US20060213499A1

US20060213499A1 - Baffle design for a gas-fired unit heater

Info

Publication number: US20060213499A1
Application number: US11/386,190
Authority: US
Inventors: Kevin Alphs; Robert Cooley; Mark Krupo; Norman Mattson; James Palmer; Harold Sindelar; Michael Strande; Colette Van Beek; Gerald Thomas
Original assignee: Modine Manufacturing Co
Current assignee: Modine Manufacturing Co
Priority date: 2005-03-24
Filing date: 2006-03-22
Publication date: 2006-09-28
Also published as: GB0604818D0; GB2424695A; CA2541013A1

Abstract

A gas-fired unit heater (10) is provided and includes a burner (20), a heat exchanger tube (18) located to receive a flow of the combustion products from the burner (20), the tube (18) including at least one linear tube run (30) extending along a longitudinal axis (18), and a corrugated baffle (40) received in the tube run (30).

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to provisional application Ser. No. 60/664,878, filed Mar. 24, 2005, entitled “Improved Baffle Design for a Gas-Fired Unit Heater”.

BACKGROUND OF THE INVENTION

Gas-fired unit heaters are known and are commonly used to heat relatively large open and closed areas, such as residential and commercial garages or warehouses. Such units will often include a plurality of gas burners that combust natural or propane gas, with the heated combustion products being drawn through one or more heat exchange tubes by a exhaust blower or fan. Heat is transferred from the combustion products or flue gas to air that is passing over the exterior of the heat exchanger tubes, with the heated air then flowing into the area that is to be heated.
Given the ever-increasing cost of heating fuel, such as natural and/or propane gas, there is a continuing need to improve the efficiency of such unit heaters, this includes the efficiency of the transfer of heat from the combustion products to the air passing over the exterior of the tube.

SUMMARY OF THE INVENTION

In accordance with one form of the invention, a gas-fired unit heater is provided and includes a burner, a heat exchanger tube located to receive a flow of the combustion products from the burner, the tube including at least one linear tube run extending along a longitudinal axis, and a corrugated baffle received in the tube run. The tube run has an inner wail.
The baffle includes a corrugated strip of material having a length extending parallel to the longitudinal axes, with alternating peaks and valleys joined by side walls defining corrugations along the length and each of the peaks and valleys extending non-parallel to the longitudinal axis. In a preferred form, the peaks and valleys extend perpendicular to the longitudinal axis.
In one feature, opposite edges of the strip engage the inner wall of the tube run at at least one of the peaks and at at least one of the valleys.
In one feature, the inner wall is cylindrical with an inside diameter D. The corrugations have a height dimension H from the peaks to the valleys perpendicular to the longitudinal axis, and a width dimension W perpendicular to both the height dimension and the longitudinal axis. The ratio of (W×H)/D is in the range of 0.60 to 0.80. In a highly preferred embodiment, the ratio of (W×H)/D is 0.66 within the range of normal manufacturing tolerances.
In one form, the gas-fired unit heater includes a blower and is configured to provide a volumetric flow rate of the combustion products through the heat exchanger tube in the range of 2 cubic feet per minute (cfm) to 8 cfm under normal operating conditions, with a preferred optimum of 5 cfm.
As one feature, the inner wall includes a recess and the corrugated strip of material includes a longitudinal end tab that is configured to engage in the recess to retain the baffle within the tube run. In a further feature, the recess is an annular relief in the inner wall of the tube run adjacent an outlet end of the tube run.
Other objects, advantages, and features of the invention will become apparent from a detailed review of the specification, including the appended claim and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a unit heater including a baffle constructions embodying the present invention;
FIG. 2 is a perspective view of selected components of the unit heater of FIG. 1;
FIG. 3 is a reduced size, perspective view of a plurality of heat exchanger tubes of the unit heater of FIG. 1;
FIG. 4 is a plan view of the heat exchanger tubes of FIG. 3;
FIG. 5 is a side elevation of the heat exchanger tubes of FIG. 3;
FIG. 6 is an end view of the heater exchanger tubes of FIG. 3;
FIG. 7 is a reverse angle perspective view of the components of FIG. 2 with a heat exchanger tube broken away to reveal a baffle;
FIG. 8 is an enlarged section view of any one of the tubes taken from the line 8-8 in FIG. 5;
FIG. 9 is a perspective view of one form of the baffle of FIG. 8 shown in smaller scale than FIG. 8;
FIG. 10 is a side view of the baffle of FIG. 9 shown in larger scale than FIG. 9;
FIG. 11 is a view taken from line 11-11 in FIG. 10;
FIG. 12 is an enlarged section view of any of the tubes taken from the line 12-12 in FIG. 4 and showing another form of the bracket embodying the present invention;
FIG. 13 is a view taken from line 13-13 in FIG. 12;
FIG. 14 is a section view taken from line 14-14 in FIG. 12;
FIG. 15 is a side elevation view of the baffle of FIG. 12, removed from the tube run; and
FIG. 16 is a section view of the burner box looking towards the inlets to the burners.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A unit heater 10 is shown in FIG. 1 and includes an outer housing 12 with a hot air outlet 14 that includes a plurality of louvers 16 (only one shown in FIG. 1) with a plurality of heat exchanger tubes 18 located within the housing 12 behind the outlet 14 such that air is heated as it flows over the heat exchanger tubes 18 and passes from the outlet 14 into an area or room to be heated. It should be understood that while the invention is described in connection with the illustrated embodiment of a unit heater 10, no limitation to a specific type or construction of unit heater is intended unless expressly recited in the claims.
With reference to FIG. 2, the unit heater 10 includes a plurality of burners 20 (only one shown in FIG. 2), each aligned with an inlet opening 22 for a corresponding one of the heat exchanger tubes 18 such that hot combustion products from each of the burners 20 is received in the corresponding tube 18. The burners 20 are housed within a burner box 23, only part of which is shown in FIG. 2. The unit heater 10 further includes a fan or blower (power exhauster) 24 that draws the combustion products through the heat exchanger tubes 18 and blowing the combustion products (flue gases) from a flue collecting chamber 25 that gathers the combustion products as they exit each of the heat exchanger tubes 18. The blower 24 also serves to draw air into the unit heater 10 for combustion with the gas at the burners 12.
Each of the heat exchangers tubes 18 includes one or more linear tube runs 30, and in the case of the illustrated embodiment in FIGS. 1-7, each of the heat exchangers tubes 18 includes four linear tube runs 30A, 30B, 30C and 30D, with tube bends 32A, 32B and 32C connecting the tube runs 30A, 30B, 30C and 30D, as best seen in FIG. 3. Each of the tube runs 30A-30D extends along a corresponding longitudinal axis 33, as shown for the tube runs 30D in FIG. 3. Each of the tubes 18 further includes an inlet end 34 at the end of the tube 18 opposite from an outlet end 36. It should be appreciated that by providing four of the tube runs 30 for each of the heat exchanger tubes 18, the inlet and outlet ends 34 and 36 can be located in the same plane. It should also be appreciated that an odd number of tube runs 30 would allow for the ends 34 and 36 to be located in spaced planes.
As best seen in FIG. 7, a corrugated or wave baffle 40 is provided in the tube run 30 d of each of the heat exchanger tubes 18. It has been found that the baffle 40 improves the heat transfer efficiency of the unit heat 10. As best seen in FIGS. 9-12, The baffle 40 is preferable formed by a strip 42 of material having a length L extending parallel to the longitudinal axis 33, with alternating peaks 44 and valleys 46 joined by side walls 48 defining waves or corrugations 50 along the length L. Each of the peaks 44 and valleys 46 extends non-parallel, and preferably perpendicular, to the longitudinal axis 33. The corrugations have a height dimension H from the peaks 44 to the valleys 46 perpendicular to the longitudinal axis 33 and a width dimension W perpendicular to both the height dimension H and the longitudinal axes 33 It is preferred for the corrugations 50 to be sized and configured so that opposite edges 52 of the strip 42 engage an inner wall 54 of the tube run 30D at at least one of the peaks 44 and at at least one of the valleys 46. In this regard, each of the adjacent side walls have an angular spacing α which is preferably the same for each of the corrugations 50, except for one or more of the middle corrugations 50 which may have a smaller angle α so as to create the desired engagement of the side edges 52 of the strip. This engagement can reduce or prevent rattling of the baffle 40 in the corresponding tube 18.
In a preferred embodiment, the angles α are in the range of 102 degrees to 121 degrees, with a preferred optimum of 109 degrees.
With or without the desired engagement, it is also preferred that the ratio of the multiple of the width W and the height H to the diameter D [(W×H)/D] be in the range of 0.60 to 0.80 with an optimum being at 0.66 within the standard manufacturing tolerances of the baffle 40 and tube 18. These ranges create a desirable amount of free flow area 55 (illustrated with cross hatching in FIG. 8) between the baffle 42 and the inner wall 54 of the tube run 30D.
Preferably, the strip 42 is a strip of sheet metal with bends forming the alternating peaks 44 and valleys 46 of the corrugations 50
With reference to FIGS. 9, 10 and 11, the illustrated baffle 40 further includes a mount flange 56, which in the illustrated embodiment is part of the strip 42, and which extends outside of the outlet end 36 of the corresponding tube 18 so that it can be joined to the housing 12 using a suitable fastener (not shown) which extends through a mount hole 58 in the flange 56 to engage the housing 12. This structure retains the baffle 40 in the tube run 30D.
With reference to FIGS. 12-15, another embodiment of the baffle 40 is shown wherein the flange 56 is replaced by a longitudinal end tab 60 that is configured to engage in an annular recess 62 of the tube 18 with a spring force that is reacted through the baffle 40 to the edges 52 of the strip 42 that engage the inner wall 54 of the tube run 30D to retain the baffle 40 in the tube 18. This design has the benefit of being easily installed and not requiring a separate fastener. This design also can reduce or prevent rattling between the baffle 40 and the corresponding tube 18.
The blower 24 is sized to provide the movement of the combustion products from the flue collecting chamber 25 while sustaining the draft for the combustion process and entraining air for the combustion process. To accomplish this, the blower 24 must overcome the pressure resistance caused by the heat exchange tubes 18, the baffles 40, the collecting chamber 25, the restriction of any vent associated with the chamber 25 or flue, the restriction associated with any vent terminal, and any reasonable natural external force. In this regard, in one preferred form, the blower 24 is sized to create a volumetric flow rate of the combustion products in the range of 2 CFM to 8 CFM through each of the tubes 18 under normal operating conditions, and in highly preferred form to deliver 5 CFM.
It should be understood that, while some of the drawings include specific numbers of the corrugations 50 and specific dimensions in inches and degrees for the baffle 40 and the tubes 18, these dimensions are for one preferred form of the unit heater 10, and that the specific dimensions and number of corrugations 50 required to optimize the efficiency of the unit heater 10 will be highly dependent upon the specific parameters of each application, including for example, the number of tube runs 30 in each tube 18, the length of the tube run(s) 30 including the length of the tube run 30 in which the baffle 40 will be installed, the shape of the tube 18, the size of the inner wall 54, and the desired flow rate of the combustion products through each tube 18.
With reference to FIGS. 2 and 16, another feature is the provision of a burner mount/secondary air bracket 64 that is designed to mount the burners 20 in their appropriate relationship to the tubes 18 while minimizing the disturbance of the secondary air flow that must flow past the burners 20 to the gaps 66 between the outlet ends of the burners 20 and the openings 22. In order to provide as complete combustion as possible, it is important for the secondary air to be as undisturbed as possible over the entire 360° extent of the gap 66 as the secondary air flows into the combustion products exiting the burners 20 and entering the opening 22. To this end, the bracket 64 has been designed so that it is spaced from the side walls 68 of the burner box 23 to provide gaps 70 and 72 on either side of the bracket 64, and further have cutouts or window openings 74 and 76 so as to allow an air flow through the bracket 64 itself while still providing the appropriate structural integrity required for the bracket 64.

Claims

1. A gas-fired unit heater comprising:

a burner;

a heat exchanger tube located to receive a combustion gas flow from the burner, the tube including at least one linear tube run extending along a longitudinal axis, the tube run having an inner wall;

a corrugated baffle received in the tube run, the baffle comprising a corrugated strip of material having a length extending parallel to the longitudinal axis, and alternating peaks and valleys joined by side walls defining corrugations along the length with each of the peaks and valleys being non-parallel to longitudinal axis.

2. The unit heater of claim 1 wherein opposite edges of the strip engaging the inner wall at at least one of the peaks and at at least one of the valleys.

3. The unit heater of claim 1 wherein:

the inner wall is cylindrical with an inside diameter D;

the corrugations having a height dimension H from the peaks to the valleys perpendicular to the longitudinal axis and a width dimension W perpendicular to both the height dimension and the longitudinal axis; and

the ratio of (W*H)/D is in the range of 0.60 to 0.80.

4. A corrugated baffle for use in a linear tube run of a gas-fired unit heater: the baffle comprising a corrugated strip of material having a length extending parallel to the longitudinal axis, and alternating peaks and valleys joined by side walls defining corrugations along the length with each of the peaks and valleys being non-parallel to longitudinal axis.

5. The baffle of claim 4 wherein opposite edges of the strip engaging the inner wall at at least one of the peaks and at at least one of the valleys.

6. The baffle of claim 4 wherein:

the inner wall is cylindrical with an inside diameter D;

the ratio of (W*H)/D is in the range of 0.60 to 0.80.