Patent Application
20180259179
The present disclosure is directed to HVAC systems and more particularly to gas-air mixers.
The use of gas-air mixers helps to provide a homogenous or proper ratio supply of gas and air to a premix burner in a heat exchanger system. A poorly mixed, improper ratio of gas and air can result in poor lighting, flame flashback, and poor combustion. Some HVAC systems accomplish mixing by use of an upstream blower assembly. However, such blower assemblies have drawbacks that prevent their use in residential applications. These drawbacks can include creating a positive pressure in burner and heat train creating potential safety concerns, space constraints, and expensive construction requirements.
One embodiment of the present disclosure comprises a fuel-air mixer assembly for use in HVAC systems comprising: a tube comprising an inlet and an outlet, the tube comprising a bend between the inlet and the outlet, the inlet configured to receive a supply of air; an orifice body at a location upstream of the bend, the orifice body comprising a first portion extending from a tube wall into the interior of the tube and a second portion extending upstream within the interior of the tube, the first and second portions connected by a curve, the second portion comprising a tip distal to the curve, the tip comprising one or more orifices operable to direct a supply of fuel into the tube.
Another embodiment under the present disclosure comprises a fuel-air mixer assembly for use in an HVAC system, comprising: a first portion comprising a tubular shape and comprising an inlet and an orifice body, the inlet operable to receive a supply of air, the orifice body comprising an elbow-shape and extending into the interior of the fuel-air mixer assembly and then extending upstream, the orifice body comprising one or more orifices operable to direct a supply of fuel to the first portion; and a second portion connected to the first portion by a bend downstream of the orifice body, the second portion comprising a tubular shape and an outlet operable to deliver a mix of fuel and air to another component of the HVAC system; wherein a first distance comprises a length between the outlet and a first axis defined by the center of the first portion, and a second distance comprises a length between the one or more orifices and a second axis defined by the center of the second portion, and wherein the second distance is greater than the first distance.
Another embodiment under the present disclosure comprises a method of constructing a fuel-air mixer assembly for an HVAC system, comprising: providing a mixer body, the mixer body comprising an elbow shape, an inlet, and an outlet, the inlet operable to receive a supply of air and the mixer body comprising a bend between the inlet and the outlet, the mixer body further comprising an opening upstream of the bend; coupling an orifice body to the opening, the orifice body comprising an elbow shape, and extending into the interior of the mixer body and then extending upstream toward the inlet, the orifice body operable to receive fuel from outside of the mixer body, the orifice body comprising one or more orifices operable to direct fuel into the mixer body.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention.
For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
Mixing of the gas-air stream for premix combustion is typically accomplished by mechanical agitation via an up-stream blower assembly. While this method provides a well blended gas-air mixture to the burner, it is undesirable for residential furnaces for several reasons. One, the blower creates a positive pressure in the burner and heat exchanger (a possible safety concern if leaks occur). Two, it's bulky and it's difficult to fit the blower/gas valve assembly into the required space. Three, it requires a costly specialized blower and gas valve assembly. Maintaining a proper ratio of gas and air is critical to the performance of a premix burner. A lean gas-air supply can result in poor lighting, noise and poor combustion while a rich gas-air supply can result in high emissions and combustion resonance. A venturi manifold is commonly used in combination with a 1:1 regulating gas valve. While this method can provide a consistent gas-air ratio to the burner, it can take up a lot of space, require a specialized gas valve assembly, and the venturi manifold must be sized for a target input rate requiring multiple parts to meet the needs of a residential furnace line. A venturi manifold can therefore be hard to implement.
Solutions under the present disclosure help to solve the shortcomings of the prior art. Turning to
Referring to
Both the orifice body 390 and the mixer assembly (or mixer body) 310 can have an elbow shape. Orifice body 390 can extend in a direction perpendicular to air flow in mixer assembly 310, and then extend parallel to air flow. However, the exact angles can differ, possibly by up to ±15 degrees. It is generally desired for the orifice to extend into the interior of mixer assembly 310, and then against the direction of airflow. Similarly, regarding the mixer assembly 390, a line bisecting the first portion 384, and a line bisecting the second portion 386, will preferably be at a right angle (90 degrees, ±5 degrees). However, various embodiments can use other angles to achieve a desired mix of fuel and air, and to fit within given space constraints.
The exact shape and size of orifice(s) 395 can differ. In a preferred embodiment, orifices 395 are located on the lateral sides of the tip of body 390. Example embodiments can include four small orifices equidistant around the circumference of body 390, a plurality of orifices 395 along the length of body 390, a plurality of slots around the tip and circumference of body 390, one or more orifices 395 on the very tip of body 390, or other layouts. A preferred embodiment comprises six orifices around the top tip along the circumference of body 390.
Alternative forms of this invention could include different tube diameters or shapes to vary clearances between gas orifice and outer walls to maximize mixing while maintaining acceptable pressure drop. Mixer length could be varied to help attenuate combustion resonance. Another alternate construction might add inlet and outlet effects to the outer tube to vary flow rate, improve mixing, or provide a useful signal pressure for gas-air control linkage. For instance, a fixed orifice, venturi or flow tube could be applied to the mixer inlet to create a useful signal pressure for control, safety monitoring, or combustion airflow measurement. Another alternate feature might incorporate a screen or mesh material at the mixer inlet as a debris shield. Screen size could vary to provide more or less filtering for specific applications as required. Another alternate feature might incorporate a connection port for combustion resonance attenuation devices, such as a quarter-wave tube or Helmholtz resonator.
Certain embodiments of the fuel-air or gas-air mixer assembly, or mixer body, described in the current disclosure can comprise an elbow shape that helps to assist in the mixing of the fuel and air. In a preferred embodiment, the elbow bends at approximately a 90 degree angle, ±5 degrees. However, the elbow shape can vary, using smaller or larger angles, such as ±15 degrees. The angles described can be measured by taking an axis from the center of a first and second portion of the mixer assembly. The first portion being upstream of the elbow bend, and the second portion being downstream of the bend.
The tip of the orifice body will preferably comprise one or more orifices to direct fuel into the mixer assembly to mix with air. The form, shape, size, and layout of the orifices can vary. They can be located at various locations on the orifice body. The orifice body will preferably be tubular or cylindrical, but can take other shapes.
A gas valve, such as described above, can provide fuel or gas to the orifice body. However other arrangements can comprise different embodiments under the present disclosure. The gas valve may be local or remote. A controller, thermostat, switch, or other controlling means can be coupled to the gas valve. Such coupling can be wired or wireless.
Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.
