US3016893A - Heater - Google Patents

Description

Jan. 16, 1962 J. w. BROWN, JR

HEATER Filed May 29 1959 xxxxx INVENT BY 6M A OF/VEY 3,016,893 HEATER John Wesley Brown, .ln, Lakewood, Ohio, assignor to Brown Fintuhe Company, Elyria, Ohio, a corporation of Ohio Filed May 29, 1959, Ser. No. 316,795 3 Claims. (Cl. 126116) This invention relates to heat exchangers and more particularly to heat exchangers adapted for service at high temperatures in which a fluid to be heated flows in an annular space between an outer or shell tube and an inner tube having longitudinally extending external fins thereon.

Heat exchangers of this general type are used Widely as heaters for heating air or other gases and various liquids to relatively high temperatures. The fluid to be heated flows in the annular space between the shell tube and the finned tube while heat is supplied by a gas or oil burner which discharges its products of combustion directly into the interior of a shell tube or by a high tempertaure electric heater or the like. The inlet and the outlet to the annular space extend laterally through the wall of the shell tube. In the past it has been necessary to stop the fins on the inner, finned tube short of the inlet and outlet in order to provide annular zones in which the incoming and outgoing fluid can flow circumferentially around the finned tube. At the inlet end, the fluid is distributed to the longitudinal channels formed by the fins and at the outlet end of the heater the fluid discharged from the channels can flow circumferentially around the tube and reach the laterally extending outlet.

The termination of the longitudinally extending fins has presented an operational problem because the lack of fins on the exterior of the tube results in a reduced rate of heat exchange in these zones of circumferential flow. Since the fluid to be heated removes heat from the finned tube at a reduced rate in these zones, a localized increase in temperature of the finned tube results. Not only is the efliciency of the heat transfer reduced, but also in some services the temperature of the finned tube may become so high that the life of the tube is considerably shortened or the tube must be constructed from an expensive heat resistant alloy rather than ordinary low alloy steel. The problem is particularly acute in heaters in which a gas or liquid fuel burner is connected to one end of the exchanger so that the finned tube acts in effect as a combustion tube for the burner. In a counterfiow heat exchanger embodying such an arrangement, the outlet from the annular space is adjacent the zone where the burner supplies heat to the finned tube at the greatest rate.

A general object of the present invention therefore is the provision of a heater, of the general type described, in which longitudinally extending fins are provided that extend throughout the zone of circumferential flow for the inlet or for the outlet or both, if desired, whereby the rate of heat transfer in these zones is increased over conventional practice and whereby the efliciency of the heat exchanger and the life of the finned tube are both increased. Another object is the provision of such a heat exchanger which can be manufactured at reasonable cost. Further objects and advantages of my invention will become apparent from the following description of a pre ferred form thereof, reference being made to the accompanying drawings in which:

FIGURE 1 is a longitudinal view, partially in section, illustrating a fired heater embodying my invention.

FIGURE 2 is a section taken along the line 2-2 of FIGURE 1.

FIGURE 2a is a fragmentary view on an enlarged States atent O 3,016,893 Patented Jan. 16, 1962 scale, showing one of the fin members in the zone of circumferential flow, and

FIGURE 3 is a perspective detail illustrating one of the fin members before it has been secured to the finned tube.

As shown in the drawing, the invention may be adapted to a heat exchanger of generally conventional construction comprising a shell tube 10 having an inlet 11 and an outlet 12 extending laterally through the wall of the shell tube at opposite ends thereof. The shell tube is also preferably provided with an expansion joint 13 and is supported by any convenient means such as the pedestal supports 14, 15 and 16, supports 15 and 16 being provided with rollers as shown to permit expansion of the shell tube.

An inner tube 20 is disposed within the shell tube 10. Inner tube 20 has a plurality of channel section fin members 21 secured to the exterior thereof as by welding. The fin members extend longitudinally throughout substantially the entire length of the finned tube, and extend radially as shown into close proximity to the inner surface of the shell tube. Each end of the finned tube is connected to the shell tube to block the ends of the annular space by connections 22 and 23. These connections may take any suitable form such as a conventional packing gland arrangement as indicated at 22 and a flanged connection as indicated at 23. If desired, connections such as shown in United States Patent No. 2,745,683, issued May 15, 1956, and assigned to the assignee of the present application may be employed, and

- Where there is no necessity to provide for cleaning the finned tube, a permanent welded connection can bemade. At one end of the finned tube a liquid or gaseous fuel burner 25 is mounted in any conventional manner; for example, the burner may extend through an opening in an insulated plate 26 that is secured to flange 27 at the end of the finned tube near the outlet 12. Combustion of the fuel takes place within the finned tube, the combustion gases being at very high temperatures in the zone adjacent the outlet 12 and radiating heat at a high rate to the inner surface of the finned tube in this zone. As

the gases travel down the length of the finned tube, transfer by radiation becomes of lesser importance and heat is transferred to the finned tube by convection, the temperature of the gases being gradually lowered. At the end of the finned tube adjacent the inlet 11 suitable connections to a stack 29 may be made. This arrangement provides a counterflow heat exchanger which is preferred where the discharge temperatures of the heated fluid are required to be high. It is evident that the heater can be adapted for concurrent flow if desired.

The elements of the heat exchanger thus far described are all conventional. However, in the usual heat exchanger of this general type the longitudinally extending fins 21 stop short of the outlet 12 to provide a distribution zone so that the heated air or other fluid can flow circumferentially around the finned tube from the channels provided by the fin members to reach the laterally extending outlet. With such an arrangement, particularly with a fired heater such as illustrated in the present drawings, serious overheating of the finned tube in the zone near the outlet can take place because of the reduced rate of heat transfer on the outside of the finned tube and the high rate of input of heat to the inside of the finned tube. The tube in the zone beyond the ends of the fins becomes much hotter than the finned zone, setting up thermal stresses in the tube as well as subjecting it to corrosion and other damaging influence of excessive temperature. It has been proposed to ameliorate these influences by welding studs to the finned tube in the zone beyond the fins but the provision of studs has not been entirely satisfactory and entails considerable additional expense in the manufacture of the heat exchangers.

According to the present invention, the fins 21 are not stopped at the edge of the opening 30 that leads to the discharge conduit 12 but are extended at least all of the way across the opening and preferably slightly beyond, as shown in the drawing. In this zone, however, the fin members 21 are provided with perforations 31 which, as shown in FIGURES 2 and 3, provide circumferential paths around the finned tube for the circumferential flow of fluid in the distribution zone and into the outlet 12. Preferably, the openings occupy about half of the total area of the fins but this proportion may be varied considerably. The openings are shown in the drawing as being round, but obviously they can be oval, rectangular or any other convenient shape. This provides adequate passages for the circumferential flow of the fluid and sufficient extended surface area so that heat exchange takes place at a high rate between the fins and the fluid flowing over and through them. Because of the increase in turbulence in the distribution zone, the rate of heat exchange in this region of the finned tube is substantially as great as in the regions where there are no perforations. Thus, the efficiency and heat exchange ability of the heat exchanger is substantially increased and at the same time the rapid transfer of heat to the fluid to be heated by means of the perforated sections of the fin members prevents overheating of the finned tube in this zone. The temperature of the finned tube in this area is reduced as compared to the temperature of a tube in a similar heater where the fins are stopped short of the outlet, and there is a corresponding reduction in corrosion and in thermal stresses on the finned tube,

Preferably the fin members are in the form of channels as shown in FIGURE 3, each fin member having a pair of of fin portions 33 and a base portion 34. The fin portions are perforated as at 31 While the base is imperforate. The perforations are preferably stamped into the metal from which the fin members are formed while it is in flat strip form; then the fin members are formed into channel sections as shown and Welded to the exterior of the finned tube preferably in accordance with the method and apparatus disclosed in my Patents Nos. 2,298,249 and 2,298,250, issued October 6, 1942. The presence of the perforations in the fin members does not affect the welding operation in any way; hence, the improvement of the present invention can be incorporated in heat exchangers at little additional cost and Without requiring the use of any additional equipment in the welding operation.

In the form of the invention disclosed herein, the fins 21 stop short of the inlet 11. It will be understood that in some services it may be desirable to have perforated fins adjacent the inlet as well as adjacent the outlet; and in some instances, depending upon the materials employed, the commodities to be heated and the nature of the heating medium, it may be desirable to employ perforated fins adjacent the inlet but to stop the fins short of the outlet. It will also be appreciated that the invention may be adapted to heat exchangers of different types from that specifically disclosed herein, which is given by way of example only. The essential characteristics of the invention are set forth in the appended claims,

I claim:

1. A heater comprising an elongated shell tube, a fluid conduit opening laterally into said shell tube, an elongated inner tube within said shell tube and defining with it an elongated annular space having an annular zone adjacent said conduit opening, said inner tube having fixed to its outer surface a plurality of spaced elongated fins which extend into close proximity to the inner surface of said shell tube and which extend longitudinally of said inner tube and into said zone adjacent said conduit opening, said fins being imperforate except in said annular zone wherein they have openings therethrough permitting fluid to flow circumferentially around said inner tube in said annular zone, and means for supplying heat to the interior of said inner tube comprising a fluid fuel burner disposed adjacent the end of said inner tube located nearest said fluid conduit.

2. A heater comprising an elongated shell tube, a fluid conduit opening laterally into said shell tube, an elongated inner tube within and concentric with said shell tube and defining with it an elongated annular space having an annular zone adjacent said conduit opening, said inner tube having fixed to its outer surface a plurality of circumferentially spaced elongated channel section fin members which extend into close proximity to the inner surface of said shell tube and which extend longitudinally of said inner tube and into said annular zone adjacent said conduit opening, said fins being imperforate except in said annular zone wherein they have openings therethrough permitting fluid to flow circumferentially around said inner tube in said annular zone, and means for supplying heat to the interior of said inner tube comprising a fluid fuel burner disposed adjacent the end of said inner tube located nearest said fluid conduit.

3. A heat exchanger comprising an elongated shell tube, a fluid conduit opening laterally into said shell tube, an elongated inner tube within said shell tube and defining with it an elongated annular space having an annular zone adjacent said conduit opening, said inner tube having fixed to its outer surface a plurality of spaced elongated fins which extend into close proximity to the inner surface of said shell tube and which extend longitudinally of said inner tube into said zone adjacent said conduit opening, said fins being imperforate except in said annular zone wherein they have openings therethrough permitting fluid to flow circumferentially around said inner tube in said annular zone, and means for supplying heat to the interior of said inner tube disposed adjacent the end of said inner tube located nearest said fluid conduit.

References ited in the file of this patent UNITED STATES PATENTS 1,558,848 Doble Oct. 27, 1925 1,920,800 McCausland Aug. 1, 1933 2,404,646 McCollum July 23, 1946 2,483,489 De Lancey Oct. 4, 1949 2,752,128 Dedo June 26, 1956 2,843,367 Bogus et al. July 15, 1958 FOREIGN PATENTS 105,745 Sweden Oct. 20, 1942

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