[0001] The present invention relates to a gas fire.
[0002] In particular, the present invention relates to a gas fire incorporating a heat exchanger
for use in transferring heat from the gaseous products of combustion in the gas fire
to a passage through the fire for convection air. In certain such gas fires, the heat
exchanger is of a complex and expensive construction providing a tortuous path for
both the convection air and the combustion products so that the air gains the maximum
exposure to surfaces heated by the combustion products.
[0003] The aim of the present invention is to provide a gas fire with a simple heat exchanger
which is relatively cheap to manufacture whilst being efficient in operation.
[0004] According to the present invention there is provided a gas fire comprising at least
one heat exchanger in the form of a hollow tubular element made of a thermally conducting
material, which extends across a path for convection air in the fire and provides
a passage for gaseous combustion products passing to a flue from the fire.
[0005] In one embodiment of the present invention the hollow tubular element is generally
cylindrical and preferably made of aluminium, with a number of groups of three generally
radially projecting fins formed on its outer periphery, the fins each extending axially
of the element. It is envisaged that the element may be formed by extrusion and cut
into the desired lengths. Alternatively, however, the tubular element may be fabricated
or die cast.
[0006] In another embodiment of the present invention, the generally radially projecting
fins extend circumferentially of the hollow tubular element, the element being die
cast or fabricated.
[0007] In a still further embodiment of the present invention, the or each heat exchanger
is formed by a hollow tubular element which is partially flattened to present an oval
transverse cross-section, i.e. a lozenge-shaped cross-section. This design maximises
the surface area available for heat transfer but reduces the resistance to convection
air flow; the narrow section facing into the air flow. If desired, one or more fins
may project from the outer surface of the tubular element to further enhance heat
transfer, e.g. a fin can project from each end of the flattened transverse cross-section.
[0008] A number of these generally cylindrical heat exchanger elements are positionned between
the walls defining a convection air passage through a gas fire, with the passage through
each element interconnecting the front of the fire with an appropriate flue. Thus,
hot combustion products pass through the elements and convection air passes over the
outside of the elements which the fins, if provided, scrubbing i.e. imparting turbulence,
to the air flow to enhance heat transfer. If desired, fins may be provided on the
inside wall of the tubular element defining said passage, to thus improve heat transfer.
[0009] As an alternative to securing the heat exchanger element of the present invention
between the walls defining a convection air passage, part of one of the walls may
be formed by casting with the tubular elements cast integrally therewith. The precast
wall section may also include a multi-fin facia for use in radiating heat from the
front of the fire.
[0010] The present invention will now be further described, by way of example, with reference
to the accompanying drawings, in which:-
Fig.1 is a perspective view of one embodiment of a heat exchanger for use in the present
invention;
Fig.2 is a cross-sectional view through part of a gas fire incorporating a number
of the heat exchangers shown in Fig.1;
Fig.3 is a rear perspective view of the fire shown in Fig.2;
Fig.4 is a perspective view of another embodiment of a heat exchanger suitable for
use in the present invention;
Fig.5 is a perspective view of a precast section of a wall of the convection air passage
including integrally cast heat exchanger elements as per Fig.4,
Fig.6 is a perspective view of a further embodiment of heat exchanger for use in the
present invention; and
Fig.7 is a schematic illustration of the preferred relative arrangement of the heat
exchangers of Fig.6, in a gas fire.
[0011] The gas fire constructed according to the present invention and illustrated in Figs.
1, 2 and 3 of the accompanying drawings, comprises a hollow generally cylindrical
heat exchanger element 1 made of aluminium, with three groups 3 of three generally
radially projecting fins 5 which extend axially of the element 1. The heat exchanger
element 1 is formed by extrusion, the extrusion being cut to the desired length and
the end regions machined to form axial extensions 7 for use in sealingly mounting
the element 1 in a gas fire as shown in Fig.2 of the accompanying drawings.
[0012] As seen in Fig.2, a number of the elements 1 are in use located in the top part of
a fire 9, between the walls 11 and 13 defining a convection air passage 15. The elements
1 each connect the upper region 17 of the front of the fire 9 with the rear region
19 of the fire which is in use sealingly connected with a flue (not shown). Thus,
in use the hot combustion products pass through the heat exchanger elements 1 to the
flue, the convection air being moved over the outside of the heat exchanger elements
1 and scrubbed by the fins 15 to enhance heat transfer.
[0013] Whilst the elements 1 are described hereabove as being made by the extrusion of aluminium,
any suitable thermally conductive material can be alternatively used, as can any suitable
method of manufacture, e.g. fabrication or die casting.
[0014] An alternative construction of heat exchanger is illustrated in Figs. 4 and 5 of
the accompanying drawings. This heat exchanger comprises a hollow generally cylindrical
element 21 with a number of axially spaced apart, circumferentially extending fins
23 projecting generally radially outwardly from the outside surface thereof. As shown
in Fig.5, these heat exchangers (Fig.4) can be integrally formed, e.g. by casting,
as part of the convection air passage wall 13 - see Fig.1 between points 'X' and 'Y'
- this section of wall being provided with a front facia portion 25 carrying a number
of fins 27 for radiating conducted heat from the front of the fire. Alternatively,
the heat exchanger of Fig. 1 or any other heat exchanger within the scope of the present
invention, can be formed as part of the wall section X-Y.
[0015] A still further embodiment of heat exchanger element 25 is shown in Figs. 6 and 7
of the accompanying drawings, the element being formed by a partially flattened tubular
element which has a generally oval or lozenge-shaped transverse cross-section. These
heat exchanger elements 25 are arranged in a gas fire such as shown in part in Fig.1,
with the heat exchanger elements relatively positioned as shown in Fig.7, with the
narrow cross-section being presented to the air flow. In this way the surface area
available for heat transfer is maximised whilst the resistance to air flow is minimised.
Fins 28, as shown in dashed lines, can be provided one at each end region of the flattened
transverse cross-section, to increase surface area and further enhance heat transfer.
Alternatively any number of fins can be provided in any desired configuration and
arrangement.
[0016] In any of the heat exchangers 1, 21, 25 described hereabove heat transfer can be
further enhanced by the provision of fins 29 on the inside wall of the passage through
the heat exchangers, said fins extending generally radially inwardly and axially of
the passage. Again, any desired number, configuration and/or arrangement of fins 29
can be selected.
[0017] The present invention thus provides an efficient heat exchanger for use in a gas
fire, which is both simple and inexpensive to manufacture.
1. A gas fire characterised by at least one heat exchanger in the form of a hollow
tubular element (1;21;25) made of a thermally conducting material, which extends across
a path (15) for convection air in the fire (9) and provides a passage for gaseous
combustion products passing to a flue (19) from the fire (9).
2. A gas fire as claimed in claim 1, wherein the hollow tubular element (1;21;25)
is generally cylindrical.
3. A gas fire as claimed in claim 1 or claim 2, wherein a number of fins (5) project
outwardly from the hollow tubular element (1), each fin (5) extending axially of said
hollow tubular element (1).
4. A gas fire as claimed in claim 3, wherein the fins (5) are arranged in groups (3)
of three fins.
5. A gas fire as claimed in claim 3 or 4, wherein the hollow tubular element (1;25)
is formed by extrusion.
6. A gas fire as claimed in claim 1 or claim 2, wherein a number of fins (23) project
outwardly from the hollow tubular element (21), each fin (23) extending circumferentially
of the hollow tubular element (21).
7. A gas fire as claimed in claim 1, wherein the hollow tubular element (25) has a
partially flattened transverse cross-section.
8. A gas fire as claimed in claim 7, wherein a fin (28) projects outwardly from each
end region of the partially flattened hollow tubular element (25), each fin (28) extending
axially of the hollow tubular element (25).
9. A gas fire as claimed in claim 7 or 8, wherein the hollow tubular element (25)
is arranged so that its reduced transverse dimension is, in use, presented to the
flow of convection air along said path (15).
10. A gas fire as claimed in any one of the preceding claims, wherein fins (29) are
provided on the inside wall of the tubular element (1;21;25) defining the said passage
for gaseous combustion products.
11. A gas fire as claimed in claim 1, wherein a number of said hollow tubular elements
(21) are cast as an integral part of a section of a wall (13) used to define said
path (15) for convection air.