SPACE HEATING APPLIANCE

Abstract: Radiant tube space heating appliance includes a burner assembly (12), air flow therethrough being induced by a fan (14) by way of a restricted air inlet orifice (34) communicating with a stabilising chamber (32) leading to the burner head (26) for smoothing and silencing the air flow; the burner head including a flame stabilising matrix (40), conveniently formed from windings of flat and corrugated stainless strips (42,43) which define through apertures of substantial axial length. The appliance may further include a turbulator insert (50) in the radiant tube formed as a corrugated strip (52) of stainless steel or similar material which is twisted to form a helix.

Description: This invention relates generally to space heating appliances of the kind known as radiant tube heaters comprising a U-shaped or other tube operatively carrying a flow of hot gases from a burner at an upstream end of the tube, typically gas fuelled, said flow being induced by a fan or other flow inducing means, typically located at the downstream end of the tube, drawing air through air feed means to provide combustion air to a combustion chamber of the burner; the space heating effect being largely provided by radiation from the tube walls which may be directed by means of a reflector adjacent to the tube, e.g. downwardly, where the appliance is suspended in an upper region of the room or other space being heated. Said appliances are hereinafter described as "radiant tube heater assemblies". An example of a radiant tube heater assembly is known from FR-A-2560359. A head of the burner may advantageously be provided with a flame stabilising matrix as shown by GB-A-892067. The object of the invention is to provide a radiant tube heater assembly which is particularly quiet in operation yet which is economic and efficient to provide and run, and reliable and safe in use. A further object is to provide for the simple, economical and durable construction of said heaters. According to the invention there is provided a radiant tube heater assembly as defined and characterised by Claim 1 of the appended claims. An example of the invention is more particularly described with reference to the accompanying drawings wherein: Figure 1 is a diagrammatic perspective view of a burner assembly; Figure 2 is a side elevation thereof; Figure 3 is a horizontal section on line 3-3 of Figure 2; Figure 4 is a perspective view of a burner head of the assembly; Figure 5 is a vertical section of an outer end of said head; Figure 6 is an end view thereof; Figure 7 is a perspective view of strip material used to form a matrix of said head; Figure 8 is a diagrammatic plan view of a radiant tube heater incorporating the burner assembly; Figure 9 is a part sectional view of part of a radiant tube of the heater; and Figure 10 is a perspective view of an insert for said tube at one stage of its manufacture. The radiant tube heater assembly of this example comprises a U-shaped radiant tube 10 (Figure 8) having a burner assembly 12 at the upstream end and a flow inducing extraction fan 14 at the downstream end. Assembly 12 includes a control section 16 of generally conventional type incorporating automatic ignition, operation and safety controls and a combustion chamber section 18 which is now further described in detail with reference to Figures 1-3. Section 18 is a box-like structure defining a combustion chamber 20 defined in part by an L-shaped interior wall 22 having a smoothly radiused corner 23. An outlet 24 in the front wall of chamber 23 forms a connection with the upstream end of tube 10 and spaced in axial alignment to the rear of this is a burner head 26 described in greater detail below which projects into chamber 23 from the division wall 28 between said sections 16 and 18. The head is operatively supplied with gas fuel from a gas feed pipe 30 through regulating and control valves (not shown) in section 16. Air infeed means of the assembly comprises an L-shaped stabilising chamber 32 defined between internal wall 22, rear wall 28 and a side wall of section 18, air being drawn into said chamber by the action of fan 14 in operation by way of a restricted air inlet orifice 34 in the front wall of section 18. A baffle 36 (not shown in Fig. 1) protects the exterior of orifice 34. The restriction of air flow due to the dimensions of orifice 34 ensures that there is a degree of depression within the burner assembly when fan 14 is operating with normal unobstructed flow through tube 10 and a vacuum sensor (not shown) operates in known manner to prevent or shut off operation of the burner if such depression is not maintained, eg due to a blockage or a fault in fan 14. However, with many known burner assemblies of this type the operation is unduly noisy due to the turbulence induced by the restricted orifice and due to constrictions and irregularities in the air path from the orifice to the combustion chamber. Excessive noise is a nuisance and unpleasant and has, in the past, precluded the use of this type of heater in such buildings as halls for public meetings and social functions, churches and other places of worship and the like. The shaping of stabilizing chamber 32 allows for smoothing and slowing to a lower velocity of the air flow passing through orifice 34, it is then swept around the radiused corner 23 of wall 22 without any unduly abrupt change of direction and passes into combustion chamber 20 by way of a large diameter cylindrical sleeve 38 in surrounding relationship and co-axial with burner head 26, the inner end of sleeve 38 merging with wall 22 at a radiused corner. Thus there is a smooth transition for the air flow into chamber 20 and it is directed along burner head 26 axially of the latter in an even flow along and in the head so that there is gentle laminar mixing with the gas fuel, and noise at the mixing and combustion areas is again substantially reduced. The efficient and quiet operation of burner head 26 itself is further assured by its manner of construction now described in greater detail with reference to Figures 4-7. A tubular casing constituting the outlet end of head 26 is occupied by a matrix 40 built up from stainless steel strip metal, in this example 10 mm wide using flat and corrugated strips 42, 43 (Figure 7) wound in alternate layers to form a honeycomb like disc having a large number of through apertures of substantial axial length (in this case 10 mm). The matrix is located in head 26 by means of a pair of press fitted spiders 44, 45 at front and back each comprising an outer ring which is a press fit within the cylindrical sleeve of head 26, a diametral cross-bar and a central boss abutting the centre of matrix 40 for its axial location. Matrix 40 smoothes the outflow of gas/air mix from head 26 and stabilizes combustion at the outer end of the head and therebeyond into the combustion chamber again giving substantial noise reduction and efficient and safe operation. Any tendency for the flame to "burn back" into the head is resisted by the cooling or quenching effect of the matrix yet its through passages can be of substantial size in comparison with mesh or gauze used in some applications to prevent burning back, thus there is less likelihood of blockage and improper functioning. The matrix is also stronger and more durable than mesh or gauze, can readily be removed for cleaning or replaced if necessary, and is simple and economical to manufacture. For maximum heating effect it is important that there is good heat transfer from the gas flow to the walls of the U-shaped tube 10 for radiation from the latter. To enhance such transfer, particularly in the downstream limb of the tube, it is preferred that a spiral turbulator or insert 50 is positioned in a portion of tube 10 as best seen in Figure 9. Insert 50 is formed from a strip of sheet metal 52, for example stainless steel of 0.3 mm gauge, the strip having a width slightly less than the internal diameter of tube 10, for example 70 mm width for use in 75 mm internal diameter tube. The strip is subjected to a crimping process by passing it through a pair of meshing toothed rollers to form transverse corrugations along its full length. This is a very simple process which merely involves bending the light gauge metal without any actual stretching or other deformation and the axial length of the rollers used can be sufficient to accommodate a wide range of strip widths for making inserts for tubes of varying diameters. The pitch of the corrugations may, for example, be 12 mm and their trough to crest height 4 mm for 70 mm width strip. This stage of manufacture is shown in Figure 10 and the strip so formed can readily be stored or transported as a coil until required for use. Corrugations 54 enable strip 52 to be readily twisted about a longitudinal axis to form a helix, and the pitch of the turns thereof can very readily be varied according to requirements . This process can readily be carried out by hand or using simple tools either before or at the time of the insertion of the strip into tube 10, indeed if an insert has to be positioned in the tube in a confined space, for example positioning a long insert in a tube where there is restricted clearance at the tube mouth, the flexibility of the strip prior to or during twisting will be found to be particularly convenient. There is also the possibility of feeding the strip around a bend in the tube while forming the twist. In forming a helix in a flat metal strip the outer borders of the strip have to be stretched relative to the centre area which necessitates special tools and processes and also means that heavier gauge material must be used which can be stretched without tearing. On the other hand, the corrugations 54 of strip 52 permit its outer borders to expand longitudinally relative to its central area without difficulty and the rigidity provided by the lateral corrugations also facilitate easy and even twisting. Typically the strip 52 is twisted to a pitch of from 250 to 350 mm using 70 mm wide strip. Corrugations 54 themselves provide a slight increase in gas turbulence in the region of tube 10 occupied by insert 50 as well as the improved heat transfer provided by the scrubbing effect of the spiral gas flow on the wall of tube 10 due to the helical shaping of insert 50. The twisting impetus imparted to the gases as they exit from the downstream end of the insert 50 continues this scrubbing effect giving increased heat transfer in regions of tube 10 downstream of the insert again giving increased efficiency of operation. As in the case of the strips 42 and 43 used to form matrix 40 of burner head 26 the use of light gauge strip material gives considerable economy of material (e.g. of costly corrosion and heat resistant stainless steel) and a possible reduction in weight as well as the economies of manufacture and assembly referred to above.

Claims: A heater assembly comprising: a) a radiant tube (10) for carrying a stream of hot gases to provide space heating by radiation from the tube; b) gas flow inducing means (14) at a downstream part of said tube for inducing flow of said gases therealong; c) a burner head (26) including a flame stabilising matrix (40) at its mouth defining a plurality of through passages of substantial length for stabilising combustion at the downstream end of the head while restricting burning back into the head interior; d) a combustion chamber (20) surrounding the burner head having an outlet (24) in operative communication with the tube upstream of the flow inducing means, and an inlet in co-axial relationship with the head for directing combustion air axially along and in encircling relationship to the head; e) air feed means upstream of the burner head for providing combustion air to said combustion chamber inlet and comprising a stabilising chamber (32) having a restricted inlet orifice (34); and f) a vacuum sensor for monitoring the degree of depression within the air feed means to check that correctly induced flow along the tube is operatively maintained: characterised in that the combustion chamber inlet is defined by a sleeve (38) having a downstream end located within the combustion chamber in surrounding relationship to the burner head for directing the combustion air evenly axially along and in encircling relationship to the head in a smooth path with little restriction or abrupt change of direction and an inner end which smoothly merges with an interior wall (22) separating the combustion and stabilising chambers, and in that the stabilising chamber is L-shaped, said interior wall being smoothly curved to extend along one side of the latter chamber, the inlet orifice and said sleeve being spaced from and substantially parallel to one another whereby the stabilising chamber operatively changes the direction non-abruptly and smooths the flow of the combustion air drawn therethrough to silence turbulence in said flow. An assembly as in Claim 1 characterised in that the flame stabilising matrix comprises windings (42, 43) of strip material arranged to define said plurality of through passages. An assembly as in Claim 2 characterised in that said windings are of alternate layers of corrugated strip material (43) and flat strip material (42). An assembly as in Claim 2 or 3 characterised in that said strip material is stainless steel or other metal. An assembly as in any preceding claim characterised in that the radiant tube (10) includes a flow modifying insert (50). An assembly as in Claim 5 characterised in that said insert (50) is formed at least in part of a longitudinal strip (43; 52) of sheet material having transverse corrugations and wound or twisted to form a coil or helix locating in the tube (10).

Inventors: FLETCHER, JOHN EDWARD, YALE, WILLIAM
Applicants: AMBI-RAD LIMITED
Application year: 1987
Main classification: F24D5
IPC codes: F23M9, F23D14, F24D5, F23C3, F28F13, F23M99