US 3705621 A
An air cooled heat exchanger, having U-tubes, for cooling gases or liquids. Each tube is connected at one end to an inlet manifold and at the other end to a collection manifold. Cooling air flows co-currently with the condensing vapor or cooling liquid, thus preventing subcooling and freezing.
Description (OCR text may contain errors)
United States Patent [151 3,705,621 Schdonman [4 1 Dec. 12, 1972 [s41 AIR-COOLED HEAT EXCHANGER 3,598,179 8/1971 Giauque ..l65/l 11  Inventor: Willem Schoonman, Voorschoten, Primary Examiner wmiam Wayner Neheflands Attorney-Richard J. Holton et al. 73 Assi nee: The Lummus Com an Blo Infield, 1 g NJ. p  ABSTRACT  Filed: June 25 1971 An air cooled heat exchanger, having U-tubes, for coolmg gases or l1qu1ds. Each tube 1s connected at one  Appl. No.2 156,844 end to an inlet manifold and at the other end to a collection manifold. Cooling air flows co-currently with the condensing vapor or cooling liquid, thus prevent-  0.8. CI. ..l65/l12, 165/124, 165/176 ing b li and f e i  Int. Cl ..F28b 1/06  Field of Search ..165/l1l,110,124,176,112
[ 56] References Cited 7 Claims, 3 Drawing Figlll'GS UNITED STATES PATENTS 1/1969 Schoonman ..16s/122 x Condensate AIR-COOLED HEAT EXCHANGER BACKGROUND OF THE INVENTION Numerous types of air cooled heat exchangers for condensing steam and other vapors by indirect heat exchange with flowing air have been described and patented. A common factor in the design of such equipment is the necessity of preventing subcooling and consequent freezing of condensate in the tubes of the exchanger. However, few of the designs devised to overcome or prevent this problem have proven suitable for use in extreme weather conditions, e.g., at low ambient temperatures. Nor are most designs sufficiently versatile so as to be used in areas of the world in which the temperature may vary widely from season to season.
SUMMARY OF THE INVENTION This invention comprises a design for an air cooled heat. exchanger; particularly a vapor condenser, in which subcooling of the condensate is prevented, even at low ambient temperatures. However, the invention is not limited to use at such temperatures; it can be used in any. situation in which vapor is to be condensed by indirect heat exchange with cooling air. In fact, subcooling does not only occur at low ambient temperatures; it can take place at higher temperatures in situations in which the vapor flows at a low rate, and condensate accumulates in the tubes.
In general, the invention relates to an air cooled heat exchanger for condensing vapors, comprising an inlet manifold, a first condensate manifold, a second condensate manifold, a first plurality of substantially U- shaped tubes connecting the inlet manifold to the first condensate manifold, a second plurality of substantially U-shaped tubes connecting the inlet manifold to the second condensate manifold, means for directing air to flow over the outsides of the tubes to condense vapor therein, means for draining condensate from the condensate manifolds, means for removing vapor from the condensate manifolds, the first plurality of tubes having an upstream leg connected to he inlet manifold and a downstream leg connected to the first condensate manifold, the second plurality of tubes having an upstream leg connected to the inlet manifold and a downstream leg connected to the second condensate manifold, the first and second pluralities of tubes being so disposed that the air flows first over the upstream legs of the first plurality of tubes, then over the upstream legs of the second plurality of tubes, then over the downstream legs of the second plurality of tubes, and finally over the downstream legs of the first plurality of tubes.
DETAILED DESCRIPTION OF THE INVENTION The invention is more clearly shown and described in the accompanying drawings, in which:
FIG. 1 is an elevational view of an embodiment of the invention, in a vertical arrangement;
FIG. 2 is a section of FIG. 1 taken along line 2-2;
FIG. 3 shows schematically an inclined arrangement of two exchangers embodying the invention, with a common source of vapor.
The exchanger of FIGS. 1 and 2 generally comprises an inlet manifold 5, condensate manifolds 6 and 7, tubes 1 and 2, vapor outlet 8 and condensate outlet 9.
Steam or other vapor enters the inlet manifold 5 from an external source (e.g., 12 in FIG. 3). From the manifold it flows into the upstream legs la, 2a of tubes 1 and 2, which are generally of the finned type. Tubes 1 and 2 are of a generally U-shaped configuration, with the upstream legs of the U (la, 20) connected to the corresponding downstream legs lb, 2b by bends 14, 13. The tubes may be integral or composed of several sections connected together, as by welding. The ends of legs 2b are connected to condensate manifold 6; the ends of legs 2a to condensate manifold 7, which is separate from, but located adjacent to manifold 6. In the embodiment of FIGS. 1 and 2, the lower ends of manifolds 6 and 7 are connected by a connecting pipe 11 which carries the condensate via loop seal 10 to the bottom of manifold 5, from which it is removed in outlet 9. Air and uncondensed vapor are removed from manifolds 6 and 7 through outlet 8, which connects the upper ends of both manifolds.
Airis passed over the exchanger by means of a fan 0 other device in the direction shown by the arrows FIGS. 1 and 2; that is, cocurrently with the flow of vapor and condensate. As shown in the figures, the cold air first encounters the hottest steam, in tubes la. The slightly warmed air is then heat exchanged against an additional quantity of the hottest steam in tubes 2a, followed by heat exchange against condensate in tubes 2b. Finally the warmed air is heat exchanged against the coldest condensate in tubes 1b.
Some heat exchange may also take place between cold air and the steam in manifold 5, but this is not detrimental as it contributes to the heating of the air and the condensate thus formed can easily be removed, through outlet 9 or otherwise.
The tubes 1a, 2a are arranged :in what is known as a triangular pitch, that is, the tubes 2a are staggered with respect to tubes 1a so that a combination of two tubes in any row (for example row 1a) with the nearest tube in the other row (2a) forms a triangle. Similarly, the tubes 2b are arranged with tubes 1b in a triangular pitch. This allows for maximum use of the cold air, since that portion of the cooling air which passes between the tubes 1a will be encountered by tubes 2a. Preferably, as shown in FIGS. 1 and 2, the row of tubes 2a, 2b is situated within the area enclosed by the U- shape of tubes 1a, lb.
The Figures depict the exchanger as having two sets of tubes (1,2) joined by U-bends, with two condensate manifolds. However, the exchanger may have three or more sets of tubes, each with its accompanying condensate manifold.
Because of the cocurrent flow of air and steam, and the danger of subcooling the condensate in tubes 2b, and particularly in tubes lb, is eliminated, since the air which is heat exchanged against the condensate has been warmed by previous contact with hot steam. Similarly, even though condensate may accumulate in the bottom of manifolds 6 and 7, there is no danger of subcooling since the air passing over the manifolds has been sufficiently warmed.
As shown in FIG. 1, the tube bundles are preferably sloped so that the downstream legs 1b, 2b of the tubes are located at a lower level than the upstream legs 1a, 2a to permit drainage of condensate from the tubes by gravity.
Under some operating conditions the amount of steam condensed in the outer row of tubes 10, 1b can be appreciably higher than that condensed in tubes 20, 2b. This will result in a higher pressure drop across tubes la, lb than across tubes 2a, 2b, with an accompanying loss of sensible heat. The condensate outlet construction shown in FIG. 1 enables this heat loss to be recovered by contact of exiting condensate with hot steam in the lower part of the steam manifold 5. The higher level of condensate in manifold 7, resulting from the higher pressure drop in tubes la, 1b, combined with the loop seal construction 10, causes some increase in the flow of condensate, resulting in a greater heat transfer. Additionally, the direct contact with hot steam prevents any subcooling of the exiting condensate which might take place owing to its proximity to the coldest air. The lower portion of manifold 5 can also be insulated to prevent such subcooling.
However, this construction is but a preferred embodiment of the invention; the condensate manifolds may be drained in any convenient manner, by separate drain pipes or by a simple common drain.
FIG. 3 depicts an inclined arrangement of two condensers of the present design, operating from a common vapor inlet 12. The drawing depicts the vapor inlet connected to the top of vapor manifolds 5, but it may in fact be connected wherever convenient. Air is supplied by fans here shown located below the exchangers, with guides 17 for guiding the air across the exchangers. The fans may also be located above the exchangers, causing air to flow over them by induced draft.
While the apparatus of the present invention has been described mainly in terms of condensing steam, it is equally applicable to the cooling of other vapors, such as hydrocarbons, and to the cooling of liquids such as hydrocarbons and water.
While this invention has been described in terms of certain preferred embodiments and illustrated by way of particular drawings, these are only illustrative, as many equivalents and alternatives will present themselves to those skilled in the art as within the spirit and proper scope of the invention. The invention is therefore not to be construed as limited, except as set forth in the following claims:
1. An air cooled heat exchanger for condensing vapors comprising an inlet manifold, a first condensate manifold, a second condensate manifold, a first plurality of substantially U-shaped tubes connecting the inlet manifold to the first condensate manifold, a second plurality of substantially U-shaped tubes connecting the inlet manifold to the second condensate manifold, means for directing air to flow over the outsides of the tubes to condense vapor therein, means for draining condensate from the condensate manifolds, means for removing vapor from the condensate manifolds, the first plurality of tubes having an upstream leg connect= ing to the inlet manifold and a downstream leg connected to the first condensate manifold, the second plurality of tubes having an upstream leg connected to the inlet manifold and a downstream leg connected to the second condensate manifold, the first and second pluralities of tubes being so disposed that the air flows first over the upstream legs of the first plurality of tubes,
then over the the upstream le s of the second pluralit of tubes, then over the downs ream legs of the secon plurality of tubes, and finally over the downstream legs of the first plurality of tubes.
2. The apparatus of claim 1 in which the first and second pluralities of tubes are disposed in a triangular pitch arrangement.
3. The apparatus of claim 1 further comprising means for gravity draining liquid from each of the pluralities of tubes.
4. The apparatus of claim 1 wherein the tubes of the second plurality of tubes are located within the space enclosed within the U-bends of the first plurality of tubes.
5. The apparatus of claim 1 wherein the first and second condensate manifolds are connected by a common liquid drain means.
6. The apparatus of claim 5 wherein the common liquid drain means comprises a collection pipe connected to the inlet manifold by a loop-seal structure, and means for draining liquid from the inlet manifold.
7. Apparatus according to claim 6 further comprising means in the inlet manifold for bringing liquid drained from the condensate manifolds into direct heat exchange contact with vapor.