US2696976A - Element set for air preheaters - Google Patents

Description

Dec. 14, 1954 G. K. w. BOESTAD ETAL 2,696,975

ELEMENT SET FOR AIR PREHEATERS Filed May 17, 1950 a 3 Sheets-Sheet 1 A INV'ENTORK s 7 AV 1 5 ifii' ATroRNl-zv 14, 1954 e. K. w. BOESTAD ETAL 2,595,976

ELEMENT SET FOR AIR PREHEATERS F iled May 17, 1950 I 3 Sheets-Sheet 2 T211215 Tll:'.5. ."i

Dec. 14, 1954 G. K. w. BOESTAD ETAL 2,696,976

ELEMENT SET FOR AIR PREHEATERS Filed May 17, 1950 3 Sheets-Sheet 3 l I I I A ATTORNEY 2,696,976' ELEMENT SET FOR AIR PREHEATERS Gustav K. W. Boestad, Lidingo, and --Knrt S'v'en'ningson, Johanneshof, Sweden, assignors, by mesne assignments,

to Jarvis C. Marble, New York, N. Y., Leslie Merrill, Westfield, N. 1., and Prcy H. Batten, Racine, Wis., trustees Application May 17, 1950; Serial'No. 162,524 Claims priority, application Sweden Jnne 22, 1949 13 Claims. (c1; 257-6) The present invention relates to element plates forheat exchangers of the regenerative type in which, as is known,

the heat emitting and heat absorbing media alternately flow through the channels between the suitably arranged plates in an element set which thereby is alternately heated and cooled. The rotating Ljungstrem-preheatei may be mentioned as a typical example of a" heatexchanger of the regenerative type.

In order to obtain the best possible result from lth 'ei.

viewpoint of heat economy, the heat transfer between gas and element plate should be as high as possiblewhileatthe same time maintaining a minimumpressured'ro'p'of.

thegases through the channel and'also maintaining the cost of the plate structure and its assembly. at aminimumu The possibility of blowing the plate surfaces free from soot and the like by means of air-or steam jets .isalso of importance for the desig'n'of the channels between the plates and thusfor the design of the'plates' themselves.

Furthermore, said plates should also be of such construc-;

tion that they are soiled as little as possible by flue gas particles.

A conventionalembodiment'of element plates is'. dis closed in U. S. Patent No'. 2,023,965. According to that patent the plates in the elementset are' 'made alternately as corrugated and ridged plates. Between each pairof plates channels are formed which ar'e completely separated from the other channels'which are formed between the same adjacent pair of plates.

The corrugations or undulations in the plates have for their object the deflection of the main gas current so that in each channel, defined between two distance ridges, there are formed laterally directed secondary eddies whereby the heat exchange is improved. However, this improvement of the heat exchange evidently is due not only to the creation of secondary eddies but also due to the fact that the boundary layer formed along each plate surface at the passage of the gas is agitated. The more effectively this boundary layer is interrupted or agitated in some other way and the more often the gaseous medium impinges the plate surfaces, the more effective becomes the heat exchange. Therefore, the invention has for its object a novel plate construction for element sets for heat exchangers of the kind mentioned, through which this purpose is satisfied to a very great extent.

For this purpose, the element set according to the invention is substantially characterized in that it contains plates which are provided with slits and which are deformed between the slits in such a manner that each plate surface becomes composed of a number of surface portions partially separated from each other by means of slits or spaces and deviating from the base plane of the plate.

In order to reduce the heat conduction in the plate material itself from hot to colder portions, it has previously been suggested to provide the plate with a number of narrow apertures or spaces formed by means of punching operations carried on the plate material. This way of proceeding is only of importance if the plate thickness is great in relation to the channel length, because the efficiency of the heat exchanger without said apertures would be reduced due to the heat flow in the plate proper.

Thus, the invention is substantially characterized in that the element plates consist of surface portions displaced in different directions relative to each other and tit partially separated from each other by spaces. By this means, favourable conditions arepreated for the; heat transmission as the bondary layeralongthe plate surfaces isbrokenudown and destroyed before/ it reaches the nextplate' strip and the eddies vthus formech in combination with the repeated impingement against the following:

plate edges, acts to increase the heat transmission to a higher extent than that corresponding to the increase in pressure drop.

The invention will be described hereinaftenmore in.

detail with-reference to the accompanying. dr'awings in which some suitable embodiments are shown by way: of m l In the drawings Fig. 1 is an elevationof a structure embodying the invention;

v Figs- 2 and 3 are sectionstaken on lines 2"2 and"3 -3 of 1 respectively; I I T Fig. 4 is a modified form of the structure shown in Fig. 1; Y

Fig, Sis aview similar to Fig. 1 of another structure embodying the invention; v

Figs. 6-7 are sections indicated on the lines 66 and 7'7 respectively of Fig.5; v

Fig. 8 is a view similar to Fig. 1,,of'still another form of structure embodying the invention;

Figs. 8a and 9 are sections taken on thelines 8 a-8a and 9 9 respectively of Fig. 8';

Fig...l0 is a. section of amodification of the structure shownin Fig; 8'; t v.

Fig., 1 1 is a" view similar. to Fig. lshowingstill another form of structure embodying the invention; p

lla'is a section taken on the line 11a11a of Fig. 12 is a View similar to Fig.1 showing still another structure embodying the invention;

. F'g. 12a is a section taken on the line 12tl-12t1 of Fig; .13; v

Fig; 13 is a'sec'tion on the line 13-13 of Fig. 12;. Fig'.. 141is a section showing a modified form of the structure illustrated in Fig. 12;

Fig. 15 is a view similar to Fig. 1;

Figs. 15a; and.16 are sections taken on lines 15a15a ahd."16 16 respectively of Fig. 15;

Fig. 17'isa'v1ew similar to Fig. 1 showing still another structure embodying the invention; and

Fig. 18 is a section taken on the line 18-18 of Fig. 17.

In Figs. 1 to 3, the reference numeral 10 designates an element plate provided with pressed-up straight ridges 12 which serve as distance elements between the different plates and at the same time create straight flow passages 14 for the gas. Between the ridges 12 the plates are cut as indicated at 16, and the surface portions 18 thus obtained are pressed out to oblique position as is clearly seen from Figs. 2 and 3. In usual cases the pressing should be carried out so that not more than at least one-half of the channel width, that is, the distance between two element plates is free from the oblique surface portions 18. g The ridges 12 are of the usual design but they may also be designed in another manner. The smooth plate 20 shown in Fig. 3 constitutes part of the casing of a heat exchanger and encloses the element plates 10 proper.

Fig. 4 shows plates 10 of the same design as that of Figs. 1 to 3, but in this case every second plate 10a is placed up and down with respect to the position of the pressed-out surface portions 18 and preferably turned in such a manner that the surface portions between two adjacent plates form an angle to each other instead of running parallel in the same direction.

The element plate shown in Figs. 5 to 7 is ridged and slit in the same manner as in the previous embodiments, but the surface portions 18 are displaced in parallel relative to each other instead of obliquely positioned, so that every second strip or surface portion 18 has been pressed out or that all of them have been displaced alternatingly in opposite directions.

From the viewpoint of solidity and in order to further increase the heat transmission, it is advantageous to press the surface portions in vaulted or bent form as shown in the two similar embodiments according to Figs. 8 and 9, or Fig. 10, or according to the two alternatives in Figs. 12, 13 and 14.

The surface portions need not necessarily be formed by means of slits 16 situated at right angles to the ridges 12, but the slits may also be positioned obliquely, as will be clearly seen from Fig. 11.

The ridges 12 may also be slit and deformed in the same manner as the surface portions 18, the heat transition being improved because the whole element plate is effectively utilized according to the principles of the invention. Such an embodiment is shown by way of example in Figs. 15 and 16.

According to another embodiment of the invention the surface portions may in connection with the cutting, or subsequently, be pressed out from the original plate surface to yoke shape and thereby at the same time serve as distance ridges. An embodiment according to this principle is clear from Figs. 17 and 18. A plane plate without ridges is divided into groups of slits 16 of suitable length, between which slits remaining parts 22 of the plate 10 serve to hold the surface portions 18 together which are bending back upon themselves in such a manner that the element plate has the aspect shown in Fig. 18. The element plates shaped according to this embodiment may either rest directly on each other, or special plane or slightly corrugated plates 24 may be inserted between the element plates according to Fig. 18, in which last-mentioned case the pitch indicated need not be maintained.

We claim:

1. A pack of elements for heat exchangers comprising a plurality of juxtaposed plates providing between them a plurality of parallel channels for flow of gaseous heat exchanging medium in paths of flow generally parallel with the plates, the plates forming at least one of the side walls of each of the channels being slit at a plurality of spaced places along the length of the channel and at an angle to its length and the portions of the plates between said slits being bent out of the planes of the plates to extend generally lengthwise of the channels.

2. A structure as defined in claim 1 in which the slit plates include spaced parallel distance ridges engaging adjacent plates to form relatively wide and shallow channels between the adjacent plates and the slits extend across substantially the entire distance between adjacent ridges.

3. A structure as defined in claim 1 in which each of the opposite sides of the respective channels is formed by a slit plate.

4. A structure as defined in claim 2 in which the bent out portions are inclined at an acute angle with respect to the planes of the plates.

5. A structure as defined in claim 4 in which the bent out portions are in the form of shallow arches considered in the direction of gas flow through the channels.

6. A structure as defined in claim 4 in which the bent out portions are sinuous considered in the direction of gas flow through the channels.

7. A structure as defined in claim 2 in which the major parts of the bent out portions are parallel to the planes of the plates and offset therefrom by a distance less than the height of said ridges.

8. A structure as defined in claim 7 in which alternate bent out portions along the length of an individual plate extend from opposite sides of the plane of the plate of which they form a part.

9. A structure as defined in claim 8 in which the distance ridges are also slit at a plurality of spaced places along the length of the channels, the portions of the distance ridges between the slits being bent out alternately from opposite sides of the plate.

10. A structure as defined in claim 2 on which the slits are oblique with respect to the lengths of the channels.

11. A structure as defined in claim 1 in which the bent out portions are yoke shaped to provide rows of distance elements for engaging and spacing adjacent plates.

12. A structure as defined in claim 11 in which alternate bent out portions of individual rows project from opposite sides of the plane of the plate.

13. A structure as defined in claim 12 in which the pack 'comprises alternating slit and imperforate plates.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,762,446 Ljungstrom June 10, 1930 2,023,965 Lysholm Dec. 10, 1935 2,227,836 Linderoth Jan. 7, 1941 FOREIGN PATENTS Number Country Date 67,903 Norway June 5, 1944 512,265 Great Britain Aug. 31, 1939

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