Abstrict A single-stage desiccant regeneration system for use in an air
conditioning system, the regeneration system comprising a falling
film heat exchanger for transferring heat from concentrated desiccant
to dilute desiccant, a boiler for regenerating dilute desiccant,
piping for flowing dilute desiccant from the air conditioning system
upward through the heat exchanger, and a flow path for directing
concentrated desiccant from the boiler through the heat exchanger
and to the air conditioning system.
Claims Having thus described our invention, what we claim as new and desire
to secure by Letters Patent of the United States is:
1. A single-stage desiccant regeneration system for use in an air
conditioning system, said regeneration system comprising:
a falling film heat exchanger for transferring heat from concentrated
desiccant solution to dilute desiccant solution, said heat exchanger
comprising a housing, a vertical cylindrical tube disposed in said
housing, a generally helically wound tube mounted on and around
said vertical cylindrical tube, a distributor for distributing concentrated
desiccant evenly onto an outer surface of said vertical cylindrical
tube, a spacer separating said vertical cylindrical tube and said
helically wound tube from side walls of said housing, said spacer
comprising a plurality of fins connected together and arranged in
radial fashion, each of said fins having therein a notch in which
is received an upper edge portion of said vertical cylindrical tube,
said fins extending radially outwardly from said vertical cylindrical
tube a distance further than the extent of any portion of said helically
wound tube from said vertical cylindrical tube, outer edges of said
fins being adjacent said side walls of said housing, said housing
having a bottom portion for trapping concentrated desiccant,
a boiler for regenerating dilute desiccant and vaporizing moisture
absorbed in said dilute desiccant,
means for flowing dilute desiccant from said air conditioning system
upward through said heat exchanger wound tube to said boiler, and
means for directing concentrated desiccant from said boiler through
said heat exchanger to said air conditioning system.
2. The single stage desiccant regenerator system according to claim
1 wherein said vertical cylindrical tube, said helically wound
tube and said housing are configured such that concentrated desiccant
flowing down said outer surface of said vertical cylindrical tube
contacts said helically wound tube and exchanges heat with diluted
desiccant flowing therein, and are further configured such that
a portion of concentrated desiccant flows along an outer surface
of said helically wound tube in a downward helical path, and a remaining
portion of said concentrated desiccant spills over said helically
wound tube and onto a lower portion of said helically wound tube
and said bottom portion of said housing, and a concentrated desiccant
outlet in said housing proximate said bottom portion and adapted
to convey concentrated desiccant from said housing.
3. The single stage desiccant regeneration system according to
claim 2 wherein said vertical cylindrical tube, said helically
wound tube, said housing, said distributor and said spacer are composed
of non-corrosive material.
4. The single stage desiccant regenerator system according to claim
3 wherein said vertical cylindrical tube and said helically wound
tube are composed of material with a high thermal conductivity thereby
facilitating said heat exchange from concentrated desiccant to dilute
desiccant.
5. A falling film heat exchanger for use in a desiccant regeneration
system, said heat exchanger comprising:
a vertical cylindrical tube adapted to direct the flow of concentrated
desiccant by gravity down its outer surface,
a generally helically wound tube fixed on and about said vertical
cylindrical tube for transporting diluted desiccant in an upward
direction in a generally helical path,
a housing in which said vertical cylindrical tube and said helically
wound tube are disposed, said housing having a bottom portion for
trapping concentrated desiccant, said housing further having a diluted
desiccant inlet and a concentrated desiccant outlet at said bottom
portion, and a diluted desiccant outlet and a concentrated desiccant
inlet at a top portion thereof,
said vertical cylindrical tube, said helically wound tube and said
housing being configured such that concentrated desiccant flowing
down said outer surface of said vertical cylindrical tube contacts
said helically wound tube and exchanges heat with diluted desiccant
flowing therein, and such that a portion of concentrated desiccant
flows along an outer surface of said helically wound tube in a downward
helical path while a remaining portion of concentrated desiccant
spills over said helically wound tube and onto a lower portion of
said helically wound tue and into said bottom portion of said housing,
a distributor for evenly distributing concentrated desiccant on
said outer surface of said vertical tube, and
means for separating side walls of said housing from said vertical
and helically wound tubes, comprising a spacer member, said spacer
member comprising a plurality of fins connected together and arranged
in radial fashion, each of said fins having therein a notch in which
is received an upper edge portion of said vertical tube, said fins
extending radially outwardly from said vertical tube a distance
further than the extent of any portion of said helical tube from
said vertical tube, outer edges of said fins being adjacent said
side walls of said housing, whereby to space said vertical tube
and said helical tube from said housing side walls.
6. The falling film heat exchanger according to claim 5 wherein
said distributor comprises a cylindrical shell with a bottom and
with holes arranged in a plane parallel to said bottom in a periodic
fashion around the circumference of said cylindrical shell, said
distributor being adapted to be disposed on top of said vertical
tube such that concentrated desiccant enters said housing through
said concentrated desiccant inlet in said housing and is received
by said distributor and fills said distributor until the level of
concentrated desiccant reaches said planar periodically arranged
holes, whereupon concentrated desiccant flows through said holes
and onto said vertical cylindrical tube in said even manner.
7. The falling film heat exchanger according to claim 6 wherein
said vertical cylindrical tube, said helically wound tube, said
housing, said distributor and said spacer are composed of non-corrosive
material.
8. The falling film heat exchanger according to claim 6 wherein
said vertical cylindrical tube and said helically wound tube are
composed of material with a high thermal conductivity, thereby facilitating
said heat exchange from said concentrated desiccant to said dilute
desiccant.
Description BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to liquid desiccant regeneration systems
for use in air-conditioning systems, and is directed more specifically
to a single stage desiccant regeneration system including a falling
film heat exchanger.
2. Description of the Prior Art
Devices that use hygroscopic liquids, such as lithium chloride
(LiCl), to dehumidify air are well known in the art. One of the
principal limitations of such systems is the need to regenerate
the desiccant once it has become diluted through absorption of water.
Regeneration usually requires heating the desiccant to drive off
the excess moisture, or exposing the desiccant to a hot gas which
absorbs the excess moisture. Regenerators in which air serves as
the hot gas are often employed, but are expensive to run, especially
when waste heat for heating the air is not readily available. Boiler-type
regenerators are also used, but are expensive inasmuch as a heating
means must be provided and non-corrosive metals must be employed.
An improved boiler-type regenerator is disclosed in U.S. Pat. No.
4939906 to Spatz, et al, which uses natural circulation of the
desiccant being heated. The boiler in the '906 patent is provided
with finned tubes through which desiccant being heated passes in
an upward direction. The finned tubes are inside a housing containing
gas combustion products which serve as a heat source for the boiler.
Natural circulation is achieved by providing downcomer tubes which
are outside the housing and at a lower temperature. The '906 patent
also discloses a means for preheating the diluted desiccant before
it enters the boiler for final regeneration. The means employed
comprises a two-stage heat-exchanger for transferring heat from
concentrated desiccant exiting the boiler to dilute desiccant exiting
the air conditioner. The heat transfer takes place in a heat exchanger
formed by stacking corrugated plates to form alternating flow channels--one
for diluted desiccant and one for concentrated desiccant. The plates
are sealed from each other by gasketing. Although the system provides
for higher efficiency and lower costs, it is not without drawbacks.
The need for gasketing to seal the plates from each other causes
pressure to build up unevenly in the flow channels, which can lead
to formation of "hot spots" and, thus, lower heat transfer
efficiency.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a single stage
desiccant regeneration system which overcomes the above-mentioned
problems and is more efficient and less complex than the prior art
desiccant regeneration systems.
A further object of the invention is to provide as a part of the
single stage desiccant regeneration system a novel falling film
heat exchanger.
With the above and other objects in view, as will hereinafter appear,
a feature of the present invention is the provision of a single-stage
desiccant regeneration system for use in an air conditioning system,
the regeneration system comprising a falling film heat exchanger
for transferring heat from concentrated desiccant solution to dilute
desiccant solution from an air conditioner, the falling film heat
exchanger comprising a housing, a vertical cylindrical tube disposed
in the housing, a generally helically wound tube mounted on and
around the vertical cylindrical tube, a distributor for distributing
concentrated desiccant evenly onto an outer surface of the vertical
cylindrical tube, a spacer separating the vertical cylindrical tube
and the helically wound tube from the housing, the housing having
a bottom portion for trapping concentrated desiccant, a direct fired
natural circulation desiccant boiler for regenerating dilute desiccant
and vaporizing moisture absorbed in the dilute desiccant, means
for flowing dilute desiccant from the air conditioning system upward
through the heat exchanger wound tube to the boiler, and means for
directing concentrated desiccant from the boiler through the heat
exchanger to the air conditioning system.
In accordance with a further feature of the invention, there is
provided a falling film heat exchanger for use in a desiccant regeneration
system, the heat exchanger comprising a vertical, cylindrical tube
adapted to direct the flow of concentrated desiccant by gravity
down its outer surface, a generally helically wound tube fixed on
and about the vertical cylindrical tube for transporting diluted
desiccant in an upward direction in a generally helical path, a
housing in which the vertical cylindrical tube and the helically
wound tube are disposed, the housing having a bottom portion for
trapping concentrated desiccant, the housing further having a diluted
desiccant inlet and a concentrated desiccant outlet at the bottom
portion, and a diluted desiccant outlet and a concentrated desiccant
inlet at a top portion thereof, the configuration of the vertical
cylindrical tube, the helically wound tube and the housing being
such that concentrated desiccant flowing down the outer surface
of the vertical cylindrical tube contacts the helically wound tube
and exchanges heat with diluted desiccant flowing therein, and being
such that a portion of concentrated desiccant flows along an outer
surface of the helically wound tube in a downward helical path while
a remaining portion of the concentrated desiccant spills over the
helically wound tube and onto a lower portion of the helically wound
tube and into the bottom portion of the housing, and a concentrated
desiccant outlet disposed in the housing and proximate the bottom
portion, a distributor for evenly distributing concentrated desiccant
on the outer surface of the vertical tube, and means for separating
the housing from the vertical and helically wound tubes.
The above and other features of the invention, including various
novel details of construction and combinations of parts, will now
be more particularly described with reference to the accompanying
drawings and pointed out in the claims. It will be understood that
the particular devices embodying the invention are shown by way
of illustration only and not as limitations of the invention. The
principles and features of this invention may be employed in various
and numerous embodiments without departing from the scope of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
Reference is made to the accompanying drawings in which are shown
illustrative embodiments of the invention, from which its novel
features and advantages will be apparent.
In the drawings:
FIG. 1 is a diagrammatic view of one form of desiccant regeneration
system, illustrative of an embodiment of the invention; and
FIG. 2 is a side elevational view, partly in section, of one form
of falling film heat exchanger, illustrative of an embodiment of
the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1 it will be seen that the regeneration process
includes flowing of desiccant d from an air conditioner 2 through
a falling film heat exchanger 4. In the heat exchanger 4 heat from
concentrated desiccant D exiting a boiler 6 is transferred to the
dilute desiccant d exiting the air conditioner 2. The regeneration
process continues by piping heated dilute desiccant d' to the gas
fired natural circulation desiccant boiler 6 where the desiccant
is heated and excess moisture M is driven off. Newly-concentrated
desiccant D is then piped back through the falling film heat exchanger
4 to exchange heat with the dilute desiccant d from the air conditioner
2. The concentrated and cooled desiccant D' then continues on to
the air conditioner 2 where it is utilized for dehumidifying purposes.
Referring to FIG. 2 it will be seen that the falling film heat
exchanger 4 of the present invention uses falling film technology
to improve the heat exchange effectiveness over previous systems.
In the falling film heat exchanger 4 the hot concentrated desiccant
D flows by gravity downward along the exterior of a central, vertical
tube 8. Wrapped around the central tube 8 in a generally helical
fashion is another tube 10 which carries the dilute desiccant d,
d'. The dilute desiccant d, d' is pumped upward through the helical
tubing 10. As the concentrated desiccant D falls, it contacts the
helical tubing 10 and transfers heat through the walls of the tubing
10 to the dilute desiccant contained therein. The concentrated desiccant
D then continues falling by gravity, in part spilling over the helical
tubing 10 to a lower portion of the tubing, and in part flowing
down and around on an outside surface 12 of the helical tubing.
This extended contact with the helical tubing improves the efficiency
of the falling film heat exchanger as compared to other heat exchangers.
The effectiveness is further enhanced by the absence of pressure
differentials resulting in "hot spots" and uneven heat
transfer. No pressure problems exist as the concentrated desiccant
simply falls in an open chamber 14 that does not have to be sealed.
The effectiveness is also enhanced by the concentrated desiccant
being evenly distributed over the outside surface 13 of the central
tube 8 by a distributor (described herein below) designed for that
purpose. A heat exchange effectiveness of 89% has been realized.
A typical liquid desiccant, such as LiCl, may be employed by the
air conditioner 2 for removing excess moisture from air being conditioned.
As the desiccant dehumidifies the air being conditioned, the moisture-absorbing
capability of the desiccant is lessened, and it must be regenerated.
The dilute desiccant d is collected in a sump 16 in the air conditioner
2 (FIG. 1). From the sump 16 the dilute desiccant d is flowed,
as by a pump 18 to a dilute desiccant inlet 20 (FIG. 2) in a housing
22 of the falling film heat exchanger 4. In the falling film heat
exchanger, the temperature of the dilute desiccant d is raised.
The warmer dilute desiccant d' is then piped out of a dilute desiccant
outlet 24 of the housing 22 to the gas fired natural circulation
desiccant boiler 6 (FIG. 1). In the desiccant boiler 6 the desiccant
d' is regenerated by being heated, and the excess moisture M being
driven off. In addition to being concentrated, the desiccant D is
now at an elevated temperature. To make effective use of this heat,
the concentrated desiccant D is piped into a concentrated desiccant
inlet 26 of the housing 22 (FIG. 2). From there, the concentrated
desiccant D continues through the falling film heat exchanger 4
and imparts heat to the dilute desiccant d, d' therein. The cooler
concentrated desiccant D' then leaves the falling film heat exchanger
through a concentrated desiccant outlet 28 in the housing 22 and
flows back to the sump 16 in the air conditioner 2 (FIG. 1).
As noted above, the hot, concentrated desiccant D enters the falling
film heat exchanger 4 (FIG. 2) through the concentrated desiccant
inlet 26 in the housing 22. All of the motion of the concentrated
desiccant D is caused by gravity, thus obviating any need to pump
the concentrated desiccant, and further obviating any possible accompanying
pressure differentials.
The concentrated desiccant D is first directed to a distributor
30. The distributor 30 is adapted to evenly distribute the concentrated
desiccant D. The distributor 30 momentarily contains the flow of
the concentrated desiccant D. The concentrated desiccant falling
into the distributor 30 fills the distributor until the desiccant
level in the distributor reaches the level of holes 32 spaced about
the periphery of the distributor. The concentrated desiccant D flows
through the holes 32 and onto the central tube 8 in an even manner.
As the concentrated desiccant falls down the central tube, the desiccant
makes contact with the helical tubing 10. The helical tubing 10
contains the dilute desiccant d, d' being pumped from the sump 16
of the air conditioner 2 to the gas fired natural circulation desiccant
boiler 6. Contact between the falling concentrated desiccant D and
the helically wound tubing 10 causes the concentrated desiccant
to transfer heat to the wall of the helically wound tubing and thus
to the dilute desiccant contained d, d' therein. From the point
of contact, the concentrated desiccant follows one, or both, of
two paths. The falling desiccant maintains contact with the helically
wound tubing 10 and thereby follows a first downward helical path,
while portions of the concentrated desiccant may spill over the
helically wound tubing and fall to lower portions of the helically
wound tubing. As the concentrated desiccant continues downward by
either the first, or both paths, it continues to exchange heat with
the dilute desiccant in the helical tubing whenever it is in contact
with the helical tubing. When the concentrated desiccant reaches
a bottom portion 33 of the housing 22 it is trapped and begins
to fill the housing until reaching the level of the concentrated
desiccant outlet 28 in the housing, whereupon the concentrated and
cooled desiccant D' flows out of the housing and to the sump 16
of the air conditioner 2.
A spacer member 34 may be provided at the upper end of the heat
exchanger 4 to insure location of the central tube 8 centrally of
the housing 22 and to insure that the periphery of the helical tubing
10 is spaced from the housing 22. The spacer member 34 may comprise
a plurality of fins 36 connected together and arranged in radial
fashion. Each of the fins 36 is provided with a notch 38 adapted
to receive an upper edge portion 40 of the central tube 8. The fins
36 extend radially outwardly from the central tube 8 a distance
further than the extent of any portion of the helical tube 10 from
the central tube, including the dilute desiccant inlet 20 and the
dilute desiccant outlet 24. In assembly, after placement of the
vertical central tub 8 and helical tube 10 in the housing 22 the
spacer member 34 is placed over the upper edge portion 40 of the
central tube 8 with the notches 38 receiving the upper edge portion
40. A housing top plate 42 when fixed to the housing 22 locks
the spacer in place. The spacer, in turn, locks the central tube
8 in place. The central location of the central tube 8 insures that
the helical tube 10 is appropriately centered and therefore distanced
from housing side walls 44.
The high heat exchange effectiveness of the falling film heat exchanger
4 derives largely from the fact that the concentrated desiccant
D, D' maintains contact with the helical tube 10 for a majority
of the time the desiccant is in the heat exchanger. Also, the low
pressure drop from top to bottom of the falling film heat exchanger
insures that no "hot spots" develop to impede heat transfer
effectiveness. Heat transfer effectiveness is also increased by
selecting a material with a high thermal conductivity for the vertical
central tube 8 and the helically wound tube 10. In one embodiment,
a non-corrosive metal alloy such as copper-nickel is used. In an
alternative embodiment, polysulfone is used. Since liquid desiccant
is a corrosive liquid, all of the elements of the falling film heat
exchanger are composed of non-corrosive materials.
The present invention thus provides an efficient and economic means
to regenerate liquid desiccant used in an air conditioning system
for dehumidification. The single stage regenerator reconditions
the desiccant by utilizing a falling film heat exchanger and a gas
fired natural circulation desiccant boiler. The falling film heat
exchanger makes effective use of the heat imparted to concentrated
desiccant in the boiler by transferring it to dilute desiccant that
is pumped through the falling film heat exchanger. The preheated
desiccant is then piped to the boiler where it is heated, and the
excess vapor is driven off, concentrating the desiccant. The concentrated
desiccant is then passed through the falling film heat exchanger
where it imparts heat to dilute desiccant before returning to the
air conditioner where it is used for dehumidifying air.
While the foregoing invention has been described with reference
to its preferred embodiments, various alterations and modifications
will occur to those skilled in the art. For example, a variety of
materials can be utilized to fabricate the elements of the falling
film heat exchanger. Also, various liquid desiccants can be used
with the present invention. These and other such alterations are
intended to fall within the scope of the following claims. |