Practical Working Conditions Research Articles

Is C3N4 Chemically Stable toward Reactive Oxygen Species in Sunlight-Driven Water Treatment?

Reactive oxygen species (ROS) are key oxidants for the degradation of organic pollutants in sunlight-driven photocatalytic water treatment, but their interaction with the photocatalyst is easily ignored and, hence, is comparatively poorly understood. Here we show that graphitic carbon nitride (C3N4, a famous visible-light-responsive photocatalyst) is chemically stable toward ozone and superoxide radical; in contrast, hydroxyl radical (•OH) can tear the heptazine unit directly from C3N4 to form cyameluric acid and further release nitrates into the aqueous environment. The ratios of released nitrogen from nanosheet-structured C3N4 and bulk C3N4 that finally exists in the form of NO3- reach 9.5 and 6.8 mol % in initially ultrapure water, respectively, after 10 h treatment by solar photocatalytic ozonation, which can rapidly generate abundant •OH to attack C3N4. On a positive note, in the presence of organic pollutants which compete against C3N4 for •OH, the C3N4 decomposition has been completely or partially blocked; therefore, the stability of C3N4 under practical working conditions has been obviously preserved. This work supplements the missing knowledge of the chemical instability of C3N4 toward •OH and calls for attention to the potential deactivation and secondary pollution of catalysts in •OH-involved water treatment processes.

Enhanced Performance and Stability of Perovskite Solar Cells Using NH4I Interfacial Modifier.

Despite organic-inorganic hybrid perovskite solar cells have rapid advances in power conversion efficiency in recent years, the serious instability of the device under practical working conditions is the current main challenge for commercialization. In this study, we have successfully inserted NH4I as an interfacial modifier between the TiO2 electron transport layer and perovskite layer. The result shows that it can significantly improve the quality of the perovskite films and electron extraction efficiency between the perovskite and electron transport layer. The devices with NH4I are obtained an improved power conversion efficiency of 18.31% under AM 1.5G illumination (100 mW cm-2). More importantly, the humidity and UV light stability of the devices are greatly improved after adding NH4I layer. The uncoated devices only decrease by less than 15% of its original efficiency during 700-h stability tests in a humidity chamber (with a relative humidity of 80%) and the efficiency almost maintains 70% of its initial value over 20 h under UV light stress tests. This work provides a potential way by interfacial modification to significantly improve photovoltaic performance and stability of perovskite solar cells.

Thermal effects on the structural response of planar serpentine interconnects

Serpentine-shaped interconnects are widely employed to achieve high level of stretchability in stretchable electronic devices. In the current work, an analytical model for the mechanical response of planar serpentine interconnects with thermal effect is developed and verified by finite element method (FEM). Specifically, the closed-formed expressions to compliance and stretchability are derived based on curved beam theory and energy method. The numerical results indicate that a considerable error (e.g., >10% relatively) could be induced for many representative configurations using the model with thermal loads absent. The present work provides more accurate predictions for the structural response of serpentine interconnects in practical working conditions, which help in optimal design in future applications.

ERGONOMICS EDUCATION IN ORTHOPEDIC SURGERY

The motivation of research was poor quality of working conditions in orthopedic practice which results from lack of use of ergonomics principles by medical staff. Hence, the research objective was to indicate the most important determinants for creating high-quality working conditions in operating room, particularly when performing orthopedic procedures. As methodology, the observations, video-registrations and interviews with orthopedic professionals were conducted. Based on the research material, the ergonomic and workflow assessments were examined. The research outcomes confirmed a problem of low quality working conditions during orthopedic surgeries resulted from insufficient knowledge and awareness of orthopedists regarding ergonomics. There was diagnosed a need for creation of a specialized guide for orthopedists and medical decision makers of how to improve working conditions in operating room on the background of the human and technical perspectives. As a result there was proposed the comprehensive online course on ergonomics for orthopedists and all medical staff who are interested in and are responsible for safety and comfortable conditions at their workplace. Hence the future scope is formulated as the monitoring and evaluation of working conditions after implementing ergonomics course within medical staff.

An improved model for remaining useful life prediction on capacity degradation and regeneration of lithium-ion battery

The regeneration phenomena of the lithium-ion battery are widely existed in reality but rarely studied due to the gap between experiment conditions and practical working conditions. In this paper, the capacity regeneration phenomena are considered during the degradation process of batteries. An improved empirical model incorporating both rest time and discharge cycles for remaining useful life (RUL) prediction is proposed. The degradation process and regeneration process have been described by different components and integrated to formulate the whole model. The dual estimation framework is employed to decouple the states and parameters during the degradation and regeneration process. The datasets from NASA Prognostics Center of Excellence (PCoE) have been adopted for model validation. The proposed model is compared with other empirical model and also different estimation methods. The results are satisfactory, and demonstrate the capability of the proposed model for the RUL prediction of Lithium-ion battery.

Accurate approach to the temperature effect on state of charge estimation in the LiFePO4 battery under dynamic load operation

This paper presents a simple approach to estimate the state of charge of the LiFePO4 batteries in electric vehicles under dynamic loads and variable temperature, which are inevitable during practical working conditions. This approach employs a highly adaptive estimation algorithm based on the recursive least-squares method and an original simple model of the open circuit voltage to the state of charge over a wide range of temperature. The modeling and the estimation in this approach are based on a new term for the state of charge, which is defined based on experimental findings to take into account the battery recovery capacity due to temperature variations. The proposed approach is validated through Urban Dynamometer Driving Schedule experiments including harsh temperature conditions, which have been mostly overlooked in previous research. The obtained results show that this approach maintains an accurate state of charge estimation, with an error of less than 5.2% under such conditions. The accuracy and the simplicity of the proposed algorithm are crucial for a feasible battery management system to be used in electric vehicles.

Boundary for aviation bearing accelerated life test based on quasi-dynamic analysis

Full-scale bearing accelerated life test experiment is an effective way to achieve the demand of modern aero-engine bearing. However, its premise is how to determine the boundary reasonably. In this study, the factors leading bearing abnormal failure are presented by the fault tree analysis. Then, the boundary conditions of aero-engine bearing are analysed by the quasi-dynamic method. The relationship between status parameters associated with failure modes (such as lubricating oil film thickness, etc.) and working parameters (such as rotation speed, external load) is discussed. It revealed the interrelation between practical working condition and status parameters in graphical form. The analysis provided theoretical bases for the choice of working parameters and the ultimate failure judgment in the accelerated life test.

Magnetically Controlled Saturable Reactor Core Vibration Under Practical Working Conditions

In order to seek new vibration reduction method for magnetically controlled saturable reactors (MCSRs), this paper studies the stress characteristic which is the inherent reason of vibration and noise. Under the practical working condition, dc and ac excitations make iron cores work in a magnetic saturation state. Meanwhile, the stress in reactor cores always exists and influences on magnetic properties of the core material. Because the core material shows different magnetization and magnetostrictive properties under dc bias and stress, a database of magnetization and magnetostrictive curves of silicon steel under different tensile stresses with different dc bias excitations is tested. Based on the measured constitutive relations, an electromagneto-mechanical two-way coupled numerical model for MCSRs is presented. Vibrations considering magnetostrictive effect, electromagnetic force effect, and the combination of them are calculated to compare the influence of the two forces on MCSR vibration. From the computation results, it can be seen that the total vibration stress is not a simple superposition of electromagnetic stress and magnetostrictive stress. Finally, vibration stress of an MCSR prototype under working conditions is tested to prove the validity of the proposed model.

Experimental investigations and an updated correlation of flow boiling heat transfer coefficients for ammonia/lithium nitrate mixture in horizontal tubes

In this work, experiments have been performed to investigate the flow boiling heat transfer coefficients (HTC) of ammonia/lithium nitrate mixture in horizontal smooth tubes with different internal diameters (4mm, 6mm). According to the practical working conditions of absorption refrigeration system, the ammonia concentration for the tested ammonia/lithium nitrate mixture was selected as 45.0 wt%, and the boiling temperature of tests were in the range of 78–90°C. The effects of boiling temperature, heat flux, mass flux and tube size on the flow boiling HTCs were investigated in this article. Results show that higher heat and mass fluxes as well as heat transfer tube with larger diameter tend to exert positive influence on flow boiling HTCs of the present study cases. Based on more than 600 groups of experimental data, a new correlation was proposed to predict the effects of mass flux, heat flux, and tube size on flow boiling HTCs for NH3/LiNO3 mixture under investigated conditions, with a mean deviation less than ±10%. The new correlation will be of great significance to the design and optimization of generators in the practical absorption refrigeration units using ammonia/lithium nitrate mixture.

Experimental investigation on potential of a concentrated photovoltaic-thermoelectric system with phase change materials

Since the influence of temperature on the conversion efficiencies of photovoltaic (PV) cells and thermoelectric (TE) generators are totally different and opposite, the system operating temperature becomes a key parameter which significantly determines the utilization efficiency of the common PV-TE system on solar energy. In order to make the PV-TE system obtain higher energy utilization efficiency, phase change material (PCM) is incorporated to construct a novel PV-PCM-TE hybrid system to maintain the system operating at the ideal working temperature. The performance of such a novel hybrid system is experimentally studied corresponding to a number of practical working conditions. The temperature, efficiency, and output power of the hybrid system are compared with those of the pure PV system under the same circumstance. The effects of the optical concentrations ratio and cooling approaches on the conversion efficiency of the hybrid system are experimentally investigated. The whole conversion efficiencies of the hybrid system incorporated with TE generators with different values of dimensionless thermoelectric coefficient (ZT) are discussed. The present work reveals that such a hybrid system possesses a promising potential on the full-spectrum utilization of solar energy.

Flow boiling heat transfer characteristics and pressure drop of ammonia-lithium nitrate solution in a smooth horizontal tube

This paper presents experimental results of flow boiling heat transfer coefficient of ammonia/lithium nitrate solution in a smooth horizontal tube with diameter of 10mm. The test conditions are selected based on practical working conditions of absorption refrigeration system with ammonia/lithium nitrate solution. The ammonia concentration of the solution at the inlet of test section is around 45.5wt%. The mass flow rate and boiling temperature of the solution are in the ranges of 20–55kg/h and 76.7–93.2°C, respectively. The effects of the heat flux, mass flux and exit vapor quality has been investigated. The maximum flow boiling heat transfer coefficient reaches 2100W·m-2K-1. Results show that heat fluxes have significant influence on boiling heat transfer coefficients (HTCs). Nucleate boiling is found to be predominant during the tests. The experimental results are also compared with the available flow boiling heat transfer coefficients of NH3/LiNO3 solution and predicting correlations in literature. Kandlikar’s correlation is appropriate to characterize the experimental boiling heat transfer coefficients with a mean deviation of ±12.56%. Pressure drops in the solution side are also measured under different working conditions. The results of the present study will be of great significance to the design and optimization of generators in the absorption refrigeration units using ammonia/lithium nitrate solution.

A wireless visualization monitoring, evaluation system for commercial photovoltaic modules solely in MATLAB/Simulink environment

This paper proposes a wireless photovoltaic (PV) visualization monitoring, evaluation, and fault detection system based on the STM32F4DISCOVERY board with Bluetooth data transmission in the MATLAB/Simulink platform. All of the irradiance, the cell temperature, voltage, and current of PV devices are acquired through the microcontroller-based DAQ board. These measurements data are transferred to a host computer by both Bluetooth slave module and Bluetooth master one built in a laptop. These measurement data are visually displayed in the form of dashboard in the MATLAB/Simulink environment and are simultaneously input to PV model for theoretical simulation. The functions of evaluation and fault detection for PV modules under practical working conditions are conducted and displayed at the same software platform.The proposed system has been proved with sufficient accuracy and confidence in the functions of visualization monitoring, evaluation, and fault detection. As compared with the well-developed ones, the proposed system has the advantages such as: reduce both cable and hardware configuration and integrate the all visualization monitoring, evaluation, and fault detection solely in the MATLAB/Simulink environment.

A theoretical investigation of the effects of the low-temperature reforming products on the combustion of n-heptane in an HCCI engine and a constant volume vessel

A new concept of the flexible cylinder engine for the combustion in the engine cylinders is developed to optimize the combustion process, according to the practical working conditions. By the new concept, the fuel is reformed in the flexible cylinder, mixed with the same fresh fuel, and then introduced into the normal cylinders to finish the normal combustion process. The reformed fuel may alter the combustion reaction pathways of the fresh fuel and hence may improve the combustion in the engine cylinders potentially. In this work, the effects of the reformed fuel on the combustion of the fresh fuel were investigated by using n-heptane as the model fuel to demonstrate this new concept theoretically. It was found that the reformed fuel may decrease the ignition delay time of the fresh fuel by about 6 TDCA (top dead crank angle) at a typical engine condition. Among the reformed species, ketohydroperoxides and hydrogen peroxide are the key species to decrease the ignition delay time besides the radicals. The reformed fuel may increase the laminar flame speed of the fresh fuel, with H2 and CO being the key species. Finally, the reformed fuel may also decrease the harmful emissions, such as the unburned hydrocarbons, including acetylene, ethylene, propyne, propylene, 1,3-butadiene, and the partially oxidized species, including formaldehyde, ketone, acetaldehyde, etc. These simulation results indicate that the new concept of the flexible cylinder engine is a potential clean combustion strategy for the engines.

Experimental study on the anti-jacking-up performance of a screw pile for photovoltaic stents in a seasonal frozen region

The soils in seasonal frozen regions freeze and thaw frequently, causing severe frost heave and thaw settlement problems, which bring challenges to piles of photovoltaic stents. In this paper, laboratory tests are conducted with different types of screw piles under freezing conditions, with also using smooth piles for contrast. The aim is to simulate the freezing process of screw piles according to practical working conditions based on the similarity principle. Internal thermal resistance is ignored. The change laws of temperature, displacement, as well as the influence factors of types of screw piles are analyzed. The results indicate that: with a freezing depth of 30 cm, which is half of the pile length, large-double-bladed screw piles perform the best in antijacking-up, while all-bladed screw piles perform the worst, independent of the types of soil samples tested. The fitting relationship between jacking-up displacement and freezing depth is also proposed for each type of pile. Results obtained can provide an important reference to site construction in seasonal frozen regions.

Acid Mist Cyclone Separation Experiment on the Hydrochloric Acid Regeneration System of a Cold Rolling Steel Plant

In the hydrochloric acid regeneration system of a cold rolling steel plant, the large amounts of hydrochloric acid droplets and iron oxide dust in the flue gas at the absorption column outlet cause serious air pollution. To reduce pollution, a high-precision cyclone separator is utilized to recycle hydrogen chloride acid mist and iron oxide dust simultaneously. The key factors of the high-precision cyclone separator, such as pressure drop, separation efficiency, and fluid density, are investigated to determine the optimal operation parameters under practical working conditions. Results show that the separation efficiency of the cyclone separator increases rapidly initially and then decreases gradually with an increase in pressure drop. Pressure drop and separation efficiency increase slightly with an increase in inlet fluid concentration. When the velocities of the inlet gas are 4.8-10 m s^(-1) and 5.0-9.2 m s^(-1), the separation efficiencies of hydrochloric acid and iron oxide are both higher than 80%. When the velocity of the inlet gas is 6.67 m s^(-1), the separation efficiencies of hydrochloric acid and iron oxide reach the highest values of 92% and 89%, respectively.

A new kind of transparent and self-cleaning film for solar cells.

A kind of one step and in situ etching method is developed to fabricate a highly optically transparent and flexible self-cleaning superhydrophobic film (SSF). This SSF exhibits a very rough surface morphology with hierarchical structure, which makes it have a contact angle of 154.6° and a sliding angle of smaller than 1°. And the SSF can also be self-cleaned in the wind. The SSF hierarchical structure scatters the incident light, but it almost doesn't attenuate the light. So the SSF has antireflection properties and a high light transmittance of 94%. The excellent self-cleaning property, high light transmittance and antireflection property mean that the SSF greatly enhances the performance of solar cells in practical working conditions. The solar cell's efficiency maintains at 95.8% of its initial value after covering with the SSF, which is about 1.7 times higher than that of the solar cell covered with dust, as in practical conditions.

Heat analysis of ball bearing under nonuniform preload based on five degrees of freedom quasi-static model

Bearing preload has a great impact on the service performance of high-speed spindle, such as the temperature rise and stiffness. Because of the flatness error of spacer, the axial parallelism error of the spindle, the nonuniform heat distribution of ball bearing and the external loads, the outer ring of the bearing is often subjected to nonuniform distributed loads, which will result in the misalignment between outer ring and spindle. In such conditions, traditional uniform preload method may not meet the requirements for bearing temperature rise and spindle rotation accuracy. In this paper, a nonuniform preload is presented which not only includes the preload magnitude in traditional way, but also involves the preload distribution nonuniformly. Firstly, an equivalent transformation for nonuniform preload is built to simplify the nonuniform preload acting on the outer ring. Then based on the Hertz contact theory and ball bearing geometry theory, a five degrees of freedom quasi-static model of ball bearing under nonuniform preload is established. On the basis of this model, internal load and other contact parameters in bearing are calculated and the heat mechanism of ball bearing is analyzed. Finally, according to the heat generation model under nonuniform preload which include both preload magnitude and distribution, effects of both uniform and nonuniform preload on bearing heat and its distribution are investigated and compared, and the contact forces in bearing are then analyzed. The results show that compared with uniform preload, proper nonuniform preload could effectively improve the contact status between balls and rings, decrease the heat generation rate, and reduce the excessive local heat in ball bearing under practical working conditions.

Contact Stress Analysis and Fatigue Life Prediction of a Turbine Fan Disc

AbstractFan discs are critical components of an aero engine. In this paper, contact stress and life prediction of a turbine fan disc were investigated. A simplified pin/disc model was conducted to simulate the practical working condition under applied loads using finite element (FE) analysis. This study is devoted to examining the effects of interface condition of pin/disc such as gap and coefficient upon the maximum stress. The FE model indicated that the maximum stress occurs at the top right corner in the second pin hole, and larger gap or friction coefficient has a significant effect on the maximum stress. In addition, FE analysis without considering friction is also conducted. The results show that the dangerous point is similar to the result which considers friction and the stress state is relatively larger than that of considering friction. Finally, based on FE analysis result, life prediction for the fan disc is conducted to combine the material

Development and verification of compact transient heat exchanger models using transient effectiveness methodologies

Heat exchangers are important units in HVAC systems, such as the cooling systems used in data centers. The effectiveness of the heat exchangers significantly influences the thermal performance and energy efficiency of the cooling systems. Normally, the heat exchangers are designed for steady state operations. However, under practical working conditions, the events of changing operational conditions and working load may influence temperature and mass flow rate variations to the heat exchangers. For instance, typically data centers are dynamically operated due to the time and temperature dependent workload allocations. Therefore, the heat exchangers used in a data center operate under transient scenarios. Therefore, it is important to characterize the dynamic response of the heat exchanger. In this study, two compact transient modeling methods for heat exchangers are proposed. A transient effectiveness concept and model are used to develop transient modeling methodologies. Also, Computational Fluid Dynamic (CFD) heat exchanger models are developed using the compact transient methodologies. Verifications of the CFD compact models are carried out by comparing them with physics based thermal dynamic heat exchanger models and experimental measurements. The results show good agreement. Different heat exchanger configurations, including counter flow and cross flow heat exchangers are modeled and verified. The transient response of the heat exchanger under temperature variation, mass flow rate variation, and multiple variation combination scenarios are performed using the CFD compact models.

Dynamic response and control analysis of cross flow heat exchangers under variable temperature and flow rate conditions

Abstract Crossflow heat exchangers are important facilities that are widely used in HAVC systems, such as data center cooling systems. The dynamic performance of the heat exchanger may have a significant effect on the performance of cooling systems. Characterizing and modeling the dynamic behaviors of cross flow heat exchangers in practical working conditions is important for both thermal management and control system design. Multiple variable input scenarios are common occurrences to the heat exchangers under practical operating conditions. In this paper, an established thermal dynamic model is solved numerically to predict the transient response of an unmixed–unmixed cross-flow heat exchanger, of the type that is widely used in data center cooling equipment. Detailed analyses of the transient response due to the time dependent fluid inlet temperature and flow rate are conducted. Cases for two fluid mass flow rate variation combinations, hot fluid inlet temperature and hot and cold fluid mass flow rate variation combinations are modeled and analyzed. Some of the most meaningful transient conditions such as step and linear ramp functions are used for the flow rate variation type for the hot and cold fluids, and step, ramp and exponential functions are applied to the fluid temperature at the entrance. Some of the modeling scenarios are based on control strategy design. The transient response results are also used to analyze some actual situations which are commonly seen for the cross flow heat exchangers used in data centers. The study and corresponding analysis provide fundamental insights into a cross flow heat exchanger which can be used to improve cooling unit performance and aid in the design of thermal control systems.