Valve Opening Ratio Research Articles

Modelling of a Floating-Type Hybrid Wind-Wave System with Oscillating Water Column Wave Energy Converters: A Study Towards Floater Motion Reduction

The integration of floating offshore wind turbines with wave energy converters is regarded as a promising solution for offshore renewable energy development. Given the early stage of wave energy conversion technologies and the substantial influence of control methods on overall system dynamics, a faithful aero-hydro-thermo-elastic-servo-mooring coupled model, along with an engineering environment offering high flexibility for control implementations, is essential. To address the requirement, a numerical modeling framework is developed in this study based on Simulink, known for its superiority in control design and implementation, and OpenFAST, which offers a reliable floating wind turbine model. The model incorporates the thermodynamics of the air in chambers, power take-off dynamics, and oscillating water column dynamics. Furthermore, bypass valves are utilized for the wave energy converters to adjust chamber pressure and reduce floater motion, with a control law proposed to regulate the valve opening ratio. A case study is conducted under harsh ocean conditions to validate the model. The numerical results not only demonstrate the feasibility of the model but also underscore the effectiveness of the control law in improving floater motion performance.

Evaluating the effects of cavitating refrigerant flow on noise radiation from electronic expansion valve: a numerical study

The electronic expansion valve (EEV) is a critical component in air conditioners, responsible for regulating refrigerant flow rate and controlling the cooling or heating performance. However, it is also a significant source of noise. When the valve opening ratio is low, the increased flow velocity of the refrigerant can cause pressure to drop below the vapor pressure and result in a cavitation flow. This type of flow is known to produce higher levels of flow noise compared to single-phase liquid refrigerant flow. A Large Eddy Simulation is utilized to compute the internal flow of the EEV, incorporating a homogeneous mixture model to model cavitation phenomena. The structural vibration of the EEV and its inlet/outlet pipe wall is computed using high-resolution finite element methods with excitation force from internal wall pressure fluctuations. The near and far field noise radiation from the structure is calculated using finite and boundary element methods, respectively. The developed numerical methods are applied to two operating conditions: single-phase and two-phase. The results indicate that the noise radiation from the EEV is 6.5 dB higher in the cavitating flow than in the single liquid flow, closely matching the measured data. The current numerical methodology is expected to be useful in designing low-noise EEV units.

Performance research and optimization of marine dual-fuel engine based on RSM and NSGA-II

ABSTRACT In order to improve the economic efficiency of the ship when sailing and reduce the engine optimization cost. We propose the Response Surface Methodology (RSM) combined with NSGA-II to optimize the engine parameters. First, a simulation model of a marine four-stroke dual-fuel engine is established in AVL-BOOST software. Then, control parameters such as engine speed, exhaust valve opening (EVO) and compression ratio (CR) are planned by design of experiments. The response surface model was established in Design-Expert software. The significant influence of control parameters on performance parameters was studied by analysis of variance (ANOVA). Finally, with the output power, indicated fuel consumption rate and nitrogen oxide emissions as the optimization objectives. Non-dominated Sequential Genetic Algorithm (NSGA-II) is used to optimize the parameters to improve engine performance and reduce emissions. The results show that the established response surface model has good prediction accuracy. The response surface model visualizes the mathematical relationship between the control parameters and the optimization targets. The ANOVA results show that engine speed, EVO and CR have significant effects on engine performance and emissions. The optimization results show that the engine speed is 793 rpm, the EVO is 145°CA, and the CR is 12.3. Compared to standard settings, the optimized data shows a 3.4% increase in power, a 0.3% reduction in ISFC, and a 6.2% reduction in nitrogen oxide (NOx) emissions. The combination of response surface analysis and NSGA-II algorithm to optimize engine performance and emissions is thereby a feasible method.

PHM for Spacecraft Propulsion Systems: Similarity-Based Model and Physics-Inspired Features

This paper presents a methodology designed for the Prognostics and Health Management (PHM) Asia-Pacific 2023 Conference Data Challenge. In particular, this study targets the health assessment of spacecraft propulsion systems. The challenge involved analyzing and categorizing a simulation-generated dataset that included four unique spacecraft and multiple health conditions, such as normal operation, bubble anomalies, and solenoid valve faults in various system locations. The proposed approach uses a two- step process. First, a model based on similarity measures is employed to classify the data into one of four health states. Then, a model incorporating physics-inspired features is utilized in solenoid valve faults to identify the fault location and estimate the valve opening ratio. The validity of the model is confirmed through cross-validation with the training dataset, which achieved a flawless total score across all permutations. Our method effectively categorizes the test data, including cases from a spacecraft not covered in the training, thereby securing a top position in the competition. The findings highlight the strength of our proposed model, which uses physics-inspired features to predict valve opening ratios, proving useful in managing and interpreting complex, unfamiliar spacecraft health data.

Optimal design of a hydrogen tube skid for stable charging, storage, and discharging

This research investigates the optimization of a hydrogen tube skid's design for stable charging, storage, and discharging. It aims to propose an optimized manifold design based on the analysis of temperature and pressure changes within the cylinders. Using an experimentally validated model, the study analyzes cylinder pressure and temperature. The temperature and pressure in the cylinders increase and decrease during the charging and discharging processes, respectively. Specifically, the central cylinder in the skid exhibits a temperature 9% higher than the corners. Controlling the valve opening ratio effectively regulates temperature and pressure in the nine cylinders. Reducing the valve opening ratio to 75% from 100% decreases the temperature by 13 °C and the pressure by 10 MPa. Furthermore, it reduces temperature and pressure variations between the cylinders during charging to 1 °C and 0.1 MPa, respectively. These findings contribute to achieving a safe hydrogen delivery system and realizing an economically efficient hydrogen infrastructure.

Evaluation of correlations for mass flow rate of refrigerant through electronic expansion valve in air—water heat pump system using R32

To measure mass flow rate of R32 through EEVs under real operating conditions, a commercially available air-water heat pump (AWHP) system was operated in as wide a range as possible. Measurements showed that the effect of oil circulation on the refrigerant mass flow rate of the test system was negligible. To examine whether they were able to predict refrigerant mass flow rate of R32 in a real operating heat pump systems, previous empirical correlations available in the open literature were compared against these measured data. Previous empirical correlations, except for those of Park et al. (2007), showed poor agreement with the present experimental data, with mean absolute percentage error (MAPE) from 9.1% to 334.5% for EEV#1 (D: 2.40 mm) and from 24.1% to 122.2% for EEV#2 (D: 1.65 mm). These large differences were caused by differences in internal geometry of flow passage and operating conditions due to different refrigerants. A new empirical correlation was developed considering these aspects. The valve opening ratio was considered in terms of the valve flow coefficient variation. The thermodynamic state of refrigerant at the EEV inlet was represented by the enthalpy difference, so as to avoid discontinuity of the mathematical expression at the saturated liquid point. The new correlation showed good agreement with mass flow rate measured through both EEVs, with MAPE values of 9.3% and 14.5% for EEV#1 (D: 2.40 mm) and EEV#2 (D: 1.65 mm), respectively.

DSMC Simulation of the Effect of Needle Valve Opening Ratio on the Rarefied Gas Flows inside a Micronozzle with a Large Length-to-Diameter Ratio

The cold gas micro-propulsion system can provide low noise and ultra-high accuracy thrust for satellite platforms for space gravitational wave detection, high-precision earth gravity field measurement. In this study, the effect of different needle valve opening ratios on the rarefied flow characteristics of a micro-nozzle in a cold gas micro-propulsion system was investigated based on DSMC method. The special feature of the currently studied micro-nozzle is that it has a section of micro-channel with a large length–diameter ratio up to 4.5. Due to the extremely small needle valve displacement of the nozzle (minimum needle valve displacement up to 1.7 μm), a finely structured mesh was used. The molecular particle and macro flow characteristics inside the micro-nozzle were calculated for the conditions of a needle valve opening ratio from 5% to 98%. The throttling effect of the throat has a significant effect on the rarefied flow in the micro-nozzle; especially under the tiny opening, this effect is more significant. The spatial distribution of continuous flow, transition flow, and free molecular flow in the micro-nozzle varies at different needle valve opening ratios. As the needle valve opening ratio increases, the continuous flow will gradually fill the microfluidic region.

Numerical study on the behavior and design of a novel multistage hydrogen pressure-reducing valve

Applying hydrogen fuel-cell vehicles (HFCVs) is feasible to achieve net zero carbon emission in transportation sector. The energy density requirements of these vehicles are fulfilled via high-pressure gaseous hydrogen storage; therefore, an effective pressure-reducing system is necessary. In this work, a novel multistage pressure-reducing valve (named as T–M valve) combining a sleeve pressure structure valve and a Tesla-type orifice valve is proposed. A computational fluid dynamics (CFD) model is developed to analyze the influence of operating parameters on pressure and velocity distributions. Results show that the large pressure and velocity gradients’ region is concentrated on the throttling elements. The valve opening and pressure ratio significantly affect energy consumption. In addition, the Mach number in the valve less than one is proposed. This study is conducive to further energy conservation and emission reduction and the research of multistage flow pressure-reducing devices. •A novel multistage hydrogen pressure-reducing valve using a sleeve pressure structure and Tesla-type orifice valves. •Analyze the novel valve behavior using a computational fluid dynamics model. •Large pressure and velocity gradients area is concentrated on the throttling elements. •The valve opening and pressure ratio significantly affect energy consumption.

Highly Articulated Tube Mechanism With Variable Stiffness and Shape Restoration Using a Pneumatic Actuator

Recently, soft robotics research has focused on mechanisms to control the stiffness of robot structures. There are several types of variable stiffness mechanisms that can change the stiffness of such structures by altering friction force. Among these, the negative-pressurization method applies negative pressure to the particles or layers that are filled inside a bag so that they contact each other and increase stiffness. However, the maximum driving pressure that can be achieved using the negative-pressurization method is 0.1 MPa, which limits the stiffness. In this study, we devised a new fluid-driven mechanism that can change the stiffness through positive pressurization using pneumatic artificial muscles. The proposed structure constructed with hollow beads and inner muscles can hold arbitrary joint angles by the contraction force generated when a pressure is applied. We measured the torque in the pitch direction due to friction when the internal pressure and inner segment diameter were changed. We confirmed that the error between the measured and theoretical torque value was within a 20% at any inner diameter. Also, since a pneumatic artificial muscle is enclosed inside the structure, an actuation effect can occur when the pressure is applied. We measured the restoring angle and force of this effect when the valve opening ratio and inner segment diameter were changed. We confirmed the function that can change the shape restoration characteristics by changing the flow rate with a single rubber tube. Our approach will help design effective stiffening mechanisms using positive pressurization in soft robotics applications. In future, we will design a tensioner mechanism for arbitrarily changing the distance of segments in the axial direction, and we will investigate the holding torque, restoring angle and force when the distance of the segments is changed.

Comparison of Loss Coefficient using 1-inch Ball and Glove Valve Opening Ratio

Comparison of Loss Coefficient using 1-inch Ball and Glove Valve Opening Ratio

Experimental investigation on control of temperature asymmetry and nonuniformity in a pilot scale thermal flow reversal reactor

Temperature asymmetry along flow direction and nonuniformity vertical to flow direction have been the prominent obstacles to the stable operation of thermal flow reversal reactor (TFRR) devices in industry. However, the relevant investigations are sorely lacking especially through the experiment method due to the limitation of laboratory test conditions. In this study, temperature asymmetry and nonuniformity for extra lean CH4/air combustion (feed methane concentration below 1 vol%) in a pilot TFRR were investigated experimentally. The effects of the preheating process and feed methane concentration were investigated. The switching time of 120 s and feed rate of 400 m3/h were determined for the preheating process. In the transition period between preheating completion and cyclic steady state achievement, the operation pattern with preheater off was beneficial to heat storage. Stable combustion for minimum feed methane concentration of 0.2 vol% was confirmed in the experiment. When feed methane concentration was decreased from 0.8 vol% to 0.2 vol%, higher feed methane concentration was easier to intensify temperature nonuniformity. To restrain the increase of temperature asymmetry and nonuniformity, an electronically controlled adjustment was adopted. Valve opening ratio could be monitored to obtain more equivalent average temperature values of two sections of the packed bed. A 55-min process and a 116-min process were picked out from the cyclic steady-state period to eliminate temperature nonuniformity through adjusting valve opening ratio. As a result, the gaps in the high-temperature section width of two sections get narrowed and the average temperature of two sections is almost the same. The switching time ratio could be regulated to shift high-temperature cores of two sections to middle height position. A 58 min long process was selected with a switch time ratio of 1.25 and the temperature center height of both two sections dropped obviously. Synchronous adjustment of the valve opening ratio and the switching time ratio accelerated the adjustment process and double effects could be acquired in the meantime. A 36-min long process and a 28-min long process are chosen for simultaneous adjustment. The average temperature of two sections reach good agreement in the end and the temperature center height of two sections both drop obviously. This work is beneficial to the development of TFRR for better dealing with ventilation air methane and other lean gaseous fuel streams.

A pre-test analysis of ATLAS SBO with RCP seal leakage using MARS code

The accident in Fukushima Daiichi nuclear power plants shows the important of developing coping strategies for extended station blackout (SBO) scenarios of the nuclear power plants (NPPs). Many NPPs in United State of America are applying FLEX approach as main coping strategies for extended station blackout (SBO) scenarios. In FLEX strategies, outside water injection to reactor cooling system (RCS) and steam generators (SGs) is considered as an effective method to remove residual heat and maintain the inventory of the systems during the accident. This study presents a pretest calculation using MARS code for the Advanced Thermal-hydraulic Test Loop for Accident Simulation (ATLAS) SBO experiment with RCP seal leakage scenario. In the calculation, the turbinedriven auxiliary feed water pumps (TDAFPs) are firstly used after SBO initiation. Then, the outside cooling water injection method is used for long term cooling. In order to minimize operator actions and satisfy requirements of APR1400 emergency operation procedure (EOP), the SGs Atmospheric Dump Valve (ADV) opening ratio, auxiliary feed water (AFW) and outside cooling water injection flow rates were investigated to have suitable values. The analysis results would be useful for performing the experiment to verify the APR 1400 extended SBO optimum mitigation strategy using outside cooling water injection.

Experimental study for a high efficiency cascade heat pump water heater system using a new near-zeotropic refrigerant mixture

Single-stage water-source heat pumps have some disadvantages such as high pressure ratio and lower coefficient of performance at high water outlet temperature, and normally the temperature promotion cannot exceed 50 °C. To surmount these disadvantages, a high temperature water-source cascade heat pump (HTWSCHP) was suggested; the HTWSCHP system demonstrates a much more competitive performance at high water outlet temperature of 142 °C and the temperature promotion can reach 90 °C. Lots of researches have been performed to analyze the cascade heat pump system, but they are normally about the low ambient temperature and there is very little information about the high water -outlet temperature. In this study, a HTWSCHP system was investigated experimentally. The high and low refrigerant cycle employed BY-3(A&B) and R245fa respectively. The experimental test was performed under different conditions: different electronic expansion valve opening ratio combination for low and high cycle, different refrigerants for the low cycle, different temperature for low-temperature heat source, different heating capacity, and varying water-outlet temperature. The final results shows that the water-outlet temperature of 142 °C can be achieved which is the highest level in the open literature with the total coefficient of 1.669, and the pressure ratio for low and high cycle are 3.9 and 3.4 respectively.

Dynamic model of a transcritical CO2 ejector expansion refrigeration system

This paper presents a dynamic model of a transcritical CO2 ejector expansion refrigeration cycle (EERC) which is a promising refrigeration system due to its environment-benign nature and low throttling loss. The mathematical models for gas cooler, evaporator and separator are formulated by using the mass and energy conservation equations. Based on the real properties of CO2, the ejector model is developed and the variable ejector component efficiencies are taken into account because they vary with operation conditions. The compressor and expansive valve are modeled in a set of algebraic equations. The presented transient simulation results are in good agreement with the experimental data. The dynamic behaviors of the system undergoing the change of expansion valve opening and ejector area ratio are observed by the developed model, which helps to understand the characteristics of the EERC and guide the system control.

Modeling and Model-based Analysis of a Solid Oxide Fuel Cell Thermal-Electrical Management System with an Air Bypass Valve

For stand-alone solid oxide fuel cell (SOFC) power systems without grid connection, delivering demanded power, maintaining system temperature constraints, and achieving high system efficiency are the key design objectives. A typical SOFC system consists of an SOFC stack and a blower, a heat exchanger, an exhaust-burner as the primary components in its balance of the plant. In this work, a novel SOFC system design with an air bypass valve and a target operating range of 1 to 5kW is considered. A system dynamic model, which captures the spatial electrical and thermal distributions of stack, is developed and optimal operating points to maintain the maximum steady state system efficiency are explored while enforcing four constraints on temperature and temperature gradient. Furthermore, the effects of the control variables, namely the bypass valve opening ratio (BP), voltage (U), fuel utilization (FU), and air excess ratio (AR) in improving system performance and expanding feasible operating range are quantified. In addition, the open-loop optimal operation strategy is obtained. The analysis demonstrates that the design of the stand-alone SOFC system is feasible and the bypass valve plays an important role in improving the overall system performance and operation ability.

IMPACT OF THERMOMECHANICAL REFINING CONDITIONS ON FIBER QUALITY AND ENERGY CONSUMPTION BY MILL TRIAL

Fiber thermomechanical refining is a critical step for the manufacturing of medium density fiberboard (MDF). To increase productivity and improve fiber quality with a reduction in energy consumption during refining, it is essential to determine appropriate refining conditions, such as the chips retention time (accumulated chip height, CH) in the pre-heater, feeding screw revolution speed (SR) in the chip feeding pipe, and the opening ratio of the discharge valve (OV) in the discharge pipe. Using multiple regression analysis, relationships between the response variables (the total fibers, the specific energy consumption obtained by the motor power consumption/the total amount of dry fibers, and the percentage of qualified fibers) and the predictor variables (OV, CH, and SR) were modeled. Specific energy consumption decreased with an increase in CH. When more chips were stored in the pre-heater, the chips were softened by the extended steam-treatment time, reducing the energy consumption. There were negative relationships between the percentage of qualified fibers and the predictor variables (OV and SR). It was reasoned that a greater proportion of coarse fibre was produced when the discharge valve opening ratio or the feeding screw speed increased. This resulted in a reduction in the percentage of qualified fibers. Due to the large sample size (1667 measurements for each variable) in this study, the resulting regression equations can be applied to estimate the productivity, energy consumption, and fiber quality during refining in an MDF mill.

Development and experimental validation of a new one-dimensional valve boundary condition based on the method of characteristics

One-dimensional (1D) engine gas dynamic simulations are necessary in order to develop control laws for specific valve systems such as variable valve timing or the pneumatic hybrid engine. The keystone of 1D engine models is the valve boundary condition, where the pressure wave phenomenon into a pipe is created and the in-cylinder mass flowrate is determined. Most commercial or research simulation codes embed the method of characteristics (MOC) constant-pressure valve boundary condition from Benson. This constant-pressure model in its original form provides good results in most cases, but this paper shows that it does not converge for low valve opening and pressure ratio values, for which the characteristic lines become vertical. A solution to this problem cannot be found in the literature. The current paper presents a new MOC-based valve boundary condition that obviates convergence problems. The computational time of the proposed model is evaluated and compared with that of Benson’s model. The new valve boundary condition is validated experimentally on a valve gas dynamics test bench and compared with the original constant-pressure model. The study shows that results obtained with the proposed model are similar to data from both experiments and Benson’s model.

Pressure Pulsation Behavior in Actual Size Mock-Up Piping System

In this study, the influence of valve closing and opening operations to change inner pressure during pump operations on the pulsation boundary condition was investigated to improve the prediction accuracy of pressure pulsation. Vibration experiments were conducted by using an actual size mock-up piping system with 40 m long as found in nuclear power facilities. A drastic change in the boundary condition of the acoustic resonance by a slightly different valve opening ratio to set a different inner pressure was seen in the experimental results. The simulation results by using the method of characteristics showed that the boundary condition of the acoustic resonance changed when the valve opening ratio was changed slightly from 10 % to 15 %. This indicated that the boundary condition of the acoustic resonance had a pulsed change and changed even at the small valve opening ratio, which was approximately 15% though the design threshold value was 25 %. It was concluded that the boundary condition of the acoustic resonance was sensitive to a slight change of the valve opening ratio and this was one of the reasons why it is difficult to predict the pressure pulsation behavior including acoustic resonance accurately in actual plants.

A Study of Flow Induced Vibration in a Steam Control Valve

The flow field in a steam control valve is investigated by using the 2-D experiment and CFD to clarify the causes of serious pressure fluctuations. The experiments are carried out by changing the pressure ratio and valve opening ratio. Five types of flow patterns are observed in the experiment. Two types of them are stable and one of them is asymmetric attached flow and other is symmetric free jet flow. Three types are unsteady with symmetric, asymmetric oscillations and their mixture. These types of flows could be simulated by a 2-CFD fairly well. From these results, the characteristics of each flow fields are clarified.

High-Pressure Steam Flow in Turbine Bypass Valve System Part 1: Valve Flow

This paper presents a study of steam e ow behavior through a high-pressure turbine bypass valve when it suffers a high-pressure reduction in an electric-power-plant cogeneratorsystem. Efforts have been mainly directed at investigating the process of steam e ow and property variations in the aforementioned bypass valve as well as at obtaining correlations between the e ow rate and the valve opening ratio. Modeling of the high-pressure turbulent steam e ow was performed on a three-dimensional nonstaggered grid system by employing the e nite volume differencing method and by solving the three-dimensional, turbulent, compressible Navier ‐Stokes and energy equations. Through this research numerous data have been acquired and analyzed. These efforts enable us to obtain a correlation data set for the valve-opening vs the e ow rate coefe cient of the valve. One of the signie cant accomplishments isto use the model presented here to further improvethedesign of a high-pressuresteam turbine bypass e ow valve to reduce a high-velocity spot in the valve e ow pass so that noise can be suppressed.