Abstract:
The present invention discloses a heat exchanger with microchannel, parallel flow, all-aluminum flat tube welding structure, wherein the heat exchange part of the heat exchanger is formed by flat tubes composed of extruded thin-wall aluminum profiles in parallel arrangement. Compared to existing technology, the present invention has the following advantages: 1. The heat exchange efficiency of refrigerant and the inner wall of flat tubes is increased by 40%, and the flow resistance of the refrigerant in the heat exchanger is reduced by 40%. 2. The heat exchange efficiency of fins on air side is increased by 40%, and the wind resistance of the heat exchanger on air side is reduced by 40%. 3. The heat exchange performance of the entire heat exchanger is improved by 40%. 4. The refrigerant covered is 40% less than that in the conventional technology. 5. All-aluminum structure features longer service life due to no copper-aluminum potential difference when comparing with copper-aluminum structure. The flat tubes adopted by the present invention are provided with the advantages of resistance to high pressure restricted by the existing refrigerant, compact product structure, light unit weight, short process flow, and high manufacturing reliability and relatively low cost. The present invention also discloses the application of the abovementioned heat exchanger.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Technical Field 
         [0002]    The present invention relates to a heat exchanger and its application, and in particular, relates to a heat exchanger with microchannel, parallel flow, all-aluminum flat tube welding structure and its application. The new series of heat exchangers all adopt aluminium as the main material: it is a recyclable material with stronger corrosion resistance than copper-tube aluminium-sheet heat exchanger; moreover, the microchannel flat tube design improves the efficiency on the refrigerant side of the heat exchanger, the advanced design of the parallel flow structure+fin greatly increases the air side efficiency of the heat exchanger, so as to substantially upgrade the overall efficiency of the heat exchanger. The new series of heat exchangers have the advantages of environmental protection, low consumption of refrigerant, resistance to pressure, high efficiency, high reliability, low cost for recovery, and no potential difference or primary cell effect. 
         [0003]    2. Description of Related Art 
         [0004]    The heat exchanger in the conventional heat exchanger system mainly adopts the copper-tube aluminium-sheet expansion tube form; as shown in  FIG. 1 , as for the outdoor unit in the conventional heat exchanger system, the heat exchanger part  10  uses the expansion tube structure combining copper tube  11  and aluminium sheet  12  as shown in  FIG. 3  and  FIG. 4 ; as for the indoor unit in conventional heat exchanger system as shown in  FIG. 2 , the heat exchanger  20  uses the expansion tube structure combining copper tube  21  and aluminium sheet  22  as shown in  FIG. 5 . The conventional heat exchanger system has the following problems: 
         [0005]    1. Low heat exchange efficiency between the refrigerant on the refrigerant side and the inner wall of the copper tube, and strong flow resistance of refrigerant in the copper tube of the heat exchanger. 
         [0006]    2. Low heat exchange efficiency of fin on air side and strong wind resistance. 
         [0007]    3. High consumption of refrigerant and inconsistent with environmental protection requirements. 
         [0008]    4. Existence of potential difference between aluminium sheet and copper tube, erodes easily, and short service life. 
         [0009]    5. Thickness of the heat exchanger, heavy weight and high logistics cost. 
         [0010]    6. High power of fan and compressor and high energy consumption. 
         [0011]    The applicant invented an extruded thin-wall aluminium profile in 2006, and submitted it to the State Intellectual Property Office of the P.R.C for patent application of utility model. It has been granted the publication number for granting of CN201007423. The extruded thin-wall aluminium profile, formed by smelting and extruding aluminum ingot, is composed of at least one flat channel tube. The channel tubes are independent, parallel to each other and transversely connected through connectors, so as to form multi-channel parallel flow tubes with symmetrical structure or asymmetric structure. At least one cold-heat agent flow channel is set in the channel tube. And at least the section of one part of the cold-heat agent flow channel is in the shape of round or ellipse or polygon or undulation or any combination of the shapes, so as to fit for the requirements for the design of various products and the requirements for different cold-heat agents. Various cold-heat agent flow channels are parallel to each other to form double-flow-channel extruded thin-wall aluminium profile or multi-flow-channel extruded thin-wall aluminium profile. The cold-heat agent flow channels are separated by fins to replace conventional electrolytic copper tubes, effectively reducing energy consumption and environmental pollution, and improving the effective utilization of resources. The profile has the advantages of low cost for recovery, wide application in industries and so on. 
         [0012]    The applicant also invented a cool-heat exchanger in 2006 according to the extruded thin-wall aluminium profile mentioned above, and submitted it to the State Intellectual Property Office of the P.R.C for patent application of utility model. It has been granted the publication number for granting of CN2932273. The heat exchanger is comprised of a first collecting tube and a second collecting tube with coupling holes, a plurality of flat tubes parallel to each other which are inserted into the coupling holes in the first, second collecting tubes and link the first, second collecting tubes, and outer fins between adjacent flat tubes, wherein each flat tube unit is composed of at least one flat channel tube, and a parallel connection part is provided between flat channel tubes. This cool-heat exchanger is applicable to the parallel-flow oil coolers for automobile automatic gearbox cooling oil, and parallel-flow water tank for automobile engine cooling water and parallel-flow heating air core for heating air for automobile air conditioners. 
         [0013]    There is no related news for the application of the heat exchanger composed of the abovementioned extruded thin-wall aluminium profile in refrigerant-based heat exchange rooms through gas-liquid physical change via R12, R22, R410A, R407C, R123, HFC134A and so on, and in similar-purpose air conditioning systems, freezing and refrigeration systems, air conditioning systems for refrigeration and dehumidification, heat pump heating and water cooling/heating and air conditioning systems, computer cooling modules in the IT industry, cooling systems in equipment and other air heat exchange systems in other industries. 
       SUMMARY OF THE INVENTION 
       [0014]    The technical problem to be solved by the present invention is, on one hand, to provide a heat exchanger with microchannel, parallel flow, all-aluminum flat tube welding structure applicable to heat exchange for refrigerant and made of the abovementioned extruded thin-wall aluminium profiles and high effective fins through assembly. 
         [0015]    The technical problem to be solved by the present invention is, on the other hand, to provide the application of the abovementioned heat exchanger with microchannel, parallel flow, all-aluminum flat tube welding structure. 
         [0016]    The heat exchanger with microchannel, parallel flow, all-aluminum flat tube welding structure as in the first aspect is characterized in that the heat exchange part of the heat exchanger is formed by flat tubes composed of extruded thin-wall aluminium profile in parallel mode. 
         [0017]    In the first preferred embodiment of the heat exchanger for the present invention, there is one flat tube which forms the heat exchange part of the heat exchanger by multiple reciprocated bending horizontally. 
         [0018]    In the second preferred embodiment of the heat exchanger for the present invention, there is one flat tube which forms the heat exchange part of the heat exchanger by multiple reciprocated bending vertically. 
         [0019]    In the third preferred embodiment of the heat exchanger for the present invention, there are two flat tubes which form the heat exchange part of the heat exchanger by multiple reciprocated bending horizontally or vertically. 
         [0020]    In the abovementioned first, second and third preferred embodiments of the heat exchanger for the present invention, one end of the flat tube is the inlet of heat exchange medium, and the other end of the flat tube is the outlet of heat exchange medium. 
         [0021]    In the fourth preferred embodiment of the heat exchanger for the present invention, there are over two flat tubes which are arranged in one row at horizontal interval in parallel mode; the heat exchanger in this embodiment further is comprised of a first collecting tube on one end of the over two flat tubes and a second collecting tube on the other end of the over two flat tubes. 
         [0022]    In the fifth preferred embodiment of the heat exchanger for the present invention, there are over two flat tubes which are arranged in a row at vertical intervals in parallel mode; the heat exchanger in this embodiment further is comprised of a first collecting tube on one end of the over two flat tubes and a second collecting tube on the other end of the over two flat tubes. 
         [0023]    In the sixth preferred embodiment of the heat exchanger for the present invention, there are over two flat tubes which are arranged in two rows at vertical intervals in parallel mode; the heat exchanger in this embodiment further is comprised of a first collecting tube connecting one end of the first row of the flat tubes, a second collecting tube connecting the other end of the first row of the flat tubes, a third collecting tube connecting one end of the second row of the flat tubes, and a fourth collecting tube connecting the other end of the second row of the flat tubes; wherein the first collecting tube and the third collecting tube are located in the same direction of two rows of the flat tubes, parallel to each other, and communicated according to the flow direction of heat exchange medium, the second collecting tube and the fourth collecting tube are located in the same direction of two rows of the flat tubes, parallel to each other, and communicated according to the flow direction of heat exchange medium. 
         [0024]    In the seventh embodiment of the heat exchanger for the present invention, there are over two flat tubes which are arranged in two rows at horizontal interval in parallel mode; the heat exchanger in this embodiment further is comprised of a first collecting tube connecting one end of the first row of the flat tubes, a second collecting tube connecting the other end of the first row of the flat tubes, a third collecting tube connecting one end of the second row of the flat tubes, and a fourth collecting tube connecting the other end of the second row of the flat tubes; wherein the first collecting tube and the third collecting tube are located in the same direction of two rows of the flat tubes, parallel to each other, and communicated according to the flow direction of heat exchange medium, the second collecting tube and the fourth collecting tube are located in the same direction of two rows of the flat tubes, parallel to each other, and communicated according to the flow direction of heat exchange medium. 
         [0025]    In the eighth embodiment of the heat exchanger for the present invention, there are over two flat tubes which are arranged in two rows at horizontal or vertical intervals in parallel mode; the heat exchanger in this embodiment further is comprised of a first collecting tube connecting one end of the flat tubes, and a second collecting tube connecting the other end of the flat tubes. 
         [0026]    In the abovementioned embodiment, the heat exchanger formed by arranging flat tubes at horizontal or vertical intervals in parallel mode is placed vertically or horizontally or at an included angle of 15°˜25° with the horizontal ground. 
         [0027]    In the abovementioned embodiment, the flat tubes are twisted into spiral shapes with the helix angle less than 68.2°, namely thread pitch ≦2.5 times of flat tube width. The thickness of the flat tubes is 1.0 mm-2.5 mm, 1.3 mm-2.0 mm preferably. 
         [0028]    In the ninth embodiment of the heat exchanger for the present invention, the flat tubes are over two U-shaped flat tubes, wherein various U-shaped flat tubes are arranged in one row at horizontal or vertical interval in parallel mode, the both ends of each U-shaped flat tube are connected by a first collecting tube and a second collecting tube respectively, the first and the second collecting tubes are parallel to each other and communicated according to the flow direction of heat exchange medium. 
         [0029]    In the abovementioned ninth embodiment, the U-shaped flat tubes are twisted into spiral shapes with the helix angle less than 68.2°, namely thread pitch ≦2.5 times of flat tube width. The thickness of the flat tubes is 1.0 mm-2.5 mm, 1.3 mm-2.0 mm preferably. 
         [0030]    In the abovementioned embodiment, the inlet and outlet of the heat exchange medium can be set on the ends of the collecting tubes; or in the wall of a collecting tube simultaneously. When the length of the connecting tube with the inlet or outlet for the heat exchange medium is no less than 300 mm, the inlet or outlet of the heat exchange medium is multiple, the distance between two adjacent inlets of heat exchange medium or two adjacent outlets of heat exchange medium is less than 150 mm and all inlets or outlets of the heat exchange medium are distributed at equal spacing. 
         [0031]    In the abovementioned fourth and fifth embodiments, the heat exchanger can be an odd-loop single-row parallel-flow heat exchanger or an even-loop single-row parallel-flow heat exchanger. With regard to the odd-loop single-row parallel-flow heat exchanger, the inlet and outlet of heat exchange medium are set on the ends of the first collecting tube and the second collecting tube respectively in diagonal distribution, while in regard to the even-loop parallel-flow heat exchanger, the inlet and outlet are both set on the first collecting tube or the second collecting tube. In particular, when the fifth embodiment is an odd-loop single-row parallel-flow heat exchanger, it can functions as a condenser or an evaporator, wherein when it is used as an evaporator, the inlet of the heat exchange medium is set at the bottom of the heat exchanger; when it is used as a condenser, the inlet of the heat exchange medium is set on the top of the heat exchanger, and the outlet is set at the bottom of the heat exchanger. When the fifth embodiment is an even-loop single-row parallel-flow heat exchanger, regardless if it functions as a condenser or an evaporator, the inlet and outlet of the heat exchange medium are both located at the bottom of the heat exchanger. 
         [0032]    With regard to the odd-loop single-row parallel-flow heat exchanger and the even-loop single-row parallel-flow heat exchanger, when the loop number is over one, the volume of various loops shall be distributed according to appropriate proportion, for instance, as for double-loop single-row parallel-flow heat exchanger, the volume of the first loop is 80% of the total volume of loops, and that of the second loop is 20% of the total volume of loops. With regard to the three-loop single-row parallel-flow heat exchanger, the volume of the first loop is 55% of the total volume of loops, that of the second loop is 30% of the total volume of loops, and that of the third loop is 15% of the total volume of loops. With regard to the four-loop single-row parallel-flow heat exchanger, the volume of the first loop is 40% of the total volume of loops, that of the second loop is 27% of the total volume of loops, that of the third loop is 20% of the total volume of loops and that of the fourth loop is 13% of the total volume of loops. With regard to the five-loop single-row parallel-flow heat exchanger, the volume of the first loop is 34% of the total volume of loops, that of the second loop is 24% of the total volume of loops, that of the third loop is 18% of the total volume of loops, that of the fourth loop is 13% of the total volume of loops and that of the fifth loop is 13% of the total volume of loops. With regard to the six-loop single-row parallel-flow heat exchanger, the volume of the first loop is 30% of the total volume of loops, that of the second loop is 20% of the total volume of loops, that of the third loop is 17% of the total volume of loops, that of the fourth loop is 14% of the total volume of loops, that of the fifth loop is 10% of the total volume of loops and that of the sixth loop is 9% of the total volume of loops; the abovementioned loops are isolated by baffles set in the first collecting tube or the second collecting tube. 
         [0033]    In the sixth embodiment, the length of heat exchange medium axially flowing in the first collecting tube and the third collecting tube is more than that of heat exchange medium axially flowing in the second collecting tube and the fourth collecting tube, and the axially flowing length in the first collecting tube and the third collecting tube is as long as possible, while the axially flowing length in he second collecting tube and the fourth collecting tube as short as possible. In particular, the length of heat exchange medium axially flowing in the first collecting tube and the third collecting tube take up over 70% of the length of heat exchange medium axially flowing in the first, second, third and fourth collecting tubes, while the length of the heat exchange medium axially flowing in the second collecting tube and the fourth collecting tube accounts for less than 30% of the length of heat exchange medium axially flowing in the first, second, third and fourth collecting tubes. 
         [0034]    In the sixth embodiment, the first collecting tube and the third collecting tube are not directly interconnected, while the second collecting tube and the fourth collecting tube are directly interconnected via a part. In particular, in this embodiment, the axially flowing of heat exchange medium is completed in the first collecting tube and the third collecting tube, while the flowing of heat exchange medium between the first row of the flat tubes and the second row of the flat tubes is completed via the part (for example, a hole) interconnecting the second collecting tube and the fourth collecting tube; the heat exchanger is isolated into several loops through baffles in the collecting tubes, wherein these loops are interconnected in series. In particular, the volume of various loops along heat exchange medium flowing direction is increasing, but the volume of the last loop shall be no more than 2.5 times of the volume of the first loop. Preferably: the volume of the latter loop is 20-60% higher than that of the former loop; and more preferably: the volume of the latter loop is 40-50% higher than that of the former loop. 
         [0035]    In the sixth embodiment, a feeder for supplementing the heat exchange medium to the last two loops is set on the two loops, wherein the feeder can be designed in any shape, quantity and location as long as the medium amount supplemented is incapable of substantially destroying the original medium flow rate; the heat exchange medium supplemented to the last loop can be 15-20% of the total weight of heat exchange medium. 
         [0036]    In the sixth embodiment, the inlet and outlet of the heat exchange medium is set in the side walls of the first collecting tube or the third collecting tube. 
         [0037]    In the abovementioned technical solution, several orifice plates are configured in the collecting tubes at certain interval, each orifice plate is provided with orifices to play a part of turbulence and spraying and realize gas-liquid separation. The spacing distance between the orifice plates is less than 80 mm, 50 mm preferably. 
         [0038]    In the abovementioned technical solution, the thickness of the flat tubes is 1.0 mm-2.5 mm, preferably 1.0 mm-2.0 mm for cooling-only condenser, preferably 1.6 mm-2.5 mm for cooling-only evaporator; preferably 1.3 mm-2.0 mm for heat-pump indoor and outdoor heat exchangers. The section of single orifice in perforated microchannel inside flat tubes is 0.36 mm 2 -1.00 mm 2  preferably. 
         [0039]    In the abovementioned technical solution, fins are set between the flat tubes, wherein the window angle of fins at the wind speed of 1.5M/s-2M/s is 22°-45°, preferably 27°-33°. The pitch of fins at the wind speed of 1.5 M/s-2 M/s is 2.0 mm-5.0 mm, 2.2 mm-2.8 mm in preferred solution of high-efficiency heat exchanger, 2.6 mm-3.0 mm in the preferred solution stressing both high-efficiency heat exchange and dehumidification; 3.6 mm-5.0 mm in preferred solution in freezing &amp; refrigeration or dehumidification-only or sand-dust regions. When the abovementioned heat exchanger with flat-tube fins and bent tubes is applied in heat exchange systems without air blowers, windowless design is adopted, wherein the pitch of fins is equal to the height of fins. 
         [0040]    In the abovementioned heat exchanger, the condensate water discharge problem is addressed by using the design of flat tube length perpendicular to the ground, gas-liquid separation problem is solved by utilizing the turbulence and spraying of orifice plates, and heat exchange efficiency is improved by means of changing loop volume. 
         [0041]    In the abovementioned heat exchanger, the gas-liquid separation problem caused by gravity can be solved by utilizing the design of horizontal placement of the parallel-flow heat exchanger, and condensate water discharge problem can be addressed by means of hydrophilic treatment of fins of the parallel-flow heat exchanger fin+gravity action. 
         [0042]    In the abovementioned heat exchanger, at least one microchannel extensible along the flat tube length direction is mounted in the flat tubes. 
         [0043]    In the abovementioned heat exchanger, the section of the collecting tubes is D-shaped to further reduce the loss of heat exchange medium in collecting tubes. 
         [0044]    To increase the intensity of the collecting tubes, reinforcing ribs are configured on the three sides of tube walls of the D-shaped collecting tubes without connecting the flat tubes along collecting tube length direction, with the interval of two adjacent reinforcing ribs being 25.4 mm. 
         [0045]    In the abovementioned embodiment, the flat tubes are Zinc-coated with the thickness of zinc coating of 12˜18 g/m 2 . 
         [0046]    The abovementioned heat exchanger with microchannel, parallel flow, all-aluminum flat tube welding structure can be applied in air conditioners for housing and commercial use, and many other specialized heat exchange systems, and in particular, in rooms and similar-purpose air conditioning systems, freezing and refrigeration systems, air conditioning systems for refrigeration and dehumidification, heat pump heating and water cooling/heating and air conditioning systems, computer cooling modules in IT industry and cooling systems in equipment. 
         [0047]    The present invention is designed to adopt microchannel flat tubes to form effective heat exchange flow channels and heat exchange areas through tube bending, and assemble high-efficiency fins between adjacent two flat tubes after flat tube bending, and then form all-aluminium heat exchanger. The heat exchanger with this design has the advantages of resistance to pressure to a maximum degree, compact product structure, light unit weight, short process flow, high manufacturing reliability and relatively low cost. The special design allows the product to exert better heat exchange effect when the frontal area is less than 0.2 m 2  and obtain a performance 20% higher than the conventional copper tube+aluminium sheet structure. 
         [0048]    Comparing with the existing technology, the present invention has the following advantages due to the adoption of the abovementioned technical solutions: 
         [0049]    1. The heat exchange efficiency of refrigerant and the inner wall of flat tubes is increased by 40%, and the flow resistance of the refrigerant in the heat exchanger is reduced by 40%. 
         [0050]    2. The heat exchange efficiency of fins on air side is increased by 40%, and the wind resistance of the heat exchanger on air side is reduced by 40%. 
         [0051]    3. The heat exchange performance of the whole heat exchanger is improved by 40%. 
         [0052]    4. The refrigerant covered is 30% less than that in the conventional technology. 
         [0053]    5. All-aluminium structure features longer service life due to no copper-aluminium potential difference when compared to copper-aluminium structure. 
         [0054]    The flat tubes adopted by the present invention are provided with the advantages of resistance to high pressure, compact product structure, light unit weight, short process flow, high manufacturing reliability and relatively low cost. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0055]    The present invention is further explained in combination with the drawings and embodiments. 
           [0056]      FIG. 1  is the schematic view of the outdoor unit structure in the conventional heat exchanger system. 
           [0057]      FIG. 2  is the schematic view of the indoor unit structure in the conventional heat exchanger system. 
           [0058]      FIG. 3  is the schematic view of the structure of the heat exchanger adopting copper-tube aluminium-sheet expansion tubes for the outdoor unit in the conventional heat exchanger system. 
           [0059]      FIG. 4  is the left view of  FIG. 3 . 
           [0060]      FIG. 5  is the schematic view of the structure of the heat exchanger adopting copper-tube aluminium-sheet expansion tubes for the indoor unit in the conventional heat exchanger system. 
           [0061]      FIG. 6  is the schematic view of embodiment 1 of the heat exchanger for the present invention. 
           [0062]      FIG. 7  is the schematic view of embodiment 2 of the heat exchanger for the present invention. 
           [0063]      FIG. 8  is the schematic view of embodiment 3 of the heat exchanger for the present invention. 
           [0064]      FIG. 9  is the thermogram of embodiment 3 during performance testing for the present invention. 
           [0065]      FIG. 10  is the schematic view of embodiment 4 of the heat exchanger for the present invention. 
           [0066]      FIG. 11  is the schematic view of the structure of embodiment 5 of the heat exchanger for the present invention. 
           [0067]      FIG. 12  is the bottom view of  FIG. 11 . 
           [0068]      FIG. 13  is the left view of  FIG. 11 . 
           [0069]      FIG. 14  shows the connection relations between flat tubes and fins in embodiment 5. 
           [0070]      FIG. 15  is the view from A of  FIG. 14 . 
           [0071]      FIG. 16  is the schematic view of the structure of embodiment 6 of the heat exchanger for the present invention. 
           [0072]      FIG. 17  is the schematic view of the structure of embodiment 7 of the heat exchanger for the present invention. 
           [0073]      FIG. 18  is the schematic view of the structure of embodiment 8 of the heat exchanger for the present invention. 
           [0074]      FIG. 19  is the schematic view of the structure of embodiment 9 of the heat exchanger for the present invention. 
           [0075]      FIG. 20  is the bottom view of  FIG. 19 . 
           [0076]      FIG. 21  is the left view of  FIG. 19 . 
           [0077]      FIG. 22  is the schematic view of the structure of embodiment 10 of heat exchanger for the present invention. 
           [0078]      FIG. 23  is the schematic view of the structure of embodiment 11 of heat exchanger for the present invention. 
           [0079]      FIG. 24  is the top view of  FIG. 23 . 
           [0080]      FIG. 25  is the left view of  FIG. 23 . 
           [0081]      FIG. 26  is the schematic view of the structure of embodiment 12 of heat exchanger for the present invention. 
           [0082]      FIG. 27  is the schematic view of the structure of embodiment 13 of heat exchanger for the present invention. 
           [0083]      FIG. 28  is the bottom view of  FIG. 27 . 
           [0084]      FIG. 29  is the left view of  FIG. 27 . 
           [0085]      FIG. 30  is the schematic view of the structure of embodiment 14 of heat exchanger for the present invention. 
           [0086]      FIG. 31  is the schematic view of the structure of embodiment 15 of heat exchanger for the present invention. 
           [0087]      FIG. 32  is the top view of  FIG. 31 . 
           [0088]      FIG. 33  is the left view of  FIG. 31 . 
           [0089]      FIG. 34  is the schematic view of embodiment 15 of the heat exchanger during refrigeration for the present invention. 
           [0090]      FIG. 35  is the schematic view of  FIG. 34  enlarged from I. 
           [0091]      FIG. 36  is the thermogram of embodiment 15 during refrigeration operation. 
           [0092]      FIG. 37  is the schematic view of embodiment 15 of the heat exchanger during heating for the present invention. 
           [0093]      FIG. 38  is the schematic view of  FIG. 37  enlarged from I. 
           [0094]      FIG. 39  is the thermogram of embodiment 15 during heating operation. 
           [0095]      FIG. 40  is the schematic view of the structure of embodiment 16 of the heat exchanger for the present invention. 
           [0096]      FIG. 41  is the top view of  FIG. 40 . 
           [0097]      FIG. 42  is the left view of  FIG. 40 . 
           [0098]      FIG. 43  is the schematic view of the structure of embodiment 17 of the heat exchanger for the present invention. 
           [0099]      FIG. 44  is the top view of  FIG. 43 . 
           [0100]      FIG. 45  is the left view of  FIG. 43 . 
           [0101]      FIG. 46  is the schematic view of embodiment 18 of the heat exchanger for the present invention. 
           [0102]      FIG. 47  is the schematic view of embodiment 19 of the heat exchanger for the present invention. 
           [0103]      FIG. 48  is the schematic view of embodiment 20 of the heat exchanger for the present invention. 
           [0104]      FIG. 49  is the schematic view of embodiment 21 of the heat exchanger for the present invention. 
           [0105]      FIG. 50  is the schematic view of the connection relations between round collecting tubes and flat tubes in the conventional structure. 
           [0106]      FIG. 51  is the schematic view of flow resistance in round collecting tubes of the conventional structure. 
           [0107]      FIG. 52  is the schematic view of the connection relations between D-shaped collecting tubes and flat tubes for the present invention. 
           [0108]      FIG. 53  is the schematic view of flow resistance in D-shaped collecting tubes for the present invention. 
           [0109]      FIG. 54  is the schematic view of the structure of the D-shaped collecting tube for the present invention. 
           [0110]      FIG. 55  is the schematic view of the structure of the reinforcing ribs in the D-shaped collecting tube for the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0111]    The present invention is further explained in combination with embodiments in order to make the technical means, invention features, purposes and functions of the present invention easily understood. 
       Embodiment 1 
       [0112]    The heat exchanger with microchannel, parallel flow, all-aluminum flat tube welding structure in this embodiment is a double-loop single-row parallel-flow heat exchanger, and used for heating as a heat pump type indoor heat exchanger. As shown in  FIG. 6 , the heat exchanger is comprised of a first collecting tube  100 , a second collecting tube  200  and several flat tubes  300  linking the first collecting tube  100  and the second collecting tube  200 , wherein the flat tubes  300  are composed of extruded thin-wall aluminium profiles with the thickness of the flat tubes  300  from 1.3 mm to 2.0 mm. 
         [0113]    In this embodiment, several flat tubes  300  are arranged in one row at vertical intervals in parallel mode; the first collecting tube  100  is located on top of the whole heat exchanger, the second collecting tube  200  is at the bottom of the heat exchanger; the inlet  400  of heat exchange medium is located on the left end of the first collecting tube  100 , the outlet  500  is located on the right end of the second collecting tube  200 . Baffles  110 ,  210  which ( 110 ,  210 ) isolate the whole heat exchanger into the first loop  610  and the second loop  620  are set in the first collecting tube  100  and the second collecting tube  200  respectively. The volume of the first loop  610  takes up 80% of the total volume of loops, and the volume of the second loop  620  covers 20% of the total volume of loops. Three orifice plates  700  are configured in the second collecting tube  200  at certain interval. Each orifice plate  700  is provided with orifices  710  to play a part of turbulence and spraying. The spacing distance between the orifice plates  700  is less than 80 mm, 50 mm optimally. The working principles of the embodiment: heat exchange medium such as refrigerant enters from the inlet  400  on the left end of the first collecting tube  100 , flows downwards vertically to the side of the second collecting tube  200  with orifice plates  700  installed through the flat tubes of the first loop  610 , and then flows to the side of the second collecting tube  200  without orifice plates  700  after throttling, afterwards, flows upwards into the first collecting tube  100  vertically through the flat tubes of the second loop  620 , and then flows out from the outlet  500 . 
       Embodiment 2 
       [0114]    The heat exchanger with microchannel, parallel flow, all-aluminum flat tube welding structure in this embodiment is a double-loop single-row parallel-flow heat exchanger, and used for refrigeration as a heat pump type indoor heat exchanger. As shown in  FIG. 7 , the structure is the same as embodiment 1, but the inlet  400  and outlet  500  of heat exchange medium are in different locations. In this embodiment, the inlet  400  of heat exchange medium is located on the right end of the first collecting tube  100 , and the outlet  500  is on the left end of the first collecting tube  100 . 
         [0115]    The working principles of the embodiment: heat exchange medium such as heating agent enters from the inlet  400  on the right end of the first collecting tube  100 , flows downwards vertically to the side of the second collecting tube  200  without orifice plates  700  through the flat tubes of the second loop  620 , and then flows to the side of the second collecting tube  200  with orifice plates  700  installed; after throttling by orifice plates  700 , flows upwards into the first collecting tube  100  vertically through the flat tubes of the first loop  610 , and then flows out from the outlet  500 . 
       Embodiment 3 
       [0116]    The heat exchanger with microchannel, parallel flow, all-aluminum flat tube welding structure in this embodiment is a three-loop single-row parallel-flow heat exchanger, and its refrigerant flow direction is designed for heating use as a heat pump type indoor heat exchanger. As shown in  FIG. 8 , the heat exchanger is comprised of first collecting tube  100 , a second collecting tube  200  and several flat tubes  300  linking the first collecting tube  100  and the second collecting tube  200 , wherein the flat tubes  300  are composed of extruded thin-wall aluminium profiles with the thickness of the flat tubes  300  from 1.3 mm to 2.0 mm. 
         [0117]    In this embodiment, several flat tubes  300  are arranged in one row at vertical intervals in parallel mode; the first collecting tube  100  is located on the top of the whole heat exchanger, the second collecting tube  200  is at the bottom of the whole heat exchanger; the inlet  400  of heat exchange medium is located on the left end of the first collecting tube  100 , the outlet  500  is located on the right end of the first collecting tube  100 , the inlet  400  and outlet  500  are diagonally distributed. Baffles  110 ,  120 ,  210 ,  220  which ( 110 ,  120 ,  210 ,  220 ) isolate the whole heat exchanger into the first loop  610 , the second loop  620  and the third loop  630  are set in the first collecting tube  100  and the second collecting tube  200  respectively. The volume of the first loop  610  takes up 55% of the total volume of loops, the volume of the second loop  620  covers 30% of the total volume of loops and the volume of the third loop  630  accounts for 15% of the total volume of loops. Three orifice plates  700  are configured in the second collecting tube  200  at certain interval. Each orifice plate  700  is provided with orifices  710  to play a part of turbulence and spraying. The spacing distance between the orifice plates  700  is less than 80 mm, 50 mm preferably. The working principles of the embodiment: heat exchange medium such as refrigerant enters from the inlet  400  on the left end of the first collecting tube  100 , flows downwards vertically to the side of the second collecting tube  200  with orifice plates  700  installed through the flat tubes of the first loop  610 , and then flows to the middle side of the second collecting tube  200  without orifice plates  700  after throttling by orifice plates  700 , afterwards, flows upwards into the first collecting tube  100  vertically through the flat tubes of the second loop  620 , and then flows downwards vertically to the other side of the second collecting tube  200  without orifice plates  700  through the first collecting tube  100  and via the flat tubes of the third loop  630 , finally flows out from the outlet  500 . 
         [0118]    As shown in  FIG. 9 , the thermogram in this embodiment shows that the refrigerant inside the microchannel parallel-flow heat exchanger exhinbits reasonable layout, effective supper-cooling degree control and high heat exchange efficiency. 
       Embodiment 4 
       [0119]    The heat exchanger with microchannel, parallel flow, all-aluminum flat tube welding structure in this embodiment is a three-loop single-row parallel-flow heat exchanger, and its refrigerant flow direction is designed for refrigeration use as a heat pump type indoor heat exchanger. As shown in  FIG. 10 , the heat exchanger is comprised of a first collecting tube  100 , a second collecting tube  200  and several flat tubes  300  linking the first collecting tube  100  and the second collecting tube  200 , wherein the flat tubes  300  are composed of extruded thin-wall aluminium profiles with the thickness of the flat tubes  300  from 1.3 mm to 2.0 mm. 
         [0120]    In this embodiment, several flat tubes  300  are arranged in one row at vertical intervals in parallel mode; the first collecting tube  100  is located on the top of the whole heat exchanger, the second collecting tube  200  is at the bottom of the whole heat exchanger; the inlet  400  of heat exchange medium is located on the right end of the second collecting tube  200 , the outlet  500  is located on the left end of the first collecting tube  100 , the inlet  400  and outlet  500  are diagonally distributed. Baffles  110 ,  120 ,  210 ,  220  which ( 110 ,  120 ,  210 ,  220 ) isolate the whole heat exchanger into the first loop  610 , the second loop  620  and the third loop  630  are set in the first collecting tube  100  and the second collecting tube  200  respectively. The volume of the first loop  610  takes up 55% of the total volume of loops, the volume of the second loop  620  covers 30% of the total volume of loops and the volume of the third loop  630  accounts for 15% of the total volume of loops. Three orifice plates  700  are configured in the second collecting tube  200  at certain intervals. Each orifice plate  700  is provided with orifices  710  to play a part of turbulence and spraying. The spacing distance between the orifice plates  700  is less than 80 mm, 50 mm preferably. The working principles of the embodiment: heat exchange medium such as refrigerant enters from the inlet  400  on the right end of the second collecting tube  200 , flows upwards vertically to one side of the first collecting tube  100  through the flat tubes of the third loop  630 , and then flows to the middle side of the first collecting tube  100  through the middle side of the first collecting tube  100  and the second loop  620 , and then flows to the side of the second collecting tube  200  with orifice plates  700  installed, after the throttling by the orifice plates  700 , flows upwards vertically into the first collecting tube  100  through the flat tubes of the first loop  610 , finally flows out from the outlet  500 . 
       Embodiment 5 
       [0121]    The heat exchanger with microchannel, parallel flow, all-aluminum flat tube welding structure in this embodiment is a double-loop single-row parallel-flow heat exchanger, and used for refrigeration and heating as a heat pump type indoor heat exchanger. As shown in  FIGS. 11-13 , the heat exchanger is comprised of a first collecting tube  100 , a second collecting tube  200  and several flat tubes  300  linking the first collecting tube  100  and the second collecting tube  200 , wherein the flat tubes  300  are composed of extruded thin-wall aluminium profiles with the thickness of the flat tubes  300  from 1.3 mm to 2.0 mm. 
         [0122]    In this embodiment, several flat tubes  300  are arranged in a row at vertical intervals in parallel mode; the first collecting tube  100  is located on the top of the whole heat exchanger, the second collecting tube  200  is at the bottom of the whole heat exchanger; the inlet  400  and outlet  500  of heat exchange medium are located on the second collecting tube  200 . Baffles  210  which ( 210 ) isolate the whole heat exchanger into the first loop  610  and the second loop  620  are set in the second collecting tube  200  respectively. The volume of the first loop  610  takes up 80% of the total volume of loops, the volume of the second loop  620  covers 20% of the total volume of loops. 
         [0123]    The working principles of the embodiment: heat exchange medium such as refrigerant enters from the inlet  400  on the left side of the second collecting tube  200 , flows upwards vertically to one side of the first collecting tube  100  through the flat tubes of the first loop  610 , then flows to the other side of the first collecting tube  100 , then flows upwards vertically to the other side of the second collecting tube  200  through the flat tubes of the second loop  620 , and finally flows out from the outlet  500 . 
         [0124]    As shown in  FIGS. 14 and 15 , the fins  800  which are snake-shaped folding type are set between adjacent two flat tubes  300 , wherein the window angle of fins at the wind speed of 2 M/s is 22°-45°, preferably 27°-33°. The pitch H of fins at the wind speed of 1.5 M/s-2 M/s is 2.0 mm-5.0 mm, preferably 2.2 mm-3.6 mm. When the abovementioned heat exchanger is applied in heat exchange systems without air blowers, windowless design is adopted and pitch H for the fins  800  is equal to the height of the fins  800 . 
         [0125]    The flat tubes  300  along draft direction adopt A° design to guide condensate water of the heat exchanger, wherein 30°≦A°°60°; the window length of the fins  800  is utilized to stop the formation of condensate water, the windowless length of fins, namely the distance from window bottom to the edge of fins B is no more than 0.3 mm, optimally from 0.10 mm to 0.15 mm. 
       Embodiment 6 
       [0126]    The heat exchanger with microchannel, parallel flow, all-aluminum flat tube welding structure in this embodiment is a single-loop single-row parallel-flow heat exchanger, and used as an evaporator or a condenser in water-cooling system. As shown in  FIG. 16 , the heat exchanger is comprised of a first collecting tube  100 , a second collecting tube  200  and several flat tubes  300  linking the first collecting tube  100  and the second collecting tube  200 , wherein the flat tubes  300  are composed of extruded thin-wall aluminium profiles with the thickness of the flat tubes  300  from 1.6 mm to 2.0 mm. 
         [0127]    In this embodiment, several flat tubes  300  are arranged in one row at vertical interval in parallel mode; the first collecting tube  100  is located on the top of the whole heat exchanger, the second collecting tube  200  is at the bottom of the whole heat exchanger; the inlet  400  of heat exchange medium is located on the left end of the first collecting tube  100 , the outlet  500  is on the right end of the second collecting tube  200 , the inlet  400  and outlet  500  are diagonally distributed. The flat tubes  300  are twisted into spiral shape with the helix angle ≦68.2°, thread pitch ≦2.5 times of the width of the flat tubes  300 . Wherein, the flat tube width refers to the dimension other than length and thickness among the three dimensions of a flat tube. 
         [0128]    The working principles of the embodiment: heat exchange medium such as refrigerant enters from the inlet  400  on the left side of the first collecting tube  100 , flows downwards vertically to the second collecting tube  200  through the flat tubes  300 , and then flows out from the outlet  500 . 
       Embodiment 7 
       [0129]    The heat exchanger with microchannel, parallel flow, all-aluminum flat tube welding structure in this embodiment is a single-loop single-row parallel-flow heat exchanger, and used as an evaporator or a condenser in water-cooling system. As shown in  FIG. 16 , the heat exchanger is comprised of a first collecting tube  100 , a second collecting tube  200  and several flat tubes  300  linking the first collecting tube  100  and the second collecting tube  200 , wherein the flat tubes  300  are composed of extruded thin-wall aluminium profiles with the thickness of the flat tubes  300  from 1.6 mm to 2.0 mm. 
         [0130]    In this embodiment, several flat tubes  300  are arranged in one row at horizontal interval in parallel mode; the first collecting tube  100  is located on one side of the whole heat exchanger, the second collecting tube  200  is on the other side of the whole heat exchanger; the inlet  400  of heat exchange medium is located on the bottom end of the first collecting tube  100 , the outlet  500  is on the top end of the second collecting tube  200 , the inlet  400  and outlet  500  are diagonally distributed. The flat tubes  300  are twisted into spiral shape with the helix angle ≦68.2°, thread pitch ≦2.5 times of the width of the flat tubes  300 . 
         [0131]    The working principles of the embodiment: heat exchange medium such as refrigerant enters from the inlet  400  on the bottom end of the first collecting tube  100 , flows horizontally to the second collecting tube  200  through the flat tubes  300 , and then flows out from the outlet  500 . 
       Embodiment 8 
       [0132]    The microchannel, all-aluminium single flat tube in this embodiment forms effective refrigerant flow channel and heat exchange space through bending and then is welded with high-efficiency heat exchange fins to form a single-loop single-row microchannel heat exchanger. It is used as an evaporator in cooling-only system. As shown in  FIG. 18 , the heat exchange part of the heat exchanger is formed by a flat tube  300  through multiple reciprocated bending vertically. The fins  800  which are snake-shaped folding type are set between adjacent two flat tubes  300 , as shown in  FIGS. 14 and 15 , wherein the window angle of fins at the wind speed of 2 M/s A is 22°-45°, preferably 27°-33°; the pitch H of fins at the wind speed of 2 M/s is 2.0 mm-5.0 mm, preferably 2.2 mm-3.6 mm. When the abovementioned heat exchanger is applied in heat exchange systems without air blowers, windowless design is adopted and pitch H for the fins  800  is equal to the height of the fins  800 . 
         [0133]    The flat tube  300  is provided with the inlet  400  of heat exchange medium on one end and the outlet  500  of heat exchange medium on the other end. 
         [0134]    The working principles of the embodiment: heat exchange medium such as refrigerant enters into the flat tube  300  from the inlet  400 , and then flows out from the outlet  500  after heat exchange by the flat tube  300 . 
       Embodiment 9 
       [0135]    The heat exchanger with microchannel, all-aluminium single flat tube welding structure in this embodiment is a single-loop single-row heat exchanger. It is used as an evaporator in water-cooling system. As shown in  FIGS. 19-21 , the heat exchange part of the heat exchanger is formed by a flat tube  300  through multiple reciprocated bending vertically. The flat tube  300  is provided with the inlet  400  of heat exchange medium on one end and the outlet  500  of heat exchange medium on the other end. The flat tube  300  is twisted into spiral shape with the helix angle ≦68.2°, thread pitch ≦2.5 times of the width of the flat tube  300 . 
         [0136]    The working principles of the embodiment: heat exchange medium such as refrigerant enters into the flat tube  300  from the inlet  400 , and then flows out from the outlet  500  after heat exchange by the flat tube  300 . 
       Embodiment 10 
       [0137]    The heat exchanger with microchannel, parallel flow, all-aluminum flat tube welding structure in this embodiment is a double-loop single-row parallel-flow heat exchanger. It is used as a condenser for housing or commercial purposes. As shown in  FIG. 22 , the heat exchanger is comprised of a first collecting tube  100 , a second collecting tube  200  and several flat tubes  300  linking the first collecting tube  100  and the second collecting tube  200 , wherein the flat tubes  300  are composed of extruded thin-wall aluminium profiles with the thickness of the flat tubes  300  from 1.0 mm to 2.0 mm. 
         [0138]    In this embodiment, several flat tubes  300  are arranged in one row at horizontal intervals in parallel mode; the first collecting tube  100  is located on one side of the whole heat exchanger, the second collecting tube  200  is on the other side of the whole heat exchanger; the inlet  400  and outlet  500  of heat exchange medium are located on the top end and bottom end of the first collecting tube  100 . 
         [0139]    The working principles of the embodiment: heat exchange medium such as refrigerant enters into the top side of the first collecting tube  100  from the inlet  400 , flows into the top side of the second collecting tube  200  through the flat tubes  300  of the whole heat exchanger, and then flows downwards along the second collecting tube  200  and returns to the bottom side of the first collecting tube  100  through the flat tubes  300  at the bottom of the heat exchanger, and finally flows out from the outlet  500 . 
       Embodiment 11 
       [0140]    The microchannel, all-aluminium single flat tube in this embodiment forms an effective refrigerant flow channel and heat exchange space through bending and then is welded with high-efficiency heat exchange fins to form a single-loop single-row microchannel heat exchanger. It is used as a condenser in cooling-only system. As shown in  FIGS. 23 and 24 , the heat exchange part of the heat exchanger is formed by a flat tube  300  through multiple reciprocated bending horizontally. The fins  800  which are snake-shaped folding type are set between adjacent two flat tubes  300 , as shown in  FIGS. 14 and 15 , wherein the window angle of fins at the wind speed of 2M/s A is 22°-45°, preferably 27°-33°; the pitch H of fins at the wind speed of 2M/s is 2.0 mm-5.0 mm, preferably 2.2 mm-3.6 mm. When the abovementioned heat exchanger is applied in heat exchange systems without air blowers, windowless design is adopted and pitch H for the fins  800  is equal to the height of the fins  800 . 
         [0141]    The flat tube  300  is provided with the inlet  400  of heat exchange medium on one end and the outlet  500  of heat exchange medium on the other end. 
         [0142]    The working principles of the embodiment: heat exchange medium such as refrigerant enters into the flat tube  300  from the inlet  400 , and then flows out from the outlet  500  after heat exchange by the flat tube  300 . 
       Embodiment 12 
       [0143]    The heat exchanger with microchannel, all-aluminium single flat tube welding structure in this embodiment is a single-loop single-row heat exchanger. It is used as a condenser in water-cooling system. As shown in  FIG. 26 , the heat exchange part of the heat exchanger is formed by a flat tube  300  through multiple reciprocated bending horizontally. The flat tube  300  is provided with the inlet  400  of heat exchange medium on one end and the outlet  500  of heat exchange medium on the other end. The flat tube  300  is twisted into spiral shape with the helix angle ≦68.2°, thread pitch ≦2.5 times of the width of the flat tube  300 . 
         [0144]    The working principles of the embodiment: heat exchange medium such as refrigerant enters into the flat tube  300  from the inlet  400 , and then flows out from the outlet  500  after heat exchange by the flat tube  300 . 
       Embodiment 13 
       [0145]    The heat exchanger with microchannel, all-aluminium flat tube welding structure in this embodiment is a non-inverting parallel connection single-loop single-row heat exchanger. It is used as an evaporator. As shown in  FIGS. 27-29 , the heat exchange part of the heat exchanger is formed by two flat tubes  300  through multiple reciprocated bending horizontally and vertically. The fins  800  which are snake-shaped folding type are set between adjacent two flat tubes  300 , as shown in  FIGS. 14 and 15 , wherein the window angle of fins at the wind speed of 2 M/s A is 22°-45°, preferably 27°-33°; the pitch H of fins at the wind speed of 2 M/s is 2.0 mm-5.0 mm, preferably 2.2 mm-3.6 mm. When the abovementioned heat exchanger is applied in heat exchange systems without air blowers, windowless design is adopted and pitch H for the fins  800  is equal to the height of the fins  800 . 
         [0146]    The two flat tubes  300  are provided with the inlet  400  of heat exchange medium in parallel connection on one end and the outlet  500  of heat exchange medium in parallel connection on the other end. 
         [0147]    The working principles of the embodiment: heat exchange medium such as refrigerant enters into the two flat tubes  300  from the inlet  400 , and then flows out from the outlet  500  after heat exchange by the two flat tubes  300 . 
       Embodiment 14 
       [0148]    The heat exchanger with microchannel, all-aluminium flat tube welding structure in this embodiment is a non-inverting parallel connection single-loop single-row heat exchanger. It is used as a condenser. As shown in  FIG. 30 , the heat exchange part of the heat exchanger is formed by two flat tubes  300  through multiple reciprocated bending horizontally and vertically. The fins  800  which are snake-shaped folding type are set between adjacent two flat tubes  300 , as shown in  FIGS. 14 and 15 , wherein the window angle of fins at the wind speed of 2 M/s A is 22°-45°, preferably 27°-33°; the pitch H of fins at the wind speed of 2 M/s is 2.0 mm-5.0 mm, preferably 2.2 mm-3.6 mm. When the abovementioned heat exchanger is applied in heat exchange systems without air blowers, windowless design is adopted and pitch H for the fins  800  is equal to the height of the fins  800 . 
         [0149]    The two flat tubes  300  are provided with the inlet  400  of heat exchange medium in parallel connection on one end and the outlet  500  of heat exchange medium in parallel connection on the other end. 
         [0150]    The working principles of the embodiment: heat exchange medium such as refrigerant enters into the two flat tubes  300  from the inlet  400 , and then flows out from the outlet  500  after heat exchange by the two flat tubes  300 . 
       Embodiment 15 
       [0151]    The heat exchanger with microchannel, parallel flow, and all-aluminum flat tube welding structure in this embodiment is a double-row double-exchange parallel-flow heat exchanger. It is used as a heat pump type evaporator or condenser. As shown in  FIGS. 31˜33 , the heat exchanger is comprised of a first collecting tube  100 , a second collecting tube  200 , a third collecting tube  100   a,  a fourth collecting tube  200   a  and several flat tubes  300 , wherein the flat tubes  300  are composed of extruded thin-wall aluminum profiles, the thickness of the flat tubes in heat pump type heat exchanger is 1.3 mm-2.0 mm preferably, and the section of single hole flow channel in the perforated microchannel in the flat tubes is 0.36 mm 2 -1.00 mm 2  preferably. Several flat tubes  300  are arranged in two rows at vertical intervals in parallel mode, wherein the upper end of the first row of the flat tubes  300  is connected with the first collecting tube  100 , the lower end of the first row of the flat tubes  300  is connected with the second collecting tube  200 , the upper end of the second row of the flat tubes  300  is connected with the third collecting tube  100   a,  the lower end of the second row of the flat tubes  300  is connected with the fourth collecting tube  200   a.  The first collecting tube  100  and the third collecting tube  100   a  are parallel to each other and facing the same direction of the two rows of the flat tubes  300 , on the top of the whole heat exchanger, wherein the two tubes are not directly connected, and only connected by the flat tubes  300  according to the flow direction of heat exchange medium. The second collecting tube  200  and the fourth collecting tube  200   a  are parallel to each other and facing the same direction of the two rows of the flat tubes  300 , on the top of the whole heat exchanger, wherein the two tubes are communicated according to the flow direction of heat exchange medium. 
         [0152]    The fins  800  which are snake-shaped folding type are set between adjacent two flat tubes  300 , as shown in  FIGS. 14 and 15 , wherein the window angle of fins at the wind speed of 1.5 M/s-2 M/s A is 22°-45°, preferably 27°-33°. The pitch H of fins at the wind speed of 2 M/s is 2.0 mm-5.0 mm, 2.2 mm-2.8 mm preferably in high-efficiency heat exchanger, 2.6 mm-3.0 mm preferably when stressing both high-efficiency heat exchange and dehumidification, 3.6 mm-5.0 mm preferably in freezing &amp; refrigeration or dehumidification-only or sand-dust regions. When the abovementioned heat exchanger is applied in heat exchange systems without air blowers, windowless design is adopted and pitch H for the fins  800  is equal to the height of the fins  800 . 
         [0153]    As shown in  FIGS. 34 and 35 , when the heat exchanger in this embodiment is applied in refrigeration places, there are two inlets  400  of heat exchange medium which are arranged on the right side of the first collecting tube  100 . There are three outlets  500  of heat exchange medium which are placed on the left side of the first collecting tube  100  and distributed at equal intervals. A baffle  110  is set between the right side and left side of the first collecting tube  100 , and an orifice plate  700  is set between the right side and left side of the second collecting tube  200 , wherein the orifice plate  700  is provided with orifices  710 . A baffle  210   a  is configured between the left side and right side of the fourth collecting tube  200   a.  The baffle  210   a,  orifice plate  700  and baffle  110  are all in the same plane. The right side of the second collecting tube  200  and that of the fourth collecting tube  200   a  are directly connected, such as through small holes (not shown in the drawings). The left side of the second collecting tube  200  and that of the fourth collecting tube  200   a  are directly collected, such as through small holes (not shown in the drawings). The working principles of the embodiment during refrigeration: heat exchange medium enters into the right side of the first collecting tube  100  through two inlets  400 , and then flows downwards to the right side of the second collecting tube  200  along part of the flat tubes  300 . One part of liquid phase entering into the right side of the second collecting tube  200  flows into the left side of the second collecting tube  200  through the orifices  710  in the orifice plates  700  so as to balance the gas and liquid phases on the left side of the second collecting tube  200 , the other part of liquid phase flows into the right side of the fourth collecting tube  200   a  transversely. The liquid phase entering into the right side of the fourth collecting tube  200   a  flows upwards into the right side of the third collecting tube  100   a  along part of flat tubes  300 , while the liquid phase entering into the right side of the third collecting tube  100   a  axially flows into the left side of the third collecting tube  100   a  through the third collecting tube  100   a,  and then flows into the left side of the fourth collecting tube  200   a  along part of flat tubes  300 . At this time, the heat exchange medium flowing into the left side of the fourth collecting tube  200   a  is gas and liquid phases. Under the action of gravity, the two phases are difficult to be divided into layers. The gas and liquid phases then transversely flow into the left side of the second collecting tube  200 , and flow upwards into the left side of the first collecting tube  100  along part of flat tubes after mixing with the liquid from orifice plates  700 , and then flow out from the three outlets  500 . Since the orifice plates  700  are set in the second collecting tube  200  and area of the superheat degree for the entire heat exchanger is small (see  FIG. 36 ) compared to the existing technology, close to a small area of the outlet  500  only, high-efficiency conversion of energy in the parallel-flow heat exchanger system can be realized. 
         [0154]    As shown in  FIGS. 37 and 38 , when the heat exchanger in this embodiment is applied in refrigeration places, there are three inlets  400  of heat exchange medium which are arranged on the left side of the first collecting tube  100  and distributed at equal intervals. There are two outlets  500  of heat exchange medium which are placed on the right side of the first collecting tube  100 . A baffle  110  is set between the right side and left side of the first collecting tube  100 , and an orifice plate  700  is set between the right side and left side of the second collecting tube  200 , wherein the orifice plate  700  is provided with orifices  710 . A baffle  210   a  is configured between the left side and right side of the fourth collecting tube  200   a.  The baffle  210   a,  orifice plate  700  and baffle  110  are all in the same plane. The right side of the second collecting tube  200  and that of the fourth collecting tube  200   a  are directly connected, such as through small holes (not shown in the drawings). The left side of the second collecting tube  200  and that of the fourth collecting tube  200   a  are directly collected, such as through small holes (not shown in the drawings). The working principles of the embodiment during heating: heat exchange medium enters into the left side of the first collecting tube  100  through three inlets  400 , and then flows downwards to the left side of the second collecting tube  200  along part of the flat tubes  300 . One part of gas phase entering into the right side of the second collecting tube  200  flows into the right side of the second collecting tube  200  through the orifices  710  in the orifice plates  700  so as to balance the gas and liquid phases on the right side of the second collecting tube  200 , the other part of gas phase flows into the left side of the fourth collecting tube  200   a  transversely. The gas phase entering into the left side of the fourth collecting tube  200   a  flows upwards into the left side of the third collecting tube  100   a  along part of flat tubes  300 , while the gas phase entering into the left side of the third collecting tube  100   a  axially flows into the right side of the third collecting tube  100   a  through the third collecting tube  100   a,  and then flows into the right side of the fourth collecting tube  200   a  along part of flat tubes  300 . At this time, the heat exchange medium flowing into the left side of the fourth collecting tube  200   a  is gas and liquid phases. Under the action of gravity, the two phases are difficult to be divided into layers. The gas and liquid phases then transversely flow into the right side of the second collecting tube  200 , and flow upwards into the right side of the first collecting tube  100  along part of flat tubes after mixing with the gas from orifice plates  700 , and then flow out from the two outlets  500 . Since the orifice plates  700  are set in the second collecting tube  200  and area of the supercooling degree for the whole heat exchanger is small (see  FIG. 37 ) compared to the existing technology, close to a small area of the outlet  500  only, high-efficiency conversion of energy in the parallel-flow heat exchanger system can be realized. 
         [0155]    The heat exchanger can be also horizontally placed: the collecting tubes, flat tubes and fins form a plane parallel to the ground during system installation, this design solves the problem of gas-liquid separation caused by gravity of refrigerant in the heat exchanger, and the condensate water discharge problem can be addressed by means of hydrophilic treatment of fins of the parallel-flow heat exchanger fin+self gravity of condensate water. 
       Embodiment 16 
       [0156]    The heat exchanger with microchannel, parallel flow, and all-aluminum flat tube welding structure in this embodiment is a double-row double-exchange parallel-flow heat exchanger. It is used as an evaporator. As shown in  FIGS. 40-41 , the heat exchanger is comprised of a first collecting tube  100 , a second collecting tube  200  and several flat tubes  300  with thickness of the flat tubes  300  from 1.6 mm to 2.0 mm. Each flat tube  300  is bent into a U shape and each U-shaped flat tube is arranged into one row at vertical intervals in parallel mode. Both ends of each U-shaped flat tube are connected with the first collecting tube  100  and the second collecting tube  200 , wherein the first collecting tube  100  and the second collecting tube  200  are parallel to each other and located on the top of the whole heat exchanger. The two tubes ( 100 ,  200 ) are not directly connected, and only connected by the flat tubes  300  according to the flow direction of heat exchange medium. The fins  800  which are snake-shaped folding type are set between two adjacent flat tubes  300 , as shown in  FIGS. 14 and 15 , wherein the window angle of fins at the wind speed of 2 M/s A is 22°-45°, preferably 27°-33°; the pitch H of fins at the wind speed of 2 M/s is 2.0 mm-5.0 mm, preferably 2.2 mm-3.6 mm. When the abovementioned heat exchanger is applied in heat exchange systems without air blowers, windowless design is adopted and pitch H for the fins  800  is equal to the height of the fins  800 . The inlet  400  and outlet  500  are alternately set on the first collecting tube  100 . 
         [0157]    The working principles of this embodiment: heat exchange medium flows into the left side of the first collecting tube  100  through the inlet  400 , and flows into the left side of the second collecting tube  200  from the left side of the whole heat exchanger; the heat exchange medium entering into the second collecting tube  200  axially flows into the right side of the second collecting tube  200  along the second collecting tube  200 , and then flows into the right side of the first collecting tube  100  from the right side of the whole heat exchanger, and finally flows out from the outlet  500 . 
       Embodiment 17 
       [0158]    The heat exchanger in this embodiment is basically the same as that in Embodiment  16 . As shown in  FIGS. 43-45 , the flat tubes  300  are twisted into spiral shapes with the helix angle ≦68.2°, thread pitch ≦2.5 times of the width of the flat tubes  300 . The fins  800  are not provided between two adjacent flat tubes  300 . 
       Embodiment 18 
       [0159]    The heat exchanger with microchannel, parallel flow, and all-aluminum flat tube welding structure in this embodiment is a double-row double-exchange parallel-flow heat exchanger. It is used as an evaporator or condenser. As shown in  FIG. 46 , the heat exchanger is comprised of a first collecting tube  100 , a second collecting tube  200 , a third collecting tube  100   a,  a fourth collecting tube  200   a  and several flat tubes  300 , wherein the flat tubes  300  are composed of extruded thin-wall aluminum profiles, the thickness of the flat tubes  300  is 1.6 mm-2.5 mm. Several flat tubes  300  are arranged in two rows at vertical intervals in parallel mode, wherein the upper end of the first row of the flat tubes  300  is connected with the first collecting tube  100 , the lower end of the first row of the flat tubes  300  is connected with the second collecting tube  200 , the upper end of the second row of the flat tubes  300  is connected with the third collecting tube  100   a,  the lower end of the second row of the flat tubes  300  is connected with the fourth collecting tube  200   a.  The first collecting tube  100  and the third collecting tube  100   a  are parallel to each other and facing the same direction, on the top of the whole heat exchanger; the second collecting tube  200  and the fourth collecting tube  200   a  are parallel to each other and facing the same direction of the two rows of the flat tubes  300 , at the bottom of the heat exchanger. The outlet is set on one end of the third collecting tube  100   a.  The inlet  400  and outlet  500  are located on the same side of the top of the whole heat exchanger. Baffles  110 ,  110   a  are configured in the middle of the first collecting tube  100  and the third collecting tube  100   a.  The inlet  400  of heat exchange medium is set on one end of the first collecting tube  100 . The baffles  110 ,  110   a  isolate the flow channel of the whole heat exchanger into the first loop  610 , the second loop  620 , the third loop  630  and the fourth loop  640 , wherein the side of the first collecting tube  100  and the third collecting tube  100   a  away from the inlet  400  and outlet  500  is directly connected through small holes  900 , the second collecting tube  200  and the fourth collecting tube  200   a  are not directly connected. 
         [0160]    The working principles of this embodiment: the heat exchange medium enters into the side of the first collecting tube  100  close to the inlet  400  through the inlet  400 , and then flows downwards into one side of the second collecting tube  200  along the first loop  610  under the action of the baffle  110 ; the heat exchange medium flowing into one side of the second collecting tube  200  axially flows into the other side of the second collecting tube  200  along the second collecting tube  200 , and then flows upwards to the side of the first collecting tube  100  away from the inlet  400  through the second loop  620 ; the heat exchange medium flowing into the side of the first collecting tube  100  away from the inlet  400  flows into the side of the third collecting tube  100   a  away from the outlet  500  through small holes  900 ; the heat exchange medium entering into the side of the third collecting tube  100   a  away from the outlet  500  flows downwards into one side of the fourth collecting tube  200   a  along the flat tubes  300  in the third loop  630  due to the blocking of the baffle  110   a,  and the heat exchange medium flowing into one side of the fourth collecting tube  200   a  axially flows into the other side of the fourth collecting tube  200   a  along the fourth collecting tube  200   a,  afterwards, flows upwards into the side of the third collecting tube  100   a  close to the outlet  500  through the flat tubes  300  in the fourth loop  640 , and finally flows out from the outlet  500 . 
         [0161]    The heat exchanger can be also horizontally placed: the collecting tubes, flat tubes and fins form a plane parallel to the ground when system installation, this design solves the problem of gas-liquid separation caused by gravity of refrigerant in the heat exchanger, and condensate water discharge problem can be addressed by means of hydrophilic treatment of fins of the parallel-flow heat exchanger fin+self gravity of condensate water. 
       Embodiment 19 
       [0162]    The heat exchanger with microchannel, parallel flow, and all-aluminum flat tube welding structure in this embodiment is a double-row double-exchange parallel-flow heat exchanger. It is used as an evaporator or condenser. As shown in  FIG. 47 , the heat exchanger in this embodiment is comprised of a first collecting tube  100 , a second collecting tube  200 , a third collecting tube  100   a,  a fourth collecting tube  200   a  and several flat tubes  300 , wherein the flat tubes  300  are composed of extruded thin-wall aluminum profiles, the thickness of the flat tubes is 1.6 mm-2.5 mm. Several flat tubes  300  are arranged in two rows at vertical intervals in parallel mode, wherein the upper end of the first row of the flat tubes  300  is connected with the first collecting tube  100 , the lower end of the first row of the flat tubes  300  is connected with the second collecting tube  200 , the upper end of the second row of the flat tubes  300  is connected with the third collecting tube  100   a,  the lower end of the second row of the flat tubes  300  is connected with the fourth collecting tube  200   a.  The first collecting tube  100  and the third collecting tube  100   a  are parallel to each other and facing the same direction of the two rows of the flat tubes  300 , on the top of the whole heat exchanger; the second collecting tube  200  and the fourth collecting tube  200   a  are parallel to each other and facing the same direction of the two rows of the flat tubes  300 , at the bottom of the heat exchanger. The outlet is set on one end of the third collecting tube  100   a.  The inlet  400  and outlet  500  are located on the same side of the top of the whole heat exchanger. Baffles  110 ,  110   a  are configured in the middle of the first collecting tube  100  and the third collecting tube  100   a.  The inlet  400  of heat exchange medium is set on one end of the first collecting tube  100 . The baffles  110 ,  110   a  isolate the flow channel of the whole heat exchanger into the first loop  610 , the second loop  620 , the third loop  630  and the fourth loop  640 , wherein the side of the first collecting tube  100  and the third collecting tube  100   a  away from the inlet  400  and outlet  500  is directly connected through small holes  900 , the second collecting tube  200  and the fourth collecting tube  200   a  are not directly connected. Three orifice plates  700  are set in the second collecting tube  200  and the fourth collecting tube  200   a  respectively with each orifice plate  700  provided with the orifices  710 . 
         [0163]    The working principles of this embodiment: the heat exchange medium enters into the side of the first collecting tube  100  close to the inlet  400  through the inlet  400 , and then flows downwards into one side of the second collecting tube  200  along the first loop  610  under the action of the baffle  110 ; the heat exchange medium flowing into one side of the second collecting tube  200  axially flows into the other side of the second collecting tube  200  along the second collecting tube  200  after throttling by the three orifice plates  700  in the second collecting tube  200 , and then flows upwards to the side of the first collecting tube  100  away from the inlet  400  through the second loop  620 ; the heat exchange medium flowing into the side of the first collecting tube  100  away from the inlet  400  flows into the side of the third collecting tube  100   a  away from the outlet  500  through small holes  900 ; the heat exchange medium entering into the side of the third collecting tube  100   a  away from the outlet  500  flows downwards into one side of the fourth collecting tube  200   a  along the flat tubes  300  in the third loop  630  due to the blocking of the baffle  110   a,  and the heat exchange medium flowing into one side of the fourth collecting tube  200   a  axially flows into the other side of the fourth collecting tube  200   a  along the fourth collecting tube  200   a  after throttling by the three orifice plates  700  in the second collecting tube  200 , afterwards, flows upwards into the side of the third collecting tube  100   a  close to the outlet  400  through the flat tubes  300  in the fourth loop  640 , finally flows out from the outlet  400 . 
         [0164]    The heat exchanger can be also horizontally placed: the collecting tubes, flat tubes and fins form a plane parallel to the ground when system installation, this design solves the problem of gas-liquid separation caused by gravity of refrigerant in the heat exchanger, and condensate water discharge problem can be addressed by means of hydrophilic treatment of fins of the parallel-flow heat exchanger fin+self gravity of condensate water. 
       Embodiment 20 
       [0165]    The heat exchanger with microchannel, parallel flow, and all-aluminum flat tube welding structure in this embodiment is a double-row double-exchange parallel-flow heat exchanger. It is used as an evaporator or condenser. As shown in  FIG. 48 , the heat exchanger in this embodiment is comprised of a first collecting tube  100 , a second collecting tube  200 , a third collecting tube  100   a,  a fourth collecting tube  200   a  and several flat tubes  300 , wherein the flat tubes  300  are composed of extruded thin-wall aluminum profiles, the thickness of the flat tubes is 1.6 mm-2.5 mm. Several flat tubes  300  are arranged in two rows at vertical intervals in parallel mode, wherein the upper end of the first row of the flat tubes  300  is connected with the first collecting tube  100 , the lower end of the first row of the flat tubes  300  is connected with the second collecting tube  200 , the upper end of the second row of the flat tubes  300  is connected with the third collecting tube  100   a,  the lower end of the second row of the flat tubes  300  is connected with the fourth collecting tube  200   a.  The first collecting tube  100  and the third collecting tube  100   a  are parallel to each other and facing the same direction of the two rows of the flat tubes  300 , on the top of the whole heat exchanger; the second collecting tube  200  and the fourth collecting tube  200   a  are parallel to each other and facing the same direction of the two rows of the flat tubes  300 , at the bottom of the heat exchanger. 
         [0166]    The first collecting tube  100  and the third collecting tube  100   a  are not directly connected, and the second collecting tube  200  and the fourth collecting tube  200   a  are partially connected in a direct manner, in this way, the first collecting tube  100 , the second collecting tube  200 , the third collecting tube  100   a,  the fourth collecting tube  200   a  and flat tubes  300  constitute the whole heat exchange flow channel of the embodiment. The inlet  400  and outlet  500  of heat exchange medium for the whole heat exchange flow channel are set on the side tube wall of the first collecting tube  100 . 
         [0167]    A baffle  110  and a baffle  210  are set in the first collecting tube  100  and the second collecting tube  200  respectively, wherein the baffles  110  and  210  isolate the flat tubes  300  between the first collecting tube  100  and the second collecting tube  200  into N 1 -row flow channel and N 2 +N 3 -row flow channel, the baffles  110  and  210  are in the same plane. 
         [0168]    A baffle  210   a  is set inside the fourth collecting tube  210   a,  an orifice plate  700  is set in side the third collecting tube  110   a,  wherein the baffle  210   a  and orifice plate  700  isolate the flat tubes  300  between the third collecting tube  100   a  and the fourth collecting tube  200   a  into N 1 +N 2 -row flow channel and N 3 -row flow channel. The N 1 -row flow channel in the second collecting tube  200  and the N 1 +N 2 -row flow channel in the fourth collecting tube  210   a  are communicated through the small holes  910  between the second collecting tube  200  and the fourth collecting tube  210   a.  The N 2 +N 3 -row flow channel in the second collecting tube  200  and the N 3 -row flow channel in the fourth collecting tube  210   a  are communicated through small holes  920  between the second collecting tube  200  and the fourth collecting tube  210   a.  The flat tubes  300  of the N 1 -row flow channel between the first collecting tube  100  and the second collecting tube  200  constitute the first loop  610 . The flat tubes  300  of the N 1 +N 2 -row flow channel between the third collecting tube  100   a  and the fourth collecting tube  200   a  form the second loop  620 . The flat tubes  300  of the N 3 -row flow channel between the third collecting tube  100   a  and the fourth collecting tube  200   a  constitute the third loop  630 . The flat tubes  300  of N 2 +N 3 -row flow channel between the first collecting tube  100  and the second collecting tube  200  constitute the fourth loop  640 . 
         [0169]    The flow direction of the refrigerant in the whole flow channel is as below: enter into the N 1 -row flow channel of the first collecting tube  100  through the inlet  400 , flow downwards into the N 1 -row flow channel of the second collecting tube  200  along the flat tubes  130  of the first loop, and then transversely flow into the N 1 +N 2 -row flow channel of the fourth collecting tube  200   a  through the small holes  910 , afterwards rise to the N 1 +N 2 -row flow channel of the third collecting tube  100   a  along the flat tubes  300  of the second loop. The refrigerant entering into the N 1 +N 2 -row flow channel of the third collecting tube  100   a  axially flows into the N 3 -row flow channel of the third collecting tube  100   a  along the third collecting tube  100   a  through the orifice plates  700 , and then flows downwards into the N 3 -row flow channel of the fourth collecting tube  100   a  along the flat tube  300  of the third loop  630 , afterwards, transversely flows into the N 2 +N 3 -row flow channel of the second collecting tube  200  through the small holes  920 . The refrigerant flowing into the N 2 +N 3 -row flow channel of the second collecting tube  200  flows upwards into the N 2 +N 3 -row flow channel of the first collecting tube  100  along the flat tubes  300  in the fourth loop  640 , and finally flows out from the outlet  500 . 
         [0170]    The flowing process of the whole refrigerant includes four loops, namely the first loop  610 , the second loop  620 , the third loop  630  and the fourth loop  640 . The volumes of the four loops of the refrigerant during flowing are in the ascending trend, namely, the volumes of various flow channels are: the first loop  610 &lt;the second loop  620 &lt;the third loop  630 &lt;the fourth loop  640 , wherein the volume of the second loop  620  is more than 40-50% of that of the first loop  610 , the volume of the third loop  630  is more than 40-50% of that of the second loop  620 , the volume of the fourth loop  640  is more than 40-50% of that of the third loop  630  and the volume of the fourth loop  640  is 2.5 times of that of the first loop  610 . 
         [0171]    As shown in  FIG. 48 , the length of the refrigerant axially flowing in the fourth collecting tube  200   a  along the fourth collecting tube  200   a  is N 1 +N 2  at most, while the axially flowing length in the third collecting tube  110   a  is N 2 +N 3 . Since the length of N 3  is more than N 1 , the length of the refrigerant axially flowing in the third collecting tube  100   a  is more than the axially flowing length in the fourth collecting tube  200   a  along the fourth collecting tube  200   a.    
         [0172]    The length of the refrigerant axially flowing in the third collecting tube  110   a  can be set as long as possible, taking up 70% of the summation of the refrigerant axially flowing length in the first collecting tube  100  and the third collecting tube  100   a  along the first collecting tube  100  and the third collecting tube  100   a  as well as the axially flowing length in the second collecting tube  200  and the fourth collecting tube  200   a  along the second collecting tube  200  and the fourth collecting tube  200   a;  while the axially flowing length in the fourth collecting tube  200   a  along the fourth collecting tube  200   a  can be as short as possible, accounting for 30% of the summation of the refrigerant axially flowing length in the first collecting tube  100  and the third collecting tube  100   a  along the first collecting tube  100  and the third collecting tube  100   a  as well as the axially flowing length in the second collecting tube  200  and the fourth collecting tube  200   a  along the second collecting tube  200  and the fourth collecting tube  200   a.    
         [0173]    The heat exchanger can be also horizontally placed: the collecting tubes, flat tubes and fins form a plane parallel to the ground when system installation, this design solves the problem of gas-liquid separation caused by gravity of refrigerant in the heat exchanger, and condensate water discharge problem can be addressed by means of hydrophilic treatment of fins of the parallel-flow heat exchanger fin+self gravity of condensate water. 
       Embodiment 21 
       [0174]    The heat exchanger with microchannel, parallel flow, and all-aluminum flat tube welding structure in this embodiment is a double-row double-exchange parallel-flow heat exchanger. It is used as an evaporator or condenser. As shown in  FIG. 49 , the heat exchanger in this embodiment is comprised of a first collecting tube  100 , a second collecting tube  200 , a third collecting tube  100   a,  a fourth collecting tube  200   a  and several flat tubes  300 , wherein the flat tubes  300  are composed of extruded thin-wall aluminum profiles, the thickness of the flat tubes is 1.6 mm-2.5 mm. Several flat tubes  300  are arranged in two rows at vertical intervals in parallel mode, wherein the upper end of the first row of the flat tubes  300  is connected with the first collecting tube  100 , the lower end of the first row of the flat tubes  300  is connected with the second collecting tube  200 , the upper end of the second row of the flat tubes  300  is connected with the third collecting tube  100   a,  the lower end of the second row of the flat tubes  300  is connected with the fourth collecting tube  200   a.  The first collecting tube  100  and the third collecting tube  100   a  are parallel to each other and facing the same direction of the two rows of the flat tubes  300 , on the top of the whole heat exchanger; the second collecting tube  200  and the fourth collecting tube  200   a  are parallel to each other and facing the same direction of the two rows of the flat tubes  300 , at the bottom of the heat exchanger. 
         [0175]    The first collecting tube  100  and the third collecting tube  100   a  are not directly connected, and the second collecting tube  200  and the fourth collecting tube  200   a  are partially connected in a direct manner, in this way, the first collecting tube  100 , the second collecting tube  200 , the third collecting tube  100   a,  the fourth collecting tube  200   a  and flat tubes  300  constitute the whole heat exchange flow channel of the embodiment. The inlet  400  of heat exchange medium for the whole heat exchange flow channel is set on one end of the third collecting tube  100   a,  and the outlet  500  is set on one end of the first collecting tube  100 . 
         [0176]    Two baffles  210  and  220  are set in the second collecting tube  200 , wherein the baffles  210  and  220  isolate the second collecting tube  200  into N 1 -row flow channel, N 2 -row flow channel and N 3 +N 4 -row flow channel; a baffle  110  and an orifice plate  700  are set in the first collecting tube  100 , wherein the baffle  110  and orifice plate  700  isolate the first collecting tube  100  into N 1 -row flow channel, N 2 -row flow channel and N 3 +N 4 -row flow channel. 
         [0177]    Two baffles  210  and  220  are set in the fourth collecting tube  200   a,  wherein the two baffles  210  and  220  isolate the fourth collecting tube  100   a  into N 1 -row flow channel, N 2 +N 3 -row flow channel and N 4 -row flow channel; a baffle  110  and an orifice plate  700  are set in the third collecting tube  100   a,  wherein the baffle  110  and orifice plate  700  isolate the third collecting tube  100   a  into N 1 -row flow channel, N 2 +N 3 -row flow channel and N 4 -row flow channel. A guide tube  410  is inserted into the third collecting tube  100   a.  Its entrance is connected with the inlet  400  and an exit is located within the N 1 -row flow channel of the third collecting tube  100   a.    
         [0178]    The N 1 -row flow channel in the second collecting tube  200  and the N 1 -row flow channel in the fourth collecting tube  200   a  are communicated through the small holes  910  between the second collecting tube  200  and the fourth collecting tube  200   a.  The N 2 -row flow channel in the second collecting tube  200  and the N 2 +N 3 -row flow channel in the fourth collecting tube  200   a  are communicated through small holes  920  between the second collecting tube  200  and the fourth collecting tube  200   a.  The N 3 +N 4 -row flow channel in the second collecting tube  200  and the N 4 -row flow channel in the fourth collecting tube  200   a  are communicated through the small holes  930  between the second collecting tube  200  and the fourth collecting tube  200   a.    
         [0179]    The flat tubes  300  of the N 1 -row flow channel between the third collecting tube  100   a  and the fourth collecting tube  200   a  constitute the first loop  610 . The flat tubes  300  of the N 1 -row flow channel between the second collecting tube  200  and the first collecting tube  100  form the second loop  620 . The flat tubes  300  of the N 2 -row flow channel between the first collecting tube  100  and the second collecting tube  200  constitute the third loop  630 . The flat tubes  300  of N 2 +N 3 -row flow channel between fourth collecting tube  200   a  and the third collecting tube  100   a  constitute the fourth loop  640 . The flat tubes  300  of the N 4 -row flow channel between the third collecting tube  100   a  and the fourth collecting tube  200   a  form the fifth loop  650 . The flat tubes  300  of the N 4 -row flow channel between the second collecting tube  200  and the first collecting tube  100  constitute the sixth loop  660 . 
         [0180]    The flow direction of the refrigerant in the whole flow channel is as below: enter into the guide tube  410  through the inlet  400 , and then flow into the N 1 -row flow channel in the third collecting tube  100   a  from the guide tube  410 , flow downwards to the N 1 -row flow channel of the fourth collecting tube  100   a  along the flat tube  230  of the first loop  610 , afterwards, transversely flow into the N 1 -row flow channel of the second collecting tube  200  through small holes  122 , and flow upwards into the N 1 -row flow channel of the first collecting tube  100  along the second loop  620 . The refrigerant entering into the N 1 -row flow channel of the first collecting tube  100  axially flows along the first collecting tube  100 , and then flows into the N 2 -row flow channel of the first collecting tube  100  through the orifice plates  700 . 
         [0181]    The refrigerant entering into the N 2 -row flow channel of the first collecting tube  100  flows into the N 2 -row flow channel of the second collecting tube  200  along the flat tubes of the third loop  630 , and then transversely flows into the N 2 +N 3 -row flow channel of the fourth collecting tube  100   a  through the small holes  123 . The refrigerant entering into the N 2 +N 3 -row flow channel of the fourth collecting tube  200   a  flows upwards into the N 2 +N 3 -row flow channel of the third collecting tube  100   a  along the flat tubes  300  of the fourth loop  640 . 
         [0182]    The refrigerant entering into the N 2 +N 3 -row flow channel of the third collecting tube  100   a  axially flows into the N 4 -row flow channel of the third collecting tube  100   a  along the third collecting tube  100   a  through the orifice plates  700 , and then flows downwards into the N 4 -row flow channel of the fourth collecting tube  100   a  along the flat tube  300  of the fifth loop  650 . Afterwards, the refrigerant entering into the N 4 -row flow channel of the fourth collecting tube  200   a  transversely flows into the N 4 -row flow channel of the second collecting tube  200  through the small holes  935 , and then flows upwards into the N 3 +N 4 -row flow channel of the first collecting tube  100  along the flat tubes  300  in the sixth loop  660 , and finally flows out from the outlet  500 . 
         [0183]    The flowing process of the whole refrigerant includes six loops, namely the first loop  610 , the second loop  620 , the third loop  630 , the fourth loop  640 , the fifth loop  650  and the sixth loop  660 . The volumes of the six loops of the refrigerant during flowing are in the ascending trend, namely, the volumes of various loops are: the first loop  610 &lt;the second loop  620 &lt;the third loop  630 &lt;the fourth loop  640 &lt;the fifth loop  650 &lt;the sixth loop  660 , wherein the volume of the second loop  620  is more than 40-50% of that of the first loop  610 , the volume of the third loop  630  is more than 40-50% of that of the second loop  620 , the volume of the fourth loop  640  is more than 40-50% of that of the third loop  630 , the volume of the fifth loop  650  is more than 40-50% of that of the fourth loop  640 , the volume of the sixth loop  660  is more than 40-50% of that of the fifth loop  650  and the volume of the sixth loop  660  is 2.5 times that of the first loop  610 . 
         [0184]    As shown in  FIG. 49 , the refrigerant almost does not make axial movement in the fourth collecting tube  200   a  and the second collecting tube  200 , but the axially flowing length in the third collecting tube  100   a  along the third collecting tube  100   a  is N 4 +N 3 +N 2 +N 1 +N 2 +N 3 +N 4 , and the axially flowing length in the first collecting tube  100  along the first collecting tube  100  is N 1 +N 2 +N 4 . Therefore, it is far more than the length of the refrigerant axially flowing in the fourth collecting tube  200   a  and the second collecting tube  200 . 
         [0185]    The length of the refrigerant axially flowing in the third collecting tube  100   a  along the third collecting tube  100   a  and the axially flowing length in the first collecting tube  100  along the first collecting tube  100  can be set as long as possible, taking up 70% of the summation of the refrigerant axially flowing length in the first collecting tube  100  and the third collecting tube  100   a  along the first collecting tube  100  and the third collecting tube  100   a  as well as the axially flowing length in the second collecting tube  200  and the fourth collecting tube  200   a  along the second collecting tube  200  and the fourth collecting tube  200   a;  while the axially flowing length in the second collecting tube  200  and the fourth collecting tube  200   a  along the second collecting tube  200  and the fourth collecting tube  200   a  can be as short as possible, accounting for below 30% of the summation of the refrigerant axially flowing length in the first collecting tube  100  and the third collecting tube  100   a  along the first collecting tube  100  and the third collecting tube  100   a  as well as the axially flowing length in the second collecting tube  200  and the fourth collecting tube  200   a  along the second collecting tube  200  and the fourth collecting tube  200   a.    
         [0186]    To prevent overheating, the guide tube  410  is provided with holes in section of the N 3 -row flow channel and N 4 -row flow channel in the third collecting tube  100   a.  The holes supplement refrigerant to the N 3 -row flow channel and N 4 -row flow channel in the third collecting tube  100   a,  wherein the refrigerant amount supplemented to N 4 -row flow channel takes up 15-20% of the total amount of the refrigerant. 
         [0187]    The heat exchanger can be also horizontally placed: the collecting tubes, flat tubes and fins form a plane parallel to the ground when system installation, this design solves the problem of gas-liquid separation caused by gravity of refrigerant in the heat exchanger, and condensate water discharge problem can be addressed by means of hydrophilic treatment of fins of the parallel-flow heat exchanger fin+self gravity of condensate water. 
         [0188]    As shown in  FIG. 50 , the collecting tube a in the existing technology is round tube structure, forms high flow resistance after connection with the flat tubes  300  (See  FIG. 51 ). The collecting tube adopted by the present invention in the abovementioned embodiments is D-shaped collecting tube b which can further reduce the loss of heat exchange medium in the collecting tube after connection with the flat tubes  300  (See  FIG. 53 ). 
         [0189]    As shown in  FIGS. 54 and 55 , to increase the intensity of the collecting tubes, reinforcing ribs b 1  are configured on the three sides of tube walls of the D-shaped collecting tubes without connecting the flat tubes along collecting tube length direction alternately, with the intervals of two adjacent reinforcing ribs b 1  being 25.4 mm, wherein the reinforcing ribs b 1  are semicircular concave bars with the depth of 1 mm, radius of R 1 . 
         [0190]    In these embodiments, the flat tubes are all Zinc-coated with the thickness of zinc coating of 12˜18 g/m 2  so as to prolong the service life. 
         [0191]    The abovementioned heat exchanger with microchannel, parallel flow, all-aluminum flat tube welding structure can be applied in air conditioners for housing and commercial use, and many other specialized heat exchange systems, and in particular, in rooms and similar-purpose air conditioning systems, freezing and refrigeration systems, air conditioning systems for refrigeration and dehumidification, heat pump heating and water cooling/heating and air conditioning systems, computer cooling modules in IT industry and cooling systems equipment. 
         [0192]    The abovementioned displays and describes the basic principles, main features and advantages of the present invention. The technical personnel in this art shall be aware that the embodiments and the specification above only explain the principles of the present invention and are not intended to limit the present invention in that the invention is subject to modifications and improvements, without departing from the spirit and scope of the present invention. Such modifications and improvements are intended to be within the protection scope of the present invention defined by the Claims and the equivalents attached.