This invention relates to a heat exchanger construction. More specifically, this invention relates to a plate-fin heat exchanger core including means for strengthening the core and for protecting the peripheral edges thereof against thermal stress failure.
Heat exchangers in general are well known in the prior art, and typically comprise a heat exchanger core having dual fluid flow paths for passage of two fluids in heat exchange relation with each other without intermixing. The fluid flow paths commonly comprise a plurality of relatively small and/or intricately shaped passages formed within a heat exchanger core so as to maximize the available core surface area for absorbing and transferring heat from one fluid to another.
In the prior art, plate-fin heat exchangers have become popular largely because of their simplicity of fabrication and ease of assembly. Such plate-fin heat exchangers comprise a core formed by a stacked series of thin plates connected together in a spaced relationship so as to provide fluid flow regions between the plates. Extended surface fin elements are interposed between the plates to form a multiplicity of relatively small fluid flow paths within the flow regions, and to increase the available surface area for absorbing and transferring heat. Suitable manifolds supply the two fluids to the heat exchanger for flow through the flow paths in the core without intermixing.
A common problem with plate-fin heat exchangers comprises stress failure of the thin plates, particularly at their outer, peripheral edges. More specifically, the heat exchanger experiences substantial thermal gradients and stresses upon start-up and/or shut down, and these thermal gradients are particularly pronounced at the peripheral edges of the core. The thermal gradients result in substantial expansion or contraction of the thin core-forming plates which all too frequently causes the plates to crack or separate. Such cracking or separation of the plates allows undesirable leaking and intermixing of the fluids, and thereby shortens the useful life of the heat exchanger.
Another common problem with plate-fin heat exchangers comprises so-called creep failure of the relatively thin core-forming plates. That is, during sustained thermal loading at operating temperatures, the thin plates experience a relatively slight and random stretching and contracting known as creep. This slight creeping of the plates with respect to each other contributes to eventual cracking or separating of the plates, particularly at the peripheral plate edges.
Some prior art heat exchangers have included devices for protecting the peripheral edges of the plates in a plate-fin heat exchanger. In one arrangement, these protective devices have comprised outwardly projecting fins which are primarily intended to protect the plates against damage from erosion or contact with foreign objects. See, for example, British Pat. No. 585,192. Other protective devices have included plate-like shields for shielding the plates against high temperature radiant heat energy. See, for example, U.S. Pat. Nos. 370,865; 2,093,686; 3,150,714. Still other prior art techniques have involved the attachment of fin-like elements to designated areas exposed to high heat. See, for example, German Pat. No. 1,122,080. However, none of these prior art techniques satisfactorily resolve the problems of stress failures resulting primarily from the substantial thermal gradients experienced at the peripheral edges of a plate-fin heat exchanger.
The present invention overcomes the problems and disadvantages of the prior art by providing an improved heat exchanger construction including appropriately sized masses mounted at the peripheral edges of the core-forming plates in a plate-fin heat exchanger for controlling expansion and contraction of the plates so as to reduce stress failures.