US1690108A - Heat exchanger - Google Patents

Description

Nov. 6, 1928. 1,690,108

C. B. GRADY HEAT EXCHANGER Filed Oct. 30, 1924 5 Sheets-$heet l lb TUBE cm a avaldllrtt'l Nov. 6, 1928.

c. B. GRADY' HEAT EXCHANGER Filed Oct. 30, 1924 5 Sheets-Sheet 2 I gvweutoz Char/e55 6 0 351 GM I Nov. 6, 1928. 1,690,108

- C. B. GRADY HEAT EXCHANGER Filed Oct. 50, 1924 s Sheets-Sheet s /10 'r qns 77 j r: I v 56 751 Q Svwemtoz Char/65D. Grog Nov. 6, 1928.

C. B. GRADY HEAT EXCHANGER 5 Sheets-Sheet 4 Filed Oct. 30, 1924 {inventor Char/e513. Gro Gum,

Nov. 6, 1928.

601.0 WAT Filed Oct. 30, 1924 c. B. GRADY HEAT EXCHANGER 5 Sheets-Sheet 5 Patented Nov. 6, 1928. 5

UNITED STATES PATENT OFFICE.

HEAT EXCHANGER.

Application filed October 30, 1924. Serial No. 746,736.

The present invention aims to provide a heat exchanger adapted for various uses, a modification and certain clearly indicated parts of which are shown in my application Serial No. 665,266, filed September 28, 1923.

Several alternative improvements of the invention are illustrated in the accompanying drawings in which Fig. 1 is a vertical longitudinal section of a portion of a heat exchanger."

Fig. 2 is a vertical section through a modified form of heat exchanger.

Fig. 3 is a fragmentary front view showing the staggered arrangement of heat exchanging elements of Figs. 1 and 2.

Fig. 4 is a vertical section of the heat exchanger similar to that shown in Fig. 2, but showing certain of the heat exchan ing elements inclined and others disposediiorizontally.

Figs. 5 and 6 illustrate a combined heat exchanger and dust catcher, Fig. 6 being a section on line 66 of Fig. 5.

Fig. 7 illustrates in horizontal section a form of heat exchanger adapted to absorb heat from various hot liquids issuing from industrial apparatus and for transferring said heat to another fluid.

Fig. 8 illustrates a heat exchanger similar to Fig. 7, but adapted to absorb heat from hot fluids coming from two separate sources;

Fig. 9 shows an apparatus adapted to absorb heat of waste gases coming from a boiler or the like and adapted to transfer the heat to another medium such as a body of water;

Fig. 10 illustrates diagrammatically a further modification of heat exchanger adapted to transfer the heat of waste gases issuing from a boiler to two other mediums one of which is gaseous and the other of which is liquid;

Figs. 11 and 12 illustrate alternative constructions.

Referring in detail first to Fig. 1 of the drawings 10 is a duct through which hot gases are passed. for example, from the inlet end 12 toward the outlet end 14. Extending transversely across this duct are a plurality of heat exchanging elements designated as a whole by -numeral 16. Each of these elements comprises a hollow tubular member containing a fluid 18 in the bottom thereof and a vapor of such fluid in the remainin space 20. The elements 16 are preferably hermetically sealed and practically all of the air is exhausted therefrom. Extending longitudinally through the space 20 of each heat exchanging element is a pipe or conduit 22. As thus arranged it is evident that by circulating a fluid through the several pipes 22 a transfer of heat can be obtained. The hot gases flowing through the duct 10 contact with the multiplicity of tubular heat exchanger units 16, the latter containing a liquid which is evaporated.

In Fig. 1 the relatively cool fluid to be beated is fed from a header 24 and circulated through the several pipes 22 which extend longitudinally through the heat exchanger elements 16. Fluid thus heated passes out as indicated by the arrow to an outlet header 26, the several pipes 22 being connected by bends 28 at the ends of the exchanger elements 16. The exchanger elements are arranged in banks and the banks are staggered as illustrated in Fig. 3.

In Fig. 2 I have shown a duct 30 in which the hot gases are circulated in the direction of the arrows from the inlet end 32 to the outlet end 34. This duct is provided with a vertical wall or partition 36 which with the wall 38 at the left forms another duct 40 through which a fluid is circulated as indicated by the arrows. In this figure I also show a supply header 42 to which is connected a series of pipes 44 which project into the heat exchanger units 16 which in this case are inclined. The pipes 44 extend only a short distance into one end of each unit 16 and are formed with return bends 46 at their inner ends so that the cool fluid to be heated can flow serially through the several pipes 44 and outward to the header 46. The upper most unit 16 in Fig. 2 contains the greatest volume of liquid 18 and the lowest unit contains the least amount. the intermediate units being substantially uniformly graded between these two extremes. It is apparent that the amount of absorption for the diiferent parts of the exchanger may vary and that by using a greater or less amount of liquid 18 in different parts of the exchanger this variation may be compensated for and thus prevent bursting of the units in the hottest zone.

The hot gas or other fluid to be cooled passes through the duct 30 progressively giving up its heat to the successive exchanger elements 16 and evaporating the liquid contained therein. The fluid to be heated which is circulated through the pipes 44 progressively condenses the vapor in the said exchanger elements 16. thus absorbing the heat therefrom. There will be a different pressure and temperature inside of each horizontal row of heat exchanger elements. There is therefore a perfect counterflow action. It is apparent that in the embodiment of the invention shown in Fig. 2 there is a heat transfer from the gases circulated through the duct 30, to a fluid such as gas or air circulated through the duct 40 and also a transfer of heat to a fluid which may be a liquid circulated through the pipes 44 from the header 42. I have discovered that with such an apparatus and method of operating the heat transfer is of much higher order than that obtained in the usual form of direct type air heaters in which the gases and air pass either in parallel or countercurrent through separate passages. I have also determined that when water or other fluid is circulated through the pipes 44 which are in contact with a vapor the heat transfer is much more.

rapid than that obtained in forms of exchanges heretofore used.

In Fig. 4 I have illustrated in vertical section a heat exchanger combining in one structure the arrangements shown-in Figs. 1 and 2. In this figure the upper heat exchanger units 16 are disposed horizontally like those shown in Fig. 1 and the pipes 22 extend horizontally through the vapor space of such elements. The lower section of this heat exchanger is made up of elements 16 which are inclined to the horizontal and provided with return bend pipe sections 44 substantially the same as those shown in Fig. 2. As before, the hot gases circulate upward in the direction of the arrows through a duct 30 and the air or other fluid to be heated circulates downwardly through a duct 40.

In Figs. 5 and 6 I have illustrated a heat exchanger well adapted to absorb the heat from the waste gases coming from a' boiler or like piece of industrial apparatus and adapted to transfer the heat thereof to two other mediums, one being a gaseous fluid such as air and the other being a liquid such as water. This apparatus is particularly well adapted for use as a combined air heater and economizer and is also provided with means for trapping the solid material such as flue dust and carbon particles entrained in the waste gases. In this form of the apparatus the heat exchanger elements 16 are disposed vertically and filled with a suitable fluid 18 as before with a space 20 at the top which is filled with a vapor of the liquid 18. The hot waste gases from the steam boiler or other apparatus flow in the direction of the arrows from the inlet end 48 toward the outlet end 50 of a duct 52. A partition wall 54 separates the duct 52 from a second duct 56 through which air or other fluid is adapted to be circulated in the direction of the arrows so as to absorb the heat from the upper portion of the units 16. Certain of the units 16 terminate as indicated at 58 just below transversely extending pipes 60 which connect headers 62 and 64. Similar units, two of which are shown in dotted lines staggered with relation to the units shown in full lines in Fig. 5, extend upwardly to the top surface 62 of the apparatus, so that the heat thereof can be in part transferred to the feed water or other fluid circulated from the headers 62 and 64 through the pipes 60. The space surrounding the pipes 60 and upper portions of the units 16 will be packed with a suitable heat conducting material as indicated at 66. A dust catcher 68 comprising a substantial rectangular tank is disposed below the units 16 and is adapted to trap dust particles entrained in the gases flowing through the duct 52. This dust catcher is provided with a plurality of partition walls 70 dividing the same into a plurality of compartments, each compartment communicating by means of a branch 72 with a pipe 74 through which the dust may be sucked out by vacuum or washed by a stream of water circulating through the pipe.

In Fig. 7 I have illustrated an apparatus adapted to absorb heat in the liquid coming from various types of industrial apparatus and for traiisferring such heat to another fluid such as water. In this form of device hot liquid such as oil coming from an industrial apparatus through a pipe 76 will flow through a conduit 78, giving up its heat by vaporizing a liquid in the heat exchanger elements 16. The cooled oil or other liquid will be carried off by a suitable outlet pi e or header 80. The water or other fluid to lie heated will be supplied from a main 82 and flow through the conduit 84 in contact with the upper ends of the heat exchanger elements 16 and the heated water or other liquid will flow in the direction of the arrow to the outlet main 86.

i Fig. 8 exemplifies a heat exchanger adapted to absorb the heat from two hot fluids coming from an industrial apparatus and for transferring such heat to another fluid. In this apparatus hot air passes through a duct 88 in the direction of the arrows and gives up its heat to the liquid contained in the exchanger elements 16. Hot oil passes from a main header 90 through a conduit 92, also giving up its heat to the liquid within the unit 16 the oil thus cooled, passing out by way of a pipe 94. This particular type of apparatus adequately meets the cooling needs of a large steam turbo electric generating apparatus. With such apparatus it is highly desirable to cool the oil and air and to recirculate them. It isedvantageous in many localities to use salt water as a cooling me dium. In such cases the different parts of the apparatus wit-h which the salt water contacts will be protected by a suitable coating to avoid corrosion. The water will be supplied through a main 96 and passed through a conduit 98 in contact with the upper portion of the exchanger units 16 and will be discharged through an out-let main 100.

Fig. 9 illustrates a heat exchanger adapted to absorb heat from waste gases coming from a boiler or the like, and for transferring the heat to another medium such as water. In this case the hot gas issuing from the boiler passes through the duct 102, giving up its heat to the liquid in the exchanger units 16 which in turn transfer the heat to water or other fiuid circulating through a conduit 104 from an inlet main 106 to the outlet main 108.

Fig. 10 illustrates an apparatus adapted to absorb heat from the waste gases emanating from a boiler or the like and for transferring such heat to two other mediums one of which is a gaseous fluid such as air and the other of which is a liquid. This particular embodiment of the invention is adapted to serve as a combined air heater, economizer and dust catcher. In this figure 110 represents a conventional type of water tube boiler having an outlet port 112 for the hot waste gases, the latter starting their journey toward the stack through a duct 114 disposed horizontally over the tube banks of the boiler. Projecting into the duct 114 are a series of heat exchanger elements 16 which, like those previously described, contain liquid in their lower parts and a vapor in their upper parts. Part of the heat of the waste gases is transferred through the units 16 to a current of air flowing through a duct 116 and the re mainder of the heat is transferred'to' water or other liquid which enters a pipe 118 and passes through a duct 120 into which the upper ends of the heat exchanger elements 16 project as shown in dotted lines, the heated water passing out by way of pipe 122.

This apparatus is also provided with a catch hopper 124 having an upper portion 126 slightly elevated above the lower wall of the duct 114 so that a portion of the dust en-v trained in the waste gases flowing through said duct- 114 will be trapped and flow into the hopper. 124. Beyond the hopper 124 is located asecond hopper 128 of relatively greater capacity. This connects with the duct 114 by means of a vertical duct 130 of gradually decreasing sectional area so that the velocity of the fluid stream passing therethrough is substantially increased. That portion of the dust entrapped by the hopper 124 will be discharged downwardly into the bot-tom of the hopper 128 and the dust-free waste gas will escape to the "stack through a pipe 132. At the point of connection between the hopper 128 and the hopper 124, I provide a pivoted valve or damper 134.

The hot gases in their passage through the duct 114 of necessity strike the heat exchanger elements 16 and the dustparticles entrained 1n such gases impinge on these elements and fall on the comparatively smooth plate 136 which forms the lower portion of the duct 114. The greaterproportion of the dust thus precipitated is trapped in the hopper 124 and is gradually discharged past the damper 134 to the hopper 128 and the remainder of the dust particles are trapped in the hopper 128 a after their passage through the duct 130.

In the various embodiments of the invention herein illustrated the ducts or passages may be constructed of steel plate or other suitable material properly reinforced, fitted and fabricated, and will of course be covered air from the remaining portion so'that it will contain substantially only water vapor, and then hermetically seal said elements by Welding or otherwise, it is to be understood that I may construct these elements of any suitable material of any desired shape, the important point bein that I partially fill such elements with any desired liquid or mixture of liquids and keep them substantially free from air in any desired manner.

The invention ma be utilized in industrial applications othert ian those specifically referred to hereinbefore, for example, the heat exchanger elements may be incorporated in apparatus for abstracting a sensible heat and obnoxious fumes from waste gases coming from a smelter or similar industrial ap paratus. Such gases frequently contain fumes which are both dangerous and obnoxious and form a nuisance to the surrounding neighborhood when discharged into the atmosphere. The apparatus herein described provides the easiest, most feasible and most economic method for preventing such obnoxious fumes from being discharged into the atmosphere. The apparatus disclosed being adapted to cool such fumes to a point where sublimation occurs, that is to say such gases change almost instantly from a gaseous to a solid state without becoming a liquid, and in most cases they sublime into a fine powder or dust. y

In Fig. 12.1 have illustrated a slightly modified form of heat exchangers unit in which the'tops of the heat exchanger elements 16 are joined to pipes 16 which carry a cool medium to be heated, the lower portions of said pipes being exposed to the vapor in said elements. The joining of the elements to the pipes may be accomplished by welding, or in an desired way. The units thus formed will be economical to manufacture, convenient for shipment, easy to erect, and will permit a close nesting of the elements.

In Fig. 11 I have illustrated a slightly modified form of heat exchanger unit in the form of a U-tube having vertical legs 16 and 16 joined by a bridge portion 10*. The lower portion of the legs 16 and 16 are filled with a suitable liquid adapted to absorb the heat passed through the duct into which the lower part of the U-tube projects. The upper legs 16 and 16 contain a vapor which 1s adapted to be condensed by the fluid passed through the upper conduit. The U-tubes may be either arranged in the conduits in the manner illustrated or they may be turned 90 so as to permit of closer nesting. This type of exchanger unit is somewhat less expensive to manufacture it being apparent that because of the U-connection at the bottom, the closures corresponding to the closures in the lower ends of the single tubes is done away with. In other words, with the U-tube type there are two closures necessary at the top of the legs 16 and 16 On the other hand for a given capacity using simple stralght tubes we would require two straight tubes each of which would have to be closed at the top and bottom, that is four closures for the simple straight tubes against two closures for the U-tube type.

In experiments which I have made heat exchangers of the type herein described with tubes of steel and with tubes of brass, I have secured a much higher heat transfer in British termal units per degree difference in temperature per hour from the hot surface of the tubes to the air, and also from the vapor to the water in the pipes exposed thereto, than has been obtained in the air heaters and economizers now enerally in service. The data obtained indicate that the more nearly complete the air exhaustion, the better the heat transfer. They also indicate that the pressure in the tubes will not rise to an amount that will distort them past the elastic limit, or burst them, with the hot fluid entering the heat exchanger at 900 F. These experiments also show that there is an extremely fast, rapid, efficient and continuous circulation existing in each element when the heat exchanger is in service..

There are many advantages of my indirect type of heat exchanger as compared with the usual direct type of heat exchangers now in use in industrial and generating plants. In most of the power stations now in operation the gases are leaving the boilers at a fairly high temperature, many of them up as high as 600 F. and some even higher. Some power stations are equipped with economizers, some with air heaters, and a few with both economizers and air heaters arranged in series. With an economizeritispossible to savealarge percentage of the waste heat in the gases if we feed the economizer with low temperature water, such as water at or somewhat near the hotwell temperature from a condenser. By this means we make an efiicient recovery from our waste gases, but we sacrifice to a great extent, the economy that can be derived by bleeding the steam turbines. A well designed air heater can extract a fairly large percentage of the heat in the waste gases coming from the boiler, but inasmuch as the mass flow of the gas is always substantially greater than the mass flow of the air needed for combustion, the air heater alone is inherently inefficient. The combination of an economizer and an air heater in series is more efiicient, but such an arrangement is costly and requires a large amount of space. A very ellicient apparatus for extracting the heat from the gases coming from a boiler is the novel arrangement shown in Figs. 2 and 5. In this apparatus there is a progressive serial heat transfer from the hot medium to be cooled, namely, the waste gases from a boiler to the cool mediums to be heated, namely, the air for combustion and the feed water for the boiler. The heat transfer takes place in one small compact apparatus, each of my heat exchanger tubes extracting heat from the gases and transferring part of it to the air and part to the water. My apparatus is flexible in design. For instance, the area exposed to the hot gases may be proportioned for any desired heat drop. The areas receiving the condensed vapor for transmitting the heat to the air and water may be definitely proportioned so that this heat will properly be divided. In the usual forms of direct type air heaters the gases and air pass through a plurality of small channels, sometimes parallel, sometimes perpendicular to one another. Most of the air heaters in present practice are constructed of thin metal. It is a well known fact that the transfer of heat from one gas to another in such prior apparatus is of a-low order. In the usual form of direct transfer economizer the gas passes over a number of tubes inwhich the water to be heated flows. While the transfer rate in this case is somewhat higher than in the air heater, it is still of a comparatively low order.

In my apparatus the hot gases are in contact with tubes containing a liquid which is evaporating and I have discovered that the heat transfer in this case is of a much higher order than in either of the first mentioned cases. The air to be heated is in contact with tubes containing condensing liquid, and this transfer is also of a much higher order than that of the ordinary air heater. The water fer obtained in a condenser. For instance,

in the ordinary direct cconomizer the rate of heat transfer into the water would probably be of the order of about 5 B. t. u. per square foot per degree difierence per hour. In a condenser this rate of transfer is of the order of 400 to 800 B. t. u. per square foot per degree difference per hour.

For example, my heat exchanger shown in Fig. 10 above and receiving the waste gas from a cross drum water tube boiler, the gases would leave such a boiler under normal operating conditions at, say, 550 F., leaving the heat exchanger at any desired tempera.- ture. The air heating surface would be proportioned so as to receive any desired percentage of the heat absorbed in the lower por tion of the heat elements and the waterhcating surface proportioned to absorb the remainder. In an old power station where no provision has been made for bleeding the steam turbines, it would probably be advis able to pass all of the condensate through the heat exchanger, entering same at a temperature at or near the hotwell temperature. In a new station it may be advisable to pass only a portion of this low temperature water' through the heat exchanger, then to discharge said Water into the suction lines of the boiler feed pumps or into a closed heater forming an integral part of the usual water heating system utilizing steam bled from the turbines, such as are now installed in most modern ower stations. With such an arrangement cut down the enormous waste of heat carried by gases into the atmosphere, and am still able to take advantage of the efficiencies gained by bleeding the steam turbines to a point almost equal to the usual practice, thus giving us a substantial gain in economy over ;the present practice.

In the usual type'of air heater and economizer, if one of the elements comprising the apparatus should break it is necessary to shut the apparatus down, as soon as possible repair and replace said element, as they are always connected together. In my apparatus each individual heat exchanger tube is a separate and distinct element, and if a few should break there is no necessity of shutting the apparatus down, and the result would simply be a very small decrease in efficiency.

In many industrial enterprises where heat exchangers are used or where they may be used in future, the fluids or mediums to be cooled have corrosive effects and in such cases my heat exchanger is superior to the direct forms now in use. For example, the waste gases leaving boilers and many other apparatuses deriving their heat from coal burning furnaces, contain sulphur dioxide and 9ther gases together with water vapor. At a cer tain temperature which is usually less than the exit temperature of the gases leaving a highly eflicient heat exchanger, an acid is formed which deposits on the heat absorbing elements of the heat exchanger, corroding and finally destroying them. The same is also true of some-fluids used as a cooling medium. For instance, for industrial plants located near an ocean, salt water is one of the most easily obtainable and economical agents for use as a cooling fluid or medium. It is a well known fact that saltwater, especially when it is heated, has a severe corrosive effect upon many metals. In my indirect heat exchanger only a portion of the heat absorbing or heat releasing surfaces are exposed to the fluids .or mediums to be heated or cooled, and if only one of said mediums has a corrosive action, then said action is limited to the area exposed. Said area with my heat exchanger built of individual elements, having much higher transfer rates than the usual elements now in use for direct heaters, will obviously be smaller andcan be far more easily and economically protected by a non-corrosive coating or by using'a non-corrosive material for the particular part exposed to corrosive action. Considering a case where we are ex tracting the heat from a corrosive fluid, such as waste gas from coal fired boilers and at or near the rear end of our heat exchanger, we desire to maintain an exit temperature of 150 F., and our fluids to be heated have an entering temperature of F., itis a well known fact that with usual conditions of humidity and moisture in the coal, aporrosive liquid will be deposited upon the elements of any direct type of heat exchanger. The temperature of the-heat absorbing surface will necessarily be an arithmetical means between the above mentioned temperatures irrespective of the areas of the heat absorbing and releasing surfaces. Inasmuch .as the surfaces in my heat exchangers are separate and distinct by themselves, and my transfer is indirect instead of direct, itis possible with my heat exchanger to maintain a. temperature of the heat absorbing surfaces above the dew point of the waste gas leaving the exchanger.

My heat exchanger elements are well adapted for the application of any form of extended surface. If my heat exchan ers are manufactured of round metallic tu es, the application of extended surface would of course decrease the amount of round tube area necessary. I

My apparatus is well adapted for the application of any desired soot-blowing or washing arrangement to keep the elements free from too great an amount of dirt and dust. For instance, in using my heat exchanger as an air heater with waste gases from a boiler, a. soot-blowing apparatus similar to that now used for water tube boilers may be installed and the problem of cleanin" the apparatus is satisfactorily taken care 01'. Such an ap )aratus or any method as etiicient or as satisiiictory could not be installed on the usual types of air heaters now in service, and it is clear that m indirect heat exchanger has a distinct advantage in the matter of cleaning.

Though I have described with great particularity the specific construction of the various structures embodyin the invention it is not to be construed that ffilll limited thereto as various changes and substitution of mechanical equivalents may be made by those skilled in the art without departing from the invention as defined in the appended claims.

hat I claim is 1. A heat exchanger comprising a. plurality of containers each carrying a liquid in its lower portion which is exposed to the hot medium to be cooled and adapted to carry a vapor generated from said liquid in an upper portion which is exposed to the cool medium to be heated, and pipes arranged to carry the cool medium and in contact with said vapor in the successive containers.

2. A heat exchanger comprising a number of containers, each carrying a liquid in its lower portion which is exposed to a hot fluid to be cooled, and adapted to carry a vapor generated from said liquid in an upper portion, the tops of said containers being attached to pipes arranged to carry the cool medium, said vapor being in contact with a portion of the surface of said pipes.

3. A heat exchanger comprising in combination a duct for the passage of a hot gaseous medium, a second duct adjacent to the first for the passage of a gaseous medium to be heated, means for effecting an exchange of heat comprising a plurality of evacuated containers partially filled with liquid to be vaporized having portions extending into the path of the gases in each duct, and means for transferring a portion of the heat to a liquid comprising a third duct in contact with the containers to absorb heat from the vapor by conduction.

4. A heat exchanger comprising in combination a duct for the passage of a hot gaseous medium, a second duct adjacent to the first for the passage of a. gaseous medium to be heated, means for effecting an exchange of heat comprising a plurality of evacuated containers partially filled with liquid to be vaporized extending into each duct in the paths of the two gases, and means for transferring a portion of the heat to a liquid in circulation comprising a third duct extending into the containers and exposed to the vapor thereinf 5. [a heat exchanger comprising in combination a. duct for the passage of a hot fluid medium, a second duct adjacent. and. parallel to the first for the passage of a gaseous medium, means for transferring heat from the hot medium to the gas comprising a plurality of evacuated containers carrying liquid to be vaporized in their lower portions, the lower portions of the containers extending into the first mentioned. duct, the upper portions carrying the vapor of the liquid extending into the other duct, and means for trans ferring a portion of the heat to a liquid medium consisting of a third duct in contact with the containers.

6. A heat exchanger comprising in combination a duct for the passage of a hot fluid medium, a second duct adjacent and parallel to the first for the passage of a gaseous medium, means for transferring heat from the hot medium to the gas comprising a plurality of evacuated containers carrying liquid to be vaporized in their lower portions, the lower portions of the containers extyending into the first mentioned duct, the upper portions carrying the vapor of the liquid extending into the other duct, and means i or trans ferring a portion of the heat to a liquid medium consisting of a third duct in contact with the containers and exposed to the heat of the vapor therein.

7. A heat exchanger comprising in combination a duct for the passage of a hot fluid medium, a second duct parallel and adjacent to the first for the passage of a gaseous medium, means for transferring heat from the hot medium to the gas comprising a plurality of inclined evacuated containers carrying liquid to be vaporized in their lower portions, the lower portions of the containers extending into the firstmentioncd duct, the upper portions carryin the vapor of the liquid extending into the other duct, and means for transferring a portion of the heat to a liquid medium comprising a third duct in n contact with the containers.

8. A heat exchanger comprising in coinbination a duct for the passage of a hot fluid medium, a second duct parallel and adjacent to the first for the passage of a gaseous me 115 dium, means for transferring heat from the hot medium to the gas comprising a plurality of inclined evacuated containers carrying liquid to be vaporized in their lower portions, the lower portions of the containers 120 extending into the first mentioned duct, the upper portions carrying the vapor of the liquid extending into the other duct, and means for transferring a portion of the heat to a liquid medium comprising a third duct 1 5 in contact with and exposed to the heat of the vapor in the containers.

9. A heat exchanger comprisin in combi nation a duct for the passage of aliot aseous medium, a second duct adjacent to t e first 130 for the passage of the gaseous medium to be comprising a third duct through which liquid heated, means for effecting an exchange of flows in heat exchange relationship with the heat comprising a plurality of evacuated conportions of said containers in which Vapor 10 tainers partially filled with liquid to be vais present.

5 porized having portions extending into the In witness whereof, I have hereunto signed path of the gases in each duct and means for my name transferring a portion of the heat to a liquid CHARLES B. GRADY.

Images