US2545028A - Falling film heat exchanger - Google Patents

Description

March 13, 1951 AN 2,545,028

FALLING FILM HEAT EXCHANGER Filed Dec. 5, 1945 2 Sheets-Sheet l FIGQI FIG.2.

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@NVENTOR GEORGE W.HALDEMAN BY mm; W

ATT NEYS G. W. HALDEMAN FALLING FILM HEAT EXCHANGER March 13, 1951 2 Sheets-Sheet 2 Filed Dec. 5, 1945 INVENTOR GEORGE W.HALDE-MAN BY ymmmgm ATTO NEYS 'pipe. .as it overflows the top periphery of the pipe'is 1 zero or nearly zero and the 'rate down the pipe ifsaccelerated by gravity until a steady state Patented Mar. 13, 1951 UNITED STATES PATENT OFFICE FALLING FILM HEAT ExcnANGEn GeorgeW. HaIde'mamOak Ridge, Tenn. I Application December 5, 194 Serial Ne. 632,993.

an abnormal amount of heating or cooling energy. The rate of heat transfer from a liquid or, a gas to a liquid, or a gas, depends primarily on the contact area, the difierence in temperature and the heat transfer coefficient. The unsatisfactory operation of prior forms of heat exchangers is due to a large extent to the restriction of the contact area which limits the 'manner in which heating or cooling effects of the two fluids are associated with one another.

Most types of heat exchangers incorporate the idea of two liquids or gases separated by a wall of metal or other solid material. in'g film type of heat exchanger the heating or cooling medium is caused to overflow the top periphery of a vertical pipe to flow by gravity down the inside wall in the form of a thin layer or a falling film of liquid. Due to the thinness of this layer, the turbulence and relatively high rates of flow considerable heat transfe coeflicients are obtained. While this type of heat exchanger gives a certain amount of satisfaction, it is subject to a number of factors which greatly reduce its efliciency of operation.

. One primary defect is the non-uniformity of flow of the thin liquid layer down the vertical The initial vertical velocity of the liquid condition is reached atwhich point the average vertical velocity is constant. It is therefore apparent that the upper part-of the tube or pipe, due to the lower velocities in'this region, is not utilized for heat transfer at its maximum ciliciency. The liquid velocity down the tube is limited to the steady state velocity caused by gravity because it is only inthis direction that 'Ithefliquid can flow since-it takes the shortest path between the top and the bottom of the tube; In addition to the difficulties discussed immediately above, there is also the problem of. even distribution of liquid around the periphery of the tube where it overflows the pipe and v,thenlmoves over the interior surface of the p p 'Onfoccasion, the upper edge of the pipe is sometimes notched to assist distributing theliquid 3 Claims. (01.261-) v provide heat transfer apparatus which will, not be subject to the difficulties set forth above and In the fallbut even this expediency is not altogether successful unless the tube be perfectly vertical and its upper edge be maintained strictly horizontal.

In these prior forms of heat exchangers the quantity of liquid per unit of time which can be passed down the tube is limited. When quantities become too great, the liquid breaks loose from the pipe wall where it overflows since the liquid must change direction at this point. This results in liquid falling free down through the space in the middle of the tube or pipe, resulting in poor heat transfer and large entrainment losses if a gas is being passed through the center of the tube. H

The primary object of the invention is to one in which greater quantities of fluids canb'e accommodated and the heattransferfrom one fluid'to another is effected ata relatively high efficiency. A

Another object is to provide a heat exchanger of the so-called falling film" type in which the movement of the liquid through the exchanger is at a much greater rate than in the earlier types of apparatus.

Still another object is to provide a heat exchanger which is of inexpensive design, easy to assemble and operate and one which will handle considerable quantities of fluids per unit weight and per unit space taken by the apparatus. w

As'will be explained in detail, my improved device can, on account of its design, be used for other purposes than transferringheat from one liquid solutions. Accordingly, another object is "to provide apparatus, the primary purposejof which is to efiect highly efficient interchange of heat betweentwo adiacent. but separated fluids but may also be usedj'for efliciently dissolving gases in liquids or for removing such gases from the liquids at room or elevated temperatures.-

By reason Qf. Iits vefficient-.h,eating effects or rather the transfer of heat from onemedium-to another," my. improved apparatusv lends itself readilyto a rapid concentration of mixturesor colloidal compositions. providing a jacketed cylinder and admitting one The above objects can be attained in brief by of the fluids under pressure into the cylinder in such a way that the fluid is caused to closely hu thesinterior surface of the cylinder and to take K ispiral path through the device asa thin layer so land boss being omittedin this-figure. r

3 that the contained heat can be readily transferred through the wall of the cylinder to the fluid in the jacket. Inasmuch as the liquid is caused to be localized or concentrated around the interior wall of the cylinder leaving an open core down through the middle, a column of gas can be caused to flow through this core and if desired closely to intermingle with the liquid layer. Thus, the liquid is distributed over awide area determined by the interior surface of the container and the thickness of the layer is substantially uniform throughout the area so that the rate of travel of the liquid through itsspiral path is substantially uniform throughout the" length of the cylinder.

Other objects and features will. bev apparent as the improved heat exchanger.

Figures 2, 3 and 4 are sectional views taken along lines 2-2, 3-3 and 44, respectively, in

Fig. 1 and looking in the direction of the arrows.

Figure 5 is a vertical sectional view of a modi- Lfied form of heat exchanger, while Fig. 6 is a transverse sectional view taken along line 6-6 in Fig. 5. I

Figure 7 is a fragmentary sectional view of sti lanother modified type of the improved-heat ex-.; .changer and Figure 8 is a' transverse sectional view taken along line 8 8 in Figure 7,lthe pipe Referring Particularly tOF SUrGs 1 'tof i,

paratus. The casing 1 contains an annularly arranged cylinder 2 preferably formed integral with the casing by a casting process.

The inner cylinder 2 is flared outwardly and upwardly as indicated at 3 to join with the outer ..cylinder or casing l and the latter terminates at Q the top and bottom in a relatively heavy cylin- 'drical portion 4. The lower portion 4, may have integrally joined thereto a plate 5. It is evident that the elements I, 2, 4 and may conveniently be formed by casting and the annular opening 6 between the walls I, 2 obtained through a icoring operation. The casing I is-provided at the upper end with a boss i which contains a threaded opening for receiving a pipe 8. 'At the lower end of the casing, there is a tangentially extending projection 9 (Fig. 4) which receives a pipe 9a leading through a conduit to a source 90 of heated or cooled fluid. It is apparent that the opening in the boss I and the opening 911 in the pipe 9a should be sufficiently large through which to remove the sand core which forms the, annular space 6 in the casting operation. The

heated or cooled fluid in the reservoir 96 is maintained under sufficient pressure in any suitable and well known manner to causean upward flow I of the fluid through the jacket or compartment E in a spiral path due to the tangential position of I the opening 901.

The end of the upper casing portion} is also numeral l designates a casing, preferably of cylin- -drical configuration and made of-any suitable ;metal such as cast iron and depending on the character of the fluids passing through the. ap-

, is dependent on many factors including the quantity ofthe fluid which is caused to pass through ,the casing and the amountof space between the ing patterns and the cores. 3 is preferably of a spherical shape in order to j'facilitate the ready movement of the fluid.

means of an annular recess and is secured to the casing by screws 15 or in any other suitable manner. The closure plate has a downwardly extending centrally disposed tube 16, preferably hollow at its interior, as indicated at ll, for reasons which will be explained presently and the upper end of the opening is threaded to receive a plug it. The tube [6 extends into the compartment 5 8' formed bythe inner cylinder 2 for an appreciable distance. This tube preferably has an outside diameter slightly less than the interior diameter of the cylinder 2 so as to permit a thin .layer of liquid or gas to pass therebetween as will be explained presently. A conduit I9 is connected with the pipe I! in communication with a pump 25) of any suitable type. The opposite or suction side of the pump is taken from a source of fluid or liquid (not shown) which it is desired to heat, or to cool, by passing through the heat exchanger. p h

In order to reducefriction and eddy current loss as much as possible, it is preferred that all the corners be roundedby the use of fillets or gradual curves and surfaces of this character are readily obtainable by properly shaping the cast- As'shown, the wall In operation, heated fluidfrom the.reservoir j ,(not'shown) is caused by the pump 20 to enter the space ZS atiJ e upper end; of the casing "th ugh the ta gentia y position d e ing 19- li flu d com l ly fil s e. 2. nd l se [tqmovef downwardly t r u h t e t t n in a spiral path due'to thejacquired tangential or com trifugal velocity and 'the composite sheet of gravity so that a layer. 24 of fluid emerges from the annular space between 2 and IE along the interior surface of cylinder 2 beginning. at the bottom of tube H5. The thickness of this layer elements 2 and [6. Its rate of movement, disregarding the downward pull of gravity, is, in

general, dependent on the pressure at which the fluid is introduced into the upper portion 4. This pressureand the velocity obtained thereby should be such that all of the fluid is caused tightly to hug the interior surface of the casingthroughout its length so that the layer will represent an unbroken body of fluid travelling around the casing and in a constantly downward direction. This spiralmovement of the fluid has been broadly indicated by the arrows 25, 28. Due to the presence of higher velocities at thetop of the ca sing the an leof travel .ofthefluid at this point would be considerably less than at positions farther down the casing,'and this change in angle has distances between the spiral loops. For optimum results, although not necessary, the spiral angle :sh'ould'be approximately 30 at the top of the been indicated on the drawings by the changing j i nner-c asing 3 and not more than 60 at the lower end of that casing. The fluid eventually reaches the lower casing portion 4, as indicated at 21, and is withdrawn at the'pipe l3, either by a pump lair-space as a filnrof fluid;

"to the continuity of the layer, the heat transfer 'coei ficient at the wall 2 is relatively high. The ithermal resistances of the laminar layer becomes low and the rate at which the liquid passes by the metal wall is essentially increased. The

1 initial velocity of the liquid emerging through the annular space between cylinder 2 and tube H5 is even greater than the steady state velocity since it is dependent primarily'on the pressure of the entering liquid, although eventually if the "tube were long enough, the steady state velocity 'would be reached in normal lengths and average velocity would he obtained greatly in excess of the --steady state velocity. In addition, the liquid-in it'ravelling the spiral path, has a rotary velocity that greatly increases the net velocity. Conversely, the liquid travels through a much greater distance in reaching the lower end of the tube.

"Approximately 5' to times as much liquid can be passed down the inside wall with the improved "type of heat exchanger.

The centrifugal force caused by the rotary motion forces the liquid against the tube wall and if a part of the liquid breaks away from the tube wall, it will be thrown back into the stream, thus insuring good control'of the liquid at alltimes.

Thus, as the fluid in the central compartment is caused to flow in the manner described and as- Isuming' that the'fluid is at'higher temperature than the fluid in the annular compartment 6, 'the circularly moving fluid is caused readily to give up its excess heat to'the'surrounding column of fluid. The fluid in this column is kept at a lower temperature than the'fluid in the central compartment by a continual movement :of the fluid through the compartment 6 from ,the reservoir So. It is apparent that the reverse operation takes place in the event that the fluid passing through the central compartment is at 5 a lower temperature than the fluid in the an- -nular compartment because the central compartment fluid would abstract heat from the adj jacent column of fluid through the action of the r falling layer 24.

The tangential manner in which the outer column of fluid is caused-to enter the casing l .7 at the pipe 9a reduces turbulence which in turn j causes some increase in the velocity of the fluid moving through the casing. Itwill be understood that, if desired, the fluid in casing i could be introduced through a diametral connection, rather than tangential. Accordingly, my improved thin layer. or falling film type of heat exchanger lends itself to all .of the advantages to "which prior 'forms' ofheat exchanges are dapted but to a greater degree dueto tlie increase of the heat exchange coefficientobtainable from the-device. This coefficient is greatly increased 7 over prior heat exchangers :insofar as-the'transfer of heat is concerned through the wall 2. ioperates in both directions so, that the device can i be, used :to cool liquids orfluids quite as well as heat the; same. depending :onthe relative temperaturesof the fluid contained in the two compartments B and..l.8'......

' Ini'Figurcsaand 6, there summits fm improved heat exchange apparatus which has been adapted to the simultaneous treatment of gaseous as well as liquid fluids. In this case, the plug [6 of the structure shown in Fig. 1 has been removed and replaced by a threaded pipe 28 which is in communication with the interior of liquid-is caused to spread out over large areas then be drawn through the pipe 30.

.tween the two compartments custom is. The pipe may be conveniently held in position by means of a flange 29. The lower end of the casing is apertured to receive av relatively long centrally disposed tube 36 held in position by a flanged element 3| secured to the lower side of the plate 5. Gas of any desired kind could be introduced at the tube 28 and caused to pass downwardly through the tube l6 and the gas can be caused to be dissolved into the liquid as it falls as a layer overthe interior surface of the casing 2. The excess gas may It is apparent that the moving thin film of liquid may be caused, not only to abs-orb gas but also to disassociate therefrom any gas that is dissolved in "the liquid and the disassociated gas can be :pumpedout through the pipe 3%. In the latter event, the upper pipe 28 would be plugged similar to the structure shown in Fig. 1 and a suction pump would be connected with the tube 30.

It is further evident that if the liquid in the cen tral pipe 2 is heated by a surrounding body of heated fluid in the compartment 6, the disassociation of gas from the central column of liquid is facilitated. As in the case of the structure shown in Fig. 1, the device illustrated in Fig. 5 provides a highly eflicient exchange of heat be- 5 and I8 so that the disassociation of the gases contained within :the liquid is facilitated at these elevated temperatures. l

The heat transferring fluid is introduced into -:.thechamber 6 through a pipe 8' which is threaded in a boss I, the fluid being placed un- -der pressure at a reservoir 90. upwardly through the chamber and leaves at the pipe 3 as was explained in connection with Fig. 1.

The fluid moves The casings l and 2 have been shown as being made separate and secured together at their ends although if desired, the e ements could be cast integral as indicated in Fig. 1.

The layer formation of the liquid serves to cause ready absorption of the gas if the latter were maintained under considerable pressure. Other advantageous results may be obtained by admitting the gas through the tube 30 and exhausting the same from the tube 28, thus causing the gas to move through the central container in a direction opposite the downward spiral movement of the liquid. In some cases,

- it may even be desirable to have the middle portion evacuated of gas and operated under a partial vacuum. In fact, the versatility or adapt- ..ability' of the device is practically limitless as to i uid, that may be employed in each of the compartments 6 and I8, and the manner in which -such fluids are introduced.

the various combinations of fluids, gas and liq- The primary feature or consideration in all of these uses or adaptations is the fact that the in the form ofa relatively thin but thoroughly continuous layer which offers the greatest exposure both to the wall 2 and also to any gases contained within the wall.

' Figures '7 and 8 show still further modifications I which are based, for the most part, on the structure as illustrated in Figure 1 except that the plug 118 is provided with an opening which tightly and 8. When gas under pressure is forced through the pipe 32 from a source (notshown), the gas column is caused to rotate around the interior surface of the wall 2 and also to move downwardly over the wall in a spiral path. Thus, the gas is caused to strike the liquid layer which is also travelling through a spiral path at many areas, causing the liquid to absorb or in some other manner to react with the gas during the downward travel and particularly, if the liquid is maintained at an elevated temperature.

From the foregoing, it is evident that I have disclosed an improved form of heat exchanger in which the velocity is increased by spiraling the liquid so that the average net liquid velocity is much greater than can be obtained with conventional falling film heat exchangers. These high net liquid velocities result in exceptionally high heat transfer rates. The turbulence in the liquid layer next to the tube wall is also increased and this increase of turbulence enhances still further the heat transfer effect which is obtained at the "higher liquid velocities. The spiral motion and the use of a chamber leading into an annulus results in good distribution of liquid around the periphery of the tube, and in addition, the centrifugal force exerted at all sections of the tube results in a uniform thickness of the liquid layer. When gas is admitted to the tube, the spiral motion prevents small droplets of liquid from breaking away from the liquid layer and entering the gas stream. Any such droplets that do leave the liquid ar immediately thrown back into the "layer'due to the spiral motion of the liquid. The

heat exchanger is unique in that it provides a restrictive; reference being bad to the appended claims rather than to the foregoing descripton to indicate the scope of the invention.

Having thus fully described my invention, what I claim as new and desire to secure by Letters Patent, is:

1. Heat exchange apparatus comprising a hollow cylindrical container terminating in portions of enlarged diameter, a cylindrical jacket secured to the end portions 01" the container to leave an annular space between the intermediate portion cf the container and the jacket, a tangential port in one of said enlarged portions of the container to admit fluid and to provide a whirling action thereof within the said container portion, a cylindrical tube having a diameter slightly less than the size of the intermediate portion of the container to leave an annular space between the tube and said intermediate portion of-the container,

whereby the whirling fluid as it leaves said annular space is confined as a layer'against the container, inlet and outlet ports at opposite ends of 8 said-jacket for introducing liquidin heat transferring relation with respect to the liquid in said container. 1 Y

2. Heat exchange apparatus comprising a hollow cylindrical container terminating in portions of enlarged diameter, a cylindrical jacket secured to the end portions of the container to leave an annular space between the intermediate portion of the container and the jacket, a tangential port in one of said enlarged portions of the container to admit fluid and to provide a whirling action thereof within the said container portion, a cylindrical tube having a diameter slightly less than the size of the intermediate portion of the container to leave an annular space between the tube and said intermediate portion of the container, whereby the whirling fluid as it leaves said annular space is confined as a layer against the container, an inlet port in said jacket at the end of the apparatus opposite from said tangential port and tube, an outlet port in said jacket at the end of the apparatusadjacent said tangential port and tube, and means for maintaining the interior of the jacket full of liquid and to cause the liquid to move in a direction opposite from the direction in which the fluid layer moves through said container.

3. Heat exchange apparatus comprising a hollow cylindrical container terminating in portions of enlarged diameter, a cylindrical jacket secured to the end portions of the container to leave an annular space between the intermediate portion of the container and the jacket, a tangential port in one of said enlarged portionsof the container to admit fluid and to provide a whirling action thereof within the said container portion, a cylindrical tube having a diameter slightly less than the size of the intermediate portion of the container to leave an annular space between the tube and said intermediate portion of the container, whereby the whirling fluid as it leaves said annular space is confined as a layer against the container, inlet and outlet ports at opposite ends of said jacket for introducing liquid in heat transferring relation with respect to the liquid in said container, means for introducing gas into said tube to cause th gas to intermix with the fluid as it flows through the container in the form of a whirling layer, and a pipe extending into the container at the end opposite from said gas introducing means for carrying away the gas which remains free of said fluid.

GEORGE W. HALDEMANQ REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Linderman Feb. 25, 1941

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