U.S. patent number 3,744,272 [Application Number 05/210,661] was granted by the patent office on 1973-07-10 for refrigeration system with heat exchanger employing eutectic.
This patent grant is currently assigned to The United States of America as represented by the Secretary of the Army. Invention is credited to Oscar Oldberg.
United States Patent |
3,744,272 |
Oldberg |
July 10, 1973 |
REFRIGERATION SYSTEM WITH HEAT EXCHANGER EMPLOYING EUTECTIC
Abstract
This invention is a unique environmental control unit of the
vapor-compreon system type which incorporates a dual operation heat
exchanger of the circulated air variety. The heat exchanger
embodies spaced plate containers of eutectic material with
evaporator coils effectively embedded therein such that air
circulation and the normal evaporation process is not unduly
impeded during regular operation and holdover cooling is provided
when electric power for the compressor fails. In accordance with
the invention, a separately powered air circulation means is
provided.
Inventors: |
Oldberg; Oscar (Springfield,
VA) |
Assignee: |
The United States of America as
represented by the Secretary of the Army (Washington,
DC)
|
Family
ID: |
22783765 |
Appl.
No.: |
05/210,661 |
Filed: |
December 22, 1971 |
Current U.S.
Class: |
62/439; 252/67;
62/262; 62/515; 165/104.11; 423/599; 62/498; 165/10 |
Current CPC
Class: |
F24F
1/027 (20130101); F25B 39/02 (20130101); F25D
11/006 (20130101); F24F 5/0017 (20130101); F28D
20/02 (20130101); Y02E 60/14 (20130101); Y02E
60/145 (20130101); F25B 2400/24 (20130101); Y02E
60/147 (20130101) |
Current International
Class: |
F24F
13/00 (20060101); F24F 1/02 (20060101); F25D
11/00 (20060101); F25B 39/02 (20060101); F24F
13/30 (20060101); F25d 011/04 () |
Field of
Search: |
;62/439,515K,DIG.7,498
;260/414,429,439 ;252/67,68,69,71 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Perlin; Meyer
Claims
I claim:
1. An extended cooling period, vapor-compression cooling system
incorporating a condenser for dissipating heat energy to an outside
area; a compressor operative on a refrigerant fluid; an evaporator
for absorbing heat energy from an interior area to be cooled,
including a forced air circulation means; and a refrigerant fluid
adapted to be circulated within said system wherein:
said evaporator consists of refrigerant fluid containing tubing
adapted and disposed with respect air circulation produced by said
forced air circulation means to absorb heat energy from said
interior area to be cooled, said tubing has a plurality of sections
with each section having at least two tubing portions, with each
tubing portion disposed in spaced relation with respect other
portions;
wherein at least one sealed container is intrinsically disposed in
direct contact with each of said tubing portions along its length
and disposed, with respect air circulation produced by said forced
air circulation means, to absorb heat energy from said interior
area to be cooled;
wherein each of said sealed containers contains an eutectic
material having a fusion temperature characteristic greater than
the normal operating temperature of said refrigerant fluid when
circulating in said evaporator and less than the ambient
temperature to be maintained in said interior area and a heat of
fusion characteristic above 40 BTU, said eutectic material is a
composition material selected from the group of composition
materials consisting of:
sodium chloride - sodium sulphate decahydrate, having a chemical
symbol NaCl.sup.. Na.sub.2 SO.sub.4.sup.. 10H.sub.2 O;
sodium chloride - ammonium chloride - sodium sulphate hydrate,
having a chemical symbol NaCl.sup.. NH.sub.4 Cl.sup.. 2Na.sub.2
SO.sub.4.sup.. 20H.sub.2 O;
sodium manganate decahydrate, having a chemical symbol Na.sub.2
MnO.sub.4.sup.. 10H.sub.2 O;
sodium chromate decahydrate, having a chemical symbol Na.sub.2
CRO.sub.4.sup.. 10H.sub.2 O; and
nickel oleate, having a chemical symbol Ni(C.sub.18 H.sub.33
O.sub.2).sub.2.
2. A vapor-compression cooling system as defined in claim 1 wherein
said eutectic material is sodium chloride - sodium sulphate
decahydrate, having a chemical symbol NaCl.sup.. Na.sub.2
SO.sub.4.sup.. 10H.sub.2 O.
3. A vapor-compression cooling system as defined in claim 1 wherein
said eutectic material is sodium chloride - ammonium chloride -
sodium sulphate hydrate, having a chemical symbol NaCl.sup..
NH.sub.4 Cl.sup.. 2Na.sub.2 SO.sub.4.sup.. 20H.sub.2 O.
4. A vapor-compression cooling system as defined in claim 1 wherein
said portions of said tubing are folded such that each folded
portion is in planar form and said planar portions are disposed in
spaced parallel relation, and each of said sealed containers has a
relatively narrow, substantially parallel wall configuration and is
intrinsically disposed substantially within its respective planar
portion, each of said substantially parallel walls being of heat
conductive material and wherein said eutectic material is sodium
chloride - sodium sulphate decahydrate, having a chemical symbol
NaCl.sup.. Na.sub.2 SO.sub.4.sup.. 10H.sub.2 O, and each of said
planar tubing portions is substantially encased by its respective
sealed container with said substantially parallel walls thereof in
heat conductive relation with said folded tubing along its
length.
5. A vapor-compression cooling system as defined in claim 1 wherein
said sealed container substantially encompasses said tubing along
its length and said tubing includes outwardly extending radiation
fin members disposed in heat conductive relation with respect said
sealed container and extending therefrom and wherein said eutectic
material is sodium chloride - ammonium chloride - sodium sulphate
hydrate, having a chemical symbol NaCl.sup.. NH.sub.4 Cl.sup..
2Na.sub.2 SO.sub.4.sup.. 20H.sub.2 O.
Description
GOVERNMENT USE
The invention described herein may be manufactured and used by or
for the Government of the United States of America for governmental
purposes without the payment to me of any royalties therefor.
BACKGROUND OF THE INVENTION
Environmental control units of the vapor-compression cooling system
variety normally are utilized to control the temperature in a room
size, closed area. In a closed room application, when an electric
power interruption occurs and the temperature reduction process
ceases, obviously, the temperature rapidly increases if the heat
source continues to generate heat. When temperature sensitive
equipment is contained within the closed area, even a short term
interruption in electric power to the environmental control unit
can be disasterous. However, recognizing the relatively high
current demand of the compressor unit in such systems, it is
desirable, in military applications especially, to minimize power
consumption by programmed shutdown of the compressor unit for short
periods of time.
Various thermal holdover systems have been devised to maintain a
controlled temperature in a closed room size area when such
programmed interruptions occur. In general, temperature is
maintained by an alternate cooling system which may be activated
automatically when power ceases. For example, battery powered
equipment which provides outside air ventilation of the room may be
turned on. In other instances, the air conditioning unit may
incorporate several different types of heat exchangers whereby upon
deactivation of one heat exchanger by loss of power, for example, a
second heat exchanger in the system, essentially a heat sink which
does not require electric power, affords a "holdover" for a period
of time. It will be appreciated that a heat sink or an alternate
cooling system may be precluded by size or weight considerations
alone in many military applications requiring environmental control
units.
In a generally related technical area, small volume portable cold
storage applications, cooling often is provided by use of frozen
wall surfaces and in one known example, the U.S. Patent to G. G.
Lorch, U.S. Pat. No. 3,006,167, a narrow wall container containing
a liquid eutectic material has been utilized as the wall surface.
In such small volume portable applications, no vapor-compression
cooling system maintains the temperature of the chamber; the frozen
wall surfaces are the sole cooling means, essentially a substitute
for dry ice; and no air circulation system is involved.
It is readily apparent that a means for extending the cooling
period provided by a vapor-compression cooling system which
utilizes available components of the cooling system is needed and
would be welcomed as a substantial advancement of the art.
SUMMARY OF THE INVENTION
The environmental control unit of this invention performs its
cooling function in a relatively conventional manner when operating
in its normal mode. An evaporator coil, which is subjected to a
forced flow of air, serves to cool the air passing therethrough as
the refrigerant circulates in the cooling system. As the invention
primarily is directed to military application, provision is made
for continued operation upon loss of the heavy power drain
compressor unit. Sufficient power to maintain forced air flow is
required.
In the unique system of the invention, standard components are
utilized for the compressor, condenser and expansion valve. The
evaporator coil, however, is a more complex structure which cools
the air passing through the evaporator in a conventional manner
when refrigerant is circulating and continues to cool the air
passing therethrough for a limited time period after the
refrigerant stops circulation. The useful cooling period is
extended by selective disposition of a liquid container in direct
contact with the evaporator coil along its entire length, by use of
a eutectic material, having a desirable heat of fusion as the
contained liquid and by continued operation of the evaporator
forced air circulation means. In normal operation of the
environmental control unit, the eutectic material is in a frozen
solid state. In the event of compressor power shutdown, the air
which continues to pass through the evaporator is cooled by the
walls of the container housing the frozen eutectic material. A
significant cooling advantage is obtained as the eutectic material
changes from its solid to its liquid state.
It will be appreciated that the principal objective of the
environmental control unit of this invention is to provide a
relatively short term holdover cooling for use during planned or
unscheduled electric power to the compressor interruptions.
Other objects of the invention will become apparent upon a more
comprehensive understanding of the invention for which reference is
had to the following description of preferred embodiments and the
drawings wherein:
FIG. 1 is illustrative of a typical vapor-compression cooling
system which affords holdover cooling in accordance with the
present invention.
FIG. 2 is a graphical presentation of a typical temperature cycle
for eutectic material utilized in the environmental control unit of
this invention.
FIG. 3 is a more detailed cutaway showing of one embodiment of an
evaporator suitable for use in the system of this invention
depicted in FIG. 1.
FIG. 4 is a cross-section showing of a portion of an evaporator
section of the type utilized in the embodiment of FIG. 3.
FIG. 5 is a cutaway showing of a section of another type of
evaporator tubing also suitable for use in this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE PRESENT
INVENTION
The vapor-compression cooling system of FIG. 1 comprises a
condenser 11, a compressor 12, an expansion valve 13, an evaporator
14, an inside air circulator 15 of the squirrel cage variety and a
direct drive outside air circulator 16. In accordance with the
invention, the inside air circulator 15 is adapted, by battery
means, not shown, for example, for separate powered operation when
the principal power for the system is shut down. The system is
installed through a wall 17 such that the evaporator 14 is exposed
to the interior air of the chamber to be cooled and the condenser
11 is exposed to the outside air. The evaporator 14 consists of a
plurality of planar coil sections connected via different ports of
the expansion valve 13. While a three outlet port expansion valve
with three lines leading to the evaporator sections is shown, it
will be appreciated that the expansion valve may have a greater
number of outlet ports, if desired. In FIG. 1, the coils and
sections thereof are vertically disposed in planar and parallel
relation. In place of the finned section normally attached to the
cooling coil-evaporator 14, however, the planar region defined by
each coil is completely filled by a parallel wall, sealed
compartment which contains an eutectic material. The eutectic
material may be, for example, sodium chloride - sodium sulphate
decahydrate, NaCl.sup.. Na.sub.2 SO.sub.4.sup.. 10H.sub.2 O, which
has a liquid state similar to heavy oil and a solid state similar
to pliable plastic. The heat of fusion of NaCl.sup.. Na.sub.2
SO.sub.4.sup.. 10H.sub.2 O, that is, the quantity of heat required
per unit mass, without any change in temperature, to solidify this
crystaline substance is 70 BTU. The above-mentioned eutectic
material, which has a fusion temperature of 55.degree.F, has been
found to have an acceptable expansion characteristic which, when
appropriately contained, will not cause rupture of its container
upon expansion incident to solidification.
Selection of the proper eutectic material is determined primarily
by the fusion temperature and the heat of fusion benefit derived at
change of state, of course. However, selection also may involve a
consideration of compatibility with the container material and
tubing material. Frequently, aluminum is utilized as the tubing
material and container material and corrosion is minimized by
anodizing. Sealing the unit, in itself, reduces the corrosive
effect, of course. Other eutectic materials which have been found
suitable for use in the evaporator structure described herein are
sodium chloride - ammonium chloride - sodium sulphate hydrate -
NaCl.sup.. NH.sub.4 Cl.sup.. 2Na.sub.2 SO.sub.4.sup.. 20H.sub.2 O;
sodium manganate decahydrate Na.sub.2 MnO.sub.4.sup.. 10H.sub.2 O;
sodium chromate decahydrate Na.sub.2 CrO.sub.4.sup.. 10H.sub.2 O;
nickel oleate Ni(C.sub.18 H.sub.33 O.sub.2).sub.2 which have fusion
temperatures of 58.degree.F, 63.degree.F, 66.degree.F and
64.degree.-68.degree.F, respectively. Sodium chloride - ammonium
chloride - sodium sulphate hydrate NaCl.sup.. NH.sub.4 Cl.sup..
2Na.sub.2 SO.sub.4.sup.. 20H.sub.2 O has been found to be
especially useful in that it has a 78 BTU heat of fusion
characteristic.
FIG. 2 illustrates the temperature response of the first identified
eutectic material when the refrigerant flow stops in the
environmental control unit of this invention. During normal
operation of the unit, the ambient temperature in the immediate
vicinity of the evaporator is maintained at a selected temperature,
for example, 75.degree.F and the temperature of the refrigerant
R-12 Freon, for example, is 40.degree.F. In accordance with the
invention, the fusion temperature of the eutectic material is
intermediate these temperatures and might be, for example,
55.degree.F.
At time A, when refrigerant flow stops, the ambient temperature in
the immediate vicinity of the evaporator 14 and the temperature of
the eutectic material contained as an internal part thereof,
gradually rises, as shown, until the fusion temperature of the
eutectic material, for example 55.degree.F is reached. The rate of
increase in temperature is, of course, a function of the heat
source load, the nature of air flow in the vicinity of the
evaporator and other factors peculiar to the environmental control
application.
As the temperature of the eutectic material increases, heat energy
is removed from the room as the air continues to circulate through
the evaporator and at time B, when the eutectic material begins to
melt, the amount of heat energy which is removed is substantially
increased as the change in state occurs. Thus, the cooling effect
of the evaporator 14 increases during the melting period. Assuming
the heat source is introducing heat energy at a determined BTU
rate, the temperature of the room increases in proportion to the
difference in heat energy introduced by the heat source and removed
by the evaporator 14. Obviously, the capability of the evaporator
14 to remove heat energy determines the time period of acceptable
temperature control of the room area. Thus, the vapor-compression
system of this invention with its single unit, dual action, heat
exchanger-evaporator provides a significant extension of the
cooling time period after compressor power shutdown. In actual
operation of the system of this invention in an instrument and
equipment room temperature control application, it has been found
that system easily will afford a thirty minute extension beyond the
normally expected holdover period, that is, beyond the time B on
the FIG. 2 curve to time C. After time C, the cooling effectiveness
of the evaporator 14 would diminish, of course, unless the
refrigerant circulation is resumed as shown in FIG. 2.
As shown in more detail in FIG. 3, the evaporator 14 normally is
made up of a plurality of sections, indicated at 21. Each section
is connected via a respective port of the expansion valve 13 to
enable a predetermined, sequential refrigerant flow therethrough.
While an expansion valve with three ports is shown in FIG. 1 and a
five section evaporator is shown in FIG. 3, it will be appreciated
that the number of ports and sections must conform. The number of
expansion valve ports and the corresponding number of evaporator
sections, of course, is determined by the optimum pressure drop in
the evaporator, normally 2-3 lbs/square inch.
In FIG. 3, each of the sections 21 comprises three portions of the
evaporator in which each portion consists of tubing folded upon
itself in a planar form as indicated at 22. The sections 21 and
respective portions 22 thereof are disposed in spaced parallel
relation such that air to be cooled may be moved through the planar
section defined spacing by the air circulator 15. While the
sections are shown in horizontal disposition for purposes of
illustration in FIG. 3, it will be recognized that the vertical
disposition shown in FIG. 1 is preferred for condensate drainage
purposes.
In the FIG. 3 embodiment of this invention, the folded tubing is
embedded in a eutectic material, indicated at 23, and both the
tubing 22 and the eutectic material are sandwiched between thin
sheets of aluminum or other material of high heat conductivity,
indicated at 24. As more clearly shown in FIG. 4, the sheets 24 are
disposed in direct contact heat conductive relation with the
outward facing sides of the tubing 22 in its planar form. Also, in
accordance with the change of state concept of the invention, the
edges of the sheet material 24 are folded and crimped, as indicated
at 25, or otherwise interconnected to form a sealed container for
the eutectic material which confines the eutectic material in its
fluid state.
It is not essential to the invention that the eutectic material be
confined in the precise manner shown in FIGS. 3 and 4, of course.
For example, the sheet material 24 may be embossed to conform to
the folded tubing to provide a greater exposure of the outward
facing side surface of the folded tubing to the circulating air, if
desired. Conversely, the sheet material walls may be embossed to
provide a eutectic material container which is wider than the
tubing 22 and thus contains a greater amount of eutectic material
23, if desired. In the latter instance, of course, it is especially
important that sufficient air circulation be provided to insure a
full functioning of the evaporative process during normal operation
of the vapor-compression cooling system.
Indeed, it is not essential that the eutectic material container be
formed of parallel sheet material, embossed or otherwise. In an
alternative construction, a container having a configuration which
fills the voids between folds of the tubing in each section may be
formed of any heat conductive material and placed in direct heat
conductive relation with the interfacing walls of the folded tubing
22 along its length.
It will be appreciated that for efficient heat transfer, the
eutectic material should substantially fill its container but that
allowance must be made for a limited expansion of the eutectic
material upon solidification. It has been found that the narrow
parallel wall configuration shown in FIG. 3 is particularly
desirable in that the parallel walls may bulge to a limited degree
upon expansion of the eutectic material with no adverse effect upon
the container over an extended period of operation provided, of
course, the eutectic material is selected from those having an
expansion characteristic within reasonable limits. The degree of
bulge permitted is determined by the air circulation in the
particular application.
In actual test of the system of this invention, utilizing 1/4 inch
o.d. tubing and a eutectic material consisting of sodium sulphate
(69%) - sodium chloride (31%) hydrate in a 9,000 BTU military air
conditioning application, it has been found that operation is
improved by closer spacing between folds in the folded tubing
planar sections and by closer disposition of the planar sections
with respect one another.
FIG. 5 depicts another evaporator tubing configuration suitable for
use in the vapor-compression system of this invention. Spiral
finned tubing, as shown in FIG. 5, may be adapted for use in planar
folded tubing sections of the variety in FIG. 3, if desired. More
commonly in evaporator design, however, spiral finned tubing is
disposed in a spiral coil configuration with air circulation
through the core of the coil.
In the configuration of FIG. 5, the conventional spiral finned
tubing consisting of tubing 31 and continuous spiral fin 32 has
been modified by the addition of a tubular wall member, indicated
at 33, which encompasses the tubing 31 and is terminated at its
ends by conventional means, not shown, to form a container about
the tubing 31 along its length. As in the configuration of FIG. 3,
a eutectic material, indicated at 34, is contained within the
container formed by the wall section 33 and the outer surface of
the tubing 31.
It will be noted that the continuous spiral fin member 32 is
directly attached in heat conductive relation to the tubular wall
member 33 for manufacturing simplification purposes. Ideally, the
spiral fin member 32 is connected directly to the tubing 31 and may
be so connected periodically along its length by means, not shown,
if desired. In the finned tubing configuration, the heat
conductivity characteristic of the eutectic material as well as its
fusion temperature, heat of fusion, and expansion characteristics
must be considered in selection of the appropriate eutectic
material.
Of those eutectic materials presently known, sodium chloride -
ammonium chloride - sodium sulphate hydrate NaCl.sup.. NH.sub.4
Cl.sup.. 2Na.sub.2 SO.sub.4.sup.. 20H.sub.2 O is preferred for use
in the spiral finned tubing configuration. It should be recognized,
however, that the spiral finned tubing configuration inherently
introduces a preliminary cooling time delay in normal operation of
the vapor-compression cooling system in that the eutectic material
must be cooled to the requisite temperature of the refrigerant in
the evaporator before normal cooling operation can begin.
Consequently, the configuration shown in FIGS. 3 and 4 is preferred
in the cooling system of this invention.
Although this disclosure of invention is directed to the more
conventional vapor-compression cooling system and the invention is
considered as a patentable improvement thereover, it will be
recognized that the invention is not restricted to the particular
illustrated cooling system. For example, the invention is not
restricted to cooling systems for maintaining a temperature within
any specific temperature range and eutectic materials, having an
appropriate fusion temperature and a desirable heat of fusion
characteristic, other than those specifically disclosed herein, may
be substituted. Likewise, the evaporator forced air circulation
means may be powered by the principal power means which energizes
the compressor during normal operation, if desired, provided, of
course, an auxiliary power means, which may be switched on in event
of principal power means outage, is available.
* * * * *