Heat exchange – Flow passages for two confined fluids – Interdigitated plural first and plural second fluid passages
Patent
1996-11-04
1998-09-15
Leo, Leonard R.
Heat exchange
Flow passages for two confined fluids
Interdigitated plural first and plural second fluid passages
165167, F28F 308
Patent
active
058065849
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
This invention relates to a plate-type heat exchanger made up of a stack of corrugated plates delimiting channels of variable section.
Corrugations have the general purpose of disturbing the flow of fluids to increase the heat transfers through the plates, but they have the drawback of making the pressure drops much larger than with flat plates. An earlier French patent (FR-A-2 648 220) described a particular form of corrugated plate which made it possible to reduce the volume of dead or recirculation zones in which the fluid stagnates substantially, which is one of the main causes of losses in heat exchange efficiency and the fouling of plates if the fluid is charged with particles, because they then deposit much more easily. The plates of that earlier invention had facets of two alternately different lengths and were assembled together such that the corrugations of the consecutive plates formed angles of preference of nearly 180.degree. C., i.e. such that, in each channel, the long facets were oriented substantially in the same direction corresponding to the direction of fluid flow in the channel: the short facets thus faced the fluid and, owing to their steeper slope, deviated it strongly towards the long facets of the other plate delimiting the channel. The result was that the fluid stream licked the long facets over a large part of their surface, and the recirculation zones which formed behind the corrugations which restricted the channel, namely in front of the long facets, were reduced as a consequence. One thus obtained better heat exchange performance as well as easier flow.
The objectives assigned to that invention were thus met, but certain drawbacks may be found to such a configuration of plates. First of all, the corrugations composed of a long facet and a short facet have, for the same pitch (the pitch designating the width of the corrugation), a smaller height than the corrugations of a conventional corrugated plate composed of two similar facets. In other words, the channels have a smaller average section. In practice, it is however desirable not to reduce this section, thus requiring the use of plates of similar shape but with larger corrugations having a larger pitch. The lines of corrugations then have a larger spacing and the number of contact points between the plates is smaller, thus reducing the mechanical strength of the stack.
Another drawback stems from the fact that the beneficial effect is obtained only for one direction of fluid flow in each channel, alternating in adjacent channels, thus imposing countercurrent circulation of fluids which is not always desired. Finally, if pressure drops are lower than with conventional corrugated plates, they remain significant.
The present invention may be regarded as an improvement of the earlier invention, because it offers substantially equivalent advantages as concerns the heat exchange performance and the reduced fouling of the walls of the plates, but also substantially smaller pressure drops by the reduction of vortex movements, while still involving the same number of contact points between plates as ordinary corrugated plates. In its best embodiments, the invention also lends itself to similar flows of fluids in both directions, thus allowing the free choice of parallel current flows as well as counterflows.
The invention relates, in its most general form, to a heat exchanger composed of corrugated plates placed side by side to delimit channels, the plates being similar, composed of facets joined by bottom and top lines, with the plates joined to each other at contact points, characterized in that the plates are alternately turned over and joined either through their top lines or through their bottom lines, and in that the facets include bosses near the top lines and hollows near the bottom lines.
This thus provides an arrangement in which the corrugations are flattened and squeeze the section of the channels near the contact points of the corrugations, thanks to this combination of hollows and bosses as described and t
REFERENCES:
patent: 2550339 (1951-04-01), Ehrman
patent: 3661203 (1972-05-01), Mesher
patent: 4014385 (1977-03-01), Wright
patent: 4563314 (1986-01-01), Ernst et al.
patent: 4668443 (1987-05-01), Rye
Grillot Jean-Michel
Roussel Claude
Thonon Bernard
Vidil Roland
Commissariat a l''Energie Atomique
Leo Leonard R.
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