US2893705A - Heat exchanger - Google Patents

Description

July 7, 1959 A. A. FENNELL HEAT EXCHANGER Filed July 5, 1957 INVENI OR.

United States Patent HEAT EXCHANGER Anthony A. Fennel], Homewood, Ill. Application July 5, 1957, Serial N 0. 670,029 7. Claims. (Cl. 257-26215) The present invention relates to a novel heat exchanger structure, and more particularly to a novel heat exchanger for transferring heat from one stream of fluid to another, whichheat exchanger is, for example, especially'useful in an industrial furnace as a recuperator.

Ithas been proposed to provide a heat exchanger including conduit means and a plurality of elements or pins extending through thewall of the conduit means for promoting heat transfer between one fluid within th'econduit means and another fluid outside of the conduit means. When such a heat exchanger is used as a recuperator in. an'industria'l furnace or in some other installation where it is subjected to high temperature gases or fluids, there is danger that portions of the pins exposed to the'hot gases will be burned.

'An important object of the present invention is to provide novel'he'at exchanger structure of the type contemplated abovewhereinthe pins or similar elements areconstructed and arranged so as to reduce any possibility of injury thereto or burning'thereof while at'the sa'metime promoting eflicient'operation of the heat' ex changer:

A moresp'ecificobject of the presentiinven-tionis to provide anovel heat exchanger of theab'ove described type having elements or pins with opposite en'd'portions' res'p'ectively"projecting outwardly of and inwardly of-the wallof the conduit means, which pin portions are'con structed so as to. provide a predetermined ratio between the=sizes or areas thereof, and said ratios of pins ar ranged at different locations b'eing varied'in accordance with the temperature environment at such location-so asto'pro'mote more eflicient heat exchange while re sisting damage or burning of the pins. 2 V

Gther objects and" advantages of the present inven: tion will becomeapparent from the following description and? the accompanying drawings 'wl iereinf V Fig. 1 is'an" elevational view of a furnace or the like ofknown construction having a heatexchanger em-, hodyin'g the principles of the. present invention associated therewith; i

' Fig. 2. is J an enlarged fragmentary perspective viewshowing the novel'heat exchanger of the present invention" disposed in assembled relationship with aflue pipe,

of a furnace; V Fig; 3'isfan enlarged crosssectionalview taken gene'ral-ly along the lines 33- in Fig. 1;

line 44 in" Fig. 3;

Fig. 5 is a fragmentary enlarged partial sectional. view taken-alongline 5 -5 in Fig. 4;

'Fig. 6 is a fragmentary enlarged partial sectional view taken along line 6-6' in Fig. 4; and

Fig. 7'is a fragmentary enlarged partial sectional view throughout the various figures; a heat-exchanger assemlily 10incorporating the features of the present'inve'm Fig. 4is; afurther enlarged cross sectional vieav along ice tion is shown mounted in a flue pipe 12 of a furnace 14 of knownconstruction. I

As will be understood, the heat exchanger in: this installation is adapted to transfer heat from escaping flue gases to another fluid such as air and, in this installation, the air is to be used as combustion air in'the furnace. The heat exchanger assembly is provided with an air supply manifold 16 which directs air to conduit means generally designated by the numeral 18 extending into the flue pipe 12, which conduit means has outlet means connected with another manifold 20 which extends to the furnace.

In the embodiment shown for the purpose of illustrating the present invention, the conduit means 18 is provided by a plurality of generally U-shaped pipes 22; 24, 26 and 28. Each of the pipes or tubes 22-28 has an inlet end connected with the manifold 16 and extends transversely into the flue pipe 12 through an open} ing which is sealed by suitable packing means 30. An outlet leg of each of'the U-shaped tubes or pipes ex; tends through a similar opening in the flue pipe 12 that is closed by suitable packing means 22, and each of the outlet legs of the tube is Welded or otherwise suitably connected to the outlet manifold 20. In order to pro mote intimate contact of the flue gases flowing'in' a stream through the flue pipe 12 with the heat exchanger tubes, each of the tubes is provided with a substantially streamlined transverse cross sectional shape identical to the cross sectional shape of the tube 22 shown in Fig; 4. As shown in Fig. 4, this cross sectional shape'has an enlarged upstream or leading marginal or edge portion 34; tapering oppositeside portions 36 and 38 and a smaller trailing'or downstream marginal or edge por tion 40-. Pins 42 are spaced longitudinally and transversely ofthe leading edge portion 34'of each tube and somewhat similar pins 44land id-are respectively spaced longitudinally and transversely of the oppositesi'des and trailing or downstream edge portions of thetubes. These pins serve to increase theheat exchanger area exposed to the fluids and also to reduce or eliminate laminar flow of the-gases around the streamlined tube toPFQe mote more intimate contact oftlie gases with the'tube and thereby increase the efliciency of "the heat exchanger.

Itwill be appreciated that the temperature of theflue gases approaching the upstream or leading tube 22' of the heatexchanger assembly will-frequently be sufficient ly high to cause injury-or burning of the pins in the. absence of proper cooling. of the pins. Furthermore, as the gases pass over the heat exchanger the temperaturethereof is progressively reduced so-that theleading pins 42' will be subjected to higher temperatures than" the trailing pins 44 and the pins 44'will' be subjected to a higher'temperature than the trailing pins 46. Injury or. burning. of outer ends of the pins may he prevented by correlating the ratio between the sizes or surface areas of outer and inner end portions of the-pins and the expectedtemperatures of the within'the tubes. so tha t' heat is conductedfrom the, outer or heated'ends of the pins to the inner or cooler ends of the pins and thence to the cooler gasesat a'rate which" is suflicient to prevent overheatingof the pins. In accordance with a feature of'the present invention; the pins are constructed in this manner so as to avoid injury thereto and at the same time the ratio betweenthe sizes or areas of opposite ends of the pins is changed,

for pins disposed at spaced'locations subjected to dif-I gases flowing; over andsmall as compared with the size of area of inner end portions 50 thereof. In other words, in the embodiment shown the outer end portion 48 of the pin has a diameter smaller than the inner end portion 50 so that the inner end portion is effective for transferring heat from the ,outer end portion and to a relatively cool fluid stream flowingthrough the tube at a rate which is suflicient, when compared with the rate at which the outer smaller end portion 48 absorbs heat from the flue gases, to prevent overheating of the pin portion 48. As the flue gases pass the pins 42 they are cooled sufficiently so that outer end portions 52 of the pins 44 may be enlarged as compared with the outer end portions 48 of the pins 42 for absorbing heat at about the same rate as the outer pin end portion 48 even though the temperature of the flue gases is lower. Inner portions 54 of the pins 44 are also constructed so as to prevent overheating of the outer end portions 52, but in view of the lower flue gas temperatures at this location the ratio of the inner end portion 54 area to the outer end portion 52 area is less than the corresponding ratio between the areas of the inner and outer end portions of the pins 42. This change in the ratio has been illustrated in the drawings by making the inner and outer end portions of the pins 44 substantially equal in size.

The temperature of the gases passing the pins 42 is further reduced so that outer end portions 56 of the pins 46 are further enlarged as compared with outer end portions of the preceding pins in order to maintain the desired rate of heat transfer. Inner end portions 58 of the pins 46 are also of a size suflicient to prevent overheating of the outer end portions 56 and, in view of the lower temperatures of the flue gases, the inner end portions 58 may, in many cases, be smaller in size or area than the outer end portions 56. In addition to decreasing the ratio between the areas of the inner and outer portions of pins spaced transversely of each tube in the direction of flow of the flue gases, the ratio between the areas of inner and outer pin portions of pins on each of the tubes 24-28 may be decreased with respect to the corresponding ratio of the pins on each preceding tube since the temperature of the flue gas will be reduced as it passes from tube to tube. It is also to be noted that the rate of heat transfer from the outer ends to the inner end portions of the pins will vary for pins spaced along each of the U-shaped tubes from the entering to the outlet ends of the tubes since the air will be heated as it passes through the tubes so that the temperature difierential between the air and the pins decreases. Thus, in addition to varying the ratio between the areas of the inner and outer ends of the pins spaced transversely of the tubes and in the direction of flue gas flow, said ratio may also be varied for the pins on each tube and spaced along the tube in the direction of air flow through the tube. More specifically, the pins 42 at the leading marginal portion of a tube are formed in the manner shown and described above so that the ratio between the inner end portion 50 and the outer end portion 48 is smallest for pins adjacent the inlet of the tube and is increased for pins spaced along the tube toward the outlet end thereof. Said ratios for the remaining pins 40 and 46 may similarly be varied. With this arrangement, it will be appreciated that all of the pins may be formed so as to minimize any possibility of injury or burning thereof, and at the same time more rapid and efficient heat transfer in all portions of the heat exchanger assembly is accomplished.

While the preferred embodiment of the present invention has been shown and described herein, it is obvious that many structural details may be changed without departing from the spirit and scope of the appended claims.

The invention is claimed as follows:

1. A heat exchanger comprising tube means for a first fluid stream which enters at a first temperature, said tube means being disposable in a second fluid stream which approaches a leading portion of the tube means at a second and different temperature, one of said temperatures being sufficiently high to cause injury to the heat exchanger in the absence of cooling thereof, and a plurality of elements secured to said tube means and spaced on the tube means in the direction of flow of the high temperature fluid stream, each of said elements passing through a wall of the tube'rneans and including oppositely extending portions respectively for projecting into said high temperature fluid stream and the other of said fluid streams, each of said elements having a predetermined ratio between the surface areas of said portion projecting into the other of said fluid streams and the portion projecting into the high temperature fluid stream, said ratio for certain of said elements located upstream of the high temperature fluid stream being greater than said ratio of other of said elements located downstream of the high temperature fluid stream so as to reduce any possibility of injury to the elements while promoting eflicient operation of the heat exchanger.

2. A heat exchanger, as defined in claim 1, wherein said tube means is disposable transversely of said second mentioned stream, which second mentioned stream is the high temperature stream, a plurality of said spaced elements being arranged on said tube means with said ratio of the elements adjacent a leading edge of the tube means being greater than said ratio of the elements adjacent a trailing edge of the tube means.

3. A heat exchanger, as defined in claim 1, wherein said tube means includes a plurality of separate tubes disposable transversely of said second mentioned fluid stream which is the high temperature stream, each of said tubes having a plurality of said spaced elements arranged thereon with said ratio of elements adjacent leading edges thereof being greater than said ratio of elements adjacent trailing edges thereof.

4. A heat exchanger, as defined in claim 3, wherein said ratio of substantially all of said elements on a tube disposable downstream of said second stream from a preceding tube is less than said ratio of substantially all of the elements on said preceding tube.

5. A heat exchanger, as defined in claim 1, which includes additional elements similar to said first mentioned elements spaced along said tube means in the direction of flow of said other of said fluid streams, said ratio of certain of said additional elements located upstream of said other fluid stream being less than said ratio of other of said additional elements located downstream of said other fluid stream.

6. A heat exchanger comprising tube means for a first fluid stream which enters at a first temperature, said tube means being disposable in a second fluid stream which approaches a leading portion of the tube means at a relatively high temperature sufiicient to cause injury to the heat exchanger in the absence of cooling thereof, and a plurality of elements secured to said tube. means and spaced on said tube means in the direction of flow of said first mentioned fluid stream, each of said elements passing through a wall of said tube means and including oppositely extending end portions respectively.

for projecting into said first mentioned fluid stream and said high temperature fluid stream, each of said elements having a predetermined ratio between surface areas of the end portions projecting into said first mentioned fluid stream and said high temperature fluid stream, said ratio for certain of said elements located upstream of said first mentioned fluid stream being less than said ratio of other of said elements located downstream of said first mentioned fluid stream so as to reduce any possibility of injury to the elements while promoting eflicient operation of the heat exchanger.

7. A heat exchanger comprising a generally U-shaped tube for a first fluid stream which enters at a first. temperature, said tube being disposable transversely in.

a second fluid stream which approaches a leading edge of the tube at a difierent temperature, said tube having a substanitally streamlined transverse cross sectional shape for promoting intimate contact of fluid in said second stream with the outer surface of said tube, one of said temperatures being sufficiently high to cause injury to the heat exchanger in absence of cooling thereof, and a plurality of pins secured to and spaced transversely of and longitudinally of said tube, each of said pins having inner and outer end portions respectively for projecting into said first and second mentioned fluid streams, each of said pins having a predetermined ratio between surface areas of its inner and outer end portions, said ratio of pins disposed at various locations being varied in accordance with the temperatures of said first and second mentioned fluid streams at said locations so as to reduce any possibility of injury to the pins while promoting eflicient operation of the heat exchanger.

References Cited in the file of this patent UNITED STATES PATENTS 166,461 Houghton Aug. 10, 1875 1,421,247 Keenan June 10, 1922 2,004,252 Sorenson June 11, 1935 2,779,573 Kuroda Jan. 29, 1957

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