US2814415A - Heat exchanger head thermal shield construction - Google Patents

Description

F..BONI, JR, ETAL Filed July 6, 1954 Nov. 26, 1957 HEAT EXCHANGER HEAD THERMAL SHIELD CONSTRUCTION fi r s 1 m 1% n W m m i T S T in .A nlh um F .r 0 9 Y B All 3mm;

Patented N 0v. 26, 1 95.7

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HEAT EXCHANGER HEAl THERMAL SHIELD CONSTRUCTION Frank Bani, lira, Massillon, Philip S. Otten, Canton, and Cornelius J. Wilson, Massillon, Ohio, assignors to The Griscom-Russell Company, Maissillon, ()hio,a corporation of Delaware Application .luly6, 1954, Serial No. 441,432

4 Claims. (Cl. 220-68) This invention relates to heatexchangers and it pertains' particularly to athermal shield for a headcover diaphragm'of a heat exchanger.

Theuseof higher and higher pressures in installationsutilizing heat exchangers has required the head barreland cover to be designed with thicker and thicker walls in order tosustain and-contain the high'pressures. Such high pressures andthickhead Walls have created problems in providing and maintaining a liquid-tight seal between the head cover plate and the head barrel walls ofa heat-exchanger. These problems have been satisfied by a construction in which a thin diaphragmis welded about its periphery to theopen end of the head barrel wall toprovidethe liquid-tight joint, and a head-cover plate is then secured to the head barrelwallbyany suitable means so as to overlie and-support the diaphragm.

However, such construction involves other difliculties- Where there may be sudden and extreme changes intemperature of the fluid entering the heat exchanger head chamber, because, due to the thickness of the. head barrel and cover plate walls there may beonly a: gradual change in the average temperature thereof, while the thin diaphragm wall is subjected to a sudden and extreme change in average temperature.

When sudden temperature changes take place within the head due to temperature changes in the fluid passing therethrough, the diaphragm,-beingrelatively thin with respect to the-heavier head barrel and head cover plate, responds almost immediately to the fluid temperature change. Severe stresses develop due to different expan sion rates of the diaphragm and the barrel towhich it is secured.

Where the fluid temperature increases, the diaphragm expands and is subjected to radial compression at its periphery due to a-smaller expansion rate of the heavier headbarrel. Thus, if the fluid temperature increases substantially, the diaphragm may buckle. On the other hand, if the fluid temperature decreases, the diaphragm contracts to a greater extent than the barrel creating radial tensile stresses; and if such temperature decreases substantially, there is a possibility of tensile failure around the periphery of the diaphragm.

We have found that these disadvantages may be overcome by providing a thermal shield plate spaced. from the diaphragm. The shield plate preferably has a radius slightly less than the inner diameter of the head barrel to permit slow passage of fluid therebetween, and provides a layer of stagnant fluid between the thermal shield plate and the diaphragm. The effect is the provision of a thermal buffer which minimizes the development of thermal stresses in the diaphragm due to sudden temperature changes in the fluid in the head. Thus, thermal stresses are greatly alleviated.

Accordingly, it is one object of this invention to pro vide means for minimizing the thermal stresses in a head of a heat exchanger resulting from sudden changes in heat exchanger fluid temperature.

It is another object of this invention to provide athermal'shield plate spaced from the head cover plate for the creation of a fluid thermal gap adjacent to the cover plate.

Another object of this invention istoprovide means for preventing the deterioration-and eventual failure. of fluidtight connections between thehead cover plate and head barrel.

Anothercbject of this invention is to p-rovidesafluid baflie plate for a head-covervdiaphragm for the-entrapment ofv a fluid layer against.the:diaphragm..

Another object of this invention is to'provide a layer of stagnant fluidadjacent the fluid .seal diaphragm for insu-- lating the same from transientthermal effects.

Finally, it is an objectofthis inventionto provide a thermalshield fora head cover of'a'v heat exchanger in-.. corporating the foregoing features that is simpleand inexpensive to manufacture and repair.

These and other. objectsand advantages apparent tothose skilled in the artfrom the following description and claims may be attained, the stated results achieved, andthe described difficulties. overcome, by the discoveries, principles, apparatus, parts, combinations, subcornbinations and elements which comprise the present invention, the nature of which is set forth in the following statement, a preferred embodiment of whichillustrative of" the best mode in which applicantshave contemplated applying the principles-is set forthdn the following description, and Which is particularly and distinctly pointed out and set forth in the appended'claims forming part hereof.

In general terms the head closure thermal shield construction of the present invention may be stated as including in a heat exchanger, a head including a tube sheet portion, a head barrel portion-having a fluidport therein, the barrel terminating at an open end opposite the tube sheet; a thin metallic diaphragm welded continuously about its periphery to the head barrel closing the open.

end; a head cover plate adjacent and coextensive with the diaphragm on the external side thereof and having, a peripheral portion marginally overlapping and secured to the head barrel; and a fluid baffle plate within the. barrel spaced from the diaphragm adapted for providing a layer of stagnant fluid adjacent the plate.

Referring to the accompanying drawings which are illustrative of the preferred embodiment of the invention, by way of example, and in which similar numerals refer to similar parts throughout:

Fig. 1 is a perspective view of a portion of a heatexchanger showing a head member and shell separated by a tube sheet;

Fig. 2 is a vertical sectional view taken on the line 2-2 of Fig. 1; and

Fig. 3 is a chart comparing'stress-time curves for the liquid seal diaphragm with and without the thermal shield plate.

The exchanger is generally indicated at 1 in Fig. 1. It comprises a head barrel 2 and a shell3 havinga flange 4- by which the shell is secured to the head barrel by means of bolts 5. As shown in Fig. 1 the shell 3 forms a chamber 6 and is provided with a fluid port 7 which communicates with the chamber 6 and through which a liquid enters the chamber.

Likewise, the head barrel 2 is provided with a fluid port 8 which communicates with a head chamber 9 formed by the barrel 2. Between the chamber 6 and the'charnber 9 is a tube sheet 10 which may be integral with the head barrel as shown in Fig. 1. The tube sheet 10 includes a plurality of tube-receiving openings 11 to which are connected in a fluid-tight manner a corresponding number of heat exchange tubes 12.

The tubes 12 extend through the chamber 6 within the shell 3 to the opposite end thereof where is disposed a head barrel similar to head barrel 2 and including a similar tube sheet in which opposite ends of the tubes 12 are secured. The present invention, however, is equally applicable to other types of heat exchangers, such as one having U-tubes with opposite ends secured in the same tube sheet.

The end of the head barrel 2 opposite to the tube sheet is closed in fluid-tight manner by means of a thin diaphragm 13 preferably composed of metal. The periphery of the diaphragm 13 is welded at 14 to a radial flange 15 which is integral with the wall of the head barrel 2 and partially isolated therefrom by means of an annular radial groove 16 formed in the interior wall of the barrel head 2. The diaphragm is welded at 14 to the lip or flange 15 so that its outer surface is flush with the end of the barrel head 2. Overlying the diaphragm 13 is a head cover plate 17 the peripheral portion of which is secured to the end of the barrel 2 by means of a plurality of bolts 18.

As shown in Fig. 1 the walls of the head barrel 2, of the tube sheet 10, and of the head plate 17 are relatively thick compared to the diaphragm 13. The thick walls sustain the pressure of the fluid entering the head barrel chamber 9 through the fluid port 8 and passing through the heat exchange tube 12 which communicates with the chamber 9. The fluid to be cooled normally enters the chamber 9 at a high temperature and pressure, and is cooled in passing through the tubes 12. The thin diaphragm 13, welded to the head barrel 2 as stated, and backed up by the overlying head cover plate 17, provides a fluid-tight seal for the head chamber 9 capable of withstanding and containing very high pressures without leakage, such as can occur where a gasketed seal is provided between the head barrel wall and head cover plate unless extremely thick head walls are used, and inordinately heavy securing means are provided between the cover plate and barrel walls to maintain the gasket seated under all conditions.

In certain high pressure heat exchanger installations, there may be sudden and extreme temperature changes in the temperature of the fluid entering the head chamber 9, and these sudden temperature changes cause unusual and peculiar effects, particularly where a thin diaphragm 13,is used to provide the fluid-tight seal for the head chamber 9.

Sudden changes in the temperature of the fluid within the chamber 9 results in gradual changes in the average metal temperature of the walls of the barrel 2, of the tube sheet 10, and of the head cover plate 17. However, such sudden temperature changes may result in the creation of severe stresses within the thin diaphragm 13.

On the one hand, if the temperature of the fluid entering the chamber 9 suddenly increases substantially, the diaphragm 13 will expand radially, creating compression stresses due to the rigid walls of the surrounding barrel 2. As a result such stresses may produce buckling of the diaphragm 13.

On the other hand, if the temperature of the fluid entering the chamber 9 suddenly decreases substantially, the diaphragm 13 would tend to contact radially and thereby be subjected to radial tensile stresses due to the resistance to contraction caused by the barrel 2 to which the periphery of the diaphragm 13 is welded at 14. The ultimate possibility is a tensile failure of the diaphragm 13 at the weld 14.

To overcome the foregoing difliculties, a thermal shield, plate or balfle 19 is provided in spaced relationship with respect to the inner side of the diaphragm 13. The plate 19 may be mounted in place as shown in Fig. 1 in any desired manner, but preferably may be mounted by welding or otherwise securing a number of U-shaped clips 20 to the facing sides of the diaphragm 13 and plate 19 prior to assembling and welding the diaphragm 13 in the open end of the head. The clips 20 are formed in such manner as to space the plate 19 from the diaphragm 13 a substantial distance so as to provide a compartment 19a therebetween.

The thermal shield plate 19 preferably has a diameter only slightly less than the interior diameter of the head barrel wall 2, as indicated at 21, thus providing means communicating between the head chamber 9 and the compartment 19a through space 21. This communicating means, however, because of the small spacing 21, only permits very slow flow of fluid between the head chamber 9 and the compartment 19a.

When the heat exchanger is in operation, fluid in the head chamber 9 passes into the compartment 19a and fills the same. However, because fluid can only slowly enter or leave compartment 19a, the same is effectively trapped in the compartment 19a and the temperature thereof normally reaches an equilibrium temperature substantially the same as the temperature of the fluid in the head chamber 9 and of the head chamber walls 2 and 17.

When a sudden change occurs in the temperature of the fluid passing through the head chamber 9, this sudden temperature change does not directly affect, either immediately or suddenly, the temperature of the diaphragm 13 because the stagnant layer of fluid in compartment 19a forms in effect a layer of fluid insulating the diaphragm 13 against sudden temperature change.

In other words, there will only be a temperature change in the diaphragm wall 13 by slow conduction of the temperature change in the head chamber 9 through the thermal shield 19 and the stagnant layer of fluid trapped within compartment 19a.

In this connection, it is important that the communication between chamber 9 and compartment 19a, as through space 21, be such as to provide for extremely slow fluid flow; so as to prevent convection currents of fluid from flowing from chamber 9 through compartment 19a which would impair the temperature insulation value of the stagnant layer of fluid trapped in compartment 19a.

In this manner, thermal stresses within the diaphragm 13 caused by sudden changes in the temperature of the fluid passing through head chamber 9 are substantially reduced.

Two time-stress curves (A and B) are shown in Fig. 3 for thermal shock on the diaphragm 13. The horizontal line C indicates the allowable stress permitted in the diaphragm. Curve A shows the stress created in the diaphragm 13 when no thermal shield plate 19 is used. As shown the stress, either tensile or compressive, increases rapidly to a maximum well above the allowable stress level, and then gradually decreases as time elapses. Curve B shows the ideal conditions which prevail when a thermal shield plate 19 is used. With the plate 19 in use the stress in the diaphragm first decreases in the opposite direction from that later developed. Then the stress increases gradually to a maximum well below the allowable stress and then decreases as time elapses. The thicker the trapped liquid layer, the lower and later the maximum stress developed. Moreover, the maximum stress peak is attained later than is the case without the plate 19.

Hence, by using the foregoing thermal shield plate construction it is possible to entrap or isolate a layer of stagnant or slow-moving fluid adjacent the thin diaphragm to serve as an initial absorbent for sudden temperature changes in the fluid entering the head chamber of the heat exchanger. The thermal shield plate constitutes a definite improvement over similar heat exchanger heads lacking such plate, because the effect of temperature variations is diminished resulting in substantial decreases in thermal stresses within the diaphragm and preventing eventual failure in extreme cases. By permitting only a gradual change of the entrapped fluid the temperature changes are absorbed by the fluid layer whereby the diaphragm is insulated from transient thermal effects, by a fluid layer equal to the space between the diaphragm and the thermal shield plate.

The advantages of the improved thermal shield construction may also be realized in a heat exchanger construction involving a gasketed joint rather than a welded diaphragm between the head barrel walls and head cover plate. The danger in a gasketed joint from sudden temperature changes lies in the tendency of the head to slide on the gasket or to tear the gasket with possible failure of the seal as a result, when the head cover plate is subjected to extreme or sudden temperature changes. In such gasketed construction, the improved thermal shield may be secured directly on the inside face of the head cover plate to trap a stagnant layer of temperature insulating fluid between the thermal shield and head cover and thereby reduce the thermal shock on the inside face of the head cover plate when extreme temperature changes occur in the head barrel.

In the foregoing description certain terms have been used for brevity, clearness and understanding, but no unnecessary limitations are to be implied therefrom beyond the requirements of the prior art, because such words are used for descriptive purposes herein and are intended to be broadly construed.

Moreover, the embodiment of the thermal shield construction illustrated and described herein is by way of example, and the scope of the present invention is not limited to the exact details of construction shown.

Having now described the features, constructions and principles of invention, the characteristics of the new thermal shield plate for heat exchangers, and the ad vantageous, new and useful results provided; the new and useful discoveries, principles, parts, elements, combinations, subcombinations, structures and arrangements,

and mechanical equivalents obvious to those skilled in the art, are set forth in the appended claims.

We claim:

1. Head closure construction for a heat exchanger including metal head barrel walls forming an annular chamber through which heat exchange fluids circulate terminating in an open end having an end surface lying in a plane, a flat metal diaphragm having inner and outer surfaces, the diaphragm being Welded about its periphery to the barrel wall at the open end of the barrel wall, and with one surface of the diaphragm lying in the plane of the barrel wall end surface, a cover plate having a flat inner surface engaging the flat outer surface of the diaphragm and overlapping the end surface of the barrel wall, means engaging the cover plate and barrel wall removably securing the cover plate to the barrel wall in pressure-supporting engagement with the diaphragm, a fluid baffle plate located within the chamber spaced from the diaphragm and forming with the diaphragm a thermal insulating compartment, and at least a portion of the edge of the baflle plate being slightly spaced from the barrel wall to provide means forming limited fluid flow communication between the compartment and chamber.

2. Head closure construction for a heat exchanger including metal head barrel walls forming an annular chamber through which heat exchange fluids circulate terminating in an open end having an end surface lying in a plane, a flat metal diaphragm having inner and outer surfaces, the diaphragm being welded about its periphery to the barrel Wall at the open end of the barrel wall, a cover plate having a flat inner surface engaging the flat outer surface of the diaphragm and overlapping the end surface of the barrel wall, means engaging the cover plate and barrel wall removably securing the cover plate to the barrel wall in pressure-supporting engagement With the diaphragm, a fluid baflle plate located Within the chamber, means mounting the bafile plate on and in spaced relation with the diaphragm, a thermal insulating compartment being formed between the spaced plate and diaphragm, and the periphery of the plate being spaced slightly from the chamber wall to provide means forming limited fluid flow communication between the compartment and chamber.

3. Head closure construction for a heat exchanger, including metal barrel walls forming a head chamber through which heat exchange fluids subject to extreme and sudden temperature changes circulate, a thin metal plate diaphragm welded to the barrel walls forming a liquid-tight closure for one end of the head chamber, a cover plate engaging the diaphragm, means engaging the cover plate and barrel wall removably securing the cover plate to the barrel wall in pressure-supporting engagement with the diaphragm, fluid baflie plate means mounted in the chamber spaced from the diaphragm and forming therewith a thermal insulating compartment, and the periphery of the baflle plate being spaced slightly from the barrel wall to provide means forming limited fluid flow communicating between the compartment and the chamber.

4. Head closure construction for a heat exchanger, including metal barrel walls forming a head chamber through which heat exchange fluids subject to extreme and sudden temperature changes circulate, a thin metal plate diaphragm welded to the barrel walls forming a liquid-tight closure for one end of the head chamber, a cover plate engaging the diaphragm, means engaging the cover plate and barrel Wall removably securing the cover plate to the barrel wall in pressure-supporting engagement with the diaphragm, fluid baflle plate means mounted in the chamber spaced from the diaphragm and forming therewith a thermal insulating compartment, means communicating between the compartment and chamber limiting fluid flow therebetween, and the baffle plate means being mounted in the chamber on the diaphragm substantially parallel thereto.

References Cited in the file of this patent UNITED STATES PATENTS 1,057,485 Knollmann Apr. 1, 1913 1,767,989 Leek June 24, 1930 2,009,877 Dodd July 30, 1935 2,219,659 Price Oct. 29, 1940 2,547,521 Buehler Apr. 3, 1951 2,647,656 Frisch Aug. 4, 1953

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