Bypass Valves 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.

Nitrogen precooling heat exchanger replacement and control system upgrade in superfluid cryoplant at CMTF

Liquid nitrogen precooling is used in most cryoplants to achieve cooldown to 80 K temperature range. In one such system at Fermilab’s CMTF superfluid cryoplant, where the helium supply directly exchanges heat with liquid nitrogen, freezing of nitrogen occurred inside the heat exchanger due to heat exchanger flow imbalance during a cryoplant trip. Trapped vapor pockets of nitrogen within the frozen heat exchanger channels were formed while warming up the heat exchanger, creating high localized pressure and subsequent damage/rupture of the heat exchanger. Replacement of the heat exchanger was done, and modifications were made in the system to rectify future occurrences. The control system was updated to bypass the heat exchanger entirely if the incoming helium stream temperature drops below 76 K. This was done by repurposing two control valves as heat exchanger bypass valves that were previously used for a redundant 80 K adsorber in the coldbox. Additional modifications were made to further prevent return of large amount of cold helium gas from cold end during abrupt cryoplant shutdown. This modification has ensured high reliability of heat exchanger with prevention of freezing of nitrogen which can damage the heat exchanger.

ИССЛЕДОВАНИЕ ОСНОВНЫХ ПАРАМЕТРОВ ГИДРОМЕХАНИЧЕСКОГО ДЕМПФЕРА ТРАНСПОРТНЫХ СРЕДСТВ, ИСПОЛЬЗУЕМЫХ В АГРОПРОМЫШЛЕННОМ КОМПЛЕКСЕ

The article presents materials related to the development of a promising design of a hydraulic damper in-stalled in the suspension of vehicles used in the agro-industrial complex. A special feature of the hydraulic damper design is the transition from vertical channels to horizontal channels in the piston and stem of the vi-bration damper. In this case, the vertical sections of the rod channels are mated with the horizontal sections of the piston channels. The presence of such calibrated holes in the piston and rod, as well as due to the ab-sence of bypass valves, can significantly reduce sudden pressure changes in the vibration damper during high-speed movements of both the rod and the piston. This significantly increases the smoothness of the ride, and, consequently, the comfort and safety of the vehicle and, thus, improves the working conditions of the personnel operating it. Analytical studies have been carried out, as well as hydrodynamic and strength calcu-lations of such determining parameters as the pressure of the working fluid and its flow rate. Recommenda-tions are given on the choice of rod and piston material for a promising design of a hydraulic damper for ve-hicles. A method of engineering calculations for determining the parameters of the throttling system is pro-posed, which allows to establish the criteria for the operability of the developed technical solution with a view to its possible application in industrial conditions.

Experimental investigation on acceleration of working fluid of heat pipe under bypass line operation

In a conventional heat pipe, the flow resistance is generated by the opposing flow of liquid and vapor across the phase-change interface. The flow resistance can impose a limitation on the heat transfer rate within the heat pipe, which can have an adverse effect on its overall efficiency. Therefore, reducing the flow resistance is essential for improving the heat transfer of heat pipe. The method of inducing a decrease in flow resistance is classified as an essential technology for improving the heat transfer performance of a heat pipe. In this study, experiments were conducted to induce operating fluid acceleration by decreasing the hydrodynamic resistance inside a heat pipe to improve thermal performance. A liquid bypass line connecting the three points of the condenser to the beginning of the evaporator was designed and installed, with four flow rate control valves attached to control the bypass flow rate at each bypass port. In this study, the working fluid acceleration was observed experimentally in bypass mode (all bypass valves opened) and normal mode (all bypass valves closed). According to the experimental results, the heat transfer efficiency of the heat pipe system improved by up to 106.5% in relation to the thermal resistance. The maximum thermal load in a horizontal position increased by up to 45.8% in the bypass mode.

Development of control strategies for novel systems of a full scale OWC for the WEDUSEA project

The WEDUSEA project is a €19.6 million European wide joint venture between 14 partners spanning industry and academia from Ireland, the UK, France, Germany, and Spain that will culminate with a two-year, grid connected deployment of a 1MW rated oscillating water column (OWC) wave energy converter (WEC) at the EMEC test site in Orkney, Scotland, UK. 
 The WEDUSEA project will incorporate a number of novel systems and control strategies to improve device performance, annual power production, and grid integration. During the initial planning and design phases of the project, a wave-to-wire numerical model has been created to investigate the impact these new systems will have on device performance and allow for the testing and development of the control strategies necessary to operate the 1MW power take-off (PTO) system as efficiently as possible. This paper will detail the novel systems added to the OWC, the control strategies developed for the new additions, and the modelled performance of the OWC. 
 The WEDUSEA OWC will rely on a Wells turbine for the pneumatic-to-mechanical conversion. As Wells turbines are susceptible to aerodynamic stall, a flow control system using 4 bypass valves of varying size will be added, and it will allow for up to 16 different variations for flow control. The performance of the valves will be tested via CFD and MATLAB-Simulink modelling.
 The nature of WECs result in fluctuations in the power delivered to the grid, and this can lead to undesirable impacts on the grid. To mitigate these power fluctuations, the WEDUSEA OWC electrical system will include a controllable super capacitor energy storage system that will be used to improve the power quality of the electricity delivered. The objective will be to absorb power peaks and use that stored energy to minimise energy troughs. The power output is aimed to be levelized by mitigating fluctuations in a certain frequency range. The ability of the super capacitor to improve power delivery to the grid may also facilitate improved performance and increased annual power production by the mechanical PTO by enhancing the turbine-generator control system flexibility. 
 To incorporate the bypass valves and the super capacitor into the WEDUSEA OWC, more complex algorithms will need to be created for control of the mechanical and electrical components of the PTO. These algorithms will be tested and sharpened through testing using the wave-to-wire model developed using MATLAB Simulink and Simscape. The MATLAB-Simulink software simulations will allow for in-depth analysis of the impact the bypass valves will have on the behaviour of the pneumatic-to-mechanical section of the PTO. The Simscape Electrical software will allow for thorough modelling and evaluation of the electrical system and the impact the control strategies will have on the output power quality. The full model will allow for estimations of annual power production, and with improved kWh/yr, the LCOE could see significant reductions. The model testing and control development performed during this early stage of the project will help to maximise the deployment phase of the project and estimate annual power production.

Multiphysics Model of Quench for the ITER Central Solenoid

The ITER Central Solenoid (CS), the backbone of the ITER magnet system, is composed of 6 modules, each made of 40 pancakes, for a total conductor length of about 36 km. More than 4 km of pipes, about 30 bypass or control valves, the heat exchangers and a cold circulator are part of the cryogenic distribution used to maintain the nominal operating conditions (flow and temperature). During the plasma scenario, several loss sources – such as AC losses, heat from supports and structures, joule heating at joints – can affect the magnet stability. A reliable analysis of quench is therefore of great importance to guarantee the safe operation of the CS superconducting coils. In this work, the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SuperMagnet</i> code, a state of the art software for the numerical modelling of hydraulic, electrical and thermal phenomena occurring in superconducting magnets, is applied to study the CS and its cryogenic distribution during quench events.

Thermal management of bypass valves for temperature difference elimination in a 5 kW multi-stack solid oxide fuel cell system

Large-scale solid oxide fuel cell (SOFC) stationary power generation systems require multi-stack SOFC integration. System consistency has a significant impact on stable, long-term operations. Investigations on the flow and temperature distributions of the system and effective thermal management are necessary to improve system consistency. In this study, a multi-stack SOFC system homogeneity thermal management method and its decision process are proposed based on the flow network method. The flow and thermal distributions and performance are investigated by considering air stoichiometries of 1.5, 2.0, and 2.5. A thermal management strategy using bypass valves is proposed to solve the maldistribution issue of the system. Both the flow characteristics calculated by the flow network and the electrothermal characteristics of the stack determine the bypass valve opening (or air mixing ratio). The results indicate that a maximum temperature difference of 60 K can be reduced to 0 K through the proposed thermal management strategy in a 5 kW multi-stack system. The application of the bypass valve enables the system to attain temperature consistency, and the thermal efficiency of the entire SOFC combined heat and power system can be increased by up to 50% at the set temperature.

By‐pass valves in hydropower plants: An ecologically important measure to mitigate stranding in rivers due to emergency turbine flow shutdown

AbstractHydropeaking operations or accidental shutdown in hydropower (HP) plants lead to rapid reduction in river flows downstream HP outlets and cause severe stranding of biota. Stranding of fish in dewatered riverbeds is a major consequence of hydropeaking. To mitigate the direct negative impacts of accidental powerplant shutdown implementation of automated by‐pass valves (BPVs) is suggested as an efficient measure. Proper configuration and operation of the BPV is crucial. At present, more than 110 Norwegian HP plants have BPVs as a license requirement. We found that the function of the BPVs in small‐scale HP plants (HPPs &lt;10 MW) were found to be inadequate. Re‐configuration to better mitigate the ecological impacts were required to minimize stranding risk for juvenile salmonids. The valves were found to come into operation too late, did not open automatically, or were found to reduce the flow too rapidly. Hence, the function of the valves did not meet best practice. This is alarming seen both from a governance perspective as well as from an ecological standpoint. Our second objective was to develop a generic cost‐efficient formula for BPVs configuration to dampen severe flow dewatering in case of HP fallout. Our configuration formula is adjustable to meet down‐ramping flow rules, and hence may helps to mitigate stranding of key species in rivers. For most of the large‐scale HPPs (&gt;10 MW), the BPVs seems to operate as expected, namely to secure base‐flow until the HP turbine is re‐started and hence mitigate the most severe dewatering events. Potentially more than 650 HPPs in Norway, and hence several thousand of river km downstream HPP outlets may need well‐operated BPVs to mitigate accidental stranding of riverine biota worldwide.

Equivalent model-based optimal matching for two-stage turbocharging systems with bypass valves

A bypass valve can effectively distribute the energy of a two-stage boosting system and adapt to the demand for air intake regulation in multiple combustion modes. Gradually, it has become the direction of evolution of boosting technology. However, the existing two-stage turbocharging system matching methods do not consider the selection of bypass valves simultaneously. This study proposes an optimal matching method (H-TCB) for the critical parameters of a two-stage turbocharging system with a bypass valve based on the equivalent model of a two-stage turbocharging system. Taking the lowest comprehensive energy consumption as the constraint boundary, the theoretical constraint equations for the optimal distribution principle of the pressure and expansion ratios of the two-stage turbocharger with a bypass valve were obtained. The cooperative optimal relationship between the bypass coefficient and flow area of the high-pressure stage turbine and the similar flow of the high-pressure stage compressor were analyzed. The research results show that, as the bypass coefficient increases, the optimized matching high-pressure stage turbocharger efficiency increases gradually, the effective flow area of the high-pressure stage turbine reduces, and the flow of the high-pressure stage compressor increases.

Detailed simulations of an aircraft fuel system by means of Simulink

The fuel system is one of the most important and complex parts of aircraft, being tasked with suppling the correct quantity of fuel to the aircraft engine during all operative conditions, from flight to ground operation. It must operate efficiently in any condition to guarantee safety and reliability. A fuel system for kerosene-based fuels (i.e., jet fuels) is a combination of hydraulic components, namely, tanks, pumps, bypass valves, safety valves, servovalves. The aim of this paper is to provide an accurate simulation model of an entire fuel system for gas turbine (turboprop and turbofan) engines, which can be used by manufacturers and researchers to evaluate the performance of the fuel system under different operating conditions for given components or to select the geometries of the components to obtain specific performance levels. The numerical code is developed in the Simulink environment, which is a software package widely used in industry. A detailed description of the model is provided in this paper, and results under specific operating conditions are shown and discussed. The power consumption of the system is assessed as well, with indication of the main sources of losses, which will be useful for current EU projects aimed at reducing the power consumption of aircraft.

Experimental Proof-of-Concept of a Hybrid Wave Energy Converter Based on Oscillating Water Column and Overtopping Mechanisms

This paper presents the results of laboratory tests on a hybrid wave energy converter concept, the O2WC (Oscillating-Overtopping Water Column) device. The proposed device aims at providing an alternative to the classical OWC concept, storing part of the wave energy of the highly energetic sea states in a second chamber at atmospheric pressure, through overtopping phenomena. In this way, the maximum airflow rate and air pressure in the OWC chamber are reduced, possibly aiding the safe functioning of the air turbine, and allowing to exploit the excess of energy instead of dissipating it through by-pass valves. The performance of the device is investigated under different incident wave conditions, for different design parameters. The height of the overtopping threshold from the second chamber of the device which allows to maximize the performance has been selected. Results show that the decrease of the primary conversion efficiency of the OWC component of the device caused by the decreased air pressure in the OWC chamber can be partially compensated by the additional energy stored in the overtopping chamber of the O2WC device. Overall, the studied O2WC device has capture width ratio values ranging between 0.3 and 0.7.

Optimal selection of supercritical CO2 Brayton cycle layouts based on part-load performance

The supercritical CO2 (S–CO2) Brayton cycle is considered a promising power generation system owing to its high efficiency and compactness. This cycle has numerous layouts which have been extensively investigated for design condition performance, whereas it often operates under part-load conditions, Therefore, it is vital to compare layouts based on part-load performance. Because part-load performance is influenced by control strategies and layout elements such as recompression, reheating, and intercooling processes, the part-load performance of four typical S–CO2 Brayton cycles including simple recuperated cycle, recompression cycle, reheating cycle, and intercooling cycle with different control strategies are explored using dynamic models. The results indicated that the thermal efficiency of the four layouts was simultaneously influenced by the layouts and control strategies. Safety performance is mainly determined by the control strategies. Moreover, when the turbine bypass valve and inventory are adopted to follow the load, the intercooling cycle overtakes the reheating cycle to attain the maximum thermal efficiency at low and medium loads. There was no overpressure or surge for the four layouts with the necessary controllers. However, when using bypass valves following the load, the four layouts are at risk of operating with overloaded drive motors at low loads. This is beneficial for guiding the selection of layouts and corresponding control strategies in different operation scenarios.

Acceptability assessment of casting defects under transient thermal loading

Weld repairs of castings during manufacture is a well-known and acceptable practice if conducted in accordance with approved standards and procedures. However, either original casting induced cracks or cracking of these weld repairs in high temperature and aging plant is not uncommon. Structural integrity assessments of such components must not only consider reduced material toughness, due to temper embrittlement, but also the stress intensities generated during transient thermal events such as start/stops and quenching incidents. In the first of two case studies the acceptability of weld repair defects in a high pressure turbine outer casing is presented. Metallurgical assessments concluded significant temper embrittlement had occurred which was taken into account in a finite element based structural integrity assessment that considered design operating conditions as well as a hypothetical quenching event. Low pressure turbine bypass valves are considered in the second case study. In this case the material temper embrittlement was found not to be as severe but the criticality of pre-warming to reduce transient thermal stress and by extension crack stress intensities during trips or shutdowns was clearly demonstrated. Remaining life assessments concluded the defects to be acceptable for operation to the next planned outage.

Assessment of flow ramping in water bodies impacted by hydropower operation in Norway – Is hydropower with environmental restrictions more sustainable?

Hydropower production is a key electricity generation technology in many parts of the world which can play a significant role in the transition towards a green and clean energy system. Hydropower can mobilize flexible energy on demand (hydropeaking) to balance out intermittent electricity from wind and photovoltaics. Adoption of hydropower as a peaking power source could lead to increased frequency of flow ramping in rivers downstream hydropower tailraces, which is one of the main stressors for riverine biota in alpine rivers. Both planned and accidental shutdowns of hydropower turbines need ecological mitigation. Our survey revealed that >3000 km of rivers downstream ca 800 hydropower plants in Norway may be ecologically impacted by non-natural flow fluctuations, and few have appropriate mitigation thresholds. A considerable eco-friendly peaking service may come from the Norwegian hydropower portfolio of over 19 GW installed capacity, with outlets into fjords, reservoirs or other large water bodies which normally dampen the ecological impacts of flow ramping. Intensive flow ramping occurs with irregular intervals from most types of hydropower. Although the highest frequency of stops were revealed in hydropower turbines not impacting river flow from storage hydropower, a significant number of turbine flow stops lasting over half a day in most types and categories of diversion hydropower.We suggest that further emerging ecosystem-based mitigations need to be adapted in hydropower licenses. This includes operational thresholds for both up and down ramping, constructional measures like by-pass valves, retention basins and increased base-flow or flow cap to ensure sustainability for hydropower operations.Our data reveal some of the most intensive hydropeaking operations from hydropower impacting longer rivers. Hence, our data underpins the potential for restoring downstream modified flow by ecosystem based measures related to both up and down ramping events in many regulated rivers.

Performance analysis of multi-level high voltage direct current converter

&lt;p class="Abstract"&gt;The conventional three-phase alternating current (AC) to direct current (DC) converter can be modified using two isolated-gate bipolar transistor (IGBT) as by-pass switches connected to tapping points on the secondary side of the transformer. This scheme yields a reduction in both harmonic contents and reactive volt-ampere absorption. This modified converter possibly eliminates the need for an on-load tap-changer on the converter transformer. The modified AC/DC converter is fully analyzed and implemented under balanced conditions using MATLAB-Simulink. The expressions of the output DC voltage are derived for different cases. The supply current harmonic contents, the reactive power absorption and the power factor have been compared for three schemes; the conventional bridge, the modified bridge using one by-pass IGBT valve and the modified bridge with two by-pass IGBT valves. &lt;/p&gt;

Automatic detection system for performance curve of exhaust valve of tractor turbocharger

The matching of the tractor turbocharger and the engine has a great influence on the vehicle’s dynamics, economy and other parameters. The bypass air release adjustment scheme has been widely used due to its simple structure and high reliability. Therefore, a platform capable of qualification testing is needed to test and evaluate the performance of the air release valve. This article carried out the design of the hardware detection platform of the bypass valve, and completed the program design based on the force control configuration program platform, which mainly includes manual static, automatic static and dynamic detection of the tractor turbocharger exhaust valve Procedures etc. The detection system has the characteristics of low cost, high degree of automation, high detection accuracy, and strong stability, and can perform detection of different types of bypass valves. The performance of the hardware platform and software was verified through experiments. The experimental results show that the detection system can meet various requirements and can be used for the detection of actual vent valve production.

A study on characteristics of vacuum solenoid valves

Vacuum solenoid valves have been widely used in internal combustion engine engines. They are used to regulate various processes in the car’s systems by controlling actuators – for example, variable geometry of the turbocharger, exhaust gas recirculation (EGR) valves, various bypass or throttle valves. The vacuum solenoid valves are controlled by the electronic control unit (ECU) by means of a constant frequency and pulse width modulation of the controlling signal. In operation, these valves change their characteristics over time, which leads to a change in the control of the actuators, and hence to the overall operation of the engine and systems related to the environmental performance of the vehicle. Often there is no feedback on the actual value compared to the demand and their correct diagnosis is difficult. In this work an experimental study was performed, which shows dependence of pressure characteristics from possible deviations of some parameters (vacuum system, power supply) in operation of the vehicle.

Double Loop Network for Combined Heating and Cooling in Low Heat Density Areas

This study investigated a double loop network operated with ultra-low supply/return temperatures of 45/25 °C as a novel solution for low heat-density areas in Denmark and compared the proposed concept with a typical tree network and with individual heat pumps to each end-users rather than district networks. It is a pump-driven system, where the separate circulation of supply and return flow increased the flexibility of the system to integrate and displace heating and cooling energy along the network. Despite the increased use of central and local water pumps to operate and control the system, the simulated overall pump energy consumption was 0.9% of the total energy consumption. This was also an advantage at the design stage as the larger pressure gradient, up to 570 Pa/m, allowed minimal pipe diameters. In addition, the authors proposed the installation of electrically heated vacuum-insulated micro tanks of 10 L on the primary side of each building substation as a supplementary heating solution to meet the comfort and hygiene requirements for domestic hot water (DHW). This, combined with supply water circulation in the loop network, served as a technical solution to remove the need for bypass valves during summer periods with no load in the network. The proposed double loop system reduced distribution heat losses from 19% to 12% of the total energy consumption and decreased average return temperatures from 33 °C to 23 °C compared to the tree network. While excess heat recovery can be limited due to hydraulic issues in tree networks, the study investigated the double loop concept for scenarios with heat source temperatures of 30 °C and 45 °C. The double loop network was cost-competitive when considering the required capital and operating costs. Furthermore, district networks outperformed individual heat pump solutions for low-heat density areas when waste heat was available locally. Finally, although few in Denmark envisage residential cooling as a priority, this study investigated the potential of embedding heating and cooling in the same infrastructure. It found that the return line could deliver cold water to the end-users and that the maximum cooling power was 1.4 kW to each end-user, which corresponded to 47% of the total peak heat demand used to dimension the double loop network.

Surge analysis in a centrifugal compressor using a dimensionless surge number

Surge protection via the installation of an anti-surge control valve is indispensable in centrifugal compression systems, and the designs of such valves are often specified in the early design phase of centrifugal compression systems. However, additional recycle valve piping, such as hot or cold gas bypass valves, could be required in the case of emergency shutdowns. Furthermore, design verification via dynamic simulations is crucial in the engineering workflow. Because of the unavailability of design guidelines in the early design phase, only late verification is possible, necessitating system redesign when dynamic simulation results evidence the need for additional protection. This study presents a compressor surge distribution map by analyzing sensitivity parameters and establishing a new dimensionless number called the “surge number” (Ns). The surge distribution map is used to classify the safe and unsafe areas for surge protection using numerical threshold values. The map is to be used as a preliminary guideline for surge protection for engineers to quickly review the system and take additional protection measures in the early phase of design.

Off-design performance analysis of a turbocharged solid oxide fuel cell system

The aim of this study is to analyse the off-design performance of an innovative turbocharged solid oxide fuel cell system, fed by biogas and designed to generate 30 kW during nominal operating conditions. The layout of such a plant combines the high efficiencies of the solid oxide fuel cell with a reduced-cost option for fuel cell pressurization: fuel cells are usually pressurized by a micro gas turbine, but the alternative use of a turbocharger, a mass-produced component widely used in the automotive field, could reduce significantly the capital cost of the system. This kind of layout has been rarely investigated in literature, and a detailed performance analysis of a turbocharged SOFC system would be a valuable source of information for both academia and industry. To perform this analysis, a steady-state model has been created using a modular tool developed in Matlab®-Simulink® that includes off-design models of the system components. The model has been used to compare different control strategies. The most suitable control strategy, based on wastegate and cold bypass valves, was adopted, obtaining compliance with the operative constraints and high system efficiency. Afterward, the system steady-state operation was simulated for various electric power loads and ambient temperatures. The performance analysis focused on the effect of these two variables on the system behaviour and has provided insight on the influence on the most significant system outputs, including global efficiency, temperatures and pressures. A system efficiency increase was observed at part load, with values growing from 50.8% to 57.3%. Higher values of ambient temperature resulted in a more significant pressurization of the fuel cell, affecting positively the system efficiency: from 50.5% at 0 °C to 51.0% at 30 °C. Great attention was paid to the system constraints, to verify that the plant could operate properly in all the considered conditions. The proposed control strategy was tested and proved to be effective at achieving this objective.