Start-up Time Research Articles

Analysis of characteristics of seawater desalination-solar chimney power plant under double-layer collector

To improve the output characteristics of seawater desalination-solar chimney power plants, enrich the theoretical research basis and promote its commercial application, this paper introduces the concept of multilayer flow channel, establishes four new types of multilayer collector flow channel, and constructs the corresponding heat and mass transfer mathematical models, revealing the mechanism of the influence of different flow channel and structural parameters on the system performance. The results showed that the surround-flow system extended the heat absorption time of the airflow, had two thermal storage layers, and had the best performance. The daily average power generation was 43.3 kW, and the average water production rate was 87.2 g/(h·m2), which was 132.8 % and 91.2 % higher than the traditional type’s, respectively, but had the longest start-up time. For the surround-flow system, the main reason for the flow loss increasing is swirling regions below the inlet and the transition section caused by the structure itself. Both the inlet width increasing and the roof’s inclination angle decreasing can increase power generation, with little impact on water production. Corner width increasing results in a significant decrease in water production, with little impact on power generation. The determination of structural parameters should also consider operational costs.

Evaluation of the Heat Transfer Performance of a Device Utilizing an Asymmetric Pulsating Heat Pipe Structure Based on Global and Local Analysis

PHPs (pulsating heat pipes) are widely used as an efficient heat transfer element in equipment thermal management and waste heat recovery due to their flexibility. The purpose of this study was to design a heat transfer device that utilizes an asymmetric pulsating heat pipe structure by adjusting the lengths of selected pipes within the entire circulation pipeline. In the experiment, a constant temperature water bath was used as the heat source, with heat dissipated in the condensing section via natural convection. An infrared thermal imager was used to record the temperature of the condensing section, and the local wall temperature distribution was measured in different channels of the condensing section. Based on an in-depth analysis of the wavelet frequency, the following research conclusions are drawn: Firstly, as the heat source temperature increases, the start-up time of the pulsating heat pipe is shortened, the operating state changes from start–stop–start to stable and continuous oscillation, and the oscillation mode changes from high amplitude and low frequency to low amplitude and high frequency. These changes are especially pronounced when the heat source temperature is 80 °C, which is when the thermal resistance reaches its lowest value of 0.0074 K/W, and the equivalent thermal conductivity reaches its highest value of 666.29 W/(m·K). Secondly, the flow and oscillation of the working fluid can be effectively promoted by appropriately shortening the length of the condensing section of the pulsating heat pipes or the heat transfer distance between the evaporation and condensing sections. Third, under a low-temperature heat source, the oscillation frequency of each channel of a pulsating heat pipe is found to be low based on wavelet analysis. However, as the heat source temperature increases, the energy content of the temperature signal of the working fluid in each channel changes from a low- to a high-frequency value, gradually converging to the same characteristic frequency. At this point, the working fluid in the pipes no longer flows randomly in multiple directions but rather in a single direction. Finally, we determined that the maximum oscillation frequency of working fluid in a PHP is around 0.7 HZ when using the water bath heating method.

A Study of High Transient Response Low Dropout Linear Regulator Chips

Abstract. With the rapid development of the microelectronics industry in the world, electronic products are being updated more and more quickly. This has created a growing large market demand for power management chips. Low drop-out linear regulators have become one of the most widely used types of power management chips due to their advantages of high stability, low drop-out voltage, and fast response. This paper is a data collection study and comparison of improvement methods based on high transient response low drop-out linear regulators. It describes the basic principles of LDOs as well as the principles, advantages and disadvantages of different improvement methods. It was found that the method of shortening the overshoot and undershoot durations by constructing transient enhancement circuits was the best in terms of performance among the following research methods. The stability of capacitor-less LDO is harder to control. Using compensation circuits to improve stability will increase circuit complexity. The capacitor-coupled current mirror method has a longer startup time, because it takes some time for it to reach homeostasis. The high complexity and energy consumption of the dual feedback loop structure makes the circuit costly.

Single-Loop Triple-Diameter Pulsating Heat Pipes at Reduced Heat Input: A CFD Study on Inner Diameter Optimization

The geometric configuration, particularly the inner tube diameter, plays a significant role in the thermal performance of pulsating heat pipes (PHPs). Previous experimental research has demonstrated that single-loop triple-diameter PHPs (TD-PHPs) outperform single-loop single-diameter PHPs (SD-PHPs) and dual-diameter PHPs (DD-PHPs) in terms of thermal performance under moderate heating input powers ranging from 25 W to 75 W. However, a reduction in heat input from 75 W to 25 W leads to a diminished impact of TD-PHPs on the thermal performance. Therefore, to improve the overall performance of TD-PHPs, this study used two-dimensional transient computational fluid dynamics simulations to identify the optimal inner tube diameters for TD-PHPs at a low heat input by evaluating the thermal resistance of five TD-PHPs with various inner diameters. The findings reveal that the TD-PHP configuration exhibits minimum thermal resistance, with inner diameters of 4.5 mm for the upper arch (the condenser section), 4.0 mm for the wide branch, and 2.5 mm for the narrow branch, primarily due to its full circulation flow pattern. Furthermore, the overall heat transfer performance of the optimal TD-PHP was compared with that of an SD-PHP at low heat inputs (10 and 18 W), indicating that although the optimal TD-PHP shows lower thermal resistance, it does not significantly affect the start-up time.

Modelling and theoretical research on transient lubrication and wear coupling behavior of main bearing during start-up of low-speed diesel engine

This study endeavors to establish a transient mixed lubrication model for time-varying wear of main bearings under dynamic loading conditions during the startup process. This model accounts for variations in oil film thickness attributable to deformation, wear profiles, and journal misalignment throughout the operational cycle. The evolution of main bearing lubrication characteristics during the startup process was analyzed, as well as the evolution of wear profiles and their effects on lubricating properties under different numbers of startups. The results indicate that as the number of startup cycles increases, the wear rate gradually levels off. With increasing startup times, there is a decrease in contact pressure and a slight reduction in oil film pressure, resulting in enhanced lubricating performance. Furthermore, the influence of startup duration on wear is significantly greater than that of radial clearance.

Aerobic granular sludge enhances start-up and granulation in single-stage partial nitritation anammox granular sludge systems: Performance, mechanism, and shifts in bacterial communities

The rapid start-up and granulation of a single-stage partial nitritation anammox granular sludge (PN/AnGS) system under limited seed sludge conditions is crucial for its practical application. This study proposed an aerobic granular sludge (AGS) − based strategy, enhanced the enrichment of anammox bacteria (AnAOB), and shortened the start-up time of PN/AnGS system by 20.5%. In addition, the inoculation of AGS can ensure the stable operation of the system during the selective sludge discharge to washout the flocs. Microbial community structure, particle size distribution, morphology results showed that niche shift was the key to promote the enrichment of AnAOB and AGS played a decisive role in the particle characteristics of PN/AnGS. Since AGS can be directly obtained from full-scale AGS wastewater treatment plants, integrating PN/AnGS with AGS processes can transition wastewater treatment from a “linear economy” to a “circular economy”, enhancing nitrogen removal efficiency and delivering significant economic and environmental benefits.

Characterization of a highly integrated, natural convection-driven, condensing methanol reactor

A highly integrated, natural convection-driven, condensing methanol reactor with the catalyst bed, heat integration section and liquid product separation in a single pressure vessel without moving parts is successfully tested. Space-time yields of up to 600kgMeOHmcat.−3h−1 are demonstrated, comparable to other CO2-to-methanol processes. The internal recycle by natural convection is successfully achieved as well as significant heat integration. A further reduction of heat losses to the environment is needed for autothermal operation. The dynamic characteristics of the process, with fast start-up times, a high turn-down ratio add to the potential to deal with intermittent feed supply. Overall the LOGIC 2.0 reactor concept is a promising process configuration for green methanol production.

Determination of steady-state for continuous powder mixing: Analysis of mixture properties and signal processing

Continuous powder mixing offers many advantages over batch processes, but its industrial implementation requires control of transient phases due to startup or variations in operating conditions. Detecting the steady-state by observing the mixture properties, obtained through in-line analysis of the mixture composition, is challenging due to the significant fluctuations in these properties. However, there is no quantitative method for identifying the steady-state for continuous powder mixing. We therefore propose in this work a methodology for steady-state detection by comparing several methods of mixture property analysis and signal processing. We show that conventional methods of mixture property analysis cannot reliably and accurately detect steady-state. We conclude that the best methodology is to perform signal processing on the content of the key component in the mixture. To do this, the signal of the content of the key component is first smoothed by the Savitzky-Golay filter. Then, the standard deviation of the filtered signal is compared with a tuning parameter to detect the beginning of steady-state. This method could be used to determine the mixing conditions leading to the smallest startup time, hence avoiding costly waste.

Estimating radial attenuation of vacuum pressure for dredged clays

The radial attenuation of vacuum pressure in dredged clays limits the effectiveness of vacuum consolidation. In this study, a series of model tests were conducted on five dredged clays with varying initial water contents to investigate this radial attenuation. The significant radial attenuation can be divided into two stages: the increasing and stabilization stages. In the stabilization stage, exponential radial attenuation is observed. Lower initial void ratio (e 0) and higher void ratio at liquid limit (e L) lead to a decrease in radial attenuation. Additionally, higher applied vacuum pressure (p v) results in a greater reduction in the magnitude of the radial vacuum pressure. In the increasing stage, the radial vacuum pressure increases exponentially to a stable state after start-up. The radial attenuation is attributed to the differential start-up time (i.e., initial time-point at which the increase begins) and varying increase rates. Lower e 0, higher e L, and higher p v values reduce the start-up time and raise the increase rate. A changing pattern is proposed to describe the exponential radial attenuation using three parameters: radial attenuation coefficient (k 2), increasing coefficient (k 3), and time-delay coefficient (D t). Furthermore, an empirical estimation for the radial attenuation is also suggested without relying on time-consuming tests

Electricity production and nutrient recovery from waste activated sludge via microbial fuel cell and subsequent struvite crystallization: Effect of low temperature thermo-alkaline pretreatment

Microbial fuel cell (MFC) and subsequent struvite crystallization are available low-carbon environmental- friendly techniques for resource utilization of waste activated sludge (WAS). In this study, low temperature thermo-alkaline pretreatment (LTTAP) was innovatively proposed for enhancing MFC electricity generation and subsequent struvite crystallization from WAS. The results indicated that LTTAP at 75 °C and pH 10 not only substantially shortened the start-up time of MFC to 3–4 days, but also significantly increased maximum power density to 5.38 W/m3. Moreover, thermo-alkaline pretreated WAS effectively exhibited stable and high output voltage over long period, compared to unpretreated WAS. Furthermore, pretreated WAS can provide an effective pH buffering function for MFC operation. In addition, about 90 % of phosphate in the pretreated WAS supernatant was recovered by struvite crystallization. The findings herein provided a new route for enhancing electricity production and nutrient recovery from WAS, which can realize the full-scale applicationof WAS resource utilization.

The start-up characteristics of a novel loop heat pipe with stainless steel capillary wick

Loop heat pipe (LHP) is an advanced thermal management technology that utilizes liquid–vapor phase change and capillary action to achieve efficient heat transfer across long distances and in various directions. The start-up of an LHP is crucial for its reliable and stable operation. This study aims to explore the start-up characteristics and temperature variations of various components under different heating conditions by designing a cost-effective flat plate evaporator LHP with a stainless-steel casing and acetone as the working fluid. The experimental analysis examined the performance of the LHP under varying heating powers from 28 to 60 W, positions, and gravity angles. The findings revealed that the LHP successfully started at 28 W, and a temperature overshoot occured when the heating position was near the compensation chamber. Notably, the start-up time was 400 s faster compared to the heating condition near the mean pressure chamber. When the evaporator was tilted such that the compensation chamber was above the evaporator’s pressure equalization chamber, circulation within the LHP could not be established. The thermal resistance of the LHP decreased with increasing heating power, achieving a maximum reduction of 51.51 %. When both the compensation chamber and the mean pressure chamber were heated simultaneously, the impact of the gravity inclination angle on thermal resistance was minimized. This study introduces an innovative capillary wick LHP with high start-up success rates and cost-effectiveness, providing both empirical data and theoretical insights for the refinement and optimization of civilian LHP designs.

Effect of magnetic powder (Fe3O4) on heterotrophic-sulfur autotrophic denitrification efficiency and electron transport system activity for marine recirculating aquacultural wastewater treatment

As an efficient nitrogen removal process, heterotrophic-sulfur autotrophic denitrification (HSAD) has attracted extensive attention in wastewater treatment. However, the effects of magnetic powder (Fe3O4) on the electron transport activity in HSAD process remain unclear. Therefore, in this study, a heterotrophic-sulfur autotrophic denitrification system was established to remove nitrogen from marine recirculating aquacultural wastewater for evaluating the effects of Fe3O4. At the optimal Fe3O4 concentration of 50 mg/L, the nitrogen removal efficiency reached 100% with lower sulfate accumulation, and the start-up time was shortened. The assays of denitrifying enzymes and electron transport system activity showed that Fe3O4 improved the activities of nitrate and nitrite reductases, and increased the efficiency of electron transport. Microbial community analysis revealed that Fe3O4 enriched heterotrophic denitrifier Thauera and sulfur autotrophic denitrifier Canditatus Thiobios, and thus enhanced denitrification efficiencies. This study demonstrated that Fe3O4 is an efficient denitrification accelerator in HSAD for treating marine recirculating aquacultural wastewater.

Heat transfer performance and startup characteristics of separated gravity heat pipe

Separated gravity heat pipes, with distinct arrangements of evaporating and condensing sections, offer low thermal resistance, high heat transfer efficiency, and a simple structure, making them suitable for passive cooling of spent fuel pools through gravity-driven processes. In this study, a steady-state, one-dimensional, two-phase flow model is developed to analyze phase change heat transfer in a separated gravity heat pipe. The research investigates the impact of liquid filling rate and vacuum level on heat pipe operation. The findings reveal a notable increase in pressure drop inside the tube with higher liquid filling rates, which diminishes the adaptability of the heat pipe as pressure rises, resulting in a narrower range of effective liquid filling rates. Specifically, the liquid filling rate of the heat pipe ranges from 38 % to 72 % at P = 13.75 kPa and from 44 % to 68 % at P = 15.75 kPa. Additionally, a startup prediction model is formulated based on a thermal resistance network model using the ideal gas assumption. Two startup states—namely, the initial startup state and the subsequent startup state—are proposed for large-scale separated gravity heat pipe arrays. The heat pipe achieves the large-temperature-difference initial startup state at a 50 % liquid filling rate within 7 min before transitioning to the subsequent startup state. The vapor mass, heat transfer coefficient, and working fluid temperature initially increase and then decrease over time, with varying peak times. As the liquid filling rate increases, the maximum vapor mass also increases. The heat transfer coefficient peaks at a 60 % liquid filling rate before subsequently declining. The optimal liquid filling rate of 60 % is identified based on startup time, heat transfer coefficient, and overall heat transfer efficiency.

OASR-WFBP: An overlapping aware start-up sharing gradient merging strategy for efficient communication in distributed deep learning

Wait-Free-Back-Propagation (WFBP) is a practical method for distributed deep-learning, but it suffers from a high communication overhead. To address this issue, the communication overhead can be reduced by overlapping gradient communication and computation, and sharing the startup time among multiple gradient communication phases. However, existing optimizations choose to share the startup time greedily and fail to coordinately exploit the overlapping opportunity between computation and communication. We propose an overlapping aware startup sharing Wait-Free-Back-Propagation (OASR-WFBP). An analytic model is designed to guide the sharing procedure. Evaluations show that OSAR-WFBP achieves a 5%-16% optimization in iteration time over the state-of-the-art WFBP algorithm.

Cationic polymer-mediated interbacterial aggregation: A novel approach for rapid aerobic granules development

This study introduces a novel approach to aerobic granular sludge technology that minimizes the start-up time and guarantees the formation of stable granules. This is achieved by seeding the reactor with a cationic polymer without using inoculated sludge. Three cationic polymers (Hydrofloc C4400SA, C8896, and polyelectrolyte emulsion) were tested to determine the most appropriate polymer for aerobic granular sludge (AGS) startup based on the optimal dose and formation of aerobic granules. Hydrofloc cationic polymer C4400SA has excellent granule-forming properties in the AGS reactor compared to their counterparts. The formation of granules was boosted by adding 15 ppm of polymer, resulting in densely packed aerobic granules after 10 days. This improvement can be due to the more cationic properties of hydrofloc, which play a key role in bridging between cells and particles because the cationic charges of hydrofloc attract negatively charged bacteria in wastewater, thereby promoting aggregation and the formation of initial flocs. These flocs serve as the foundation for the development of granules. After 80 days of operation, 40–50% of particles with an average size range from 0.6 to 0.9 mm were observed. The AGS SBR operation was closely monitored and showed consistent efficiency in removing solids, where TP, TN, NH+4 –N, and the total soluble COD were removed at average efficiencies of 62%, 73%, 97%, 93%, and 79% respectively, during steady-state cycles conducted at room temperature. Overall, this study highlights the potential of hydrofloc cationic polymer C4400SA to enhance the performance and resilience of AGS in wastewater treatment applications.

Experimental study on Start-Up and heat transfer characteristics in loop heat pipes with dual heat sources for battery thermal management system

Electric vehicles represent a breakthrough in sustainable transportation, significantly diminishing global emissions. The efficacy of lithium-ion batteries is significantly influenced by the operating temperature, with elevated temperatures potentially resulting in thermal runaway. A proficient battery thermal management system (TMS) must resolve this concern and uphold safe temperatures. Loop heat pipes (LHPs) offer passive cooling technology and have garnered the attention of researchers. Nonetheless, research on LHPs for battery thermal management systems is scarce, and prior investigations have concentrated on a singular heat source. A liquid heat pipe with a dual heat source evaporator has been engineered to simulate the battery arrangement of electric vehicles, which typically comprises multiple battery cells. This study seeks to examine the starting and heat transmission characteristics of LHP. Two battery simulators are fabricated from steel blocks equipped with cartridge heaters. A copper evaporator (121 × 56 × 20 mm) is equipped with a stainless-steel screen mesh capillary wick, and thermocouples are linked to a National Instruments data acquisition (NI DAQ) system for the LHP. Ethanol serves as the working fluid at a filling ratio of 60 %. The startup characteristics of the LHP are examined by altering the heat load, coolant flow rate, and coolant temperature. The experimental findings indicate that the LHP effectively initiates operation at heat loads ranging from 20 to 100 W. The LHP with multiple heat sources demonstrates reduced temperatures compared to a single heat source. The best performance of coolant flow rate and temperature for the quickest startup times are 1.5 L/min and 25 °C, respectively. The lowest thermal resistance achieved is 0.17 °C/W.

Improved sprayed water boiler design for steam production

The lengthy time required for conventional boilers to attain a steady state, their sizable size, the substantial pressure drop, and their high cost are all disadvantages. The objective of this study was to develop a novel design for a boiler to achieve better performance based on a sprayed water boiler (SWB) through injectors with a specific spray rate in a near-atomized form over tubes containing hot gases. As the water temperature in the SWB is equal to the temperature of the water sprayed by the injectors, the temperature difference between the hot gases and the water is higher than in the conventional boiler. A parametric study was conducted to investigate the main parameters affecting the boiler performance, such as the steam quantity and quality, the time required to reach the steady state condition, the size of the boiler, and the drop pressure on the hot-gas side. The results showed that the size of the SWB was significantly smaller than that of a conventional boiler. When generating steam of the same quantity and quality, the size of the SWB is one-third of the conventional size. This reduces the manufacturing costs of the boiler and the pressure drop of the hot gases inside the boiler. It was also found that the thermal efficiency of the SWB was higher, and the start-up time to reach a steady state of operation was less than 1% of the time required for the conventional boiler. To close the gaps in the theoretical design, an experimental test should be performed.

Dynamic Simulation and Performance Analysis of Alkaline Water Electrolyzers for Renewable Energy-Powered Hydrogen Production

This paper presents a comprehensive study on the dynamic simulation modeling of alkaline water electrolyzers. Detailed experimental testing and characteristic analysis reveal that alkaline water electrolyzers have long startup times, rapid dynamic responses, and poor dynamic stability. These characteristics are critical for the development of accurate models and effective strategies. A dynamic simulation model was established in MATLAB R2022b and Simulink, enabling standalone simulation operation and module encapsulation. This model facilitates the construction of hydrogen production clusters and serves as a foundational tool for system strategy research. Simulations of rated current loading and unloading for four electrolyzers over 6 h showed significant differences in startup and operation. Key parameters such as cell voltage, maximum loadable power, hydrogen production efficiency, and energy consumption were analyzed. Temperature simulations indicated significant differences in thermal equilibrium points and cooling modes among the electrolyzers, as determined by structural design and cooling system efficiency. These findings highlight the need for efficiency improvements in high-current density electrolyzers. Overall, the model effectively represents commercial electrolyzer characteristics and offers a reliable tool for future research on control strategies for adapting hydrogen production systems to renewable energy power fluctuations, laying a solid foundation for the optimization of electrolyzer design and operation strategies.

Understanding Powder Behavior in Continuous Feeding: Powder Densification and Screw Layering

Background: Precise continuous feeding of active pharmaceutical ingredients (APIs) and excipients is crucial in a continuous powder-to-tablet manufacturing setup, as any inconsistency can affect the final tablet quality. Method: This study investigated the impact of various materials on the performance of a continuous twin-screw loss-in-weight (LIW) feeder. The materials tested included spray-dried lactose, anhydrous lactose, granulated lactose, microcrystalline cellulose (MCC), an MCC–lactose preblend (50%:50% w/w ratio), and a co-processed excipient (lactose–lactitol at a 95%:5% w/w ratio). The feeding performance of these excipients was systematically assessed, focusing on powder densification and screw layering within the LIW feeder. Results: The results demonstrated densification for the spray-dried lactose and preblend. Densification was more pronounced during the initial feeding cycles for spray-dried lactose, but decreased gradually over time. In contrast, the densification remained relatively constant throughout the feeding process for the preblend. Notably, minor screw layering was observed for both spray-dried lactose and anhydrous lactose, with the extent of this issue reducing over time for the spray-dried lactose. Interestingly, granulated lactose grades did not show screw layering, making them preferable for blending with APIs prone to severe screw layering. The LIW feeder control system successfully managed powder densification and minor screw layering, maintaining the mass flow rate at the set point for all investigated materials. Conclusions: These findings inform the selection of optimal excipients, appropriate tooling for LIW feeders, and the enhancement of control strategies to shorten startup times. By addressing these factors, the precision and reliability of continuous feeding processes can be improved.

Robust integral super-twisting controller for enhanced photovoltaic integration with hybrid battery and supercapacitor storage in DC microgrid

This study relates to the enhancement in performance of a Hybrid Energy Storage System (HESS) over a DC microgrid, particularly toward a fast-accurate controller of the DC bus voltage. Conventional control methods are particularly difficult to implement in order to reduce start-up time with minimum overshoot, resulting in a significant disturbance of the DC bus voltage. To circumvent these problems, we propose an innovative hybrid controller method that combines the Integral Super-Twisting Algorithm (ISTA) controller technique with adaptive gain in regulating DC bus voltage and current. The capacity of ISTA to greatly enhance the system's dynamic responsiveness, guaranteeing steady operation with effective output voltage control, is by far its greatest benefit. Comparative testing found that the conventional PI controller had a rise time of 0.0666 s, a settling time of 0.165 s, and a 17 % overshoot with a steady-state error of 0.02 %. The proposed ISTA controller had a rise time of 0.0016 s, a settling time of 0.0667 s, zero percentage overshoot, and a minimal steady-state error of only 0.0003 %. The above-mentioned issues mostly focused on better sharing power in HESS and a more effective controller of the DC bus voltage. Furthermore, we evaluate the practical feasibility of the suggested controller through hardware-in-the-loop testing. This research lays a foundation for advancing renewable energy integration in DC microgrid, offering a promising avenue for sustainable and resilient power systems. Finally, the effectiveness and applicability of the proposed ISTA controller for DC microgrid use are proven with Controller Hardware-in-the-Loop (C-HIL) simulations.