Glass manufacturing – Processes – Fusion bonding of glass to a formed part
Patent
1994-09-08
1998-11-03
Ford, John K.
Glass manufacturing
Processes
Fusion bonding of glass to a formed part
165165, 165166, F28D 900, F28F 308
Patent
active
058295135
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a tubeless heat exchanger for transferring heat between two gasflow paths.
STATE OF THE ART
Heat exchangers for transferring heat between two isolated gas-flow paths have developed along different lines from liquid heat exchangers. This has resulted from the fact that gas, unlike a liquid, is incompressible and has a lower heat content per unit volume than a liquid. This has led to the development of heat exchangers in which the gas-flow paths have a large cross-sectional area so that there is an insignificant pressure drop between the gas inlet and outlet apertures of the heat exchanger. Also, thin materials are preferred because the transfer of heat from a gas to a surface along which it is travelling, takes place more slowly than is the case with a liquid which wets the surface.
The conventional form of heat exchanger for use with gases is the parallel plate heat exchanger. This comprises a stack of spaced, parallel metal plates which define, between them, pockets through which the gas flows. Alternate pockets are connected to carry one of the two gas streams between which heat is to be transferred, and the remaining pockets carry the other gas stream.
In order to extend the dwell time of the gases in the heat exchanger, it has been proposed to provide metal baffles in the pockets which extend the length of the gas-flow path through them and are in good thermal contact with the plates. Such an arrangement is disclosed in the Applicant's U.S. Pat. No. 5,078,208. This Patents discloses the feature of providing the parallel plates from a sinuously wound metal foil successive spaced areas of which provide the parallel spaced plates. It has also been proposed in the said Patent to use metal spacers between rectangular plates of a heat exchanger and which are shaped to produce counterflow passages in successive pockets so that the heat exchange efficiency is enhanced (see said Patent, column 8, between lines 36 and 55). Amongst other Patents disclosing the use of a sinuously wound metal strip are U.S. Pat. Nos. 4,131,159 and 4,343,355.
Recent developments in heat-conductive plastics have created interest in the use of plastics materials in place of metals in heat exchangers. Plastics sheeting can be made thinner than metal sheeting so that the reduced heat-transfer co-efficient of the plastics is offset by its reduced thickness. Also, pressing thin metal sheets into different shapes, which is normal practice for creating turbidity in the pockets of a heat exchanger, can result in stress creases and other problems occurring which make the construction of a heat exchanger from thin metal sheeting more difficult. Plastics on the other hand can be moulded without the formation of stress creases and is also capable of being vacuum-formed and hot-pressed into virtually any contour required, while being capable of being securely attached to a supporting frame at room temperature by the use of resinous cement.
Patent Specifications suggesting the use of plastics in the construction of heat exchangers are U.S. Pat. Nos. 4, 631,213; 4,907,648 and 5, 050671. These three U.S. Patents and other proposals which have come to the Applicant's attention, suggest the use of plastics materials in heat exchangers as substitutes for components which previously were made of metal. Where such proposals have involved the use of plastics baffles in parallel pockets of the heat exchanger, such baffles have been held in place by being rigidly and continuously attached along one edge to one plastics plate of a parallel plate heat exchanger, built up by stacking such plates one above the other. Obviously, it is not practical to use such a technique with a sinuously wound strip of plastics, as the formation of such a strip with the baffles walls projecting from one face, would pose formidable manufacturing problems . Also, the thickness of the plastics sheet necessary to support the baffle edgewise on its surface is naturally large and consequently stiff and the heat transfer quality of
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