Note: Descriptions are shown in the official language in which they were submitted.
6 BACKGROUND OF THE Ih-VENTION
7 This invention is an improvement to the cooling
~ ~ 8 capacity of a parallel path gas-liquid heat exchanger
¦ 9 ~.articularly a parallel flowpath air-water cooling tower
by internally recirculating all or a portion of the liquid
11 to be cooled. All or a portion of the liquid flow o.~ a
12 heat exchanger which has been cooled by being in parallel
~;~ 13 path relationship with the ambient gas and thus has increased
¦ la the temp~rature of the L~mediate surrounding gas approximately
5~ j 15 equal to the temperature of the liquid therefore exhausting
~ 16 the gas's ability to further cool; is transported (recircu-
'~1' 17 lated) to a cooler ambien~ wet bulb within the ~arallel path
18 heat exchanser and re-exposed thereto for further cooling
' ~ 19 thereby increaslng the cool~ing capaclty of the heat exchanger.
,~ ~ 20 In the prior art (U.S. Patent 3,922,153) there is
~,
21 shown a water collection shelf about half w2y down the height
i 22 of the cooling tower wherein water is collected and passed
23 into a sump region without tricXling over the mist eliminators
24 therebelow. The sole reason for the collection shelf in
this case is to enable water collected in the upper bank of
~¦ 26 mist eliminators to bypass the lower bank of mist eliminators
27 thus preventing the lower bank from becoming excessively
1 28 flooded with water which could result in this water being
L8~3~
1 carried out along with the exhaust air. In addition this
2 flooding creates resistance to air flow thereby reducing tne
3 quantity of air and thus the efficiency of the unit. It
4 should also be realized that the water which passes through
these by-pass openings is at approximately the same tempera-
6 ture as the surrounding air. Consequently, very little
7 cooling, if any, occurs as the water alls to the sump or to
8 the next lower collection shelf.
9 In U.S. Patent 3,929,435, the overall size of an
injector cooling tower therein shown was reduced by having
11 two separate conduits and two separate transfer maans, such
12 that all the water that passed through the first stage then
13 passed through the second stage. This U.S. Patent teaches
14 the use of a new fresh secondary source of air for re-exposing
the water thereto. The instant invention differs in that
16 the same source of gàs induced by the primary source of
17 l~quid is also used for cooling the secondary liquid source.
18 Furthermore, the instant invention differs from said U.S.
19 Patent in that the secondary liquid circuit is created
within the unit itself and does not rPquire a second source
21 of energy. In fact, no additional energy is being axpended
22 in the instant case, because the secondary source energy ~7as
23 initially created by the height potential (potential energy)
24 of the initially spra~ed water from the primary liquid
source. The instant invention recovers a portion of that
26 energy and re-uses it.
8~3~
1 SUM~RY OF THE INV~3TION
2 This invention is an improvement to the cooling
3 capacity of a parallel path gas-liquid heat exchanger by
4 internally recirculating all or a portion of the liquid to
be cooled. More particularly the invention relates to an
6 improvement to the cooling capacity of a parallel path
7 air-water cooling tower by recirculatlng all or a portlon
8 of the water to be cooled. All or a portion of the heat
9 exchanger flow that has been cooled in parallel path rela-
tionship with the ambient gas and thus increased the tempera-
11 ture of the immediate surrou~ding gas approximately equal to
12 the temperature of the water thereore exhausing the gas's
13 ability to further cool; is transported (recirculated) to a
1~ cooler ambient wet bulb and re-exposed thereto for further
cooling within the parallel path gas-liquid heat exchanger
16 thereby increasing the cooling capacity of the heat exchanger.
17 An object of this invention is to provide a liquid
18 cooling system which results in a lower liquid out tempera-
19 ture for the same heat load (i.e. the same flow and same
c~oling range) when compared with a par211el path gas-liquid
21 heat exchanger which does not employ ir.ternal recirculation.
22 A further object is to increase the load capacity
23 by cooling through a greater range for either the same
24 li~uid inlet or outlet ~emperature as compared `o an unre-
cycled parallel path gas-liquid flow heat exchanger.
26 Another object of this invention is to take advan-
27 tage of a liquid water collection shelf or shelves to re-
28 cover a portion of the energy that has been expended in
2g spraying the liquia into the conduit o the cooling tower.
This recovered energy is in the form of potential energy.
1 Another ob~ect of this invention is to transport a
2 portion of the initially entering liquid to the front of Lhe
3 unit and to re-introduce it or re-spray it into the conduit
4 thus exposing liquid that has been partially cooled .Lo
additional cooling by the ambient gas.
6 It is another object of this invention to provide
7 means for xecirculating and redistributing said liquid for
8 re-exposure by several methods including a) nozzles dis-
9 charging water in a parallel relationship with the incoming
gas or b) by a series of troughs or nozzles which distributes
11 the liquid in a crossflow relationship to the gas flow.
12 Other objectives and advantages of the invention
13 will be apparent from the following detailed description
14 thereof in conjunction with the annexed drawings, ~EP~IN
FIG. 1 is an isometric ~iew of a typical injection
16 type cooling tower having parallel gas-liquid flow charac-
17 teristics;
18 FIG. 2a is a cut-away view of a gas-liquid
19 parallel flow path device of the instant invention wherein
liquid is redistributed in back of the initial nozzles by
21 additional nozzles;
22 FI5. 2b is a front view looking directly into the
23 cooling tower of FIG. 2a;
24 FIG. 3a is a side view of a parallel path gas-
liquid device of the instant invention wherein liquid is re-
26 circulated and redistributed by nozzles pointing downward;
27 FIG. 3b is a view looking into the cooling device
28 Of FIG. 3a;
~ ` 10~ 338
1 FIG. 4a is a parallel gas-liquid cooling d~vice
2 of the instant invention wherein liquid is recirculated and
3 redistributed by means of troughs;
4 FIG. 4b is a view looking into the front of the
device of FIG. 4a;
6 ` FIG. 5 is another parallel gas-liquid flow heat
7 exchanger of the instant invention wherein liquid from the
8 collection sump is recirculated and resprayed into the
9 cooling unit;
FIG. 6a is a side view of an injection type gas-
11 liquid parallel flow cooling unit having more than one
12 collection tray therein, and which does not utilize the
13 instant invention;
14 FIG. 6b is a side view of a gas-liquid parallel
flow cooling device having three liquid collection shelves
16 wherein said liquid collected on these shelves is resprayed ``
17 in front of the unit;
18 FIG. 7 is another version of the parallel flow
19 gas-liquId cooling unit of FIG. 6b.
Referring first to FIG. l,~it will be seen that a
21 typical injector type evaporative cooling tower is illus-
22 txated. The details of the injector towers of FIG. 1 are
23 shown in U.S. Patent Nos. 3,807,145 and 3,922,153.
24 The unit comprises an air entry mouth 10, an air
and water mixing region 11, and down stream region 12.
26 Beyond the downstream reglon there is a bank of mist elimi-
27 nators 13, and an air exhaust region 14, provided with.vanes
28 15, to direct the exhausting air upwardly and outwardly rom
29 the apparatus.
`
--5--
838
1 Water to have neat extracted from it is pumped by
2 a pump 16 through a heat load to header 17. Header 17
3 supplies a series of horizontal conduits 18 extending across
4 the air entry mouth 10 of the unit. Each of the conduits 18
is provided with nozzles 19 spaced along its length. The
6 water to have heat extracted from it is sprayed from these
7 nozzles into the air and water mixing region 11, and this
8 has the effect of drawing in air from the surrounding a~mo-
9 sphere which thus constitutes the source of air for the
present system. The air and water co-mingle, some of th~
ll water evaporates, the air is exhausted through the outlet 14
12 and the cooled water is collected in a sump 20.
13 Although FIG. 1 shows a typical injector cooling
14 tower wherein the air flow is caused by the sprayed liquid
itself, the alr flow can also be caused by a centrifugal or
16 axial fan located,-for example in the exhaust region. It
17 will be realized by those skilled in the art that applicant's
18 ~ invention is applicable to any parallel gas-liquid flow de-
19 vice whether the gas flow is induced by the sprayed li~uid
itself or whether it is caused by other means such as by
21 fans.
22 In ~IG. 2a and 2b, there is~represented an embodi-
23 ment of this in~ention wherein a portion of the water sprayed
24 into the cooling device, namely, about half the water is
recycled and reintroduced into the confined region of the
26 cooling device. Thus, liauid is sprayed from nozzles in
27 headers 34 to form sprays 35 which, in this case, induce air
28 flo~ into the cooling tower. The moisture laden air passing
29 through mist eliminators 13 exits the cooling tower through
louvers 15. The water sprayed in the top half of the cooling
`109'~838
1 tower is channeled down the mist eliminators 13 to a collec-
2 tion tray 30. From there this liquid is channeled through
3 conduit 31 and exits as sprays 33 through nozzles in a
secondary header system header 32. The sprayed liquid is
then reintroduced to the confined region of the cooling
6 tower.
7 Although the reintroduced water is shown in FIG.
8 2a and 2b as being reintroduced before the intersection of
9 original sprays 35, it can be reintroduced anywhere in the
confined region even at a point behind the general area of
11 intersection of original sprays 35; the ultimate criteria
12 being that the ambient gas temperature at the area where the
13 liquid is reintroduced is lower than the temperature of the
14 liquid at that point.
It is most advantageous, to reintroduce the liquid
16 into an area which is in front of the original sprays, pre-
17 ferably in front of the area of intersection of said original
18 sprays or the area in front of a pressure seal point to ex-
19 pose said secondary sprays, to fresh ambient gas ~air).
This is normally the most effective area for reintroduc~ion
21 since the ambient gas temperature is normallv the coolest.
22 Throughout the remainder of FIG. 37 the reintro-
23 duced liquid is thus shown being reintroduced in an area
24 which is prior to or in front of the intersection or pressure
seal area of the original sprays, but those skilled in the
26 art will realize from the above explanation that said re-
27 introduced liquid can be reintroduced anywhere in the con-
28 duit as long as the temperature of the gas at the point of
29 reintrGduction is lower than that of the introduced liquid.
1 The sprays 33 in FIG. 2a and 2b are caused ~y
2 gravity, in that the liquid collected ln the tray 30 has to
3 drop down to the bottom half of the cooling tower wh~re the
4 liquid is then reintroduced by spray 33. The liquid origin-
ally introduced in the lower half of the cooling tower and
6 the reintroduced liquid is stripped of moisture by elimina-
7 tor 13 and the cooled liquid eventually collected in sump
8 36. The liquid from sump 36 is then pumped to the heat
9 source. After being used in the heat source whereupon the
liquid emerges hotter than when it entered said heat source
11 it is pumped back to the original spray header 34. E~IG. 2b
12 shows that the secondary or reintroduced liquid sprays 33
13 eminate from nozzles on headers 32 and are in such a position
14 as to flow between the headers 34 of the original sprayed
liquid~
16 In FIG. 3a and 3b there is shown another embodiment
17 of this invention wherein llquid in the top half o~ the
18 cooling tower therein shown is caught by tray 40 and communi-
19 cated to a secondary tray 46 by means of a com~.unicating con-
duit 48. This tray 46 cont~ins nozzles or openings facing
21 downward so that this liquid is reintroduced just prior to
22 the mixing region 47 of the original spray 44. As stated
23 previously the liquid can be reintroduced anywhere in the
24 conduit and the above is merely the preferred embodiment.
The tray 46 is located generally between two original spray
26 headers 43 as shown in FIG. 3b. The remainder of the water
~7 not recycled and the recycled spray water along with the
28 original sprays in the lower half of the cooliny tower are
2~ all collected in sump 45 and then put to use in the heat
source~
3~
1 In FIG. ~a and 4b, there is shown another embodi-
2 ment of this invention wherein the portion of the recycled
3 liquid collected in the top half of the cooling to~er in
4 tray 50 is recycled and reintroduced to areas just prior to
the mixing region 58 of the original spray 56 by means of a
6 communicating conduit 51 and notched cross trough 52 as can
7 be seen in FIG. 4b. These troughs 52 which are preferably
8 Ushaped, and have notches 53 through which the recycled
9 liquid overflows are located generally in a position between
two original headers 55. Again, the total liquid separated
11 from the air stream by eliminators 13 is collected in sllmp
12 57 and used in the particular heat source.
13 In FIG. 5, there is shown a device having a pri-
14 mary spray 68 which induces an air flow. The iiquid from
these sprays after being passed through the cooling device
16 is collected in sump 61. By means of a secondary pump 63,
17 energy is imparted to create a secondary flow of liquid and
18 it is reintroduced to a region just prior to the mixing
19 region 69 of the original spray by means of a header 64
and cross headers 65 which cross headers 65 contain nozzles
21 which spray out the recycled liquid.
22 In all the above devices shown in FIG. 1-5 and
23 also in the device shown in FIGS~ 6b and 7, the collection
24 trays for collecting liquid to be reintroduced into the heat
exchanger, are shown splitting the liquid-gas separator
26 means 13 i.e. they are located within the liquid-gas sepa-
27 rator means to catch the liquid falling down the separator
28 means. The collection trays how2ver can be located anywhere
2~ within tne conduit although they are most preferably located
within the separator means as shown.
3~
1 In order to better demonstrate the value of the
2 recirculation of li¢uid operation which constitutes the
3 present invention, reference is made to the following
4 examples.
EXAMPLE 1
; 6 In this example, a comparision will be made be-
7 tween a typical standard parallel air-water low device as
; 8 shown in FIG. 1 and a parallel air-water device with re-
9 circulated water typically shown in FIG. 2, 3 or 4. Both
devices have the same entering water temperature and other
11 data as shown below and it is assumed that these de-
12 vices are perfect machines. All calculations zre theoreti-
13 cal.
14 Flow: 650 GPM
Cooling Range: 15
16 Æir Velocity: 650 FPM
17 Cross Section Area: 61.25 Ft
18 Air Flow: 39,812.5 CFM
19 Ambient Wet Bulb
Temperature: 78F.
21 A. Standard Parallel Flow Machine:
h
22 Water Heat Load = Air Heat Load ( out-41.~8)
39,812.5 CFM 60 Min/Hr
23 650 GPM x 15 Range x 500 5 (14.1 Spec Vol)
24 4,8i5,000 Btu~Hr - 169,414.89 ( out - 41.58)
hout = 4,875,000 + 41.58
169,414.89
26 = 28.776 + 41.58
27 = 70.356
28 . .Tout - 99.23F.
29 Approach = 99.23F. - 78F. - 21.23F.
In water Temp = 99.23F ~ 15F Range - 114.23F.
--10--
'
~ot~
1 Water in 114.23F
2 ~
3 ___~ Out Water Temp = Out Wet
,o' Bulb = 59.23F
4 Air Velocity /
650 FPM /
~ Approach = 21.23F.
/
6 Ambient WB 78F / A:r ~
7 B. Recirculated Water: Where 50~ of the flow is caught
; 8 and additionally cooled.
~ 114.23
~ 99.23F
78F ~ ~ 325 ~PM
11114.23F ~
~ 103.4F
1299.23F ~ ~ ~
~ 91.01F
1378F WE ~
, _
14 Since the upper half is identical to a standard
parallel machine, temperatures must be identical,
16 i.e., in water = 114.23F, out water = 99.23F,
17 ambient air 78 ws, out WB = 99.23F.
18 In the lower half, the out water from the upper
19 half at 99.23F is re-exposed to the ambient 78
WB t~Jmperature and is further cooled in a
21 parallel manner.
38
1 Water heat load = air heat load
(~out - 41,5
2 325 GPM x R x 500 = 19,906.25 CFM x 60 Min~Hr
3 14.1
4 R = .5213 (hout - 41.58)
R = .5213 hout - 21.675
6 In addition Tout + R = 99.23
7 out = f (Tout)
8 , Substituting h
9 99.23 - Tout = . 5213 out - 21.675
Tout = -.5213 out + 120.905
11 ` Solving out = 91.01F
12 The primary system lower half will then be entering
13 at 114.23F at 91.01WB
14 Water Load = Air Heat Load h
( out - 57.34)
(325 GPM) R x 500 = 19,906.25 CFM x 60
16 14.1
17 R = .5218 out - 29.89
.
I8 Tout + R = 114.23
19 114.23 - Tout = .5218 hout - 29.89
Tout = .5218 hout ~ 114.12
21 Solving Iteratively
22 Tout = 103.40F ;~
23 The sump temperature ~ould then be:
24 325 GPM at 91.01 + 325 GPM at 103.40 =T
650 GP~ at sump
2Ç ~ Tsump = 97.205F
27 Therefore, the total range is now 114.2~-g7.205= 1?~ 025F
28 or 2.025F more range or 13.5~ more capacity for the
2 - same in water tempe ~ature .
- 12 -
3~
1 EXAMPLE 2
2 As a second example one can compare the difference
3 in water temperatures for the same load and same flow:
4 A. As determined previously, the parallel device
would have an in water temperature of 114.23
6 and out water temperature equal to out air tempera-
7 ture of 99.23.
B. In order to determine the actual in water tempera-
9 ture for this internally recirculated system, it is
necessary to use a trial and error method by assuming
11 an initial in water temperature and determining the
12 resulting out water temperature. The difference be-
13 tween the two temperatures is the cooling range.
14 In the first example, it was found that for an in
water temperature of 114.23F, the resulting out
16 water temperature was 97.205~ and thus the range
17 was 17.025F. If a lower in water temperature is
18 selected, the out water temperature range will be
19 lower. In this manner, one can determine what in
water temperature results in exactly a 15 range.
21 After several trials, the final temperatures are
22 as ~follows:
23 The upper half would cool one-half the system
24 flow from 110.48F to 97.25F at 78F WR. In
the lower half this 97.25F water would be
26 cooled to 89.87F at 78F WB first and then
27 the other half of the flow would be cooled
28 from 110.48F to 101.10F at 89.87F wet bulb.
29 The mlxing effect of half the wate of 89.87F
with half ~he water at 101.10F yields a
31 final temperature of 95.48F.
,, ,
~13-
'- : ,
3~3
1 Comparing the two systems, it is found that the
2 second produces water that is 3.75F cooler than the unrecir-
culated system~
3 EXAMPLE 3
4 As a third example, one can consider the increased
~low capacity for the same range and same in water tempera-
6 ture for the recirculated unit using the same cross section
7 area of 61.25FT as for the standard parallel syste~.
8 Example 1 showed that for the same in water temperature, a
9 recirculated unit hadrange capacity of 17.025F at 650 GPM
vs. a 15F range for the standard parallel system. Example
11 2 showed that if one held the range to exactly 15 along with
12 the flow at 650 GPM, the recirculated system's in water and
13 out water would drop 3.75F lower than the parallel systems'.
14 In this example, which most closely relates to how this in-
vention would be used in actual practice, an exact 15 range
16 will be maintained and the in water temperature will be held
17 to that of the parallel system, namely, 114.23F. The com-
la parison will be between the flow capacity of the recirculated
19 system vs. the ~50 GPM for the unrecirculated system.
The method of determining this flow capacity involves
21 a trial and error procedure similar to Example 2. An initial
22 estimate is made for flow capacity and then the resulting
23 temperatures are calculated holding the in water constant at
24 114.23F. If the resulting range is grea er than 15, then
2~ a higher flow capacity is possible. An additional factor in
26 this example (for an ejector type cooling tower) is that the
27 air flow (CFM) is a function of the water flow (GPM) by the
28 following relationship:
-14-
1/3
2 CFM2 = ¦ GPM2
CFMl \ GPMl J
4 or for this example, ~ ~
/ \ 1/3
GPM2 ~
7 CFM2 = 39,812.5 650 J
8 Trying a flow of 895 GPM, induces an air flow of 44,291.7 CFM.
9 Equating the heat load in the upper half results in an out
water temperature of 100.867F~ This water is recirculated
11 and cooled down to ~3.002F where it returns to the sump.
12 The lower half primary water is cooling from 114.23F at a
13 wet bulb of 93.002F to a final temperature of 105.186F.
14 The sump temperature is then the average of 93.002F plus
105.186F or 90.094F for a cooling range ~f 15.136~
16 In this same manner, new flows have tc be tried
17 until one finds the flow that results in exactly a 15
18 range. That flow is 916.12 GPM which induces 44,633 CFM.
19 The upper half then cools water fxom 114.23F to 100.9~9F.
This water is recirculated and cooled to 93.155F. The lower
21 half primary water i5 cooled from 114.23F at a wet bulb of
22 93.155F to a final temperature of 105.310F. The sump temper-
.
23 ature is then the average of 93.155F plus 105.310F or39.23~F-
24 for a range of 15.000F. The flow capacity of the internally
recirculated system is then 916.12 GPM vs. 650 GPM for the
26 standard parallel system or 40.9~ increased flow capacity~
27 FlGo 6b shows another embodiment of the instant in-
28 vention. A comparision of a device shown in FIG. 6b which
29 embodies the instant invention and of a device shown in FIG 6a
which daes not embody the instant invention ~will be made
31 using theoretical calculation based on the assumption tha'
32 both devices are perfect machines~
-15-
L8~3~
1 In a device shown in FIG. 6a wherein the liquid is
2 sprayed from nozzles in crossheaders 100 into a cooling device,
3 said liquid spray 101 causing an air flow for comparision
4 purposes with FIG. 6b of about 39,812 cu. ft. per minute.
The moisture laden air is then stripped of liquid by mist
6 eliminators 13, after which the moisture laden air exits
7 through louvers 15. All of the water stripped by eliminators
8 13 is collected in three trays 102, 103 and 104, the liquid
g falling from each tray into sump 105 and pumped by pump 107
to a heat load shown as 108. After being used in the heat
11 load, the water is sprayed back into the cooling device as in
12 normal operation. It can be seen from FIG. 6a that assuming
13 a 78 wet bulb temperature o~ entering air at 10 a liquid
14 (water) temperature of initially sprayed liquid at 114F.
liquid is cooled to 99.1F. and is collected in the sump at
I6 99.1F. The air exits at a wet bulb temperature 99.1F.
17 In FIG. 6b, there is shown the same type device
18 modified by the instant invention by having three collectisn
19 trays 72, 76 and 82 vertically spaced along the exit end of
the device to catch the initially spxayed water at different
21 levels and reintroduce the water caught at the three levels
22 to the ambient air in the region in front of the initial
23 nozzle spray 71. Thus, liquid collected in txay 72 is
24 reintroduced through conduit means 73 to spray ~rom nozzles
at 94, again in the front of the initial spray 71. Sir.ce
26 this recycled liquid is being sprayed by gravity, the
27 recycled liquid sprays at 94 themselves collect in a
28 collection tray 75 al~o located in front of the initial
29 spray area. Water from this collec~ion tray 75 is
then xecycled using communicating means and gravity to another
838
1 nozzle spray outlet shown as 80 which is located in front of
2 the initial spray nozzles 71 and even in front of a second
3 recycled spray system coming from the second collection tray
4 76. As seen in FIG. 6b, this system follows for two more
S levels. The last portion of the original liquid spray
6 which is not recycled shown as 90 in FIG. 6b exits into a
7 sump. All the other liquid which was caught by any of the
_ 8 intermediate trays 7~, 76 and 82 had been-recycled and re-
9 - introduced prior to initial spray 71. These ex~t to the
sump as shown at the res~ec~ive tempera~ures. As shown,lthe
11 overall temperature of the liquld in sump 91 of FIG. 6a is
12 -95.7F.~ ~This compares with 9~1F ln the device in FIG. 6b
13 which had no recycling. ~ `
14 - This illustrates the advantage of applicants' in- -
~,
vention in that in botA FIG. 6a and 6b ~ne ,ame size primary
16 cooling device was used. ~he same alr flow namely 39,812
,
17 cfm was used in both devicésO The sàme~entering air tempera-
,, ~ .
]8 ture of 78F wet bulb is also used.` Agàin as can be seen,
19 the temperature of the water coIiected in the sump 91 of the
.
device in FIG. 6b W2S 3.4~ lower than that shown in the sump
21 of the device i~ FIG. 6a which had no recycling of the
22 liquid. In actual practice, if water at 99.1F was needed,
23 (the sump temperature o~ the water in the device in FIG~ 5a)
24 the device in FIG. 6~ can be smaller in size that the device
in FIG. 6a.
26 In FIG. 7, there is shown another modification of
27 the device in FIG. 6b. The difference here is that the
28 original spray header 110 from which crossheaders 111 exits
29 therefrom causing spray 112 from the nozzles located along
crossheaders 111 is at an anyle such that the bottom of
- 17
~483~
1 such spray header 110 is closer to the mist eliminators 13
2 than the top of the header as can be seen from FIG. 7. The
3 additional space caused by the angular design of header 110
4 can be utilized to house the additional spray headers and
S collection trays through which the recycled liquid passes.
6 This type configuration allows a compact rectangular shape
7 cooling device having no projections or appurtenances beyond
8 the rectangular profile shape.
9 The invention may be embodied in other specific
forms withou-t departing from the spirit or essential charac-
11 teristics hereof. The embodiment and the modification des-
12 cribed are therefore to be considered in all respects as
13 illustrative and not restrictive, the scope of the invention
~4 being indicated by the appended claims rather than by the
lS foregoing description, and all changes which come within the
16 meaning and range of equivalency of the claims are therefore
17 intended to be embraced therein.
~ ' ,
,, ~
~.~
~ -18-
