GB2168140A - A heater - Google Patents

Abstract

A heater comprises a heat exchanger housing 1 adjacent the bottom of which there is arranged a burner tube 6, an air case 2 communicating with said housing 1 and a wall-traversing tube 4 for discharging combustion gases, and an outer tube 3 for air supply surrounding said discharge tube 4, as well as a gas control block 8 arranged in a gas supply duct 7 to said burner tube. The connection between the air case 2 and the heat exchanger housing 1 includes one or more stub tubes 16 adapted to receive a ring 17 for limiting the quantity of air supplied. A finned heat exchanger block 12 is arranged in at least one wall of the heat exchanger housing. The fins 13 have longitudinal discontinuities to prevent the build-up of a barrier layer. <IMAGE>

Description

SPECIFICATION A heater This invention relates to a heater comprising a heat exchanger housing with a burner tube adjacent the bottom thereof, an air case communicating with said heat exchanger housing, and a wall-traversing tube for discharging combustion gases, an outer tube for air supply, surrounding said discharge tube, as well as a gas control block arranged in a gas supply duct to said burner tube.

Such a heater is known e.g. from Dutch patent application 67.01804.

It is an object of this invention not only to improve the efficiency of such an apparatus but moreover to construct the apparatus from standard elements, so that it can be rendered suitable for a different capacity at minimal cost, while maintaining a high efficiency.

To this end, the heater according to this invention is characterized in that the connection between the air case and the heat exchanger housing consists of one or more stub tubes adapted to receive a ring for limiting the quantity of air supplied. During the assembly of the heater, the efficiency of the apparatus can be maintained at different capacities by using a ring having a different inner diameter.

In other words, use can be made of the same standard parts for a large number of capacities, but exclusively the inner diameter of the ring disposed within the stub tubes, as well as the nozzle determining the quantity of gas supplied should be altered.

An improved efficiency can be obtained by arranging a finned heat exchanger block in at least one wall of the heat exchanger housing.

For instance, the combustion gases flow along the inside of the block and the ambient air flows along the outside of the block. In order to obtain maximum heat transfer between the heat exchanger block and the fluid flowing along it, (i.e., a maximum efficiency), the elongate fins disposed on the outer surface of the heat exchanger block may be discontinuous.

The result is that no boundary layer of substantial thickness can be built up, which would limit heat transfer. This "boundary layer" effect can be improved still further by providing the discontinuities in adjacent fins at different levels.

It is observed that in many cases the fins with discontinuities are not provided on the "inside", i.e. the side along which the flue gases flow, since this would lead to undue resistance, thereby adversely affecting combustion.

In the heater according to this invention, use is made of an aluminum heat exchanger block, since aluminum ensures satisfactory proper heat transfer. However, it is impossible from the viewpoint of cost to manufacture the entire heater from aluminum. The other part of the heater therefore consists usually of steel sheet or similar material. In order to avoid problems in case of expansion of the parts when being heated due to an incorrect assembly, such a mutual attachment has been chosen as to allow a mutually different expansion. Such an attachment may consist e.g. of a metal strip having outstanding ends abutting at room temperature against the sides of two fins oriented towards the centre.

For the sake of completeness, it is observed that a heater comprising a finned heat exchanger is known per se from British patent 847,141. However, the heat exchanger block disclosed therein is integral with the housing.

It is further observed that the casing around the housing is made of enameled steel sheet, except for the "cool" side panels, which may be made of a high quality synthetic plastics material.

One embodiment of the heater according to this invention will now be described, by way of example, with reference to the accompanying drawing, in which: Figure 1 is a partly exploded, perspective diagrammatic view of a heater according to the present invention; and Figure 2 shows an enlarged detail of the heater shown in Fig. 1.

According to the drawing, a heater comprises a heat exchanger housing 1 and a juxtaposed air case 2, which communicates with the atmosphere by means of an outer tube 3 extending through a wall, not shown. Inside said outer tube 3 there is disposed a flue gas discharge tube 4 communicating with the top of heat exchanger housing 1. As shown in Fig. 1, air supply tube 3 and gas discharge tube 4 are fitted at their free end with a known per se wall grid 5 for preventing recirculation of the exhaust gases and trouble caused by wind fiow.

As shown in the drawing, the lower end of the heat exchanger housing contains a burner tube 6 (moved sideways for clarity here) to which gas can be supplied through a duct 7 containing a gas control block 8 and on which is mounted a nozzle 18 that can be operated by a control knob 9 disposed on the top of a casing 10 shown in part only.

The front top of said casing includes a louvre-shaped portion 11 allowing an effective air flow from the casing, which has an open bottom, along the heat exchanger block 12 through the louvre-shaped portion 11. As shown in Fig. 1, heat exchanger block 12 includes elongate fins 13 having longitudinal discontinuities therein (only the two fins at the outer ends have no discontinuities). As already observed, the discontinuities in the fins serve to limit the boundary layer flow along the fins.

Such a boundary layer, resulting in poor heat transfer, increases in thickness with its distance from the point of inflow. By interrupting the fins lengthwise the boundary layer is lim ited. More effective turbulence, i.e. restriction of the thickness of the boundary layer, will be produced when, as in the embodiment shown, the discontinuities in adjacent fins are at different levels.

The heat exchanger block 12 can be mounted in the heat exchanger 1 by means of a supporting strip 14, which may be attached to the wall or walls of the heat exchanger housing 1 by screws, not shown. The retention of the heat exchanger block in lateral direction, i.e. so that different expansions are possible, is ensured by fitting the ends of the supporting strip 14 with outstanding ends 15 (see Fig. 2). The form and sizes of the ends and the supporting strip are chosen in such manner that, at room temperature, the distal edges of the outstanding ends 15 about the mesial sides of the fins concerned. The mesial edges of the ends 15 are slightly sloped.

There is thus created a clear possibility of mutually different expansions of the supporting strip 14 and the heat exchanger housing 1 relative to the heat exchanger block 12.

As further shown in the drawing, heat exchanger housing 1 and air case 2 are in open communication with each other at their lower ends through stub tubes 16. The stub tubes contain rings 17 by means of which the air supplied to the heat exchanger housing and/or the burner tube can be limited and controlled.

By incorporating rings of a different inner diameter and adjusting the nozzle, the capacity of the heater can be changed in a simple manner, while maintaining its efficiency, the other parts of the heater being the same. For the sake of completeness, it is observed that a limited amount of control is possible by increasing or decreasing the length of the flue gas discharge tube.

It will be clear that a great many modifications and/or additions are possible within the scope of this invention. Thus, for example, protective plates may be provided adjacent the burner tube to limit the load on the surrounding material.

Furthermore, there is a calculable relation between the height and the width of, and the interspace between, the fins and the locations where the discontinuities have to be made.

Claims (7)

1. A heater comprising a heat exchanger housing adjacent the bottom of which there is arranged a burner tube, an air case communicating with said housing and a wall-traversing tube for discharging combustion gases, and an outer tube for air supply surrounding said discharge tube, as well as a gas control block arranged in a gas supply duct to said burner tube, characterized in that the connection between the air case and the heat exchanger housing includes one or more stub tubes adapted to receive a ring for limiting the quantity of air supplied.

2. A heater according to claim 1, characterized in that a finned heat exchanger block is arranged in at least one wall of the heat exchanger housing.

3. A heater according to claim 2, characterized in that one or more fins have a longitudinal discontinuity.

4. A heater according to claim 3, characterized in that the discontinuities in adjacent fins are at different levels.

5. A heater according to claim 2, 3 or 4, characterized in that the heat exchanger housing and the heat exchanger block consist of materials having different coefficients of expansion and the mutual attachment allows an expansion relative to each other.

6. A heater according to claim 5, characterized in that the attachment comprises a metal strip having outstanding ends abutting at room temperature against the mesial sides of two fins.

7. A heater substantially as hereinbefore described with reference to the accompanying drawings.