US 3675710 A
Apparatus for and method of condensing hot vapor at increased efficiency wherein the initial flow path for hot vapor is so related to that in downstream areas as to provide relatively high velocity contact of hot vapor with the heat exchange wall, thereby to promote heat transfer. Provision for drainage of condensate at closely spaced intervals facilitates condensate removal and enables the vapor to have wiping contact with a maximum interior surface area of the heat exchange wall. If tubes of similar size are employed throughout, control of vapor velocity is obtained by selecting a varying number of tubes in parallel at different flow levels and additionally by causing the vapor to flow in a spiral path to increase its velocity and wiping contact with the heat exchange surfaces.
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Description (OCR text may contain errors)
United States Patent Ristow [451 July 11,1972
 Inventor: Roderick E. Ristow, 1441 W. 190th St.,
Gardena, Calif. 90247 22 Filed: March 8,1971
21 Appl.No.: 121,755
Related U.S. Application Data  Continuation-impart of Ser. No. 825,496, May 19,
 U.S. Cl ..165/1, 165/111, 165/147, 165/176, 165/109 [51 1 Int. Cl. ..F28b l/00  Fleldoi'Seanch ..165/1, 110, 111, 146,147, 165/174, 176, 145, 109
 References Cited UNITED STATES PATENTS 1,578,830 3/1926 Jones et a1. ..165/146 1,759,011 3/1930 Huet ..165/1 FOREIGN PATENTS OR APPLICATIONS 284,413 2/1928 GreatBritain ..165/117 913,270 12/1962 Great Britain ..165/147 Primary ExaminerALbert W. Davis, Jr. A!!omeySellers and Brace  ABSTRACT Apparatus for and method of condensing hot vapor at increased efiiciency wherein the initial flow path for hot vapor is so related to that in downstream areas as to provide relatively high velocity contact of hot vapor with the heat exchange wall, thereby to promote heat transfer. Provision for drainage of condensate at closely spaced intervals facilitates condensate removal and enables the vapor to have wiping contact with a maximum interior surface area of the heat exchange wall. If tubes of similar size are employed throughout, control of vapor velocity is obtained by selecting a varying number of tubes in parallel at different flow levels and additionally by causing the vapor to flow in a spiral path to increase its velocity and wiping contact with the heat exchange surfaces.
9Clnims,4Drawingiigures PATENTEnJuL 1 1 1972 Ea. Z
HIGH EFFICIENCY VAPOR CONDENSER AND METHOD This application is a continuation in part of my copending application for U.S. Letters Patent Ser. No. 825,496, filed May 19, 1969 titled High Efficiency Vapor Condenser and Method, now abandoned.
This invention relates to evaporative condensers, and more particularly to an improved heat exchange apparatus and method wherein heat exchange efficiency is enhanced by so proportioning the flow path as to assure relatively high velocity flow initially and lower flow velocity as condensation progresses.
It has been found that a substantially smaller, lighter weight, more efficient condenser is provided by varying the velocity of vapor flow in different portions and by taking steps to pass the vapor in wiping contact with a maximum percentage of the heat exchange surface throughout the length thereof. These objectives are achieved according to the principles of this invention by varying the cross sectional flow area so as to provide relatively high flow velocity for the incoming vapor as contrasted with the vapor velocity as it approaches the dew point and begins to liquify and additionally by causing the vapor to follow a spiral path thereby further increasing its velocity, turbulence and the effectiveness of the wiping contact with interior surfaces of the heat exchanger. The high initial velocity promotes heat transfer by fast wiping contact with the exchanger walls as well as internal turbulence to aid in bringing all portions of the vapor into contact with the wall surface. The variable velocity flow is obtained without need for specially constructed tubes simply by utilizing a smaller number of tubes in the higher velocity passes. By this technique the same size of tubes may be used throughout. A thin spiral strip extending lengthwise of tubing conducting superheated vapor is found beneficial. The number of tubes in a pass may be determined by the location of partitions in the headers. Maximum surface contact is obtained by collecting condensate as it forms and draining it away in a path out of contact with vapor.
Accordingly, it is a primary object of the present invention to provide an improved high efliciency vapor condenser and method designed to provide relatively high velocity vapor flow initially decreasing to a substantially lower velocity as the vapor temperature approaches the dew point.
Another object of the invention is to provide an improved vapor condensing heat exchanger of variable velocity flow achieved with tubes of similar size so arranged as to provide a substantially smaller cross sectionalflow .area for hot vapor than for vapor dissipating latent heat of condensation.
Another object of the invention is the provision of a high efficiency, low cost, lightweight condenser utilizing a plurality of similar sized tubes arranged between headers partitioned to provide a much smaller number of tubes in the flow path for incoming hot vapor than for vapor undergoing condensation thereby to provide much higher velocity flow initially than for vapor passing through the condensing phase.
Another object of the invention is the provision of a high efficiency vapor condenser and method utilizing a plurality of passes for vapor through heat exchange tubing of substantially the same diameter and spacing which tubing is arranged and constructed to provide a relatively high velocity spiralling flow for entering superheated vapor and relatively slower flow for vapor cooled substantially to the dew point.
Another object of the invention is the provision of a heat exchange apparatus and method for use in condensing vapor having a plurality of passes formed from similar sized tubing and forming one or more relatively high velocity vapor passes at the upper level of the exchanger and relatively low velocity passes in lower portions of the exchanger along with means for collecting condensate as it forms and draining it away in a path out of contact with the uncondensed vapor.
These and other more specific objects will appear upon reading the following specification and claims and upon considering in connection therewith the attached drawing to which they relate.
Referring now to the drawing in which a preferred embodiment of the invention is illustrated:
FIG. 1 is a view partially in vertical cross section through one preferred embodiment of a heat exchanger embodying the principles of this invention;
FIG. 2 is a cross sectional view taken along line 2-2 on FIG. 1 with portions of the header casing broken away;
FIG. 3 is a cross sectional view on an enlarged scale through a single tube of the exchanger; and
FIG. 4 is a cross sectional view through a lower tube of the exchanger and illustrative of operating conditions in a conventional heat exchanger lacking means for purging condensate.
Referring initially more particularly to FIG. 1, there is shown a preferred arrangement of an evaporative condenser, designated generally 10, incorporating the features of this invention. The heat exchanger comprises a pair of similar headers ll, 12 fabricated from sheet stock welded or brazed together and interconnected between their adjacent faces by a multiplicity of tubes 13 of the same size and preferably inclined slightly to the horizontal in the direction of fluid flow. One or more hot vapor supply tubes 14, 14. open into the upper end of header l2 and condensate is drained away by conduits 15 leading from the lower end of this same header.
Various expedients may be employed to provide relatively high velocity flow in upper passes and lower velocity flow in lower passes of exchanger 10 including the use of different numbers of tubes in adjacent passes and the use of tubes of smaller diameter in the higher velocity paths than in the low velocity passes. However, numerous advantages reside in the use of a variable number of similar size tubes in certain passes and this is the arrangement shown here. When using this technique, it is only necessary to inventory the same size tubing, tools and jigs employed in prearing the header plates to receive the tubes as well as the same equipment for welding and cutting the tubes to length. The higher velocity flow is readily obtained in part by the use of appropriately located partitions 18 crosswise of the interior of headers 11 and 12 and/or in part by the use of baffling in tubing carrying superheated vapor. Partitions 18 are welded in place between the interior walls of the header as in the manner shown in FIGS. 1 and 2. Note that the uppennost partition 18 in header 12 is immediately below the top row 19 of tubes whereas the upper partition 18 in header 11 is located between the second and third rows 20, 26 of tubes. The next lower partition 18 in header 12 is located between the fourth and fifth layers of tubes, whereas the second partition 18 from the top of header 11 is below the sixth layer of tubes.
Greatly extending the flow path and the velocity of the vapor with highly beneficial results is accomplished merely by installing barrier means such as spiral conductive strips 22 in upper rows 19 and 20 and possibly in one or more of the next lower rows of tubing if the vapor passing through these rows is still in a super heated condition. It is usually undesirable to employ the strips 22 in tubing conveying condensate as the presence of the strips interferes with proper drainage of condensate'and this is undesirable because restricting the flow area and direct contact of vapor with the heat exchange surface. The axial distance between convolutions or the pitch distance of the spiral in strips 22 found to provide excellent results is two to three inches when using nominal three quarter inch tubing. Strips 22 are proportioned to have a snug fit within the tubing to aid efficient heat transfer to the tube walls and preferably are smooth surfaced. As will be recognized, the limited number of flow paths together with the spiralling path of flow along the two upper passes of tubign 19, 20 causes the hot vapor to flow at high velocity and in brisk turbulent rubbing contact with all interior surfaces thereby providing unusually high efficiency heat transfer.
It follows from the foregoing that the velocity of the vapor passing through the two top rows or passes 19, 20 flows at high velocity. However, vapor discharging from the ends of the tubes in pass 20 enters chamber 23 of header 12 from which it can return to chamber 24 in header 1 l in parallel flow through passes 26, 27. it follows that the velocity of flow along the parallel layers of tubes 26 and 27 will be very substantially less than the velocity in each of the overlying passes 19, 20.
Likewise the arrangement of partitions 18 relative to each pass in lower portions of the heat exchanger provides multiple paths of flow and accordingly relatively low velocity. Although in nowise essential, the drawings herein illustrate the same number and size of tubes in each horizontal pass.
The relatively high velocity flow in layers 19, 20 assures high efficiency heat exchange and turbulent action within the tubes resulting in all portions of the superheated vapor coming repeatedly into contact with the tube surface.
An evaporative cooling medium is preferably passed over the exterior of all tubes in accordance with customary practice to can-y away the sensible heat and later the latent heat of evaporation. As the vapor temperature lowers and approaches the dew point, high velocity flow is not found particularly helpful in expediting condensation. However, it is important that a maximum interior surface area of the exchanger be maintained free of condensate. For this purpose each of headers 11 and 12 is provided with a plurality of condensate drain pipes 29 extending at intervals between holes in partitions 18 and condensate collecting sumps 30 in the bottoms of the headers. Tubes 29 have their lower ends nonnally submerged in condensate in sumps 30 to safeguard against vapor by passing from a higher level of the exchanger to the drain outlet conduit 15. Drain pipes 29 are of sufficient capacity to drain condensate as it forms in the tubes directly to the collection sumps. In consequence the maximum level of condensate in any tube 32 normally does not exceed that inidcated generally at 33 in FIG. 3. In sharp contrast a typical similar tube 32' in a conventional prior art condenser, particularly in lower passes thereof, would be at a much higher level such as at indicated 33' in FIG. 4. Under these conditions, it is at once apparent that a major portion of the heat exchange tube is isolated from contact with the vapor.
It will be appreciated from the foregoing that there is provided by this invention a simple, compact, high capacity, high efficiency condensing apparatus. It has been found that particularly high efiiciency is obtained if the condensir is constructed to provide approximately double or higher vapor velocity in uppermost levels as compared to the velocity in levels where the vapor temperature is approaching and close to the dew point. However, as is well known to those skilled in this art, the temperature differential between the vapor and the cooling medium, the nature of the vapor being condensed, its initial pressure and other criteria have an effecton the design factors. For example, if the initial temperature of the vapor is very substantially above the dew point a larger number of high velocity passes should be employed to achieve higher initial velocities than with vapor possessing a lower amount of sensible heat. A typical design providing excellent results as a refrigerant vapor condenser operates at a vapor velocity of approximately 50 feet per second along the upper passes 19, 20 and 26 and at approximately 25 feet per second along the lower passes. The presence of spiral strips 22 in the superheated passages can further and materially increase this velocity advantageously. It will be understood that these velocities and this relative flow ratio is not critical and that the advantages of the invention are obtainable at other values provided the flow velocity of the hot vapor is substantially higher than vapor in the process of condensing.
While the particular high efficiency vapor condenser and method herein shown and disclosed in detail is fully capable of attaining the objects and providing the advantages hereinbefore stated, it is to be understood that it is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the detail of construction or design herein shown other than as defined in the appended clarms' ing fluid in contact with the exteriors of said tubular walls, varying the aggregate flow area for hot vapor interiorly along said tubes to provide very substantially lesser flow area for relatively hot superheated vapor than for the relatively cool vapor approaching the dew point thereby to assure a relatively high flow velocity of hot vapor and enhanced heat exchange with said tubular walls, and continuously draining away condensate from a plurality of points distributed along the vapor flow path thereby to assure that a maximum of the interior surface area of said tubular walls will be free of condensate and available for direct wiping contact with vapor undergoing condensation.
2. That method defined in claim 1 characterized in the steps of providing approximately one-half asmuch vapor flow area along the initial length of said serpentine flow path as along the remainder thereof thereby to provide an initial vapor flow velocity of the order of double the vapor flow velocity along the remainder of said serpentine flow path.
3. That method defined in claim 1 characterized in the steps of forming said serpentine flow passages from tubular walls of substantially the same length arranged generally parallel to one another and supporting their adjacent opposite ends by respective header assemblies formed from metal plates welded together.
4. That method defined in claim 1 characterized in the step of utilizing tubular walls of substantially the same cross-sectional area to form all of said vapor flow passages.
5. That method defined in claim 3 characterized in the step of utilizing tubular walls of substantially the same diameter to interconnect said headers.
6. That method defined in claim 3 characterized in the step of carrying out the step of draining away condensate from points confined within said header assemblies.
7. That method defined in claim 1 characterized in the step of providing barrier means in the flow path of said superheated vapor to increase the velocity thereof and the wiping action between the vapor and the interior surfaces of said vapor flow passages thereby enhancing the efficiency of heat exchange between said vapor and the heat absorbing fluid in contact with the exterior of said tubular walls.
8. That method defined in claim 1 characterized in the step of inserting spiralling barrier means of heat conductive material axially of the interior of those flow passages along which superheated vapor passes to increase the length of the flow path.
thereby increasing the flow velocity therealong and increasing the surface area of heat conductive material in contact with said superheated vapor.
9. That method defined in claim 1 characterized in the steps of utilizing a substantially lesser number of tubular walls in parallel with one another to provide flow passages for superheated vapor than for flow passages for vapor approaching the dew point, inserting spiral strips of heat conductive material lengthwise of the interior of said lesser number of tubular walls whereby said superheated vapor flows therethrough at relatively high velocity and in a spiralling path tending to throw the vapor by centrifugal action into firmer wiping contact with said tubular walls to enhance heat exchange.
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