Start-up Conditions Research Articles

The effect of low-temperature starting on the thermal safety of lithium-ion batteries

With the widespread application of lithium-ion batteries (LIBs) in the field of energy equipment, their probability of starting or operating in low-temperature environments is also increasing. However, there is currently a lack of research on the changes in thermal safety of batteries after use in corresponding environments. In this work, the thermal safety performance, degradation mechanisms and evaluation method of LIBs at low-temperature start-up conditions are studied. The results show that starting at low temperature leads to the decrease of cell capacity. Electrochemical characterization and cell disassembly analysis indicate that the loss of active lithium ions is mainly caused by the evolution of lithium and the growth of solid electrolyte interface films. In addition, the low-temperature startup results in the decrease of thermal runaway (TR) onset temperature and the advance of TR time. In order to quantitatively evaluate the safety state of the LIBs, an evaluation model based on Informer algorithm is established. The model extracts the discharge capacity, discharge energy and dV/dQ as aging characteristic parameters, and extracts TR temperature as thermal safety characteristic parameters. The data set is processed by cubic spline interpolation. After training and verification, the accuracy of the model reaches 80 %.

Study on Internal Flow Characteristics and Pressure Pulsation Features of Pump-Turbine under the no-load Startup Condition with Different Heads

Study on Internal Flow Characteristics and Pressure Pulsation Features of Pump-Turbine under the no-load Startup Condition with Different Heads

A study of capacity demands for heat pumps intermittent heating of China’s residences

Heat pump heating is one of the most promising solutions for transitioning residential heating in China’s cold regions, as well as hot summer and cold winter regions from centralized, continuous heating to decentralized, intermittent heating, promoting low-carbon transformation. However, the fundamental issue of the actual capacity requirements for heat pumps in intermittent heating has not yet been addressed. In view of this, this study developed a numerical model that considers the dynamic coupling characteristics between the heat pump and the building environment. Using the model, the worst startup conditions for heat pumps in intermittent heating, actual heat pump capacity demands, and the differences in capacity compared to continuous heating mode for residential buildings in 230 Chinese cities are analyzed. The findings revealed an exponential relationship between intermittent heating capacity demands and time constraints, as well as a linear relationship with heating temperature. Specifically, the impact of the set temperature on capacity demands in cold regions and hot summer and cold winter regions is 22.8 W/(m2·°C) and 32 W/(m2·°C), respectively. These findings provide insights into the planning and design of future intermittent heating renovation projects in China.

Dual-time scale optimal dispatch of the CSP-PV hybrid power plant considering dynamic operation

The concentrating solar power (CSP) plant, renowned for its flexibility, environmental friendliness, and energy storage capabilities, has become integral components of large-scale renewable energy projects in China. However, the grid connection methods for CSP plants, wind farms, and photovoltaic (PV) plants are independent. To enhance renewable energy consumption and improve the revenue of CSP and PV plants, this paper proposes a dual-time scale dispatch model for the dynamic operation of the CSP-PV hybrid plant. This model considers the actual startup conditions and dynamic switching models of the subsystems involved in the receiver, thermal storage subsystem, and power cycle. Based on the dynamic operation characteristics of the CSP-PV hybrid power plant, different time scales are used for prediction during day-ahead and intraday periods, improving the efficiency of the hybrid power plant and adapting to weather changes. The dispatch optimization outcomes of the CSP-PV hybrid plant serve as the reported curve for the day-ahead and intraday rolling optimal scheduling process, aiming to minimize the operating costs of the power system. A simulation is conducted to demonstrate the effectiveness of the proposed model, utilizing data from the Dunhuang area, Gansu Province, China.

Performance and economic study of a novel high-efficiency PEMFC vehicle thermal management system applied for cold conditions

This paper proposes three different heating management systems, sysse (self priming thermal management system), syslow (low temperature thermal management system), and syssp (split flow thermal management system), which are mainly composed of PEMFC and heat pump subsystems. Simulations were conducted to compare the comprehensive performance of these systems under cold startup and cold operating conditions, and analyzed the effect of different factors on these three system. The results show that under the influence of cell stack parameters, compared to sysse and syslow, the syssp has an average power consumption reduction of 29.95 % and 20.94 %, with a maximum power reduction of 31.46 % and 27.61 %, the average range power increases by 35.09 % and 23.58 %, with a maximum range power increase of 107.53 % and 75.57 %, the average COPPEMFC (Coefficient of Performance of heating Proton Exchange Membrane Fuel Cell) increases by 0.56 and 0.37. Under the influence of heat pump parameters, the evaporating temperature has a larger impact on the performance gains of the syssp, while condensing temperature has a greater effect on power consumption, range power, and COP variations. Compared to sysse and syslow, the syssp can recover costs as quickly as 3.12 and 3.68 years.

Influence of mass conservation cavitation boundary on transient performance of water-lubricated bearings

Given the current research gap regarding cavitation phenomena and startup conditions in water-lubricated bearings (WLBs), this study offers an innovative approach by integrating the mass conservation boundary condition proposed by Jakobsson, Floberg, and Olsson (known as the JFO boundary condition) with a transient mixed lubrication model of WLBs. It also considers the impact of elastic deformation and surface roughness peaks, thus establishing a transient startup model of WLBs that incorporates the cavitation effect. Furthermore, the dynamic behaviors of this boundary condition are contrasted with the commonly used Reynolds boundary condition during the startup process of the bearings, as well as under eccentric and step load impacts. The findings demonstrate that the JFO boundary condition, accounting for cavitation effects, significantly influences the transient performance of WLBs. The presence of a cavitation region diminishes the damping of the bearing system following step load impacts, leading to increased overshoot and adjustment time while weakening the system's self-adjusting ability against step loads. This study offers valuable insights for theoretical analysis of ship propulsion systems operating under complex conditions.

Performance of MT-I spherical tokamak with upgraded power supplies

This paper describes the upgradation of power supply systems for the improved performance of a small spherical tokamak (MT-I) with an aspect ratio of 1.67 in operation at the Pakistan Tokamak Plasma Research Institute (PTPRI), Islamabad. Three mutually independent power supplies are designed to generate current pulses of desired shape and magnitude in central solenoid (CS), toroidal field (TF) and vertical field (VF) coil systems. The main parts of a power supply are capacitor banks as energy storage devices, ignitrons and thyristors as fast switches for controlled power switching. A double capacitor bank topology with enhanced second capacitor bank voltage is found to be suitable for CS to improve the plasma startup conditions. Simulations are performed in MATLAB Simulink for confirmation of the designed power supply system. The Rogowski coil and current transformers are employed to measure plasma current and the coil’s current waveforms during the experiment in the presence of hydrogen as working gas. An ocean spectrometer and a photron high-speed camera (SA-8) are used for optical measurements and fast plasma imaging. An improvement in startup conditions is observed, enhancing the plasma current duration and light emission intensity recorded in the high-speed camera masked with a Hα filter.

A semiconductor wafer manufacturing system scheduling start-up and decision mechanism considering bottleneck drift characteristics

The development of Artificial Intelligence (AI) requires a significant amount of high-performance semiconductor chips. Scientifically and effectively scheduling and optimizing semiconductor wafer manufacturing systems can improve the productivity of the production system, equipment utilization, and semiconductor chip output. Therefore, scheduling optimization and decision-making for semiconductor wafer manufacturing systems have become a hot research topic for current researchers. However, bottleneck drift is an important feature of semiconductor wafer manufacturing systems, and is also a key factor that constrains scheduling and decision-making in semiconductor wafer manufacturing systems. Currently, there is a lack of research on the specific characteristics of bottleneck drift in semiconductor wafer manufacturing systems in the literature, which leads to problems such as ineffective planning and scheduling decisions by managers, and affects the performance of semiconductor wafer manufacturing systems. This paper considers the triggering conditions, occurrence time, and impact on production plan objectives of bottleneck drift, and improves two methods for bottleneck identification and bottleneck drift, based on which a new semiconductor wafer manufacturing systems scheduling start-up mechanism is proposed, which includes three parts and nine steps. Firstly, the semiconductor wafer manufacturing system scheduling process is given, including bottleneck identification, impact analysis, prediction, and planning for the impact of bottleneck drift on production plan objectives. Secondly, bottleneck identification and impact factors are predicted based on bottleneck drift, and the trigger conditions and drift time of bottleneck drift are determined. Then, based on the delivery time of the production plan objectives, the impact of bottleneck drift on production plan objectives is analyzed to determine the scheduling start-up conditions for the semiconductor wafer manufacturing system. Experimental results show that the mechanism proposed in this paper can timely and accurately identify the triggering conditions and drift time of bottleneck drift, avoid ineffective scheduling decisions before bottleneck drift, avoid unnecessary production scheduling decisions, and reduce additional performance losses. In addition, it can analyze the impact of bottleneck drift on production plan objectives according to the production plan objectives, so as to formulate scheduling decision-making schemes better, avoiding production plan delays and waste of production capacity.

Numerical study of the self‐priming process of a prototype pump based on coupled calculations of circulatory system

AbstractTo understand the self‐priming characteristics of a self‐priming pump, a closed‐loop piping system that includes the self‐priming pump, valve, tank, and piping system is established. The acceleration–constant speed operation processes of the impeller are controlled through a user‐defined function that ensures that the computational model and startup conditions are consistent with the real situation. Based on numerical calculations of the self‐priming process with two different self‐priming heights, the gas–liquid distributions during the self‐priming startup process are obtained. The results show that the self‐priming startup process can be divided into three stages: rapid inhalation, oscillating exhaust, and accelerated exhaust. Under the two self‐priming heights, the time required for the rapid inhalation and accelerated exhaust stages is basically the same. Thus, the difference in self‐priming time is mainly concentrated in the oscillating exhaust stage. The rate at which the liquid level rises in the vertical pipe is not proportional to the self‐priming height, and the difference in the self‐priming time is not proportional to the change in the self‐priming height.

Annular unidirectional slip Couette flow with heat transfer and variable viscosity by Laplace transform and homotopy perturbation method

This article investigates the thermal, variable viscosity axial Couette flow between two con- centric circular cylinders, taking into account both the Navier and the dynamic slip boundary conditions. In order to put in evidence the effect of dynamic slip on the behavior of the solution, we have kept the flowing fluid to a simple Newtonian viscous fluid. The nonlinear governing equations for momentum and energy balance are solved under startup condition using the Laplace transform (LT) technique, in conjunction with the Homotopy Perturbation Method (HPM). The first two orders of approximation for temperature and velocity are obtained, as well as the entropy generation in the space occupied by the flow and the volumetric flux. Numerical results and graphical representations of the solution are provided and discussed to depict the effects of the slip parameters on the velocity and the temperature profiles, on the entropy generation rate and on the volumetric flux.

Dynamic modelling of supplemental cooling systems with vapor compression refrigeration units in civil aircrafts

Newly developed airliners have adopted supplemental cooling systems (SCS) to provide for non-cabin cooling requirements. In the present study, dynamic component models for compressor and phase change heat exchangers were developed with dynamic decoupling and explicit solution methods, and pressure zone separation and solution methods are developed based to obtain dynamic pressures as key values. A dynamic VCRU subsystem model is established, and the result under single-unit startup condition shows pressure deviations less than 0.16 %, with a simulation time ratio of 5.65 %, exhibiting good overall performance at both precision and speed. A dynamic SCS system model is developed, and the simulation of a 9000 s flight took 1973.3 s to complete. Result in the cruise phase shows the condensation and evaporation temperatures are in the ranges of 28.39–31.33 °C and −17.93 to −10.71 °C, respectively, meeting their respective designed ranges of 30 ± 5 °C and −15 ± 5 °C. These results reflects good consistency of the model with actual system characteristics. Control optimization is conducted based on the developed model to eliminate temperature fluctuation. The optimization reduced the maximum temperature deviation from 0.4004 K to 0.0019 K after system starting process, proving the feasibility of control method optimization based on the developed dynamic simulation model.

Performance Comparison of a DC–DC Boost Converter With Conventional and Non-linear SMC Controller in Dual Loop Structure

Generally, the control system confronts various control techniques in the dual-loop control concept. Most of the studies deal with two different controllers in their loops, which increases the problem of designing two distinct procedures with lengthened calculations. In this article, different control techniques like conventional proportional integral (PI), proportional integral derivative (PID), and nonlinear sliding mode control (SMC) have been discussed, and the implementation of SMC in the Dual loop control of a DC–DC Boost converter is presented. The converter’s dynamic behavior is observed by driving their analytical equations. The effective controller for the proposed converter is ascertained by their comparative analysis. The proposed concept is validated with MATLAB/Simulink and a hardware prototype. The controller’s response is compared for various disturbances. Here, dual-loop SMC is put forward in both loops and its competence is confirmed with a minimal settling period of 0.005 sec and a percentage overshoot of 0.2% during the startup conditions, whereas during the line disturbances a minimum peak time of 0.0001 sec is achieved with a settling time of 0.025 sec. Additionally, a nil percentage overshoot and a settling time of 0.02 sec with a 0.001 sec peak time are attained during the load variations. Furthermore, a settling time of 0.01 sec and a percentage overshoot of 0.8% is reached during the reference voltage variations. From the numerical analysis, it is contemplated that an appropriate selection of SMC controllers in both the outer and inner loop results in optimal performance of the converter during the closed loop operation. Finally, the SMC + SMC controller exhibits superior controlling action compared to PI + PI and PID + PID controllers.

Thermal and structural analysis of the DONES target system under steady state and transient loading conditions

One of the crucial steps in the European Roadmap to the realisation of fusion energy is the design and construction of the Demo-orientated NEutron Source (DONES) facility. DONES is a fusion-like neutron source, based on the International Fusion Materials Irradiation Facility (IFMIF) concept, aimed at qualifying and testing the materials to be used in fusion reactors. The Target System (TSY) is a crucial system as it is the component where the interactions between deuterons and a liquid lithium target, flowing on a solid surface (i.e. the Back Plate), take place to produce neutrons for irradiating the testing materials. In this regard, an investigation campaign has been performed to evaluate the thermo-mechanical behaviour of the DONES TSY under selected steady state and transient loading conditions, in light of the most recent design updates (new bellows and connection systems). The first part of the assessment concerned the analysis of the TSY under the normal operation steady state loading scenario. A detailed 3D FEM model has been set up, considering the newest updates of the TSY geometry and of the operational parameters, and a thermo-mechanical analysis has been launched. Results have been mainly checked in terms of TSY global deformation, focusing on the Back Plate and on the connecting bellows displacements, in order to exclude overlapping with the High Flux Test Module and misalignments with the beam footprint. Afterwards, since the lithium inlet temperature has been increased from 250 °C to 300 °C, a transient thermo-mechanical analysis of the TSY under the start-up loading conditions has been performed to check if it is able to withstand the hotter lithium flow according to the RCC-MRx criteria. Therefore, the reference pre-heating strategy has been adopted, assessing the thermal and mechanical behaviour of the TSY, focusing on the Back Plate. The obtained results are presented and critically discussed, suggesting important recommendations for the follow-up of the design.

Visual observations of steam–air submerged horizontal jets at low mass flux

Steam jet condensation at low mass flux is important especially in start-up, shutdown or accident conditions of various applications. Visual experiments of steam–air submerged jets through horizontal pipe were conducted in the ranges of mass flux 0–––20 kg/m2s, air mass fraction 0–––0.02, and water temperature 20 − 80℃. In pure steam jets, three condensation regimes of no bubbling, intermittent bubbling, and continuous bubbling were identified in steam jets. In no bubbling regime, rolling up and billows of plane shear flow were observed. In intermittent bubbling regime, large bubble was generated, detached and collapsed intermittently, accompanied by fluid oscillations. The bubble forming frequency increased with the rise of water temperature. Condensation heat transfer coefficients tends to decrease as the steam mass flux increases. In continuous bubbling, fluid oscillation no longer occurred. The bubble forming frequency decreased with the rise of water temperature. Condensation heat transfer coefficients increase as the steam mass flux increases. In the cases with shallow submerged depth, air-entrained vortex, surface water jets, and splash were observed after bubble condensation. In steam–air jets, condensation became stable and small bubbles increased. The condensation regime transitioned from intermittent bubbling to continuous bubbling earlier.

Model-free adaptive optimal control for fast and safe start-up of pumped storage hydropower units

Pumped storage unit (PSU) is a special kind of hydropower unit, that undertakes the task of power generation, and performs the function of energy storage. Due to its unique advantages, pumped storage power stations have been extensively developed in China in recent years and play an important role that is difficult to be performed by other energy sources. Although many studies have been carried out on the control of PSUs, most of the control algorithms are based on object models, which results in the control performance depending on the model accuracy to a large extent, limiting the practical application of these algorithms. For this reason, a preliminary application of model-free adaptive control in PSUs is investigated in this paper. Firstly, a refined nonlinear model of PSU is established, secondly, the model-free adaptive controller of PSU and its parameter optimization strategy are designed, and finally, verification is carried out by simulation studies for four different start-up conditions, and a comprehensive comparison is made with control strategies such as proportional-integral-derivative (PID), fractional-order PID, and nonlinear generalized predictive control. The results show that the proposed method has significant improvement in both speed and head control performance compared with other methods, with the regulation time being on average at least 5.53 s faster and the overshoot being on average at least 2.85 % lower. It proves the effectiveness and superiority of the method. In addition, the proposed method reduces energy consumption in the regulation process, and the computational cost meets the real-time control requirements, which has a wide range of application prospects.

Multiphysics Analysis of PLOFC and DLOFC Accidents in the HTGR-TR

High-temperature, gas-cooled reactors (HTGRs) are promising advanced reactor designs. Leveraging passive safety features, higher core outlet temperatures, previous commercial operational experience, and potential coupling with nonelectrical systems, HTGRs present many advantages over traditional light water reactors and other advanced reactor designs. The High-Temperature, Gas-Cooled Test Reactor (HTGR-TR) is a point design developed by Idaho National Laboratory as a response to the need for the expansion of U.S. test reactor capabilities. The HTGR-TR was designed to serve as a test reactor for Generation-IV small modular prismatic block HTGRs and to provide irradiation data, two crucial contributions to the development of advanced reactors. As in any reactor design, it is necessary to understand the behavior of the reactor during accident scenarios to determine the overall safety of the design. Pressurized loss of forced cooling (PLOFC) and depressurized loss of forced cooling (DLOFC) are two accidents that can occur in HTGRs and that present challenges to decay heat removal. In order to understand the behavior of the fuel during these accidents, the resulting mechanical behavior and fission product migration in the fuel are evaluated. Using the HTGR-TR design, which utilizes tristructural isotropic (TRISO) fuel, a multiphysics analysis during the PLOFC and DLOFC transients was performed. This study utilizes neutronics, thermal hydraulics, and fuel performance modeling to analyze the behavior of TRISO particles during steady-state operation and the described transients. This analysis aims to characterize the hoop stress and strain during the transients, as well as predict fission product migration and radiological release. Due to the startup conditions of the HTGR-TR, the silicon carbide (SiC) layer for both of the transients and steady-state conditions are initially in compression for both the hoop stress and strain. The DLOFC transient at the beginning of cycle was the most challenging overall to the fuel, having the closest to tensile behavior and the closest to tensile strain. Because the integrity of the SiC layer was not challenged during any of the transients, the release of 90Sr and 137Cs was found to be negligible. The PLOFC transient at the end of cycle resulted in the largest 110mAg release and subsequent radioactivity increase. However, the increase in radioactivity was minor when compared to typical operating conditions due to the relatively large diffusivity of 110mAg though SiC at normal operating temperatures. Highlights include Neutronics and thermal-hydraulic modeling generating steady-state and transient conditions for use in fuel performance analysis.2. Detailed BISON analysis demonstrating the excellent performance of TRISO fuel during PLOFC and DLOFC transients.3. Fuel behavior showing negligible fission product release.

Optimization of purge strategy under fuel cell startup conditions based on CFD-Simulink collaborative simulation

Optimization of purge strategy under fuel cell startup conditions based on CFD-Simulink collaborative simulation

Calculation Method for Structural Dynamics of Material Ropeway under Startup and Shutdown Conditions with Single Concentrated Loads and Distributed Multiple Loads

In light of the unique structural features of material ropeway of transmission line, this paper presents a calculation method for the structural dynamics of material ropeway when subjected to single concentrated loads and distributed multiple loads. Taking into account the geometric nonlinearity and significant flexible deformation features of carrying rope and pulling rope in material ropeways, a finite mass point method is utilized for theoretical derivation to investigate the effects of varying load weights and speeds on tension fluctuations in carrying rope and pulling rope during the startup and shutdown processes. The results indicate that the proposed method can accurately calculate the tension and structural variations in carrying rope and pulling rope of multi-span material ropeway when subjected to single concentrated loads and distributed multiple loads. This method not only satisfies the requirements for transmission line engineering applications but also offers insights into the safe utilization of material ropeway of transmission line.

Effects of different stocking density start-up conditions on water nitrogen and phosphorus use efficiency, production, and microbial composition in aquaponics systems

Controlling environmental parameters, including nitrogen and phosphorus use efficiency, is a crucial aspect of maintaining effective aquaponic systems. In this study, we evaluated the impact of start-ups under high (20 kg/m3) and low (5 kg/m3) stocking density conditions on water quality, productivity, nitrogen use efficiency (NUE), phosphorus use efficiency (PUE), microbial community compositions, and functional genes in the aquaponics system. Six experimental units (three replications per treatment) were categorized into two groups. The experimental process was divided into two phases: Phase I (Days 1–40) and Phase II (Days 41–145). During Phase I, the two system groups were initiated under high and low stocking densities. Phase II constituted the fish and vegetable production phase, with all aquaponics systems standardized at a stocking density of 10 kg/m3 and a planting density of 12 plants/m2. The results indicated superior water quality in the low aquaponics systems than that in the high aquaponics systems during Phase I, whereas the opposite was observed during Phase II. The final weight, specific growth rate, and fish weight gain of jade perch (Scortum barcoo), as well as the plant weight gain of tomato plants, were significantly higher in the high aquaponics system than those in the low aquaponics system. The NUE and PUE of the high aquaponics system were 49.55 ± 1.02% and 60.12 ± 1.28%, respectively, surpassing those of the low aquaponics system (43.41 ± 2.16% and 49.06 ± 1.59%). The microbial diversity in the moving bed biofilm reactor and roots of the high aquaponics system was lower than in the low aquaponics system. However, the relative abundances of nitrifying and denitrifying bacteria were higher than those in the low aquaponics system. The number of copies of functional genes for nitrification and denitrification, including amoA, nxrB, nirS, nirK, and nosZ, was higher in the high aquaponics systems. Overall, the results indicated that high aquaponics systems initiated with high stocking density yield more products, improved water quality, and higher NUE and PUE by altering the composition of microbial communities. This study presents a method for enhancing the functional microbial community of a system by optimizing conditions during the initiation period.

Analysis of internal flow characteristics of a multistage pump during start-up

In order to study the transient characteristics during the startup process of a multi-stage pump, the Flowmaster software was used to obtain the rotating speed and flow characteristic curves of the pump under different valve openings, and analyze its internal flow and structural characteristics based on numerical simulation. The study results indicate that the time required for the flow to reach a steady state lags significantly behind the time required for the rotational speed to reach a stable state during the initial stage of pump start-up. By comparing the pressure distributions of a multistage pump under quasi-steady state and transient conditions, it can be seen that the internal flow field evolution of the pump under transient condition during the startup process lagged behind that under quasi-steady state condition, which makes using quasi-steady state laws were not suitable for describing the changes in transient flow field. The deformation law of the first-stage impeller under stable and start-up conditions was similar. The impact of increased flow rate on deformation was relatively weak and the difference in deformation values under different flow rates was relatively small under transient condition.