Operating Temperature Limit Research Articles

Dielectric properties of cryogenic gas mixtures for superconducting power applications

Dielectric breakdown strengths of ternary mixture of gaseous helium, hydrogen, and nitrogen at room temperature and cryogenic temperatures (77 K) have been investigated experimentally in an effort to identify a gaseous cryogen with higher dielectric strength than pure helium for high temperature superconducting (HTS) power applications. Building on our previous success in enhancing the dielectric strength of helium gas by 80% by using a binary mixture containing4 mol% hydrogen + 96 mol% helium, a ternary mixture with a composition of 4 mol% hydrogen + 88 mol% helium + 8 mol% nitrogen was investigated. The composition of the ternary mixture was the result of theoretical modelling studies which used the Boltzmann equation to calculate the dielectric strength of various ternary mixture ratios. The dielectric breakdown strength of the ternary mixture was measured at room temperature and at 77 K at several pressures up to 2 MPa. A 300 % enhancement in dielectric strength was observed for the ternary mixture compared to pure gaseous helium. The dielectric strength of the ternary mixture was measured to be 12 kV/mm at 1 MPa and 77 K, which is approaching the dielectric strength range of liquid nitrogen. The results on the new mixture are compared to the previous studies on helium-hydrogen binary mixtures and the implications of the observed enhancement for gas cooled HTS power devices is discussed. The challenges posed by the addition of nitrogen in terms of limited operating temperature and pressure due to the condensation of nitrogen at higher pressures and/or lower temperatures is also discussed.

Cooling circle design and testing for ITER radial X-ray camera

The ITER radial X-ray camera (RXC), which is installed in the middle diagnostics shield module (DSM) of equatorial port plug 12, is an important piece of diagnostic equipment in the tokamak system. A cooling circle is vital for RXC detectors because it can protect them from being damaged during the DSM baking phase when the temperature reaches 240 (±10)°C. Helium is used as a cooling medium in this cooling circle owing to its low activation and good heat exchange with copper. To increase the gas resistance and expand the heat transfer area, a labyrinth structure is introduced into the internal structural design of a heat exchanger. In this paper, an analysis of the heat load of the RXC and its cooling circle is presented, along with the thermal simulation and test results. Thermal simulation results indicate that the cooling circle design can meet the requirements. A test platform is built to validate the cooling circle design. The experimental results are presented, and the problems encountered during the testing are analyzed. The test results indicate that the maximum temperature of the detector is lower than 65°C with the cooling circle during the platform baking phase, which is lower than the detector operation temperature limit of 75°C.

Renewable jet fuel company Velocys shares jump 40% after British Airways deal

The ITER radial X-ray camera (RXC), which is installed in the middle diagnostics shield module (DSM) of equatorial port plug 12, is an important piece of diagnostic equipment in the tokamak system. A cooling circle is vital for RXC detectors because it can protect them from being damaged during the DSM baking phase when the temperature reaches 240 (±10)°C. Helium is used as a cooling medium in this cooling circle owing to its low activation and good heat exchange with copper. To increase the gas resistance and expand the heat transfer area, a labyrinth structure is introduced into the internal structural design of a heat exchanger. In this paper, an analysis of the heat load of the RXC and its cooling circle is presented, along with the thermal simulation and test results. Thermal simulation results indicate that the cooling circle design can meet the requirements. A test platform is built to validate the cooling circle design. The experimental results are presented, and the problems encountered during the testing are analyzed. The test results indicate that the maximum temperature of the detector is lower than 65 °C with the cooling circle during the platform baking phase, which is lower than the detector operation temperature limit of 75 °C.

Bulk and Nanostructured Closo-Hydroborate Salts of Lithium and Sodium As Superionic Electrolytes for Solid-State Batteries

Liquid organic electrolytes continue to dominate metal-ion battery technologies despite lingering concerns over safety, capacity loss due to parasitic side reactions, limited operating temperature range, and costly packaging needed to prevent electrolyte leakage. Although several solid-state electrolytes with ionic conductivity approaching that of liquid organic electrolytes have been recently demonstrated, including perovskites, garnets, and sulfides, challenges exist in integrating these into durable battery systems. The main issues of the existing solid electrolytes are their low ionic conductivity, low electrochemical stability and large interfacial resistance between the electrodes and the solid electrolyte. We propose a new class of superionic solid electrolytes based on closo-borate and carborate anions, such as B12H12 2-, CB11H12 -, B10H10 2-, CB9H10 -. The facile cation conduction pathways in these materials are enabled by the spacious, vacancy-rich, interstitial network afforded by a sub-lattice of large, orientationally mobile anions. Many of these materials display superionic conductivity in bulk, for instance a conductivity as high as 0.03 S cm-1 was achieved in NaCB9H10 at room temperature. This talk will describe three strategies used to further improve the conductivities of bulk closo-hydroborate and carborate anions by 1) ball-milling to create vacancies and stabilize disordered phases, 2) anion mixing to create preferred pathways for facile cation diffusion, and 3) nanoconfinement of salts inside mesoporous silica or alumina with functionalized surfaces to enhance ion-transport through nano-channels. We will show examples where nanostructuring was efficient in increasing the Li and Na-ion conductivity, in some cases by two orders of magnitude compared to bulk. We will present results from neutron scattering and nuclear magnetic resonance techniques which provide invaluable insights into the dynamical nature of the reorienting anions. Finally, we will describe the remaining challenges and barriers which remain to be solved to enable the use of nanostructured electrolytes in all-solid-state batteries at device-relevant temperatures.

Thermoelectric generator for industrial gas phase waste heat recovery

A technical solution recycling exhaust gas sensible heat based on thermoelectric power generation is proposed by using finite time thermodynamics. The effects of some key parameters such as exhaust gas inlet temperature, exhaust gas and cooling water heat transfer coefficient on the optimum length of the thermoelectric elements are analyzed. It is found that the gas temperature drops rapidly because of the small specific heat of the exhaust gas. Enhancing the heat transfer of gas can effectively improve the power, but not the efficiency. Exhaust gas inlet temperature and transfer coefficient have significant effects on the optimal thermoelectric element length. Due to the highest hot surface operating temperature limit 200 °C, the optimal length of the thermoelectric elements is about 2 mm. About 1.47 kW electrical energy can be produced per square meter and the conversion efficiency of 4.5% can be achieved for exhaust gas at 350 °C. The payback period of the waste heat recovery device is about 4 years for the price and performance of thermoelectric products made in China.

Thermal properties enforcement of carbonate ternary via lithium fluoride: A heat transfer fluid for concentrating solar power systems

A novel eutectic of Li2CO3-Na2CO3-K2CO3 improved by LiF, when employed as a heat transfer fluid in concentrating solar power systems, is prepared to eliminate the disadvantage of limited operating temperature range and low specific heat as well as thermal conductivity. Using the static melting method, Li2CO3-Na2CO3-K2CO3 with 15.0 wt.% LiF which is simply physical mixture determined by X-ray diffraction, is chosen as the optimized candidate. Results indicate that, at 10 °C/min of heating rate, LiF-Li2CO3-Na2CO3-K2CO3 reached melting point of 368 °C and upper temperature limit of 753 °C, allowing it to be effectively employed in thermal storage and heat transfer in high temperature CSP systems. During temperature range from 400 to 600 °C, the liquid quaternary exhibited notably mean specific heat of 1.917 J/(g·°C), which is larger than that of the original ternary eutectic. Thermal conductivity of solid LiF-Li2CO3-Na2CO3-K2CO3 reached the stable level of 1.021 W/(m·°C) at 320 °C. Density of improved eutectic tested by the archimedean principle is approximately 1.95 g/cm3. In conclusion, LiF-Li2CO3-Na2CO3-K2CO3 can be employed as the admirable heat transfer fluid for thermal storage and heat transfer in high-temperature CSP plants. This investigation will provide useful information for further improvement of molten salt based heat transfer fluids.

Comprehensive Experimental and Computational Analysis of a Fully Contained Hybrid Server Cabinet

The rapid growth in the number of data centers combined with the high-density heat dissipation of computer and telecommunications equipment has made energy efficient thermal management of data centers a key research area. Localized hybrid air–water cooling is one approach to more effectively control the cooling when there is wide variation in the amount of dissipation in neighboring racks while the traditional air cooling approach requires overprovisioning. In a closed, hybrid air–water cooled server cabinet, the generated heat is removed by a self-contained system that does not interact with the room level air cooling system. Here, a hybrid-cooled enclosed cabinet and all its internal components were characterized experimentally in steady-state mode (e.g., experimentally determined heat-exchanger effectiveness and IT characterization). Also, a comprehensive numerical model of the cabinet was developed and validated using the experimental data. The computational model employs full numerical modeling of the cabinet geometry and compact models to represent the servers and the air/water heat exchanger. The compact models were developed based on experimental flow and thermal characterization of the internal components. The cabinet level model has been used to simulate a number of operating scenarios relevant to data center applications such as the effect of air leakage within the cabinet. The effect of the air side and the water side failure of the cooling system on the IT performance were investigated experimentally. A comparison was made of the amount of time required to exceed the operating temperature limit for the two scenarios.

Background–limited long wavelength infrared InAs/InAs1− xSbx type-II superlattice-based photodetectors operating at 110 K

We report the demonstration of high-performance long-wavelength infrared (LWIR) nBn photodetectors based on InAs/InAs1− xSbx type-II superlattices. A new saw-tooth superlattice design was used to implement the electron barrier of the photodetectors. The device exhibited a cut-off wavelength of ∼10 μm at 77 K. The photodetector exhibited a peak responsivity of 2.65 A/W, corresponding to a quantum efficiency of 43%. With an R × A of 664 Ω·cm2 and a dark current density of 8 × 10−5 A/cm2, under −80 mV bias voltage at 77 K, the photodetector exhibited a specific detectivity of 4.72 × 1011 cm·Hz/W and a background–limited operating temperature of 110 K.

Electromagnetic and Thermal Analyses of High-Performance Magnetic Shape Memory Actuators for Valve Applications

Magnetic shape memory (MSM) alloys are relatively new smart alloys, which have enormous potential to be used in actuators, sensors, and other electrical devices. Their large strain and considerable stress output can be controlled by magnetic fields or mechanical stresses. Maximum magnetic field-induced strain varies from 6% to 12% of the MSM element’s length depending on its microstructure. However, very low operational temperature limit is one of the main drawbacks of conventional MSM alloys. This makes their application in high-performance actuators challenging due to considerable power losses. This paper discusses different MSM actuator designs, optimized particularly for large force output for pneumatic electromagnetic valve applications. The thermal problem is addressed through analyzing the heat transfer conditions of each particular design and the effects of different cooling systems. An energy-efficient operating cycle for varying actuator loads that takes advantage of the shape memory effect is also proposed. This allows the minimization of energy losses, resulting in an acceptable increase in the temperature ensuring stable continuous actuation.

A silicon field-effect hall sensor with an extended operating temperature range

The characteristics of thin-film Si MISIM magnetic transistors with a built-in accumulated channel and partially depleted quasi-neutral area are studied. The design of transistors is integrated with a Hall element. It is shown experimentally that transistors of this type, which were named field-effect Hall sensors (FEHSs) and made by the “silicon-on-insulator” (SOI) technology, provide measurements of the magnetic induction in a temperature range of 1.7–605 K. Theoretical estimates show that the upper operating temperature limit of the FEHS can be about 850 K.

Efficient Enrichment Applications for Capacitive Deionization in Conventional Carbon Capture Processes

Liquid amine carbon capture systems have been in use for decades, but there remain certain drawbacks that need to be addressed before large-scale implementation of this technology will be more appreciably adopted. Many of these limitations are related to the energy cost of the capture process, but secondary emissions are a pervading limitation due to adverse health and environmental effects related to amine emissions and their degradation products. Secondary emissions from the CO2 absorber column (process unit shown in Figure 1) include vapors and aerosols of amine molecules as well as smaller amounts of their by-products, such as nitrosamines.(1) Currently, to limit the emission of these molecules, water wash sections are added to the top of the absorber that contact the exiting gas and reduce the concentrations of vapors, aerosols, and by-products being potentially emitted to the atmosphere. This system subsequently produces a liquid stream containing rather dilute concentrations of dissolved amine molecules (less than 1 wt%) and a small fraction of other contaminants. To reduce their accumulation in the water wash section for which emissions are controlled by their vapor-liquid equilibrium, they need to be removed using an efficient separation process capable of high water recovery rates. Established methods to concentrate ionic content from aqueous streams, such as the amine molecules being adsorbed and concentrated here, include polymeric membranes, distillation, and ion exchange techniques. In the ideal concentration process, high water recovery and subsequently high concentrations of amine in the concentrate are desired with minimal energy input. While polymeric membranes can provide quite pure water streams, high pressures are typically required to obtain high water recoveries and resulting high concentrations in their concentrate streams. In addition, membranes have stability issues at high and low pH and suffer from limited operating temperature windows above 40 °C. Distillation techniques are dependent on high energy inputs, and corrosion persists as a notable problem in these units over longer periods of time. Therefore, a capacitive deionization (CDI) system is proposed here to concentrate and return amine molecules from the water wash section to the CO2 capture system. In fact, a similar capacitive mixing process has been shown previously for energy recovery from flue gas streams with dilute bicarbonate and monoethanolamine solutions.(2, 3) Due to CDI’s reported lower energy costs of separation, high water recoveries, and ability to concentrate ionic species at a range of temperatures, pressures, and pH levels, CDI could be an ideal candidate for this application.(4, 5) Flow-through CDI and recently demonstrated inverted capacitive deionization (i-CDI) cells will be shown here to reversibly separate and concentrate CO2-loaded piperazine (PZ) molecules, an advanced carbon capture solvent currently under investigation, using cell potentials less than 1.5 V.(6) Longer-term performance characteristics including charge efficiency and salt adsorption capacity of the separation process will be evaluated for implementation at larger scales. Liquid chromatography-mass spectrometry (LC-MS) will be used to complement conductivity measurements and confirm piperazine concentrations for the adsorption and desorption profiles from these separation cells. Finally, energy assessments and water recoveries will be shown for this separation process and compared to conventional processes. Preliminary separation results using a batch-mode CDI system operated at 1.2/0 V for adsorption-desorption are shown in Figure 2.

Outline Design of ITER Radial X-Ray Camera Diagnostic

The radial X-ray camera (RXC) is designed to measure the poloidal profile of plasma X-ray emission with high spatial and temporal resolution. Its primary diagnostic role includes measuring low (m, n) magnetohydrodynamic modes, sawteeth and disruption precursors, H-mode, edge-localized modes, and L-H transition. The RXC comprises two subsystems, i.e., in-port and ex-port cameras that view the outer and core regions, respectively, through vertical slots in the diagnostics shield module of an equatorial port plug. Detailed camera design is in progress including design of the camera structure, electronics, data acquisition and control, calibration, and pretest on the EAST tokamak. The sight path and neutron shielding have been optimized. The secondary vacuum, heat insulation, cooling, positioning, and calibration have been designed. The structure analysis results for the external camera indicate that even under five times gravity acceleration, the maximum stress was still below the allowable stress. The heat analysis results indicate that the maximum temperature on the detector box was ~56°C, which is within the detector operation temperature limit. The neutronics analysis results indicate that the detectors can be operated during the whole deuterium-deuterium phase without detector replacement. The electronics group and instrumentation and control group have also made good progress.

SELF-LUBRICATING PROPERTIES OF THIN COATINGS BASED ON MOLYBDENUM DISULPHIDE

The paper presents an analysis of the friction and wear processes of a composite coating based on molybdenum disulphide doped by tungsten and titanium, taking into account the impact of load and temperature in the contact zone. The tribological tests were performed at room temperature and at 300°C and 350°C in non-lubricated sliding contact with an Al2O3 ball. The characterization of the micromechanical properties and the adhesion of coatings to steel substrates were done by scratch testing. The analysis of the coatings wear and the sliding tribolayer formation was conducted by the observation of the friction track using light microscopy (LM) and scanning electron microscopy (SEM). The low hardness of the MoS2(Ti,W) coating, equal to 6 GPa, with the predominantly amorphous structure, allows for quick formation of the tribological contact and the sliding tribolayer creation. Due to self-lubricating properties, the coating has a high wear resistance and a low friction coefficient (below 0.1), both at room and elevated temperatures. The study allowed the determination of the operating temperature limit of the coating-substrate system in sliding point contact, which helped to specify the application area of such material.

Thermal design of air cooled condenser of a solar adsorption refrigerator

The objective of this paper is to study the design of a condenser of a solar adsorptionrefrigerator which will be tested in the region of Biskra (Algeria). The LMTD (log mean temperaturedifference) method is used to calculate the size of the condenser applying experimental dataobtained from the literature. For this purpose, a calculation code has been developed todetermine the total heat transfer area of the heat exchanger. Therefore, we present a comparisonbetween calculated and experimental results obtained from the literature. This comparisonallowed the validation of the calculation method by applying the same experimental conditions.The discussion of the results indicates that we cannot use the ambient air in free convection modeas a cooling fluid if its temperature exceeds 30°C. This problem presents the greatest obstacleespecially in the Saharan regions, such as in Biskra, where the average ambient air temperatureduring the summer exceeds 35°C. As a solution, we propose in this article the improvement of theheat transfer by the air-forced convection mode. Thus, it is established that the use of the air fancan extend the operating temperature limits of the condenser above 35°C.

Investigation of Engine Oil-cooling Problem during Idle Conditions on Pusher Type Turbo Prop Aircraft

AbstractAircraft engines need a cooling system to keep the engine oil well within the temperature limits for continuous operation. The aircraft selected for this study is a typical pusher type Light Transport Aircraft (LTA) having twin turbo prop engines mounted at the aft end of the fuselage. Due to the pusher propeller configuration, effective oil cooling is a critical issue, especially during low-speed ground operations like engine idling and also in taxiing and initial climb. However, the possibility of utilizing the inflow induced by the propeller for oil cooling is the subject matter of investigation in this work. The oil cooler duct was designed to accommodate the required mass flow, estimated using the oil cooler performance graph. A series of experiments were carried out with and without oil cooler duct attached to the nacelle, in order to investigate the mass flow induced by the propeller and its adequacy to cool the engine oil. Experimental results show that the oil cooler positioned at roughly 25 % of the propeller radius from the nacelle center line leads to adequate cooling, without incorporating additional means. Furthermore, it is suggested to install a NACA scoop to minimize spillage drag by increasing pressure recovery.

The effect of smaller turbulent motions on heat transfer in the annular gap flow of flywheel

The forced convective heat transfer in the gap of a flywheel is affects the safety of reactor coolant pump (RCP), such as the operation temperature limit of the bearing, therefore it is necessary to analyze the heat transfer in the annular gap flow of a flywheel. The current study provides evidence that the convective heat transfer depends on the flow structure. When the Taylor number of this flow is about 1E12, the flow structure has a special pattern likes Herringbone near the wall, and consists of many smaller Görtler vortices. Although the earliest experimental studies found the Görtler vortex with laser-induced fluorescence (LIF), these vortices are difficult to study by numerical analysis with direct numerical simulation (DNS) or the large eddy simulation (LES), and the Reynolds-averaged Navier–Stocks (RANS) cannot capture the smaller scale vortices in the wall boundary layers with overestimated eddy viscosity. In this paper, we adopt the partially-averaged Navier–Stokes (PANS) model to observe the smaller turbulent motions in the annular gap flow of a flywheel, and analyze the effect of Görtler vortices on convective heat transfer. Compared with k–ε, PANS simulation suggests that there are larger temperature gradients at the Görtler vortices region, and two temperature mixing processes occur at the boundaries of a pair of Taylor vortices.

The Effect of Additives on the High‐Temperature Stability of the Vanadium Redox Flow Battery Positive Electrolytes

AbstractSeveral inorganic additives are investigated as potential precipitation inhibitors for the positive half‐cell electrolyte of the vanadium redox flow battery (VRB) at elevated temperatures. Electrolyte stability tests on the more concentrated 2 m vanadium electrolyte show that of the additives tested, the best results are obtained with the addition of 1 % phosphoric acid that give induction times of 40, 22 and 18 days for 80, 90 and 95 % state of charge (SOC) solutions at 50 °C, compared with 5, 2 and 1 days respectively for the corresponding blank solution. Several additives are also evaluated at 45 °C in a vanadium redox flow cell operating with a 2 m vanadium electrolyte. In the case of the cell employing the blank solution, a sudden drop in capacity, followed by pump failure is observed after around 70 cycles, while the cells with the additives continue to cycle without failure for 120 and 150 cycles for ammonium sulphate and ammonium phosphate additives respectively. A similar stabilising effect has previously been observed with these additives at low temperatures in the negative half‐cell electrolyte of the VRB, confirming that these stabilising agents have the potential to extend the upper and lower operating temperature limits of a 2 m vanadium electrolyte in the VRB to 45 and 5 °C respectively, while also significantly enhancing its energy density without the need for potentially hazardous chloride additions.

Degradation Behavior in Lithium Iron Phosphate Secondary Cells Under High Rate Pulsed Discharge

LiFePO4 secondary cells cycled under a ultra-high rate pulsed discharge profile are dismantled to study the changes in surface chemistry in pulse power load systems. Three cells lost the ability to charge (0 Ahrs) in less than 50 cycles at 15C (40A) pulsed discharge/continuous recharge conditions. Electrode samples show varying levels of solid electrolyte interphase growth. However, x-ray absorption near edge structure analysis conducted on the cathode material shows minimal loss of active lithium. A cell cycled under the same conditions with a 60°C operating temperature limit showed more gradual capacity fade and a higher degree of shift in the photon energy of the XANES spectrum. XPS analysis shows thicker SEI formation in the 60°cells. This indicates that the additional thermal energy in the 75°C cells provide more favorable conditions for the evolution of a degradation mechanism that is more complex than lost active material. Increased concentration in oxygen at the anode surface indicates heavy reduction in the electrolyte salt forming LixPFy-Oz. The 0 Ahr cells showed higher concentration of Fluorine and an SEI that contains mostly LiF. Results suggests that high temperature, ultra-high rate pulsed cycling favors LiPF6 reduction into LiF and thus the concentration of Li2CO3 in the SEI is reduced creating a high impedance film.

Characterization of PTFE-Based Gaskets at High Temperature

The objective of this work is to analyze the hot blow-out test procedure (HOBT) used to determine the maximum operating temperature of Teflon-based gaskets. The study focuses on the effect of thermal cycles and a few considerations that can be made to improve the characterization procedure for better prediction of the long-term performance of these types of gaskets at high temperature. The determination of their safe operating temperature limit requires a good knowledge of their capacity to resist creep-relaxation due to temperature exposure in the short and long terms. The study investigates the effects of the cumulative gasket deformation due to thermal cycling, gasket stress level, and holding time on the relaxation of these materials. In parallel, an experimental fixture has been developed to measure the thermal expansion coefficient and the short-term creep resistance of such materials. Based on this study, the introduction of thermal cycling in the HOBT test procedure shows that ratcheting damage has some impact on the reduction of the gasket lower bound stress and therefore on the temperature limit of polytetrafluoroethylene (PTFE) gaskets. The effect of holding temperature for a short period of time is also investigated. The modified HOBT rig allows measurement of the gasket deflection during the test in order to accurately quantify the cumulative permanent deformation. Tests on small size PTFE-based gaskets are conducted to demonstrate the above mentioned effects.

The Blue LED Nobel Prize: Historical context, current scientific understanding, human benefit

The Blue LED Nobel Prize: Historical context, current scientific understanding, human benefit