Recommended Operating Temperature Research Articles

Post-irradiation examination of commercial tantalum alloys following neutron irradiation

Post irradiation examination of two commercial tantalum alloys (based on Ta-8 %W) revealed significant irradiation hardening following neutron irradiation in the High Flux Isotope Reactor at Oak Ridge National Laboratory. Tensile samples of commercial Ta alloys T-111 and ASTAR-811C were irradiated to a total neutron fluence (E > 0.1 MeV) in the range (2–4)x1021 n/cm2 (0.39–0.75 dpa) at an irradiation temperature near 900 °C. Tensile testing conducted at room temperature and at 800 °C revealed significant irradiation hardening under all test conditions. Samples that were tensile tested at room temperature exhibited brittle failure, whereas ductility was maintained for elevated temperature testing. The irradiation hardening and embrittlement noted for both alloys was attributed to irradiation-induced dislocation loop formation as confirmed through scanning transmission electron microscopy analysis. Corresponding energy dispersive x-ray spectroscopy revealed radiation-induced segregation of Hf in these loop populations. This Hf enrichment is shown to result in eventual co-precipitation of elongated (Hf,O)-rich precipitates along the dislocation loops. These results show that irradiation hardening is enhanced via irradiation-enhanced precipitation at elevated irradiation temperatures. Consequently, the minimum recommended operating temperature window for Ta alloys should be increased to account for observed hardening/embrittlement at irradiation temperatures as high as 900 °C (1,173 K).

Effects of Current Collector on Internal Visualization of Solid Oxide Cells

Introduction Visualization of spatial distribution in solid oxide fuel cells (SOFCs) operating under high temperature is difficult to use various measurement equipment and sensors due to their recommended operating temperature. Therefore, it is difficult to reveal the distributions of gas species and reactions in the cell, as well as the loading current, using only electrochemical measurement methods. Simulation technology can be used to visualize various distributions in the cell and predict cell performance. While many simulation studies have revealed various spatial distributions in the SOFCs such as current density, they have also indicated that it is essential to accurately reflect the cell shape and multiphysics to simulate the cell performance1, 2.In our previous study, simulation and experimental thermal imaging combined temperature visualization method was developed. It was suggested that the temperature distribution under actual operating conditions is affected by Joule heating due to loading current distribution depending on the current collector geometry. Therefore, in order to evaluate the influence of the collector shape on the spatial temperature distribution, the influences of Joule heating and the collector geometry on the temperature distribution are evaluated. Then, we also analyze the influence of the current collector on the SOFC performance and propose a current collection method suitable for visualizing the reaction in an SOFC. Simulation Method In this study, the calculation was performed using a three-dimensional model that simulates the actual cell geometry used in the experiments. The simulated 3-D model was based on an electrolyte-supported plate cell with Scandia-stabilized Zirconia (ScSZ, 5 cm × 5 cm in size) as the support, LSM ((La0.8Sr0.2)0.98MnO3) and LSM-ScSZ composite material for the air electrode, and Ni-ScSZ cermet for the fuel electrode, respectively. The electrode area was 4 cm × 4 cm (16 cm2), and a platinum mesh and wire were used as a current collector. A schematic diagram of one of these examples is shown in Fig. 1. COMSOL Multiphysics (Ver. 6.0) was used as the 3-D simulation software to calculate the I-V characteristics and cell temperature distribution.The cell operating conditions were set to 800 ℃ for the operating temperature, 100 ml min-1 of 3 % humidified hydrogen as the incoming fuel, and the air electrode side opened to the atmosphere. I-V characteristics and cell temperature distributions were calculated under current density loading conditions ranging from 0.01 A cm-2 to 0.15 A cm-2. Based on each result, the relationship between current density and cell temperature distribution was evaluated. Results and Discussion As a result of numerical analysis and experiments focusing on the effect of the current collector shape, it was confirmed that the influence of the current collector shape appeared significantly in the cell temperature distribution as shown in Fig. 2. In addition, it was found that the visualization of the spatial distribution may be difficult because the effect of the heat generated by the Pt wire used as the current collector appears in the results of the temperature distribution on the surface. Based on these findings, we improved the current collector shape. Although the effect of the improvement on the Joule heating at Pt wire appeared in the temperature distribution result, the temperature distribution change was confirmed due to the loading current flow pattern, which depends on the shape of the current collector. The simulation results of the further improved collector shape showed that the temperature distribution change depending on the collector shape became smaller, suggesting that this collector shape is promising as a current collecting method suitable for visualizing the cell inside. In this presentation, we report the simulation results and discussion on the changes in current density distribution, gas distribution, and I-V characteristics, in addition to the changes in temperature distribution. References (1) M. Andersson, H. Paradis, J. Yuan, and B. Sundén, Electrochimica Acta, 109, 881 (2013).(2) A. Li, C. Song, and Z. Lin, Applied Energy, 190, 1234 (2017). Figure 1

Indoor experimental analysis of Serpentine-Based cooling scheme for high concentration photovoltaic thermal systems

High concentration photovoltaic thermal hybrids are expected to play an important role in meeting growing energy demands. When approaching concentrations over 1000 suns, a cooling system is needed to maximise both the thermal and electrical performance of the multi-junction solar cell without producing excessive parasitic losses.This study develops a novel simulation model to provide an in-depth understanding of the functionality of a concentrated photovoltaic thermal hybrid system with serpentine-based cooling systems. An ultra-high concentrator photovoltaic optic irradiance profile (peak effective concentration ratio: ∼1500 suns) is considered within the simulation model, which has been validated through indoor experimentation. The effectiveness of cooling is also evaluated through maximum thermal stresses generated in the multi-junction solar cell. The double serpentine design was deemed the highest performing, primarily because of the single serpentine’s excessive pressure drop. Copper as the heat sink material yielded superior performance because of its higher thermal conductivity. The maximum total exergetic efficiency achieved by the receiver was ∼ 10.9% with this configuration. Compared to some examples in the literature this value may seem low, however, it is more accurate due to the inclusion of a specific irradiance profile. All serpentine-based cooling systems could maintain the recommended operating temperature.

Transient Finite Element Simulation of a Lithium-Ion Battery Pack Thermal Management System Based on Latent Heat System Materials

Battery packs in high-intensity use run the risk of overheating, potentially inducing catastrophic thermal runaway. Thermal runaway occurs when an individual cell in a connected system fails and subsequently applies increased stress on the remaining cells, leading to cascading failures and destruction of the battery pack as a whole. One method for controlling battery temperature during usage is utilizing the battery pack casing as a latent heat system (LHS), specifically incorporating phase-change materials (PCMs). Using this method, the transient thermal response of a 84-cell, 270 V lithium-ion battery pack for an aircraft application was simulated using ANSYS FLUENT. Heat generation rates and specific heat capacity of a single cell were experimentally measured and used as input to the thermal and mechanical model. A heat generation load was applied to the entire battery pack, and natural convection film boundary conditions were applied to the exterior of the enclosure. The maximum temperature of the battery pack without any casing reached 69.8 ᵒC after 800 s of usage at a simulated peak power draw of 1013 W or 16 A. This exceeds the manufacturer’s maximum recommended operating temperature of 60 ᵒC. For other materials, we found the maximum temperature of the batteries reached 57.0 ᵒC with plastic casing and 45.0 ᵒC with aluminum casing. We present a design of the pack that incorporates a passive thermal management system using a composite material consisting of phase-changing material, Puretemp60®, mixed with expanded graphite (EG). Simulations of the battery pack showed a decrease in the maximum temperature with the Puretemp60® as the sole material reaching a maximum of 54.2 ᵒC and the Puretemp EG composite matrix having a maximum temperature of 51.1 ᵒC, both after 800 s at the same power draw.The optimal material combination was then determined through evaluating several PCM and EG composites in several ratios using ANSYS FLUENT, followed by experimental testing. The mixture was cost effective, easy to mix, and demonstrated good mechanical properties. Results illustrated that a mixture of 25% expanded graphite with 75% Puretemp60® (PCM) was capable of maintaining battery temperatures within the acceptable operating range under moderate load conditions and therefore preventing thermal runaway. A resulting weight reduction of about 23.5% was also achieved using the Puretemp EG composite matrix in comparison to aluminum casing, and about a 7.2% reduction compared to plastic casing.Differential scanning calorimetry (DSC) was utilized to determine the phase transformation of the composites. The addition of expanded graphite minimally affected the phase transformation temperature, while decreasing the latent heat of transformation by about 40%. Scanning electron microscope (SEM) pictures visualized the morphology of the graphite during each stage of the composite fabrication process. The Puretemp60® and expanded graphite were easily mixed and the backscattering electron images indicated the composition was homogenous.The heat generation rate of the battery was calculated using the q̇gen= mCp(dT/dt) + UA∆T. The change in temperature with respect to time was experimentally determined from a series of discharges. Heat generation in the batteries was modeled as uniformly distributed. The average of the experimentally measured heat generation rates for a 1P constant power discharge were divided by the volume of the battery to yield a curve for the average body heat flux load in W/m3 over the discharge of the battery. A polynomial curve fit to the average heat generation rates was applied as a heat load to each battery in the simulation. The heat generation due to discharge was tested with a setup where the battery was insulated in polyurethane foam in order to reduce convection heat transfer during the experiments. A polyurethane foam block was cut such that the battery could be placed in the center, along with three T-type thermocouples to measure the surface temperature and external air temperatures. Two metal cylinders, one consisting of copper and the other of 6061 aluminum, were machined to the same cylindrical dimensions as the battery. These cylinders were then used to determine the heat loss, or UA value, of the foam insulation block setup. A National instruments NI 9147, Chroma Programmable DC Power Supply, and LabView software were used for the experiments. Figure 1

INVESTIGATION OF THE PHYSICOCHEMICAL PROPERTIES OF A NEW SYNTHETIC LUBRICANT FOR PASSENGER CAR INTERNAL COMBUSTION ENGINES

The subject of the article is a synthetic lubricant for the latest generation internal combustion engines, used especially in passenger cars, equipped with both spark ignition engines and compression ignition engines, which is used in particular in passenger cars operating in urban conditions, overcoming relatively short distances, and therefore working usually below the recommended operating temperature of the engine. The developed 5W30 oil maintains excellent rheological properties (fluidity) also before reaching the correct operating temperature of the engine, especially at negative temperatures, which results in lower oil pump resistance and reduced friction of key engine components, which ensures better engine working conditions and affects its service life.

Instrumentation for quantitative analysis of volatile compounds emission at elevated temperatures. Part 2: Analysis of carbon fibre reinforced epoxy composite

We have investigated the release of gases and volatile organic compounds (VOCs) from a carbon fibre reinforced epoxy composite matrix used in aircraft structural components. Analysis was performed at several temperatures both up to and above the recommended operating temperature (121 °C) for the material, to a maximum of 250 °C. Gas chromatography-mass spectrometry (GC-MS) combined with thermal desorption (TD-GC-MS) was used to identify and quantify VOCs, and in parallel real-time gas detection with commercial off-the-shelf (COTS) gas sensors. Under hydrocarbon free air, CO, SO2, NO, NO2 and VOCs (mainly aldehydes, ketones and a carboxylic acid) were detected as the gaseous products released during the thermal exposure of the material up to 250 °C, accompanied by increased relative humidity (4%). At temperatures up to 150 °C, gas and volatile emission was limited.

Estimation of the performance limits of a concentrator solar cell coupled with a micro heat sink based on a finite element simulation

Concentrated photovoltaic (CPV) technology makes use of cheap optical elements to amplify the irradiance and focus it on small-sized solar cells enabling the extraction of higher amounts of electricity. However, increasing the solar concentration raises the temperature of the PV cell which can deter its performance and can also cause its failure. To combat this issue both active and passive cooling mechanisms are utilized for different types of CPV systems. In this study, we determine the limits of passive cooling systems and establish when an active cooling system is needed based on the recommended operating temperature of the solar cell. We investigate the temperature characteristics of the solar cells bonded to three different substrate materials under different solar concentrations. Results showed that cell temperature is linearly dependent on the concentration ratio and ambient temperature independent of the substrate material. Further, the integration of a micro-finned heatsink results in higher heat dissipation by 25.32%, 23.13%, and 22.24% in comparison with a flat plate heatsink for Direct Bonded Copper (DBC), Insulated Metal Substrate (IMS), and Silicon Wafer (Si wafer) substrates respectively. The low thermal resistance of the IMS substrate compared to the DBC and the Si wafer substrates result in the best thermal performance in terms of maintaining the cell temperature < 80 °C and allowing a wider range of high concentration ratio.

Characteristics of particulate matter from four coal–fired power plants with low–low temperature electrostatic precipitator in China

The performance of traditional electrostatic precipitators (ESPs) is strongly affected by the flue gas temperature. Operating under much lower temperatures (e.g., ~90 °C), the low–low temperature electrostatic precipitators (LLT–ESPs) are considered as an effective technology to improve the particulate matter (PM) removal efficiency in coal–fired power plants (CFPPs). Wet flue gas desulfurization (WFGD) can also be affected by the decrease in the operating temperature of the ESP. This study evaluates the influence of various ESP operating temperatures on ESP performance, PM2.5 (particles with an aerodynamic diameter of ≤2.5 μm), and total dust emission characteristics at the ESP and WFGD outlets in CFPPs equipped with LLT–ESPs. PM2.5 and total dust concentrations at the ESP and WFGD outlets in CFPPs installed with LLT–ESPs are much lower than those with traditional ESPs. The PM concentrations at both the ESP and WFGD outlets show a decreasing trend with a decrease in the operating temperature. However, the concentration of total water–soluble ions (mainly SO42−, Cl−, and NH4+) in the total dust at the outlet of ESPs increases from 0.3 to 0.8 mg/m3 as the temperature decreases from > 90 °C to 80–90 °C, which is contrary to that at the WFGD outlet (decreases from 4.7 to 0.8 mg/m3). The PM2.5 and total dust concentrations increase by 10.2–80.2% and 13.7–77.0%, respectively, through the WFGD unit due to the entrainment of a gypsum slurry. A relatively lower operating temperature of LLT–ESPs in power plants is also beneficial to decrease the incremental effect of PM emissions in the process of WFGD. The recommended operating temperature for LLT–ESPs is ~90 °C, and limited improvement on PM reduction can be achieved with a further temperature decrease from 90 to 80 °C.

Design and Simulation of Passive Thermal Management System for Lithium-Ion Battery Packs on an Unmanned Ground Vehicle

The transient thermal response of a 15-cell, 48 V, lithium-ion battery pack for an unmanned ground vehicle (UGV) was simulated using ANSYS fluent. Heat generation rates and specific heat capacity of a single cell were experimentally measured and used as input to the thermal model. A heat generation load was applied to each battery, and natural convection film boundary conditions were applied to the exterior of the enclosure. The buoyancy-driven natural convection inside the enclosure was modeled along with the radiation heat transfer between internal components. The maximum temperature of the batteries reached 65.6 °C after 630 s of usage at a simulated peak power draw of 3600 W or roughly 85 A. This exceeds the manufacturer's maximum recommended operating temperature of 60 °C. We present a redesign of the pack that incorporates a passive thermal management system consisting of a composite expanded graphite (EG) matrix infiltrated with a phase-changing paraffin wax. The redesigned battery pack was similarly modeled, showing a decrease in the maximum temperature to 50.3 °C after 630 s at the same power draw. The proposed passive thermal management system kept the batteries within their recommended operating temperature range.

Solid Electrolytic Capacitors Designed for High Temperature Applications

For decades the maximum recommended operating temperature of solid electrolytic capacitors was 125°C. Responding to needs in the automotive and downhole drilling industries passive component manufacturers developed surface mount tantalum capacitors rated at 150°C in 2002–2003. Since that time the industry has introduced high temperature capable tantalum capacitors generally in 25°C increments roughly every four years. Today multiple manufacturers have products rated at 230°C poised for market release. The tantalum anode, tantalum pentoxide dielectric and manganese dioxide primary cathode material stand up well to these temperatures, although some optimization of the design and manufacturing process for these materials have been required. The primary challenges encountered when developing solid electrolytic capacitors with high temperature capabilities are associated with the carbon, silver and epoxy encapsulant materials used in conventional surface mount tantalum capacitors. Capacitor manufacturers have taken different paths to overcome these challenges. We have developed a metallized plating process to avoid issues associated with silver paints utilized in conventional Ta capacitors. We have worked with suppliers, or developed in house capabilities, to manufacture the other materials required to withstand the rigors of high temperature applications. This paper will discuss these challenges and provide reliability test data on a recently developed tantalum surface mount series capable of continuous operation at 230°C.

Thermorheological behaviour of a lithium lubricating grease

Thermal-induced changes in the viscous and viscoelastic responses of lubricating greases have been investigated through different rheological techniques in a temperature range of 0–175 °C. Small-amplitude oscillatory shear and viscous flow measurements were carried out on a model conventional lithium lubricating grease prepared by inducing the in situ saponification reaction between 12-hydroxystearic acid and hydrated lithium hydroxide. The linear viscoelasticity functions dramatically decrease above 110 °C, but not below this critical temperature, which determines the maximum recommended operating temperature in relation to its durability and resistance under working conditions. Two different regions, below and above this critical temperature, in the plateau modulus versus temperature plot have been detected. From this thermal dependence, a much larger thermal susceptibility of the lubricating grease at temperatures above 110 °C is apparent. The thermo-mechanical reversibility of this material has been studied by applying different combined stress–temperature protocols. Regarding the viscous flow, a minimum in the shear stress versus shear rate plots appeared at temperatures above 60 °C, more pronounced as temperature increases, resulting from material instabilities. The experimental results obtained have been explained on the basis of the thermo-mechanical degradation of the lubricating grease microstructure.

Unbreakable Solid-Phase Microextraction Fibers Obtained by Sol−Gel Deposition on Titanium Wire

Solid-phase microextraction commercial fibers present a few drawbacks such as relatively low recommended operating temperature, instability and swelling in organic solvents, breakage of the fiber, stripping of coatings, and bending of the needle. Some of these problems have been obviated by covalent bonding of the polymer phase to the fused-silica substrate by sol-gel, but the easy breakage of the fiber remains a problem. In the present work, the known occurrence of titanol groups at the surface of titanium wire was exploited to produce sol-gel fibers supported on this unbreakable substrate. Scanning electron microscopy analysis revealed the film formation on titanium wire surface while temperature and solvent stability as well as durability tests showed that the sol-gel film was tightly attached to the substrate, thus suggesting covalent bonding. The use of this type of fiber is currently generalized in our laboratory without any breakage or stripping out incidents up to the moment.

Separation of Polysaccharides from Industrial Syrup Using Tubular Membranes

The mass‐transfer plot and gel‐polarization aging of a number of tubular membranes made of hydrophilic polymers, ceramic, and sintered stainless steel was compared under their recommended operating temperature, transmembrane pressure, shear velocity, and cycle time for the separation of polysaccharides from composite industrial syrup. The results showed that more than 98% of the polysaccharides that correlate with the turbidity in the syrups were separated from the syrups. At the same time, the purity of the syrup was increased by up to 3% after membrane ultrafiltration. The comparison clearly showed that there were distinct differences in performance between different tubular membranes.

Anhydrous esterification of myristic acid with propylene: Ion exchange resin and acid‐treated clay as catalysts

Anhydrous esterification of myristic acid with propylene was carried out in the temperature range of 110–145°C and pressure from 190–195 psig in the presence of Amberlyst‐15 (cation exchange resin) and Filtrol‐24 (acid‐treated clay) as catalysts. The product ester, isopropyl myristate finds use in cosmetic and topical medicinal preparations where good absorption through the skin is desired. Filtrol‐24 is the catalyst of choice, and the recommended operating temperature is 130°C with a pressure of 190 psig.

KANTHAL 70

Abstract KANTHAL 70 alloy was designed to provide a high positive temperature coefficient to electrical resistance comparable with that of pure nickel; however, it has much higher electrical resistivity than pure nickel. This makes it useful as a voltage regulator when placed in series with another electrical device across a fluctuating voltage source. Kanthal 70 has a maximum recommended operating temperature of 600 C and is used widely in resistance thermometers and in various appliance and automotive applications. This datasheet provides information on composition, physical properties, and tensile properties. It also includes information on corrosion resistance as well as forming, heat treating, and joining. Filing Code: Ni-270. Producer or source: The Kanthal Corporation.

NIKROTHAL 6

Abstract NIKROTHAL 6 is a nickel-chromium-iron electrical-resistance alloy for use in appliances and industrial furnaces. Its maximum recommended operating temperature is 1125 C (2055 F). It is highly suitable for heating elements in domestic appliances. This datasheet provides information on composition, physical properties, and elasticity. It also includes information on corrosion resistance as well as forming, heat treating, machining, and joining. Filing Code: Ni-265. Producer or source: The Kanthal Corporation. Originally published October 1980, revised February 1981.

DRIVER 180 ALLOY

Abstract DRIVER 180 ALLOY is a copper-nickel alloy for use where moderate electrical resistance is required. The number designation refers to its specific resistivity (180 ohms/cir mil/ft) which is combined with a fairly low coefficient of resistance (180 x 10^-6 per C). Its maximum recommended operating temperature is 1000 F. This datasheet provides information on composition, physical properties, and tensile properties. It also includes information on corrosion resistance as well as forming, heat treating, machining, and joining. Filing Code: Cu-348. Producer or source: Wilbur B. Driver Company.

DRIVER 90 ALLOY

Abstract DRIVER 90 ALLOY is a copper-nickel alloy for use where only moderately low electrical resistance is required. The number designations refers to its specific resistivity (90 ohms/cir mil/ft) which is combined with a moderate coefficient of resistance. Its maximum recommended operating temperature is 800 F. This datasheet provides information on composition, physical properties, and tensile properties. It also includes information on forming and heat treating. Filing Code: Cu-343. Producer or source: Wilbur B. Driver Company.

DRIVER 60 ALLOY

Abstract DRIVER 60 ALLOY is a copper-nickel alloy for use where fairly low electrical resistance is required. The number designation corresponds to its specific resistivity (60 ohms/cir mil/ft) which is combined with a fairly high temperature coefficient of resistance. Its maximum recommended operating temperature is 600 F (316 C). This datasheet provides information on composition, physical properties, and tensile properties. It also includes information on corrosion resistance as well as forming, heat treating, machining, and joining. Filing Code: Cu-339. Producer or source: Wilbur B. Driver Company.

DRIVER 30 ALLOY

Abstract DRIVER 30 ALLOY is a copper-nickel alloy for use where low electrical resistance is required. The number designation corresponds to its specific resistivity (30 ohms/cir mil/ft) which is combined with a relatively high temperature coefficient of resistance. Its maximum recommended operating temperature is 600 F (316 C). This datasheet provides information on composition, physical properties, and tensile properties. It also includes information on corrosion resistance as well as forming, heat treating, machining, and joining. Filing Code: Cu-337. Producer or source: Wilbur B. Driver Company.