Thermal Working Conditions Research Articles

Structural electrochemistry of poly(3,4-ethylenedioxythiophene) and its applicability as simultaneous sensor of environmental surroundings: self-sensing electrical, thermal, and chemical working conditions

An extensive electrochemical investigation of PEDOT has been carried out with a particular focus on understanding the structural electrochemistry during its faradaic process, a topic that has not been previously explored in such detail.

Pre-expansion ejector absorption power cycle for ocean thermal energy conversion

Ocean thermal energy conversion technology has limited applications due to low energy utilization efficiency. This study proposes a pre-expansion ejector absorption power cycle for ocean thermal energy conversion. To enhance the turbine output, a pre-expansion separator heated by discharged warm seawater, along with an ejector, was introduced between the generator and absorber. A thermodynamic analysis strategy for the proposed cycle was conducted using MATLAB and Aspen Plus. A performance comparison between the pre-expansion ejector absorption cycle, traditional ejection cycle, and non-ejection two-stage absorption cycle under the ocean thermal energy working conditions was conducted. Parametric analysis was performed to investigate the cycle performance. In addition, the working range of the pre-expansion ejector was analyzed. The results show that the ejection-driven turbine output work effectively increased by 79.38% with the pre-expansion process, although the thermal efficiency slightly decreased. When the temperatures of warm and cold seawater were 26–32 °C and 4–7 °C, the lower and upper boundaries of the pre-expansion pressure are 560 kPa and 680 kPa, respectively. When the pre-expansion pressure varied from 600 to 660 kPa, the entrainment ratio and turbine outlet pressure drop were 0.541–1.018 and 344.9–348.9 kPa, respectively. The pre-expansion pressure and temperature of the cold source influence the cycle performance in a more complex manner because there exists a working range for the ejector, which is dominated by the pre-expansion pressure and influenced by the temperature of the heat and cold source.

Tropical deforestation accelerates local warming and loss of safe outdoor working hours

<h2>Summary</h2> Climate change has increased heat exposure in many parts of the tropics, negatively impacting outdoor worker productivity and health. Although it is known that tropical deforestation is associated with local warming, the extent to which this additional heat exposure affects people across the tropics is unknown. In this modeling study, we combine worker health guidelines with satellite, reanalysis, and population data to investigate how warming associated with recent deforestation (2003–2018) affects outdoor working conditions across low-latitude countries, and how future global climate change will magnify heat exposure for people in deforested areas. We find that the local warming from 15 years of deforestation was associated with losses in safe thermal working conditions for 2.8 million outdoor workers. We also show recent large-scale forest loss was associated with particularly large impacts on populations in locations such as the Brazilian states of Mato Grosso and Pará. Future global warming and additional forest loss will magnify these impacts.

Multi-parameter optimization and uncertainty analysis of multi-stage thermoelectric generator with temperature-dependent materials

It plays crucial importance for practical application to clarify the coupled nonlinear effects of multi-parameter uncertainty from temperature-dependent material properties, electrical and thermal working conditions, configuration, and geometry size on the performance of thermoelectric generator (TEG). This paper develops a comprehensive tool for optimal geometry design of the multi-stage TEG and identifies the synergistic impacts of the multi-parameter uncertainty on its optimal performance. A novel balanced impedance matching model is established for the first time to balance the optimal output power and conversion efficiency. The developed method is then efficiently integrated with optimization and uncertainty analysis methods. The designed three-stage TEG could achieve better performance due to the optimal working temperature range obtained for each stage, reaching an optimal efficiency of 18.06% under a temperature difference of 500 K. Compared to the single-stage TEG, a remarkable increase of 36.40% for output power and 34.47% for conversion efficiency are achieved for the convective heat transfer conditions, respectively. Uncertainty analysis has indicated that the uncertainty of Seebeck coefficients, leg length ratios, and working temperature conditions have significant impacts on the performance of multi-stage TEG. In contrast, the uncertainty of leg cross-section area ratios and external electrical loading have less effect. The coupled effects of multiple parameters with a total number up to 26 for three-stage TEG are studied in detail. Overall, this work provides a promising comprehensive tool for intensifying TEG performance and clarifying the nonlinear coupled effects of multi-parameter inherent uncertainty.

Heat Balance Determination Methods for Mining Areas in Underground Mines - A Review

Mine operation in presence of aerological hazards is a challenging issue for mine ventilation services. Increasing depth of exploitation and growing level of mechanization, due to the demand for intensification of extraction, makes it even more difficult regarding thermal hazard. As air temperature is a decisive factor shaping underground thermal working conditions it is extremely important to predict its value. This task determines the possibility of carrying out works in regions with the highest thermal hazard, where, due to the applicable regulations, it is necessary to use air conditioning to ensure appropriate working conditions for people. To determine the required cooling capacity for mining regions, it is crucial to identify the individual heat sources, as well as to define the amount of heat they generate. For this purpose, heat balances need to be set, taking into account the mentioned issues. The main goal of this paper is a presentation of methods available in the literature for determining the thermal balances of mining areas. The article also presents and characterizes the most important heat sources in underground mines. In addition, methods of determining heat fluxes from individual sources were indicated, as well as potential difficulties in the applicability of the above-mentioned methods for mining areas heat balances determination, in which, due to the current depth of exploitation, the thermal hazard is the most important natural hazard that determines the possibility of mining works.

Simulation and Multi-Objective Optimization of the Vehicle Thermal Management System of Electric Cars

The research on the vehicle thermal management (VTM) system is very important for ensuring the driving reliability of electric cars, however, currently there’re few research concerned about this topic, and the existing ones mostly focus on matching and optimizing parameters to improve the management of driving kinetic energy, and the heat dissipation and cooling performance of the cars; however, there isn’t a uniform standard for evaluating these performances, and the research on closed thermal energy management and control based on the evaluation results is pending. This paper studied the simulation and multi-objective optimization of the VTM system of electric cars, and proposed accurate methods and ideas for evaluating the heat dissipation efficiency of the engine cooling system, the cooling efficiency of the air conditioning system, and the thermal management performance of the VTM of electric cars. Based on the model predictive control (MPC) algorithm of vehicle motion control, this paper constructed temperature control optimization objective functions for electric cars under various thermal adaptation working conditions such as low-speed slope climbing, medium-speed gentle slope climbing, high-speed driving, and idling; and it designed several strategies for the coordinated control of the VTM system of electric cars. At last, this paper used test results to verify the effectiveness of the proposed strategies.

A new developed semi-full-scale approach to facilitate the CFD simulation of shell and tube heat exchangers

The full-scale CFD simulations may not be recommended in preliminary steps of STHEs’ design and sensitivity analyses because of heavy computations. This work benefits from the sequential geometry repetitions in STHEs and presents a new semi-full-scale approach, which alleviates the need for full-scale simulation of STHEs. This approach first isolates the smallest zone, say block, which is sequentially repeated in the STHE domain. Second, this block is carefully simulated considering various thermal and flow working conditions. Third, the data collected from these CFD simulations are used to generate the required thermal and flow correlations for the chosen block at various working conditions. Fourth, the proposed performances are suitably assembled to calculate/study/rate/design one STHE considering all proposed conditions. Generally, the results of semi-full-scale simulation approach show great agreement with both experimental data and analytical calculations. The developed approach can be readily used to facilitate the CFD simulation of large STHEs.

Numerical Simulation of Thermal Performance for the Reaction Tubes in a Miniaturized Methanol Synthesis Reactor

The reaction of methanol synthesis via hydrogen and carbon dioxide which has a broad application prospect in the energy field should be carried out in a reasonable temperature range. Thus, a comprehensive thermal analysis under different work conditions for the reaction tube which is the really reaction place in the miniaturized methanol synthesis reactor is of great significance to its temperature control and thermal design. In this paper, the thermal analysis models of reaction tube in methanol synthesis reactor via hydrogen and carbon dioxide are established, through numerical simulation, the thermal performance results which include the molar ratio of methanol synthesis and temperature distribution inside reaction tubes changing with the reaction tube diameter, inlet gas temperature, and space velocity are obtained. Based on the results, the change laws of the methanol synthesis molar ratio and temperature distribution change with the three parameters are summed, which provide a reference to the thermal design and working conditions setting for the miniaturized methanol synthesis reactor of hydrogen and carbon dioxide.

The research on the levelling process of thick slabs based on the electric motor parameters monitoring

For the leveling machines in conditions of a small batch production which is typical for manufacturing sheets of non-ferrous alloys, in particular, titanium, the rollers heating is very influential. In order to expand the technological possibilities of the main equipment in non-stationary thermal working conditions of rollers that is an actual new scientific problem the experimental study of the loading in the hot leveling of slabs made from hardly-deformed titanium alloys was carried out on the 9-roll leveling machine. To achieve this goal the methodology of the complex experimental study of the actual loading definition of the leveling machine drive was developed. The experimental study was carried out for alloys Ti6Al4V (Vt-6s) and PT-3V with the initial heating temperature of the rolled product from 750 to 850°C. The slab leveling process was logged for slabs with the thickness from 20 to 68 mm, the width from 985 to 1720 mm by the number of passes through the leveling machine from 2 to 8. The treatment and analysis of experimental data was conducted on the basis of which the summary of permissibility of assortment expansion of leveling slabs has been formulated.

A coupled electrical-thermal impedance matching model for design optimization of thermoelectric generator

Based on the definition of numerical-type equivalent thermoelectric parameters through developing a 1D self-consistent numerical method, this paper established a novel coupled electrical-thermal impedance matching (CETIM) model for prediction of the maximum output power and the highest conversion efficiency of thermoelectric generator (TEG). CETIM model could highlight the impacts of thermal working conditions and temperature-dependent properties on the TEG performance. It also clarifies the unreasonable assumption of the impedance matching conditions in the literature, which would lead to underestimation by 10.9% for the maximum output power prediction under a large thermal resistance between TEG and heat reservoirs. The analytical expressions of the output power and conversion efficiency obtained through CETIM model were used to derive the single- and two-parameter geometry optimization models, which could be quickly and accurately solved without needing the complicated optimization methods. It is found that the two-parameter optimization model could lead to a higher output power compared with that based on the single-parameter model, such as the observed improvement by 27.8% for the maximum output power and 21.6% for the corresponding conversion efficiency, respectively. Impacts of the coupled thermal-electrical working conditions and geometric sizes on the TEG performance were also investigated in detail. The results indicated that decreasing the thermal resistance between TEG and heat sink could acquire a larger output power and conversion efficiency compared with that through reducing the thermal resistance between TEG and heat source, such as increase by 15% for the output power and by 4% for the conversion efficiency, respectively. The present study provides an accurate and time-efficient comprehensive modeling tool for geometric optimization of TEG, which was implemented by MATLAB open source codes presented in supplementary materials.

Нормализация теплового режима протяженных тупиковых выработок при высоких температурах пород на основе шахтных передвижных кондиционеров

Thermal working conditions in the deep mines of Donbass are the main deterrent to the development of coal mining in the region. Mining is carried out at the lower technical boundaries at a depth of almost 1,400 m with a temperature of rocks of 47.5-50.0 °C. The air temperature in the working faces significantly exceeds the permissible safety standards. The most severe climatic conditions are formed in the faces of blind development workings, where the air temperature is 38-42 °С. It is due to the adopted coal seam mining systems, the large remoteness of the working faces from the main air supply openings, the difficulty in providing blind workings with a calculated amount of air due to the lack of local ventilation fans of the required range. To ensure thermodynamic safety mine n.a. A.F.Zasyadko we accepted the development of a draft of a central cooling system with ground-based absorption refrigerating machines with a total capacity of 9 MW with the implementation of the three types of generation principle (generation of refrigeration, electrical and thermal energy). However, the long terms of design and construction and installation work necessitated the use of mobile air conditioners in blind development faces. The use of such air conditioners does not require significant capital expenditures, and the terms of their commissioning do not exceed several weeks. The use of a mobile air conditioner of the KPSh type with a cooling capacity of 130 kW made it possible to completely normalize the thermal working conditions at the bottom of the blind workings 2200 m long, carried out at a depth of 1220-1377 m at a temperature of host rocks 43.4-47.5 °С. It became possible due to the closest placement of the air conditioner to the face in combination with the use of a high-pressure local ventilation fan and ducts, which ensured the air flow produced by the calculated amount of air. The use of the air conditioner did not allow to fully normalize the thermal conditions along the entire length of the blind face but reduced the urgency of the problem of normalizing the thermal regime and ensured the commissioning of the clearing face.

Research on susceptibility of 7075 aluminium alloy to extrusion welding

Abstract Extrusion welding of the 7xxx series aluminium alloys, especially these of high strengthened containing copper is still a barrier difficult to overcome. The main limitations are: poor weldability of the material which decreases a product quality, low permissible exit speed from the die decreasing the production efficiency, as well as severe thermal and mechanical working conditions for the die. The paper presents the results of weldability testing of the 7075 aluminium alloy, containing 5,59 % of Zn, 2,36 % of Mg and 1,49 % of Cu, with the use of an original authorial device. This device enables modelling the behavior of a material in the welding chamber of a porthole die. The tested material was submitted to non-conventional homogenization, what permitted to increase the solidus temperature of the alloy in comparison to the for cast material. The tests were conducted at 520°C and under the pressure of 200 MPa. The microstructure of the material was investigated both in the region of welds and in the basic material by using light microscope and scanning microscopy SEM. In addition, the chemical composition of the alloy was examined by using the ESD method. The microhardness test was performed perpendicularly to the surface of welding. The results indicate that the high-quality welds were not obtained. As it was stated, for the given temperature of welding, the welding factor limit value, i.e. relation of unit pressure to the yield strength (σn/k), was not reached.

Heat Strain and Hydration of Japanese Construction Workers during Work in Summer.

The aim was to ascertain hydration and heat strain of construction workers in Japan during the summer who are at the highest risk of heat-related disorders. The subjects were 23 construction workers, whose average age was 41, average weight was 69 kg, and average height was 170 cm. We measured thermal working conditions with a wet bulb globe temperature (WBGT) measurement instrument affixed to the helmet of each worker, at fixed points outdoors in the sun and indoors. Heat strain was evaluated for water intake, urine specific gravity (Usg), urine temperature (UT), heart rate (HR), and body weight during work. The average WBGT measured on the worker helmets over 3 consecutive days was 28.0 ± 0.7, 27.6 ± 0.8, and 27.6 ± 1.1°C. The average water intake was 2.6 l during a work shift. The average Usg, UT, and % HR reserve were the highest in the first half of afternoon work. Seventy-eight percent of the subjects exceeded at least one of the ACGIH TLV physiological guidelines for heat strain in terms of HR and weight loss or a clinically dehydrated level of Usg. Heat strain was the highest in the first half of afternoon work. The number of dehydrated workers increased during this shift because of insufficient water intake. Adequate hydration is required to decrease the risk of heat-related disorders among construction workers in the summer.

Research on operation mode of abrasive grain during grinding

The processing of materials by cutting with an abrasive tool is carried out by means of thousands of grains bonded together as a single whole. The quality of the abrasive tool is defined by cutting properties of abrasive grains and depends on features of spreading the temperature field in time and in the abrasive grain volume. Grains are exposed to heating and cooling during work. It leads to undesired effects such as a decrease of durability of grain retention in the binder, hardness, intensification of diffusion and oxidation processes between the binder and the grain, the occurrence of considerable temperature stresses in the grain itself. The obtained equation which allows calculation of temperature field of grain for one rotation of grinding wheel shows that the temperature of the wheel depends on grinding modes and thermophysical properties of abrasive material. Thus, as the time of contact of grain with processed material increases, the temperature in the cutting area rises. As thermophysical properties increase, the temperature in cutting area decreases. Thermal working conditions are determined to be different from each other depending on contact time of the grain and the material. For example, in case of creep-feed grinding, the peak value of temperature is higher than during multistep grinding; the depth of expansion is greater. While the speed of the thermal process in creep-feed grinding is 2-3 times lower than in multistep grinding, the gradient reduces 3-4 times. The analysis of machining methods shows that creep-feed grinding ensures greater depth of grain heating, a smaller heating rate and a reduced velocity gradient. It causes a decrease of probable allotropic modifications and prevents from occurring of heat strokes - cracking of grains due to high temperature falls. Consequently, it is necessary to employ creep-feed grinding to increase the efficiency of abrasive tool employing. Three operation modes of grinding wheel including blunting, full self-sharpening, emergency wear and tear are determined as the result of the research on evaluation of cutting ability of grinding wheels. Recommendations for working capacity of grinding wheels in each operation mode and with a transition from one mode to another are given. As a result of the research, different dependencies were determined. They include dependencies, governing the extent of influence of granularity, difference in height and concentration of grains, geometry parameters of the detail to be machined and the grinding wheel on machining modes and the thickness of the layer cutoff by one grain. They have an influence on the grinding process.

The cooperative actuation of multistep electrochemical molecular machines senses the working temperature: voltammetric study

Electrochemical reactions of conducting polymers drive conformational movements of the constitutive polymeric chains (molecular motors or molecular machines), generating or destroying the required free volume to exchange balancing counterions and solvent. The influence of the temperature on the reversible oxidation/reduction of a polypyrrole film in NaCl aqueous solutions was studied here by cyclic voltammetry. Under constant potential limits, constant scan rate and constant electrolyte concentration the extension of the reversible reaction, defined by the coulovoltammetric charge, increases for rising experimental temperatures. That means that the reaction charge is a function of, and senses, the working temperature. Based on the empirical chemical kinetics of the reactions a theoretical description was attained resulting in a sensing equation. The attained results could explain how muscles from cold-blooded animals work and are aware of the thermal working conditions.

Quantitative Characterization of Structural and Mechanical Properties of Boron Nitride Nanotubes in High Temperature Environments

The structural stability and mechanical integrity of boron nitride nanotubes (BNNTs) in high temperature environments are of importance in pursuit of their applications that are involved with extreme thermal processing and/or working conditions, but remain not well understood. In this paper, we perform an extensive study of the impacts of high temperature exposure on the structural and mechanical properties of BNNTs with a full structural size spectrum from nano- to micro- to macro-scale by using a variety of in situ and ex situ material characterization techniques. Atomic force microscopy (AFM) and high resolution transmission electron microscopy measurements reveal that the structures of individual BNNTs can survive at up to 850 °C in air and capture the signs of their structural degradation at 900 °C or above. In situ Raman spectroscopy measurements reveal that the BN bonds in BNNT micro-fibrils undergo substantial softening at elevated temperatures of up to 900 °C. The AFM-based nanomechanical compression measurements demonstrate that the mechanical integrity of individual BNNTs remain intact after being thermally baked at up to 850 °C in air. The studies reveal that BNNTs are structurally and mechanically stable materials in high temperature environments, which enables their usages in high temperature applications.

Physical modelling of tire wear for the analysis of the influence of thermal and frictional effects on vehicle performance

The tire and vehicle setup definition, able to optimise grip performance and thermal working conditions, can make the real difference as for motorsport racing teams, used to deal with relevant wear and degradation phenomena, as for tire makers, requesting for design solutions aimed to obtain enduring and stable tread characteristics, as finally for the development of safety systems, conceived in order to maximise road friction, both for worn and unworn tires. The activity discussed in the paper deals with the analysis of the effects that tire wear induces in vehicle performance, in particular as concerns the consequences that tread removal has on thermal and frictional tire behaviour. The physical modelling of complex tire–road interaction phenomena and the employment of specific simulation tools developed by the Vehicle Dynamics UniNa research group allow to predict the tire temperature local distribution by means of TRT model and the adhesive and hysteretic components of friction, thanks to GrETA model. The cooperation between the cited instruments enables the user to study the modifications that a reduced tread thickness, and consequently a decreased SEL (Strain Energy Loss) and dissipative tread volume, cause on the overall vehicle dynamic performance.

Thermal Power Of The TS-300B Refrigerator in the Aspects of Statistical Research / Moc Cieplna Chłodziarki TS-300B W Aspekcie Badań Statystycznych

Abstract The article discusses the improvement of thermal working conditions in underground mine workings, using local refrigeration systems. It considers the efficiency of air cooling with direct action air compression refrigerator of the TS-300B type. As a result of a failure to meet the required operating conditions of the aforementioned air cooling system, frequently there are discrepancies between the predicted (and thus the expected) effects of its work and the reality. Therefore, to improve the operating efficiency of this system, in terms of effective use of the evaporator cooling capacity, quality criteria were developed, which are easy in practical application. They were obtained in the form of statistical models, describing the effect of independent variables, i.e. the parameters of the inlet air to the evaporator (temperature, humidity and volumetric flow rate), as well as the parameters of the water cooling the condenser (temperature and volumetric flow rate), on the thermal power of air cooler, treated as the dependent variable. Statistical equations describing the performance of the analyzed air cooling system were determined, based on the linear and nonlinear multiple regression. The obtained functions were modified by changing the values of the coefficients in the case of linear regression, and of the coefficients and exponents in the case of non-linear regression, with the independent variables. As a result, functions were obtained, which were more convenient in practical applications. Using classical statistics methods, the quality of fitting the regression function to the experimental data was evaluated. Also, the values of the evaporator thermal power of the refrigerator, which were obtained on the basis of the measured air parameters, were compared with the calculated ones, by using the obtained regression functions. These statistical models were built on the basis of the results of measurements in different operating conditions of the TS-300B refrigerator, both on the test stand in the manufacturer’s laboratory and in the workings of underground mines. The evaluation of the measurement data distributions, as well as an analysis of the basic descriptive statistics of the mentioned variables were carried out, determining their measures of central tendency, location, dispersion and asymmetry.

Design of 40-W AlGaN/GaN MMIC High Power Amplifiers for $C$-Band SAR Applications

Two C-band monolithic high power amplifiers (HPAs) have been designed and implemented exploiting a 0.25-μm AlGaN/GaN HEMT process on an SiC substrate. The circuits have been designed for use in transmit/recevie modules of satellite synthetic aperture radar antennas for Earth observation. The design was accurately focused on the HEMTs' electrical and thermal working conditions in order to guarantee the reliable operation required by space applications. The HPAs operate in pulsed conditions with typical pulsewidth of 50 μs and 10% duty cycle: in that regime, the circuits deliver about 40 W with more than 21-dB associated gain and 40% to 45% power-added efficiency in the 5-5.8-GHz band. The achieved performance clearly demonstrates the very high potentiality of this technology for the replacement of GaAs-based HPAs in new generations of this type of systems.

On the Transition Thermal Discomfort to Heat Stress as a Function of the PMV Value

ISO 15265 Standard - Ergonomics of the thermal environment - Risk assessment strategy for the prevention of stress or discomfort in thermal working conditions - can be considered as a key document for helping responsible for the health protection and prevention of working situations. According to the SOBANE strategy, this standard provides a three-step protocol aimed to the prevention, elimination or reduction of risks affecting the workplaces. Although both methods and procedures suggested by ISO 15265 appear very clear, this standard could bring in confusion both beginners and not specialists in occupational health concerning Predicted Mean Vote (PMV) threshold values consistent with comfort - hot discomfort and the discomfort - hot stress transitions. In this work such matter has been extensively discussed showing a certain difficulty in the definition of an unambiguous PMV threshold value for each working situation in any microclimate.