Heat exchange – Casing or tank enclosed conduit assembly – With distinct flow director in casing
Utility Patent
1999-01-26
2001-01-02
Lazarus, Ira S. (Department: 3743)
Heat exchange
Casing or tank enclosed conduit assembly
With distinct flow director in casing
C165S159000
Utility Patent
active
06167951
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a regenerative heat exchanger that can be used in a flow-through water treatment system to kill pathogenic microorganisms.
INTRODUCTION AND BACKGROUND OF THE INVENTION
In dire personal need water can be purified by boiling. Boiling kills microorganisms hazardous to human beings. However, the energy cost of boiling large quantities of water for municipalities or other large-scale requirements is exorbitant, and unless continued over a period of 15 minutes or more, it does not necessarily destroy all pathogens potentially harmful to humans or fish and it does not remove inorganic minerals or any organic contaminants.
However, if instead of simply boiling the water, the water is passed through a heat exchanger, the process would be advantageously efficient. Patents that describe various heat exchangers are discussed below.
Cameron, U.S. Pat. No. 4,357,991 recognizes the intrinsic high efficiency of the disk and donut baffle configuration in shell and tube heat exchangers, but U.S. Pat. No. 4,357,991 requires an equal diagonal spacing between all tubes and their nearest neighbors on adjacent rows and a minimum tube-to-tube separation of twice this distance between tubes on the innermost row. This causes the incurrence of a larger unproductive void volume in the center of the heat exchanger than the configuration which is the subject of the present work. We have found, at least in the turbulent flow regime where operation is most economic, that twice the diagonal tube-to-tube spacing distance between tubes in the first row is not required or even desirable. Such configuration is not desired because tubes in the first row have only two nearest neighbors instead of four and therefore unless the spacing between tubes on the first innermost row is less than twice the diagonal spacing between a tube on the first row and its nearest neighbors on the second row the heat exchange is not balanced and the tubes in the first row become less effective than the tubes on other interior rows. The desired design configuration is one where the external heat transfer coefficient is the same or nearly the same for all tubes and not necessarily an equal spacing between all tubes and their nearest neighbors on adjacent tube rows. The mistaken requirement, for the purposes of obtaining uniform or near uniform heat transfer, that the spacing between tubes in the innermost row be twice the diagonal spacing between each tube and its nearest neighbors on the second adjacent tube row diminishes the number of tubes which can be inserted within a given shell volume, and accordingly limits heat transfer. As subsequently noted in Cameron in U.S. Pat. No. 5,044,431 in col. 1 lines 46-53 there is a problem with the economy of the tube spacing in U.S. Pat. No. 4,357,991 and;
Although the approach in the Cameron patent [U.S. Pat. No. 4,357,991] allows a second family of rings [tube rows] to be placed outside the main series with smaller ligaments and more tubes per ring, the discontinuity caused by the change in the ring tubing density significantly moves the outer edge of the bundle outwardly and makes the heat exchanger larger. In addition there is a discontinuity in flow between the families of rings . . .
Also noted by Cameron in col. 4, lines 13-15 of U.S. Pat. No. 5,044,431 with regard to the tube spacing in the innermost tube ring;
can be designed so that [the spacing between tubes] in the two inner arcs, “b”=1.5a [“a” being the diagonal separation between each tube and its nearest neighbors in the adjacent tube rows], rather than 2a . . . While this will create a slightly increased pressure drop in the inner rings, this will not have a major effect on the performance of the heat exchanger.
U.S. Pat. No. 4,357,991 also fails to recognize or at least specify the much greater efficiency, and therefore desirability of operation in the all turbulent flow regime. We have found, especially for the regenerative heating of water, a fluid with high specific heat and low thermal conductivity, that: (1) operation in the all turbulent range becomes an economic necessity from a cost benefit point of view; and (2) for balanced or near equal heat transfer to every tube, which is an object of U.S. Pat. No. 4,357,991, the tube spacing between at least: the tubes on the first or innermost row should be less than twice the diagonal spacing between tubes and their closest neighbors on adjacent rows. Equal shell-side heat transfer to the tubes on the outermost tube row cannot be accomplished without inserting rods or other turbulence enhancing expedient to compensate for the fact that the tubes on the outermost row have only two nearest neighbors. However, this would also increase tube-bundle volume and entail additional fabrication cost. It is better to add one more tube row and accept ≈80% effectiveness from the tubes in the outermost row.
Finally, U.S. Pat. No. 4,357,991 fails to disclose the multiple parallel tube bundle configurations shown in
FIGS. 4 and 5
of the present application, which comprises a more economic means of heat exchange within a single shell, and extends only to the specific design of a heat exchange element rather than high efficiency heat exchange as a component or means of thermal water purification and/or sterilization.
Cameron, in U.S. Pat. No. 5,044,431 claims another disk and donut baffle configuration for shell and tube heat exchangers, which is similar to U.S. Pat. No. 4,357,991. This configuration differs from the present invention in that the tubes are spaced on a multiplicity of arcs having centroids which are not coincident with the shell axis. The object of U.S. Pat. No. 5,044,431 is to minimize the unproductive core volume interior to the first row of tubes thereby enhancing the advantage of the disk and donut baffle configuration via a greater density of tube packing. However, the configuration of U.S. Pat. No. 5,044,431, somewhat defeats the uniformity of flow which U.S. Pat. No. 4,357,991 and the present work seek to capitalize upon. Beyond the general disk and donut baffle configuration, U.S. Pat. No. 5,044,431 does not present a geometry which is similar to that of the present work. Further, U.S. Pat. No. 5,044,431 is concerned with the specific design of the heat exchange element and not a high efficiency heat exchanger as a component of a thermal water purification and/or sterilization system.
Burne, U.S. Pat. No. 3,587,732, claims a heat exchange configuration where one fluid flows into the inner diameter of a large porous or skeletal metal tube and is forced to percolate from the inner to outer diameter while it receives heat from, or transfers heat to, a secondary fluid which is caused to flow through a parallel set of smaller tubes which are imbedded in and in close thermal contact with the porous or skeletal metal, as by brazing. Obviously the primary fluid flow could be from the outside diameter inward with essentially the same effectiveness. However, this configuration is a completely different heat transfer configuration than the flow configuration according to the invention. According to the present invention, the heat transfer is expedited by an efficient, uniform radial flow across, in general, a substantially greater number of small tubes and a suitable shell-side flow velocity and a high level or turbulence is achieved by utilizing a large number of baffle plates. In contrast, the heat transfer in Burne is expedient by enhanced thermal conduction available from a thermally conductive porous media such as a skeletal aluminum or copper matrix. The design and principle of operation of U.S. Pat. No. 3,587,732 are different from the present work.
In addition, the shell-side flow in the Burne configuration is radially symmetric but it is not a disk and donut configuration and therefore is different from the heat exchanger according to the invention. In Burne U.S. Pat. No. 3,587,732, the total shell-side flow makes only one radial pass: percolating from the central cavity through
Couch Harold Matthew
Couch Harold Thompson
Lazarus Ira S.
McKinnon Terrell
Smith , Gambrell & Russell, LLP
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