Liquid heaters and vaporizers – Stand boiler – Fluid fuel burner
Reexamination Certificate
2000-11-09
2001-11-20
Lu, Jiping (Department: 3749)
Liquid heaters and vaporizers
Stand boiler
Fluid fuel burner
C122S018400, C122S019200, C122S494000
Reexamination Certificate
active
06318304
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to water heaters, such as water heaters for domestic or commercial applications, and boilers e.g. for hydronic heating systems and the like.
BACKGROUND OF THE INVENTION
One known type of water heater provides a water tank and a burner located below the tank arranged so that combustion products from the burner are directed to flow up the sides of the tank to thereby heat the water in the tank. The tank is mounted and centred within a casing so as to define a flue path for the combustion products between the outside surface of the tank and the casing. An example of this kind of water heater is shown in the present assiginee's Australian patent specification No. AU-28685/97 (Patent No. 720,062).
A problem or difficulty with this kind of arrangement is that the heat extraction efficiency may not be optimised and, in particular, combustion products may still have some significant heating capacity after being wastefully discharged from the unit.
Another kind of water heater, such as shown in Australian patent specification AU-38573/93, uses a flue for combustion products passing vertically through the centre of the water tank. The flue is provided with convolutions and baffles intended to improve the heat extraction efficiency. It would be possible to use convoluted shapes and baffles along the outside of the tank of the kind shown in our patent specification AU-28685/97 but this would be complicated and undoubtedly very costly to manufacture and assemble.
OBJECT OF THE INVENTION
It is an object of the present invention to provide a water heater enabling an improvement in efficiency of heat extraction from combustion products.
SUMMARY OF THE INVENTION
According to the present invention there is provided a water heater including a water tank having an outside surface and a lower portion thereof, a burner producing hot combustion products located at or towards the lower portion of the tank, a casing around at least part of the outside surface of the tank and spaced therefrom so as to define a flue path within the casing and along the outside surface of the tank whereby combustion products can flow along the outside surface of the tank and can therefore heat water within the tank the water heater further including at least one flow restriction located in the flue path and extending inwardly from the casing towards the outside surface of the tank and forming in generally horizontal section through the flue path a region of restricted flow area whereby the combustion products flowing along the flue path encounter the flow restriction and are restricted and disturbed in flow pattern at said at least one flow restriction, the or each one of said at least one flow restriction being of limited vertical extent so that combustion products flowing past the flow restriction are again disturbed in their flow upon passing the flow restriction and encountering an increased flow area of the flue path past the flow restriction.
The restriction of the area of the flue path around the outside of the tank followed by expansion of the flow area produces an improvement in the heat extraction efficiency. Although the precise mechanism and thermodynamics resulting in the improved efficiency are not known for certain, it is possible that at least one effect is occurring. The effects that produce or contribute to the heat extraction improvement include (i) the slowing of the average flow velocity through the entire flue path which can produce a greater residence time of combustion products within the water heater before being discharged. and (ii) the or each restriction is contributing to turbulence in the flow of combustion products which can increase the heat transfer efficiency. It is possible and perhaps even likely that both of these effects are contributing to an improvement in heat exchange efficiency.
In the preferred embodiment multiple flow restrictions are provided, e.g. three restrictions spaced apart in the direction of flow of combustion products so that the combustion products are repeatedly encountering the restrictions in passing from the burner before being discharged from the water heater.
Preferably the flow restrictions are provided no lower along the height of the tank than about one third to one half of the overall height up from the bottom. The extraction of heat from combustion products towards the lower portions of the tank is quite effective because the combustion products in that zone are hottest and also most turbulent. However as the combustion products travel further up the sides of the tank, they become cooler and the flow becomes less turbulent. The first restriction may be approximately at or above the mid-point in the height of the tank so as to restrict and disturb the flow pattern after the combustion products have travelled up and cooled significantly. As mentioned above preferably further flow restrictions are provided spaced above the first and before the combustion products reach the top of the tank.
In the case of a tank having cylindrical walls, the casing may define a flue path around the entire circumference of the tank. i.e. the flue path is substantially cylindrical. In this arrangement the flow restriction preferably in a cloud ring which extends inwardly from the casing so as to define a restricted flow area of annular shape in horizontal cross-section. The flow restriction may be defined by a formation constituting part of the casing. Alternatively the flow restriction may be defined by a body, such as ring or collar located within the casing and projecting inwardly therefrom towards the outside surfaces of the water tank. The flow restriction may restrict the flow area by in the order of 50% or more. For example if the radial width of the flue path is about 11 mm, the flow restriction ring or collar may extend inwardly by say 6.5 mm, leavinig a restricted flow passage of 4.5 mm radial width.
In the preferred embodiment, the flow restriction extending inwardly from the casing towards the outside surface of the tank also provides a tank centering formation which contacts the outside surface of the tank so as to thereby locate and maintain the tank relatively centered within the casing and so that the flue path is of uniform cross-sectional shape wherever a horizontal sectional view therethrough may be taken. The centering formations for example may comprise fingers, bosses or other projections which extend inwardly at points around the circumference of the flow restriction ring or collar and which contact the outside surfaces of the tank at points or small area contact zones around the circumference. The projections provide further restrictions to the flow although these are of relatively small dimension in the overall flow area at the flow restriction.
REFERENCES:
patent: 2263031 (1941-11-01), Estes
patent: 2506336 (1950-05-01), Bock
patent: 5415133 (1995-05-01), Noh
patent: A-38573/93 (1993-12-01), None
patent: 720062 (2000-05-01), None
Aqua Max Pty LTD
Bloom Leonard
Lu Jiping
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