WO2007097856A2

WO2007097856A2 - Heat exchanger and finned tube therefor

Info

Publication number: WO2007097856A2
Application number: PCT/US2007/001758
Authority: WO
Inventors: Joseph E. Schroeder
Original assignee: Nooter/Eriksen, Inc.
Priority date: 2006-02-16
Filing date: 2007-01-23
Publication date: 2007-08-30
Also published as: WO2007097856A3

Abstract

A heat exchanger (A) includes a succession of side-by-side tubes (6), each having a tubular core (20) and circular fins (22) surrounding the core. In addition, each tube has a pair of baffles (26) attached to the ends of its fins and extended generally axially along the fins. The baffles lie along the downstream sides of the fins and deflect the flow of fluid toward the downstream face of the core so as to enhance the transfer of heat between that fluid and the core and fins.

Description

HEAT EXCHANGER AND FINNED TUBE THEREFOR

CROSS-REFERENCE TO RELATED APPLICATIONS

This application derives and claims priority from U.S. Provisional Application 60/773,901, filed 16 February 2006, which is incorporated herein by reference. TECHNICAL FIELD

This invention relates in general to heat exchangers and more particularly to heat exchangers with finned tubes. BACKGROUND ART

Heat exchangers that transfer heat from flowing gases of elevated temperature to other fluids, such as liquids or other gases, typically have tubes that extend transversely through a duct. The high temperature gas flows through the duct. The lower temperature fluid flows through the tubes that traverse the duct. As a consequence, heat transfers from the high temperature gas through the wall of the tube to the low temperature fluid, elevating the temperature of the latter.

Most heat exchangers of the foregoing type have tubes that include fins to enhance the transfer of heat. With these tubes the high temperature gas not only heats the tube cores, but also the fins as well, and the fins, being in contact with the tube cores, conduct heat to the cores.

Where a finned tube exists within a flowing stream of high temperature gas, the gas impinges on the face of the tube core that is presented upstream, so the transfer of heat at the upstream face is quite good. But the downstream face is largely shielded, and transfers less heat. Moreover, the impingement generates some turbulence at the upstream face and at the fins in the region of that face and that enhances the transfer of heat at the upstream face even more. BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a sectional view of a duct containing several heat exchangers constructed in accordance with and embodying the present invention; Fig. 2 is a perspective view of a bank of tubes for any one of the heat exchangers, with the tubes being constructed in accordance with and embodying the present invention;

Fig. 3 is a transverse view of one of the tubes and showing the flow of fluid past one of the tubes; and Fig. 4 is a fragmentary elevational view along line 4-4 of Fig. 3.

BEST MODE CONTEMPLATED FOR CARRYING OUT INVENTION

Several heat exchangers A (Fig. 1) exist within a duct 2 through which a fluid flows, usually at a relatively high velocity on the order of 30 to 100 ft/sec. The fluid in the duct 2 may be a liquid or a gas, but typically it is a gas, such as the gaseous products of combustion. Each heat exchanger A may include at least one bank 4 (Fig. 2) of tubes 6 that lie along parallel axes X and extend between a supply header 8 and a discharge header 10. Usually each heat exchanger A will have multiple banks 4 of tubes 6 and headers 8 and 10, and they may be organized side by side or one after the other or both. The tubes 6 of each bank 4 extend through the duct 2 generally transversely with respect to the flow of the fluid in the duct 2. To be sure, the tubes 6 in the banks 4 disrupt the flow of the fluid, but immediately upstream from each heat exchanger A the flow is generally laminar, and the tubes 6 are oriented with their axes X generally perpendicular to that flow.

Another fluid flows through the tubes 6 of the bank 4 at a temperature different from that of the fluid in the duct 2, so that heat transfers from the one fluid to the other. Normally the fluid in the duct 2 flows at an elevated temperature considerably hotter than the fluid in the tubes 6 and typically is a gas, whereas the fluid in the tubes 6 may be a gas or a liquid or a combination. For example, the tubes 6 of the first or upstream heat exchanger A may contain superheated steam, the next heat exchanger A water and saturated stream, and the last heat exchanger A feed water.

At least some of the tubes 6 are configured to maximize the transfer of heat between the two fluids. Each tube 6 that is so configured has (Figs. 2-4) a tubular core 20 and fins 22 around the core 20. The fins 12 may take the form of a spiral that is wound about the core 20 or individual disks. Moreover, they may be segmented into individual fingers 24. Where the fins 22 take the form of a spiral, each convolution is considered a fin 22. The core 20 and the fins 22 are formed from metals that resist reacting with the fluids with which they are in contact.

In addition to the core 20 and fins 22, the tube 6 has baffles 26 that are attached to the fins 22 - indeed, to the outside edges of the fins 22 — and extend parallel to the axis X of the tube 6 preferably for at least that much of the tube 6 that is occupied by the fins 22. They are formed from a metal that resists reacting with the fluid in the duct 2 and are preferably attached to the ends of the fins 22 at welds. The baffles 26 are arranged (Figs. 3 & 4) in pairs on the downstream sides of the fins 6 and are equally spaced from a plane P within which the centerline of the tube 6 lies, which plane P is parallel to the direction of flow for fluid through the duct 2 immediately upstream from the heat exchanger A of which tube 6 is a component. Each baffle 26 measured from its center should lie at an angle <χ between 40° and 90° from the center plane P. Typically the tubes 6 have an outside diameter of 1.25 to 3.0 inches, whereas the fins 22 have an outside diameter of 1.75 to 4.5 inches. When the tubes 6 and fins 22 are so configured, the baffles 26 can vary in width from 0.5 inch to one inch. Each baffle 26 should cover 2% to 20% and preferably should cover 2% to 15% of the perimeter of the fin 22 over which it extends.

In the operation of the heat exchanger A, the gas in the duct 2 encounters each tube 6 at the upstream edges of its fins 12. Here it flows between the fins 12 heating them. It also impinges against the tubular core 20 on the upstream face of the core 20, generating some turbulence along the upstream face and within the upstream spaces between the fins 22 as well. The turbulence enhances the transfer of heat between the gas in the duct 2 and the fins 22 and core 20. Downstream, generally beyond the core 20, the gas encounters the baffles 26 that deflect it inwardly along the downstream surfaces of the fins 22. Indeed, the baffles 26 divert the gas toward the downstream face of the core 20 and more turbulence there and along the fins 22 at the downstream face. The result is greater heat transfer through the downstream face of the core 20 and downstream surfaces of the fins 22 for each tube 6 and greater heat transfer through the tubes 6 of the tube bank 4, all with a minimal drop in pressure across the tube bank 4.

Claims

CLAIMS:

1. A tube for a heat exchanger, said tube lying along an axis and comprising: a tubular core through which a fluid may flow; fins surrounding the core and projecting outwardly from the core such that individual fins are spaced axially along the core; and at least one baffle extended along the peripheral edges of successive fins and covering between 2% and 20% of the perimeters of the fins.

2. A tube according to claim 1 wherein the baffle is one of two baffles.

3. A tube according to claim 2 wherein the angle between the centers of the two baffles ranges between 80° and 180°.

4. A tube according to claim 2 wherein the baffles are attached to the fins at the ends of the fins.

5. A heat exchanger according to claim 4 wherein the baffles are welded to at least some of the fins.

6. A heat exchanger comprising a succession of side-by-side tubes located along generally parallel axes, each tube including: a tubular core through which a first fluid flows and around which a second fluid flows at a different temperature; fins attached to and surrounding the core, with the individual fins being spaced axially apart along the core; and baffles attached to the fins at their peripheries for deflecting the flow of the second fluid toward the downstream face of the core, the baffles being remote from and detached from the other side- by-side tubes.

7. A heat exchanger according to claim 6 wherein the baffles for each tube are two in number and are attached to the fins of the tubes at the peripheries of the fins.

8. A heat exchanger according to claim 7 wherein the two baffles for each tube are spaced equally from a plane that lies parallel to the flow of the second fluid immediately upstream from the heat exchanger and contains the axis of the tube, so that the plane bisects the space between the two baffles.

9. A heat exchanger according to claim 8 wherein the angle between the center of each baffle and the plane bisecting the baffles ranges between 40° and 90°.

10. A heat exchanger according to claim 9 wherein each baffle covers between 2% and 20% of the periphery of the fin along which it lies.

11. A heat exchanger according to claim 7 wherein each baffle covers between 2% and 20% of the periphery of the fin along which it lies.

12. A heat exchanger according to claim 7 wherein the baffles are attached to the fins by welds.