Fast Temperature Rise Research Articles

Design and application of high-precision calibration blackbody for space optical remote sensing sensor

Radiation calibration is a crucial step in producing high-quality images for spaceborne infrared cameras. Blackbody radiation sources, as the standard equipment for infrared thermometers, play an increasingly important role in radiation calibration. But as the camera aperture increases, blackbody faces challenges such as poor temperature uniformity, slow heating and cooling rates, large mass, and large volume. This article proposes a design scheme for spaceborne calibration blackbody based on a combination of rope pull fixation and limit block positioning. The temperature uniformity, temperature stability, temperature rise and fall rate, thermal stress characteristics, and anti-emission vibration characteristics of the blackbody under this scheme are analyzed and optimized in detail. The analysis results show that the conduction thermal resistance between the blackbody and the environment is nearly two orders of magnitude higher than that of the conventional scheme. The blackbody has excellent temperature uniformity, temperature stability, wide calibration temperature range, light weight, small volume, and fast temperature rise and fall speed. The blackbody scheme with a thickness of only 1.5 mm was implemented and applied on orbit.

Fast identification of machine tool spindle system temperature rise based on multi-model fusion and improved D-S evidence theory

Thermal equilibrium test is the key means to obtain the thermal characteristics of machine tools. In order to shorten the test period and reduce the research and development cost, a novel fast temperature rise identification method for machine tool spindle systems is proposed. The existing prediction identification methods ignore the limitation of the single prediction model, leading to large error fluctuations in different environments. In this study, various intelligent prediction models are combined with the improved D-S evidence theory to improve the accuracy and robustness of the prediction. Firstly, based on the virtual prediction, the evidence identification framework is established through the multiple evaluations of the data information in the evidence segment. Then, the weight allocation of each basic prediction model is carried out by the evidence combination theory. In this process, the evidence identification framework is reconstructed according to the improved strategy to avoid the high conflict problem in classical evidence theory. Finally, the fusion prediction of multiple models can be realized. The VM-850L machining center was selected as the research object for the thermal equilibrium test to evaluate the proposed method. The results show that the proposed multi-model fusion prediction method can accurately predict the temperature rise of selected points in a short time. Moreover, the prediction accuracy is significantly improved compared with the traditional single model. The proposed method has good universality and is expected to be popularized and applied more widely.

Relation between hydrophilic/hydrophobic characteristics of sludge extracellular polymeric substances and sludge moisture-holding capacity in hot-pressing drying

Sludge poses a serious threat to the environmental health. Hot-pressing drying has been proven efficient in sludge treatment because of the reduced thermal contact resistance, rapid increase in sludge temperature, and high drying rate. Sludge extracellular polymeric substances (EPS) significantly influence moisture transfer. However, whether in hot-pressing or traditional thermal drying, the effect of EPS on sludge moisture-holding capacity is rarely reported. Thereby, this study investigated the relationship between hydrophilic/hydrophobic characteristics of EPS and sludge moisture-holding capacity at various drying time and mechanical compression using XAD resin fractionation. Thermodynamic analysis indicated that sludge moisture desorption isotherms, net isosteric heat of desorption, and differential entropy presented a downward trend with the increase in drying time and mechanical compression, suggesting reduced sludge moisture-holding capacity. EPS analysis showed that at the same drying time, applying 25 kPa mechanical compression increased sludge temperature by 16 % and protein content by 13.8 %. At the same sludge temperature, protein content rose by 7.3 % compared to the drying without mechanical compression. It was concluded that the fast rise in sludge temperature and the mechanical extrusion facilitated the destruction of sludge microbial flocs, accelerating the release of intracellular and EPS-bound moisture and contributing to the decrease in moisture-holding capacity. Besides, tryptophan protein-like substances were the major source of hydrophilic/hydrophobic organic matter, compared to polysaccharide and humic acid-like substances. The gradually reduced sludge moisture-holding capacity was divided into three stages. Below 67 °C, the moisture desorption was dominated by the release of intracellular moisture. Below 85 °C, the increase in protein and the enhanced exposure of hydrophobic functional groups in protein improved the hydrophobicity of EPS. Above 85 °C, protein consumption due to thermal decomposition and browning reaction facilitated the desorption of EPS-bound moisture. Hence, this study provided novel insights into the mechanism of sludge drying.

Variation Of Air Speed On Energy-Saving Stoves With Waste Coconut Oil Frying Getas

Waste coconut oil (WCO) from brittle draining can be used as fuel for multifuel stoves and can be used to boil water. Combustion air velocity is one of the factors that affect the combustion process. Air velocity in a multi-fuel stove with WCO fuel greatly affects the character of the fire produced. The research was conducted with the aim of obtaining the character of the fire and the temperature of the water boiling process at variations in air speed and the length of the WCO combustion flame. This research process was carried out with a multifeul stove by measuring the temperature and boiling time of 0.5 liters of water using variations in air velocity of 10 m / s, 12 m / s and 14 m / s by using 20 ml of WCO for each test. The results at a speed of 14 m / s tejadi the highest flame this occurs high air flow velocity causes a faster temperature rise. The greater the air supplied will accelerate the oxidation process, so that the fuel decomposition process will be faster.

Spatiotemporal changes in Universal Thermal Climate Index in the Middle East and North Africa

A fast temperature rise has made the Middle East and North Africa (MENA) region a global hotspot of extreme heat events. Previous studies conducted in the region to evaluate extreme heat based on temperature were inadequate for assessing heat based on human thermal impacts. The present study employed the Universal Thermal Climate Index (UTCI). This index evaluates the changes in heat related to human thermal stress in MENA. This analysis employed the ERA5-HEAT dataset, derived from the Copernicus climate change service portal. The results showed that all the regions experienced an average daily UTCI representing extreme heat stress for 1 to 25 days. The daily maximum UTCI goes to the extreme level on average of 1 to 175 days a year, with the highest in the east and southwest. The annual mean UTCI in MENA is increasing from 0.1 to 0.7 °C/decade, with the highest increase in the northeast, covering eastern Saudi Arabia and most parts of Iraq and Syria. This caused a decrease in cold stress and an increase in hot stress days, with the highest increase in strong thermal stress days in the range of 4 to 16 days/decade in most of MENA. The trend in daily maximum UTCI also showed an increase in the range of 0.1 to 0.6 °C/decade, which caused an increase in the number of daily maximum UTIC above 46 °C or extreme level by 1 to 16 days/per decade, with the highest increase in central Saudi Arabia, northern Sudan and southern Mauritania. This study is the first to investigate UTCI trends in the MENA region and is expected to provide valuable information on hotspots and temporal trends in UTCI, serving as a foundation for future heat action plans to prevent heat-related illnesses throughout the region.

Photothermal superhydrophobic copper nanowire assemblies: fabrication and deicing/defrosting applications

Ice and frost buildup continuously pose significant challenges to multiple fields. As a promising de-icing/defrosting alternative, designing photothermal coatings that leverage on the abundant sunlight source on the earth to facilitate ice/frost melting has attracted tremendous attention recently. However, previous designs suffered from either localized surface heating owing to the limited thermal conductivity or unsatisfied meltwater removal rate due to strong water/substrate interaction. Herein, we developed a facile approach to fabricate surfaces that combine photothermal, heat-conducting, and superhydrophobic properties into one to achieve efficient de-icing and defrosting. Featuring copper nanowire assemblies, such surfaces were fabricated via the simple template-assisted electrodeposition method, allowing us to tune the nanowire assembly geometry by adjusting the template dimensions and electrodeposition time. The highly ordered copper nanowire assemblies facilitated efficient sunlight absorption and lateral heat spreading, resulting in a fast overall temperature rise to enable the thawing of ice and frost. Further promoted by the excellent water repellency of the surface, the thawed ice and frost could be spontaneously and promptly removed. In this way, the all-in-one design enabled highly enhanced de-icing and defrosting performance compared to other nanostructured surfaces merely with superhydrophobicity, photothermal effect, or the combination of both. In particular, the defrosting efficiency could approach ∼100%, which was the highest compared to previous studies. Overall, our approach demonstrates a promising path toward designing highly effective artificial deicing/defrosting surfaces.

Application of Microwave Technology in Different Fields for Energy Saving and Emission Reduction

In today's world, security of energy supply and greenhouse gas emissions due to rising energy demand are seriously threatening sustainable energy development, and it is urgent to promote energy structure reform. Microwave, as a clean and environmentally friendly green energy source, has developed rapidly in recent years. Unlike traditional heating methods, microwave heating generates heat through the random motion of polar molecules. This results in microwave heating having the advantages of selective heating, fast temperature rise, easy control and high heating efficiency. This allows microwaves to make a contribution in advancing the reform. of the energy mix. This paper investigates the use of microwave technology in different industries to save energy and reduce emissions. It finds that in the ironmaking industry, microwaves can speed up the reduction time of iron ore, reduce carbon dioxide emissions, while making iron ore more easier to crush and magnetically sort during iron ore pretreatment process. In the food industry, microwaves can reduce the time required to cook and dry, and maximise the retention of nutrients in food. In the field of waste recycling, microwaves reduce the volume of bottom radioactive waste in a shorter time and improve the efficiency of desulphurisation of waste rubber. In the Budur reaction, microwaves reduce the temperature required for the reaction and increase the conversion of carbon dioxide. After summarising the advantages of microwave technology, this paper also analyses the current shortcomings of microwave technology, introduces microwave-related patents and concludes with an outlook on the future of microwave technology.

Experimental study on the effect of passive retardation method for thermal runaway mitigation of lithium-ion battery

To delay and suppress the thermal runaway of 18650-type lithium-ion battery, three TRRs (thermal runaway retardants) with various mitigation mechanisms were proposed, and the results were compared to the commonly used thermal management material PA (paraffin). A 200 W heating rod was used to trigger thermal runaway, the flame height, battery temperature, and mass loss were recorded and the suppression effects of different materials were discussed. The results show that PA delays the onset of thermal runaway, however, the higher flame, faster temperature rise, and longer burning time are all a sign of increased danger. TRRH (phenoxy cyclophosphazene) with radical capture effect enables the reduction in flame height and peak temperature by 60.87% and 30.31% compared to a single battery. However, the lack of heat absorption prevents TRRH from reducing the battery surface temperature. TRRM (magnesium hydroxide) and TRRS (sodium acetate trihydrate) have a positive effect on the reaction rate, temperature rise, and flame of the battery. TRRS performs better, and lowering the battery surface temperature to below 400 °C and delaying the onset of thermal runaway by more than 25 min. This study brings novelty to the thermal runaway suppression of lithium-ion batteries, especially from the perspective of pre-filled materials.

Photoliquefiable Azobenzene Surfactants toward Solar Thermal Fuels that Upgrade Photon Energy Storage via Molecular Design.

Photoresponsive phase change materials (PPCMs) are capable of storing photon and heat energy simultaneously and releasing the stored energy as heat in a controllable way. While, the azobenzene-based PPCMs exhibit a contradiction between gravimetric energy storage density and photoinduced phase change. Here, a type of azobenzene surfactants with balance between molecular free volume and intermolecular interaction is designed in molecular level, which can address the coharvest of photon energy and low-grade heat energy at room temperature. Such PPCMs gain the total gravimetric energy density up to 131.18 J g-1 by charging solid sample and 160.50 J g-1 by charging solution. Notably, the molar isomerization enthalpy upgrades by a factor of up to 2.4 compared to azobenzene. The working mechanism is explained by the computational studies. All the stored energy can release out as heat under Vis light, causing a fast surface temperature rise. This study demonstrates a new molecular designing strategy for developing azobenzene-based PPCMs with high gravimetric energy density by improving the photon energy storage.

An electroless nickel plating fabric coated with photothermal Chinese ink for powerful passive anti-icing/icephobic and fast active deicing

The icing phenomenon has caused much inconvenience to people's life. With the continuous progress of technology, it has been found that hydrophobic materials can be used in the anti-icing field, however icing still occurs on hydrophobic surfaces with long-term using in extremely harsh environments. Therefore, materials with anti-icing/icephobic and deicing functionalities have become an innovative strategy. In this paper, photothermal hydrophobic materials with anti-icing/icephobic and photothermal deicing properties are prepared using the photothermal nickel, Chinese ink and polydimethylhydrosiloxane with low surface energy. Due to the synergistic effect of the photothermal nickel nanoparticles and carbon nanoparticles in Chinese ink, the prepared material has a fast temperature rise rate at 1000 W/m2, which can reach the equilibrium temperature of 72 °C within 80 s. The freezing time of water droplets can be delayed to 1018 s at −15 °C, which is 11 times longer than that of nickel-plated materials. The ice on the coating melts rapidly and slides off along the inclined surface under the sunlight, proving that the material has a good photothermal deicing performance. Additionally, the coated surface has excellent wear resistance and UV resistance, which can be used outdoors for a long time. This powerful electroless nickel plating fabric, integrated with anti-icing/icephobic and fast deicing functionality with photothermal and drag reduction effect, provides a new approach to solve the icing problem in outdoor clothing.

Numerical analysis of the performance of a PID control based real-time mechanical ventilation system to prevent smoke back-layering in tunnel fires

Longitudinal mechanical ventilation systems are widely employed to prevent smoke back-layering in tunnel fires. Correlations for the critical velocity of ventilation in tunnels have already been extensively studied, for given fire and tunnel (cross-sectional) dimensions. This work describes the potential of a novel concept of an automatic ventilation system based on a PID (Proportional-Integral-Derivative) controller for preventing smoke back-layering under a priori unknown fire size. A few different tunnel dimensions and heat release rates (HRR) are addressed in order to illustrate how the ventilation velocity adapts automatically. Two methods to identify the location of the smoke front are proposed, based on temperature information. Simulation results show that the proposed approach can control the smoke well, preventing back-layering in real-time. It has excellent adaptability for the unknown fire size, which is considered an advantage compared to a system based on constant ventilation velocity. The smoke front becomes stable more quickly for higher HRR, while it takes longer to stabilize for increased tunnel height. This relates to the flame height: sufficiently high flames (compared to the tunnel height) induce a fast rise in temperature, which is the input parameter for the PID system. The tunnel width therefore has little impact. The values for the critical velocity and for the ventilation velocity at maximum smoke back-layering length (BL), as obtained with the proposed method, agree well with existing correlations. The influence of the set-point value for temperature is briefly discussed.

Measurement report: Long-term measurements of aerosol precursor concentrations in the Finnish subarctic boreal forest

Abstract. Aerosol particles form in the atmosphere via the clustering of certain atmospheric vapors. After growing into larger particles by the condensation of low-volatility gases, they can affect the Earth's climate by scattering light and acting as cloud condensation nuclei (CCN). Observations of low-volatility aerosol precursor gases have been reported around the world, but longer-term measurement series and any Arctic data sets showing seasonal variation are close to nonexistent. Here, we present ∼7 months of aerosol precursor gas measurements performed with a nitrate-based chemical ionization atmospheric pressure interface time-of-flight (CI-APi-TOF) mass spectrometer. We deployed our measurements ∼150 km north of the Arctic Circle at the SMEAR I (Station for Measuring Ecosystem–Atmosphere Relations) continental Finnish subarctic field station, located in the Värriö strict nature reserve. We report concentration measurements of the most common compounds related to new particle formation (NPF): sulfuric acid (SA), methane sulfonic acid (MSA), iodic acid (IA) and the total concentration of highly oxygenated organic molecules (HOMs). At this remote measurement site, SA originates from both anthropogenic and biological sources and has a clear diurnal cycle but no significant seasonal variation. MSA shows a more distinct seasonal cycle, with concentrations peaking in the summer. Of the measured compounds, IA concentrations are the most stable throughout the measurement period, except in April during which time the concentration of IA is significantly higher than during the rest of the year. Otherwise, IA has almost identical daily maximum concentrations in spring, summer and autumn, and on NPF event or non-event days. HOMs are abundant during the summer months and low in the autumn months. Due to their low autumn concentrations and high correlation with ambient air temperature, we suggest that most HOMs are products of biogenic emissions, most probably monoterpene oxidation products. NPF events at SMEAR I happen under relatively low-temperature (1–8 ∘C) conditions, with a fast temperature rise in the early morning hours as well as lower and decreasing relative humidity (RH, 55 % vs. 80 %) during NPF days compared with non-event days. NPF days have clearly higher global irradiance values (∼450 m−2 vs. ∼200 m−2) and about 10 ppbv higher ozone concentrations than non-event days. During NPF days, we have, on average, higher SA concentrations, peaking at noon; higher MSA concentrations in the afternoon; and slightly higher IA concentration than during non-event days. In summary, these are the first long-term measurements of aerosol-forming vapors from SMEAR I in the subarctic region, and the results of this work will help develop an understanding of atmospheric chemical processes and aerosol formation in the rapidly changing Arctic.

Experimental Study on Fe3O4 Nanoparticle-Assisted Microwave Enhancing Heavy Oil

Nanoparticle-assisted microwave heating of heavy oil has the advantages of fast temperature rise and high thermal efficiency. Compared with traditional heating methods, it can reduce viscosity in a shorter time. In addition, the heavy components in the heavy oil are cracked into light components at high temperatures (this high temperature cannot be reached by conventional heating methods). This process is irreversible and avoids the problem of viscosity recovery of heavy oil after the temperature is reduced. Through absorbing microwave heating experiments, study the effect of nanoparticles on the improvement of the ability of heavy oil to absorb waves and raise temperature; through the heavy oil upgrading experiment and the four-component analysis experiment, the effect of adding hydrogen donor to assist microwave on the viscosity reduction of heavy oil upgrading by nanoparticles was studied, and the problem of viscosity recovery was determined; Through the gravity drainage experiment, the mechanism of nanoparticle-assisted microwave to improve the recovery of heavy oil is studied, and the influence of water content, nanocatalyst, and microwave power on the production of drainage is analyzed. The results show that nanoparticles can improve the wave absorption and heating capacity of heavy oil, and adding 0.6 wt% of nanomagnetic iron oxide catalyst can increase the heating rate of heavy oil in microwave by 60.6%; nanoparticle-assisted microwave heating method can effectively upgrade heavy oil and reduce viscosity. The experimental conditions are 2 wt% tetralin mass concentration, 0.5 wt% nano-Fe3O4 particle mass concentration, microwave heating time 50-60 min, and microwave power 539 W. Under this experimental condition, the viscosity is reduced by 40%. This method has viscosity recovery problems, but final viscosity reduction effect is still very significant. Obtaining the mechanism of nanoparticle-assisted microwave to enhance oil recovery, one of which is that nanoparticles improve the wave absorption and heating capacity of heavy oil and increase the heating speed of heavy oil; the second is that the nanoparticles form local high temperature under the action of microwave, which catalyzes the hydrocracking reaction between the heavy components in the heavy oil and the hydrogen donor, upgrading and reducing the viscosity of the heavy oil, and accelerating the production of heavy oil.

Vertically Aligned Polyamidoxime/Graphene Oxide Hybrid Sheets’ Membrane for Ultrafast and Selective Extraction of Uranium from Seawater

AbstractWith the continuous research and development of amidoxime (AO)‐based adsorbents, industrialization production of uranium from seawater gradually becomes a reality. However, the currently available AO‐based adsorbents still suffer from low adsorption rate and poor selectivity. Herein, vertically aligned polyamioxime–graphene oxide (VA‐PG) sheet membrane is fabricated by directional freeze casting. The run‐through microchannels contribute to the free diffusion of uranyl ions (UO22+), leading to the fast adsorption kinetics. Furthermore, partially reduced graphene oxide allows high photothermal conversion efficiency and rapid in‐plane heat transfer, resulting in the fast temperature rise under simulated sunlight irradiation. Because of the endothermic behavior of UO22+, light‐irradiated VA‐PG can simultaneously satisfy the requirements of high adsorption capacity (13.63 mg‐U g‐Ads−1), high adsorption rate (0.43 mg g−1 day−1), and excellent selectivity toward U(VI) over V(V) (U/V = 1.24) in natural seawater, indicating the right direction for a breakthrough in the field of uranium extraction from seawater.

Thermal, mechanical and ultrasonic properties of cemented tailings backfill subjected to microwave radiation

Cemented tailings backfill (CTB), which is normally prepared by mixing tailings, binder and water, is applied to fill underground mined-out areas for ground control and waste disposal. When the CTB is placed underground, it should quickly gain satisfactory strength to ensure safe and efficient mining production. However, in some high-altitude areas, such as the Qinghai-Tibet Plateau, the low temperature limits the strength development in the CTB. As a result, it is necessary to develop a method, such as microwave technique, to provide fast and effective temperature rise for the CTB. In this paper, the thermal, mechanical and ultrasonic properties of CTB subjected to microwave radiation are studied. The obtained results indicate that the microwave technology can significantly affect the temperature distribution, strength development and structural compactness of the CTB. When the same microwave energy is applied, the thermal, mechanical and ultrasonic behaviors of the CTB vary with different curing age, solid content and binder-to-tailings ratio. The current study reveals that the microwave technique can reliably improve the stability and durability of the prepared CTB structures. Therefore, this study can contribute to a further step for the practical application of the microwave technique to the CTB technology.

Rapid thermal response and sensitivity analysis of proton exchange membrane fuel cell stack with ultra-thin vapor chambers

Vapor chamber (VC) embedded in proton exchange membrane fuel cell (PEMFC) stacks is an effective approach for thermal management of PEMFC stacks due to high thermal conductivity and temperature uniformity of VC. To quantitatively analyze the effect of VC on the dynamic thermal response of PEMFC stacks, a thermal equivalent circuit model is developed for PEMFC stacks cooled by VC. Each component in the stacks is regarded as a corresponding thermal resistance in the heat transfer process. The heat capacity of components is also applied on the model to couple the dynamic response. A series of key parameters on the thermal performance of the stacks are analyzed. The analysis result shows that the stacks have the fast temperature rise within 60 s of the start-up phase and VC nicely decrease the thermal response time of stacks. Parameters on temperature sensitivity of the stacks are also discussed. Thermal contact resistance and cooling velocity are significant factors on temperature sensitivity of stacks, but the temperature sensitivity becomes lower and even less than 0.01 with the increase of velocity. These works will help to design and optimize the thermal management system of PEMFC stacks.

Two-Dimensional MoO2 Nanosheet Composite Hydrogels with High Transmittance and Excellent Photothermal Property for Near-Infrared Responsive Actuators and Microvalves.

Stimulus-responsive intelligent hydrogel actuators have highly promising applications in the fields of soft robotics, smart manipulators, and flexible devices. Near-infrared (NIR) light is considered an ideal method to trigger the response behavior remotely and precisely. In order to realize the excellent optical transmittance and photothermal property of NIR-responsive hydrogels at the same time, two-dimensional nonlayered MoO2 nanosheets (2D-MoO2) with excellent photothermal efficiency (62% under an NIR light irradiation of 808 nm), splendid chemistry stability, and low preparation cost are used as photothermal agents and incorporated into the poly(N-isopropylacrylamide) (PNIPAM) hydrogel network, forming the 2D-MoO2/Laponite/PNIPAM ternary nanocomposite hydrogel (TN hydrogel). It is remarkable that compared with the GO and MXene hydrogels with the same agent content (1.0 mg mL-1) and thickness (1 mm) whose transmittance values are only ∼5% at 600 nm, the TN hydrogel shows a similar NIR-responsive temperature, but much higher optical transmittance (∼53%). Besides, of the three hydrogels with similar transmittance, the TN hydrogel shows a much higher NIR-responsive temperature. The TN hydrogel with a low loading of 2D-MoO2 (1.5 mg mL-1) can produce a significant temperature increase of ∼30 °C after the application of 0.8 W cm-2 NIR light irradiation for 15 s. Impressively, the TN hydrogel exhibits excellent anti-fatigue property, keeping a fast response and temperature rise behavior even after 50 times of heating-cooling cycles. The flexibly controllable and reversible deformation is realized by a well-designed bilayer structure even in harsh environments. The transparent and asymmetric bilayer hydrogel is further used as a soft manipulator to capture objects visually and accurately. The NIR light-controlled microvalve based on this composite hydrogel is also demonstrated. This work provides a novel kind of transparent hybrid NIR response hydrogel for the further development of smart, programmable, reversible hydrogel-based actuators and soft robotics.

Modeling of fast ionization waves in pure nitrogen at moderate pressure

The fast ionization wave (FIW) discharges in pure nitrogen in a capillary tube at 27 mbar, initiated by positive polarity, high-voltage nanosecond pulses, are numerically studied by coupled two-dimensional plasma fluid modeling. The 2D fluid code based on local mean energy approximation is validated and used, an extended three-exponential Helmholtz photoionization model is proposed for pure nitrogen. The development and structure of the nitrogen FIW is analyzed, the electric field and current are calculated compared with experimental measurements. The evolution of radial distribution of electrons and N2(C 3Π u ) during the FIW development stage and in the afterglow are analyzed, the radial profiles of electron density show a ‘hollow’ structure in the FIW development stage, the temporal-spatial evolution of N2(C 3Π u ) is dominated by the competition between the pooling reaction of and the quenching by electrons. The role of photoionization on the nitrogen FIW radial morphology is discussed, the equivalent background electron density of photoionization in nitrogen discharge is suggested to be (4–6) × 1013 m−3. Spatial distribution of specific energy deposition (SED), fast gas heating (FGH) energy and temperature rise are obtained, heating efficiency varies with electric field E/N and SED and tends to be 10% at high SED. The dominating reactions responsible for FGH and their fractional contribution in space and time are analyzed, in the near axis region, pooling reactions of and N2(B 3Π g ) contribute up to 80% FGH energy, electron impact dissociation of molecular nitrogen contributes about 10%, while e- recombination and quenching of N(2 D) atoms by N2 molecules contribute rest.

Influence of thermal shock of piezoelectric pressure sensors on the measurement of explosion pressures

Piezoelectric pressure sensors are susceptible to changing temperatures, because resulting mechanical deformations of the sensor membrane and housing may exert a positive or negative force on the piezo crystal, thus changing the reading of this sensor. The consideration and compensation of this influence quantity is a frequent topic of many investigations in the field of combustion chambers, of spark-ignition engines and internal combustion engines. However, this is not the case in the field of the type of protection “flameproof enclosures”. Here a peculiarity is the fast temperature rise during a single explosion and the concurrent influence of the temperature gradient, which is often described as thermal shock. The whole event has a typical duration time of the order of seconds and less. Thermal shocks have so far received little attention, as was also a lesson learnt from the evaluation of an interlaboratory comparison between Ex testing laboratories. The laboratories handle thermal shock in a variety of ways, starting from complete ignorance up to various sophisticated coatings. This was a main source of different results within the field of participants. This work evaluates the behavior of different piezoelectric pressure sensor types with respect to thermal shock. Different temperature protection measures are investigated regarding their functionality, practicability and stability. Possible influences on the sensitivity of the sensors due to the used protective measures regarding thermal shock are shown. The transient temperature load of the sensor membrane is estimated by physical calculations as well as numerical analysis based on surface temperature measurements transformed in a surface heat flux density. This work provides guidelines for typical end-users in the field of flameproof enclosures how to handle thermal shock correctly.

Research on fast real-time calculation model for transient temperature rise of power cables in ducts

A straightforward and fast transient temperature rise calculation model is necessary for electrical engineers to manage power cable load. A self-heating lumped parameter model (LPM) without the requirement of monitoring cable surface temperature is developed to evaluate the real-time transient temperature rise of the power cable in ducts. A mutual-heating lumped parameter model to describe the mutual heat interaction between any two cables is proposed in this paper as well. The transient temperature rise of any power cable in duct is the sum of the self-heating temperature rise and the mutual-heating temperature rise from all the other power cables in ducts. All parameters of these two models are obtained by transient thermal circuit analysis, CYMCAP calculation results and generic algorithm. A case study has been conducted to verify the feasibility of the proposed LPMs and the self and mutual temperature rise for each cable in ducts have been obtained. These results agree with the accurate data obtained from CYMCAP well, indicating that LPM can be used as a fast and straightforward tool to calculate the transient temperature rise of power cables in duct.