US1810912A - Method of heat transfer at high temperatures - Google Patents

Description

June 23, 1931. c. FIELD 1,810,912

METHOD OF HEAT TRANSFER AT HIGH TEMPERATURES Original Filed April 17. 1922 3 Sheets-Sheet l iii-3;; 15

j o z E I 7? I Z' J INVENTOR [iwyfield 71m ATTORNEY C. FIELD June 23, 1931.

METHOD OF HEAT TRANSFER AT HIGH TEMPERATURES Original Filed April 17. 1922 3 Sheets-Sheet 2 L/ZQ 5'.

INVENTOR 1 d ATTORNEY June 23, 1931. 'c. FIELD 1,810,912

METHOD OF HEAT TRANSFER AT HIGH TEMPERATURES Original Filed April 17. 1922 3 Sheets-Sheet 3 Patented June 23, 1931 UNITED STATES PATENT OFFICE CROSBY FIELD, OF BROOKLYN, NEW YORK, ASSIGNOB' TO CHEMICAL MACHIIil'EBY COB- POB-ATION, A CORPORATION OF NEW YORK I METHOD OF HEAT TRANSFER AT HIGH TELEPEBATUBES Original application filed April 17, 1922,

, 1927. Serial My present invention is more or less closely related to certain heat transferring operations of the clases described in my Patent No. 1,403,471, granted J anuar 10, 1922. In the present case, as inmy Pat nt No: 1,619,- 661 granted March 1, 1927, on application Ser. No. 553,640 filed A ril 17, 1922, of which this is a division, t e heat transferring medium is a liquid of boiling point much above that of water, preferably mercury; the temperatures at which heat is to be transferred are usually far above said boiling point of water; the temperatures of heat transfer either to the transferring medium or from the transferrin medium, or both, are determined by the internal pressures at the boiling or the condensing points, or both; and these pressures may be controlled either b hand manipulation 'or automatic action 0 valves, pumps or other suitable pressure controlling devices.

My present invention includes regulating the temperature in the heat transferring-system by controlling the internal pressure by and in accordance with the temperature of a region or substance to be heated or cooled; or by the difierence between the internal and external pressures; and the external pressure may be atmosphere or may be one maintained in an auxiliary part of the system by a vacuumizing or other pressure controllin pump.

In tlie preferred embodiment and in normal operation the ressure is approximately uniform throug out the circuit ofthe heat transfer medium, although the pressure at the boiling or heat absorption point may be higher than at the condensing or heat yielding point.

While the system may be employed partly or exclusively for cooling, the rimary purpose illustrated is heating substances, for distillation, sublimation or chemical reaction which require limiting the temperatures for a predetermined maximum or minimum, or between a maximum and a minimum; or for different temperatures successively.

My present invention includes systems wherein there is a supplemental condenser located beyond the primary condensing re-..

said circulating system.

Serial No. 553,640. Divided and this application filed February a,

gion and adapted to return its condensate to the circulating system. In certain cases the supplemental condenser is beyond the ressure controlling valverin others it is etween the primary condensation or heat yielding} region and the pressure controllingcirculatin system and in others the return is contro ed by a valve opened only when conditions of operation permit.

Preferably all of the systems have pumps, adapted to withdraw foreign gases and impurities from the circulation and these-are preferably arranged to dischar e the impurities into the atmosphere wit out interferin with return of condensate to the circulation and without interferin with the desired vacuum or pressure con ltio'ns within In certain cases the desired operation is continuously endothermic or heat absorbing. In such case the heatin is b the condensation portion of the eye e an the control of however, concerns a'system which will auto- 35 matically control the temperature of a desired region when'the operation in said region requires heating at one time and cooling at another time under conditions where the operation of the fluid medium must shift from a rimary condition of condensing to impart eat, .over to avsecondary condition of boiling to absorb heat; and to do this automatically. This very difiicult special case is frequently met with in the chemical 915 industry. Certain chemicals in the mixture must be heated to a predetermined critical temperature. In certain cases, notably oxidation or partial oxidation of organic compounds, heating to a certain critical temper- 1 0 ature will initiate an exothermic or heat evolving reaction. The heat thus evolved necessarily raises the 5 temperature further and the higher temperature thus produced may cause a decomposition of the product or even an explosion and in most cases it will create a condition unsuitable for the best performance of the desired reaction. Hence one part of my invention concerns'maintaining a body of liquid medium in heat absorbing relation to the same region which is initially heated by condensation of the heated vapor. Where the heat transferring wall is thin sheet steel and the temperature drop between exterior and interior is small," the two operations will come into effect successively and automatically upon change of a few degrees in the temperature of a chemical mixture, even without chan e of the internal pressures. Moreover, w ere there is automatic, thermostatic control of pressures by and in accordance with the heat of the chemicals, as above mentioned, the regulation may be even closer.

Another feature of my invention concerns various methods .of electrically heating and boiling the mercury to be circulated to the region of condensation for imparting heat therein.

The above and other features of my invention-will be more evident from the following description in connection with the accompanying drawings, in which 7 Figs. 1, 3, 4 and 7 are diagrammatic vie s of systems embodying various features of my invention.

Fig. 2 is a sectional-detail on the line 2-2, Fig. 1.

F ig; 5 shows in longitudinal and cross section modifications of the iron filler pieces shown in Figs. 4 and 6.

Fig. 6 is a vertical section on the line 66, Fig. 4.

Figs. 8 and 9 are respectively end and side elevations of one form of electrically heated boiler. v, g

Fig. 10 is an end elevation of another form of electrically heated boiler.

In these drawin the boiler, ipes, valves, condensers, and a other parts likely to contact with mercury are preferably of iron or steel, since such materials are ordinarily not attacked or even wettedby mercury. The

various containers and pipes for performance of the heating function are understood to be properly heat insulated.

Fig. 1 shows a system articularly adapted for certain cases of eating operations where the operation is one of impartin heat and the substance or region to be heate does nbt generate heat in excess of its own radiation losses. That is to say, the sistem is one for continuous or intermittent eat application.

The system comprises a heat absorbing charges through pigs 12 as 9.

come in contact with it. As shown it is hermetically closed by a top 6 communicating through a pipe 7 with a cooling chamber 8, the whole being vacuumized throu h pipe 9 by a ump diagrammatically in cated at 10. istillate or sublimate caught in chamber 8 may be removed through asuitable outlet, as for instance, the 'valve controlled pipe diagrammatically indicated at 11. These parts ma be the ordina vacuum distilling or sub imating unit, su l i as commonly em loyed in the manufacture of petroleum an coal tar products; and the usual mechanical stirring means (not shown) may be emplo ed if desired.

While the mercury oiling element 1 may be usefully em loyed as a cooling element for any desire heat evolving system, it is shown in this case as being electrically heated from any desired source of ower.

As will be evidentfrom the d i'awin the coil 3 is a down-flow condenser and 1t disfrom which the condensed mercury return flow path through pipes 13, "14 and branch pipes 15 15, to the ends of boiler 1. Any uncondense vapor can its further the pressure control instrumentalities.

The internal pressure is controlled b controlling the escape of such" vapor. 1X1 the present case there are two controls either of which may be em loyed separately butwhich are especially a vantageous when einplo ed in combination.

'lhie vapor from 12 is discharged into i 22, from which in normal operation of t device it will be permitted to flow through certain controlling devices into pi e 23, upflow condenser coil 24, vacuuming through pipe 25, check valve 26, pump 10 and dis charge outlet 29. The jacket of condenser 24 is supplied with cooling water thro 11 pipe 240, which water esca es through t e pipe 246. A trap 29a may interposed in pipe 29 containing material adapted to comme with the last traces of mercury vapor,

.thus preventing any mercury from escaping to the outer air.

The suction pump 10 is utilized to maintain in the condenser 24 and pipe 23 a ressure which is usually less than atmosp eric and which in any event is preferably less pass up through. pipe 22 whence progress will be determined by than the. ressureipe.22, which latter is refera I that of t e circulating system. ne of e controls for the pressure is valve 16, operated b fluid pressure through pipe 17, controlled y the thermometric or eat sensitive element 18, the. o eration of which is controlled by ad'usta le mechanism diagrammaticall indicated at 19.

Another control is y means of pressure relief valve 30 arranged in a parallel pipe connection 31. There is also a down-flow check valve 34 in a third parallel pipe 35 through which condensed mercury may flow back into the system.

As shown in the drawin the pressure relief valve 30 may be set or above-atmosphere ressures in the system as by having the weight 300 to the light of fulcrum 301) as shown in Fi 1; or for below-atmosphere pressures as w an the weight is to the left of said fulcrum. When the predetermined pressure is exceeded the valve automatically opens andvents the vapor into pipe '23 and condenser 24. For below-atmosphere pressures the pump will be operated in the usual way. For above-atmosphere pressures escape may be throu h pipe 27, check'valve 28 and outlet 29. i check valve ma be rovided at 26 to revent accidental back ow of gaseous ro ucts from the still into the mercury con enser 24. I

As before mentioned, valves 16 and'30 are ada ted for operation as follows: I

ntainer 5 bein supplied with the .de-

sired amount of su stance 4 to be heated,

pump 10 is started vacuumizing the heating system throu h pipe 25, condenser 24, pipe 23, and one o the valves 1 6 or 30, which may be held open for'the purpose. The resistance 40 being pro is closed, current ows through mercury in the container 1 and also through the walls of the container heating and eventually boiling the same. The hot vapor flows through pipe 2 and condenser coil 3. Material 4 be-' mg cold, practically all of the mercury will be condensed; also the heat sensitive element 18 will be cold so the valve 16 will be closed.

Valve 16 will remain closed until the substance 4 is heated u to the desired critical temperature for which the device 18 is adjusted and ressure relief valve 30 will sta closed unti the internal pressure excee that for. which said valve is set. Normally the boiling, condensing :and heating ma proceed until the internal pressure excee s that for which valve 30 is set and thereafter venting through 30 will control until the mixture 4 ,reaches the critical temperature for which the thermostat 18 is set.

Preferably the thermostat 18 will be set to control at lower pressures than the pressure relief valve 30. Hence when theinaterial 4 is once heated enou h to bring the valve. 16 into action, it wil control exclurly a usted, switch 41 against back flow sively unless or until va or is generated excess of the capacity 0 said valve 16, in

which case the pressure relief valve will act a as an ordina safety valve blowing off at the predetermined higher pressure for which it is set.

Preferably the valve 16 is used for close regulation of below-atmosphere pressures, pipe 23Vbeing vacuumized so that the pressures therein will always be less than that in the circulating system. Usually valve 30 will be set for control where internal pressures above atmosphere are desired and in such dcase valve 16 may be permanently close The liquid condensate can return through said valve 16 whenever it is open, but when- -54 inlpipe 2 or in pipe 31.

The container in which mercury is boiled to absorb heat is long as compared with its ,cross section and is'formed with a central vapor collecting dome 40 and also with reduced ends 44, 44. 'The heating current is supplied through electrodes 42, 42, mounted in insulated blocks 43, '43, in said reduced ends 44. The reduced ends afi'ord the small-. est cross section and greatest heat development tends to localize therein; also the" return of condensate through branch pipes 15,

15, is to these regions of greater heat development. The mass'of mercury in boiler'l 'afiords a 'ath for electric current which is of so muc lower resistance than any other path that the leakage losses in other directions are minimized but insulation ma be employed for parts above the level 0 the liquid mercury, as diagrammatically indicated at 50.

In the apparatus of Figs. 1 and 2, the level of the mercur is referably at or near that indicated by otte line 46, 46. This level is high up in the boiler, is well above the level of return pipe 13, 14, and is well below the level of return pipe 12. Thus the flow of vapor and condensate through pipe 12 is free and unthrottled by any static back pressure of mercury, while the body of mercury in pipes 13, 14, maintainsa liquid seal of mercury vapor through said pipes.

The system shown in Fi 3 resembles that of, Fig. 1 in many respects at has im ortant differences. Analogous elements inc ude reids gion 101 in which the fluid medium absorbs heat and boils, the pipe 102 for up-flow of the vapor, the gauge 139 indicatin internal pressure por condenses for imparting heat to the material 104, the container 105 for the latter, the ipe 112 for outlet of condensate and uncon ensed vapor, the down flow'pi e 113 and the return pipe 114 for return ow of the condensate to the boiler element 101, all being substantially as above described.

A In the present case the boiler 101 is heated by a current from the secondary of transformer T, the primary of the transformer supplied with alternating current through suitable controlling devices including the switch 141. The transformer is particularly useful because of convenience in ste ping down the voltage to-get correspondingy great amperage -or heating eifect. on the mic! 101. t

The pipe 112 leads to and the pipe 113 drains out .of the bottom of a tubular u flow condenser 124, which in this case is between the primary or heating condenser 103, and the. pressure regulating devices. The upper part of the condenser has an outlet through pipe 125 which may be vacuumized b pump 110. In place of the thermostatically controlled valve 16 of Fi 1, there is a pressure relief valve 130 adjustable for ventin at the desired internal pressures, indicate by position of wei ht 1300 as bein less than atmosphere. is valve may ,set for internal ressures greater than atmosphere by shi ting the weight to the other side of the fulcrum. When internal pressures above atmosphere are required, the pump may be cut oil by valves 110a, 1106. Then the outlet will be through parallel pipe 127 which provides a by-pass from the intake 125 to the dischar 129 oflpum 110. This by-pass 127 may contro ed a ressure relief .valve 1306 adapted to be set or venting internal premures above atmosphere. These valves 130 and 1306 are adapted for simultaneous or successive operation somewhat as valves 16 and 30 of Fig. 1, except that the primary valve is controlled by internal pressure instead of thermostatically.

The uncondensed gases passing either through pump 110 or the by-pass 127 flow to the residual condenser 124a. The lower end of this condenser connects through a barometric U-leg 113a, and pipe 1136 with the return pi 114 which leads back to the boiler 101. e level of the mercury is indicated by the dotted line 47, 47, as being near the top of boiler 101; below the draina e pipe 112 and condensers 124,124w but above the barometric U pipe 113a, and the return flow pipes 1136 and 114.

There is a pipe 129! affording an atmospheric outlet from pipe 113w, below the re-.

the worm coil 103 wherein the va-' sidual condenser 12401, but above the level of the mercury. Outlet pipe 129a: may have interposed therein a trap 29h; like the trap 29a in Fi 1. I

It will ie understood that the closed circuit through the residual condenser 124a and the barometric U, 113a, may be used in conjunction with the system shown in Fig. 1, as may also the pipe 129a through whlch uncondensed gases may be discharged to the atmosphere.

In the system shown in Fig. 4, the vacuumizingpump 210, the supplemental condenser 224, residual condenser 22401, the primary pressure relief valve 230, secondary relief valve 230a, container 205 for the material 204 which is to be heated, as also the ad-- justments to be, made and the operations to be performed, may be substant1ally the same 'as in Fig. 3. It is noted, however,

that the supplemental condenser 224 is a down-flow condenser and residual condenser 2240 is a tubular condenser instead of a worm.

The important differences are that the primary or heat imparting condenser 203 is in an external jacket 2030; instead of the internal worm 103 and that instead of a single outlet 112 for both condensate and uncondensed vapor, there are two separate outlets, one a pipe 212' from a low point of the jacket for return of the condensate and the other a pipe 212a from a high point in the jacket for escape of the uncondensed vapor.

This arrangement whereby the ressure of the liquid mercury in the jacket oes not interfere with the circulation of the condensing vapor -facilitates employment of an important feature not found in Fig. 3; namely, an arrangement whereby the normal level of the mercury, indicated byline 47-47, is substantially above the bottom of the container 205, so that the lower portion of said container is continuously bathed in a body of liquid mercury. In normal operation, this mercury will be hot ,condensate which ma be at or near the temperature of condensation as determined by the particular internal pressure then being maintained by the pressure regulating valves. This body of condensate in the jacket is in an im ortant strategic position in several partic ars.

- the same manner The vapor resulting from the boilin has a higher pressure vapor may circulate from the header.

the bottom p movably secured by pins 201:}; so that each the; header and mercury therein por sup 1y tube 502, the

' base of a three? important a vantage of this arrange;

. I5 ment is that the; boiler requires no insulation.

ressure controlling devices. The boiled 05 'quid is replenished through pipe 212 after as the primary boiler 201.

free path of escape through the regu ar' vapor outlet 2120. to condenser 224 and its ressure, condensation and return flow to the acket or secondary boiler may be automatically controlled by the instrumentalities above described for the primary boiler. Obviously however, the ad uStment of the pressure ief valves may be changed if it is desired-to conduct the heat generating reaction at a different temperature from that which initiated it,

' Moreover, where said reaction may be desirably contlnued at a higher temperature requiring a higher internal 'pressure of the mer vapor the sudden and great increase in the total volume of va r due to ilingjnthe Iiacket becoming a mercury stea of a mercury condensing device may be taken advantage of to cause control to shift to a pressure relief and tem erature than the one which controls the iiutfal heating. In such case the sudden increase in volume of exceed the condensing capacity of the first condenser, in which case a valve like 230 set for a below-temperature pres-' sure maybe forced open continuously. and if the pumping capacity of pump 210 is also exceeded valve 230a will become the pressure determining instrumentality.

If the pressure control system of Fig. 1 be em loyed under conditions above describe he thermostatic valve 16 is likely to be too small to sufliciently relieve the increaslngpressure even when wide open, in

which case a back pressure'will be built up e until the pressure relief valve 30 becomes the controlling instrumentality In such case said v'alve30 be set for the desired exothermic reaction temperature and will come into operation automatically whenever said reaction commences.

Another novel feature in Fig.4 is the ri-v mary heat absorbing element or b01812 -This is preferablyof iron and comprises a header 201 having a plurality of depending tubes 201a forming mercury containing pockets into and out of which mercury may These tubes are airs which are connected across y conducting element 2016 rearranged in pair of tubes with 201a is the rimary As indicated in Fig. 6,1; are are preferably three such pairs of tubes, each energized by a difierent current.

valve set for a .ment is for three-phase as in Fig. 6.

that if the mercur formsa single turn secondary of a; transformer of which-201d ,isthe core and usual control devices represented by switch 241. Such control devices may be operated to reduce current or open the circuit in response to excessive or sudden increases of pressure or heat either in the mercury systemor in the container 205. Such automatic regulation is also contemplated for the other s stemsdescribed herein.

Within the depending tubes are referably arran ed iron filler pieces 201;: which normally fioat in the mercury. Their cross sections are shaped so as to aliord separate paths foru ward fiow of hot mercury and vapor and own-flow of cool mercury. Various cross sections suitable for this purpose are shown in Fi 5.

Another nove arrangement for heating mercur' therein is shown in Figs. 8 and 9. Here t e rimary coils 301a encircle the tubes and t e iron filler pieces 201 together with the iron of the tubes, header and cross bar constitute the iron core of the transformer. In this case the heating is entirely by the eddy currents generated in the iron core by the reversals of magnetism thereof in response to the alternating current in said coils 3016. In Figs. 8 and 9 the arran ea 1 10 shows a variationof the above whereiil the primary coil 401d encircles the iron connecting bar 201?) instead of the tubes.

In the system of Fig. 4, it will be noted level were lowered below the bottom of 1acket 203 there would be no body of liquid mercury in the jacket and the entire space would be available for mercury vapor heating. Asystem better adapt d or operation with the mercury above'or below the bottom of the container or at any desired level is illustrated in Fig. 7.

In this figure, the boiler-501 is upright and extends from below the lowest level of mercu indicated by line 147 I47, to a point well a vs the higher level indicated by 47, 47 the former. line bein below the bottom of the jacket 503 and t erlatter above the bottom of container 505. Thisboiler 501 i forms art of a single turn secondary, circuit 0 which isIcompleted through copper bar 501w which is 'of low enough resistance to practically short circuit the rest of. the system. This single secondary is ener ize by primary coil 501e, and controlled; by

cury in the system. In this system, the pressure controlling valve 530 is located in the pipe 5120 between the jacket 503 and the condenser 524 and, as diagrammatically indicated, it is adapted to be set for pressures either above or below atmosphere. The exhaust pump is beyond the condenser and consists of a well-known form of barometric jet condenser com rising the upwardly extending suction tu e 525 for the vapor, dischargin downwardly through the jet 510a in cham r 510 supplied with water through 0 nin 5106 controlled b valve 5100. i h is Slumber connects wit downwardly extending tube 529 which is long enough to afford a barometric column when water is the fluid. The ipe 529 has an outlet at 550 below the leve of the liquid in container 551. This container has two water outlets, one 552 at the proper level to drain off water when the mercury level is at 47, 47, and the other 553, when it is at level 47,, 47. The mercury vapor is condensed by the water and settles out in the container 551.

It might be returned to the system through a barometric U-tube like that in Fig. 3, but as shown there is a hand operated valve at 554 which is opened only when the internal pressures are suitable for in-flow of mercury without disturbing the adjustment of the ap aratus.

the ystem of Figs. 4 and 7, where a body of liquid mercury may be and preferably is maintained in contact with the lower portion of the same container which is being eated by condensation of the mercury vapor, there is special advantage in employing a vertical] arranged propeller to afford vertical (Sire ation of the mixture, andin Fig. 7 I have shown for this purpose a screw ro- Her on the lower end of vertical s aft 1 ournalled in the cover 507 and power driven through an suitable means, as for instance, a gear 72 riven by gear 73 on horizontal shaft 74 which is supfported in a bearing 75 and may be rotated rom any desired source of power diagrammatically indicated by belt pulle s 76, 77, one of which ma be an idler whi e the other is keyed to sai shaft 74. The vertical circulation thus;

rovided is important not only for mixin ut also for driving hot mixture into coo ing relation with. the liquid mercury for boiling the latter during exothermic reactionsand also for displacing the cooler material upward in heating relation with the condensing area of the container when the operation is endothermic.

It willbe understood that the presence of liquid mercury in bathing contact with the same container which is heated by condensation of hot vapor supplied from an outside source is of great importance, not only for controlling the temperature during desired exothermic eactions, but also as an ever 55 present refrigerating medium which will at 430 Fahrenheit under a automatically come into operation as a safety appliance in cases where undesired exothermic reactions may occur by accident as in case of certain im urities in certain mixtures or in case of faulty regulation by the pressure controlling devices.

A not uncommon case is where there is a small amount of impurity capable of oxidizing or other exothermic reaction within the range of the desired operating temperature. 75 In such case the cooling action of the boiling mercury will be su cient to keep down the temperature until the exothermic reaction has been completed, after which the process will proceed as before. In other cases, as'where the amount of material for the exothermic reaction is considerable, it ma be necessary to have expert attendance an regulation to completely take care'of the situation. Even in cases where the dan er never materializes, the advantage of the l lquid mercury as a precautionary safety device is obvious.

It will be understood as to all of the systems shown herein that adjustment of heat- 9o ing current may be such as to boil mercury at rates suflicient to supply more vapor than will be condensed in the heating coil or i'acket. Such excess represents waste but uness maintained the system controls will operate only as upper limit regulators. If, however, the vapor is always 1n excess, the working temperature will be kept up to the predetermined limit as well as prevented rom falling below it.

While the various systems disclosed herein are capable of being operated either above or below atmosphere, as heretofore explained, there are great advantages in emloyin them for t e operations e per ormed at or below atmospheric pressure, that is, for temperatures at orv below 357 centigrade, the atmospheric boiling point of mercury. Hence, as-will be evident, a great variety of heating operations, particularl for chemical reactions can be accomplis ed with the secondary yalve, as for instance, valve 30, Fig. 1, set to open at or below atmosphere. In the below-atmosphere operation there can be no leaks of mercury to the exterior. Any leaks must be inward into the system and an im urities thus introduced, are drawn o wit the excess um I condensed vapor and are gradually worked out of the system by continued olperation of the vacuumizing pump. While t e leaks are thus in the direction of safety as regards human life and are taken care of as above described, it isto be understood that they are highly undesirable and the greatest pos- 1 25 sible care is taken to prevent them.

Inm prior Patent No. 1,619 661 I have stated that mercury vapor may be obtained pressure of only nine-tenths pounds to the square inch.

which can 195,

Higher degrees of heat may be obtained with corresponding increase in pressure. And I have also described how these pressures, required for desired temperatures, can be maintained by a vacuum pump operated and controlled in the usual manner in connection with an ordinary pressure gauge which indicates the boiler pressure. While the methods claimed in. said application can be practised by manual control of the pump in connection with the gauge, there are 1mportant advantages in employing automatic means for the purpose. Hence my present application concerns certain varieties of automatic means which may be used for controlling internal pressures. Also said automatic means include devices that are capable of operation at pressures above as well as below atmosphere. Specifically considered, the principal regulating means are in the nature of relief valves and, to take care of the specific case where the internal pressures are below-atmosphere, there are the various forms of vacuumizing pumps. Such pumps require no special description or illustration, being well-known in the art, and they may be continuously operated for predetermined low vacuum without special regulation. It will be noted, however, that in ordinary operation they are not required to maintain vacuum any greater than is necessar to give internal pressures free vent when t e relief valve is open. Hence said vacuum pumps may be supplied with automatic control mechanism to maintain only the required degree of vacuum; and when the valves are set for above-atmosphere pressures, the pumps may be cut oil either by hand valves as indicated in Figs. 3 and 4, or by any desired automatic mechanism.

It will be understood that the pressure relief valves, such as 30, 130, 130a, 230, 2300i,

and 530, are diagrammatically indicated as having the internal pressure on the valve element directly opposed by external atmospheric pressure which latter is adjustably counterbalanced or an ented by the weighted lever. It will e understood, of course, however, that various other valveoperating means may be utilized with a view to more accurate regulation.

In systems of the type herein described, transfer of a given amount of heat requires boiling and condensing of relatively large amounts of mercury. Hence the velocity of the vapor flow is great and the resulting friction may give rise to a certain amount of back pressure. Hence it will be understood as to all of the systems the mercury level in the boiler may be somewhat below that in the pipes leadin from the Condensers and it will sometimes fie necessary to make allowance for this.

In this same connection it may be noted that the level of the condensed mercury may be raised to a desired higher level than the mercury in the boiler b throttling of the return flow of the con ensed vapor. For instance, in Fig. 7 the mercury may be raised to or above the level 47'47 in the condensing jacket while the mercury in the boiler is at a much lower level by suitably adjusting a valve like 230 which can be inserted in i e 512. The back pressure could be varied by partially closing a similar valve, which can be arranged in pipe 502. Preferably, however, the should be kept as small as possible so that the pressure throughout the entire system may be more nearly uniform.

I claim:

1. The method of transferring heat which consists in imparting heat to mercury to boil ofi' mercury vapor in one region of a circulating system, mercury vapor at another region of the system to condense it; and governing the temperature in the region to which the heat is transferred by governing the pressure of the condensing vapor by and in accordance with the temperature of the latter region.

2. The method of transferring heat which consists in imparting heat to mercury to boil oil mercury vapor in one region of a circulating system, absorbing heat from the mercury vapor at another region of the system to condense it; and governing the temperature of condensation by boiling ofi amounts of mercury vapor in excess of the condensing capacity of the region of condensation and maintaining a desired pressure in the circulating system by venting the necessary amounts of said vapor.

3. The method specified by claim 2, and wherein the desired internal pressure is below atmosphere and a partial vacuum is maintained in the region to which the pressure is vented.

4. The method specified by claim 2, regulating the boiling of the mercury to produce a desired minimum excess of heat transferring vapor, by applying electric current of low voltage and large amperage to generate heat in the mercury, and controlling the current to vary the amount of heat produced thereby.

5. A method of accurately controlling transformation of form or nature of chemical compounds which includes imparting heat to mercury to boil off mercury vapor in one region of a circulating system, absorbing heat in said compound from said mercury vapor in another region of the system to condense mercury; maintaining a body of the condensate in heat absorbing relation to saidcompound in said latter region; and governing the temperature in said latter region by boiling ofl' mercury in excess of the condensation while governing the interback pressure nal pressure of the condensing vapor; the

of the mercury to ensure a desired minimum excess of vapor, by applying electric current of low voltage andlarge amperage in heating relation to the mercury, and

5 regulating the amount of the current so ap lied.

igned at New York city in the county of New York and State of New York, this 2nd day of February, A. D. 1927.

CROSBY FIELD.

5 regulatin boiling of the mercury to ensure a desired minimum excess of vapor, by applying electric current of low voltage and large amperage in heating relation to the mercury, and

g the amount of the current so ap lied.

igned at New York city in the county of New York and State of New York, this 2nd day of February, A. D. 1927.

CROSBY FIELD.

CERTIFICATE OF CORRECTION.

Patent No. 1,810,912. Granted 111111523, 1931, m

CROSBY FIELD.

It is hereby certified that error appears in the printed specification oi the above numbered patent requiring correction as follows: Pages 7 and 8, strlke out lines 117 to 130, and lines 1 to 6, respectively compris ng clami 5; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent 0ff1ce.

Signed and sealed this 6th day of October, A. I). 1931.

M. J. Moore, (Seal) Acting Coimnissiouer of Patents.

CERTIFICATE OF CORRECTION.

Patent No. 1,810,912. Granted June 23, 1931, to

CROSBY FIELD.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Pages 7 and 8, strike out lines 117 to 130, and lines I to 6, respectively, comprising claim 5; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 6th day of October, A. D. 1931.

M. J. Moore, (Seal) Acting Commissioner of Patents.

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