A Prediction Method for Slug Limit of Scroll Compressor using CFD Two-Phases Flow Simulation

Slug test is used to simulate a real application work condition in lab. During operation, a compressor eventually gets to endure dynamic slugging which is characterized by the arrival of a liquid refrigerant at the suction side when the compressor is already running. Because of this dynamic, the liquid is able to reach the compression side. The presence of incompressible liquid in the scrolls (volumetric compression) involves mechanical strength quickly becoming unbearable for the compressor involute breakage or Oldham coupling breakage are the consequences suffered by the compressor following a severe slugging. In this paper, a prediction method of slug limit is introduced which is based on simulation result numerical fitting to experimental result. In laboratory, engineers use dynamometer to monitor the image of compressor current intensity which shows a steep peak when more and more liquid refrigerant injected. Once the current peak ratio exceeds our goals, we would take the corresponding liquid quantity as slug limit of the compressor. And this liquid injection process is transient simulated by CFD method using two-phases flow model – Eulerian multiphases model which allows for the modeling of multiple separate yet interacting phases. The phases can be liquids, gases, or solids in nearly any combination. Liquid refrigerant is thought as granular phase and calculated. Mass flow rate of each phase at outlets is recorded during calculation process and divided by normal mass flow rate (only gas suction). The maximum ratio of mass flow rate is used to predict slug limit comparing to experimental criterion. Using this method, it’s easier to comparing with different parts structure which one is better for slug performance and which one is worse, saving time and cost and more and more helpful for engineering design

Influence of hole-drilling diameter on aluminum alloy residual stress measurement

A hole-drilling method and finite element (FEM) numerical simulation are used to estimate the residual stress of aluminum alloy welding joints. In order to study the influence of hole diameter on measurement accuracy, a group of experiments are conducted. Experiment results show that the measuring error can be the minimal when the drilling hole diameter is 4 mm. Residual stress of 2219-T87 aluminum alloy welding joints under this optimal hole diameter are obtained. The distribution of the residual stress from the welding seam to the outward is first tensile stress and then compressive stress. And the maximum residual stress is 123.2 MPa

Effect of Hf additions on microstructure and mechanical properties of a Co-9Al-9W-2Ta alloy at room and high-temperatures

AbstractIn The microstructural evolution, room/high-temperature mechanical properties of a Co-9Al-9W-2Ta alloy with 2, 5, 6, 9 at.% Hf additions (referred as to 2Hf, 5Hf, 6Hf and 9Hf alloy hereafter, and content of W+Hf = 9 at.% for all alloys) prepared by arc-melting were investigated. It was found that the as-cast 2Hf∼6Hf alloys showed a microstructure composed of Co-base solid solution γ phase (γ-CoSS) and eutectic of γ+ intermetallic compound Co23Hf6, and the 9Hf alloy was composed of primary Co23Hf6 and (γ+ Co23Hf6) eutectic. While after 1170°C/8h solution and 800°C/100h aging, the cubic γ’ phase with a size of 200nm∼700nm homogeneously and coherently precipitates on the γ matrix for the 2Hf ∼ 6Hf alloys, no γ’ particles were found in the 9Hf alloy. The 2Hf alloy exhibits yield stress anomaly at temperatures above 600°C, and the temperature corresponding to the anomalies stress peak is at about 700°C. However, the other three alloys show no yield stress anomalies

Role of Customized Bus Services in the Transportation System: Insight from Actual Performance

After attaining great prevalence from the end of 2013, customized bus (CB) transit services have experienced a huge decline in China. The feasibility of this new bus sharing system is thus being questioned. Therefore, it is imperative to investigate the actual role of CB services in the overall transportation system based on successful cases, as the role of the CB service determines its primary service object, system construction, marketing orientation, and even government function. To examine the role of CB services, this study investigates the practical performance, advantages, and spatial and temporal coverage of a successful CB system based on practical subscription data for more than two years. The results illustrate that the CB service is an eclectic choice that can balance service quality and cost between traveling by traditional public transportation (PT) and private cars/taxis. Even though the travel cost increased to a limited extent, the CB service significantly improved the travel experience in terms of the travel time, travel speed, number of stations, and difference arrival time compared to PT services. The multinomial logit model and regression models demonstrate a significant positive relationship between the relative advantage and amount of demand for the CB services. Furthermore, the CB service primarily serves trips generated during the peak traffic hours of the city and supplements traditional PT service in areas with poor coverage levels. Document type: Articl

The Improvement of Motor Cooling Through Stator Profile Optimization using CFD Analysis in Hermetic Scroll Compressors

With the increased pressure of cost, hermetic compressor sizing become an important part of the design optimization process, while maintain the same performance level in the same time. Hermetic compressor motor design also face the same challenge. However, reducing motor size for same compressor capacity will increase the motor power density, with the same motor cooling design as before, motor running temperature will be increased and this affect both motor life and reliability as well as passing UL certification requirement for compressors using OLP ( internal overload protector). Hermetic motor cooling improvement using thermal modelling has been investigated before by using thermal network method, with limited accuracy since this do not taken all thermal correlation between motor and compressors. (refer to Purdue paper: thermal modelling ro the motor in semi-hermetic screw refrigeration compressor under part load conditions) However, the real situation in terms of thermal and fluid distribution which affect motor cooling inside the compressor in much more complicated than a pure thermal lumped circuit can represent. With the usage of fluid and thermal coupled simulation method today, we can simulate and understand more accurately the correlation between motor and compressor heat transfer and fluid distribution to optimize motor cooling channel, both in static and dynamic stage, and keep motor temperature under the accepted level while main a good flow for the overall compressor performance. In this paper, different geometry of stator outer diameter profiles are investigated, to balance between the motor efficiency impacts versus the motor temperature increase, compressor and conclude the optimization in terms of stator outer profile for the compressor structure discussed in this paper. Motor efficiency results are calculated and also tested, motor cooling optimization also calculated and tested inside compressor. From the research work done here, we can see that by using CFD tool (ANSYS), compressor motor design engineers can find the optimal stator lamination design, and understand the biggest influence factor to motor cooling, but not important for motor electromagnetic design and performance. In future, if the design concentrated on the important factors, and optimize the motor cooling, compressor design in terms of sizing and cooling correlation would be well balanced between cost and performance

Modeling Human Performance on Statistical Word Segmentation Tasks

Harnessing the orbital angular momentum (OAM) of light is an appealing approach to developing photonic technologies for future applications in optical communications and high-dimensional quantum key distribution (QKD) systems. An outstanding challenge to the widespread uptake of the OAM resource is its efficient generation. In this work we design a new device that can directly emit an OAM-carrying light beam from a low-cost semiconductor laser. By fabricating micro-scale spiral phase plates within the aperture of a vertical-cavity surface-emitting laser (VCSEL), the linearly polarized Gaussian beam emitted by the VCSEL is converted into a beam carrying specific OAM modes and their superposition states, with high efficiency and high beam quality. This new approach to OAM generation may be particularly useful in the field of OAM-based optical and quantum communications, especially for short-reach data interconnects and QKD

Sorting full angular momentum states with Pancharatnam-Berry metasurfaces based on spiral transformation

Full angular momentum states constitute a complete and higher state space of a photon, which are significant not only for fundamental study of light but also for practical applications utilizing cylindrical optics such as optical fibers. Here we propose and demonstrate a simple yet effective scheme of combining the spiral transformation with Pancharatnam-Berry (PB) metasurfaces for high-resolution sorting of full angular momentum states. The scheme is verified by successfully sorting full angular momentum states with 7 orbital angular momentum states and 2 spin angular momentum states via numerical simulations and experiments. We expect that our work paves the way for simple high-resolution sorting of full angular momentum states, which could be highly useful in both classical and quantum information systems