U.S. patent application number 10/186253 was filed with the patent office on 2002-12-26 for evaporator with enhanced condensate drainage.
Invention is credited to Bhatti, Mohinder Singh, Falta, Steven R., Joshi, Shrikant Mukund, Vreeland, Gary Scott.
Application Number | 20020195235 10/186253 |
Document ID | / |
Family ID | 26868642 |
Filed Date | 2002-12-26 |
United States Patent
Application |
20020195235 |
Kind Code |
A1 |
Falta, Steven R. ; et
al. |
December 26, 2002 |
Evaporator with enhanced condensate drainage
Abstract
An evaporator (10) with opposed pairs of generally vertically
oriented flow tube surfaces (14) has corrugated air fins in which
the tube surface spacing c, the interior radius r of a crest (20)
joining adjacent pairs of fin walls (18), the fin pitch p
separating adjacent crests (20), and the length l of louvers (22)
cut out of the fin walls (18) bear the following relationship:
0.ltoreq.r/c.ltoreq.0.057, 0.89.ltoreq.l/c.ltoreq.1.01, and
0.29.ltoreq.p/c.ltoreq.0.43. This has been found to substantially
improve condensate drainage, while not significantly penalizing
heat transfer or air side pressure drop.
Inventors: |
Falta, Steven R.;
(Ransomville, NY) ; Bhatti, Mohinder Singh;
(Amherst, NY) ; Joshi, Shrikant Mukund;
(Williamsville, NY) ; Vreeland, Gary Scott;
(Medina, NY) |
Correspondence
Address: |
PATRICK M. GRIFFIN
DELPHI TECHNOLOGIES, INC.
Legal Staff, Mail Code: 480-410-202
P.O. Box 5052
Troy
MI
48007-5052
US
|
Family ID: |
26868642 |
Appl. No.: |
10/186253 |
Filed: |
June 28, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10186253 |
Jun 28, 2002 |
|
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|
09637733 |
Aug 11, 2000 |
|
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6439300 |
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60172949 |
Dec 21, 1999 |
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Current U.S.
Class: |
165/152 ;
165/153 |
Current CPC
Class: |
F25D 21/14 20130101;
F28F 17/005 20130101; F25B 39/02 20130101; F28F 1/128 20130101 |
Class at
Publication: |
165/152 ;
165/153 |
International
Class: |
F28D 001/02 |
Claims
1. In an evaporator (10) having substantially parallel,
substantially vertically oriented refrigerant flow tubes (12), said
tubes having opposed pair of surfaces (14) spaced apart by a
distance c, between which tube surfaces (14) corrugated air fins
(16) are located, said fin corrugations comprised of adjacent pairs
of fin walls (18) joined at integral crests having an interior
radius r and a fin pitch p, said fin walls (18) also comprising
louvers (22) having a length l, characterized in that, said tube
surface spacing c, crest interior radius r, fin pitch p, and fin
louver length l have the following relationship:0.ltoreq.r/c.l-
toreq.0.0570.89.ltoreq.l/c.ltoreq.1.010.29.ltoreq.p/c.ltoreq.0.43
2. In an evaporator (10) having substantially parallel,
substantially vertically oriented refrigerant flow tubes (12), said
tubes having opposed pair of surfaces (14) spaced apart by a
distance c, between which tube surfaces (14) corrugated air fins
(16) are located, said fin corrugations comprised of adjacent pairs
of fin walls (18) joined at integral crests having an interior
radius r, said fin walls (18) also comprising louvers (22) having a
length l, characterized in that, said tube surface spacing c, crest
interior radius r, and fin louver length l have the following
relationship:0.25 mm.ltoreq.r.ltoreq.0.58
mm0.89.ltoreq.l/c.ltoreq.1.01
Description
PRIOR PATENT APPLICATION
[0001] This application is a continuation application of U.S.
application Ser. No. 09/637,733, filed Aug. 11, 2000, an
application that claims priority of prior provisional patent
application Ser. No. 60/172,949 filed Dec. 21, 1999.
TECHNICAL FIELD
[0002] This invention relates to air conditioning evaporators in
general, and specifically to an improved air fin design that
enhances the drainage of condensate.
BACKGROUND OF THE INVENTION
[0003] Automotive air conditioning system evaporators are subject
to water condensate formation, by virtue of being cold and having
humid warm air blown almost continually over them. Water condenses
on the tube or plate outer surfaces and fins, partially blocking
air flow, increasing thermal resistance, and potentially even
shedding or "spitting" liquid water into the ductwork of the
system. A screen is often installed downstream of the evaporator to
block water shedding, adding considerable expense.
[0004] To the extent that condensed water can be forced or
encouraged to drain down and out of the evaporator, the above noted
problems are reduced. Some obvious and low cost expedients include
orienting the evaporator core so that the flat outer plate or tube
surfaces are oriented vertically (or nearly so), with open spaces
between them at the bottom of the core, so that downward drainage
is assisted, and at least, not blocked. Vertical troughs or
channels have been formed in the outer plate surfaces, as well, for
the same reason.
[0005] An inherent problem with vertical plate or tube orientation
is that it creates a resultant air fin orientation that is not
conducive to condensate drainage. That is, the corrugated fins
brazed between the flat plate surfaces are given a nearly
horizontal orientation when the plates are arranged vertically,
thereby acting as dams to block drainage flow down the plate
surfaces. Numerous fin designs have been proposed with notches cut
through, or stamped into, the fin corrugation peaks or crests, to
thereby provide drains through the fins. Such designs would be
considerably more difficult to manufacture, and also remove
substantial contact area between the fin crest and plate surface.
reducing thermal conduction efficiency between the two.
[0006] Fins also typically include banks of thin, angled louvers
cut through the fin walls, oriented perpendicular to the air flow,
which are intended to break up laminar flow in the air stream,
enhancing thermal transfer between the fin wall and the air stream.
Louvers are invariably arranged in sets of oppositely sloped pairs
or banks, so that the first louver pattern will turn the air stream
in one direction, and the next will turn it in the other direction,
for an overall sinuous flow pattern. The cutting of the louvers
inevitably leaves narrow gaps through the fin walls through which
condensate can drain, under the proper conditions.
[0007] At least one prior art design claims a connection between
the louvers and condensate handling. U.S. Pat. No. 4,580,624 simply
proposes to assure that the last, most downstream pattern of
louvers on the fin wall be sloped inwardly, toward the interior of
the core, rather than sloped toward the exterior. It is claimed
that this orientation causes condensate drainage at this downstream
point to also flow inward, rather than being blown out into the
duct. This is a somewhat odd claim, especially since, with the
essentially universal louver pattern of oppositely sloped pairs or
banks, the most downstream louvers would be sloped inwardly,
anyway, and would inherently do what is claimed. Moreover, a fast
air stream moving up through the most downstream louver bank could
overwhelm the drainage force, shedding the water regardless, unless
the last louver pattern were very steeply sloped. It would be
essentially impossible to manufacture a fin in which only the most
downstream louver bank was steeply sloped, and putting a very steep
louver angle on all louvers in the fin would increase the air side
pressure drop considerably.
[0008] Another apparent trend in evaporator air fins is the use of
corrugated fins in which the fin walls are oriented parallel to
each other (or nearly so), in a U shaped corrugation, or in a
shallow V with a relatively large radiused crest, rather than a
sharper crested V. At least part of the impetus for this trend is
the desire for a dense fin pattern or fin pitch, one that puts more
fin walls per unit length within the available volume. A wider V
shape, in general, would create a less dense pattern of fewer fin
walls per unit length, at least for a given radius of the crest.
Furthermore, a more rounded, less sharply radiused corrugation
crest would be considered desirable in that it provides the only
surface area of the fin that directly contacts the plate or tube
outer surface. A corrugation crest with a smaller radius ( a
sharper "V") would provide less mutual contact area. While denser
fin patterns theoretically provide more fin-to-air-stream contact,
and more fin-to-plate mutual surface contact, which would increase
thermal efficiency, the effect on condensate retention has
apparently not been closely considered.
[0009] An example of an evaporator fin design with parallel walls,
and large radiused or U-shaped crests joining the fin walls, is
disclosed in U.S. Pat. No. 4,892,143. The design claims lower
condensate retention, but claims that such a result is due to a
factor that is very much at odds with the actual operation of an
evaporator fin of that type, as described further below. The patent
claims that by reducing the unlouvered length of the outside of the
fin wall and holding it within a small range, that the amount of
condensate "trapped" on the exterior of the crest between adjacent
fin walls is reduced. In point of fact, with a fin of this design,
it is found that water condensate is strongly retained between the
facing inner surfaces of the fin walls, on the interior of a fin
corrugation, but not on the exterior of the fin crest to any
significant extent. It may have been assumed, from observation,
that where condensate was not seen, it was somehow being drained or
removed, when in fact it had simply not formed in the first
instance. In actuality, fin shape design disclosed in the patent,
with parallel fin walls and large radiused, U-shaped crests, is the
worst performing in terms of retained condensate.
SUMMARY OF THE INVENTION
[0010] The invention provides an evaporator with a fin pattern that
provides enhanced drainage of water condensate from between the fin
walls and out of the evaporator, without degrading the performance
of the evaporator otherwise.
[0011] In the embodiment disclosed, a laminated type evaporator has
a series of spaced tubes, the opposed surfaces of which are
separated by a predetermined distance. A corrugated air fin located
in the space between opposed plate surfaces is comprised of a
series of corrugations, made up of a pair of adjacent fin walls
joined at a radiused crest. Each fin wall is pierced by a louver,
the length of which is determined by that portion of fin wall not
taken up by the radiused crest. Adjacent crests joining adjacent
pairs of fin walls are separated by a characteristic spacing or
pitch, with smaller pitches yielding higher fin densities, and vice
versa. For a given pitch and tube spacing, a volume or cell is
defined between the tube surfaces within which each corrugation
(pair of fin walls and crest) is located.
[0012] According to the invention, the shape of the corrugation
within that cell, in terms of radius and relative louver length, is
determined and optimized as a function of a series of defined
ranges variously of both the absolute values of and the relative
ratios of parameters including fin pitch, louver length, and crest
radius, normalized, in some cases, to plate spacing. Based on a
combination of empirical testing and computer modeling, optimal
ranges of those parameters that determine corrugation shape have
been determined based on practical considerations of desirable heat
flow performance, air pressure drop through the fin, and water
retention on and in the fin. For a given tube spacing, the designer
can choose a corrugation shape (crest interior radius, fin pitch,
and louver length) that will improve condensate drainage
significantly, while not significantly degrading the evaporator
performance in other areas.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a partially broken away view of the front of a
typical evaporator core of the laminated type;
[0014] FIG. 2 is an enlarged view of a section of an evaporator
core in general showing a complete fin corrugation;
[0015] FIG. 3 is a view similar to FIG. 2, showing an actual view
of an existing or baseline evaporator fin in operation, with
retained water condensate formation;
[0016] FIG. 4 is a view similar to FIG. 3, showing an actual view
of an evaporator fin designed according to the invention, with its
reduced and improved water condensate formation;
[0017] FIG. 5 is a graph showing a comparison of water retention
performance for the baseline fin and other fins of varying shape
and density;
[0018] FIG. 6 is a graph showing a comparison of heat transfer
performance for the baseline fin and other fins of varying shape
and density;
[0019] FIG. 7 is a graph showing a comparison of air pressure drop
performance for the baseline fin and other fins of varying shape
and density;
[0020] FIG. 8 is a graph that captures the data from FIGS. 5-7 on a
single graph to indicate the optimal fin parameter ranges of the
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0021] Referring first to FIGS. 1 and 2, a laminated type
evaporator, indicated generally at 10, is comprised of a series of
spaced refrigerant tubes 12, the opposed outer surfaces 14 of which
are separated by a regular, predetermined distance "c". A
corrugated air fin, indicated generally at 16, is located in the
space between each pair of opposed tube surfaces 14. Fin 16 is
comprised of a series of corrugations, each of which, in turn, is
comprised of a pair of adjacent fin walls 18, joined at an integral
radiused crest 20. The inside or interior radius of each crest 20
is indicated at "r". Each fin wall 18 is pierced by a louver 22,
which would have a conventional width and angle relative to fin
wall 18. The length "l" of each louver 22 is basically the length
of that portion of fin wall 18 not occupied by the radiused crest
20, and the converse is true, as well. Significantly, the basic
construction and manufacture of fin 16 according to the invention
is conventional with no holes, or notches to promote drainage, and
no differing of varying louver angles, etc, that would impair
manufacture. As with any corrugated fin, adjacent crests 20 are
separated by a characteristic spacing or pitch, indicated at "p",
which has an inverse relationship to the density "n", or number of
fin corrugations encountered per unit length of the tube surface
14. That inverse relationship is indicated as p=2/n. For any given
pitch "p" and tube spacing "c", a volume or cell is defined between
the tube surfaces, indicated by the dotted line rectangle in FIG.
2. According to the invention, a means is provided for optimizing
the shape of a corrugation within that available cell, especially
as related to louver length and crest radius.
[0022] Referring next to FIG. 3, the performance of a currently
used, conventional or baseline fin, indicated at 16', is
illustrated. Fin 16' is located between the same opposed, flat tube
surfaces 14, and has all of the same basic structural features as
fin 16 of the invention, so numbered with a prime. Each corrugation
of baseline fin 16' is shaped, within the available cell, so as to
be more U than V shaped, with a relatively large radiused crest
20'. The fin walls 18' are substantially parallel or, in many
cases, actually buckled back in on themselves. The exterior
surfaces of each corrugation crest 20' are convex, and thus do not,
because of the nature of surface tension forces, act to form or
"trap" a water condensate film, in spite of the claims of the
patent discussed above. The interior surfaces of the corrugation
crests 20', however, are concave, and thus do form and retain water
condensate, very readily. The retained condensate grows beyond a
film to become a meniscus that bridges the facing fin walls 18', as
indicated by the shaded areas. This drawing was produced from a
photograph of the actual operation of the evaporator. The result is
a series of restricted open areas "O" (areas in cross section, but
volumes in fact) bounded by the tube surfaces 14', the exterior
surfaces of two adjacent crests 20', and the terminal edge of the
retained water meniscus. These areas O are very small relative to
the potential open area between the fin walls 18', most of which is
blocked. The potential impact on performance is clear. Air passing
between the fin walls 18' is restricted, increasing pressure drop
and reducing thermal performance. Of course, retained water can
lead to the shedding or "spitting" phenomenon referred to above.
The fan air forced through the restricted areas O is accelerated,
making it even more prone to stripping water out from between the
fin walls 18'. This problem has been serious enough to require a
screen covering the downstream face of the core, which adds cost
and is itself an air flow restriction. Table 1 below gives the
relative dimensions and performance parameters for this baseline
case.
1TABLE 1 Geometric and Performance Information Pertaining to the
Baseline Evaporator English Units Metric Units Fin height c 0.400
in. 10.2 mm Fin pitch p = 2/n 0.143 in. 3.6 mm Louver length l
0.332 in. 8.4 mm Fin radius r 0.036 in. 0.91 mm Fin density n = 2/p
14 fins/in. 5.5 fins/cm Heat transfer rate q.sub.o 470 Btu/min 8.26
kW Water retention in operation m.sub.o 1.56 lb.sub.m 0.71 kg
Airside pressure drop .DELTA.P.sub.o 0.47 in. H.sub.2O 0.12 kPa
[0023] Referring next to FIG. 4, the performance of a fin 16 made
according to the invention is illustrated. The view shows the same
evaporator 10, tubes 12, vertically oriented, flat tube surfaces
14, with the same spacing c. Fin 16 has the same pitch as baseline
fin 16' described above. As a consequence, the same basic cell
within which a corrugation of fin 16 is located is defined. Within
that available cell, however, it is evident that the fin 16 is more
V shaped than the baseline fin 16', with fin walls 18 that are
joined at a sharper, smaller radius crest 20. It is also very
evident that the retained water meniscus is much smaller, and the
open areas "O" are, consequently, much larger. Before describing
the mechanisms that are thought to be at work, a corresponding
Table 2 gives the comparative dimensions and measured performance
for fin 16:
2TABLE 2 Geometric and Performance Information Pertaining to the
Test Evaporators English (metric) Fin height c, in. (mm) 0.400
(10.2) Fin pitch p = 2/n, in. (mm) 0.143 (3.6) Louver length l, in.
(mm) 0.374 (9.5) Fin radius r, in. (mm) 0.016 (0.40) Fin density n
= 2/p. fins/in. (fins/cm) 14 (5.5) Heat transfer rate q, Btu/min
(kW) 485 (8.5) Water retention in operation m, lb.sub.m 1.10 (0.50)
(kg) Airside pressure drop AP, in H.sub.2O (kPa) 0.54 (0.13)
[0024] Comparing Tables 1 and 2, a few points are immediately
apparent. For an equivalent plate spacing and fin pitch, the heat
transfer rate and airside pressure drop are essentially equivalent
(the former somewhat better, the latter somewhat worse), but the
water retention is significantly improved, by nearly 30%. This is
achieved just by the differing corrugation shape within the same
available volume or cell, a shape difference reflected in the
significantly smaller radius and longer louver length. No major
structural change is made to the fin, that is, it has no extra
holes or voids added for water drainage, (beyond the attendant
louver openings), no special number of, or angle for, or
orientation of, the louvers 22. Consequently, manufacture of fin 16
according to the invention can, and would be, done conventionally.
But, by the seemingly simple (with hindsight) expedient of shaping
the fin as noted, the greatly improved water retention performance
is achieved. Not all of the mechanisms at work are perfectly
understood, but it is thought that at least two factors are the
most significant, and these two factors work in a synergistic or
cooperative fashion. One factor is the sharper radiused crest 20,
which results in the more "V shaped" walls 18, which, in turn,
tends to pull the meniscus of retained water deeper into the
interior of the crest 20, deeper into the "V," in effect. That
factor alone, however, would not cause the retained water to drain
out any more readily. The second factor is the relatively longer
louver 22 (and the relatively longer louver opening that inherently
lies next to a longer louver 22.) That provides a drainage path
which, advantageously, also extends deeper into the "V,"
overlapping with the meniscus of water that is continually pulled
in. So, the surface tension force pulling the water continually
toward the extended drainage path allows an equilibrium to be
achieved as water continually drains down, fin to fin, from top to
bottom and, eventually, out between the vertically oriented tubes
12. This is an improved drainage equilibrium in which, on balance,
significantly less water is retained.
[0025] Referring back to FIG. 4, the result of this improved
drainage equilibrium is evident. The retained meniscus of water is
smaller, so the open areas O are conversely larger. Air flow is,
due to that factor alone, less restricted, and the air velocity
through the larger open spaces O less, leading to less shedding or
"spitting" of the already reduced retained condensate. (Overall
airside pressure drop is greater, on balance, because of the longer
louvers 22, which increase resistance to air flow). Heat flow
performance is improved, since the fin walls 18 are less insulated
or "jacketed" by retained condensate. Other advantages of improved
condensate drainage include less potential evaporator odor and
corrosion, as well as the potential for eliminating add on
structures, such a downstream screens, that have been used in the
past to block or reduce water shedding. This can represent a
significant cost saving.
[0026] The invention is broader than just the particular embodiment
disclosed in Table 1, of course, and a method is provided by which
a designer can achieve a similar result in evaporators with
different tube spacings, and achieve it with fins that have
different absolute dimensions, but in which the dimensions adhere
to optimal ranges defined below. Referring next to FIGS. 5 through
8, a series of graphs is presented, which are computer generated
depictions of the expected performance of a range of fin shapes and
geometries, presented in the form of ratios of parameters that are
not normally so considered. For example, in FIGS. 5-7, a ratio of
fin radius r to fin height (tube spacing) c is shown at the lower x
axis, and the corresponding ratio of louver length l to fin height
c is shown at the top x axis. The y axis indicates the ratio of
various performance measures to the baseline case (distinguished by
the subscript o), such as water retention, heat transfer rate, and
pressure drop. The various curves represent the fin geometries at
various fin pitches p, again, represented not in absolute terms,
but as a ratio of p relative to c. These curves end at a point
which represents the limiting factor for 1 as a ratio of c. That
is, for a ratio greater than 1, as the louver 22 becomes very long
and essentially as long as the entire fin height, the fin wall 18
could be expected to buckle or curl up, which would be undesirable.
Likewise, the curves are not drawn beyond the points where the
ratio is so small that the louver 22, in turn, would be too short
to be effective in condensate drainage.
[0027] In determining what is an improved performance, in FIGS. 5
and 7, a ratio of less than 1 is considered better than the
baseline case, since it is desired to decrease water retention. For
FIG. 6, a ratio of greater than one is an improvement, of course,
since it is desired to improve heat transfer (or at least keep it
relatively constant). As a practical matter, a hypothetical
automotive designer would be satisfied with keeping heat transfer
constant, and even increasing the airside pressure drop to an
extent, if water retention could be substantially reduced, since it
is water retention that is seen as the real problem in this area.
The discussion below indicates how an optimal range of the above
described ratios can be identified based on these general
guidelines. That is, a method is provided by which a designer can,
having chosen a given fin height c, in turn determine the other fin
dimensions that will yield the desired general result. Stated
differently, the designer can, having determined the available room
within a cell for a corrugation, then determine the shape of the
corrugation within the cell that can be expected to yield the
desired result of substantially improved (decreased) water
retention, without substantially decreased performance in the areas
of heat transfer and air side pressure drop.
[0028] Specifically, referring to FIG. 5, it is a given that an
evaporator would be considered to be improved if the water
retention ratio, m/m.sub.0, were less than 1. Referring to the
broken horizontal line, corresponding to m/m.sub.o=1, and the
upward sloping water retention curves, it is apparent that for
m/m.sub.0.ltoreq.1, the ranges of the geometric parameters would
be:
0.ltoreq.r/c.ltoreq.0.125
0.73.ltoreq.l/c.ltoreq.1.01
0.25.ltoreq.p/c.ltoreq.0.50
[0029] This general restriction or condition does not cull anything
out of the range of fin dimension possibilities. However, practical
experience has shown that to significantly improve the condensate
"spitting problem", the ratio should be less than 0.75. Using the
broken horizontal line corresponding to m/m.sub.o=0.75 in FIG. 5 as
the determinate, the ranges of r/c and l/c for
m/m.sub.o.ltoreq.0.75 are narrowed giving the following set of
ranges of the geometric parameters:
0.ltoreq.r/c.ltoreq.0.090
0.82.ltoreq.l/c.ltoreq.1.01
0.25.ltoreq.p/c.ltoreq.0.50
[0030] These ranges of r/c, l/c and p/c corresponding to
m/m.sub.o.ltoreq.0.75 are indicated by the shaded area in FIG.
5.
[0031] Referring next to FIG. 6, the further constraint of heat
transfer rate is illustrated. As noted, FIG. 6 shows variation of
the heat transfer rate q with r/c, l/c and p/c. Heat transfer rate
q appears as a parameter for the family of the heat transfer rate
curves, with the heat transfer rate q is normalized relative to the
heat transfer rate q.sub.o for the baseline evaporator given in
Table 1. Imposing the additional condition that q/q.sub.o.gtoreq.1,
the ranges of the geometric parameters derived from are further
narrowed as follows:
0.ltoreq.r/c.ltoreq.0.057
0.89.ltoreq.l/c.ltoreq.1.01
0.25.ltoreq.p/c.ltoreq.0.43
[0032] These further narrowed ranges of r/c, l/c and p/c are
indicated by the shaded area in FIG. 6.
[0033] Referring next to FIG. 7, the consideration of airside
pressure drop places yet a further limitation on the ranges of the
geometric parameters derived from the water retention and heat
transfer constraints defined above. FIG. 7 shows variation of the
pressure drop .DELTA.P with r/c, l/c and p/c, which also appears as
a parameter for the family of the pressure drop curves. Also it may
be noted that the pressure drop .DELTA.P is normalized with the
pressure drop .DELTA.P.sub.o for the baseline evaporator given in
Table 1. For a high performance evaporator, it is desirable that
the pressure drop .DELTA.P should be less than or equal to the
pressure drop in the baseline evaporator .DELTA.P.sub.o. In other
words, .DELTA.P/.DELTA.P.sub.o.ltoreq.1. As a practical matter,
however, a modest pressure drop penalty is acceptable, on the order
of approximately 20%, which is less limiting on the range of
parametric ratios defined. The horizontal broken line drawn at
.DELTA.P/.DELTA.P.sub.o=1.20 in FIG. 7 completes this final
narrowing, and the optimal ranges of the parametric ratios are
determined to be:
0.ltoreq.r/c.ltoreq.0.057
0.89.ltoreq.l/c.ltoreq.1.01
0.29.ltoreq.p/c.ltoreq.0.43
[0034] This final, further narrowing is also represented by the
shaded area in FIG. 7.
[0035] Referring finally to FIG. 8, the three optimal parametric
ranges noted above are regraphed on the various axes, and with the
three constraints of q/q.sub.o, m/m.sub.o and
.DELTA.P/.DELTA.P.sub.o represented as bounding curves, enclosing a
shaded area. The additional constraint that would occur if
.DELTA.P/.DELTA.P.sub.o were further limited to be either 1.0 or
1.1 is indicated by the additional two broken and nearly vertical
lines in the graph. Clearly, the acceptable range of parametric
ratios would encompass a much smaller shaded area, with the more
restrictive pressure drop constraint. The baseline evaporator is
also indicated for purposes of comparison, and the evaporator
referred to in Table 2 above is shown as a data point that is
within the preferred range.
[0036] In conclusion, given the guidelines above, a designer can
use a predetermined fin height c as a scaling factor, and from that
determine a range radius and relative louver length that would be
expected to be particularly effective. As noted above, what is
especially significant are the dual factors of crest radius and
louver length, and those two factors alone could be designed for.
To repeat, the crest radius should be sufficiently sharp to both
create a V shape (as opposed to a U shape) within the corrugation,
and also to pull the meniscus of condensate strongly toward and
into the bottom inner surface of the crest, as opposed to bridging
the fin walls of the corrugation, as occurs in the old design. In
addition, the louver length should be sufficient to reach down into
that meniscus and drain it. As such, the range of radius values
that would be workable would be an absolute range, really
independent of fin spacing c or fin wall length. A crest radius
would be sharp or not regardless of how long the fin walls, the
"sides of the V", were. However, any louver like 22, in order to
enhance drainage, must be "long" not in absolute terms, but "long"
relative to the length of the fin wall 18, or, stated more
universally, long relative to the fin spacing c. It is that
relative length of the louver 22 compared to the fin wall 18 (or
fin spacing c) that assures that the co extensive louver opening
will reach into and drain the water condensate meniscus at the
bottom of the V. For the particular fin spacing c disclosed here,
of 10.2 mm, crest radius r would range from 0 to 0.58 mm, based an
r/c ratio ranging from 0 to 0.057. Since 0 is not a practical
radius to manufacture, a lower limit of about 0.25 mm could be
expected to be practically useful, in conjunction with the
relatively long louver, to enhance drainage.
* * * * *