This specification relates generally to the field of heat exchangers, and more particularly, to non-adiabatic catalytic heat exchangers.
Heat exchangers in which heat is transferred between a tube-side fluid contained within multiple tubes comprising a bundle of tubes and a shell-side fluid surrounding the bundle of tubes are known. Shell and tube heat exchangers embody such art.
Baffles are used in existing shell and tube heat exchangers to cause the shell-side fluid to impinge the outer surface of the tubes in a cross flow pattern and thereby increase the outside film heat transfer coefficient of the tubes relative to equivalent shell-side fluid where the flow is parallel to the axis of the tubes, but cross flow is less efficient than counter flow for the most complete or effective exchange of heat. To the extent that each cross flow pass of shell-side fluid impinges a large length of the tubes, the difference in temperature between the tube-side fluid and shell-side fluid (the ΔT) has a wide range of values across the width of the shell-side pass with respect to distance along the length of the tube bundle. A wide range of ΔT introduces inefficiency relative to counter current flow. Baffles may cause the shell-side fluid to impinge surfaces that are not primary heat transfer surfaces to undergo virtually 180° changes of direction, such that the considerable pressure drop in the shell-side fluid from the change of direction does not directly impinge a primary heat transfer surface to break down a boundary layer impeding heat transfer or thereby provide a useful heat transfer function.
It is desirable for changes of fluid flow direction to be useful in impinging only heat transfer surfaces to improve the film heat transfer coefficient in exchange for the associated pressure drop. The inherently non-uniform velocity across the cross section of the flow path of a fluid undergoing changes of flow direction through wide cross sectional paths as in shell-side fluid passing between successive baffles introduces further inefficiency in that the higher velocity fluid improves heat transfer at disproportionately greater expense of pressure drop than the lower velocity fluid. It is therefore desirable that flow through the shell-side fluid be at uniform velocity in all locations and that changes of fluid flow direction only occur as a result of impingement onto heat transfer surfaces, and preferably primary heat transfer surfaces.
Helical baffles having a common helicoid surface through which multiple tubes project are known. Shell-side baffles in the shape of a single helicoid of the approximate transverse cross section as the tube bundle are known for creating a helical shell-side fluid path through a tube bundle, the helical path being laterally bounded by the shell, resulting in the deficiency of forcing changes of direction of shell-side fluid flow via surfaces that are not primary heat transfer surfaces and of creating cross flow rather than countercurrent flow. Because the baffle forms an acute angle to the tube wall in the direction of the inlet on one side of a given tube and forms an acute angle to the tube wall in the direction of the outlet on the other side of the given tube, the fluid passing between the tubes is only directed to impinge the tube wall from one direction as opposed to the distinct, multiple oblique fins associated with individual tubes in a bundle as disclosed herein to cause fluid passing between the tubes to impinge the tube wall on multiple sides and from multiple directions. Helical baffles cause uneven heat transfer around the tube perimeter and normally undesirably limit or render impractical the maintenance of heat exchangers, such as for the reduction or removal of fouling on the outside surfaces of a bundle of tubes.
Both longitudinal and transverse externally finned tubes for increasing the effective surface area of the outside of a tube are known. Fins provide additional or extended surface area for tube outside film heat transfer at the expense of masking primary heat transfer surface area and reducing the fluid velocity and film heat transfer coefficient of those primary heat transfer surfaces. These types of fins replace primary heat transfer surface area having a limited film heat transfer coefficient with area intimately contacting high thermal conductivity solids having much greater surface area than the primary heat transfer surface itself. Longitudinal and transverse fins are advantageously used in systems where the heat transfer through the fin material exceeds the heat transfer through the film layer of the fluid at the primary heat transfer surface, such as with copper or aluminum fins contacting a low conductivity fluid such as a gas. In such cases, the fins can have high aspect ratio of length (distance from primary heat transfer surface) to fin thickness. Conventional fins, whether transverse or longitudinal, are less effective if they must be composed of lower conductivity material, such as but not limited to iron or nickel alloys including carbon steel, stainless steel, Inconel® or plastic, wood, and the like, or when the thermal conductivity of the shell-side fluid is high such as with liquids. Applications at elevated temperature or in corrosive conditions may necessitate the use of fin or tube materials of much lower conductivity than Al or Cu, requiring less effective fins and/or thicker low aspect ratio fins. The material consumption, fabrication cost, and weight to be supported by tube sheets for finned tubes of these relatively lower conductivity materials are disadvantageous. Further, fins often require expensive joining to the tubes for good solid state thermal conductivity and make cleaning of the heat transfer surfaces difficult or impractical.
In accordance with an embodiment, a heat exchanger is provided. The heat exchanger includes a packing comprising at least one external oblique fin having a surface, and a plurality of tubes, each tube having an inlet, an outlet, a wall, an outer surface, and an axis. The plurality of tubes are substantially parallel and separate from each other.
In another embodiment, the packing includes a plurality of fins arranged in a plurality of columns. Each column includes a plurality of external oblique fins associated with a respective tube disposed along at least part of a length of the respective tube, and first fins in a first column have substantially the same first orientation. The first orientation of the first fins in the first column is different from a second orientation of second fins in a second column.
In another embodiment, each tube includes a reference plane. A defining intersection is an intersection between the reference plane and a surface of the at least one external oblique fin. An angle between the defining intersection and the tube axis in the direction of the inlet is greater than 0° and less than 90°.
In another embodiment, the angle between the defining intersection and the tube axis in the direction of the inlet is greater than 0° and less than 45°.
In another embodiment, the heat exchanger further includes at least one of a plurality of transitional members, a plurality of supports and a plurality of skids.
In another embodiment, the heat exchanger further includes a helicoid transition member.
In another embodiment, the heat exchanger is a tube and shell type heat exchanger.
In accordance with another embodiment, a heat exchanger is provided. The heat exchanger includes a packing and a plurality of tubes. Each tube has an inlet, an outlet, a wall, and an axis. The plurality of tubes are substantially parallel to each other and separate from each other. The packing includes one or more external fins having a helicoid shape and having an axis of rotation that does not coincide with the tube axis.
In another embodiment, the axis of rotation is external to each of the plurality of tubes.
In another embodiment, the packing includes first external helicoidal fins twisted in a first direction and second external helicoidal fins twisted in a second direction opposite the first direction.
In accordance with another embodiment, a heat exchanger is provided. The heat exchanger includes a plurality of tubes, each tube having an inlet, an outlet, a wall, an outer surface, and an axis. The heat exchanger also includes a packing comprising a plurality of fins arranged in a plurality of columns, each column including at least one external oblique fin associated with a respective tube disposed along at least part of a length of the respective tube.
In one embodiment, the heat exchanger also includes a first fin in a first column having a first orientation, and a second fin in a second column having a second orientation different from the first orientation.
In another embodiment, each tube has a reference plane, wherein a defining intersection is an intersection between the reference plane and a surface of the at least one external oblique fin. The angle between the defining intersection and the tube axis in the direction of the inlet is greater than 0° and less than 90°. In another embodiment, the angle between the defining intersection and the tube axis in the direction of the inlet is greater than 0° and less than 45°.
In another embodiment, the heat exchanger includes at least one of a plurality of transitional members, a plurality of supports and a plurality of skids.
In another embodiment, the heat exchanger includes a helicoid transition member.
In another embodiment, the heat exchanger is a tube and shell type heat exchanger.
In another embodiment, the plurality of tubes are substantially parallel and separate from each other.
These and other advantages of the present disclosure will be apparent to those of ordinary skill in the art by reference to the following Detailed Description and the accompanying drawings.
The following detailed description discloses various exemplary embodiments and features of the invention. These exemplary embodiments and features are not intended to be limiting.
In accordance with an embodiment, a heat exchanger is provided containing a packing and a plurality of tubes (sometimes referred to herein as a bundle of tubes), wherein the individual tubes have an inlet, an outlet, a wall, an outer surface, an axis, and a reference plane, wherein the tubes are substantially parallel to each other and are separated from each other, and wherein the packing contains at least one external oblique fin. The packing may additionally contain transitional members, supports, struts, skids, or helicoids, and may include multiple and preferably identical sub-assemblies, which sub-assemblies may be individually inserted into or removed from the bundle of tubes for maintenance purposes.
The fins may be constructed of low thermal conductivity materials. The packing may or may not be permanently joined to the tubes. The fins are proximate the tube walls and may or may not contact the tube walls. The fins are preferably are less than 0.25 tube diameters from the tubes, and more preferably are less than 0.1 tube diameters from the tubes. The fins may be flat or curved sheets, and may be rigid or non-rigid. The fins are preferably substantially impervious.
The design of the packing causes shell-side fluid passing between the tubes to be deflected in its flow direction primarily by primary heat transfer surfaces and not by the fins themselves or by a shell or housing of the tube bundle such as to exploit all such deflections for breaking down boundary layers at primary heat transfer surfaces for the improvement of film heat transfer coefficients of the primary heat transfer surfaces. Generally helical flow patterns are created, the angle of which is determined by the relative values of the heat exchanger being small, being light weight, and having low pressure drop. The shell-side fluid is further directed to impinge tubes from multiple directions as opposed to impinging tubes from one lateral direction as is known with shell-side baffles.
In a heat exchanger in which heat is transferred between a first fluid within a plurality of tubes or a bundle of tubes and a second fluid surrounding the tubes, it is desirable that the heat transfer coefficient be high, the pressure drop of the respective fluids, gross consumption and net finished weight of materials of construction and fabrication cost be minimal, and that the materials of construction be durable in the given application environment.
Systems, methods, and apparatus described herein offer numerous advantages. For example, systems, methods, and apparatus described herein provide a heat exchanger having a tube or a plurality (bundle) of tubes that will cause a fluid to impinge greater portions of the outside surface of the tube or of the bundle of tubes in such a way that the ratio of the outside film heat transfer coefficient divided by the pressure drop is higher than in other known art for equivalent applications. Systems, methods, and apparatus described herein also reduce the material consumption, finished weight, and fabrication cost of heat exchangers containing bundled tubes. Certain systems, methods, and apparatus described herein provide a heat exchanger packing that is installable, removable, and maintainable, both in fouling and non-fouling conditions. Systems, methods, and apparatus described herein also provide fins of less expensive materials. Other advantages will become clear to one reasonably skilled in the art upon reading the disclosure set forth herein.
For the purposes of this invention, the following terms shall have the indicated meanings:
A tube includes tubes, pipes, channels and conduits having an inlet, an outlet, an axis, a length, a reference plane, and a lateral wall enclosing a volume, such wall having an outer surface. The cross section of a tube may be round, triangular, square or any other shape.
A baffle is a common sheet that completely engulfs, or is penetrated by, multiple tubes.
A fin is a flat or curved sheet having a thickness wherein the sheet is associated with a tube for extending the surface area of the tube or for directing the flow of a fluid through or around a tube. A sheet may be associated with a tube either by way of being joined to the tube or by being proximate to the tube and in fixed orientation or position with respect to the tube during use or operation. A fin may be proximate multiple tubes, but only completely engulfs at most one tube as opposed to a baffle.
An external fin is a fin that either extends from the external surface of a tube or directs the flow of fluid outside or around the associated tube.
A tube axis is a line running longitudinally along the tube's length at the tube's mid-transverse cross section.
A reference plane is a plane that includes and is aligned with the tube axis such that the intersection of the reference plane and the tube axis is the tube axis, as opposed to a plane that does not intersect the tube axis or that intersects the tube axis at a single point.
A fin surface is the surface coinciding with the mid thickness of a fin. Fins are classified herein by the shape of the intersection between a reference plane and the fin surface, wherein said intersection is referred to as the defining intersection.
A transverse fin is a fin for which the defining intersection is a line that is perpendicular to the tube axis.
A longitudinal fin is a fin for which the defining intersection is one of the fin surface itself or a line that is parallel to the tube axis.
An oblique fin is a fin for which the defining intersection is a line that is oblique to the tube axis. A fin for which the defining intersection is a curved line is defined as the straight line passing through the ends or extremities of the curved line, such as in the case of a helicoidal fin rotating about an axis that is external to the tube or otherwise does not coincide with the tube axis.
A fin for which reference planes within one or more arcs about the tube axis create defining intersections that define the fin as a transverse fin and reference planes within one or more arcs about the tube axis create defining intersections that define the fin as an oblique fin is defined herein as being of the type represented by the larger cumulative angles of arcs. For example, a flat fin at an oblique angle to a tube encompassing a 360° arc about the tube that creates defining intersections that define the fin as transverse at two diametrically opposite reference planes and creates defining intersections that define the fin as oblique for all other angles over two arcs of about 180° each is defined as oblique. All of the exemplary fins illustrated in the present disclosure fall within arcs of only 120° of reference planes about their respectively associated tubes in which arcs, all reference planes and defining intersections define the fins as oblique and not transverse or longitudinal.
Elements depicted in the Drawings with corresponding numeral references in more than one figure are corresponding elements.
In various embodiments, the tube and fin components are constructed of materials that are compatible with the specific application such as in strength and resistance to corrosion and erosion. The tubes preferably have high thermal conductivity. In various embodiments, high temperature and corrosion resistance metal alloys may be used, including, but not limited to, low and high alloy steels such as stainless steels and nickel alloys such as Inconel®. In some embodiments, the packing does not predominantly rely on solid state thermal conduction through the fins, but instead enhances convection through the boundary layers surrounding the tubes; packings composed of low cost materials of construction of low thermal conductivity and/or high corrosion resistance such as polymers, refractory, glass, wood, cardboard, cloth and the like may be used. The fins may be only as thick as is necessary for structural purposes and may or may not be rigid. The fins may or may not be attached to the tubes. The gap between the fins and the tubes is preferably as small as possible. A fin may or may not contact the tube; contact between the fin and the tubes is not necessary. The tubes may be of any cross sectional shape. The shape of the fins may be altered to accommodate different tube packing patterns, tube spacing, tube diameters, tube shapes, prescribed ratios of heat transfer coefficient to pressure drop, and different fluid properties. It is preferred that the horizontal projections of the fins as depicted in
Similarly, cross section B-B1 and cross section C-C1 (indicated in
All fins 5, 6, and 7 of
Although the tubes in the examples are arranged in hexagonal close packing or triangular arrays, other tube patterns may be used, such as square arrays of tubes, etc. The tube spacing and patterns may be varied at the edges of a tube bundle from those within a tube bundle. The tubes may additionally enclose other tubes.
The packing around the tubes consists of multiple sub-assemblies of fins and members and rods (not shown), supports (not shown) and skids (not shown) surrounded by triangular groups of three tubes in an arrangement similar to that of the sub-assemblies shown in
Shell-side fluid flows vertically downward through the packing such that its path consists of counterclockwise helical paths between certain groupings of three tubes as indicated with reference to members 31, 32, and 33 and clockwise helical paths between certain other groupings of three tubes as indicated with reference to members 34, 35, and 36. The relative areas of the fins and of the members may be altered such that fins have a broader projected area at the expense of the members or the members have a broader projected area at the expense of the fins, as compared to those shown in
Thus, in accordance with an embodiment, a heat exchanger is provided. The heat exchanger includes a packing comprising at least one external oblique fin having a surface, and a plurality of tubes, each tube having an inlet, an outlet, a wall, an outer surface, an axis, and a reference plane. The plurality of tubes are substantially parallel and separate from each other.
In another embodiment, the packing includes a plurality of fins arranged in a plurality of columns. Each column includes a plurality of external oblique fins associated with a respective tube disposed along at least part of a length of the respective tube, and first fins in a first column have substantially the same first orientation. The first orientation of the first fins in the first column is different from a second orientation of second fins in a second column.
In another embodiment, a defining intersection is an intersection between the reference plane and a surface of the at least one external oblique fin. An angle between the defining intersection and the tube axis in the direction of the inlet is greater than 0° and less than 90°.
In another embodiment, the angle between the defining intersection and the tube axis in the direction of the inlet is greater than 0° and less than 45°.
In another embodiment, the heat exchanger further includes at least one of a plurality of transitional members, a plurality of supports and a plurality of skids.
In another embodiment, the heat exchanger further includes a helicoid transition member.
In another embodiment, the heat exchanger is a tube and shell type heat exchanger.
In accordance with another embodiment, a heat exchanger is provided. The heat exchanger includes a packing and a plurality of tubes. Each tube has an inlet, an outlet, a wall, and an axis. The plurality of tubes are substantially parallel to each other and separate from each other. The packing includes one or more external fins having a helicoid shape and having an axis of rotation that does not coincide with the tube axis.
In another embodiment, the axis of rotation is external to the plurality of tubes.
In another embodiment, the packing includes first external helicoidal fins twisted in a first direction and second external helicoidal fins twisted in a second direction opposite the first direction.
In accordance with another embodiment, a heat exchanger is provided. The heat exchanger includes a plurality of tubes, each tube having an inlet, an outlet, a wall, an outer surface, and an axis. The heat exchanger also includes a packing comprising a plurality of fins arranged in a plurality of columns, each column including at least one external oblique fin associated with a respective tube disposed along at least part of a length of the respective tube.
In one embodiment, the heat exchanger also includes a first fin in a first column having a first orientation, and a second fin in a second column having a second orientation different from the first orientation.
In another embodiment, each tube has a reference plane, wherein a defining intersection is an intersection between the reference plane and a surface of the at least one external oblique fin. The angle between the defining intersection and the tube axis in the direction of the inlet is greater than 0° and less than 90°. In another embodiment, the angle between the defining intersection and the tube axis in the direction of the inlet is greater than 0° and less than 45°.
In another embodiment, the heat exchanger includes at least one of a plurality of transitional members, a plurality of supports and a plurality of skids.
In another embodiment, the heat exchanger includes a helicoid transition member.
In another embodiment, the heat exchanger is a tube and shell type heat exchanger.
In another embodiment, the plurality of tubes are substantially parallel and separate from each other.
The present description anticipates that one skilled in the art will be able to calculate or experimentally determine optimal angles, shapes, spacings, overlaps, thicknesses, supports, skids, and materials of construction of the listed components and of divisions of the described components into sub-components, and such common and often necessary adjustments are within the scope of the present invention.
Although the present invention has been described in terms of certain preferred embodiments, various features of separate embodiments can be combined to form additional embodiments not expressly described. Moreover, other embodiments apparent to those of ordinary skill in the art after reading this disclosure are also within the scope of this invention. Furthermore, not all of the features, aspects and advantages are necessarily required to practice the present invention. Thus, while the above detailed description has shown, described, and pointed out novel features of the invention as applied to various embodiments, it will be understood that various omissions, substitutions, and changes in the form and details of the heat exchanger or process illustrated may be made by those of ordinary skill in the technology without departing from the spirit of the invention. The inventions may be embodied in other specific forms not explicitly described herein. The embodiments described above are to be considered in all respects as illustrative only and not restrictive in any manner. Thus, scope of the invention is indicated by the following claims rather than by the foregoing description.
This application claims the benefit of U.S. Provisional Patent Application No. 61/960,674 filed on Sep. 24, 2013, which is hereby incorporated by reference in its entirety for all purposes.
Number | Date | Country | |
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61960674 | Sep 2013 | US |