Storage material for heat transfer

Details Storage material for heat transfer Storage material for heat transfer

1985-03-22

1986-03-25

Davis, Jr., Albert W.

Heat exchange

Regenerator

Heat collector

165905, F28D 1702, F28D 1904

Patent

active

045776784

DESCRIPTION:

BRIEF SUMMARY
The invention relates to a storage material for the transfer of heat between gas streams in heat exchangers, composed of stick-like profiled spacing elements and a plurality of plate-like molded elements serving as storage elements made of heat-resistant plastic, which are assembled into storage blocks.
Such a storage material is known from German publication DE-A No. 32 07 213. In it, the stick-like profiled spacing elements and the heat-storing, plate-like molded elements are made from polyphenylene oxide or a copolymer of polyphenylene oxide and polystyrene, or from polyblends of polyphenylene oxide and polystyrene.
On the other hand, it is the object of the invention further to improve the long-term stability of the storage material while simultaneously achieving a higher temperature level. Moreover, the preparation of the storage material from the plate-like and stick-like molded elements is to be facilitated.
Setting out from a storage material of the kind mentioned above, this object is achieved by making the molded elements from polyetherimide. Imides of high molecular weight are known in the plastics art mainly as heat-resistant thermosets. By the incorporation of imides of high thermal stability and strength into amorphous polyethers by means of ether bonds, i.e., compounds of higher molecular weight having numerous ether bonds, polyetherimides are now available which have thermoplastic properties, i.e., they are easy to form into molded elements on account of their good rheological qualities and melt stability, and can be fabricated by all methods commonly used with thermoplastics. Thus, both injection-molding and extrusion methods can be used for making them into stick-like and plate-like molded elements. Due to the high thermal stability, the mass temperatures are to be selected between 340.degree. and 425.degree. C., preferably around 400.degree. C. Care must be taken only to see that heated tools are used for fabrication whose surface has a temperature between 70.degree. and 170.degree. C., preferably around 95.degree. C. By selecting optimum fabricating temperatures, optimum properties are obtained in the finished molded elements on account of the better rheological characteristics of the material, such as for example high strength in the flow seams and high resistance to heat and chemicals, combined with optimum cycle times despite the amorphous material.
The joining of the stick-like spacing elements and of the plate-like heat-storing elements can then be performed, as in the known storage material, by ultrasonic welding, transitions in the form of studs of triangular cross section, for example, being provided in the areas to be joined so as to give a particularly great strength to the bond after the ultrasonic welding.
Alternatively, the molded elements can also be joined to one another to form storage blocks by cementing, and this refers both to joining the molded elements by an adhesive cementing using cements on the basis of polyurethane, silicone, nonaminic epoxy resins or polyamide hot-melt adhesives, and to joining by means of diffusion cementing using a solvent for polyetherimide, preferably methylene chloride in concentration of 1% to 5%. In the latter case, the parts to be joined are softened by the solvent in the area of the junction, and these surfaces are bonded together under pressure. After the solvent evaporates, a virtually monolithic bonding of the molded elements is achieved, i.e., no foreign matter having material properties different from those of the molded elements is left in the seam. To join by cementing, the areas to be joined are to be fitted accurately to one another, and before they are cemented they must be cleansed thoroughly of grease, oil and dust; isopropyl alcohol is suitable for this purpose. In all cementing processes, furthermore, the application of pressure for a certain length of time after joining is important to the integrity of the bond.
Independently of such cementing of the profile elements, or in addition to such cementing, it is desirable, on

REFERENCES:
patent: 2706109 (1955-04-01), Odman
patent: 4114597 (1978-09-01), Erb

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