Safe Operating Region Research Articles

Development of Adiabatic Criterion for Runaway Detection and Safe Operating Condition Designing in Semibatch Reactors

To prevent the occurrence of thermal runaway accidents in semibatch reactors (SBRs), it is desirable and practicable to develop criteria that can distinguish between the safe and runaway operating regions. In this article a new safety criterion, namely, the adiabatic criterion, has been developed for SBRs in which liquid homogeneous as well as liquid–liquid heterogeneous reactions with arbitrary reaction orders occur. It states that an SBR is operated in the potential runaway situation if the value of the adiabatic criterion exceeds zero at a segment of the reaction path. Numerical results show that the adiabatic criterion is more conservative than the two other criteria (divergence criterion and target temperature criterion). However, the adiabatic criterion is not suitable to reactions with autocatalytic behaviors. Also knowledge of activation energies and reaction enthalpies is necessary to utilize the adiabatic criterion.

Vertical arrangement of SRF particles in a stationary fluidized bed

Flexibility against fuel properties makes Fluidized Bed Conversion a markedly successful technology also for climate change mitigation. Solid Recovered Fuel is a standardized waste-derived fuel of inherently inhomogeneous character regarding particle size, shape, and composition. It is a crucial question, how much of these particles can utilize the advantages of the FBC technology, that is, how much of them will be located in the bed body – instead of floating to the top or sinking to the bottom. The bed-frozen method was used in this research, and the relative weight, concentration, density, and size distribution of the particles found at the three vertical locations were measured. Relative fluidization velocity and bed particle mean diameter were varied as independent variables. A bi-directional segregation phenomenon was observed on an area of the space spanned by the independent variables, and a region of safe and robust operation was recognized as well. A successive change can be observed between the two extremes of these areas regarding total mass, concentration, and size distribution of the particles found in the three referred vertical locations. Densities of the SRF particles alone do not explain the measured vertical arrangements.

Process operational safety using model predictive control based on a process Safeness Index

It has been repeatedly suggested that the common cause-and-effect approach to evaluating process safety has deficiencies that could be addressed by a systems engineering perspective. A systems approach should consider safety as a system-wide property and thus would be required to integrate all aspects of the process involved with monitoring or manipulating the process dynamics, including the control, alarm, and emergency shut-down systems while operating them independently for redundancy. In this work, we propose initial steps in the first systems safety approach that coordinates the control and safety systems through a common metric (a Safeness Index) and develop a controller formulation that incorporates this index. Specifically, this work presents an economic model predictive control (EMPC) scheme that utilizes a Safeness Index function as a hard constraint to define a safe region of operation termed the safety zone. Under the proposed EMPC design, the closed-loop state of a nonlinear process is guaranteed to enter the safety zone in finite time in the presence of uncertainty while maximizing a stage cost that reflects the economics of the process. Closed-loop stability is established for a nonlinear process under the proposed implementation strategy.

Design of a Premixed Fuel–Oxidizer System to Arrest Flashback in a Rotating Detonation Engine

Rotating detonation engines offer the promise of pressure gain combustion in aeronautical combustors where (normally) stagnation pressure decreases. For practical reasons, current experimental rotating detonation engine designs include separate streams of fuel and air injected into a detonation channel. Experimentation with a fully premixed rotating detonation engine has repeatedly failed due to flame flashback into the premixed plenum. That fundamental problem is the subject of this paper: understanding the relevant principles and parameters that contribute to flashback and investigating a scheme for arresting the flashback phenomenon. This investigation quantifies the flashback susceptibility for a proposed rotating detonation engine feed slot with parameterization of channel height, channel length, equivalence ratio, fuel type, and feed pressure. The design principles of quenching distance and critical boundary-layer velocity gradients are shown to describe the safe operation region to deliver a safe premixture of fuel and air to a rotating detonation engine when adjusted for experimental conditions and applied in unison. This research leads to a design that is capable of avoiding flashback while enabling detonation to occur in a rotating detonation engine.

Perspectives on safe operating region and field weakening operation in electrical machines

This paper discusses the issue of safe operating speed torque zone and field weakening in electrical machines from a somewhat different viewpoint than in the existing literature, including textbooks. At present, field weakening in electrical machines is viewed as an issue due to limitation of available input voltage which prevents a desired current to flow into the motor due to back emf at high speeds. This issue, along with the issue of safe operating zone, is examined in this paper with elaborations on the total loss in the machine which includes magnetic loss, copper loss, and also rotational and windage losses. The author believes that this gives a more complete and accurate picture of the situation and leads to a more scientifically accurate reasoning towards implementation of field weakening (if necessary), and also describing the safe operating zone in electrical machines.

Determination of safe reliability region over temperature and current density for through wafer vias

Circular and slot backside vias are stressed over current and temperature and the resulting failure times are fitted to Black's equation. Contour plots of the FIT rate are generated and the reliability of circular and slot vias are compared. It is demonstrated that in most cases the FIT rate of the circular via is statistically significantly lower than that of the slot via. However, both types are easily able to meet a goal of 100 FITs in 10years at T=125°C and J=0.25×106A/cm2. The contour map of the FIT rate defines the region where the via can operate reliably. By use of the 95% upper confidence bound, the region of safe operation is reduced in size, adding a layer of margin to the prediction of via reliability. The approach described here provides a “reliability map” for designers allowing trade-offs between temperature current to be made when designing for high reliability.

Analysis of explosion characteristics of combustible wood dust in confined system using the thermal decomposition rate and mass loss rate

In this study, dust explosion experiments were conducted to investigate the explosion characteristics of three samples of dust from wood particleboard that had exploded in the manufacturing process. Explosion tests were conducted by utilizing a standardized Siwek 20L apparatus according to the standardized test procedures in the European Standard CEN EN 14034 series and CEN EN 13821. To understand the physiochemical properties of the tested dust samples, the element composition, particle size distribution, and heat release rate were obtained by utilizing an element analyzer, particle-size analyzer, and cone calorimeter, respectively. Explosion pressure and rising explosion pressure featured log-linearly increasing trends in dust concentration and equivalence ratios until the maximum. They then decreased linearly as the dust concentration and equivalence ratios increased. Dust particles of smaller sizes and non-spherical shapes achieved higher maximum explosion pressure and maximum explosion pressure rising rates. The dust concentration at maximum explosion pressure decreased as the dust particle size decreased. Thermal decomposition rates and mass loss rates of dusts, which were calculated from the results of the cone calorimeter test, were mainly affected by the content of noncombustible materials such as nitrogen and inorganic residuals. To suggest a proper method to analyze dust explosion characteristics, the correlations among the tested dust samples were calculated with four variables: dust concentration, equivalence ratio, equivalence ratio based on thermal decomposition rate, and mass loss rate. The results showed that the latter two variables were considered to be more proper methods than the dust concentration and showed slightly better correlation than the equivalence ratio. A bubble graph and a contour diagram of the explosion pressure were also utilized to visualize the degree of explosion risk and to determine a safe region of operation. The test results and analytical methods proposed in this study could be utilized to design methods for the prediction, prevention, and protection of dust explosions.

Fuzzy Logic-Based Fault Prevention of the Battery System in Hybrid Electric Vehicle

Due to high energy and power density, lithium-ion batteries (LIBs) have become one of the most popular choices for electric vehicle (EV) and hybrid electric vehicle (HEV) applications. However, reliability and durability of LIBs are highly affected by the operational and environmental conditions. The Battery Management System (BMS) is responsible for guaranteed performance and safety of batteries. Typically, the battery system protection against current or voltage fault conditions is performed using a simple on/off command from the BMS to a power contactor. However, the sudden elimination of power due to transient current or voltage changes (e.g. vehicle launch or climbing a slope) reduces the amount of energy that can be delivered and in some cases may be dangerous for the components in connection with the batteries. This paper presents the design of a closed-loop fuzzy-based control system to achieve maximum performance of the battery with regard to driving conditions such that safe operation of the battery is ensured. To do so, battery voltage or current is limited using a control input from a fuzzy controller implemented in the BMS. The vehicle Central Control Unit (CCU) corrects the traction motor torque command according to the control input received from the BMS in order to maintain battery safe operating region. This way, the battery current and voltage is limited before reaching the fault conditions, thereby improving the durability of the battery and preserving its life. Performance of the designed control system is evaluated in various driving regimes using a Hardware-in-the-Loop (HiL) test bench. Results show the efficacy of the designed control system toward the prevention of voltage and current fault conditions.

Flammability and volatility attributes of binary mixtures of some practical multi-component fuels

Gasoline compression ignition (GCI) engines could be more efficient than most advanced SI engines while running on lower octane fuel. GCI engines may utilize a mixture of different fuels and fuel components such as gasoline and diesel or diesel and naphtha. The risks and hazards associated with such mixtures must be studied to ensure safe fuel storage, shipping and dispensing. In this work, flash point and vapor pressure measurements of different binary multi-component hydrocarbon mixtures are presented along with calculated lower and upper flammability limits. An equation has been developed to correlate flash point with other fuel properties. The flash point of a mixture approaches the flash point of the more volatile component, falling rapidly in some cases, as the more volatile component concentration increases. Vapor pressure is inversely related to flash point for a given mixture. Diesel/light straight run naphtha mixtures and diesel/gasoline mixtures exhibit similar flash point versus vapor pressure trends. Flammability limits were calculated using Le Chatelier’s Mixing Rule and modified Burgess–Wheeler Law. Hydrocarbon mixtures have similar lower and upper flammability limits over a range of temperatures. The vapor pressure of fuels and fuel blends has been used to determine the safe operating region as a function of blending formula and temperature. This work demonstrates that normal butane can be used to formulate blends of gasoline and naphtha with diesel, which are safe to handle and meet seasonal vapor pressure requirements.

Torsional Microresonator in the Nonlinear Regime: Experimental, Numerical and Analytical Characterization

The dynamic behavior of a torsional microresonator is characterized analytically, numerically and experimentally both in the linear and nonlinear regime. Starting from the work presented in [1], here, the highly nonlinear regime is considered and the dynamic pull-in is experienced. Very good agreement between experimental data and numerical model is found also when the analytical methods usually employed to describe the nonlinear dynamic behavior of MEMS (multiple scale methods) are no more accurate. Finally, a numerical limit domain for the microresonator safe operation region in terms of bias and actuation voltages is computed and validated with experimental data.

An approach to the microscopic study of wear mechanisms during hard turning with coated ceramics

The influence of tool edge microgeometry on the wear of tool inserts made from mixed oxide ceramics is investigated. The microgeometry of ceramic inserts is described using quantifiable data, including, tool edge radius (rn), roughness of the rake face (Ra) and tool edge roughness (sometimes called ‘tool edge sharpness’) Rt. Applied coatings affect these quantifiable data. Total force and mean temperature were measured to identify the safe operating region in which the tool edge is not chipped or damaged. The effect of tool microgeometry on wear progress for two types of mixed oxide ceramics-TiN-coated and uncoated, were compared using both macroscopic and microscopic tool wear data. A geometrical approach was used to determine the effective chip area at the chamfered tool edge. This involved mathematical modelling where the effective chip area, effective tool edge length and maximum distance between two subsequent transient surfaces were determined. The total forces were divided into cutting parts and parasitic parts, using both effective chip area and effective tool edge length. Total force division during hard machining operations with uncoated and TiN-coated ceramic inserts, enabled us to compare the effects of tool edge microgeometry on the main mechanisms of wear. Secondary wear areas at the chamfered tool edge were identified for both ceramic types. Hard machining produced abrasive wear pattern and smearing particles due to thermal load for uncoated ceramics; while it produced particles with iron content in the secondary wear area of TiN-coated ceramics.

Modeling and Stability Analysis of Islanded DC Microgrids Under Droop Control

The stability of dc microgrids (MGs) depends on the control strategy adopted for each mode of operation. In an islanded operation mode, droop control is the basic method for bus voltage stabilization when there is no communication among the sources. In this paper, it is shown the consequences of droop implementation on the voltage stability of dc power systems, whose loads are active and nonlinear, e.g., constant power loads. The set of parallel sources and their corresponding transmission lines are modeled by an ideal voltage source in series with an equivalent resistance and inductance. This approximate model allows performing a nonlinear stability analysis to predict the system qualitative behavior due to the reduced number of differential equations. Additionally, nonlinear analysis provides analytical stability conditions as a function of the model parameters and it leads to a design guideline to build reliable (MGs) based on safe operating regions.

Analysis of jet blast impact of embarked aircraft on deck takeoff zone

The jet blast impact of embarked aircraft on the takeoff zone is studied to support carrier–aircraft adaptation. The geometric model of carrier–aircraft system is built in CATIA Software and an unstructured mesh of the model is generated in Workbench Software. The jet blast impact of embarked aircraft on flight deck and jet blast deflector while taking off from takeoff zone is numerically simulated with standard k–ε and three dimensional N–S equations based on CFD theory. Thermal coupling of wind over deck and jet blast is also taken into consideration. The distribution of temperature, pressure, velocity and streamline of the coupling flow is numerically simulated through Fluent Software and the temperature characteristics distribution on axes is also obtained. The results indicate: (1) the method presented in the paper can analyze fluid mechanics problems of complicated geometric models and obtain highly reliable simulation results; (2) the safe operation region for personnel, the suitable outfitting of jet blast deflector and proper layout of takeoff zone can be obtained.

Effects of delayed time active controller on the vibration of a nonlinear magnetic levitation system to multi excitations

In this paper, a time-delayed positive position feedback controller is proposed to reduce the horizontal vibration of a magnetically levitated body subjected to multi force excitations. This controller is coupled to the main system with 1:1 internal resonance. The method of multiple scales perturbation technique is employed to obtain an approximate solution which clarifies the nonlinear behavior for both amplitude and phase of the whole system. The effects of time delay magnitude are investigated to indicate the safe region of operation. Validation curves are involved to compare the approximate solution with the numerical simulation.

Interactive buckling tests on steel cones subjected to axial compression and external pressure – a comparison of experimental data and design codes

The plastic buckling of thick steel conical shells subjected to combined action of axial compression and external pressure is of considerable interest in the offshore and the nuclear industries. However, design information on this subject area is limited. At present, only the ASME B&PV code case 2286-2 provides design information for cones subjected to axial and hoop compressions acting simultaneously. This design rule has not been validated both experimentally and numerically, especially in the elastic–plastic region. Past results on interactive buckling tests carried out at the University of Liverpool, Liverpool, UK on 13 computer numerically controlled (CNC)-machined cones having r2/r1 = 2.02, r2/t = 34.3, h/r2 = 1.01, and β = 26.56° were compared with predictions of design loads obtained from ASME code case 2286-2. This was done in order to check the applicability of this design rule and suggest a safe operating region. The paper consider the general procedure adopted by the ASME case code 2286-2 to predict the interactive buckling curve and identifies some discrepancies in the predictions. It further suggests region of safe operational design level. Combined stability plots for the master cone and equivalent cylinder have also been derived. Results of this study show that ‘the equivalent cylinders’ do not represent a safe design substitute for a relatively thick cone under combined loading.

On-line nonlinear model predictive control of a PEM fuel cell system

The aim of this work is to develop and deploy an advanced model-based control framework for a polymer electrolyte membrane (PEM) fuel cell system. The framework relies on nonlinear model predictive control (NMPC) using a reliable and efficient dynamic optimization approach which discretizes both manipulated and state variables. The optimization is performed using a direct transcription method that handles the optimal control problem as a nonlinear programming (NLP) problem. The motivation for the control is to ensure optimum power generation following a variable load demand with acceptable response time while avoiding oxygen starvation and minimizing hydrogen consumption. To validate the applicability, efficiency and robustness of the NMPC scheme a small-scale fully automated unit was used and an experimentally validated semi-empirical dynamic model was utilized at the core of the optimization scheme. The on-line application of the multivariable controller shows that the proposed framework can accomplish the desired objectives for power demand in the context of a safe operating region. Furthermore the controller exhibits excellent performance in terms of computational requirements and can follow load changes with a negligible error in its response, even at varying operating conditions.

Development of a Thermal Model for Lithium-Ion Batteries for Plug-In Hybrid Electric Vehicles

This paper describes a novel thermal model for lithium-ion battery technology. The model has been developed in Matlab/Simulink, which is based mainly on the electrical parameters such as thermal resistance, thermal capacitance, and thermal convection. In this study, a new methodology is presented for extraction of the model parameters based on the Matlab/Simulink parameter optimization tool. The results exhibit that the error percentage between the simulated and experimental results is less than 5%. According to this model, the battery cell temperature can be kept in a safe operating region by coupling the surface temperature of the battery with the heating and cooling systems. This will allows to enhance the battery performances on one hand and to avoid thermal runway effect on the other hand. The proposed battery model is not only useful for pouch battery cells but can be employed for any battery design concept.

A QMU approach for characterizing the operability limits of air-breathing hypersonic vehicles

The operability limits of a supersonic combustion engine for an air-breathing hypersonic vehicle are characterized using numerical simulations and an uncertainty quantification methodology. The time-dependent compressible flow equations with heat release are solved in a simplified configuration. Verification, calibration and validation are carried out to assess the ability of the model to reproduce the flow/thermal interactions that occur when the engine unstarts due to thermal choking. quantification of margins and uncertainty (QMU) is used to determine the safe operation region for a range of fuel flow rates and combustor geometries.

Vibration and shock reliability of MEMS: modeling and experimental validation

A methodology to predict shock and vibration levels that could lead to the failure of MEMS devices is reported as a function of vibration frequency and shock pulse duration. A combined experimental–analytical approach is developed, maintaining the simplicity and insightfulness of analytical methods without compromising on the accuracy characteristic of experimental methods. The minimum frequency-dependent acceleration that will lead to surfaces coming into contact, for vibration or shock inputs, is determined based on measured mode shapes, damping, resonant frequencies, and an analysis of failure modes, thus defining a safe operating region, without requiring shock or vibration testing. This critical acceleration for failure is a strong function of the drive voltage, and the safe operating region is predicted for transport (unbiased) and operation (biased condition). The model was experimentally validated for over-damped and under-damped modes of a comb-drive-driven silicon-on-insulator-based tunable grating. In-plane and out-of-plane vibration (up to 65 g) and shock (up to 6000 g) tests were performed for biased and unbiased conditions, and very good agreement was found between predicted and observed critical accelerations.

Experimental and numerical analysis of blade channel vortices in a Francis turbine runner

PurposeThe purpose of this paper is to investigate, experimentally and numerically, the pressure pulse characteristics and unsteady flow behavior in a Francis turbine runner for moderate flow heads. The pressure pulses in the runner blade passage were predicted numerically for both moderate and high heads. The calculations were used to partition the turbine operating regions and to clarify the various for the unsteady flow behavior, especially the blade channel vortex in the runner.Design/methodology/approachExperimental and numerical analyses of pressure pulse characteristics at moderate flow heads in a Francis turbine runner were then extended to high heads through numerical modeling with 3D unsteady numerical simulations performed for a number of operating conditions. The unsteady Reynolds‐averaged Navier‐Stokes equations with the k‐ω‐based shear stress transport turbulence model were used to model the unsteady flow within the entire flow passage of a Francis turbine.FindingsThe dominate frequency of the predicted pressure pulses at runner inlet agree with the experimental results in the head cover at moderate flow heads. The influence of the blade passing frequency causes the simulated peak‐to‐peak amplitudes in the runner inlet to be larger than in the head cover. The measured and predicted pressure pulses at different positions along the runner are comparable. At the most unstable operating condition of 0.5a0 guide vane opening, the pressure pulses in the runner blade passage are due to the blade channel vortex and the rotor‐stator interference. The predictions show that the frequency of the blade channel vortex is relatively low and it changes with the operating conditions.Originality/valueThe paper describes a study which experimentally and numerically investigated the pressure pulses characteristics in a Francis turbine runner at moderate flow heads. The pulse characteristics and unsteady flow behavior due to the blade channel vortex in the runner at high heads were investigated numerically, with the turbine operating regions then partitioned to identify safe operating regions.