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.     

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.     

Influence of liquid refrigerant injection on the performance of an inverter-driven scroll compressor

The operation of a scroll compressor at high compression ratios can cause excessively high discharge temperatures, which can be detrimental to the reliability and efficiency of the compressor. In the present study, the performance of an inverter-driven scroll compressor with liquid refrigerant injection was measured with a variation of compressor frequency, injection pressure, and injection location. The influence of the liquid injection on the performance is presented as a function of operating parameters and injection location by comparing the results with those for the non-injection case. It was found that liquid injection under high frequency was very effective at attaining higher performance and reliability of the compressor, but injection under low frequency showed some disadvantages. For high frequency at a given injection ratio, the injection at α=180°, for an injection angle at an injection port, yielded slightly better performance of the compressor as compared to that at α=90°.     

Comparative study of the impact of the dummy port in a scroll compressor

A dummy port plays an important role in the porting process and the improvement of the performance of a scroll compressor. This paper documents an investigation on the working mechanism of the dummy port in a scroll compressor. To characterize the dummy port effects on the different parts of the scroll compressor, two scroll compressors, one with and the other without a dummy port, are studied comparatively. The flow through the dummy port is examined in the background of an integrated compressor working process. The assembly of the compressor under investigation includes the upper bearing housing, scrolls, check valve, and discharge plenum. The Navier–Stokes equations with a k– turbulence model are solved at the standard operating conditions of a scroll compressor. Refrigerant-22 is used as the working fluid. The thermodynamic and transport properties of the refrigerant gas are modeled by the Martin–Hou equation of state and power laws, respectively. Global flow physics is investigated first to lay a foundation to understand the working mechanisms that control the porting process before averaging techniques are applied. The behavior of the gas pockets in the porting process is characterized in both geometric and dynamic nature. The time-dependent variation of volume, mass, energy, and volume-averaged field quantities inside the gas pockets are studied throughout the porting process. The impact of the dummy port on the compressor performance is defined.     

Variable wall thickness scroll geometry modeling with use of a control volume approach

In a scroll-type compressor, compression is achieved through relative contact between two spiral curves. Since the scroll invention by Leon Creux (1905), multiple methods have been developed for calculating scroll geometry. What can generally be considered the most classical method, is defining each scroll curve as the involute of a circle. Gravesen and Henriksen (2001) introduced a new method to calculate scroll geometry by deriving each scroll curve from the radius of curvature parameterized with involute angle. This allows a wide range of involute geometries to be considered not included in the classical method. In this paper, Gravesen's method is extended to the tip region to include all tip geometries involved in a two arc configuration resulting in a more comprehensive scroll geometry definition. Lastly, with parametric representation of all scroll geometry, the pocket volume can be easily solved using a derived control volume approach.     

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.     

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.     

A lumped-parameter thermal model for scroll compressors including the solution for the temperature distribution along the scroll wraps

A lumped-parameter thermal model is presented to predict the temperature in different chambers and components inside scroll compressors with particular attention to gas superheating in the suction process. Thermal resistances between the components are based on global heat transfer conductances, whereas conduction heat transfer through the scroll wraps is solved via a one-dimensional finite volume method. The thermal model was coupled to a thermodynamic model of the compression cycle and then applied to simulate the compressor performance under different conditions of speed and pressure ratio. The model was able to correctly predict the compressor temperature for operating conditions within the range of those adopted for its calibration. The results showed a strong coupling between the compressor thermal profile and the temperatures of the motor and lubricating oil. It has also been found that heat conduction through the scroll wraps reduces slightly the discharge temperature.     

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.     

Unsteady state analysis of the compression cycle of a hermetic reciprocating compressor

In this work, an unsteady state analysis of the compression cycle of a small hermetic reciprocating compressor for domestic refrigeration was carried out. A specific one-dimensional model of the valves was developed and the mass and energy balances were applied to the refrigerant inside the cylinder to determine the mass, pressure and temperature behaviour and the heat and work transfer through the compression process. This analysis was inserted into a traditional steady state model of the compressor to evaluate the efficiency of the compression cycle and the performance of the compressor unit. The whole simulation code was validated against the experimental measurements carried out on a R134a commercial unit in a wide range of operative conditions: a fair agreement was found between predicted and measured performances. The simulation code can be a useful tool for the analysis, the design and the development of small hermetic reciprocating compressors for domestic refrigeration.     

低温热泵用涡旋压缩机性能的试验研究

制定低温热泵用涡旋压缩机试验方案,对研制的原型机进行性能测试。试验结果表明：在冷凝温度不变的情况下,随着蒸发温度的降低,原型机的制热量有所减少,但减少的速度低于普通热泵系统用涡旋压缩机;压缩机的电功率有所增加,但增加的幅度不大,且压缩机的排气温度也有所降低,故在低温工况下采用准二级压缩热泵用涡旋压缩机比采用普通热泵用涡旋压缩机可以更有效地提高空气源热泵的低温制热性能,是寒冷地区用小型空气源热泵比较适宜采用的压缩机。     

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.     

涡旋式压缩机在低温冷冻领域应用的实验研究

针对带HVE阀设计的半封闭卧式涡旋式压缩机,与当前冷冻市场上广泛使用的一款活塞式压缩机的性能进行对比测试。测试结果表明:由于喷气增焓的作用,随着系统压比的增大,涡旋式压缩机在制冷量方面表现出明显的优势。当蒸发温度为-25℃时,其制冷量与活塞式压缩机的比值,从25℃冷凝温度的约90%,提高到50℃冷凝温度的约130%。与活塞式压缩机相比,在上述运行工况下,涡旋式压缩机的性能也有所提升,当蒸发温度为-25℃时,R404A涡旋式压缩机的EER比活塞式压缩机的提高约2%~8%;R22涡旋式压缩机的EER比活塞式压缩机的提高2%~3%(冷凝温度为25℃时),冷凝温度为50℃时提高4%~5%。     

The effect of scroll wraps on the performance of scroll compressors

A number of geometrical curves have been used to form the wraps of scroll compressors. When the suction pressure, pressure ratio, scroll wrap height and thickness, and suction volume are constant, the effect of the involute curves of a cricle, square and line segment on the performances of the scroll compressor, such as geometrical parameters, leakage line length and various gas forces acting on the orbiting scroll are analysed in this paper. The effects of these scroll wraps on the performance of the scroll compressor vary as the suction volume changes. The results in this paper should be considered in scroll compressor design.     

Defrost cycle performance for an air-source heat pump with a scroll and a reciprocating compressor

A 10.6 kW nominal cooling capacity air-source heat pump was tested according to ANSI/ASHRAE Standard 116-1983 for the frost acumulation and defrost cycle. These tests required indoor conditions of 21.1°C (70°F) dry-bulb, 15°C (60°F) maximum wet-bulb, with outdoor conditions of 1.7°C (35°F) dry-bulb, 0.5°C (30°F) wet-bulb. The unit was tested with the original scroll compressor and a reciprocating compressor that yielded similar heating performance. Heating capacity for the scroll system peaked at 8.4 kW (2.38 tons), while the reciprocating system heating capacity peaked at 8.5 kW (2.42 tons) during the frosting period. Heating capacities for the two system configurations differed by less than 1% during the frosting period. Power demand for the scroll system peaked at 2.9 kW, and the reciprocating system power demand peaked at 3.1 kW. During the frosting period, the reciprocating system power demand averaged 7% higher than the scroll system power demand. The reciprocating system completed a defrost 5% faster than the scroll system. Scroll system defrost time was 6.8 min while reciprocating system defrost time was 6.5 min. The volume of condensate produced differed by less than 3% with 1680 ml (102.5 in³) and 1640 ml (100 in³) produced by the scroll and reciprocating systems, respectively. Discharge pressures during defrost were within 3% with peak values of 1315 kPa (191 psia) and 1351 kPa (196 psia) for the scroll and reciprocating systems respectively. The reciprocating compressor produced higher levels of discharge superheat, peaking at 53°C (95°F) compared to the scroll system peak discharge superheat of 47°C (85°F). Overall, discharge superheat for the reciprocating system averaged 18% higher than the scroll system. The reciprocating system produced defrost refrigerant flowrates that averaged 3% higher than the scroll system. Refrigerant flowrates for the scroll and reciprocating systems peaked at 3.7 kg min⁻¹ (8.2 lbm min⁻¹) and 4.0 kg min⁻¹) (8.8 lbm min⁻¹) respectively.     

含运动副间隙的涡旋压缩机动平衡仿真研究

为了研究运动副间隙对涡旋压缩机动平衡的影响,根据涡旋压缩机机构运动副间隙特点,采用非线性等效弹簧阻尼模型和Coulomb摩擦模型建立考虑摩擦作用的运动副间隙接触碰撞模型,并将其嵌入到ADAMS动力学仿真软件中,建立了含运动副间隙的涡旋压缩机动力学模型,针对小轴防自转机构、间隙大小和间隙数目三种情况,进行了动力学仿真。仿真结果表明：小轴防自转机构、间隙大小和间隙数目对涡旋压缩机的动平衡有显著影响,为合理选用轴承游隙提供了参考,并为提高涡旋压缩机的动力特性提供了理论依据。     

涡旋压缩机涡旋型线的研究现状及展望

涡旋压缩机作为第三代容积式压缩机,具有效率高、能耗低、噪声低、结构紧凑等诸多优点,被广泛应用于制冷空调与气体压缩等方面。由于涡旋压缩机的寿命、加工性能、效率和功耗等都受到涡旋型线的制约,所以涡旋型线的研究是开展涡旋压缩机其他研究的基础和关键。本文总结了国内外相关的研究成果,从型线类型和型线修正两个方面出发,对现有涡旋型线的研究现状进行综述分析,并对未来涡旋型线发展方向和趋势进行预测和展望,对于今后涡旋压缩机型线的研究与工程应用具有指导和借鉴作用。     

R32涡旋式压缩机开发

R32是一种具有巨大应用潜力的制冷剂,但其适用的涡旋式压缩机的开发尚不成熟,尤其是排气温度过高的问题严重影响R32制冷剂的应用。本文指出R32涡旋式压缩机开发的重点与难点,并探讨R32涡旋式压缩机未来的开发方向。     

空压机轴承箱蜗壳温度探头油封改造

由于空压机进气侧轴承箱蜗壳温度探头密封效果不好,使空压机及其后续管道受到油污染。后将温度探头的O形圈密封改为骨架油封,杜绝了轴承箱漏油问题。文章简介空压机的结构和技术参数,详细介绍了骨架油封的制作和优点。