US3479948A - Louver - Google Patents

Description

Nov. 25, 1969 Filed Feb. 26, 1968 R. T. MATHEWS LOUVER 5 Sheets-Sheet 1 IN EWYOR fia lph Zfiiaiiwws ATTORNEY Nov. 25, T1969 MATHEWS 3,479,948

LOUVER Filed Feb. 26, 1968 5 Sheets-Sheet 2 mmrroza fialph YTMws ATTORNEY Nov. 25, 1969 R. T. MATHEWS 3,479,948

LOUVER Filed Feb. 26, 1968 5 Sheets-Sheet 5 Max. Operung' For Waer C Radian E Q) E5 U N f g M 0 e ax. Q: 04 p 9 40 v Q50 l\ g C- o a??- C m 9p posihzi fr 2- T 20 Low/ens Conqdlele Closed @[120 fiwmHoz izoml Based 0n4CerderTa Center Spacirz'y QfLauvarBLwdes 1230 I IN VEN T012 Ill, parsed Z'Mathewa /w ywe m ATTORNEY 5 Sheets-Sheet 4 LOUVER R. T. MATHEWS INVENTOR (pk TMkiheem AH TURNEY w: QQ

Nnv. 25, 1969 Filed Feb. 26, 1968 Nov. 25, 1969 R. T. MATHEWS LOUVER 5 Sheets-Sheet 5 Filed Feb. 26, 1968 INVENTUR @PWW My 3,479,948 LOUVER Ralph T. Mathews, Wallingford, Pa., assignor to E. I. do Pout de 1 emours and Company, Wilmington, Del., a corporation of Delaware Filed Feb. 26, 1968, Ser. No. 708,120 Int. Cl. F24f 13/08; F25d 21/14 US. Cl. 98121 3 Claims ABSTRACT OF THE DISCLOSURE An air flow-regulating louver shaped to an inwardly directed concave moisture-collecting transverse profile and provided with moisture-collecting gutter means on the leading edge.

CROSS REFERENCE TO RELATED APPLICATIONS The louver of this invention is a particularly useful auxiliary for air-cooled heat exchangers of the design taught in US. application S.N. 524,712, now Patent No. 3,384,165, filed in the name of the same applicant.

BRIEF SUMMARY OF THE INVENTION Generally, this invention comprises an elongated airimpervious member provided at the ends with journal means for rotation of the member about a line substantially co-parallel with the longitudinal axis of the member, the member being sigmoid-like, formed to an arcuate transverse cross-section presenting a concave liquid reception space on the inwardly directed trailing portion of the member and to a reverse arcuate transverse cross-section of relatively small convexity on the inwardly directed leading portion of the member, and gutter means on the leading edge entrapping liquid draining by gravity transverse the member.

DRAWINGS The following drawings detail the construction and operation of a louver according to this invention, as to which:

FIG. 1 is a side elevation cross-sectional view of a typical air-cooled heat exchanger provided with the louvers,

FIG. 2 is a transverse cross-sectional view of the multiple louver installation alone shown in FIG. 1,

FIG. 3 is a transverse end view showing a pair of louvers according to this invention in fully closed position,

FIG. 4 is a transverse end view showing the pair of louvers of FIG. 3 in near fully open position,

FIG. 5 is a plot of Opening in percent v. blade angle in percent for a preferred design of louver of this invention,

FIG. 6 is a plot of actual cubic feet/min. of air flow v. static pressure in inches of water for an air-cooled heat exchanger provided with a multiple louver air supply of this invention, and

FIG. 7 is a schematic automatic louver control diagram for an air-cooled heat exchanger shown in side elevation cross-section, as in FIG. 1.

DETAILED DESCRIPTION There is a great need for moisture-collecting or otherwise protective louvers in cooling and ventilating practice, and especially in the cooling of chemical process fluids and the like by the use of air-cooled heat exchangers of the general design shown in FIG. 1, described in complete detail in said US. application Ser. No. 524,712.

Such heat exchangers comprise a pair of tube bundles indicated generally at 10 and 11, respectively, mounted in upright V arrangement, preferably at a 60 included angle, the individual finned tubes of which can be advannited States Patent 3,479,948 Patented Nov. 25, 1969 tageously relatively long (e.g., 36') and supported at intervals by horizontally disposed support straps (not here detailed) which space the tubes uniformly and stably, thereby insuring uniform cooling air throughput along the course indicated by the arrows. Process fluid to be cooled is circulated interiorly of the tubes, a wide variety of flow patterns being obtainable by the use of bafiies or other flow regulators not detailed.

Cooling air is drawn through the exchanger by induction fan 15 driven by motor 27 through gear box 28, which fan is supported on mountings (not shown) disposed across the mouth of stack opening 22 exhausting the air upwardly into the atmosphere. The entire apparatus is mounted within an open-bottomed housing indicated generally at 14, to shield operation from the disturbing effects of drafts and unfavorable weather conditions, which housing is supported on elevating legs, indicated at 17, which usually are mounted high overhead in order to allow open cool air access and discharge of the heated exhaust air remote from plant personnel and equipment.

It is highly desirable during periods of high ambient outside temperatures or humidities, which may occur approximately 5-10% of the time, or when an overload in terms of cooling demand exists, to supplement the ordinary cooling achieved by air transit past the finned tubes of tube bundles 10 and 11 with cooling water projected against the tubes by spray nozzles supplied with water under pressure by pump 92 via supply lines 101 and 102, with gravitational drainage return etfected via gutters 103 and drain pipes 104 discharging into sump 91.

It is usually necessary to employ spray w-ater considerably in excess of the amount required for evaporative heat removal because: (1) excess water washes any solids or foreign material from the fin surfaces, thereby improving heat transfer, (2) water in excess of the evaporation rate prevents build-up of solids, thereby greatly reducing pitting type corrosion from galvanic cells and (3) circulation of excess water insures evaporative cooling closely approaching ambient air wet bulb temperatures, thereby obtaining lower outlet process fluid temperatures from the exchanger while using higher temperature inlet makeup water.

It is also occasionally necessary to cleanse the surfaces of the finned tubes of bundles 10 and 11 by spraying independently supplied water thereon, detergents or other adjuvants being added, to scrub away dust or incrustations deposited from evaporated cooling water, so that clean metal-to-cooling air contact is assured so far as practicable. Wetting agents are also advantageously added to the spray water, thereby obtaining thin wetted surfaces on the finned tubes contributing greater effectiveness in evaporative cooling and also better wetting of louver blade surfaces, thus improving drop collection, as the drop spatter is reduced and the water made to adhere as a liquid film.

The intermittent use of cooling water requires the employment of air flow-controlling louvers for the reasons hereinafter explained. Also, even though the bulk of the cooling water is retrieved by gutters 103, there is always a residual water spray problem resulting from objectionable spray dissemination over personnel and neighboring plant equipment, which can have serious consequences, especially as regards electrical equipment in the area. Louvers according to this invention, seen in longitudinal side elevation at 20, FIG. 1, are conjointly employed to entrap such spray, as well as even larger water accumulations, such as those arising from tube washing operations, heavy rainstorms or the like. To automatically drain collected water to a safe collection point, trough-like louvers 20 can be inclined inwardly, as indicated in FIG. 1, so as to discharge Water by gravity runoff into sump 91, which can be especially desirable from the standpoint of water conservation, particularly in arid regions.

Referring to FIGS. 2, 3 and 4, the louvers are mounted within a squat, square cross-section breeching 88 located beneath the upright V tube bundle assembly and athwart the lowermost air passage of the apparatus, which is provided with a pair of end walls 88a upon which are pivotally mounted on common horizontal level E the co-parallel individual louvers 20. These louvers have a length a (FIG. 3) of typically 8 measured tip-to-tip, and are spaced at uniform distances apart of about 4", so that they overlap when closed, as will be apparent from the right-hand broken-line representation of a single louver shown in closed position in FIG. 2, but even more clearly in FIG. 3, which details the closed louver positional arrangement.

In FIG. 2 it will be noted that the left-hand louver 20' is of shortened construction, so that it presents no interference troubles in the course of closure.

Louvers 20 are formed with reverse curvatures as regards the trailing blade portions 20a and the leading blade portions 20b, both being formed, typically, on 5" radii (R, FIG. 3). Blade portions 20b are provided with oppositely disposed U cross-section water collection gutters 89 and 90, respectively, each serving an individual side of a louver 20 upon which it is mounted, these gutters also discharging into central sump 91 hereinbefore described.

Louvers 20 are operated in unison through bar connector 93, which is provided with upstanding finger portions 94, pinned to bar connector 93 and individually fixedly attached to the ends of the blade portions 2011, via actuating crank 95, pinned to bar connector 93, through a connecting linkage (not shown) at the right-hand end of the subassembly. In order to coordinate the actuation of the abbreviated right-hand louver with its neighbors, there is provided a short connector bar 96 securely attached through finger portions 97 to the tip ends of the two rightmost louvers shown in FIG. 2.

The ends of louvers 20 provided with the pivot pins permitting predetermined louver rotational positioning clear end walls 88a with a small spacing through which some water can leak. Preferably, the lower inside periphery of breeching 88 is fitted with an appropriately sloped, weldattached angle iron gutter 152 defined by upstanding outboard angle iron legs 151, which not only receives any water draining down the surfaces of the walls of breeching 88 but also any excess which may drain from the highlevel ends of louvers 20, as best seen in FIG. 1. This water is then drained to sump 91 via drain lines 153.

In addition, water draining from the abbreviated righthand louver 20 of FIG. 2 is preferably preliminarily collected within a V cross-section gutter 150 constituting also an air seal against the underside of which the adjacent full-size louver 20 bears. Gutter 150 is located approximately three-fourths of the way up the right-hand wall of breeching 88 and is slit at the ends (not shown) in order to drain moisture therefrom down the wall surface into gutter 152.

A particularly preferred transverse louver cross-section is the relatively thin sigmoid defined by the angle A, FIG. 3, of approximately extent. This angle is that included within the line tangent to the leading edge of the louver curling into gutter 90 and the line MN drawn tangent to the trailing tip of the louver and passing through the 282 point, referred to conventional polar coordinate axes, of a circle drawn about center B of the central boss 23 carrying the journal pins (not shown) constituting the means for preselected rotational positioning of the louver. Boss 23, which incidentally provides a reinforcement adding structural strength, is disposed along the central lon gitudinal axis of the upper face of the louver, so as to constitute a retaining dike for water collected within the concavity of blade portion a. Also, boss 23 is disposed exclusively on the upper side of the louver, thereby eliminating any depending drip point on the underside, which could otherwise interfere with smooth drainage transverse the louver blade into gutter 89. The trailing (uppermost) edges of the louver blades are shaped to a teardrop cross-section for increased blade strength with minimum increase in air flow resistance.

As shown in FIG. 3, the water collected within the concavity of blade portion 20a is somewhat exaggerated in amount as, usually, runoff to sump 91 safeguards against excessive water accumulation on the louvers. However, in any case, overflow occurring from boss 23 will still be collected within gutter on the louver upper side, leading edge, which thus constitutes a moisture collection backup.

If desired, the lowermost ends of both gutters 89 and 90 can be provided with depending lips (not shown) which lead draining water smoothly into sump 91 without any possibility of reverse flow along the louver undersides. Also, if high service water levels are anticipated for these gutters, it is preferred to close ofi the high level ends remote from sump 91 with polymeric slip-on caps, which thus constitute dams barring flow of water out of the upstream louver extremities.

In this connection, it is preferred that gutter 90 extend well outboard from the continuation line of blade portion 20b, 2. very effective design being that shown for the righthand louver of FIG. 4 in which a line D, drawn tangent to the convexity of blade portion 20b and parallel to the base line for angle A, FIG. 3, approximately bisects the gutter width. This insures entrapment of Water sliding oIf the louver front side, even when it is draining at relatively high velocity. Gutter 89 can be relatively narrower, because draining conditions are not so severe here.

The water collecting action of louvers 20' is portrayed by the force vector diagram of FIG. 4, showing a pair of associated louvers in near full open position which res'ults in virtually complete entrapment of any droplet water draining from tube bundles 10 or 11 in their upright V mounting, since the resultant of forces (gravitational and air supply velocity) acting on water drops, as shown schematically in FIG. 4, is a component of a force at directed against louvers 20 over a 12 to 60 range of blade settings of the louvers. Accordingly, the water droplets impinge on the louvers and drain via gutters 89 and 90 into sump 91.

Extensive observation coupled with mathematical analysis has confirmed that the force vectors acting upon water droplets of, typically 1 dia. (or about 1600 microns) under a cooling air face velocity of 1200'/min. positively deflect the droplets across the space between louver blades of the proportions hereinbefore given to the trailing concave blade portions 20a. It will be understood that, as the blades rotate towards the closed position from that shown in FIG. 4, the air velocity increases through the blade-to-blade throat passage, thereby increasing the moisture collection action.

Louvers 20, of course, have the dual purpose of not only collecting reject water as hereinbefore described but also of regulating air flow for best cooling utilization under conditions where: (1) dry air operation is the desirable mode or (2) during periods when cooling water is sprayed on the tubes as a supplementary measure.

Louvers having the general dimensions detailed are particularly preferred because of the near-linear relationship of opening in percent to blade angle in percent, plotted in FIG. 5. Such a linear relationship is highly advantageous from the standpoint of louver positioning control, because unit control adjustment enables corresponding unit louver positioning. The angular range of adjustment with the specific louvers described is sketched on the FIG. 5 plot, which shows complete closure of the louvers at a 12 clockwise displacement measured to line MN from the horizontal (X axis), with liquid collection achieved during the succeeding 48 of louver placement,

up to the maximum liquid collection position at the 60 point and maximum opening for air throughput at 83.

As best seen in FIG. 4, the reverse curvature of the louver blades defines a variable cross-sectional venturi for the control of air flow with minimum pressure drop through the louver assembly. This is accomplished by the streamline flow of air into the venturi and the regain of static pressure at the blade discharge end, thereby reducing the net air pressure drop across the louver.

Progressive closing of the louver blades increases the projected horizontal area of the blades in the top half to collect water droplets by gravity while, at the same time, increasing the velocity of the air passage through the blade-defined venturis. This increased air velocity, plus the fiat inclination to the vertical at which the air is flowing, deflects water droplets from their vertical trajectories caused by gravity towards the concave blade portions 20a, from whence the water drains by gravity to sump 91.

The reverse curvature of the lower blades always establishes the minimum (venturi throat) opening near the center 50% expanse of blade width, which bars fine water spray downward escape through this throat section while deflecting large water droplets to the collection concavities of blade portions 20a.

The operating characteristics ascertained from a model of a typical multiple louver assembly such as hereinbefore described with particular reference to the aircooled heat exchanger of FIGS. 1 and 2 is plotted in FIG. 6, which details the pressure drop losses due to (1) louvers 20, (2) other (lumped) losses and (3) the fin coils for the conditions of both full and half blower speed. Thus, with dry air operation, i.e., with spray nozzles 100 shut oft, a given cooling load is dissipated by 143,000 actual cubic feet of air flow with the development of a static pressure of 0.73" H O measured at the cooling fins. Now, if spray nozzles 100 are turned on to supply supplemental cooling by wetting the tube fins in an amount dissipating 25% of the heat load by water evaporation, the air flow requirement is quickly reduced to about 106,000 actual cubic feet/min. of air flow, or about 75% of the original requirement with air cooling solely. Louver 2t) positioning to reduce the air flow from the first level to the second increases the trans-louver loss from about 0.05" H O to about 0.39" H O, or about eight times the original pressure drop. The blade regulatory position necessary to achieve this must now be altered from near full open position to a position well within the angular range (refer FIG. 5) for water collection. Under these circumstances the increased pressure drop across the louvers coupled with the change in the attack angle of the blades accelerates the air flow to a higher velocity through the louver venturis. This prevents escape of water droplets downward therefrom without their coming into contact with the louver blade surfaces, to thereby form a film of water which is either blown upwardly off the blades as atomized droplets or drains off into gutters 89 and 90. It is thus seen that the louver air flow regulating action simultaneously establishes ideal conditions producing water droplet throwout.

Moreover, progressive closing of the louver blades to the fully closed state of FIG. 3 presents a larger water collection volume which is particularly advantageous for the recovery of large water amounts which must be accommodated when heavy water washing is periodically resorted to in order to scrub dirt and insects from the fin coils, or to recirculate detergent solutions employed for most efiicient cleansing action. A particularly eflfective cleaning procedure is to locate special cleaning spray nozzles above the finned tubes and oriented in the direction of the tubes inside the V defined by tube bundles and 11. Then, if the rotation of fan is temporarily halted, wash water can be collected in sump 91 and recycled or run to the sewer, as desired, after which the apparatus can be restored to service when the fin washing is completed.

It is usually the best engineering practice to distribute the air-moving load between a plurality of side-by-side mounted fans 15 disposed lengthwise of the same heat exchanger tube bundles 10 and 11, which can then be isolated as individual cells one from another by curtain walls extending from top to bottom inside the V defined by tube bundles 10 and 11, leaving the outside space as an open interconnection between fan cells. Such an arrangement permits convenient exhaust of reversely propelled air out of individual fan cells during occasional cleanings horizontally through the interconnections between neighboring units, and thence upwardly out of these in the normal flow pattern shown by the arrows of FIG. 1, the wash water being then collected as fall out on louvers 20.

It "sometimes happens that cooling tubes leak or break and discharge inflammable or explosive process materials into housing 14. When this occurs, emergency full closure of louvers 20 to FIG. 3 position isolates the dangerous substances, while simultaneously diluting them with cooling water.-This tends to extinguish fires by both cooling and drowning action and is a highly advantageous incidental feature of my invention.

It is sometimes desirable to shield heat exchangers of the general design shown in FIGS. 1 and 2 from the effects of driving rain, intense sunlight or high winds entering via stack opening 22. A louver assembly such as that detailed in FIG. 2 is well-adapted to this service and can be mounted above opening 22, either alone or together with a separate louver assembly mounted as hereinbefore described across the bottom air ingress. It will be understood that the operation of the two louver assemblies will then be entirely independent of each other, the upper one being normally full open and partially closed only when adverse weather conditions require. It is desirable to provide a separate water reception sump for the exit end louvers, since rain water often contains adulterants, or at least is not carefully pre-conditioned, as is usually preferred for the cooling spray nozzle water.

As hereinbefore mentioned, supplementary water spraying is not resorted to as the usual operating mode; however, where exceedingly high dry bulb air temperatures occur over protracted periods, or where manufacturing requirements temporarily necessitate preselected extraordinary amounts of cooling, it is highly advantageous to resort to spray supplementation. Moreover, since upward air flow in the direction indicated by the arrows in FIGS. 1 and 7 is usually provided on a modular basis by a plurality of independently operated induction fans 15 disposed in parallel one to another with respect to the relatively long-length tubes of bundles 10 and 11, it is practicable to shut down individual fans for repairs or maintenance while taking over the cooling load by water spray cooling supplementation as regards the remaining modules.

Referring to FIG. 7, from which spray nozzles 100 are omitted for simplicity, there is shown a typical automatic louver control system adapted to accommodate both dry air operation and water spray supplementation.

In this instance, the hot process fluid is introduced to the heat exchanger via line 109, which is divided into separate branches 109a and 109!) leading to the inboard tubes of tube bundles 10 and 11, respectively. A box header construction, as taught fully in said application Ser. No. 524,712, routes the flow into the plane of the figure and then on a reverse course. This produces a cooled product fluid withdrawn from lines 110a and 110b, which latter are manifolded into line 111.

Supplementary spray water is supplied from sump 91, which collects spray water recovered via gutters 103 and louvers 20, any fresh make up water being obtained from line 32 connected through float control valve 33. Spray water is pumped from the bottom of sump 91 by pump 92 driven by electric motor 141, the water being circulated in sequence through line 101, filter 132, and water delivery throttling valve 140 to spray nozzles 100 (not shown in FIG. 7). Drive motor 141 for pump 92 is placed in power circuit via signal line 142 provided with an electrical thermal switch 143 disposed in the heat exchanger air intake passage. Thus, when the intake air attains a temperature too high for effective cooling, thermal switch 143 closes the power circuit to drive motor 141 to commence supplementary water spraying. If desired, for increased control flexibility, as the ambient air temperature increases, temperature controller 37 can be made to modulate the supply of cooling water delivered through throttling valve 140 by control imposed via signal line 140a.

Direct air flow restriction is effected by conventional pneumatic temperature controller 37, which operates in the usual 315 p.s.i. instrument air pressure range, for control of louver blades throughout their full rotational range for dry air cooling depending upon ambient air temperatures with the upper portion of the 3-15 p.s.i. range being utilized during high ambient air temperatures for essentially full-open blade 20 disposition under the usual condition where dry air cooling is the operating mode, whereas the 310 lbs. portion is then reserved to water spray supplementation as hereinafter detailed. Rotational positioning of louvers 20 from full open to closed position is effected by direct-connected air-powered actuators 138 responsive to controller 37 via line 38. Temperature controller 37 in turn is under the general operating pressure range control of air temperature switch 143 via signal line 142a, which constrains controller operation to the 3-10 p.s.i. range reserved for spray supplementation operation. However, the primary control is that achieved by sensing of the temperature of process fluid product delivered via exchanger discharge line 111, to which controller 37 is connected via temperature sensing line 37a.

From the foregoing, it will be understood that this invention can be modified extensively within the skill of the art without departure from its essential spirit and it is accordingly intended to be limited only within the scope of the following claims.

What is claimed is:

1. An inclined air flow-regulating louver comprising an elongated air-impervious member provided at the ends with journal means for rotation of said member about a line substantially co-parallel with the longitudinal axis of said member, said member 'being formed to an arcuate transverse cross-section presenting a concave liquid reception space on the upper inwardly directed trailing portion of said member and to a reverse arcuate transverse crosssection of relatively small convexity on the lower inwardly directed leading portion of said member, first gutter means on the leading edge entrapping liquid draining by gravity transverse said member and second gutter means on the opposite side of said louver from said first gutter means and adjacent thereto for collecting transverse gravity runoff from the opposite face of said member.

2. An air flow-regulating louver according to claim 1 wherein said journal means are disposed to provide an inclination of said member to the horizontal, maintaining gravity runoff of liquid collecting on said member.

3. An air flow-regulating device comprising, in combination, a plurality of inclined substantially co-parallel louvers each comprising an air-impervious member provided at the ends with journal means for rotation of said member about a line generally co-parallel with the iongitudinal axis of said member, said journal means being disposed in a substantially common plane, each said member being formed to an arcuate transverse cross-section presenting a concave liquid reception space on the upper inwardly directed trailing portion of said member and to a reverse arcuate transverse cross-section of relatively small convexity on the lower inwardly directed leading portion of said member, first gutter means on the leading edge entrapping liquid draining by gravity transverse said member and second gutter means on the opposite side of said louver from said first gutter means and adjacent thereto for collecting transverse gravity runoff from the opposite face of said member, said louvers being journaled in said common plane at spacings such that adjacent edges overlie one another in a direction perpendicular to said common plane when said louvers are in air flow close-off position.

References Cited UNITED STATES PATENTS 1,486,084 3/1924 Gearhart.

1,785,682 12/1930 Hamilton.

2,456,311 12/1948 Paget.

2,480,562 8/ 1949 Ewing.

2,962,956 12/1960 Magyar.

2,997,939 8/1961 Snyder 98l2l 3,413,905 12/1968 Johnson 98-37 MEYER PERLIN, Primary Examiner U.S. c1. X.R.'

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