Records with Subject: Process Operations
Showing records 1 to 25 of 696. [First] Page: 1 2 3 4 5 Last
A Flexible Heat Exchanger Network Synthesis Method Adapted to Multi-Operation Conditions
Sibei Ji, Li Zhou, Bozhou Dang, Xu Ji, Yagu Dang
February 10, 2024 (v1)
Keywords: flexibility, Heat Exchanger Network, multiperiod, stream phase changes
This paper presents a flexible HEN (heat exchanger network) synthesis methodology for designing a multiperiod HEN with streams involving phase changes. The methodology is based on an MINLP (mixed integer nonlinear programming) model, identification of critical points, and flexibility index analysis considering phase changes. A nominal multiperiod HEN topology is constructed in the first step. Then each process operating condition’s critical points and flexibility index are calculated to verify the feasibility of the designed HEN under multiple operating conditions. To verify the validity of the method, the proposed methodology will be applied to a case study on an ammonia synthesis process heat transfer network design based on renewable energy. The results show that the method can obtain a flexible heat transfer network that is cost-effective and adaptable to multi-condition production for green ammonia synthesis.
Small-Scale Solids Production Plant with Cooling Crystallization, Washing, and Drying in a Modular, Continuous Plant
Stefan Höving, Thomas Schmidt, Maximilian Peters, Hendrik Lapainis, Norbert Kockmann
January 5, 2024 (v1)
Keywords: continuous downstream processing, cooling crystallization, filter cake drying, filter cake washing, filtration, integrated small-scale production
Small-scale continuous apparatuses for solid product manufacturing are receiving increasing interest due to the demand for the fast market availability of specialty chemical products manufactured in integrated and modular processing plants. Relevant unit operations span from crystallization over solid−liquid separation and filter cake washing to drying. For this purpose, the quasi-continuous filter belt crystallizer (QCFBC) was developed and is presented here. The newly integrated unit operations with positive pressure filtration (Δpmax = 0.8 bar), filter cake washing (V˙wash = 55 mL·min−1), and convection drying (Tdry = 60 °C) have been individually characterized and integrated into the filter apparatus that has been modified for continuous operation. They were synchronized with the flexible cooling crystallization, enabling for a seamless production process. Sucrose in water was used as model substance system. Long-term operations of up to 14 h were successfully performed with dry pr... [more]
Effect of Cavitating Hydraulic Elements on Pump Characteristics
Jana Jablonská, Milada Kozubková, Sylva Drábková, Tomáš Blejchař
November 30, 2023 (v1)
Keywords: cavitation, converging-diverging nozzle, NPSH, pump, suction piping
The effective and reliable performance of any pump can be significantly impacted by the piping system design. One of the essential points is the pump suction pipe. Poor design and dimension of the suction piping can lead to cavitation in the pump which affects its head and efficiency. The primary objective is to reduce the hydraulic losses of the suction piping in order to maintain a Net Positive Suction Head required by the pump. Suction piping is recommended to be short and straight, and branch connections, valves and elbows should be avoided, which is not always possible. In addition, cavitation can occur in the actual hydraulic elements installed on the pump suction. This work is focused on the investigation of cavitating hydraulic element in the suction pipe on the pump performance. A converging-diverging nozzle with a circular cross-section was used for this purpose. A straight pipe segment of constant diameter and the same length was used for comparison. Both elements were chara... [more]
Monitoring and Characterizing the Flame State of a Bluff-Body Stabilized Burner by Electrical Capacitance Tomography
Liuyong Chang, Boxuan Cui, Chenglin Zhang, Zheng Xu, Guangze Li, Longfei Chen
September 21, 2023 (v1)
Keywords: electrical capacitance tomography, flame flashback, flame liftoff, flame state, flame state index
Unstable combustion phenomena such as flame flashback, flame liftoff, extinction and blowout frequently take place during the operation of the bluff-body stabilized burner. Therefore, flame state monitoring is necessary for the safe operation of the bluff-body stabilized burner. In the present study, an electrical capacitance tomography (ECT) system was deployed to detect the permittivity distribution in the premixing channel and further characterize the flame states of stabilization, flashback, liftoff, extinction and blowout. A calderon-based reconstruction method was modified to reconstruct the permittivity distribution in the annular premixing channel. The detection results indicate that the permittivity in the premixing channel increases steeply when the flame flashback takes place and decreases obviously when the flame lifts off from the combustor rim. Based on the varied permittivity distribution at different flame states, a flame state index was proposed to characterize the fla... [more]
Prediction of Physical Properties and Phase Characteristics of Ethane and Ethane Mixture in the Ethane Pipeline
Jiuqing Ban, Changjun Li, Wei Yang, Wei Zhang, Xiaoyun Yuan, Yingying Xu
September 20, 2023 (v1)
Keywords: equation of state, ethane pipeline, phase characteristics, physical properties
In order to realize the safe transportation of liquefied ethane pipeline in the Oilfield of China, it is necessary to fully study the process of pipeline replacement, operation and shutdown. The accurate calculation of physical property parameters and critical parameters is the basis of studying the gas-liquid two-phase flow and heat and mass transfer process of liquefied ethane in the pipeline. In this paper, different equations of states (EOSs) were used to predict the physical properties (such as density, dew point and dynamic viscosity) of ethane or ethane mixture, and the predicted results were compared with the corresponding experimental data from the literature. The prediction performance of different EOSs were evaluated by using two evaluation indicators, including average absolute deviation (AAD) and average relative deviation (ARD). The results showed that the PR-Peneloux EOS has the best performance for predicting the density of CH4-C2H6-N2 mixture with an ARD value of 4.46%... [more]
Effect of Flexible Operation on Residual Life of High-Temperature Components of Power Plants
Jun Heo, Mingyu Park, Jeong-Myun Kim, Dong-Won Jang, Ji-Hoon Han
July 7, 2023 (v1)
Keywords: creep–fatigue behavior, flexible operation, response surface model
Electricity generation from renewable energy sources is emerging as a result of global carbon emission reduction policies. However, most renewable energy sources are non-dispatchable and cannot be adjusted to meet the fluctuating electricity demands of society. A flexible operation process has been proposed as an effective solution to compensate for the unstable nature of renewable energy sources. Thermal load fluctuations during flexible operation may cause creep−fatigue damage to the high-temperature components of thermal power plants, as they are designed with a focus on creep damage under a constant power level. This study investigated the residual life of high-temperature components, such as a superheater tube and a reheater header, to failure under flexible operation conditions using finite element analysis and empirical models. First, we determined an analytical solution for the straightened superheater tube under thermal conditions and compared it with the numerical solution to... [more]
Gas/Liquid Operations in the Taylor-Couette Disc Contactor: Continuous Chemisorption of CO2
Georg Rudelstorfer, Rafaela Greil, Max Vogi, Matthäus Siebenhofer, Susanne Lux, Annika Grafschafter
July 4, 2023 (v1)
Keywords: chemisorption, continuous process, gas/liquid, multiphase, Taylor-Couette flow
Gas/liquid contactors are widely used in chemical and biotechnological applications. The selection and design of bubble-column-type gas/liquid contactors requires knowledge about the gas distributor design to provide appropriate gas flow patterns. This study presents the continuous chemisorption of CO2 in 0.1 molar sodium hydroxide solution in a counter currently operated gas/liquid Taylor-Couette disc contactor (TCDC). This vertical-column-type contactor is a multi-stage agitated gas/liquid contactor. The performance of a lab-size TCDC contactor in gas/liquid mass transfer operations was investigated. The apparatus design was adjusted for gas/liquid operations by installing perforated rotor discs to provide a rotational-speed-dependent dispersed gas phase holdup in the column. The parameters of dispersed gas phase holdup, volumetric mass transfer coefficient and residence time distribution were measured. In the first step, hydraulic characterization was performed. Then, the efficiency... [more]
Vibration Characteristics of Concrete Pump Trucks with Multiple Postures and Multiple Conditions Based on the Secondary Development of HyperWorks
Yafeng Ren, Weifeng Yang, Xiaohui Sun, Jinning Zhi, Jie Li, Haiwei Wang
June 7, 2023 (v1)
Keywords: boom posture, concrete pump truck, dynamic response analysis, finite element model, secondary development
Due to the excitation generated by the periodically alternate pumping of dual-hydraulic cylinders, vibration of concrete pump trucks (CPT) occurs. Excessive boom vibration will seriously affect the service life and operation safety of CPT. At the same time, the long boom structure of a CPT makes it very sensitive to the posture and pumping conditions, which directly affect the vibration characteristics of CPT in different postures and different working conditions. This paper establishes a finite element model of a type of CPT. Through force analysis of concrete in the straight pipe and elbow pipe during the pumping and reversing stages, an excitation model of the conveying pipe is established. Based on the secondary development of HyperWorks, a finite element model of CPT with multiple postures is built, and the dynamic response under multiple conditions is analyzed. Finally, the accuracy of the finite element model of CPT and the excitation model of the conveying pipe is verified by e... [more]
Impact of the Operation of Distribution Systems on the Resilience Assessment of Transmission Systems under Ice Disasters
Zhiwei Wang, Xiao Ma, Song Gao, Changjiang Wang, Shuguang Li
May 23, 2023 (v1)
Keywords: distribution system, ice disaster, load shedding, resilience evaluation, transmission system
Ice disasters, such as ice storms, can cause serious damage to power systems. To understand ice disasters’ influences on power systems, this paper introduces a resilience evaluation frame for transmission and distribution systems during ice disasters. First, we built a vulnerability model for transmission and distribution systems under ice disaster weather. Then, we established an optimal load power shedding model for transmission and distribution systems. After this, according to the vulnerability model and the optimal power load power shedding model, we generated the fault scenario set of a system in the influence of an ice disaster. According to the curve of system resilience, we propose two resilience evaluation indices of transmission and distribution systems under ice disaster weather. Finally, we verified the efficacy and rationalization of the established resilience evaluation framework with an example in which a transmission and distribution system is coupled with a six-bus tr... [more]
Experimental Performance Evaluation of a PV-Powered Center-Pivot Irrigation System for a Three-Year Operation Period
Juan Ignacio Herraiz, Rita Hogan Almeida, Manuel Castillo-Cagigal, Luis Narvarte
May 23, 2023 (v1)
Keywords: performance, PV irrigation system, stand-alone PV system, water pumping system
High-power diesel-based or grid-connected irrigation systems are being replaced by battery-free, high-power stand-alone Photovoltaic Irrigation Systems (PVIS) that reduce energy costs by up to 80% and for which no experimental performance data are available. The operation of PVIS is affected by various factors, some unrelated to the quality of the PV system itself, that generate losses that affect their performance: losses that vary with the crop and its irrigation period, losses intrinsic to the PVIS design, and losses that happen as a consequence of the behavior of the end-user. To better understand the impact of each type of loss, the traditional performance ratio was factorized. This paper provides the PV community with experimental data on the performance of a battery-free 160 kWp PV-powered constant-pressure center-pivot irrigation system. The system was analyzed over three years of real operation, during which the performance ratio ranged from 49.0 to 53.2%.
Some Logarithmic Intuitionistic Fuzzy Einstein Aggregation Operators under Confidence Level
Khaista Rahman, Ibrahim M. Hezam, Darko Božanić, Adis Puška, Miloš Milovančević
April 28, 2023 (v1)
Keywords: CLIFEHA operator, CLIFEHG operator, CLIFEOWA operator, CLIFEOWG operator, CLIFEWA operator, CLIFEWG operator, MAGDM problem
The objective of this paper is to introduce some new logarithm operational laws for intuitionistic fuzzy sets. Some structure properties have been developed and based on these, various aggregation operators, namely confidence logarithmic intuitionistic fuzzy Einstein weighted geometric (CLIFEWG) operator, confidence logarithmic intuitionistic fuzzy Einstein ordered weighted geometric (CLIFEOWG) operator, confidence logarithmic intuitionistic fuzzy Einstein hybrid geometric (CLIFEHG) operator, confidence logarithmic intuitionistic fuzzy Einstein weighted averaging (CLIFEWA) operator, confidence logarithmic intuitionistic fuzzy Einstein ordered weighted averaging (CLIFEOWA) operator, confidence logarithmic intuitionistic fuzzy Einstein hybrid averaging (CLIFEHA) operator have been presented. To show the validity and the superiority of the proposed operators, we compared these methods with the existing methods and concluded from the comparison and sensitivity analysis our proposed techniq... [more]
Integration of PV Sources in Prosumer Installations Eliminating Their Negative Impact on the Supplying Grid and Optimizing the Microgrid Operation
Rozmysław Mieński, Irena Wasiak, Paweł Kelm
April 28, 2023 (v1)
Keywords: 3-phase 4-wire PV inverter, power quality improvement, prosumer installation, PV integration, voltage unbalance
This paper concerns the mitigation of voltage disturbances deteriorating power quality and disrupting the operation of LV distribution grids due to the high penetration of PV energy sources in prosumer installations. A novel control strategy for 3-phase 4-wire PV inverters is proposed, which ensures the transmission of PV active power and simultaneous compensation of load unbalance and reactive power, making the prosumer installation balanced and purely active. It results in the balance of phase voltages and the mitigation of their variability. Unlike other methods used for voltage regulation in LV grids, the proposed solution contributes to the reduction in losses, is simple, and does not require additional costs. In the paper, a control algorithm for the PV inverter is described. Its effectiveness was tested by simulation using a model of the real LV distribution grid developed in the PSCAD/EMTDC program. The results of the simulations are presented and evaluated.
Issues Related to Power Supply Reliability in Integrated Electronic Security Systems Operated in Buildings and Vast Areas
Jacek Paś
April 28, 2023 (v1)
Keywords: integrated security systems, operation, power supply, power supply system model, reliability
The article presents basic issues associated with the power supply of integrated electronic security systems (IESS) operated in various facilities. Ensuring the reliability of an IESS power supply is an important issue associated with the operation of these systems that are responsible for the safety of people, accumulated property, natural environment, and cooperating structures—e.g., storage facilities. IESSs are operated under harsh external or internal environmental conditions. In such a case, we are dealing with processes of beneficial or adverse impact, which actively affects IESS operation. The IESS operation process is also associated with ensuring power supply continuity under normal operating conditions. This also means ensuring transition to backup power supply systems in the event of failures. Therefore, an IESS should exhibit high reliability related to the power supply process. To this end, the article presents two representative IESSs operated in buildings and in a vast... [more]
Raiffa-Kalai-Smorodinsky Bargaining Solution for Bilateral Contracts in Electricity Markets
Reinaldo Crispiniano Garcia, Javier Contreras, Matheus de Lima Barbosa, Felipe Silva Toledo, Paulo Vinicius Aires da Cunha
April 25, 2023 (v1)
Keywords: bilateral contracts, electricity market, game theory, Raiffa–Kalai–Smorodinsky bargaining solution
In electricity markets, bilateral contracts (BC) are used to hedge against price volatility in the spot market. Pricing these contracts requires scheduling from either the buyer or the seller aiming to achieve the highest profit possible. Since this problem includes different players, a Generation Company (GC) and an Electricity Supplier Company (ESC) are considered. The approaches to solve this problem include the Nash Bargaining Solution (NBS) equilibrium and the Raiffa−Kalai−Smorodinsky (RKS) bargaining solution. The innovation of this work is the implementation of an algorithm based on the RKS equilibrium to find a compromise strategy when determining the concessions to be made by the parties. The results are promising and show that the RKS approach can obtain better results compared to the Nash equilibrium method applied to a case study.
Automatic Energy-Saving Operations System Using Robotic Process Automation
Toru Yamamoto, Hirofumi Hayama, Takao Hayashi, Taro Mori
April 25, 2023 (v1)
Keywords: automatic operation, building management device, continuously and optimally operation, energy-saving operation system, reduction of carbon dioxide emissions, robotic process automation
We have developed an energy-saving operations system featuring remote operation of central monitoring equipment installed in a building. This system applies robotic process automation to remote operation to automatically perform energy-saving operations on behalf of the operations manager. Furthermore, as another feature, the system requires only a local area network to connect to the central monitoring equipment enabling automatic operation to be performed regardless of the specifications of the central monitoring equipment. The items targeted for energy-saving operation by this system are the optimal operation of a heat source system, setting of the supply water temperature of heat source equipment, setting of room temperature, and setting of outside-air intake volume. At present, the operations manager has the role of performing these energy-saving operations, but finding the optimal value for each of these operations is a difficult task. An operations manager, moreover, is responsi... [more]
Analysis of the Operation of an Unheated Wooden Church to the Shaping of Thermal and Humidity Conditions Using the Numerical Method
Grzegorz Nawalany, Paweł Sokołowski, Małgorzata Michalik
April 25, 2023 (v1)
Keywords: Carbon Dioxide, indoor microclimate, numerical method, religious building, wooden structure
The article deals with the problem of the effects of using a wooden church on thermal and humidity conditions forming inside. Religious services in the studied site were provided several times a year. The building was not used in the remaining time. The analysis of the effects of the frequency of religious services and the number of people at the services on the formation of temperature and humidity conditions in the wooden church is provided in this paper. The effect of the presence of people in the church on CO2 concentration fluctuations was also studied. Analysis of the results showed that external conditions have the greatest effect on internal microclimate substitutions. The presence of people affects temporary fluctuations in internal parameters. Both the number of people attending the service and the time of year are important. An indoor air temperature amplitude of 9.4 °C was recorded during the winter period. The CO2 level in the church during the service exceeded the limit v... [more]
Diagnostic Protocol for Thermal Performance of District Heating Pipes in Operation. Part 1: Estimation of Supply Pipe Temperature by Measuring Temperature at Valves after Shutdown
Peter Lidén, Bijan Adl-Zarrabi, Carl-Eric Hagentoft
April 24, 2023 (v1)
Keywords: cooling method, district heating network, non-destructive testing, polyurethane, thermal response time, valve
This study evaluates temperatures measured at district heating (DH) valves in manholes and their usability for non-destructively assessing the thermal performance of buried DH pipes. The study was conducted as a field test in which part of a DH network was shut down and the temperature decline in the valves was analysed in terms of absolute temperature and thermal response time from the DH pipe to the top of the valve. The calculated and measured supply pipe temperatures by the drainage valves were in good agreement, with 1% deviation. The valve measurement analysis from this study shows that the drainage valve has good potential to serve as a measurement point for assessing the thermal status of a DH network. However, the shutdown valve measurements were greatly affected by the manhole environment.
Operation Characteristics of Mechanical DC Circuit Breaker Combined with LC Divergence Oscillation Circuit for High Reliability of LVDC System
Sang-Yong Park, Hyo-Sang Choi
April 24, 2023 (v1)
Keywords: DC circuit breaker, LC divergence oscillation circuit, LVDC, zero point
DC systems are modernly starting to come into the spotlight again due to the carbon-neutral policy, the development of semiconductor devices for power, and the increase in digital loads. We need to prepare in advance solutions to problems that may arise from fault currents due to transients for future DC power grid models. In the case of DC, there is no current zero-point because there is no frequency. Therefore, a large switching surge is generated when the circuit breaker cuts off the fault current. The possibility of insulation breakdown is greater than that of AC in severe cases. We consider power semiconductors or superconducting current limiters as an alternative. However, DC breaking cannot be safely achieved by itself. For reliable DC breaking, mechanical circuit breakers must be used with them. Among the mechanical shut-off methods, we adopted the divergence oscillation method. It has the biggest advantage compared to other methods in that it has a simple structure by composin... [more]
Analysis of the Effect of Mass Parameters on Motorcycle Vibration and Stability
Andrzej Dębowski
April 24, 2023 (v1)
Keywords: Bode plot, LabVIEW, motorcycle dynamics, shimmy, steering system, vibrations, wobble
This paper presents a vibration analysis method and an example of its application to evaluate the influence of mass parameters on torsional vibration frequencies in the steering system of a motorcycle. The purpose of this paper is to analyze to what extent vibration frequencies can change during their daily operation. These changes are largely due to the ratio of vehicle weight to driver and load. The complex dynamics make it very difficult to conduct research using simple models. It is difficult to observe the influence of individual parameters because they are strongly interrelated. This paper provides a description of the vibration analysis method, and the results are presented in the form of Bode diagrams and tables. On this basis, it was found that the driver, deciding on the way of using the vehicle and introducing modifications in it, influences the resonant frequencies of the steering system. Typical exploitation factors, on the other hand, do not cause significant changes, alt... [more]
Technology for Preventing the Wax Deposit Formation in Gas-Lift Wells at Offshore Oil and Gas Fields in Vietnam
Mikhail Konstantinovich Rogachev, Thang Nguyen Van, Aleksandr Nikolaevich Aleksandrov
April 24, 2023 (v1)
Keywords: asphalt-resin-paraffin deposits (ARPD), associated petroleum gas, high-wax oil, injection depth, offshore fields, operation of gas-lift wells
Within the past few decades, the production of high-wax oils at offshore fields in Vietnam has been fraught with severe problems due to the intense formation of asphalt-resin-paraffin deposits (ARPD) in the downhole oil and gas equipment. The formation of organic wax deposits in the tubing string led to a significant decrease in gas-lift wells production, efficiency of compressor units, transport capacity of the piping systems, along with an increase in equipment failure. Subsequently, the efficiency of gas-lift wells dramatically decreased to less than 40% as a whole. The existing methods and technologies for combating organic wax deposit formation in downhole equipment have many advantages. However, their use in producing high-wax anomalous oil does not entirely prevent the wax formation in the tubing string and leads to a significant reduction in oil production, transport capacity, and treatment intervals. The results of theoretical and experimental studies presented in this article... [more]
Temperature Estimation of SiC Power Devices Using High Frequency Chirp Signals
Xiang Lu, Volker Pickert, Maher Al-Greer, Cuili Chen, Xiang Wang, Charalampos Tsimenidis
April 24, 2023 (v1)
Keywords: frequency response analysis, junction temperature estimation, reliability of power devices, signal injection, silicon carbide metal–oxide–semiconductor field-effect transistor, temperature sensitive electrical parameters
Silicon carbide devices have become increasingly popular in electric vehicles, predominantly due to their fast-switching speeds, which allow for the construction of smaller power converters. Temperature sensitive electrical parameters (TSEPs) can be used to determine the junction temperature, just like silicon-based power switches. This paper presents a new technique to estimate the junction temperature of a single-chip silicon carbide (SiC) metal−oxide−semiconductor field-effect transistor (MOSFET). During off-state operation, high-frequency chirp signals below the resonance frequency of the gate-source impedance are injected into the gate of a discrete SiC device. The gate-source voltage frequency response is captured and then processed using the fast Fourier transform. The data is then accumulated and displayed over the chirp frequency spectrum. Results show a linear relationship between the processed gate-source voltage and the junction temperature. The effectiveness of the propose... [more]
Improvement of Stand-Alone Solar PV Systems in the Maputo Region by Adapting Necessary Parameters
Paxis Marques João Roque, Shyama P. D. Chowdhury, Zhongjie Huan
April 24, 2023 (v1)
Keywords: PV efficiency, PV installation, PV operation, PV power generation
With the energy crisis and the constant blackout in the Mozambique Power Company grid, the option of applying solar photovoltaic (PV) systems has been one of the most used alternatives in the neighborhoods of the Maputo region. However, inefficient power delivery caused by unproper sizing and installation of stand-alone solar PV systems has been contributing to the low utilization of solar energy potential in the Maputo region. The optimal sizing and installation of the solar PV system is addressed to evaluate the influence of installation and operation parameters on the power output of PV modules. In this topic, PV modules parameters such as cell temperature, the module’s slope and azimuth angles, the losses caused by excessive heating of the module cells, shadows and dust on the PV module and the cooling process at the back of the module are assessed in order to find out the consequence of inadequate installation and operation parameters of solar PV systems in the Maputo region. The... [more]
Circuit Breaker Failure Protection Strategy for HVDC Grids
María José Pérez-Molina, Dunixe Marene Larruskain, Pablo Eguia, Oihane Abarrategi
April 24, 2023 (v1)
Keywords: algorithm, circuit breaker failure, HVDC grid, protection
HVDC grids demand the fast and reliable operation of the protection system. The failure of any protection element should initialize a backup protection almost immediately in order to assure the system’s stability. This paper proposes a novel backup strategy that covers the failure of the primary protection including the malfunctioning of the HVDC circuit breaker. Only local voltage measurements are employed in the proposed backup protection and the voltage derivative is calculated at both sides of the limiting inductor. Consequently, the speed and reliability of the protection system are enhanced, since no communication channel is needed. This paper contains a thorough specification of the proposed protection strategy. This strategy is validated in a four-terminal HVDC grid with various fault case scenarios, including high-resistance fault cases. The operation of the backup protection is reliable and remarkably fast.
Improvement of DC Fault Current Limiting and Interrupting Operation of Hybrid DC Circuit Breaker Using Double Quench
Sang-Jae Choi, Jun-Hyup Lee, Jin-Wook Lee, Sung-Hun Lim
April 21, 2023 (v1)
Keywords: DC fault current limiting and interrupting operation, double quench, hybrid DC circuit breaker (DCCB), superconducting elements
In this paper, direct current (DC) fault current limiting and interrupting operation of hybrid DC circuit breaker (DCCB) using double quench, which consists of DCCB, a series resonance circuit, power electronic switch, surge arrestor, two separated current limiting reactor/resistor, and two superconducting elements, were suggested. The suggested hybrid DCCB can perform the interrupting operation after twice or once DC fault current limiting operation according to DC fault current amplitude. To verify the effective operation of the suggested hybrid DCCB, the modeling for the components of DCCB, the surge arrestor, and the SCE was carried out and its DC operational characteristics were analyzed. Through the analysis of the modeling results for the suggested hybrid DCCB, the advantages of hybrid DCCB were discussed.
A Study of Moist Air Condensation Characteristics in a Transonic Flow System
Jie Wang, Hongfang Gu
April 21, 2023 (v1)
Keywords: Laval nozzle, moist air, non-equilibrium condensation, relative humidity, transonic flow
When water vapor in moist air reaches supersaturation in a transonic flow system, non-equilibrium condensation forms a large number of droplets which may adversely affect the operation of some thermal-hydraulic equipment. For a better understanding of this non-equilibrium condensing phenomenon, a numerical model is applied to analyze moist air condensation in a transonic flow system by using the theory of nucleation and droplet growth. The Benson model is adopted to correct the liquid-plane surface tension equation for realistic results. The results show that the distributions of pressure, temperature and Mach number in moist air are significantly different from those in dry air. The dry air model exaggerates the Mach number by 19% and reduces both the pressure and the temperature by 34% at the nozzle exit as compared with the moist air model. At a Laval nozzle, for example, the nucleation rate, droplet number and condensation rate increase significantly with increasing relative humidi... [more]
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