IES960243A2 - Convective heat exchangers - Google Patents

Abstract

In a heat exchanger having tube sections (4) for flow of heating medium and heat transfer elements in the form of plates (5a,5b,25a,25b) associated with the tube sections for transfer of heat from the sections (4) to the plates (5a, 5b, 25a, 25b), the plates (5a,5b,25a,25b) extend across a region between substantially parallel spaced apart tube sections (4). Each plate (5a, 5b, 25a, 25b) has a multiplicity of louvre-form openings (6,7) for directed flow of air through the openings. According to the invention, at least three heat transfer plates (5a, 5b, 25a, 25b) extend across the region between each pair of substantially parallel spaced apart tube sections (4), and preferably four such plates (5a, 5b, 25a, 25b) are provided. <fig.6>

Description

CONVECTIVE HEAT EXCHANGERS This invention relates to tubular heat exchangers, in particular for use as radiators in heating systems. The invention is especially directed to a radiation/convection heating unit having a box-like casing containing a generally finned tubular pipe assembly.

British Patent Specification No. 946,650 discloses a heat exchanger of this kind in which an upper and a lower pipe are interconnected by tubes, each of which has a central rising portion. Heat transfer elements are secured to the tubes and comprise fins for directing the airflow for maximum convective heat transfer.

Preferably the heat transfer elements consist of plates, provided with fins, attached one to each side of each upwardly directed tube. The fins are bent out from the plates in such a manner as to form louvre openings appropriately directed for the required convective airflow.

British Patent Specification No. 2,044,910A provides further variations in heat exchangers of the foregoing kind. This patent specification provides an improved external appearance for a unit of - 2 /E 560243 the kind identified above by replacing the louvred front panel arrangement of the earlier design with an apertured or slotted front panel behind which the heat exchange structure itself is disposed.

In a particular construction described in this patent specification, referred to as an extra-deep unit, the heat exchange structure of the radiator includes a diagonally arranged pipe assembly within the casing of the unit by virtue of which enhanced heat exchange is established.

According to Irish Patent Specification No. S58054, there is provided a heat exchanger comprising an upper header, a lower header, a plurality of tubes extending between the headers and communicating with each header for fluid flow between the headers by way of said tubes, a front panel extending between the upper and lower headers, each header being in substantial proximity to the said front panel, at least one heat transfer element associated with each of said plurality of tubes, said heat transfer element comprising fins, and each of said plurality of tubes having a first portion extending divergingly away from said front panel and upwardly from said lower header, said first portion communicating with a second portion of said tube, and said second portion extending in a direction away from said first portion convergingly towards said front panel and upwardly towards the upper header, a bent tube structure being thereby provided, at least a section of said bent tube structure being at a greater spacing from said front panel than those sections of said tube structure connected to said upper and lower headers.

A copending patent application provides a heat exchanger in which a plurality of tube portions is located between an inlet for a heating medium and an outlet for the heating medium, for flow of the heating medium between said inlet and said outlet, said plurality of tube portions extending in series between said inlet and said outlet, each of said plurality of tube portions suitably comprising a substantially horizontal tube section and each upstream tube section being connected to a downstream tube section by a 180° bend IE 960243 - 3 portion, said plurality of tube portions then preferably defining an array of tube sections in which each upstream substantially horizontal tube section is located substantially vertically above a downstream horizontal tube section and each successive 180° bend portion is disposed at an opposite end of the array, so that the heat exchanger defines a substantially serpentine tubular array in front view, and a plurality of heat convective features being suitably associated with the tube portions, such as louvred or slotted panels welded to the front and rear of the serpentine tube.

It is an object of the present invention to effect further improvements in units of any of the foregoing kinds to enhance the heat output of the unit. It is a particular objective of the present invention to provide an improved finning structure which enables enhancement of the heat output of a unit of any of the foregoing kinds.

According to the invention there is provided a heat exchanger comprising: (a) a plurality of tube sections for flow of heating medium therethrough, (b) a plurality of heat transfer elements associated with said plurality of tube sections, wherein (i) each of said heat transfer elements consists of a plate associated with one or more of said plurality of tube sections for transfer of heat from said tube section(s) to said plate, (ii) said plates extend across a region between substantially parallel spaced apart tube sections, and (iii) each said plate has a multiplicity of louvre-form openings formed therein for directed flow of air through said openings, characterised in that at least three of said plates extend across said region between substantially parallel spaced apart tube sections.

IE 960243 - 4 In a preferred embodiment of the invention, four said plates are provided to extend across said region between substantially parallel spaced apart tube sections, for example in a heat exchanger in which the tube sections are defined by vertical elements disposed between spaced apart upper and lower headers, or alternatively in a unit in which the tube sections are defined by successive transverse runs of a generally serpentine tube assembly.

Two of said plates are substantially planar louvred outer plates, while the or each inner plate has a substantially planar louvred central region and cranked curved side or end regions for embracing a said tube section so that the or each inner plate is spaced from the outer plates. The curved edges allow the inner plates to engage snugly around the tubes and the outer plates to be put in position over the inner plates where they pass across the tube sections.

The or each inner plate is then welded to said substantially parallel spaced apart tube sections, while each outer plate is welded either to an inner plate or to a tube section. Thus in the four-plate construction, the outer and inner plates are welded to each other where they pass over the tube sections, and the inner plates are welded to the tube sections.

The invention also extends to a heat exchanger substantially as described herein with reference to and as shown in any one or more of Figures 6, 7, 10 and 11 of the accompanying drawings, of these Figures taken together with one or more of the remaining Figures.

Known constructions of heat exchanger will now be described having regard to certain of the accompanying drawings, together with embodiments of improved heat exchanger according to the invention and certain features and variants thereof, again with reference to others of the following drawings.

IE 960243 - 5 In the drawings, Figure 1 is a pictorial representation of a known construction of tubular heat exchanger or radiator, Figure 2 is a cross-sectional end view of the radiator of Figure 1, Figure 3 is a pictorial representation of three of the louvres of the fin construction of the arrangement of Figures 1 and 2, looking upwardly towards the downwardly directed limbs of the louvres, Figure 4 is a cross-sectional side view of a portion of the louvred structure of Figure 3, Figure 5 is a top view of the fin arrangement of the heat exchanger according to Figure 2, Figure 6 is a top view of an assembled fin arrangement according to the invention, Figure 7 is an exploded view of the construction of Figure 6, Figure 8 shows a tubular heat exchanger construction suitable for application of the present invention, Figure 9 shows an alternative serpentine tube assembly for application of the system according to the invention, Figure 10 shows a side-sectional view of a tube arrangement according to Figure 8 incorporating the improvement of the present invention, and Figure 11 is a side-sectional view in diagrammatic form of IE 960243 - 6 the arrangement of Figure 9, showing a manner of application of the improvement of the present invention.

Referring first of all to the known construction of Figures 1 and 2, the heat exchanger 1 includes an upper horizontal or header pipe 2 located substantially vertically above a lower horizontal or header pipe 3. Pipe 2 is a supply pipe and pipe 1 is a discharge pipe. The headers 2 and 3 are interconnected by vertical tubes or elements 4, each of which is welded at the top and bottom respectively to the upper header 2 and the lower header 3. Two heat-conducting plates 5a, 5b are welded onto the opposite sides of the vertical elements or tubes 4. Each plate 5a, 5b is provided with respective outwardly bent fins 6 and 7. The fins 6 of the front plate 5a are downwardly directed, while the fins 7 of the rear or inward plate 5b are arranged to open upwardly. Each plate has two rows of fins between each pair of vertical elements or tubes 4. The vertical elements 4 are welded to the fronts of the headers 2 and 3, and the array of heat-conducting plates 5a welded to the sides of the vertical elements 4 directed away from the headers define the front face of the radiator or heat exchanger unit 1. In an alternative construction, the front plates 5a may be spaced back from the front wall structure of a separate casing arangement enclosing the heat exchanger, so that front plate 5a does not then define any portion of the casing structure itself, which is wholly independent of the heat exchanger.

The headers and heating elements are accommodated within a frame structure defined by suitable framework members, and the upper side of this structure is covered over by a grid 8, while the ends are closed in by plates 9, which may optionally also be apertured or louvred. The lower side of the structure may also be enclosed as required.

Referring now in particular to Figure 2, the manner of operation of this heating unit is shown. Radiant heat is directed /E 960243 - 7 outwardly from the vertical elements and their attached heat-conducting plates in the direction of arrows 11. Significant convective heat distribution also takes place by virtue of air, heated by contact with the vertical elements and their heat-conducting plates, rising along the front of the unit, where it is engaged by the downwardly directed outer lips of the fins or louvres 6 to be thereby conducted inwardly to pass between the vertical tubes 4 and to then emerge through the upwardly directed fins or louvres 7 of the inner heat-conducting plate 5b. The direction of this airflow is shown by arrows 12. It continues upwardly through the interior of the unit to the top grid 8, where the heated air emerges into the space to be warmed. In engineering terms, this arrangement is highly effective and of substantially greater efficiency than a flat panel radiator. The downwardly directed fins or louvres on the front panel of the radiator break up any boundary layer of air inclined to develop along this front face. In addition, there is less diminution in the thermal gradient or temperature difference between the radiator and the air immediately adjacent to it as between the bottom and top of the radiator than is the case for a panel construction of heat exchanger. The arrangement and disposition of the louvres is highly effective in generating effective convective heat transfer.

Figure 3 is a detailed pictorial representation of the louvres of the heat convective panels. As shown in Figure 3, louvres 6 of plate 5a are seen looking upwardly from below, i.e. there is depicted a construction in which the louvres open downwardly. In other words, the louvres 6 as represented intercept upwardly flowing air and direct it through the panel 5a from the downwardly extending louvre lip inwards. The louvres 6 are suitably formed by slitting the plate member 5a and then twisting the metal between the slits through an appropriate angle. The pitch of the slits is typically 4 mm and the bending is such as to provide a flow area approximately 1.8 mm in depth. These features of the invention are furrther indicated in the side sectional view of Figure 4, where IE 960243 - 8 dimension X represents the depth of the free flow area.

Figure 5 is a top view of the structure of Figure 2, in which a front 5a and a rear 5b louvred plate are welded onto the vertical radiator elements 4. The louvred regions 6, 7 are indicated and the downwardly directed louvres 5 of the front plate 5a intercept the upward air flow, direct it through the space between the louvre plates 5a, 5b where it undergoes further heating, and the air flow then passes out through the rear louvres 7 to continue upwards within the radiator structure. In an arrangement of this kind, if 100 units of heat, measured on any basis, are typically transferred to the air by the front louvred plate 5a, then approximately 60 units on the same measurement basis are transferred by the second louvred plate 5b.

Referring now to the top view of Figure 6, there is shown the arrangement of the present invention, wherein a further two louvred plates 25a, 25b are interposed between the front 5a and rear 5b louvred plates of the prior art construction. The louvering features of these additional plates 25a, 25b are identical with those previously described, namely, the louvres on the forwardly-directed side of each plate are profiled to intercept rising air and conduct it through the plate for upwardly-oriented discharge at the rear of the plate. The arrangement results however in four louvred plates 5a, 5b, 25a, 25b being associated with the vertical elements 4, so that the air flows initially through the front plate 5a, then through the second plate 25a and the third plate 25b and finally emerges through the rear plate 5b. If the front plate 5a is again postulated to deliver 100 units of heat to the air passing through it, and the second plate 25a, namely that immediately behind the front plate 5a, delivers 60 units, then the second additional louvred plate, i.e. the third plate 25b, may be expected to add approximately 40 units of heat to the air, while the innermost plate 5b now transfers just 20 units of heat. Thus the aggregate convective heat transferred by the improved system of the invention is 220 units, as - 9 compared with 160 in the prior art. An increase in heat output of substantially one-third is thus gained without any change in the package size of the radiator unit. This is a significant advantage in achieving improved performance of space heating systems.

Figure 7 shows the arrangement of Figure 6 in exploded view. The inner louvred plates 25a, 25b are profiled or curved at each end 26 so as to pass over but embrace the vertical elements 4 at the spot welding locations while also providing the required disposition of the louvred plates 25a, 25b between the elements 4, spaced inwardly from the outer plates 5a, 5b but spaced apart from one another. The profiled inner plates 25a, 25b and the generally planar outer plates 5a, 5b are brought together during assembly and are welded to one another and to the vertical elements 4 by means of spot welding.

The improved heat convective structure of the invention in the form of the additional louvred plates or fin features 25a, 25b are suitably not only to radiators of the type shown in Figures 1 and 2, but may also be applied to the improved serpentine tube constructions 31, 41 shown in Figures 8 and 9, heat exchangers of this type being described in a copending patent application. As applied to the unit 31 of Figure 8, the additional plates 36a, 36b are interposed between the outer finned or louvred plates 35a, 25b in the manner shown in diagrammatic sectional form in Figure 10. For the horizontally louvred structure of Figure 9, essentially the same result is achieved, but by means of a segmental inner and plate structure 45a, 45b, 46a, 46b, as viewed in the side sectional representation of Figure 11. Thus an upper group of finned plates engages the two uppermost runs of tubing 41, the next group encloses the following three runs, and the lowermost plates are welded to the two final tube runs.

The multiple louvre plate construction of the present invention may be applied not only to any of the arrangements shown, IE 960243 - 10 but may also be applied to constructions in which the tube assemblies are tilted within the overall casing structure, so as to optimise heat exchange. In conjunction with tilting of the overall tubing assembly, the degree of opening or inclination of the individual louvres may also be varied, with or without pitch variation, so as to achieve total optimisation of unit performance.

Claims (5)

1. A heat exchanger comprising: (a) a plurality of tube sections for flow of heating medium therethrough, (b) a plurality of heat transfer elements associated with said plurality of tube sections, wherein (i) each of said heat transfer elements consists of a plate associated with one or more of said plurality of tube sections for transfer of heat from said tube section(s) to said plate, (ii) said plates extend across a region between substantially parallel spaced apart tube sections, and (iii) each said plate has a multiplicity of louvre-form openings formed therein for directed flow of air through said openings, characterised in that at least three of said plates extend across said region between substantially parallel spaced apart tube sections.

2. A heat exchanger according to Claim 1, comprising four said plates extending across said region between substantially parallel spaced apart tube sections.

3. A heat exchanger according to Claim 1 or Claim 2, wherein two of said plates are substantially planar outer plates, and the or each inner plate has a substantially planar central region and cranked curved side or end regions for embracing a said tube section so that the or each inner plate is spaced from the outer plates.

4. A heat exchanger according to Claim 4, wherein the or each inner plate is welded to said substantially parallel spaced apart tube sections, and each outer plate is welded either to an inner plate or to a tube section. IE 960243 - 12

5. A heat exchanger substantially as described herein with reference to and as shown in any one or more of Figures 6, 7, 10 and 11 of the accompanying drawings, of these Figures taken together with one or more of the remaining Figures.