US1845690A - Apparatus for the extraction of heat - Google Patents

Description

J. F. WAIT Feb. 16, 1932.

APPARATUS FOR THE EXTRAGTION OF' HEAT Original Filed Dc. 13, 1924 iff/77145.55.'

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`Patented Feb. 16, 1932 UNITED STATES PATENT oFFl JUSTIN F. WAIT, OF NEW YORK, N. Y., ASSIGNOR TO SUN OIL COMPANY, F PHILADEIP' PHIA, PENNSYLVANIA, A CORPORATION OF lil'EW` JERSEY APPARATUS IEOIR. THE EXTRACTION OF HEAT 'Original application filed December 15, 1924, Serial No. 755,708. Divided and this application iiled August 16, 1927. Serial No. 213,350.

This invention relates to apparatus for the abstraction of heat from high temperature fluids by means of a boilingmetal held in thermal Contact therewith.` It includes improvements and refinements which render possible commercial application of such theoretical operation. Some features included in my previous applications of July 26, 1923, Serial No. 654,054 now Patent #1,760,095 of May 27, 1930, and December 21, 1922, Serial No. 608,347, are amplie'd in accordance with more recent findings and others are further substantiated by certain phases of this invention correlated therewith.

In view of "the improved heat transfer which I have obtained with boiling metals when in contact with metals having surfaces which they wet, I have further extended my equipment design to facilitate such wetting. In pretreating the surfaces I have found it desirable to increase the thickness of the wetted metal until it has sufficient strength to render possible complete elimination of the steel parts previously used'.

My invention, therefore, includes the use of commercially pure nickel and nickel alloys, as for example, nickel steel, for use in those parts of the abstracting unit in contact with the high temperature Huid and which transfers heat therefrom. By limiting the use of the parts containing an appreciable percentage of nickel to the main heat transfer surfaces, a substantial reduction in construction cost is possible. Other metals, for example, platinum, which are wetted or form alloys which are wetted, may likewise be used. I have also discovered that ordinary iron can be effectively wetted by liquid mercury, if the iron beA first plated with a substance, as for example, copper, with which the mercury will forni an amalgam of a nature which will be subsequently dissipated in the body of the mercury. The formation and dissipation of the amalgam permits such intimate contact between the mercury and the iron as to result in wetting of the iron.

In addition to increase in heat transfer, the use of a wetted surface greatly precludes possibility of plugging of passages by oxides of the boiling metal or construction material or such other im urities as might accumulate. This invention filrther relates to use of this principle in connection with special design of surfaces and passages to insure continuous and highest rate of heat transfer. This matter is of utmostimportance in equipment involving metals, the value of which makes necessary the use of passages and voids of maximum volume.

Plugging of the passages is further prevented and improved heat transfer is further obtained by provision for .more rapid re- `Circulation of the metal whereby vapor kformed at the surfaces of the container is quickly swept away by unidirectional flow thereover of liquid metal, thus ,insuring a more constant wetting of all portions of the heat transferring surfaces and preventing the formation of a relatively poorly conductingk film of vapor. During any given period, the amount of metallic liquid flowing past a portion of a heat transferring surface will'be preferably more than two hundred times' the amount of vapor evolved during the same period from the surface. Accordingly, notwithstanding the increase in volume .of the metal attending vaporization, the liquld will be sufficient in amount to cleanse the surface from vapor. This ra id unidirectional flow of liquid contrasts with the relatively local disturbances produced when liquids are ordinarily heated, from which disturbances there results only a random production 0f eddles and whirls of the liquid, inoperative to re, l

move vapor films.

By further improving the recirculation rate I have been able to insure practically constant composition in all parts of a boiling mass 'when mixed metals are involved. Uniformi heat abstraction may be obtained with the special means provided for recirculation. Vith the improved design operating with mixed metals, the more volatile component on being returned to the vessel is sufliciently well mixed to give practically the same boiling point for instantaneous samples at several portions of the metal mass.

A limit to both efficiency and capacity of a heat abstractor is the rate of heat transfer between thc metal walls and the fluid on one side I makin and the boiling metal on the other side. Decided improvement may be obtained with a coating or platin of the walls in contact with the heated uid such that the boiling metal would wet the said walls. n As a further improvement, however, I have developed a means which permits of even better and more permanent results. It consists of greatly increasing the thickness of the special coating until it is sufficiently lheavy that the nonwetting metal-may be definitely eliminated. For example, pure nickel tubes'may be used thus yielding highvrate of heat transfer, and lessening the possibility of plugging with impurities.

An economical construction may be had by Y only those parts, conducting heat from t e hot fluid to the boiling metal, of a 1 metal which Vis wetted. Spacers and other parts may be made of other metal l and improved in operation by a light plating of aI wetting metal, although the latter feature is not essential.

IVhile, perhaps, the common construction materials suitable for this improvement in Operation of the abstractor are nickel and nickel alloys such as copper and iron containing alloys, other suitable materials may likewise be used. I do not, therefore, limit my claims to metals or alloys containing nickel.

The use of a single special metal rather than a coating for the heat transfer surface insures continuity of operation and eliminates possibility of cracking or peeling by overheating,

and inequal expansions inherent with a thin coat. The use of the recirculation principle, developed for maintaining uniform mixtures of alloys previously described1 together with l the use of a .heavy plate or entire wall of the passage during the same period.

wetting metal, insures permanent and uniform operation.

Use of a naturally wetted surface not only gives better direct heat transfer results but also exerts a secondary influence on heat `transfer rate by greatly facilitating the circulation rate across the surface. The reduction in coefficient of friction obtained when the surface is wetted thus also increases heat transfer and betters the heat abstraction efficiency. Circulation rates much in excess of those heretofore obtained maythus be obtained. By circulation rate`is meant the ratio of the total amount of metal passing a particular datum to the weight of that part thereof which is vaporized because of such he ii ure is a sectional view of one form l l of heat a stractor.

represents a casing enclosing the hot fluid and containing a heat abstractor consisting of a` wallB and a boiling metal F 'thus held in thermal contact with the hot fluid. C and D are the hot fluid inlet and' outlet, respectively. My invention includes the use of a metallic inner spacer to both decrease the mercury volumeI and to furnish definite passages of such design as to assist in the natural circulation. To this end, the spacer G is provided with a central opening H, and the slopes and passages so designed as to give definite unidirectional flow of the boiling liquid upward across the surface of at such a rate that the vapor bubbles are quickly removed. I have found that with one or two hundred times the amount of metal vaporized sufficient metal is circulated to insure ractically continuous wetting of the surgace, thus eliminating the flashing tendlency and' obtaining the most eilicient heat transfer.` Vapor is led to a condenser orto a point of use by an attachment to the. outlet y vwith a unidirectional flow of the metallic liquid is greatly assisted if the surfaces are pretreated soas'to eliminate absorbed gases and vapor and permit of actual contact between the wall and the metallic liquid. y.

A tendency to prevent wetting of the surface exists in commercial installations because of the accumulation of impurities in the liquid metal. A metallic oxide is frequently met and will coat the surfaces and occupy space'in chamber B, preventing proper wetting and therefore lowering the heat transfer. To prevent this, the rapidly moving l1qu1d which continuously wets the surface is greatly decreased in volume near its upper surface and before it is started on its downward trip. This important hase of my invention whereby I inflict di erential velocities on the boiling metal has rendered commercial applications'possible, as otherwise frequent cleaning of these passages would be necessary. This is a phenomenon not heretofore apparent and which is peculiar only to operation of metallic liquids which are naturally very dense as compa-red with ordinary liquids,I as water and oil. v Continuous wetting of the surface is therefore rendered positive and certain kby that phase of my invention, illustrated 1n the figure. Here the volume occupied by F increases towards the top of the column of metallic liquid, thus reducing its velocity as `it flows upward. Above the upper edge of spacer G the vertical velocity is at a minimum. The upper end of the channel H may be greatly increased in sectional area as shown at L to insure low velocity as the liquid assumes a downward motion. This low velocity permits the impurities to rise to the surface due to the buoyant effect of the heavy metallic liquid so that they will not be subsequently carried, due to the high velocity of flow, downwardly into the chamber B: They may be skimmed from the surface of the liquid when the apparatus is shut down. The de- Langeac crease in upward velocity by increasing the area of the space occupied by the metal F materially decreases splashing, thus aiording a secondary preventitive for downward passage of impurities. Battles P and N are desirable for high velocities, the former guiding returning liquid to the central down-take section and preventing its return through a region of uptlowing material, thus further extending the principle of unitiow necessary to efficient operation.

The application oi a .bonded coating of low melting metal such as lead is shown as Q. This may cover all or part of the shell B and is in contact with parts of the liquid being heated.

One of the features necessary to good design is the fastening of the fingerlike chamber B at one end only, preferably the upper end, that the opposite end is free :for expansion. The inner spacer G is likewise fastened at one point with reference to its longitudinal axis that it may be free to expand. Obviously the number of fingers B may be multiplied.

These `features are of major importance in heat abstractors embodied in this invention because of the high temperature which gives an unusual amount of expansion at a temperature approaching the weakening point or" the metals used in the construction of the abstractor.

This application is filed as a division of my application Serial No. 7 55,708, filed December 13, 1924.'

Having now fully described my invention, what T claim and desire to protect by Letters Patent is Tn a heat interchanger for the transference of heat Jfrom a. source of heat to a boiling metal, an upright wall interposed between the source and metal, the surface of the Wall adjacent the metal being capable of being wetted thereby, means within the boiling metal for producing a rapid upward circulation otboiling metal across the wetted surface. means providing an enlarged space into which the upwardly circulating metal may pass and in which its velocity may decrease to Jfacilitate separation 'of liquid metal from vapors or impurities, and baiiies in said enlarged space.

Tn testimony of which invention, I have hereunto set my hand, at New York city, on this 13th day of August, 1927.

\ JUSTIN F. WAIT.

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