US3508608A - Condenser tubes - Google Patents

Description

A ril 28, 1970 R. C. ROE

CONDENSER TUBES Filed April 17, 1968 INVENTOR. fiLP/l 6' $6 Arr-0e N56 United States Patent 3,508,608 CONDENSER TUBES Ralph C. Roe, Tenafly, N.J., assignor to Saline Water Conversion Corporation, Oradell, N.J., a corporation of New York Filed Apr. 17, 1968, Ser. No. 722,011 Int. 'Cl. 192% N42 US. Cl. 165-179 6 Claims ABSTRACT OF THE DISCLOSURE Condenser tubes having longitudinal external grooves for attracting and channeling condensate and internal longitudinal fins tapered in cross section to optimize heat transfer paths through the tubes.

This invention relates to fluid heat transfer systems and more particularly it concerns novel arrangements for effecting condensation of liquids from their vapors.

The present invention is particularly suited to steam condensers, such as may be used in saline to fresh water conversion systems, or as may be used in steam power plant operations.

One feature of the present invention lies in the fact that it makes practical the use of vertical tube arrangements in condensers. In general, a steam condenser comprises an outer jacket or shell into which steam is admitted. A plurality of condenser tubes pass through the interior of the shell, and a coolant fluid, usually a liquid, passes through these tubes to maintain their outer, steam exposed, surfaces below the condensing temperature of the steam inside the outer shell. Thus, when the steam in the shell impinges on the tube surfaces it cools and condenses into liquid droplets. These droplets eventually fall off the tubes and drop into a fresh water collection basin near the bottom of the shell.

The condenser tubes in prior condenser arrangements have, in nearly all cases, been oriented to extend horizontally through the outer shell. The reason for this was that the liquid droplets which condensed on the tube surfaces would form a thin liquid film which, in the case of a vertical tube, would flow down and cover nearly the entire outer surface of the tube. This liquid film, though quite thin, presented an extraordinarily large resistance to heat transfer and thereby severely impaired the condensing ability of the condenser. In order to avoid or at least minimize this situation, the condenser tubes were arranged horizontally so that the liquid which formed on any one portion of the tube length would fall off from that one portion without flowing to another portion and impairing the condensing function there.

The present invention in one aspect makes it possible to provide a vertical tube condenser arrangement without the above-described impairment of the condensing function. In this aspect, use is made of the relatively high surface tension of water in its liquid form. This is done through the provision of a plurality of elongated narrow grooves which extend along and open out to the outer surface of each condenser tube. As condensate forms along the outer surface of each tube and begins to flow down the length of the tube, its cohesiveness or tendency toward self attraction results in the water in the grooves being effective to attract the Water on the remaining surfaces and pull this water also into the grooves. This leaves the remaining surface of the tubes free of liquid film and therefore at their maximum effectiveness.

According to a further aspect of the present invention, there is provided a condenser tube configuration which maximizes the heat transfer characteristics between the tube and the liquid coolant flowing through it. It is, of

3,508,608 Patented Apr. 28, 1970 ice course, known that heat transfer can be increased by increasing the surface area over which the heat transfer takes place and that one means of achieving this is by the use of fins or projections on the heat transfer surface. The present invention, however, provides arrangements by which the effectiveness of heat transfer fins is increased. According to the present invention, there are provided along the inner surface of the condenser tubes, inwardly projecting fins which are wider toward the condenser tube surfaces. As specifically embodied, these fins in cross section are triangular, and their apexes point toward the axis of the tube. As a result of this arrangement, not only is the inner surface area of the condenser tubes increased, but, in addition, this increased surface area is evenly distributed. Consequently, heat flow through the tubes is improved evenly all about the tubes and not just in discrete regions. Because the heat flow is evenly distributed, there are no isolated regions of high heat flow through the tube walls and the overall resistance to heat transfer by the tubes is minimized.

The present invention in a still further aspect makes possible a condenser tube structure in which the improved heat transfer features described above can be cooperatively combined. According to this aspect, there is provided a condenser tube having exterior grooves and interior wide base fins which are properly positioned to accommodate the grooves. Thus, essentially the same structural configuration simultaneously provides both internal and external features which operate in different ways (i.e. the one by removing a water film and the other by evenly increasing the heat transfer surface area) to produce a cooperative eifect, namely the improved ability to effect condensation.

Various further and more specific objects, features and advantages of the invention will appear from the description given below, taken in connection with the accompanying drawings, illustrating by way of example a preferred form of the invention.

In the drawings:

FIG. 1 is a perspective view, partially cut away, and somewhat diagrammatic, of a vertical tube condenser in which the present invention is embodied;

FIG. 2 is an enlarged elevational view of a condenser tube used in the condenser of FIG. 1; and

FIG. 3 is a cross sectional view taken along line 33 of FIG. 2.

In the arrangement of FIG. 1, there is provided a condenser 10 comprising an outer steel jacket or shell 12, and a plurality of vertically extending elongated condenser tubes 14 positioned within the shell 12.

The shell 12 is of generally cylindrical configuration and it encloses a condensing region 16 through which the tubes 14 pass. A steam inlet 18 is provided on the side of the shell 12 for admitting steam to be condensed into the region 16.

Within the shell 12 there are provided upper and lower tube sheets 20 and 22 which define the upper and lower extremities of the condensing region 16. The ends of the condenser tubes 14 are tightly fitted to the tube sheets so that the interiors of the condensing tubes are open to end regions 24 and 26 between each tube sheet and its respective end of the shell 12. At the same time, the interiors of the tubes 14 are isolated from the condensing region 16. Coolant inlet and outlet means 28 and 30 are provided respectively at the ends of the shell 12 to permit coolant liquid to flow through the end regions 24 and 26 and the interiors of the tubes 14.

A condensate collection basin 32 is formed in the lower tube sheet 22, and a condensate outlet 34 is arranged to permit the collected condensate to flow from the basin 32 to the exterior of the condenser 10.

The overall operation of the condenser as thus far described is similar to that of conventional condensers. That is, steam to be condensed is admitted via the inlet 18 into the condensing region 16 where it contacts the external surfaces of the condensing tubes 16. At the same time, coolant liquid flows through the interiors of the tubes between the end regions 24 and 26 to maintain the temperature of the tubes below the vaporization temperature of the steam. Heat thus passes from the steam through the tube walls and into the coolant liquid; and as the steam loses its heat it condenses in liquid form on the external surfaces of the tubes 14 and eventually flows down the tubes and into the collection basin 32.

The condensing tubes 14 are each of similar configuration and construction. As shown in FIGS. 2 and 3, a representative tube 14 is of elongated, tubular configuration. The tube may be made of any material normally used for conventional condenser tubes. In addition, it may be formed by extrusion or any other known process which will produce the configuration described below.

It can be seen that the exterior surface of the tube 14 is formed with a plurality of spaced grooves 40 which extend along the length of the tube in parallel fashion. The grooves 40 are of generally rectangular cross section and their depth into the surface of the tube 14 is greater than their width. The grooves 40 open out to the outer surface of the tube 14; and they define between them lands 42 upon which condensate forms. Actually, condensate initially forms also in the grooves 40; and as it flows downwardly along the grooves, it attracts the condensate formed on the lands 42. This attraction is produced by the inherent cohesiveness of water, especially of pure water such as fresh condensate. This in turn is produced through the effects of surface tension of the water. In essence, the surface tension effects are such that the water attempts to maximize its volume while minimizing its surface area. Thus, since the configurational situation inside the grooves is more amenable to these conditions than is that on the lands themselves, the water becomes drawn off the lands and into the grooves. This leaves the lands bare and free of liquid film so that their heat transfer characteristics are not deteriorated.

The interior configuration of the tube 14 is defined by a plurality of longitudinally extending fins 50. The fins 50 in cross section are of generally triangular configuration with apexes 52 which point toward the longitudinal axis of the tube, and wide bases 54 at the inner surface of the tube 14. It will be noted that the fins 50 thus provide straight sloping surfaces 56 which contact the liquid flowing through the tube. In addition, the fins 50 are positioned in close positional relationship so that the base ends of the sloping surfaces 56 of adjacent fins actually touch each other. As a result, every segment on the exterior of the tube 14 has a corresponding segment on the interior of increased surface area. Thus, the increased heat transfer surface area provided by the fins 50 is uniformly distributed about the tube 14.

The increased surface area serves to improve the flow of heat from the tube walls to the coolant liquid flowing through the tube. In addition, however, the tapered or triangular configuration of the fins serves to establish heat flow paths from the outer to the inner surfaces of the tube 14 which are substantially uniformly distributed. As a result, the increased heat transfer obtained by virtue of the fins 50 is not concentrated in isolated regions of the tube walls but instead, it is spread evenly about the tube. In this manner, the overall heat transfer characteristic of the condenser tube system is substantially improved.

It will be noticed that the internal fins 50 and the external grooves 40 of the tube 14 are so positionally related that each groove 40 is adjacent the base of a corresponding fin 50. This arrangement is especially advantageous since the generally complementary configurations of the fins and grooves serves to minimize the amount of 4 metal (i.e. the wall thickness), required in the construction of the tube 14. At the same time, each element opcrates in its own manner to improve heat transfer from the steam surrounding the outside of the tube, to the coolant liquid inside the tube.

Although a certain specific embodiment of the invention is herein disclosed for purposes of explanation, further modifications thereof, after study of this specification, will be apparent to those skilled in the art to which the invention pertains. Reference should accordingly be had to the appended claims in determining the scope of the invention.

What is claimed and desired to be secured by Letters Patent is:

1. In a condenser tube having an external surface and an internal surface for exchanging heat therethrough, the improvement which comprises:

a plurality of alternating elongated lands and grooves forming the external surface of said tube and extending along the length thereof, said lands and grooves being substantially equally spaced around said tube; and plurality of elongated fins projecting inwardly and forming the internal surface of said tube and extending longitudinally therealong, said fins being of generally triangular cross section and in close sideby-side relation such that the bases of their sloping surfaces touch.

2. An improved condenser tube as in claim 1 wherein there are provided a like number of said grooves and fins and wherein each of said grooves is positioned opposite the central portion of the base of a corresponding fin.

3. A condenser tube as in claim 1 wherein said grooves have a depth greater than their width.

4. A condenser tube as in claim 1 wherein said grooves are of generally rectangular cross section.

5. In a condenser for converting vapor to a liquid having an outer shell enclosing a condenser region the improvement which comprises:

a pair of spaced tube sheets positioned within said shell and separating said condenser region from end regions;

means for admitting a vapor into said condenser region;

a plurality of condenser tubes extending in a vertical direction through said condenser region between said tubes each being provided with a plurality of alternating elongated lands and grooves forming the external surface of said tubes and extending along the length thereof, and a plurality of elongated triangular shaped fins projecting inwardly and forming the internal surface of said tube and extending longitudinally therealong, said fins being in close side-by-side relation such that the bases of their sloping surfaces touch;

means for admitting a coolant fluid into said end region-s to pass through said condenser tubes; and

means at the lower ends of said tubes for collecting condensate from said grooves.

6. An improved condenser as in claim 5 wherein the grooves on said tubes are generally parallel and equally spaced, and wherein said grooves are positioned opposite to said fins.

References Cited UNITED STATES PATENTS 626,924 6/1899 Ortmans --177 1,519,673 12/1924 Doble 165-179 X 2,467,668 4/1949 Hallberg 165-179 X 2,978,797 4/1961 Ekelund 165179 X LLOYD L. KING, Primary Examiner T. W. STREULE, Assistant Examiner

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