A variable flow double-row microchannel heat exchanger and control method thereof

Abstract

A variable flow double-row microchannel heat exchanger and a control method thereof, the double-row microchannel heat exchanger comprising four collecting pipes, flat tubes, fins, three partitions, five distribution pipes, and seven ball valves. When the double-row microchannel heat exchanger works as an evaporator, it is sensitive to changes in the refrigerant pressure drop and requires fewer processes to reduce the pressure drop. When the double-row microchannel heat exchanger works as a condenser, the refrigerant flow rate has a significant impact on the heat exchange effect and requires more processes to increase the flow rate. The conventional heat exchanger process is fixed and cannot achieve changes in the refrigerant process. The variable flow double-row microchannel heat exchanger proposed in the present invention can adjust the process according to three different load conditions when the heat exchanger works as an evaporator or condenser, so that the pressure drop and flow rate changes on the refrigerant side can better meet the heat exchange requirements, thereby improving the performance of the heat exchanger.

Description

Technical Field

[0001] The invention relates to the technical field of microchannel heat exchangers, and in particular to a variable-flow double-row microchannel heat exchanger and a control method thereof. Background Art

[0002] Microchannel heat exchangers have been widely used in the field of automotive air conditioning due to their compact structure, high heat exchange efficiency, and low refrigerant charge. With the rapid development of refrigeration technology, microchannel heat exchangers are also gradually being used in the field of refrigeration and air conditioning.

[0003] When a conventional microchannel heat exchanger works as an evaporator or condenser, the refrigerant can only flow through a fixed flow path. However, such a design cannot meet the optimal flow path corresponding to the heat exchanger under different cooling and heating conditions. For the evaporator, the pressure drop on the refrigerant side has a greater impact on the heat exchanger, and fewer flows are required to reduce the pressure drop. For the condenser, the flow rate of the refrigerant has a greater impact on the heat exchanger, and more flows are required to increase the flow rate. In addition, when the microchannel heat exchanger is operating at a low load, the refrigerant flow rate decreases sharply, and the refrigerant does not need to flow through all the flat tubes to meet the heat exchange requirements. On the contrary, the refrigerant flowing through all the flat tubes will bring about a greater pressure drop and reduce the heat exchange performance. Summary of the invention

[0004] In view of the problems existing in the microchannel heat exchanger described above, the object of the present invention is to provide a variable flow double-row microchannel heat exchanger and a control method thereof. The present invention adopts the structure of a double-row microchannel heat exchanger. The flow of the refrigerant needs to be determined according to the different loads when the heat exchanger is used as an evaporator or a condenser. When the heat exchanger works at full load or intermediate load as an evaporator, the refrigerant flows through all flat tubes and the flow is 1 or 2 flat tubes respectively. When the heat exchanger works at full load or intermediate load as a condenser, the refrigerant flows through all flat tubes and the flow is 5 or 4 flat tubes respectively. When the heat exchanger works at a small load, the refrigerant only flows through the front row of heat exchangers to reduce the pressure drop on the refrigerant side and improve the heat exchange performance.

[0005] In order to achieve the above technical purpose, the present invention adopts the following technical solutions:

[0006] A variable flow double-row microchannel heat exchanger, comprising a first collecting pipe 01, a second collecting pipe 02, a third collecting pipe 05 and a fourth collecting pipe 06, a plurality of flat tubes 04 arranged between the first collecting pipe 01 and the second collecting pipe 02, the third collecting pipe 05 and the fourth collecting pipe 06 and connecting the first collecting pipe 01 and the second collecting pipe 02, the third collecting pipe 05 and the fourth collecting pipe 06, and fins 03 installed between adjacent flat tubes. The first collecting pipe 01, the second collecting pipe 02, the flat tubes 04 and the fins 03 constitute a front-row microchannel heat exchanger, and the third collecting pipe 05, the fourth collecting pipe 06, The flat tubes 04 and the fins 03 constitute a rear microchannel heat exchanger; the first partition 14 is arranged at 1 / 2l inside the second manifold 02, the second partition 13 is arranged at 1 / 2l inside the third manifold 05, and the third partition 12 is installed at 1 / 3l near the left end of the fourth manifold 06, where l is the length of the manifold; the first distribution pipe 11 is installed inside the first manifold 01, the second distribution pipe 10 is installed inside the second manifold 02 and is located on the right side of the first partition 14, and the third distribution pipe 09 is also installed inside the second manifold 02 and passes through the first partition 1 4, the fourth distribution pipe 08 is installed inside the third liquid collecting pipe 05 and passes through the second partition 13, the fifth distribution pipe 07 is installed inside the fourth liquid collecting pipe 06 and passes through the third partition 12, the length of the first distribution pipe 11, the fourth distribution pipe 08 and the fifth distribution pipe 07 is l and has holes evenly opened along the pipe length direction, the length of the second distribution pipe 10 is 1 / 2l and has holes evenly opened along the pipe length direction, the length of the third distribution pipe 09 is l and has holes evenly opened only in the rear half, and all the opening sections are located on the left side of the first partition 14; the first ball valve 18 and the fifth ball valve 21 are respectively connected to the first distribution pipe 11 and the fifth distribution pipe 08. The distribution pipe 11 is connected to the third distribution pipe 09, and the third ball valve 16 and the sixth ball valve 20 are connected to the two ends of the fourth distribution pipe 08; the second ball valve 17 and the fourth ball valve 15 are respectively connected to the left ends of the second collecting pipe 02 and the fourth collecting pipe 06, but are not connected to the third distribution pipe 09 and the fifth distribution pipe 07; the first ball valve 18, the second ball valve 17 and the third ball valve 16 are connected to the inlet pipeline of the heat exchanger; the second distribution pipe 10, the sixth ball valve 20, the fifth ball valve 21 and one end of the seventh ball valve 19 are connected, and the other end of the seventh ball valve 19 is connected to the fourth ball valve 15 and the outlet pipeline of the heat exchanger.

[0007] By installing the second partition 13 and the third partition 12 at different positions in the third collecting pipe 05 and the fourth collecting pipe 06, and installing the second distribution pipe 10 and the third distribution pipe 09 of different lengths in the second collecting pipe 02, combined with the switch of the ball valve, different flow designs can be realized when the double-row microchannel heat exchanger is used as an evaporator and a condenser, and the flow design of the double-row microchannel heat exchanger under different load conditions can also be realized. When the heat exchanger works as an evaporator, fewer flows can reduce the pressure drop on the refrigerant side, thereby improving the heat exchange performance; when the heat exchanger works as a condenser, more flows can increase the flow rate of the refrigerant, thereby improving the heat exchange performance. In addition, when the heat exchanger works under low load conditions, the refrigerant flow is small, and only a small heat exchange area is required to meet the heat exchange requirements.

[0008] When the double-row microchannel heat exchanger works at full load as an evaporator, the first ball valve 18, the third ball valve 16, the fourth ball valve 15, the fifth ball valve 21 and the seventh ball valve 19 are opened, and the refrigerant enters the front row microchannel heat exchanger and the rear row microchannel heat exchanger through the first ball valve 18 and the third ball valve 16 respectively, and the refrigerant flows through all the flat tubes and the process is one flat tube; when the double-row microchannel heat exchanger works at intermediate load as an evaporator, the first ball valve 18, the fourth ball valve 15, the fifth ball valve 21 and the sixth ball valve 20 are opened, and the refrigerant flows from the first The refrigerant enters the front row microchannel heat exchanger through the ball valve 18, then flows out of the front row microchannel heat exchanger through the second distribution pipe 10 and the third distribution pipe 09, and then flows through the sixth ball valve 20 into the rear row microchannel heat exchanger. The refrigerant flows through all the flat tubes and the flow path is 2 flat tubes; when the double-row microchannel heat exchanger works as an evaporator with a small load, the first ball valve 18, the fifth ball valve 21 and the seventh ball valve 19 are opened, and the refrigerant enters the front row microchannel heat exchanger through the first ball valve 18. The refrigerant only flows through the flat tubes of the front row microchannel heat exchanger and the flow path is 1 flat tube.

[0009] When the double-row microchannel heat exchanger works at full load as a condenser, the second ball valve 17, the fourth ball valve 15 and the sixth ball valve 20 are opened, and the refrigerant enters the rear-row microchannel heat exchanger through the fourth ball valve 15. Under the action of the second partition 13 and the third partition 12, the refrigerant flows through the process of 3 flat tubes, and then flows out of the rear-row microchannel heat exchanger through the sixth ball valve 20, and then flows into the front-row microchannel heat exchanger from the second distribution pipe 10. The second distribution pipe 10 evenly supplies liquid to the rear half of the front-row microchannel heat exchanger. The refrigerant flows through the process of 2 flat tubes. The total refrigerant process under full load conditions is 5 flat tubes; when the double-row microchannel heat exchanger works as a condenser at intermediate load, the first ball valve 18, the fourth ball valve 15, the fifth ball valve 21 and the sixth ball valve 20 is opened, and the refrigerant enters the rear-row microchannel heat exchanger through the fourth ball valve 15. Under the action of the second partition 13 and the third partition 12, the refrigerant flows through the process of 3 flat tubes, flows out of the rear-row microchannel heat exchanger from the sixth ball valve 20, and then evenly supplies liquid to the front-row microchannel heat exchanger through the second distribution pipe 10 and the third distribution pipe 09. The refrigerant flows through the process of 1 flat tube. The total refrigerant process under the intermediate load condition is 4 flat tubes; when the double-row microchannel heat exchanger works as a condenser with a small load, the second ball valve 17 and the seventh ball valve 19 are opened, and the refrigerant enters the front-row microchannel heat exchanger only through the second distribution pipe 10. The second distribution pipe 10 evenly supplies liquid to the rear half of the front-row microchannel heat exchanger, and the refrigerant only flows through the process of 2 flat tubes.

[0010] Compared with the prior art, the present invention has the following advantages:

[0011] 1. The present invention proposes a variable-flow double-row microchannel heat exchanger and a control method thereof, which can adjust the flow of the heat exchanger according to different working conditions of the double-row microchannel heat exchanger to achieve the optimal flow design corresponding to the evaporator and the condenser.

[0012] 2. The present invention proposes a variable-flow double-row microchannel heat exchanger and a control method thereof, which can adjust the heat exchange area through which the refrigerant flows according to the working conditions of the double-row microchannel heat exchanger under different loads, reduce the pressure drop on the refrigerant side, and improve the heat exchange performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a schematic diagram of the refrigerant flow when the variable-flow double-row microchannel heat exchanger described in the present invention works at full load as an evaporator.

[0014] Figure 2 This is a schematic diagram of the refrigerant flow when the variable-flow double-row microchannel heat exchanger described in the present invention works as an evaporator at intermediate load.

[0015] Figure 3 This is a schematic diagram of the refrigerant flow when the variable-flow double-row microchannel heat exchanger described in the present invention is used as an evaporator working at a low load.

[0016] Figure 4 This is a schematic diagram of the refrigerant flow when the variable-flow double-row microchannel heat exchanger described in the present invention works as a condenser at full load.

[0017] Figure 5 This is a schematic diagram of the refrigerant flow when the variable-flow double-row microchannel heat exchanger described in the present invention works as an intermediate load of the condenser.

[0018] Figure 6 This is a schematic diagram of the refrigerant flow when the variable-flow double-row microchannel heat exchanger described in the present invention is used as a condenser working at a low load. DETAILED DESCRIPTION

[0019] The specific implementation modes of the present invention are described in detail below with reference to the accompanying drawings.

[0020] like Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 and Figure 6As shown, the variable flow double-row microchannel heat exchanger of the present invention comprises a first collecting pipe 01, a second collecting pipe 02, a third collecting pipe 05 and a fourth collecting pipe 06, a plurality of flat tubes 04 arranged between the first collecting pipe 01 and the second collecting pipe 02, the third collecting pipe 05 and the fourth collecting pipe 06 and connecting the first collecting pipe 01 and the second collecting pipe 02, the third collecting pipe 05 and the fourth collecting pipe 06, and fins 03 installed between adjacent flat tubes. The first collecting pipe 01, the second collecting pipe 02, the flat tubes 04 and the fins 03 constitute a front-row microchannel heat exchanger, and the third collecting pipe 05 and the fourth collecting pipe 06 constitute a front-row microchannel heat exchanger. 06, flat tubes 04 and fins 03 constitute a rear microchannel heat exchanger; the first baffle 14 is arranged at 1 / 2l inside the second collecting tube 02, the second baffle 13 is arranged at 1 / 2l inside the third collecting tube 05, and the third baffle 12 is installed at 1 / 3l near the left end of the fourth collecting tube 06, where l is the length of the collecting tube; the first distribution pipe 11 is installed inside the first collecting tube 01, the second distribution pipe 10 is installed inside the second collecting tube 02, and is located on the right side of the first baffle 14 without passing through the first baffle 14, and the third distribution pipe 09 is also installed inside the second collecting tube 02, and passes through the first partition 14. The fourth distribution pipe 08 is installed inside the third liquid collecting pipe 05 and passes through the second partition 13. The fifth distribution pipe 07 is installed inside the fourth liquid collecting pipe 06 and passes through the third partition 12. The length of the first distribution pipe 11, the fourth distribution pipe 08 and the fifth distribution pipe 07 is l and has holes uniformly opened along the length of the pipe. The length of the second distribution pipe 10 is 1 / 2l and has holes uniformly opened along the length of the pipe. The length of the third distribution pipe 09 is l and has holes uniformly opened only in the rear half. The opening sections are all located on the left side of the first partition 14. The first ball valve 18 and the fifth ball valve 21 are separated. The first ball valve 18, the second ball valve 17 and the third ball valve 16 are connected to the first distribution pipe 11 and the third distribution pipe 09 respectively, and the third ball valve 16 and the sixth ball valve 20 are connected to the two ends of the fourth distribution pipe 08; the second ball valve 17 and the fourth ball valve 15 are connected to the left ends of the second collecting pipe 02 and the fourth collecting pipe 06 respectively, but are not connected to the third distribution pipe 09 and the fifth distribution pipe 07; the first ball valve 18, the second ball valve 17 and the third ball valve 16 are connected to the inlet pipeline of the heat exchanger; the second distribution pipe 10, the sixth ball valve 20, the fifth ball valve 21 and one end of the seventh ball valve 19 are connected, and the other end of the seventh ball valve 19 is connected to the fourth ball valve 15 and the outlet pipeline of the heat exchanger.

[0021] By installing the second partition 13 and the third partition 12 at different positions in the third collecting pipe 05 and the fourth collecting pipe 06, and installing the second distribution pipe 10 and the third distribution pipe 09 of different lengths in the second collecting pipe 02, combined with the switch of the ball valve, different flow designs can be realized when the double-row microchannel heat exchanger is used as an evaporator and a condenser, and the flow design of the double-row microchannel heat exchanger under different load conditions can also be realized. When the heat exchanger works as an evaporator, fewer flows can reduce the pressure drop on the refrigerant side, thereby improving the heat exchange performance; when the heat exchanger works as a condenser, more flows can increase the flow rate of the refrigerant, thereby improving the heat exchange performance. In addition, when the heat exchanger works under low load conditions, the refrigerant flow is small, and only a small heat exchange area is required to meet the heat exchange requirements.

[0022] like Figure 1 As shown, when the double-row microchannel heat exchanger works at full load as an evaporator, the first ball valve 18, the third ball valve 16, the fourth ball valve 15, the fifth ball valve 21 and the seventh ball valve 19 are opened, and the refrigerant enters the front row and the rear row of microchannel heat exchangers through the first ball valve 18 and the third ball valve 16 respectively, and the refrigerant flows through all the flat tubes and the process is one flat tube.

[0023] like Figure 2 As shown, when the double-row microchannel heat exchanger works as an evaporator intermediate load, the first ball valve 18, the fourth ball valve 15, the fifth ball valve 21 and the sixth ball valve 20 are opened, and the refrigerant enters the front-row microchannel heat exchanger from the first ball valve 18, and then flows out of the front-row microchannel heat exchanger through the second distribution pipe 10 and the third distribution pipe 09, and then flows through the sixth ball valve 20 to enter the rear-row microchannel heat exchanger. The refrigerant flows through all the flat tubes and the process is 2 flat tubes.

[0024] like Figure 3 As shown, when the double-row microchannel heat exchanger works as an evaporator with a small load, the first ball valve 18, the fifth ball valve 21 and the seventh ball valve 19 are opened, and the refrigerant enters the front-row microchannel heat exchanger through the first ball valve 18. The refrigerant only flows through the flat tubes of the front-row microchannel heat exchanger and the process is one flat tube.

[0025] like Figure 4 As shown, when the double-row microchannel heat exchanger works at full load as a condenser, the second ball valve 17, the fourth ball valve 15 and the sixth ball valve 20 are opened, and the refrigerant enters the rear-row microchannel heat exchanger through the fourth ball valve 15. Under the action of the second partition 13 and the third partition 12, the refrigerant flows through the process of 3 flat tubes, and then flows out of the rear-row microchannel heat exchanger through the sixth ball valve 20, and then flows into the front-row microchannel heat exchanger from the second distribution pipe 10. The second distribution pipe 10 evenly supplies liquid to the rear half of the front-row microchannel heat exchanger. The refrigerant flows through the process of 2 flat tubes. The total refrigerant process under full load conditions is 5 flat tubes.

[0026] like Figure 5 As shown, when the double-row microchannel heat exchanger works as a condenser at an intermediate load, the first ball valve 18, the fourth ball valve 15, the fifth ball valve 21 and the sixth ball valve 20 are opened, and the refrigerant enters the rear-row microchannel heat exchanger through the fourth ball valve 15. Under the action of the second partition plate 13 and the third partition plate 12, the refrigerant flows through the process of 3 flat tubes, flows out of the rear-row microchannel heat exchanger from the sixth ball valve 20, and then uniformly supplies liquid to the front-row microchannel heat exchanger through the second distribution pipe 10 and the third distribution pipe 09. The refrigerant flows through the process of 1 flat tube. The total refrigerant process under the intermediate load condition is 4 flat tubes.

[0027] like Figure 6 As shown, when the double-row microchannel heat exchanger works as a condenser with a small load, the second ball valve 17 and the seventh ball valve 19 are opened, and the refrigerant enters the front-row microchannel heat exchanger only through the second distribution pipe 10. The second distribution pipe 10 evenly supplies liquid to the rear half of the front-row microchannel heat exchanger, and the refrigerant only flows through the process of two flat tubes.

Claims

1. A variable flow double-row microchannel heat exchanger, characterized in that: The invention comprises a first collecting pipe (01), a second collecting pipe (02), a third collecting pipe (05) and a fourth collecting pipe (06); a plurality of flat tubes (04) arranged between the first collecting pipe (01) and the second collecting pipe (02), the third collecting pipe (05) and the fourth collecting pipe (06) and connecting the first collecting pipe (01) and the second collecting pipe (02), the third collecting pipe (05) and the fourth collecting pipe (06); and fins (03) installed between adjacent flat tubes; the first collecting pipe (01), the second collecting pipe (02), the flat tubes (04) and the fins (03) constitute a front-row microchannel heat exchanger; the third collecting pipe (05), the fourth collecting pipe (06) and the flat tubes (04) and fins (03) form a rear-row microchannel heat exchanger; the first baffle (14) is arranged at 1 / 2l inside the second collecting tube (02), the second baffle (13) is arranged at 1 / 2l inside the third collecting tube (05), and the third baffle (12) is installed at 1 / 3l near the left end of the fourth collecting tube (06), where l is the length of the collecting tube; the first distribution pipe (11) is installed inside the first collecting tube (01), the second distribution pipe (10) is installed inside the second collecting tube (02) and is located on the right side of the first baffle (14), the third distribution pipe (09) is also installed inside the second collecting tube (02) and passes through the first baffle (14), and the fourth distribution pipe (09) is installed inside the second collecting tube (02) and passes through the first baffle (14). The distribution pipe (08) is installed inside the third liquid collecting pipe (05) and passes through the second partition (13). The fifth distribution pipe (07) is installed inside the fourth liquid collecting pipe (06) and passes through the third partition (12). The length of the first distribution pipe (11), the fourth distribution pipe (08) and the fifth distribution pipe (07) is l and holes are evenly opened along the length of the pipe. The length of the second distribution pipe (10) is 1 / 2l and holes are evenly opened along the length of the pipe. The length of the third distribution pipe (09) is l and holes are evenly opened only in the rear half. All the opening sections are located on the left side of the first partition (14). The first ball valve (18) and the fifth ball valve (21) are respectively connected to the first distribution pipe (11) and the third The first ball valve (18), the second ball valve (17), and the third ball valve (16) are connected to the distribution pipe (09); the third ball valve (16) and the sixth ball valve (20) are connected to the two ends of the fourth distribution pipe (08); the second ball valve (17) and the fourth ball valve (15) are connected to the left ends of the second collecting pipe (02) and the fourth collecting pipe (06) respectively, but are not connected to the third distribution pipe (09) and the fifth distribution pipe (07); the first ball valve (18), the second ball valve (17), and the third ball valve (16) are connected to the inlet pipeline of the heat exchanger; the second distribution pipe (10), the sixth ball valve (20), the fifth ball valve (21) and one end of the seventh ball valve (19) are connected, and the other end of the seventh ball valve (19) is connected to the fourth ball valve (15) and the outlet pipeline of the heat exchanger; By installing the second baffle (13) and the third baffle (12) at different positions in the third collecting pipe (05) and the fourth collecting pipe (06), and installing the second distribution pipe (10) and the third distribution pipe (09) of different lengths in the second collecting pipe (02), and combining with the switch of the ball valve, different flow designs when the double-row microchannel heat exchanger is used as an evaporator and a condenser can be realized, and the flow design of the double-row microchannel heat exchanger under different load conditions can also be realized; when the heat exchanger works as an evaporator, fewer flows can reduce the pressure drop on the refrigerant side, thereby improving the heat exchange performance; when the heat exchanger works as a condenser, more flows can increase the flow rate of the refrigerant, thereby improving the heat exchange performance; in addition, when the heat exchanger works under a small load condition, the refrigerant flow is small, and only a small heat exchange area is required to meet the heat exchange requirements.

2. The control method of a variable flow double-row microchannel heat exchanger according to claim 1, characterized in that: When the double-row microchannel heat exchanger works at full load as an evaporator, the first ball valve (18), the third ball valve (16), the fourth ball valve (15), the fifth ball valve (21) and the seventh ball valve (19) are opened, and the refrigerant enters the front row microchannel heat exchanger and the rear row microchannel heat exchanger through the first ball valve (18) and the third ball valve (16) respectively, and the refrigerant flows through all the flat tubes and the flow process is one flat tube; when the double-row microchannel heat exchanger works at intermediate load as an evaporator, the first ball valve (18), the fourth ball valve (15), the fifth ball valve (21) and the sixth ball valve (20) are opened, and the refrigerant The refrigerant enters the front row microchannel heat exchanger from the first ball valve (18), then flows out of the front row microchannel heat exchanger through the second distribution pipe (10) and the third distribution pipe (09), and then flows through the sixth ball valve (20) into the rear row microchannel heat exchanger. The refrigerant flows through all the flat tubes and the flow path is two flat tubes. When the double-row microchannel heat exchanger works as an evaporator with a small load, the first ball valve (18), the fifth ball valve (21) and the seventh ball valve (19) are opened, and the refrigerant enters the front row microchannel heat exchanger through the first ball valve (18). The refrigerant only flows through the flat tubes of the front row microchannel heat exchanger and the flow path is one flat tube. When the double-row microchannel heat exchanger works at full load as a condenser, the second ball valve (17), the fourth ball valve (15) and the sixth ball valve (20) are opened, and the refrigerant enters the rear-row microchannel heat exchanger through the fourth ball valve (15). Under the action of the second baffle (13) and the third baffle (12), the refrigerant flows through the process of three flat tubes, then flows out of the rear-row microchannel heat exchanger through the sixth ball valve (20), and then flows into the front-row microchannel heat exchanger from the second distribution pipe (10). The second distribution pipe (10) evenly supplies liquid to the rear half of the front-row microchannel heat exchanger. The refrigerant flows through the process of two flat tubes. Under full load conditions, the total refrigerant process is five flat tubes. When the double-row microchannel heat exchanger works at intermediate load as a condenser, the first ball valve (18), the fourth ball valve (15), the fifth ball valve (21) and the sixth ball valve (22) are opened. The valve (20) is opened, and the refrigerant enters the rear microchannel heat exchanger through the fourth ball valve (15). Under the action of the second partition plate (13) and the third partition plate (12), the refrigerant flows through the process of three flat tubes, flows out of the rear microchannel heat exchanger from the sixth ball valve (20), and then is evenly supplied to the front microchannel heat exchanger through the second distribution pipe (10) and the third distribution pipe (09). The refrigerant flows through the process of one flat tube. Under the medium load condition, the total refrigerant process is four flat tubes; when the double-row microchannel heat exchanger works as a condenser with a small load, the second ball valve (17) and the seventh ball valve (19) are opened, and the refrigerant enters the front microchannel heat exchanger only through the second distribution pipe (10). The second distribution pipe (10) evenly supplies liquid to the rear half of the front microchannel heat exchanger, and the refrigerant flows through the process of only two flat tubes.

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