Design of experimental bench and internal pressure measurement of scroll compressor with refrigerant injection

Experiments on the inner compression process of scroll compressor with refrigerant injection can reveal the essence of refrigerant injection. The difficulty of the experiment is the design of location of measuring ports, measuring system of dynamic pressure and design of the injection system. Focusing on the dynamic pressure measurement of inner compression process during refrigerant injection, an integrated bench design method for refrigerant injection research in scroll compressor is presented in this paper. The location design of injection ports and measuring ports, frequency spectrum analysis of pressure signal, selection of the sensor type and configuration, and design of the pressure-leading system are expressed, respectively. Finally, a test bench is set up. Based on it, several elementary experiments were carried out. The results show that: this design method solves most problems in the experimental research of scroll compressor with refrigerant injection and works reliably; the refrigerant injection effects the majority of the inner compression process and should not be considered as a transient process; gas injection can increase the system performance greatly and there is an optimal injection pressure for a certain scroll compressor.     

Performance improvement of air source heat pump using gas-injected rotary compressor through port on blade

Gas injection has been a crucial technology to avoid the serious degradation of air source heat pumps in low ambient temperature. A novel injection structure on the blade for rotary compressors has been put forward in previous research to overcome the drawback of traditional injection structures. Based on a verified numerical model, the thermodynamic performance of an air source heat pump with the new gas-injected rotary compressor is investigated. The results indicate that, compared to the air source heat pump with the regular single-stage rotary compressor, the proposed injection structure can enhance heating capacity and COP of the air source heat pump by 23.1–28.2% and 4.5–8.1%, respectively.     

电动汽车空调热泵型涡旋压缩机结构分析

为了解决电动汽车空调系统冬季采暖问题,针对冬季空调工况下压缩机单级压比增大的运行特性,以涡旋压缩机制热性能系数为热力学优化目标函数,确定了制冷剂循环系统中的最佳补气压力,优化了涡旋压缩机静涡旋盘上的中间补气口的几何位置和形状,使其具备了准双级压缩功能。将研发的热泵型电动涡旋压缩机安装于电动汽车空调系统,利用空气焓差法对系统进行了制热、制冷性能实验。实验结果表明,静涡旋盘结构优化后的热泵型电动涡旋压缩机,其制热和制冷能力可以满足5人座电动汽车司乘人员的冬季和夏季舒适性要求,并且具有较高的制热和制冷性能系数,从而提升了汽车空调系统热泵循环和制冷循环的热经济性,达到了节能的目的。     

Experimental investigation on heating performance of gas-injected scroll compressor using R32, R1234yf and their 20wt%/80wt% mixture under low ambient temperature

In this paper, an integrated gas-injected scroll compressor heat pump system using R1234yf, R32 and its binary mixtures as working fluid was developed and their heating performances under low ambient temperature were quantitatively evaluated. A composite test system consisting of second-refrigerant calorimeter and water-cooled condenser was used to test the system working performance. The condensing temperature, evaporating temperature, compressor power input and other variables were analyzed to evaluate the system heating capability and energy efficiency. Test results showed that the R1234yf system can run at an evaporating temperature of −25 °C. R1234yf/R32 mixture can run at an evaporating temperature of −20 °C and it has the highest heating COP value among other refrigerants; R1234yf/R32 gas injection system provided very significant performance improvements for heating performance, compared with no gas injection, the heating capacity and heating COP can improve 16%~20% and 13%~16%, respectively.     

涡旋式单机准双级压缩系统的分析与应用

目前,制冷行业内关于双级压缩的理论和研究都是相对于活塞式压缩机和螺杆式压缩机而言,在涡旋式压缩机日益盛行的今天,迫切需要关于涡旋式双级压缩的试验和应用。本文从实际应用出发,介绍涡旋式单机准双级压缩系统的优点、计算及其在机组中的实际应用,最后从试验的角度验证涡旋式单机准双级压缩机的优点。     

Theoretical and experimental investigation on the performance of screw refrigeration compressor under part-load conditions

Slide valve is normally employed in screw refrigeration compressor to meet the cooling capacity demanded by the load variation. A mathematical model describing the working process of screw refrigeration compressor with a slide valve assembly under part-load conditions is established based on the calculation of the effective by-pass area and radial discharge area. Experimental investigation on a screw refrigeration compressor under part-load conditions with several evaporation and condensation temperatures is also carried out. Simulation results are in good agreement with the experimental ones. With the validated model, effects of key design parameters, i.e. the installation angles of the slide valve relative to the cylinder and the slide stop length, on the working process and performance of screw refrigeration compressor have been analyzed. These results can be useful for optimum design of the slide valve assembly to improve the energy efficiency of refrigeration system with screw compressor under part-load conditions.     

容积式制冷压缩机电效率分析

对制冷压缩机的发展进行了简单的概述,统计计算了市场上几种主要容积式压缩机的电效率,并进行了对比和分析,结果表明： 涡旋压缩机的电效率基本上在0.5~0.75之间,主要集中于0.6~0.7之间;活塞压缩机的效率基本上在0.4~0.7之间,而主要集中于0.5~0.65之间;螺杆压缩机的电效率基本在0.5~0.75之间,主要集中于0.65~0.75之间;压比为2~4时压缩机电效率达到最大。为制冷压缩机的设计、校核和计算提供基础和依据,为制冷系统的性能改进提供方向。     

Evaluation of two-phase suction,liquid injection and two-phase injection for decreasing the discharge temperature of the R32 scroll compressor

R32 has been considered as an important alternative in the phase-out of hydrochlorofluorocarbons (HCFCs) due to its advantages such as relatively low global warming potential compared to R410A, favorable thermal properties. However, the increased discharge temperature of the R32 compressor, compared with R410A, is the main barrier affecting the wide and quick adoption. In this work, three promising methods to decrease the discharge temperature of R32 scroll compressor, namely, two-phase suction, liquid injection and two-phase injection, have been investigated. By considering the variations of motor efficiency and leakage rate, an improved distributed parameter model of the scroll compressor is rebuilt based on a previously developed one (Wang et al., 2008). By that model, the effectiveness of these three methods in decreasing discharge temperature and their influence on thermodynamic performance are researched. It is concluded that all the three methods show excellent potential in decreasing the discharge temperature of R32 scroll compressor. Besides, two-phase injection outperforms the other two methods in cooling capacity and COP by 11.8% and 4.8%, respectively.     

制冷压缩机机壳散热研究

许多机房专用空调的制冷压缩机置于室内机的机壳内,用回风冷却制冷压缩机,良好的冷却对于延长制冷压缩机的寿命非常有利,但是,会增大空调房间的冷负荷,制冷系统的能耗增大。本文研究了与制冷压缩机机壳散热有关的因素,计算了全封闭蜗旋压缩机机壳散热量,分析了机壳散热量与压缩机制冷量之间的关系和制冷压缩机置于室内与室外的利弊。     

梯形截面涡旋压缩机的型线设计及泄漏特性

电动汽车整车热管理系统需要搭载大排量的涡旋压缩机以适应多工况高负载的设计需求。本文提出一种大排量涡旋压缩机的型线设计方法,通过经实验校正的仿真模型研究了梯形截面涡旋压缩机的几何特性及泄漏特性。计算结果表明：梯形截面涡旋压缩机在保证齿根强度校核的前提下,平均壁厚降低29.9%,排量提升19.5%。研究型线设计参数对泄漏特性的影响,发现梯形截面涡旋压缩机的内泄漏率与等壁厚涡旋压缩机相差不足2%,具有良好的应用前景。     

Effects of liquid refrigerant injection on the performance of a refrigeration system with an accumulator heat exchanger

Liquid refrigerant injection technique can be a very effective method for controlling subcooling and the compressor discharge temperature of a refrigeration system at high ambient temperatures. In this study, the effects of liquid refrigerant injection on the performance of a refrigeration system with an accumulator heat exchanger were investigated by varying the liquid injection rate at the conditions of constant expansion valve opening in the evaporator and constant total flow rate. During the tests, the ambient temperature was maintained at 43 °C. With the increase of the liquid injection rate, the subcooling at the inner heat exchanger outlet increased and the superheat at the accumulator outlet decreased. However, unacceptable results such as the increase of the compressor discharge pressure and decrease of the system performance were also observed depending on the control method applied. To obtain high system performance and reliability, optimum control methods for liquid injection in the accumulator heat exchanger are suggested. The liquid injection technique for the refrigeration system with an accumulator heat exchanger was found to be an effective method for controlling adequate subcooling and the compressor discharge temperature of the refrigeration system at high ambient temperatures.     

Two-stage heat pump system with vapor-injected scroll compressor using R410A as a refrigerant

Refrigerant vapor-injection technique has been well justified to improve the performance of systems in refrigeration applications. However, it has not received much attention for air conditioning applications, particularly for air conditioning in hot climates and for heat pumping in cold climates. In this study, the performance of an 11 kW R410A heat pump system with a two-stage vapor-injected scroll compressor was experimentally investigated. The vapor-injected scroll compressor was tested with the cycle options of both flash tank and internal heat exchanger configurations. A cooling capacity gain of around 14% with 4% COP improvement at the ambient temperature of 46.1 °C and about 30% heating capacity improvement with 20% COP gain at the ambient temperature of −17.8 °C were found for the vapor-injected R410A heat pump system as compared to the conventional system which has the same compressor displacement volume.     

滚动转子式补气压缩机在热泵系统中的实验研究

介绍了滚动转子式补气压缩机的设计,并将其在热泵系统中进行了实验研究。分析了不同制热工况下滚动转子式补气压缩机的性能,对比了带闪发器与过冷器的经济器热泵系统、滚动转子式与涡旋式补气压缩机的性能。结果表明:随着室外环境温度的下降,滚动转子式补气压缩机补气后制热量提升比例逐步增大;滚动转子式补气压缩机制热实验中,带闪发器系统的制热量较高;在超低温制热工况下滚动转子式补气压缩机制热量提升18%左右,与涡旋式补气压缩机相比制热量相当,性能略高。     

Experimental investigation on convective heat transfer mechanism in a scroll compressor

This paper describes an experimental study on the convective heat transfer inside the scroll compressor. An experimental refrigeration system is composed with extensive instrumentations in the compressor that is operated at variable speeds. The 13 thermocouples installed inside the compressor monitor the temperatures of the scroll wrap during compression process of refrigerant. The temperature and the pressure of refrigerant at suction, and the pressure at discharge ports are measured, and applied to the numerical simulation as the operating condition parameters. The temperature measured at the discharge port is used to verify the simulation result with relevant heat transfer coefficient. This paper describes the effect of motion of the orbiting scroll on the convective heat transfer in the scroll wraps. Separate experiments are performed to investigate the heat transfer in such a peculiar physical condition. With this experimental result, the effect of the oscillation of the wall on the heat transfer is quantitatively analyzed and applied to the simulation of compression process in scroll compressor. The whole consecutive compression processes in the scroll compressor is simulated in detail by solving equations of mass and energy balance for the refrigerant. The modified heat transfer coefficient correlation considering the effect of motion of the orbiting scroll predicts the discharge temperature better than other typical heat transfer coefficients.     

Theoretical study of a novel refrigeration compressor – Part II: Performance of a rotating discharge valve in the revolving vane (RV) compressor

A new refrigeration compressor, named ‘Revolving Vane (RV) compressor’, has been introduced in Part I of this paper series. For a first time in refrigeration compressors, a rotating discharge valve is employed in the RV compressor mainly due to the rotation of the entire cylinder. This paper presents a theoretical investigation on the dynamic behavior of a reed-type discharge valve undergoing rotatory motion, with the primary objective of elucidating the applicability of such valves in refrigeration compressors. Under the application of the Euler–Bernoulli beam theory, a mathematical model of the rotating valve is formulated and the transient response of the valve under centrifugal loads in addition to pressure forces is analyzed. Results have shown that under careful design considerations, the performance as well as the reliability of the rotating discharge valve can be enhanced as compared to a non-rotating valve that has been used in all refrigeration compressors currently.     

An investigation of the performance of a scroll compressor under liquid refrigerant injection

In this study, fundamental and practical influence of liquid refrigerant injection on the performance of a refrigerant scroll compressor has been investigated experimentally and theoretically. In the theoretical analysis, a compression model of vapor/liquid mixture is developed by taking account of heat transfer from the cylinder wall to suction, compression and injection refrigerant. An experiment has been done under the condition of keeping the oil temperature constant in order to investigate the fundamental influence of the liquid refrigerant injection on the compressor performance, and the results were compared with the theoretical ones. It was found that the injection basically increases the compression power and decreases the compressor efficiency, though the situation depends on the condition of the heat transfer to the injection refrigerant. And furthermore, the performance of the liquid refrigerant injection compressor under practical operating condition without controlling the oil temperature has been investigated. Under this condition, the compressor showed recovery and slight improvement of performance due to the decrease of the oil and cylinder temperatures by the injection. In addition, influence of the refrigerant injection on the oil viscosity and refrigerant solubility in the oil, which relate mechanical loss and reliability of the compressor, have been discussed.     

R32涡旋压缩机两相喷射制冷系统的设计与控制

R32涡旋压缩机存在排气温度过高的问题,利用两相制冷剂喷射可降低排气温度同时提升性能。基于经济器系统,提出了R32涡旋压缩机的两相喷射制冷系统,利用模拟仿真对其设计和控制方法进行了研究。从压缩机的角度,分析了喷射口等效直径对两相喷射压缩机性能的影响,并指出了两相喷射时喷射压力和喷射干度的优化方向。通过对两相喷射系统的模拟分析,在系统层面上对中间换热器的换热能力进行了优化配置和对中间喷射压力进行了优化控制,并提出根据排气温度来确定最优中间压力的方法,即将排气温度控制为135℃对应的中间压力为最优中间压力。经过优化后的两相喷射系统,不仅解决了排气温度过高的问题,而且能够提升制冷量7.1%~11.4%,提升COP 2.6%~6.2%。     

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.     

Advanced control systems for single compressor chiller units

In this paper the problem of designing advanced control systems for increasing the performances of low capacity HVAC system with single scroll compressor is addressed. In particular, a simulation environment based on Matlab/Simulink that has been validated on a state-of-the-art experimental facility and used to design an adaptive controller for single scroll compressor, packaged air-cooled water chillers is presented. The capability of the controller to substantially increase the energy performance of the system, as well as to achieve excellent regulation performances in process applications is demonstrated.     

Dynamic simulation and optimal matching of a small-scale refrigeration system

This paper describes a principle and method of optimal matching to reduce energy consumption in small-scale refrigeration systems, based on systems analysis. A knowledge of the dynamic characteristics of a refrigeration system is important for predicting the performance of the system. A simulation model of a refrigeration system consisting of a compressor, an evaporator, a condenser and a capillary tube has been established to illustrate optimal matching. For each component a mathematical model has been developed, in which the concept of transient and distributive is introduced. On the basis of dynamic simulation, a method of optimal matching to minimize power consumption is recommended. To test the reliability of the theoretical models, an experiment was carried out on a small-scale refrigeration system. The experimental data were compared with the theoretical results and it is shown that the theory is valid.