Radial Heat Flux Transformer

Abstract

A radial heat flux transformer adapted to be employed in the transfer of thermal energy, particularly suited for use in delivering energy radially and characterized by two concentric cylinders interconnected by a network of groups of radially extended capillary channels having vapor spaces defined therebetween, a particular feature of the transformer being the capability of radially delivering vapor as well as its condensate in opposite radial directions between the concentric cylinders, whereby the device may be employed interchangeably as a flux concentrator or a flux radiator.

Description

ORIGIN OF INVENTION

The invention described herein was made in the performance of work under a NASA contract and is subject to the provisions of Section 305 of the National Aeronautics and Space Act of 1958, Public Law 85-568 (72 stat. 435; 42 U.S.C. 2457).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to heat pipes and more particularly to a radial heat flux transformer wherein thermal energy is delivered radially between concentric cylinders for use in heating and cooling processes.

2. Description of the Prior Art

A heat pipe essentially is a closed, evacuated chamber whose inside walls are lined with capillary structure saturated with a volatile fluid. Normally, a heat pipe includes an evaporator section located at an energy input end of the pipe and a condenser section located at an energy output end of the pipe.

Energy in the form of heat is delivered from the evaporator section to the condenser section by a working fluid employing vapor heat transfer processes, while capillary action serves to deliver the liquid condensate to the evaporator section, for thus providing a closed circuit for the working fluid as it repeatedly is evaporated and condensed for purposes of transferring heat from the evaporator to the condenser sections.

The purpose and functions of heat pipes are well known. It should be appreciated that heat pipes have been made to operate at various temperatures spanning significantly wide ranges extending from below the freezing temperature of water to an excess of 3,600.degree. F. In achieving an operative condition, various types of working fluids have been employed including methanol, acetone, water, fluidated hydrocarbons, mercury, idium, cesium, potassium, sodium, lithium, lead, bismuth and a range of inorganic salts, depending upon the working temperatures. The containment vessels have been made of glass, ceramic materials, various copper alloys, stainless steel, and the like, while capillary channels have been formed of sintered porous matrixes, woven mesh, fiber glass, longitudinal slots and various combinations of these structures.

The evaporation and condensation functions of a heat pipe are essentially independent operations connected only by streams of vapor and liquid condensate. The patterns and areas of evaporation and condensation are independent. Thus, the process occurring at one end of the pipe can take place uniformly or nonuniformly over a large or small surface area without significantly influencing what is occuring at the opposite end. This separation of functions is particularly significant since it permits the heat pipe to be employed to concentrate or dispense thermal energy. This property often is called "heat flux transformation." If energy in the form of heat is introduced into the heat pipe at a slow rate over a large surface area, the same total amount of working fluid can be evaporated as when energy is introduced at a high rate over a small surface area. Similarly, vapor can be condensed rapidly over a small area or slowly over a large area. It is the ratio of the surface area of the evaporator to the area of the condenser that determines the rate at which the energy is concentrated or dispersed at a constant temperature.

Heretofore, it has been common to employ heat pipe principles for delivering heat by establishing a flux field extending longitudinally of the heat pipe with radial delivery being merely incidental to the operation of the heat pipe.

OBJECTS AND SUMMARY OF THE INVENTION

This invention employs a new approach to heat flux transformation, in that it utilizes heat pipe principles to move heat radially from a shell of a small diameter to a shell of a large diameter, or from a large diameter outer shell to a small diameter inner shell with a negligible temperature drop adapted to be employed in those environments where it is desirable to achieve a heating or a cooling of concentrically arranged materials, substances and structures.

Accordingly, an object of the instant invention is to provide an improved radial heat flux transformer.

Another object is to provide a simplified device capable of being employed for heating or cooling concentrically arranged substances.

Another object is to provide a heat transfer device which may interchangeably be employed as a heat flux radiator or a heat flux concentrator.

Another object is to provide a simplified radial heat flux transformer employing a plurality of registered wafers to provide a cylindrical member having radially extended bundles of capillary channels and interposed vapor spaces formed of a multiplicity of registered wafers of a similar configuration and particularly adapted to utilize heat pipe principles for achieving heat flux transformation.

These together with other objects and advantages will become more readily apparent by reference to the following description and claims in light of the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a partially exploded perspective view of a transformer illustrating the arrangement of the wafers employed in forming the wicking member of the transformer embodying the principles of the instant invention.

FIG. 2 is a cross-sectional side view taken generally along the longitudinal axis of the transformer of FIG. 1.

FIG. 3 is a cross-sectional end view of the transformer of FIG. 1, taken along a transverse axis.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Turning now to FIG. 1, the transformer embodying the principles of the present invention includes a first cylinder 10 about which is concentrically arranged a second cylinder 12. The cylinders 10 and 12 serve as inner and outer shells which together define the elongated housing for the transformer.

About the cylinder 10 there is arranged a plurality of waferlike, planar screens 14 formed of a similar configuration and registered in a manner such that between the cylindrical shells there is provided a cylindrical body 16. The body serves as a wicking member for a transformer.

The wafers 14 are stamped or otherwise formed of any convenient material capable of establishing capillary channels. As presently employed, the wafers are formed of moly screen stamped to provide waferlike screen members. The specific materials employed in the fabrication of the wafers is dictated by the intended operating temperature of the transformer. Various materials can be employed such as, for example, stainless steel, molybdenum, or other refractory materials. Since the material employed may be selected from various types of materials normally employed in wicking members, a detailed description thereof is omitted.

Each of the wafers 14 is so stamped as to provide an inner ring portion 20 having extended therefrom radial portions 22. These portions terminate in a circumscribing annulus 24 whereby capillary channels are established between the inner surface of the portion 20 and the outer surface of the annulus 24. Between adjacent radial portions 22 there is defined a plurality of voids serving as vapor spaces 26 through which a vapor is radially propagated employing the well-known principles of the heat pipe.

The wafers 14, which define the body 16, are stacked in registration so that the capillary portions define axially elongated and radially extended bridges operatively coupling the annulus 24 with the ring 20.

Within the transformer, there is deposited a premeasured quantity of working fluid 30. The specific quantity of working fluid employed is not deemed critical. However, it is to be understood that a quantity sufficient to completely saturate the capillary channels is provided. Therefore, as illustrated, the working fluid is deposited in the interstices of the wafers 14 and, in operation, is displaced through the capillary channels from the cooled to the heated surfaces of the transformer employing capillary action.

As best illustrated in FIG. 3, the working fluid 30 progresses, in a liquid form, between the cylinders 10 and 12 through the capillary portions 22 and is returned, in vapor form, through the vapor spaces 26. Solid lines serve to illustrate the path of the working fluid, when the transformer is employed as a radiator, while the dotted lines serve to illustrate the paths of the working fluid when employed as a concentrator.

In assembling the transformer embodying the principles of the instant invention, the first, or inner cylinder 10, is placed within the outer cylinder shell 12. The two shells are then connected by means of an end plate 40, welded in place with an electron beam welder, in a manner such that a concentric relationship is established. The wafers 14, having been stamped to a desired configuration, such as that shown in FIGS. 1 and 3, are inserted into the resulting structure in a manner such that the ring 20 is in sliding engagement with the external surface of the first cylinder 10, and the external surface of the annulus 24 is in engagement with the internal surface of the second cylinder 12.

With the transformer thus assembled a premeasured quantity of working fluid is placed in the openings or vapor spaces 26. If the working fluid is of a very high purity, then it is distilled into the housing employing high temperature degassing and processing techniques which form no specific part of this invention. The resulting structure is then closed by a second cover plate 42 seated at the opposite end of the transformer from the plate 40, and welded in place. It is to be understood that the entire fabrication is performed in a vacuum so that a vacuum is established within the transformer. As a practical matter, the process may be carried out in an argon atmosphere so that an inert atmosphere is established within the transformer.

OPERATION

It is believed that in view of the foregoing description, the operation of the device will be readily understood and it will be briefly reviewed at this point. With the transformer assembled in a manner heretofore described, the capillary portions 22 provide a myriad of capillary channels arranged in groups and extending radially from the ring 20 to the annulus 24, while the voids between the groups serve to provide vapor spaces through which are established paths for the flow of vaporized working fluid. It is to be understood that the term "radially" is intended to encompass any disposition having a sufficient radial component to permit the capillary heat pipe transfer of thermal energy and is not intended to mean precise radial disposition even though efficiency is normally enhanced by relatively closely approaching precise radial disposition.

When the transformer is to be employed as a radiator, thermal energy first is transferred through the first cylinder 10, so that this cylinder functions as an evaporator, for driving the evaporated working fluid radially toward the annulus 24, where the energy is given up, as indicated by solid lines in FIG. 3. As the vapor traverses the vapor space, condensation occurs at the annulus 24, whereupon capillary action is employed to deliver the cooled working fluid along a plurality of return paths to the ring 20, also as best illustrated in solid lines in FIG. 3.

When the transformer is used as a flux concentrator, that is for concentrating thermal energy at the internal surface of the cylinder 10, energy is applied to the external surface of the cylinder 12, which now serves as an evaporator for establishing a flow of vapor toward the cylinder 10, as illustrated in the dotted lines in FIG. 3. In such instances, heat applied to the external surface of the cylinder 12 evaporates and drives the working fluid toward the cylinder 10 whereupon the working fluid is condensed and caused to return toward the cylinder 12 through capillary attraction in the manner consistent with the principles of the heat pipe. When the transformer is employed as a flux concentrator, the outer shell becomes the evaporator and the inner shell becomes a condenser. The flux concentration ratio can be expressed as a ratio of diameters or DI/DO where DI and DO are the inner and outer diameters, respectively, of the the heat flux transformer.

Although the invention has been herein shown and described in what is conceived to be the most practical and preferred embodiment, it is recognized that departures may be made therefrom within the scope of the invention.

Claims

What is claimed is:

1. A radial heat flux transformer comprising:

A. a first tubular shell;

B. a second tubular shell concentrically related to said first shell and radially spaced therefrom;

C. a tubular wicking member interposed between said first and said second tubular shells comprising a plurality of longitudinally registered, unitary wafers of a similar configuration, each including a center ring, means defining a multiplicity of channels radially extended from said ring, and an annulus integrally related with the distal ends of said means defining said radially extended channels; and

D. a working fluid disposed within said channels.

2. The transformer of claim 1, wherein said means defines said channels is fabricated from a woven screenlike material.