Optimization of Nonlinear Pressure-flow Characteristics of a Spring- Loaded Pressure Relief Valve Based on CFD Simulation

In this study, the nonlinear pressure-flow characteristics of a spring-loaded pressure relief valve (PRV) which is used in the automotive fuel supply system for pressure control is analyzed, and its characteristics are improved by means of geometrical modifications of the valve structure. Given the complexity of the coupling mechanism between the valve internal flow characteristics and spring system, a quasi-steady computational fluid dynamics (CFD) method is introduced to predict the nonlinear pressure-flow characteristic curve of the valve and the accuracy is validated by experimental data. The total hydraulic force on the valve spool and diaphragm are divided into three parts according to the position of action and the correlation between the internal flow characteristics, hydraulic force, and pressure-flow characteristics of the valve are explained by CFD analysis and visualization. The result shows that the quasi-steady CFD method can accurately predict the trends of the valve nonlinear pressure-flow characteristic curve which is mainly determined by the hydraulic force produced in the middle chamber of the valve, when the valve opening reaches a certain value, a main vortex would be formulated in the middle chamber and lead to the sudden increase of hydraulic force which causes the fluctuation of the pressure-flow characteristic curve of the valve. It was also found that by increasing the round corner size, the valve opening value of flow pattern change will be promoted and the valve pressure-flow characteristic can be optimized.

An investigation on using MDCs for an efficient desalination process as pretreatment of reverse osmosis

Microbial desalination cell (MDC) is a new bio-electrochemical technique which converts chemical energy into electrical energy, and at the same time desalinates water and treats wastewater. In this study, MDC performance and water biofouling conditions were tested as an efficient pretreatment desalination process of reverse osmosis (RO). The experiments were designed in a three-chamber reactor to compare the performance of batch and continuous fed modes, using bio-cathode and synthetic wastewater in four different hydraulic retention times and 17 and 35 g/L NaCl concentrations. According to the results, maximum salt removal of about 52.3% was obtained in the continuously fed MDC at 35 g/L NaCl concentration. The maximum salt removal at 17 g/L NaCl was also observed in continuous mode. The anolyte pH in both batch and continuous modes dropped from 7 to 6.32, 6.47 and 6.37, 6.48 in 17 and 35 g/L NaCl concentrations respectively. The chemical oxygen demand (COD) removal values in the continuous mode were 61 and 65% in the anolyte and catholyte respectively, higher than those of fed-batch MDC. The biofouling of the middle chamber solution was confirmed by conducting bio-microbial tests. Our results suggest that the type of hydraulic flow can improve the performance of MDC in different concentrations of NaCl.

Soft Robotic Gripper with Chambered Fingers for Performing In-Hand Manipulation

In this work, we present a soft robotic gripper for grasping various objects by mimicking in-hand manipulation. The soft robotic gripper consists of three fingers. Each finger contains three air chambers: Two chambers (side chambers) for twisting in two different directions and one chamber (middle chamber) for grasping. The combination of these air chambers makes it possible to grasp an object and rotate it. We fabricated the soft finger using 3D-printed molds. We used the finite element method (FEM) method to design the most effective model, and later these results were compared with results from experiments. The combined experimental results were used to control the range of movement of the whole gripper. The gripper could grasp objects weighing from 4 g to 300 g just by inflating the middle chamber, and when air pressure was subsequently applied to one of the side chambers, the gripper could twist the object by 35°.

Influence of perforation and sound-absorbing material filling on acoustic attenuation performance of three-pass perforated mufflers

The finite element method is employed to calculate the transmission loss of three-pass perforated reactive and hybrid mufflers. The effects of perforated tubes and bulkheads on the transmission loss of three-pass reactive mufflers are investigated numerically. Two types of hybrid mufflers are considered, and the effects of sound-absorbing material filling and packed outlet tube on the acoustic attenuation performance of mufflers are analyzed. The perforations of the tubes and bulkheads and sound-absorbing material filling are demonstrated to have significant influence on the acoustic attenuation behaviors of the mufflers. The perforation of the tubes and bulkheads may shift the resonance from the low- to middle-frequency range. The sound-absorbing material filling in the middle chamber improves the acoustic attenuation performance at middle to higher frequencies and provides a relatively flat and broadband acoustic attenuation. It is found that the solid inlet or outlet tube replacing the perforated tube and sound-absorbing material filling in the middle chamber increases the pressure drops, while the rest configurations change the pressure drops slightly.

Simultaneous Desalination of Sea water and Electricity Production with New Membrane Technology, Air-Cathode Microbial Desalination Cells

Water and energy shortages, has increased the need for methods that can provide low energy for desalination of sea water. Microbial desalination cell is one of the most important of these methods. In this study we use air cathode MDC for desalination of seawater. The maximum voltage, power and current density was 607mV, 521mW/m2 and 858mA/m2 (25mM PBS) and 701mV, 695mW/m2 and 992mA/m2 (50mM PBS) respectively. During the period of the voltage generation in 50mM PBS was about 1.5 times of 25mM PBS. Under this situation, EC of seawater with initial electrical conductivity declined by 48.31±3% (25mM PBS) and 46.71±2.73% (50mM PBS). As well as decrease of salt from sea water in the middle chamber, EC in synthetic wastewater and catholyte slightly increased. So that Change percent of EC in synthetic wastewater was 44.20 ± 11.94(25mM PBS) and 27.94 ± 3 (50 mM PBS) and in catholyte was 211.66 ± 22.41(25mM PBS) and 119.24 ± 11.25 (50 mM PBS) respectively. These results show that the MDC can also be used as a pretreatment to reverse osmosis; simultaneously the energy required in this process is also partly meet.

Removing As, Ba, Cu and Zn from Waste Plasma Display Panel Glass by Electrokinetics

Due to shorter and shorter life span and the rapid development of flat panel display, plasma display panel (PDP) is now becoming a new kind of e-waste. In order to remove heavy metals, such as As, Ba, Cu, Zn, from waste PDP glass, electro-kinetic process was introduced and factors that affect heavy metal removing rate were investigated. Results showed that HNO3 concentration and PDP adding amount could significantly impact heavy metal removing rate, while current density was on the opposite. Heavy metal removing rate increased first and then decreased as the time extension. When PDP powders was 2 g, 9 mL 5 mol/L HNO3 was added, current density was 200 mA/cm2 and time was 6 h, the removal rate of As, Ba, Cu, Zn were 71.02%, 95.87%, 92.50% and 97.70%, respectively. As, Ba, Cu and Zn distributions in the cathode, anode and middle chamber varied as changing particle size, HNO3 concentration, current density. Generally, most Cu was concentrated in cathode chamber, and Zn in the anode chamber, while As and Ba would be in both cathode and anode chamber. As, Ba, Cu and Zn, in the middle chamber, no more than 10%, were the lowest among the three.

Research on Dynamic Characteristics of Anti-Reverse Valve for Hydraulic Excavator Rotary Motor

Hydraulic excavator slewing system is an important component of the excavator and its core-component is the rotary motor. When the rotary hydraulic system starts, stops, and reciprocating works, dynamic characteristic of rotary motor anti-reverse valve has a great influence for working condition of the whole system. Through researching working principle of hydraulic system anti-reverse valve, establish dynamic mathematical model of anti-reverse valve, analyze dynamic response of the model, and get the theoretical foundation of the impact of anti-reverse valve middle chamber throttle opening on hydraulic system. According to the actual working condition of the excavator slewing hydraulic system, establish the system AMESim simulation model, take different parameters of the anti-reverse valve throttle opening, conduct simulation and analysis of the anti-reverse valve characteristics, and validate throttle opening has a great influence on dynamic characteristics of the hydraulic system.

Flow Characteristics of Micro Diffuser/Nozzles for a Valveless Micropump

In this study, the flow characteristics have been experimentally investigated for various shapes of the diffuser/nozzles, and the results are compared with the numerical simulation. Three chambers (inlet, exit, and middle) and two identical diffuser/nozzles are fabricated on a silicon wafer. The inlet and middle chamber is connected by one diffuser/nozzle; and the middle and exit chamber is connected by another diffuser/nozzle. The experiments are performed in a pump mode in which pressure is applied to the middle chamber and a supply mode in which pressure is supplied to the inlet and exit chamber. The net flow rate is determined by the flow difference between the pump and supply mode. The important parameters considered in this study are the throat width (30–12μm) and the taper angle (3.15–25.2°). For the taper angle and the throat width, it is found that there exists an optimum at which the net flow rate is the greatest. The optimal taper angle is in the range of 10–20° for all the pressure differences; and the throat width indicates an optimal value near 90μm for the case of 35kPa pressure difference. This tendency has been verified by the numerical simulation. From the numerical simulation, it is also found that the net flow rate is influenced by the size of the middle chamber. With decreasing chamber size, the net flow rate is reduced because of the interference between two streams flowing into the middle chamber.