1. Field of the Invention
The present invention relates generally to burners for use in water heaters and boilers, and more particularly to a flow distribution member used with such burners for providing an improved pressure distribution of fuel and air mixture throughout the burner.
2. Description of the Prior Art
One well known architecture for water heaters and boilers is that utilized in the series of water heaters produced by Lochinvar LLC, the assignee of the present invention, as its POWER-FIN® water heaters and boilers. The general construction of such water heaters may be similar to that disclosed for example in U.S. Pat. No. 4,793,800 to Vallett et al. or that in U.S. Pat. No. 6,694,926 to Baese et al.
Such water heaters utilize a generally cylindrical burner concentrically received within a circular array of fin tubes.
Water heaters of this type use a premix blower to supply air and gas mixture to the cylindrical burner. One issue which is encountered in designing in such a water heater is the desire to provide a balanced uniform flow of fuel and air mixture throughout the burner, and particularly to avoid any negative pressure zones in the burner which could cause flashback into the burner.
In one embodiment a pre-mix burner apparatus includes a burner having a generally cylindrical burner surface, the burner having a central axis and having a generally circular burner inlet at one end of the burner. The burner inlet has an inlet diameter. A flow distribution member is arranged to distribute flow of fuel and air mixture into the burner. The flow distribution member includes a closed axially central portion configured to block flow of fuel and air mixture axially centrally into the burner. The flow distribution member further includes a plurality of vanes extending radially outward from the closed axially central portion. The vanes are configured to generate a swirling flow of fuel and air mixture flowing past the vanes into the burner.
The closed axially central portion may be disc shaped and may have a disc diameter in a range from about 10 percent to about 20 percent of the inlet diameter.
The burner inlet may define an inlet plane generally perpendicular to the burner central axis, and each of the vanes may be oriented at a vane angle to the inlet plane in a range from about 30 degrees to about 60 degrees.
Each of the vanes may be planar.
Each of the vanes may be generally triangular in shape.
Each of the vanes may have a radial length in a range from about 40 percent to about 45 percent of the inlet diameter.
The array of vanes may include at least 12 and no greater than 20 vanes substantially equally circumferentially spaced about the central axis of the burner.
The flow distribution member may comprise a formed integral sheet, the vanes each being generally triangular shaped with two free sides and one attached side, the attached side extending generally radially relative to the central axis of the burner.
The flow distribution member may have a total open area in a range from about 50 percent to about 70 percent of a cross sectional area of the burner inlet.
The flow distribution member may include a plurality of spokes extending outward from the closed axially central portion, each of the vanes being attached to one of the spokes.
The flow distribution member may include a radially outer planar flange connected to radially outer ends of the spokes, the flange being configured to mount the flow distribution member.
The apparatus may further include a blower configured to provide fuel and air mixture to the burner inlet, the blower having a blower outlet having a blower outlet cross sectional area, wherein the burner inlet has an inlet cross sectional area greater than the blower outlet cross sectional area.
The vanes may be configured such that the spiral flow pattern adjacent and downstream of the burner inlet prevents flame flow back into the burner adjacent the burner inlet.
The burner apparatus may be used in combination with a water heater, the water heater being in heat exchange relationship with the burner.
In another embodiment a method is provided for operating a burner comprising:
(a) providing an inlet stream air mixture to an inlet of the burner, the inlet being generally circular;
(b) blocking an axially central portion of the inlet and thereby preventing axially central flow of the inlet stream into the inlet; and
(c) swirling the inlet stream and creating a spiral flow pattern as the stream passes through an annular area between the axially central portion and a diameter of the burner inlet, such that negative pressure is avoided in the burner adjacent the burner inlet.
The method may further include in step (a) the burner being a cylindrical burner having a cylindrical burner surface and having an axial length, and in step (c) the spiral flow pattern extending along the entire length of the burner.
The spiral flow pattern may cause the fuel and air mixture to exit the burner surface at substantially uniform velocities along the entire length of the burner.
The spiral flow pattern may avoid the creation of negative pressures at any location along the entire length of the burner.
The burner may be operated at an output in excess of 1.0 MM BTU/HR.
The inlet stream of step (a) may be provided by a blower having a blower outlet with an outlet cross sectional area less than an inlet cross sectional area of the burner inlet.
The method may further comprise the step of heating water with a heat exchanger in heat exchange relationship with the burner.
Numerous objects, features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the following disclosure when taken in conjunction with the accompanying drawings.
Referring now to the drawings, and particularly to
The general construction of the heat exchanger 12 may be similar to that disclosed for example in U.S. Pat. No. 4,793,800 to Vallett et al., or that in U.S. Pat. No. 6,694,926 to Baese et al., the details of which are incorporated herein by reference. The heat exchanger may be a multiple pass exchanger having a plurality of fin tubes arranged in a circular pattern with a burner located concentrically within the circular pattern of fin tubes. In
A burner 26 is concentrically received within the circular array of fin tubes 24. The burner 26 is operatively associated with the heat exchanger 12 for heating water which is contained in the water side 14 of the heat exchanger 12. Within each fin tube 24, the water receives heat from the burner 26 that is radiating directly upon the exterior fins of the fin tubes 24.
The burner 26 is of the type referred to as a premix burner which burns a previously mixed mixture of combustion air and fuel gas. In the system shown in
In order to provide the variable output operation of the burner 26 a variable flow blower 34 delivers the premixed combustion air and fuel gas to the burner 26 at a controlled blower flow rate within a blower flow rate range. The blower 34 may be driven by a variable frequency drive motor 36. Alternatively, a variable speed motor with a Pulse Width Modulation drive may be used to drive the blower 34.
The gas line 32 will be connected to a conventional fuel gas supply (not shown) such as a municipal gas line, with appropriate pressure regulators and the like being utilized to control the pressure of the gas supply to the venturi 28.
The gas control valve 33 is preferably a ratio gas valve for providing fuel gas to the venturi 28 at a variable gas rate which is proportional to the flow rate entering the venturi 28, in order to maintain a predetermined air to fuel ratio over the flow rate range in which the blower 34 operates.
An ignition module 40 controls an electric igniter 42 associated with the burner 26.
Combustion gasses from the burner 26 exit the boiler 10 through a combustion gas outlet 44 which is connected to an exhaust gas flue 46.
The water inlet and outlet 16 and 18 may be connected to a flow loop 38 of a heating system. A pump 39 may circulate water through the flow loop 38 and thus through the water side 14 of the heat exchanger 12.
A plurality of temperature sensors are located throughout the boiler apparatus 10 including sensor T1 at the water inlet 16, sensor T2 at the water outlet 18, and sensor T3 at the exhaust gas outlet 44.
A blower to burner transition duct 48 may connect a blower outlet 50 to a burner inlet 52. A flow distribution member 54 may be located at the burner inlet 52.
As best seen in
Thus, as schematically illustrated in
The blower outlet 50 of blower 34 has a blower outlet which may generally be rectangular in shape, and has a blower outlet cross sectional area which may be less than the circular inlet cross sectional area of the circular inlet 52 of burner 26. This can best be appreciated by viewing the diverging enlarging cross section of the blower to burner transition duct 48 which is best seen in the cross sectional view of
When using a pre-mix blower such as blower 34 to supply fuel and air mixture to the cylindrical burner inlet 52, in the absence of the flow distribution member 54, the high velocity flow of fuel and air mixture exiting the blower 34 and entering the burner inlet 52 can cause a negative pressure zone at the inlet of the burner 52 and for a short distance downstream thereof, which can result in pulling flame back into the burner 26. Also, the velocity profile exiting the blower outlet 50 across the cross section thereof is typically not even and equal across the entire cross sectional area of the blower outlet 50, which can result in uneven loading of the burner 26. Furthermore, high velocity flow from the blower outlet 50 through the burner 26 can cause noisy operation of the water heater apparatus 10 under normal running conditions. This problem may be more severe in arrangements where the blower outlet 50 cross-section is substantially smaller than the burner inlet 52 cross-section. But there can be other causes of unequal velocity profile entering the burner inlet 52, such as for example the unequal distribution due to centrifugal effects within the blower 34, or flow disturbances due to ducting between the blower 34 and the burner 26. The flow distribution member 54 described herein may be used in any suitable situation, including arrangements where the cross-section of the blower outlet 50 is greater than the cross-section of the burner inlet 52.
The flow distribution member 54 is provided to break up the flow pattern of the fuel and air mixture exiting the blower outlet 50 and to redirect that fuel and air mixture into a spiral flow pattern 106 (see
This spiral flow pattern 106 creates an outward pressure at the neck of the burner adjacent and just downstream of the burner inlet 52, and also throughout the entire burner length 62, thus causing the fuel and air mixture to exit the burner 26 at an equal or approximately equal flame velocity throughout the entire length of the burner 26, thus eliminating negative pressure zones.
Additionally, the flow distribution member 54 may eliminate the effect of blower velocity profile on the burner balancing. The inherently unequal velocity profile at the outlet 50 of the blower 34 is redirected into the spiral flow pattern 106 by the flow distribution member 54, which results in a balanced burner 24.
Finally, by breaking up the flow pattern exiting the blower outlet 50, the flow distribution member 54 reduces the noise level of the combustion system of water heater 10 during normal operation.
One preferred construction of the flow distribution member 54 is shown in more detail in
The flow distribution member 54 includes a closed axially central portion 70 configured to block flow of fuel and air mixture axially centrally into the burner 26 along the burner axis 58.
The flow distribution member 54 further includes a plurality of vanes 72 extending radially outward from the closed axially central portion 70. The vanes 72 are configured to generate the swirling flow 106 of fuel and air mixture flowing past the vanes 72 into the burner 26.
As best shown in
As seen in
In the embodiment illustrated, each of the vanes 72 may be described as being generally planar and as being generally triangular in shape. It will be appreciated, however, that the vanes 72 could also be curved.
In the embodiment illustrated in
In the embodiment illustrated in
The flow distribution member 54 includes a plurality of spokes 88 extending radially outward from the closed axially central portion 70, to a annular outer flange portion 90.
It will be appreciated in the view of
The flow distribution member 54 may be described as having a plurality of triangular openings in the plane or cross sectional area thereof, each of which openings is defined as a triangular opening between the attached side 84, and a radially open edge 92 and an outer open edge 94. The total open area of the flow distribution member 54 is preferably in a range from about 50 percent to about 70 percent of the cross sectional area of the circular burner inlet 52. It will be appreciated that the effectiveness of this open area is also dependent upon the vane angle 78.
The flow distribution member 54 may also have a radially outward upturned annular wall 96 formed thereon for aid in placement and retention of the flow distribution member 54 in the inlet 52 of the burner apparatus 26.
One example of flow distribution member 54 has an outside diameter 98 of 7.727 inches. The closed axially central portion 70 has a disc diameter 74 of 1.0 inches. Each of the fourteen vanes 72 has a radial length 86 of 3.16 inches. Each of the first free sides 80, and the corresponding outer open edge 94 has a length of 1.25 inches. This provides a flow distribution member 54 having a total open area of approximately 58 percent of the cross sectional area of the burner inlet 52. The vanes 72 are at a vane angle 78 of approximately 40 degrees.
The flow distribution member 54 just described is designed for use with a burner 26 designed for a heat output at maximum rated capacity of 4.0 Btu/Hr. In general, the apparatus 10 may be described as having a heat output at maximum rated capacity in excess of 1.0 MM Btu/Hr. For the burner 26, designed to have a maximum rated capacity of 4.0 Btu/Hr, the inlet stream 100 may have a flow velocity of 10.4 ft/sec at the inlet 52 of the burner 26 at low fire, and 52.2 ft/sec at high fire.
The example flow distribution member 54 was tested to compare pressure distribution in the burner, both with and without the flow distribution member.
The test was performed by blowing air into the burner 26 with the blower 34 operating at 5500 RPM, and measuring the air pressure in the four quadrants of the cross-section at each of the six different elevations 1-6 along the length of the burner 26. The data is displayed in the following Table I, with the pressure data being displayed in “inches of water”.
As is seen in Table I, very low pressures are experienced for pressure detection tube 110D at elevation locations 1 and 2, and for pressure detection tube 110A at elevation location 1. These locations correspond to the width centerline 112 of the outlet 50, and they are locations where back flow of flame into the burner could occur. Also there is a substantial lack of uniformity of the pressure data in the four quadrants for any selected elevational location near the burner inlet 52.
It is noted that as compared to Table I there are much higher pressures adjacent the burner inlet 52, and there are no negative pressure zones. Also, with the use of the flow distribution member 54 there is much better cross-sectional pressure uniformity across the four quadrants for any given elevational location, as compared to the data of Table I.
In
Finally,
The methods of operating the burner apparatus 26 may be described as follows with reference to the schematic illustration of
An inlet stream 100 of fuel and air mixture is provided to the inlet 52 of burner 26 from the outlet 50 of blower 34 via the blower to burner transition duct 48.
An axially central portion 102 of inlet 52 is blocked by the closed axially central portion 70 of flow distribution member 54 thereby preventing axially central flow of the inlet stream 100 into the inlet 52.
This diverts the inlet stream 100 through an annular area 104 between the axial central portion 102 and the outside diameter 60 of the burner inlet 52. Additionally, the vanes 72 swirl the inlet stream 100 as it passes across the vanes 72 thus creating the spiral flow pattern schematically illustrated at 106 in
As a result of the spiral flow pattern 106 and the absence of axially central flow adjacent the inlet 52 to burner 26, negative pressures are avoided along the entire length 62 of the burner 26, particularly adjacent the burner inlet 52.
Furthermore, the spiral flow pattern 106 causes the fuel and air mixture to exit the burner outer surface 56 at substantially uniform velocities along the entire length 62 of the burner 26.
The vanes 72 serve as a directional guide to the fuel and air mixture. The angle 78 of the vanes 72 can vary, but should be great enough to create a swirling motion of the fuel and air mixture to form the spiral flow pattern 106.
With the spiral flow pattern 106, an outward pressure is provided against the perforated burner wall 56 which in turn provides an even and substantially equal flame pattern throughout the length 62 of the burner 26.
Thus it is seen that the apparatus and methods of the present invention readily achieve the ends and advantages mentioned, as well as those inherent therein. While certain preferred embodiments of the invention have been illustrated and described for purposes of the present disclosure, numerous changes in the arrangement and construction of parts and steps may be made by those skilled In the art, which changes are encompassed within the scope and spirit of the present invention as defined by the appended claims.