United States Patent 3828762

A heat exchanger, especially useful for warm air furnaces alone or in combination with air-conditioning apparatus, in which a flame is directed into the end of an elongated tube, the hot products of combustion flowing into the tube and being vented from the opposite end. Novel features include a push-pull, forced draft blower arrangement combined with positive pressure, tangential air entry to the heat exchanger tube in order to control the combustion rate and promote heat flux in said tube.

Application Number:
Publication Date:
Filing Date:
Primary Class:
International Classes:
F24H3/06; F23M9/00; F23M9/08; F24H3/08; F24H9/18; F28D7/06; (IPC1-7): F24C3/00
Field of Search:
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US Patent References:
3315655N/A1967-04-25Stone et al.
2796118Burner for tube firing1957-06-18Parker et al.
2787318Burner with tangential air admission and restricted throat1957-04-02Wolfersperger
2385854Gas burner1945-10-02Wolfersperger
2226816Heating apparatus1940-12-31Hepburn
2188133Heating apparatus1940-01-23Hepburn

Primary Examiner:
Dority Jr., Carroll B.
Attorney, Agent or Firm:
Banner, Donald W.
What is claimed is

1. In combination with a furnace of the type having a heat exchange zone through which air to be heated is circulated (26), said heat exchange zone being defined, in part, by a wall (22) which divides said zone from ambient atmosphere: a generally U-shaped heat exchange element (14) arranged in the path of said air to be heated and extending through said wall (22), said element having an inlet (16) and an outlet (18); a combustion chamber (12) at the inlet of said heat exchange element; an inshot-type burner assembly (10) spaced from said combustion chamber and disposed entirely within said ambient atmosphere, said burner assembly being arranged to direct a flame into said combustion chamber; a flue collector (38) cooperating with the outlet of said heat exchange element; a first blower (30) adapted to deliver a combustion supporting gas under pressure to said combustion chamber; means (48) for directing said gas tangentially to the axis of said inlet to produce a swirling path for products of combustion flowing through said heat exchange element; and a second blower (40) having its suction side connected to the outlet of said heat exchange element for inducing flow from said heat exchange element toward said flue collector.

2. The combination as defined in claim 1 including a single drive means (34) for driving both said first and second blowers.


This invention relates generally to fuel fired (preferably gas fired) heat exchangers commonly used in warm air furnaces or roof top units which combine an air heating unit and an air cooling unit in the same housing. More specifically, the invention deals with heat exchangers in which a flame is directed into a tube and the products of combustion flow through the tube and are vented through a flue at the opposite end. In the present arrangement, it is convenient to use a U-shaped tube so that a dual blower assembly can be used for force air (or other combustion supporting gas) to flow under pressure to the combustion chamber and also to induce the flow of combustion products through the tube and into the flue.

Several of the features which are described and claimed in this application may be found individually in various prior art patents and publications. For example, in Hepburn, U.S. Pat. No. 2,226,816, there is disclosed a heat exchanger in which a single blower draws the products of combustion through a U-shaped tube. The Hepburn patent also discloses a spiral shaped element to stir up the exiting gases.

Also of interest is Wolfersperger, U.S. Pat. No. 2,787,318, which provides a tangential air inlet into the burner assembly which promotes mixing of the fuel (oil) with the air.

In the present invention, a novel push-pull blower system is combined with a tangential air inlet to improve the overall efficiency of the burner assembly and promote heat flux within the tubes. In the design of such heat exchangers, size is a critical limitation. This is especially true in roof top units which are designed for a compact, low profile assembly. The reduction in size of the heater unit per se is therefore very important. It has been found that the combination of the tubular type heat exchanger with a blower system, in which air is forced under pressure into the combustion chamber to induce tangential flow directed into the length of the tube, greatly enhances the heat flux and overall efficiency. Moreover, the same motor can be used to operate a second blower unit having its suction side connected to the distal end of the burner tube to draw the products of combustion into the flue and discharge the same into the atmosphere.


FIG. 1 is a cross-sectional view of certain portions broken away for clarity, of a heat exchanger constructed in accordance with the principles of the present invention; and

FIG. 2 is a cross-sectional view taken along the plane of line 2--2 of FIG. 1.


Referring now to FIG. 1, there is shown a heat exchanger including a burner assembly 10, a combustion chamber 12, a U-shaped tubular heat exchange element 14 (hereinafter referred to simply as the U-tube) having an entrance end or inlet 16 and discharge end or outlet 18. Burner assembly 10 may be of any known design, but preferably is of the inshot type which operates in an atmospheric ambient independent of the heat exchanger.

U-tube 14 extends through one wall 22 of the furnace in the path of air to be heated as indicated by the arrows 26. At the inlet 16 there is a combustion chamber 12 into which pressurized air is supplied by a first blower 30, said blower including a centrifugal blower wheel 32 driven by motor 34. The outlet of the blower is connected to the combustion chamber at 36. At the exhaust end or outlet of the U-tube 16 there is a flue collector 38 into which the products of combustion flow from the tube. A second blower unit 40 includes centrifugal blower wheel 44 having its suction side 42 in communication with the flue collector and its outlet side 44 connected to a flue vent 46 or other means for discharging gases to atmosphere. The second blower unit is also driven by motor 34. The induced draft of blower 40 maintains negative pressure throughout the length of the U-tube.

An important feature of the invention includes a means for supplying pressurized air from the blower to the combustion chamber in an manner to produce a rapid swirling of the flame and combustion air which causes the products of combustion to continue on a helical path through substantially the entire length of the tube. The swirling motion of these hot products of combustion greatly increase the heat transfer between such gases and the inside wall of the tube, thereby promoting the efficiency of the heat exchanger. Also, the spinning secondary air controls the rate (or length) of combustion.

As seen in FIG. 2, the tangential air inlet comprises a cylindrical shaped element or spinner 48 inside combustion chamber 16, said spinner having a plurality of tangentially directed inlet openings 49 formed by bent tabs 50 cut out of the side wall of the cylinder. As the pressurized air is forced into annular combustion chamber 16, it is forced to be directed through the tangential openings to swirl through the inside of the cylinder mixing with the axially directed flame from burner 10.

It will be understood that the heat exchange tube shown is only one of several which are ordinarily included in a warm air furnace section. Each such tube utilizes its own burner assembly although it will be apparent to those skilled in the art that various modifications and arrangements may be made without departing from the scope of the invention.

While the invention has been described in connection with a certain specific embodiment thereof, it is to be understood that this is by way of illustration and not by way of limitation; and the scope of the appended claims should be construed as broadly as the prior art will permit.