Heat exchanger

Abstract: A heat exchanger comprises a plurality of heat transfer tubes (1) arranged in parallel to each other at predetermined intervals, and a plurality of ring fins (4) of a fine wire, having a substantially circular shape of a diameter greater than the outside diameter of the heat-transfer tubes. Eath ring fin has a portion of the inner circumference fixed to the outer surface of the heat-transfer tube so that the respective centers of the ring fins are dislocated from the center axes of the heat-transfer tubes toward the upper side with respect to the flowing direction (A) of the external fluid.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a heat exchanger according to the preamble of claim 1. Such a heat exchanger is known from JP-A-61-153 388. Description of the Prior Art Fig. 1 is a perspective view of a prior art heat exchanger for an air conditioner, disclosed in Japanese Patent Laid-open (Kokai) No. 61-153388 and Fig. 2 is a sectional view of the heat exchanger of Fig. 1. Referring to Figs. 1 and 2, the heat exchanger is formed by alternately passing fine wires 2a and 2b, which serve as fins, over and under heat-transfer tubes 1 through which a heat exchanging fluid, such as a cooling medium, flows in the direction of the arrow B so that the fine wire fins 2a and 2b are in close contact with the heat-transfer tubes 1. In this heat exchanger, the thermal contact between the fine wire fins 2a and 2b, and the heat-transfer tubes 1 is secured and the positions of the heat-transfer tubes 1 and the fine wire fins 2a and 2b relative to each other are fixed by alternately passing the fine wire fins 2a and 2b over and under the heat-transfer tubes 1. The heat-transfer tubes 1 are very thin tubes having, for example, an outside diameter in the range of 1 to 2 mm and an inside diameter in the range of 0.7 to 1.7 mm. In operation, as shown in Fig. 2, a current of an external fluid, for example, air, flowing in the direction of the arrow A (Fig. 1) toward the plurality of parallel heat-transfer tubes 1 threads its way through spaces between the fine wire fins 2a and 2b, exchanging heat with the heat-transfer tubes 1 and the fine wire fins 2a and 2b. The current of the external fluid is disturbed by the fine wires 2, the current of the external fluid falling on the fine wire fins is deflected to right and left as shown by arrows in Fig. 3, and part of the external fluid flows along the fine wire fins and rises along the surfaces of the heat-transfer tubes 1, so that the external fluid is able to be in contact with the heat-transfer tubes 1 for a comparatively long contact time. When cold water is passed through the heat-transfer tubes 1 of the heat exchanger or a low-temperature cooling medium is evaporated in the heat-transfer tubes 1, air flowing past the heat-transfer tubes 1 is cooled for air cooling. If the air passing by the surfaces of the heat-transfer tubes 1 and the fine wire fins 2a and 2b is cooled to a temperature below the dew point, water droplets form over the surfaces of the heat-transfer tubes 1 and the fine wire fins 2a and 2b. The water droplets flow along the surfaces of the heat-transfer tubes 1 and the fine wire fins 2a and 2b, and drain off from the heat exchanger. In the heat exchanger of this construction, the contact area in which the fine wire fins 2a and 2b are in contact with the heat-transfer tubes 1 is very small. Therefore, the fine wire fins 2a and 2b do not reduce the contact area in which the external fluid comes into contact with the heat-transfer tubes 1 and hence heat can effectively be transferred between the external fluid and the heat-transfer tubes 1. Although the heat-transfer rate of this prior art heat exchanger is greater than that of a conventional heat exchanger for air conditioner, the heat-transfer area of the prior art heat exchanger is 1/5 or below that of a conventional heat exchanger having the same front area because the prior art heat exchanger has a very small thickness in the range of 1 to 3 mm. A heat exchanger formed by stacking a plurality of heat exchanging units of the type similar to this prior art heat exchanger may be used to secure a necessary heat exchanging quantity. However, the heat exchanger having the plurality of heat exchanging units increases the pressure loss of air, the flow of air is reduced and, consequently, it is impossible to secure a necessary heat exchanging quantity unless the power of the blower is increased. The heat exchanging ability Q of a heat exchanger is expressed by: Q = K x A x ΔT , where K is the overall heat-transfer coefficient, A is the heat-transfer area and ΔT is the temperature difference between air and the medium flowing through the heat-transfer tubes 1. Since the prior art heat exchanger is constructed by passing the fine wire fins 2a and 2b alternately over and under the heat-transfer tubes 1, it is difficult to increase the heat-transfer area per unit front area and it is difficult to increase the overall heat-transfer coefficient by enhancing the disturbance of the flow of air. After all, it has been impossible to enhance the heat exchanging quantity through the improvement of the factors that contribute to the enhancement of the heat exchanging quantity and there has been a limit to the enhancement of the heat exchanging efficiency. Such problems are remarkable particularly when the heat exchanger is used as an evaporator and vapor contained in air condenses into water droplets over the heat-transfer surface. If water droplets form over the surfaces of the heat-transfer tubes 1 and the fine wire fins 2a and 2b, the spaces between the fine wire fins 2a and 2b are clogged with the condensation to hinder the flow of air through the heat exchanger. Consequently, the flow of air is reduced due to pressure loss and the reduction of the heat exchanging efficiency results. It is generally known that, when a nonazeotropic cooling medium is used as a cooling medium which is passed through the heat-transfer tubes, the performance of the heat exchanger formed by arranging a plurality of heat exchanging units in layers is improved considerably when the nonazeotropic cooling medium is passed in a crossflow mode from the rear heat exchanging unit sequentially through the intermediate heat exchanging units toward the front heat exchanging unit so that the heat exchanger functions virtually as a crossflow type heat exchanger. The number of the heat exchanging units of a heat exchanger for the conventional air conditioner is two at the most, because an excessively large number of heat exchanging units increase the thickness of the heat exchanger and the size of the air conditioner increases accordingly. Therefore it has been very difficult to construct a crossflow type heat exchanger capable of functioning virtually as a counterflow type heat exchanger. GB-A-636615 discloses a fin to form a heat-exchanger for exchanging heat between a solid surface and a fluid arranged to pass through the fin. The fin comprises a flattened helix of wire of high thermal conductivity having a substantial portion of each half turn of the helix straight and having the straight portions of alternate half turns lying in an imaginary surface substantially parallel to an imaginary surface in which the straight portions of the remainder of the half turns lie. The planes in which the curved portions of each half turn lie are inclined to the imaginary surfaces of angles of the order of 45 degrees. SUMMARY OF THE INVENTION It is the object of the present invention to provide a heat exchanger for an air conditioner, provided with a heat exchanger for an air conditioner, provided with heat transfer area capable of exchanging heat at an increased heat exchanging quantity, and capable of passing air at a reduced pressure loss and of suppressing reduction in heat exchanging quality due to reduction in the flow of air. Further of the present invention is to provide a heat exchanger for an air conditioner, having an increased heat-transfer area capable of exchanging heat at an increased heat exchanging quantity, and requiring a reduced space for installation. Still further object of the present invention is to provide a heat exchanger for an air conditioner, capable of increasing heat-transfer coefficient outside a heat-transfer tube and of promoting heat transfer, having an increased heat-transfer area to increase heat exchanging quantity and capable of suppressing reduction in heat exchanging quantity due to reduction in the flow of air and of reducing the pressure loss of air. Still further object of the present invention is to provide a heat exchanger for an air conditioner, having a simple construction and an increased heat-transfer area, and capable of exchanging heat at an increased heat exchanging quantity and of suppressing reduction in the heat exchanging quantity due to reduction in the flow of air. For solving this object, a heat exchanger according to the invention is characterized by the features of claim 1. Preferred embodiments of the heat exchanger according to the invention are defined in the subclaims. A heat exchanger for an air conditioner, according to the present invention comprises a fin section including a plurality of first ring fins which are substantially circular fine wire fins, having a diameter greater than the diameter of the heat-transfer tubes, and fixed to the heat-transfer tubes with their inner circumferences in contact with the outer surface of the heat-transfer tube and with their centers dislocated from the axes of the heat-transfer tubes toward the upper side with respect to the flowing direction of the external fluid, which in operation flows in one direction towards the heat-transfer tubes. The heat exchanger has an increased heat-transfer area, the rings disturb the current of the external fluid on the upper side of the heat-transfer tubes so that the external fluid comes into contact with the heat-transfer in turbulent currants, which increases the heat exchanging quantity. Since spaces are formed between the heat-transfer tubes and the ring fins, condensed water droplets are hardly able to stay on the heat exchanger, and the heat exchanger is hardly clogged with condensed water droplets even if the surface of the heat exchanger is wet during operation, so that reduction in the heat exchanging quantity due to reduction in the flow of the external fluid can be suppressed. The two adjacent ring fins may fixedly be joined at least at one position. When the adjacent ring fins are joined together, the heat-transfer surface has a firm construction, the heat-transfer tubes can be arranged at reduced intervals to increase the heat-transfer area. A heat exchanger for an air conditioner, in a preferred mode of the present invention additionally comprises a plurality of second fins which are substantially circular fine wire fins, having an inside diameter greater than the outside diameter of the heat-transfer tubes, and fixed to the heat-transfer tube with their inner circumferences in contact with the outer surface of the heat-transfer tube and with their centers dislocated from the axis of the heat-transfer tube toward the lower side with respect to the flowing direction of the external fluid. The ring fins of the first and the second fin sets are arranged alternately along the axis of the heat-transfer tube. The current of the external fluid is disturbed on the upper side of the heat transfer tubes so that the external fluid comes into contact with the heat-transfer tubes in turbulent currants, which increases the heat exchanging quantity. Since spaces are formed between the heat-transfer tubes and the ring fins, condensed water droplets are hardly able to stay on the heat exchanger, and the heat exchanger is hardly clogged with condensed water droplets even if the surface of the heat exchanger is wet during operation, so that reduction in the heat exchanging quantity due to reduction in the flow of the external fluid can be suppressed. A heat exchanger for an air conditioner, in a preferred mode of the present invention comprises 8-shaped fins each having two loops, formed by bending a fine wire in the shape of the digit "8". One of the loops of each 8-shaped fin is put on each heat-transfer tube. The heat exchanger has an increased heat-transfer area. The 8-shaped fins further disturbs the turbulent currants of an external fluid three-dimensionally to promote heat-transfer efficiency on the lower side. One of the loops of each 8-shaped fin may be put on and fixed to a plurality of heat-transfer tubes, which forms a firm heat-transfer surface of a simple construction having an increased heat-transfer area in the flowing direction of the external fluid and increases the heat exchanging quantity. Since spaces are formed between the 8-shaped fins and the heat-transfer tubes, condensed water droplets are hardly able to stay on the heat exchanger, the heat exchanger is hardly clogged with condensed water droplets even if the heat exchanger is wet during operation, and reduction in the heat exchanging quantity due to reduction in the flow of the external fluid can be suppressed. In a heat exchanger for an air conditioner, in a preferred mode of the present invention, said first ring fins are formed by a plurality of first coil rings formed by helically winding fine wires at a pitch twice the diameter of the fine wire or above. The fin can easily be mounted around the heat-transfer tube, and the heat exchanger has a simple construction and an increased heat-transfer area. The centers of the ring fins are dislocated from the axis of the heat-transfer tube toward the upper side with respect to the flowing direction of an external fluid to disturb the currant of the external fluid on the upper side of the heat-transfer tubes so that the turbulent currants of the external fluid come into contact with the heat-transfer tubes, which increases the heat exchanging quantity. Since spaces are formed between the ring fins and the heat-transfer tubes, condensed water droplets are hardly able to stay on the heat exchanger and the heat exchanger is hardly clogged with condensed water droplets even if the surface of the heat exchanging unit is wet during operation, and reduction in the heat exchanging quantity due to reduction in the flow of the external fluid can be suppressed. Each coil-shaped fin on one heat-transfer tube may fixedly be joined at least at one point to the fin on the adjacent heat-transfer tube. The heat exchanger has a firm heat-transfer surface. Since the heat-transfer tubes can be arranged at small intervals, the heat exchanger has a simple construction and a large heat-transfer area. The heat exchanger may be provided further with second coil-shaped fin having a plurality of ring fins. The current of the external fluid is disturbed on the upper side of the heat exchanger and the turbulent currants of the external fluid come into contact with the heat-transfer tubes and hence the heat exchanging quantity can be increased. In a heat exchanger in a preferred mode of the present invention, a plurality of heat-transfer tubes are attached to the inner surface of each coil-shaped fin. In a heat exchanger in a preferred mode of the present invention, ring fins are attached fixedly to heat-transfer tubes so as to extend obliquely downward. The ring fins extending obliquely downward facilitate condensed water droplets dropping by gravity when the heat exchanger is used in a moist atmosphere where moisture contained in the atmosphere condenses, the heat exchanger is hardly clogged with condensed water droplets even if the surface of the heat exchanger is wet during operation, and reduction in the heat exchanger is wet during operation, and reduction in the heat exchanging quantity due to reduction in the flow of the external fluid can be suppressed. A heat exchanger for an air conditioner, in a preferred mode of the present invention comprises a plurality of heat-transfer tubes through which a nonazeotropic cooling medium flows, a plurality of fine wires, and a plurality of heat-transfer members arranged perpendicularly to the flowing direction of an external fluid in a plurality of banks and parallel to each other, and connected to each other. The cooling medium is supplied so as to flow from the heat-transfer member disposed at the lowermost position with respect to the flow of the external fluid through the heat-transfer tubes toward the heat-transfer member disposed at the uppermost position. The heat exchanging performance of this heat exchanger is higher than that of a heat exchanger of a simple crossflow type (a heat exchanger with a single crossflow heat exchanging unit). BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a fragmentary perspective view of the heat transfer plane of a conventional heat exchanger for an air conditioner; Fig. 2 is an enlarged fragmentary sectional view of a conventional heat exchanger, showing the flow of air on the heat exchanger; Fig. 3 is a fragmentary plan view of the heat transfer plane of a conventional heat exchanger; Fig. 4 is a fragmentary sectional view of the main part of a heat exchanger for an air conditioner in a first embodiment according to the present invention; Fig. 5 is a fragmentary sectional view of the main part of a heat exchanger for an air conditioner in a second embodiment according to the present invention; Fig. 6 is a fragmentary sectional view of the main part of a heat exchanger for an air conditioner in a third embodiment according to the present invention; Fig. 7 is a fragmentary sectional view of the main part of a heat exchanger for an air conditioner in a fourth embodiment according to the present invention; Fig. 8 is a fragmentary perspective view of the main part of a heat exchanger for an air conditioner in a fifth embodiment according to the present invention; Fig. 9 is a fragmentary sectional view of the main part of a heat exchanger for an air conditioner in a ninth embodiment according to the present invention; Fig. 10 is a fragmentary perspective view of the main part of a heat exchanger for an air conditioner in a seventh embodiment according to the present invention; Fig. 11 is a fragmentary view of the main part of a heat exchanger for an air conditioner in an eight embodiment according to the present invention; Fig. 12 is a fragmentary perspective view of a heat exchanger for an air conditioner in a ninth embodiment according to the present invention; Fig. 13 is a fragmentary sectional view of a heat exchanger for an air conditioner in a tenth embodiment according to the present invention; Fig. 14 is a fragmentary sectional view of a heat exchanger in a modification of the exchanger in Fig. 13; and Fig. 15 is a graph showing the dependence of heat exchanging quantity on the number banks of the heat-transfer surfaces in the heat exchanger in the tenth embodiment when a nonazeotropic cooling medium is used. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Fig 4 showing a heat exchanger for an air conditioner, in a first embodiment according to the present invention in a fragmentary sectional view, there exist heat-transfer tubes 1 and ring fins 4 realizing heat transfer fins. An external fluid, such as air, flows in the direction of the arrow A. The inside diameter of the ring fins 4 is greater than the outside diameter of the heat-transfer tubes 1, the centers of the ring fins 4 are dislocated toward the upper side with respect to the direction of the windward or upper part of the flow form the center axes of the corresponding heat-transfer tubes 1 so that parts of the inner surfaces of the ring fins 4 on the lower side are in contact with the outer circumference of the corresponding heat-transfer tubes 1. The plurality of ring fins 4 are arranged axially of each heat-transfer tube 1 at a pitch not smaller than the diameter of the fine wire forming the ring fins 4. The ring fins 4 are fixed to the heat-transfer tubes 1 at the contact points. In operation, the air flow velocity increases as the air flows through spaces between the portions of the ring fins 4 on the upper side of the heat-transfer tubes 1, and the ring fins 4 disturb the currents of the air flows in Kármán vortex streets toward the heat-transfer tubes 1. The air does not flow straight toward the heat-transfer tubes 1, threads its way through the spaces between the ring fins 4 and the heat-transfer tubes 1, generating small vortices. The vortices disturb the currents of the air at the rear portions of the ring fins on the lower side and the heat-transfer tubes 1. Since the ring fins 4 are dislocated toward the upper side relative to the heat-transfer tubes 1 and the rear portions of the ring fins 4 are in contact with the heat-transfer tubes 1, the flow of the air is deflected by the ring fins 4 and air reaches the rear sides having a low heat-transfer coefficient of the heat-transfer tubes 1. Consequently, heat transfer is promoted and the heat exchanger transfers heat at a high heat-transfer rate. The ring fins 4 increases the heat-transfer area. Since the inside diameter of the ring fins 4 is greater than the outside diameter of the heat-transfer tubes 1, comparatively large spaces are formed between the heat-transfer tubes 1 and the ring fins 4 and hence condensed water droplets are hardly able to stay on the heat exchanger even if the heat exchanger is used in a moist atmosphere where moisture contained in the atmosphere condenses in water droplets. Therefore, the heat exchanger is hardly clogged with condensed water droplets and reduction in heat exchanging quantity due to reduction in the flow of the air can be suppressed. The heat exchanger may be provided with elliptic ring fins instead of the ring fins with their major axes in parallel to the flowing direction of the air, and the heat transfer tubes 1 may be arranged at smaller intervals to increase the overall heat-transfer area. Referring to Fig. 5 showing a heat exchanger for an air conditioner, in a second embodiment according to the present invention in a fragmentary sectional view, there exist a heat-transfer tube 1 and ring fins 4 realizing heat transfer fins. An external fluid, such as air, flows in the direction of the arrow A. The inside diameter of the ring fins 4 is greater than the outside diameter of the heat-transfer tubes 1, the centers of the ring fins 4 are dislocated from the center axes of the corresponding heat-transfer tubes 1 toward the upper side of the external operating fluid so that parts of the inner surfaces of the ring fins 4 on the lower side are in contact with the outer circumference of the corresponding heat-transfer tubes 1. The transverely adjacent ring fins 4 cross each other and joined together at crossing points 8a and 8b. In operation, the air flow velocity increases as the air flows through spaces between the front portions of the ring fins 4, and the ring fins 4 disturbs the currents of the air and the air flows in Kármán vortex streets toward the heat-transfer tubes 1. The air is unable to flow straight toward the heat-transfer tubes 1 and threads its way through spaces between the ring fins 4 and the heat-transfer tubes 1, generating small vortices. The small vortices swirl around the rear portions of the ring fins 4 and the heat-transfer tubes 1 in turbulent currents. Since the rear portions on the lower side of the ring fins 4 are attached to the heat-transfer tubes 1, the ring fins 4 deflects the currents of the air so that the air is able to reach the rear portions having a low heat-transfer coefficient on the lower side of the heat transfer tubes 1. Consequently, heat transfer is promoted and the heat exchanger transfers heat at a high heat-transfer rate. Since the transversely adjacent ring fins 4 cross each other and joined together at crossing points 8a and 8b, the heat-transfer suface has a firm construction, the heat transfer tubes 1 can be arranged at comparatively small intervals, and the heat exchanger has a comparatively large heat-transfer area. Since the inside diameter of the ring fins 4 is greater than the outside diameter of the heat-transfer tubes 1, comparatively large spaces are formed between the ring fins 4 and the heat-transfer tubes 1. Therefore, condensed water droplets are hardly able to stay on the heat exchanger even if the heat exchanger is used in a moist atmosphere where moisture contained in the atmosphere condenses in water droplets, the heat exchanger is hardly clogged with condensed water droplets and reduction in heat exchanging quantity due to reduction in the flow of the air can be suppressed. Referring to Fig. 6 showing heat exchanger for an air conditioner, in a third embodiment according to the present invention in a fragmentary sectional view, there exist a heat-transfer tube 1 and ring fins 4 realizing heat transfer fins. An external fluid, such as air, flows in the direction of the arrow A. The inside diameter of the ring fins 4 is greater than the outside diameter of the heat-transfer tubes 1, and portions of the ring fins are attached to the outer surface of the corresponding heat-transfer tubes 1, so as to function as heat transfer fins. A ring fin 4a is dislocated from the heat-transfer tube 1 toward the rear side with respect to the direction of the arrow A and another ring fin 4b is dislocated from the heat-transfer tube 1 toward the front side with respect to the direction of the arrow A. A pair of ring fins 4a and 4b are arranged alternately axially of the heat-transfer tube 1. The transversely adjacent rear ring fins 4a, and the transversely adjacent front ring fins 4b may cross each other and joined together at least one crossing point similarly to the ring fins 4 of the first and the second embodiment. In operation, the air flow velocity increases as the air flows through the spaces between the ring fins 4b which extend to the front direction of the heat-transfer tube 1, the ring fins 4a disturbs the currents of the air, and the air flows in Kármán vortex streets toward the heat-transfer tubes 1. The air is unable to flow straight toward the heat-transfer tubes 1 and threads its way through the spaces between the ring fins 4 and the heat-transfer tubes 1 in small vortices and the turbulent currents of the air having the small vortices reach the ring fins 4b and the heat-transfer tubes 1. Since the ring fins 4b is in contact with the rear side of the heat-transfer tubes, the ring fins 4b deflects the flow of the air toward the rear side having a low heat-transfer coefficient of the heat-transfer tube 1. The rear ring fins 4a increases the heat-transfer area. Consequently, heat transfer is promoted, the heat exchanger transfers heat at a high heat-transfer rate. Since the front ring fin 4b and the rear ring fin 4a are arranged alternately axially of the corresponding heat-transfer tubes 1 and contiguously with each other, the pitch of the rear ring fins 4a and that of the front ring fins 4b are determined automatically. Since the inside diameter of the ring fins 4 is greater than the outside diameter of the heat-transfer tubes 1, comparatively large spaces are formed between the ring fins 4 and the heat-transfer tubes 1. Therefore, condensed water droplets is hardly able to stay on the heat exchanger when the heat exchanger is used in a moist atmosphere where moisture contained in the atmosphere condenses in water droplets, the heat exchanger is hardly clogged with condensed water droplets and reduction in heat exchanging quantity due to reduction in the flow of the air can be suppressed. Fig. 7 is a fragmentary sectional view of a heat exchanger for an air conditioner, in a fourth embodiment according to the present invention. This heat exchanger is provided with a heat transfer tube 1 and 8-shaped ring fins 4 instead of the ring fins 4 of the first embodiment. Portions of the 8-shaped ring fins 4 are attached to the outer surface of heat-transfer tubes 1 arranged at predetermined intervals. An external fluid, such as air, flows in the direction of the arrow A. In operation, the front portions of the 8-shaped ring fins 4 disturb the currents of the air in vortices and the twisted portions of the 8-shape ring fins 4 further disturb the turbulent currents of the air so that vortices of the air spread over the entire surface of the heat exchanger to promote the heat transfer function of the heat-transfer tubes 1 and, consequently, the heat exchanging quantity of the heat exchanger is enhanced. Mechanisms of this embodiment effective in promoting heat transfer are the same as those of the first embodiment and hence the description thereof will be omitted. Referring to Fig. 8 showing a heat exchanger for an air conditioner, in a fifth embodiment according to the present invention, there exist a heat-transfer tube 1 and a coil ring fin 5 formed like a coil and realizing a heat transfer fin. An external fluid, such as air, flows in the direction of the arrow A. The inside diameter of the coil ring fin 5 is greater than the outside diameter of the heat-transfer tubes 1, the pitch of the coil ring fin 5 on each heat-transfer tube 1 is twice the diameter of the fine wire or above, and portions of the inner sufaces of the coil ring fin 5 are attached to the outer surfaces of the corresponding heat-transfer tubes 1. As the coil ring fin 5 is formed by helically connecting of ring fins, it can comparatively easiliy be formed and be firm and strong. Mechanisms of this embodiment effective in promoting heat transfer are the same as those of the first embodiment and hence the description thereof will be omitted. Referring to Fig. 9 showing a heat exchanger for an air conditioner in a sixth embodiment according to the present invention in a fragmentary sectional view, there exist heat-transfer tubes 1 and a coil ring fins 5 formed like a coil and realizing a heat transfer fin. An external fluid, such as air, flows in the direction of the arrow A. The inside diameter of the coil ring fin 5 is grater than the outside diameter of the heat-transfer tubes 1, the pitch of the coil ring fin 5 on each heat-transfer tube 1 is twice the diameter of the fine wire or above, and portions of the inner surfaces of the coil ring fin 5 are attached to the outer surfaces of the corresponding heat-transfer tubes 1. Since the transversely adjacent coil ring fins 5 cross each other and joined together at crossing points 8a and 8b, the coil ring fins 5 are firm and strong, the heat-transfer tubes 1 can be arranged at comparatively small intervals to increase heat-transfer area. The coil ring fins 5 can comparatively easily formed. Mechanisms of this embodiment effective in promoting heat transfer are the same as those of the first embodiment and hence the description thereof will be omitted. Referring to Fig. 10 showing a heat exchanger for an air conditioner, in a seventh embodiment according to the present invention, there exist a heat-transfer tube 1 and coil ring fins 5a, 5b (which are designated inclusively by "5") realizing heat-transfer fins, respectively. An external fluid, such as air, flows in the direction of the arrow A. The inside diameter of the coil ring fins 5 is greater than the outside diameter of the heat-transfer tubes 1, and the pitch of the coil ring fins 5 is twice the diameter of the fine wires or above. Portions of the inner surfaces of the coil ring fins 5 are attachted to the outer surfaces of the corrsponding heat-transfer tubes 1. The coil ring fins 5a are attached to the front side of the heat-transfer tube 1 in view of the direction of the flow A, and the coil ring fins 5b are attached to the rear side of the heat-transfer tube 1 in view of the direction of the flow A. Mechanisms of this embodiment effective in promoting heat transfer are the same as those of the first embodiment and hence the description thereof will be omitted. Referring to Fig. 11 showing a heat exchanger for an air conditioner, in an eighth embodiment according to the present invention, there exist heat-transfer tubes 1 and coil ring fins 4, which is similar to those of the first to the fifth embodiment. The inside diameter of the ring fins 4 is greater than the outside diameter of the heat-transfer tubes 1. Portions of inner surfaces of each ring fin 4 is attached to the outer surfaces of the three heat-transfer tubes 1. An external fluid, such as air, flows in the direction of the arrow A. Since each ring fin 4 is in contact with the plurality of heat-transfer tubes 1, the heat-transfer rate of the heat exchanger enhanced by the current disturbing action of the heat-transfer tubes 1 is higher than those of the first to the fifth embodiment, in which each ring fin is in contact with a single heat-transfer tube. The ring fins 4 can easily be fixed to the heat-transfer tubes and the heat exchanger has a firm construction. Mechanisms of this embodiment effective in promoting heat transfer are the same as those of the first embodiment and hence the description thereof will be omitted. Referring to Fig. 12 showing a heat exchanger for an air conditioner, in a ninth embodiment according to the present invention in a fragmentary perspective view, heat-transfer tubes 1 are arranged at predetermined intervals, and ring fins 4, i.e., heat-transfer fins, having an inside diameter greater than the outside diameter of the heat-transfer tube 1 are attached to the heat-transfer tube 1 so as to extend obliquely downward. An external fluid, such as air, flows in the direction of the arrow A. When the heat exchanger is used in a moist atmosphere and moisture contained in the atmosphere condenses in water drops on the heat exchanger, condensed water droplet drain off by gravity along the ring fins 4, so that the heat exchanger will not be clogged with condensed water drops. Mechanisms of this embodiment effective in promoting heat transfer are the same as those of the ninth embodiment and hence the description thereof will be omitted. Referring to Fig. 13 showing a heat exchanger for an air conditioner, in a tenth embodiment according to the present invention in a fragmentary sectional view, there exist heat-transfer tubes 1, fine wires are passed alternately over and under heat-transfer tubes 1 of each row to form fine wire fins 2, and headers 3. An external fluid, such as air, flows in the direction of the arrow A. The heat exchanger in this embodiment has a plurality of heat-transfer surfaces. A nonazeotropic cooling medium is used as an internal operating fluid in the heat-transfer tubes 1. The nonazeotropic cooling medium flows from the rear header 3 into the heat-transfer tubes 1 of the rear row in the direction of the arrow B, flows sequentially through the headers 3 and the heat-transfer tubes 1 of the intermediate rows toward the heat-transfer tubes 1 of the front row, and flows into the front header 3. Thus, the nonazeotropic cooling medium flows across the flow of air flowing in the direction of the arrow A in a virtually counterflow mode. Suppose that the nonazeotropic cooling medium is used as an internal operating fluid that flows through the heat-transfer tubes 1, the temperature of the nonazeotropic cooling medium, which phase change occurs in the heat exchanger, changes. In case the temperature of the nonazeotropic cooling medium at the inlet of the heat exchanger is fixed, the heat exchanging quantity of a heat exchanger provided with heat-transfer tubes arranged in a plurality of rows, in which the nonazeotropic cooling medium flows across the air flow in a virtually counterflow mode, is higher than that of a heat exchanger provided with heat-transfer tubes arranged in a single row, in which the nonazeotropic cooling medium flows simply across the air flow, which will be obvious from Fig. 15. Therefore, ba the construction of the heat exchanger as shown in Fig. 13, the heat exchanging quantity of the heat exchanger becomes higher. It is also possible to bent heat transfer surfaces without intermediate headers 3 as shown in Fig. 14.

Claims: A heat exchanger comprising: a plurality of heat transfer tubes (1) arranged in parallel to each other at predetermined intervals, and fin means characterized in that the fin means comprises a plurality of ring fins (4) of a fine wire, having a substantially circular shape of a diameter greater than the outside diameter of the heat-transfer tubes (1), and each having a portion of the inner circumference fixed to the outer surface of the heat-transfer tube (1), the respective centers of the first ring fins (4) are dislocated from the center axes of the heat-transfer tubes (1) toward the upper side with respect to the flowing direction of an external fluid, which in operation flows in one direction towards the heat-transfer tubes (1). A heat exchanger according to claim 1, wherein the fin means comprises adjacent first ring fins (4) being in contact with and joined to each other at least at one position. A heat exchanger according to claim 1, wherein the fin means comprises a plurality of second ring fins (4a) of a diameter greater than the outside diameter of the heat-transfer tubes (1), each having a portion of the inner circumference fixed to the outer surface of the heat-transfer tube (1), the second ring fins (4a) disposed with their centers dislocated from the center axes of the heat-transfer tubes (1) toward the lower side with respect to the flowing direction of the external fluid that flows outside the heat-transfer tubes (1); and the first (4b) and the second (4a) ring fins are arranged alternately along the axis of each heat-transfer tube (1). A heat exchanger according to claim 1 or 2, wherein each ring fin (4) is an 8-shaped ring fin having two loops, and the heat-transfer tube (1) is inserted in one of the two loops. A heat exchanger according to claim 1 wherein the fin means comprises first ring fins being formed by a plurality of first coil rings (5) formed by helically winding fine wires, and the pitch of the first coil rings (5) is twice the diameter of the fine wire or above. A heat exchanger according to claim 5, wherein the adjacent first coil rings (5) are in contact with and fixed to each other at least at one position. A heat exchanger according to claim 5, wherein the fin means comprises second coil rings (5a) formed by second ring fins helically connected each other in a substantially circular shape, having a diameter greater than the outside diameter of the heat-transfer tubes (1) and each having a portion of the inner circumference fixed to the outer surface or the heat-transfer tube (1) so that the centers of the ring fins are dislocated from the center axes of the heat-transfer tubes toward the lower side with respect to the flowing direction of the external fluid that flows outside the heat-transfer tubes (1). A heat exchanger according to any of claims 5 to 7, wherein a plurality of heat-transfer tubes (1) are inserted in each coil ring (5) and fixed to the inner circumference of the respective coil ring (5). A heat exchanger according to any one of claims 1 to 7, wherein portions of the inner circumferences of the ring fins (4, 5) are fixed to the heat-transfer tubes (1) so that the ring fins (4, 5) extend obliquely downward. A heat exchanger according to any one of claims 1 to 9, wherein the heat exchanger is provided with a plurality of heat-transfer members each comprising the plurality of heat-transfer tubes (1) through which a cooling medium flows and the plurality of ring fins, arranged in parallel to each other along and perpendicularly to the flowing direction of an external fluid that flows outside the heat-transfer tubes (1) and connected to each other, the cooling medium in operation flows from the heat-transfer member disposed at the lowermost position with respect to the flowing direction of the external fluid sequentially through the heat-transfer members toward the heat-transfer member disposed at the uppermost position with respect to the flowing direction of the external fluid.

Inventors: COTOH TAKASHI, IKEJIMA KAORU, TAKESHITA MICHIMASA, YOSHIDA TAKAYUKI, YUMIKURA TSUNEO, COTOH, TAKASHI, IKEJIMA, KAORU, TAKESHITA, MICHIMASA, YOSHIDA, TAKAYUKI, YUMIKURA, TSUNEO, Cotoh, Takashi, c/o Mitsubishi Denki K.K., Ikejima, Kaoru, c/o Mitsubishi Denki K.K., Takeshita, Michimasa, c/o Mitsubishi Denki K.K., YOSHIDA, TAKAYUKI, C/O MITSUBISHI DENKI K.K., Yumikura, Tsuneo, c/o Mitsubishi Denki K.K.
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1995
Main classification: F28F1
IPC codes: B23K1, F28F1