Steady-state Operating Conditions Research Articles

Power Flow and Generator-Converter Schemes Studies in Ship MVDC Distribution Systems

The medium-voltage dc (MVDC) distribution system is a new shipboard power distribution technology that has been extensively discussed and studied by many shipbuilding corporations and ship-owners in recent years. As different types of power converters and ac and dc power distributions simultaneously involved in the system, the system performance for different connections of generators to MVDC converters under varying steady-state operating conditions is essential and important in the design stage of the electrical power distribution system. This type of problem can be analyzed by performing power flow studies. This paper aims presenting a methodology for power flow studies in ship MVDC distribution systems for system planning purpose. A power flow model of the power converters in steady-state is derived to consider medium and low voltage characteristics of electric power system on this type of ship. An ac/dc power flow solution approach then is developed to incorporate ac-system and dc-system models and the ac/dc interface buses in the analysis for determining an appropriate connection of generators and MVDC converters and power converter setting values. Test results of two alternatives for the direct connection of generators to MVDC converters under varying steady-state operating conditions are presented and compared to determine the proper generator-power converter scheme.

생물증강법을 이용한 오염해양준설토의 환경친화적 정화 및 재활용

Korea Maritime and Ocean University, Busan 49112, Republic of Korea(Received December 7, 2015; Accepted December 21, 2015)ABSTRACT: Occurrences of coastal dredged materials are ever increasing due to port construction, navigational course maintenance and dredging of polluted coastal sediments. Ocean dumping of the coastal dredged materials has become virtually prohibited as L ondon Treaty will be enacted as of the year 2012. It will be necessary to treat and recycle the dredged materials that may carry organic pollutants and heavy metals in a reasonable and effective process: collection of the dredged materials, liquid and solid separation, and treatment of organic compounds and heavy metals. In this study we have developed a continuous bioreactor system that can treat a mixture of silt and particulate organic matter using a microbial consortium (BM-S-1). The steady-state operation conditions were: pH (7.4–7.5), temperature (16°C), DO (7.5–7.9), and salt concentration (3.4–3.7%). The treatment efficiencies of SCOD, T-N and T-P of the mixture were 95–96%, 92–99%, and 79–97%. The system was also effective in removal of heavy metals such as Zn, Ni, and Cr . Levels of MLSS during three months operation period were 11,000 –19,000 mg/L. Interestingly, there was little sludge g enerated during this period of operation. The augmented microbial consortium seemed to be quite active in the removal of the organic component (30%) presen t in the dredged material in association with indigenous bacteria. The dominant phyla in the treatment processes were Proteobacteria and Bacteroidetes while dominant genii were Marinobacterium , Flaviramulus , Formosa, Alteromonadaceae_uc, Flavobacteriaceae_uc. These results will contribute to a development of a successful bioremediation technology for various coastal and river sediment s with a high content of organic matter, inorganic nutrients and heavy metals, leading to a successful reuse of the polluted dredged sediments.Key words: bioaugmentation, bioremediation, coastal dredged materials, reuse

Compressive Sensing of a Taylor-Fourier Multifrequency Model for Synchrophasor Estimation

Synchrophasor measurements, performed by phasor measurement units (PMUs), are becoming increasingly important for power system network monitoring. Synchrophasor standards define test signals for verification of PMU compliance, and set acceptance limits in each test condition for two performance classes ( $P$ and $M$ ). Several PMU algorithms have been proposed to deal with steady-state and dynamic operating conditions identified by the standard. Research and discussion arising from design, implementation, testing and characterization of PMUs evidenced that some disturbances, such as interharmonic interfering signals, can seriously degrade synchrophasor measurement accuracy. In this paper, a new compressive sensing (CS) approach is introduced and applied to synchrophasor measurements using a CS Taylor–Fourier (TF) multifrequency (CSTFM) model. The aim is to exploit, in a joint method, the properties of CS and the TF transform to identify the most relevant components of the signal, even under dynamic conditions, and to model them in the estimation procedure, thus limiting the impact of harmonic and interhamonic interferences. The CSTFM approach is verified using composite tests derived from the test conditions of the synchrophasor standard and simulation results are presented to show its potentialities.

Adapting the Existing District Heating Systems to Dynamic Operating Conditions

District heating systems operating under dynamic conditions without proper hydronic balancing is one of the causes of discomfort for heating consumers. Moreover, from the point of view of producers, unbalanced heating networks generate low energy efficiency. The study analyzes the operation conditions in three cases, on the same network: the first simulates the operating conditions of the network without balancing, the second when just balancing valves set to corresponding nominal flow rate values are used and the third when balancing valves and differential pressure controllers are used, the so-called total balancing method. Results highlight the importance of the hydraulic balancing under steady state and dynamic operating conditions, as a source to increase the energy efficiency and assure thermal comfort by better distribution of fluid flow rates between consumers.

Modeling of Start-Up From Engine-Off Conditions Using High Fidelity Turbofan Engine Simulations

Engine models are widely used to simulate the engine behavior at steady state and transient operating conditions over the full flight envelope. Within the engine development process such simulations are used to support component design, evaluate engine performance, operability and test data, as well as to develop and optimize the engine controls. Recent developments have raised interest in the modeling of start-up processes of turbofan engines in order to support the definition of sufficient engine control laws. This implies that simulations are started at a condition where the engine shafts are static and temperatures and pressures are equal to ambient. During start-up the engine can only be operated transiently through the sub-sub-idle region (near zero speed) using a starter torque. The activity presented here was targeted to support the development of industrial-standard high-fidelity turbofan engine models capable of simulating start-up, shutdown or windmilling operation. Within the three previously mentioned cases starting from an engine-off condition, ground start from zero-speed is the most challenging in terms of physical and numerical modeling. For this reason, this paper concentrates on that case only. Zero mass flow and speed at the beginning of the simulation impose a set of special problems that do not exist in standard simulations: the modeling of a static engine-off condition, the modeling of static friction, and the modeling of reverse flows. The requirement to support an existing industrial model development process also made it necessary to apply the same quality of physical modeling to start-up simulations as would be the case for above-idle engine simulations. The physical effects present during engine start are discussed and modeling solutions are presented. Finally, results of a dry crank simulation are presented and discussed, illustrating that the expected effects are present and that the simulation is capable of predicting the correct trends.

Modeling and Characterization of Organic Light-Emitting Diodes Including Capacitance Effect

This paper presents a new theoretical equivalent model (TEM) for organic light-emitting diodes (OLEDs). The parameters of TEM are identified using a simple characterization procedure based on auxiliary circuits and low-cost equipment. From this TEM, a method for intrinsic capacitance identification is proposed. This model is useful to simulate and analyze OLED devices considering dynamic and steady-state operation conditions. In addition, it provides guidelines for manufacturers and lighting designers to enhance the device performance and to design dedicated OLED drivers. In order to validate the proposal of this paper, four commercial OLEDs are tested, and the comparison between the theoretical and the experimental results is satisfactory.

Emissions from a Diesel Engine using Fe-based Fuel Additives and a Sintered Metal Filtration System.

A series of laboratory tests were conducted to assess the effects of Fe-containing fuel additives on aerosols emitted by a diesel engine retrofitted with a sintered metal filter (SMF) system. Emission measurements performed upstream and downstream of the SMF system were compared, for cases when the engine was fueled with neat ultralow sulfur diesel (ULSD) and with ULSD treated with two formulations of additives containing Fe-based catalysts. The effects were assessed for four steady-state engine operating conditions and one transient cycle. The results showed that the SMF system reduced the average total number and surface area concentrations of aerosols by more than 100-fold. The total mass and elemental carbon results confirmed that the SMF system was indeed very effective in the removal of diesel aerosols. When added at the recommended concentrations (30 p.p.m. of iron), the tested additives had minor adverse impacts on the number, surface area, and mass concentrations of filter-out (FOut) aerosols. For one of the test cases, the additives may have contributed to measurable concentrations of engine-out (EOut) nucleation mode aerosols. The additives had only a minor impact on the concentration and size distribution of volatile and semi-volatile FOut aerosols. Metal analysis showed that the introduction of Fe with the additives substantially increased Fe concentration in the EOut, but the SMF system was effective in removal of Fe-containing aerosols. The FOut Fe concentrations for all three tested fuels were found to be much lower than the corresponding EOut Fe concentrations for the case of untreated ULSD fuel. The results support recommendations that these additives should not be used in diesel engines unless they are equipped with exhaust filtration systems. Since the tested SMF system was found to be very efficient in removing Fe introduced by the additives, the use of these additives should not result in a measurable increase in emissions of de novo generated Fe-containing aerosols. The findings from this study should promote a better understanding of the benefits and challenges of using sintered metal systems and fuel additives to control the exposure of underground miners and other workers to diesel aerosols and gases.

Effective Density and Volatility of Particles Emitted from Gasoline Direct Injection Vehicles and Implications for Particle Mass Measurement

The effective density and volatility of particulate emissions from five gasoline direct injection (GDI) passenger vehicles were measured using a tandem differential mobility analyzer (DMA) and centrifugal particle mass analyzer (CPMA) system. The measurements were conducted on a chassis dynamometer at three steady-state operating conditions. A thermodenuder was employed to find the volatility and mixing state of the particles as well as the effective density of nascent and non-volatile particles (defined as particle phase remaining after denuding at 200°C). The mass–mobility exponent ranged between 2.4 and 2.7 for nascent (or undenuded) particles and between 2.5 and 2.7 for non-volatile particles; higher than typical diesel soot. The effective density function was 4278dm−0.438 ± 76.3 kg/m3 (for mobility diameter, dm, in nm) for nascent particles and 3215dm−0.395 ± 37.9 kg/m3 for non-volatile particles. The effective density functions of the non-volatile particles were fairly similar for the conditions stu...

Assessment of pollutants emission and aftertreatment efficiency in a GTDi engine including cooled LP-EGR system under different steady-state operating conditions

Nowadays, EGR systems are being incorporated in the research focused on spark-ignition direct-injection engines as a solution to the problems presented by them; i.e. knock risk and high combustion temperature which produces high NOx emission. Since the major part of the investigations are centered on engine performance or engine simulation aside pollutants emission and aftertreatment evaluation, this paper focuses on these topics: gaseous and particle emission analysis and aftertreatment efficiency evaluation when cooled LP-EGR system is applied to a GTDi engine.This work has been performed in a 4-cylinder, turbocharged, direct-injection gasoline engine with 2.0 L displacement. The equipment used in this study are TSI-EEPS for particle measurement and HORIBA MEXA 1230-PM for soot measurement being HORIBA MEXA 7100-DEGR with a heated line selector the system employed for regulated gaseous emission measurement and aftertreatment evaluation. A reduction around 50% of NOx with an increase of HC and CO emissions was found in medium-load operating points. At full-load conditions, the suppression of fuel enrichment including EGR leads in a drastically reduction in CO maintaining similar HC and NOx emissions. Furthermore, PN and soot emissions also decrease as EGR is included and spark timing advanced in all the tested conditions.

Transient 1D heat exchanger model for the simulation of domestic cooling cycles working with R600a

Generally, domestic refrigerators and freezers are running in non-continuous operation mode most of the time, which is a necessity to match cooling capacity to thermal loads. In currently available domestic appliances, this matching is realized either by on/off or variable frequency control of the hermetic compressor, leading to a repetitive and transient change of the system state. In case of longer compressor runtimes when cooling capacity demand is high (e.g., pull-down cycles, initial operation), steady-state operating conditions might be reached. The cycling transients cause losses in system efficiency; thus, they should be reduced or avoided. To understand the complex transient physical processes and to optimize the cooling system efficiency, the use of numerical methods has turned out to be a promising approach. For this reason, a 1D heat exchanger model, which has been successfully implemented in a domestic cooling cycle simulation tool, is presented in this work. The heat exchanger model is a further development of the model being presented in Berger et al. (2012). The same mathematical framework is used for modeling the evaporator and condenser. To compute the void fraction, pressure drop and heat transfer in the case of evaporation and condensation special empirical models, which are proposed in the literature, have been implemented. Finally, the numerical predictions are compared to experimental data gained from a purpose-built test rig.

Online Detection of High-Resistance Connections in Multiphase Induction Machines

High-resistance connections in electrical machines cause unbalances in the stator resistances, reduce the efficiency, and increase the fire hazard. In this paper, the problem of detection of high-resistance connections is investigated for multiphase induction machines with an odd number of phases. The main contribution of this paper is a control scheme that can determine the stator resistance unbalance of all phases, under transient and steady-state operating conditions. The theoretical analysis and the feasibility of the control scheme are confirmed by experimental tests.

Defining Thermophysical Parameters of Electric Devices Based on Solution of Inverse Heat Transfer Problem

This paper describes application of the study methods based on the solution of inverse problems of mathematical physics to define thermophysical parameters of electric devices. The mathematical model of the device is developed based on equations of non-stationary heat conductivity. The algorithm to define thermohysical parameters is developed; this algorithm uses the finite element method to solve a direct heat transfer problem and the gradient method to minimize the objective function. Examples of the algorithm application are given. The problem to define an equivalent heat transfer coefficient of the solenoid area covered with heavy winding and a heat emission from its inside surface is considered. In the second example thermophysical parameters of electromagnetic valve actuator of an ICE (internal combustion engine) gas distribution mechanism are defined. The obtained results show that thermophysical parameters and temperature distribution in non-stationary and steady-state operating conditions of electrical devices may be evaluated with adequate efficiency based on the solution of inverse heat transfer problems.

Hydraulic lift-off issues for application of high performance annular fuels in pressurized water reactors

In the PWR core, the fuel assembly is firmly seated on the lower core plate during operation. However, if the hydraulic force exerted on the fuel assembly by coolant flow is too large and the fuel assembly is lifted-off from the lower core plate, the excessive vibration will cause fuel failure. Therefore, the hydraulic lift-off issue needs to be addressed when the advanced fuel assembly is developed. It has been shown that the advanced annular fuel design with internal cooling allows power uprating up to 50% while the peak temperature of the fuel can be reduced and the MDNBR can be maintained. However, if the coolant condition in the core is kept unchanged, increasing the core power by 50% requires the core flow rate also increase proportionally, which will give rise to the hydraulic lift-off, an important issue to be addressed. In this paper, taking the 17×17 solid fuel design as the reference, the hydraulic lift-off issue is investigated for proposed 12×12 and 13×13 annular fuel designs. Both the steady-state and start-up operating conditions are evaluated. It is found that the hydraulic lift-off indeed is an issue for annular fuel design which requires careful analysis. By comparison, the lift-off forces and hold-down forces required for the externally and internally cooled annular fuels (13×13 and 12×12 arrays) are several times larger than that of the referenced solid fuel (17×17 array). Therefore, the hold-down mechanism for annular fuel needs to be carefully designed.

Solid Oxide Cell and Stack Testing, Safety and Quality Assurance (SOCTESQA)

The market penetration of fuel and electrolysis cell energy systems in Europe requires the development of reliable assessment, testing and prediction of performance and durability of solid oxide cells and stacks (SOC). To advance in this field the EU-project “SOCTESQA” was launched in May 2014. Partners from different countries in Europe and one external party from Singapore are working together to develop uniform and industry wide test procedures and protocols for SOC cell/stack assembly. In this project new application fields which are based on the operation of the SOC cell/stack assembly in the fuel cell (SOFC), in the electrolysis (SOEC) and in the reversible SOFC/SOEC mode are addressed. This covers the wide field of power generation systems, e.g. stationary SOFC µ-CHP, mobile SOFC APU and SOFC/SOEC power-to-gas systems. The paper presents the results which have been achieved so far in the SOCTESQA project. Besides a summary of existing test procedures a so called “test matrix” was created. This document includes generic test modules, e.g. current-voltage curves, electrochemical impedance spectroscopy, thermal cycling, electrical current cycling and long term tests both under steady state and dynamic operating conditions. The application specific test programs are created by combining several of these test modules. In a next step defined test modules will be applied for the initial test bench validation, which will be improved by several validation loops. The final test protocols will be confirmed by round robin tests.

Transient simulation of heat pumps using low global warming potential refrigerants

Due to the relatively high global warming potential value of R410A, a lot of effort has been devoted to the exploration of potential refrigerants to replace R410A in heat pump applications. Natural refrigerants with single-digit global warming potential values have not yet shown readiness. Therefore, some synthetic refrigerants with global warming potential values significantly lower than R410A, such as R32 and the R32-based blend D2Y60, are getting more attention. To evaluate the transient performance of these two drop-in low-global warming potential refrigerants, two dynamic heat pump models, based on different platforms, have been developed to simulate a heat pump cycle during both steady state and transient operations. Both models include an efficiency-based compressor model, two control volume-based heat exchanger models, a control volume-based valve model, a segmented pipe model and a lumped-capacitance accumulator model. In order to speed up the simulations, accelerated refrigerant property routines were developed for R32 and D2Y60 based on National Institute of Standards and Technology's (NIST's) REFPROP database (2013). The simulation results have been compared with the published experimental data. The data includes steady-state operation data based on ASHRAE steady-state tests, and transient data from ASHRAE's cyclic operation D-test. The validation of R410A, R32 and D2Y60 cycles under steady-state operating conditions (ASRHAE A and B tests and one in-house ‘extended’ condition) shows that most of the simulations are within 5% measured values. The transient simulation results demonstrate that both models capture the dynamic performance of vapor compression cycle during start-up and shut-down.

Single‐phase single‐stage multifunctional grid interfaced solar photo‐voltaic system under abnormal grid conditions

This study deals with a single-phase single-stage multifunctional grid interfaced solar photo-voltaic (SPV) system. The proposed SPV system is multifunctional as it has MPPT (maximum power point tracking) and it provides harmonics elimination, reactive power compensation and feeding SPV energy into the grid at unity power factor. The PV array is connected at the DC link of voltage source converter. The MPPT controller estimates reference PV voltage and a proportional integral controller is used to maintain the PV string voltage to the reference value. Feed-forward terms are used for SPV array and load components for fast dynamic response. The performance of the system is analysed under abnormal grid (sudden sag and swell) conditions. Simulation studies are performed on MATLAB-based platform. Simulation results are verified experimentally on a developed SPV system. Under steady-state operating conditions, the total harmonic distortion of grid voltage and currents are found well under IEEE-519 standard. A wide range of simulation and experimental results are presented to demonstrate all the features of the proposed SPV system.

A generic physical model for a thermally integrated high-temperature PEM fuel cell and sodium alanate tank system

We study the thermal coupling potential between a Sodium Alanate tank and a High-Temperature PEM fuel cell using a heat transfer fluid to redirect a fraction of the thermal power produced during normal fuel cell operation towards the walls of the metal hydride tank in order to maintain hydrogen desorption. The remaining thermal power is then rejected to the environment by introducing an appropriately adjusted excess of air directly to the fuel cell cathode. Assuming a typical tubular geometry for both the metal hydride tank and the fuel cell, we propose a generic physical model that accounts for heat transfer in all the components of the integrated system (fuel cell, metal hydride tank and heating jacket), as well as H2 desorption kinetics and flow in the tank. Based on this model we study the dynamics of the coupled storage/usage system in terms of H2 pressure in the tank and temperatures in the tank and the fuel cell. Focus is primarily placed on the parameters that lead to steady-state operating conditions (i.e. the flow rate of air towards the fuel cell and the velocity of the heat transfer fluid in the heating jacket), with respect to the electrical power of the fuel cell.

Large-Signal Reliability Analysis of SiGe HBT Cascode Driver Amplifiers

This paper presents the results of an investigation of the steady-state safe operating conditions for large-signal silicon-germanium (SiGe) heterojunction bipolar transistor (HBT) circuits. By calculating capacitive currents within the intrinsic transistor, avalanche inducing currents through the transistor junctions are isolated and then compared with dc instability points established through simulation and measurement. In addition, calibrated technology computer-aided design simulations are used to provide further insight into the differences between RF and dc operation and stress conditions. The ability to swing the terminals of a SiGe HBT beyond the static $I$ – $V$ conditions coincident with catastrophic breakdown is explained. Furthermore, hot-carrier effects are also compared from multiple perspectives, with supporting data taken from fully realized $X$ -band and $C$ -band cascode driver amplifiers. This analysis provides microwave circuit designers with the framework necessary to better understand the full-voltage-swing potential of a given SiGe HBT technology and the resultant hot carrier damage under RF operation.

Family of quadratic step‐up dc–dc converters based on non‐cascading structures

The interconnection of basic switching converters to increase power handling capabilities in dc applications has been widely reported in technical literature. This study presents a family of switching step-up dc-dc converters based on the principle of reduced redundant power processing ( R 2 P 2 ). This principle states that the power transfer from input port and output port on interconnected converters is reduced when a non-cascading connection is used. As shown in this study, the principle R 2 P 2 is useful for developing new converters. These have wide conversion ratios and quadratic dependence with respect to the duty ratio. In this study, the voltage conversion ratios, average models and steady-state operating conditions for proposed converters are derived, which are verified by experimental results.

Transient analysis of an FHR coupled to a helium Brayton power cycle

The Fluoride salt-cooled High-temperature Reactor (FHR) features a passive decay heat removal system and a high-efficiency Brayton cycle for electricity generation. It typically employs an intermediate loop, consisting of an intermediate heat exchanger (IHX) and a secondary heat exchanger (SHX), to couple the primary system with the power conversion unit (PCU). In this study, a preliminary dynamic system model is developed to simulate transient characteristics of a prototypic 20-MWth Fluoride salt-cooled High-temperature Test Reactor (FHTR). The model consists of a series of differential conservation equations that are numerically solved using the MATLAB platform. For the reactor, a point neutron kinetics model is adopted. For the IHX and SHX, a fluted tube heat exchanger and an offset strip-fin heat exchanger are selected, respectively. Detailed geometric parameters of each component in the FHTR are determined based on the FHTR nominal steady-state operating conditions. Three initiating events are simulated in this study, including a positive reactivity insertion, a step increase in the mass flow rate of the PCU helium flow, and a step increase in the PCU helium inlet temperature to the SHX. The simulation results show that the reactor has inherent safety features for those three simulated scenarios. It is observed that the increase in the temperatures of the fuel pebbles and primary coolant is mitigated by the decrease in the reactor power due to negative temperature feedbacks. The results also indicate that the intermediate loop with the two heat exchangers plays a significant role in the transient progression of the integral reactor system.