US2505774A - Multifluid heat exchange passage construction - Google Patents

Description

y 1950 v s HOLM EI'AL 2,505,774

MUL'IIFLUID HEAT EXCHANGE PASSAGE QONSTRUCTION Filed April 16, 1947 2 Sheets-Sheet 1 mmaqzu r I j SVEIV HOl M End PER .H/L MEI? 6719155 0/\/ IN VENTOR5 Patented May 2, 1950 UNITED" "PATENT, OFFICE m'rrrwm m-zA'r ExcnANcn PASSAGE coNs'rauc'rroN Application April 1c, 1941, Serial No. wars The present invention relates to heat exchange apparatus and particularly to apparatus in which heat is transferred between several streams of fluid and wherein two fluids flowing through contiguous passages in heat transfer relationship are periodically switched so that each fluid flows for a time through a passage previously traversed by the other.

In an application filed in our names on November 3, 1944, under Serial No. 561,766 we disclosed multi-fluid heat exchangers of the plate type through the passages of which one fluid is circulated to be cooled by indirect contact with two other fluids. One use contemplated for the apparatus is to cool air to very low temperatures using oxygen and nitrogen both at temperatures substantially below F. The air entering at a temperature around 100 F. carries a certain amount of water vapor which sublimes to ice at low temperatures. To dispose of the ice it is necessary to periodically transpose the air and nitrogen streams so that the nitrogen're-evaporates the ice deposited from the air. The apparatus, therefore, works in two cycles, each of which must give the same performance as to heat exchange between the nitrogen and air and a uniform pressure drop must be maintained in the passages for these gases. The oxygen enters the apparatus at a lower temperature than'the nitrogen but is required to leave at the same temperature and, therefore, receives heat from both the air and the nitrogen.

A feature of the invention is a heat exchanger construction in which two of the streams of fluid may be switched or transposed with respect to their relation to each other while maintaining the rate of heat transfer between nitrogen and air and without changing the pressure drop through the exchanger for any fluid.

The invention will be best understood upon consideration of the following detailed description of illustrative embodiments thereof when considered in conjunction with the accompanying drawings in which:

Figure 1 is a vertical sectional elevation of a heat exchanger embodying the invention in apparatus having a series of concentric annular passages;

Figure 2 is a transverse sectional view of a heat exchanger having two groups of passages in place of the single group in Figure 1 illustrating the connection of inlet and outlet duets with the passages of the exchanger.

Figure 3 is an enlarged sectional viewon line 33 in Figure 1, illustrating contiguous passages 2 Claims. (Cl. 257-246) 2 V for the flow of two fluids with extended surface in the form of fins internal with their common intermediate wall arranged to maintain the same heat transfer relationships when either fluid is switched to flow through the passage for the, other;

Figure 4 is a further enlarged view of fragmentary portions of two of the contiguous fluid passages;

Figure 5 is a diagrammatic view of a heat exchanger embodying the invention and showing the relation of its inlet and outlet connections to the supply and discharge ducts for the various fluids.

In Figure 1 the four concentric wall members II, I2, I! and I4 define a pair of adjacent annular passages i5, i8 extending from end to end of the apparatus outwardly of a channel l1. Additional groups of passages may be provided to increase the capacity of the apparatus as illustrated in Fig. 2 showing two groups each made up of three concentric passages and Fig. 3 showing three groups. One of the cooling fluids (oxygen) enters thechannels I! through an inlet connection is at one end of the apparatus and is discharged from the opposite end of the exchanger through an outlet connection 20.

At the upper end of the apparatus air to be cooled enters on the left hand side through an inlet connection 2| which communicates with the outermost annular passage l5 and by a sleeve 22 penetrating the second and third annuli with the fourth annulus I5A and every third annulus thereafter, as the seventh in Fig. 3. At the lower amid the apparatus the outlet connection 2| for air communicates in like manner with the lower ends of the first, fourth and seventh annuli IE, ISA, I53 etc.

The cold nitrogen enters the bottom of the apparatus at the left hand side through an inlet connection which extends toward the center of the apparatus and pierces the oxygen and air annuli ii, I'I where necessary but communicates only with the second, fifth and eighth, i. e. annuli I8, I 6A, IIB, every third annulus counting from the second. At the upper right hand side of the apparatus the nitrogen is discharged through a subdivided. if desired. as disclosed in the parent application. As described herein, the central space is beyond the innermost annulus is not utilized as a heat exchange passage.

Fundamentally the apparatus comprises a plurality of adjacent parallel fluid passages. In the form described these are in groups of three concentric annuli. It may be noted that it no special provisions were made and the air. were to flow in the entire outer annulus I in cycle I and then in the intermediate annulus IS in cycle 11, it is evident that the air would be cooled to a much lower temperature in cycle II, where it would flow between the cold oxygen in channel I1 and the cold nitrogen in passage I5. The discrepancies in the diameters of the annuli could also result in a difference in pressure drop due to dif- Ierence in mass velocity. In switching the fiuids in the inner groups of annulae the air would be in channels ISA and IGB in cycle II with cool nitrogen in channels ISA, I513 and cool oxygen in channels I1, "A so that the air would remain between relatively cooler fluids; but the heat exchange conditions between air and nitrogen would not be the same in both cycles because oi the difierent areas and gas swept wall surfaces in the sets of annular passages.

In accordance with the invention the air and nitrogen streams flow in contiguous passages (shown as annular) whose heat transfer relationships and the total flow area for each of the two gases is the same in both cycles so that the apparatus is balanced as to heat exchange relationship between air and nitrogen in the two cycles. This is so because the relations that exist between an air passage I5 and a nitrogen passage IS in one cycle have their counterparts in the second cycle as between a passage I6 used for air and a passage i5 used for nitrogen, as a result of constructing the apparatus so that the hydraulic diameters of contiguous passages as I5,

I6 and ISA, IBA are the same despite differences in diameter due to their concentricity. Heat is also exchanged at the same rate between these two gases in either cycle.

The air and nitrogen flow through the apparatus in substantially greater amount than the oxygen; therefore, extended surfaces in the form of fins ill, 42, MA, MA, MB, and 423; project from the walls I2, I2A and 52B between annulae I5, I8, I5A, ISA, I513, IBB into the passages for these gases. The hydraulic diameter of the channels between fins must be the same for air as for nitrogen because the pressure drop increases inversely as the hydraulic diameter. l br pressure drop, the hydraulic diameter (also called equivalent diameter) is defined as equal ,to our times the area of channel divided by the circumference. In heat transfer the hydraulic diameter of a passage depends on what portion oi. its perimeter is efiective as heat transfer surface,

and is defined as four times the cross-sectional area divided by the portion of perimeter through which heat exchange takes place. The walls II and I2; I2 and I3; I4 and A and HA etc. are therefore spaced radially at such distances that the hydraulic diameters of any two contiguous annuli for air and nitrogen such as I5 IE or ISA, ISA etc. (Fig. 2) are the same. This applies also to Fig. 3 wherein the passages ISA and IGB are made of greater radial width than passages ISA and I5B to obtain the same area for flow in the contiguous annuli of each pair and the same hydraulic diameter of passages between the fins in these passages. For the same reason the fins are be considered to illustrate the space between walls such as Ii and I3, I4 and ISA etc. divided into the two contiguous passages I5, It by a double comb-like annular member 40 of which wall I2 is a part. The fins ll in passage it are of greater length than the fins 42 in passage is and the member 40 is positioned oil center in the space between walls I I and I3 so that the overall area (A) of passage I8 is greater than that (A) for passage IS in order to maintain the same ratio between the area A of passage I6 and its periphery 43, 45, ll, 49 (Fig. 4) as between the smaller area A of passage I5 and the smaller periphery M, 48. 48 in such manner as to preserve the ratio:

Thus, wall I2, for example is not midway between walls II and I3 inasmuch as to preserve the ratios desired the fins H are not only longer than fins 42 but their distal ends are spaced further (at El) from the opposite wall I3 of the passage I6 in which they are located than the fins 42 are (at 52) from wall II of passage I. It is therefore evident that by equalizing flow areas in contiguous pairs 01' annulae the two heat exchange cycles between nitrogen and air in these passages are equal, whereas if the streams were to occupy entire concentric annulae of equal width the two cycles would not be equal because the areas and perimeters would not produce equivalent diameters." For passage I5, I6 the heat loss from the outside through insulation (not shown) has the same effect on temperature of nitrogen and air in both cycles since both of these gases contact the same portion of outside shell I I in both cycles.

In Fig. 5 the fins 53 in passage I6 are staggered with respect to the fins 54 in passage I! so as to increase the elastic stability of wall I2 under high pressure.

There is complete balance of the heat transfer relation of the several fluids because the streams of nitrogen and air, respectively, are always in passages of equivalent diameter at opposite sides of an intervening wall I2, I'2A etc. while the owgen flowing through the channels I'I, IIA always has a stream of air at one side and of nitrogen at the other. In Fig. 2 the air is in the passage ISA inwardly of the channel I! through which the oxygen flows and the nitrogen is in the outer passage section I6. The relation is reversed in the following cycle where the nitrogen is in the inner passage ISA and the air is in the outer passage IS. When the air is caused to fiow through channels previously filled with nitrogen and vice versa, the respective positions of these fluids with respect to oxygen are changed but the heat transfer relationships remain the same. With apparatus having several groups of passages each of which comprises 3 passages as in Figures 2 and 3, the streams of oxygen in both cycles are between a stream of nitrogen and a stream of air regardless of which of the latter is on the inner or outer side of the oxygen and the slight differences of temperature between the nitrogen and air streams does not materially alter the heat transfer relationship because of the much smaller amount of oxygen. Although air in the outside annular passage 15 and nitrogen in the inner passage ISA (Figure 2) sweep in one cycle against walls ii and 13A respectively which are not heat transfer surfaces, the air and gas streams are in reversed relation in the second cycle and any discrepancy in heat transfer efilciency is so slight, for all practical purposes, that it is inconsequential. Moreover, when several heat exchangers, even those having only one group of three passages as in Fig. 1, are employed in parallel or series connection in the manner dis- "I as indicated in Fig. 5, all of the valves 50 to 53 are open when air flows through the passage sections 15, ISA, Fig. 2 (and also I513, Fig. 3) in the first cycle and nitrogen flows through the sections IE, ISA, HB while all the valves 55 to 56 are closed. Conversely, in the second cycle all ,1 of the valves 55 to 58 are open when the nitrogen is to flow through the annular sections I 6, 16A, "5B. The relative counter current relation of the flow of air to nitrogen and oxygen is maintained in both cycles as the directions of flow are not changed.

The invention described above embodies the generic principle of cooling (or heating) one fluid by means of two others while providing for transposing all the relations of the treated fluid and one of the treating fluids due to the requirements of a process. Likewise, it is possible to preserve the same heat exchange relationship among the fluids passing through the heat exchanger and maintain the same pressure drop through the various passages in each cycle of operation.

What we claim is:

1. In a heat exchanger for gaseous media;

means forming a pair of contiguous, concentric passages including a common intervening wall provided with radial fins extending into both passages to points short of the opposite walls bounding the latter with the fins in the inner passage that has the smaller radius being of greater length and having their distal ends further from the opposite wall of said passage than the corresponding iins in the outer passage of larger radius so as to maintain the same ratio of flow area to gas swept surface in the inner passage as in the outer.

2. In a heat exchanger for gaseous media; means forming a pair of contiguous parallel passages including a non-centrally located common intervening wall provided with fins extending into both passages to points short of the opposite walls bounding the latter with the fins in the passage that has the greater width being of great er length and having their distal ends located further from the opposite wall of said passage than corresponding fins in the adjacent passage of narrower width so as to maintain the same ratio of flow area to gas swept surface in both passages.

SVEN HDLM. PER HIIMER KARL-$80M.

REFERENCES man The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 448,521 Horner Mar. 17, 1891 1,615,658 Shipman Jan. 25. 192? 2,362,571 McCollum Nov. 14, 194i FOREIGN PATENTS Number Country Date 4,832 Great Britain Mar. 2, 1903 20,175 Great Britain Sept. 19, 1903 469,943 Great Britain Aug. 3 1937 538,391 Great Britain July 31, 1941 OTHER REFERENCE "Heat Transmission" by William H. McAdams, 2nd edition. 1942 McGraw-Hill Book Co. N. Y.

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