MXPA02000709A

MXPA02000709A - Enhanced crossflow heat transfer.

Info

Publication number: MXPA02000709A
Application number: MXPA02000709A
Authority: MX
Inventors: Thomas L Larsen
Original assignee: Washington Group Int
Priority date: 1999-07-21
Filing date: 2000-07-18
Publication date: 2003-01-28
Also published as: DE60043227D1; CZ2002250A3; JP2003509650A; ES2331405T3; EP1203195B1; CN1292221C; ATE447154T1; WO2001007857A8; WO2001007857A1; CA2379283C; BR0012680B1; AU6955000A; KR100768763B1; BR0012680A; TW512219B; KR20020073327A; CA2379283A1; EP1203195A4; PT1203195E; CN1361856A

Abstract

Baffles (20, 22) arranged alongside a plurality of conduits (12).

Description

HEAT TRANSFER WITH IMPROVED CROSSOVER FLOW FIELD OF THE INVENTION The present invention relates in general to methods and a related apparatus for improving heat transfer to or from a fluid flowing transversely in contact with the thermally conductive outer walls of a plurality of axially oriented heat exchange conduits. able to act as heat sources or heat sinks. By channeling the flow of the transverse fluid, to flow in a generally orthogonal manner with respect to the axes of the heat exchange conduits, and by contouring it upstream, downstream and / or around or along the heat exchange conduits By using slotted or apertured plates, screens or surrounding sleeve elements, a surprisingly more effective and efficient heat transfer is made between the fluid flowing and the thermally conductive surface.

BACKGROUND OF THE INVENTION It is well known to heat or cool process fluids, which can be liquids or gases, making them flow so that they come in contact with a surface of thermal transfer that is maintained at a temperature that is different from that of the upstream process fluid, thereby resulting in heat transfer, either to or from the process fluid (depending on whether the thermal transfer surface is maintained at a temperature higher or lower than that of the fluid). In a familiar version of this technology, the thermal transfer surface that acts as a heat source or heat sink is the outside of a thermally conductive wall of a heat transfer tube or pipe, for example, which is heated or It is cooled by a liquid that flows axially through the inside of the tube or pipe. In a variation of this technology, the heat can be supplied directly into a heat exchange conduit, by the combustion without flames of combustible gas (such as hydrogen or a hydrocarbon) as described, for example, patents of the United States of America Numbers 5,255,742 and 5,404,952, which are incorporated herein by reference. It is also known in the art to make a process fluid flow axially along a heat transfer surface, either in favor of the current or countercurrent with respect to the direction of the liquid flow within the heat transfer tube, or flow the flow of the process flow with cross flow, with connection to the shaft of the thermal transfer tube, or some combination of the two. Typical applications of heat transfer between a fluid flowing with cross flow and heat exchange ducts are found in air coolers, economizers associated with furnaces or direct-fired heaters, and in shell and tube heat exchangers. Various types of reactor designs known as radial or axial / radial flow reactors are known for various applications, whereby at least a part of a process fluid stream is moved, at some point, through the reactor, at a radial direction , with cross flow (that is, from the inside out or out inside), which contrasts with the more familiar designs of reactors with axial (ie end to end) flow. Examples of reactor designs that incorporate at least in part the radial, cross flow of a process fluid, relative to a plurality of axially placed heat transfer tubes, are presented in the United States of America Patent Numbers 4,230,669; 4,321,234; 5,594,227; 4,714,592; 4,909,808; 5,250,270 and 5,585,074, each of which is incorporated herein by reference. Although the cross-flow contact of a process fluid with a heat transfer surface can be an attractive option for many applications, the Cross-flow contact utility, for industrial applications, has been limited by certain inefficiencies in heat transfer that have been experienced in practice. Typically in cross flow designs, a certain portion of the process fluid is in contact with the heat transfer surface, for a shorter time than in a comparable axial flow design. In addition, the contact between the cross-flow process fluid and the heat transfer surface is not uniform due to the separation and recirculation of the process fluid. Short contact time with the surface, non-uniform contact, and limited mixing of the fluid, can lead to an inefficient, insufficient, and / or non-uniform thermal energy transfer. In this way, in an article entitled ^ Heat transfer by shock in a circular cylinder, due to a slotted, off-centered or non-off-center jet ", which appears in Int. J. Heat Mass Transfer., Vol. 27, No. 12, pp. 2297-2306 (1984 ), the authors Sparrow and Alhomoud report on the experimental efforts to vary the heat transfer coefficients associated with the cross flow of a process gas relative to a heat transfer tube, by placing a grooved surface, at some distance upstream of the heat transfer tube, to create a gas jet Sparrow and Alhomoud varied the width of the jet-inducing slot, the distance between the slot and the tube, the Reynold number (degree of turbulence of the fluid), and the fact that the jet of the slot was aligned with the tube or off-center thereof. The authors concluded that the heat transfer coefficient was increased with the slot width and with the Reynold number, but that it decreased with the distance between slot and tube and the offset. Because the study by Sparrow and Alhomoud concluded that the heat transfer coefficient increased with the width of the groove, the general utility of a groove located upstream, to increase heat transfer, is, at best, cases, ambiguous based on these results. It can only be concluded that, in the experimental design used by Sparrow and Alhomoud, a relatively wider groove led to a higher heat transfer coefficient than a relatively narrow groove, and if an upstream groove was not entirely found, this could produce the greatest value. Tests were not carried out using a plurality of heat transfer tubes, or using pairs located upstream and downstream, or around or along means • for the constriction of the flow to preferentially contour the trajectories of the fluid with cross flow, in contact with the outer surface of each of a plurality of heat transfer tubes, and reasonable extrapolations can not be made to those alternative configurations and designs, very different, based on the data presented, which are extremely limited. These and other disadvantages, as well as limitations of the cross flow heat exchange designs of the prior art, are overcome in whole or in part with the methods and designs of heat transfer, with improved cross flow, of this invention. .

OBJECTS OF THE INVENTION Accordingly, a principal object of this invention is to provide methods and designs for cross-flow, improved heat transfer between a process fluid and a heat transfer surface. A general object of this invention is to provide methods and designs for directing and shaping, in particular, the cross-flow paths of the fluid, in contact with one or more heat transfer surfaces, in order to improve heat transfer between the fluid and the heat transfer surface. A specific object of this invention is to provide means for constricting the flow of the fluid, located upstream, downstream and / or around or along a heat transfer surface, in order to preferentially contour the flow of a process fluid that flows transversely beyond the heat transfer surface, to improve heat transfer between the fluid stream and the heat transfer surface. A further specific object of this invention is to provide plates with openings, curves or planes, or sleeves with openings, placed in relation to each conduit in a heat exchange conduit arrangement, in order to preferentially contour the trajectory of flow of the fluid stream that flows transversely beyond the exterior of each of the conduits, to realize the improved heat transfer. Still another object of this invention is to provide arrangements of heat transfer conduits, of different sizes and configurations, wherein each conduit of the arrangement is associated with its own means for constricting the flow of the fluid, upstream, downstream and / or around or along the conduit, in order to preferentially contour the portion of the fluid stream flowing transversely beyond the exterior of the conduit, to perform an improved heat transfer.

Other objects and advantages of the present invention will be partly obvious and in part will appear later in the present. Accordingly the invention comprises, but is not limited to, the methods and related apparatus, which involve the different stages and the different components, and the relationship and order of one or more of those steps and components, with respect to each of the others, as exemplified by the following description and the accompanying drawings. Various modifications and variations of the method and apparatus as described herein will be apparent to those skilled in the art, and all such modifications and variations are considered within the scope of the invention.

SUMMARY OF THE INVENTION In the present invention a screen structure comprising at least one group in pairs of fluid flow constrictors, is used to preferentially contour the flow path of a fluid of a process flowing transversely, or in substantially transverse form, in contact with a heat transfer surface, in order to improve the heat transfer between the fluid and the surface. The apparatus is designed to substantially restrict the bypassing the fluid flow, such that a predominant portion of the process fluid is forced to flow past the heat transfer surface. The heat transfer surface will typically be one or 5 a configured arrangement of heat exchange conduits, oriented such that they have parallel axes placed in an axial direction, which is generally orthogonal with flft with respect to the direction of fluid flow, and having a thermally conductive wall. The outer surface of the The wall of each of these conduits is maintained at a temperature different from that of the upstream process fluid, so that thermal energy is transferred to . ^^ or from the process fluid, by conduction, convection, radiation or some combination thereof, to As the fluid flows beyond the outer surfaces of the heat exchange conduits and contacts them. The heat exchange conduits or ducts of this invention may broadly comprise pipes, pipes, or any other housing with heat sources or heat sinks. The outer surfaces of the heat exchange conduits may be smooth, or as discussed below, may have fins or any combination of the two. The cross section of the conduits or ducts can be circular, elliptical or any other closed forms. Where a plurality of those heat exchange conduits are used, they will typically be arranged with some predetermined configuration, such as in a triangular array, a square array, a circular array, an annular array, or other such patterns, depending on the selection of the design and / or requirements of a particular application. With regard to the direction of fluid flow, the adjacent conduits may be aligned, staggered or placed in another form, again depending on the selection of the design and / or the requirements of the application. The size of the heat exchange conduits can be dictated, at least in part, by the process requirements with respect to the heat transfer rate. In general, conduits having larger cross sections (for any given conduit geometry) will provide larger surface areas and therefore higher heat transfer capacity. Fin elements, screens or other structures can be provided to improve heat transfer, on the outer surface of some or all of the heat exchange conduits, to further increase the surface area and improve the characteristics of the heat transfer. A preferred embodiment uses circumferential alps, closely spaced, applied in a spiral along the outer length of the conduit. This arrangement increases the surface area of heat transfer exposed to the cross flow without impeding the flow. It will be understood that the nature and flow velocity of the process fluid, and the desired temperature change in the fluid, between the upstream part of the heat exchange conduits, and the part located downstream of the conduits, will affect also these design selections. The means for constricting the fluid flow, to contour the transverse flow of the process fluid, may comprise inlets, outlets and orifices of various shapes and sizes, in screen structures located upstream, downstream and / or around or along the heat exchange conduits. In a further preferred embodiment, each heat exchange conduit has its own associated pair of fluid flow constrictors, upstream and downstream, or its own flow constrictors, around or along length, as described below. The aperture screen structures, which function as a means for constricting fluid flow, may comprise plates, sleeves or other screens comprising substantially planar surfaces, or curved surfaces, or a combination of flat and curved surfaces. It has been found that aperture structures of this type, placed in upstream and downstream pairs of an array of heat exchange conduits, improve heat transfer by a factor from about one and a half times to about twice. In a particularly advantageous embodiment for certain applications, the structure for the constriction of the fluid flow is a larger, generally concentric, sleeve-like structure that at least partially surrounds each conduit in an arrangement of tubular heat exchange conduits, each one of these sleeve structures has openings upstream and downstream of the centrally located heat exchange tube. It has been found that sleeves with openings, of this type, which at least partially surround the individual heat exchange conduits, in an arrangement of those conduits, improve heat transfer by a factor of about five times or more. The openings in the structure for the constriction of fluid flow comprise any combination of perforated holes or axial grooves (ie, elongated openings having a longer axis generally parallel with respect to the axial orientation of the heat exchange conduits) . The holes or slots, in different portions of the apparatus, may have a different or equal curvature, size and shape. The edges around the entrances and exits can be straight, round, toothed or some combination of the same ones. The structure for constricting the fluid flow is preferably positioned relative to an associated heat exchange conduit, such that the distance between the center line of an opening located upstream or downstream, and the centroid of the conduit associated heat exchange varies from about 0 to about 2.0, preferably from about 0.50 to about 1.00 times the outer diameter (or the largest cross-sectional dimension of a non-circular conduit) of the conduit. In any case, the separation between the opening and the conduit must be close enough to realize a substantially improved heat transfer. The width (shorter side) of an elongated opening for constricting the flow, or the diameter of a constriction opening in the form of a generally circular hole, may preferably vary from about 0.02 to about 1.5, preferably from about 0.05 to about 0.25 times the outer diameter (or larger cross-sectional dimension of a non-circular conduit) of the conduit. The structure for the constriction of the fluid flow is preferably placed in relation to an associated heat exchange conduit, Such that the offset between the center of the opening and the centroid of the heat exchange conduit varies from 0 to 0.5, preferably 0 times the outer diameter (or largest cross-sectional dimension of a non-circular conduit) of the conduit. The improved cross-flow heat transfer apparatus of this invention improves heat transfer between the cross flow fluid and the plurality of heat exchange conduits through one or more of the following mechanisms: (a) ) increase the speed of the fluid around the heat exchange conduits; (b) preferentially directing the fluid to closely follow the outer surface of the heat exchange conduits; (c) restricting the fluid from flowing to or through areas that are distant from the outer surface of a heat exchange conduit; (d) reducing the "dead" regions and recirculating the flow around the heat exchange conduits; (e) improve fluid turbulence; and (f) improving mixing between cooler and hotter portions of the fluid.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic top sectional view of a first embodiment of an apparatus for heat exchange with cross flow, with the heat transfer improvement in accordance with the present invention, wherein a substantially circular array of heat exchange conduits, placed axially, is located within an annulus with fluid flow restricted. Figure 2A is a schematic plan view of a second embodiment of an apparatus for heat exchange with cross flow, with heat transfer improvement, in accordance with the present invention, showing an arrangement, substantially circular , of axially placed heat exchange conduits, each surrounded by a tubular sleeve with restricted fluid flow, substantially concentric, and also showing the different sleeves for constricting the flow of fluid joined together to produce a first ring-like structure. Figure 2B is a side view of a duct and sleeve combination, illustrating a preferred configuration of offset, stepped grooves. Figure 3 illustrates a variation of the structure of Figure 2 showing a circular, double, concentric arrangement of heat exchange ducts, where the radially adjacent ducts are shown in an alignment such that the openings for flow restriction of the fluid, of the sleeves with restricted flow, respectively, associated with these radially aligned conduits, are also in radial alignment. Figure 4 is a schematic top sectional view of another embodiment of an apparatus for heat exchange with cross flow, with heat transfer improvement in accordance with the present invention, showing a double row of exchange conduits of heat placed axially and arranged in a substantially rectangular arrangement with a first screen with flow of restricted fluid, upstream, and a second intermediate screen with flow of restricted fluid, separating the first and second rows of ducts, and a third screen with flow of the restricted fluid, located downstream, which follows the second row of conduits, wherein the corresponding openings of the first, second and third bulkheads are shown substantially in alignment with the respective conduits and with each other. Figure 5 illustrates yet another embodiment of an improved cross-flow heat transfer apparatus according to this invention, showing an array of multiple (ie three or more) rows of heat exchange conduits arranged with one triangular separation and showing two alternative fluid flow paths, through the arrangement.

Figure 6 illustrates another embodiment of an improved cross-flow heat transfer apparatus according to this invention, showing an arrangement of multiple (ie, three or more) rows of heat exchange conduits arranged in a square separation and showing two alternative fluid flow paths through the array. Figure 7 illustrates yet another embodiment of an improved cross flow heat transfer apparatus according to this invention, showing how one or a plurality of plates can be placed along two sides of each exchange conduit. of heat, to cause the preferential contouring of a cross-flow fluid stream, to achieve improved heat transfer characteristics. Figure 8 illustrates still another embodiment of an improved cross flow heat transfer apparatus according to this invention, showing an alternative type of sleeve structure, which is formed by placing curved plates having a contour corresponding to two sides of a conduit, about two sides of each heat exchange conduit, to cause the preferential contouring of a fluid flow with cross flow, to achieve the improved heat transfer characteristics.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES Figure 1 shows an apparatus 10 for cross-flow heat exchange, in accordance with this invention, having an arrangement, generally circular, of heat exchange conduits 12, positioned axially and distributed around the interior of an annular region 28 defined by an inner cylindrical wall 20 and an outer cylindrical wall 22, each of which has a common center point 14. As shown in Figure 1, the conduits 12 have a substantially equal diameter, which is smaller than the radial width of the annular region, and are substantially substantially equidistant from each other. Associated with each heat exchange conduit 12 is an opening 24 located upstream, in an interior wall 20 and an opening 26 located downstream, in the exterior wall 22. As shown in Figure 1, the respective pairs of openings 24 located upstream and openings 26 located downstream, are substantially in radial alignment with the associated conduit 12 and each other. Thus in Figure 1, a process fluid 30 is made to flow axially into the inner cylindrical region 16 of the apparatus 10 for heat exchange, and then it is directed radially outwardly and through the openings 24 located upstream, flowing transversely to make contact with the conduits 12 for heat exchange, as denoted by the fluid flow arrows in Figure 1, thereby heating or cooling the process stream, to form a stream of thermally conditioned fluid 32, which it leaves the annular region 28 through the openings 26 located downstream. It will be understood that while Figure 1 illustrates a flow path of the fluid, radially outward, the same apparatus could be used for the thermal treatment of a process stream that flows radially inwardly and towards the central region 16 and that is subsequently removed axially. of the region 16. In this variation the openings 26 that are in the outer wall 22 would be the openings located upstream, and the openings 24 that are in the inner wall 20 would be the openings located downstream. Figures 2A and 2B show a particularly preferred cross-flow heat exchange apparatus 110 according to this invention, having an arrangement, generally circular, of axially placed heat exchange conduits 112, each surrounded by a sleeve 120 with openings, having either an opening 124 located upstream and an opening 126 located downstream, or pairs of off-center openings 174, 176 and 184, 186 as described later. The individual sleeves 120 are joined together to form a larger cylindrical or ring-like structure by connecting walls 122. The openings 124 and 126 may comprise columns of axially oriented perforated holes or elongated slots that are radially aligned with the conduits 112. Alternatively, in a preferred embodiment illustrated also in a portion of Figure 2A, the pairs of openings 174, 176 and 184, 186 are slightly off-center from the radial alignment in a stepped slot arrangement. The arrangement of stepped slots, for the pairs of openings 174, 176 and 184, 186 is illustrated in Figure 2A, with further detail in Figure 2B, wherein the pairs of offset slots 174, 176 and 184, 186 (which replace the pairs of openings 124, 126) are staggered in elevation and offset slightly from the radial line from the center point 114 by equal angles?. Figure 2B shows a side view, taken along the line 2B-2B in Figure 2A of a heat exchange conduit 112 having a cylindrical sleeve 124 with the arrangement of stepped slits, preferred. The plan view of this duct / sleeve combination with stepped grooves, as shown in Figure 2A, is taken along line 2A-2A in Figure 2B. The ends of the slots, from the pairs of off-center, alternating slots, can be slightly overlapped or at equal elevation, so that there is no interruption of flow along the axial direction of the apparatus for heat exchange. This design with spacing and overlap of the offset grooves also leaves connection regions between the axially overlapping portions of adjacent offset grooves, indicated generally with the reference number 190 in Figure 2B, to provide the sleeves 120 with better mechanical integrity circumferential, without blocking any fluid flow. By simplified illustration, Figure 2A shows a sleeve 124 with openings having the configuration of off-center openings, in two pairs, while the other sleeves have the configuration of aligned openings, in a pair. However, in practice, all sleeves with openings for a particular appliance 110 will typically have the same opening configuration. Thus, in Figure 2A, a process fluid 130 is flowed axially into the inner cylindrical region 116 having the center point 114 of the heat exchange apparatus 110 and then directed radially outwardly and through the openings 124. located upstream, flowing transversely to make contact with the exchange conduits 112, as denoted by the fluid flow arrows in Figure 2A, thereby heating or cooling the process stream to form a thermally conditioned fluid stream 132, which leaves the interior regions defined by the sleeves 120 to the openings 126 located downstream. In the stepped slot mode, the fluid flowing radially outward would flow either through the opening 174 located upstream, to make contact with the conduit 112, and would exit through the opening 176 located downstream, or, depending of the axial lift, it would then flow through the pair of openings 184, 186. It will be understood that although Figure 2A illustrates a flow path of the fluid radially outward, the same apparatus could be used for the thermal treatment of a process stream that flow radially inward and towards the central region 116 and then be removed axially from the region 116. In this variation, the openings 126 (or 176 and 186) would be the openings located upstream, and the openings 124 (or 174 and 184) would be the openings located downstream. Figure 3 shows an apparatus 160 for cross-flow heat exchange, which is a variation of the cross-flow heat exchange apparatus 110, shown in Figure 2. The apparatus 160 differs from the apparatus 110 in the use of a double, circular, concentric arrangement of heat exchange ducts, instead of the simple, circular arrangement of Figure 2. As seen in Figure 3, there is a second circular array of heat exchange conduits 142, each in radial alignment with a corresponding conduit 112 of the first circular array. Each conduit 142 is surrounded by a sleeve 150 with openings, having an opening 164 located upstream, and an opening 166 located downstream. The f openings 164 and 166 for a given sleeve 150 associated with a particular conduit 142 are shown substantially in radial alignment with the openings 124 and 126 in the sleeve 120 of the correspondingly radially adjacent conduit 112. The individual sleeves 150 are joined together to form a larger cylindrical or ring-like structure through the walls 152. Although Figure 3 shows only a single conduit 142 of the second circular array of heat exchange conduits, it will be understood that each duct 112 of the first circular array is associated with a corresponding duct 142 of the second circular array. Thus, in Figure 3, a fluid stream 132 partially conditioned thermally, exiting through the first openings 126 located downstream, in the sleeves 120, is directed radially outwardly and through the second openings 164 located current upstream, flowing transversely to make contact with the second array of heat exchange conduits 142, then heating or cooling, additionally, the process stream, to form a fluid stream 162 fully thermally conditioned, exiting the interior region defined by the sleeves 150 through the second openings 166 located downstream. It will be understood that although Figure 3 illustrates a flow path of the fluid radially outwardly, the same apparatus could be used for the thermal treatment of a process stream that flows radially inwardly and towards the central region 116 and be removed later, axially, of the region 116. In this variation, the openings 166 and 126 would be respectively the first and second openings located upstream, and the openings 164 and 124 would be respectively the first and second openings located downstream. Figure 4 shows a portion of another apparatus 210 for heat exchange with cross flow, in accordance with this invention. In Figure 4 a double row of heat exchange conduits placed axially, comprising a first row of conduits 212, located upstream, and a second row of conduits 216, located downstream, is placed in a generally rectangular arrangement in conjunction with: a first plate 220 with openings, located upstream, having openings 226; a second plate 222 with intermediate openings having openings 228, plate 222 separates the first and second rows of ducts; and, a third plate 224 with openings, located downstream, having the openings 230. Each set of openings 226, 228 and 230 associated with an adjacent pair of conduits 212 and 216, upstream and downstream, is substantially shown in FIG. linear alignment with each other and with the associated pair of conduits 212 and 216, located upstream and downstream, respectively. Thus, in Figure 4, a process fluid 232 is directed, as denoted by the fluid flow arrows in Figure 4, through the openings 226 and flowed transversely to make contact with the first heat exchange conduits 212, located upstream, then heating or cooling the process stream partially to form a partially thermally conditioned fluid stream 234. The stream 234 is then directed through the openings 228 and flows transversely to make contact with the second heat exchange conduits 216, located downstream, to thereby heat or cool, in addition, the process stream and form a fluid stream 236 fully thermally conditioned, which is flowed out of the apparatus 210 through the outlet openings 230. Figure 5 illustrates two flow paths of the fluid, alternative, through a set of heat exchange conduits 312, in multiple rows, arranged in an off-center or triangular arrangement in accordance with another embodiment of an apparatus 310 for heat exchange with cross flow, in accordance with this invention. Thus, in Figure 5, alternating rows of heat exchange conduits are off-center from the adjacent rows, instead of the conduits in adjacent rows being substantially in linear alignment as shown in Figures 4 and 6. In this configuration the center points of three adjacent conduits, in two adjacent rows, form an equilateral triangle 340. Although not shown in Figure 5 it is understood that the apparatus of Figure 5 includes plates with openings, located upstream and downstream, located respectively before the first row of ducts and after the last row of ducts, as well as plates with openings, intermediate, separating adjacent rows of ducts. Alternatively, each conduit 312 may be surrounded by a sleeve structure with openings, as previously described for other figures. The flow arrows of the fluid 332 in the Figure 5 illustrate a first possible orientation of the fluid flow, which can be used with the triangular conduit arrangement of the apparatus 310. Fluid flow arrows 334 in Figure 5 illustrate a second possible orientation of the fluid flow, which can also be used with the triangular duct arrangement of the apparatus 310. Although Figure 5 shows four rows of heat exchange ducts, in the triangular array , a smaller or greater number of duct rows can be used in this configuration, as appropriate. Figure 6 illustrates two possible fluid flow paths, alternative, through a multi-row assembly, of heat exchange conduits 412 arranged in a square arrangement in accordance with yet another embodiment of an apparatus 410 for heat exchange with cross flow, in accordance with this invention. Thus, in Figure 6, the adjacent ducts 412 and rows are substantially in a linear alignment. In this configuration, the center point of four adjacent conduits, in two adjacent rows, forms a square 440. Although not shown in Figure 6, it will be understood that the apparatus of Figure 6 includes plates with openings, located upstream and current below, located respectively before the first row of ducts and after the last row of ducts, as well as plates with openings, intermediate, separating the rows of ducts, adjacent. Alternatively, each conduit 412 may be surrounded by a sleeve with openings, as previously described. The fluid flow arrows 432 in Figure 6 illustrate a first possible orientation of the fluid flow, which can be used with the square, duct arrangement of the apparatus 410. The fluid flow arrows 434 in Figure 6 illustrate a second possible orientation of the fluid flow, which can be used with the square, duct arrangement of apparatus 410. Although Figure 6 shows five rows of heat exchange ducts, in the square arrangement, in this configuration a smaller or greater number of duct rows, as appropriate. Figure 7 illustrates yet another variation of an improved cross flow heat transfer apparatus 510 in accordance with this invention. In Figure 7 each heat exchange conduit 512 is associated with one or more side plates 520, 522, 524, 526 and 528, for the constriction of the flow, placed along the conduit 512 and oriented in generally orthogonal manner with respect to the direction of fluid flow, as indicated by arrows 530 and 532. The edges of side plates 520, 522, 524, 526 and 528 closest to conduit 512 are separated from the outer walls of conduit 512 a In order to create two channels or holes for the fluid, between the edges of the plate and the wall of the conduit, one along the each side of each conduit 512. The separation between the edges of the plate and the wall of the conduit, can be adjusted through routine experimentation, to optimize the contouring of the fluid flow path, to maximize heat transfer. Where two or more flow constriction plates are used, laterally, for each conduit 512, the separation between the edges of the plate and the wall of the conduit may be the same or different in order to optimize the contour of the flow path of the fluid. As seen in Figure 7, the side plates for flow constriction can be positioned along the duct 512, such that the plane of the plate passes through the centroid 518 of the duct 512 (such as the plate 524), or else it is positioned such that the planes of the plates intersect the upstream duct 512 (such as plates 520 and 526) of the centroid 518, or downstream (such as the plates 522 and 528) of the centroid 518 , or any combination thereof. The distance 542 between the opening and the centroid 518 of the conduit may be less than half the diameter 544 as shown, with a distance approaching zero as a limit, for example the plate 524. This differs from the structures of screen shown in Figures 1 and 4 wherein the distance between the openings and the centroid of the duct is greater than half the diameter of the duct. conduit. As used herein, the phrase "side plate positioned along a heat exchange conduit" means plates such as 520, 522, 524, 526 and 528 in Figure 7, generally oriented orthogonally with with respect to the direction of fluid flow, wherein the plane of the plate intersects any part of the heat exchange conduit. Figure 8 illustrates another variation of an improved cross flow heat transfer apparatus 610 in accordance with this invention, which shows a variation of the aperture sleeve configuration shown in Figure 2. In Figure 8 each The heat exchange conduit 612 is partially surrounded by a pair of opposingly curved plates 620 which generally conform to the curvature of the outer wall of the conduit 612 in a clam-shell configuration. Each curved plate 620 is attached to a wall or side plate 622 positioned generally orthogonal to the direction of fluid flow, as indicated by arrows 630 and 632. The pair of curved plates 620 around each side of a given conduit 602 does not touch each other and does not extend upstream or downstream of the outer wall of conduit 612. In this manner, as shown for purposes of illustration in Figure 8, a line or plane connecting the edges located upstream or downstream, of a pair of curved plates 620, would intersect conduit 612. The holes located upstream and downstream, between pairs of curved plates 620 are the openings through which the stream of process fluid is directed to perform the preferential contouring of the fluid stream. The distance 642 between the opening and the centroid 618 of the conduit may be less than half the diameter 644 cal as shown, where a distance approaches zero as a limit, for example, when the lengths of the curved plates 620 approach zero leaving only the side plate 622, a configuration corresponding to Figure 7 with a single plate 524. This differs from the screen structures shown in Figures 1 and 4 where the distance between the openings and the centroid of the duct It is greater than half the diameter of the duct. The shell-like shell configuration of Figure 8, wherein each pair of curved plates 620 is around the sides of each conduit 612, differs from the groove sleeve configuration, of Figure 2, because in Figure 8 a line or plane connecting the edges of the fluid orifices, located upstream and downstream, intersects the conduit 612, which is not the case for the slotted sleeves shown in Figure 2A. In one sense the modality of Figure 8 can be seen as a version end of the diment of Figure 7 wherein the individual side plates placed along the heat exchange conduit, are not separated, as seen in Figure 7, but instead are face-to-face with each other, such that their edges on the duct side form the curved plates 620 of Figure 8. It will be apparent to those skilled in the art, that other changes and modifications may be made to the apparatus and methods described above, to improve heat transfer with cross flow, without departing from the scope of the present invention, and it is intended that any matter contained in the foregoing description be interpreted in the illustrative and non-limiting sense.

Claims

CLAIMS 1. An apparatus for contouring the flow of a fluid, to preferentially contour the flow path of a process fluid that flows transversely through a plurality of heat transfer surfaces, separated, and contacting therewith, the The apparatus is characterized in that it comprises at least one set in pairs of constrictors of the fluid flow, in a screen structure substantially surrounding each heat transfer surface and isolating the fluid flow around that heat transfer surface, the flow of the fluid around adjacent heat transfer surfaces, located transversely to the direction of fluid flow, the fluid flow constrictors are located symmetrically and respectively upstream and downstream of the associated heat transfer surface, at least in partial alignment upstream and downstream, some with others and with the associated heat transfer surface, whereby the partition structure contours the flow path of the process fluid to establish a substantially uniform fluid flow pattern around the contour of a heat transfer surface. 2. The apparatus for contouring the flow of a fluid, according to claim 1, characterized in that the heat transfer surfaces comprise the outer surfaces of an array of heat exchange conduits, cylindrical, oriented to have parallel axes. 3. The apparatus for contouring the flow of a fluid, according to claim 2, characterized in that each partition structure comprises a sleeve-shaped element that is substantially concentric with respect to the associated heat exchange conduit. 4. The apparatus for contouring the fluid flow, according to claim 3, characterized in that the sets, in pairs, of fluid flow constrictors comprise openings located upstream and downstream, in the sleeve-shaped elements. 5. The apparatus for contouring the flow of a fluid, according to claim 1, characterized in that at least two of the screen structures are interconnected in a larger apparatus to contour the flow, in order to contour the fluid flow around of a plurality of heat transfer surfaces. 6. The apparatus for contouring the flow of a fluid, according to claim 2, characterized in that the heat exchange conduits are arranged in a generally circular arrangement. The apparatus for contouring the flow of a fluid, according to claim 6, characterized in that the individual screen structures, associated with the heat exchange conduits, are interconnected to form a larger apparatus for contouring the flow, of cylindrical shape. 8. The apparatus for contouring the flow of a fluid, according to claim 7, characterized in that the pairs of fluid flow constrictors comprise radially aligned upstream and downstream openings in the individual screen structures. 9. The apparatus for contouring the fluid flow, according to claim 7, characterized in that the pairs of fluid flow constrictors comprise openings, located upstream and downstream, in the individual screen structures, which are off-center from the radial line. 10. The apparatus for contouring the flow of a fluid, according to claim 1, characterized in that the heat transfer surfaces comprise the outer surfaces of at least one arrangement, generally circular, of heat exchange conduits, cylindrical, aligned axially, at least some of which are substantially surrounded by a sleeve-shaped structure, with openings, substantially concentric, having pairs of openings, located upstream and downstream, in columns parallel to the axis of the duct • 5 associated, and furthermore where a sleeve-shaped structure is secured by a plate member, to an adjacent sleeve structure, to form a more cylindrical structure (large) 11. The apparatus for contouring the flow of a 10 fluid, according to claim 10, characterized in that the pairs of openings comprise elongated grooves, each groove has a longitudinal axis in general fetal parallel with respect to the axes of the heat exchange conduits. 12. The device for contouring the flow of a fluid, according to claim 11, characterized in that the pairs of elongated slots are in radial alignment. 13. The apparatus for contouring the flow of a fluid, according to claim 11, characterized in that a heat exchange conduit is associated with two pairs of elongated slots, each pair of slots is offset from the radial alignment with the shaft of the largest cylindrical structure. 25 14. The device for contouring the flow of a fluid, according to claim 13, characterized in that the two elongated slots, located upstream and the two located downstream, associated with each heat exchange duct, are axially offset from one another, but axially aligned with the member of the pair opposite. 15. The apparatus for contouring the flow of a fluid, according to claim 10, characterized in that the heat transfer surfaces comprise the outer surfaces of at least two arrangements, generally circular, of heat exchange conduits, cylindrical, oriented to have parallel axes and where one arrangement is concentric with respect to the other. 16. The apparatus for contouring the flow of a fluid, according to claim 15, characterized in that the pairs of openings comprise elongated slots in radial alignment, each slot having a longitudinal axis generally parallel with respect to the axes of the ducts. heat exchange. 17. The device for contouring the flow of a fluid, according to claim 15, characterized in that the screen structures, of adjacent pairs of heat exchange conduits, radially aligned, are interconnected in such a way that an opening between the structures of screen serves as the Constrictor of the fluid flow, located downstream, for one of the conduits, and as the constrictor of the fluid flow, located upstream, for the other. 18. The apparatus for contouring the flow of a fluid, according to claim 17, characterized in that the pairs of openings comprise elongated slots, in radial alignment, wherein each slot has a long axis generally parallel with respect to the axes of the heat exchange conduits. The apparatus for contouring the flow of a fluid, according to claim 1, characterized in that the heat transfer surfaces comprise the outer surfaces of a substantially rectangular array, comprising at least three rows, axially aligned, of ducts heat exchange, cylindrical, oriented to have parallel axes, and wherein the associated screen structures comprise, in general, concentric sleeve-shaped elements, having pairs of openings located upstream and downstream. 20. The apparatus for contouring the flow of a fluid, according to claim 1, characterized in that the heat transfer surfaces comprise the outer surfaces of a substantially rectangular array comprising at least three rows of heat exchange ducts, cylindrical , where the rows Alternating are axially offset from the adjacent rows located upstream and downstream, the heat exchange conduits are oriented to have parallel axes, and wherein the associated partition structures generally comprise concentric, sleeve-shaped elements having pairs of openings located upstream and downstream. 21. The apparatus for contouring the flow of a fluid, according to claim 1, characterized by the partition structure associated with a heat transfer surface, comprising a set of substantially flat plate members, placed in pairs at the edges and on the sides of two sides of a heat transfer surface, in proximity but without touching the surface, the planes of the plate members are oriented in a generally orthogonal manner with respect to the flow path of the process fluid, in order of defining regions for flow of generally annular fluid, having pairs of openings located upstream and downstream around the heat transfer surfaces. 22. The apparatus for contouring the flow of a fluid, according to claim 1, characterized in that the partition structure associated with a heat transfer surface comprises plate members, contoured, placed in pairs along two sides of the heat transfer surface, in proximity but not touching the surface, the plate members have an outline that corresponds respectively to the two sides of the heat transfer surface, In order to define regions for fluid flow, generally annular in shape, having holes, located upstream and downstream, around the heat transfer surfaces, the plate members are attached to other associated plate members, with adjacent heat transfer surfaces. 23. A method for improving heat transfer to or from a fluid flowing transversely and contacting the outer surfaces of a plurality of heat exchange conduits, characterized in that it comprises the step of preferentially contouring the flow of the fluid through the heat transfer surface, by flowing the fluid through a first set in pairs of fluid flow constrictors, in a screen structure substantially surrounding each heat transfer surface and isolating the fluid flow around of that heat transfer surface, of the flow of the fluid around the adjacent heat transfer surfaces, located transversely with respect to the direction of fluid flow, the fluid flow constrictors are located symmetrically and respectively, upstream and downstream of the associated heat transfer surface, at least in a partial alignment upstream and downstream, with each other, and with the associated heat transfer surface, whereby the partition structure contours the fluid flow path, to establish a substantially uniform fluid flow pattern, around the contour of a heat transfer surface. 24. A method according to claim 23, characterized in that the heat transfer surfaces comprise the outer surfaces of an array of heat exchange conduits, cylindrical, oriented to have parallel axes. 25. A method according to claim 24, characterized in that each of the partition structures comprises a sleeve-shaped element that is substantially concentric with respect to the associated heat exchange conduit. 26. A method according to claim 25, characterized in that the sets, in pairs, of fluid flow constrictors, comprise openings located upstream and downstream, in the sleeve-shaped elements. 27. A method according to claim 23, characterized in that at least two of the screen structures are interconnected in a larger apparatus to contour the flow, in order to contour the fluid flow around a plurality of heat transfer surfaces. 28. A method according to claim 25, characterized in that the heat exchange conduits are arranged in a generally circular arrangement. 29. A method according to claim 28, characterized in that the individual partition structures, associated with the heat exchange conduits, are interconnected to form a larger cylindrical flow-contouring apparatus. 30. A method according to claim 29, characterized in that the pairs of fluid flow constrictors comprise openings, located upstream and downstream, aligned radially, in the individual screen structures. 31. A method according to claim 29, characterized in that the pairs of fluid flow constrictors comprise openings, located upstream and downstream, in the individual screen structures that are offset from the radial line. 32. A method according to claim 1, characterized in that the heat transfer surfaces comprise the outer surfaces of at least one generally circular arrangement of heat exchange conduits, cylindrical, axially aligned, at least some of which are substantially surrounded by a sleeve-like structure, with openings, substantially concentric, having pairs of openings located upstream and downstream, in columns parallel to the axis of the associated conduit, and furthermore where a sleeve-like structure It is secured by a plate member to an adjacent sleeve structure to form a larger cylindrical structure. 33. A method according to claim 32, characterized in that the pairs of openings comprise elongated slots, each slot having a longitudinal axis generally parallel with respect to the axes of the heat exchange conduits. 34. A method according to claim 33, characterized in that the pairs of elongated slots are in radial alignment. 35. A method of compliance with the claim 33, characterized in that a heat exchange conduit is associated with two pairs of elongated slots, each pair of slots is offset from the radial alignment with the axis of the larger cylindrical structure. 36. A method according to claim 35, characterized in that the two elongated grooves located upstream and the two grooves located downstream, associated with each heat exchange conduit, are axially off-center from one another, but are axially aligned with the other. member of the opposite pair. 37. A method according to claim 32, characterized in that the heat transfer surfaces comprise the outer surfaces of at least two arrangements, generally circular, of heat exchange ducts, cylindrical, oriented to have parallel axes, and a The arrangement is concentric with respect to the other. 38. A method according to claim 37, characterized in that the pairs of openings comprise elongated slots in radial alignment, each slot having a longitudinal axis generally parallel with respect to the axes of the heat exchange conduits. 39. A method of compliance with the claim 37, characterized in that the partition structures, of adjacent pairs of heat exchange conduits, radially aligned, are interconnected in such a way that an opening between the partition structures serves as the constrictor of the fluid flow located downstream, for one of the conduits, and as the constrictor of the fluid flow, located upstream, for the other. 40. A method according to claim 39, characterized in that the pairs of openings comprise elongated slots in radial alignment, each slot having a longitudinal axis generally parallel to the axes of the heat exchange conduits. 41. A method according to claim 23, characterized in that the heat transfer surfaces comprise the outer surfaces of an array, substantially rectangular, comprising at least three axially aligned rows of heat exchange conduits, cylindrical, oriented for having parallel axes, and wherein the associated screen structures comprise sleeve-like elements, generally concentric, having pairs of openings located upstream and downstream. 42. A method according to claim 24, characterized in that the heat transfer surfaces comprise outer surfaces of a substantially rectangular arrangement comprising at least three rows of cylindrical heat exchange conduits, in which alternate rows are axially offset from the adjacent rows located upstream and downstream, the heat exchange conduits are oriented to have parallel axes, and wherein the associated screen structures comprise sleeve-shaped elements, generally concentric, having pairs of openings located upstream and downstream. 43. A method according to claim 23, characterized in that the partition structure associated with a heat transfer surface comprises a set of substantially flat plate members, placed in pairs at the edge and along two sides of a surface of heat transfer in proximity but without touching the surface, the planes of the plate members are oriented in a generally orthogonal manner with respect to the flow path of the process fluid, in order to define regions for fluid flow , in general annular form, having pairs of openings located upstream and downstream, around the heat transfer surfaces. Four . A method according to claim 23, characterized in that the partition structure associated with a heat transfer surface comprises contoured plate members, placed in pairs along two sides of the heat transfer surface, in proximity but not touching the surface, the plate members have an outline corresponding respectively to the two sides of the transfer surface of heat, in order to define regions for fluid flow, generally annular in shape, having holes, located upstream and downstream, around the heat transfer surfaces, the plate members are attached to other members of associated plate, with adjacent heat transfer surfaces.