适用于制冷系统动态仿真的全封闭式压缩机准动态模型

制冷系统动态仿真中要求压缩机模型能够适用于吸入制冷剂状态从两相到气相的宽变化范围,并且能够快速地反映其关键的动态特性,为了解决这个问题,提出了可覆盖进口状态从气相到两相制冷剂的准动态压缩机模型。此模型按其热力过程分解为吸入气相或两相制冷剂与腔内制冷剂混合过程的动态模型、壳体换热过程的动态模型和气缸内制冷剂压缩过程的稳态模型。此压缩机模型克服了通常压缩机模型中忽略腔内制冷剂混合过程所导致预测的流量大于实际流量的缺点,以及全部采用动态模型导致计算复杂的问题。通过某压缩机厂生产的全封闭式压缩机的稳态实验数据和模型预测值的比较,结果表明:模型预测的稳定工况时的质量流量和输入功率与实验数据误差小于5%;开机过程质量流量和输入功率与实验测量值趋势一致,误差小于10%。     

跨临界二氧化碳压缩机热力性能仿真与分析

针对跨临界二氧化碳半封闭式往复式活塞压缩机建立了一个通用数学模型,既包括热力学模块,也包括机械模块。热力学模块主要描述气缸内部的气体压缩过程。机械模块包括运动学模型和曲轴连杆机构模型,考虑了轴承上的功耗损失。采用一台压缩机样机对模型进行了不同运行工况下的实验验证,结果显示压缩机流量和耗功的最大误差分别不超过5%和8%。通过仿真分析了变结构和变工况条件下的压缩机性能,结果表明:在不同的运行工况下,存在最佳缸径行程比;容积效率和等熵效率都随着转速的增加而下降;吸排气阀门内径存在最佳值;对于容积效率的影响,吸气阀间隙比排气阀间隙更大,活塞与汽缸间隙比活塞环与汽缸间隙更大。     

A comprehensive model of a novel rotating spool compressor

A comprehensive simulation model of a novel rotating spool compressor is presented. The spool compressor provides a new rotary compression mechanism with easily manufactured components. A detailed analytical geometry model of the spool compressor is presented, which includes the geometry of the vane. This geometry model is included in an overall comprehensive compressor model that includes sub-models for friction, leakage, and heat transfer. The results of the comprehensive model were validated using experimental data from a prototype compressor. The prototype compressor has an overall displacement of 23.9 cm³, and was operated using R410A as the working fluid. The model predicts the volumetric efficiency, discharge temperature, and shaft power of the prototype compressor to within 3.13% MAE, 16.5 K and ?13.2 W average deviation, respectively. The trends and spread in the data indicate that additional effort should be focused on the operation of the active sealing elements within the compressor.     

Performance representation of variable-speed compressor for inverter air conditioners based on experimental data

Variable speed control of compressors is one of the best methods to regulate the capacity of heat pumps and air conditioners. An analysis is conducted for modeling the variable speed compressor for simulation of inverter air conditioner and heat pump. Having scattered the real operation performance of inverter compressor into infinite operation performance of constant speed compressor, the map-based method is utilized to fit the performance curves of inverter compressor. The model is built at the basic frequency and the map condition as the second-order function of condensation temperature and evaporation temperature. Then it is corrected by the compressor frequency as the second-order function of frequency and by the actual operating condition as the actual specific volume of the suction gas. This method is used to set up simulation models of three different compressors. Compared with the data provided by the compressor manufacturers, the average relative errors are less than 2, 3 and 4% for refrigerant mass flow rate, compressor power input and coefficient of performance (COP), respectively. This model of variable speed compressor is suitable for the simulation of inverter air conditioner and heat pump systems. Based on the experimental data and simulation model, the frequency at zero mass flow rate and power input at zero frequency are discussed and the relation between COP and compressor frequency is analyzed.     

Modeling and performance study of a water-injected twin-screw water vapor compressor

Due to the reason of water injection, twin screw water vapor compressor can realize higher pressure ratio and saturated temperature lift of compressed vapor. Its application in mechanical vapor compression (MVC) heat pump systems has drawn much attention recently because of the great energy-saving potential and reliability. In this paper, a thermodynamic model of the working process in water injected twin screw water vapor compressor is established, in which heat and mass transfer between water liquid and vapor are considered. Its accuracy is validated by the experimental recorded p–V indicator diagrams. With the proposed model, the compressor performance is simulated and studied. According to the simulation results, water injection can increase the volumetric efficiency 5% and adiabatic indication efficiency 6%. Once the discharged vapor has been cooled to saturation, the shaft power of the compressor will increase while the adiabatic indication efficiency and the volume flow rate together with the volumetric efficiency change little with the continuous increase of injected water. Since the sensible heat of water is much smaller than latent heat, the temperature of injected water has little effect on the performance. Both the volume flow rate and shaft power increase linearly with the rotor speed. In addition, the volume flow rate of injected water should be adjusted with the regulation of rotor speed to guarantee a saturate discharge temperature. The volumetric efficiency will increase and the adiabatic indication efficiency will decrease slowly with the rise of rotor speed. Due to the cooling and evaporation effects of liquid water at the discharge chamber, the adiabatic indication efficiency does not decline when it operates at under compression condition. Water injection can greatly improve the compressor performance when the compressor operates at under compression or over compression condition, especially where a high saturated temperature lift of compressed vapor is in demand.     

Development of one-dimensional model for initial design and evaluation of oil-free Co2 turbo-compressor

A 1-dimenional tool for preliminary design and performance prediction of oil-free CO₂ compressor is presented. The model describes high speed centrifugal compressor in a hermetic configuration supported on foil gas bearings. To give possibly comprehensive overview of the technology, a wide range of loss mechanisms is considered. The model predicts aerodynamic performance of the compressor as well as losses related to the windage of rotor and bearings and due to the internal cooling. Numerical investigation of different compressor stages was used to validate aerodynamic predictions of the 1D model. Maximal prediction discrepancy amounted 2% for efficiency and 5% for pressure ratio. The prediction of the total compressor efficiency was compared with test data from a 50 kW compressor published Sandia Laboratories. The predicted peak compressor efficiencies are between 66 and 67.5% while experimentally measured values are within 65–70% region.     

Thermodynamic analysis on the performance of a variable speed scroll compressor with refrigerant injection

A thermodynamic model for a variable speed scroll compressor with refrigerant injection was developed using continuity, energy conservation and real gas equation. The model included energy balance in the low-pressure shell compressor, suction gas heating, motor efficiency, and volumetric efficiency considering gas leakages as a function of compressor frequency. The developed model was verified by comparing the predicted results for the no injection condition with the experimental data. The deviations of the predicted from the measured values were within 10% for approximately 90% of the experimental data. Based on the model, mass flow rate, suction gas heating, cooling capacity and power consumption of the compressor were estimated and analyzed as a function of frequency. The effects of refrigerant injection on the performance of the compressor were also discussed as a function of frequency, injection conditions, and injection geometry.

Résumé

A thermodynamic model for a variable speed scroll compressor with refrigerant injection was developed using continuity, energy conservation and real gas equation. The model included energy balance in the low-pressure shell compressor, suction gas heating, motor efficiency, and volumetric efficiency considering gas leakages as a function of compressor frequency. The developed model was verified by comparing the predicted results for the no injection condition with the experimental data. The deviations of the predicted from the measured values were within 10% for approximately 90% of the experimental data. Based on the model, mass flow rate, suction gas heating, cooling capacity and power consumption of the compressor were estimated and analyzed as a function of frequency. The effects of refrigerant injection on the performance of the compressor were also discussed as a function of frequency, injection conditions, and injection geometry.     

Sensitivity analysis of a comprehensive model for a miniature-scale linear compressor for electronics cooling

A comprehensive model of a linear compressor for electronics cooling was previously presented by Bradshaw et al. (2011). The current study expands upon this work by first developing methods for predicting the resonant frequency of a linear compressor and for controlling its piston stroke. Key parameters governing compressor performance – leakage gap, eccentricity, and piston geometry – are explored using a sensitivity analysis. It is demonstrated that for optimum performance, the leakage gap and frictional parameters should be minimized. In addition, the ratio of piston stroke to diameter should not exceed a value of one to minimize friction and leakage losses, but should be large enough to preclude the need for an oversized motor. An improved linear compressor design is proposed for an electronics cooling application, with a predicted cooling capacity of 200 W a cylindrical compressor package size of diameter 50.3 mm and length 102 mm.     

Modeling of rotary vane compressor applying artificial neural network

The thermal modeling of rotary vane compressor (RVC) was performed in this paper by applying Artificial Neural Network (ANN) method. In the first step, appropriate tests were designed and experimental data were collected during steady state operating condition of RVC in the experimental setup. Then parameters including refrigerant suction temperature and pressure, compressor rotating speed as well as refrigerant discharge pressure were adjusted.With these input values, the operating output parameters such as refrigerant mass flow rate and refrigerant discharge temperature were measured. In the second step, the experimental results were used to train ANN model for predicting RVC operating parameters such as refrigerant mass flow rate and compressor power consumption. These predicted operating parameters by ANN model agreed well with the experimental values with correlation coefficient in the range of 0.962-0.998, mean relative errors in the range of 2.79-7.36% as well as root mean square error (RMSE) 10.59 kg h⁻¹ and 12 K for refrigerant mass flow rate and refrigerant discharge temperature, respectively. Results showed closer predictions with experimental results for ANN model in comparison with nolinear regression model.     

A model for exergy analysis and thermodynamic bounds of Stirling refrigerators

A thermodynamic model based on exergy flow through a Stirling Refrigerator is developed. Important irreversibilities of the refrigerator due to external heat transfer with the reservoirs, heat leak, flow and heat transfer in regenerator are included in the model. Expansion and compression efficiencies are introduced in the model to account for the losses in these processes. The effect of a control phase shift between the mass flow rate and pressure across regenerator on the performance of the refrigerator is presented. Analytical solutions representing important quantities in the design of Stirling refrigerators such as the load curve, cooling power and efficiency in terms of basic system input parameters are developed. Thermodynamic bounds for the performance of Stirling refrigerators are obtained. Results indicating a compromise between cooling power and efficiency that are dependent on the constraint of the system are presented and discussed.     

New characterization methodology for vapor-injection scroll compressors

This paper presents a characterization methodology for vapor-injection scroll compressors (SCVI). An SCVI was characterized in a modified calorimetric test bench, which is able to control the intermediate pressure and the injection superheat independently. Based on the characterization results, the injection mass flow rate was correlated with the intermediate pressure through a linear expression, and a modified AHRI polynomial was proposed to estimate the compressor power input. The correlations were used in a simple model to predict the intermediate conditions of the SCVI installed in a heat pump prototype with an economizer. The deviations obtained for the evaporator mass flow rate, injection mass flow rate, intermediate pressure, and compressor power input were lower than 5% in all cases. The proposed methodology allows evaluating SCVI in a wide range of operating conditions, being only dependent on compressor characteristics and totally independent of the system in which it is installed.     

准等温压缩技术在转子式压缩机上的应用

根据热力学理论,制冷压缩机内气态制冷剂压缩过程越趋近等温过程消耗的输入功越少,等温压缩技术是提高压缩机性能的一个重要途径。降低运行过程中的压缩机整机及主要部件温度可以有效降低汽缸内的制冷剂温度,获得近似等温压缩的效果。本文通过具体算例明确准等温压缩技术可以节省的压缩机输入功率消耗,以滚动转子式压缩机为对象,探讨压缩机的汽缸部和电机部的冷却方案,以期为转子式压缩机准等温压缩技术提供支持。     

A comprehensive model of a miniature-scale linear compressor for electronics cooling

A comprehensive model of a miniature-scale linear compressor for electronics cooling is presented. Linear compressors are appealing for refrigeration applications in electronics cooling. A small number of moving components translate to less theoretical frictional losses and the possibility that this technology could scale to smaller physical sizes better than conventional compressors. The model developed here incorporates all of the major components of the linear compressor including dynamics associated with the piston motion. The results of the compressor model were validated using experimental data from a prototype linear compressor. The prototype compressor has an overall displacement of approximately 3 cm³, an average stroke of 0.6 cm. The prototype compressor was custom built for this work and utilizes custom parts with the exception of the mechanical springs and the linear motor. The model results showed good agreement when validated against the experimental results. The piston stroke is predicted within 1.3% MAE. The volumetric and overall isentropic efficiencies are predicted within 24% and 31%, MAE respectively.     

Mathematical modeling of scroll compressors — part II: overall scroll compressor modeling

This paper presents the development of a comprehensive simulation model of a horizontal scroll compressor, which combines a detailed compression process model (Chen Y., Halm N., Groll E., Braun J. Mathematical modelling of scroll compressors — part I: compression process modeling, International Journal of Refrigeration 2002;25(6):731–750) and an overall compressor model. In the overall model, compressor components are analyzed in terms of nine different elements. Steady state energy balance equations are established applying the lumped capacitance method. In combination with the detailed compression process model, these equations were implemented into computer code and solved recursively. In this way, the temperature and pressure of the refrigerant in different compressor chambers, the temperature distributions in the scroll wraps, and the temperatures of the other compressor elements can be obtained. Thereafter, power consumption and efficiency of the compressor can be calculated. Tests were used to verify the overall model on a macroscopic basis. Using the simulation program based on the overall compressor model, a parametric study of the scroll compressor was performed, and the effects of internal leakage and heat transfer losses were investigated and some preliminary results were obtained. These results indicate that the comprehensive scroll compressor model is capable of predicting real compressor behavior and useful to the design and optimization of scroll compressors.     

Twin screw oil-free wet compressor for compression–absorption cycle

The performance of a twin screw compressor operating under wet (two-phase) compression conditions in an ammonia–water compression absorption heat pump cycle is investigated both theoretically and experimentally. The paper reports on the influence of the location of liquid intake or, depending what applies, injection angle and mass flow rate of the injected liquid on compressor performance. Labyrinth seals separate the oil-free process side from oil lubricated bearing housing. Labyrinth seals leakage is modelled and its impact on performance is theoretically and experimentally investigated. The need for liquid injection from the discharge side to obtain acceptable performance is discussed based on experimental results.     

Development and evaluation of virtual refrigerant mass flow sensors for fault detection and diagnostics

Refrigerant mass flow rate is an important measurement for monitoring equipment performance and enabling fault detection and diagnostics. This paper presents and evaluates three different virtual refrigerant mass flow (VRMF) sensors that use mathematical models to estimate flow rate using low cost measurements. The first model uses a compressor map that relates refrigerant flow rate to measurements of condensing and evaporating saturation temperature, and to compressor inlet temperature measurements. The second model uses an energy-balance method on the compressor that uses the compressor power consumption. The third model is developed using an empirical correlation for an electronic expansion valve (EEV) based on an orifice equation. The three VRMFs are shown to work well in estimating refrigerant mass flow rate for various systems under fault-free conditions with less than 5% RMS error. The combination of the three VRMFs can be utilized to detect and diagnose when the compressor and/or expansion device is not providing the expected flow.     

涡旋式水源热泵系统性能仿真

为了预测涡旋式水源热泵系统变结构和变工况稳态性能,建立了稳态涡旋式热泵系统仿真模型.其中涡旋式压缩机模型考虑了吸、排气换热对工质流量和排气温度的影响以及流量、排气温度和输入功率三者的耦合关系;通过增加电子膨胀阀开度对蒸发器出口过热度的控制模型,反映了过热度对膨胀阀流量的影响.系统算法综合了顺序模块法和连续迭代法,改善了迭代收敛性,且易于实现部件模型的模块化.与实验结果对比表明:模型预测值与实验值的误差小于4.4％.     

Modelling of the non-reactive deposits impact on centrifugal compressor aerothermo dynamic performance

The centrifugal compressor blockage is considered an important issue in compressor operation and one of the main causes of machine failure. This is normally initiated by the presence of deposits with the process gas yielding to reduce the effective flow area, increase the frictional losses and distort the pressure distribution profile. The influences of flow blockage cover the thermodynamic, aerodynamic and rotordynamic performance parameters of centrifugal compressor as will be investigated further in this study. Accordingly, this paper introduces a novel approach to model the impact of non-reactive deposits flow on the centrifugal compressor aerothermodynamics performance. The developed set of empirical equations in this study provides a new way to derive the equivalent compressor performance map at various degrees of fouling with a consideration of gas properties and stage efficiency variation and without a prior knowledge of the detailed geometrical features. In order to emphasize the validity of the new method, it has been tested with two operating cases and the obtained results were compared with the internal inspection findings from the stage overhauling process. Besides, this approach has been proven to be valid for the modelling of flow blockage effect at the suction side, compressor internals and downstream equipment. Furthermore, a new methodology has been established to assess the possibility of deposits accumulation in the gas path of the compression system based on the operational data of the discharge parameters.     

Development of capacity modulation compressor based on a two stage rotary compressor – part I: Modeling and simulation of compressor performance

Two-stage rotary compressors are gaining popularity because of their ability to reduce operating and energy costs over the entire compressor life cycle. In this work, a capacity modulation compressor based on a two-stage rotary compressor (CMCTR) is developed to improve the performance of the rotary compressor system. The working principle of the CMCTR is presented and the cycle efficiency of the compressor through two-stage compression is numerically investigated. The CMCTR model considers mass and energy balance for a control volume, the internal leakage condition for all leakage paths, the discharge valve motion, and the force and moment balance. For simulation results, the motor efficiency is estimated with respect to shaft power and the pressure during an entire cycle is obtained with respect to the compression volume for saving mode and power mode. The optimum efficiency of the CMCTR is obtained for the modulation for these modes.     

A simulation approach for hermetic reciprocating compressors including electrical motor modeling

The design of a high-efficiency reciprocating compressor requires an understanding of the interactions between different phenomena occurring inside the compressor. This paper describes a comprehensive simulation approach for hermetic reciprocating compressors including modeling of the electrical motor. The simulation of the compression cycle follows an integral control volume formulation for mass and energy conservation. A thermal model is adopted with steady-state thermal energy balances applied to the compressor components via global thermal conductances. The equivalent circuit method is employed to form a steady-state model of a single-phase induction motor. The coupling between the three models provides the motor slip and mean compressor speed, which are seen to affect the compressor efficiency. The simulation model is validated through comparisons between predictions and measurements of the parameters associated with the compressor efficiency, temperature distribution and motor performance. A parametric analysis is carried out to investigate the dependence of the motor temperature on the input voltage and the results are discussed.