Heat Exchanger Having Resiliently Mounted Tubular Members

Abstract

The invention relates to tubular heat exchange devices and in particular to improved arrangements of tube sheets for flexibly securing radiating tubes to the liquid containing chambers of the tube exchangers. Heat exchange devices commonly comprise a plurality of parallel tubes extending between input and output liquid containing chambers or liquid tanks. The temperature of liquid circulated by the tubes from the input to the output tank is modified by the region intermediate the tanks, commonly referred to as the cooling region. Each tank comprises a wall portion and a tube sheet or header. The tube sheet serves as a wall of the tank and secures the tubes thereto.

Description

BACKGROUND OF THE INVENTION

Some cooling systems subject the tubes of the radiator to extremely large variations in temperature. For example, in the system described in U.S. Pat. No. 3,067,817 hereinafter referred to as "dry type of heat exchanger," the tubes may pass liquids having a temperature in excess of -200.degree. F. or alternatively may be devoid of liquid and exposed to ambient temperatures as low as 60.degree.F. Moreover, the hot coolant does not simultaneously reach all radiating tubes or all portions thereof at the same time so that individual radiating tubes are subjected to widely varying temperatures and temperature gradients. Thus some of the radiating tubes may be rapidly increasing in length due to the presence of a hot liquid while adjacent tubes, having no coolant therein, may remain contracted.

In arrangements of this type, it is essential to provide for a resilient connection between the radiating tubes and the tube sheets. As disclosed in Applicant's U.S. Pat. No. 3,447,603, it is desirable to utilize a rigid tube sheet containing apertures into which tubes can be flexibly secured so as to absorb the differential thermal expansions. Specifically, sleeves are resiliently secured thereto by an elastomeric material which is suitably bonded to the tube sheet and the sleeve. This permits the pattern to be maintained during curing so that the heat exchanger tubes can be readily installed in the sleeves, such as by soldering, and also allows for individual movement of the tubes secured thereto.

Initially, it was attempted to mount the sleeves flush to the tube sheet so as to provide a flat plane on that surface of the tube sheet which constitutes the interior wall of the tank, i.e. the surface exposed to the liquid in the tank. The bond between the sleeve and the tube sheet frequently failed because of the shrinkage of rubber during the curing cycle, and additionally because of the action of the flux during soldering of the bonded sleeves to the tubes. This problem was alleviated by positioning the sleeves to project inwardly into the tank past the surface of the tube sheet and by extending the elastomeric material over substantially the entire surface of the tube sheet on the tank side. This arrangement was intended to protect the tube sheet, which was usually made of steel, from the corrosive action of the liquid in the tank. A perforated tube sheet was used having a bonded elastomeric material on each side. The perforations in the tube sheet were required to minimize blistering of the elastomeric material which subsequently can result in water leakage and failure of the system. However, even constructions utilizing perforated tube sheets were still subject to blistering and ultimate failure. It is believed that this deficiency resulted from residual liquid deposits in the undrained areas of the tank which would initiate blistering. Heat exchangers, particularly those of the dry type, are frequently mounted so that the tubes extend substantially horizontally one above the other. In some applications, the heat exchanger assemblies are canted so that the plane comprising the parallel tubes is inclined slightly in respect to a vertical plane. For example, such canted assemblies are utilized in diesel electric locomotives, wherein the assemblies are flush mounted in inclined sections intermediate the vertical side wall and the horizontal roof section of the locomotive. The canted location of the heat exchanger increases the lower surface area of the elastomeric material which is subjected to residual liquid contained in the tank. Additionally, the sleeve and tube portions extending from the tube sheet into the tank preclude complete draining of the residual liquid in the tank.

The referenced U.S. Pat. No. 3,447,603 discloses one solution for further minimizing blistering and tube sheet failure. Therein the elastomeric material continues to be bonded to substantially the entire surface of the perforated tube sheet which is exposed to the heated fluid in the tank. However, the major portion of the surface area of the elastomeric material, which directly exposed to the heated fluid of the heat exchange system, is rendered vapor impervious, by a layer of suitable material, such as a metal or fluorocarbon polymer. Such an arrangement appears to further reduce blistering and rupture. However, the application of a vapor impervious material entails additonal manufacturing steps and is very costly and time consuming. Additionally, the sandwich structure of this arrangement, wherein the layer of elastomeric material is interposed between two water impervious surfaces, may still be susceptible to blistering.

It is an object of this invention to provide a new and improved tube sheet arrangement for heat exchange devices which substantially overcomes one or more of the prior art difficulties and exhibits increased operating lifetime.

It is another object of this invention to provide such an improved arrangement for heat exchange devices which exhibits improved operating lifetime while providing for less complex and expensive manufacturing procedures.

SUMMARY

Briefly stated in accordance with one aspect of the invention a plurality of radiating tubes are flexibly connected to tube sheets on first and second liquid containing chambers. Each tube sheet comprises a reinforcing plate having a first surface constituting an interior wall portion of the chamber which is impervious to water vapor and is directly exposed to the liquid in the chamber. The plate is provided with a plurality of apertures, displaced in a discrete pattern, but has no other openings in the region which defines the interior wall portion. A plurality of sleeves adapted to be secured to the periphery of the radiating tubes, are provided with one sleeve being positioned within each aperture. An elastomeric material is intimately and irreversibly bonded to substantially the entire area of the second surface of the plate to provide an elastomeric surface on the side of the tube sheet defining the cooling region of said heat exchanger. The elastomeric material is applied so as to further extend over substantially the entire external circumference of each of said sleeves whereby the only elastomeric material on the first surface of said plate within the area defining the interior wall portion of the chamber comprises discrete collars extending about each sleeve member. In this arrangement, the elastomeric material and plate are arranged so that moisture migrating through the elastomeric material is not condensed and blocked by the plate to cause blistering.

The novel features believed characteristic of this invention are set forth with particularity in the appended claims. The invention itself, however, together with its organization and method of operation will best be understood by reference to the following description taken in conjunction with the accompanying drawing in which:

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of the heat exchange device incorporating this invention with the structural support members removed and the inlet and outlet tanks being illustrated in simplified fashion;

FIG. 2 is a partial section view of one embodiment of the tube sheet construction of this invention;

FIG. 3 is a perspective view of a portion of the tube sheet structure illustrating the side of the reinformcement plate which constitutes the interior wall surface of the tank; and

FIG. 4 is a partial view of the reinforcement plate taken in section A--A of FIG. 3 and illustrating mold members utilized in applying the elastomeric material.

DESCRIPTION OF PREFERRED EMBODIMENT

FIG. 1 illustrates a heat exchange device comprising a plurality of heat exchange, or radiating, tubes 11 extending between an input tank 2 and an output tank 4. The input tank 2 has an outer wall portion 6 and an input liquid coupling 8. A first tube sheet 12 is connected to wall portion 6, by fastening means 17. The output tank 4 has an outer wall portion 7 and an output liquid coupling 9. A second tube sheet 13 is connected to wall portion 7 by fastening means 17. The tubes 11 extend between tube sheets 12 and 13 so that one fluid, such as water, may, for example be circulated through the tubes and a second fluid, such as air, may be circulated externally of the tubes. In order to increase the heat exchange between the fluids, the radiating tubes are generally provided with external fins 14.

Means are provided for resiliently mounting the radiating tubes between the input and output tanks to accommodate individual changes in their lengths under varying temperature conditions while maintaining a perfect liquid seal at all times. For this purpose the ends of the radiating tubes are each secured to a metal sleeve, or ferrule which has been resiliently mounted to the tube sheet.

The arrangement for resiliently securing the radiating tubes to the tube sheets in accordance to the invention is illustrated in FIG. 2. The tube sheet comprises a reinforcing plate 18 constructed out of a suitably rigid material. Steel plates have commonly been utilized for this purpose. Although the liquid normally contains a rust inhibiting substance, it is desirable to utilize therefore a rust proof material, such as brass clad or coated steel, or a suitable plastic composition. The plate has a first surface 19 which constitutes an interior wall portion of the tank chamber. As illustrated in FIG. 3, a peripheral region 22 of said first surface is provided to contact an extending portion of the outer wall portion 6 of the tank chamber and is fastened thereto in a leak proof manner. A series of holes 26 may be provided in the peripheral region to permit the plate to be screwed to the wall portion. Suitable gaskets of elastomeric material may be bonded about these holes. These may be applied during the molding process described subsequently.

The plate member comprises a plurality of apertures 16 punched, or otherwise suitably provided, in a preselected pattern. A sleeve, or ferrule, 15 is resiliently secured within each aperture as subsequently descried. Prior arrangements required a plate member containing plural perforations intermediate the apertures. These were required in order to assist water migration and to minimize blistering. In such arrangements water vapor penetrated the elastomeric material on the tank side and condensed as it approached the cooled plate member. In accordance to the invention, however, this problem is avoided and accordingly, the plate member has no openings interior of said peripheral fastening region, except for the aforesaid apertures 16.

The ends of the radiating tubes extend through the sleeves 15 and are rigidly secured thereto in a known manner, such as by soldering, brazing, welding, expanding or any other suitable means of providing a rigid leak proof connection. One preferred method is to dip solder the tubes and sleeves subsequent to the sleeves having been resiliently secured to the plate member.

The sleeves have an interior circumference adapted for rigid connection to the radiating tubes and an and intimate length substantially greater than the thickness of the plate. As illustrated in FIG. 2, the sleeves 15 are positioned within the apertures of the plate member so the locomotive to extend substantially on each side thereof. The sleeves are intimately and irreversibly bonded within the apertures whose interior circumference is greater than the outer circumference of the sleeves. For this purpose a suitable elastomeric material of the type disclosed in U.S. Pat. No. 3,067,817 is utilized which effects an intimate bond to metal and which is capable of resisting the fluid employed in the heat exchange system. As described subsequently, it is particularly desirable to utilize an elastomeric material which may be applied by transfer molding techniques. One elastomeric material which is particularly satisfactory is compounded from a silicon rubber gum sold by the General Electric Company, Silicon Products Department under the designation No. CE-407. Such material is self-bonding and provides a very strong and intimate bond to the metal sleeves and the material of the member 18, which bond is not affected by the coolant at the temperatures encountered, for example, in the locomotive engine cooling system shown and described in U.S. Pat. No. 3,067,817.

In accordance to the invention a layer 20 of the elastomeric material is bonded to substantially the entire area of the second surface 21 of the plate member, i.e. the surface exposed to the cooling region of the heat exchanger. Additionally, the elastomeric material is bonded to substantially the entire external circumference of the ferrules. As illustrated in FIGS. 2 and 3, a surrounding collar of elastomeric material extends about the ferrule portions projecting on each side of the plate member. Thus a collar portion 25 extends outwardly into the cooling region from the second surface 21 of the plate and a collar portion 24 extends outwardly into the liquid chamber from the first surface 19 of the plate. This arrangement precludes bond failures between the collar 24 and sleeve 25 due to flexures, curing shrinkage and actions incident to joining the tubes to the sleeves, such as the effects of flux used in connection with the soldering operation. In the preferred embodiment illustrated in FIG. 2, the opposing end portions of the sleeve 15 are flared outwardly. This flaring, in addition to assisting the insertion of the radiating tubes into the sleeves, is believed to contribute to the formation of an effective bond between the ends of the sleeves and the elastomeric material. The curing shrinkage of the elastomeric material is believed to place the bond between the ferrules and the elastomeric material under compression and thus improve the elastomeric seal on the ends of the ferrules. Similarly, the above described arrangement is not subject to the blistering problems encountered in described prior art arrangements, while obviating the requirement of costly perforated plates and the applications of additional leakage proof laminations on the surface of the elastomeric material. It is believed that the blister phenomena occurred in prior arrangements because heated fluid migrated through the elastomeric material, condensed upon contacting the plate member and was blocked from further migration by the plate member. In the present arrangement the plate does not constitute a barrier to fluid which permeates through the elastomeric material. This permits retention of a layer 20 of elastomeric material on the plate which in addition to providing structural support to the elastomeric seal between the plate and the ferrules provides the manufacturing advantages described subsequently. The extending collars 24 and 25 about the sleeve while providing further structural support to the seal between the plate and seal do not promote blistering despite the absence of a vapor impervious coating about the surface of collar 24, i.e. the elastomeric surface which is exposed to the heated fluid in the liquid tank. Whereas the fluid vapors penetrate the elastomeric material of collar 24, the vapors freely migrate to the air cooled region of the heat exchanger without encountering a metal barrier. Additionally, it is believed that the intermittent passage of heated fluid through the radiating tubes minimizes the condensation of vapors contained in the elastomeric regions surrounding the sleeves and tubes.

FIG. 4 illustrates a transfer mold arrangement for applying the elastomeric material. The mold arrangement, while not a part of this invention, is described to further explain the tube sheet arrangement. A first mold comprises a plurality of mold sections 32 which are secured, by screws 34 to a mold backing or support, plate 36. The mold sections, which are illustrated in cross-section, incorporate an extending annular member 33 and an inner projecting member 38 so as to form therebetween a toroidal cavity. The projecting member preferably flares outwardly at its base. When the mold is positioned onto the sleeves 15, as illustrated in FIG. 4, the flared configuration of the projecting member 38 flares the ends of the ferrules. The first mold is positioned so that the lower surface of the mold is displaced from the second surface 21 of plate 18 by a distance corresponding to the desired thickness of elastomeric layer 20. This can be accomplished by appropriate setting of the mold apparatus or alternatively by extension of screws 34, so that a portion of the screws extending outwardly of the mold sections provides for appropriate displacement.

The wall of the projecting member abuts against the inner surface of the sleeve so as to prevent the application of elastomeric material to the inner walls of the sleeve. The inner wall of the annular member 33 extends about the ferrule with a clearance equivalent to the thickness of the elastomeric collar 25.

A second mold member abuts against the first surface of plate member 18. The second member is similar to the first comprising mold sections 42 secured by screws 44 to a mold support plate 46.

During the transfer molding operation, the elastomeric material is introduced through one or more sprues 37 of the first mold against the second surface of plate 18. The elastomeric material thus forms layer 20 and by entering the cavities of the mold sections 32 forms collars 25. Additionally, the elastomeric material flows through the annular spaces formed by apertures 16 and sleeves 15 into the cavities of the mold sections 42 to form collars 24. Accordingly, the application of the elastomeric material can be performed in a single transfer molding operation. The application of layer 20 not only provides structural support, but additionally obviates the requirement to include sprues into each individual mold section. Various modifications may be made in the molding operation and the structural parts used therefor.

The above described arrangement provides a reliable arrangement for resiliently securing radiating tubes to the liquid containing tanks of the heat exchanger. It minimizes bonding failures, and provides for economies of manufacture and parts. While only a preferred embodiment has been described in detail herein, it will be apparent to those skilled in the art that many changes and modifications may be made without departing from the invention in its broader aspects. It is intended therefore, in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention:

Claims

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a tubular heat exchange device wherein a plurality of radiating tubes are flexibly connected between first and second liquid containing chambers, each chamber comprising:

a. an outer wall portion;

b. a reinforcing plate having a first and a second planar surface;

c. means for fastening a peripheral fastening region of said first surface in a leak proof manner to said outer wall portion, said first surface of said plate constituting an interior wall portion of said chamber directly exposed to any liquid contained therein;

d. a plurality of sleeve members having a longitudinal length substantially greater than the thickness of said plate, an interior circumference adapted for rigid connection about one of said radiating tubes, and a predetermined exterior circumference;

e. said plate comprising a plurality of displaced apertures having an interior circumference greater than the external circumference of said sleeve members; said plate having no openings interior of said peripheral fastening region, excepting for said apertures;

f. one of said sleeve members being disposed within each of said apertures;

g. an elastomeric material intimately and irreversibly bonded to substantially the entire area of said second planar surface to provide an elastomeric surface on the side of said tube sheet defining the cooling region of said heat exchanger;

h. said elastomeric material further being intimately and irreversibly bonded to substantially the entire external circumference of each of said sleeve members, whereby the only elastomeric material on the first surface of said plate and within said peripheral fastening region comprises discrete collars extending about each sleeve member and fluid vapors permeating said elastomeric material from said liquid containing chamber are not blocked by said reinforcing plate so as to avoid formation of blisters within said elastomeric material.

2. The arrangement of claim 1 wherein each of said sleeve members has opposing end portions flared outwardly and the elastomeric material extends about the external circumference of said sleeve members to form collars extending from each end portion to said plate member.

3. The arrangement of claim 2 wherein the elastomeric material comprises a self-bonding silicon rubber material.