Effect of particle mass concentration on erosion characteristics of self-priming pump

The self-priming pump is widely used in conveying the solid-liquid two-phase flow medium. The particles in the medium erode the components, leading to structural damage and failure. The computational fluid dynamics (CFD) model of the 65ZW30-20 self-priming pump is built to study erosion characteristics and mechanisms. FLUENT, along with the Discrete Phase Model and Oka erosion model, is applied for the numerical simulation. The particle distribution, impact times and velocity, and trajectories are taken into consideration to investigate the erosion characteristics in each component. The results show that with the increase of the particle concentration, the head and efficiency decreases gradually. The volute wall and blade leading edge are the most vulnerable regions to erosion, because of a large number of impact times and high impact velocity. Also, the particles impact the front gap wall for fewer times and the hub with lower velocity, which leads to a slighter erosion. Besides, the particle trajectories indicate that some particles impact the blade suction surface and the paraxial area of the shroud, rendering considerable erosion.

The driven flow vacuum infusion process: An overview and analytical design

This article describes a novel variant of the vacuum infusion process based on a multifunctional elastomeric reusable vacuum bag. The main innovation of this process is an elastomeric membrane having resin flow channels that can be controlled during the infusion process: they can be activated for the impregnation stage to enhance resin flow and removed during the curing stage to provide a smooth surface finish to the part. In addition, the size of the resin flow channels can be modified during the infusion providing control on the impregnation rate. This article describes the driven flow vacuum infusion (DFVI) process and presents analytical calculations regarding the effect of the geometrical design of the membrane and the processing variables on the porosity, permeability, and volume of resin transported by the flow medium. Preliminary results of unidirectional resin infusion tests comparing the DFVI process to traditional vacuum infusion and SCRIMP are also presented.

Simulation Research of Hydraulic Stepper Drive Technology Based on High Speed On/Off Valves and Miniature Plunger Cylinders

The technology for stepper drive that can achieve accurate motion in the hydraulic field has always been urgently needed in the industry. This paper proposes a hydraulic stepper drive based on five high speed on/off valves and two miniature plunger cylinders. The stepper drive discretizes the continuous flow medium into fixed small steps through the miniature plunger cylinder and realizes the state control of the drive through the logic action of the high speed on/off valve. This paper improves the current stepper drive and establishes a mathematical model to analyze the error of the drive and calculate the position of the actuator. In addition, through simulation research, the performance parameters such as the single-step step characteristic and pressure characteristic of the stepper drive are studied. The results show that, compared with the technology of current stepper drive, this stepper drive can effectively remove the “post step” phenomenon, greatly improve the stepper accuracy of the stepper drive, and have a more excellent performance.

Particle Deposition by Thermophoresis Under High-Temperature Conditions in a Helium Flow

The continuous generation of graphite dust particles in the core of a high-temperature reactor (HTR) is one of the key challenges of safety during its operation. The graphite dust particles emerge from relative movements between the fuel elements or from contact to the graphitic reflector structure and could be contaminated by diffused fission products from the fuel elements. They are distributed from the reactor core to the entire reactor coolant system. In case of a depressurization accident, a release of the contaminated dust into the confinement is possible. In addition, the contaminated graphite dust can decrease the life cycle of the coolant system due to chemical interactions. On one hand, the knowledge of the behavior of graphite dust particles under HTR conditions using helium as the flow medium is a key factor to develop an effective filter system for the discussed issue. On the other hand, it also provides a possibility to access the activity distribution in the reactor. The behavior can be subdivided into short-term effects like transport, deposition, remobilization and long-term effects like reactions with material surfaces. The Technische Universität Dresden has installed a new high-temperature test facility to study the short-term effects of deposition of graphite dust particles. The flow channel has a length of 5 m and a tube diameter of 0.05 m. With helium as the flow medium, the temperature can be up to 950 °C in the channel center and 120 °C on the sample surface, the Reynolds number can be varied from 150 up to 1000. The particles get dispersed into the accelerated and heated flow medium in the flow channel. Next, the aerosol is passing a 3 m long adiabatic section to ensure homogenous flow conditions. After passing the flow straightener, it enters the optically accessible measurement path made from quartz glass. In particular, this test facility offers the possibility to analyze the influence of the thermophoretic effect separately. For this, an optionally cooled sample can be placed in the measuring area. The thickness of the particle layer on the sample is estimated with a three-dimensional laser scanning microscope. The particle concentration above the sample is measured with an aerosol particle sizer (APS). Particle image velocimetry (PIV) detects the flow-velocity field and provides data to estimate the shear velocity. In combination with the measured temperature-field, all necessary information for the calculation of the particle deposition and particle relaxation times are available. The measurements are compared to results of theoretical works from the literature. The experimental database is relevant especially for computational fluid dynamics (CFD)-developers, for model development, and model verification. A wide range of phenomena like particle separation, local agglomeration of particles with a specific particle mass, and selective remobilization can be explained in this way. Thus, this work contributes to a realistic analysis of nuclear safety.

Experimental Characterisation of Acoustic Damping Generated by Perforated Screens at High Frequencies

Modern low-emission gas turbine combustion systems often experience thermo-acoustic instabilities at certain operating conditions, which adversely affect the performance of the engine. One way to mitigate the detrimental effect of such instabilities is to place passive damping devices along the wall of the combustion chamber. To achieve greatest overall damping requires good understanding of the acoustic properties of the damping devices at engine conditions and determination of the undesired acoustic mode shapes for optimal placement at the wall. This paper presents an experimental study which characterises the acoustic properties of bias flow liners operating at frequencies in the low kilohertz regime (> 1 kHz). The engine conditions are simulated in the experiment at ambient conditions by maintaining dynamic similarity, i.e. by matching a number of non-dimensional parameters in the experiment which characterise the engine conditions. The present experimental study contributes to the existing measurement database by taking into account the strong gradient in characteristic impedance between grazing and bias flow medium. The acoustic properties of the investigated damper configurations are assessed in terms of the surface impedance at the interface between grazing and bias flow. An impedance model is suggested which accounts for the strong gradient in characteristic impedance between grazing and bias flow medium. The impedance model may serve conveniently as input to an acoustic mode shape prediction in the combustion chamber to identify the optimal placement of the damping devices.