US3125159A - Apparatus for transferring heat - Google Patents

Description

March 17, 1964 J. E. LINDBERG,JR 3,125,159

APPARATUS FOR TRANSFERRING HEAT Original Filed Nov. 8, 1957 INVENTOR. JO/M' Ala/08mm United States Patent 2 Claims. c1. 165--86) This invention relates to improvements in turbines,

especially to means for cooling turbine blades. This application is a division of application Serial No. 695,357, filed November 8, 1957, now Patent 3,075,361.

Conventional heat transfer methods depend almost solely on the product of the specific heat and the quantity of a heat transfer medium that is cycled between the source and the sink. For example, when water is used to cool an engine, the amount of heat removed from the engine by the water is the product of the difference in temperature between the engine and the air, the mass of water circulated, and the specific heat of water. While this method has its advantages and is satisfactory for many purposes, it also has many disadvantages, and in some circumstances they outweigh the advantages. Thus, some temperature ranges are too hot for use of liquid water, and even steam becomes very difficult to handle. In fact, it is well known that some atomic energy installations use liquid sodium in spite of its relatively low specific heat (about .294). The liquid sodium, considered abstractly, is less than one-third as eflicient as water, but water cannot be used in the liquid state above 100 C., and the liquid sodium is preferred to most other materials because its specific heat is high in comparison with most other metals.

When practicing the conventional methods of heat transfer, it is necessary to move the entire medium from the source to the sink. A relatively low amount of heat is transferred per quantity of medium moved. More-' over, large-capacity pumps have to be used if large amounts of heat are to be transferred.

The present invention differs from the prior art by placing substantial reliance on the heat energy associated with certain types of thermodynamic transformations, particularly those accompanying chemical reaction and physical solution. In some transformations, the energy change is orders of magnitude larger than that involved in heating conventional heat exchanger media. When considered in terms of the heat energy transferred per unit mass of medium moved, the present invention achieves rather astounding results.

Two requirements of my invention are: (1) In the thermodynamic transformation, heat must be absorbed from the source and released to the sink; (2) in a cyclic system, the transformation must be reversible between the temperature of the source and the temperature of the sink.

Many chemical compounds and solutions do not produce enough heat during their formation or dissolution to be of practical use in my invention. Moreover, many transformations are not reversible within practical ranges of temperature. The present specification therefore considers certain transformations that are reversible within practical temperature ranges and that absorb much heat per unit weight from the source and release it to the sink.

The method of this invention makes it possible to absorb a large proportion, in some cases the major portion, of the heat energy produced at the source in an endothermic transformation and to liberate that heat at the sink in an exothermic transformation. For example,

3,125,159. Patented Mar. 17, 1964 hydrogen may be liberated from certain metals at the source and recombined at the sink.

In this invention, the amount of heat Q which may be transferred by the heat-exchange medium of mass M may be expressed as:

where Q is the heat of formation of the compound, S is the specific heat content of the compound, M is its mass, and Tsoum and Tsink are the respective temperatures of the source and the sink. For heat to be transferred from the source to the sink, Q must be a positive quantity, which in turn implies that Q must be greater than c source sink) if sink source- This require? ment for heat transfer from source to sink can usually be met by a proper choice of the heat-exchange medium ac cording to the present invention, for while S is a relatively small quantity, Q is quite large for many materials employed in this invention, as is shown in several examples on following pages. In the conventional style of heat transfer, however, the term Q is absent in the above expression and such methods would fail if T T source, since in that event heat would be carried from the sink to the source. Since Q is large for many reactions, the present invention will operate atsuperior efiiciency over very wide temperature ranges.

Another important advantage of the invention is that often only a part, frequently a small part, of the medium need be transferred between the source and the sink. Instead of having to pump the entire mass, only a small fraction is pumped. For example, in certain applications where a metallic hydride is used, only the hydrogen need be transferred. In certain particular reactions explained below, a tremendous amount of heat energy can be transferred per unit mass of the hydrogen pumped.

The present invention also distinguishes from the prior art in being practical at very high temperatures. Heat can be transferred at temperatures not heretofore feasible, and this fact demonstrates the utility of this invention in chemical, petroleum, metal-processing, and atomic energy applications, among others.

Other objects and advantages of the invention will appear from the following description of several preferred embodiments thereof.

The drawing is a schematic view of a type of a heat exchange system embodying the invention and primarily a moving envelope system that oscillates or rotates between having one side at the source and one at the sink bodying the invention have been found to be exceptionally mic).

useful, and they will serve as examples illustrating the principles of this invention. These transformations concern the interaction between certain gases and certain metals.

Hydrogen combines with some metals to produce actual stoichiometric hydrides. With some other metals it forms what are often called hydrides but are not stoichiometric compounds; actually the hydrogen is physically dissolved in these metals. Except for careful chemical investigation, it would be difficult to tell the difference between the solutions and the true reactions; in fact, only recently has there been any differentiation. In both cases considerable heat is produced during combination (exothermic), and in both cases heat is required for dissolution (endother- Both produce 'hydrides, and the principal difference is only that in one case reaction is stoichiometric and in the other it is not. Both reactions are reversible; both release heat as hydrogen is taken into the metal due to temperature decrease or pressure increase or both, and both absorb heat when the hydrogen is removed from the or metal due to decrease in pressure or increase in hydride temperature or both.

The stoichiometric reaction is between hydrogen and the alkali and alkaline earth metals. Specifically, hydrogen reacts with lithium, sodium, potassium, rubidium, cesium, calcium, radium strontium, francium and barium, in stoichiometric proportions to form hydrides. The heats of formation and dissolution of all these hydrides is quite large, of the order of 10,000 calories per mole. Moreover, the ranges of temperatures between formation and dissolution are quite practical for use in many applications of heat exchange. Some specific examples are given below, and Tables I and II are furnished to show some of the heat properties of some of these compounds.

Note: In this and in the following tables, the following relations hold true:

Mm (1) Sm=Cm (3) Sc=Sm+Sg Where Mg is the formula mass of the gas,

Mm is the formula mass of the metal,

Me is the formula mass of the hydride,

Cm is the specific heat of the metal (gram calories per gram per degree Centigrade), and

Cp is the specific heat of the gas at constant pressure.

(For H this is 3.50 over the 01000 C. range.)

TABLE 11 Heat Properties of Certain Alkaline Earth H ydrides [The units in the table headings are the same as in Table 1] Heat of Heat Heat Heat Hydride Formation Content Content Content Q of Metal 01 Gas of Hydride Sm Sg Sc Also, useful is the solution of hydrogen in what are known as the group B metals, the class consisting of scandium, titanium, vanadium, ytterbium, zirconium, niobium, hafnium, tantalum, the rare earth metals (atomic numbers 57 through 71), and the actinide metals (atomic numbers 89 through 103); palladium is a member of this group at temperatures greater than about 300 C. This solution is often termed a hydride, though it is not a stoichiometric compound. The solubility of hydrogen in group B metals varies (at least over a wide range of temperatures and pressures) according to the equation:

where s is the solubility at saturation at room temperature,

0 is a constant of proportionality,

s is the solubility of molecular hydrogen in the metal, P is the pressure,

e is the base of natural logarithms,

Q is the heat absorbed in calories per mole of H and T is the temperature, in degrees Kelvin.

Some of the heat properties of some of these hydrides are shown in Table III.

TABLE III Heat Properties of Certain Group B Hydrides [The units in the table headings are the same as in Table I] Heat Heat H eat Heat of Content Content Content Hydride Formaof of 01 tion Metal Gas Hydride Q Sm Sg So 634 0.120 0. 126 0.246 ZrHr.n2 417 0. 065 0.074 0. 139 PdHQjQ 23. 7 0.058 0. 021 0. 079

Oxygen also combines in an analogous manner with several metals, particularly silver, mercury and palladium, in stoichiometric relation, in reactions that are reversible within ranges of temperatures making their use in heat transfer practicable. The temperature ranges are different from those of the hydrides; and this diiference makes the reactions of great interest. Large heats of formation, in the order of scores or hundreds of calories per gram of compound, result, as Table N indicates.

The examples which follow disclose specific embodiments of the invention using some of the oxides and hydrides discussed above.

An example will now be given of a heat exchanger using relative motion between an envelope system and the heat source and sink; the example involves a metal hydride but also utilizes the specific heats of the gas and of the metal as well as the total heat of [formation of the compound. The purpose of this system is to avoid the problem of pumping metal and hydride, by actually moving the whole heat-transfer system in such a manner that the roles of symmetric end elements are reversed cyclically. The only component which is required to flow in this system is the hydrogen gas.

The system is shown diagrammatically in the drawing, where the heat exchanger consists of two vessels 70 and *71 connected by a :gas line 72 and mounted pivotaltly at 73. By way of example, it will be assumed that the vessels 70 and 71 are charged with partially hydrided sodium metal. In the drawing the transfer system is designed to rotate about the center 73 so that the end elements 70 and 71 sweep through two regions 74 and 75 which are opposed from each other, one of which may be regarded as the heat source, at temperature T while the other is a heat sink at temperature T When the element 70 is immersed in the source 74, the element 71 will be immersed in the sink 75. The heat received in the element 70 causes dissociation of the sodium hydride into sodium metal and hydrogen gas. The metal is retained in the element 70, while the gas flows through the transfer line 7-2 to the element 71, where it combines with free sodium metal to form sodium hydride. This result-s in the production of heat associated both with the formation of the compound and the specific heat of the hydrogen gas. When the element 71 is sufficiently filled with sodium hydride so that most of its originally tree sodium has been combined, the system may be rotated about the center 73 to place the element 71 at the source 74 and the element 70 at the sink 75. The same reaction will take place at the source 74 and at the sink 75, but the sodium hydride, which is now in the element 71 and is now at the source 74, will be decomposed, internally cooling the element 71, and the by drogen flow to the element 70 and recombine there, again transferring heat from the source 74 (internally cooling the element being heated) to the sink 75 (internally heating the element being cooled). When the cycle has been completed, or at any earlier time, another rotation is given and the materials are restored to their original position. The cycle can be smooth and even con tinuous if desired. It is not, of course, necessary to carry each step to completion.

Obviously, this transfer device, consisting of two elements may, if desired, be replaced by a circular system containing a continuous distribution of sodium hydride. It should also be noted that source 74 and sink 75 can rotate while the elements 7 and 71 remain fixed; alternatively, the elements 70 and 71 can, in general, partake of any type of motion such as transl-atory, rotational, reciprocating, oscillating, etc. The only requirement for heat transfer is that there be relative motion between the elements 70 and 71 and the source and sink 74 and 75 respectively to accomplish cyclic alternate heating and cooling of alternate elements.

A specific example of the general system shown in the drawing and described above is that of a getter-cooled turbine rotor. It will be assumed that this rotor is comprised of an even number of hollow blades, one of each pair being filled initially with hydride and the other of each pair being filled with metal (sodium hydride and sodium, for example) and connected to the rotor hub in such a manner that the blades may freely pass outgassed hydrogen between one another: the element 70 might represent one hollow blade of a pair and the element 71 the other blade of the pair, rotating (with the other blade pairs, which are not shown for reasons of clarity) about the hub 73 and connected by a gas transfer line 72. In the operation of a turbine most of the heat which the material comprising the rotor is required to withstand is concentrated in a relatively small region (as at a nozzle in a steam or gas turbine), which region may be designated the heat source 74; at the same time the region opposite source 74 is a relatively cool one and is designated the heat sink 75.

In operation, it is very desirable to equalize the temperature of the various rotor blades as well as possible since their material must be able to stand the peak temperature encountered, even if that temperature is experieneed by a given blade only during a traction of a revolution. This means of cooling the blades achieves that result in the following manner: assume that blade 70 contains ingassed hydride and has just entered the high temperature source region 74, while its companion blade 71, containing outgassed metal, has entered the cooler region 75. Heat transferred from the source 74 to the blade 71 will cause the hydride contained therein to outgas hydrogen, the heat transferred from the source 74 to the blade 70 being absorbed in this reaction thus cooling the blade 70. The outgassed hydrogen is allowed to flow through the line 72 to the metal contained within the blade 71; the consequent ingassing of the metal there will liberate the transferred heat, the heat being dissipated at the sink 75.

After a half cycle, the blades 70 and 71 will have changed places, the blade 71 then being exposed to the heat source 74 and the blade 70 being at the sink 75. Since the blade 71 has contained hydride due to its ingassing as described above, it can now transfer heat to the blade 70 at the sink via hydrogen outgassed from its hydride and flowing through the line 72. When the blade 70 again is in the heat source region 74, the cycle has been completed. Each other blade on the rotor experiences the same cycle of outgassing and ingassing in turn, depending upon the temperature distribution around the rotor.

It should be pointed out that the process of heat distribution described here can take place under any conditions around the rotor, so long as there exist temperature differentials among blades; for while a discrete gas transfer line 72 has been shown to connect a single blade pair 70 and 71 in the drawing, all of the rotor blades would normally be connected together by lines 72 so that hydrogen may seek those elements which are at lowest vapor pressure which are those most nearly outgassed and coolest. The heat source 74 may thus be present at several positions (such as would be the case in the normal turbine, which contains more than one nozzle and hence more than one source 74), either fixed or varying, and the rotor may revolve in either direction, without afiecting the transfer of heat herein described. :If half the blades are initially filled with hydride and the other half initially filled with metal, the proper relation of ingassed material at a source 74 and outgassed material at a sink 75 will be established after one revolution of the rotor.

To those skilled in the art to which this invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing lfrom the spirit and scope of the invention. The disclosures and the description herein are purely illustrative and are not intended to be in any sense limiting.

'F or example, although all of the examples given above use only single-metal hy drides, it should be noted that mixtures or alloys of suitable metals may be used. Alloying techniques offer a number of advantages. For one thing, the quantity of hydrogen that may be contained in an alloy may be larger than the quantity contained by equivalent amounts of the separate metals. For another, the transition temperatures of the pure metals may be modified by the addition of small quantities of alloying metals. For yet another, some alloys may be more convenient to handle than the constituent metals. In particular, lithium might be handled as a solid at high temperatures by alloying it with more refractory alkali metals.

What is claimed is:

1. In a turbine having an axial hub, a heat source and a diametrically opposite heat sink, a plurality of rotor blades rotatably mounted on said hub in diametrically opposite pairs, each blade being hollow, passage means connecting together the hollows in each pair of blades, a metal that ingasses and outgasses hydrogen reversibly, retained at all times in the hollow of each said blade, and a supply of hydrogen for circulation through said passage means between said blades from one said metal to the other, whereby said hydrogen is ingassed into the metal in one blade when that blade is at the heat sink, thereby imparting heat from the blade to the sink, while the metal in the opposite blade is outgassing hydrogen at the heat source, thereby cooling said opposite blade, only said hydrogen being circulated while the metal remains fixed.

2. In a turbine having an axial hub, a heat source and a diametrically opposite heat sink, at least one pair of diametrically opposite hollow rotor blades mounted on said hub for rotation thereon, passage means connecting together the space inside said hollow blades, metal that in-gasses and outgasses hydrogen reversibly inside each said blade, and a circulating supply of hydrogen in said blades, whereby said hydrogen is ingassed into the metal in one blade and outgassed at the same time from the metal in the other blade, depending on which blade is at the heat sink and which at the heat source, thereby imparting heat from one blade to the sink and cooling the opposite blade at the source, only said hydrogen being circulated While the metal remains in its position in each said blade.

References Cited in the file of this patent UNITED STATES PATENTS 2,708,564 Erickson May 17, 1955 8 Reed May 22, 1956 OTHER REFERENCES A Survey Report on Lithium Hydride (Gibbs, Jr., et 5 al.), published by the Atomic Energy Commission, Document NYO-3957, May 2, 1954, pages 1 and 22 relied on. Dissociation-Cooling (McKisson), published by Atomic Energy Commission, Document -L-RL-86, March 1954, pages 5, 6, 17, 18 and 19 relied on.

Claims (1)

1. IN A TURBINE HAVING AN AXIAL HUB, A HEAT SOURCE AND A DIAMETRICALLY OPPOSITE HEAT SINK, A PLURALITY OF ROTOR BLADES ROTATABLY MOUNTED ON SAID HUB IN DIAMETRICALLY OPPOSITE PAIRS, EACH BLADE BEING HOLLOW, PASSAGE MEANS CONNECTING TOGETHER THE HOLLOWS IN EACH PAIR OF BLADES, A METAL THAT INGASSES AND OUTGASSES HYDROGEN REVERSIBLY, RETAINED AT ALL TIMES IN THE HOLLOW OF EACH SAID BLADE, AND A SUPPLY OF HYDROGEN FOR CIRCULATION THROUGH SAID PASSAGE MEANS BETWEEN SAID BLADES FROM ONE SAID METAL TO THE OTHER, WHEREBY SAID HYDROGEN IS INGASSED INTO THE METAL IN ONE BLADE WHEN THAT BLADE IS AT THE HEAT SINK, THEREBY IMPARTING HEAT FROM THE BLADE TO THE SINK, WHILE THE METAL IN THE OPPOSITE BLADE IS OUTGASSING HYDROGEN AT THE HEAT SOURCE THEREBY COOLING SAID OPPOSITE BLADE, ONLY SAID HYDROGEN BEING CIRCULATED WHILE THE METAL REMAINS FIXED.

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