Safe Operating Conditions Research Articles

A 30 MeV-cyclotron-based quasi-monoenergetic neutron source

This study developed a quasi-monoenergetic neutron source (QMN) for the semiconductor device's soft error rate test (SER). Quasi-monoenergetic neutrons are generated by Be(p,n)B99 nuclear reaction with a 1 mm beryllium target and 30 MeV protons from a cyclotron. An 8 mm water in the back of the beryllium target is used for avoiding proton penetration. The neutron spectra simulated by MCNP showed that the peak energy was around 26.5 MeV. The heat flow and mechanical properties are numerically analyzed, and the safe operating conditions are therefore determined.

Analysis of damage origin of bevel gear wheels

The safety and smooth operation of manufacturing facilities also depends on ensuring the failure-free operation of technical equipment. Power transmission failures in particular are usually the cause of shutdown of the entire manufacturing facility. The characterization of gear failures according to their origin plays an important role in determining safe operating conditions. The presented paper is dedicated to the problem of damage of specific gears, defining the extent of damage, determining the possible causes of damage. The problem is solved for a single-stage helical bevel gearbox with, which is a part of the mechanism of a small hydroelectric power plant. The aim is to determine the conditions for proper operation, based on the evaluation of the extent of damage to this gearbox, so that the gearbox is no longer damaged to such a large extent.

Optimal dispatching rules of hydropower reservoir in flood season considering flood resources utilization: A case study of Three Gorges Reservoir in China

Making full use of flood resources on the basis of ensuring flood control safety plays a positive role in improving the comprehensive benefit of reservoirs during flood season. To improve the utilization rate of flood resources of hydropower reservoirs, taking the Three Gorges Reservoir (TGR) as an example, an optimal forecast dispatching model for flood resources utilization (FRU) in flood season is established first based on the safety requirements of flood control, combining the power demand and the safe operating conditions of the power grid. Then, considering the uncertainty of runoff forecast, the stochastic simulation method of inflow forecast based on the gaussian mixture model (GMM) is used to assess the flood control risk of FRU dispatching. Finally, the optimal dispatching rules of TGR in flood season considering FRU are derived by using the gradient boosting regression tree (GRBT). The experimental results show that the optimal dispatching rules can effectively improve the utilization rate of flood resources and increase the generation benefit of TGR during flood season without an additional increase in flood control risk. Compared with routine dispatching, the hydropower generation of the TGR by rule dispatching considering inflow forecast information of 3, 5, and 7 days can be increased by 3.38%, 5.57%, and 6.93% respectively. This shows that the dispatching rules derived are very reliable and promising, which can provide decision support for reservoirs operation in flood season.

Performance management of EV battery coupled with latent heat jacket at cell level

This numerical study evaluates the cell level performance management of an Electric Vehicle (EV) battery with Latent Heat (LH) jacket (as passive cooling). In this regard, a battery cell is conjugated with Phase Change Material (PCM) is assessed under continuous cycles of discharging and re-charging. This study is validated with numerical and experimental data with less than 1% deviation captured from literature for a Panasonic 18650 PF Lithium-ion (Li-ion cell). The thermal and electrical performance of key parameters is assessed with and without the existence of a PCM under various climatic conditions including extreme winter −20 °C, winter 0 °C, ambient 25 °C, hot summer 40 °C, and extreme hot/desert 55 °C temperatures. In addition, the choice of PCMs and circumferential jacket thicknesses around the battery (1 mm, 3 mm, 5 mm, and 7 mm) is evaluated in terms of thermal performance for multiple discharge/charge cycles under safe manufacturer operating conditions. Initially the PCM is in a solid state and results indicate that the conjugated thermo-chemical and electrical system is stable whilst LH is active however once fully melted, Sensible Heat (SH) dominates. This study shows, passive cooling maintains the thermal performance of the battery cell for longer, i.e., a 3 mm jacketed PCM as passive cooling results in a 340% thermal performance improvement in the number of consecutive discharge/charge cycles at ambient weather, 25 °C. At higher ambient temperatures (40 °C and 55 °C) improvement in thermal performances of up to 275% and 440% are achieved, respectively. At lower ambient temperatures at −20 °C and 0 °C thermals stability up to 162% and 160% with PCM respectively as opposed without for consecutive cycling. It is therefore concluded that efficient passive management is a feasible approach in reducing the harmful effects of overheating, including thermal runaway, thus improving the safety and performance of the electrical energy storage system (EES) in Electric Vehicles (EVs) and Hybrid Electric Vehicles (HEVs).

Solid oxide electrolysis cells – Interplay between operating conditions, fuel electrode overpotential and degradation

With the integration of increased share of energy from renewable, but fluctuating, energy sources there will be an increased demand for large-scale flexible conversion of electrical energy into easily storable chemical fuels. Electrolysis will be a key component in the future of energy conversion and storage solutions. Solid oxide cells (SOC) can provide the most efficient electrolysis technology. Furthermore, solid oxide electrolysis cell (SOEC) technology has improved tremendously in terms of initial performance, long-term durability, and up-scaling of cell and stack sizes; and with respect to commissioning and operation of SOEC plants. Nevertheless, it is evident that further improvement of electrochemical performance and especially long-term durability is crucial for the coming up-scaling and integrated SOEC systems as part of our energy grid. This calls for research within 1) thorough mapping of degradation mechanisms, 2) determination of thresholds for the onset of irreversible degradation processes, 3) safe operating conditions and means to mitigate known degradation processes, etc. However, degradation is not a simple singular property and there is often a puzzling interplay between parameters such as: the chosen electro-catalysts, the manufacturing of cell components, obtained microstructures, the resulting initial electrochemical performance, operating conditions, and the nature and extent of different degradation processes. This work will present11This work has been presented as invited keynote speak at symposium E01.07 as part of the 23rd International Conference on Solid State Ionics, MRS Meeting, Boston (US), July 2022. an overview of the puzzling interplay between initial electrochemical performance and long-term durability. It will then provide examples of multiple complementary characterization techniques applied for the analyses of these features and processes (e.g., SEM, TEM, Raman spectroscopy and electrochemical impedance spectroscopy). Furthermore, strategies to mitigate and/or limit specific degradation processes and insight into data required to establish degradation wise safe operating conditions are discussed. The present work will touch upon multiple performance characteristics and degradation processes: 1) triple-phase-boundaries (TPB) and critical micro/nano-structural parameters of the porous nickel/yttria-stabilized-zirconia (Ni/YSZ) electrode; 2) the perception of electrode overpotential and why this parameter is more important than the set current density or operating cell/stack voltage, 3) the effect of impurities, 4) the interplay between impurities and carbon deposition and 5) the degradation caused by Ni migration and actions to mitigate this degradation process.

Investigation of the capabilities of a supersonic transport system in a rarefied environment

The paper is devoted to the study of problems in organizing high-speed ground transport traffic. The solution to this problem may be the organization of a combined transport system, which involves the movement of a transport unit in a rarefied environment of limited space, using the principles of magnetic levitation. The use of such a system will significantly increase the speed of a transport unit up to the supersonic range due to the following factors: reduced aerodynamic air resistance when moving; the absence of direct contact of the transport unit with the lower structure of the track and, as a result, the complete absence of friction; separate dedicated lines allow the use of structures that allow for a significant increase in freight traffic. The paper explores the possibilities of developing the basic principles of movement of a transport system based on magnetic levitation in a rarefied environment, modeling key processes, determining the main parameters of a new transport system and establishing their optimal ratio, reduced to conditions of safe and energy-efficient operation. As well as an assessment of possible risks associated with the use of this type of transport, both for freight and passenger transportation.

ОБОСНОВАНИЕ ПАРАМЕТРОВ ТЕХНОЛОГИИ ОЧИСТКИ ИЛОНАКОПИТЕЛЕЙ УГЛЕОБОГАТИТЕЛЬНЫХ ФАБРИК ГИДРОЭЛЕВАТОРНЫМИ ЗЕМСНАРЯДАМИ

A methodological approach has been developed to determine the conditions that ensure the stable and safe operation of a hydraulic elevator dredger during the development of enrichment tailings. The conditions of stable and safe operation of a hydraulic elevator dredger during the development of enrichment tailings are determined. An algorithm has been developed for calculating the hydraulic transport system, performance and the main parameters of this technology, depending on the mining conditions of the complex. The productivity and the area of use of the UGB-2M hydraulic elevator dredger in the development of enrichment tailings for each of the technically possible diameters of the pulp duct under various mining conditions of its operation - the distances of transportation of the hydraulic mixture and the geodetic height of its lifting.

Validation of a balancing model based on master-slave battery management system architecture

The battery management system (BMS) performs the monitoring and control of the charging/discharging process of the cell, state of charge estimation, battery safety and protection, state of health estimation, cell balancing, and thermal management. These control operations ensure accurate, safe, and reliable operating conditions, individual cell damage on battery string, and increase the cell life. Battery balancing is one of the key technologies in the BMS, which affects the actual usable capacity range, performance, and lifetime of the entire battery module. However, it is difficult to evaluate or compare the performance of the overall BMS under the multi-series battery module structure. Most of the proposed battery energy storage system (ESS) models focus on energy distribution and system estimation (microgrid or renewable energy). This study develops a balancing model for estimating the balancing performance of the BMS. A Master-Slave BMS (MS-BMS) is proposed to validate the balancing model. The Master and Slaves of the BMS employed a traditional flyback converter with a MOSFET switching array and bidirectional flyback converters with photoMOS arrays, respectively, to perform the balancing behavior. The balancing skill, balancing circuit power, equalization speed, control simplicity, modularization simplicity, and cost has been considered in designing the proposed BMS. The simulation results are verified with the experimental results, which are then compared with the balancing model's results under the five balancing conditions, and the average absolute error of the balancing duration results is 3.12%. The performance of the proposed BMS is also compared with the existing modular BMS architecture, which validates the advantages of the proposed BMS including equalization speed, control simplicity, modularization simplicity, and cost.

Assessment of ship manoeuvring safety in waterway systems by relative navigational risk

The safety of vessels navigating in the sea waterway system is ensured by fulfilling the acceptable restrictions called safe ship operation conditions in that system. The assessment of navigation safety is particularly important when the conditions for safe operation of ships in the waterway system are changed concerns increasing the maximum parameters of vessels, increasing the allowable hydrometeorological conditions or changing the minimum tug assistance. The article presents a method for assessing navigation safety when the conditions for the safe operation of vessels in the waterway system get changed. The method uses two indicators, which are difference in navigation risks and relative navigation risk. To determine the navigational risk, algorithms were developed for calculating the probability of accidents caused by the deterioration of navigation conditions and technical failure of ship equipment and tugs. Another algorithm was developed for calculating the consequences of the accidents that involve blocking a waterway by a ship anchoring in an emergency, grounding, impact of the ship against a port structure or moored ship and a collision with another ship in motion. The method developed for assessing navigation safety by means of relative navigation risk can be used in practice when changing the conditions for safe operation of vessels in the waterway system and when the system is modernized. Navigational safety management is a decision process that is implemented in the loop presented in the article. The acceptable risk is determined on the basis of vessel traffic intensity and ship parameters defined by safe operation conditions for a given waterway system. Relative navigational risk may be used in assessment and comparison of various conditions of safe ship operation. The probability of an accident caused by ship's moving outside the available navigable area due to technical failures of ship equipment or tugs is determined, depending on the type of port waterway and the manoeuvres performed.

Effect of Electrical Accelerated Aging on DC Resistivity of Mineral Oil Used in Power Transformers

Power transformers are still equipment of primary importance within power grids. The recent paradigm changes registered in the field of energy require the interconnection of electrical grids of much larger areas, even up to the level of an entire continent. In this context, knowing the state of the electrical equipment and that of the power transformers is an essential aspect to ensure safe operation conditions. The present work is related to the vulnerability of the oil–paper insulation systems of power transformers to different aging factors and their quick degradation under certain conditions. In this regard, the study proposed in this paper considers the measurement of DC resistivity on mineral oil samples contaminated with small amounts of accelerated aging oil under the action of high-strength electric field and partial discharges. In the absence of standardized procedures for accelerated electrical aging of mineral oil, an original method presented and discussed in previous articles is used. The obtained results clearly indicate that under the action of electrical stress, the mineral oil resistivity decreases significantly, showing that the oil’s electric properties worsen.

About preliminary statistical processing of information on the study of fatigue strength of machine parts

A generalized approach to statistical processing of the results is proposed fatigue parameters of static strength using methods of mathematical statistics and conventional statistics using the following probabilistic parameters: the mean square deviation, the initial moment, the central moment of dispersion and the coefficient of variation of the distribution series of physical and mechanical characteristics of the part material. Further, the analysis of fatigue strength research at the initial stage is carried out according to statistical information processing, graphical design of a number of stress distributions, statistical stress analysis, a graphical approach is applied in the form of a histogram of a number of distributions, a polygon of frequencies, a polygon of accumulated frequencies, the selection of theoretical stress distribution laws with their empirical confirmation is compared with a more rigorous assessment of the conformity of the distribution laws, which is performed using special consent criteria, for example, the Pearson criterion, a parallel verification of the correctness of the chosen approach using classical dependences of the resistance of materials is proposed. the total error is estimated in the form of a methodological error and a direct discrepancy between the theoretical and experimental values of stresses and temperatures of the physico-mechanical process according to experimental and theoretical normal and tangential stresses arising during the operation of the part as a result of the application of external force factors, a temperature-time superposition is used, in the form of a function of the predicted durability of the fluctuating kinetic theory of strength, in which the temperature, as a linear function, it can be replaced by any energy or force criterion, in particular: specific energy, relative deformation, normal or tangential stresses. The proposed approach requires substantial experimental study on a basic batch of the same type of samples and coordination according to schematized diagrams of the limiting amplitudes of Goodman, Sorensen - Kinasoshvili, Kogaev, subject to the conditions of safe operation of parts in the field of low-cycle fatigue. The proposed probabilistic model of statistical processing of fatigue strength can be recommended for solving applied problems of the theories of mechanics of materials, elasticity, plasticity and creep, resistance of materials, structural mechanics

A Dynamic Principal Component Analysis and Fréchet-Distance-Based Algorithm for Fault Detection and Isolation in Industrial Processes

Fault Detection and Isolation (FDI) methodology focuses on maintaining safe and reliable operating conditions within industrial practices which is of crucial importance for the profitability of technologies. In this work, the development of an FDI algorithm based on the use of dynamic principal component analysis (DPCA) and the Fréchet distance δdF metric is explored. The three-tank benchmark problem is studied and utilized to demonstrate the performance of the FDI method for six fault types. A DPCA transformation for the system was established, and fault detection was conducted based on the Q statistic. Fault isolation is also of critical importance for proper intervention to mitigate fault effects. To identify the type of detected faults, the fault responses within the PC subspace were analyzed using the δdF metric. The use of the Fréchet distance metric for the isolation of faults combined with DPCA for feature extraction is a novel technique to the best of the authors’ knowledge that provides a robust computational tool with low computational cost for FDI purposes that fits well into the Industry 4.0 framework.The robustness and sensitivity of the method was validated for a wide variety of signal-to-noise ratio (SNR) conditions, with findings indicating a possible average false and missed alarm rate of 0.1 and a macro-averaged F-score above 0.8 in all cases.

Intelligent Control with Artificial Neural Networks for Automated Insulin Delivery Systems.

Type 1 diabetes mellitus is a disease that affects millions of people around the world. Recent progress in embedded devices has allowed the development of artificial pancreas that can pump insulin subcutaneously to automatically regulate blood glucose levels in diabetic patients. In this work, a Lyapunov-based intelligent controller using artificial neural networks is proposed for application in automated insulin delivery systems. The adoption of an adaptive radial basis function network within the control scheme allows regulation of blood glucose levels without the need for a dynamic model of the system. The proposed model-free approach does not require the patient to inform when they are going to have a meal and is able to deal with inter- and intrapatient variability. To ensure safe operating conditions, the stability of the control law is rigorously addressed through a Lyapunov-like analysis. In silico analysis using virtual patients are provided to demonstrate the effectiveness of the proposed control scheme, showing its ability to maintain normoglycemia in patients with type 1 diabetes mellitus. Three different scenarios were considered: one long- and two short-term simulation studies. In the short-term analyses, 20 virtual patients were simulated for a period of 7 days, with and without prior basal therapy, while in the long-term simulation, 1 virtual patient was assessed over 63 days. The results show that the proposed approach was able to guarantee a time in the range above 95% for the target glycemia in all scenarios studied, which is in fact well above the desirable 70%. Even in the long-term analysis, the intelligent control scheme was able to keep blood glucose metrics within clinical care standards: mean blood glucose of 119.59 mg/dL with standard deviation of 32.02 mg/dL and coefficient of variation of 26.78%, all below the respective reference values.

A novel thermal management system for battery packs in hybrid electrical vehicles utilising waste heat recovery

• Waste heat from HEVs is applied to the ejector battery thermal management system. • Accurate prediction of complex flow behaviors in ejector by the condensation model. • Ejector's COP and ER shows inverse trend with increasing inlet superheating. • Ejector's performance reaches maximum with an increase of 11 K inlet superheating. Thermal management system generally ensures the safe operating conditions and heat resilience of battery packs in hybrid electric vehicles (HEVs). The current study raised a novel approach to reduce fire risks related to HEVs through a novel battery thermal management system powered by low-grade combustion waste heat running on steam ejectors for the first time. In this paper, an ejector operating at a low temperature under 100 °C for HEV's battery thermal management system is proposed and investigated. An in-house wet-steam model considering the condensation effect has been developed to characterise the ejector's internal flow structure and further analyse its feasibility as a thermal management system. The results show that the model considering the condensation process is more feasible in evaluating the performance of the steam ejector than the dry gas assumption. To improve the performance of the proposed ejector battery thermal management system, the effect of superheating of primary steam has been investigated. The results showed that an optimum point exists with 11 K superheating between improvement of entrainment ratio, the system's coefficient of performance and the power efficiency for the current case. The entrainment ratio at that point reaches around 0.45, while the coefficient of performance reaches 0.225.

A design framework for optimized economic and inherently safe operation conditions for isoperibolic semi-batch reactors

Thermal runaway in the semi-batch reactors (SBRs) involving exothermic reaction can have serious consequences and the primary driver of process design in the SBRs is economic performance. Hence, in this article, a general framework for safe-economic design and operation of isoperibolic SBRs via integrating advanced process optimization and inherently safe operation condition identification criteria is proposed, and is applied to homogeneous solution polymerization. First, a criterion is proposed to identify the thermally safe operation condition (QFS region, quick onset, fair conversion, and smooth temperature) of homogeneous solution polymerization and the comparison with the other common criteria is conducted. The adiabatic temperature diagrams are also extended to homogeneous solution polymerization considering avoiding triggering side or decomposition reactions under cooling failure. Furthermore, a large accumulation can occur due to the rapid decomposition of the initiator when the jacket temperature in the QFS region exceed a threshold value. Therefore, a new temperature diagram is introduced via combination initiator decomposition temperature and adiabatic temperature diagrams. Finally, the optimal safety-economic design of the simulation case is conducted. The process optimization algorithm is genetic algorithm and runaway criteria are the proposed criterion in this article and the target temperature criterion. The comparison between the target criterion and proposed criterion shows there are almost approximately identical conversion profiles and temperature profiles. This result proves the general proposed framework and further proves the validity of the proposed criterion. This general framework can be extended to other kinetic schemes and this work can contribute to the inherent safety design of semi-batch reactors.

Technical, environmental, and economic feasibility investigation of an innovative dry washing process for metal degreasing

Industrial washing is essential in manufacturing and many other technological fields. Nowadays, steam washing is the most common technique. However, it involves chemical solvents which are potentially noxious for the environment and difficult to be disposed of. Therefore, there is a growing demand for alternative washing techniques that would ensure low operating costs, extensive productivity, high efficiency, environmental sustainability, good compatibility with different materials, and safe operating conditions. A fluidized bed (FB) represents a promising alternative to satisfy market requirements. In this study, a prototype of FB machine for the degreasing of pressure vessels was designed, built, and compared to the current solvent washing machine. The scope of the work is to assess the technical, environmental, and economic feasibility of a FB device for industrial washing. The analysis of variance (ANOVA) was carried out to detect the process parameters influencing the cleaning. The optimal process parameters were identified based on the experimental results. Life cycle assessment (LCA) and cost analysis were performed to evaluate environmental impacts, and operating costs. The results confirmed the validity of FB technology as an alternative to current washing techniques thanks to its higher cleanness, minor environmental impact and costs, and comparable productivity.

Lightweight methane-air gas turbine controller and simulator

• Lightweight CH4/air gas turbine simulator. • System identification, cycle, and sensitivity analyses CH4/air gas turbines. • Developing and calibrating a CH4/air gas turbine controller. • The potential of utilizing waste heat utilization mechanisms. • Control measures to eliminate turbine overheating. Due to the uncertainties of determining stable, efficient, and safe operating conditions of methane-air gas turbines and the complexity of involving multivariable parameters, the task of controlling and analyzing methane-gas turbines remains a challenge despite the existing methods of control and analyses in the literature. In fact, as far as the methane-air gas turbines are concerned, there is still much room for improvement within the criterion of (computation effort, settle time, its capacity to adjust with a variable range of set-points, as well as its stable, steady, and dynamic outputs can all be enhanced). Furthermore, an accurate system-identification phase has been adopted in this paper to initiate the process of advancing an efficient gas turbine controller by determining the system's sensitivities towards the involved multivariable parameters. Therefore, this paper presents a control and analysis tool for methane-air gas turbines. This tool is a ‘light code (the time to reach the desired set-point (i.e., settle period reaches 1 s)) to serve as a methane-air gas turbine controller that can be used for experimentation or applied on an industrial scale. Moreover, the code is designed with a user interface that enables the simulations and system identification for the methane-fueled gas turbine, thus; ensuring that the governing parameters are calibrated precisely. The code was created using LabVIEW and GASEQ and is driven by conventional gas turbine cycle assessments. A simulation case study has been utilized as a system identification phase to determine the system's sensitivity of temperatures and works at the three primary stages of a simple cycle methane-air gas turbine (compressor, combustion chamber, and turbine) toward the multivariable input parameters of the compression stage (compressor pressure ratio, efficiency, inlet pressure, and temperature), the combustion phase (methane, airflow rates) and the expansion phase (turbine ratio of pressures and isentropic efficiency). Based on the sensitivity analysis performed through the developed code, the turbine output temperature is shown to be very sensitive to the turbine's parameters ( P 04 / P 03 and ε t ). This essentially emphasizes the possibility of including waste heat utilization mechanisms (i.e., heat exchangers, combined cycles) for turbines with high P 04 / P 03 or/and low ε t , resulting in a high turbine outlet temperature. Based on the performed system identification phase and sensitivity analyses, the intervals of the Proportional controller gain ( K c ) , Integral time ( t i ) , and Derivative time ( t d ) have been identified to guarantee a settling period ( T s ) within [1 s-60 s] to achieve the desired temperature set-point which eliminates turbine overheating.

Stack-Scale Modeling of Ammonia-Fueled Solid Oxide Fuel Cell

Ammonia is one of the promising fuels that can be used as a hydrogen source for solid oxide fuel cells (SOFC) due to its high energy density, high hydrogen content, no carbon emission at the consumption site, easy storage and transportation, and potential for low cost owing to a well-developed infrastructure. Ammonia-fueled SOFCs have been studied through several experimental works at both cell and stack levels, while a limited number of numerical models at cell levels have been devoted to this subject. Both experimental and numerical studies show that the ammonia decomposes chemically in the fuel support layer at the common operating temperatures of the SOFCs due to the catalytic role of the nickel particles for the ammonia decomposition.Here, we present the first Multiphysics model of an ammonia-fueled SOFC stack, which couples and solves the transport equations of mass, momentum, species, charges, and heat. The model includes the whole stack with manifolds, active domain, headers, and sealings. For the layered domains of the stack, a homogenization approach is used, which replaces them with an equivalent domain and solves for the effective variables [1-3]. Several research groups and stack manufacturers have been using this homogenization approach to model SOFC stacks due to the advantage of reasonable computational expenses and so runtimes. This makes systematic studies of operating conditions, design changes, and even degradation at the stack-scale computationally feasible [1].An ammonia decomposition reaction rate model has been developed and validated thoroughly in [4]. The model shows that the ammonia decomposition occurs over the thickness of the fuel support layer, depending on the amount of ammonia in the fuel channel and the operating temperature. With the homogenized model, the variations over the thickness of the electrode are effectively described by a well-accepted 0D model developed, see e.g. [5].Here, we present such a 0D model that has been validated with a 2D through-plane model of the fuel side of a single cell. We show that the 0D model can describe the effective penetration depth of the ammonia in the fuel support layer through the balance of the fluxes to/from the support layer. The developed relation for the effective ammonia penetration depth in the support layer approximates well the one obtained from the detailed 2D model. A similar idea can be used to find the effective penetration depth of methane in the support layer for the case of a methane-fired SOFC and facilitate its stack-scale modeling with the homogenized model.Ammonia is added to the stack-scale model with the 0D model, which correctly describes the decomposition rate per unit area. The model reproduces well-reported trends from experiments with ammonia-fueled SOFC stacks. Internal cracking of the ammonia is advantageous from a cost/efficiency perspective as the heat consumption of the cracking process facilitates stack cooling; however, depending on the conditions of operation, the ammonia decomposition could be too fast, making a sharp temperature drop at the inlet. This leads to increased thermal stresses in the region and increases the risk of mechanical failure. The model is used to investigate the effects of the operating conditions, e.g. temperature and flow rates of the fuel and air, and flow configuration on the temperature gradients at the inlet to identify safe operating conditions.

Investigation on pressure fluctuations induced by flow instabilities in a centrifugal pump

To investigate the pressure fluctuations induced by internal flow instabilities with flow rate variations in a centrifugal pump, combining numerical and experimental methods are applied to detect the complex flow state and identify safe and stable operating conditions of the pump. An analysis of the velocity and vorticity field based on the Q-criterion shows that a region of intensely unstable flow, including rotating stall, leakage vortices, wake flow, backflow and secondary flow, is concentrated upstream of the flow channel near the pump hump point. It was found from the experiments that the extremum of the main frequency of the pressure fluctuations at the pump inlet rapidly decreases to the local minimum value near the pump hump point. And an apparent broadband of the pressure fluctuations at the pump outlet is created between 100 and 150 Hz as the flow rate increases from 0 to 0.4 Qd. Relationships between the flow instabilities and the pressure fluctuations at the pump inlet and outlet are determined to formulate an effective detecting method for the flow state, while the pump outlet pressure fluctuations can serve as indicators of instabilities induced by flow rate variations in the centrifugal pump.

Piece-Wise Linear (PWL) Probabilistic Analysis of Power Grid with High Penetration PV Integration

This paper aims at presenting a novel effective approach to probabilistic analysis of distribution power grid with high penetration of PV sources. The novel method adopts a Gaussian Mixture Model for reproducing the uncertainty of correlated PV sources along with a piece-wise-linear approximation of the voltage-power relationship established by load flow problem. The method allows the handling of scenarios with a large number of uncertain PV sources in an efficient yet accurate way. A distinctive feature of the proposed probabilistic analysis is that of directly providing, in closed-form, the joint probability distribution of the set of observable variables of interest. From such a comprehensive statistical representation, remarkable information about grid uncertainty can be deduced. This includes the probability of violating the safe operation conditions as a function of PV penetration.