Bypass Valves Research Articles

Traitement de l’hydrocéphalie de l’enfant par ventriculocisternostomie endoscopique au Sénégal

IntroductionSince its advent, endoscopic third ventriculostomy (ETV) has been an effective alternative to shunt placement for the treatment of hydrocephalus. The aim of this study was to report the results of our experience with this technique in children in Senegal. Materials and methodsThis was a retrospective study of 70 cases of children aged between 5 months to 15 years who were treated by ETV in the Neurosurgery Department of Fann Hospital in Dakar, between January 2010 to December 2012. The results were evaluated based on the clinical criteria of Drake and the Canadian Pediatric Neurosurgery Study Group. The mean follow-up duration was 24 months (9–32 months). ResultsThe mean age at diagnosis was 29 months. A male predominance (sex-ratio 1/3) was observed. We also noted a macrocephaly in 64.4 % of cases, psychomotor retardation in 40 % and decreased vision in 31.4 %. Headache and vomiting were found in 42.8 % and 61.4 % respectively. The main etiology was a stenosis of the mesencephalon aqueduct (30 %), followed by a Dandy-Walker malformation (25.7 %). Significant intraoperative bleeding was found in 2.8 % of patients. The most common postoperative complication was CSF leakage (18.6 %), followed by infections (14.2 %). The success rate according to the clinical criteria of Drake was 71.4 %. This success rate was influenced by the age of patients and the hydrocephalus etiology. No deaths occurred. ConclusionThe endoscopic third ventriculostomy is a simple, safe and effective technique. Its advantages in terms of quality of life and morbidity compared with bypass valves makes it the technique of choice, particularly in developing countries.

Co-surge in bi-turbo engines: Measurements, analysis and control

In parallel turbocharged V-engines, with two separate air paths connected before the throttle, an oscillation in the flow can occur. If the compressor operates close to the surge line, typically during low speed and high load, and a disturbance alters the mass flow balance, the compressors can begin to alternately go into surge. This phenomenon is called co-surge and is unwanted due to high noise and risk of turbocharger destruction. Co-surge is measured on a test vehicle in a chassis dynamometer and the system analyzed and modeled using a mean value engine model. The investigation shows that alternating compressor speeds have an important role in the prolonged oscillation. A reconstruction of the negative flow from measurements is made and compared to simulation results, showing similar amplitudes, and supports the model validation. A new co-surge detection algorithm is presented, suitable for a pair of sensors measuring either mass flow, boost pressure or turbo speed in the two air paths. Furthermore, a new controller is proposed that uses a model based feedforward for the throttle, together with wastegate actuation to force the compressor speeds together and improve balance at the recovery point. This has been shown to be sufficient for moderate to high pressure ratios over the throttle, and only for zero or very low pressure drop the use of bypass valves is necessary. The advantage of not opening the bypass valves is a smaller drop in boost pressure which also reduces the torque disturbance. The performance of the controller is evaluated both in simulation and in the test vehicle.

Changing Landscape and Disease-specific Considerations of Therapeutic Bronchoscopy in Clinical Trials

Changing Landscape and Disease-specific Considerations of Therapeutic Bronchoscopy in Clinical Trials

Miller-Cycle Regulatable, Two-Stage Turbocharging System Design for Marine Diesel Engines

The increasingly stringent NOx emission regulations of the International Marine Organization (IMO) have demanded new design concepts and architectures for diesel engines. The Miller cycle, which reduces the in-cylinder combustion temperature by reducing the effective compression ratio, is the principal measure used for reducing NOx specific emissions; however, this is at the cost of volumetric efficiency and engine power. Therefore, it is essential to combine the Miller cycle with a highly boosted turbocharging system, two-stage turbocharging for example, to recover the power. While much work has been done in the development of Miller-cycle regulatable two stage turbocharging system for marine diesel engines, there are nonetheless few, if any, thorough discussions on system optimization and performance comparison. This study presents a theoretical optimization design process for a Miller-cycle regulatable, two-stage turbocharging system for marine diesel engines. First, the different scenarios and regulation methods of two-stage turbocharging systems are compared according to the system efficiency and equivalent turbine flow characteristics. Then, a multizone combustion model based on a one-dimensional cycle simulation model is established and used for the optimization of valve timings according to the IMO NOx emission limits and fuel efficiencies. The high- and low-stage turbochargers are selected by an iterative matching method. Then, the control strategies for the boost air and high-stage turbine bypass valves are also studied. As an example, a Miller-cycle regulatable, two-stage turbocharging system is designed for a highly boosted high-speed marine diesel engine. The results show that NOx emissions can be reduced by 30% and brake specific fuel consumption (BSFC) can also be improved by a moderate Miller cycle combined with regulatable two-stage turbocharging.

Laser Treatment of Textured X20Cr13 Stainless Steel to Improve Water Droplet Erosion Resistance of LPST Blades and LP Bypass Valves

X20Cr13, a martensitic stainless steel, is commonly used for the manufacture of low pressure steam turbine (LPST) moving blades and LP bypass valves of fossil fuel and nuclear power plants. The LPST blades, at present, are laser surface treated to improve their water droplet erosion (WDE) resistance. The laser-treated X20Cr13 stainless steel has improved the water droplet resistance (WDER) several times compared to untreated ones. Further improvements are being carried out by providing a carbide-based HVOF coating having appropriate surface roughness or by creating textured surfaces and treating with a high power diode laser. The surfaces, having appropriate roughness, absorb more laser energy, resulting in improved microstructure, microhardness, modified ultimate resilience, and thicker hardened layer. The WDER of laser-treated textured X20Cr13 stainless steel has improved significantly compared to the untextured ones. The WDE test results of laser-treated textured and untextured X20Cr13 stainless steel along with their microhardness, modified ultimate resilience, microstructure, SEM, and XRD analysis are discussed and reported in this paper. The laser-treated textured X20Cr13 stainless steel is highly suitable for LP bypass valves and LPST blades for achieving a thicker hardened layer with lesser heat input to the components.

Experimental Research of Granular Silica Pneumatic Conveying System in Tyre Factory

Through the experimental research of granular silica in dense phase pneumatic conveying in the tyre plants, the characteristic parameters of granular silica pneumatic conveying have been obtained. By adjusting the main and bypass pipe pressure values, the stable plug flow conveying of granular silica can be realized, which considerably reduces the broken ratio of the granular silica. The plug flow conveying will be even more stable, when the opening blow tank pressure is set at zero. Additionally the same research has also proven that bypass valves open pressure in the end of pipeline will affect the stability of the entire conveying system as well.

Accurate Pressure Management of Parallel Choke Manifold

The conventional valves used in the choke manifold for well control usually have intensely nonlinear characteristic of the match between pressure choking and vale opening. Therefore, it is difficult to achieve the precise choking pressure that is essential to the managed pressure drilling (MPD) through a single throttle within the scope of full opening. However, the parallel choke manifold proposed in this paper, i.e. a program of parallel throttling, can enhance the accurate choking wellhead backpressure for MPD. The fine linear choking principle and feasibility of the parallel choke manifold were analyzed in detail by calculating the resistance modulus of bypass valves. The formula calculated the resistance modulus of each valve under different working state. Furthermore, the laboratory tests shown the parallel throttle method can achieve the control of fine choking pressure by switching one or more valves in the branch pipes. Therefore, the proposed parallel choke manifold system can reduce the requirements for the linear capability of valves and provide some references to further study the surface fine choking pressure system for MPD.

Mechanical Extrusion Offers Advantages Over Ball Activation for Downhole Tools

Technology Update One of the most innovative recent advances in downhole drilling tool activation has been the introduction of mechanical extrusion technology, incorporating the use of rigid metal darts to improve the cycling and control of a variety of processes and devices. Increasingly, operators are recognizing mechanical extrusion by means of dart activation as a time-, cost-, and labor-saving alternative to traditional ball activation methods. For example, conventional cycling of drilling bypass valves has used a polymer extrusion process that relies on balls as the activation device. However, Churchill Drilling Tools has developed an effective and accurate mechanical extrusion method that uses a dart-based valve. The system can perform activations up to five times faster than polymer methods. The company’s MX (mechanical extrusion) system allows the use of rigid Smart Darts for multicycle control and exploits their robustness and resilience at high pressures and temperatures (up to 660°F) to deliver greater operating speed, reliability, and performance. The system’s unique feature is its two configurable shearing modes, which solves reliability and power delivery problems. It requires a radius as small as 0.0075 in. for power transmission, thereby making implementation extremely compact. With the ability to control and power three or more tools independently, users eliminate the conventional inner diameter (ID) and obstruction conflicts between different tools in a string. This has implications for mono-cycling ball and shear systems, which commonly obstruct the bore after use. These can be turned into multicycling, nonobstructive, and multi-tool systems. The system can also enhance multicycling ball-activated tools that are based on polymer extrusion by improving performance and delivering greater multitool compatibility and interoperability. The system allows the mechanical extrusion to be delivered in a range of settings to suit the specific cycle application. With a variety of latching, sealing, and flow path geometries, as well as the adjustable shear mode ratings, this element of the system provides a tangible change in string design and program implementation. For example, in bypass valve implementation, users can cover multiple flow path contingencies with a single valve in hole and choose from the range of darts to establish the optimal setting for the situation encountered. The system advances the capability of simple hydromechanical control and its power and reliability benefits into areas that previously needed more complex electronic systems. Being mechanical, it is not subject to the same high pressure and high temperature limits that affect electronics and electrical components. Smart Darts enable a multicycle circulating sub (circ sub) tool to deliver a reliable and versatile bypass on demand. Whatever the drilling application, whether planned or a contingency, the system enables a rapid and reliable switching to the optimal flow path configuration.

Co-Surge Detection and Control for Bi-Turbo Engines with Experimental Evaluation

A V-type engine with a bi-turbocharger configuration utilizes the exhaust energy well which gives a fast torque response. An unwanted instability, called co-surge, can occur in such engines where the two interconnected compressors alternately go into flow reversals. If co-surge occurs, the control system must quell the oscillations with as little disturbance in engine torque as possible. A model of a bi-turbocharged engine is presented, combining a mean value engine model and a Moore-Greizer compressor model for surge. The model is validated against measurements on a vehicle dynamometer, showing that it captures the frequency and amplitude of the co-surge oscillation. The model is used to develop detection and control strategies for co-surge that rapidly returns the turbo to a stable operating point. Both simulations and experimental evaluation on the vehicle show that the developed strategies are successful in rapidly detecting and quelling co-surge. The selection of actuators is also studied. With no or small pressure drops over the throttle, it is necessary to use the bypass valves. However, for operating conditions with moderate and high pressure drops over the throttle, it is shown that it is sufficient to only open the throttle. This has the advantage, compared to opening the bypass valves, that it reduces the drop in boost pressure and thus reduces the drop in engine torque.

Validation of the 4C code against data from the HELIOS loop at CEA Grenoble

We complete the first validation campaign of the Cryogenic Circuit Conductor and Coil (4C) code, focusing on the cryogenic circuit module of 4C, which is based on the component models from the recently developed “Cryogenics” Modelica library. Measured data from the HELIOS facility (HElium Loop for hIgh LOads Smoothing) at CEA Grenoble, France, are used as reference. HELIOS includes a supercritical He loop (cold circulator, pipes equipped with resistive heaters, control and bypass valves, heat exchangers) and a saturated He bath. A repetitive heat pulse test is simulated with 4C. The computed evolution of temperature, pressure and mass flow rate at different circuit locations, both in the loop and in the bath, shows a very good agreement with the measurements.

Simultaneous Turbine Speed Regulation and Fuel Cell Airflow Tracking of a SOFC/GT Hybrid Plant With the Use of Airflow Bypass Valves

This paper studies a novel control methodology aimed at regulating and tracking turbo machinery synchronous speed and fuel cell mass flow rate of a SOFC/GT hardware simulation facility with the sole use of airflow bypass valves. The hybrid facility under consideration consists of a 120 kW auxiliary power unit gas turbine coupled to a 300 kW SOFC hardware simulator. The hybrid simulator allows testing of a wide variety of fuel cell models under a hardware-in-the-loop configuration. Small changes in fuel cell cathode airflow have shown to have a large impact on system performance. Without simultaneous control of turbine speed via load or auxiliary fuel, fuel cell airflow tracking requires an alternate actuator methodology. The use of bypass valves to control mass flow rate and decouple turbine speed allows for a greater flexibility and feasibility of implementation at the larger scale, where synchronous speeds are required. This work utilizes empirically derived transfer functions (TF) as the system model and applies a fuzzy logic (FL) control algorithm that can be easily incorporated to nonlinear models of direct fired recuperated hybrid plants having similar configurations. This methodology is tested on a SIMULINK/matlab platform for various perturbations of turbine load and fuel cell heat exhaust.

Model-based development of low-level control strategies for transient operation of solid oxide fuel cell systems

The exploitation of an SOFC-system model to define and test control and energy management strategies is presented. Such a work is motivated by the increasing interest paid to SOFC technology by industries and governments due to its highly appealing potentialities in terms of energy savings, fuel flexibility, cogeneration, low-pollution and low-noise operation. The core part of the model is the SOFC stack, surrounded by a number of auxiliary devices, i.e. air compressor, regulating pressure valves, heat exchangers, pre-reformer and post-burner. Due to the slow thermal dynamics of SOFCs, a set of three lumped-capacity models describes the dynamic response of fuel cell and heat exchangers to any operation change. The dynamic model was used to develop low-level control strategies aimed at guaranteeing targeted performance while keeping stack temperature derivative within safe limits to reduce stack degradation due to thermal stresses. Control strategies for both cold-start and warmed-up operations were implemented by combining feedforward and feedback approaches. Particularly, the main cold-start control action relies on the precise regulation of methane flow towards anode and post-burner via by-pass valves; this strategy is combined with a cathode air-flow adjustment to have a tight control of both stack temperature gradient and warm-up time. Results are presented to show the potentialities of the proposed model-based approach to: (i) serve as a support to control strategies development and (ii) solve the trade-off between fast SOFC cold-start and avoidance of thermal-stress caused damages.

ICONE19-43754 RETRAN Analysis of Feedwater Controller Failure Transient for Lungmen ABWR

This study used RETRAN-3D program to analyze the FWCFWB transient at 100% rated power/111% rated core flow and under EOC operating condition where the ΔCPR response was worst. Important system operational actions included (1) the turbine and the feedwater pumps tripped on high water level (L8), (2) fast bypass valves opening which inhibited reactor scram and RIPs trip on turbine trip, (3) reactor scram and the four RIPs which are not connected to the Motor Generator (M-G) sets tripped on low water level (L3), (4) low-low water level (L2) initiation of the Reactor Core Isolation Cooling System (RCIC). The ΔCPR of this event was 0.05 and the results were compared with those from FSAR. It showed that there was a significant difference in the change rate of vessel water level, but other transient trends were in good agreement with FSAR. A test of all bypass valves failed to open was also covered in this study. In this situation, the reactor scram occurred on high water level turbine trip, and the ΔCPR would rise to 0.17.

Enhanced Droplet Erosion Resistance of Laser Treated Nano Structured TWAS and Plasma Ion Nitro-Carburized Coatings for High Rating Steam Turbine Components

This article deals with surface modification of twin wire arc sprayed (TWAS) and plasma ion nitro-carburized X10CrNiMoV1222 steel using high power diode laser (HPDL) to overcome water droplet erosion occurring in low pressure steam turbine (LPST) bypass valves and LPST moving blades used in high rating conventional, critical, and super critical thermal power plants. The materials commonly used for high rating steam turbines blading are X10CrNiMoV1222 steel and Ti6Al4V titanium alloy. The HPDL surface treatment on TWAS coated X10CrNiMoV1222 steel as well as on plasma ion nitro-carburized steel has improved water droplet resistance manifolds. This may be due to combination of increased hardness and toughness as well as the formation of fine grained structure due to rapid heating and cooling rates associated with the laser surface treatment. The water droplet erosion test results along with their damage mechanism are reported in this article.

Multivariable Robust Control of a Simulated Hybrid Solid Oxide Fuel Cell Gas Turbine Plant

This paper presents a systematic approach to the multivariable robust control of a hybrid fuel cell gas turbine plant. The hybrid configuration under investigation comprises a physical simulation of a 300 kW fuel cell coupled to a 120 kW auxiliary power unit single spool gas turbine. The facility provides for the testing and simulation of different fuel cell models that in turn help identify the key issues encountered in the transient operation of such systems. An empirical model of the facility consisting of a simulated fuel cell cathode volume and balance of plant components is derived via frequency response data. Through the modulation of various airflow bypass valves within the hybrid configuration, Bode plots are used to derive key input/output interactions in transfer function format. A multivariate system is then built from individual transfer functions, creating a matrix that serves as the nominal plant in an H-infinity robust control algorithm. The controller’s main objective is to track and maintain hybrid operational constraints in the fuel cell’s cathode airflow and the turbo machinery states of temperature and speed under transient disturbances. This algorithm is then tested on a SIMULINK/MATLAB platform for various perturbations of load and fuel cell heat effluence.

Relative Gain Array Analysis of a Solid Oxide Fuel Cell Gas Turbine Hybrid Plant

This paper presents a relative gain array (RGA) analysis of a simulated solid oxide fuel cell/gas turbine plant, based on a multivariate empirical formulation of a 300 kW hybrid system. The HyPer test facility at the National Energy Technology Laboratory, served as the test bed for deriving frequency response data and subsequent multivariable model of a direct-fired, recuperated hybrid cycle plant. Through the modulation of various airflow bypass valves, magnitude and phase data are used to formulate transfer function (TF) equations that describe input/output system interaction. A frequency dependent RGA calculation of the empirical TF matrix provides a means of quantifying the degree of coupling between system inputs and outputs for the configuration studied. Various input/output interaction time scales are obtained to identify frequencies where fully developed system coupling occur. Analysis of the RGA matrix leads to a better understanding of the inherent properties and the hybrid configuration, and can serve as a validating tool to existing analytical RGA calculations of similar types of hybrids.

Large-scale diesel engine emission control parameters☆

Abstract Emission tests were carried out on a large-scale medium-speed supercharged diesel engine (∼1 MW per cylinder) with control parameters compression ratio, start of ignition (SOI) and fuel type (light and heavy fuel oil, LFO and HFO). Emissions of NO x , CO, hydrocarbons (HC), smoke (FSN) and particulate matter (PM) were measured and are discussed in relation to the control parameters. Regarding turbocharger influence on emissions the control parameters by-pass and waste-gate are also briefly addressed. The results show that NO x , CO and FSN decrease while HC emissions increase with later SOI (more delay) for all loads (25–100%). The influence of compression ratio (CR) on NO x is the inverse of this; decreasing CR gives increased NO x . Nozzle design is important for emissions control and less holes and bigger diameter for a certain injection angle seems preferable. Fuel type is important too, and in general LFO produces less gaseous or particulate emissions. Diesel engine turbocharger by-pass and waste-gate valves do affect the emissions. PM emissions were found to decrease with the load (∼Bmep) for propulsion mode, showing an increase with load for generator mode for HFO; for LFO decreasing PM emissions were found with increasing load for both generator and propulsion mode.

EXPERIMENTS ON THE PERFORMANCE SENSITIVITY OF THE PASSIVE RESIDUAL HEAT REMOVAL SYSTEM OF AN ADVANCED INTEGRAL TYPE REACTOR

A set of experiments has been conducted on the performance sensitivity of the passive residual heat removal system (PRHRS) for an advanced integral type reactor, SMART, by using a high temperature and high pressure thermal-hydraulic test facility, the VISTA facility. In this paper the effects of the opening delay of the PRHRS bypass valves and the closing delay of the secondary system isolation valves, and the initial water level and the initial pressure of the compensating tank (CT) are investigated. During the reference test a stable flow occurs in a natural circulation loop that is composed of a steam generator secondary side, a secondary system, and a PRHRS; this is ascertained by a repetition test. When the PRHRS bypass valves are operated 10 seconds later than the secondary system isolation valves, the primary system is not properly cooled. When the secondary system isolation valves are operated 10 or 30 seconds later than the PRHRS bypass valves, the primary system is effectively cooled but the inventory of the PRHRS CT is drained earlier. As the initial water level of the CT is lowered to 16% of the full water level, the water is quickly drained and then nitrogen gas is introduced into the PRHRS, resulting in the deterioration of the PRHRS performance. When the initial pressure of the PRHRS is at 0.1MPa, the natural circulation is not performed properly. When the initial pressures of the PRHRS are 2.5 or 3.5 MPa, they show better performance than did the reference test.

Transient of modified HVDC converters

The bridge circuit used in high voltage direct current (HVDC) converters may be modified by including by-pass thyristor valves connected to tapping points on the secondary windings of the transformer to give a reduction in both harmonic generation and reactive volt–ampere absorption for the rectifier and inverter modes of operation. In this paper, control strategies for the transient response of the HVDC converter with either thyristor or GTO thyristor by-pass valves are investigated using several types of firing angle control logic. Fast and continuous control of the DC voltage is possible using the proposed scheme without the conventional on load tap-changer on the converter transformer. Experimental results on a laboratory model compare well with the predicted values.

A Snubber Configuration for Modified Bridge Converter

Semiconductor switches are subjected to high voltage and high current simultaneously during turn-on and turn-off. A snubber is a set of components that reduce the stress on the power semiconductors during switching intervals and transient. This article reports on the design of snubbers for modified bridge using gate-turn-off thyristor (GTO) by-pass valves. The snubber gives switching stress reduction. It has better performance than other equivalent snubbers described in the literature. Both theoretical and experimental results are discussed in detail.