Abstract:
A multiplicity of parallel heat transfer tubes each sealed with refrigerant are journaled for rotation at each end and in a bulkhead that separates the air flow channel in a counterflow heat exchanger into ingoing and outgoing parallel channels. Each heat transfer element has closely spaced circular fins extending radially outward from each tube, the spacing between adjacent fins being less than the fin radius. A motor and transmission cause each heat transfer element to rotate about its longitudinal axis.

Description:
This application is a continuation-in-part of application Ser. No. 631,097 filed July 16, 1984, now abandoned. 
    
    
     This invention relates to new and useful improvements in heat exchangers and, more particularly, heat exchangers of the finned tube in cross flow type. 
     BACKGROUND OF THE INVENTION 
     A search of the prior art uncovered U.S. Pat. Nos. 1,844,308, 3,344,854, 3,989,101, 4,066,119, 4,076,072 and 4,405,013. U.S. Pat. No. 3,344,854 discloses an engine radiator having a movable endless belt screen around the heat exchanger for preventing clogging of heat exchangers by foreign particles entrained in the cooling medium. 
     SUMMARY OF THE INVENTION 
     According to the invention, there is heat exchanging apparatus comprising a plurality of substantially parallel heat transfer elements each having a plurality of closely spaced heat radiating fins extending radially outward from the element axis, means for rotatably supporting the heat transfer elements at at least one end and intermediate the ends in a dividing member that divides the heat exchanging apparatus into portions for receiving air flow perpendicular to the plane of the substantially parallel elements in opposite directions so that air flowing in one of the directions releases heat to the heat transfer elements that is absorbed by the air moving in the opposite direction so that rotation of the elements allows particles stuck to fins upon entering to be expelled by the air flow over them as the fin portion bearing the stuck particles advances from the upstream to the downstream side of the incident air stream. Preferably, there is means, such as a motor and transmission means for coupling the motor to the rotatable heat transfer elements for rotating the heat transfer elements. Preferably, the heat transfer elements comprise conducting tubes sealed with refrigerant, such as Freon refrigerant. 
     The general object of this invention is to provide a simple means of manufacturing a heat exchanger which, when placed in the flow of a fluid laden with suspended lint or other complex contaminant particles, will be generally self cleaning and nonclogging. 
     Other important objects of this invention are to provide a heat exchanger of the type with low power consumption, and low labor requirement in the cleaning process. 
     Additional objects of this invention are to provide a heat exchanger of the type with low costs of manufacture, installation, and maintenance. 
     An additional object of this invention is to provide a heat exchanger of the type which is mechanically simple and reliable. 
     A further object of the invention is to produce an exchanger of the type wherein high fin densities needed for high thermal performance do not adversely affect the nonclogging nature of the device. 
     Still another object of this invention is to provide a heat exchanger of the type without need for external filtration and with total design flexibility with respect to size. 
     These, together with other objects and advantages which will become subsequently apparent, reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof and in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a perspective view of a heat exchanger in a typical embodiment for air to air heat recovery; 
     FIGS. 2 and 3 are transverse sectional views of various embodiments of the invention utilizing additional means for cleaning with the heat exchange elements; and 
     FIGS. 4 and 5 are transverse sectional views showing adjacent elements arranged to rotate in opposite directions. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawing in detail and more particularly FIG. 1, a feature of the invention is the rotating heat transfer elements 1, of a suitable material, which, being driven by suitable transmission means 2, rotates about an axis 3. 
     FIG. 1 shows one basic embodiment in which each heat transfer element 1 is a discrete sealed circular cylindrical tube with transverse circular external fin means. The heat transfer element is charged with a refrigerant, such as Freon, which provides heat transfer means by evaporating throughout part of the length of the heat transfer element and condensing elsewhere along the length of the element. 
     When these heat transfer elements are exposed to, for instance, a flow of exhaust air from a laundry drier, the leading or upstream edges of these fins catch and hold a certain amount of the lint in the airstream. As each heat transfer element 1 rotates about its axis, these leading edges with their buildup of lint move to the area of high air velocity between the tubes and then to the rear of the tubes, during which rotation the same air flow which initially deposited the lint acts to remove the lint from the fins then trailing or downstream edges. The separation between adjacent fins is significantly less than the span across each fin between extreme upstream and downstream points on leading and trailing edges, respectively. 
     Where the heat exchanger consists of a number of banks of heat transfer elements 1 situated sequentially with respect to the air flow, lint will move from one bank to the next and finally out of the heat exchanger after being removed from the final bank. 
     This self cleaning system allows all debris in the air flow to pass through the heat exchanger, and it eliminates the need for filtering prior to the heat exchanger. Thus eliminated is the need to clean filters and remove the waste from filter cleaning collection points. This represents a significant savings in man hours to the user, and also a savings in electrical energy to run compressors or other mechanical devices commonly used in the self cleaning filters and air jet or water jet cleaning systems in heat exchangers. The energy required to rotate the heat transfer elements in the current invention is minimal in comparison with that to run air compressors or water pumps. 
     In the preferred embodiment, the heat exchanger is an air-to-air heat recovery system wherein a bulkhead 4 with journal bearing means separates the exhaust air flow from the makeup air flow. Differential pressure sensing switch 10 via conduits to ducting on either side of the exhaust portion of the heat exchanger, may activate a mechanical power means in the form of a simple low powered geared reduction electric motor assembly 2, which rotates the heat transfer elements slowly via the transmission means in the form of gears, pullies, chain drives, or other standard transmission means. Depending on the application, this differential pressure switch may be set to operate whenever any differential pressure is detected, or with the use of appropriate standard relays and time delays, may be used to rotate the elements only when an excessive pressure drop indicating clogging is detected. 
     If additional cleaning means are required, a preferred method is the appropriate placement of sonic transducers such as 5 about the heat exchanger, for instance, at the end of each heat transfer element, which will additionally help to loosen lint from on or between fins and allow it to be blown free by the normal air flow. 
     In FIG. 2 the cleaning action provided by the exhaust air stream over the rotating heat transfer elements is augmented by a more traditional cleaning method, for example an air jet 6. In this embodiment, the air jet means, activated periodically, merely loosens whatever material was not blown free by the exhaust air stream, allowing it to be removed in the normal manner by the exhaust air stream and subsequent rotating elements. This substantial improvement over previous uses of air jets for cleaning finned tubes eliminates the need to collect the freed lint at each bank of elements. 
     In FIG. 3 the cleaning action of the exhaust air stream over the rotating elements is augmented by mechanical brush means 7 on an endless belt 8. In one embodiment the brush means intermittently or constantly traverse one or more banks of rotating elements. In another embodiment brush means are fixed with respect to individual heat transfer elements. And still another embodiment brush means may move in other ways, for instance rotating about their longitudinal axes, whether in a fixed or traversing configuration. 
     The advantage to such embodiments over brush means on nonrotating elements is that in the present invention the brush means need only loosen the clogging material, and not remove it completely. Once loosened the rotating heat transfer elements and air flow through the heat exchanger will cause removal of the clogging materials. 
     Other mechanical cleaning systems will be apparent to those skilled in the art, for instance pressurized water jet means or steam cleaning means, but in all cases the cleaning action of these additional systems is enhanced by the action of the rotating elements in the air flow. 
     Referring to FIGS. 4 and 5, there are shown embodiments of the invention in which adjacent elements rotate in opposite directions as indicated by the arrow on each element. As indicated above each heat transfer element rotates slowly. By slowly rotating each element as is evident from the use of a low powered gear reduction motor assembly used in a practical system, the velocity of air flow is significantly greater than the tangential velocity of a piece of lint on a rotating thin tip. 
     Having the transmission means rotate each adjacent pair of heat transfer elements oppositely helps roll large clumps of lint through a pair of elements to the next bank of heat transfer elements. To help insure that clumps of lint are not trapped in alternate gaps between heat transfer elements, the mechanical power source or transmission device may include means for periodically changing the direction of rotation of the heat transfer elements. 
     The present invention has several advantages over the prior art in the areas of simplicity, flexibility, and effectiveness in keeping heat transfer surfaces clean. 
     Vehicle radiators having first and second opposed surfaces in the prior art exemplified by U.S. Pat. Nos. 4,066,119 and 4,076,072 lose performance during the rotation process, and thus can not provide continuous self cleaning without a significant penalty. In the present invention, the rotation of the heat transfer elements creates no changes in the heat transfer surface or frontal area. Additionally, in the present invention the bulk of the lint is removed as the lint passes through the high velocity area in the gaps between adjacent heat transfer elements. The prior art does not teach this benefit. 
     U.S. Pat. No. 4,405,013 discloses a rotor made up of a plurality of heat pipes with no motion of one heat pipe rotationally relative to another. This apparatus has the disadvantage that an accumulation of lint or other complex material trapped between rows of heat pipes (if they are closely spaced heat pipes) will merely be tossed back and forth between two banks of heat pipes as the direction of flow alternates during the rotation. In the present invention the flow direction is constant with respect to the banks of heat pipes, and the rotational action of the individual heat pipes with respect to one another aids in the freeing of lint. Additionally, the pesent invention allows the heat pipes to remain fixed with respect to the temperature gradient in the air flow, thereby providing maximum thermal effectiveness duplicating that of pure counterflow heat exchange. The prior art apparatus loses the benefits of counterflow heat exchange as the heat pipes move throughout the temperature gradient of the air flow. 
     U.S. Pat. No. 2,813,698 discloses a heat exchanger having rotating heat elements with disks that spin in hot gases at high velocity to improve heat transfer when operating in high temperature air streams. The high rotational velocity also throws off soot particles which may gather on the spinning disks. 
     This patent and the other prior art does not address the problem of lint, such as that in the air stream of a laundry dryer at significantly lower temperature than the 2300° F. mentioned in this patent. Lint differs from other solids found in airstreams in a number of ways. The volume of space defined by a lint fiber is orders of magnitude greater than the actual volume of the lint itself. That is, a lint fiber is long and twisted, defining a large three-dimensional space, compared to a speck of soot, which is a simple shape of comparatively high density. Lint has the capacity to form large mats of randomly interlocked fibers. 
     The present invention operates at a rotational speed about one revolution per minute, believed to be about 1000 times slower than the apparatus in U.S. Pat. No. 2,813,698. Lint is lodged on the leading edge of the rotating element fins and slowly rotated to the position of maximum air velocity discussed above, where the lint is blown from the fins. Furthermore, the counter rotating elements shown in the embodiments of FIGS. 4 and 5 may function to roll large mats of lint through the heat exchanger system as sometimes may be desirable. 
     The individually installed nature of the heat pipes in the present invention allows for a greater ease of removal and replacement, and also allows for total flexibility in the size and shape of the heat exchanger. A fixed pattern of parallel banks is economically preferable and structurally preferable to radially dispersed concentric banks fixed to a rotating support structure. 
     Tests have shown the configuration of parallel banks of thin tubes described in the present invention to generate extremely low pressure drops in the air flow in comparison with other commercially available heat exchangers of similar thermal performance. 
     A benefit of the present invention with respect to the prior art is that higher fin densities along the length of the heat transfer elements, which higher densities are desirable to produce higher thermal performance, actually improve the clog free nature and cleanability of the exchanger by increasing the chances of the lint particles being caught on the leading edges of the fins rather than wedging between the fins, after which the rotation of the elements causes the previously described removal of the linty material. 
     Manufacture of the claimed exchanger is not limited to the materials or processes described above. Other methods are suitable. Transmission means, for instance may range from automatically controlled powered system for commercial applications to a manually powered system wherein the home owner manually rotates each element or gang of elements in a small system attached to a home laundry dryer. 
     The foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described. Accordingly, all suitable modifications and equivalents may be resorted to if they fall within the scope of the invention as claimed.