Method Of Heat Exchange Using Rotary Heat Exchanger

Abstract

A rotary heat exchanger comprising an array of closely spaced parallel annular thermally conductive fins mounted coaxially for rotation as a unit. A plurality of thermally conductive heat exchange tubes extends longitudinally through the array of fins circumferentially about the rotational axis and the fins are dimensioned and spaced and rotationally driven at a speed operable to convey a gaseous fluid radially between said fins essentially by viscosity shear forces and accelerate such fluid substantially to the velocity providing optimum total heat exchange between said fluid and another fluid flowing through the heat exchange tubes.

Parent Case Text

This application is a continuation-in-part of my application Ser. No. 110,478 filed Jan. 28, 1971, which was a continuation-in-part of my earlier application Ser. No. 25,857, filed Apr. 4, 1970, now abandoned.

Description

The present invention relates to rotary heat exchangers, and more particularly to rotary heat exchangers having an arrangement of rotating fins through which a gaseous cooling or heating fluid is entrained and accelerated by viscosity shear forces to the velocity providing optimum total heat exchange between said fluid and another fluid in thermal contact with the fins.

Rotating heat exchangers comprising an array of heat exchange fins are known in the art. However, prior to the present invention such heat exchangers customarily employed conventional lift forces to convey fluid through the array of heat exchange fins. The use of lift forces causes cavitation and renders such heat exchange devices noisy in operation. Also, such heat exchangers are characteristically inefficient and are necessarily of substantially bulky and heavy construction so that substantial power is required to rotationally drive the exchanger at the desired speed. For these reasons such rotary heat exchangers have not experienced wide usage or marked commercial success.

With the foregoing in mind, an object of the present invention is to provide a rotary heat exchange apparatus of the type described having high-performance characteristics affording optimum total heat exchange between two selected fluids.

Another object of the invention is to provide a rotary heat exchange apparatus as set forth which is of relatively small compact size and lightweight construction requiring low power consumption to rotationally drive the apparatus at the desired speed.

Another object of the invention is to provide a rotary heat exchange apparatus of the type described which is substantially devoid of cavitation and relatively noiseless in operation.

More particularly, an object of the invention is to provide a high-performance rotary heat exchange apparatus comprising an array of closely spaced parallel annular fins operable by viscosity shear forces to entrain a gaseous heat exchange fluid radially outward between the fins and accelerate said fluid to the velocity affording optimum total heat exchange between said fluid and another fluid having thermally conductive relation therewith.

A further object of the invention is to provide a rotary heat exchange apparatus which is suitable for use as a condenser and is particularly adapted for use as a condenser for the exhaust vapors from the expander in high-performance closed Rankine cycle power systems having a rotary boiler to which the condenser can be directly mounted coaxially for rotation with the boiler as a unit.

These and other objects of the invention and the various features and details of the construction and operation thereof in accordance with the invention are hereinafter set forth and described with reference to the accompanying drawings, in which:

FIG. 1 is a sectional view diametrically of a rotary heat exchange condenser made according to and embodying the present invention;

FIG. 2 is a view, partially in section, taken on line 2--2, FIG. 1;

FIG. 3 is a detached fragmentary view, in expanded or exaggerated form, of a continuous spiral or helicoidal fin arrangement;

FIG. 4 is an end elevational view of the fin arrangement shown in FIG. 3;

FIG. 5 is a sectional view similar to FIG. 1 showing a modified form or arrangement of apparatus embodying the present invention;

FIG. 6 is a sectional view taken on line 6--6, FIG. 5;

FIG. 7 is a detached view showing one of the U-shaped heat exchange tubes embodied in the condenser shown in FIG. 5;

FIG. 8 is a fragmentary sectional view diametrically of a rotary heat exchanger showing another modification of the invention, and

FIG. 9 is a fragmentary sectional view on line 9--9, FIG. 8.

Referring now more particularly to FIG. 1 of the drawings, the illustrated embodiment of a rotary condenser made according to the present invention comprises a cylindrical body or casing 1 of selected diameter and relatively short axial length having a continuous circumferentially extending wall 2 and axially spaced side walls 3 and 4, respectively. Fixedly secured to and extending coaxially outward from the casing side wall 3 is a tubular shaft member 5 that is in communication with the interior of the casing 1 through an axial opening in said side wall 3. The shaft 5 is rotatably mounted in bearings 6 and 7 and said shaft 5 and casing 1 are rotationally driven at the desired speed by means of an electric motor M driving a gear 8 which in turn drives a gear 9 secured on the shaft 5.

Mounted outwardly adjacent the opposite side wall 4 of the casing 1 for rotation therewith, is an array of annular fins 10 arranged coaxially of the casing 1 in predetermined equally spaced parallel relation and defining internally thereof a coaxial inlet chamber C for gaseous heat exchange fluid to be discharged outwardly between the fins 10 as hereinafter described. The fins 10 consist of separate or independent annual disk elements supported and secured in the desired closely spaced parallel relationship with respect to one another and the casing 1 by means of a plurality of heat exchange tubes or pipes 11 that extends longitudinally through the array of fins 10 circumferentially about the rotational axis thereof. The fins 10 and tubes 11 are fabricated of metal having high thermal conductivity such as, for example, copper or aluminum, and said fins preferably are bonded to said heat exchange tubes 11 by brazing, soldering or the like, to provide maximum thermal conductivity therebetween.

The tubes or pipes 11 are arranged in equally spaced radially staggered relation circumferentially of the fins 10 and casing 1 as shown in FIG. 2 of the drawings. The inner ends of the tubes 11 are mounted and secured in corresponding openings 12 provided through the casing side wall 4 so that the interiors of the tubes 11 are in communication with the interior of the casing 1. The outer ends of the tubes 11 are mounted and secured in recesses 13 provided in an annular end ring 14 that is disposed coaxially of the apparatus adjacent the outermost of the fins 10. The end ring 14 effectively closes the outer ends of the tubes 11 and also supports them in the desired relationship.

As shown in FIG. 1, the outer radius of all of the fins 10 is the same and conforms substantially to the radius of the casing 1. The inner radius of all the fins is also the same. More particularly, the inner and outer radii of the fins 10 are predetermined and interrelated to provide an inner to outer radii ratio within a predetermined relatively narrow range of limits hereinafter described.

The array of annular fins 10 does not extend axially inward entirely to the casing wall 4 and the innermost of the fins 10 is spaced from the adjacent surface of said wall to provide between the wall 4 and fins 10 an annular passage P for the radial discharge of dirt, dust and other solid particles that become entrained and carried into the chamber C by the gaseous heat exchange fluid. Such particles have greater density and momentum than the gaseous fluid and tend to travel to the inner end of the chamber C. Thus, the particles are discharged outwardly through the discharge passage P and do not accumulate in the heat exchanger.

Extending coaxially into the chamber C from the casing wall 4 is a tapered guide member G having a curvilinear concave lateral circumferential surface that functions to guide the foreign solid particles outwardly through the discharge passage P and also to guide and distribute the gaseous heat exchange fluid outwardly between the fins. The guide member G may be formed as an integral part of the casing wall 4 as shown, or separately and secured thereto, as desired.

The outer diameter of the end ring 14 is substantially the same as the outer diameter of the fins 10 and the inner diameter of said ring is substantially the same as the inner diameter of the adjacent group of fins so as not to restrict the flow of fluid into the chamber C. An outwardly flared or bell shaped fluid intake member 15 is fixedly mounted on a stationary base or support 16 and disposed coaxially adjacent the outer face of the end ring 14. The smaller end of the intake member 15 adjacent the ring 14 has a diameter substantially the same as the inner diameter of said ring 14 to provide smooth uninterrupted flow of fluid inwardly through the member 15 and ring 14 to the chamber C.

In the condenser embodiment of the invention shown in FIG. 1 the vapor to be condensed enters the casing 1 through the tubular shaft 5 and then passes into the tubes 11 where the vapor is condensed by heat exchange with a gaseous cooling fluid, such as ambient air, discharged outwardly between the spaced fins 10 as herein described. The condensate thus formed in the tubes 11 flows back into the casing 1 from which it is discharged radially by centrifugal force generated by rotation of the condenser. In the arrangement shown, the condensate discharged from the casing 1 through a plurality of U-shaped tubes 19 that form liquid traps which prevent discharge of the vapor directly from the casing and cause the vapor to be diverted into the heat exchange tubes 11. Upon leaving the U-shaped tubes 19 the vapor condensate is discharged radially outward against the inner surface of the cylindrical peripheral wall 20 of a stationary annular housing 2l that circumscribes the rotating casing 1 and has spaced apart side wall portions 22 and 23 which lie closely adjacent the peripheral portions of the casing side walls 3 and 4, respectively. Condensate collecting in the housing 21 discharges therefrom through a drain 24.

An alternative fin construction is shown in FIGS. 3 and 4 of the drawings wherein the fins 10a are formed by adjacent turns or coils of a continuous spiral or helical arrangement of a flat strip of high thermally conductive material. As in the case of the fins 10 in the first embodiment, the adjacent fins 10a are disposed coaxially of the casing 1 in predetermined equally spaced parallel relation and are supported and secured in the desired relationship with respect to one another and the casing 1, for rotation with the latter as a unit, by means of heat exchange tubes or pipes 11a extending therethrough and arranged and secured in the casing wall 4 and end ring 14 as previously described for the tubes 11 in FIG. 1.

The axial spacing or distance between the adjacent fins 10 or 10a is determined with relation to the rotational speed at which the fins are driven, the inner and outer radii of the said fins and the kinematic viscosity of the gaseous fluid so as to utilize the viscous properties of the fluid and the shear forces exerted thereon by the rotating fins 10 and 10a to pump the fluid radially outward between said fins. Thus, upon rotation of the fins 10 or 10a at the predetermined speed related to the spacing of the fins 10 or 10a, their inner and outer radii and the fluid kinematic viscosity, gaseous fluid is caused to flow inwardly through the intake member 15 and ring 14 to the chamber C and enter radially into the spaces between the fins 10 or 10a where it is accelerated by the shear forces generated by the difference or slip between the speed of the fins and the velocity of the fluid. As the fluid is accelerated and forced outwardly between the fins the fluid follows a spiral trajectory and is pressurized and ultimately discharged at the outer edges of said fins.

For optimum results the axial spacing of the fins, their speed of rotation and their inner and outer radii are correlated so that the gaseous fluid passing between the fins is accelerated to a velocity substantially less than the outer peripheral speed of the fins in order to retain the fluid between the fins 10 or 10a the longer time required to provide the optimum total heat flux or total heat exchange between the fluid passing between the fins and another fluid in the tubes or pipes 11 or 11a.

The axial spacing between the fins 10 and 10a or the relationship of the inner radius of the fins to their outer radius may vary within predetermined ranges or limits for any given range of speeds of rotation (r.p.m.) of the condenser. The nature of the flow for rotational shear force devices is completely described by the Taylor number, N.sub.Ta, where:

N.sub.ta = d.sup.2 w/v

d = distance between fins

w = angular velocity (radians per sec.)

v = kinematic viscosity

We have found that most efficient pumping occurs when N.sub.Ta = 3.25. However, efficient fluid pumping does not lead to an efficient heat exchanger. Efficient pumping occurs when the energy transfer to the fluid is maximized. Efficient heat exhange depends upon both the fin area and the difference between the speed of the fins and the velocity of the fluid flowing between them. Thus, for heat transfer, the Taylor number is not adequate by itself to completely describe an optimum configuration. We have found that for various combinations of inner radius (Ri) and outer radius (Ro) of the fins the Taylor number for an efficient heat exchanger will always be greater than 4.5. The precise values of Taylor number and the ratio of the inner to outer radii of the fins depend upon the thermodynamic and transport properties of the fluids exchanging heat and whether the heat transfer mechanism for the fluid in the heat exchange tubes is boiling, condensing or convective. For heat transfer to or from air on the fin side to or from a boiling or condensing fluid within the tubes, it has been determined that the Taylor number for an efficient heat exchanger is within the range of from 5.0 to 10.0 and the inner to outer radii ratio of the fins is within the range of from 0.70 to 0.85. For optimum results the Taylor number will be in the neighborhood of 6.0 and the fin radii ratio in the neighborhood of 0.77, and these values constitute good starting points for the design of an efficient heat exchanger according to the present invention. The particular optimum design and operating conditions for any given heat exchanger installation can be determined by a person skilled in the art. It has been determined that the values of Taylor number and fin radii ratio for other gaseous fluids are essentially the same as the values stated for air.

For example, in the case of an air cooled condenser comprising fins having an outer radius of 7.00 inches and driven at a speed of 2400 r.p.m., optimum results are obtained where the Taylor number is 6.3 and the inner radius of the fins 10 and 10a is 5.25 inches, giving a fin radii ratio of 0.75, and the axial spacing between the adjacent fins 10 or 10a is 0.027. The total number of fins 10 or 10a employed is directly proportional to the heat load of any given installation. Increasing the number and/or diameter of the heat exchange tubes which pass through the fins will provide more heat exchange surface for the fluid inside the tubes but this increased area is obtained at the expense of reduced fluid flow between the fins. That is, the presence of the tubes tends to impede slightly the air flow between the fins. Tube shapes other than round are possible. For example, heat exchange tubes having air foil cross-section shape with the chord of the air foil disposed substantially parallel to or in the direction of the flow streamline between the fins tend to reduce fluid flow resistance between the fins and may be desirable in certain installations.

A rotary condenser made according to the present invention is characterized by its comparatively small compact size and lightweight construction and the minimum power that is required to rotationally drive the heat exchanger at the desired speed. Also, the use of viscosity shear forces to convey the fluid between the spaced fins 10 or 10a with the inherent absence of flow separation, produces a very low operating noise level free of cavitation such as frequently occurs when conventional lift forces are employed to accelerate a fluid.

By reason of these characteristics and advantages, a rotary condenser embodying the present invention is particularly suited for use in high-performance closed Rankine cycle power systems having a rotary boiler to which the condenser can be directly mounted or coupled coaxially for rotation with the boiler as a unit. In such a power system incorporating a rotary condenser according to the present invention, the vapor from a power generator, for example, a turbine, enters the condenser through shaft 5 where it is condensed in the tubes 11 or 11a by heat exchange with cooling air moving outwardly between the fins 10 or 10a and then is discharged into the housing 21 from which it is returned directly to the rotary boiler for regeneration into vapor and the cycle is repeated continuously. A rotary boiler construction and power system suitable for use with a condenser of the present invention is disclosed in my U.S. Pat. No. 3,590,786 issued July 6, 1971.

The use of a rotary heat exchanger embodying the present invention is not limited to use as a condenser for boiler vapors as previously described. For example, another embodiment of the invention is shown in FIGS. 5, 6 and 7 of the drawings which may be used to provide high-performance heat exchange between a cooling or heating fluid and another fluid. Referring to FIG. 5, the heat exchanger illustrated is essentially similar in construction and operation to the first embodiment of the invention previously described. Accordingly, it is not necessary to repeat a detail description of the heat exchanger, and the parts thereof which are similar to the parts shown and described with reference to the embodiment in FIGS. 1 and 2 have been correspondingly referenced with the addition thereto of the letter b.

The principal difference between the two embodiments of the invention shown in the drawings resides in the casing structure 1b and the heat exchange tubes 11b. Thus, referring to FIG. 5, the casing 1b is subdivided by a partition 28 into inlet and outlet chambers I and O, respectively, and the heat exchange tubes 11b are of elongated U-shape provided with longer and shorter leg portions 11c and 11d, respectively. The ends of the shorter leg portions 11d of the U-shaped tubes 11b are mounted and secured in openings 12b provided through the casing side wall 4b so that said tubes are in communication with the interior of the inlet chamber I of the casing 1b. Similarly, the ends of the longer leg portions 11c are mounted and secured in openings 28b provided through the casing partition 28 so that said tubes are in communication with the interior of the outlet chamber O in the casing 1b. The tubes 11b extend through an end ring 14b with their U-shaped ends projecting outwardly beyond said ring as shown.

The tubular shaft 5b is journaled in bearings 6b and 7b and communicates with the interior of the outlet chamber O of the casing 1b to constitute the outlet passage for vapors or liquids from the heat exchange tubes 11b. The inlet passage for vapors or liquids is provided by a smaller tubular shaft 29 disposed coaxially within the shaft 5b and the inner end of said shaft 29 communicates with the interior of the inlet chamber I of the casing 1b from which the incoming vapor or liquid enters the shorter leg portions 11d of the tubes 11b. In the embodiment shown in FIG. 9 the heat exchanger is driven at the desired speed of rotation by a motor M' through a conventional multiple belt drive including pulley 30, belts 31 and pulley 32 secured on the shaft 5b.

The operation of the embodiment of the invention shown in FIGS. 5, 6 and 7 is essentially the same as previously described with reference to the first embodiment. Thus, the vapor or liquid to be cooled or heated enters the heat exchanger through shaft 29 to inlet chamber I from which the fluid enters the tubes 11b, passing first through the shorter leg portions 11d and then through the longer leg portions 11c, during which the fluid is cooled or heated, as the case may be, by heat exchange with a gaseous cooling or heating fluid discharged from the chamber C' outwardly between the spaced fins 10b and 17b in the manner previously described. The fluid, cooled or heated in the tubes 11b, enters the outlet chamber O of the casing 1b from which it is discharged through the tubular shaft 5b.

In some installations guide members such as G are not completely effective in distributing the gaseous first fluid outwardly between the fins 10 uniformly throughout the entire axial length of the fin array, and there is a tendency for less fluid to flow outwardly between the several fins adjacent to the inlet to the chamber C than between the more inward fins of the array. Also, the amount of fluid discharged between the fins at the inlet end of the chamber C becomes less as the axial length of the array of fins is increased.

I have discovered that in installations where there is less fluid flow between the fins at the inlet end of the chamber C, as described, this can be corrected and the flow of fluid outwardly between all of the fins in the array made substantially uniform by providing at the inlet end portion of the array of fins, an axially spaced pair of continuous annular radially projecting flanges or flange portions F and F' that extend a predetermined distance outwardly beyond the outer peripheral edges of the fins 10 and rotate as a unit with the array of fins.

As shown in FIG. 8 of the drawings, the flange F is disposed at the extreme outer or fluid inlet end of the array of fins 10 and can be provided simply by increasing the radial dimension of the end ring 14 previously described. The flange F' is provided by an annular ring member 31 having openings therethrough for the heat exchange tubes 11 and mounted in spaced relation inwardly from the flange F a distance to include or bracket between the flanges F and F' a predetermined relatively small number of the fins 10 depending upon the requirements of the particular heat exchange installation.

As in the case of the end ring 14 the inner diameter of the ring 31 is the same as the inner diameter of the fins 10 and the ratio of the outer radius of the flanges F and F' to the outer radius of the fins will vary according to the dimensional specifications for a particular heat exchanger and usually will be of the order of about 1.3.

The volume of fluid flow outwardly through the several fins bracketed by the flanges F and F' can be further increased as desired or required by providing circumferentially about the fins between the flanges F and F' a plurality of axially extending radially disposed blades 32 that rotate with the array of fins as a unit. The inner edges of the blades 32 are spaced outwardly from the outer edges of the fins, and the number of blades 32 employed in a particular installation will vary according to the design and operation specifications of the heat exchanger.

The invention may be employed for heat exchange purposes generally, including other condenser applications as well as the cooling or heating of liquids, gases, and vapors where high-performance optimum total heat exchange is desired along with the accompanying advantages of compact lightweight construction, minimum power requirement and substantially noise-free operation. Rotary heat exchangers of the present invention can be used as condensers for closed Rankine cycle engines in vehicles for land use, such as the automobile, in which case air would be the preferred exterior fluid. Also, air-cooled engines using the present invention are useful in total energy systems wherein the heat rejected by the condenser in the form of hot air could be used to heat homes, shops, and other buildings, and the shaft energy can be simultaneously converted to electric power by means of a generator. In the case of a total energy system in which hot water is the preferred means of rejecting heat, the rotary heat exchanger of this invention can be optimized for silence, high efficiency, and low power consumption and thus could be used for total energy on land and in boats. Other applications of the present invention include its use for assisting in the cooling of other types of engines, such as the internal combustion engines, for refrigeration cycle condensers and evaporators, and for chemical process cooling.

While certain embodiments of the present invention have been illustrated and described, it is not intended to limit the invention to such disclosures and changes and modifications may be made and incorporated as desired within the scope of the claims.

Claims

1. In rotary heat exchange apparatus comprising

an array of a plurality of annular fins disposed coaxially in predetermined spaced parallel relation for rotation as a unit about a common axis, each fin having the same inner radius and the same outer radius and a predetermined inner to outer radii ratio in the range of 0.70 to 0.85,

a plurality of heat exchange tubes each extending longitudinally through said fins in spaced relation to the common axis and arranged circumferentially thereabout,

means for introducing a gaseous first fluid interiorly of said array of annular fins,

means for introducing and withdrawing a second fluid into and from said heat exchange tubes,

and means for rotationally driving said plurality of fins about said common axis,

the improvement which comprises rotationally driving the plurality of fins at a predetermined speed of rotation correlated to the axial spacing of said fins and the kinematic viscosity of said gaseous first fluid to provide a Taylor number in the range of 5.0 to 10.0 and operable at said inner and outer radii ratio of the fins to convey and accelerate said gaseous first fluid by viscosity shear forces spirally outward between the fins substantially to the velocity providing optimum heat exchange between the gaseous first fluid and the second fluid in said heat exchange tubes.

2. In rotary heat exchange apparatus as claimed in claim 1, wherein the fin radii ratio is about 0.77, comprising rotationally driving the plurality of fins at a speed of rotation to provide a Taylor number of about 6.0.