Abstrict A liquid desiccant dehumidifier includes a liquid desiccant absorber
arranged to receive concentrated liquid desiccant and absorb moisture
contained in ambient air passed through the absorber thereby diluting
the liquid desiccant. A first heat exchanger is operative to heat
dilute liquid desiccant received from the desiccant absorber prior
to passage to a boiler that evaporates moisture from the diluted
liquid desiccant to create steam and reconstitute the desiccant
into a concentrated liquid desiccant. Dilute liquid desiccant from
the first heat exchanger first passes to a condenser that receives
steam from the boiler and sensibly heats the dilute liquid desiccant
to a higher second temperature without direct exposure to steam
or air. A second heat exchanger communicates with the condenser,
the boiler and the first heat exchanger and is operative to further
heat diluted liquid desiccant received from the condenser to a higher
third temperature prior to entry into the boiler by recovering waste
heat from the boiler. A pump draws concentrated liquid desiccant
from the boiler through the heat exchangers and passes it to the
absorber.
Claims What is claimed is:
1. A liquid desiccant dehumidifier, comprising:
a liquid desiccant absorber for absorbing moisture contained in
ambient air entering the dehumidifier and passing through said desiccant
absorber, said desiccant absorber constructed and arranged for receiving
concentrated liquid desiccant and dispensing dilute liquid desiccant,
said desiccant absorber including a plurality of absorber pads disposed
in upstanding side-by-side relation, said desiccant absorber further
including a distributor pan disposed above said pads for distributing
liquid desiccant to said pads, said absorber pads being secured
together at least adjacent upper ends thereof so as to substantially
prevent liquid desiccant from said distributor pan passing downwardly
between said pads and thereby cause said desiccant to wick downwardly
through said pads, and a drain pan disposed below said pads for
collecting dilute liquid desiccant from said pads;
a boiler for boiling dilute liquid desiccant to evaporate moisture
to reconstitute the liquid desiccant into concentrated liquid desiccant;
and
a condenser fluidly communicating with said boiler to receive steam
generated by boiling liquid desiccant in said boiler, said condenser
further fluidly communicating with said absorber to receive dilute
liquid desiccant from said absorber, said condenser being operable
to sensibly heat the dilute liquid desiccant therein by recovering
the latent heat of condensation as steam delivered from said boiler
is condensed so as to preheat said dilute liquid desiccant prior
to delivery to said boiler.
2. A liquid desiccant dehumidifier as defined in claim 1 wherein
said absorber pads are bonded together in spaced sealed relation
at said upper ends thereof so as to prevent liquid desiccant from
passing downwardly between said pads.
3. A liquid desiccant dehumidifier as defined in claim 1 wherein
said upper ends of said absorber pads are received in slots formed
in said distributor pan in sealed relation with said pan so that
liquid desiccant flows only into said pads from said pan.
4. A liquid desiccant dehumidifier, comprising:
a liquid desiccant absorber for absorbing moisture contained in
ambient air entering the dehumidifier and passing through said desiccant
absorber, said desiccant absorber constructed and arranged for receiving
concentrated liquid desiccant and dispensing dilute liquid desiccant,
a boiler for boiling partially preheated dilute liquid desiccant
to evaporate moisture to reconstitute the liquid desiccant into
concentrated liquid desiccant, said boiler including an inner vessel
and an outer vessel, a heating element disposed in said inner vessel,
and a pipe communicating heated liquid desiccant from said inner
vessel and disposed within said outer vessel, whereby liquid desiccant
is returned to said outer vessel from said condenser and is heated
in said outer vessel by hot liquid desiccant passing through said
pipe prior to entering said inner vessel; and
a condenser fluidly communicating with said boiler to receive steam
generated by boiling liquid desiccant in said boiler, said condenser
further fluidly communicating with said absorber to receive dilute
liquid desiccant from said absorber, said condenser being operable
to sensibly heat the dilute liquid desiccant therein by recovering
the latent heat of condensation as steam delivered from said boiler
is condensed, to preheat said dilute liquid desiccant prior to delivery
to said boiler.
5. A liquid desiccant dehumidifier, comprising:
a liquid desiccant absorber for absorbing moisture contained in
ambient air entering the dehumidifier and passing through said desiccant
absorber, said desiccant absorber constructed and arranged for receiving
concentrated liquid desiccant and dispensing dilute liquid desiccant,
a boiler for boiling partially preheated dilute liquid desiccant
to evaporate moisture to reconstitute the liquid desiccant into
concentrated liquid desiccant, said boiler including and inner vessel
and an outer vessel, a heating element disposed in said inner vessel,
and an interchange heat exchanger disposed in said outer vessel,
said interchange heat exchanger including an inner tube and an outer
tube defining an annulus therebetween, said interchange heat exchanger
including an inlet disposed to admit desiccant rising to the top
of a desiccant puddle in said outer vessel to enable heat transfer
with hot desiccant leaving said inner vessel, whereby liquid desiccant
returned to said outer vessel from said condenser is preheated in
said outer vessel and said interchange heat
exchanger prior to entering said inner vessel; and
a condenser fluidly communicating with said boiler to receive steam
generated by boiling liquid desiccant in said boiler, said condenser
further fluidly communicating with said absorber to receive dilute
liquid desiccant from said absorber, said condenser being operable
to sensibly heat the dilute liquid desiccant therein by recovering
the latent heat of condensation as steam delivered from said boiler
is condensed, to preheat said dilute liquid desiccant prior to delivery
to said boiler.
6. A liquid desiccant dehumidifier, comprising:
a liquid desiccant absorber for absorbing moisture contained in
ambient air entering the dehumidifier and passing through said desiccant
absorber, said desiccant absorber constructed and arranged for receiving
concentrated liquid desiccant and dispensing dilute liquid desiccant;
a boiler for boiling partially preheated dilute liquid desiccant
to evaporate moisture to reconstitute the liquid desiccant into
concentrated liquid desiccant; and
a condenser fluidly communicating with said boiler to receive steam
generated by boiling liquid desiccant in said boiler without direct
exposure to air said condenser further fluidly communicating with
said absorber to receive dilute liquid desiccant from said absorber,
said condenser being operable to sensibly heat the dilute liquid
desiccant therein by recovering the latent heat of condensation
as steam delivered from said boiler is condensed to preheat said
dilute liquid desiccant prior to delivery to said boiler, said condenser
including an air vent.
7. The liquid desiccant dehumidifier recited in claim 6 wherein
said air vent comprises a hydrophobic membrane enabling the free
passage of air but preventing liquid desiccant leakage.
8. The liquid desiccant dehumidifier recited in claim 7 wherein
said hydrophobic membrane tape is laminated between a polypropylene
mesh.
9. The liquid desiccant dehumidifier recited in claim 6 wherein
said air vent comprises a float-type air vent.
10. A liquid desiccant dehumidifier, comprising:
a liquid desiccant absorber for absorbing moisture contained in
ambient air entering the dehumidifier and passing through said desiccant
absorber, sand desiccant absorber constructed and arranged for receiving
concentrated liquid desiccant and dispensing dilute liquid desiccant;
a boiler for boiling dilute liquid desiccant to evaporate moisture
to reconstitute the liquid desiccant into concentrated liquid desiccant;
and
a condenser fluidly communicating with said boiler to receive steam
generated by boiling liquid desiccant in said boiler, said condenser
further fluidly communicating with said absorber to receive dilute
liquid desiccant from said absorber, said condenser being operable
to sensibly heat the dilute liquid desiccant therein by recovering
the latent heat of condensation as steam delivered from said boiler
is condensed and without directly exposing said dilute liquid desiccant
to air so as to preheat said dilute liquid desiccant prior to delivery
to said boiler, said condenser communicating with said desiccant
absorber to recirculate a fraction of the liquid desiccant leaving
said condenser to said desiccant absorber.
11. A liquid desiccant dehumidifier, comprising:
a liquid desiccant absorber for absorbing moisture contained in
ambient air entering the dehumidifier and passing through said desiccant
absorber, said desiccant absorber constructed and arranged for receiving
concentrated liquid desiccant and dispensing dilute liquid desiccant,
said desiccant absorber including a plurality of absorber pads bonded
together and disposed side-by-side, said desiccant absorber further
comprising a top distributor pan for distributing liquid desiccant
to a top side of said pads, and a drain pan for collecting dilute
liquid desiccant from a bottom side of said pan;
a boiler for boiling partially preheated dilute liquid desiccant
to evaporate moisture to reconstitute the liquid desiccant into
concentrated liquid desiccant, said boiler including an inner vessel
and an outer vessel, a heating element disposed in said inner vessel,
and a pipe communicating heated liquid desiccant from said inner
vessel and disposed within said outer vessel, whereby liquid desiccant
is returned to said outer vessel from said condenser and is heated
in said outer vessel by hot liquid desiccant passing through said
pipe prior to entering said inner vessel; and
a condenser fluidly communicating with said boiler to receive steam
generated by boiling liquid desiccant in said boiler, said condenser
further fluidly communicating with said absorber to receive dilute
liquid desiccant from said absorber, said condenser being operable
to sensibly heat the dilute liquid desiccant therein by recovering
the latent heat of condensation as steam delivered from said boiler
is condensed, to preheat said dilute liquid desiccant prior to delivery
to said boiler, said condenser communicating with said desiccant
absorber to recirculate a fraction of the liquid desiccant leaving
said condenser to said desiccant absorber, said condenser further
including an air vent.
12. A liquid desiccant dehumidifier, comprising:
a liquid desiccant absorber for absorbing moisture contained in
ambient air entering the dehumidifier and passing through said desiccant
absorber, said desiccant absorber constructed and arranged for receiving
concentrated liquid desiccant and dispensing dilute liquid desiccant,
said desiccant absorber including a plurality of absorber pads bonded
together and disposed side-by-side, said desiccant absorber further
comprising a top distributor pan for distributing liquid desiccant
to a top side of said pads, and a drain pan for collecting dilute
liquid desiccant from a bottom side of said pan;
a boiler for boiling partially preheated dilute liquid desiccant
to evaporate moisture to reconstitute the liquid desiccant into
concentrated liquid desiccant; and
a condenser fluidly communicating with said boiler to receive steam
generated by boiling liquid desiccant in said boiler, said condenser
further fluidly communicating with said absorber to receive dilute
liquid desiccant from said absorber, said condenser being operable
to sensibly heat the dilute liquid desiccant therein by recovering
the latent heat of condensation as steam delivered from said boiler
is condensed, to preheat said dilute liquid desiccant prior to delivery
to said boiler, wherein said condenser comprises at least one tube
assembly including an inner tube defining a first flow passageway
and an outer tube, said inner tube being disposed within said outer
tube to define an annular second flow passageway therebetween, wherein
liquid desiccant is communicated through a first of said flow passageways
and steam is communicated through a second of said flow passageways.
13. The liquid desiccant dehumidifier defined in claim 12 wherein
said inner tube comprises a convoluted or corrugated tube.
14. The liquid desiccant dehumidifier recited in claim 13 wherein
said tube assembly is coiled.
Description BACKGROUND
1. Field of the Invention
The present invention relates generally to room air dehumidification,
and more particularly, to a liquid desiccant dehumidifier which
is portable, energy efficient, and corrosion resistant.
2. Description of the Prior Art
It is known in the art to dehumidify ambient air using liquid desiccant
systems. These devices typically utilize hygroscopic liquids such
as lithium bromide (LiBr), lithium chloride (LiCl) or calcium chloride
(CaCl.sub.2) as the desiccant solution. Desiccant units offer advantages
over commercial dehumidifiers based on vapor compression technology,
specifically in terms of lower energy usage.
In a desiccant system, the desiccant solution absorbs moisture
from ambient air exposed to the solution. As the desiccant solution
continues to absorb moisture, it becomes dilute and must be regenerated.
In the regeneration process, the desiccant solution is heated to
evaporate the excess moisture or the desiccant solution is brought
into contact with a hot gas to desorb the excess moisture. In some
expedients, air regenerators are used to regenerate the desiccant.
These arrangements have relatively high operating costs as energy
is required to provide a source of heat and to generate a suitable
flow of air. In others, boiler-type regenerators are employed. However,
boiler embodiments are expensive, as the corrosive nature of liquid
desiccant solutions necessitates the use of costly corrosion resistant
metals.
A liquid desiccant dehumidfication system in which a liquid desiccant
is regenerated with a boiler is described in U.S. Pat. No. 4939906
("the '906 Patent"). The '906 Patent discloses a gas-fired
desiccant boiler and a combined desiccant regenerator/interchange
heat exchanger, in which the combined regenerator/heat exchanger
utilizes steam produced from the boiler to provide heat for partial
regeneration. The desiccant boiler has a liquid/vapor separator
chamber and thermosyphon recirculation to reduce scale and corrosion
of the boiler. Specifically, the overall system is shown in FIG.
1 wherein outdoor air is drawn into the system through an inlet
duct 22 and is evaporatively cooled by a water spray 24. The cooled
air is directed to a desiccant conditioner 26 to which return air
is also directed through a duct 30. In the desiccant conditioner
26 the return air is contacted with a liquid desiccant solution
from a sprayer 28. The desiccant liquid is disclosed as lithium
calcium chloride.
This dehumidified air is then supplied to the space to be dehumidified,
or it can be sensibly cooled through an evaporative cooler 32. The
desiccant dehumidifies the air stream, and in the process its moisture-absorbing
capability is reduced; this capability is regenerated by passing
a portion of the dilute desiccant from the conditioner 26 to a first
interchange heat exchanger 44 wherein the temperature of the desiccant
is raised. The weakened desiccant is partially concentrated in an
air-desiccant regenerator 46 in which heated air from a regeneration
air heater 48 contacts the liquid desiccant. This desiccant is pumped
through a second interchange heat exchanger 52 and thereafter to
a desiccant boiler 56 in which regeneration of the desiccant is
completed. The water vapor generated in the desiccant boiler 56
raises the temperature of the air passing through the regeneration
air preheater 48. The interchange heat exchangers 44 52 reduce
the temperature of the regenerated desiccant as it returns along
the pipe 60 to the conditioner 26.
The boiler 56 is depicted in FIG. 2 and operates on natural circulation,
with the density of the fluid (part liquid, part vapor) in the "fired"
tubes 70 being less than the density of the liquid in the outer
"unfired" tube 74. A porous ceramic burner 80 facilitates
combustion to provide a heat source and hot combustion gases are
blown through a combustion chamber formed by a housing 88 enclosing
the fired tubes 70 and flow across fins 90 of the fired tubes 70.
Weak desiccant is pumped into the fired tubes 70 through a manifold
94 which causes water in the desiccant to be vaporized. Accordingly,
a density differential is created between the fluid in the fired
tubes 70 and the unfired tubes 74 connected between the manifold
94 and a liquid/vapor separator 98 outside the combustion chamber
housing 88. This density differential induces a natural flow of
desiccant solution up the fired tubes 70 and down the unfired tubes
72. In this manner, the natural circulation of desiccant keeps the
inside walls of the fired tubes 70 coated with desiccant to thereby
reduce or prevent "hot spots" from forming on the inside
of the fired tubes 70 to reduce corrosion and scale build up in
the fired tubes 70.
The liquid vapor separator 98 at the top of the boiler 56 separates
water vapor from the concentrated liquid desiccant. A portion of
the concentrated desiccant is withdrawn from the bottom of the liquid/vapor
separator 98 and is returned to the desiccant conditioner 26. Water
vapor flowing out of the top of the liquid/vapor separator 98 is
subsequently condensed to heat air for use in an earlier regeneration
step shown in FIGS. 3 and 4.
The combined regenerator/interchange heat exchanger, depicted in
FIGS. 3 and 4 comprises two (2) interchange heat exchangers 44
52 the desiccant regenerator 46 and the regeneration air heater
48. The combined desiccant regenerator/interchange heat exchanger
is identified by the reference numeral 102 and is constructed by
alternately stacking two (2) different corrugated plates (see FIG.
4) to define alternating flow channels. Water vapor or steam from
the desiccant boiler 56 is introduced near the top of the regenerator/exchanger
102 in alternate channels (plate A). This water vapor is condensed,
thereby transferring heat to the air and weak desiccant entering
adjacent channels near the top of the regenerator/heat exchanger
102 (plate B). The upper portion of each plate corresponds to the
desiccant regenerator 46 and regeneration air heater 48. As the
water vapor condenses, the weak desiccant and air mixture is heated
and the desiccant is partially regenerated. Warm air and moisture
are exhausted by fan 106 to the outdoors. An entrainer 108 is provided
to prevent desiccant from escaping the combined regenerator/exchanger
102. The partially regenerated desiccant flows into the middle of
a channel plate B, and is further heated by the hot concentrated
desiccant removed from the liquid/vapor separator 98. Hot concentrated
desiccant from the boiler 56 is introduced at the middle of plate
A while the partially regenerated desiccant is removed from the
middle of plate B. The partially regenerated desiccant is then pumped
to the desiccant boiler 56. Diluted desiccant from the regenerator/heat
exchanger 102 is introduced at the bottom of the plate A and is
heated by the hot desiccant from the boiler 56. The heated dilute
desiccant from the regenerator/heat exchanger 102 is then removed
from the center of plate B and pumped to the top of plate B.
The apparatus shown and described in the '906 Patent suffers from
several disadvantages. The regeneration process described therein
requires the flow of hot air through the system in order to operate.
This necessitates the use of additional components such as fans,
air preheaters, and liquid/vapor separators, which adds system complexity.
Furthermore, the multiple stacked plate interchange heat exchanger
configuration is complex and takes up a relatively large amount
of space. This arrangement is not suitable for use in a small portable
unit.
SUMMARY OF THE INVENTION
In view of the disadvantages in the prior art, it is an object
of the present invention to provide a portable liquid desiccant
dehumidifier which efficiently regenerates the liquid desiccant
using a simple arrangement having a minimum number of components.
It is another object of the present invention to provide a portable
liquid desiccant dehumidifier which is energy efficient.
It is still another object of the present invention to provide
a portable liquid desiccant dehumidifier which utilizes primarily
plastic components to prevent corrosion.
It is yet another object of the present invention to provide a
portable liquid desiccant dehumidifier in which steam to desiccant
heat recovery takes place in a condenser.
It is still another object of the present invention to provide
a portable liquid desiccant dehumidifier in which air vents are
provided on the condenser.
It is a further object of the present invention to provide a portable
liquid desiccant dehumidifier in which plastic components are used
for the interchange heat exchangers.
It is yet another object of the present invention to provide a
portable liquid desiccant dehumidifier in which the waste heat radiating
from the boiler is utilized in an interchange heat exchanger for
desiccant regeneration.
It is another object of the present invention to provide a portable
liquid desiccant dehumidifier having a boiler including inner and
outer vessels to preheat incoming liquid desiccant entering the
outer vessel with hot liquid desiccant from the inner vessel.
It is still another object of the present invention to provide
a portable liquid desiccant dehumidifier having a boiler which is
primarily elongated in a horizontal orientation to minimize the
temperature gradient and consequent concentration differential in
the liquid desiccant.
It is yet another object of the present invention to provide a
portable liquid desiccant dehumidifier which is lightweight, energy
efficient, and inexpensive to manufacture.
It is a further object of the present invention to provide an improved
heat exchanger employing at least one polytetrafluoroethyline tube
concentrically disposed within a silicone rubber tube.
In accordance with the foregoing objects and additional objects
that will become apparent hereinafter, the present invention provides
a liquid desiccant dehumidifier, including a liquid desiccant absorber
for absorbing moisture contained in ambient air entering the dehumidifier
and passing through the desiccant absorber, the desiccant absorber
constructed and arranged for receiving concentrated liquid desiccant
and dispensing dilute liquid desiccant. A boiler is provided for
boiling partially preheated dilute liquid desiccant to evaporate
moisture to reconstitute the liquid desiccant into concentrated
liquid desiccant. A condenser fluidly communicates with the boiler
to receive steam generated by boiling liquid desiccant in the boiler,
and with the absorber to receive dilute liquid desiccant from the
absorber. The condenser and without directly exposing the dilute
liquid desiccant to air is operable to sensibly heat the dilute
liquid desiccant therein by recovering the latent heat of condensation
as steam delivered from the boiler is condensed, to preheat the
dilute liquid desiccant prior to delivery to the boiler to increase
operating efficiency.
In a preferred embodiment, the invention provides a liquid desiccant
dehumidifier including a liquid desiccant absorber for absorbing
moisture contained in ambient air entering the dehumidifier and
passing through the desiccant absorber, the desiccant absorber constructed
and arranged for receiving concentrated liquid desiccant and dispensing
dilute liquid desiccant. A boiler is provided for boiling partially
preheated dilute liquid desiccant to evaporate moisture to reconstitute
the liquid desiccant into concentrated liquid desiccant. A first
heat exchanger fluidly communicates with the desiccant absorber
and a second heat exchanger. The first heat exchanger is operable
to transfer heat from the concentrated liquid desiccant to the dilute
liquid desiccant directed to the first heat exchanger from the desiccant
absorber to raise the temperature of the dilute liquid desiccant
to a first temperature. A condenser fluidly communicates with the
boiler to receive steam generated by boiling the liquid desiccant
in the boiler, and with the first heat exchanger to receive partially
heated dilute liquid desiccant from the first heat exchanger at
the first temperature. The condenser without directly exposing the
dilute liquid desiccant to air is operable to sensibly heat the
dilute liquid desiccant therein to a second temperature by recovering
the latent heat of condensation as steam delivered from the boiler
is condensed. The second heat exchanger fluidly communicates with
the condenser, the boiler and the first heat exchanger. The second
heat exchanger is operable to transfer heat from concentrated liquid
desiccant directed to the second heat exchanger from the boiler
to the dilute liquid desiccant directed to the second heat exchanger
from the condenser at the second temperature to raise the temperature
of the dilute liquid desiccant to a third temperature. The dilute
liquid desiccant at the third temperature is directed to the boiler
and the concentrated liquid desiccant from the second heat exchanger
is directed to the first heat exchanger. The second heat exchanger
is disposed with respect to the boiler to recover waste heat from
the boiler. A pump is provided for pumping concentrated liquid desiccant
into the absorber.
In a preferred embodiment, the desiccant absorber includes a top
and a bottom and comprises: a plurality of horizontally and vertically
disposed interconnected microglass fiber plates; a distributor disposed
above the fiber plates at the top of the desiccant absorber for
introducing the concentrated desiccant into the desiccant absorber;
and a drain pan for collecting the dilute desiccant disposed at
the bottom of the desiccant absorber.
In another embodiment, the desiccant absorber includes a plurality
of absorber pads disposed side-by-side, the desiccant absorber further
comprising a top distributor pan for distributing liquid desiccant
to a top side of the pads, and a drain pan for collecting dilute
liquid desiccant from a bottom side of the pan. The pads are bonded
together at the ends inside the pans. A sealant may be used to fill
any gaps between the pads and the pans.
The first heat exchanger comprises at least one tube assembly including
an inner tube concentrically disposed within an outer tube to define
an annulus therebetween. The dilute liquid desiccant from the desiccant
absorber is passed through the inner tube, and the concentrated
liquid desiccant is passed through the annulus, or vice-a-versa.
The second heat exchanger comprises at least one tube assembly
including an inner tube concentrically disposed within an outer
tube to define an annulus therebetween. The tube assembly is coiled
around the boiler to recover waste heat passing through the walls
of the boiler. The concentrated liquid desiccant from the boiler
is passed through the annulus and the partially heated dilute liquid
desiccant from the condenser is passed through the inner tube, or
vice-a-versa.
In a preferred embodiment, the inner tubes of the heat exchangers
are fabricated from Polytetrafluoroethyline and the outer tubes
are fabricated from silicone rubber. The inner tubes may be convoluted
or corrugated to increase the available heat transfer area.
In a preferred embodiment, the condenser comprises an inner shell
disposed within an outer housing defining at least one chamber between
the inner
shell and the housing. Steam is directed to the inner shell from
the boiler through a steam inlet. The housing includes a solution
inlet to direct partially heated dilute liquid desiccant from the
first heat exchanger into the at least one chamber. A solution outlet
communicates with the chamber and directs partially heated dilute
desiccant at the second temperature to the second heat exchanger.
The inner shell is fabricated from materials including inconel,
monel, titanium, Polytetrafluoroethyline, Polytetrafluoroethyline-coated
copper, Polytetrafluoroethyline Teflon-coated aluminum, and Polytetrafluoroethyline
Teflon-coated stainless steel; and the outer shell is fabricated
from materials including Polytetrafluoroethyline, polycarbonate,
polyvinylidene fluoride, polypropylene, silicone rubber, polyethylene,
and polystyrene.
In an alternative embodiment, the condenser comprises at least
one steam inlet communicating steam from the boiler with the at
least one chamber and at least one solution inlet communicating
partially heated dilute liquid desiccant from the first heat exchanger
with the inner shell.
The condenser may incorporate a plurality of fins associated with
the inner shell and a plurality of fins associated with the housing.
The inner shell may be provided with a plurality of baffles to prevent
short circuiting from the steam inlet to the condensate outlet.
In another embodiment, the condenser comprises a housing and a
plurality of convoluted tubes. The tubes are supported by opposing
support plates, and communicate with a steam inlet to receive steam
from the boiler. The housing includes a solution inlet to receive
partially heated dilute liquid desiccant from the first heat exchanger,
and a solution outlet through which partially heated dilute liquid
desiccant is delivered to the second heat exchanger. The tubes are
fabricated from Teflon, and the support plates include at least
one silicone rubber sheet attached thereto.
In yet another embodiment, the condenser comprises at least one
tube assembly including an inner tube defining a first flow passageway
and an outer tube, the inner tube being disposed within the outer
tube to define an annular second flow passageway therebetween, wherein
liquid desiccant is communicated through a first of the flow passageways
and steam is communicated through a second of the flow passageways.
In an alternative embodiment, the tube assembly is coiled.
In all condenser embodiments, air vents may be provided to vent
air from the system. In a preferred embodiment, the air vent may
consist of Teflon tape laminated between a polypropylene mesh. Alternatively,
conventional float-type air vents may be used.
In a preferred embodiment, the boiler includes an inner vessel
and an outer vessel, a heating element disposed in the inner vessel,
and a pipe communicating heated liquid desiccant from the inner
vessel and disposed within the outer vessel, whereby liquid desiccant
is returned to the outer vessel from the condenser and is heated
in the outer vessel by hot liquid desiccant passing through the
pipe prior to entering the inner vessel.
In an alternative embodiment, the boiler includes an inner vessel
and an outer vessel, a heating element disposed in the inner vessel,
and an interchange heat exchanger disposed in the outer vessel.
The interchange heat exchanger includes an inner tube and an outer
tube defining an annulus therebetween, and an inlet disposed to
admit desiccant rising to the top of a desiccant puddle in the outer
vessel to enable heat transfer with hot desiccant leaving the inner
vessel. In this manner, liquid desiccant returned to the outer vessel
from the condenser is preheated in the outer vessel and the interchange
heat exchanger prior to entering the inner vessel.
In a preferred embodiment, the respective components are disposed
with respect to one another to take advantage of gravity feed to
communicate the liquid desiccant from the absorber to the boiler
via the first and second heat exchangers and the condenser, thereby
eliminating the need for multiple pumps in the system.
BRIEF DESCRIPTION OF THE DRAWINGS
In accordance with the above, the present invention will now be
described in detail with particular reference to the accompanying
drawings.
FIG. 1 is an exploded isometric view of the portable liquid desiccant
dehumidifier in accordance with the present invention;
FIG. 1A is a block diagram depicting the general operation of the
invention;
FIG. 2 is an exploded isometric view of a desiccant absorber assembly;
FIG. 2A is a detail view of the microglass fiber plates in the
absorber;
FIG. 2B is a side elevational view of a desiccant absorber in another
embodiment;
FIG. 2C is a detail view of the absorber pads;
FIG. 2D is an isometric view of the desiccant absorber of FIG.
2B;
FIG. 3 is an isometric view of a boiler;
FIG. 4 is a an isometric view of a coiled interchange heat exchanger
and the boiler;
FIG. 4A is an isometric view of a boiler in an alternative embodiment;
FIG. 4B is an isometric view of a boiler in another embodiment;
FIG. 5 is an isometric view of a split interchange heat exchanger;
FIG. 5A is a plan view of an inner tube for an interchange heat
exchanger having a convoluted profile;
FIG. 5B is a plan view of an inner tube for an interchange heat
exchanger having a corrugated profile;
FIG. 6 is an isometric cut-away view of a condenser in a first
embodiment;
FIG. 7 is an isometric cut-away view of an inner shell of the condenser
shown in FIG. 6;
FIG. 8 is an isometric cut-away view of a condenser in a second
embodiment;
FIG. 9 is an isometric cut-away view of a condenser in a third
embodiment;
FIG. 9A is an isometric view of a condenser in a fourth embodiment;
FIG. 9B is an isometric view of a condenser is a fifth embodiment;
FIG. 10 is an isometric cut-away view of a frame for housing the
respective components of the system; and
FIG. 11 is an isometric cut-away view depicting the frame and some
of the components installed therein.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the several views of the drawings, there is shown
a portable liquid desiccant dehumidifier ("PLDD"), generally
characterized by the reference numeral 10.
Referring now to FIGS. 1 and 1A, the PLDD 10 includes a liquid
desiccant absorber 12 for absorbing moisture contained in ambient
air entering dehumidifier 10 and passing through desiccant absorber
12. The desiccant absorber 12 is constructed and arranged for receiving
concentrated liquid desiccant at the top of desiccant absorber 12
and dispensing dilute liquid desiccant from the bottom of desiccant
absorber 12. The desiccant solution may be any one of several conventional
solutions, including aqueous LiBr, LiCl or CaCl.sub.2 as described
above, or any mixture of these solutions. Referring now to FIGS.
2 and 2A, desiccant absorber 12 includes a distributor 14 disposed
at the top of desiccant absorber 12 which receives concentrated
liquid desiccant and delivers the liquid desiccant through a plurality
of "spaghetti" tubes 16 extending radially outward from
a central hub 18. The desiccant absorber 12 includes a plurality
of horizontally and vertically disposed interconnected microglass
fiber plates. The vertical plates are identified by the reference
numeral 20 and are supported by horizontal interconnecting fiber
plates 22 as shown. The top plate 22 is referred to as a distribution
sheet. The concentrated desiccant wicks into the distribution sheet
22 and down the vertical plates 20. The vertical plates 20 contain
beads 21 which separate and support contiguous vertical plates 20.
Ambient air is drawn into the unit and forced through the microglass
fiber plates by a fan 23 (see FIG. 1), where the moisture in the
air is removed as the air makes contact with the liquid desiccant.
As the desiccant dehumidifies the air stream, the moisture-absorbing
capability of the desiccant is reduced and the desiccant must be
regenerated. This dilute desiccant is collected in a drain pan 24
disposed at the bottom of desiccant absorber 12. The drain pan 24
includes an intermediate support plate 26 defining at least one
drain hole 28 which enables the dilute desiccant to flow into a
bottom chamber defined between support plate 26 and a bottom wall
30 of drain pan 24. A drain tube 32 including a one-way or check
valve 33 extends from the bottom chamber to direct the dilute desiccant
out of absorber 12. The absorber components are disposed within
a frame 35 as shown in FIG. 10 which can be fabricated from materials
including, but not limited to, polypropylene, polyethylene, polytetrafluoroethyline,
which is commercially available under the tradename TEFLON, polyvinylidene
fluoride, polycarbonate, PVC or polystyrene. The frame 35 includes
a plurality of shelves 37a, 37b, and 37c for supporting the respective
components of the unit described below.
The dilute liquid desiccant is regenerated into concentrated desiccant
by boiling the liquid desiccant in a boiler 34 at a temperature
in the range of from approximately 260.degree. F. to 320.degree.
F. An improvement over prior art systems resides in the use of steam
to desiccant heat recovery to directly preheat the dilute liquid
desiccant. The dilute liquid desiccant is thus passed through a
condenser and preheated using the latent heat of condensation of
the steam produced by boiling the liquid desiccant. Preferably,
a series of interchange heat exchangers are employed to further
preheat the dilute liquid desiccant entering the boiler 34 by recovering
heat from the concentrated liquid desiccant delivered to absorber
12 from boiler 34 to further increase operating efficiency. These
components are described in more detail below.
In an alternative embodiment shown in FIGS. 2B-2D, a plurality
of absorber pads 20a are stacked side-by-side. The pads 20a are
received in an aperture or slots in a top tray or distributor pan
25 and a bottom tray or drain pan 27. The pads 20a are bonded to
each other at the ends thereof with an adhesive "A" (or
taped) so that the gaps between the pads 20a and the supporting
structure are completely sealed to force the liquid desiccant to
wick through the pads 20a. Any other gaps between the pads 20a and
the pans 25 27 may be filled with an RTV silicone sealant or like
material. Liquid desiccant is communicated into the distributor
pan 25 through an inlet 29. This configuration prevents the liquid
desiccant from just flowing over the surface of the pads, and consequently
increases absorber efficiency. The trays 25 27 effectively prevent
spillage of liquid desiccant from the absorber 12 in the event of
tilting. In addition, the liquid desiccant supplied to the distributor
pan 25 forms a thin film on the pan surfaces to reach every distributor
pad 20a to improve desiccant distribution.
The boiler 34 is shown in FIG. 3 and is configured in the shape
of a tub or vessel having an elongated horizontal dimension. The
horizontal elongation provides a uniform temperature gradient, and
thus a uniform concentration level of the liquid desiccant solution,
as compared to a vertically elongated boiler. The boiler 34 includes
side walls 36 a bottom wall 38 a top wall 40 and a peripheral
support flange 42 for supporting the other dehumidifier components
above the boiler. The boiler 34 is constructed from materials including,
but not limited to, polycarbonate, polyvinylidene fluoride, Teflon,
fiber glass and the like. A heating element 44 is coiled proximal
to the bottom wall 40 as shown, and is connected to a pair of leads
46 in a conventional manner. A thermocouple 48 extends into boiler
34 to monitor the internal temperature. The leads 46 and thermocouple
48 extend through top wall 40. The heating element 44 and thermocouple
48 are operably associated with a controller (not shown) for maintaining
boiler 34 at the optimum temperature. A pair of steam outlets 50
extend through top wall 40 to deliver steam generated by boiling
the liquid desiccant to a condenser described in more detail below.
Referring now to FIG. 4 a drain tube 51 is coupled to one of the
side walls 36 to enable boiler 34 to be emptied as required. A U-fitting
52 is coupled to the upper region of one of the side walls 36 to
receive preheated dilute liquid desiccant from the condenser through
an inlet port 54 and to dispense concentrated liquid desiccant
through an outlet port 56. The U-fitting 52 communicates with a
coiled interchange heat exchanger 58 which comprises at least one
tube assembly including an inner tube 60 concentrically disposed
within an outer tube 62 to define an annulus 64 therebetween. The
tube assembly is coiled around boiler 34 to recover the waste heat
radiating through side walls 36. This arrangement is exemplary,
as the tube assembly could be embedded within the side walls 36
or disposed in contact with top wall 40. The concentrated liquid
desiccant from boiler 34 enters the annulus 64 through side wall
36 and is directed to outlet port 56. The partially heated dilute
liquid desiccant from the condenser is passed through the inner
tube 60 in a direction counter to the concentrated liquid desiccant
and enters boiler 34 through side wall 36. Alternatively, the concentrated
liquid desiccant is passed through inner tube 60 and the dilute
liquid desiccant is passed through annulus 64. In a preferred embodiment,
inner tube 60 is fabricated from TEFLON, and outer tube 62 is constructed
from silicone rubber. The TEFLON inner tube 60 has relatively high
heat conductivity, while the outer silicone rubber tube 62 has a
relatively low thermal conductivity, and is a good insulator. These
components can withstand relatively high temperatures (.about.400.degree.
F.), and are not corroded by the desiccant solution. To improve
efficiency, inner tube 60 may be convoluted as shown in FIG. 5A
or corrugated as shown in FIG. 5B. It is to be understood that the
use of this type of TEFLON/silicone rubber tube-in-tube heat exchanger
is not limited to a liquid desiccant system. There are many applications
in which this arrangement may be employed. The particular operation
of the coiled interchange heat exchanger 58 will be described in
more detail below.
Referring now to FIG. 4A, there is shown an isometric view of an
boiler 34a in an alternative embodiment, having a double-wall configuration
including an inner wall 400 and an outer wall 402 which define an
inner vessel 404 and an outer vessel 406. A heating element 408
extends into the inner vessel 404 and around the floor as shown.
The incoming liquid desiccant from condenser 86 enters the outer
vessel 406 of the boiler at inlet 410. Hot liquid desiccant from
the inner vessel 404 is communicated into pipe 412 which coils through
the outer vessel 406 to effect heat transfer with the incoming liquid
desiccant. The desiccant puddle contained in the outer vessel 406
is heated and the hottest portion of the liquid is forced to rise
to the top of the vessel 406. It is then fed into the inner vessel
404 via an inlet 414. A thermocouple 416 is disposed in the inner
vessel 404 as described above to control the boiler temperature.
This arrangement forces any heat radiated or conducted from the
inner vessel 404 to flow through the desiccant puddle in the outer
vessel 406 thereby reducing thermal losses, and pressure losses
attributable to long flow paths. The heating element 408 is disposed
below the pump suction or inner vessel boiler outlet 415a so that
heating element 408 is always immersed in a pool of liquid desiccant
within the inner vessel 404. In this manner, the pump 80 stops drawing
liquid desiccant from inner vessel 404 before it is reduced to a
level beneath the heating element 408. Hot liquid desiccant leaves
the boiler through outlet 415b. This arrangement eliminates the
need for a low-level control switch. High level control in the boiler
is necessary to provide consistent dehumidification and to prevent
excess liquid buildup. A high level control switch can be eliminated
by sizing the inner vessel 404 with an internal volume equal to
approximately twice the volume of pooled liquid desiccant accumulation.
This takes advantage of the inherent desiccant properties to make
the system flexible to adapt to varying weather conditions without
compromising performance.
Referring now to FIG. 4B, there is shown an isometric view of a
boiler 34b in an alternative embodiment, having a double-wall configuration
including an inner wall 400b and an outer wall 402b which define
an inner vessel 404b and an outer vessel 406b. A heating element
408b extends into the inner vessel 404b and around the floor as
shown. The incoming liquid desiccant from condenser 86 enters the
outer vessel 406b of the boiler at
inlet 410b. An interchange heat exchanger 412a is disposed within
the outer vessel 406b. The interchange heat exchanger comprises
an inner tube 407a and an outer tube 407b defining an annulus therebetween.
The tube arrangement may be similar to that described above with
the inner tube being either convoluted or corrugated to improve
heat transfer characteristics. An inlet 417 permits liquid desiccant
to enter the annulus between inner tube 407a and the outer tube
407b. This liquid desiccant has been preheated by heat transfer
between the inner vessel 404a and the outer vessel 406b. The hottest
portion of the heated liquid desiccant in the outer vessel is forced
to rise to the top of the puddle, and enters the interchange heat
exchanger 412a through inlet 417. Hot liquid desiccant from the
inner vessel 404b is communicated into the interchange heat exchanger
412a at outlet 415a to effect heat transfer with the incoming liquid
desiccant. The preheated liquid desiccant is then fed from the interchange
heat exchanger 412a into the inner vessel 404a via an inlet 414a.
A thermocouple 416 is disposed in the inner vessel 404a as described
above to control the boiler temperature.
Referring now to FIG. 5 there is depicted a split interchange
heat exchanger 66 which includes a pair of tube assemblies 68.
Each tube assembly 68 comprises an inner tube 70 concentrically
disposed within an outer tube 72 to define an annulus 74 therebetween.
The dilute liquid desiccant from desiccant absorber 12 is gravity
fed to the interchange heat exchanger 66 where it is directed through
a manifold 76 and into the inner tubes 70. Concentrated liquid desiccant
from boiler 34 is first delivered through coiled interchange heat
exchanger 58 and thereafter directed through a U-fitting 78 coupled
to the respective outer tubes 72 and into the annuli 74. Alternatively,
dilute liquid desiccant is passed through annuli 74 and concentrated
liquid desiccant is passed through inner tubes 70. In this manner,
heat is transferred from the concentrated liquid desiccant to the
dilute liquid desiccant within split interchange heat exchanger
66. The concentrated liquid desiccant is thereafter drawn into a
pump 80 (see FIGS. 1 and 1A) through a U-fitting 82 coupled to the
respective outer tubes 72. The pump 80 delivers the concentrated
liquid desiccant to distributor 14 of absorber 12. The partially
heated dilute liquid desiccant flows through a manifold 84 to the
condenser. During this stage, the dilute liquid desiccant dispensed
from absorber 12 is raised to a first temperature. As discussed
above with respect to coiled interchange heat exchanger 58 the
inner tubes 70 may be fabricated from TEFLON and the outer tubes
72 may be constructed from silicone rubber. Likewise, the inner
tubes may be provided with a convoluted or corrugated profile as
shown in FIGS. 5A and 5B, respectively.
The partially heated liquid desiccant at the first temperature
is delivered to a condenser 86 from split interchange heat exchanger
66 as shown in FIGS. 1 and 1A. Referring now to FIGS. 6 and 7 there
is depicted a first embodiment of condenser 86 which is comprised
of an inner shell 88 disposed within an outer housing 90 defining
at least one chamber 92 between inner shell 88 and housing 90. The
housing 90 includes a plurality of side walls 94 a top wall 96
and a bottom wall 98. A pair of steam tubes 100 communicate with
inner shell 88 through top wall 96 to deliver steam from boiler
34. A pair of air vents 102 likewise communicate with chamber 92
through top wall 96 to evacuate excess air therefrom. A condensate
tube 104 communicates with inner shell 88 through bottom wall 98
to drain condensate into a condensate pan 106 (see FIG. 1A). An
inlet tube 108 communicates with chamber 92 through one of the side
walls 94 to deliver partially heated dilute desiccant to condenser
86 from split interchange heat exchanger 66. An outlet tube 110
is similarly disposed to communicate with chamber 92 on an opposite
side of condenser 86 to deliver dilute desiccant which is sensibly
heated to a second temperature by the latent heat of condensation
as the steam condenses in the inner shell 88 to the coiled interchange
heat exchanger 58 via the inlet port 54 of U-fitting 52 shown in
FIGS. 1 and 4. A fraction of the desiccant flow leaving the condenser
may be recirculated to the desiccant absorber 12. This reduces the
flow rate to the boiler 34 to lower heat loss and increase energy
efficiency. In addition, this maintains a relatively high flow through
the absorber 12 and condenser 86 to yield a higher absorption and
condensation capacity. To facilitate heat transfer, inner shell
88 is fabricated from materials including inconel, monel, titanium,
TEFLON, TEFLON-coated copper, TEFLON-coated aluminum, and TEFLON-coated
stainless steel. The housing 90 is fabricated from materials including
TEFLON, polycarbonate, polyvinylidene fluoride, polypropylene, silicone
rubber, polyethylene, and polystyrene. If a plastic such as TEFLON
is used for the housing 90 the wall thickness is made suitably
thick to provide the necessary insulating properties.
The condenser 86 may incorporate a plurality of fins 112 located
on the exterior of inner shell 88 and a plurality of fins 114 disposed
on bottom wall 98 of housing 90. The inner shell 88 may be provided
with a plurality of baffles 116 to prevent short circuiting from
steam inlets 100 to condensate outlet 104.
Although depicted with the steam being directed into the inner
shell 88 and the liquid desiccant being directed into the chamber
92 the opposite arrangement may be employed with the liquid desiccant
directed into the inner shell 88 and the steam delivered to the
chamber 92. Referring now to FIG. 8 there is shown an alternative
embodiment of a condenser 86a, including a housing 90a and inner
shell 88a, where the inner shell 88a segregates housing 90a into
two compartments 92a, 92b, respectively. A steam inlet tube 100a
communicates with compartment 92a, and a steam inlet tube 100b communicates
with compartment 92b. Partially heated dilute desiccant solution
is delivered to inner shell 88a through solution inlet 108a, and
is sensibly heated by the latent heat of condensation as the steam
condenses in the respective chambers 92a, 92b. Condensate flows
out of chambers 92a, 92b, via condensate outlets 104a, 104b, respectively.
Partially heated dilute desiccant at the second temperature flows
out of inner shell 88a through solution outlet 110a to coiled interchange
heat exchanger 58. Baffles 112a, 112b are provided in chambers 92a,
92b, respectively.
Referring now to FIG. 9 there is shown a third embodiment of a
condenser 86b, comprising a housing 90b and a plurality of tubes
118 which may be convoluted or corrugated as described above with
regard to the interchange heat exchangers and shown in FIGS. 5A
and 5B. The tubes 118 are supported by opposing support plates 120
and communicate with respective steam inlets 100c, 100d through
which steam is delivered from boiler 34. The housing 90b includes
a liquid desiccant solution inlet 108b to receive dilute liquid
desiccant from split interchange heat exchanger 66 and an outlet
110b to deliver partially heated liquid desiccant at the second
temperature to the coiled interchange heat exchanger 58. The tubes
118 are fabricated from TEFLON, and the support plates 120 include
at least one silicone rubber sheet attached thereto.
Referring now to FIG. 9A, there is shown another embodiment of
a condenser 86c, utilizing multiple double-pipe heat exchangers.
Each double-pipe heat exchanger comprises an outer straight tube
300 and an inner convoluted tube 302 concentrically disposed within
the outer tube. A small annular gap is defined between the outer
and inner tubes 300 302 which forces the fluid to follow a "screw-like"
tortuous path through the convolutions at high velocity. This arrangement
provides high heat transfer coefficients and condensation capacity.
The components can be fabricated from plastics such as polypropylene,
TEFLON, PVDF or silicone rubber. Dilute liquid desiccant from split
Interchange heat exchanger 66 is directed into a manifold 304. Similarly,
steam from boiler 34 flows into a manifold 306 through inlet ports
308. Manifold 304 communicates with the inner convoluted tubes 302.
Steam flows through the annuli formed between outer tubes 308 and
inner tubes 302 causing the dilute liquid desiccant entering the
heat exchangers from manifold 304 to be partially heated to the
second temperature. This heated liquid desiccant is delivered to
the coiled interchange heat exchanger 58 from exit manifold 310.
Condensate is collected in manifold 312 and is then delivered to
pan 106. Air vents are utilized to ensure reliable gravity assisted
drain flow of the liquid desiccant from the absorber 12 to the boiler
34. In a preferred embodiment, small pieces of TEFLON tape having
a micro-pore structure can be used in the vent assembly. The TEFLON
material is hydrophobic and has a micro-pore structure which enables
the free passage of air while preventing desiccant leakage. The
air vent 314 comprises a tube 316 extending upwardly from manifold
310. The tube 316 includes a polypropylene mesh 318 and a piece
of TEFLON tape 320 in a laminated structure. Alternatively, conventional
float-based air vents, such as air vents manufactured by Honeywell,
can be utilized to vent air from the system.
Referring now to FIG. 9B, in another embodiment the condenser 86d
comprises multiple coiled double pipe heat exchangers. Each double
pipe heat exchanger includes an outer straight tube 300a and inner
convoluted tube 302a concentrically disposed within the outer tube
300a. Steam from boiler 34 enters a manifold 306a, from where it
is communicated into the annuli formed between outer tubes 300a
and inner tubes 302a. Dilute liquid desiccant is delivered to manifold
304a and thence into the inner tubes 302a. Partially heated liquid
desiccant exits into manifold 310a, and is delivered to coiled Interchange
heat exchanger 58. Condensate flows through outlets 312a to pan
106. This condenser 86d, operates on the same principles and offers
the same advantages as the double-pipe condenser 86c described above.
Referring now to FIG. 11 the respective components of the PLDD
10 are shown stacked within frame 35.
During the operating cycle, ambient air is drawn into the unit,
through absorber 12 and exhausted to the room by fan 23. The moisture
in the air is extracted as the air makes contact with the liquid
desiccant wicking across the microglass fiber wick plates 20 22.
Dilute liquid desiccant is gravity fed from drain pan 24 of absorber
12 to manifold 76 of split interchange heat exchanger 66 wherein
it is raised to a first temperature through heat transfer from concentrated
liquid desiccant flowing through annuli 74. The dilute liquid desiccant
at the first temperature is then delivered to the condenser 86
in which the latent heat of condensation as the steam condenses
sensibly heats the liquid desiccant to the second temperature. The
liquid desiccant at the second temperature is thereafter delivered
to the coiled interchange heat exchanger 58 in which it is further
heated to a third temperature prior to introduction into boiler
34 for regeneration. The coiled interchange heat exchanger 58 recovers
waste heat radiating from the walls 36 of boiler 34. The concentrated
liquid desiccant solution produced by boiling the liquid desiccant
is drawn through the coiled interchange heat exchanger 58 and split
interchange heat exchanger 66 and thereafter delivered to distributor
14 of absorber 12 by pump 80. The stacking of the respective components
as shown in FIG. 1 provides for the gravity feed of dilute liquid
desiccant from absorber 12 to boiler 34 through the first and second
heat exchangers and the condenser, thereby eliminating the need
for multiple pumps in the system.
The present invention has been shown and described in what are
considered to be the most practical and preferred embodiments. It
is anticipated, however, that departures can be made therefrom and
that obvious modifications will be implemented by persons skilled
in the art. |