US2606006A - Tubular heat exchanger - Google Patents

Description

Aug 5, 1952 P. H. KARLssoN ETAL 2,606,006

TUBULAR HEAT EXCHANGER 2 SHEETS-SHEET 1 Filed April 3, 1946 mi N NQ NY SM Y Rx www@ al. R www@ 1,3 y @www ug. 5; 1952 P, H, KARLSSON ETAL, 2,606,006

TUBULAR HEAT EXCHANGER Filed April 5, 19:5 2 SHEETS-SHEET 2 INVENTORS Per Hz lm er Karlsson Sven Holm Patented Aug. 5, 1952 TUBULAR HEAT EXCHANGER v Per Hilmer Karlsson and `Sven* Holm, Wellsville, v

tion, New York, N. Y.

N. Y., assignors to The :Brehater Corpora- Application April s, 1946, serial No, 659,272

The present invention relates to heat exchange apparatus and more particularly to a tubular heat exchanger adapted, for example, for use in a gas turbine or other gas engine cycle to recover the heat inthe gases exhausted from the turbine for preheating the working medium (air).

A feature of this invention is a heat exchange apparatus having a rate of heat transfer above what is ordinarily attained with heat recovery apparatus transmitting the heat from one gas to another.

An object of the invention is to attain a minimum flow resistance in the exchanger. The exhaust gases enter at a very high velocity and an object is to utilize the velocity of the gases to the best advantage in overcoming flow resistance.

Other objects and advantages of the invention will become apparent upon consideration of the following detailed description of illustrative embodiments of the invention when read in conjunction with the accompanying drawings in which:

Figure 1 is a longitudinal sectional view through a tubular heat exchanger embodying thel invention; n

Figures 2 and 3 are fragmentary sectional views on the correspondingly designated section lines in Figure 1 and illustrate two diierent tube spacing arrangements at points spaced longitudinally of the heat exchanger;

Figures 2a and 3a are diagrammatic views indicating the areas occupied by the tubes at the positions where the section lines for Figs. 2 and 3 are located; f

Figure 4 is a diagram illustrating the relation between the areas forfree ow of gases through the tube bundle and the pressure and velocity conditions existing at several locations longitudinally of the heat exchanger; l

Figure 5 is a diagram showing the relation between the gas velocities and areas for gas flow in the rst pass through the tube bundle.

Figure 6 is a view partially in plan and partially in diagrammatic section of another arrangement of a multi-pass heat exchanger embodying the invention wherein the heat transfer tubes are arranged in several banks and disposed normally to the direction of gas flow rather than extending in the general direction thereof and Figure '7 is a sectional view on the line 1-1 in Figure 6.

The heat exchanger illustrated in Figure 1 has -an annular tube bundle I made u p of a multiplicity of tubes H of a diameter ofg" or less 3 Claims. (Cl. 251-235) with thin walls and rolled at theirends intothe tube sheets I2 and I3. The air to -be heatedis 'distributed to the tubes Il through` an inlet header I4 at the right and discharged from the exchanger. through an outlet header I5. The tubes l l vinstead of being dispersed over the entire 'area of the circular or rectangular tube sheets as'in conventional tubular heat exchangers are disposed in a plurality of concentric rows to form the annular tube bundle l0..whose tubes surround the central space 20 within the heat exchanger. .The heating gas entersthrough a duct 2l extending through the header l5 to the centralspace 20 within the bundle so that the gas flows longitudinally towards a baille which is constituted by the central imperforate portion 22A of aA tube spacing plate 23. Intermediate portionsbf the tubes I0 extend through plate 23 and asecond plate 21 of annular form maintains the tubes in desired mutually spaced relations. The wrapper sheet or shell 24 surrounding vthe tubev bundle I0 is spaced .away from the latter between tube sheet l2 andthe tube spacing plates 23, 21 so that the gases flowing from the central space 20 radially outward across' portions of the tubes l0 in the first pass may flow longitudinally in a passage 26 formed between the shell 24 and the tube bundle, over the periphery of the baille 23 and to the second pass. Thel spacing plate 21, being annular `in form, provides a central aperture 28 through which thel gases ow to enter the third pass wherein they flow radially outward across the right hand portions of the tubes I0 into a co1- lecting chamber 30 from which they are discharged through an outlet 3|.

The tubes l l are connected into the tube sheet l2 at the gas inlet end of the exchanger in closely spaced relation in concentric circular rows and may be staggered in .adjacent rows, if desired. Between the tube sheet l2 and the baille plate 23, the axes ofthe tubes forming each of the concentric rows are parallel but becomeA more closelyspaced circumferentially dueto the fact that the circles in which their holes are distributed in the plate 23 are made of smaller diameter than in the tube sheet I2. Consequently the intertube area free for gas flow is less between tube portions at baille 23 than adjacent that part of the rst pass contiguous to the inlet 2|. In passing through the second spacing plate 21 the tubes project through openings Which are arranged in circles of larger diameter than in the plate 23 but with the inner and outercircles lla, lib (Fig. 3) closer together ati the. vinner end of. the first pass.

radially than at baille 23 (Fig. 2) thereby still further decreasing the free area for gases to iioW among the tubes as may be noted by examination of Figs. 2 and 3. At the tube sheet I3 the tubes may be located in concentric rows that are of smaller diameter than in the spacing plate 21, thus repeating the relationship that exists between thevtube spacings at the inlet tube sheet I2 and the rst baille plate 23.

This variation in the spacings between adjacent tubes longitudinally thereof enables full use to be made of the velocity head of the gas K entering inlet 2l (at 100 feet per secondand over) and produces so-called stagnationA point flow in the first pass of the unit. This-type of flow is an almost perfect conversion from velocity head to static pressure head. Its simplest form is a jet of gas impinging on a flat plate whose surface is perpendicular to the axis of the f Si to S3 and is a maximum. This increased static pressure is. then usedvto create velocity through the tube bank .for overcoming the greater resistance R3 due to closer tube spacings Thus, to obtain substantially uniform distribution of flow over the tube bank and avoid the tendency of gas to' rush toward the inner end oi.' the pass and iiow over the tube Vportions near bafiie 22 while largely bypassing. the, outer end portions of. the tubes, the annular bundle l is tapered so as to give smaller gas iiow area A1 for flow between the tubes at the far end of the first pass where static pressure is at a maximum Sa', and a larger area A3 at the entrance end where static pressure is at a minimum S1.'

` Figure 5 shows the basis of calculations forproportioning the taper of the tubebank. For

this particular design it has .been assumed that the static pressure (Ps) at the entrance necessary for now through the tube bank at a given velocity is equal to one .velocity head (HU) In the central space Within the tube bank the static pressure increases from the inlet end to the baille 22v as indicated by Sg .due to `conversion from velocity pressure to static pressure. The static pressure existing in the outer passage 26 between the tube bundle I0 and casing 241 decreasesas represented by Sd, this decrease resulting from the increase in velocity of thegases discharging over tube portions near baille 22 into the space 26.' This diagram graphically shows that, assuming 100% conversion from velocity head to pressure head, P=Hv=Sg=Sdand therefore the pressure differential (P-i-Sg-i-Sd) atthe inner end of .the rst pass or at the baiile 22 is three times that (P) at the outer end.

Figure 5 shows diagrammatically that at baille 22 there is a drop in static Pressure through the bank amounting .to SH12 while near inlet 2l the drop is Ho. Where V1 and V2 represent velocities through bundle l0 near inlet 2|. and at'baie 22 where. V is velocityand g is acceleration dueto gravity indicates the pressure differential at bafrie 22 is 5g 3 2g Since the iiow through any section is equal to velocity times density times ow area, then for uniform mass rate of flow through the tube bank (if area for flow per unit/length of tube bank is represented by A and D represents density of fluid) Vi D A1=Vz D Az it follows that for the assumed Ho=P the area ratio to obtaina velocity ratio V: rfi/'5 Itis evident that if the resistance through the tube bank is less than H12, the ratio .4 1 Az will be igreaterjthanV V3 and smaller than V5 if the resistancethrough the tube `*bank is greater than Hv. It has been lassumed herein thatY conversion from velocity'head to static head and vice versa would be This is, of course, not possible-With -any' kind -of apparatus, due to friction etcpbut 100% conversion has been usedv tov simplify the explanation.

The ratio-between areas for flow through the outerand inner ends of the rst pass is there- Iore'in reverse proportion for uniform mass ilowvelocity rate for the whole length of Pass, So that the area at the inner end is approXimately58% Tof that at the outerend. Itis evident that a'higher rate ofv heat transfer results from the higher velocity as compared with a tube bundle having tube .rows thatare parallel from end .to end. Astudy of Figs, 4 and 5 makes it clear that this additional velocity through the bank and increased heat transfer is obtained by using Athe high velocity head of the entering gas. The same area ratio can .be had in the second pass by narrowing 4the radial `depth of the tube bank at the second. baille 21 where the static pressure is builtup at the far end of theannular space 26; The same principle may be applied again in the `third pass by reducing the diameter of the tube circles as was done at baille 23.

At the baiile 2 3 the gas iiows across the tube bank atsubstantially Aright angles and at very high'velocity. To prevent this gas stream. from bridging across the annular passage 426 and thus choking off the stream of gases from the inlet end of this passage a deiiector 32 is provided. The frusto-conical deiiectors 34 are forthe purpose of directing parts of the gas stream along their' outer faces to iiow over the front partof the respective passes.

In the heat exchanger illustrated in Figs. 6 and 7 there are two banks 40. ineach pass .each comprising tubes 4I (represented by dots in Fig..6) disposed so as to extend normally to the general direction of gas flow. These tubes are arranged in spaced relation in a plurality of parallelrows With the tube banks 40 disposed at opposite sides of the central space 42 through which the gas entering throughinlet 43 flows toward `the baie should plate 45. Here the banks 40 are of rectangular form and in the rst pass are arranged with their inner ends in convergent relation to each other and disposed between the inlet 43 and the baffle 45. In the second pass the banks 40A are arranged in divergent relation. These inclined relations provide the required passage 46 between the outer portion of each bank and the casing 44 through which gas may ilow to pass over the tubes in the banks 40A in the second pass to be finally discharged through the outlet 41.

In order to obtain substantially uniform mass flow through the banks 40, the tubes in each longitudinal row of each bank are more closely spaced adjacent the baiiie 45 than at the portion of the bank adjacent the inlet 43. Likewise in the banks 40A in the second pass of the heat exchanger the tubes at the far end near the outlet 41 are more closely spaced than at the inner end of these banks near baille 45. Thus, the same principles of conversion of Velocity head into static pressure and effective utilization thereof to attain better heat transfer apply to this construction also.

In this form the air to be heated enters through a bottom inlet 50 at the right hand end of the apparatus and flows into the lower ends of the tubes of both banks 40A at this end of the apparatus, the tubes 4I being connected at their ends to tube sheets 5| and 52. The top part of the casing 44A is spaced above the tube sheet 52 to provide a passage 53 for gases to flow longitudinally to enter the upper ends of the tubes lll in the tube banks 40. The lower ends of the tubes in the banks 40 are seated in the tube sheet 55 located in the chamber 56 into which the outlet duct 51 is connected. Thus air which is first heated in the banks 45A absorbs further heat in the tubes of the banks 4i) before being discharged through the air outlet 51.

The arrangement of tubes shown in Figs. 6 and 7 has the advantage that the tube spacing can be varied within a greater range than is possible with tubes continuous through all passes. For instance, due to stagnation point ilow, and. velocity head conversions, there is always a higher pressure differential between a and l) (Fig. 6) than between b and c. Therefore, the resistance to iiow should be higher between a and b than between b and c and the tube spacing closer where the higher resistance is required and good distribution can therefore be obtained. This is not possible with continuous tubes because next to the baile the tube spacing must remain the same from one pass to the other. Another advantage with this arrangement of tubes is that the. tube rows can be arranged in any desired angle in relation to the direction of flow of the gas entering the unit so that the gas stream passing through tube bank at the gas inlet end will contact all the tubes without dead corners and ineiective heating surface.

This application is a continuation-in-part of that filed in our name on November 17, 1944, under Serial No. 563,816, now abandoned.

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What We claim is:

l. In a heat exchanger; an elongated casing formed in one end wall with an inlet opening directly into a narrow gas passage alined there- With and extending longitudinally of said casing and which is several times as long as it is wide; a baffle extending transversely within said casing perpendicular to the axis of said passage with the periphery of the baiile spaced from the adjacent wall of said casing; and tube banks at opposite sides of the axis of said passage comprising tubes normal to the axis of said passage disposed in alinement in spaced parallel rows that extend longitudinally of said passage from said iniet to said baille and inclined at an angle with respect to its longitudinal axis with the banks being located further from said axis at the inlet end of said passage and the tubes in the end portions of said rows adjacent said bafile being spaced closer together in said rows than tubes adjacent said inlet.

2. In a heat exchanger; an elongated casing formed in opposite end Walls with an inlet and an outlet communicating directly with a narrow gas passage alined therewith and extending longitudinally of said casing and which is several times as long as it is wide; a. baliie extending transversely within said casing intermediate said inlet and outlet with the periphery of the baffle spaced from the enclosing casing to permit gas flow between portions of the passage located along its said longitudinal axis at either side of said baille; and pairs of tube banks bounding opposite sides of said passage at each side of said baiile comprising tubes normal to the axis of said passage disposed in alinement in spaced parallel rows that extend longitudinally of said passage at angles inclined toward the baile with respect to the longitudinal axis of said passage with the banks being located closer to said axis adjacent said baffle and the tubes in the end portions of said rows adjacent said batlie being spaced closer together than tubes adjacent said inlet.

3. A heat exchanger as recited in claim 2 including inlet and outlet headers for another fluid located at one side of said casing parallel to the longitudinal axis of said passage and in uid communication with the tubes in said tube banks.

PER HILMER KARLSSON. SVEN HOLM;

REFERENCES CITED The following references are of record in the le oi this patent:

UNITED STATES PATENTS Number Name Date 898,932 Schmug Sept. 15, 1908 1,740,318 Smith Dec. 17, 1929 2,149,007 Cassidy Feb. 28,1939 2,232,935 Bailey Feb. 25, 1941 2,519,084 rIull Aug. 15, 1950

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