Flexible acoustic baffle for staggered tube banks

Abstract: A corrugated-shaped acoustic baffle unit (12) for insertion into a tube bundle (10) of a tubular-type heat exchanger (13) having parallel staggered tubes to prevent flow-induced vibrations in the heat exchanger (13). The baffle unit (12) is formed of at least two helical-shaped spacer members each rotatably attached to a flexible connecting barrier member, such as a fabric or metal mesh material or formed by multiple adjacent bars or tubes each attached to the rotatable spacer members. The flexible corrugated-shaped baffle unit (12) can be inserted between adjacent parallel tubes of a heat exchanger by rotating simultaneously the helical-shaped members. After insertion of the baffle unit, the ends of the helical-shaped members are connected together so as to prevent their further rotation and thereby secure the baffle unit firmly in place between adjacent tubes of the heat exchanger (13).

Description: This invention pertains to acoustic baffles provided between adjacent rows of tubes in tubular type heat exchangers. It pertains particularly to flexible corrugated-shaped baffles located between adjacent staggered rows of tubes in a tube bank to prevent flow induced acoustic vibrations in a tubular heat exchanger. Flow channels of heat exchangers or steam generators containing tube arrays can be subject to acoustical resonance vibrations excited by flow of air, gas, or steam transversely across the tubes. Such resonance occurs when the frequency of a flow periodicity inside the tube bank coincides with an acoustical (standing wave) mode of the flow channel. The acoustical modes primarily excited are those which are related to the dimension perpendicular to both the fluid flow direction and the tubes axes. At resonance, an intense sound can be generated which is typically sufficient to cause noise and vibration problems within the heat exchanger. The elimination of such resonant condition and vibration may be achieved by suppression of the excited acoustic (standing wave) modes. The commonly used method of suppressing standing waves is by use of acoustic baffles. Typically, plate baffles are placed within the tube bank parallel with the flow direction. These baffles divide the flow chamber into separate flow channels, each having a higher natural acoustic frequency than the natural frequency of the unbaffled chamber. The number of baffles used and their location within the width of the flow channel will depend on the acoustical mode frequencies which need to be achieved in order to prevent resonances. In tubular heat exchangers having a staggered tube arrangement, there is ordinarily no room to place a baffle in the direction parallel with the flow. The only way a baffle could be inserted into the staggered tube bundle would be if space for a baffle was made by eliminating a number of tubes in alignment. However, such a solution represents a great complication in construction in that it affects the uniformity of the tube bundle and reduces the total heat transfer surface. Also for a retrofitting arrangement in heat exchangers for which acoustic baffles have to be inserted to eliminate noise in an operating unit, a structural modification involving tube removal would be prohibitively expensive. The general use of baffles in tubular heat exchangers is known. For example, U.S. Patent No. 1,711,622 to Vennum discloses a baffle arrangement used for water tube steam boilers in which a bank of vertically extending tubes have a plurality of straight baffles which extend at an angle through spaces between some of the rearward tubes, so as to protect those tubes from direct contact with the hot furnace gases. U.S Patent No. 2,655,346 to Corbitt et al discloses a heat exchanger having a matrix of parallel tubes carrying a first fluid, and having flat baffles arranged in various configurations to control transverse flow of a second fluid past the tubes. Such baffles are spaced apart so as to control fluid flow generally transverse to the tubes, but they do not support the tubes. U.S. Patent No. 3,163,208 to Cuzzone et al discloses use of transverse braces for supporting and inhibiting vibration of elongated finned tubes used in heat exchangers; but corrugated shaped baffles are not utilized. U.S. Patent No. 3,720,259 to Fritz et al discloses a heat exchanger having spirally wound tubes which are supported by a spacer structure. The spiral tubes are separated into groups by a series of conical-shaped straight baffles which are oriented upwardly and provide flow passages generally transverse to the tube bundle. The tubes are each supported by upwardly extending curved wires each having a wave-shaped configuration. U.S. Patent No. 4,204,570 to Eisinger discloses helical-shaped tube spacers placed between adjacent tubes in heat exchanger to support the tubes, but the spacers do not provide any useful baffling function for fluids passing transversely through the heat Exchanger. U.S. Patent No. 4,662,434 to Porowski discloses use of straight vibration dampening spacer tubes which extend transversely between adjacent tubes in a heat exchanger to laterally support the tubes, but the spacer tubes provide no significant acoustic baffling function for fluids flowing external to the heat exchanger tubes. U.S. Patent No. 4,796,695 to Cannon discloses tubular heat exchanger having parallel tubes supported by corrugated slats positioned in empty lanes to separate adjacent rows of tubes. The corrugations extend along the length of the slat to support the tube and generate turbulence in transverse flow of gas, and are made of resilient material such as spring steel so as to press against the adjacent rows of tubes. Although the prior art has disclosed various types of baffles for use in tubular heat exchangers, it has apparently not provided flexible acoustic baffles which are corrugated shape and which can be inserted into staggered tube banks of heat exchangers to eliminate resonant flow conditions and acoustic vibrations in the heat exchangers. According to the invention there is provided an acoustic baffle unit adapted for insertion between adjacent tubes of a tubular type heat exchanger, comprising a flexible barrier and at least two elongated helical-shaped rotatable spacer members, the spacer members being rotatably attached to the the flexible barrier, the barrier including means for rotatable attachment of the forward and rear ends of the spacer members to leading and trailing ends of the barrier, and means for rotating each spacer member provided at the rear ends of the spacer member whereby the spacer members and the barrier can be inserted between the adjacent tubes of a heat exchanger by simultaneously rotating the spacer members. The acoustic baffle unit according to the invention can be inserted between adjacent staggered rows of tubes in tubular heat exchangers so as to press against the tubes and so prevent flow-induced acoustic vibrations within the tube bank. The helical-shaped spacer members are made of a rigid material such as metal or reinforced plastics material and have a pitch spacing consistent with the pitch of the tube bank in which the baffle unit is installed. The flexible barrier can be made of woven material, such as cloth or metal mesh construction. Alternatively, the barrier member can be formed by multiple adjacent parallel bars, strips or tubes each flexibly attached together and rotatably attached to each of the rotatable helical spacer members. After installation of the baffle unit in a tubular heat exchanger, the helical-shaped spacer members are connected together at least at their trailing or rear ends or preferably at both their leading and trailing ends, so as to prevent further rotation of the spacer members and thereby maintain the baffle unit in place between the tubes of the tube bank. The invention also provides a tubular type heat exchanger assembly having a plurality of adjacent parallel tubes and at least one flexible acoustic baffle unit according to the invention inserted between adjacent rows of tubes in the heat exchanger. The flexible acoustic baffle unit can be inserted into the tube bundle in the transverse flow direction by rotation of the helical-shaped spacer members. The invention also includes the method steps required for inserting the flexible acoustic baffle unit between adjacent rows of tubes of a tubular type heat exchanger by simultaneously rotating the spacer members, and comprises: (a) placing the leading edge of a baffle unit according to the invention between two adjacent rows of tubes; (b) simultaneously turning the helical-shaped rotatable spacer members connected to the flexible barrier, so that the forward end of the baffle unit enters the space between the two adjacent rows of tubes, and (c) continuing turning the helical-shaped spacer members until the baffle unit is entirely inserted into the tube bundle. Advantages of the acoustic baffle unit according to the invention for tubular heat exchangers are that it can be installed between adjacent tubes in existing heat exchangers, so as to prevent flow induced acoustic vibrations therein, all without the need for substantial modification or reconstruction of the heat exchanger assembly. The sinewave-shaped acoustic baffle unit according to the invention is especially suited for being retrofitted into a heat exchanger tube bundle for the elimination of noisy resonant conditions in such heat exchangers. Embodiments of the invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 shows schematically a corrugated acoustic baffle unit inserted into a staggered tube bank of a tubular heat exchanger in accordance with the invention; Fig. 2 shows a sinewave-shaped flexible acoustic baffle unit made of a flexible woven material attached to rotatable helical spacer members; Fig. 3 shows an end view taken at lines 3-3 of Fig. 2; Fig. 4 shows an alternative embodiment of the invention in which the acoustic baffle unit is made of a plurality of adjacent parallel bars or tubes attached to rotatable helical spacer rod members; Fig. 5 shows a partial end view taken at lines 5-5 of Fig. 4; Fig. 6 shows some details of the adjacent bars or tubes which form the barrier member of the acoustic baffle unit of figs. 4 and 5; Fig. 7 shows typical hinged connecting joints provided between adjacent barrier bars or tubes; Fig. 8 shows a schematic view of an acoustic baffle unit in position to be inserted into a staggered tube bank; Fig. 9 shows the baffle unit after being inserted in the staggered tube bank of a heat exchanger; and Figs. 10, 11, and 12 show various useful configurations of acoustic baffle units after being inserted into a tube bank of a heat exchanger. As seen in Fig. 1, a bank of parallel staggered tubes 10 are provided within a pressurizable enclosure or shell 11 of a heat exchanger 13, such that a first fluid can flow within the tubes 10 and a second fluid can flow generally transversely across the tubes at a velocity sufficient to produce acoustic vibrations within the enclosure. The enclosure 11 can be made either generally rectangular or cylindrical-shaped depending upon the configuration desired for the heat exchanger 13. A corrugated shape acoustic baffle unit 12 is shown installed between adjacent tubes 10. As shown in greater detail in Figs. 2 and 3, the flexible acoustic baffle unit 12 is composed of two principal components, including a plurality of elongated helical-shaped spacer rod members 14 each rotatably attached to a flexible barrier member 16. The spacer members 14 are each rotatably attached at points 14a, 14b, 14c, etc. to the flexible barrier members 16, so as to form the acoustic baffle unit 12. The helical spacers 14 serve the dual function of maintaining the sinewave-shaped baffle geometry and permitting insertion of the flexible acoustic baffle unit 12 transversely into a tube bundle between adjacent staggered rows of tubes 10 during manufacture of heat exchanger 13. The acoustic barrier member 16 provides the body of the baffle unit 12, and serves as an acoustic wall for dividing the second fluid flow channel 11a into separate chambers having different acoustic properties. In one useful embodiment of the invention, the flexible barrier member 16 is made of a woven material such as cloth or fabric including a metal wire mesh, as shown in Figs. 2 and 3. The flexible barrier member 16 has suitable multiple attachment means 15 such as loops or rings provided at each end and also at intermediate positions along the width dimension W of the barrier member 16 for its attachment to each of the rotatable spacer members 14. Each rotatable spacer member 14 has its forward end rotatably attached at 17 to the leading end 16a of the barrier member 16, and its rear end rotatably attached at 18 to the trailing end 16b of the barrier member 16. Also, a rotation means 19 such as a nut is provided attached to the rear end of each helical spacer member 14. By this construction, it will be understood that by substantially simultaneous rotation of all the spacer rod members 14 by the rotation means 19, the flexible barrier unit 12 will be drawn incrementally into the space between adjacent rows of staggered tubes 10. As shown in Figs. 2 and 3, at least three helical spacer rod members 14 are preferably provided substantially equally spaced along the length L of the baffle unit 12. Each spacer member 14 spans the entire height or width W of the acoustic baffle unit 12, and the spacer members 14 are each rotatably attached to the baffle barrier 16 by the multiple loops 15 which encircle the rotatable spacers 14. Because the ends of the spacer members 14 are each firmly rotatably attached at 17 and 18 to the leading and trailing edges, respectively, of the acoustic baffle member 12, so as to permit rotation of the spacer members at these connection points, the baffle unit can be conveniently inserted between adjacent tubes 10 in a tube bundle. The relative dimensions of the helical-shaped spacer members 14 and the loops 15 are determined by the need to allow ease of rotation of the spacer members and also provide firm lateral support and control of the flexible barrier member 16. Suitable relative dimensions between the spacer members 14 and the loops 15 should provide diametrical clearance of 1.5-3.2 mm (0.060-0.125 inches). The preferred construction for the attachments of the barrier 16 to the spacer members 14 in a fabric-type baffle unit are metal rings attached to the fabric at suitable spaced intervals. Alternatively, a continuous flexible tube-like containment member for the spacer members 14 can be either made an integral part of the barrier fabric or attached to the barrier fabric by suitable fasteners. Suitable materials for the flexible baffle unit 12 will be determined by the fluid temperatures encountered as well as cost considerations. Steel spacer members and barriers made of steel mesh are preferred primarily because of stiffness provided in the high flow and pulsation environment, and barriers made of a ceramic fibre material are desired where low weight is an important consideration. In an alternative embodiment of this invention as shown in Figs. 4 and 5, the baffle unit 22 is formed of a plurality of adjacent narrow parallel metal strips, bars or tubes 20 which are flexibly attached together, and are also attached to at least two rotatable helical spacer members 24. Cross-sectional shapes of suitable bars, strips or tubes which can be adapted for use as the barrier member 26 of the Figs. 4 and 5 embodiment as shown by Fig. 6. For this alternative embodiment, the helical-shaped spacer rod members 24 are each inserted through transverse holes 25 provided in each of the bars or tubes 20 near their opposite ends. Also, transverse holes 25 can be provided at an intermediate position or positions as needed along the length of the barrier bars or tubes 20 for receiving an additional spacer rod 24. The diameter or major width dimension of the barrier bars or tubes 20 exceeds that of the spacer rod members 24. The spacer rod diameter will usually be approx. 5.0 to 12.7 mm 0.20 to 0.50 inch, and the barrier bars or tubes will have a diameter or width of approx. 7.6 to 19.1 mm 0.30 to 0.75 inch. The adjacent parallel bars, rods or tubes 20 are also each attached together by a flexible connection member 23, such as a connecting cable strung through transverse holes 25a, as generally shown by Fig. 6, so that a tensile force can be transmitted transversely across the barrier member 26 during its installation in a tube bank. Alternatively, the adjacent bars, rods or tubes 20 can be connected together by multiple hinged joints 23a provided between the adjacent bars, rods or tubes 20, as shown by Fig. 7. The construction of the barrier member 26 must be sufficiently flexible to offer very little resistance for it being shaped into the sinewave geometry needed during insertion of the baffle unit 22 between adjacent tubes 10 of a heat exchanger using the helical-shaped rotatable spacer members 24. The spacing between adjacent helical spacer member rods 14 is determined by the type of baffle unit construction used. A baffle unit 12 having a barrier 16 made of flexible fabric per Figs. 2 and 3 requires relatively closely spaced spacer rods located approx. 229 to 305 mm 9 to 12 inches apart, in order to maintain the flexible baffle unit 12 aligned and sufficiently stiff along the tubes of the tube bundle. However, a baffle unit 22 made of multiple adjacent bars, rods or tubes 20 per Figs. 4 and 5 can tolerate a larger spacing between the spacer member rods 24, because the bars, rods or tubes 20 are relatively stiff as compared to the fabric barrier 16, and the spacing of the spacer rods 24 will be determined by the need to limit deflections of the bars, rods or tubes 20 of the barrier member 26. The spacing between the helical spacer rods 24 of a typical baffle unit construction can be in the range of approx. 914 to 1829 mm (36 to 72 inches). The entire baffle unit 22 including the connected rods or tubes 20 is constructed so as to withstand a tensile force applied at its leading edge 26a by the helical spacer members 24 during insertion of the baffle unit into a tube bank. The helical spacer members each have their forward end 27 rotatably attached to the leading end 26a of the baffle unit in such a way that the spacers can exert a forward force upon the leading edge in the direction of the baffle insertion, per Fig. 8. Similarly, the spacer members rear end 28 is rotatably attached to the trailing end 26b of barrier 26. Also, a rotation means 29 such as a nut is attached to the rear end of each helical spacer member 24 to provide for rotation of the spacer members by a suitable tool (not shown) as required for installation of the flexible baffle unit 24 in a tube bank. The preferred construction material for the spacer members and the barrier bars or tubes 20 is steel. Carbon steel is used for spacers and baffle units which are exposed to cold air or gas temperatures up to about 426°C (800°F), and alloy steel including stainless steels are used for higher gas temperature environments up to 648-981°C (1200-1800°F). This invention also includes within its scope a tubular type heat exchanger 13 containing multiple rows of parallel tubes 10, and which has the corrugated acoustic baffle unit 12 installed therein as generally shown in a schematic cross-sectional view by Fig. 1. A description of such a tube type heat exchanger is provided by U.S. Patent No. 4,204,570, which is incoporated herein by reference to the extent necessary. The method or procedure for insertion of the flexible acoustic baffle unit 12 into a tube bundle 10 is generally shown by Figs. 8 and 9. The geometry of the helical spacer members 14 and the geometry of the sinewave-shaped barrier member 16 must conform to the geometry of the tube bundle and the direction of the insertion of the baffle unit between the adjacent tubes 10. The overall thickness of the acoustic baffle unit 12 must also conform to the available gap or space between adjacent tubes 10, both for ease of insertion and firmness of support provided by the tubes. Depending upon the orientation of the tube bundle cross-section relative to the fluid flow direction, the baffle unit insertion can be done in either the direction of a triangle apex (no see-through direction) as shown by Fig. 10, or in the direction of the triangle base (see-through direction) per Fig. 11, or in a diagonal direction for an in-line tube bank as shown by Fig. 12. The normal method or procedure for installation insertion of the corrugated acoustic baffle unit 12 into the tube bundle is described below: (a) Inspect the baffle unit 12, 22 to determine that it is truly sinewave-shaped along its entire length, i.e., the helical spacer members 14,24 holding the shape are oriented substantially parallel to each other, and the "peaks" and "valleys" of all the spacer members are in the same relative positions. (b) Determine that the barrier member 16, 26 can take a "tensile" load in the direcion of its height. This is achieved by the integrity of the fabric barrier material. For a barrier member made of adjacent multiple bars or tubes, the tensile load-carrying ability is provided by the cable-type ties 23 extending between the bars being capable of withstanding tensile loading. (c) Determine that the leading edge of the baffle barrier member is firmly attached to the leading ends of each helical spacer member, with sufficient allowance for rotation of the spacer relative to the barrier. Similar end ties are also necessary at the trailing edge of the baffle unit. (d) Determine that each helical spacer member 14, 24 can be rotated freely relative to the acoustic baffle barrier 16, 26. The features listed above are normal characteristics of a properly designed and manufactured acoustic baffle unit according to the invention. Insertion of the baffle unit into a heat exchanger tube bank includes the following steps: (a) Select location for baffle unit insertion between tubes of the heat exchanger. (f) Hold the baffle unit 12, 22 so that along its entire length the baffle unit faces the particular tube gap within which it is to be inserted. (g) Commence inserting the baffle unit by rotating all helical spacer members 14, 24 substantially simultaneously. For spacer members having a right-handed helix, turn the spacers in a clockwise direction. (h) Continue turning the helical spacer members until the entire baffle unit 12, 22 is inserted into the heat exchanger tube bundle to its full height or width. (i) Connect the trailing ends of all helical spacer members to each other by a bar 30 rigidly attached such as by welding to each helical spacer member 14, 24. This connection will prevent the acoustic baffle unit 12, 22 from moving further relative to the tube bundle. Also similarly connect together the leading ends of the helical spacers. (j) Provide stops at each end of the acoustic baffle unit in tube axial direction,so as to prevent the entire baffle from sliding in a tube axial or longitudinal direction. This invention will be better understood by reference to the following examples, which should not be construed as limiting the scope of the invention. EXAMPLE 1 A flexible acoustic baffle unit is constructed which consists of four helical-shaped steel spacer rods which are rotatably attached to a flexible ceramic fabric barrier member at several places along the length of the rods. The helical spacer rods are inserted through a plurality of loops which are attached on to the flexible fabric at spaced intervals along the width of the barrier member. Important structural details of the baffle unit are provided below: This flexible acoustic baffle unit containing fabric barrier can be inserted between adjacent tubes of a heat exchanger having 0.750 in. (approx. 19 mm) diameter tubes on a staggered pattern with a pitch spacing of 1.0 in. (approx. 25.4 mm) and a triangular (staggered) tube pattern. EXAMPLE 2 An alternative flexible baffle unit is constructed which consists of two helical-shaped metal spacer rods which are each rotatably attached to a series of adjacent parallel metal tubes which form a barrier member. The tubes each contain two transverse holes in alignment with the metal helical spacer rods, which are inserted through each of the transverse holes in each tube. The tubes are also tied together by two steel cables, which each extend transversely through holes in the tubes so that the entire baffle unit can take a "tensile" force in the direction of its insertion into a tube bank. Important structural details of this baffle unit are as follows: Any desired number of this baffle unit containing multiple parallel tubes can be inserted between adjacent parallel tubes of a heat exchanger in which the tubes are 5 inches (approx. 127 mm) diameter with a pitch of 6 inches (approx. 152 mm) in a staggered pattern.

Claims: An acoustic baffle unit (12,22) adapted for insertion between adjacent tubes (10) of a tubular type heat exchanger (13), comprising a flexible barrier (16,26) and at least two elongated helical-shaped rotatable spacer members (14,24), the spacer members being rotatably attached to the flexible barrier (16,26), the barrier (16,26) including means (15,25) for rotatable attachment of the forward and rear ends (17,18,27,28) of the spacer members (14,24) to leading and trailing ends (16a, 16b, 26a, 26b) of the barrier (16,26), and means (19,29) for rotating each spacer member (14,24) provided at the rear ends (18,28) of the spacer member (14,24), whereby the spacer members (14,24) and the barrier (16,26) can be inserted between adjacent tubes (10) of a heat exchanger (13) by simultaneously rotating the spacer members (14,24). An acoustic baffle unit as claimed in Claim 1 in which said spacer members (14,24) are rotatably attached to the flexible barrier (16,26) by being inserted through a plurality of loops (15) attached to the barrier (16,26) at spaced intervals. An acoustic baffle unit as claimed in Claim 1 or Claim 2 in which there are at least three rotatable spacer members (14,24). An acoustic baffle unit as claimed in any preceding claim in which flexible barrier (16) is formed of a flexible woven material. An acoustic baffle unit as claimed in any of Claims 1 to 3 in which the flexible barrier (26) is formed of a plurality of adjacent elongated parallel members (20) attached together by at least two flexible connecting members (23,23a). An acoustic baffle unit as claimed in Claim 5 in which the adjacent elongated parallel members (20) are attached together by at least two connecting cable means (23) extending laterally through the parallel members (20). An acoustic baffle unit as claimed in Claim 5 in which the adjacent elongated parallel members (20) are attached together by multiple hinged joints (23a). Use of an acoustic baffle unit (12,22) as claimed in any preceding claim to prevent flow induced acoustic vibrations in a heat exchanger by inserting it between two adjacent rows of tubes (10) in a heat exchanger (13) so as to direct a fluid flowing transversely past the tubes (10). A tubular type heat exchanger (13) comprising a plurality of parallel extending tubes (10) provided within a pressurizable enclosure (13), and at least one acoustic baffle unit (12,22) as claimed in any of Claims 1 to 7 extending between adjacent rows of the parallel tubes (10) so as to direct a fluid flowing transversely past the tubes (10) and prevent flow-induced acoustic vibrations in the heat exchanger (13). A heat exchanger as claimed in Claim 9 in which the parallel tubes (10) are provided in staggered rows within the pressurizable exchanger (13). A method of inserting a flexible corrugated acoustic baffle unit (12,22) between adjacent rows of tubes (10) of a tube bundle, comprising: (a) placing the leading edge of a baffle unit as claimed in any of Claims 1 to 7 between two adjacent rows of tubes; (b) simultaneously turning the helical-shaped rotatable spacer members (14,24) connected to the flexible barrier (16,26), so that the forward end of the baffle unit (12,22) enters the space between the two adjacent rows of tubes (10), and (c) continuing turning the helical-shaped spacer members (14,24) until the baffle unit (12,22) is entirely inserted into the tube bundle. A method as claimed in Claim 11 including after step c connecting together at least the rear ends (18,28) of the helical-shaped spacer members (14,24) to stabilize the baffle unit (12,22) in place in the tube bundle.

Inventors: EISINGER FRANTISEK L, EISINGER, FRANTISEK L.
Applicants: FOSTER WHEELER ENERGY CORP, FOSTER WHEELER ENERGY CORPORATION
Application year: 1990
Main classification: F28F9
IPC codes: F28F9, G10K11