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Description  |
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BACKGROUND OF THE INVENTION
While this invention relates generally to heat exchangers, it more
specifically involves flexible heat exchangers that can be conformed to
the outer cylindrical surface of tanks or the like. For example, wine vats
are closely controlled in temperature, which is usually accomplished by
circumferentially attaching a stainless steel jacket (heat exchanger) to
the outer surface of the tank and pumping cooled fluids through the
jacket. Since the stainless steel jacket is metal, a great deal of rime
ice forms on its outer surface.
Although the stainless steel jackets work, their cost is substantial and
the condensation of rime ice is a continuing problem. Also, they are
difficult to install, and cannot be easily brought into integral contact
with the surface of a cylindrical tank, even when custom made. In
addition, these jackets usually have relatively high pressure drops across
the inlet and outlet, resulting in high energy consumption in the pump
transfer system circulating the heating or cooling fluid.
The good insulating characteristic of plastics is a drawback for their use
in heat exchange elements. However, by using polyolefins, such as
polypropylene and polyethylene, for the novel heat exchanger of this
invention and designing it with large flat contacting surfaces, plus a
high capacity flow rate of cooling or heating fluids on the opposite side
of the thin plastic contacting surface, most of the prior problems of
plastic heat exhangers have been minimized. The foam insulation adhered to
the exterior surface eliminates the rime ice because it is sealed to the
outer sheet forming the exchanger element so that no moisture-laden air
can contact this surface. As a result, there is no condensation on this
surface or on the exterior surface of the foam due to its insulating
characteristics.
Economically, the heat exchangers according to this invention cost less
than one-sixth of the prior art stainless steel jackets, and are much more
easily conformed to the surface of a tank due to the flexibility of the
plastic. Because it is constructed of plastic, the novel heat exchanger
can be "stretched" slightly to fit properly when installed on a
cylindrical surface, thereby ensuring positive contact with a tank or
other cylindrical surface over the entire surface area where thermal heat
exchange is to be accomplished.
Many factors determine the efficiency of heat exchangers, but with the
innovations employed in this invention and the features achieved, this
plastic exchanger rivals the prior art stainless steel jacket in
efficiency. This is a totally unexpected result for a plastic exchanger.
Manifolds are specially designed for high flow rates and are securely
connected to the thermal exchange portion so that a complete heat
exchanger modular unit can be fitted to a surface by holding the manifolds
with clamps or the like and stretching the unit slightly under tension
across a cylindrical surface through adjusting bolts on the clamps. As the
insulating foam is bonded only to an outer surface sheet of modular units,
it is not placed under tension by this action. Further, the thickness of
the thermal exchange is less than one-quarter inch (excluding the
thickness of the foam insulation), which allows it to be conformed easily
to cylindrical surfaces with diameters of over three feet without placing
undue stress on its internal structures.
Polyolefins are non-corrosive, non-scaling and chemically inert, making
this novel heat exchanger useful in corrosive and caustic environments.
However, very strong oxidizing acids can cause slow oxidation, and organic
solvents at temperatures of about 180.degree. F. may cause some
deterioration. Thus due to the construction and the characteristics of
polyolefins, this novel heat exchanger has service temperatures from
-40.degree. F. to +300.degree. F., and is useful with corrosive fluids of
nearly all types.
SUMMARY OF THE INVENTION
The above advantages and economies can be recognized in a modular plastic
heat exchanger having at least one thermal exchange means composed of
parallel inner and outer plastic sheet means separated by a plurality of
parallel flat ribs oriented normal to said sheet means and fused to said
sheet means to form a plurality of parallel channels, an insulating foam
layer co-extensive with the outer sheet means and sealingly adhered to its
exterior surface, a first manifold means having a central large flow tube
and a distributor means operably connected to said thermal exchange means
at one edge so said flow tube is normal to the longitudinal axes of said
channels and fluidly communicating said channels with said flow tube, a
second manifold means having a large central flow tube and a distributor
means operably connected to the opposite edge of said thermal exchange
means to fluidly communicate said channels and its flow tube, whereby
fluids can enter one flow tube and simultaneously pass through said
thermal exchanger means to the other flow tube. The modular heat exchanger
can include U-shaped fittings to interconnect said flow tubes so a number
of modules can be placed in series to circumferentially extend around
large tanks or the like.
DESCRIPTION OF THE DRAWINGS
This novel heat exchanger will be better understood by reference to the
description thereof in conjunction with the following drawings, wherein:
FIG. 1 is a perspective of a tank (wine vat) with the novel plastic heat
exchanger cinched to its outer circumference with clamps and arrows
illustrating the direction of the fluid flow patterns;
FIG. 2 is a top view of the tank and heat exchanger shown in FIG. 1;
FIG. 3 is a broken-away perspective of one corner of the heat exchanger
illustrating its structure, and also a clamp used for securing the modular
unit on a cylindrical surface;
FIG. 4 is a sectional end view of the tank showing the modular heat
exchanger attached and illustrating the connection of the clamps employed;
FIG. 5 is a broken-away perspective of the thermal exchange element with
the manifold removed and enlarged to show its structural details;
FIG. 6 illustrates in elevation the U-shaped connectors for connecting
multiple modular panels in series;
FIG. 7 is an elevation of the end plug used to close off the ends of the
flow tubes in the manifold when desired;
FIG. 8 illustrates an elevation of two modular units stacked vertically
(with parts broken away), along with a coupling to interconnect them for
tanks of heights over four feet; and
FIG. 9 is a perspective of an end portion of a manifold unit illustrating
its construction details.
DESCRIPTION OF A PREFERRED EMBODIMENT
Referring to FIGS. 1 and 2, the general construction of the novel plastic
heat exchanger 10 can be seen. It is shown installed on a cylindrical tank
A, such as a wine vat. As can be seen in FIG. 2, three separate modular
units are connected in series whereby an inlet pipe 11 provides a
pressurized feed of heated or cooled liquid from a source (not shown)
which flows circumferentially around the tank (illustrated by arrows B) to
a return outlet pipe 12 which is connected to return the feed to the
source. The pumping system is conventional, and therefore is not described
or illustrated.
More specifically, the construction of the thermal exchange element 13 is
best illustrated in FIGS. 3 and 5. Basically, it is composed of an outer
sheet 14 and an inner sheet 15 which are separated by ribbons or ribs 16.
Normally the sheets are plastic, and preferably a polyolefin, such as
polyethylene or polypropylene. Also, the ribs 16 are of similar material.
As can be seen, the ribs have their edges fused to inside surfaces of the
sheets where they are arranged in a spaced-apart relationship forming a
series of parallel channels having a rectangular cross-section. With
appropriate dies, the sheets and ribbons can be extruded as a composite
unit to form this element.
On the exterior surface of the outer sheet 14 a foam layer 17 having a
thickness from 1/8 inch to 3/4 inch is secured by sealing it to this
surface. This foam layer is co-extensive with the exterior surface of this
sheet, and is usually attached with an adhesive which joins the foam and
the surface so no air space exists therebetween. Normally a closed
cellular foam is employed which is not air permeable. Due to the tight
continuous seal of the foam layer with sheet 14 and the non-permeable
character of the foam layer, no rime ice forms on the exterior surface of
the outer sheet.
While the foam layer 17 is co-extensive with the exterior surface of sheet
14 of the thermal exchange element 13, portions of the opposite edges 18
thereof where the channels are accessible are not covered with the foam
layer where they are inserted into the manifold unit 20. This manifold
unit includes a hollow tubular structure 21 having a central flow tube 22
and a tangentially extending distributor element 23 which is usually fused
to the tubular structure, or alternatively made integral therewith in a
single extrusion. By making the distributor project tangentially from the
manifold, as can be seen in FIGS. 3 and 9, the inner sheet 15 of the
thermal heat exchange element can be maintained flat against a cylindrical
surface in the area of its connection to the manifold unit.
An edge 18 of the thermal exchange 13 is inserted between the separated
lips 24 of the distributor element 23 until it contacts shoulder 25 (see
FIG. 9). Prior to the insertion of the edge 18, a plurality of holes 27
are drilled parallel to and between the lips to intersect the central flow
tube 22 of the manifold. As a result of these holes and the large
lengthwise duct 26 adjacent shoulders 25, fluids from the flow tube can
simultaneously communicate with all the channels in thermal exchange means
13. After the edge 18 is sealed with the inner surfaces of the lips, the
opposite ends of duct 26 are plugged thereafter to eliminate leakage.
The completed modular unit 10 is then ready to be installed on and retained
on a tank or the like. As can be seen in FIGS. 1, 2, 3 and 4, this can be
conveniently done with clamping devices. Specifically, C-shaped clamps can
be used to grip one of the manifold units 20 and a similar clamp can be
used on an adjacent manifold unit (see FIG. 4). A bolt 32 of an
appropriate length is used to connect the flanges 31 and then tightened to
cinch the modular unit against the tank A. Multiple clamps are used which
are spaced axially along the manifold units as necessary. Multiple modular
units are used, depending on the circumference of the tank. On a tank ten
feet in diameter, three ten-foot modules would be used. The bolts are
tightened to ensure that the inner surface of sheet 15 of each thermal
exchange element 13 is faced tightly against the tank surface. If desired,
a thermal conducting grease can be disposed between this surface and the
tank surface. Such greases are well-known in the heat exchange art.
Once the modular units are assembled on the tank, they are connected for
series flow. This is accomplished with U-shaped adjustable fittings 40.
These fittings have two elbows 41 with an interconnecting pipe 42 which is
cut to the appropriate length C to fit the assembled modules. The fittings
also have a nipple 43 inserted into each elbow with an O-ring 44 disposed
in a groove near the distal end of the nipple. Once a fitting has been
adjusted to fit the modular unit (pipe 42 cut to length), the joints are
solvent-welded and the nipples are inserted into the flow tubes 22 of the
modular units and pushed in so the O-rings extend past a screw 45 near the
opposite ends of the manifold units 20. Thereafter, this screw is turned
in to lock the fitting in the manifold unit.
For best flow characteristics, these fittings 40 are used at both the top
and bottom ends of the manifold units that are connected in series. End
plug 46 which includes a cap 47 and a nipple 48 also uses an O-ring
similarly located to the ones on the fitting 40 so it can be used to close
off the ends of manifold units when desired (see FIG. 8). It is locked in
place by screw 45 in the same manner as fitting 40. In all cases, the
locking screw 45 is outside the O-ring seal to eliminate leakage.
Obviously, the fittings can be easily removed from the manifold unit for
maintenance, repair or removal by removing screws 45.
In FIG. 8, a connecting nipple 50 is illustrated. It is constructed like
the U-shaped fittings 40, but connects side-by-side modular units where
tanks of heights greater than five feet are involved.
Normally, the modular units are sized with ten foot lengths and the thermal
exchange elements 13 are normally forty-eight inches wide to offer maximum
flexibility in fitting tanks with various fittings connected thereto.
Also, the exterior piping is connected with a nipple of a construction
similar to those of fittings 40 and the end plug 46.
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