Existing heat exchangers for use in a heating boiler for heating water of a central heating system and/or tap water, are usually cast round a sand core. Using the sand core a duct can be left free in he casting which can form for instance the duct for water of a central heating system or tap water. A drawback of this method is that it is relatively labour-intensive to first manufacture and then remove a sand core from the casting. Another drawback to this method is that the duct wall is formed by the casting. The material properties of the wall of the duct are thus determined by the choice of material from the casting material. This causes problems in practice. An aluminum duct wall is thus undesirable in the case of a liquid for transporting which has a pH greater than 8.5; this can occur with water in a closed central heating circuit, while aluminum is very suitable as casting material.
From the international patent application, published under number WO 85/01101, a heat exchanger according to the preamble of claim 1 is known, comprising at least one straight liquid pipe incorporated in a casting, which casting is provided in at least one side with a profiled heat exchanging surface. By placing at least a part of the liquid pipe in the mould the sand core has become superfluous.
EP-A-0 495 762 discloses a heat exchanger element, comprising three parallel tubes, which are cast into a body. The portion of the tubes enclosed by the body are externally provided with helical rills, before the casting operation.
It is an object of the present invention to provide a heat exchanger suitable for domestic purposes, such as a central heating system and/or tap water.
The present invention provides a heat exchanger with at least one liquid pipe incorporated in a casting, said casting being provided on at least one side with a profiled heat exchanging surface, characterized in that said liquid pipe is spirally wound or arranged in a zig zag form prior to pouring of the casting material, said profiled heat exchanging surface and said bent pipe being incorporated in a single casting body.
Different materials can be chosen for the duct wall and the casting material. It thus becomes possible to optimize these materials, and further allows great freedom in respect of the form and the position of the duct in the casting. The heat exchanger thus has at least one profiled side without the direction of the duct, i.e. the position of the liquid pipe, being hereby determined. It is moreover possible to embody the heat exchanger very compactly.
A preferred embodiment of the heat exchanger is characterized in that the profiled surface comprises a substantially lengthwise oriented profile and the liquid pipe is arranged in the casting substantially perpendicularly of the lengthwise oriented profile. With this construction it is possible to realize greater efficiency using the counterflow principle. By supplying a heating gas in lengthwise direction along the lengthwise oriented profile and supplying a counterflow liquid through the liquid pipe a high efficiency can be realized due in part to the comparatively large heat-exchanging surfaces.
Another preferred embodiment of the heat exchanger is characterized in that at least two liquid pipes are arranged in the casting. This heat exchanger can be applied for combined heating of a plurality of liquids, wherein can be envisaged use in a so-called combi-boiler for heating tap water and water of a central heating system. Both pipes are encased with casting material and mutually separated by casting material, whereby the danger of leakages is very small.
Yet another preferred embodiment of the heat exchanger is characterized in that the liquid pipes are arranged practically parallel to each other in the casting. This step enables arrangement of relatively long pipes in the casting, which will enhance the efficiency of the heat exchanger.
The casting is preferably manufactured from aluminum. The liquid pipe preferably manufactured from copper or stainless steel. Aluminum has the advantage that is has good heat-exchanging properties with a relatively small specific mass. Copper and stainless steel have the advantage that they are not rapidly affected by aggressive liquids.
Further the present invention provides a method for manufacturing a heat exchanger, comprising the following successive steps:
The present invention will be further elucidated with reference to the non-limitative embodiments shown in the following figures. Herein:
Fig. 1 shows a round heat exchanger 1 according to the invention in which is placed a burner 2. The burner 2 is connected to a mixing chamber 3 to which air and flammable gas are supplied via an air inlet 4 and a flammable gas inlet 5. The inner surface of heat exchanger 1 is provided with ribs 6 which enlarge the heat-exchanging surface. The ribs 6 form part of casting 7 in which two liquid pipes 8, 9 are arranged. Liquid pipe 8 herein forms the conduit through which water of a central heating system is carried, while liquid pipe 9 forms the conduit through which flows tap water for heating. The liquid in liquid pipes 8, 9 flows spirally upward from below as according to arrows S1, S2. The combustion gases flow downward from above as according to arrow S3, whereby the heating medium and the media for heating flow in opposing directions. The cooled combustion gases are further discharged via an outlet 10. Due to the high efficiency it is probable that condensation occurs on the underside of heat exchanger 1 and in outlet 10. Condensed liquid is drained via a condensation drain 11.
Fig. 2 shows a flat heat exchanger 12 comprising a casting 13 of which ribs 14 form part and two liquid pipes 15, 16 incorporated in a casting 13. Liquid pipes 15, 16 are incorporated in casting 13 such that the heat-exchanging surface is large. To this end liquid pipes 15, 16 are incorporated in casting 13 in zigzag form. The flow direction of the liquid in the liquid pipes is indicated with arrows S4, S5, while arrow S6 indicates the flow direction of the combustion gas. Use is also made in this situation of the counterflow principle to optimize the efficiency of heat exchanger 12. The heat exchanger 12 shown in this figure can for instance be incorporated into a so-called combi-boiler for household use.
Fig. 3 shows a mould 17 with which the heat exchanger 12 shown in fig. 2 can be manufactured. The liquid pipes 15, 16 are already arranged in the mould 17. Casting material will subsequently be poured into mould 17 via an opening 18. A profiled mould wall 19 comprises a main profile 20 whereby the ribs 14 are formed. After the casting material introduced into the mould 17 has hardened a top plate 21 is removed, whereafter the casting 13 with the pipes 15, 16 arranged therein is removed together with side walls 22, 23 from the mould 17. Finally, the side walls 22, 23 are taken from the casting. Such a method is also known as investment casting method.