US2049748A - Heat exchanger - Google Patents

Description

Aug 1936- J; P. RATHBUN 2,049,748-

HEAT EXCHANGER Filed July 7, 1954 REMOVABLE F G 1 WITH TUBE BUNDLE III EQF'l-LE WELDED *ro SHELL.

FIG..2.'

INVENTOR WITNESSES:

' JOHN P. RATHBUN.

BY Wgfi, ATTORNEY My invention relates PATENT OFFICE 2,049,748 HEAT EXCHANGER John P. Rathbun,

to Westinghouse Prospect Park, Pa., assignor Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application July 7, 1934, Serial No. 734,095

3 Claims; (Cl. 25'7-239) to heat exchanger apparatus, more particularly to a heat exchanger in which a smaller between the two fluids is terminal temperature difierence desired at one end of the flow path than at the other, and it also relates particularly floating head and shell into two passes.

An object of my proved apparatus to such apparatus having a a single baiile dividing the invention is to provide im-.

of the character set forth.

A further object is to provide smaller terminal temperatureidifference at one end of the flow path than at the other.

In accordance with my invention,

a shell, a tube bundle having a floating head,

and a bafile dividing the shell into two passes.

The baiile is disposed off center, toward the terminal at which minimum temperature difference is desired, providing a shell pass of greater cross section and a tion. The tubes are divided into a plurality of tube passes, there being shell pass of lesser cross seca greater number of tube passes extending through the shell pass of greater cross section.

The above and other objects are effected by my invention as will be apparent from the following description and claims, taken in conand Figs. 3, 4 and 5 are cross-sectional views taken on the section lines of Fig. 2 designated by the corresponding roman numerals.-

Referring to the drawing 1n detail, I show in Fig. 1 a heat exchanger comprising a shell I0,

a stationary head the head I I, a floating site end of the heat exchanger, tubes a tube sheet I2 adjacent tube sheet I3 at the oppo- I4 extending between the tube sheets I2 and I3, a floating head I5 secured member I6 for the the head I5. The plurality of tube pa 20 respectively. The head II inlet 2I, an outlet 23 and 24. The he zontal partition 25.

to the tube sheet I3, and a closure end of the shell I0 adjacent tubes I4 are divided into a sses designated II, I8, I9 and is formed with an 22, and horizontal partitions ad I5 is formed with a hori- The shell I I is formed with an inlet 26 and an outlet 21 adjacent the stationary head II. A

longitudinally extending baflie 28, disposed between the inlet to divide the shell 26 and the outlet 21, is provided into two shell passes 29 and I provide 30, extending longitudinally or parallel to the tubes I4 and communicating with said inlet and said outlet, respectively. Preferably, and as shown, the bafile' 28 is in the form of a fiat horizontal plate. The bafile 28 is disposed off center, 5 in this case toward the outlet 21, thereby providing a first shell pass 29 with greater cross sectional area than the second shell pass 30. The shell pass 29 may have, for example, a crosssectional area three times that of the shell pass 10 30. The baffle is formed with a slot 3|, adjacent the floating head I5, to connect the shell passes 28 and 30. Bafiles 32, extending transversely of the tubes, may be provided in each shell pass, to cause the fluid admitted through the inlet 15 26 to pass back and forth across the tubes as indicated by the arrows on the drawing. In the embodiment of Fig. l, the baflle 28 is removable with the tube bundle, being preferably secured to the tube sheet I2.

In order to illustrate the utility of the present invention, I shall give an example of one application to which it is particularly suitable. The heat exchanger may be used to cool and partially condense hydrocarbon vapor which is admitted 25 through the inlet 26 at a temperature of 200 F., for example, and cooled to a temperature of 90 F. Cooling water enters the inlet 2| at a temperature of 80 F. and leaves the outlet 22 at a temperature of 120 F. In this case, it is 30 not necessary to obtain a close temperature difference between the cooling water discharged. through the outlet 22 and the vapor entering through the inlet 25. However, it is desired to obtain as low an outlet temperature of the hydro- 35 carbon fluid as is possible, in order to condense the greatest possible amount of that portion of the hydrocarbon fluid known as the lighter ends, which means that as low a temperature difference as possible should be obtained between the inlet 2| and the outlet 21.

The operation of the above described apparatus is as follows: the fluid to be cooled, such as hydrocarbon vapor, enters through the inlet 26 and flows to the right through the shell pass 29.

- It then flows through the slot 3| in the baiile 28 to the second shell pass 30, through which it flows to the left to the outlet 21. Cooling water enters the inlet 2I and flows to the right through the tube pass II, opposite to the direction of flow of the hydrocarbon vapor through the shell pass 30-, wherefore the tube pass I! is designated a counterflow pass, and then through the shell passes I8, I9 and 20 successively, to the outlet 22. The flow through the tube passes I8 and 20 is counterflow or opposite to the flow of the vapor through the shell pass 29, while the flow through the tube pass I9 is parallel flow or in the same direction of flow.

In the present case, ample cooling water is provided to efiect the desired cooling without a great increase in temperature of the cooling water, hence, in the shell pass 29 there is ample temperature diflerence to effect coolingand partial condensation of the hydrocarbon vapor.

Inasmuch as approximately three-fourths of the tubes are in the shell pass 29, and the mean temperature diflerence therein is greater, by far the greater percentage of the total heatload is transferred there. With the assumed conditions, approximately 90% of the heat, a portion of which is heat of vaporization of the hydrocarbon vapor, will have been transferred when the hydrocarbon fluid passes from the shell pass 29 to the shell pass 30 with a resulting temperature of 115 F. at this point. The difference between this temperature and that of the cooling water is now materially decreased. In accordance with my invention, I convey this hydrocarbon fluid through the shell pass 30 in which there is a single tube pass I! through which the cooling water flows in the direction opposite to the hydrocarbon fluid. As the hydrocarbon fluid flows to the left through the shell pass 36 it is in contact with successively cooler water, until, adjacent the outlet 21, it is in heat exchange relation with the coolest water being admitted to the heat exchanger. Hence, the coldest possible temperature of the hydrocarbon fluid is obtained. The ma- -jor portion of the hydrocarbon fluid is condensed when it passes through the outlet 21.

An analysis, taking the assumed conditions of the above example, shows that the.construction shown in Fig. 1, with the balile located off center, produces an average of the effective mean temperature diiferences in the two shell passes which is 30% greater than that obtained when the bafile is centrally located as in previous constructions.

In Figs. 2 to 5, I show an embodiment of my invention which is applicable, for example, when a baille is welded to the shell and 6 or more tube passes are desired. The heat exchanger includes a shell 40, a stationary head 4| and a stationary tube sheet 42 at one end of the shell, and tubes 43 secured at one end to the tube sheet 42. The shell 40 is formed with an inlet 38 and an outlet 39 adjacent the stationary head. A bafile 44 is welded to the shell 40, dividing the shell into two passes 45 and 46, communicating with the inlet 38 and the outlet 39, respectively. The baflle 44 is disposed ofl-center toward the outlet 39, so as to provide a shell pass 45 of greater cross-sectional area than the shell pass 46, for example, the shell pass 45 may be twice the crosssectional area of the shellpass 46.

Due to the fact that the baflie 44 is welded in, it is necessary'to provide a split floating'head and floating tube sheet. Accordingly, I show a floating tube sheet portion 41 and a floating head portion 46 which are formed to pass through the upper shell pass 45, and a floating tube sheet portion 49 and a floating head portion 50 formed to be passed through the lower shell pass 46.

The baflle 44 is formed with a slot 5| to provide communication between the shell passes 45 and 46 adjacent the floating head. Bailles 52 may be provided in each shell to cause the fluid passing through the shell passes to pass back and forth across the tube surfaces, arrows on the drawing.

Due to the floating head construction, it is necessary to have an even number of tube passes in each shell pass. Accordingly, I provide two tube passes 53 and 54 which extend through the shell pass 46, and tube passes 55, 56, 51 and 58, which extend through the shell pass 45. The stationary head 4| is formed with an inlet 59, an outlet 60, and partitions forming a chamber 6| for admitting cooling water from the inlet 59 to the tube pass 53, a chamber 62 for admitting as indicated by the cooling water from the tube pass 54 to the tube pass 55, a chamber 63 providing communication between the tube passes 56 and 51, and a chamber 64 for conveying the cooling water from the tubes 58 to the outlet 66. The floating head portion 50 comprises a single chamber for directing the flow of cooling water from the tube pass 53 to the tube pass 54. The floating head portion 48 is divided by a horizontal partition into a chamber 65 which directs the flow of cooling water from the tube pass to the tube pass 56 and a chamber 66 which directs the cooling water from the tube pass 51 to the tube pass 58.

The operation of this embodiment is generally similar to that of the first embodiment. Hydrocarbon vapor or other fluid to be cooled, or cooled and condensed, is admitted through the inlet 38 at a relatively high temperature, passes, to the right through the shell pass 45 and through the slot 5| to the shell pass 46, then to the left through the latter to the outlet 39. Cooling water enters through the inlet 59, passes to the right through the tube pass 53 and then to the left through the tube pass 54. The cooling water then passes through the tube passes 55, 56, 57 and 58, successively, in the shell pass 45.

Due to the fact that the volume of the shell pass 45 is twice as great as the volume of the shell pass 46, and due to the fact that there is a greater temperature difference in the shell pass 45, morethan of the temperature reduction of the fluid to be cooled will have been effected when the fluid enters the shell pass 46. The cooling water flowing through the tubes in the shell pass 46, on the other hand, having passed through but of the tube passes when it leaves the tube pass 54, and having passed through that portion of its path in which there is the smaller temperature difierence be tween the two fluids, has acquired not more than /3 of its temperature rise and, when it leaves the tube pass 54, is still at a lower temperature than the hydrocarbon fluid. Consequently, it is able to effect a relatively low temperature of the fluid discharged through the outlet 39.

From the above description, it will be seen that I have provided a heat exchanger which is particularly suitable for certain applications, namely, where it is desired to obtain the lowest possible terminal temperature difference at one end of the fluid flow while the temperature difierence at the other end of the fluid flow need not be as small. It will be noted that I have provided a larger number of tube passes. some of which are counterflow and other parallel flow. in the larger shell pass in which a higher temperature diflerence may exist, and that I have provided a smaller number of tube passes adjacent the terminals where a lower temperature difference is desired.

While I have shown and described my invention in connection with a heat exchanger in which minimum terminal temperature difierence is obtained at the cold end, it is also applicable to a heat exchanger in which minimum terminal temperature difference is obtained at the hot end. In the latter case, the baiiie is disposed nearer said hot end, to provide a smaller shell pass and v a smaller number of tube passes adjacent said end. It is also to be understood that my invention is applicable both to heat exchangers in which there is transfer only of sensible heat and to heat exchangers in which there is transfer also of latent heat.

While I have shown my invention in several forms, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various other changes and modifications, without departing from the spirit thereof, and I desire, therefore, that only such limitations shall be placed thereupon as are imposed by the prior art or as are specifically set forthin the appended claims.

What I claim is:

1. A heat exchanger comprising a shell, a stationary head at one end thereof and a floating head at the other end thereof, tubes extending between said heads, saidshell having an inlet and an outlet adjacent said stationary head, a bafile disposed in said shell between said inlet and outlet and dividing said shell into a larger shell pass on the inlet side and a smaller shell pass on the outlet side, and means for circulating fluid through the tubes, first in a single counterflow pass through thetubes in the smaller shell pass from the stationary head to the float ing head, and then through the tubes in the larger shell pass, the latter tubes being divided into a plurality of tube passes of which the number of counterflow passes is one greater than the number of parallel flow passes.

2. A heat exchanger comprising a shell, a stationary head at one end thereof and a. floating head at the other end thereof, tubes extending between said heads, said shell having an inlet and an outlet adjacent said stationary head, a battle disposed in the shell between said inlet and said outlet and dividing said shell into two lon- '-gitudinally extending passes through which a first fluid flows successively externally of tubes therein, and means for circulating a second fluid first through tubes of one shell pass and then through tubes of the other shell pass, said tubes shell passes so that one larger number of tube being arranged in the shell pass contains a passes than the other pass has at least one counterflow tube pass and at least one of the shell passes has at least one parallel flow tube pass and one more counterflow than parallel flow tube passes.

3. A heat exchanger comprising a shell, a stationary head at one end thereof and a floating head at the other end thereof, tubes extending between said heads, said shell having an inlet and an outlet adjacent said disposed in the shell between said inlet and said outlet and dividing said shell into two longitudinally extending passes throughwhich a first 'fluid flows successively, one of said shell passes being larger than the other, and means for circulating a second fluid first through tubes in one shell pass and then through tubes in the other shell pass, said tubes being arranged in passes with the number of tube passes in the larger shell pass greater than said tubes being arranged in passes with the number of tube passes in the smaller shell pass, and each shell pass having at least one counterflow tubepass and one of the shell passes having at least one parallel flow tube pass and one more counterflow tube pass than parallel flow tube passes.

JOHN P. RA'I'HBU'N.

stationary head, a baffle,

shell pass and each shell

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