US2713994A - Heat exchanger - Google Patents

Description

July 26, 1955 H. W. A NGELERY HEAT EXCHANGER 4 Sheets-Sheet l Filed May 5, 1950 ehm Ee! Hfs ATTORNEYS July Z6, 1955 H. w. ANGELERY 2,713,994

HEAT EXCHANGER Filed May 5, 1950 4 Sheets-Sheet 2 INVENTOR. HENRY W. ANGELERY l HIS M7/44 er m ATTORNEYS July 26, 1955 H. w. ANGELERY HEAT EXCHANGER 4 Sheets-Sheet 3 Filed May 3, 1950 July 26, 1955 H. w. ANGELERY 2,713,994

HEAT EXCHANGER Filed May 3, 1950 4 Sheets-Sheet 4 Unite States Patent O HEAT EXCHANGER Henry W. Angelery, Englewood, N. I.

Application May 3, 1950, Serial No. 159,695

5 Claims. (Cl. 257-2) This application is a continuation-in-part of my earlier abandoned application Serial No. 40,959, led July 27, 1948.

The present invention relates to improvements in heat exchangers designed to effect a transfer of heat between two fluids, to a system for maintaining a mass of fluid at a predetermined temperature, and more particularly to improvements in controlling the rate of heat transfer between two fluids when the flow of the subject fluid varies or becomes intermittent.

The term subject iluid as used herein, is applied to the fluid whose final temperature and, if desired, state is to be controlled. The term regnant fluid as used herein, is applied to the uid used to control the temperature or state or both, of the subject fluid.

The subject fluid may be a liquid or vapor Whose final temperature or state, or both, upon leaving the heat exchanger of this invention is controlled by the rate of heat transfer to or from the regnant uid, which may likewise be a liquid or vapor. Thus, for example, where it is desired to heat water to a predetermined outlet temperature by bringing it into out of contact heat exchange relation with steam, the water is the subject fluid and the steam is the regnant fluid.

rl`he heat requirements of a subject fluid, i. e., the amount of heat required to be added to or absorbed therefrom to bring it to a predetermined final temperature, is determined by the volume and specific heat of the iluid and by the difference between its initial and final temperatures. The volume of the fluid is in turn determined by, and a direct function of, its rate of flow. lnasmuch as the rate of ilow of the subject iluid often varies substantially and the initial temperature thereof may vary as well, it follows that its heat requirements likewise vary widely.

The rate of heat transfer between two fluids depends upona number of factors which include the mean temperature differential between them and the area and heat conductivity of the surface separating them if they are out of contact with one another. The principles governing heat transfer between iluids are essentially the same whether the fluids involved be liquid or vapor and whether, if they are a liquid and a Vapor, the heat be transferred from the vapor to the liquid or vice versa.

For this reason, and in order to promote a most thorough and complete understanding of the principles of this invention, the following description is directed primarily to the application of the invention to the transfer of heat from steam to water, wherein steam is the regnant fluid and Water is the subject iluid. It is to be understood, however, that it is not intended to limit the application of the invention solely to such use.

In conventional out of contact heat exchangers, the rate of flow and heat content of the regnant fluid and the effective heat transfer area remain substantially constant although the heat requirements of the subject iluid may vary considerably. The only variations in the amount of heat transferred to or from the subject iluid are, therefore, due to changes in the mean temperature differential between the subject and regnant fluids. This haar is fairly satisfactory when the subject fluid is Withdrawn at a more or less constant rate. It is unsatisfactory, however, when the rate of withdrawal' of the subject iluid varies appreciably or is intermittent.

Thus, for example, when conventional heat exchangers are used to heat water with steam, diiculties arise due to the overheating of the water when its rate of flow is reduced to a minimum or stopped completely. This is usually due to the simple fact that the amount of heat available from the steam greatly exceeds the amount of heat required by the water at small or zero rates of flow. When, on the other hand, the rate of flow of the water is increased to above average the amount of heat that can be absorbed by a given volume of water is too small to raise its temperature to the desired point for the simple reason that the amount of heat made available by the steam is not suiiicient to satisfy the heat requirements of the water.

One object of the present invention is to provide a heat exchanger that is capable of anticipating or sensing the heat requirements of the subject fluid and regulating the flow of the regnant fluid in such a manner as to satisfy those requirements at all times to the end that the final temperature of the subject fluid will remain substantially constant at widely varying rates of flow.

Another object of the invention is to provide, in a heat exchanger, a means for varying the eective area of the surface available for the transfer of heat.

These objects are accomplished by including in the heat exchanger of my invention a novel arrangement of tubular heat transfer elements and utilizing a temperature responsive device to sense the heat requirements of the subject fluid and control the ow of regnant iluid. In its preferred form, my heat exchanger comprises a shell, one or more units of tubular, heat conductive-elements in the form of concentric spirals for the passage of steam, and means for circulating water past a thermostat to regulate the flow of steam into the tubular elements.

Another object of the invention is to provide a heat exchanger through which the more viscous fluid such as water, for example, can pass with a minimum pressure drop.

One advantage of the present invention is that it provides a method and means for delivering a iluid at a substantially constant temperature even though the uid is withdrawn intermittently or at varying rates of How.

This heater can be used as a booster after a storage tank or accumulator with or without recirculation, because of its ability to accommodate wide changes in the flow rate or temperature differential and still properly control the outlet temperature accurately.

These and other advantages will become apparent from the following detailed description made with reference to the accompanying drawing, wherein Figure 1 is a sectionalized view in perspective illustrating one preferred embodiment of the apparatus of this invention.

Figure 2 is a plan view in cross section through a heat exchanger designed for relatively large capacities;

Figure 3 is a cross sectional View in elevation illustrating another preferred embodiment of the apparatus of this invention; and

Figure 4 is a diagrammatic view showing a typical piping arrangement with which the heat exchanger of this invention may be employed to advantage as a hot Water heater.

The embodiment illustrated in Figure l includes a shell 10 having a bottom 11 and a top l2, a bank of concentric spiral tubular elements 14, a vapor inlet 16. a condensate return 17. a vapor feed header 19, a

vapor or condensate return header Ztl, a drain plug 2l, liquid inlet and outlet connections 22 and 24, a tubular member 25, a conduit 27, a temperature responsive element 29, such as a thermostat, and a circulating tube 30.

The bank of tubular elements ld consists of a plurality of units 3l, each unit including two pairs of spiral coil members substantially as shown. The innermost spiral coil member 32 begins at a unit vapor feed header 34 connected to the vapor feed header t9 and, after making four turns, reverses its direction and becomes the outermost spiral coil member 36. After again making four turns, spiral coil member 36 ends at a unit vapor or condensate return header 37 connected to the vertical vapor or condensate return header 2u. The spiral coil member 39 next to the innermost spiral coil member 32 begins at the unit vapor feed header 34, makes four turns upwardly adjacent the iirst spiral coil member 32 and then reverses its direction to become the neXt to the outermost downward spiral coil member 4t) terminating in the unit vapor or condensate return header 37 adjacent the outermost spiral coil member 36.

The four coil members shown in Figure l are each of a different diameter but the tubes forming them are preferably of the same diameter. The sum of the coil diameters of spiral coil members 32 and 36 is equal to the sum of the coil diameters of coil members 39 and 40 with the result that the length of the path through one pair of coils, connected in series as shown, is equal to that of the other pair. inasmuch as the tube diameters and the number of turns of each coil member are the same, it follows that the pressure drop through one pair of coils must be equal to that through the other.

It is to be understood, of course, that the unit 3l of spiral tubular elements 14 is representative only of a plurality of such units that are connected in parallel between the vertical vapor feed header 19 and the vertical vapor or condensate return header Ztl. lr the pres sure drop of the vapor flowing through the pairs of spiral coil members and the design capacity of the heat exchanger permit, it is, of course, within the contemplation of this invention to use only one unit of one or more pairs of spiral coil members and to eliminate the vertical vapor feed and vapor or condensate return headers t9 and 2i).

By the same token, it is within the contemplation of this invention to have three, four 0r more pairs of spiral coil members in each of one or more coil units, so long as the sums of the diameters of the coil members in the various pairs are equal.

lt is also to be understood that while the members in the various coil units are most advantageously arranged concentrically to utilize to a maximum the space available within the shell, the invention is not limited to such an arrangement but is intended to include any arrangement wherein the heat transfer elements are connected in parallel and offer the same resistance to the flow of uid.

The tubular member 2o is supported from the bottom 1l by a number of feet 4l. The upper end of the tubular member 26 is open for the passage thereinto of the conduit 27 and a tube 42 enclosing the thermostat leads 4d. A partition 46 is provided in the lower portion of the tubular member 26 to form a closed well for fluid entering the tube at the open upper end and to support the circulating tube 39 which encloses the thermostat 29 and the thermostat lead enclosing tube 42. The circulating tube 3i) is open at the top and opens into an aspirating chamber i7 to permit circulation of at least part of the fluid in the shell through the tube. The conduit 27. after passing through the .partition 46, terminates in a nozzle 43 that is in line with a ditfuser 49 in the otherwise closed end Sil of l increased to any desired degree.

the tubular member 26, said diffuser terminating above the level of the bottom 11.

in operation, when it is desired to utilize the heat exchanger for heating a liquid with a vapor, the liquid enters the shell through the conduit 27 whenever liquid is withdrawn from the outlet connection 24 and, by reason of its passage through the aspirator, consisting of the chamber 47, the nozzle 48, and the diffuser 49, induces a circulation of at least part of the liquid in the shell through the circulating tube 3i) and past the thermostat 29. The ow of cold liquid through the conduit 27 withdraws heat from the liquid in the well formed by the tubular member 27 and the partition 46. This in turn withdraws heat from and thereby lowers the temperature of the liquid liowing through the circulating tube Si). The thermostat 29 thereupon operates to open a valve Si, such as a. Spence T 1GO temperature regulator valve shown in Figure 4, and thereby controls the rate of flow and pressure of vapor through the tubular elements 14. If the temperature drop at the thermostat is slight, the pressure of the vapor admitted to the tubular elements by the valve 51 will be suriicient to lill only a portion thereof with the vapor, with the result that the effective area of the heating surface will be small. lf, on the other hand, the temperature drop is appreciable and therefore reflects a high heat demand, the pressure of the vapor admitted by the valve 5l will be suiiicient to overcome the pressure drop through the coils with the result that the effective area of the heating surface will be increased to the maximum.

When the flow of liquid withdrawn from the heat exchanger ceases or is brought to a minimum, the ow of liquid through conduit 27 decreases correspondingly. This results in a decrease in the amount of heat withdrawn from the liquid trapped in the well and brings about a rise in the temperature of the liquid in circulating tube 30 that surrounds the thermostat 29. The thermostat 29 thereupon operates to close the control valve so that the amount and pressure of the vapor fed to the tubular elements 14 is decreased. This in turn results in the condensation of a portion of the vapor within the coils and, due to the action of check valves in the vapor supply and condensate return lines, operates to decrease the effective surface area of the tubular elements that is available for transfer of heat from the vapor to the liquid.

lf no heated liquid is withdrawn for a period of time sui'licient to result in the cooling thereof due to radiation losses from the shell, the liquid will circulate due to thermal action through the circulating tube 30 and any appreciable temperature drop will be sensed by the thermostat 29 and be retlected in a resumption or increase in ow of vapor through the tubular elements i4.

The embodiment illustrated in Fig. 2 is intended to show how a heat exchanger constructed in accordance with the principle of this invention may have its capacity Any one bank of coils 14 can be increased practically without limit but, in order to avoid toogreat a pressure drop in the fluid flowing therethrough, it has been found to be desirable to utilize two or more sets of vertical headers i9 and 2u for the feed and return of vapor and vapor condensate. In this event the top unit will be connected to one set of headers 19 and 20, the next unit to the other set of headers, and so on. Still more capacity may be obtained by utilizing two or more banks of coils i4. The modification illustrated in Fig. 2 shows how four banks of coils may be placed in a single heat exchanger, each bank having two sets of feed and return headers. In this event, it is not necessary to have a well and thermostat within each bank of coils. lt is sufhcient to have one such control means in only one of the coil banks and it is preferred. as shown in the drawing, to position the control means, including a tubular member 26, conduit 27 and circulating tube Sil, centrally among the various banks of coils. The essential details of the control means are the same as described with reference to TFigure l.

The operation of this modification is likewise essentially the same as that of the embodiment illustrated in Fig. 1. If desired, the heat exchanger of this type may be provided with any suitable arrangement of vertical and horizontal baflies to secure maximum contact of the fluids in the shell with the surfaces of the reverse spiral coils.

The embodiment illustrated in Figure 3 is a modification of that illustrated in Figure l and is designed to reduce to an absolute minimum the hunting of the temperature control system and to increase to a maximum the sensitivity of the thermostat to changes in the temperature and/or flow conditions of the subject fluid in the heat exchanger. n

The heat exchanger illustrated in Figure 3 includes a shell 10 having a bottom 11a and a top 12a, a bank of concentric spiral tubular elements 14, a vapor inlet 16, a condensate return 17, a vapor feed header 19, a vapor or condensate return header 20, liquid inlet and outlet connections 22 and 24 and a thermostat 29. The bank of tubular elements 14 of Figure 3 is substantially identical with the bank of tubular elements 14 illustrated in Figure 1 of the drawing. The unit vapor feed headers 34'and unit vapor or condensate return headers 37 (behind headers 34 in Figure 3) are likewise similar to those illustrated and described with reference to Figure 1.

An inlet conduit 52 is secured to the inlet connection 22 and is provided with a constriction or nozzle 54 at a point spaced from its lower end 56. The thermostat leads 44 are enclosed in a cable or tube 42 which is, in turn, enclosed in a circulating tube 57 that is substantially parallel to the conduit 52. The upper end of the tube 57is spaced from the top 12a of the shell or suitably provided with one or more openings 58 to permit the entry into the tube of at least a part of the liquid from within the shell. A support bracket 59 may be provided between conduit 52 and tube 57 to support the latter. A by-pass 60 is provided between the conduit 52 and the tube 57, the connection of the by-pass with conduit 52 being upstream of the nozzle 54 and the connection of the by-pass to the tube 57 being upstream of the location of the thermostat 29 therein. It will be understood that additional by-pass or sensing tubes may be connected to the tube 57, these additional tubes taking uid from one or more points at lower levels than the by-pass 60. The lower end of the tube 57 communicates with the aspirating chamber and diffuser 61.

It will be apparent from this description that the thermostat 29 will sense immediately the introduction of fresh water due to the admixture thereof, at a point upstream from the thermostat, with the heated water in the interior of the shell and in the upper portion of the tube 57 and that the operation of the thermostat does not depend solely upon the withdrawal of heat from the water in tube 5'7. Consequently, the thermostat 29, in effect, anticipates the heat `transfer requirements within the shell 10 prior to an actual change in the temperature of the water 'within the body ofjthe shell.

When the discharge of water by way of the outlet connection 24 is suddenly stopped, the ow of fresh water through the by-pass 60 also ceases immediately. If the water entering through inlet connection 22 is colder than the water within the shell, as it will be when the heat exchanger is utilized as a water heater, and the movement of water through the heat exchanger is stopped, the water surrounding the thermostat 29 quickly reaches the average temperature or" the water in the shell and is thus able to control effectively the further entry'of steam into the tubular elements 14.

While the circulating means illustrated in Figures 1-3 and described in detail herein are preferred as being the most simple in construction and dependable in performance, it is to be understood that it is within the contemplation of the invention to place the thermostat and recirculating tubes in a separate vessel connected with the shell for circulation of the water.

Figure 4 illustrates a typical manner in which the heat exchanger of the present invention can be utilized as a hot water heater. A steam line 62 having a thermostatically controlled pressure valve 51 of the type exemplied by the Spence T 100 temperature regulator valve, is connected to the vapor inlet 16. The water inlet 22 is connected to a suitable source 64 of water, a valve 66 being provided in the line 64. When the thermostat 29 senses a preselected maximum temperature, it operates to completely close the valve 51 in a known manner. If the temperature at the thermostat goes below said preselected temperature, it will operate to open the valve 51 sufficiently to permit steam to enter the tubular elements 14 under a preselected pressure until sufficient heat is absorbed by the liquid to raise the temperature to the preselected temperature at which the thermostat will operate to close the valve 51.

it is to be understood that the arrangement illustrated in Figure 4 may be utilized with either of the embodiments illustrated in Figures 1, 2 or 3.

When it is desired to cool or condense vapor with a liquid, the conditions within the heat exchanger are approximately the same because the direction of the heat transfer is the same. inasmuch, however, as the liquid is the regnant or working fluid and the vapor is the subject fluid whose temperature and state is to be controlled by the liquid, the thermostat is connected by well known means to actuate a valve, such as valve 66 of Figure 4, for the control of the ow of liquid into the heat exchanger. If the rate of introduction or the heat content of the vapor is increased orfthe withdrawal'of condensed or cooled vapor from the coils is increased, the temperature of the liquid in the vicinity of the thermostat will increase and the thermostat will thus sense the demand for more rapid heat absorption by the liquid. In this modification, the thermostat is connected to actuate the valve 66 controlling the rate of ow of the incoming liquid to increase the rate of flow until the correct heat balance is restored. If the rate of introduction of vapor is decreased or the heat transfer requirements thereof are otherwise diminished, or if the flow of vapor into the tubular elements 14 is stopped altogether, the amount of heat that is absorbed by the liquid from the tubular elements will also decrease and the resultant lower temperature thereof will be sensed by the thermostat 29 due to the circulation of the liquid past it. The thermostat 29 will therefore actuate the ow control valve for the incoming liquid to decrease the rate of ow or stop it altogether until the correct heat balance is restored.

It is` obvious that the principle of this invention can be applied likewise to the cooling of a fluid with a vapor wherein the tubular elements are utilized as expansion coiis for the vapor. In this event, however, the heat exchanger would be used in a position upside down from that shown in Figures l-3 so as not to interfere with the thermal circulation of the fluid around the coils. Furthermore, the headers for the`coils, if more than one unit of coils is used, would be reversed, i. e., the inlet for the vapor would be the smaller of the two or they may be ofthe same size.

In operating a heat exchanger thus modified, the subject Huid would enter the top of the heat exchanger after passing upwardly through the circulating system and descend around the coils as the heat-is being absorbed from it. The aspirator would operate to induce upward circulation of the fluid past the thermostat 29.

lf the demands of the cooled Huid are increased to above normal, the increased flow of the warm input Huid will be reected in the temperature of the Huid circulating past the thermostat 29 which will then actuate a compression pump or valve to increase the rate of expansion of the vapor within the coilsand thus increase the heat absorbing capacity thereof to meet the higher demand. If, on the other hand, the ow 0f cooled uid is decreased to below normal or stopped, the transfer of heat from the liuid will decrease correspondingly with a further reduction in the temperature thereof, with the result that the thermostat will sense the lowering of demand for heat absorption. This in turn will result in the actuation of a compressor or control valve to limit the amount of vapor introduced for expansion in the coils and thereby reestablish the desired heat balance.

In order to more fully illustrate the invention without, however, intending to limit its scope in any way, the following example is included.

Example A heat exchanger similar to that illustrated in Fig. 1 was designed to operate on steam at a pressure of 30 lbs. per square inch gauge and to raise the temperature of water from 65 F. to 160 F. while ilowing at a rate of 50 gallons per minute.

The shell had an internal diameter of 101/2 inches i and a height of 31 inches. lt contained three coil units, each unit consisting of four concentric coil members having nine turns each and coil diameters of 5, 61/2, 8 and 91/2 inches. The 5" and the 9%. coil members were connected in series and the 61/2 and 8 coil members were likwise connected in series to form two pairs of spiral coils, the sum of the diameters of the coil members in each pair being 141/2 inches. Each coil was a 5A" diameter copper tube.

A thermostat located within the bank of coils as shown in Fig. 1 was connected to a Spence T l0() temperature regulator valve on the steam line. A thermometer having scale graduations at 5 F. intervals was inserted into the water line at the outlet connection.

It was found a sudden increase in ilow rate of the water from 5 to 50 gallons per minute, and vice versa, had no perceptible effect on the thermometer reading, although the temperatures may actually vary by one or two degrees F. At the maximum rate of dow, the pressure of the steam was 26 lbs. per square inch gauge at the steam inlet and 6 lbs. per square inch gauge at the steam outlet.

It is to be understood that the embodiments of the invention described herein are the preferred forms thereof and that various changes in size, shape, location and arrangement of parts may be resorted to without departing from the principles of this invention or the scope thereof as defined in the appended claims.

I claim:

1. A heat exchanger comprising a tank for receiving liquid, a substantially vertical inlet tube having an open inner end within said tank to introduce cold liquid into said tank, an aspirator in said inlet tube for creating a Zone of reduced pressure, an outlet to discharge liquid from said tank, a conduit spaced from said inlet tube having one end communicating with the tank and the other end communicating with the inlet pipe at said zone to induce llow of liquid from said tank through said conduit in response to ow of liquid through the inlet tube, means outside of said conduit and tube and within said tank for heating the liquid therein, and a temperature-responsive device within said conduit upstream of said zone in contact with the liquid in said conduit for regulating the heating means, said temperature-responsive device being shielded from said heating means and the water in said tank by said conduit.

2 A water heater comprising a closed shell, an inlet conduit for cold water, a second conduit in the shell, a heating element in said shell outside of said conduits, said second conduit being open at one end to heated water in the shell and connected at its opposite end to the inlet conduit between the ends oi the latter, va ther- -rnostat within the second conduit, aspirator means in the inlet conduit operable by a dow of water through the inlet conduit to induce a ow of heated water through said second conduit from near the top of said shell and past the thermostat, said thermostat being upstream of said aspirator, means to supply cold water from said inlet conduit to said second conduit in proportion to the ow of water through the inlet conduit for mixing with the hot water in the second conduit prior to its 110W past said thermostat, and means responsive to the thermostat to control the operation of the heating element.

3. A heat exchanger for out of contact heat exchange between steam and water which comprises a closed shell for heated water, a bank of tubular elements within the shell for the ow of steam therethrough, a cold water inlet conduit spaced from said tubular elements for discharging cold water into the shell for 110W around `the outside of the conduit into contact with the tubular elements, said conduit extending downward from the upper portion of the shell, a second conduit in contact with the water in said tank, said second conduit being open at one end to receive heated water from the shell, a third conduit connecting and communicating with the rst and second conduits, a thermostat within the second conduit, means responsive to the flow of cold water through the inlet conduit for causing a p'ortion of the heated water and a portion of the cold water to mix and to flow through the second conduit wherein said thermostat is subjected to the temperature of the mixed cold water and hot water, and means responsive to the thermostat to control the fiow of steam into the tubular elements.

4. A heat exchanger comprising a receiver for receiving liquid, means for heating the liquid therein, an inlet pipe to said receiver having an open inner end to supply cold liquid to said receiver to be heated in said receiver by said heating means, an outlet from said receiver, a restriction said pipe between its ends, a conduit connected with said pipe downstream of said restriction and subjected to reduced pressure by ow of cold liquid through said restriction, metering connections between said conduit and the'interior of said receiver and between the conduit and `the pipe upstream of said restriction for withdrawing heated liquid from said receiver and cold liquid from said inlet pipe and metering the ow of heated and cold liquid through said conduit induced by the flow of cold liquid through said restriction, and a thermoresponsive device in said conduit responsive to the temperature of the liquid therein for controlling the means for heating the liquid.

5. The heat exchanger set forth in claim 4 in which the inner end of said inlet pipe is adjacent to the bottom of the receiver, and the means for heating the liquid comprises a plurality of substantially axially aligned coils having multiple convoiutions, the inlet pipe and the conduit extending through said coils substantially parallel with their axes.

References Cited in the file of this patent UNITED STATES PATENTS 1,485,897 West et al. Mar. 4, 1924 1,542,573 Paige `lune 16, 1925 1,714,343 Brown et al May 2S, 1929 1,727,881 Hoyt Sept. l), 1929 1,898,703 Williamson Feb. 21, 1933 1,901,761 McCorquodale Mar. 14, 1933 1,926,342 Lippencott Sept. 12, 1933 2,071,624 Graham Feb. 23, 1937 2,149,737 Jewell Mar. 7, 1939 2,266,242 Osterheld Dec. 16, 1941 2,297,768 Hutchins Oct. 8, 1942 2,337,484 McCollum Dec. 21, 1943 2,372,533 Torbett Mar. 27, 1945 2,481,630 Tramontini Sept. 13, 1949 2,501,012 St. Clair Mar. 21, 1950 2,545,966 McQuitty Mar. 20, 1951 FOREIGN PATENTS

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