Heat exchanger

Abstract: The invention describes a heat exchanger comprising a plurality of heat-transfer tubes arranged in parallel to each other at predetermined intervals, each of said heat-transfer tubes extending in a vertical direction; and a plurality of fine wire fins serving as heat-transfer fins helically wound around the plurality of heat-transfer tubes with a predetermined helix angle in its entirety.

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 DE-A-975 537. 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 fluids 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-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. DE-A-975 537 discloses a heat-exchanger comprising a plurality of heat-transfer tubes arranged in parallel to each other at predetermined intervals and a plurality of fine wire fins. The fine wire fins serve as heat-transfer fins and are fixed to the heat-transfer tubes, e.g. by soldering. The heat-transfer tubes have a rectangular shape and the fine wire fins are arranged on two opposite sides of the tubes, i.e. they are not wound around the tubes. Further, GB-A-636 615 shows a fin adapter to form part of a heat-exchanger for exchanging heat between a solid surface and a fluid arranged to pass through the fin. The fin consists of 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 said half turns lie, wherein the planes in which the curved portions of each half turn lie are inclined to said imaginary surfaces at angles of the order of 45 degrees. The solid surface is formed by an anode of an electric discharge device or a cylinder of an internal combustion engine. In this case the ends of a fin can be joined to form an annular ring whose internal diameter is approximately equal to the external diameter of the heat-transfer surface. The fin may be made longer so that its longitudinal axis follows a helical path around the surface to be cooled. SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a heat exchanger for an air conditioner, provided with a heat-transfer coefficient outside a heat-transfer tube, of promoting heat transfer and of suppressing reduction in heat exchanging quantity due to reduction in the flow of air. This object according to the present invention is solved by a heat exchanger having the features of claim 1. Preferred embodiments of the invention are defined in the subclaims. A heat exchanger for an air conditioner in accordance with the present invention comprises a plurality of parallel heat-transfer tubes arranged at predetermined intervals, each of said heat-transfer tubes extending in a vertical direction, and a plurality of fine wire fins serving as heat-transfer fins which are helically wound around the plurality of heat-transfer tubes. In operation, the external fluid that flows outside the heat-transfer tubes is disturbed three-dimensionally to promote the heat-transfer performance of the fine wire fins on the lower side with respect to the direction of flow of the external fluid. Spaces formed on the flowing path of air between the fine wire fins of the heat exchanger are large because the fine wire fins do not intersect each other in a plane perpendicular to the heat-transfer tubes. Therefore 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, and hence pressure loss is small 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 a plurality of heat-transfer tubes through which a 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 ex-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 plan view of the heat transfer plane of a heat exchanger for an air conditioner in a first embodiment according to the present invention; Fig. 5 is a fragmentary plan view of the heat transfer plane of a heat exchanger for an air conditioner in a second embodiment according to the present invention; Fig. 6 is a fragmentary plan view of the heat transfer plane of a heat exchanger for an air conditioner in a third embodiment according to the present invention; Fig. 7 is a graph showing the dependence of the area ratio on the helical angle of fine wire fins of the heat exchanger of the third embodiment; Fig. 8 is a fragmentary plan view of the heat transfer plane of a heat exchanger for an air conditioner in a fourth embodiment according to the present invention; Fig. 9 is a fragmentary plan view of the heat transfer plane of a heat exchanger for an air conditioner in a fifth embodiment according to the present invention; Fig. 10 is a fragmentary plan view of the heat transver plane of a heat exchanger for an air conditioner in a sixth embodiment according to the present invention; Fig. 11 is a perspective view of a fine wire fin employed in a heat exchanger for an air conditioner in a seventh embodiment according to the present invention; Fig. 12 is a perspective view of a fine wire fin employed in a heat exchanger for an air conditioner in the seventh embodiment according to the present invention; Fig. 13 is a fragmentary sectional view of the main part of a heat exchanger for an air conditioner in a eighth embodiment according to the present invention; Fig. 14 is a fragmentary sectional view of a heat exchanger for an air conditioner in a ninth embodiment according to the present invention; Fig. 15 is a fragmentary sectional view of a heat exchanger in a modification of the heat exchanger in Fig. 14; and Fig. 16 is a graph showing the dependence of heat exchanging quantity of the number banks of the heat-transfer surfaces in the heat exchanger in the ninth embodiment when a nonazeotropic cooling medium is used. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Fig. 4 showing an essential part of a heat exchanger for an air conditioner, in a first embodiment according to the present invention in a fragmentary plan view, heat-transfer tubes 1 and 1a to 1e are arranged at predetermined intervals to pass an internal fluid, such as a cooling medium. Portions 2a to 2c are of a fine wire fin realize heat transfer fins. The portion 2a of the fine wire fin is wound helically around the heat-transfer tubes 1a and 1c, the portion 2b of the fine wire fin are wound helically around the heat-transfer tubes 1b and 1c, and the portion 2c of the fine wire fin are wound helically around the heat-transfer tubes 1b and 1d. The portions 2a, 2c of the fine wire fin are extended on the upper side with respect to the flowing direction of an external fluid, such as air, and the portion 2b of the fine wire fin is extended on the lower side with respect to the flowing direction of the external fluid. In operation, the air flow velocity increases in spaces between the fine wire fins 2 and the fine wire fins 2 disturb the currents of air three-dimensionally. Consequently, the turbulent currents of air flow through the heat exchanger, promoting heat transfer, so that the heat exchanger transfers heat at a high heat transfer rate. Since the plurality of fine wire fins 2 are wound helically around the plurality of parallel heat-transfer tubes 1, wide spaces are formed between the fine wire fins 2 and the fine wire fins 2 obstruct scarcely the flow of condensed water droplets axially downward along the heat-transfer tubes 1. Accordingly, condensed water droplets are hardly able to stay on the heat exchanger. Therefore, 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 used in a moist atmosphere where moisture contained in the atmosphere is liable to condense, so that reduction in heat exchanging quantity due to reduction in the flow of the external fluid can be suppressed. Referring to Fig. 5 showing the main portion of a heat exchanger for an air conditioner, in a second embodiment according to the present invention in a fragmentary plan view, a plurality of pairs of heat-transfer tubes 1a and 1b are a pair of adjacent tubes among heat-transfer tubes 1 arranged at predetermined intervals to pass an internal fluid, such as a cooling medium. Portions 2a to 2d of fine wire fins as heat transfer fins are wound helically around each pair of heat-transfer tubes 1a and 1b. The portions 2a, 2b are of a fine wire fin, and the portions 2c and 2d are of another fine wire fin. The portions 2a, 2c are on the upper side with respect to the flowing direction of an external fluid, such as air, and the portions 2b, 2d are on the lower side with respect to the flowing direction of the external fluid. In operation, the air flow velocity increases in spaces between the fine wire fins 2 and the fine wire fins 2 disturb the currents of air three-dimensionally. Consequently, the turbulent currents of the air flow through the heat exchanger, promoting heat transfer, so that the heat exchanger transfers heat at a high heat-transfer rate. Since the fine wire fins 2 are wound around the pair of adjacent heat-transfer tubes 1 to form the heat transfer fins, spaces having a large area are formed in a plane perpendicular to the heat-transfer tubes 1. Therefore, condensed water droplets are hardly able to stay on the heat exchanger. Consequently, the heat exchanger is hardly clogged with condensed water droplets even if the heat exchanger is used in a humid atmosphere where moisture contained in the atmosphere is liable to condense and reduction in heat exchanging quantity due to reduction in the flow of the air can be suppressed. Referring to Fig. 6 showing a heat exchanger for an air conditioner, in a third embodiment according to the present invention in a fragmentary plan view, heat-transfer tubes 1 and 1a to 1c are arranged at predetermined intervals to pass an internal fluid, such as a cooling medium. Portions 2a, 2b are of a fine wire fins. Portions 2c, 2d are of another fine wire fins. The portions 2a, 2b of the fine wire fin are wound helically around the heat-transfer tubes 1a and 1b, and the portions 2c, 2d of the another fine wire fin are wound around the 1b and 1c. The portions 2a and 2b, and the portions 2c, 2d are wound helically around the heat-transfer tubes 1a and 1b and around the heat-transfer tubes 1b and 1c in opposite directions respectively. The portions 2a and 2d are on the upper side with respect to the flowing direction of an external fluid, such as air, and the portions 2b and 2c are on the lower side with respect to the flowing direction of the external fluid. In operation, the air flow velocity increases in spaces between the fine wire fins 2 and the fine wire fins 2 disturb the currents of the air three-dimensionally. Consequently, the turbulent currents of air through the heat exchanger, promoting heat transfer, so that the heat exchanger transfers heat at a high heat-transfer rate. As shown in Fig. 6, since the fine wire fins do not cross each other in a plane perpendicular to the heat-transfer tubes 1, i.e., since the fine wires are wound helically around the heat-transfer tubes 1 so that fine wire fin 2, does not cross the fine wire fin of the same fine wire and the fine wire fins 2 of the other fine wire and the fine wire fins 2 of the other fine wire as viewed along the axes of the transfer tubes 1, spaces having a large area are formed between the fine wire fins 2 and the fine wire fins 2 obstruct scarcely the flow of condensed water droplets axially downward along the heat-transfer tubes 1, condensed water droplets are hardly able to stay on the heat exchanger. Therefore, the heat exchanger is hardly clogged with condesed water droplets even if the heat exchanger is used in a moist atmosphere where moisture contained in the atmosphere condenses in water droplets, and reduction in heat exchanging due to reduction in the flow of the air can be suppressed. As is obvious from Fig. 7 showing the relationship between the area ratio and the helical angle  (see Fig. 6), it is established by increasing the helical angle  that the heat transfer area increases as compared with a conventional heat transfer fin where fine wire fins are linearly arranged on a heat transfer tube under the condition that the arranged wire pitches are same. Referring to Fig. 8 showing a heat exchanger for an air conditioner, in a fourth embodiment according to the present invention in a fragmentary plan view, heat-transfer tubes 1a to 1c are arranged at predetermined intervals to pass an internal fluid, such as a cooling medium. Portions 2a to 2f of fine wire fins 2 realize heat transfer fins. The portions 2a, 2b are of a fine wire fin. The portions 2c, 2d are of another fine wire fin. The portions 2e, 2f are of still another fine wire fin. The portions 2a, 2b are wound helically around the heat-transfer tubes 1a and 1b. The portions 2c, 2d and 2e, 2f are wound helically around the heat-transfer tubes 1b and 1c. The portions 2c, 2d are located between pitches of the portion 2e, 2f. The winding direction of the fine wire forming the portions 2b and 2d is opposite that of the fine wire forming the portions 2a and 2b. The portions 2a, 2c and 2e are on the upper side with respect to the flowing direction of an external fluid, such as air, and the portions 2b, 2d and 2f are on the lower side with respect to the flowing direction of the external fluid. In operation, the air flow velocity increases in spaces between the fine wire fins 2 and the fine wire fins 2 disturbes the currents of the air three-dimensionally. Consequently, the turbulent currents of the air flow through the heat exchanger, promoting heat transfer, so that the heat exchanger transfers heat at a high heat-transfer rate. Since the fine wires are wound helically around the heat-transfer tubes 1 to form the helical fine wire fins 2, the fine wire fins 2 do not cross each other in a plane perpendicular to the heat-transfer tubes 1, spaces of a large area are formed between the fine wire fins 2, and the fine wire fins 2 obstruct scarcely the flow of condensed water droplets axially downward along 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. The area ratio of the heat exchanger increases from 1 when the helical angle of the fine wire fins 2 is increased from 0 with the pitch fixed. Referring to Fig. 9 showing a heat exchanger for an air conditioner, in a fifth embodiment according to the present invention in a fragmentary plan view, heat-transfer tubes la to lc are arranged at predetermined intervals to flow an internal fluid, such as a cooling medium. Portions 2a to 2f of fine wire fins 2 realize heat transfer fins. The portions 2a, 2b are of a fine wire fin. The portions 2c, 2d are of another fine wire fin. The portions 2a, 2b are wound helically around the heat-transfer tubes la and 1b. The portions 2c, 2d are wound helically around the heat-transfer tubes 1b and lc. The winding direction of the fine wire forming the portions 2a and 2b is the same as that of the fine wire forming the portions 2c and 2d. The portions may be wound so that the bends between the portions 2a and 2b and those between the portions 2c and 2d are contiguous with each other on the heat-transfer tubes 1b to form large spaces surrounded by the helical fine wire fins 2 and the heat-transfer tubes 1 for passing an external fluid, such as air. The portions 2a and 2c are on the upper side with respect to the flowing direction of the external fluid and the portions 2b and 2d are on the lower side with respect to the flowing direction of the external fluid. In operation, the air flow velocity increases in the spaces between the fine wire fins 2 and the fine wire fins 2 disturb the currents of the air three-dimensionally. Consequently, the turbulent currents of the external fluid promote heat transfer and the heat exchanger transfers heat at a high heat transfer rate. Since the fine wires are wound helically around the heat-transfer tubes 1 so that the fine wire fins 2 do not cross each other in a plane perpendicular to the axes of the heat-transfer tubes 1, the spaces between the fine wire fins 2 are large, the fine wire fins 2 obstruct scarcely the flow of condensed water droplets axially downward along the heat-transfer tubes 1. Therefore, condensed water droplets are hardly able to stay on the heat exchanger, the heat exchanger is is hardly clogged with condensed water droplets even if the the heat exchanger is uses in a moist atmosphere where moisture contained in the atmosphere condenses in water droplets, and reduction in heat exchanging quantity due to reduction in the flow of the air can be suppressed. The area ratio of the heat exchanger increases when the helical angle is increased with the pitch fixed. Referring to Fig. 10 showing a heat exchanger for an air conditioner, in a sixth embodiment according to the present invention in a fragmentary plan view, heat-transfer tubes 1a to 1c are arranged at predetermined intervals to pass an internal fluid, such as a cooling medium. Portions 2a to 2f of fine wire fins 2 realize heat transfer fins. The portions 2a, 2b are of a fine wire fin. The portions 2c, 2d are of another fine wire fin. The portions 2e, 2f are still another fine wire fin. The portions 2a, 2b and 2c, 2d are wound helically around the heat-transfer tubes 1a and 1b. The portions 2e, 2f are wound helically around the heat-transfer tubes 1b and 1c. The portions 2a, 2b are located between pitches of the portions 2c, 2d. The winding direction of the fine wire forming the portions 2a and 2b is opposite that of the fine wire forming the portions 2e and 2f. The portions 2a and 2e are contiguous on the heat-transfer tube 1b. Thus, large spaces are formed between the helical fine wire fins 2 and the heat-transfer tubes 1 to pass an external fluid, such as air. The portions 2a, 2c and 2e are on the upper side with respect to the flowing direction of the external fluid and the portions 2b, 2d and 2f are on the lower side with respect to the flowing direction of the external fluid. The air flow velocity increases in the spaces between the fine wire fins 2 and the fine wire fins 2 disturb the currents of the air three-dimensionally. Consequently, the turbulent currents of the air promotes heat transfer and the heat exchanger transfers heat at a high heat transfer rate. Since the fine wires are wound helically so that the fine wire fins 2 do not cross each other in a plane perpendicular to the axes of the heat-transfer tubes 1, the spaces between the fine wire fins 2 for passing the air are large and the fine wire fins 2 obstruct scarcely the flow of condensed water droplets axially downward along the heat-transfer tubes 1. Therefore, condensed water drops 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. The area ratio of the heat exchanger increases when the helical angle is increased with the pitch fixed. Fig. 11 is a perspective view showing the section of a fine wire fin included in a heat exchanger for an air conditioner. As shown in Fig. 11, a fine wire fin 2, for being weaved, having a section shape other than a circular shape. The section of the fine wires for forming the fine wire fins may be any suitable concave polygon, such as a concave pentagon, a concave hexagon, a concave heptagon, a concave octagon, a concave nonagon or a concave decagon, and the corners need not necessarily be sharp edges and my be rounded. The heat exchanging quantity of this heat exchanger is greater than that of a heat exchanger formed by helically winding round fine wires having the same sectional area as that of the fine wires having a cross section resembling a concave polygon of this embodiment around heat-transfer tubes at the same pitch because the surface area of the fine wire fins 2 of the heat exchanger in this embodiment is greater than that of the fine wire fins formed by helically winding the round fine wires around the heat-transfer tubes. Other 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. The fine wire fins 2 suppresses reduction in heat exchanging quantity due to reduction in the flow of the air. When moisture contained in the atmosphere condenses in water droplets 11 on the heat exchanger, the condensed water droplets 11 are able to flow easily along grooves formed in the surfaces of the fine wire fins 2 as shown in Fig. 12. Therefore, the heat exchanger is hardly clogged with condensed water droplets even if the surface of the heat exchanger is wet during operation and hence the heat exchanger does not cause significant pressure loss of the external fluid. Referring to Fig. 13 showing a heat exchanger for an air conditioner, in a fragmentary sectional view, the heat exchanger has heat-transfer surfaces 7 formed by weaving fine wire fins and including a plurality of heat-transfer tubes 1 arranged at predetermined intervals. An external fluid, such as air, flows in the direction of the arrow A. The heat exchanger has a plurality of lines comprising heat-transfer sections 7a and 7b which are bent in a zigzag form at the heat-transfer tubes 1. The heat-transfer tubes 1 are arranged at ridges and saddles of the heat-transfer sections 7a and 7b which sectional view are zigzags. The ridges of the heat-transfer section 7b on the backward side protrude into the furrows of the heat-transfer section 7a on the front side. Since the heat transfer surfaces 7 comprising the heat-transfer sections 7a und 7b are inclined to the direction of the arrow A, the ratio of the heat-transfer area to the frontal area is large and hence the heat exchanger exchanges heat at a high heat exchanging quantity. The space required for installing the heat exchanger is small as compared with that required by a heat exchanger having flat heat-transfer surfaces of the same heat-transfer area. Since the flow of an air through a unit area of the heat-transfer surface is comparatively small, the flow velocity of the air relative to the heat-transfer surfaces is comparatively low and hence the pressure loss caused by each heat-transfer surface is small. Mechanism 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. 14 showing a heat exchanger for an air conditioner, in a fragmentary sectional view, there exist heat-transfer tubes 1, fine wires are passed alternately over and under the 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 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 temperatur 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. 16. Therefore, by the construction of the heat exchanger as shown in Fig. 14, the heat exchanging quantitiy of the heat exchanger becomes higher. It is also possible to bent heat transfer surfaces without intermediate headers 3 as shown in Fig. 15.

Claims: A heat exchanger comprising: a plurality of heat transfer tubes (1) arranged in parallel to each other at predetermined intervals, each of said heat-transfer tubes extending in a vertical direction, and a plurality of fine wire fins (2) serving as heat-transfer fins, characterized in that the fine wire fins (2) are helically wound around the plurality of heat-transfer tubes (1). A heat exchanger according to claim 1, wherein the heat exchanger is provided with a first heat-transfer member (7a) and a second heat-transfer member (7b) each comprising the plurality of heat-transfer tubes (1) around which a plurality of fine wire fins are wound helically, having a heat-transfer surface (7) including the axes of the heat-transfer tubes (1) and the fine wire fins and bent in a zigzag shape having ridges or furrows corresponding to the heat-transfer tubes (1), and the first (7a) and the second (7b) heat-transfer members are disposed one behind the other along the flowing direction of an external fluid that flows outside the heat-transfer tubes (1) so that the ridges of the second heat-transfer member (7b) protrude into the furrows of the first heat-transfer member (7a) respectively. A heat exchanger according to claim 1, 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 fine wire fins (2), the plurality of heat-transfer members are arranged in parallel to each other along the flowing direction of an external fluid that flows outside the heat-transfer tubes (1) and are connected to each other, and said cooling medium 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: GOTOH TAKASHI, IKEJIMA KAORU, TAKESHITA MICHIMASA, YOSHIDA TAKAYUKI, YUMIKURA TSUNEO, GOTOH, TAKASHI, IKEJIMA, KAORU, TAKESHITA, MICHIMASA, YOSHIDA, TAKAYUKI, YUMIKURA, TSUNEO, Gotoh, 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