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Oct. 1, 1946.-
’
J_G_RE'.D,JR_
2,408,480
EVAPORATOR FOR LOW PRESSURE REFRIGERANTS
Filed‘ Jan. 3., 1945'
M/W
ATTORNEY
Patented Oct. 1, 1946
- 2,408,480
UNITED STATES PATENT-Face
EVAPORATOR FOR- LOW-PRESSURE
>
REFRIGERANTS
'
v John G. Reid,>Jr., Evansville, Ind., ,assignor to‘, I
Servel, Inc., New York,
Y., a oorporationlof .
Delaware
Application January 3, 1945, Serial No. 571,167 I i
5 Claims. (o1.62_'119)
1
The present invention relates to refrigeration
i Fig. 1 is a diagrammatic view of an absorption
and more particularly to a refrigeration system
refrigeration system incorporating the evapora
- including a novel evaporator construction to
tor of the presentinvention'; and
adapt the system for air conditioning.
While ‘the present invention may be used with
.
g
Fig. 2 is a longitudinal sectional view of the up.
per portion of an evaporator tubeshowingvthe
internal helical groove forming a plurality of ser
other absorption refrigeration systems, it is par
ticularly adapted for use in a system of the type
rations on the inner periphery of the tube ‘andja
illustrated and described in the application for
wick to facilitate the initial'wetting of the inner
United States Letters Patent of Albert R. Thomas,
surface of the tube.
v
_
i
.
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Serial No, 560,214, filed October 25, 1944, en 10
In the drawing, the invention 'isshown ap
titled “Refrigeration.” The refrigeration system
plied to a refrigeration system'of the type illus
trated in the‘ Thomas application referred to
illustrated and described in the Thomas applica
tion operates in a partial vacuum and utilizes
water as a refrigerant and a saline ‘solution as an
absorbent.
above. In a refrigeration system of this type a
The refrigerant and absorbent; are 15
introduced into the system as a water solution of
a salt such as lithium chloride, lithium bromide,
or the like and the absorbent occurs in the sys
tem as a dilute or concentrated water solution of
the salt.
7
liquid refrigerant-such as, for‘example, water ‘is
introduced into the evaporator [0, later 'to be de
scribed in detail, from a condenser ll through a
path of ?ow including avU-shaped tube l2. rI‘he
u-shaped tube !2 has. one end connected to a
sump l3 at the bottom of the condenser II and
its opposite end extends through the top of the
evaporator H3. The refrigerant vapor ‘formed in
the evaporator it! flows 'to an" absorber [4 where
the vapor is absorbed in aliquid absorbent such
'
One of the objects of the present invention is
to provide an evaporator or cooling element hav
ing vertical tubes extending between upper and
lower headers and so constructed and arranged as
as, for example, a concentrated water solution
of lithium chloride or lithium bromide. The ab
sorber M is in the form of a horizontally arranged
to distribute liquid refrigerant equally to the
plurality of tubes.
Another object isqto provide an evaporator of
the type indicated in which the liquid refrigerant
cylindrical drum positioned below the evaporator
it. ‘A pipe l5 extends upwardly from the top of
is supplied to the open upper end of each tube in
a thin sheet or ?lm around its entire periphery for
the absorber l4 and isv connected to the emperortor ‘It to provide a path of flow for refrigerant
gravity flow therethrough.
vapor from the evaporator to the’ absorber. ‘' ‘
Absorption liquid enriched with refrigerant‘ or,
Another object is to provide an evaporator hav
ing vertical tubes of the type indicated with ser
rations on the-inner periphery of each tube to
in other words, a dilute salt solution is conducted
from the absorber l 4' to the base of- a generator I 6
in anath of'flow including a conduit l1, pump l8,
impede the flow, of liquid refrigerant and main
tain a thin ?lm of the liquid refrigerant through
out its length.
conduits i9 and 2E], liquid heat'exchanger 2| and
conduit 22. The generator’l? comprises'a plu
‘
Another object is to provide an evaporator of
the type indicated having a pump circuit for re
circulating
the
refrigerant . from
header to the upper header.
‘
the > lower
rality of riser tubes 23 enclosed Within an outer
40
'
Still another object is to provide an evaporator
of the type indicated which is adapted-to accom
modate the large volumes of refrigerant vapor
formed in a vacuum system.
These and other objects will become more'ap
parent from the following description and draw
ing in which like reference charactersdenote like '
parts throughout the several views. It is to be
expressly understood, however, that the draw 50
ing is for the purpose of illustration only and not
a de?nition of‘the limits of the invention, refer
ence being had for this purpose to the appended
claims.
In the drawing:
shell as to provide ‘a chamber therebetween.
Steam is supplied to the chamber in- the genera
tor it from a boiler 25 through a conduit 26‘. For
purposes of illustration a manually operable valve
V is shown in the conduit 25 for controlling the
amountof steam’ supplied, to the generator 16
but'it will be understood that a suitable auto
matically operable valve may be substituted for
controlling the amount of steam delivered to the
generator ity in accordance with thevload. ' The
boiler 25 isprovided with ?re tubes 21 to which
heat is supplied from’ suitable fuel burners 28.
An outlet vent 29 is provided adjacent the upper
end-of the steam chamber. in the generator l5
and a condensate return line 30' is provided ad
jacent the base thereof.v The heating of the riser
tubes 23 by the Steam causes refrigerant vapor to
2,408,480
3
4
the upper end of the conduit in the separating
chamber is protected by a shield 44.
be expelled from the absorption solution and such
expelled vapor is effective to raise the absorption
When relatively large refrigeration units uti
solution in the tubes by gas or vapor lift action.
The expelled vapor passes from the upper ends of
lizing water as a refrigerant are used for air con
the riser tubes 23 into a vapor separator 3| and
thence flows through a conduit 32 to the con
denser H where the vapor is lique?ed. Liquid
tion of refrigerant in different parts of the evap
ditioning, a uniform distribution and evapora
orator cannot be obtained in the usual types of
evaporators due to the low pressure and great
volume of refrigerant vapor. A ?ooded type
evaporator cannot be used advantageously in
such a refrigeration system because of the hy
drostatic head of refrigerant in such an evapora
refrigerant formed in the condenser ll flows
through the U-shaped tube [2 to the evaporator
ID, as explained above, to complete the refriger
ation cycle.
.
The raised absorption solution from which re
tor which raises the boiling point progressively
frigerant vapor has been expelled is conducted
from the top to the bottom of the evaporator and
from the upper portion of the generator IE to
the absorber M in a path of flow including a 15 renders the greaterportion of its surface ine?ec
tive for the transfer of heat. To avoid such hy
conduit 33, liquid heat exchanger 2| and conduit
drostatic head, it is desirable to maintain a thin
34. The end of the conduit 34 extends into the .7
?lm of the liquid refrigerant on the internal sur
upper portion of the absorber I4 adjacent the
faces of the evaporator. With relatively small
inlet from the pipe [5 and has a plurality of
apertures or nozzles therein to provide a dis
20 units using water as a refrigerant, it is the prac
tributing pipe 35 for dividing the absorption solu—
tion as it is introduced into the absorber to pro
mote absorption of the refrigerant vapor. The
heat liberated by the absorption of refrigerant
vapor in absorber I4 is taken up by a cooling
medium such as, for example, water which flows
upwardly through vertically disposed banks of
pipes or coils 36 in the absorber. The cooling
tice to flow the refrigerant from the top to the
bottom of the evaporator in a shallow stream
through a series of substantially horizontal tubes.
In such small units a substantial wetting of the
interior surfaces of the tubes is obtained and the
design can be such that all of the refrigerant will
be evaporated during a single pass through the
evaporator at full load conditions. With large
units, however, due to the increased amount of
water is introduced into the lower ends of the 30 liquid refrigerant supplied to the evaporator it is
banks of pipes 38 from a supply main 31 and is
practically impossible to maintain a thin ?lm
discharged \from the upper ends of the banks
of refrigerant on the interior surfaces of such a
of pipes through a conduit 38. Conduit 38 is
series arrangement of horizontal tubes and the
connected to the condenser ll so that the cool
liquid refrigerant in the ?rst tubes of the evap
ing water also may be utilized to effect cooling
orator is apt to be blown out of the tubes by the
of the condenser. The cooling water is discharged
from the condenser ll through a conduit 39.
The system operates in a partial vacuum with
the generator [5 and condenser H operating at
one pressure and the evaporator IE) and absorber
14 operating at a lower pressure. The pressure
differential between the high and low pressure
sides of the system is maintained by a liquid col
umn in the up-leg of the U-shaped tube l2 be
tween a condenser l l and evaporator ID. A simi
lar liquid column also is present in the conduit
34 connecting the absorber I 4 and liquid heat
exchanger 2!. The pump l8 connected between
‘the absorber M and liquid heat exchanger 2|
also maintains the pressure differential between
the absorber and generator I 6.
. The absorption solution in the absorber I4 is
circulated continuously through an auxiliary loop
circuit to promote absorption of the refrigerant
vapor. The auxiliary loop circuit for the absorp
tion solution comprises the conduit l1, pump l8
‘and conduit l9. The upper end of the conduit
l1 extends into a sump 40 in the bottom of
the absorber l4 and the lower end of the con
duit is connected to the inlet of the pump l8.
Conduit [9 is connected at one end to the outlet
from the pump I8 and its opposite end extends
‘throughout the length of the absorber l4 adja
cent the top thereof. A series of nozzles 4| are
provided in the end portion of the conduit I9 ex
tending into the absorber M to provide a liquid
distributing pipe 42 for dividing the absorption r.
liquid into a ?ne spray as it is delivered to the
absorber. During operation of the refrigeration
‘system, part Of the circulating absorption solu—
tion is diverted from the conduit l9 through the
conduit 20 and liquid heat exchanger 2| to the
generator l6~as previously described.
'
An over?ow conduit 43 is provided between the
separating chamber 3| and the absorber l4 and
rapidly expanding refrigerant vapor. Further
more, it is di?icult to design a horizontal tube
evaporator for a large unit which will vaporize
all of the refrigerant during a single pass there
through under varying load conditions.
In accordance with the present invention a
novel :form of air conditioning evaporator is pro
vided for use with relatively large refrigeration
units. The evaporator Hi comprises a casing 59
forming a central rectangular opening 5| through
which the air to be conditioned may be circu
lated. The casing is of generally hollow con
struction to provide an upper header 52 above
the opening 5|, a lower header 53 below the
opening and a relatively large passageway 54 at
one side of the opening. The bottom wall of the
upper header 52 constitutes a horizontal tube
sheet 55 and the top wall of the lower header 53
constitutes a tube sheet 56. The end of the
lower header 53 opposite the passageway 54 ex
tends horizontally and vertically to provide a
pump chamber 5?. .One end of the upper header
52 converges into a cylindrical pipe section 58
having a ?ange 59 at its end for connection ‘to
the pipe 15.
A plurality of vertical pipes or cooling tubes 60
extend across the opening 5i and through the tube
sheets 55 and 58 in the upper and lower headers
‘52 and 53. .The upper end portions of the tubes
60 extend abovethe tube sheet 55 in the upper
header 52 with all of the ends arranged at the
same level in ‘a horizontal plane.
A wall 6i ex
tends upwardly from the tube sheet 55 and be
tween the side walls ‘of the header 52 to provide
a dam for maintaining a pool of liquid refrig
erant around the upwardly projecting ends of the
tubes Bil. While a single row of the tubes 65 are
illustrated in the drawing, it will be understood
that a plurality of rows of tubes may be provided
and the tubes are provided with '?ns 63 forfin—
2,408,480
5
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' creasing the heat transfer. The internal ‘surface
.innerperiphery. thereof. Due to the equal‘height
of the tubes 60 ‘are roughened or serrated to
of the ends of the‘ evaporator tubes 58 above the '
impede the ?ow of refrigerant therethrough and
maintain a thin film of liquid refrigerant thereon.
As, illustrated in Fig.7. 2, the serrations on the
tube sheet 55 the liquid refrigerant will be dis
tributed‘ equally in all of the tubes Bi] and will
interior of each tube is formed by an internal
be supplied’ to each tube in a thin ?lm around
its entire inner periphery. When a starting de
helical groove 64 in which refrigerant flows from
the top to the bottom of the tube, by gravity.
vice 82, as illustrated in Fig. 2, is provided on
the upwardly projecting end of each of the tubes
58, a small amount of the liquid refrigerant is
Due to the size and shape of the helical groove
.64 the liquidrefrigerant creeps up along the sur 10 siphoned into the interior of the tube by capillary
face of the tube between adjacent grooves due to
action to wet the interior before the liquid refrig
erant rises to a level above the upper end of the
capillary action to wet the entire surface of the
tube and form a?lm ofliquid refrigerant thereon.
tube. Such a starting device assists in the initial
wetting of the tube to insure equal distribution
‘ While not essential to the operation of the evap
orator 10, a starting device 62 may be provided 15' of refrigerant in the plurality of tubes, "The
liquid refrigerant will flow downwardly by gravity
on the upwardly projecting end of each tube 60
to initially wet the inner surface of they tube be
> in'the helical grooves 64 from the top to thebot- _
fore the liquid rises to the level of the upper end
~ .of the tube. As illustrated in Fig. 2, the starting
tom of the tubes 60 and due to the shape and size
of the grooves the. liquid refrigerant will ‘creep
device is formed by a ?ne mesh metallic screen 20 between adjacent grooves to wet the interior sur
looped over the sides of the upwardly projecting
face of the tubes throughout their length. In
end of the tube. In place of a metal screen a
other words, the helical serrations 64 on the inte
rior of the evaporator tubes 68 will cause a thin
fabric sleeve or wicking may be used.
The liquid refrigerant in the lower header 53
?lm of the liquid refrigerant to be formed thereon.
is recirculated through the evaporator II! by‘a 25 The liquid refrigerant in excess of that evaporated
during a single pass through the evaporator tubes
pump 65in the pump chamber 51. The pump
55 is positioned below the liquid level in the lower
5i) will flow through the tubes to the lower header
53. .
header 53 and the pump'is driven by a shaft 66
extending from an hermetically sealed motor 67
The pump 65 continuously recirculates the re
mounted on the evaporator casing. A conduit 63 30 frigerant from the lower header 53 to the upper
header '52 and delivers the refrigerant through
is connected to the outlet from thepump 65 and
the nozzles 69 in the form of a spray to promote
extends upwardly and then horizontally through
evaporation of the refrigerant._ Due to the rela
out substantially the entire length of the upper
’ tively thin ?lm of liquid refrigerant on the inter
header 52. The portion of the conduit 68‘ extend
ing into the header 52 has aseries of outlet aper 35 nal surfaces of the tubes 60 the evaporation of
tures or nozzles 69 and constitutes a liquid dis
the refrigerant occurs at the surface of the liquid
tributing pipe ‘Hi for supplying the recirculated
so that liquid refrigerant will not be blown from
refrigerant to the upper header.
the tubes. Furthermore the recirculation of the
refrigerant insures complete and equal evapora
An over?ow conduit 15 is provided in the evap
orator IO to prevent the accumulation of an ex 40 tion throughout all parts of the evaporator.
The evaporation of the refrigerant in the evap
cessive amount of liquid refrigerant therein. The
orator l? will reduce the temperature of the re
upper end of the conduit ‘l5 extends into the
frigerant to a value corresponding to the pres
evaporator in to a predetermined height above
sure prevailing in the evaporator. Thus the
the bottom thereof and below the lower ends of
evaporation of the refrigerant acts to cool the
the tubes 50. The opposite end of the conduit 15
may be connected to any part of the refrigeration
7body of refrigerant supplied to the header 52
system and as hereinlillustrated it is connected ‘
from the condenser I l and recirculated by the
to the conduit 22 adjacent the base of the gen
pump‘ 65. The air to be conditioned flows
erator 16. When the level of the liquid refrig
through the opening 5| and around the tubes 59
erant in the evaporator ill rises to a level above 50 in the evaporator H! and is chilled bv its contact
the upper end of the conduit '15 the liquid refrig
with the tubes; the air transferring its heat
through the tubes to evaporate more of the re‘
erant will overflow to the base of the generator
Hi to dilute the absorption solution and maintain . frigerant'to maintain a temperature correspond
ins: to the pressure in the] evaporator.
the concentration below the saturation point at
which crystallization and precipitation of salt
The refrigerant vapor flows upwardly through
from the solution will occur. One form of the
the tubes 6!! to‘the upper header
and from
invention having now been described in detail
the lower header 53 through the relativelylarge
the mode of operation is explained as follows.
passage‘ 54 to the upper header 52 and thence
Steam supplied to the generator 55 vaporizes
flows through the pipe 85 to the absorber M
the refrigerant therein which flows upwardly 60 where it is absorbed in the absorption solution.
through the tubes 23 and raises the absorption
The absorption solution in the upper part of the
solution by vapor lift action. The refrigerant
vapor ?ows from the separating chamber 3!
through a conduit 32 to the condenser H where
generator 16 flows through the conduit 33, liquid
heat exchanger 2! and conduit 34 to the liquid
distributing pine 35 where it is delivered into the
the vapor is condensed to a liquid. The liouid 65 absorber. The absorption solution in the absorb;
refrigerant flows from the condenser H through
or M is continuously recirculated through the
the U-shaped tube !2 into the upper header 52
conduit-i7. pump it! and conduit 89 to the liquid
of the evaporator. vDue tothe dam If! in the upper
distributing pipe 42 in the absorber which deliv
header 52, a pool of the liquid refrigerant accu
‘ers the absorption solution in a ?ne spray to
mulates around the end portions of theevaporator
tubes 60 projecting above the tube sheet 55. When
a su?icient amount of liquid refrigerant has ac
cumulated in the header 52, the liquid level will
rise to the horizontal level of the upper ends of
the tubes 60 and will ?ow into the tubes at the
promote absorption. A portion of the recircu
lated absorption solution is continuously diverted
through the conduit 2!], liquid heat exchanger 2|
and conduit22 back to the base of the generator.
If for any reason the liquid refrigerant tends
to accumulate in the evaporator Hi, the overflow
2,408,480
8
conduit 15 will drain the refrigerant to ‘the con
duit 22 adjacent the base of the generator to
maintain the concentration of the absorption so
part of the system to control the amount of re
frigerant in the evaporator by draining excess
refrigerant to the other part of the system.
lution within permissible limits.
3. An evaporator for use in a refrigeration sys
tem comprising a casing forming a central open
It will now be observed from the foregoing
speci?cation that the present invention provides
ing with a header above the opening, a header
below the opening and a relatively large passage
way between the upper and lower headers at one
an evaporator of novel construction including a
plurality of vertical tubes extending between up
per and lower headers.‘ It will further be ob
served that the evaporator of the present inven
side of the opening, said upper header having an
inlet for liquid refrigerant and an outlet for re
frigerant vapor, the bottom wall of the upper
tion is so constructed and arranged as to main
header forming a horizontal tube sheet, a plu
tain a ?lm of liquid refrigerant in all parts of
rality of vertical tubes extending between the up
the evaporator and is adapted to accommodate
per and lower headers with the ends of the tubes
the large volumes of refrigerant vapor which are
formed in a vacuum system. It will still further 15 projecting above the tube sheet in the upper
header, structure in the upper header for retain
‘be observed that the present invention provides
for continuously circulating refrigerant from the
lower header to the upper header to provide an
10
ing a pool of liquid refrigerant which over?ows
into the upwardly projecting ends of the tubes,
a pump in the lower header, and a conduit con
‘ample supply of liquid refrigerant to insure the
wetting of the internal surfaces of all of the evap 20 necting the pump and the upper header to re
circulate refrigerant from the lower header to
orator tubes.
the upper header.
While a preferred refrigeration system and
4. An evaporator for use in a refrigeration sys
evaporator construction are herein illustrated and
tem comprising a casing forming a central open
described it is to be understood that other re
frigeration systems may be used and that modi 25 ing with a header above the opening, a header
below the opening and a relatively large passage
?cations may be made in the construction and
way between the upper and lower headers at one
arrangement of the elements in the evaporator
side of the opening, said upper header having an
without departing from the spirit or scope of the
inlet for liquid refrigerant and an outlet for re
invention. Therefore without limiting myself in
this respect reference is to be had to the ap 30 frigerant vapor, the bottom wall of the upper
header forming a horizontal tube sheet, a plu
pended claims for a de?nition of the limits of the
rality of vertical tubes extending between the
invention.
upper and lower headers with the ends of the
What is claimed is:
tubes projecting above the tube sheet in the up
1. An evaporator for use in a refrigeration
per header, a dam in the upper header for re
system having an upper header provided with a
taining a pool of liquid refrigerant which over
horizontal tube sheet, a lower header, a plurality
?ows into the upwardly projecting ends of the
of vertical tubes extending between the upper and
tubes, said tubes having internal serrations to
lower headers and projecting above the horizon
impede the flow of refrigerant therethrough and
tal tube sheet of the upper header, means for
cause a wetting of the internal surface of the
supplying liquid refrigerant to the upper header ’
tubes, a pump in the lower header, and a conduit
which overflows into the end portions of the
connecting the outlet from the pump to the up
tubes projecting above the tube sheet, said tubes
per header for recirculating refrigerant from the
having internal‘serrations to retard the ?ow of
lower header to the upper header.
refrigerant through the tubes to maintain a ?lm
5. A unitary evaporator comprising a casing
of liquid refrigerant on the interior surfaces 45
forming a central opening with a header above
thereof, and means for recirculating liquid re
the opening, a header below the opening and a
frigerant from the lower to the upper header.
relatively large passageway between the upper
2. In an absorption refrigeration system, a gen
and lower headers at one side of the opening,
erator, a condenser, an evaporator, an absorber,
conduit means interconnecting the elements to 60 said upper header having an inlet for liquid re
frigerant and an outlet for refrigerant vapor, the
provide circuits for a refrigerant and absorbent,
bottom wall of the upper header forming a hori
said system operating in a partial vacuum and
zontal tube sheet, a plurality of vertical tubes
utilizing water as a refrigerant and a salt solu
extending between the upper and lower headers,
tion as an absorbent, said evaporator comprising
a dam in the upper header for retaining a pool
01
Cl
a casing forming a central opening with a header
of liquid refrigerant which over?ows into the ends
above the opening, a header below the opening
of the tubes, the end of the lower header opposite
and a relatively large passageway between the
the passageway being extended horizontally and
upper and lower headers at one side of the open
vertically at the side of the opening to provide
ing, a plurality of vertical tubes extending be
a pump chamber, a pump in the pump chamber,
tween the upper and lower headers, means for iii) an hermetically sealed motor mounted on the cas
supplying liquid refrigerant to the upper header
to cause it to flow by gravity through the plu
rality of tubes, said interconnecting means in
cluding a conduit connecting the upper header to
the absorber, and a conduit having one end ex
tending a predetermined height above the bottom
of the lower header and connected to another
ing and connected to drive the pump, and a con
duit connected to the outlet from the pump and
extended into the upper header, said pump and
conduit recirculating refrigerant from the lower
to the upper header.
'
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JOHN G. REID, JR.
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