A carbon dioxide air-conditioning and heat pump system using a finless microtube heat exchanger

Abstract

The present invention discloses a carbon dioxide air-conditioning heat pump system using a finless microtube heat exchanger, which includes a compressor, a condenser, a throttling device, an evaporator and a liquid accumulator connected in sequence through pipelines to form a loop. Both the condenser and the evaporator adopt microtube heat exchangers. The microtube heat exchanger includes a metal tube array assembly and two buffer tube cavities arranged at both ends of the metal tube array assembly. A refrigerant inlet is provided on one of the buffer tube cavities, and a refrigerant outlet is provided on the other buffer tube cavity. The metal tube array assembly is composed of multiple rows of metal tubes arranged in combination. The hydraulic diameter of all the metal tubes is less than 2 mm, and there are no fins on the outer surface of the metal tubes. The microtube heat exchanger used in the present invention has a large pressure tolerance and extremely high heat transfer efficiency, and can improve the overall efficiency of the carbon dioxide refrigeration system.

Description

Technical Field

[0001] This application belongs to the technical field of air conditioning, and particularly relates to a carbon dioxide air-conditioning heat pump system using a finless microtube heat exchanger. Background Technique

[0002] Refrigeration and air-conditioning systems are widely used in various refrigeration and air-conditioning applications. Against the backdrop of widespread concern about the greenhouse effect, the air-conditioning industry has witnessed a wave of replacing existing refrigerants. In household air conditioners, traditional R22 will gradually be replaced by other environmentally friendly refrigerants such as R410A and R290 due to its certain ODP and relatively high GWP values. Based on environmental protection requirements, the application of the environmentally friendly refrigerant CO2 has attracted great attention in the academic and industrial circles. Compared with R134a and R1234yf, CO2 has obvious advantages in terms of low greenhouse effect index (GWP = 1), low ozone depletion potential (ODP = 0), non-flammability, non-toxicity, and stable chemical properties. CO₂ has a relatively large latent heat of vaporization and a quite high refrigerating capacity per unit volume, so the size of the compressor and its components is relatively small. Carbon dioxide is favored by a wide range of businesses due to its low price, safety, harmlessness, environmental friendliness, etc. However, the heat rejection and heat absorption processes of CO2 occur in the transcritical state, requiring the heat exchanger using it to have a relatively high pressure resistance. Traditional heat exchangers are not sufficient to withstand such high pressures. By optimizing the header and other means to increase the burst pressure, it is necessary to significantly increase the thickness of the header and flat tubes to improve the pressure resistance, which further increases the weight of the heat exchanger. Summary of the Invention

[0003] Aiming at the problems of insufficient pressure resistance and low refrigeration efficiency of traditional heat exchangers in the existing air-conditioning systems, the purpose of the present invention is to provide a carbon dioxide air-conditioning heat pump system using a finless microtube heat exchanger. The finless microtube heat exchanger used in the present invention has a hydraulic diameter of the microtube less than 2 mm. The smaller diameter can withstand higher pressures, which is beneficial to the safe, stable, and efficient operation of the carbon dioxide refrigerant.

[0004] The present invention is realized through the following technical solutions:

[0005] A carbon dioxide air-conditioning heat pump system using a finless microtube heat exchanger includes a compressor, a condenser, a throttling device, an evaporator, and a liquid reservoir that are sequentially connected through pipelines to form a loop. Both the condenser and the evaporator use microtube heat exchangers. The microtube heat exchanger includes a metal tube array component and two buffer cavities provided at both ends of the metal tube array component. A refrigerant inlet is provided on one of the buffer cavities, and a refrigerant outlet is provided on the other buffer cavity; the metal tube array component is composed of multiple rows of metal tubes arranged in combination, and the hydraulic diameters of all the metal tubes are less than 2 mm, and there are no fins on the outer surfaces of the metal tubes.

[0006] Furthermore, the wall thickness of the metal tube is 0.08 mm to 0.6 mm so as to be able to withstand the high-pressure requirements of the carbon dioxide system.

[0007] Furthermore, in the microtube heat exchanger structures of the condenser and the evaporator, a blower is provided on the outside of one side of the microtube heat exchanger, and the blower blows air for heat exchange on the metal tube bundle assembly; in the structure of the metal tube bundle assembly, the sizes of the metal tubes in the same row are the same, the hydraulic diameters of the metal tubes in different rows first gradually decrease and then gradually increase, the metal tubes in different rows are arranged in alignment respectively and the center points are located on the same straight line, and the air blown by the blower blows along the direction from the first row of metal tubes to the last row of metal tubes.

[0008] Furthermore, the outer tube walls of the multiple rows of metal tubes of the metal tube bundle assembly are arranged in an equidistant sequence. Along the horizontal direction of the blower blowing air, the hydraulic diameters of the metal tubes in different rows first gradually and uniformly decrease and then gradually and uniformly increase. The hydraulic diameter of the first row of metal tubes is 1 mm, and the hydraulic diameter of the adjacent lower row of metal tubes gradually and uniformly decreases at a rate of 0.15 to 0.25 mm until the hydraulic diameter of the thinnest metal tube in the middle reaches 0.4 to 0.5 mm, and then the hydraulic diameter of the metal tube gradually and uniformly increases at the same rate of 0.15 to 0.25 mm until the hydraulic diameter of the last row of metal tubes reaches 1 mm again.

[0009] Furthermore, the amplitude of the gradual and uniform decrease or the gradual and uniform increase of the hydraulic diameter of the metal tube is 0.2 mm, and the hydraulic diameter of the thinnest metal tube is 0.4 mm. That is, the sorting method of the hydraulic diameters of the metal tubes in different rows is successively: 1, 0.8, 0.6, 0.4, 0.6, 0.8, and 1 mm.

[0010] Furthermore, the blowing speed of the blower is 0.5 to 0.7 m / s, and the wall thickness of all the metal tubes is 0.1 mm.

[0011] Furthermore, the outer tube wall spacing of the metal tubes in the same row and in different rows is within the range of 0.08 to 0.2 mm.

[0012] Furthermore, the outer tube wall spacing of the metal tubes in the same row and in different rows is 0.1 mm.

[0013] Optionally, the metal microtubes are made of copper tubes, which have the advantages of easy processing and manufacturing process and less carbon emissions. The characteristics of the copper material itself, such as sterilization, corrosion resistance, and high pressure resistance, can meet the application requirements of higher air quality requirements or other special occasions, and have a large tolerance pressure and extremely high heat exchange efficiency.

[0014] Optionally, the refrigerant used is carbon dioxide.

[0015] Furthermore, a pressure sensor and a temperature sensor are provided at the outlet of the compressor. The outlet of the compressor is connected to the inlet of the condenser through a pipeline. A temperature sensor is provided at the outlet of the condenser. The outlet of the condenser is connected to the inlet of the evaporator through a throttling device. A temperature sensor is provided at the outlet of the evaporator. The outlet of the evaporator is connected to the inlet of the compressor through a liquid receiver by a pipeline, forming a refrigeration cycle path; wherein, a pressure sensor is provided on the pipeline between the liquid receiver and the inlet of the compressor.

[0016] Furthermore, the throttling device adopts a capillary tube.

[0017] Compared with the prior art, the technical effects achieved by the present invention are as follows:

[0018] 1) The present invention obtains a more efficient heat exchanger system by reducing the hydraulic diameter of the metal tube, and the metal tube with a smaller diameter described in the present invention can withstand higher pressures, which is beneficial to the safe, stable and efficient operation of carbon dioxide refrigerant; the microtube heat exchanger is arranged in sequence, and the tube diameter along the direction of the blowing wind can be appropriately changed so as to minimize the wind resistance as much as possible, thereby reducing the pressure loss and improving the overall efficiency of the carbon dioxide refrigeration system.

[0019] 2) The heat exchanger with different tube diameter arrangements adopted by the present invention can reduce the air-side pressure drop and improve the heat transfer efficiency compared with the uniform tube diameter arrangement. The cavitation zone and stagnation zone formed by the different tube diameter arrangements designed by the present invention are significantly less than those of the uniform tube diameter arrangement. The reduction of the cavitation zone and stagnation zone improves the fluidity and heat transfer performance of the particles, increases the average flow velocity during the whole process of the blowing wind passing through the metal tube bundle assembly, raises the surface heat transfer coefficient, and increases the total heat transfer amount.

[0020] 3) The overall system of the present invention only needs to appropriately change the tube diameter of the microtube heat exchanger, greatly simplifies the system structure, and makes the system have higher reliability.

[0021] 4) The present invention not only achieves better air-conditioning control and energy-saving effects, but also does not adopt a dehumidifying solution and a solid adsorbent that are toxic, harmful and strongly corrosive to the human body, and has the advantages of environmental protection, health and very high safety characteristics; at the same time, it also has the advantages of compact structure, convenient later maintenance and product upgrade, low cost and reliable operation.

[0022] 5) Compared with the heat exchanger with a traditional uniform tube diameter arrangement, the heat exchanger with different tube diameter combinations arranged consumes less material and is lighter in weight. For heat exchangers with the same power, the combined tube diameter usually saves more than 25% in cost compared with the uniform tube diameter. At the same time, the refrigerant filling amount of the heat exchanger with the combined tube diameter is also significantly reduced compared with the uniform tube diameter, usually reduced by 20% - 30%. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a schematic diagram of a carbon dioxide air-conditioning heat pump system using a finless microtube heat exchanger according to the present application;

[0024] Figure 1 It includes a liquid reservoir 1, a compressor 2, a condenser 3, an evaporator 4, a capillary tube 5, a metal tube bundle assembly 6, and a buffer tube cavity 7.

[0025] Figure 2 is a schematic diagram of the structure of the finless microtube heat exchanger according to the present application.

[0026] Figure 3 It is a schematic diagram of the sequential arrangement of the internal metal tubes of the microtube heat exchanger according to the present application.

[0027] Figure 4a It is the simulation result of the air-side pressure drop of the heat exchanger with different pipe diameter arrangements designed by the present invention.

[0028] Figure 4b It is the simulation result of the air-side pressure drop of the heat exchanger arranged with a 1mm pipe diameter uniformly. Specific Embodiments

[0029] The present invention will be further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0030] Embodiment: Control Figure 1

[0031] A carbon dioxide air-conditioning heat pump system using a finless microtube heat exchanger includes a compressor 2, a condenser 3, a throttling device, an evaporator 4, and a liquid reservoir 1 that are sequentially connected through pipes to form a loop. Both the condenser 3 and the evaporator 4 adopt the structure of a microtube heat exchanger. The microtube heat exchanger includes a metal tube bundle assembly 6 and two buffer tube cavities 7 provided at both ends of the metal tube bundle assembly 6. A refrigerant inlet is provided on one of the buffer tube cavities 7, and a refrigerant outlet is provided on the other buffer tube cavity 7; the metal tube bundle assembly 6 is composed of multiple rows of metal tubes with different hydraulic diameters arranged in combination. The sizes of the metal tubes in the same row are the same. The hydraulic diameters of all the metal tubes are all less than 2 mm, and there are no fins on the outer surfaces of the metal tubes.

[0032] Further, the throttling device adopts a capillary tube 5.

[0033] In this embodiment, in order to withstand the high-pressure requirements of the carbon dioxide system to the greatest extent, the wall thickness of the metal microtubes is 0.1 mm to 0.6 mm.

[0034] Further, the microtubes are resistant to high pressure, have a large tolerance pressure and extremely high heat transfer efficiency.

[0035] The carbon dioxide air-conditioning heat pump system of the present application includes the microchannel heat exchanger as described above.

[0036] In the system of the present invention, a blower is provided on one side of the microtube heat exchanger for blowing air to exchange heat with the metal tube assembly 6; the multi-row metal tubes of the metal tube assembly 6 are arranged in sequence at equal intervals. Along the horizontal direction of the blower blowing air, the hydraulic diameters of the metal tubes in different rows gradually and uniformly decrease first, and then gradually and uniformly increase. The hydraulic diameter of the first row of metal tubes is 1 mm, and the hydraulic diameter of the adjacent lower row of metal tubes gradually and uniformly decreases by an amplitude of 0.15 - 0.25 mm until the hydraulic diameter of the thinnest metal tube in the middle reaches 0.4 - 0.5 mm, and then the hydraulic diameter of the metal tubes gradually and uniformly increases by the same amplitude of 0.15 - 0.25 mm until the hydraulic diameter of the last row of metal tubes reaches 1 mm again. In contrast Figure 3 In it, the metal tubes in different rows are arranged in alignment respectively and the center points are located on the same straight line.

[0037] Preferably, the amplitude of the gradual and uniform decrease or gradual and uniform increase of the hydraulic diameter of the metal tubes is 0.2 mm, and the hydraulic diameter of the thinnest metal tube is 0.4 mm. That is, the sorting order of the hydraulic diameters of the metal tubes in different rows is successively: 1, 0.8, 0.6, 0.4, 0.6, 0.8, and 1 mm.

[0038] Preferably, the blowing speed of the blower is 0.5 - 0.7 m / s, the wall thickness of all the metal tubes is 0.1 mm, and the outer wall spacing between the metal tubes in the same row and between different rows of metal tubes is 0.1 mm.

[0039] In the refrigeration mode, the exhaust port of the compressor 2 is connected to the inlet of the condenser 3 through a pipeline, the outlet of the condenser 3 is connected to the inlet of the evaporator 4 through a throttling device, and the outlet of the evaporator 4 is connected to the inlet of the compressor 2 through a pipeline via the liquid receiver 1, forming a refrigeration cycle path.

[0040] Specifically, in the refrigeration mode, the exhaust port of the compressor 2 is connected to the inlet of the condenser 3, and the inlet of the compressor 2 is connected to the outlet of the liquid receiver 1. A pressure sensor is provided between the outlet of the liquid receiver 1 and the inlet of the compressor 2 to monitor the state of the refrigerant. The compressor 2 compresses the refrigerant to high temperature and high pressure and then enters the condenser 3. A pressure sensor and a temperature sensor are provided between the exhaust port of the compressor 2 and the inlet of the condenser 3 to monitor the state of the refrigerant. After the refrigerant is cooled in the condenser 3, it enters the evaporator 4 through a throttling device. A temperature sensor is provided between the outlet of the condenser 3 and the inlet of the evaporator 4 to monitor the state of the refrigerant. The refrigerant exchanges heat in the evaporator 4, and the refrigerant liquid that fails to be completely evaporated in the evaporator 4 flows into the liquid receiver 1 through the outlet of the evaporator 4, and the refrigerant vapor after further heat absorption enters the inlet of the compressor 2 to complete the refrigeration cycle.

[0041] Specifically, for the heat exchanger with different pipe diameter arrangements adopted in the design of the present invention, compared with the heat exchanger with a uniform pipe diameter of 1 mm, when the blower blows air on one side of the metal tube bundle assembly 6 at a speed of 0.6 m / s, the simulation of the air pressure drop on the other side of the metal tube bundle assembly 6 is carried out. The conditions and results of the experiment are as follows:

[0042] 1) The structure of the heat exchanger with different pipe diameter arrangements adopted in the design of the present invention includes: the hydraulic diameter of the metal pipes gradually and uniformly decreases or increases by 0.2 mm, and the hydraulic diameter of the thinnest metal pipe is 0.4 mm. That is, the sorting method of the hydraulic diameters of the metal pipes in different rows is as follows: 1, 0.8, 0.6, 0.4, 0.6, 0.8, and 1 mm. The outer wall spacing between the metal pipes in the same row and between different rows is 0.1 mm, and the wall thickness of the metal pipes is 0.1 mm.

[0043] 2) The structure of the heat exchanger with a uniform pipe diameter of 1 mm includes: the hydraulic diameter of all metal pipes is 1 mm, the outer wall spacing between the metal pipes in the same row and between different rows is 0.1 mm, and the wall thickness of the metal pipes is 0.1 mm.

[0044] 3) The simulation results of the air-side pressure drop of the heat exchanger with different pipe diameter arrangements adopted in the design of the present invention (the air-side pressure drop is the pressure drop between the upstream side and the downstream side of the metal tube bundle assembly 6 of the heat exchanger when the wind blows through) are as Figure 4a shown. The simulation results of the air-side pressure drop of the heat exchanger with a uniform pipe diameter of 1 mm are as Figure 4b shown. The results show that: the air-side pressure drop of the heat exchanger with a uniform pipe diameter arrangement is 5.173 Pa, and the air-side pressure drop of the heat exchanger with different pipe diameter arrangements is 3.951 Pa. The air-side pressure drop of the heat exchanger with different pipe diameter arrangements adopted in this design is reduced by 23.6% compared with the heat exchanger with a uniform pipe diameter arrangement.

[0045] For the heat exchanger with different pipe diameter arrangements adopted in the design of the present invention, compared with the heat exchanger with a uniform pipe diameter of 1 mm, the cavity area and stagnation area between the circular pipes formed by the different pipe diameter arrangements are significantly less than those of the uniform pipe diameter arrangement. The reduction of the cavity area and stagnation area improves the fluidity and heat transfer performance of the particles.

[0046] In addition, for the heat exchanger with different pipe diameter arrangements adopted in the design, compared with the heat exchanger with a uniform pipe diameter of 0.4 mm, although the cavity area between the circular pipes formed by the 0.4 mm pipe diameter arrangement is less, the stagnation area is still more.

[0047] Compared with the heat exchanger with a traditional uniform pipe diameter layout, the heat exchanger with a combined layout of different pipe diameters consumes less material and is lighter in weight. For heat exchangers with the same power, the combined pipe diameter usually saves more than 25% in cost compared to the uniform pipe diameter. At the same time, the refrigerant filling volume of the heat exchanger with a combined pipe diameter is also significantly reduced compared to the uniform pipe diameter, usually decreasing by 20% to 30%.

[0048] In the embodiments of the present invention, a carbon dioxide air-conditioning heat pump system using a finless microtube heat exchanger can minimize the wind resistance, thereby reducing the pressure loss and improving the overall efficiency of the carbon dioxide refrigeration system.

[0049] The content described in this specification is only a list of the implementation forms of the inventive concept, and the protection scope of the present invention should not be regarded as limited to the specific forms stated in the embodiments.

Claims

1. A carbon dioxide air conditioning heat pump system using a finless micro-tube heat exchanger, comprising a compressor (2), a condenser (3), a throttling device, an evaporator (4), and a liquid reservoir (1) connected in sequence by pipes to form a loop, characterized in that: The condenser (3) and the evaporator (4) both adopt a micro-tube heat exchanger, which includes a metal tube assembly (6) and two buffer tube cavities (7) arranged at both ends of the metal tube assembly (6), one of the buffer tube cavities (7) is provided with a refrigerant inlet, and the other buffer tube cavity (7) is provided with a refrigerant outlet; the metal tube assembly (6) is composed of a plurality of rows of metal tubes, the hydraulic diameters of all the metal tubes are less than 2 mm, and the outer surfaces of the metal tubes are not finned; The wall thickness of the metal tube is 0.08mm~0.6mm to be able to withstand the high pressure requirements of the carbon dioxide system; In the micro-tube heat exchanger structure of the condenser (3) and the evaporator (4), a fan is provided outside one side of the micro-tube heat exchanger, and the fan blows air to the metal tube assembly (6) for heat exchange; in the structure of the metal tube assembly (6), the metal tubes in the same row have the same size, the hydraulic diameters of the metal tubes in different rows gradually decrease and then gradually increase, the metal tubes in different rows are respectively aligned and arranged with their centers located on the same straight line, and the air blown by the fan blows in the direction from the first row of metal tubes to the last row of metal tubes.

2. The carbon dioxide air conditioning heat pump system using a finless micro-tube heat exchanger according to claim 1, characterized in that: The outer walls of the multiple rows of metal tubes of the metal tube assembly (6) are arranged in sequence with equal spacing. Along the horizontal direction of the fan blowing, the hydraulic diameters of the metal tubes in different rows first gradually and evenly decrease and then gradually and evenly increase. The hydraulic diameter of the first row of metal tubes is 1 mm, and the hydraulic diameter of the adjacent next row of metal tubes gradually and evenly decreases by 0.15-0.25 mm until the hydraulic diameter of the thinnest metal tube in the middle reaches 0.4-0.5 mm, and then the hydraulic diameter of the metal tubes gradually and evenly increases by the same 0.15-0.25 mm until the hydraulic diameter of the metal tubes in the last row reaches 1 mm again.

3. The carbon dioxide air conditioning heat pump system using a finless micro-tube heat exchanger according to claim 2, characterized in that: The hydraulic diameter of the metal tube gradually decreases or increases uniformly by 0.2 mm, and the hydraulic diameter of the thinnest metal tube is 0.4 mm, that is, the hydraulic diameters of different rows of metal tubes are ranked as follows: 1, 0.8, 0.6, 0.4, 0.6, 0.8 and 1 mm.

4. The carbon dioxide air conditioning heat pump system using a finless micro-tube heat exchanger according to claim 2, characterized in that: The blowing speed of the fan is 0.5~0.7m / s, and the wall thickness of the metal tube is 0.1mm.

5. The carbon dioxide air conditioning heat pump system using a finless micro-tube heat exchanger according to claim 2, characterized in that: The distance between the outer walls of metal tubes in the same row and in different rows is within the range of 0.08~0.2mm.

6. The carbon dioxide air conditioning heat pump system using a finless micro-tube heat exchanger according to claim 5, characterized in that: The distance between the outer walls of the metal tubes in the same row and in different rows is 0.1 mm, and the metal tubes are copper tubes.

7. The carbon dioxide air conditioning heat pump system using a finless micro-tube heat exchanger according to claim 1, characterized in that: The outlet of the compressor (2) is provided with a pressure sensor and a temperature sensor. The outlet of the compressor (2) is connected to the inlet of the condenser (3) through a pipeline. The outlet of the condenser (3) is provided with a temperature sensor. The outlet of the condenser (3) is connected to the inlet of the evaporator (4) through a throttling device. The outlet of the evaporator (4) is provided with a temperature sensor. The outlet of the evaporator (4) is connected to the inlet of the compressor (2) through a pipeline via the liquid accumulator (1), thereby forming a refrigeration cycle path. A pressure sensor is provided on the pipeline between the liquid accumulator (1) and the inlet of the compressor (2).

8. The carbon dioxide air conditioning heat pump system using a finless micro-tube heat exchanger according to claim 7, characterized in that: The throttling device adopts a capillary tube (5).

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