Design method for outdoor unit structure of evaporative condensation air conditioner

Abstract

The invention discloses a design method for an outdoor unit structure of an evaporative condensation air conditioner. The design method specifically comprises the following steps that S1, a main body structure of an evaporative condensation air conditioner unit is determined; s2, basic operation parameters of an outdoor unit are set according to the unit main body structure; s3, calculating according to the basic parameters of the wet film, and determining a wet film structure; s4, according to the basic parameters of the evaporative condenser, design calculation is conducted on a heat exchanger coil of the evaporative condenser, and the structure of the evaporative condenser is determined; s5, according to the basic parameters of the air-cooled condenser, the surface area of a heat exchanger coil of the air-cooled condenser, the heat transfer area of the air side and the heat transfer area of the refrigerant side are calculated, and the structure of the air-cooled condenser is determined; and S6, according to the basic parameters of the evaporator, the heat exchange surface area of the evaporator, the number of rows of evaporator tubes, the heat transfer area of the air side, the convective heat transfer coefficient of the air side, the equivalent heat transfer coefficient of the air side and the heat transfer coefficient of the refrigerant side are calculated, and the evaporator structure is determined. The method can be used for systematically designing the outdoor unit structure of the evaporative condensation air conditioner.

Description

Technical Field

[0001] The invention relates to the technical field of evaporative condensing air conditioners, and in particular to a method for designing the structure of an external unit of an evaporative condensing air conditioner. Background Art

[0002] Evaporative condensing air conditioners are air conditioners that use evaporative condensing technology. Compared with the widely used air-cooled air conditioning system, air conditioners that use evaporative condensing technology can save more than 35% of energy, and compared with the water-cooled air conditioning system, they can save more than 15% of energy. Therefore, it has attracted the attention and R&D investment of various air conditioning manufacturers. In order to improve competitiveness, how to quickly turn the concept of evaporative condensing air conditioners with excellent performance into products with actual performance has become an important R&D goal of various air conditioning manufacturers. Summary of the invention

[0003] The present invention provides a method for designing the structure of an external unit of an evaporative condensing air conditioner, which can quickly commercialize the conceptual evaporative condensing air conditioner.

[0004] The technical solution adopted by the present invention to solve the above problem is: a method for designing the structure of an external unit of an evaporative condensing air conditioner, which specifically includes the following steps:

[0005] S1 determines the main structure of the evaporative condensing air conditioning unit, wherein the main structure of the evaporative condensing air conditioning unit includes a wet film, an evaporative condenser, an air-cooled condenser and an evaporator;

[0006] S2 sets basic operating parameters of the outdoor unit according to the main structure of the evaporative condensing air conditioning unit;

[0007] S3 designs and determines the wet film structure according to the basic parameters of the wet film, and calculates the evaporative cooling efficiency of the wet film, the air state at the wet film outlet, and the water spraying amount;

[0008] S4 performs design calculation of the evaporative condenser coil according to the basic parameters of the evaporative condenser, the wet film outlet parameters, and the basic parameters of the evaporative condenser coil, and determines the structure of the evaporative condenser;

[0009] S5 determines the structure of the air-cooled condenser according to the basic parameters of the air-cooled condenser and calculates the surface area of ​​the heat exchanger of the air-cooled condenser, the heat transfer area of ​​the air side of the air-cooled condenser, and the heat transfer area of ​​the refrigerant side of the air-cooled condenser;

[0010] S6 determines the evaporator structure based on the basic parameters of the evaporator and calculates the evaporator heat exchange surface area, the number of evaporator tube rows, the evaporator air side heat transfer area, the evaporator air side convection heat transfer coefficient, the evaporator air side equivalent heat transfer coefficient and the evaporator refrigerant side heat transfer coefficient.

[0011] Compared with the prior art, the advantage of the technical solution of the present invention is that it provides a method for quickly commercializing the conceptual evaporative condensing air-conditioning, thereby more quickly commercializing the advantageously designed evaporative condensing air-conditioning to replace the existing air-conditioning equipment with high energy consumption and reduce energy consumption.

[0012] As an improvement, the main structure of the evaporative condensing air conditioning unit in step S1 also includes a water circulation system, which includes a water tank, a water pump in the water tank that is connected to the first spray device and the second spray device, and a water collecting pan that is arranged below the wet film and the evaporative condenser coil to collect the water falling from the wet film and the evaporative condenser coil, and the water collecting pan is connected to the water tank; the first spray device is arranged between the evaporative condenser coil and the air-cooled condenser coil, and the second spray device is arranged above the wet film. When passing through the wet film, the air will increase its moisture content, and the temperature of the spray water falling from the wet film will decrease. After merging into the water tank, it can be neutralized with the temperature of the spray water falling from the evaporative condenser, thereby reducing the water temperature in the water tank; and under the action of the fan, when the wind flowing through the evaporative condenser is sucked away, it will carry part of the water mist sprayed by the first spray device, and a better cooling effect can be obtained when passing through the air-cooled condenser.

[0013] Preferably, the wet film outlet parameter design calculation in step S3 includes:

[0014] Step S31, calculation of wet film evaporative cooling efficiency, the formula is:

[0015]

[0016] Where η DEC is the wet film evaporative cooling efficiency; v y is the windward velocity of the wet film filler; ε is the specific surface area of ​​the wet film filler; δ is the thickness of the wet film filler; t g1 is the inlet air dry bulb temperature of the wet film; t s1 is the wet bulb temperature of the inlet air of the wet film;

[0017] Step S32, obtaining wet film outlet air parameters according to the wet film evaporative cooling efficiency, wherein the wet film outlet air parameters include the wet film outlet air dry bulb temperature, the wet film outlet air wet bulb temperature, the wet film outlet air specific enthalpy and the wet film inlet air moisture content;

[0018] Step S33, calculation of wet film watering amount, the formula is:

[0019] qDEC1=1.2MsminF+Δqn;

[0020] In the formula: qDEC1 is the watering amount; Msmin is the minimum watering density for direct evaporative cooling; F is the watering area; Δqn is the maximum evaporation amount of the equipment.

[0021] Preferably, the actual heat exchange area of ​​the evaporative condenser coil in step S4 is calculated as follows:

[0022] A o =φ k / K c (t k -t m );

[0023] In the formula, A o is the actual heat exchange area, φ k is the enthalpy of air at the outlet of the evaporative condenser, K c is the heat transfer coefficient of the evaporative condenser, t k is the condensation temperature, t m is the average temperature of the air outside the tube;

[0024] The required number of single tubes is calculated according to the actual heat exchange area of ​​the evaporative condenser, and the evaporative condenser structure is obtained after arrangement and design.

[0025] Preferably, the heat load of the evaporative condenser is obtained by the total condensing load according to the condensing load distribution ratio of the evaporative condenser and the air-cooled condenser; the total condensing load is composed of the cooling capacity and the compressor power and the surplus.

[0026] Preferably, the total condensing load is 1.1 times the sum of the cooling capacity and the compressor power, and the ratio of the evaporative condenser to the air-cooled condenser is 0.8:0.2. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic diagram of the structure of the evaporative condensing air conditioner used as a verification example. DETAILED DESCRIPTION

[0028] The following is a description of exemplary embodiments of the present invention in conjunction with the accompanying drawings, including various details of the embodiments of the present invention to facilitate understanding, which should be considered as merely exemplary. Therefore, it should be recognized by those of ordinary skill in the art that various changes and modifications may be made to the embodiments described herein without departing from the scope and spirit of the present invention. Similarly, for clarity and conciseness, the description of well-known functions and structures is omitted in the following description.

[0029] This preferred embodiment is a method for designing the structure of an external unit of an evaporative condensing air conditioner, which specifically includes the following steps:

[0030] S1 determines the main structure of the evaporative condensing air conditioning unit, wherein the main structure of the evaporative condensing air conditioning unit includes a wet film, an evaporative condenser, an air-cooled condenser and an evaporator;

[0031] S2 sets basic operating parameters of the outdoor unit according to the main structure of the evaporative condensing air conditioning unit;

[0032] S3 designs and determines the wet film structure according to the basic parameters of the wet film, and calculates the evaporative cooling efficiency of the wet film, the air state at the wet film outlet, and the water spraying amount;

[0033] S4 performs design calculation of the evaporative condenser coil according to the basic parameters of the evaporative condenser, the wet film outlet parameters, and the basic parameters of the evaporative condenser coil, and determines the structure of the evaporative condenser;

[0034] S5 determines the structure of the air-cooled condenser according to the basic parameters of the air-cooled condenser and calculates the surface area of ​​the heat exchanger of the air-cooled condenser, the heat transfer area of ​​the air side of the air-cooled condenser, and the heat transfer area of ​​the refrigerant side of the air-cooled condenser;

[0035] S6 determines the evaporator structure based on the basic parameters of the evaporator and calculates the evaporator heat exchange surface area, the number of evaporator tube rows, the evaporator air side heat transfer area, the evaporator air side convection heat transfer coefficient, the evaporator air side equivalent heat transfer coefficient and the evaporator refrigerant side heat transfer coefficient.

[0036] The wet film outlet parameter design calculation in step S3 includes:

[0037] Step S31, calculation of wet film evaporative cooling efficiency, the formula is:

[0038]

[0039] Where η DEC is the wet film evaporative cooling efficiency; v y is the windward velocity of the wet film filler, m / s; ε is the specific surface area of ​​the wet film filler, m 2 / m 3 ; δ is the thickness of the wet film filler, mm; t g1 is the inlet air dry bulb temperature of the wet film; t s1 is the wet bulb temperature of the inlet air of the wet film;

[0040] Step S32, obtaining wet film outlet air parameters according to the wet film evaporative cooling efficiency, wherein the wet film outlet air parameters include the wet film outlet air dry-bulb temperature, the wet film outlet air wet-bulb temperature, the wet film outlet air specific enthalpy and the wet film inlet air moisture content;

[0041] Step S33, calculation of wet film watering amount, the formula is:

[0042] qDEC1=1.2MsminF+Δqn;

[0043] Where qDEC1 is the watering rate, kg / s; Msmin is the minimum watering density for direct evaporative cooling, kg / m 2 s; F is the watering area, m 2; Δqn is the maximum evaporation capacity of the equipment, kg / s.

[0044] Preferably, the actual heat exchange area of ​​the evaporative condenser coil in step S4 is calculated as follows:

[0045] A o =φ k / K c (t k -t m );

[0046] In the formula, A o is the actual heat exchange area, φ k is the enthalpy of air at the outlet of the evaporative condenser, K c is the heat transfer coefficient of the evaporative condenser, t k is the condensation temperature, t m is the average temperature of the air outside the tube;

[0047] The required number of single tubes is calculated according to the actual heat exchange area of ​​the evaporative condenser, and the evaporative condenser structure is obtained after arrangement and design.

[0048] Preferably, the heat load of the evaporative condenser is obtained by the total condensing load according to the condensing load distribution ratio of the evaporative condenser and the air-cooled condenser; the total condensing load is composed of the cooling capacity and the compressor power and the surplus.

[0049] Preferably, the total condensing load is 1.1 times the sum of the cooling capacity and the compressor power, and the ratio of the evaporative condenser to the air-cooled condenser is 0.8:0.2.

[0050] Verification example:

[0051] As Figure 1 Taking the double evaporative condensing air conditioner shown as an example, its external unit structure includes a shell 1, a wet film 2, an evaporative condenser 3, an air-cooled condenser 4, a compressor 5, a fan 6, an evaporator and a water circulation system. The lower part of the shell 1 is provided with air inlets around, the wet film 2 is arranged on the inner side of the air inlet, the top of the shell 1 is provided with an air outlet, and the fan is installed at the air outlet; the water circulation system includes a water tank 11, a water pump 12 arranged in the water tank 11 and connected with a first spray device 13 and a second spray device 14, a water collecting pan 15 arranged below the wet film 2 and the evaporative condenser 3 coils for collecting water falling from the wet film 2 and the evaporative condenser 3 coils, the water collecting pan 15 is connected to the water tank 11 and is provided with a filter 16, and flow valves are respectively provided on the water supply pipelines of the water pump 12 and the first spray device 13 and the second spray device 14; the first spray device 13 is arranged between the evaporative condenser 3 coils and the air-cooled condenser 4 coils, and the second spray device 14 is arranged above the wet film 2.

[0052] Among them, the initial basic parameters of the outdoor unit are as follows:

[0053] The atmospheric pressure is 100590Pa, the outdoor design calculated dry bulb temperature (design condition) of summer air conditioning is 35.1℃, the outdoor design calculated wet bulb temperature (design condition) of summer air conditioning is 28℃, the indoor return air dry bulb temperature is 27℃, the indoor return air wet bulb temperature is 19℃, the indoor supply air dry bulb temperature is 15℃, the refrigerant is R410A, the cooling capacity is 30kW, the condensing temperature is 40℃, the evaporating temperature is 10℃, the evaporator material and form are copper-aluminum fins, unit mm, the air-cooled condenser material and form are copper-aluminum fins, unit mm, the evaporative condenser material and form are copper tube bare tube, unit mm, the surface cooler material and form are copper-aluminum fins, unit mm, the air-cooled condenser heat exchange tube diameter is 9.52m m, the air-cooled condenser fin spacing is 1.8mm, the air-cooled condenser fin thickness is 0.105mm, the air-cooled condenser tube spacing is 25mm, the air-cooled condenser row spacing is 21.65mm, the evaporative condenser heat exchange tube diameter is 9.52mm, the evaporative condenser heat exchange tube wall thickness is 0.3mm, the evaporator tube diameter is 7mm, the evaporator fin spacing is 2.0mm, the evaporator fin thickness is 0.105mm, the evaporator tube spacing is 21mm, the evaporator row spacing is 18.19mm, the surface cooler tube diameter is 9.52mm, the surface cooler fin spacing is 1.8mm, the surface cooler fin thickness is 0.105mm, the surface cooler tube spacing is 25mm, the surface cooler row spacing is 21.65mm, and the dimensions of the four air inlets are 800mm×300mm.

[0054] Among them, the basic parameters of wet film design are as follows:

[0055] Inlet air dry bulb temperature t g1 The inlet air wet bulb temperature is 35.1℃. s1 The temperature is 28℃, the specific enthalpy of the inlet air is 89.85kj / kg, the relative humidity of the inlet air is 58.73℃, the thickness of the wet film is 200mm, the width and height of the wet film are consistent with the air inlet area of ​​the unit, and the overall size of the wet film is 800mm×300mm×200mm. The wet film is selected as model 7090.

[0056] According to the unit 6000m 3 / h air volume and the air inlet area of ​​800mm m×300m, the average wind speed is calculated to be 1.73m / s, and the specific surface area ε is generally taken as 400~500m 2 / m 3 , based on the wet film thickness of 200mm, the evaporation efficiency is calculated to be about 70%.

[0057] According to the evaporation efficiency of the air, the air state point at the wet film outlet is obtained as follows:

[0058] Outlet air dry bulb temperature t a1 The outlet air wet bulb temperature is 30.13℃.a2 It is 27.93℃, the specific enthalpy of the outlet air is 89.85kJ / kg, and the moisture content of the outlet air is 23.24g / kg.

[0059] The minimum watering density of direct evaporative cooling is determined to be 0.44kg / m·s. The maximum evaporation capacity is 7% of the watering capacity. The actual watering capacity should be greater than the minimum watering capacity. Considering the 20% surplus, the total watering capacity of the four wet films is qDEC1 = 1.2 × 0.44 × 0.8 × 0.2 ÷ 0.93 × 4 = 0.36kg / s.

[0060] The wet film structure is determined to be: 800mm×300mm×200mm.

[0061] Among them, the condensing load of the verification unit is based on a cooling capacity of 30kW, a compressor power of 6kW, a surplus factor of 1.1 times (10% surplus), and a total condensing load of 39.6kW. The condensing load distribution of the two condensers is as consistent as possible according to the calculated air volume, and the resulting condensing load distribution ratio is evaporative condenser: air-cooled condenser = 0.8:0.2, and the condensing load of the evaporative condenser is 39.6kW×0.8=31.7kW. The inlet air temperature of the evaporative condenser is calculated according to the wet film outlet temperature.

[0062] The basic parameters for calculating the evaporative condenser are as follows:

[0063] The heat load is 31.7kW, the refrigerant is R410A, and the inlet air dry bulb temperature is t g1 is 30.13℃ (i.e. the outlet air dry bulb temperature of the wet film a1 ), inlet air wet bulb temperature t s1 is 27.93℃ (i.e. the outlet air wet bulb temperature of the wet film a2 ), the inlet air enthalpy is 89.85 kJ / kg and the relative humidity is 84.71%.

[0064] This evaporative condenser coil uses copper tubes, and the copper tubes are arranged in a regular triangle cross-row. The basic parameters of the evaporative condenser coil are as follows:

[0065] Tube center distance S 1 25mm, row spacing S 2 The pipe diameter is 21.65 mm. 0 is 9.52mm, the wall thickness of the copper tube d is 0.3mm, and the inner diameter of the copper tube d i It is 8.92mm.

[0066] The design calculation process of the evaporative condenser coil is as follows:

[0067] Condensation load Q k1is 31.7kW; condensing temperature t k is 40℃; inlet air dry bulb temperature t g1 is 30.13℃; the inlet air wet bulb temperature t s1 is 27.93℃; relative humidity of inlet airΦ 1 is 84.71%; air flow L is 5930.5m 3 / h,L d =Q k1 ×ε; water volume calculation Q 1 is 0.68kg / s, Q 1 =Q k1 ×r; tube spacing s is 21.65mm; inlet air enthalpy h 1 is 89.85 kJ / kg; water film temperature (assumed) t w Assumed to be 36.5℃; air enthalpy at the water film h w 139.97 kJ / kg; outlet air enthalpy h 2 is 106.72 kJ / kg; outlet air dry bulb temperature t a1 is 32.3℃; the average enthalpy of the air outside the tube is h m is 98.86 kJ / kg, Average temperature of air outside the tube t m is 31.3℃; kinematic viscosity coefficient v m is 16.16; specific heat c is 1.055; air headwind speed u f The value is 1.62m / s; the air velocity u at the narrowest section fmax is 2.62m / s, Pipe diameter 0 9.52mm; the convection heat transfer coefficient between the water film outside the tube and the air is α wa is 68.62W / (m·K), Equivalent convection heat transfer coefficient of air outside the tube α j is 628.4W / (m·K), The tube length L is 1m; the tube wall thickness δ is 0.3mm; the heat flux Ψ is 3267.7W / m 2 , Ψ=α j (t w -t m ); The initial heat exchange area A′o is 9.695m 2 , A′o=φ k / Ψ; the thermal conductivity λ of R410A at 40°C is 0.09w / (m·k); the density ρ of R410A at 40°C is 978kg / m 3; The latent heat of vaporization h of R410A at 40°C is 159.81 kj / kg; The dynamic viscosity ν of R410A at 40°C is 0.0000985 Pa·s; β 1 / 3 is 22298.02227; cn 3260.530346w / (m 2 k), Condensation heat transfer coefficient in the tube α c,ns is 2743.872265w / (m 2 k), α c,ns =0.25Ψ 0.15 α cn ; The actual heat exchange area Ao is 9.719m 2 .

[0068] The heat transferred from refrigerant vapor to air is φ k =A o K c (t k -t m ), for the Freon system, the thermal resistance of oil pollution can be ignored, and the thermal resistance of dirt on the outer surface of the copper tube can be taken as R fou =0.0005m 2 k / W, ignoring the thermal resistance of water film and the thermal resistance of copper tube wall.

[0069] The heat transfer coefficient K of the evaporative condenser can be obtained c 374.66W / (m 2 K), according to the design Calculation can be obtained A o =9.719m 2 , which is consistent with the initial heat exchange area A′o. i is the total surface area outside the tube.

[0070] The structure of the evaporative condenser is determined as:

[0071] Total heat exchange area 9.719m 2 , the heat exchange area per meter of tube is 0.02991m 2 , the total pipe length is calculated to be 324.97m, the length of a single pipe is 1m, a total of 325 pipes, and the design is 8 rows and 41 columns. The structure of the evaporative condenser is: the section length is 1000mm, the section width is 1025mm, and the thickness is 173.2mm.

[0072] Among them, the condensing load Q of the air-cooled condenser k2 The power is 7.92kW, the air inlet temperature of the air-cooled condenser is the air outlet temperature of the evaporative condenser, the dry bulb temperature is 32.3℃, and the wet bulb temperature is 31.2℃. The cross-sectional area of ​​the air-cooled condenser is made the same as that of the evaporative condenser.

[0073] The basic parameters of air-cooled condensers are as follows:

[0074] The heat load is 7.92kW, the refrigerant is R410A, and the inlet air dry bulb temperature is t g1 32.3℃ (the outlet air dry bulb temperature of the evaporative condenser is t a1 ), outlet air dry bulb temperature t a1 is 36.3℃, the inlet and outlet air dry bulb temperature difference t a1 -t g1 =4℃, condensation temperature t k is 40℃.

[0075] Calculate the logarithmic mean temperature difference θ m Equal to 5.46℃.

[0076] According to the local atmospheric pressure Pa = 100.59 kPa, according to the air (dry air) thermophysical properties table, at the average air temperature t m =34.3℃, C pa =1060J / (kg·K),λ a =0.0267W / (m·K), v a =16.44×10 -6 m 2 / s, at the inlet air temperature t a1 =ρ at 32.3℃ a =1.121kg / m 3 .

[0077] according to The required air volume flow rate for the air-cooled condenser is 5999m 3 / h(i.e. 1.67m 3 / s).

[0078] The basic size parameters of air-cooled condenser are as follows:

[0079] Fin spacing S f is 1.8 mm, fin thickness δ f 0.105mm, tube center distance S 1 25mm, row spacing S 2 The pipe diameter is 21.65 mm. 0 is 9.52mm, the wall thickness of the copper tube d is 0.3mm, and the inner diameter of the copper tube d i It is 8.92mm.

[0080] The air-cooled condenser coil uses copper tube fins, and the copper tubes are arranged in a regular triangle cross-row. According to the above calculation parameters, the relevant heat transfer area per meter of tube length can be obtained.

[0081] Calculation of heat exchanger surface area: fin area per meter of tube length a f 0.5188m 2 / m, the surface area of ​​the tube between the fins per meter of tube length a b 0.0288m 2 / m, total outer area of ​​finned tube per meter tube length a 0f 0.5476m 2 / m, inner surface area of ​​copper tube a i 0.0280m 2 / m, surface area at average pipe diameter a m 28.95m 2 / m.

[0082] Select the headwind speed w y =1.62m / s; then the windward area Take the condenser windward width, that is, the effective single tube length l = 1m, then the condenser windward width Therefore, the number of tube rows on the windward side Take 41 columns.

[0083] Among them, the heat transfer area on the air side is calculated as follows:

[0084] The number of tube rows in the air flow direction of the condenser is expected to be n = 3, so the fin width b = 2×S 2 =64.95mm;

[0085] The equivalent diameter of the narrowest cross section of the infinitesimal element:

[0086] Wind speed at the narrowest section:

[0087] because Look up the table and use interpolation to find Ψ = 0.1897, n = 0.59, c = 1.234, m = -0.238,

[0088] Then the air surface heat transfer coefficient is:

[0089] Among them, the heat transfer area on the refrigerant side is calculated as follows:

[0090] The parameters of R410A at 40°C condensing temperature are as follows: thermal conductivity is 0.09w / (m·k), density is 978kg / m 3 , latent heat of vaporization is 159.81 kJ / kg, kinematic viscosity is 0.0000001007m 2 / s, the physical property set coefficient B is 1824.8, and the fin thermal conductivity λ is 203w / (m·k).

[0091] Heat transfer coefficient of R410A when condensing in the tube:

[0092] α ki =0.555Bd i -0.25 (t k -t wi ) -0.25 =586.03×(40-t wi ) -0.25 ;

[0093] Fin equivalent height

[0094] Take the thermal conductivity of aluminum sheet λ = 203W / (m·K) and calculate the fin parameter m, that is:

[0095] Calculate fin efficiency:

[0096] Calculate the surface efficiency:

[0097] Ignoring the influence of relevant dirt thermal resistance and contact thermal resistance, t wi =t wo =t w Substitute the calculated values ​​into the formula α ki α i (t k -t w )=α of η o α of (t w -t m ), calculate and solve for t w =38.96℃, then the heat transfer coefficient of the condensation surface of R410A in the tube is α ki =3263.32W / (m 2 k);

[0098] Take the contact thermal resistance between the tube wall and the fin r b =0.004m 2 K / W, air side dust layer thermal resistance r 0 =0.001m 2 K / W, thermal conductivity of copper tube 393W / (m·K);

[0099] Overall heat transfer coefficient for air-cooled condenser:

[0100] Among them, determine the structure of the air-cooled condenser:

[0101] Required heat transfer area for air-cooled condenser:

[0102] Required effective total length of finned tube:

[0103] Number of tube rows in air circulation direction:

[0104] The integer n=3 rows is taken, which is consistent with the number of tube rows in the air flow direction expected when calculating the air side surface heat transfer coefficient. In this way, the heat transfer requirements of the condensing load can be met. In addition, the actual headwind speed of the condenser is consistent with the taken headwind speed.

[0105] The final structure of the air-cooled condenser is determined as follows: the number of tube rows is 3, the number of tube columns is 41, the thickness is 64.95mm, the section length is 1000mm, and the section width is 1025mm.

[0106] Among them, the basic parameters of the evaporator are as follows:

[0107] The cooling capacity is 30kW, the refrigerant is R410A, the return air dry bulb temperature is 27℃, the return air wet bulb temperature is 19℃, the supply air dry bulb temperature is 15℃, the supply air wet bulb temperature is 14℃, and the evaporating temperature is 10℃.

[0108] This evaporator uses copper tubes and aluminum fins. The copper tubes are arranged in a regular triangle cross-row. The basic dimensions of the evaporator are as follows:

[0109] Fin spacing S f 2 is 15mm, fin thickness δ f 0.105mm, tube center distance S 1 21mm, row spacing S 2 The tube diameter is 18.19 mm. 0 is 7mm, the wall thickness of the copper tube is 0.3mm, and the inner diameter of the copper tube is d i It is 6.4mm.

[0110] According to the structural parameters, the parameters of each meter of fin tube are calculated, and the calculation process of the evaporator heat exchange surface area is as follows:

[0111] External fin area A f 0.34m 2 / m, Surface area of ​​intercostal tubes A p 0.02084m 2 / m, Total surface area outside the tube A i 0.3643m 2 / m,A i＝ A f +A p ; The rib coefficient τ is 18.121, A is the total heat transfer area; the rib pass coefficient a is 17.35, fa is the windward area; equivalent diameter d e 3.338mm,

[0112]

[0113] The calculation process of the number of evaporator tube rows is as follows:

[0114] The air volume can be calculated based on the cooling capacity and the state parameters of the supply and return air. The economic flow rate is selected to obtain the windward area, and then the tube length is set according to the requirements to obtain the number of tube rows. The number of tube rows is preset, and the inlet and outlet state points of the evaporator are connected on the wet air enthalpy and humidity diagram. The intersection point with the relative humidity 100% line is the average state point of the required fin tube outer surface, and the cooling efficiency η can be calculated. The number of fin tube rows is checked based on the cooling efficiency η.

[0115] Cooling capacity Q K is 30kW, evaporation temperature t k The return air dry bulb temperature is 27°C, the return air wet bulb temperature is 19°C, and the return air enthalpy value is h s1 is 54.08 kJ / kg, the supply air dry bulb temperature is 27°C, the supply air wet bulb temperature is 19°C, and the supply air enthalpy value is h s2 The air flow rate Q is 7500m 3 / h, Q = 3.6Q k / [(h s1 -h s2 )ρ]; kinematic viscosity coefficient v m is 15.31×10 -6 ·m 2 / s; specific heat capacity c is 1.026 kJ / (kg·K); wind speed u f 1.8m / s; air velocity u at the narrowest section fmax is 2.85m / s, The windward area fa is 1.166m 2 ; The number of tube rows N is preset to 4 rows; the length of a single tube L is set to 1500mm; the windward width W is 777mm, W = fa / L; the number of tube rows n is 37 rows, N = W / s1; the total heat transfer area A is 78.75m 2 , A=fa·a·N; cooling efficiency η is 0.717, Calculate the required number of rows N 1 is 3.7 (satisfied by 4 rows),

[0116] Among them, the air side convection heat transfer coefficient α a 42.85W / (m 2 ℃), Re is the air thermal resistance; the length of the fin in the airflow direction is 72.76 mm, L = N·S2 ; Index n is -0.23, n = -0.28 + 0.08Re / 1000; Index m is 0.593856, m = 0.45 + 0.0066L / d e ; Coefficient C 1 is 1.21088, C 1 =1.36-0.00024·Re; coefficient C 2 is 0.184258,

[0117]

[0118] Among them, the equivalent heat transfer coefficient on the air side is the equivalent heat transfer coefficient outside the tube α ae 44.049W / (m 2 ℃), The moisture separation coefficient ξ is 1.2, The fin shape parameter m is 69.3, The equivalent rib height L is 10.8 mm; the fin efficiency η f is 0.847,

[0119]

[0120] Among them, the heat transfer coefficient on the refrigerant side is the heat transfer coefficient of the refrigerant in the tube α b 3754W / (m 2 ℃), The heat flux of the refrigerant in the fin tube is 6716W / m 2 , The dynamic viscosity ν of the liquid is 15.59×10 -6 ·Pa·s, the thermal conductivity of the liquid is λ0.11W / (m·K), and the enthalpy value at the evaporator inlet is h 1 is 258.78 kJ / kg, and the enthalpy value at the evaporator outlet is h 2 is 425.83 kJ / kg, and the refrigerant circulation volume M R 0.18kg / s, M R =Q / (h1-h2); mass flow rate of refrigerant in the tube v m is 155kg / (m·s), v m =M R / (0.25·π·d i N), air side dirt thermal resistance R f is 0.003, and the total heat transfer coefficient K is 32.75W / (m 2 ℃),

[0121] The evaporation temperature is calibrated according to the required heat transfer temperature difference: Δtm=Q / (K·A)=30000 / (32.75×78.75)=11.316°C, which is consistent with the logarithmic mean temperature difference of 11.27°C.

[0122] Determine the evaporator structure as:

[0123] There are 4 rows of tubes, 37 columns of tubes, the height is 777mm, the length is 1500mm, and the thickness is 72.76mm.

[0124] The total design cooling capacity of the unit in this verification example is 30kW, and the indoor air design parameters are based on the return air dry-bulb temperature of 27℃, wet-bulb temperature of 19℃; the supply air dry-bulb temperature of 17℃, wet-bulb temperature of 14℃.

[0125] The design parameters of the unit heat exchanger are: dry bulb temperature 35.1℃, wet bulb temperature 28℃, relative humidity 58.7%, wet film size 800mm×300mm×200mm, evaporative condenser size 1000mm×1025mm×173.2mm, air-cooled condenser size 1000mm×1025mm×64.95mm, evaporator size 1500mm×777mm×72.76mm; the overall size of the outdoor unit is 1.5m×1.5m×2.2m.

[0126] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions may occur depending on design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for designing the structure of an external unit of an evaporative condensing air conditioner, characterized in that: The specific steps include: S1 determines the main structure of the evaporative condensing air conditioning unit, wherein the main structure of the evaporative condensing air conditioning unit includes a wet film, an evaporative condenser, an air-cooled condenser and an evaporator; S2 sets basic operating parameters of the outdoor unit according to the main structure of the evaporative condensing air conditioning unit; S3 designs and calculates the wet film outlet parameters according to the basic parameters of the wet film to determine the wet film structure; S4 performs design calculation of the evaporative condenser coil according to the basic parameters of the evaporative condenser, the wet film outlet parameters, and the basic parameters of the evaporative condenser coil, and determines the structure of the evaporative condenser; S5 determines the structure of the air-cooled condenser according to the basic parameters of the air-cooled condenser and calculates the surface area of ​​the heat exchanger of the air-cooled condenser, the heat transfer area of ​​the air side of the air-cooled condenser, and the heat transfer area of ​​the refrigerant side of the air-cooled condenser; S6 determines the evaporator structure based on the basic parameters of the evaporator and calculates the evaporator heat exchange surface area, the number of evaporator tube rows, the evaporator air side heat transfer area, the evaporator air side convection heat transfer coefficient, the evaporator air side equivalent heat transfer coefficient and the evaporator refrigerant side heat transfer coefficient.

2. The method for designing the external unit structure of an evaporative condensing air conditioner according to claim 1, characterized in that: Step S1: The main structure of the evaporative condensing air-conditioning unit also includes a water circulation system, which includes a water tank, a water pump arranged in the water tank and connected to the first spray device and the second spray device, and a water collecting pan arranged below the wet film and evaporative condenser coils for collecting water falling from the wet film and evaporative condenser coils, wherein the water collecting pan is connected to the water tank; the first spray device is arranged between the evaporative condenser coil and the air-cooled condenser coil, and the second spray device is arranged above the wet film.

3. The method for designing the external unit structure of an evaporative condensing air conditioner according to claim 2, characterized in that: The wet film outlet parameter design calculation in step S3 includes: Step S31, calculation of wet film evaporative cooling efficiency, the formula is: Where η DEC is the wet film evaporative cooling efficiency; v y is the windward velocity of the wet film filler; ε is the specific surface area of ​​the wet film filler; δ is the thickness of the wet film filler; t g1 is the inlet air dry bulb temperature of the wet film; t s1 is the wet bulb temperature of the inlet air of the wet film; Step S32, obtaining wet film outlet air parameters according to the wet film evaporative cooling efficiency, wherein the wet film outlet air parameters include the wet film outlet air dry bulb temperature, the wet film outlet air wet bulb temperature, the wet film outlet air specific enthalpy and the wet film inlet air moisture content; Step S33, calculation of wet film watering amount, the formula is: qDEC1=1.2MsminF+Δqn; In the formula: qDEC1 is the watering amount; Msmin is the minimum watering density for direct evaporative cooling; F is the watering area; Δqn is the maximum evaporation amount of the equipment.

4. The method for designing the external unit structure of an evaporative condensing air conditioner according to claim 2, characterized in that: The actual heat exchange area of ​​the evaporative condenser coil in step S4 is calculated as: A o =φ k / K c (t k -t m ); In the formula, A o is the actual heat exchange area, φ k is the enthalpy of air at the outlet of the evaporative condenser, K c is the heat transfer coefficient of the evaporative condenser, t k is the condensation temperature, t m is the average temperature of the air outside the tube; The required number of single tubes is calculated according to the actual heat exchange area of ​​the evaporative condenser, and the evaporative condenser structure is obtained after arrangement and design.

5. The method for designing the external unit structure of an evaporative condensing air conditioner according to claim 4, characterized in that: The heat load of the evaporative condenser is obtained by the total condensing load according to the condensing load distribution ratio of the evaporative condenser and the air-cooled condenser; the total condensing load is composed of the refrigeration capacity and the compressor power and the surplus.

6. The method for designing the structure of an external unit of an evaporative condensing air conditioner according to claim 5, characterized in that: The total condensing load is 1.1 times the sum of the refrigeration capacity and the compressor power, and the ratio of the evaporative condenser to the air-cooled condenser is 0.8:0.2.

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