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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a heat exchanger capable of exchanging
heat between two kinds of fluids having different temperatures and
humidities. More particularly, the invention is concerned with a heat
exchanger which can perform, in ventilating an air-conditioned room or
compartment of a house, automobile or the like, an exchange of heat
between the outgoing air discharged to the outside and the incoming air
introduced from the outside to thereby recover the heat which otherwise is
carried away by the outgoing air to be wasted.
2. Description of the Prior Art
To comply with the demand stated above, the heat exchanger must be capable
of exchanging heat in both aspects of actual heat and latent heat between
the outgoing air and incoming air. Unfortunately, however, the
conventional heat exchangers constructed with metals can make the exchange
of the actual heat only. In consequence, the heat exchanging efficiency is
undesirably lowered particularly when the latent heat occupies a large
part of the total heat including actual heat and latent heat.
In order to overcome this problem, a heat exchanger has been proposed which
incorporates a heat exchanging material having a low heat conductivity,
such as asbestos, and impregnated with a moisture adsorbent, such as
lithium chloride, thereby to recover the latent heat. This type of heat
exchanger, however, is needs a complicated process of manufacture and thus
is expensive.
Japanese Utility Model Publication No. 50-22365 (22365/1975) discloses a
heat exchanger in which the heat is exchanged across a Japanese paper. The
Japanese paper, although it can contribute to some extent to the exchange
of latent heat, has poor heat transmitting and moisture permeating
characteristics, so that the heat exchanging capacity of the heat
exchanger is low relative to the size of the heat exchanger.
It is also to be pointed out that none of the heat exchangers proposed and
used hitherto has a function to remove contaminants suspended by the
incoming fresh air, so that the contaminated air is introduced into the
room.
SUMMARY OF THE INVENTION
Accordingly, an object of the invention is to provide a heat exchanger
which is capable of effectively exchanging both of heat and moisture and
has a function to adsorb and remove any contaminant suspended by the
ambient air thereby to prevent the contaminant from being introduced into
the room.
To this end, according to the invention, there is provided a heat exchanger
having a laminated structure constituted by a plurality of flat partition
plates and corrugated spacer plates sandwiched between adjacent partition
plates, the corrugated spacer plates being arranged such that the ridges
of corrugations of adjacent layers cross each other, wherein the partition
plate is formed from a paper-like material composed of a mixture of carbon
system fibers and binding fibers in which the carbon system fibers occupy
50 to 90% of the mixture.
The above and other objects, features and advantages of the invention will
become clear from the following description of preferred embodiments of
the invention with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic illustration of a ventilation system incorporating a
heat exchanger constructed in accordance with an embodiment of the
invention;
FIG. 2 is a perspective view of the heat exchanger shown in FIG. 1;
FIG. 3 is a graph showing the relationship between the activated carbon
fiber content and the heat exchange efficiency;
FIG. 4 is a graph showing the relationship between the activated carbon
fiber content and the humidity exchange efficiency; and
FIG. 5 is a perspective view of a partition plate incorporated in a heat
exchanger of a second embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring first to FIG. 1 showing a ventilation system incorporating a heat
exchanger of the invention, a ventilation duct 1 is fixed, by means of
bolts (not shown) or the like, to a wall 2 which separates the space A in
a room from the outside space B. The space in the duct 1 is divided by
partition walls 5 into a room air passage 7 through which the air is
discharged from the inside space A to the outside space B, and a fresh air
passage 8 through which the ambient fresh air is introduced from the
outside space B into the inside space A. These passages 7 and 8 are
provided with electrically driven blowers 3 and 4, respectively, to
positively create the outgoing and incoming flows of air through these
passages. Needless to say, these blowers 3 and 4 may be driven by a common
electric motor, although independent motors 3a and 4a are provided in the
illustrated embodiment.
As will be understood from FIG. 1, the partition walls 5 are arranged such
that the air passages 7 and 8 cross each other substantially orthogonally.
A heat exchanger 6 is disposed at the point where the two air passages 7
and 8 cross each other.
Referring now to FIG. 2, the heat exchanger 6 has a laminated structure
formed by flat partition plates 9 and corrugated spacer plates 10 and 11
each sandwiched between an adjacent pair of the partition plates 9. The
corrugated spacer plates 10 and 11 are arranged such that the ridge lines
of the corrugation of the spacer plates 10 are substantially at right
angles to those of the corrugated spacer plates 11 so that the spacer
plates 10 and the partition plates 9 cooperate to define a first series of
passages for the outgoing room air indicated by an arrow X while the
spacer plates 11 and the partition plates 9 cooperate to define a second
series of passages for the incoming fresh air indicated by an arrow Y. The
first and second series of the passages are substantially at right angles
in the illustrated embodiment of the invention but may alternatively be at
an angle other than 90.degree..
In the described embodiment, the flat partition plate 9 is made from a
paper of activated carbon. This paper of activated carbon is produced by
activating carbon fibers into activated carbon fibers, mixing the
activated carbon fibers with binding fibers such as fibrous polyvinyl
alcohol and/or cellulose fibers, and then making the paper from this
mixture in the same manner as the making of the Japanese paper.
This paper made from the activated carbon fibers inherently has a
characteristics similar to those of solid carbon. Namely, it exhibits a
higher heat conductivity than the ordinary papers such as Japanese paper
consisting solely of organic cellulose material. In addition, the
activated carbon powder paper has a large surface area. For these reasons,
the paper made from activated carbon fibers provides a very high heat
exchanging efficiency. Furthermore, the exchange of moisture can be
achieved more effectively than in the case of ordinary papers, due to a
combination of the moisture permeability caused by diffusion of molecules
of vapor and due to the capillary action offered by the fine fibers of the
activated carbon.
A plurality of heat exchangers having the laminated structure shown in FIG.
2 where produced with the ratios between the activated carbon fibers and
binding fibers being widely varied. A series of tests was conducted with
these heat exchangers in order to investigate the relationship between the
mixing ratio and the performance of the heat exchanger. The test results
are as shown in FIGS. 3 and 4. Namely, FIG. 3 shows a graph in which the
abscissa represents the activated carbon content (%) while the ordinate
represents a heat exchange efficiency (%). In FIG. 4, the abscissa
represents the activated carbon content (%) while the ordinate indicates
the humidity exchange efficiency (%). In these graphs, the full line
curves show the characteristics actually measured when the flat partition
plates were not impregnated with any agent while broken line curves show
the characteristics as observed when the flat partition plates were
impregnated with lithium chloride.
As will be seen from FIG. 3, a higher heat exchange efficiency is achieved
as the activated carbon content becomes greater. In contrast, the humidity
exchange efficiency exhibits a peak value at 50% of the activated carbon
content and is slightly decreased as the activated carbon content is
increased beyond 50%, as shown in FIG. 4. Therefore, taking into account
the humidity exchange efficiency solely, the activated carbon content may
preferably be selected to range between 40 and 70%. However, in the heat
exchanger which is intended to exchange both of actual and latent heats,
it is more preferable that both of the heat exchange efficiency and the
humidity exchange efficiency are high. From this point of view, the
activated carbon content should fall within the range of between 50 and
90%.
The effect of impregnation with lithium chloride will be explained
hereinunder. As will be seen from FIG. 3, no substantial change of heat
exchange efficiency is caused by the impregnation with lithium chloride.
On the other hand, the humidity exchange efficiency is considerably
improved by the impregnation with lithium chloride. This is attributable
to the moisture adsorption and releasing effect of the lithium chloride in
combination with the aforesaid advantageous effect of the activated carbon
fibers. The effect of the lithium chloride is remarkable particularly in
the region of activated carbon content of higher than 50%. This is
considered to be because the combined effect of the lithium chloride and
the activated carbon fibers is remarkable and effective particularly in
this region of activated carbon content. Therefore, also from this point
of view, the activated carbon content preferably ranges between 50 and
90%.
The heat exchanger described above can suitably be used in a ventilation
system in which a heat exchange is made between the outgoing room air x
and the incoming fresh air Y. For instance, in the summer season in which
the temperature and humidity of ambient air are generally high, the heat
and humidity are exchanged between the hot and humid incoming air and the
cooled and less-humid outgoing air, so that the outdoor air is effectively
cooled and dehumidified before it is introduced into the air-conditioned
room. To the contrary, in the winter season in which the outdoor air is
generally chill and dry, the outdoor air is heated and humidified by the
heat and humidity exchange with the hotter and humid room air. In
consequence, the increase in the load on the air conditioner due to the
ventilation is effectively reduced or eliminated.
Furthermore, according to the invention, it is possible to obtain a
deodorant effect. Namely, an offensive odor content of outdoor air, if
any, is effectively adsorbed and removed as the incoming air contacts the
activated carbon fibers. This is also true with the removal of any noxious
component such as carbon monoxide gas contained by the outdoor air. The
paper of activated carbon fibers can hardly be burnt in ordinary state of
use and thus offers also a higher safety over the Japanese paper or the
like material.
In order to enhance the deodorant and cleaning effects stated above, it is
preferred that not only the partition plates 9 but also the spacer plates
11 faced to the passages for fresh air Y are formed from the paper of
activated carbon fibers. It is also possible to form both of the spacer
plates 10 and 11, which are faced to the passages for fresh air and room
air, from the activated carbon fibers. By so doing, it is possible to
obtain a greater surface area of the activated carbon fibers, which in
turn ensures a higher heat conductivity and, hence, a higher heat exchange
efficiency. The production of the partition plates 9 and the spacer plates
10 and 11 from the same material, i.e., the activated carbon fiber paper,
is advantageous also from the view point of efficiency of the production.
In the embodiment described above, the paper material, i.e., the activated
carbon fiber paper, is produced by activating carbon fibers and then
mixing the activated carbon fibers with the binding fibers. This, however,
is not exclusive. Namely, advantageous results substantially equivalent to
those shown in FIGS. 3 and 4 were obtained from a carbon fiber paper which
was formed by simply mixing the carbon fibers with the binding fibers. It
is, therefore, preferred that the carbon fiber content preferably ranges
between 50 and 90% also in this case. In the case where the non-activated
carbon fiber paper is used, the surface area is increased to a certain
extent over that provided by ordinary papers due to the presence of carbon
fibers projecting in a cilia-like manner, although the increase in the
surface area is smaller than that provided by the paper of activated
carbon fibers. The paper of non-activated carbon fibers, therefore, can
suitably be used as the material of the layers having the smaller demand
for deodorant and cleaning effects, such as the partition plates 9 and the
spacer plates 10 faced to the passages for the outgoing room air X.
As has been described, the present invention provides a heat exchanger
having a laminated structure including partition plates and corrugated
spacer plates each sandwiched between an adjacent pair of partition
plates, wherein at least the partition plates are formed from a paper-like
material which is made from a mixture of fibers of carbon system such as
carbon fibers or activated carbon fibers and binding fibers, the fibers of
carbon system occupying 50 to 90% of the mixture of fibers. This heat
exchanger is quite effective in exchanging not only heat but also humidity
as well between two fluids which flow through the heat exchanger in two
different directions.
Referring now to FIG. 5 showing a second embodiment of the invention, each
partition plate 9 is formed by a paper 9a of non-activated carbon fibers
and a paper 9b of activated carbon fibers. The paper 9a is disposed
adjacent to the side of the spacer plate 10 which is faced to the passages
for the room air while the paper 9b is disposed adjacent to the side of
the spacer plate 11 which is faced to the passages for the fresh incoming
air.
The non-activated carbon fiber paper which constitutes each spacer plate 10
and the side 9a of each partition plate 9 faced to the passages for the
room air is produced by mixing the carbon fibers with cellulose and
fibrous polyvinyl alcohol and then forming the mixture into paper sheets
by means of a paper making machine. On the other hand, the activated
carbon fiber paper constituting each spacer plate 11 and the side 9b of
each partition plate 9 faced to the fresh air passages is produced by
mixing activated carbon fibers with fibrous polyvinyl alcohol and forming
the mixture into paper sheets by means of a paper making machine. The
partition plate 9 can easily be formed by using a combination type paper
making machine in which a paper sheet of activated carbon fibers and the
paper sheet of non-activated carbon fibers are joined together.
In this embodiment of the invention, the spacer plate 10 faced to the
passages for the room air and the side 9a of the partition plate 9 faced
to the passages for the outgoing room air are made from carbon fiber paper
sheet having no positive adsorbing function. Therefore, the contaminants
suspended by the outgoing room air can be discharged to the outside
without attaching to the walls of the room air passages. In addition,
since the spacer plate 11 faced to the fresh air passages and the side 9b
of the partition plate 9 faced to the incoming air passages are made of
paper sheets of activated carbon fibers having the adsorbing function, the
contaminants suspended by the outdoor air, if any, can effectively be
adsorbed and removed before the air is introduced into the room.
The reason why the portions to be contacted by the outgoing room air are
made of paper sheets having no adsorption function is because, if the side
9a of the partition plate 9 faced to the outgoing room air passages were
made from the paper sheet of activated carbon fibers having the adsorption
function, it will adsorb a large amount of contaminants suspended by the
outgoing room air. In this concern, it is to be noted that the room air is
usually contaminated more heavily than the outdoor fresh air. In
consequence, a large difference in concentration of contaminants is formed
between both sides 9a and 9b of the partition plate 9 across the thickness
thereof. This in turn causes a penetration of the contaminants from the
heavier contamination side 9a to the other side 9b which is faced to the
incoming fresh air passages to thereby cause an increase in the
contaminants on the side 9b of the partition plate 9. In consequence, the
contaminants on the side 9b are removed therefrom by the incoming fresh
air flowing in contact with the side 9b of the partition plate 9 and are
conveyed thereby into the room. This problem, however, can be fairly
avoided by the embodiment of the invention shown in FIG. 5 as will be
apparent to those in the art from the foregoing description.
The invention is not limited to the described and illustrated embodiments
of the invention and may have various changes and modifications. For
example, it is possible to form the spacer plates 11 by Zeolite (Trade
Name) having an adsorption function. The two kinds of paper sheets
constituting the two sides 9a and 9b of each partition plate 11 may be
prepared separated and disposed merely in contact with each other.
Alternatively, these two kinds of paper sheets may be secured together by
means of an adhesive such as starch adhesive or the like. It is also
possible to increase the moisture adsorption effects of both sides 9a and
9b of the partition plates 9 by adding a cellulose, gypsum or the like
material to the carbon fibers or activated carbon fibers.
From the foregoing description, it will be understood that the present
invention provides an improved heat exchanger which can effectively
exchange both of actual heat and latent heat between two kinds of fluids
having different temperatures and humidities. Particularly, the second
embodiment described with reference to FIG. 5 ensures the introduction of
clean fresh air into an air-conditioned room because the sides of the
partition plates faced to the passages for the outgoing room air are made
of a material having no positive adsorption function while the sides of
the partition plates faced to the fresh incoming air passages are made of
a material having positive adsorption function.
It is to be understood that the word "plate" used herein embraces a thin
and flexible sheet material and that the word "paper" also used herein
embraces a paper-like material such as non-woven fabric.
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