FI93145C - Heat - Google Patents

Description

93145

HEAT EXCHANGE

The invention relates to a heat exchanger using a new, very thin, yet strong heat transfer surface.

Traditionally, heat transfer devices, such as lamellar heat exchangers, have been made of metal, such as stainless steel. Lamellas are made of 1-1.5 mm thick metal plates 10 as heat transfer members for evaporators, for example. Such a structure allows for considerable pressure differences, but on the other hand it is heavy and relatively expensive. If acidic solutions have to be treated, corrosion is a problem, in which case special steel or titanium has to be used as the heat transfer surface material, which considerably increases the cost of the equipment.

Lightweight, corrosion-resistant and cost-effective heat exchangers have been made using a thin plastic film as the heat transfer surface, whereby the heat exchange elements can be, for example, bag-shaped. Such heat exchangers are known, inter alia, from EP 34920 and DE 2511144. However, plastics have the disadvantage of their poor thermal conductivity and poor cheese properties as thin films.

EP 286400 discloses a plate-type heat exchanger in which a heat exchanger element is made by joining two polymer-30 panels with a thickness of 0.12-0.7 mm under the influence of heat and pressure to form flow channels between them. The surface of the second panel is coated with a certain type of material at the desired channel pattern. The facing surface of the second panel is treated with a material 35 that, when combined, adheres to the surface of the first panel from elsewhere except at the flow channels. Most preferably, the polymer is a polyamide that can be coated with a metal foil to improve heat transfer.

The object of the present invention is to eliminate the problems presented above and to provide a heat exchanger suitable for various applications, which is simple to manufacture and whose heat transfer surface conducts heat well and is thin and light, but at the same time strong.

It is essential for the heat exchanger according to the present invention that the heat transfer surface of the heat transfer members is formed of a laminate comprising at least two layers of different materials, a metal foil layer and a plastic layer, and the laminate has a thickness of less than 200 μm and a metal foil layer less than 100 μτα.

The laminate is preferably made by combining a plastic layer with a thin metal foil. The resulting heat transfer surface is light and has a decisively better strength than the metal foil alone. The disadvantage of plastic in heat transfer is small. In addition, the manufacture of a heat exchanger incurs less cost.

The invention will be explained in more detail with reference to the accompanying figure, which shows a preferred embodiment of the invention in which a lamella is formed using larinate as a heat transfer surface, a partial cross-sectional view of which is shown in the figure.

30

According to the figure, the laminate can be formed into a lamella used as a heat transfer member. The laminate 3 to be used consists of a metal foil 1 and a plastic film 2. It is produced by methods known per se, such as by gluing the metal foil and the plastic film to each other or by extruding the plastic to the surface of the metal foil. The lamella 4 is preferably made by attaching two rectangular laminate strips 3 to the opposite edges, for example with an adhesive plow 5 or the like. An opening is left on one side for the supply of heat transfer medium and on the opposite side for its removal. In the laminate strip, the plastic layer can be longer than the metal layer, in which case the outer plastic layers are also connected to each other according to the figure. There is no need for a separate support structure inside the lamella to keep the laminate paths apart. The internal pressure of the sipe 10 is slightly greater than the pressure outside of the laminate to remain tiseinämät-pressure difference due spaced so as to form between the walls of the passageway-lämmönsiirtoai the medium. In addition, the laminates can be joined together by means of point-to-point joints, e.g. by gluing, in order to limit the deformations caused by said pressure in a heat transfer medium, such as steam.

This makes it possible to produce a rigid but flexible heat transfer lamella which is corrosion-resistant, sufficiently strong and strong in structure. For example, it acts as a falling film evaporator so that the condensing steam is introduced into the lamella and the liquid to be evaporated is applied to the outer surface of the lamella. By causing a pressure difference between the heating surfaces, the condensing temperature is made higher than the vapor temperature. In this way, the heat of condensation can be transferred through the laminate wall to the evaporation (the temperature difference T is a function of the pressure difference and the increase in the boiling point of the liquid to be evaporated).

30 The vapor space does not normally need to be protected, but if necessary its surface can be coated, in which case the corrosion protection applies to both the outer and inner surface of the lamella. Protection can be done either with a film or by painting.

35 The lamella shown in the figure has a grain metal inner surface. floor. Naturally, the metal may alternatively be on the outer surface of the lamella.

93145 4

The metal layer of the laminate may contain any known metal or alloy thereof, such as aluminum, brass or copper. The most suitable metal is aluminum due to its low cost. The thickness of the metal foil layer may be very low, but it must nevertheless give the laminate sufficient rigidity. In general, it is sufficient that the thickness of the foil is less than 100 μπ ». More specifically, the thickness depends on the metal used. In the case of aluminum, a thickness of 5-25 μη »is usually sufficient, preferably 10-18 μη».

The laminate is suitable for a wide variety of plastics, the choice of which is influenced by e.g. the purpose of the heat exchanger. The plastic material must have sufficient mechanical strength 15 and corrosion resistance under the operating conditions of the heat exchanger. Preferably, the thickness of the plastic film is also less than 100 μιη. In many cases, suitable plastics are polyester and polyolefins, such as polyethylene and polypropylene, the thickness of the plastic layer being most preferably 12-25 μπ ».

20

Preferably, the total thickness of the laminate is thus less than 200 μη ».

It should be noted that the efficiency of the laminate in heat transfer depends inversely directly on the thickness of the plastic shields, while: * 25 the good thermal conductivity of the metal allows the free use of metal foils of different thicknesses without a measurable decrease in heat transfer efficiency. Thus, the thickness of the plastic layer should be adjusted to give the laminate sufficient strength, but not be unnecessarily thick at the expense of the thermal conductivity of the laminate.

In the manner known per se, heat exchanger packages can be assembled from the lamella according to the figure in units of different sizes for different uses. The lamellae are attached 35 in succession to a support frame to form a lamella cassette.

The desired number of cartridges is placed inside the same jacket as an evaporator.

5 93145

The use of at least two laminates resulting from combining different materials for the control of evaporators has been described above, but the use of the laminate is not limited to this, but can also be used as a heat transfer surface 5 in many other applications, such as heat transfer between two liquids.

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Claims (6)

A heat exchanger provided with disc-shaped heat transfer means, characterized in that the heat transfer surface of the heat transfer device is formed of laminates consisting of at least two layers, a metal foil layer and a plastic layer, and that the thickness of the laminate and metal thickness is below 200 / below 100 μπι. 10 Heat exchanger according to claim 1, characterized in that said metal foil is an aluminum foil. Heat exchanger according to claim 1, characterized in that the thickness of the plastic layer is below 100 μπι. 15 Heat exchanger according to claim 2, characterized in that the thickness of the metal foil layer is 5 - 25 μπι. Heat exchanger according to claim 4, characterized in that the thickness of the metal foil layer is 9 - 18 μπι. Heat exchanger according to claim 1, characterized in that the heat exchange means are slats which form a fall film inducer. 25