Formation law and criterion of nebulous macroscopic segregation in ZL205A alloy castings

The appearance of macroscopic segregation in ZL205A alloy castings bears a super resemblance to the appearance of shrinkage porosity, and the chemical composition of the segregation is Al2Cu whose microstructure is in the form of dentrite or skeleton crystal. According to the characteristic of nebulous segregation, the formation process could be divided into two steps by the eutectic temperature of Al2Cu. Then a criterion for each of the two steps is brought forward on the basis of the shrinkage porosity criterion of low pressure casting

On the definition of Alexandrov space

This paper shows that, in the definition of Alexandrov space with lower ([BGP]) or upper ([AKP]) curvature bound, the original conditions can be replaced with much weaker ones, which can be viewed as comparison versions of the second variation formula in Riemannian geometry (and thus if we define Alexandrov spaces using these weakened conditions, then the original definition will become a local version of Toponogov's Comparison Theorem on such spaces). As an application, we give a new proof for the Doubling Theorem by Perel'man.Comment: 12 page

Economic Assessment of Network-Constrained Transactive Energy for Managing Flexible Demand in Distribution Systems

The increasing number of distributed energy resources such as electric vehicles and heat pumps connected to power systems raises operational challenges to the network operator, for example, introducing grid congestion and voltage deviations in the distribution network level if their operations are not properly coordinated. Coordination and control of a large number of distributed energy resources requires innovative approaches. In this paper, we follow up on a recently proposed network-constrained transactive energy (NCTE) method for scheduling of electric vehicles and heat pumps within a retailer’s aggregation at distribution system level. We extend this method with: (1) a new modeling technique that allows the resulting congestion price to be directly interpreted as a locational marginal pricing in the system; (2) an explicit analysis of the benefits and costs of different actors when using the NCTE method in the system, given the high penetration of distributed energy resources. This paper firstly describes the NCTE-based distribution system that introduces a new interacting scheme for actors at the distribution system level. Then, technical modeling and economic interpretation of the NCTE-based distribution system are described. Finally, we show the benefits and costs of different actors within the NCTE-based distribution system

The Mechanism Discuss of Periodic Sound in Rolling Piston Compressor under Low Operating Frequency in Air-conditioner System

With the popularization of the inverter-driven air-conditioner and the requirement of comfort and energy saving, the operating frequency of inverter-driven air-conditioner is lower and lower, even to 1Hz. But when the air-conditioner operates under the frequency of 10Hz, a periodic sound will appear in the air-conditioner outdoor unit, which should be researched and solved. According to the experiment test and theoretical analysis, it is found that the periodic sound is the excited resonance when the valve opens. The resonator is composed by the discharge port of top-flange and discharge cavity which is made up by cylinder, roller, top-flange and bottom-flange. In one cycle the characteristic of the periodic sound is that the sound will be only taken place when the valve opens and the frequency of the sound will be higher and higher with the crank angle increasing. According to the experimental testing about different type compressor and air-conditioner outdoor unit, it is found that this sound exists in every kinds of rolling piston compressor. Using proper muffler and increasing the thickness of the valve could both reduce this periodic sound

A Novel Structure of High Efficiency Rotary Compressor

In recent years, various frequency compressors are developed rapidly and successfully in household air conditioner area. However, it is difficult to make advance progress on compressor performance, noise and reliability. The innovation of structure and technique are indispensable impetus to make a breakthrough. This paper presents a novel structure of high efficiency rotary compressor, which focuses on the connection mode between roller and vane of a compressor. On the one hand, the leakage gap between roller wall and vane tip is eliminated, which upgrades the capacity of compressor. On the other hand, through changing movement type of compressor parts, the mechanical state is meliorated and frictional loss is decreased. Several analysis are studied to validate the rationality of the above amelioration, which include strength and deformation simulation, frictional loss and leakage loss calculation. By comparison with conventional compressor, the performance of the novel compressor is improved obviously. In the end, the results of reliability and durability experiments reveal that they satisfy the national standard

Numerical Simulation Of Three-dimension Unsteady Flow In The Compression Chambers Of A Scroll Compressor

Due to the movement of orbiting scroll and leakage in scroll compressor chambers, the unsteady flow has significant influence on compression process. It\u27s necessary to takes account of both flow and thermodynamics process in analysis of compression. This paper has carried out a numerical simulation of the whole compression process in scroll compressor, involving suction, compression and discharge process. By solving mass, momentum and energy equations of the refrigerant, the velocity, pressure and temperature distribution in all compression chambers throughout the entire compression cycle has been obtained, which takes account of all the influence of flow and thermodynamics process. The field quantities have shown nonuniform distribution in every compression chamber, and leakage between different chambers is obvious. Further, the overall parameters, such as mass flow rate, discharge temperature and compression power consumption, have been calculated from the field quantities. The general comparisons between numerical and experimental results show a reasonable good agreement. The research is useful for the optimal design of the compressor geometric structure

The Finite Element Analysis of the Deflection of the Crankshaft of Rotary Compressor

The deflection of the crankshaft which transfers the power of motor to the pump of the compressor directly affects the vibration, noises and wear problems in the rotary compressor, therefore, with the requirement of higher reliability, it is important to obtain it exactly in compressor design. Various forces that the crankshaft suffers were calculated by theoretical analysis in the operation process of the compressor. And based on the finite element method (FEM), the deflection of the crankshaft was obtained by simulation in the rotary compressor. And then the measurements were performed concerning the orbit of the top dead centre of the crankshaft with non-contacting displacement sensors in the compressor. In comparison with the tests, the validity of the calculation method was verified. It was found that the results of calculation were good agreement with the tests’. In addition, several factors which affect the deflection of the crankshaft were analyzed with the FEM, and the influences of flange height, shaft diameter, mechanical air gap in the motor, rotor weight on the deflection were found distinctly, which as a primary theoretical basis is provided for the compressor design

CFD Analysis and Experiment Study of the Rotary Two-Stage Inverter Compressor with Vapor Injection

The offset angle of the upper and lower part of the crankshaft will affect the resistance of inspiration of high stage cylinder in the rotary two-stage inverter compressor with vapor injection, and then affect the performance. this paper presents the performance of the rotary two-stage inverter compressor with vapor injection in the bias angle of the crankshaft is calculated and compared with the experimental. The simulation results are in agreement with the experimental results. Under the operation of close vapor injection and open vapor injection, the performance of compressor can be improved 1% and 3% separately by optimize the bial angle of crankshaft.

Study of Novel Rotary Cylinder Compressor

A positive displacement rotary compressor is introduced:RCC(Rotary Cylinder Compressor). For implementing suction and exhaust process, the compressor\u27s cylinder and shaft revolve around their own axes while the piston reciprocates relative to the cylinder and shaft. Compared with rotary piston compressor, the RCC has the advantages of high volumetric efficiency and small torque ripple