Patent Application
20090241942
This invention relates to radiant tube heaters and burner and heating assemblies for use therewith.
A known type of radiant heater for heating the interior of buildings and other areas is a so-called radiant tube heater which has a relatively long, radiant tube made of a suitable metal and adapted to enclose an elongate flame projected from a burner head. This heater can include a combustion air blower, a burner nozzle connected to a combustible gas supply, and a burner head connected to the nozzle. The nozzle and head are positioned in a combustion air duct section forming a passage for combustion air and the outlet of the blower is attached to an inlet end of this duct section so that the blower is able to direct combustion air through the duct section. The burner head which in an exemplary embodiment is arranged centrally in the air duct section, creates an annular passageway between itself and the air duct section. Combustible gas, such as natural gas, can be delivered to the radiant heater through a gas valve governor which is connected by a line to the burner nozzle. Combustion air enters the burner head through vents or ports in the side wall of an inlet portion of the head and then mixes with the fuel, thereby producing a gas/air mixture which can exit through a perforated ceramic tile mounted in a downstream end of the head. The mixture can be ignited by a suitable electrode resulting in a long laminer flame extending down the radiant tube.
One form of radiant tube heater is described and illustrated in co-pending U.S. patent application Ser. No. 11/831,130 filed Jul. 31, 2007 and the disclosure and drawings of this co-pending application are incorporated herein by reference. This radiant tube heater in addition to including the aforementioned features, employs a tubular arrangement that includes an air duct portion forming a combustion air passage and a radiant tube portion which is heated. An airflow restricting plate is mounted in the air duct portion and extends circumferentially around the burner head. This plate can increase the flow of pressurized combustion air through the openings formed in the inlet portion of the burner head while also allowing a substantial portion of the combustion air to flow downstream between the wider outlet portion of the head and the air duct portion to provide secondary air for combustion.
The blower for the aforementioned radiant tube heater has a blower housing with a relatively straight, outlet section. Mounted on an outer wall of this outlet section are two pressure sensors in the form of pitot tubes of standard construction. These sensors are connected to differential pressure switches to ensure that the blower is in operation and is providing sufficient combustion air to the burner head when the mixture of combustion air and gas is ignited. The heater is constructed so as not to operate unless sufficient combustion air is being provided to the heater.
There is disclosed herein an air diverter for a radiant tube heater of the above-mentioned type which is mounted at or near an upstream end of the burner head which, in addition to imparting a swirling motion to the incoming combustion air, acts to direct more of this combustion air through ports formed in an inlet portion of the burner head. Thus, more primary air that enters through these ports is able to mix with the combustion gas over a greater distance prior to the mixture of air and gas exiting from the burner head.
According to one embodiment of the invention, a burner assembly for a radiant tube heater having an air duct portion forming a passage for combustion air from a blower and a radiant tube portion extending downstream from the air duct portion in relation to the flow of the combustion air includes a mixing cup device for mixing combustible gas and a portion of the combustion air and for delivering the resulting mixture to the radiant tube portion for burning. This cup device is adapted for mounting in the air duct portion and has an inlet portion and a larger, substantially cylindrical outlet portion having a diameter greater than a corresponding dimension of the inlet portion. Air inlet holes are formed in an upstream end wall of the outlet portion and air ports are formed in a peripheral wall of the inlet portion. A gas nozzle is provided in the inlet portion and connectable to a combustible gas supply line. An air diverter is adapted for mounting adjacent an upstream end of the inlet portion and has a plurality of blades distributed about a perimeter thereof. During use of the burner assembly, the air diverter directs a portion of the combustion air through the ports to provide primary air for initial mixing with the combustible gas and impart a swirling motion to the combustion air. The air diverter also allows a second portion of the combustion air to flow through the inlet holes to provide additional primary air for mixing with the combustible gas.
In an exemplary version of this burner assembly, an annual air flow restricting plate is mounted on the mixing cup device and extends circumferentially around the mixing cup device. This plate has an array of holes formed therein so that, during use of the burner assembly, the restricting plate substantially spans an annular passage for secondary combustion air formed between the outlet portion and the air duct portion.
According to another embodiment of the invention, a heating assembly is provided for a radiant tube heater having a radiant burner tube with an upstream end. The heating assembly includes a mixing cup assembly adapted for mounting centrally within the burner tube and adapted for mixing primary air and combustible gas and for delivering the resulting mixture into the burner tube. The cup assembly has an inlet portion and a substantially cylindrical outlet portion having a diameter greater than a corresponding dimension of the inlet portion. A series of air inlet holes are formed in an upstream end wall of the outlet portion for introduction of the primary air directly into the outlet portion and ports are formed in and around the inlet portion for introduction of the primary air into the inlet portion for initial mixing with the combustible gas. A gas line is provided to introduce the combustible gas into the mixing cup assembly, this gas line having one end connected to the mixing cup assembly and an opposite upstream end. A gas valve system including a gas valve unit has an outlet connected to the upstream end of the gas line. The gas valve system regulates flow of the combustible gas to the mixing cup assembly during use of the heating assembly. A blower for providing air for combustion to the radiant tube heater includes a blower outlet section adapted for connection to the upstream end of the burner tube. This air for combustion includes both primary air and secondary air. An air diverter is adapted for mounting at or near an upstream end of the mixing cup assembly and has a plurality of diverter blades distributed circumferentially around the upstream end of the mixing cup assembly. During use of the heating assembly, the diverter blades direct a portion of the combustion air from the blower through the ports to provide primary air and impart a swirling motion to the combustion air from the blower. A further portion of the combustion air enters the outlet portion of the mixing cup assembly through the air inlet holes to provide a further amount of primary air for mixing with the combustible gas. A remaining amount of the combustion air flows between the outlet portion and the burner tube to provide the secondary air for combustion.
In an exemplary form of this heating assembly, the inlet portion of the mixing cup assembly has a cylindrical end section of reduced diameter forming an upstream facing shoulder and the air diverter is fixedly mounted on this end section adjacent the shoulder.
According to a further embodiment of the invention, a radiant tube heater apparatus includes an elongate tubular arrangement having an air duct portion forming a passage for combustion air, including primary air and secondary air and a radiant tube portion which is heated by and surrounds the laminar flame during use of the heater apparatus and which extends downstream of the air duct portion in relation to the flow of combustion air in the passage. The air duct portion has an inlet at one end for receiving the combustion air. There is also a blower for providing combustion air to the inlet of the air duct portion, this blower including a blower casing with an outlet section adapted for connection to the air duct portion at the inlet. A burner assembly is mountable in the air duct portion, this burner assembly including a mixing cup assembly for mixing combustible gas and the primary air and for delivering the resulting mixture to the radiant tube portion for burning. The cup assembly has an inlet portion and a substantially cylindrical outlet portion having a diameter greater than a corresponding dimension of the inlet portion. A series of air inlet holes are formed around an annular upstream end wall of the outlet portion and the inlet portion has ports formed in a peripheral wall thereof. A gas line is provided for conducting the combustible gas to the inlet portion of the burner assembly. An air diverter is provided for mounting within the air duct portion adjacent an upstream end of the inlet portion of the cup assembly. The air diverter has a plurality of blades distributed about a perimeter thereof. An air flow restricting device is mounted on and extends around the cup assembly, this restricting device being adapted to restrict flow of secondary air between the outlet portion and an inner wall of the air duct portion during use of the tube heater apparatus. During use of the tube heater apparatus, the air diverter directs a portion of the combustion air through the ports to provide the primary air for initial mixing with the combustible gas. A further portion of the combustion air enters the outlet portion through the air inlet holes to provide an additional amount of the primary air for mixing with the combustible gas. The remaining amount of the combustion air flows between the outlet portion and a surrounding inner wall of the air duct portion to provide the secondary air for combustion.
In an exemplary version of this tube heater, the air diverter is a ring member having a plurality of diverter blades distributed about its circumference and this ring member is fixedly mountable on the inlet portion of the mixing cup assembly.
Further features and advantages will become apparent from the following detailed description of an exemplary embodiment of the invention taken in conjunction with the accompanying drawings.
In the detailed description which follows, exemplary embodiments are described, particularly with reference to the figures appended thereto. However, the particularly described embodiments are merely illustrative of radiant tube heaters and pitot tube assemblies for sensing pressure constructed according to the present disclosure.
Referring now to the drawings, wherein like reference numerals identify similar structural elements of the heating units,
The burner head or mixing cup assembly 92 is adapted for mounting within the burner tube 66 and is adapted for mixing primary air and combustible gas and for delivering the resulting mixture into an upstream end section of the burner tube as shown. The burner head is generally annular and has a cylindrical inlet portion 96 and a wider cylindrical outlet portion 102 integrally connected to the inlet portion and located at the downstream end of the inlet portion. The aforementioned nozzle 32 extends into the inlet portion and can be connected thereto by a thread connection, including internal threads 108 formed in an upstream end section of the inlet portion 96 (see
It will be understood that the heater is provided with natural gas or LPG gas indicated by the arrow G taken from a suitable source and delivered through the gas valve governor 16 and the pipe or line 20 to the burner nozzle. A portion of the combustion air enters through vents or ports distributed about the periphery of the inlet portion 96 to provide primary air. In the burner head, the gas intermingles with the primary air to produce a gas/air mixture that exits the burner head through a perforated ceramic tile 46 located at the downstream end of the outlet portion 102. The exiting mixture is ignited by an ionization electrode 48 of an igniter 50 so as to produce a long laminar flame that extends substantially the length of the tube 66. The preferred material for the radiant tube is stainless steel or aluminized steel, at least for an upstream section thereof that surrounds the flame and the burner head. The remaining downstream section can be cold rolled steel. A typical dimension for such a heating tube is four inches in diameter and the tube sections can be provided in standard lengths of ten feet each which are connected together end-to-end. Typically two to five such radiant tube sections are connected together to form a complete heating tube which can be connected at the downstream end to a suitable exhaust pipe or passage (not shown).
The illustrated heating tube is an elongate tubular arrangement that includes an air duct portion 62 forming a combustion air passage and a radiant tube portion which is the portion actually heated by and surrounding the laminar flame during use of the heater and which extends downstream of the air duct portion in relation to the flow of combustion air in the air passage 64. The air duct section has a central longitudinal axis indicated at 68 in
The blower 22 has an air outlet 74 which can be rectangular as shown in
The outlet portion 102 is substantially hollow, except for the perforated ceramic tile 46. This tile has an array of small holes distributed in a radial and circumferential pattern over its surface as shown in
The inlet and outlet portions of the burner head are rigidly and integrally connected to each other by an annular disk or wall 114 having a plurality of apertures 116 formed therein as shown in
The illustrated restricting plate 94 has a circular perimeter and is an annular plate with a central circular hole at 120 having a diameter slightly greater than the diameter of the inlet portion 96. The plate 94 substantially spans the combustion air passage 64 between the burner head and the air duct section. The plate is formed with an array of air holes 122 distributed over the plate for the passage of combustion air through the plate. The radial innermost holes 122′ can be the same in number and size as the apertures 116 formed in the radial wall 114 but it is possible to have fewer holes 122′ for some burner applications. By providing fewer holes 122′, the plate can be used to restrict air flow into the outlet portion. The holes 122′ are aligned with some or all of the apertures 116 so that combustion air can flow through them to provide additional primary air. Two outermost rows of air holes 122 are located beyond the circumferential perimeter of the outlet portion and these holes allow a substantial laminar air flow downstream of the restricting plate around the circumference of the outlet portion 102. Depending on the burner performance requirements, the number of these holes can be increased or decreased and there may be only one outer row of holes beyond the circumference of the outlet portion. The presence of the plate 94 increases the flow of pressurized combustion air through the ports 104 in the inlet portion and this increases the efficiency of the burner by providing turbulent flow in at least a central region of the outlet portion which improves mixing.
It is possible and sometimes desirable to mount the restricting plate 94 downstream from the position shown in
The radiant tube heater can be provided with an igniter 50 for mounting adjacent to the burner assembly for igniting the mixture of combustible gas and air. The igniter has an electrode 48 extending therefrom and projecting in front of the ceramic tile. In the embodiment shown in
Shown in
There can be attached to the fixed end portion 144 a reflector/shield 150 which in use receives upwardly directed radiant energy from the radiant heating tube 66. The shield can have side walls 152, 156 and end walls 158 and 160 and these walls can be formed with polished, reflecting interior surfaces in order to radiate the radiant energy downwardly or towards any desired location. The reflector/shield can be a trough-shaped channel which is open on the downward side.
Also shown mounted to the interior of the housing 132 are two differential pressure switches 170, 172 which can be of standard construction and which together provide differential pressure switch means for controlling the gas valve unit. These switches are provided to ensure the blower is in operation and is providing sufficient combustion air to the burner head when the mixture of combustion air and gas is being ignited. The switches are connected by flexible tubes to two pitot tubes 174, 176 which are part of a pitot tube assembly illustrated separately in
The pitot tube assembly, in addition to the pitot tubes, includes a mounting plate 182 for attaching the assembly to a wall 184 of the blower casing. As illustrated, the mounting plate is flat and rectangular and is sized to close both a relatively small hole 186 and a separate, larger elongate slot 188 in the wall 184 (see
The pitot tubes are substantially L-shaped as can be seen clearly in
As can be seen from
Also shown in
It is also possible to construct a diverter ring 221 wherein the whole of each blade 225 extends at an angle to the radial plane as shown in
Neither the ring 210 nor the ring 221 rotates, each being fixedly held in position by means of a screw (not shown) that extends through the connecting section 218 or 223 and into the rearwardly facing shoulder formed on the inlet portion 96′. The slope of the angular portion of each blade can vary and typically is 30, 45 or 60 degrees relative to the plane of the flat first section 220 in the case of the blade 212. In the case of each twisted blade 225, the slope of the tip of the blade can vary and in an exemplary form of this diverter ring ranges between 30 and 60 degrees relative to the plane of the connecting section 223. The best angle for a particular burner application can be determined by trial and error. These diverter rings are for low firing rate burners, typically in the 60,000 to 90,000 BTU range. Aluminized steel for the diverter is preferred as it can withstand the heat given off by the burner and it will not corrode in this environment.
The use of a diverter ring as described above has a number of advantages in this type of radiant tube heater. One significant advantage is that the blades of the ring not only impart a swirling motion to the combustion air which helps to improve combustion and the efficiency of the heater but also they direct a portion of the combustion air from the blower through the ports 104 of the inlet portion of the mixing cup assembly, thus providing more primary air for mixing in the upstream inlet portion than can be provided simply by the use of the above described restricting plate. Also, by providing more primary air through these ports, there is in effect a larger distance for this primary air to mix with the combustible gas. It will be seen from
As indicated, the diverter ring and its blades create a swirling motion in the combustion air coming from the blower and this swirling action is particularly noticeable and effective in the region between the wide outlet portion of the burner cup and the inner wall of the air duct portion of the tubular arrangement forming the burner tube. This swirling motion itself increases the burning efficiency of the tube heater. With the use of the diverter ring, one can obtain a larger flame length down the burner tube resulting in better heat distribution. If a diverter ring such as the illustrated ring is not used in the described radiant tube heater, there can be a problem of delayed ignition which can occasionally result in a small explosion-like sound during start up of the tube heater. By using the described diverter ring, on time ignition can be achieved and the aforementioned sound created by delayed ignition can be avoided. Although the cause of the aforementioned delayed ignition when one is not using a diverter ring is not known with certainty, it is believed that the delayed ignition is caused by eddies formed by the incoming combustion air creating a type of dead zone.
By controlling and properly setting the angle of the blades of the diverter ring, the user or operator can control the mixing process and the efficiency of the radiant tube heater. By having less angle to the sloping portions of the blades or at the blade tips in the case of the second embodiment of the air diverter, one can divert more air through the ports 104. The objective in setting the angle of the blades is to have a balance between the amount of primary air entering through the ports 104 and the amount of primary air entering through the series of air inlet holes 116 formed at the upstream end of the outlet portion.
While the present invention has been illustrated and described as embodied in certain exemplary embodiments, it is to be understood that the present invention is not limited to the details shown herein, since it will be understood that various omissions, modifications, substitutions and changes in the form and details of the disclosed heating assembly and burner assembly can be made by those skilled in the art without departing in any way from the spirit and scope of the present invention. For example, those with ordinary skill in the art will readily adapt the present disclosure for various other applications without departing from the spirit and scope of the present invention.
