Abstract ：

Applying an appropriate roughness model is one of the most effective ways to improve the accuracy of the numerical simulation for centrifugal compressors, and it is also the key to the study of surface deterioration such as compressor fouling and corrosion. The basis for using the roughness model is to determine the conversion relation between physical roughness and equivalent roughness. In this paper, numerical and experimental studies on the roughness conversion relation for the centrifugal compressors were performed by means of a unique self-developed "pseudo front stage (PFS)" device. An equivalent roughness conversion coefficient of 8.5 was determined on the basis of fitting performance of the U-bend and return channel model. The validity of the conversion coefficient in improving the performance prediction accuracy of the centrifugal compressors was verified by three centrifugal compressor models. The concept of weighted average roughness was proposed to quantify the roughness sensitivity and roughness level of the centrifugal compressor. Quantitative research on the roughness effect of centrifugal compressors indicated that the peak efficiency degradation due to the roughness effect in the compressors was linearly associated with the logarithm of the relative roughness when the impeller of the centrifugal compressor was in the hydraulically rough regime. Doubling or halving the roughness value of all components of a centrifugal compressor in the hydraulically rough flow regime will result in a change in the peak efficiency of the compressor by about 1.72%.

Keyword ：

centrifugal compressor equivalent roughness conversion performance prediction roughness effect sand-grain roughness

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Abstract ：

The centrifugal compressor is widely used for gas compression in various industrial fields such as aero-engine, gas turbine and turbocharger. However, the stable operating range is usually restricted by the occurrence of flow instability such as stall and surge. The paper experimentally examines the developing process of surge and stall occurring in a centrifugal compressor to advance the understanding on flow mechanism of flow instability. It is found that three types of pressure fluctuation can be observed at low flowrate region. At the critical point, the local stall firstly occurs in some specific diffuser passages and the enlarged local diffuser stall eventually induces the mild surge of compression system indicated by the sinusoidal pressure fluctuation. At lower mass flow rate, the diffuser stall cell begins to circumferentially propagate along the impeller rotating direction at 11% of rotor speed with the existence of mild surge. In comparative analysis of IGV pre-swirl angle on the occurrence of mild surge, the mild surge still occurs at the operating condition when the slope of the characteristic map of test stage is still obviously negative, in which the compression system is supposed to be stable in previous study. And a new suggested criterion for the prediction of mild surge is demonstrated that the occurrence of mild surge depends on the destabi-lization effect of downstream components about diffuser and volute. Combined with the experimental data, the streamwise distribution characteristic of diffuser stall can be used to develop the simplified model of lumped parameters for the analysis on the generation mechanism of the diffuser rotating stall. The quantitative investigation on the relation between the pressure-rise characteristic of subcomponents and the occurrence of mild surge and diffuser rotating stall not only advances the prediction of stability limit but also lays the theoretic foundation for controlling these unsteady behaviors to improve the operating range.

Keyword ：

centrifugal compressor diffuser rotating stall mild surge transient measurement

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Abstract ：

压缩机是化肥生产中的关键设备,对产能、电耗及安全生产起着至关重要的作用.气阀对压缩机的性能有着重要影响,被称为压缩机的"心脏".理论与实践表明,对压缩机气阀进行分析与改造,能有效降低压缩机的电耗,提升压缩机的排气量,保障压缩机安全可靠运行.

Keyword ：

电耗 可靠性 排气量 气阀 压缩机

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Keyword ：

闭式叶轮 堵塞流量 离心压缩机 轮盖间隙 叶片厚度 圆角

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Abstract ：

The overall perfomance of a centrifugal compressor prototype stage with shrouded impeller has been measured. Some factors influencing the numerical prediction accuracy and choke mass flow rate have been investigated numerically using different computational models generated by the component superposition method. A structure correction method using the equivalent blade thickness to replace the impeller fillet was proposed and verified. The main goal of this research was to find out a reasonable simulation strategy for the centrifugal compressor with shrouded impeller through assessing the influence of various fine structures and omitted treatments on the overall performance. A peak isentropic efficiency of 80.28% for the compressor stage was obtained experimently while the numerical model with the equivalent blade thickness correction achieved a peak efficiency of 82.02%. The results indicate that the shroud gap and seal, the impeller fillet as well as the blade machining error are the main geometric structure factors to influence the shrouded centrifugal compressor performance. The shroud gap leakage flow decreases the effective throat area of the shrouded impeller, which leads to the decrease of the choke mass flow rate, the acceleration of the fluid in the impeller passage and the reduce of the impeller diffusion ability. At a given exit pressure, the choke mass flow rate decreases with the increase of the impeller blade relative thickness. Using the equivalent blade thickness to replace the impeller fillet can make the compressor maintain an unchanged performance in the small mass flow conditions, but improve the numerical simulation accuracy in the large mass flow conditions. © 2017, Science Press. All right reserved.

Keyword ：

Blade thickness Fillet Mass flow rate Shrouded impeller Shroud gap

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Abstract ：

A numerical model has been developed for the performance analysis of solid oxide fuel cell (SOFC)/micro gas turbine (MGT) hybrid systems with prereforming of natural gas, in which a quasi two-dimensional model has been built up to simulate the cell electrochemical reaction, heat and mass transfer within tubular SOFC. The developed model can be used not only to predict the overall performance of the SOFC/MGT hybrid system but also to reveal the nonuniform temperature distribution within SOFC unit. The effects of turbine inlet temperature (TIT) and pressure ratio (PR) on the performance of the hybrid system have been investigated. The results show that selecting smaller TIT or PR value will lead to relative higher system efficiency and lower CO2 emission ratio; however, this will raise the risk to destroy SOFC beyond the limitation temperature of electrolyte.

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This paper presents the structure for a rotary six-bed adsorber that carries out a six-step PSA continuous oxygen generation process with a short cycle time and a low operation pressure ratio. The working principle of a rotary six-bed PSA oxygen generator is introduced and the effects of various operating parameters on PSA performance are experimentally investigated. The results indicate that, the adsorption pressure increases with the reduction of rotating speed and decreases with the lowering of the feed flow rate; with the acceleration of rotating velocity, the oxygen purity of the gas produced first rises and then drops, and it has an optimum rotating velocity; the higher the feed flow rate, the lower the oxygen purity of the product; the ratio of the pressurization angle to the adsorption angle has a remarkable effect on the oxygen purity with the oxygen purity increasing according to the condition of keeping the angle of the feeding ring groove and with the increase in this ratio; and the long-purging time at a low purging-gas flow rate is appropriate for miniature apparatus.

Keyword ：

Air Separation Design Mini-Scale Pressure Swing Adsorption Six-Bed Rotary Zeolite

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Abstract ：

A sliding vane expander was designed to replace the throttling valve used in the energy recovery systems with HFCs. Its performance and the coefficient of performance (COP) of the refrigeration system were tested. The experimental results show that the prototype operated in the HFC410A refrigeration system continuously and steadily. Under the air-conditioning conditions, the volumetric ratio of HFC410A reached 7.48 in the expansion process. The prototype had the volumetric efficiency of 20.58% with the maximum isentropic efficiency of 20.26%. When springs were installed at the bottom of the vane, the volumetric efficiency and isentropic efficiency increased to 44.27% and 32.07%, respectively. The COP was 3.59 and rose by 6.49% compared with that of a throttling valve system. In addition, the optimum rotation speed range of the sliding vane expander was 1100-1200 r/min.

Keyword ：

Coefficient of Performance Energy recovery Energy recovery system Experimental research Isentropic efficiency Sliding vane Volumetric efficiency Volumetric ratio

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Abstract ：

为了减小hydro-fluorocarbons(HFCs)制冷系统在节流过程中的能量损失,提高系统的效率(COP),开发出一种代替节流阀的滑片膨胀机样机,并对样机的性能进行了测试.结果表明,该样机可以满足HFCs工质在膨胀过程中的高容积比的要求.在以HFC410A为工质的制冷系统中,当空调工况下膨胀过程的容积比达到7.48时,样机运行稳定；在1100～1200 r/min的最佳运行转速下,样机等熵效率最高,对应的容积效率为20.58％.在滑片底部安装弹簧后,样机的容积效率提高到44.27％,等熵效率由原来的20.26％提高到32.07％.与节流阀系统相比,滑片膨胀机样机系统的COP提高了6.49％,达到了3.59.

Keyword ：

hydro-fluorocarbons 滑片膨胀机 空调工况 能量回收 容积比

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Abstract ：

A one dimension homogeneous steady model of adiabatic capillary tubes in CO2transcritical refrigeration systems was established to evaluate the performance and the flow characteristics of capillary tubes. The simulation results by using three different friction factor correlations (Churchill, Colebrook, Bittle & Pate) were compared with each other. The distributions of temperature, pressure, enthalpy and entropy along the tube length were investigated. The influences of four parameters (inner diameter, inlet pressure, inlet temperature, back pressure) on the mass flow rate were explored, and the chocking phenomenon was analyzed. The results show that the Churchill correlation and the Colebrook correlation predict 92% of the refrigerant mass flow rates with an error of less than 10% while the Bittle & Pate correlation may be unsuitable for simulating the flow in CO2capillary tubes due to its neglect of the inner wall roughness of capillary tubes. The back pressure has slight influence on the mass flow rate. In addition, the rate of mass flow without chocking is approximately equal to that with chocking.

Keyword ：

Adiabatic capillary tube Flow charac-teristics Friction factor correlation Inlet pressures Inlet temperature Inner diameters Refrigeration system Transcritical

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