A method and device for detecting the total refrigerant charge of a refrigeration system

Abstract

This invention provides a method and apparatus for detecting the total refrigerant charge in a refrigeration system. Before using the method, a mathematical model of heat transfer in the condenser needs to be established. The method includes the following steps: S1, condenser temperature acquisition; S2, overall heat transfer coefficient correction; S3, phase region length calculation; S4, refrigerant inventory calculation, and the total refrigerant charge of the system is calculated based on the refrigerant inventory in the condenser. The method and apparatus for detecting the total refrigerant charge in a refrigeration system described in this invention achieve the goal of detecting the total refrigerant charge in refrigeration systems, especially small household air conditioners, without requiring the installation of sensors, without interfering with system operation, and with only a small amount of data.

Description

Technical Field

[0001] This invention relates to the field of refrigerant inventory detection technology for refrigeration systems, and particularly to a method and apparatus for detecting the total refrigerant charge in small household air conditioners. Background Technology

[0002] Because the pressure in refrigeration systems is typically much higher than atmospheric pressure, all refrigeration systems are susceptible to leaks, with refrigerant leakage being the most common malfunction. Insufficient refrigerant charge leads to a significant decrease in air conditioning system performance, reduced system efficiency, and even system failure, resulting in increased power consumption and maintenance costs, energy waste, and economic losses. Furthermore, leaks of flammable refrigerants pose safety hazards. Therefore, refrigerant level monitoring is crucial for preventing refrigerant leaks in refrigeration systems.

[0003] Existing refrigerant quantity detection methods can be divided into two categories: (1) Refrigerant charge quantity detection methods based on theoretical analysis and thermodynamic models. This method requires temperature and pressure sensors to collect the required information. However, installing a large number of sensors will interfere with the system operation, increase detection costs, and consume manpower and resources. (2) Refrigerant charge quantity detection methods based on data driven by neural network models. This method requires a large amount of data support. Only large refrigeration systems have abundant data for detection, but the amount of data for small household air conditioners is insufficient to support model establishment.

[0004] Therefore, there is an urgent need for a testing method that requires a small amount of data, has high accuracy, and does not interfere with the operation of the system for testing the total refrigerant charge of small household air conditioners. Summary of the Invention

[0005] This invention presents a method and apparatus for detecting the total refrigerant charge of a refrigeration system that requires minimal data, has high detection accuracy, and does not interfere with system operation.

[0006] To address the aforementioned problems, this invention discloses a method for detecting the total refrigerant charge in a refrigeration system. Before employing this method, a mathematical model of condenser heat transfer needs to be established. Then, the total refrigerant charge in the refrigeration system is calculated using this mathematical model. The method for detecting the total refrigerant charge includes the following steps:

[0007] S1, Condenser Temperature Acquisition: Acquire temperature data of the condenser inlet and outlet and each elbow;

[0008] S2, Overall heat transfer coefficient correction: Using the temperature data obtained in step S1, the condenser heat transfer mathematical model is used to simulate the operating state of the condenser under the under-charge condition, and the calculated value of the elbow temperature is calculated. The overall heat transfer coefficient of each phase region of each flow path of the condenser is corrected in turn by the calculated value of the elbow temperature, so that the calculated value of the elbow temperature is comparable to the measured value of the elbow temperature obtained in step S1.

[0009] S3, Phase region length calculation: Based on the overall heat transfer coefficient corrected in step S2, calculate the pipe lengths of the condenser superheated zone, subcooled zone, and two-phase zone respectively;

[0010] S4, Refrigerant inventory calculation: Calculate the refrigerant inventory in the condenser based on the total heat transfer coefficient corrected in step S2 and the pipe lengths of each zone of the condenser calculated in step S3, and calculate the total refrigerant charge of the system based on the refrigerant inventory in the condenser.

[0011] Furthermore, the condenser heat transfer mathematical model is established using the distributed parameter method and calculated according to the ε-NTU method; where ε represents efficiency and NTU represents the number of heat transfer units. The calculation process of the condenser heat transfer mathematical model is as follows:

[0012] P1, input known parameters, including condenser structural parameters, air and refrigerant inlet parameters, refrigerant condensation temperature, and refrigerant mass flow rate;

[0013] P2, assuming air and refrigerant outlet parameters, given initial values ​​for air and refrigerant iterations for each heat transfer unit;

[0014] P3, according to the order in which the refrigerant flows through each heat transfer unit, calculate the air-side heat transfer coefficient, pressure drop and fin efficiency of each heat transfer unit, the refrigerant-side heat transfer coefficient, pressure drop and refrigerant mass, and use the ε-NTU method to calculate the heat exchange of each heat transfer unit.

[0015] P4, sum the calculated values ​​of all parameters of all heat transfer units;

[0016] P5, the inlet parameters of each heat transfer unit are known, or can be obtained from the outlet parameters of the previous unit. The outlet parameters of each heat transfer unit are calculated based on the inlet parameters and heat exchange of each heat transfer unit, and the air and refrigerant status in all heat transfer units are updated in sequence.

[0017] P6. Repeat steps P3 to P5 to continuously update the air and refrigerant status of each heat transfer unit until the temperature change of air and refrigerant in all heat transfer units before and after the update is less than the preset value.

[0018] P7 outputs the calculation results, including the air and refrigerant temperatures, refrigerant mass, and pipe wall temperature of each heat transfer unit.

[0019] Furthermore, step P3 includes:

[0020] P301, let i = 1, where i is the number of the heat transfer unit, and the value of i is 1, 2, 3, ... M;

[0021] P302, calculate the air-side heat transfer coefficient, pressure drop, and fin efficiency of the i-th heat transfer unit, and the refrigerant-side heat transfer coefficient, pressure drop, and refrigerant mass;

[0022] P303, calculate the heat transfer of i heat transfer units according to the ε-NTU method;

[0023] P304, determine if i = M? If yes, continue to step P4; if no, increment the value of i by 1, and execute steps P302 and P303 again until i = M.

[0024] Furthermore, in step S2, the correction method for the overall heat transfer coefficient is as follows: the calculated value of the elbow temperature obtained by the mathematical model of heat transfer of the condenser is used as the target, and the overall heat transfer coefficient is used as the correction object to continuously perform iterative correction calculations so that the calculated value of the elbow temperature is equivalent to the measured value of the elbow temperature.

[0025] Furthermore, in step S2, the correction of the overall heat transfer coefficient is performed according to formula (8):

[0026] U0'=kU0 (8)

[0027] Where U0' is the corrected overall heat transfer coefficient, k is the correction coefficient, and U0 is the overall heat transfer coefficient in the basic model.

[0028] Furthermore, in step S2, the pipe length L, correction coefficient k, and refrigerant inlet specific enthalpy H are... r，in Enthalpy H relative to exports r，out The following relationship exists between these four variables, as described in equation (9):

[0029] (H r，out Q, m r ...) = f(L, k, H r，in ,...) (9)

[0030] Among them, H r，in H is the specific enthalpy of the refrigerant inlet. r，out ν is the specific enthalpy of the refrigerant outlet; Q is the heat exchange capacity of this section of the pipeline, m r This refers to the quality of the refrigerant.

[0031] Furthermore, in step S2, the correction process for the overall heat transfer coefficient includes the following steps:

[0032] S201, Obtain the known pipe length L and refrigerant inlet and outlet specific enthalpy H.r，in H r，out ;

[0033] S202, given the initial value of the overall heat transfer coefficient k;

[0034] S203, invoke the condenser heat transfer mathematical model to calculate the refrigerant outlet specific enthalpy H'. r，out ;

[0035] S204, Determine H' r,out Is it equal to H? r,out If yes, output the calculation result; if no, adjust the value of the overall heat transfer coefficient k, and repeat steps S203 and S204 until H' r,out =H r,out .

[0036] Furthermore, the purpose of heat transfer coefficient correction is to make the phase region division of each flow path as close as possible to the actual situation, correcting errors caused by actual factors through measured elbow temperatures, and improving the accuracy of refrigerant inventory detection, rather than negating the accuracy of heat transfer calculations in the mathematical model. Therefore, the correction algorithm should follow the following principle: to make the calculated elbow temperature match the actual value while minimizing the correction to the mathematical model. In other words, when the correction coefficient k can meet the temperature requirements within a certain range, the value closest to 1 should be selected to avoid over-correction of the mathematical model.

[0037] Furthermore, in step S3, the calculation process for the pipe lengths of the condenser's superheated zone, subcooled zone, and two-phase zone includes the following steps:

[0038] S301, Obtain the known overall heat transfer coefficient k and refrigerant inlet and outlet enthalpy H. r,in H r,out ;

[0039] S302, given the initial value of the pipe length L;

[0040] S303, invoke the condenser heat transfer mathematical model to calculate the refrigerant outlet specific enthalpy H'. r,out ;

[0041] S304, Determine H' r,out Is it equal to H? r,out If yes, output the calculation result; if no, adjust the value of pipe length L and execute steps S303 and S304 again until H' r,out =H r,out .

[0042] Furthermore, in step S4, the refrigerant inventory in the condenser = total refrigerant mass in the finned tubes + total refrigerant mass in the elbows; wherein, the total refrigerant mass in the finned tubes is the sum of the refrigerant mass in each phase region of each flow path, and the total refrigerant mass in the elbows is the sum of the refrigerant mass in all elbows.

[0043] The refrigerant mass in each phase region of each flow path is calculated using the following formulas (10-12);

[0044]

[0045] In the formula, m sh For the refrigerant quality in the superheated zone, L sh ρ is the length of the pipe in the superheated zone. G Where A is the refrigerant gas density in the superheated zone, and A is the cross-sectional area of ​​the refrigerant pipe.

[0046]

[0047] In the formula, m sc For the refrigerant quality in the subcooled zone, L sc ρ is the length of the subcooled zone pipe. L This refers to the refrigerant gas density in the subcooled zone.

[0048]

[0049] In the formula, m tp For the refrigerant mass in the two-phase region, L tp ∈ represents the pipe length in the two-phase region, and ∈ represents the cavitation coefficient in the two-phase region;

[0050] The mass of refrigerant in each bend (m) r,elbow Perform according to the following formula (13):

[0051]

[0052] In the formula, R is the radius of curvature of the bend, and D... i ρ is the inner diameter of the pipe. r The density of the refrigerant fluid inside the elbow, m r,elbow The refrigerant mass inside the elbow.

[0053] A device for detecting the total refrigerant charge of a refrigeration system, wherein the device uses the above-mentioned detection method to detect the total refrigerant charge, and the device comprises:

[0054] The condenser temperature monitoring module can read the actual temperature distribution data inside the condenser of the refrigeration system for subsequent correction of the overall heat transfer coefficient.

[0055] The heat transfer coefficient correction module is used to correct the calculation error of the condenser heat transfer mathematical model, so that the calculated value of the elbow temperature is comparable to the measured value.

[0056] The zoned pipe length calculation module calculates the pipe length of the superheated zone, subcooled zone and two-phase zone of the condenser based on the corrected total heat transfer coefficient, which is used for subsequent calculation of the condenser refrigerant inventory.

[0057] The refrigerant inventory calculation module is used to calculate the refrigerant inventory in the condenser based on the calculation results of the heat transfer coefficient correction module and the partitioned pipe length calculation module, and to calculate the total refrigerant charge of the system based on the refrigerant inventory in the condenser.

[0058] The method and apparatus for detecting the total refrigerant charge of a refrigeration system described in this application achieves the goal of detecting the total refrigerant charge of a refrigeration system without installing sensors, without interfering with system operation, and with only a small amount of data. It is particularly suitable for detecting the total refrigerant charge of small household air conditioners. This solves the problems of previous detection methods that required installing a large number of sensors, which would interfere with system operation, or that the amount of data was too small to support model establishment. It provides a convenient and efficient detection solution for detecting the total refrigerant charge of a refrigeration system. Attached Figure Description

[0059] Figure 1 This is a schematic diagram of the method and apparatus for detecting the total refrigerant charge of the refrigeration system according to the present invention;

[0060] Figure 2 This is a block diagram of the refrigerant flow calculation logic for the condenser described in this invention;

[0061] Figure 3 This is a block diagram of the calculation logic of the heat transfer mathematical model described in this invention.

[0062] Figure 4 This is a logic block diagram of the heat transfer coefficient correction module described in this invention;

[0063] Figure 5 This is a logic block diagram of the partitioned pipeline length calculation module described in this invention;

[0064] Figure 6 This is a logic block diagram of the condenser refrigerant inventory calculation module of the present invention (taking the superheated zone as an example). Detailed Implementation

[0065] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0066] like Figures 1-6As shown, a method for detecting the total refrigerant charge in a refrigeration system requires establishing a condenser heat transfer mathematical model before using the method. The total refrigerant charge is then calculated based on this model. The method includes the following steps:

[0067] S1, Condenser Temperature Acquisition: Acquire temperature data of the condenser inlet and outlet and each elbow;

[0068] S2, Overall heat transfer coefficient correction: Using the temperature data obtained in step S1, estimate the refrigerant mass flow rate, use the condenser heat transfer mathematical model to simulate the condenser's operating state under under-charge conditions, calculate the elbow temperature, and use the elbow temperature calculation value to correct the overall heat transfer coefficient of each phase region of each flow path of the condenser in turn, so that the elbow temperature calculation value is comparable to the measured elbow temperature value obtained in step S1.

[0069] S3, Phase region length calculation: Based on the overall heat transfer coefficient corrected in step S2, calculate the pipe lengths of the condenser superheated zone, subcooled zone, and two-phase zone respectively;

[0070] S4, Refrigerant inventory calculation: Calculate the refrigerant inventory in the condenser based on the total heat transfer coefficient corrected in step S2 and the pipe lengths of each zone of the condenser calculated in step S3, and calculate the total refrigerant charge of the system based on the refrigerant inventory in the condenser.

[0071] Preferably, in step S1, the condenser temperature is collected by an infrared temperature detection device to obtain temperature data of the condenser inlet and outlet and each bend. It can be understood that the temperature data is the measured temperature value of each part of the condenser.

[0072] During the experiment, the applicant discovered that when the refrigerant undercharge ratio is between 80% and 100%, the ratio of the refrigerant inventory in the condenser (hereinafter referred to as "condenser refrigerant inventory") to the total refrigerant inventory in the system fluctuates around 60%. Within the refrigerant undercharge ratio range of 70% to 80%, as the RCL (ratio of initial refrigerant charge to standard charge) decreases, the ratio of the refrigerant inventory in the condenser to the total refrigerant charge in the system slightly increases, but does not exceed 67%. Therefore, within the practical application range, the ratio of the condenser refrigerant inventory to the total refrigerant charge in the system remains stable. Thus, when detecting the total refrigerant charge in the refrigeration system, the total refrigerant inventory in the system can be calculated from the condenser refrigerant inventory based on this ratio. Based on this, the applicant filed this application.

[0073] Furthermore, in step S2, it is usually difficult to make the calculated value and the measured value of the elbow temperature completely equal. Therefore, in this application, it is set that when the difference between the calculated value of the elbow temperature and the measured value of the elbow temperature obtained in step S1 is ≤ a set temperature difference value, the calculated value and the measured value of the elbow temperature are equivalent.

[0074] Preferably, the set temperature difference value is ≤0.1℃.

[0075] More preferably, the set temperature difference value is ≤0.005℃.

[0076] As some embodiments of this application, the set temperature difference value is 0.001℃.

[0077] Furthermore, the mathematical model for heat transfer in the condenser is established using the distributed parameter method, specifically using the efficiency-to-number of heat transfer units (ε-NTU method) for calculation; where ε is efficiency, NTU is the number of heat transfer units, the efficiency ε is the ratio of the actual heat transfer of the heat exchanger to the maximum possible heat transfer, and NTU is a dimensionless parameter.

[0078] Typically, refrigeration systems operate under highly variable conditions and exhibit significant inertia, incorporating nonlinear heat and mass transfer characteristics. Various thermodynamic performance parameters vary with spatial location. Distributed parameter models fully consider the distribution of parameters such as heat transfer coefficient and refrigerant dryness fraction, providing a profound understanding of the thermodynamic characteristics of refrigeration systems. Therefore, to study the heat transfer characteristics of condensers and the refrigerant mass distribution, this application employs the distributed parameter method to establish a mathematical model, resulting in more accurate detection results.

[0079] Due to the influence of various practical factors and complex interrelationships, the calculated and actual values ​​of the condenser heat transfer mathematical model inevitably contain errors. If only the condenser heat transfer mathematical model is used to calculate the refrigerant quantity within the condenser, the accuracy cannot meet practical application requirements. In this application, the errors of the condenser heat transfer mathematical model are uniformly summarized into the overall heat transfer coefficient through heat transfer coefficient correction. During use, the measured value obtained from the temperature monitoring module is used as the target, and the overall heat transfer coefficient is continuously iteratively corrected to ensure that the calculated and measured values ​​of the elbow temperature are essentially equal, thereby effectively improving the accuracy of the total refrigerant charge calculation.

[0080] Meanwhile, the total refrigerant charge detection method proposed in this application does not interfere with the normal operation of the system during use, and does not require the installation of sensors. It only requires a small amount of data to be applied to the detection of the total refrigerant charge in the refrigeration system, making it convenient to use. It realizes the calculation of the total charge of the system based on a small amount of data, solving the problem that it is difficult to apply data-driven or thermodynamic analysis to the detection of refrigerant charge in small household air conditioning refrigeration systems, and improving the convenience and accuracy of the detection of refrigerant charge in small household air conditioning refrigeration systems.

[0081] Furthermore, unlike data-driven methods such as neural networks, in the total refrigerant charge detection method proposed in this invention, the total heat transfer coefficient is not a fixed value or function obtained by pre-correcting the mathematical model based on experimental data, but is obtained by iteratively calculating the deviation between the calculated value and the measured value of the elbow temperature during the detection process. In this way, while ensuring the accuracy of the detection, the amount of data collection can be greatly reduced, and the total refrigerant charge detection method described in this application is more suitable for small household air conditioners.

[0082] It is understood that the refrigeration system described in this application includes, but is not limited to, small household air conditioners, and may also be used in other types of refrigeration systems besides small household air conditioners.

[0083] Preferably, the total refrigerant charge detection method described in this application is used to detect the refrigerant content in the condenser of a finned tube heat exchanger.

[0084] The following provides a detailed explanation of the establishment process and principle of the condenser heat transfer mathematical model, specifically:

[0085]

[0086] In equation (1), U0 is the overall heat transfer coefficient, A0 is the total heat transfer area, and q m C represents the fluid mass flow rate. p The fluid specific heat capacity at constant pressure is denoted as ; furthermore, in this application, min and max refer to the minimum and maximum values ​​of the corresponding parameters, respectively.

[0087] The formula for calculating the overall heat transfer coefficient U0 is as follows:

[0088]

[0089] In equation (2), A i h is the internal surface area of ​​the pipe. i λ is the heat transfer coefficient on the refrigerant side, δ is the pipe wall thickness, and λ is the heat transfer coefficient on the refrigerant side. p A is the thermal conductivity of the copper tube. m η is the average heat transfer area of ​​the copper tube, h0 is the air-side heat transfer coefficient, and η0 is the total efficiency of the fin surface.

[0090] Furthermore, we define a dimensionless parameter C. R As shown in the following formula:

[0091]

[0092] In equation (3), min and max refer to the minimum and maximum values ​​of the corresponding parameters, respectively.

[0093] C R Known as the heat capacity ratio, it reflects the degree of balance in a heat exchanger. If CR If C is 1, the heat exchanger is in a balanced operating state, and the heat capacity and temperature change of the hot and cold fluids are the same; if C R If the difference is very small, the heat exchanger is in an unbalanced operating state, and the heat capacity difference between the hot and cold fluids is very large. This situation generally occurs during fluid phase change.

[0094] Based on this, ε is calculated according to NTU, and the following empirical formula is used for finned tube heat exchangers:

[0095]

[0096] After determining ε according to formula (4), the heat transfer Q of the condenser is... c It can be determined based on the inlet temperatures of the air and refrigerant fluid, as shown in the following formula (5):

[0097] Q c =ε(q) m cp) min (T r，in -T air，in (5)

[0098] In equation (5), T r，in Refers to the refrigerant inlet temperature; T air，in This refers to the air inlet temperature.

[0099] In this application, heat exchange with the environment is ignored, and it is assumed that the heat exchange on the air side is Q. c，air =Refrigerant-side flow heat transfer Q c，r =Heat exchange capacity of the condenser Q c .

[0100] Furthermore, based on the heat exchange capacity Q of the condenser... c The air-side heat transfer equation (6) can be used to determine the outlet temperatures of the air and refrigerant:

[0101] Q c，air =q m，air c p，air (T air，out -T air，in (6)

[0102] In equation (6), Q c，air For heat exchange via airflow; q m，air For air mass flow rate, c p，air T is the specific heat capacity of air at constant pressure. air，out This refers to the air outlet temperature.

[0103] Furthermore, the heat transfer equation on the refrigerant side is shown in equation (7) below:

[0104] Q c，r =qm，r (H r，in -H r，out (7)

[0105] In equation (7), Q c，r For heat exchange on the refrigerant side; q m，r H is the refrigerant mass flow rate. r，in H is the specific enthalpy of the refrigerant inlet. r，out This refers to the specific enthalpy of the refrigerant outlet.

[0106] For the above formula (7), in the overall analysis of the condenser, because H r，in and H r，out Both can be obtained from infrared thermograms, meaning both enthalpy values ​​are known quantities, and Q... c，r Since the refrigerant flow rate q is a known quantity, it can be calculated using the formula (7) above. m，r .

[0107] Furthermore, due to q m，r As obtained in the overall analysis, the above formula (7) can also be used to calculate the refrigerant outlet specific enthalpy H during the analysis of each heat transfer unit. r，out And thus obtain the outlet temperature of the refrigerant.

[0108] Therefore, when calculating the refrigerant flow rate using the aforementioned condenser heat transfer mathematical model, it is necessary to first solve for the refrigerant mass flow rate q based on the condenser's energy balance. m，r The system of equations (1) to (7) is established for the entire condenser.

[0109] Based on the above reasoning and calculations, it can be concluded that the refrigerant flow rate q in the condenser heat transfer mathematical model described in this application is... m，r The process includes the following steps:

[0110] W1, input known quantities, including condenser structural parameters, air face velocity, air inlet dry bulb temperature, refrigerant inlet and outlet temperatures, condensing temperature, and condenser UA value, etc.

[0111] W2, assuming the air outlet temperature, given the initial value of the iteration, calculate the air-side heat transfer according to the air-side heat transfer equation (6);

[0112] W3, calculate the logarithmic mean temperature difference ΔT between the air side and the refrigerant side. m The heat exchange capacity Q of the condenser is calculated according to equation (5). c ;

[0113] W4, compared to Q c,air and Q c If the two are not equal, repeat steps W2 and W3, continuously resetting the air outlet temperature for iterative calculations until the iterative convergence condition, i.e., Q, is met.c,air and Q c equal;

[0114] W5, calculate the refrigerant mass flow rate according to the refrigerant side heat transfer equation (7), and output the calculation results.

[0115] After obtaining the refrigerant mass flow rate, assume that the condenser is divided into M control units along the refrigerant flow direction. For any control unit, establish the system of equations (1) to (7).

[0116] It should be noted that, in step W2, unlike the unit calculations P1 to P7 to be performed below, the refrigerant outlet temperature is already known during the overall calculation, so W2 does not need to assume the refrigerant outlet temperature, which has already been input as a known quantity in W1.

[0117] The refrigerant flow calculation process for the above condenser heat transfer mathematical model is shown in the appendix. Figure 2 The flowchart shown is shown.

[0118] Furthermore, in step W1, the air and refrigerant inlet parameters include at least the air temperature, minimum flow surface air velocity, air flow characteristic length, refrigerant type, temperature, and refrigerant flow characteristic length.

[0119] Furthermore, in step W2, at least an initial value for the air outlet temperature parameter needs to be given for iteration.

[0120] Based on the above reasoning and calculations, the calculation process of the condenser heat transfer mathematical model described in this application is as follows:

[0121] P1, input known parameters, including condenser structural parameters, air and refrigerant inlet parameters, refrigerant condensation temperature, refrigerant mass flow rate, etc.

[0122] P2, assuming air and refrigerant outlet parameters, given initial values ​​for air and refrigerant iterations for each heat transfer unit;

[0123] P3, according to the order in which the refrigerant flows through each heat transfer unit, calculate the air-side heat transfer coefficient, pressure drop and fin efficiency, refrigerant-side heat transfer coefficient, pressure drop and refrigerant mass and other parameters of each heat transfer unit in sequence, and use the ε-NTU method to calculate the heat exchange of each heat transfer unit.

[0124] P4, sum the calculated values ​​of all parameters of all heat transfer units;

[0125] P5, the inlet parameters of each heat transfer unit are known, or can be obtained from the outlet parameters of the previous unit. The outlet parameters of each heat transfer unit are calculated based on the inlet parameters and heat exchange of each heat transfer unit, and the air and refrigerant status in all heat transfer units are updated in sequence.

[0126] P6. Repeat steps P3 to P5 to continuously update the air and refrigerant status of each heat transfer unit until the temperature changes of air and refrigerant in all heat transfer units before and after the update are less than the preset value.

[0127] P7 outputs the calculation results, including parameters such as air and refrigerant temperature, refrigerant mass, and pipe wall temperature for each heat transfer unit.

[0128] Preferably, in step P6, the preset value is ≤0.01℃, and more preferably, the preset value is 0.001℃.

[0129] In step P3, the air-side heat transfer coefficient, pressure drop, and fin efficiency of each heat transfer unit are calculated based on known parameters. The refrigerant-side heat transfer coefficient, pressure drop, and other parameters are all existing technologies in the field and can be calculated using methods found in professional textbooks in the field such as "Heat Transfer". These will not be elaborated upon in this application.

[0130] In the above calculation process, it is assumed that the refrigerant is evenly distributed when flowing into each branch flow path. For each flow path in the condenser, the number of heat transfer tubes and the length of each flow path are input, and the above solution process is executed separately. Then, the calculation results are integrated, and the calculation results of all units are finally output.

[0131] The calculation process for the above condenser heat transfer mathematical model is shown in the appendix. Figure 3 The flowchart shown is shown.

[0132] Furthermore, in step P1, the air and refrigerant inlet parameters include at least air temperature, minimum flow surface air velocity, air flow characteristic length, refrigerant type, temperature, and refrigerant flow characteristic length; correspondingly, in step P2, the assumed air and refrigerant outlet parameters also include at least air temperature, minimum flow surface air velocity, air flow characteristic length, refrigerant type, temperature, and refrigerant flow characteristic length; similarly, in step P5, the outlet parameters of each heat transfer unit include at least air temperature, minimum flow surface air velocity, air flow characteristic length, refrigerant type, temperature, and refrigerant flow characteristic length.

[0133] Furthermore, in step P1, parameters such as air density, viscosity, Prandtl number, refrigerant density, viscosity, Prandtl number, property correction factor, heat transfer correlation coefficient, thermal conductivity, cavitation coefficient, and friction coefficient can be input as needed. As some embodiments of this application, these parameters can also be easily obtained via EES or REFPROP after the type and temperature are known.

[0134] Furthermore, in step P2, it is necessary to provide initial iterative values ​​for parameters such as air temperature, refrigerant type and temperature for each heat transfer unit.

[0135] Furthermore, step P3 includes:

[0136] P301, let i = 1, where i is the number of the heat transfer unit, and the value of i is 1, 2, 3, ... M;

[0137] P302, calculate the air-side heat transfer coefficient, pressure drop, and fin efficiency of the i-th heat transfer unit, as well as the refrigerant-side heat transfer coefficient, pressure drop, and refrigerant mass, etc.

[0138] P303, calculate the heat transfer of i heat transfer units according to the ε-NTU method;

[0139] P304, determine if i = M? If yes, continue to step P4; if no, increment the value of i by 1, and execute steps P302 and P303 again until i = M.

[0140] Furthermore, in step P4, the calculated values ​​of parameters such as heat exchange, pressure drop, and refrigerant mass of each heat transfer unit should be accumulated based on the calculation results of step P3.

[0141] Specifically, in step P4, based on the calculation results of step P3, the calculated heat exchange values ​​of each heat transfer unit are summed up to obtain the heat exchanger's heat exchange capacity; similarly, the calculated pressure drop values ​​of each heat transfer unit are summed up to obtain the pressure drop of the heat exchanger; and the refrigerant mass of each heat transfer unit is summed up to obtain the refrigerant mass of the heat exchanger.

[0142] Thus, based on the established mathematical model of heat transfer in the condenser, in step S2, the correction method for the overall heat transfer coefficient is as follows: the calculated value of the elbow temperature obtained by the mathematical model of heat transfer in the condenser is used as the target, and the actual measured value of the temperature monitored by the infrared thermogram is used as the correction object to continuously perform iterative correction calculations so that the calculated value of the elbow temperature is equivalent to the actual measured value of the elbow temperature.

[0143] Furthermore, in step S2, the correction of the overall heat transfer coefficient is performed according to formula (8):

[0144] U0'=kU0 (8)

[0145] Where U0' is the corrected overall heat transfer coefficient, k is the correction coefficient, and U0 is the overall heat transfer coefficient in the basic condenser heat transfer mathematical model.

[0146] Assuming a linear correlation between the overall heat transfer coefficients U0 and U0' before and after correction, when the mathematical model with correction coefficient k is used to calculate a pipe of length L, some input and output parameters are omitted, and the following relationship exists as shown in equation (9):

[0147] (H r，out Q, m r...) = f(L, k, H r，in ,...) (9)

[0148] Among them, H r,in H is the specific enthalpy of the refrigerant inlet. r,out ν is the specific enthalpy of the refrigerant outlet; Q is the heat exchange capacity of this section of the pipeline, m r This refers to the quality of the refrigerant.

[0149] That is, pipe length L, correction factor k, and refrigerant inlet specific enthalpy H. r,in Enthalpy H relative to exports r,out The four variables are correlated as described in the above formula. Therefore, if three of the variables are known, the fourth variable can be determined based on the condenser heat transfer mathematical model.

[0150] Furthermore, in step S2, the correction process for the overall heat transfer coefficient includes the following steps:

[0151] S201, Obtain the known pipe length L and refrigerant inlet and outlet specific enthalpy H. r,in H r,out ;

[0152] S202, given the initial value of the overall heat transfer coefficient k;

[0153] S203, invoke the condenser heat transfer mathematical model to calculate the refrigerant outlet specific enthalpy H'. r,out ;

[0154] S204, Determine H' r,out Is it equal to H? r,out If yes, output the calculation result; if no, adjust the value of the overall heat transfer coefficient k, and repeat steps S203 and S204 until H' r,out =H r,out .

[0155] It should be noted that in this application, the superscript "'" symbol indicates the calculated value obtained from the mathematical model of heat transfer in the condenser.

[0156] Additionally, it should be noted that in step S2, when correcting the total heat transfer coefficient of each phase region of each flow path in the condenser, the measured data is in the form of temperature, so the correction result should be based on the measured temperature.

[0157] However, during the correction process in step S204, considering the one-to-one correspondence between temperature and enthalpy, and the existence of a two-phase region where the temperature is fixed but the enthalpy changes with the dryness fraction, enthalpy is a more accurate criterion when correcting the heat transfer coefficient in the two-phase region. In other words, the correction in the two-phase region actually uses enthalpy. At the same time, in the superheated and supercooled regions, the quantities used in the program judgment and subsequent calculations are also enthalpy. Therefore, this application actually converts the measured temperature value into enthalpy for subsequent procedures. Therefore, in step S2, although the direct reference quantity is temperature, for the sake of convenient description and accurate detection, in step S204, the measured temperature value and the calculated temperature value can be converted into enthalpy value. Then, the total heat transfer coefficient of each phase region of each flow path of the condenser can be corrected by the measured enthalpy value in turn, so that the measured enthalpy value and the calculated enthalpy value are equal or equivalent. In step S204, the enthalpy value is used as the criterion for correcting the total heat transfer coefficient.

[0158] Specifically, the calculated elbow temperature value mentioned in this application is actually the outlet enthalpy value H in the model calculation. r,out The corresponding temperature value, wherein the enthalpy value is calculated using the heat transfer equation (7) on the refrigerant side.

[0159] Furthermore, in step S3, the calculation process for the pipe lengths of the condenser's superheated zone, subcooled zone, and two-phase zone includes the following steps:

[0160] S301, Obtain the known overall heat transfer coefficient k and refrigerant inlet and outlet enthalpy H. r,in H r,out ;

[0161] S302, given the initial value of the pipe length L;

[0162] S303, invoke the condenser heat transfer mathematical model to calculate the refrigerant outlet specific enthalpy H'. r,out ;

[0163] S304, Determine H' r,out Is it equal to H? r,out If yes, output the calculation result; if no, adjust the value of pipe length L and execute steps S303 and S304 again until H' r,out =H r,out .

[0164] The following specific embodiments illustrate the calculation process of the condenser refrigerant inventory and the total system charge as described in this application:

[0165] The test object is set as a double-row finned tube condenser. In this example, the refrigerant in the condenser is divided into three flow paths: upper, lower, and bottom. The upper flow path has seven bends, a1 to a7. The refrigerant flow path is divided into multiple segments by adjacent bends on the same side (e.g., a1 and a2). Each segment contains two heat transfer tubes, and the length of a single heat transfer tube is L. t .

[0166] The specific solution process for this double-row finned tube condenser is as follows:

[0167] (1) Input known quantities, including condenser structural parameters, air inlet parameters, and refrigerant condensation temperature T. c And the measured value T of the elbow temperature extracted from the infrared thermogram a1 ~T a7 Determine the phase region corresponding to elbow a2;

[0168] (2) If condition T is satisfied a2 >T c Therefore, elbow a2 is in the overheated zone, and the entire pipe section between elbows a1 and a2 is in the overheated zone. The length of this pipe section is L = 2L. t The refrigerant is superheated vapor, and the inlet and outlet temperatures are the elbow temperatures T. a1 and T a2 Based on this, the specific enthalpy of the pipeline inlet and outlet can be calculated. Figure 4 The algorithm shown can be used to calculate the correction coefficient k for the overheated zone in the upper flow path. sh，a ;

[0169] The purpose of heat transfer coefficient correction is to make the phase region division of each flow path as close as possible to the actual situation. It corrects errors caused by actual factors by using measured elbow temperatures, thereby improving the accuracy of refrigerant inventory detection, rather than negating the accuracy of heat transfer calculations in the mathematical model. Therefore, the correction algorithm should follow this principle: minimize the correction to the mathematical model while ensuring the calculated elbow temperature matches the actual value. In other words, when the correction coefficient k meets the temperature requirements within a certain range, the value closest to 1 should be selected to avoid over-correction of the mathematical model.

[0170] (3) The inlet temperature of the superheated zone is the elbow temperature T. a1 The outlet is saturated steam; based on this, the inlet and outlet enthalpies of the superheated zone can be calculated. The correction factor k is known. sh，a , call Figure 5 The algorithm shown can be used to calculate the length L of the overheated zone in the upper flow path. sh，aOutput the calculation results, including refrigerant mass and temperature, etc. It should be noted that: for the superheated zone, its outlet is the inlet of the two-phase zone, so the outlet temperature is the condensation temperature; the inlet temperature is obtained from the infrared thermogram; since the heat transfer coefficient has been corrected, the temperature at any position in the superheated zone can be naturally obtained through the refrigerant side heat transfer equation (7); on this basis, the refrigerant mass can be calculated according to formula (10~12);

[0171] (4) If condition T is not satisfied a2 >T c Then elbow a2 is in the saturation region, T a2 =T c Length of the overheated zone L sh，a ≤2L t Given an initial value k for the overheated zone correction factor. sh，a =1, call the mathematical model to calculate the pipe outlet temperature between elbows a1 and a2, that is, the temperature T' of elbow a2. a2 Compare the calculated temperature T' of the elbow. a2 and measured value T a2 If the two are equal, it indicates that the overheated zone does not require correction, and the correction coefficient k is output. sh，a =1, proceed to step S3; if the two are not equal, exclude T' a2 <T a2 In the case of (elbow a2 being too cold), then T' a2 >T a2 =T c The calculated value of elbow a2 is in an overheated state, indicating that the overall heat transfer coefficient of the overheated zone is too small, resulting in an overheated zone length L. sh，a >2L t At this point, a correction factor k should be assigned. sh，a >1, shortening the length of the superheated zone makes L sh，a ≤2L t To meet the elbow temperature T' a2 =T a2 Based on the correction principle of the condenser heat transfer mathematical model mentioned above, when the superheated zone length L... sh，a =2L t When the steam level at bend a2 is saturated, the correction to the model is minimal. The inlet and outlet enthalpies of the superheated zone are known; therefore, the model can be modified accordingly. Figure 4 The algorithm shown can be used to calculate the correction coefficient k. sh，a It outputs calculation results, including refrigerant mass and temperature.

[0172] (5) Perform a similar solution process for elbows a5 to a7 to obtain the correction coefficient k for the subcooled zone of the upper flow path. sc，a and length L sc，a The length of the saturation region in the upper flow path is equal to the total length L. aSubtract the lengths of the superheated and supercooled regions, i.e., L tp,a =L a -L sh，a -L sc，a Therefore, the correction coefficient k for the saturated region of the upper flow path can be obtained. tp,a By analyzing and solving the flow paths at the bottom and bottom of the condenser using a similar algorithm, the correction coefficients, pipe lengths, refrigerant mass, and refrigerant temperature of each phase region in each flow path can be obtained. The total refrigerant mass in the finned tube is then obtained by summing the refrigerant mass of each phase region in each flow path.

[0173] The refrigerant mass in each phase region of each flow path is calculated using the following formulas (10-12);

[0174]

[0175] In the formula, m sh For the refrigerant quality in the superheated zone, L sh ρ is the length of the pipe in the superheated zone. G Where A is the refrigerant gas density in the superheated zone, and A is the cross-sectional area of ​​the refrigerant pipe.

[0176]

[0177] In the formula, m sc For the refrigerant quality in the subcooled zone, L sc ρ is the length of the subcooled zone pipe. L This refers to the refrigerant gas density in the subcooled zone.

[0178]

[0179] In the formula, m tp For the refrigerant mass in the two-phase region, L tp ∈ represents the pipe length in the two-phase region, and ∈ represents the cavitation coefficient in the two-phase region;

[0180] Furthermore, in this embodiment, the cavitation coefficient is calculated using the Zivi slip ratio model, and the specific calculation method is shown in equation (14):

[0181]

[0182] Where S is the slip ratio, and the calculation method is shown in equation (15):

[0183]

[0184] (6) The total mass of refrigerant in the finned tube calculated in the above steps is the sum of the mass of refrigerant in the finned tube in each flow path of the condenser, and does not include the mass of refrigerant in the elbow. Therefore, it is necessary to supplement the total mass of refrigerant in the finned tube: condenser refrigerant inventory = total mass of refrigerant in the finned tube + total mass of refrigerant in the elbow.

[0185] Specifically:

[0186] In this example, the elbow length is calculated as a semicircle. The refrigerant mass within each elbow is calculated according to the following formula (13):

[0187]

[0188] In the formula, R is the radius of curvature of the bend, and D... i ρ is the inner diameter of the pipe. r The density of the refrigerant fluid inside the elbow, m r,elbow The refrigerant mass inside the elbow.

[0189] Calculate the refrigerant mass in all bends sequentially according to the refrigerant flow method in formula (13), and sum them up to obtain the total refrigerant mass in the bends. Add the total refrigerant mass in the bends to the total refrigerant mass in the finned tubes to obtain and output the refrigerant storage in the condenser. Then, based on the relationship that the ratio of the refrigerant storage in the condenser to the total refrigerant charge in the system is about 60%, calculate the total refrigerant charge in the system.

[0190] Verification shows that the maximum relative error between the calculated and measured values ​​of the refrigerant inventory in the condenser in this application is 7.0%, and the average relative error is 3.0%, indicating that the calculation accuracy meets the usage requirements.

[0191] A device for detecting the total refrigerant charge of a refrigeration system, comprising:

[0192] The condenser temperature monitoring module can read the actual temperature distribution data inside the condenser of the refrigeration system, including inlet and outlet temperatures, and temperatures of each bend, for subsequent correction of the overall heat transfer coefficient.

[0193] The heat transfer coefficient correction module is used to correct the calculation error of the condenser heat transfer mathematical model, so that the calculated value of the elbow temperature is comparable to the measured value.

[0194] The zoned pipe length calculation module calculates the pipe length of the superheated zone, subcooled zone and two-phase zone of the condenser based on the corrected total heat transfer coefficient, which is used for subsequent calculation of the refrigerant inventory in the condenser.

[0195] The refrigerant inventory calculation module is used to calculate the refrigerant inventory in the condenser based on the calculation results of the heat transfer coefficient correction module and the partitioned pipe length calculation module, and to calculate the total refrigerant charge of the system based on the refrigerant inventory in the condenser.

[0196] As some embodiments of this application, the condenser temperature monitoring module includes an infrared thermal imager, and the condenser being monitored is a double-row finned tube condenser.

[0197] Furthermore, the working process of the total refrigerant charge detection device for the refrigeration system is as follows: First, the infrared thermal imager captures an infrared thermal image of the condenser to obtain the temperature distribution information of the condenser, including at least the inlet and outlet temperatures, the temperatures at each bend, and the condensing temperature. Then, the condenser temperature monitoring module reads the actual temperature distribution data inside the condenser of the refrigeration system, including the inlet and outlet temperatures, the temperatures at each bend, etc., and transmits the information to the heat transfer coefficient correction module. The heat transfer coefficient correction module corrects the heat transfer coefficient using the condenser heat transfer mathematical model and outputs the model calculation temperature. Afterward, the heat transfer coefficient correction module transmits the corrected total heat transfer coefficient to the zone pipe length calculation module and the refrigerant inventory calculation module. The zone pipe length calculation module calculates the length of each phase zone and transmits the calculation result to the refrigerant inventory calculation module. The refrigerant inventory calculation module calculates the refrigerant inventory in the condenser using the corrected total heat transfer coefficient and the length of each phase zone. Then, it calculates the total refrigerant charge of the refrigeration system according to the ratio of the refrigerant inventory in the condenser to the total charge, thus realizing the detection of the total refrigerant charge of the refrigeration system.

[0198] Of course, the method and apparatus for detecting the total refrigerant charge of the refrigeration system described in this application can be applied to all air conditioners, especially small household air conditioners.

[0199] In summary, the method and apparatus for detecting the total refrigerant charge of a refrigeration system described in this application achieves the goal of detecting the total refrigerant charge of a refrigeration system without the need for sensor installation, without interfering with system operation, and with only a small amount of data. This solves the problems of previous detection methods that required a large number of sensors to interfere with system operation or had insufficient data to support model establishment. It provides a convenient and efficient detection solution for detecting the total refrigerant charge of a refrigeration system.

[0200] While the present invention has been disclosed above, it is not limited thereto. In the description of this specification, references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A method for detecting the total refrigerant charge of a refrigeration system, characterized in that, Before using the aforementioned method for detecting the total refrigerant charge, a mathematical model of condenser heat transfer needs to be established. Then, the total refrigerant charge of the refrigeration system is calculated using this mathematical model. The method for detecting the total refrigerant charge includes the following steps: S1, Collect condenser temperature through infrared temperature detection device: Obtain temperature data of condenser inlet and outlet and each elbow; S2, Overall heat transfer coefficient correction: Using the temperature data obtained in step S1, the condenser heat transfer mathematical model is used to simulate the operating state of the condenser under the under-charge condition, and the calculated value of the elbow temperature is calculated. The overall heat transfer coefficient of each phase region of each flow path of the condenser is corrected in turn by the calculated value of the elbow temperature, so that the calculated value of the elbow temperature is comparable to the measured value of the elbow temperature obtained in step S1. S3, Phase region length calculation: Based on the overall heat transfer coefficient corrected in step S2, calculate the pipe lengths of the condenser superheated zone, subcooled zone, and two-phase zone respectively; S4, Refrigerant inventory calculation: Calculate the refrigerant inventory in the condenser based on the total heat transfer coefficient corrected in step S2 and the pipe lengths of each zone of the condenser calculated in step S3, and calculate the total refrigerant charge of the system based on the refrigerant inventory in the condenser. The condenser heat transfer mathematical model is established using the distributed parameter method and calculated according to the ε-NTU method; where ε represents efficiency and NTU represents the number of heat transfer units. The calculation process of the condenser heat transfer mathematical model is as follows: P1, input known parameters, including condenser structural parameters, air and refrigerant inlet parameters, refrigerant condensation temperature, and refrigerant mass flow rate; P2, assuming air and refrigerant outlet parameters, given initial values ​​for air and refrigerant iterations for each heat transfer unit; P3, according to the order in which the refrigerant flows through each heat transfer unit, calculate the air-side heat transfer coefficient, pressure drop and fin efficiency of each heat transfer unit, the refrigerant-side heat transfer coefficient, pressure drop and refrigerant mass, and use the ε-NTU method to calculate the heat exchange of each heat transfer unit. P4, sum the calculated values ​​of all parameters of all heat transfer units; P5, the inlet parameters of each heat transfer unit are known, or can be obtained from the outlet parameters of the previous unit. The outlet parameters of each heat transfer unit are calculated based on the inlet parameters and heat exchange of each heat transfer unit, and the air and refrigerant status in all heat transfer units are updated in sequence. P6. Repeat steps P3 to P5 to continuously update the air and refrigerant status of each heat transfer unit until the temperature change of air and refrigerant in all heat transfer units before and after the update is less than the preset value. P7 outputs the calculation results, including the air and refrigerant temperatures, refrigerant mass, and pipe wall temperature of each heat transfer unit.

2. The method for detecting total refrigerant charge according to claim 1, characterized in that, Step P3 includes: P301, let i=1, where i is the number of the heat transfer unit, and the value of i is 1, 2, 3, ... M; P302, calculate the air-side heat transfer coefficient, pressure drop, and fin efficiency of the i-th heat transfer unit, and the refrigerant-side heat transfer coefficient, pressure drop, and refrigerant mass; P303, calculate the heat transfer of i heat transfer units according to the ε-NTU method; P304, determine if i = M? If yes, continue to step P4; if no, increment the value of i by 1, and execute steps P302 and P303 again until i = M.

3. The method for detecting the total refrigerant charge according to claim 1 or 2, characterized in that, In step S2, the correction method for the overall heat transfer coefficient is as follows: the calculated value of the elbow temperature obtained by the mathematical model of heat transfer of the condenser is used as the target, and the overall heat transfer coefficient is used as the correction object to continuously perform iterative correction calculations so that the calculated value of the elbow temperature is equivalent to the measured value of the elbow temperature.

4. The refrigerant total charge detection method according to claim 3, characterized by, In step S2, the correction of the overall heat transfer coefficient is performed according to formula (8): （8） Where U0' is the corrected overall heat transfer coefficient, k is the correction coefficient, and U0 is the overall heat transfer coefficient in the basic model.

5. The refrigerant total charge detection method according to claim 4, characterized by, In the step S2, the pipe length L, the correction coefficient k, the refrigerant inlet specific enthalpy H r,in and the outlet specific enthalpy H r,out The following relationship exists between these four variables: （9） Among them, H r,in H is the specific enthalpy of the refrigerant inlet. r,out ν is the specific enthalpy of the refrigerant outlet; Q is the heat exchange capacity of this section of the pipeline, m r This refers to the quality of the refrigerant.

6. The refrigerant total charge detection method according to claim 5, characterized by, In step S2, the correction process for the overall heat transfer coefficient includes the following steps: S201, Obtain the known pipe length L and refrigerant inlet and outlet specific enthalpy H. r,in H r,out ; S202, given the initial value of the overall heat transfer coefficient k; S203, calling the condenser heat transfer mathematical model, calculating the refrigerant outlet specific enthalpy H' r,out ; S204, judge H' r,out whether = H r,out , if yes, output the calculation result; if no, adjust the value of total heat transfer coefficient k, execute steps S203 and S204 again until H' r,out = H r,out .

7. The refrigerant total charge detection method according to claim 6, characterized by, In step S3, the calculation process for the pipe lengths of the condenser's superheated zone, subcooled zone, and two-phase zone includes the following steps: S301, acquire the known total heat transfer coefficient k, the refrigerant import and export specific enthalpy H r,in , H r,out ; S302, given the initial value of the pipe length L; S303, calling the condenser heat transfer mathematical model to calculate the refrigerant outlet specific enthalpy H' r,out ; S304, Determine H' r,out Is it = H r,out If yes, output the calculation result; if no, adjust the value of pipe length L and execute steps S303 and S304 again until H' r,out =H r,out .

8. The total refrigerant charge detection method according to claim 1, characterized by, In step S4, the refrigerant inventory in the condenser = total refrigerant mass in the finned tubes + total refrigerant mass in the elbows; wherein, the total refrigerant mass in the finned tubes is the sum of the refrigerant mass in each phase region of each flow path, and the total refrigerant mass in the elbows is the sum of the refrigerant mass in all elbows; The refrigerant mass in each phase region of each flow path is calculated using the following formulas (10~12); （10） In the formula, m sh For the refrigerant quality in the superheated zone, L sh ρ is the length of the pipe in the superheated zone. G Where A is the refrigerant gas density in the superheated zone, and A is the cross-sectional area of ​​the refrigerant pipe. （11） wherein m sc is the mass of subcooled refrigerant, L sc is the length of the subcooled pipe, p L is the density of subcooled refrigerant gas; （12） where m tp is the two-phase region refrigerant mass, L tp is the two-phase region pipe length, and is the two-phase region void fraction; The mass of refrigerant in each bend (m) r,elbow Perform according to the following formula (13): （13） where R is the bend radius, D i is the pipe inside diameter, p r is the refrigerant fluid density within the bend, m r,elbow is the refrigerant mass within the bend.

9. A refrigerant total charge detection device for a refrigeration system, characterized by The detection device uses the detection method described in any one of claims 1-8 to detect the total refrigerant charge. The detection device includes: The condenser temperature monitoring module can read the actual temperature distribution data inside the condenser of the refrigeration system for subsequent correction of the overall heat transfer coefficient. The heat transfer coefficient correction module is used to correct the calculation error of the condenser heat transfer mathematical model, so that the calculated value of the elbow temperature is comparable to the measured value. The zoned pipe length calculation module calculates the pipe length of the superheated zone, subcooled zone and two-phase zone of the condenser based on the corrected total heat transfer coefficient, which is used for subsequent calculation of the condenser refrigerant inventory. The refrigerant inventory calculation module is used to calculate the refrigerant inventory in the condenser based on the calculation results of the heat transfer coefficient correction module and the partitioned pipe length calculation module, and to calculate the total refrigerant charge of the system based on the refrigerant inventory in the condenser.

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