Discussion on the mutual matching process between air compressor and air conditioner
Usually, the air conditioning system is mainly composed of key components such as a compressor, an evaporator, a condenser, and a throttling device (such as a capillary tube). The components must be well matched to truly realize the performance of the entire air conditioning system and improve the energy efficiency ratio of the system, thereby saving energy. The method currently used in the matching of air-conditioning systems is to first give a general component composition based on experience, and then observe through experiments to see whether the parameters such as capacity and energy efficiency ratio meet the requirements; if the requirements are met, consider whether the cost can be replaced. Low parts such as heat exchangers, compressors, etc. This method has a slower matching speed and a waste of resources, so it is very important to find a faster and more economical method.
The simulation of air conditioning system provides an effective way to solve this problem.
For compressor manufacturers, it is often necessary to assist air-conditioning plants in matching experiments between compressors and air conditioners in order to better utilize the performance of the entire air-conditioning system. The air conditioner herein refers to an air conditioner system other than a compressor, and is simply referred to as an air conditioner for the sake of simplicity. An air conditioner including all components such as a compressor is called an air conditioning system. Here, the system flow of automatic matching of the compressor and the air conditioner is first established.
Secondly, in order to simulate the matching effect between the selected compressor and the air conditioner (cooling capacity, energy efficiency ratio, etc.), the VBA language is used to implement an automatic matching simulation program on the Excel software. The entire air conditioning system is divided into evaporator, condenser, compressor, capillary and other parts for simulation calculation. In order to more accurately represent the state of the system refrigerant, the system's undercooling and superheat are converted into coma for processing. The quality of the system refrigerant is kept constant as a link, and the parameters of the air conditioning system are matched by automatically adjusting the parameters such as evaporation temperature, condensation temperature, and enthalpy. In the compressor simulation, the influence of the dissolved refrigerant amount in the compressor oil pool is considered to make the simulation result more accurate.
1 system calculation flow chart
In order to match the most suitable compressor to the specified air conditioner and determine the optimal refrigerant charge, it is first necessary to establish a database of compressor characteristic parameters, and initially select the compressors that meet the requirements to form a compressor alternative database according to the design requirements of the system. Second, the selected compressor and air conditioner are simulated to give the best match. The specific steps of the system flow chart are as follows: 1) Establish a compressor alternative database Firstly, the ten coefficient method is used to fit the performance parameters such as capacity, power and current of the compressor. Typically, these fitting parameters are provided by the compressor manufacturer. Next, record the amount of refrigerant oil, high pressure chamber volume, low pressure chamber volume, etc. for each type of compressor, and build a model database of the compressor to be called when the compressor matches the air conditioner.
After the air conditioner is given, according to the design parameters of the air conditioner, the compressor with the capacity range of 100% to 150% under certain working conditions is selected, and the requirements of the compressor electric system and the applicable refrigerant are met, thereby forming the air conditioner matching. Compressor alternative database.
2) Select a certain type of compressor from the compressor alternative database, and perform simulation matching calculation between the compressor and the air conditioner to determine the optimal refrigerant charge.
3) Judging whether all compressors in the alternative database have been matched, if it is (4), otherwise the compressor output model with the highest energy efficiency ratio (COP) and the corresponding optimal refrigerant charge under the condition of meeting the capability requirements Flux.
2 compressor and air conditioner matching calculation
After the compressor is selected, the matching calculation between the compressor and the air conditioner is performed to determine parameters such as the optimal COP, the cooling capacity, and the corresponding refrigerant charge.
The entire air conditioning system is divided into evaporator, condenser, compressor, capillary and other parts for simulation calculation. In order to more accurately represent the state of the system refrigerant, the system's undercooling and superheat are converted into coma for processing. For the calculation of the coupling between the components, the mass flow of the system refrigerant remains unchanged as a link, and the state of the air conditioning system is simulated by continuously adjusting parameters such as evaporation temperature, condensation temperature, and enthalpy difference. Generally, superheat refers to the difference between the superheat temperature and the saturation temperature of the refrigerant at the same evaporation pressure in the refrigeration cycle. During the test, when the degree of superheat is 0, the state of the system refrigerant may be at 1' point or 6 points. In the calculation of the program, the calculation when the degree of superheat is 0 is required. In order to more accurately represent the state of the system refrigerant, the difference between the current refrigerant enthalpy value and the saturation gas enthalpy corresponding to the evaporation temperature is used instead of the superheat degree. Similarly, the difference between the current refrigerant enthalpy and the saturated liquid enthalpy corresponding to the condensing temperature is used instead of the subcooling.
The flow chart of the simulation calculation of the compressor and the air conditioner is as shown. Where m rmin and m rmax are the minimum and maximum refrigerant charge, respectively; ΔH c and m rc are the calculated enthalpy difference and refrigerant quantity respectively; Q com and Q cap are the mass flow rates of the compressor and the capillary, respectively.
2.1 Compressor model
In order to calculate the compressor's capacity, power, current and other related parameters, the ten-coefficient fitting method is adopted. The formula is as follows: (1) X DD capability, power or current; S DD evaporation temperature, ° C; D DD condensing temperature, ° C; C 1, C 2 C 10 is the fitting factor given by the compressor manufacturer.
Equation (1) is a numerical simulation formula under the standard test conditions of the compressor. That is, the condensing temperature is 54.4 ° C, the evaporation temperature is 7.2 ° C, the suction superheat is 11.1 K, and the simulated data under the condition of subcooling 8.3 K.
This formula needs to be corrected when the degree of subcooling and inhalation superheat changes.
Let the current subcooling degree be T sc, H sc be the ç„“ value corresponding to the (T sc-8.3) supercooling section, and G be the refrigerant mass flow rate, then the current capacity, power or current X 1 is: X 1 = X + H Sc G(2) When the superheat is T sh , the system capacity, power or current X 2 is <1>: X 2 = X + 0.00144 (T sh-11.1) X (3) In addition, when the compressor is simulated According to the refrigerant and oil mutual solubility curve, the amount of refrigerant dissolved in the oil is obtained. The solubility curve of the refrigerant in the frozen oil is shown.
Assume that the refrigerant charge in the compressor is 1700 mL, the density of the refrigerant oil is 1.2×10 3 kg/m 3 , the temperature of the compressor oil pool is 40 ° C, and the pressure is 5×10 5 Pa, which is frozen according to the available R22 refrigerant. The solubility in oil is 7.5%, that is, the amount of refrigerant dissolved in the frozen oil is 0.153 kg.
2.2 Heat exchanger model
1) The simulation of the condenser adopts a steady-state distributed parameter model, and the condenser is divided into a superheater, a two-phase zone, and a supercooling zone for numerical simulation. Each phase zone is divided into a number of micro-elements. For the single-phase zone, that is, the superheat zone and the supercool zone, the division of the micro-element is equally divided by the refrigerant side temperature drop. For the two-phase zone, since the temperature is constant, the heat transfer is represented by the change of the enthalpy value, so the division of the micro-element is equally divided according to the refrigerant enthalpy difference. If the import and export state parameters of the micro-element are known, the length L of each micro-element is: (4) where αi is the heat transfer coefficient of the refrigerant side surface, αo is the heat transfer coefficient of the air side surface, A i /A o It is the ratio of the effective heat transfer area inside and outside the condenser tube; mr represents the mass flow rate on the refrigerant side. h r1 micro-inlet side refrigerant enthalpy value, h r2 represents the refrigerant enthalpy value on the exit side of the micro-element; T rm represents the average temperature of the refrigerant side, T am represents the average temperature of the air side; di represents the inner diameter of the pipe wall.
For the single-phase zone, the refrigerant side heat transfer coefficient αi is calculated by the Dittus-Boeler heat transfer correlation. For the two-phase zone, the refrigerant side heat transfer coefficient is calculated by Shah correlation. For the air side heat transfer coefficient, the heat transfer comprehensive correlation calculation of Li Wei et al.
2) Simulation of the evaporator For the evaporator simulation, the refrigerant side consists of two phase zones: a two-phase zone and a superheat zone. Each phase region can be calculated by dividing the coma into several micro-elements. The length L of each micro-element is: (5) where Q r is the refrigerant side heat exchange amount and T w is the tube wall temperature. T r is the refrigerant side temperature, αi is the refrigerant side surface heat transfer coefficient, and the automatic matching technology study of the compressor and the air conditioner di indicates the inner diameter of the pipe wall.
For the superheat zone, the refrigerant side heat transfer coefficient is calculated by the Dittus-Boeler heat transfer correlation. For the two-phase zone, the refrigerant side heat transfer coefficient is calculated using the formula of wang.
3) Cavitation coefficient model The air conditioner simulation analysis requires accurate simulation of the actual working condition of the air conditioner. One of the important aspects is how to accurately determine the amount of refrigerant charge. The difficulty in calculating the charge amount is the determination of the refrigerant volume in the two-phase zone. The key is the calculation of the bubble coefficient in the two-phase zone.
The bubble coefficient is the total area fraction of the gas phase of the two-phase mixture in any flow section, also known as the section gas fraction. Comparing the bubble model with homogeneous model and sliding ratio model, the hughmark model is used for calculation. The formula is as follows: (6) Among them, the specific calculation of KH is shown in the literature <2>, Ïg is gas density, Ïf is liquid density, x For dryness.
2.3 Throttling device model <7> reviewed the study of capillary as a throttling element. In this paper, the practical correlation model of adiabatic capillary proposed by Jung et al. is used. The formula is as follows: (7) where, for R22 refrigerant, c 1 =0.249029, c 2 =2.543633, c 3 =-0.42753, c 4 =0.746108, c 5 = 0.013922.D is the inner diameter of the capillary, L cap is the capillary length, T in is the capillary inlet temperature, and ΔT sc is the degree of subcooling.
3 Simulation example Take the 5HP secondary energy efficiency air conditioner matching of R22 refrigerant in an air conditioning plant as an example to verify the method. It is known that the complete air conditioning system requires a nominal cooling capacity of 12 kW and a COP ≥ 3.0. Other system measurement parameters are: condenser tube diameter is 7.94 mm, wall thickness is 0.25 mm, tube spacing is 25.4 mm, row spacing is 19.04 mm, wing The sheet thickness is 0.11mm, the fin spacing is 1.3mm, the number of rows is 2, the number of branches is 8, the wind speed is 1.22m/s. The diameter of the evaporator is 9.52mm, the wall thickness is 0.35mm, the tube spacing is 25.4mm, the spacing is 21.0mm, fin thickness 0.11mm, fin spacing 18.5mm, row number 3, number of branches 6, wind speed 1.3m / s. Capillary length is 0.5m, inner diameter is 1.4mm. Fan power is 350W.
It is required to select the compressor and refrigerant charge that match the best set of air conditioners, and calculate the parameters such as COP, cooling capacity and power of the system under optimal conditions. The program is compiled on the Excel software using the VBA language, and the simulation results are compared with the actual results.
It can be seen from the simulation results that the C-SBX160H38A matches the air conditioner with the best COP of 3.102 and the cooling capacity of 11744 W. This is consistent with the actual air conditioning system matching experiment results. The cooling capacity of the two is 2.1%, the COP is 1.9%, and the refrigerant charge is 2.9%. In addition, the experimental condensation temperature is 46 ° C, the evaporation temperature is 3.8 ° C, the subcooling is 5.3 ° C, and the superheat is 4.6 ° C. . The simulated condensation temperature was 48 ° C, the evaporation temperature was 2.3 ° C, the degree of subcooling was 10 ° C, and the degree of superheat was 3 ° C. The difference between the two is 2 ° C, 1.5 ° C, 4.7 ° C, 1.6 ° C. It can be seen that the method here can accurately simulate the operating state of the air conditioner, thereby providing guidance for the matching of the compressor and the air conditioner.
4 Conclusion
Firstly, the system flow of automatic matching between compressor and air conditioner is given. Secondly, the refrigerant mass flow rate remains unchanged as the connection link, and the compressor, heat exchanger and capillary are simulated.
Among them, the evaporation temperature and the condensation temperature are adjusted according to the change of the enthalpy value, and the operating range of the simulation of the air conditioning system is expanded. When simulating the compressor, the influence of the dissolved refrigerant in the frozen oil was considered, and the accuracy of the simulation model was improved. In order to facilitate the popularization and application of this method, the VBA language is used to implement the program on Excel software. Finally, the software was applied to the air conditioner matching experiment commissioned by an air conditioner, which provided a good theoretical guidance for the experiment and saved a lot of matching time and funds.
Gas compressor is one machine used to increase pressure. For some gases, it is important to increase pressure up to 150 bars or 200 bars, this high pressure gas is filled into cylinders for storage. As different gases has different natures, some are easy to explore, some are easy to catch fire, so different gases have different compressors. For oxygen, it is Oxygen Compressor. For nitrogen, it is Nitrogen Compressor.
Oxygen/nitrogen compressor specification:
Capacity: 1-3000 Nm3/hr
Inlet pressure: 4-8 bars
Outlet pressure: 150-200 bars
Medium: Nitrogen/oxygen
Gas Compressor,Gas Air Compressor,Gas Piston Compressor,Mini Gas Compressor
Shandong Gamma Gas Engineering Co. Ltd. , https://www.gammagases.com