WO2000053992A1

WO2000053992A1 - Heat exchanger formed from tube plates having tubes joined by weaving

Info

Publication number: WO2000053992A1
Application number: PCT/CA2000/000236
Authority: WO
Inventors: Eldon Lawrence Fletcher; Pallatheri Manackal Subramanian
Original assignee: E.I. Du Pont De Nemours And Company; Dupont Canada Inc.
Priority date: 1999-03-08
Filing date: 2000-03-07
Publication date: 2000-09-14

Abstract

Heat exchangers are provided comprising plates of tubes (11) wherein the tubes (12, 13, 14, 15) are constrained supported and bonded in a parallel, essentially flat manner using a filament, thread, yarn or like material applied to the tubes (12, 13, 14, 15) in a weaving operation. Tubes (12, 13, 14, 15) are held together by weft threads (16, 17, 18). Using tubes as the warp, a woven structure is created with a thermoplastic thread as the weft. The direction of the heat exchange fluid outside the tubes (12, 13, 14, 15) is shown at 19, perpendicular to both the tubes and the weft.

Description

TITLE

Heat Exchanger Formed from Tube Plates Having Tubes Joined by Weaving

BACKGROUND Efficient plate type units (plates) used in nylon heat exchangers are produced by a twin sheet thermoforming process with internal gas assist, which gives an essentially flat plate consisting of a number of tubes joined by ligatures formed from the sheets of nylon. This process is described in US 5,195,240.

Such plates and the heat exchangers formed from them provide excellent heat transfer efficiency for the space volume occupied, but can tolerate only relatively low internal pressures, restricting their applicability. Tubing formed by extrusion can tolerate much higher internal pressure. In a high efficiency exchanger a large number of small tubes is required; constraint and support of these tubes is required. Use of tubing located between two bonded sheets of plastic to achieve this support is described in US 5,469,915. However, this still requires ligatures between the tubes, which reduces heat transfer efficiency. The following patents illustrate the state of the art and are incorporated herein by reference.

1) US 5,195,240 "Method for the Manufacture of Thermoplastic Plate Heat Exchanger", J.P.Shuster and A.J.Cesaroni, Apr.16.1992, assigned to DuPont

Canada Inc.

2) US 5,469,915 "Plate Heat Exchanger formed from Tubes and Sheet", AJ.Cesaroni, Nov. 28,1995

3) US Patent Application No. 60/014,150 filed March 25,1997 - N.A.Farkas, et al. 4) US Patent Application (Jennifer, pis substitute Ser. No. & filing date of DC-

9594-P1) "Solventless Plate Forming Process", S.R.Doshi, N.A.Farkas and K.E.Stevens

German Patent DT 2,012,883 B2 discloses weaving or braiding around tubes in a heat exchanger sheet a filament which is used to block the flow of fluid parallel to the tubes. Preferably the filament is woven or braided in part of the way from one side, then at a distance along the tubes, part of the way from the other side. Then the resulting sheet is preferably rolled so that the filaments block or interfere with the flow of fluid along the lengths of and outside the tubes. Alternatively, the sheets can be kept flat instead of being rolled, and stacked flat, with the filaments serving the same function. When the patent says either braiding or weaving can be used, the braiding is illustrated as a filament woven up and down, around the tubes, so that the tubes stay essentially flat. This patent uses the filaments to channel the flow of the fluid outside and parallel to the tubes and does not envision fluid flowing outside the tubes which flows perpendicular to and across the tubes.

SUMMARY OF THE INVENTION The present invention provides a thermoplastic heat exchanger comprising tube plates to contain a first heat-exchange medium and separate it from a second heat-exchange medium, said first medium circulating inside said tubes and said second medium circulating outside said tubes, wherein the tubes are held together as a warp by a weft which is woven or braided in a direction perpendicular to the tubes and the second medium flows in a direction perpendicular to both the tubes and the weft.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic illustration of a tube plate of the invention with the tubes essentially flat and straight.

Fig. 2 is a schematic illustration of a tube plate of the invention with the tubes in a wavy or sinusoidal arrangement.

DETAILED DESCRIPTION Heat exchanger tube plates are formed from tubes that are fed simultaneously into a conventional weaving or knitting loom, in the machine or "warp" direction. A weft of woof of a filler material, which could be a thread or filament-like material of a thermoplastic or even natural fiber, is then used to join these tubes in the loom. No chemical bond need be formed between the filler and the tubes, although materials could be selected so that such a bond would be formed at the points of contact. Alternatively, filler and weaving configuration could be adjusted so that significant tube to tube contact would occur, allowing tube to tube bonding to be introduced, for example by thermal bonding of appropriate materials. More broadly stated, polymers useful in the present invention include both isotropic thermoplastic polymers (ITP) and liquid crystal polymers (LCP), which include the following: While the invention is illustrated with certain polyamides, it will be apparent that it is not limited to the use of such materials and that other thermoplastics, preferably ITPs can be used alternatively and can be used in combination with LCPs in various structures including multilayer films, such as the following: Isotropic herein means that the polymer is isotropic when tested by the thermo-optical test (TOT) described in U.S. Patent 4,118,372, which is hereby included by reference. Any ITP may be used so long as it meets certain requirements. It must of course withstand the temperatures to which the heat exchanger id subjected and should throughout that temperature range provide sufficient strength (together with the LCP) to the heat exchanger to reasonably maintain its shape and contain the fluids in the heat exchanger, as needed. If it is exposed to one or more of the fluids in the heat exchanger (or any other adventitious materials that may contact it) it should be preferably reasonably chemically stable to those fluids so as to maintain its integrity. Although various types of heat exchangers made simply of ITPs have been described, ITPs sometimes have serious drawbacks when the are the only materials in heat exchangers. Sometimes an ITP may not be chemically stable to one or more of the fluids in the heat exchanger, for instance, many polyesters hydrolyze or otherwise degrade in the presence of water, water-alcohol, or water- glycol mixtures, especially at higher than ambient temperatures. Many ITPs are relatively permeable to many liquids and/or gases, and therefore allow losses and/or migration of these materials in or from the heat exchanger. Some ITPs may be swollen by one or more of the fluids used in the heat exchanger thereby changing their dimensions and/or physical properties. All of the above are of course problems in plastic heat exchangers.

It has been found that a layer of a thermotropic liquid crystalline polymer (LCP) used in the heat exchanger often alleviates or eliminates one or more of the above mentioned problems. By an LCP is meant a polymer that is anisotropic when tested in the TOT Test described in U.S. Patent 4,118,372. If the LCP layer is placed between a fluid and any particular ITP in the heat exchanger it usually protects that ITP from chemical degradation by the fluid, and/or also often protects the ITP from being swollen by that fluid. In addition, even if the ITP is swollen, the LCP because of its high relative stiffness, and the fact that it is not swollen by many fluids, help the overall heat exchanger maintain its shape and dimensions. Also, the LCP acts as an excellent barrier layer to many fluids. For instance, in automotive heat exchangers which help cool the engine, the commonly used internal coolant is a mixture of a glycol and water, and the external coolant is air. With many ITPs diffusion of water and/or glycol is so rapid that frequent replenishment of the water/glycol mixture is needed. If an LCP layer is included, the diffusion is greatly decreased.

In order to obtain rapid heat transfer through the heat exchanger, thickness through the material between the heat transfer fluids should be a small as possible. This would be true with any material used for an heat exchanger, but is especially important with plastics since their heat transfer coefficients are usually relatively low when compared to metals. Since the LCP is usually the more expensive of the polymers present in the heat exchanger, it is economically preferable to limit its use. Therefore, in most constructions it is preferred that the LCP is present in relatively thin layer(s) and that layer(s) of the ITP be relatively thick so as to carry much of the structural load of the heat exchanger (i.e., pressure of the fluid(s), maintain structural shape and dimensions, etc.).

The heat exchanger is made up of one or more LCP layers and one or more layers of ITP. If more than one layer of LCP or ITP is present, more than one type of LCP or ITP. respectively, can be used. In addition other layers may be present. For example, so called tie layers, also called tie or adhesive layers, may be used to increase the adhesion between various LCP and ITP layers, or between ITP layers or between LCP layers. The number and placement of the various layers in the heat exchanger will vary depending on the particular polymers chosen, the fluids used in or by the heat exchanger, temperature requirements, environmental needs, etc.

Most commonly, tie layers and LCP layers will be relatively thin compared to the ITP layer(s). Typical constructions are given below, wherein Fluids 1 and 2 represent the fluids involved in the heat transfer: (a) Fluid 1/LCP/ITP/Fluid 2

(b) Fluid l/ITP-l/LCP/ITP-2/Fluid 2

(c) Fluid l/LCP-l/ITP/LCP-2/Fluid 2

(d) Fluid l/ITP-l/LCP-l/ITP-2 LCP-2/Fluid 2

(e) Fluid l/ITP-l/ITP-2/LCP/Fluid 2 (f) Fluid l/LCP-l/ITP-l/ITP-2/LCP-2/Fluid 2

In all of the above constructions, tie layers may be present between all, some or none of the various polymer layers.

Some of the above constructions may be particularly useful in certain situations. If Fluid 1 but not Fluid 2 chemically attacked the ITP, construction (a) may be particularly useful, but (c) and (f) may also be utilized. If both Fluids 1 and 2 attacked the ITP present construction (c) or (f) may be particularly useful. If one wanted to minimize diffusion of one fluid to another, a construction having two LCP layers, such as (c), (d) or (f) could be chosen. If a special surface is required to reduce abrasive damage on the Fluid 1 side, but great stiffness is also required from the ITP, a construction such as (e) could be chosen wherein ITP-1 and ITP-2 have the requisite properties. These and other combinations of layers having the correct properties for various applications will be obvious to the artisan.

Useful LCPs include those described in U.S. Patents 3,991,013, 3,991,014 4,011,199, 4,048,148, 4,075,262, 4,083,829, 4,118,372, 4,122,070, 4,130,545, 4,153,779, 4,159,365, 4,161,470, 4,169,933, 4,184,996, 4,189,549, 4,219,461, 4,232,143, 4,232,144, 4,245,082, 4,256,624, 4,269,965, 4,272,625, 4,370,466, 4,383,105, 4,447,592, 4,522,974, 4,617,369, 4,664,972, 4,684,712, 4,727,129, 4,727,131, 4,728,714, 4,749,769, 4,762,907, 4,778,927, 4,816,555, 4,849,499, 4,851,496, 4,851,497, 4,857,626, 4,864,013, 4,868,278, 4,882,410, 4,923,947, 4,999,416, 5,015,721, 5,015,722, 5,025,082, 5,086,158, 5,102,935, 5,110,896, and 5,143,956, and European Patent Application 356,226. Useful thermotropic LCPs include polyesters, poly(ester-amides), poly(ester-imides), and polyazomethines. Especially useful are LCPs that are polyesters or poly(ester-amides). It is also preferred in these polyesters or poly(ester-amides) that at least about 50 percent, more preferably at least about 75 percent, of the bonds to ester or amide groups, i.e., the free bonds of -C(O)O- and -C(O)NRl- wherein Rl is hydrogen or hydrocarbyl, be to carbon atoms which are part of aromatic rings. Included within the definition herein of an LCP is a blend of 2 or more LCPs or a blend of an LCP with one or more ITPs wherein the LCP is the continuous phase.

Useful ITPs are those that have the requisite properties as described above, and include: polyolefins such as polyethylene and polypropylene; polyesters such as poly(ethylene terephthalate, poly(butylene terephthalate), poly(ethylene 2,6- napthalate), and a polyester from 2,2-bis(4-hydroxyphenyl)propane and a combination of isophthalic and terephthalic acids; styrenics such as polystyrene and copolymers of styrene with (meth)acrylic esters; acrylonitrile-butadiene- styrene thermoplastics; (meth)acrylic polymers including homo- and copolymers of the parent acids, and/or their esters and/or amides; polyacetals such as polymethylene oxide; fully and partially fluoropolymers such as polytetrafluoroethylene, polychlorotrifluoroethylene, poly(tetrafluoroethylene/hexafluoropropylene) copolymers, poly[tetrafluoroethylene/perfluoro(propyl vinyl ether)] copolymers, poly(vinyl fluoride), poly(vinylidene fluoride), and poly(vinyl fluoride/ethylene) copolymers; ionomers such as an ionomer of an ethylene-acrylic acid copolymer; polycarbonates; poly(amide-imides); poly (ester-carbonates); poly(imide-ethers); polymethylpentene; linear polyolefins such as polypropylene; poly(etherketoneketone); polyimides; poly(phenylene sulfide); polymers of cyclic olefins; poly(vinylidene chloride); polysulfones; poly(ether-sulfones); and polyamides such as nylon-6,6 nylon-6, nylon-6,12, nylon-6,12, nylon 4,6, and the polyamides from terephthalic acid and/or isophthalic acid and 1 ,6-hexanediamine and/or 2-methy 1-1,5 -pentanediamine. Polyamides are preferred ITPs and preferred amides are nylon-6,6, nylon-6, and a copolymer of terephthalic acid with 1 ,6-hexandiamine and 2-methyl-l,5-pentanediamine wherein 1 ,6-hexanediamine is about 30 to about 70 mole percent of the total diamine used to prepare the polymer. Especially preferred polyamides are nylon-6,6, nylon-6 and a copolymer of terephthalic acid with 1 ,6-hexandiamine and 2-methyl- 1 ,5 -pentanediamine wherein 1 ,6-hexanediamine is about 50 mole percent of the total diamine used to prepare the polymer. Included within the definition of ITP herein are blends of 2 or more ITPs or blends of one or more ITPs with an LCP provided that the ITP(s) is the continuous phase. One or more (if present) of the ITPs may be toughened. Toughening is known in the art, and may be accomplished by adding one or more of a rubber, functionalized rubber, resin which reacts with the ITP such as an epoxy resin, or other materials. Toughened polyamides are preferred.

The polymers may contain other materials conventionally found in polymers, such as fillers, reinforcing agents, antioxidants, antiozonants, dyes, pigments, etc. An especially useful material is a filler with high heat conductivity, which may increase the efficiency of the heat exchanger.

The composition of a tie layer will depend on which two polymers are on either side of it. For instance the tie layer may be an ITP functionalized or grafted to provide adhesion between the ITP and LCP layers, or may be a blend of one or more ITPs and one or more LCPs.

Typical thicknesses for ITP layers will range from about 0.025 to about 0.25 mm. Typical thicknesses for LCP layers will be about 0.01 to about 0.1 mm. Tie layers will usually be as thin as possible, consistent with their providing adhesion between polymer layers. This is usually about 0.01 to about 0.1 mm. The total thickness of the structure is preferably less than about 0.7 mm, more preferably about 0.12 to about 0.5 mm, and especially preferably about 0.15 mm to about 0.4 mm.

The tubes can be of any diameter and wall thickness, consistent with the need to transfer heat. Typical wall thicknesses are 0.005-0.015 in. (0.13-0.38 mm). In general, a minimum inner diameter of 0.030-0.060" (0.76-1.5 mm) is necessary to avoid pluggage in use. The outer diameter is determined by the internal pressure needs of the tube, generally up to 0.150-0.250 in. (3.8-6.4 mm). The weft can be a multifilament fiber or a monofilament, and could even be a stiff rod to hold the tubes in a more strongly defined sinusoidal shape. Preferred weft material is 0.17 or 0.17 to 0.25 mm diameter polyester, such as DuPont's "Delrin" polyester monofilament, or more broadly 0.1 to 0.4 mm diameter polyester or nylon 66 monofilament or other forms of fiber, including fiberglass roving.

While the plate is essentially flat, some contouring of the plate out of the flat plane may be necessary to improve heat transfer capabilities and manage noise, harshness and vibration characteristics of the heat exchanger in use. Contouring may include staggering the tubes in and out of the flat plane to present a greater surface area to the cooling medium flowing across the plate. This will happen naturally in a woven structure and can be introduced into other processes such as knitting.

Several of these plates are stacked vertically to assemble the heat exchanger; the average distance between these plates in the heat exchanger should be about 2 to 3 times the outside diameter of the tubes.

Fig. 1 shows a tubeplate atl 1 with tubes 12, 13, 14 and 15 held together by weft threads 16, 17 and 18.. Using tubes as the warp, a woven structure is created with a thermoplastic thread as the weft. This latter material could be sacrificial if consolidation occurred via a thermal bonding process, or could provide the consolidation strength itself. The direction of heat exchange fluid outside the tubes is shown at 19, perpendicular to both the tubes and the weft.

Alternatively, the weaving process can provide a shaped plate by forming a sine wave pattern by using a stiffer or more straight-through weft. This is illustrated by Fig. 2 in which tubes 21 , 22, 23 and 24 are constrained in a wave pattern by stiffer weft 25, 26 and 27, like a sine wave, but with the individual adjacent tubes out of phase with each other, as seen in comparing tubes 21 and 22 or tubes 23 with tube 24. This allows the entire tube face to be opened up for more effective exposure to surrounding fluid and provides lots of open space for reduced pressure drop and turbulence. In a heat exchanger, individual plates could be nested into each other for compact spacing.

Claims

CLAIMS:

1. A thermoplastic heat exchanger comprising tube plates to contain a first heat- exchange medium and separate it from a second heat-exchange medium, said first medium circulating inside said tubes and said second medium circulating outside said tubes, wherein the tubes are held together as a warp by a weft which is woven or braided in a direction perpendicular to the tubes and the second medium flows in a direction perpendicular to both the tubes and the weft.

2. The heat exchanger of claim 1 wherein the tubes are woven into a fabric with the tubes as the warp and the fibers or filaments as the weft

3. The heat exchanger of claim 1 wherein the thermoplastic is polyamide.

4. The heat exchanger of claim 2 wherein the tubes in a tube plate are parallel to each other.

5. The heat exchanger of claim 4 wherein the tubes are flat.

6. The heat exchanger of claim 2 wherein the tubes are arranged in a periodically undulating shape, with alternating tubes in the same plate having a curvature opposite the curvature of the adjacent tube.

7. The heat exchanger of claim 6 wherein the weft aids in holding together the shape of the tubes.

8. The heat exchanger of claim 2 wherein the tube plate has a curved shape.