gas-distribution systems without having recourse to a compressor.

To sum up, the apparatus forming the object of the invention has three important practical features.

By localizing the combustion of the gas within the actual thickness of a mattress of a metfllic gauze, it enables a reduction to be obtained of the temperature of the flame-front, an extension of the contact surface with the hot gas, and an increase in the apparent power of emission.

By creating this combustion on iron oxide, it gives rise to a mode of absorption of liberated energy which is especially efiicient, and which should not be confused with the pseudo-catalytic effect of compensation for the reduction in temperature of the flame-front obtained by means of a local concentration of the oxygen available.

Finally, it enables pre-heating of the fuel gas to be obtained by virtue of the reduction of the temperature of the flame-front, whilst this known means was not possible of application up to the present time in apparatus of the same kind.

The apparatus thus has the advantages of permitting of a very high efliciency together with a moderate injection pressure of the combustible gas, while giving a large degree of safety against back-fires.

One form of construction of the said apparatus is shown diagrammatically in the accompanying drawing.

The apparatus shown in the single figure of this drawing comprises a distribution chamber 1 for the mixture of air and fuel gas admitted to the said chamber in any known manner; for instance, through a Venturi or mixing tube 10. The chamber is open on one of its faces, and this opening is closed by a plate 2 of refractory material provided with a large number of holes 3 through which passes the mixture of air and gas under pressure.

Against the said plate 2 is applied a mattress 4 formed by means of a gauze of refractory steel. This mattress '4 is held against the plate 2 by thin metal blades 5 arranged substantially at right angles to the plane of the said mattress.

The apparatus is provided with a casing 6 of sheet metal or other suitable material, in which chamber 1 is supported by brackets 11 and blades 5 are supported by rods 12 the ends of which are bolted in or otherwise secured to the walls of the casing 6. Between said casing and chamber 1 is formed a space 7 terminating in a nozzle 8 which also terminates the casing. The burnt gases can thus rise upwards along the distribution chamber 1 through the space 7, and pass out through the nozzle 8 after having pre-heated the gaseous mixture passing into the said chamber.

It is clear that the apparatus can be given any form which is considered suitable, and can be constructed following the technique currently applied to the construction of this type of apparatus.

What I claim is:

1.. An apparatus for intense emission of infra-red raaces 3935 diation, operating with gaseous fuels, and comprising essentially: a distribution chamber for receiving the said gaseous fuel; a refractory plate provided with a plurality of perforations, said plate constituting one wall of said distribution chamber; a mattress composed of refractory metallic gauze of a thickness providing a combustion zone therewithin, said mattress being adjacent the outer face of said refractory plate, said plate serving to distribute the gaseous fuel substantially uniformly over the surface of said mattress; a plurality of blades disposed edgewise with respect to the outer face of said mattress, and holding said mattress in position against the refractory plate; a casing containing the hereinbefore specified elements and in spaced relation therewith, so as to form a space around said elements, in which space the products of combustion of said gaseous fuel pass over the outer wall of said distribution chamber; and an orifice in the upper extremity of said casing for evacuating said products of combustion.

2. Apparatus for intense emission of infra-red radiations, operating with gaseous fuels, and comprising essentially, a distribution chamber for receiving said gaseous fuel; a refractory plate provided with a plurality of perforations, said plate constituting one wall of said distribution chamber; a mattress of refractory metallic gauze constituting a combustion zone and mounted adjacent the outer face of said refractory plate, said plate serving to distribute the gaseous fuel substantially uniformly over the surface of said mattress; a plurality of blades disposed edge-wise with respect to the outer face of said mattress serving to hold said mattress in position against the refractory plate; and heat-exchanger means connected with said distribution chamber for pre-heating the fuel gas present in said distribution chamber of a capacity which utilizes a substantial portion of the heat contained in the gases of combustion of said apparatus.

3. Apparatus as claimed in claim 2, in which the thickness of said metallic gauze mattress is such that the combustion of the fuel gas can take place wholly within said mattress.

References Cited in the file of this patent UNITED STATES PATENTS 1,237,780 Hicks Aug. 21, 1917 1,677,156 Vaughn July 17, 1928 2,233,675 Narten Mar. 4,1941

FOREIGN PATENTS 494,087 Great Britain Oct. 17, 1938 847,625 France iuly 3, 1939

Claims

1. AN APPARATUS FOR INTENSE EMISSION OF INFRA-RED RADIATION, OPERATING WITH GASEOUS FUELS, AND COMPRISING ESSENTIALLY: A DISTRIBUTION CHAMBER FOR RECEVING THE SAID GASEOUS FUEL; A REFRACTORY PLATE PROVIDED WITH A PLURALITY OF PERFORATIONS, SAID PLATE CONSITUTING ONE WALL OF SAID DISTRIBUTION CHAMBER; A MATTRESS COMPOSED OF REFRACTORY METALLIC GAUZE OF A THICKNESS PROVIDING A COMBUSTION ZONE THEREWITHIN, SAID MATTRESS BEING ADJACENT THE OUTER FACE OF SAID REFRACTORY PLATE, SAID PLATE SERVING TO DISTRIBUTE THE GASEOUS FUEL SUBSTANTIALLY UNIFORMLY OVER THE SURFACE OF SAID MATTRESS; A PLURALITY OF BLADES DISPOSED EDGE-