Heat exchange – Radiator core type – Side-by-side tubes traversing fin means
Reexamination Certificate
2002-04-05
2004-08-10
Bennett, Henry (Department: 3743)
Heat exchange
Radiator core type
Side-by-side tubes traversing fin means
C165S148000, C165S160000, C165S161000, C165S172000, C165S181000
Reexamination Certificate
active
06772830
ABSTRACT:
The present invention relates generally to methods and related apparatus for enhancing heat transfer to or from a fluid flowing cross-wise in contact with the outer thermally-conductive shells of a plurality of axially-oriented heat exchange conduits capable of acting as heat sources or heat sinks. By channeling cross-wise fluid flow, flowing generally orthogonal to the axes of the heat exchange conduits and contouring it upstream, downstream and/or around or alongside the heat exchange conduits utilizing slotted or apertured plates, baffles or surrounding sleeve-like elements, a surprisingly more effective and efficient heat transfer between the flowing fluid and the thermally-conductive surface is realized.
BACKGROUND OF THE INVENTION
It is well known to heat or cool process fluids, which may be liquids or gases, by flowing them into contact with a thermal-transfer surface that is maintained at a temperature which 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 higher or lower temperature than the fluid). In one familiar version of this technology, the thermal-transfer surface that acts as a heat source or heat sink is the exterior of a thermally-conductive shell of a thermal-transfer tube or pipe, for example, which is heated or cooled by means of a liquid flowing axially through the interior of the tube or pipe. In a variation of this technology, heat may be supplied directly inside a heat exchange conduit by means of flameless combustion of fuel gas (such as hydrogen or a hydrocarbon) as taught, for example, by U.S. Pat. Nos. 5,255,742 and 5,404,952, which are incorporated herein by reference.
It is also known in the art to flow a process fluid axially along a thermal-transfer surface, either concurrently or counter-currently relative to the direction of liquid flow inside the thermal-transfer tube, or to crossflow the process fluid relative to the axis of the thermal-transfer tube, or some combination of the two. Typical applications of heat transfer between crossflowing fluid and heat exchanging conduits are found in air coolers, economizers associated with fired heaters or furnaces, and in shell and tube exchangers. Various types of so-called radial or axial/radial flow reactor designs are known for various applications whereby at least a part of a fluid process stream moves, at some point, through the reactor in a radial, crossflow direction (i.e., inward-to-out or outward-to-in), as contrasted with the more familiar axial flow (i.e., end-to-end) reactor designs. Examples of reactor designs embodying at least in part a radial, crossflow of process fluid relative to a plurality of axially-disposed heat-transfer tubes are shown in U.S. Pat. Nos. 4,230,669; 4,321,234; 4,594,227; 4,714,592; 4,909,808; 5,250,270; and 5,585,074, each of which is incorporated herein by reference.
Although crossflow contact of a process fluid with a heat-transfer surface can be an attractive option for many applications, the utility of crossflow contact for industrial applications has been limited by certain heat transfer inefficiencies which have been experienced in practice. Typically in crossflow designs, a given portion of the process fluid is in contact with the heat-transfer surface for a shorter time than with a comparable axial flow design. In addition, the contact between the crossflowing process fluid and the heat-transfer surface is uneven due to process fluid separation and recirculation. Short surface contact time, uneven contact, and limited fluid mixing can lead to inefficient, insufficient, and/or non-uniform thermal energy transfer.
Thus, in an article entitled “Impingement heat transfer at a circular cylinder due to an offset of non-offset slot jet,” appearing in Int. J. Heat Mass Transfer., vol. 27, no. 12, pp. 2297-2306(1984), the authors Sparrow and Alhomoud report experimental efforts to vary the heat transfer coefficients associated with crossflow of a process gas relative to a heat-transfer tube by positioning a slotted surface 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 Reynolds number (degree of fluid turbulence), and whether the slot jet was aligned with or offset from the tube. The authors concluded that the heat transfer coefficient increased with slot width and Reynolds number, but decreased with slot-to-tube separation distance and offset.
Because the Sparrow and Alhomoud study concluded that the heat transfer coefficient increased with slot width, the general utility of an upstream slot to increase heat transfer is at best ambiguous based on these results. It can only be concluded that, in the experimental design used by Sparrow and Alhomoud, a relatively wider slot led to a higher heat transfer coefficient than a relatively narrower slot, and no upstream slot at all might yield the highest value. No testing was performed utilizing a plurality of heat-transfer tubes, or using upstream and downstream pairs, or around or alongside flow constriction means to preferentially contour crossflow fluid paths in contact with the outer surface of each of a plurality of heat-transfer tubes, and no reasonable extrapolations can be made to such very different alternative designs and configurations based on the extremely limited data presented.
These and other drawbacks with and limitations of the prior art crossflow heat exchanged designs are overcome in whole or in part with the enhanced crossflow heat transfer methods and designs of this invention.
OBJECTS OF THE INVENTION
Accordingly, a principal object of this invention is to provide methods and designs for enhanced crossflow heat transfer between a process fluid and a heat-transfer surface.
It is a general object of this invention to provide methods and designs for specially directing and shaping fluid crossflow paths in contact with one or more heat-transfer surfaces so as to enhance heat transfer between the fluid and the heat-transfer surfaces.
A specific object of this invention is to provide fluid flow-constriction means upstream, downstream and/or around or alongside a heat-transfer surface so as to preferentially contour a process fluid stream flowing cross-wise past the heat-transfer surface to enhance heat transfer between the fluid stream and the heat-transfer surface.
A further specific object of this invention is to provide curved or flat apertured plates or apertured sleeves disposed relative to each conduit in an array of heat exchange conduits so as to preferentially contour the flow path of the fluid stream flowing cross-wise past the outside of each of the conduits to realize improved heat transfer.
Still another object of this invention is to provide heat-transfer conduit arrays of varying sizes and configurations wherein each conduit of the array is associated with its own fluid flow-constriction means upstream, downstream and/or around or alongside of the conduit so as to preferentially contour the portion of the fluid stream flowing cross-wise past the outside of the conduit to realize improved heat transfer.
Other objects and advantages of the present invention will in part be obvious and will in part appear hereinafter. The invention accordingly comprises, but is not limited to, the methods and related apparatus, involving the several steps and the various components, and the relation and order of one or more such steps and components with respect to each of the others, as exemplified by the following description and the accompanying drawings. Various modifications of and variations on the method and apparatus as herein described 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 baffle structure comprising at least a paired set of fluid flow constructors is utilized to preferenti
Jayaswal Umesh K.
Larsen Thomas L.
Bennett Henry
Hedman & Costigan ,P.C.
Patel Nihir
Stone & Webster Inc.
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