GAS TURBULATOR FOR AN INDIRECT GAS-FIRED AIR HANDLING UNIT

Abstract

A gas turbulator is inserted in a tube of a heat exchanger to increase turbulence of gases passing through the tubes of the heat exchanger. The turbulator consists of a longitudinal metal strip running the length of the heat exchanger tube. Longitudinal tabs are punched from the interior of the metal strip. The tabs protrude in opposite directions from the plane of the longitudinal strip to form a series of slanted flip up tabs and flip down tabs in a side elevation view of the turbulator.

Description

FIELD OF THE INVENTION

This invention relates to a tubular heat exchanger for an indirect gas-fired air handling unit and more particularly to a turbulator for insertion into the tubes of the tubular heat exchanger.

BACKGROUND OF THE INVENTION

A turbulator is a device that is positioned inside the tubes of a tubular heat exchanger. The turbulator prevents laminar gas flow from developing inside the heat exchanger tubes. Turbulent gas flow is preferred because turbulent gas flow inside the heat exchanger tubes promotes heat being transferred from the heated combustion gas to the tube material. High turbulence, however, also causes resistance to the gas flow through the heat exchanger tubes in the form of a pressure drop along the length of the heat exchanger tubes.

SUMMARY OF THE INVENTION

An indirect gas-fired air handling unit of the present invention includes a drum and tube heat exchanger comprising a drum combustion chamber and a tubular heat exchanger. The combustion chamber is fitted with a burner. The heated combustion gas from the burner in the combustion chamber flows through the tubes of the tubular heat exchanger before exiting through the exhaust flue. Flip-up-down single H-type turbulators of the present invention are inserted in the heat exchanger tubes to increase heat transfer from the heated gas to the heat exchanger tubes. The flip-up-down single H-type turbulators of the present invention also reduce manufacturing time for the drum and tube heat exchangers.

Further objects, features and advantages will become apparent upon consideration of the following detailed description of the invention when taken in conjunction with the drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an indirect gas-fired air handling unit with a drum and tube heat exchanger in accordance with the present invention.

FIG. 2 is perspective view of the drum and tube heat exchanger with the front plate removed to reveal internal detail in accordance with the present invention.

FIG. 3 is a side perspective view of the ends of the tubes of the heat exchanger with some of the turbulators partially withdrawn for the purposes of illustration. The heat exchanger is mounted in a demonstration cabinet with a door replacing the standard front plate for the purposes of demonstrating the present invention.

FIG. 4 is an enlarged side perspective view of the ends of the tubes of the heat exchanger with some of the turbulators partially withdrawn for the purposes of illustration. The heat exchanger is mounted in a demonstration cabinet with a door replacing the standard front plate for the purposes of demonstrating the present invention.

FIG. 5A is a top plan view of a turbulator in accordance with the present invention.

FIG. 5B is an enlarged top plan view of the turbulator in accordance with the present invention.

FIG. 6A is a side elevation view of the turbulator in accordance with the present invention.

FIG. 6B is an enlarged side elevation view of the turbulator in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGS. 1-4 illustrate the indirect gas-fired air handling unit 10 with a drum and tube heat exchanger 34 in which turbulators 40 of the present invention are used. FIGS. 5A-6B illustrate the construction of the turbulators 40 of the present invention.

FIG. 1 illustrates an indirect gas-fired and fire air handling unit 10 with a drum and tube heat exchanger 34 such as the AW-I indirect gas-fired air handling unit manufactured and sold by E. H. Price Ltd., Winnipeg, Manitoba, Canada. The air handling unit 10 comprises a cabinet 12, the drum and tube heat exchanger 34 including a gas-fired burner (not shown), a fan 22 driven by a motor 24, and controls 32 for controlling the operation of the fan 22 and the gas-fired burner. The fan 22 draws outside air into the cabinet 12 through air inlet 26 and filter 30, directs the air past the drum and tube heat exchanger 34 where the air absorbs heat, and forces the heated air out of the supply air outlet 28 into the occupied space of a building.

FIG. 2 shows the drum and tube heat exchanger 34 in greater detail. Particularly, the drum and tube heat exchanger 34 has a drum shaped combustion chamber 36 and a tubular heat exchanger 37. FIGS. 3 and 4 show an inlet side 41 of the tubular heat exchanger 37 in greater detail. A gas-fired burner (not shown) is mounted to fire into the combustion chamber 36. Combustion air is drawn into the combustion chamber 36 through a combustion air inlet (not shown). The heated combustion gases exit the combustion chamber 36 through combustion chamber outlet 17. A conduit chamber 39 connects the combustion chamber outlet 17 to the inlet side 41 of the tubular heat exchanger 37. In FIG. 2, a standard front plate for the conduit chamber 39 has been removed to show the internal detail of the heat exchanger tubes 38 at the inlet side 41 of the tubular heat exchanger 37. In FIG. 3 the heat exchanger 34 is mounted in a demonstration cabinet 12. The standard front plate has been removed from the heat exchanger 34 and replaced by a door 35 to allow easy access to the conduit chamber 39 during demonstrations and testing. Depending on the model of the indirect gas-fired air handling unit 10, the drum and tube heat exchanger 34 may have anywhere from 14 to 38 heat exchanger tubes 38. Moreover, the heat exchanger tubes 38 may vary in size from 2 inches in diameter to 3.5 inches in diameter.

As more clearly shown in FIGS. 3 and 4, flip-up-down single H-type turbulators 40 are inserted into the heat exchanger tubes 38. In FIGS. 3 and 4, the turbulators 40 have been partially pulled from the heat exchanger tubes 38 for the purposes of illustration.

Turning to FIGS. 5A-6B, the turbulator 40 is shown in greater detail. The turbulator 40 is constructed from a longitudinal strip of metal 42 with a length equal to that of the heat exchanger tubes 38 and a width approximately equal to the diameter of the heat exchanger tubes 38. H-shaped cuts 48 are made in the longitudinal strip 42 as shown in FIGS. 5A and 5B. Each H-shaped cut 48 creates a pair facing tabs, flip up tab 44 and a flip down tab 46. The flip up tab 44 remains connected to the longitudinal strip 42 along a flip up hinge line 45, and the flip down tab 46 remains connected to the longitudinal strip 42 along a flip down hinge line 47. The flip up tab 44 is bent upward from the plane of the longitudinal strip 42 along the flip up hinge line 45, and the flip down 46 is bent downward from the plane of the longitudinal strip 42 along the flip down hinge line 47. The elevation views in FIGS. 6A and 6B show the orientation of the flip up tab 44 and the flip down tab 46 once those tabs have been bent along the hinge lines 45 and 47 respectively.

The material for the turbulators 40 is stainless steel conforming to ASTM A240 Gr.409, Gr.304, or Gr.316 and has a thickness between 0.030 inch and 0.060 inch. The width of the longitudinal strip 42 conforms to the diameter of the particular heat exchanger tube 38. The width of the tabs 44 and 46 is between 40% and 60% of the width of the longitudinal strip 42. The length of each pair of the tabs 44 and 46 is approximately twice the length of the outside diameter of the tube 38 and between 4 inches and 7 inches. The total length of all of the tabs 44 and 46 is between 50% and 80% of the length of the longitudinal strip 42. The tabs 44 and 46 are bent at an angle 52 to the plane of the longitudinal strip 42 of between 15° and 25°. While the FIGS. illustrate tabs 44 and 46 that are essentially rectangular in shape, tabs in the shape of squares, triangles, circles, ellipses, pentagons, hexagons, octagons, or other geometric shapes are useful in implementing the present invention.

As previously indicated, the flip-up-down single H-type turbulators 40 of the present invention are intended for installation in the indirect gas-fired air handling unit 10, as for example the Price AW-I air handling unit. The AW-I air handling unit 10 has a heat release of 250 MBTU/hr. up to 6 MMBTU/hr. of heat output. The AW-I air handling unit 10 with prior art spiral turbulators has an efficiency of approximately 80%.

When the flip-up-down single H-type turbulators 40 of the present invention are installed in heat exchanger tubes 38 the AW-I air handling unit 10 in place of conventional spiral turbulators, a 4% increase in heat transfer occurs as evidenced by a drop in the flue temperature from 620° F. to 480° F. The flue gas pressure drops approximately 0.65 inch of water column (w.c.) as measured across the heat transfer tubes 38 when using the flip-up-down single H-type turbulators 40 of the present invention.

The flip-up-down single H-type turbulators 40 also produce increased performance even with burners that have a cylindrical flame. A cylindrical flame is longer in the direction of the length of the drum combustion chamber 34 than it is wide at the root of the flame. An efficiency of greater than 83% occurred when using a GP C-Series burner manufactured and sold by C.I.B. UNIGAS S.p.A., Via L. Galvani, 9-35011, Campodarsego (PD), Italy. Other burners have a short flame relative to the size of the flame root at maximum fire. A burner with a long cylindrical flame is able to effectively impart radiant energy onto the interior of the drum combustion chamber 36 which is on a parallel axis. At the same heat release, a burner with a short and wide flame is not able to effectively impart radiant energy onto the interior of the drum combustion chamber 36. This means that if the heat exchanger 37 needs to exchange the same amount of energy, the heat exchanger tubes 38 will need to transfer more with the short and wide flame. The H-type turbulator 40 allows for more energy to be transferred by the heat exchanger tubes 38 when the drum combustion chamber 36 is not as effective because of the flame shape. However, even when the flame is cylindrical, a shape which allows for good heat transfer through the drum, the H-type turbulators 40 still allow for improved heat transfer in the tubular heat exchanger 37. The H-type turbulators 40 ensure that laminar flow does not set up inside the heat exchanger tube 38, thereby ensuring that good heat transfer can take place between the hot flue gasses and the wall of the heat exchanger tube 38 due to the turbulent flow.

The effect of the additional pressure drop on the C-Series burner (a cylindrical flame burner) is balanced by balancing the orifice size on the tubular heat exchanger 37. The orifice of the tubular heat exchanger 37 is downstream of the heat exchanger tubes 38 which contain the turbulators 40. The orifice size can be increased when using a C-Series burner to reduce the pressure drop the orifice imparts on the flow of hot flue gases, to offset the increased pressure drop that the H-type turbulator 40 imparts on the flow of hot flue gases.

The flip-up-down single H-type turbulator 40 is easy to manufacture. The H-shaped cut 48 (FIGS. 5A and 5B) is made by a laser, and the tabs 44 and 46 are bent by hand. The heat exchanger tube 38 acts as a go/no-go jig, preventing tabs 44 and 46 from being bent too far, and also showing where tabs should be bent more. The configuration of the turbulator 40 does not require high degree of accuracy.

While this invention has been described with reference to preferred embodiments thereof, it is to be understood that variations and modifications can be affected within the spirit and scope of the invention as described herein and as described in the appended claims.

Claims

1. A gas turbulator for insertion in a tube of a heat exchanger having a length and a diameter to increase turbulence of gas passing through the tubes of the heat exchanger, the turbulator comprising a longitudinal strip of material having a width and length defining a plane and longitudinal tabs protruding in opposite directions from the plane to form a series of slanted flip up tabs and flip down tabs each bent at an angle to the plane.

2. The gas turbulator of claim 1, wherein the longitudinal tabs are formed from the longitudinal strip.

3. The gas turbulator of claim 1, wherein the longitudinal strip has a thickness between between 0.030 inch and 0.060 inch.

4. The gas turbulator of claim 1, wherein the width and the length of the longitudinal strip conforms to the length and the diameter of the tube of the heat exchanger respectively.

5. The gas turbulator of claim 1, wherein the tabs have a tab width between 40% and 60% of the width of the longitudinal strip.

6. The gas turbulator of claim 1, wherein the total length of all of the tabs is between 50% and 80% of the length of the longitudinal strip.

7. The gas turbulator of claim 1, wherein each tab has a length between 4 inches and 7 inches.

8. The gas turbulator of claim 1, wherein the tabs are set at an angle between 15° and 25° from the plane of the longitudinal strip.

9. The gas turbulator of claim 1, wherein the tabs have a geometric shape.

10. The gas turbulator of claim 9, wherein the geometric shape is selected from the group of geometric shapes including rectangles, squares, triangles, circles, ellipses, pentagons, hexagons, and octagons.

11. The gas turbulator of claim 1, wherein the longitudinal strip is metal.

12. The gas turbulator of claim 11, wherein the metal is stainless steel.

13. A method of manufacturing a gas turbulator comprising the steps of: a. providing a longitudinal strip of material with a length and a width, the longitudinal strip defining a plane;b. making a series of H-shaped cuts along the length of the longitudinal strip to create a series of pairs of facing tabs; andc. bending one of the facing tabs upwardly from the plane of the longitudinal strip and bending the other facing tab downwardly from the plane of the longitudinal strip.

14. The method of claim 13, wherein the longitudinal strip has a thickness between between 0.030 inch and 0.060 inch.

15. The method of claim 13, wherein the width and the length of the longitudinal strip conform to a length and a diameter of a tube of a heat exchanger into which the turbulator is installed.

16. The method of claim 13, wherein the H-shaped cuts are dimensioned to create a tab width between 40% and 60% of the width of the longitudinal strip.

17. The method claim 13, wherein the H-shaped cuts are dimensioned to create a tab length between 4 inches and 7 inches.

18. The method of claim 13, wherein the H-shaped cuts and dimensioned to create a total length of all of the tabs between 50% and 80% of the length of the longitudinal strip.

19. The method of claim 13, wherein the tabs are bent to an angle between 15° and 25° from the plane of the longitudinal strip.

20. The method of claim 13, wherein the longitudinal strip is metal.

21. The method of claim 20, wherein the metal is stainless steel.