GB1562662A

GB1562662A - Tubular heat exchangers and tube bundle for use therein

Info

Publication number: GB1562662A
Application number: GB4921/77A
Authority: GB
Original assignee: Phillips Petroleum Co
Current assignee: Phillips Petroleum Co
Priority date: 1976-04-29
Filing date: 1977-02-07
Publication date: 1980-03-12
Also published as: MX144609A; SE423647C; AU1985076A; FR2357852A1; DE2706049C2; FR2357852B1; PL112917B1; JPS5421579B2; DD128941A5; NO142415C; NO142415B; BR7608437A; ES456346A1; IT1085928B; NL164658B; NL7701310A; DE2706049A1; YU39672B; NO770388L; NL164658C

Description

(54) TUBULAR HEAT EXCHANGERS AND TUBE BUNDLE FOR USE THEREIN (71) We, PHILLIPS PETROLEUM COMPANY, a corporation organized and existing under the laws of the State of Delaware, United States of America. of Bartlesville, Oklahoma, United States of America, do hereby declare the invention for which wc: pray that a patent may be granted to us, and the method bv which it is to be performed. to be particularly described in and bv the following statement: This invention relates to heat exchangers such as shell and tube heat exchangers and more particularly to a means for radially supporting the tubes therein.

Heat transfer is an important part of many processes and many different tvpes of heat exchanger have been devised. For example, there are double pipe. shell and tube. plate heat exchangers and others.

Indeed, the art of heat exchanger design is developed to a very high degree: however.

there is still room for improvement in a number of areas. such as reducing pressure drop, increasing overall heat transfer coefficients, reducing fouling. and in heat exchangers utilizing a tube bundle. such as the shell and tube heat exchangers. improving tube support. In many instances the tubes in a shell and tube heat exchanger prematurely fail because the tubes vibrate or rub against one another or other parts of the heat exchanger, such as for example. a baffle or the shell.

The art has heretofore recognized the need for tube support.

Plate type baffles have been used in heat exchangers for many years. Such baffles provide support for the tubes at least to some degree. The double segmental platebaffle heat exchanger is well known to those skilled in the art. and although heat exchan gers using plate type baffles were a rclative- ly early development in heat exchanger design, such exchangers are still widely used today.In most plate type baffle heat exchangers the passages in the plate baffles through which the tubes pass are slightly larger in diameter than the outside diameter of the tubes in order to facilitate construction of the exchanger, and as a result vibration of the tubes can and does occur which frequently results in premature tube failure, U.S. ^.UlS.U37. describes a heat exchanger having a unsupported tube bundle in which a pluralitv of bars or rods is disposed in the lanes between tube rows, A bar or rod is disposed in each lane and affixed to a ring surrounding the tube bundle so that the bars form a series of parallel chords positioned in a plane perpendicular to the longitudinal axis of the tube bundle.When viewing a cross section of the longitudinal axis of the bundle as shown in Figures 2. 3 and 6 of that patent. a bar is shown in each and every lane. Thus. two groups or pluralities of bars provide radial support for each tube in the tube bundle. Although such a structure provides very good support for the tubes in the tube bundle. it incurs the penalty of a relatively large pressure loss which, besides being wasteful of energy. is usually a higher pressure loss than can be tolerated. In fact.

even though this patented design is some thirtv vears old. it is not well accepted by industry as evidenced by the fact that it is rarely if ever used.

A tube support which is used and which does provide a low pressure drop is that described in U.S. 3,70t,l42. However, the design of the present invention provides a substantial improvement in heat transfer coefficients and fouling resistance at a rela timely small increase in pressure drop as compared to the arrangement shown in U.S.

3.7()S.142. Thus. although the pressure drop is generally lower for an exchanger constructed in accordance with U.S. 3.708.142, as compared to an exchanger constructed in accordance with the present invention, the present invention provides a better overall compromise when both the pressure drop and the heat transfer coefficient are considered. In addition, tube bundles supported in accordance with the present invention are somewhat cheaper to fabricate in some instances as compared to those of the earlier invention.

It is emphasized that the present invention is a very significant breakthrough in heat exchanger design because supporting a tube bundle in accordance with the present invention limits tube failure due to such things as vibration, improves the overall heat transfer coefficient as compared to prior art heat exchangers and at the same time reduces the pressure drop as compared to the plate type baffle heat exchangers well known in the art. Also, heat exchangers employing the inventive baffles and supporting apparatus are economically competitive with heat exchangers of the prior art and at the same time provide better overall performance.

Broadly speaking. the present invention provides a tube bundle for a heat exchanger.

which comprises a plurality of tubes arranged in a plurality of spaced parallel rows, the tubes within each row being spaced one from the other. and a plurality of baffles spaced one from the other along the length of the tube bundle each baffle comprising an outer ring surrounding the tube bundle and a plurality of parallel rods extending across and forming a set of parallel chords to the ring. the rods in each baffle extending through the spaces between said tubes and serving to support said tubes in their parallel array. the number of rods in each baffle being insufficient to fill all the spaces between the adjacent rows of tubes when viewed along the axis of the tube bundle. and the number of baffles and the number of rods in each baffle being such that each tube is radially supported. as hereinbefore defined. in said bundle at points intermediate the tube ends.

Also included within this invention are heat exchangers incorporating one or more such bundles.

As used herein a tube is 'radially supported when the tube is restricted from movement in all directions perpendicular to the longitudinal axis of the tube.

The invention will be further described with reference to the accompanying drawings. in which: Figure 1 is an elevational view of a heat exchanger employing an embodiment of the invention: Figure 2 is a cross-sectional view taken substantially on line 2-2 of Figure 1 showing a baffle in accordance with the invention: Figure 3 is a cross-sectional view taken substantially as line 3-3 of Figure 1 showing another baffle of the invention suitable for use in combination with that of Figure 2:: Figure 4 is a cross-sectional view taken substantially on line 4-4 of Figure 1 showing another baffle of the invention suitable for use with those of Figures 2 and 3; Figure 5 is an elevational view of a plurality of tubes in the form of a tube bundle employing another embodiment of the invention; Figure 6 is a cross-sectional view taken substantially on line 6-6 of Figure 5 showing a baffle of the invention; Figure 7 is a cross-sectional view taken substantially on line 7-7 of Figure 5 showing another baffle of the invention suitable for use with that of Figure 6; Figure 8 is a sectional view taken substantiallv on line 8-8 of Figure 5 showing another baffle of the invention suitable for use with those of Figures 6 and 7;; Figure 9 is a cross-sectional view taken substantially on line 9-9 of Figure 5 showing another baffle of the invention suitable for use with those of Figures 6. 7 and 8: Figures 10 to 15 illustrate in sectional views a baffle set in accordance with another embodiment of the invention comprising six baffles wherein the tubes in the tube bundle are laid out on a hexagonal pitch.

Figure 16 graphically illustrates the overall heat transfer coefficient measured as a function of shell side flow rate for a heat exchanger made in accordance with applicant's invention and for two prior art heat exchangers: Figure 17 is a graphical illustration of shell side pressure drop measured as a function of shell side flow rate employing the heat exchangers used for determining the values shown in the graph of Figure 16: Figure 18 illustrates graphically the ratio of the overall heat transfer coefficient to pressure drop measured as a function of shell side flow rate employing the same heat exchangers used for determining the values shown in the graphs of Figures 16 and 17.

Figure 19 is an elevational view of a plurality of tubes in the form of a tube bundle employing another embodiment of the invention: Figure 20 is a cross-sectional view taken substantially on line '0-'() of Figure 19 showing a baffle of the invention: Figure 21 is a cross-sectional view taken substantially on line 91-'1 of Figure 19 showing another baffle of the invention suitable for use with that of Figure 20: Figllle 22 is a cross-sectional view taken substantially on line 2'-'2 of Figure 19 showing another baffle of the invention suitable for use with those of Figures 20 and 71: : and Figure 23 is a cross-sectional view taken substantially on line '3-'3 of Figure 19 showing another baffle of the invention suitable for use with those of Figures 20, 21 and 22.

High flow rates of the fluids passed through a heat exchanger frequently cause vibration of the tubes in the tube bundle if the tubes are not radially supported which in turn causes one or more of the tubes to fail prematurely, that is, before the tube or tubes would be expected to fail based upon the materials used to construct the tubes and the service of the exchanger. Two of the common methods for reducing such vibration are the addition of plate baffles to add additional support to the tubes of the tube bundle and/or the lowering of the velocity of the fluid across the tubes. The addition of plate baffles causes a substantial increase in pressure drop through the shell side of the heat exchanger and reduction in the shell side flow rate requires a larger, more expensive exchanger than is otherwise necessary.The present invention solves the vibration problem without substantialy increasing the shell side pressure drop or substantially reducing the shell side flow rate. As used herein the terms "pressure drop" and "pressure loss" are synonymous.

It is noted that the heat exchanger and tube bundle designs shown in the drawings are schematic in nature and for purposes of better illustrating the invention. Thev are not intended as drawings showing the actual relative size of the exchanger of the component parts of the tube bundle.

Referring to Figure 1. a heat exchanger, denoted generally by reference numeral 10.

employing an embodiment of the invention has two tube sheets 17a and ]7b and three baffles 12, 14 and 16 supporting the tubes 18 which are in the form of a tube bundle 20 positioned inside a shell 19.

Although each of baffles 12. 14 and 16 is shown lying in a plane which is perpendicular to the longitudinal axis of tube bundle 20, it is possible to use baffles which are not in a plane perpendicular to the longitudinal axis of tube bundle 20, see for example. our copending Application No. 6480/77 (Serial No. 1562663). however. baffles lying in the perpendicular plane as shown are easier and cheaper to construct and thus preferred.

The tube side of heat exchanger 10 has an inlet nozzle 22 and an outlet nozzle 24 to permit a first fluid to pass over the inside surface of the tubes and the shell side has an inlet nozzle 26 and an outlet nozzle 28 to permit a second fluid to pass over the outside surface of the tubes when using countercurrent flow of the heat exchange mediums. The tubes 18 in heat exchanger 10 are laid out on an equilateral triangular pitch as shown clearly in Figures 2 to 4 and the baffles 12. 14. 16 form a plurality of parallel tube rows oriented at 60" to one another. Figure 2 shows the arrangement of tubes through baffle 12. As will be seen the parallel tube rows lie on a horizontal pitch with adjacent rows forming parallel spaces 34 in which the parallel rods 31 are positioned. Figure 3 shows the arrangement of tube through baffle 14.In this case the tube rows are on a 60" diagonal pitch with the spaces 36 formed by adjacent tube rows locating the parallel rods 32. Figure 4 shows the arrangement of the tube rows through baffle 16. In this case the tube rows are on a different diagonal pitch at 60" to those of baffle 14, with the tube rows again forming parallel spaces 38 through which pass the rods 33. Baffles 12, 14 and 16 constitute a baffle set because all three baffles are required before all the tubes in the tube bundle are radially supported.

Each baffle in Figures 2. 3 and 4 is made from an outer ring 30 surrounding the tubes 18 in the tube bundle 20. Rods 31 are positioned within the space between adjacent rows of tubes 34 of Figure 2. rods 32 between adjacent rows of tubes 36 of Figure 3. and rods 33 between adjacent rows of tubes 38 of Figure 4 so as to cooperate with outer ring 30 to form a plurality of parallel chords with outer ring 30. Generally rods 31. 32 and 33 are affixed to outer ring 30.

such as by welding them to the ring or bolting them to the ring using tie down members 40, 41 for baffle 11; 49. 43 for baffle 14 and 44. 45 for baffle 16 along with bolts 46. Rods 31. 32 and 33 must be of sufficient size to provide support for tubes 18 in the tube rows adjacent each rod. The total number of rods used in each baffle must be substantiallv less than the total number of rods which could be positioned in the spaces between the tube rows of the baffle.

Where only three baffles make up a baffle set. three baffles in a baffle set being the least number of baffles that can be used in accordance with the invention where the tubes are laid out on an equilateral triangular pitch, no more rods need be used in each baffle than the number which will provide radial support for each tube in the tube bundle. Generally an equal number of rods are used in each baffle; however. there may be instances where there is some variation in the number of rods used in the individual baffles of a set. At least one baffle set is required in accordance with the invention but baffles over and above those needed to constitute one baffle set can be used includ ing partial baffle sets.For example. where three baffles are necessarv for a baffle set, five baffles can be used ir; accordance with the invention. and if the baffles are equally spaced between the tube sheets. the longest unsupported tube distance is three times the distance between any two of the baffles.

Since one of the more important aspects of the invention is the reduction of tube failure due to vibration. the maximum unsupported tube distance is very important in designing a supporting apparatus. Since it is desirable to prevent tube collisions bv adjacent tubes between support points, the supporting apparatus is generally designed so that the maximum allowable tube deflection under load is equal to something less than one-half the clearance between adjacent tubes.

Figures 5 through 9 illustrate a preferred embodiment of the invention in which the tubes 50 in tube bundle 52 having tube sheets 51a and 51b are laid out in square pitch and generally a square pitch tube layout provides greater surface area for a given shell diameter for an apparatus constructed in accordance with the invention.

For example, there are 61 tubes in the embodiment of the invention shown in Figures 5 to 9 and only 57 tubes in the embodiment of the invention shown in Figures 1 to 4, and both embodiments are drawn to the same scale. The invention as illustrated in Figures 5 through 9 shows four baffles 54. 56, 58 and 60 and a supporting apparatus requiring all four baffles to constitute a baffle set. In Figures 6 and 7 there is a first plurality of parallel tube rows (the horizontal tube rows) and in Figures 8 and 9 there is a second plurality of parallel tube rows (the vertical tube rows). Rods 62 and 6'a are positioned in the space between the tube rows in the upper half and the lower half of the horizontal tube rows of Figure 6 and Figure 7 respectively and cooperate with outer rings 66 to form a plurality of parallel chords with outer rings 66.An example of a space between adjacent tube rows is represented in Figure 6 by reference numeral 61a and in Figure 7 by reference numeral 61b. Rods 64 and 64a are also positioned in the space between the tube rows in the left half and the right half of the vertical tube rows of Figure 8 and Figure 9 respectively and cooperate with outer rings 66 to form a plurality of parallel chords with outer rings 66. an example of a space between adjacent tube rows is represented in Figure 8 by reference numeral 63a and in Figure 9 by reference numeral 63b. Rods 62, 62a. 64 and 64a are of sufficient size to provide support for the tubes in the tube rows adjacent each rod and the humber of rods in each baffle is substantially less than the total number of rods which could be positioned in the spaces between the tube rows.The rods in the baffles shown in Figures 5 to 9 are held in position by tie down members 7() bolted to rings 66 using bolts 80.

In the embodiment of the invention as shos n in Figures 5 to 9 the baffles are shown in the presently preferred embodiment wherein rings 66 are simply an annular shape as compared to rings 30 of Figures 1 to 4 in which the inside edge of rings 30 is cut to provide partial support for the tubes located adjacent the inside edge of the rings; however, it is difficult to make the circular cuts for partially supporting the tubes located adjacent the inside edge of the rings 30 so that no radial movement of the tubes is allowed. The design of baffles 54, 56, 58 and 60 of Figures 5 to 9 avoids this problem simply by not making the ring with such cuts and using one additional rod to support the tubes which would be otherwise partially supported by the cuts in the ring. The additional rod is shown as 62a in Figures 6 and 7 and as 64a in Figures 8 and 9.Further, the design of the baffles with annular rings 66 in Figures 5 to 9 is preferred because such a design further reduces the pressure loss through the heat exchanger since part of the ring which restricted the flow of the shell side fluid is eliminated. Therefore, this design simplifies the construction of the baffles and particularly rings 66. helps prevent premature tube failure due to the tubes rubbing against the relatively sharp inside edge of the rings, and further reduces the pressure loss across the shell side of the heat exchanger.

In the embodiment of the invention as shown in Figures 19 to 23 the baffles are very similar to those shown in Figures 5 to 9.

In Figures 19 to 21 rods 162 are inserted in alternate spaces between adjacent tube rows in each baffle whereas rods 62 in Figures 5 to 7 are inserted in adjacent spaces between adjacent tube rows. In Figures 19, 22 and 23 rods 164 are inserted in alternate spaces between adjacent tube rows in each baffle as compared to Figures 5. 8 and 9 wherein rods 64 are inserted in adjacent spaces between adjacent tube rows. But in any of the embodiments of the invention the rods are only inserted in a portion of the spaces between adjacent tube rows. Figures 19 to 23 further illustrate rings 166 surrounding tubes 150 which form a tube bundle 152 with the rods passing through tube bundle 152 and attached to rings 166 employing tie down members 70 bolted to rings 166 using bolts 180.

The baffles in Figures 19 to 23 are constructed in the same manner as those shown in Figures 5 to 9 in that rings 166 of Figures 19 to 23 and rings 66 of Figures 5 to 9 are simply annular rings and not the same type of ring as rings 30 shown in Figures 1 to i which are cut with an inside edge to fit partially around the tubes to give partial support thereto. Since rings 166 are the annular rings. use of additional rods 162a are required. Rods 162a are required for the same reason as rods 62a and 64a in Figures 6 to 9 as previously described. Further the baffles in any embodiment of the invention can be positioned in a plane which is not perpendicular to the longitudinal axis of the tubes as well as in a plane which is perpendicular to said axis.It is presently preferred to construct the support apparatus of the invention using baffles which are positioned in a plane perpendicular to the longitudinal axis of the tubes because the rings 166 can be circular in shape as opposed to the more difficult to construct elliptical shape required for baffles positioned in a plane which is not perpendicular to the longitudinal axis of the tubes. Of course it is understood that baffles positioned in a plane perpendicular to the longitudinal axis of the tubes as well as baffles positioned in a plane not perpendicular to said axis are within the scope of the present invention.

It is emphasized that a supporting apparatus in accordance with the present invention only requires that the rods in each baffle inserted in the spaces between adjacent tube rows in one plurality of parallel tube rows are inserted into less than the total number of such spaces and further that when the rods are inserted into such spaces in the baffles that at least three baffles are required to radially support each and every tube in the tube bundle. It is immaterial whether the rods are inserted in adjacent spaces, alternate spaces, two adjacent spaces followed by skipping two spaces or any variation desired. The baffles shown in Figures 6 to 9 are essentially identical to the baffles shown in Figures 20 to 23 for all practical purposes.

The 6 baffles shown in Figures it) to 15.

illustrating another embodiment of the invention, are required to make a baffle set using the tube layout there shown. The baffle set provides radial support for each tube and only three rods are tangent to each tube. Three rods positioned around each tube are the minimum number required to provide radial support for each tube so long as the total spacing between the three rods is in excess of 180 degrees. which is the case in Figures 10 to 15.

In Figures 10 to 15 baffles 90. 92 94. 96.

98 and 100 respectivelv are shown comprising rings 102 surrounding tubes 104 in the form of a tube bundle in which the tubes are laid out on a hexagonal pitch. Rings 102 are the same annular shape as rings 66 shown in Figures 5 to 9. In baffles 90 and 92. rods 1()6 are positioned in the space 108 between parallel tube rows in a first plurality of parallel tube rows. In baffles 94 and 96 rods 114 are positioned in spaces 116 between parallel tube rows of a second plurality of parallel tube rows. In baffles 98 and 100 rods 118 are positioned in spaces 12O be tween parallel tube rows of a third plurality of parallel tube rows. The rods of each baffle are held in place by tie down members 110 bolted to rings 102 using bolts 112.

The minimum number of rods in a baffle set is the number sufficient for the baffle set to provide radial support for each tube forming the tube bundle. It is preferred that this functional limitation also be used to determine the maximum number of rods in a baffle because the pressure drop across the shell side of a shell and tube heat exchanger is the lowest when the least number of rods are used to form the baffles; however, it is essential to use enough rods in each baffle for the baffle set to provide radial support for each tube.

Where a baffle set consists of 4 baffles, the rods in each baffle will be positioned in roughly 50 to 60 percent of the spaces between adjacent tube rows in one plurality of parallel tube rows. If a baffle set consists of 8 baffles. then roughly 25 to 35 percent of the spaces will contain rods. If the tubes of the tube bundle are laid out on a square pitch. then a baffle set must contan at least 4 baffles or a baffle set can contain even numbers above 4. such as 6. 8, 10, 12 etc. If the tubes of the tube bundle are laid out on triangular pitch. then a baffle set must contain a minimum of 3 baffles; however multiples of 3 can be used to constitute a baffle set. such as 6. 9. etc.. although it is also possible to use 4 baffles or an even number of baffles above 4 to constitute a baffle set.If the tubes are laid out on a hexagonal pitch as shown in Figures 10 to 15, then at least 6 baffles per baffle set are required to provide radial support for each tube in the tube bundle. The number of baffles constituting a baffle set as described above must not be confused with the total number of baffles used in the tube bundle as this latter number can be any number above the minimum number required in a baffle set and the total number of baffles in the tube bundle is otherwise independent of the number of baffles in a baffle set.

It is apparent from the above description of Figures 1 to 15 and Figures 19 to 23 that the minimum number of baffles per baffle set is dependent upon the tube layout.

Three different tube layouts are shown in the drawings: however. other tube layouts are possible in which the minimum number of baffles in a baffle set may be other than those specifically discussed. But with any tube lavout. at least three baffles per baffle set are required to practice the present invention and the specific tube layouts herein discussed are presented for the purposes of illustration and are not intended to limit the broad invention.

It is presently believed that the shell side pressure drop for any given exchanger designed in accordance with the invention will be largely localized at or near the inlet and outlet regions of the shell, and thus it is recommended to employ inlet and outlet shell side nozzle designs having low turbulence and pressure drop characteristics. For example, diverging nozzles, multiple nozzles and annular distributors provide low pressure drop and low turbulence in the shell side inlet and outlet regions.It is important in designing an apparatus in accordance with the invention to note that the fluid on the shell side of the apparatus flows essentially in the longitudinal direction, that is, essentially parallel to the longitudinal axis of the tubes; therefore it is recommended that longitudinal flow channels or passageways which are relatively large in relation to the clearance between the tubes be minimized either by actual elimination of such passageways or blocking off such passageway using suitable baffles.

Inherent in the design of an apparatus shown in Figures 1 to 15 and Figures 19 to 23 is the incorporation of a ring baffle and a foundation for the rods forming the rod baffle. The ring baffle restricts the flow of the shell side fluid between the shell and the tube bundle and also provides a foundation to attach the rods in order to form the rod baffle.

It is appreciated bv those skilled in the art that heat exchangers designed in accordance with the invention can be designed incorporating a variety of the configurations known in the art such as U-tubes. multiple tube passes. or floating head designs.

As mentioned previously it is preferred to position the outer rings and thus the baffles in a plane perpendicular to the longitudinal axis of the tube bundle because with the outer rings in such position it is generally easier to construct the baffles: however.

baffles lying in a plane which is not perpendicular to the longitudinal axis of the tube bundle are within the scope of the invention.

In an effort to more fullv describe the invention the following example is provided.

Exanlple Three countercurrent, single pass shell and tube heat exchangers were constructed and tested. Each heat exchanger contained 137 carbon steel tubes. 9.7 feet (2.96 m) long with a 0.5 inch (1.27 cm) outside diameter. laid out on a square pitch of 0.6875 inch (1.71(3 cm) and having a shell inside diameter of 10.25 inches (26.04 cm).

Each heat exchanger was designed to have the same tube support distance. 9.X inches (24.89 cm). Both the shell side fluid and the tube side fluid were water with the tube flow rate equal to 4.2 feet per second (1.28 m sec.). 115.80() pounds per hour.Hot fluid (shell side) inlet temperatures were generally about 165"F (73.9"C) with the cold fluid (tube side) inlet temperatures employed being appropriate values between 80"F (26.7 C) and 1300F (54.4"C). Thereby the temperature approach at each end of a tested exchanger was maintained greater than 10 F to provide adequate heat exchange driving force, as known to those skilled in this art, from which consistant test results were calculated. The shell side flow rate. W, was varied from about 2500 to 20,000 pounds per hour (1134 to 9072 Kg/hr).Figures 16, 17 and 18 graphically illustrate the results of the tests in which the overal heat transfer coefficient, U; pressure drop AP; and the ratio UlAP were determined as functions of the shell side flow rate. W, by appropriate methods of calculation known to those skilled in this art from data taken during comparable test runs.

Conversion factors are on each of the drawings for converting the data from English Units to the International System of Units.

One heat exchanger design employed was the double segmental plate baffle type referred to hereinafter as the segmental plate baffle heat exchange. The baffle cut was 50 percent that is. the baffle cut was such that it would provide an open area equal to substantially 50 percent of the total cross-sectional area of the shell less the space occupied by the tubes. This type of exchanger is frequently used and considered one of the standard designs in the industry.

The tube support distance was 9.8 inches (24.89 cm): thus the baffle spacing was 4.9 inches (12.45 cm).

The second heat exchanger design employed was that described in U.S. Patent 3,708.142, hereinafter referred to as the crisscross rod baffle heat exchanger. In this design each baffle provides radial support for each tube in the tube bundle; thus for a tube support distance of 9.8 inches (24.89 cm) a baffle spacing of 9.8 inches (24.89 cm) was used.

The third heat exchanger design was that of the present invention, referred to hereinafter as the vertical segmental rod baffle heat exchanger constructed in accordance with Figures 5 through 9 previously described except that the outer rings were constructed in accordance with the embodiment shown in Figures 2 to 4. Four baffles per baffle set were used with a baffle spacing of 2.4 inches to provide a tube support distance of 9.8 inches (24.89 cm). the same as used in the other two heat exchangers previously described. The number of rods used in each baffle was 24 which was the minimum number which provided radial support for each tube in the tube bundle.

The roods in each baffle were positioned in approximately 50 percent of the spaces between adjacent tube rows in one plurality of parallel tube rows.

As shown in Figure 16, the vertical segmental rod baffle heat exchanger provided a substantial and unexpected increase in the heat transfer coefficient over that of the other two heat exchangers. Throughout the entire range of flow rates employed the segmental rod baffle heat exchanger of the invention produced heat transfer coefficients ranging from approximately 11 to 14 percent higher than the double segmental plate baffle heat exchanger. and approximately 50 to 60 percent higher than the crisscross rod baffle heat exchanger.

Figure 17 shows that the shell side pressure loss (in pounds per square foot) of the vertical segmental rod baffle heat exchanger was almost as low as that of the crisscross rod baffle heat exchanger and that the pressure drop for either of those two heat exchangers was substantially better than the pressure loss of the double segmental plate baffle heat exchanger. The pressure drop data for the vertical segmental rod baffle exchanger of the invention is particularly surprising since it was this heat exchanger that provided the best heat transfer coefficients.Heat exchangers employing the tube support apparatus of the present invention are not only capable of operating at a much lower pressure drop than that of a double segmental plate baffle exchanger of comparable size but at the same time provide substantially higher heat transfer coefficients as compared to a comparable double segmental plate baffle heat exchanger or a comparable crisscross rod baffle heat exchanger.

Figure 18 shows that the ratio of the heat transfer coefficient to the pressure loss for a given shell side flow rate is substantially higher for the vertical segmental rod baffle heat exchanger as compared to the prior art heat exchangers. This graph, combining the results of Figures 16 and 17 provides an overall picture of the excellent results obtained employing the tube support method and apparatus of the present invention because both the pressure drop and the heat transfer coefficient are taken into consideration at the same time.

These three graphs and especiallv Figure 18 clearly establish that the present invention definitely provides unexpected results as compared to prior art heat exchangers including one in which the baffles were constructed with rods.

WHAT WE CLAIM IS: 1. A tube bundle for a heat exchanger.

which comprises a plurality of tubes arranged in a plurality of spaced parallel rows. the tubes within each row being spaced one from the other. and a plurality of baffles spaced one from the other along the length of the tube bundle, each baffle comprising an outer ring surrounding the tube bundle and a plurality of parallel rods extending across and forming a set of parallel chords to the ring, the rods in each baffle extending through the spaces between said tubes and serving to support said tubes in their parallel array, the number of rods in each baffle being insufficient to fill all the spaces between the adjacent rows of tubes when viewed along the axis of the tube bundle. and the number of baffles and the number of rods in each baffle being such that each tube is radially supported, as hereinbefore defined. in said bundle at points intermediate the tube ends.

2. A tube bundle according to claim 1, wherein the baffles lie in planes perpendicular to the axis of the tube bundle.

b 3. A tube bundle according to claim 1 or 2, wherein the number of rods in each baffle does not exceed the minimum number required to provide, in conjunction with the rods of the other baffles, said radial support for each tube.

4. A tube bundle according to any one of the preceding claims, wherein the tubes are laid out on a triangular pitch and there are at least three baffles with rods radially supporting said tubes at three points located around the circumference of each tube at 1200.

5. A tube bundle according to any one of claims 1-3. wherein the tubes are laid out on a square pitch and there are at least four baffles with rods radially supporting said tubes at four points located around the circumference of each tube at 90".

6. A tube bundle according to any one of claims 1-3. wherein the tubes are laid out on a hexagonal pitch and there are at least six baffles with rods radiallv supporting said tubes at six points located around the circumference of each tube at 60".

7. A tube bundle according to any one of the preceding claims. wherein the rods in each baffle are all located in adjacent parallel spaces between said rows of tubes.

8. A tube bundle according to any one of claims 1-6. wherein the rods in each baffle are located in alternate parallel spaces between said rows of tubes.

9. A tube bundle according to claim 1 constructed substantially as hereinbefore described with reference to Figures 1-4. 5-9 or 1()-15 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. approximately 50 percent of the spaces between adjacent tube rows in one plurality of parallel tube rows. As shown in Figure 16, the vertical segmental rod baffle heat exchanger provided a substantial and unexpected increase in the heat transfer coefficient over that of the other two heat exchangers. Throughout the entire range of flow rates employed the segmental rod baffle heat exchanger of the invention produced heat transfer coefficients ranging from approximately 11 to 14 percent higher than the double segmental plate baffle heat exchanger. and approximately 50 to 60 percent higher than the crisscross rod baffle heat exchanger. Figure 17 shows that the shell side pressure loss (in pounds per square foot) of the vertical segmental rod baffle heat exchanger was almost as low as that of the crisscross rod baffle heat exchanger and that the pressure drop for either of those two heat exchangers was substantially better than the pressure loss of the double segmental plate baffle heat exchanger. The pressure drop data for the vertical segmental rod baffle exchanger of the invention is particularly surprising since it was this heat exchanger that provided the best heat transfer coefficients.Heat exchangers employing the tube support apparatus of the present invention are not only capable of operating at a much lower pressure drop than that of a double segmental plate baffle exchanger of comparable size but at the same time provide substantially higher heat transfer coefficients as compared to a comparable double segmental plate baffle heat exchanger or a comparable crisscross rod baffle heat exchanger. Figure 18 shows that the ratio of the heat transfer coefficient to the pressure loss for a given shell side flow rate is substantially higher for the vertical segmental rod baffle heat exchanger as compared to the prior art heat exchangers. This graph, combining the results of Figures 16 and 17 provides an overall picture of the excellent results obtained employing the tube support method and apparatus of the present invention because both the pressure drop and the heat transfer coefficient are taken into consideration at the same time. These three graphs and especiallv Figure 18 clearly establish that the present invention definitely provides unexpected results as compared to prior art heat exchangers including one in which the baffles were constructed with rods. WHAT WE CLAIM IS:

1. A tube bundle for a heat exchanger.

b

3. A tube bundle according to claim 1 or 2, wherein the number of rods in each baffle does not exceed the minimum number required to provide, in conjunction with the rods of the other baffles, said radial support for each tube.

10. A tube bundle according to claim 1,

constructed substantially as hereinbefore described with reference to Figures 19-23 of the accompanying drawing.

11. A heat exchanger comprising at least one tube bundle as claimed in any one of the preceding claims.