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(11) | EP 1 146 307 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Heat exchanger |
| (57) A cast monoblock heat exchanger has heat exchange fins that span the gap between
opposed walls of primary heat exchange passageways. The fin arrangement maximises
the fin surface area to improve heat exchange efficiency and increases structural
rigidity and the transfer of stresses caused by the expansion and contraction of the
heat exchanger during use. |
[0001] This invention relates to heat exchangers, and particularly to heat exchangers cast in one piece, i.e. monoblock heat exchangers. The invention is mainly concerned with heat exchangers for domestic gas boilers.
[0002] A known form of heat exchanger has upright passages for the flow of hot gases from a gas burner. The passages are in heat exchange relationship with one or more horizontal conduits through which flows a fluid to be heated. A plurality of parallel heat exchanger fins are located in the passages and extend longitudinally from opposed walls of the passages to increase the efficiency of the heat exchange between the gases and the fluid.
[0003] The present invention aims to improve the efficiency of known cast heat exchangers, and it provides a cast monoblock heat exchanger comprising a body having at least one primary passageway for the flow of a gaseous heat exchange medium, at least one conduit for the passage of a fluid to be heated by the heat exchange with the gaseous medium between an inlet port and an associated outlet port and a plurality of generally parallel heat exchange fins spanning the gap between opposed walls of the primary passageway. For any given fin spacing, the fin arrangement of the invention maximises the fin surface area, and thereby provides an improvement in heat exchanger efficiency. The interlinking of the fins also increases the structural rigidity of the heat exchanger and improves the transfer of stresses caused by the expansion and contraction of the heat exchanger during use. Further, as the heat exchange fins span the gap between opposed walls of the primary passageway heat can be transferred between opposed passageway walls to reduce thermal stress imposed by temperature imbalances across the body of the heat exchanger.
[0004] Preferably, the heat exchange fins define an array of mutually isolated minor passageways. The present invention also encompasses a gas boiler having a cast monoblock heat exchanger as described above.
[0005] A clear understanding of the present invention will be gained from the following detailed description of a preferred embodiment with reference to the accompanying drawings, in which:
Figure 1 is a plan view of a cast monoblock heat exchanger according to the invention, shown partially sectioned; and
Figure 2 is a cross-sectional view along the line A-A of Figure 1.
[0006] The heat exchanger 1 is cast in one piece from iron, aluminium or any other suitable material. The cast heat exchanger has one or more pairs of inlet and outlet ports 2,3 and defines between associated ports a serpentine-like path for the passage of the fluid to be heated.
[0007] Three parallel flueways 4 extend through the heat exchanger 1. Hot combustion gases from a gas burner (not shown) pass through the flueways 4, which are generally rectangular with an elongate cross-section. Heat exchange fins 5 extend in general parallelism between the major faces 6a,b of the flueways to bridge the gap between the major faces and to define an array of discrete generally rectangular minor flueways disposed at right angles to the major flueways 4. As shown in the right hand half of Figure 1, alternative fins are tapered below the level of fin interconnection.
[0008] The inter-fin spaces are generally in the region of 1.8 mm and 4.0 mm. For any given inter-fin spacing, the available heat exchange area is maximised by the arrangement described above.
[0009] As the fluid to be heated passes from an inlet port 2 to the associated outlet port 3 its temperature is gradually increased through heat exchange with the hot combustion gases from the gas burner. The fluid temperature varies from a minimum at the inlet port 2 to a maximum at the associated outlet port 3, and the variation in temperature along the serpentine-like path through the heat exchanger can result in the fluid temperature in the conduit on one side of a flueway being a significantly different temperature from the fluid in the conduit on the other side of the flueway. Also, if more than one conduit is provided, a significant variation in temperature across a flueway can result. The thermal stresses on the one-piece casting that result from this temperature variation are reduced or minimised by the heat exchange fins 4 which span the gap between the major faces 6a,b of the flueway 4 to heat transfer therebetween.
[0010] For ease of comparison with a known heat exchanger, the additional area of the heat exchange fins according to the invention is shaded in the drawings. In the preferred embodiment the fins 5 bridge the gap between the major faces 6a,b of the flueways 4 in the upper half of the heat exchanger, with the end of each fin in the lower half closely confronting the end of the complementary opposite fin. A greater area of the fins could be joined.
[0011] Of course, the skilled person will appreciate that modifications to the preferred embodiment described above are possible without departing from the scope of the invention defined in the following claims. For instance, the number of flueways could be varied according to the specific performance required of the heat exchanger. Also, some but not all of the heat exchange fins could span the gap between opposed major faces 6a,b of a flueway with the other fins extending from either side of the flueway and, for example, terminating short of the longitudinal centre line of the flueway.
1. A cast monoblock heat exchanger comprising a body having at least one primary passageway
for the flow of a gaseous heat exchange medium, at least one conduit for the passage
of a fluid to be heated by heat exchange with the gaseous medium between an inlet
port and an associated outlet port, and a plurality of generally parallel heat exchange
fins spanning the gap between opposed walls of the primary passageway.
2. A heat exchanger according to claim 1, wherein the heat exchange fins define an array
of mutually isolated minor passageways.
3. A heat exchanger according to claim 1 or 2, wherein the conduit defined a serpentine-like
path through the heat exchanger for the fluid.
4. A cast monoblock heat exchanger substantially as herein described with reference to
the accompanying drawing.
5. A gas boiler comprising a heat exchanger according to any one of the preceding claims.