Diffuser plate for premixed burner box

To substantially reduce inequality in hot combustion flow rates through first and second heat exchanger tubes from a fuel-fired heating appliance burner box connected thereto and internally combusting a fuel/air mixture received therein from a source thereof to create the hot combustion gas, a perforated diffuser member having a non-uniform perforation pattern is provided. The fuel/air mixture is flowed through the perforated diffuser member into the interior of the burner box. The non-uniform perforation pattern of the diffuser member functions to alter relative combustion gas flow rates through the first and second heat exchanger tubes in a manner reducing an undesirable operating temperature differential therebetween.

BACKGROUND OF THE INVENTION

The present invention relates generally to diffuser plate apparatus that functions to beneficially lessen undesirable uneven heating of combustion product-receiving heat exchanger tubes in an array thereof during the firing of a fuel-fired heating appliance, such as a furnace, with which the tubes are operatively associated.

In fuel-fired heating appliances, such as furnaces, a known firing method is to flow a fuel/air mixture into a burner box structure in which a suitable ignition device is disposed to combust the fuel air mixture and thereby create hot combustion gases used to heat air for delivery to a conditioned space. The hot combustion gases are flowed through a series of heat exchanger tubes, externally across which the air to be heated is flowed, and then discharged from the heating appliance into a suitable flue structure.

Due to various configurational characteristics of the heating appliance, during firing of the appliance undesirable uneven heating of the combustion product-receiving heat exchanger tubes may occur such that an undesirable non-uniform temperature distribution is present in the overall heat exchanger tube array. It is to this problem that the present invention is primarily directed.

DETAILED DESCRIPTION

The fuel/air combustion system10of a fuel-fired heating appliance, representatively a furnace12, is schematically depicted inFIG. 1. The combustion system10includes a fuel/air mixture supply housing14(representatively a low NOx mixing box structure) that is connected to a burner box or housing16with which a suitable ignition device18is operatively associated. Burner box16, in turn, is coupled to a collector box20by a series of heat exchanger tubes22(representatively five in number) that extend through the furnace12and include (as shown inFIGS. 2 and 3) two outer end tubes22aand three centrally disposed tubes22b. A draft inducer fan24is positioned within the collector box20.

During firing of the furnace12, the draft inducer fan24draws a fuel/air mixture26(created in a suitable manner from separate air and fuel sources not shown herein) sequentially through the fuel/air mixture supply housing14and into the burner box16. Within the burner box16the fuel/air mixture26is combusted by the ignition device18to form hot combustion gases28which are drawn by the draft inducer fan24through the heat exchanger tubes22and into the collector box20. At the same time, air30to be heated is suitably flowed across the heat exchanger tubes22, to receive combustion gas heat therefrom, and is then discharged from the furnace12as heated air30afor delivery to a conditioned space served by the furnace12. Cooled by the heat transfer from the tubes22to the air30, cooled combustion gases28aare drawn into the collector box20by the draft inducer fan24and then discharged from the furnace12to a suitable flue (not shown).

Representatively, as shown inFIG. 2, the draft inducer fan24is generally centered in a left-to-right direction within the collector box20and with respect to the five illustratively depicted heat exchanger tubes22. Accordingly, the suction of the fan24is similarly centered relative to the array of heat exchanger tubes22. Without the incorporation in the furnace12of a subsequently described feature of the present invention, the result is that the per-tube flow of hot combustion gases28is greater for the central tubes22bthan it is for the end tubes22a. In turn, this creates an undesirable non-uniform temperature distribution across the heat exchanger tube array, with the central tubes22bhaving higher operating temperatures than those of the end tubes22a.

With reference now toFIGS. 1 and 3, according to an aspect of the present invention, a specially designed perforated diffuser plate32is installed at the juncture between the fuel/air mixture supply housing14and the burner box16. As shown inFIG. 3, the diffuser plate32illustratively has an elongated rectangular shape, and may be substantially aligned with the open inlet ends of the heat exchanger tubes22. Along substantially the entire length of the diffuser plate32are formed a series of relatively small perforations34, with relatively larger perforations36being additionally formed through the opposite end portions of the diffuser plate32. This perforation pattern, as can be seen, provides opposite end portions of the diffuser plate32(which are generally aligned with the inlets of the end heat exchanger tubes22a) with greater fuel/air mixture through-flow areas than the diffuser plate fuel/air mixture through-flow areas aligned with the inlets of the central heat exchanger tubes22b.

Accordingly, during firing of the furnace12, the presence of the diffuser plate32lessens the flow of hot combustion gases28through the central heat exchanger tubes22band increases the flow of hot combustion gases28through the end heat exchanger tubes22a, with the hole pattern in the diffuser plate32being designed to substantially alleviate non-uniform temperature distribution across the heat exchanger tube array. As can be readily be seen, principles of the present invention provide a simple and quite inexpensive solution to the problem non-uniform temperature distribution across the heat exchanger tube array. Additionally, in developing the present invention it has been discovered that the use of the diffuser plate32also provides for improved mixing of the fuel/air mixture26entering the burner box16and further provides for a beneficial reduction in the NOx level of the discharged combustion gases28a.

While a particular hole pattern in the diffuser plate has been representatively described herein, it will be readily appreciated by those of ordinary skill in this particular art that a variety of alternative hole patterns and sizes may alternatively be utilized if desired. For example, while a combination of different size holes has been representatively illustrated and described, the holes could be of uniform size but with more holes/area being disposed on the opposite ends of the diffuser plate32than in the longitudinally intermediate portion of the diffuser plate32. Further, the hole pattern could be a non-uniformly spaced pattern to suit the particular application.

While principles of the present invention have been representatively illustrated and described herein as being incorporated in a fuel-fired air heating furnace, a combustion system utilizing such invention principles could alternatively be incorporated to advantage in the combustion systems of a wide variety of other types of fuel-fired heating appliances using fire tube-type heat exchangers to heat either a gas or a liquid.

The foregoing detailed description is to be clearly understood as being given by way of illustration and example only, the spirit and scope of the present invention being limited solely by the appended claims.