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1
Fokeev, A. E., und I. N. Tumakov. „Analysis of Operating Modes of Oil-Immersed Power Transformers with a Voltage of 10 (6) / 0.4 kV“. Vestnik IzhGTU imeni M.T. Kalashnikova 24, Nr. 4 (2021): 80–91. http://dx.doi.org/10.22213/2413-1172-2021-4-80-91.
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The rate of thermal aging of the power transformers windings insulation depends on the effects of the electric field, mechanical stresses, temperature and processes that cause changes in these factors. A calculation algorithm is considered that allows determining the temperature of the most heated point of the windings of an oil power transformer at known values of the load current and ambient temperature. Calculation of the most heated winding point temperature and the rate of thermal aging of insulation for an oil power transformer at different ambient temperatures during the year, different values and different spectral composition of the electric load current showed that in some cases it is possible to violate the permissible operating conditions of power transformers. According to the calculation results, the dependences of the thermal aging rate of insulation on the ambient temperature are constructed, with different load parameters and different load coefficients of power transformers. For the considered modes, in the warm season, the value of the thermal aging rate of insulation significantly exceeds the nominal value. Based on mathematical models of oil power transformers with natural and forced oil circulation, expressions are obtained for determining the coefficient of reduction of the oil power transformers permissible load when the ambient temperature exceeds the normal value of 20 °C. On the basis of these expressions, for practical use, the dependences of the coefficient of reduction of the permissible load on the ambient temperature are constructed. The influence of ambient temperature must be taken into account when choosing the power of oil power transformers, for which it is assumed to operate in full redundancy mode or high load factor values (³ 0.8) in normal mode. To ensure the normative service life of the insulation of the windings, it is necessary to determine the design power of oil power transformers using the coefficient of reduction of the permissible load under the influence of higher harmonics of the current and the coefficient of reduction of the permissible load under the influence of ambient temperature.
2
Radziemska, E., und E. Klugmann. „Photovoltaic Maximum Power Point Varying with Illumination and Temperature“. Journal of Solar Energy Engineering 128, Nr. 1 (24.01.2005): 34–39. http://dx.doi.org/10.1115/1.2147586.
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This paper presents the experimental results and discusses the track of the maximum power point on the current-voltage curve of a PV module due to changes of the illumination level and temperature. A time decrease of the voltage and simultaneous temperature increase during the initial stage of irradiation has been observed. Some practical implementation aspects of a maximum power point tracking unit, which match the current and voltage characteristics of the load to the PV module’s maximum power point automatically, are also discussed. A linear decrease of the maximum output power Pm with temperature increase has been observed and the temperature coefficient was derivate. Temperature coefficients for Voc, Isc, Vmpp, Impp, and ηPV have been determined for the photovoltaic module. Also the radiation-rate coefficient at constant temperature has been calculated.
3
Tsao, Bang Hung, Jacob Lawson, James D. Scofield, Clinton Laing und Jeffery Brown. „3D Thermal Stress Model for SiC Power Modules“. Materials Science Forum 600-603 (September 2008): 1227–30. http://dx.doi.org/10.4028/www.scientific.net/msf.600-603.1227.
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Three dimensional models of both single-chip and multiple-chip power sub-modules were generated using ANSYS in order to simulate the effects of various substrate materials, heat fluxes, heat transfer coefficients, and device placement configurations on temperature and thermal stress contours. Alumina, aluminum-nitride, and CVD diamond were compared as substrates. Heat fluxes of 100 to 500 watts/cm2 resulted in SiC device junction temperatures in the range of 350 to 650 K. The predicted maximum operating temperature for a chip, to which 300 watts/cm2 of heat flux was applied, would be 239°C (512 K). In the applied heat flux range, the minimum and maximum Von Mises stress of a simulated single SiC device sub-module was between 1.2 MPa to 2.4 GPa. The maximum shear stress at 300 watts/cm2 was predicted to be 243 MPa. Both the maximum and minimum chip temperature decreased with increasing heat transfer coefficient from 25 to 2500 watts/m2 K. With modest cooling, represented by a heat transfer coefficient (hconv) of 250 watts/m2 K, SiC chips operated at 300 watts/cm2 power density maintained junction temperatures Tj < 400 K. If consistent with simulation results, CVD diamond integrated substrates should be superior to those comprised of AlN or Al2O3. Asymmetric device placement in the multi-chip module proved more effective at avoiding potential hot spots than the symmetric configuration.
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Konovalov, Dmytro, Ignat Tolstorebrov, Yuhiro Iwamoto, Halina Kobalava, Jacob Joseph Lamb und Trygve Magne Eikevik. „Optimizing Low-Temperature Three-Circuit Evaporative Cooling System for an Electric Motor by Using Refrigerants“. Energies 17, Nr. 16 (09.08.2024): 3942. http://dx.doi.org/10.3390/en17163942.
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This article presents modeling results and a comprehensive analysis of evaporative cooling systems designed for electric motors using the refrigerants R744 (trans-critical), R134a, R600a, and R290. This study aims to determine the most suitable refrigerant for use in a cooling system, optimize the system design, and calculate the maximum achievable motor power while adhering to specified temperature constraints. The modeling was validated by an experimental setup, which had the cooling system’s configuration featuring three circuits for motor housing, stator, and rotor cooling, respectively. The modeling of an evaporative system was used to present the cooling efficiency under varying loads and external temperature conditions. Mathematical modeling encompasses complex algorithms to simulate heat transfer phenomena, accounting for fluid dynamics and refrigeration cycle dynamics. The analyses revealed trends in winding temperature, rotor temperature, air temperature inside the motor, heat transfer coefficient, coefficient of performance (COP), and motor power across different operating conditions while using different cooling refrigerants. The maximal heat transfer coefficients were calculated for all the refrigerants for winding temperatures in the range from 32 to 82 °C, while air temperature and rotor temperatures were between 42 and 105 °C and 76 and 185 °C, respectively. Lowering the evaporation temperature of the coolant to −35 °C resulted in a significant decrease in the winding temperature to 15 °C, air temperature to 38 °C, and maximum rotor temperature to 118 °C at a motor power of 90 kW. Refrigerant R744 emerged as a promising option, offering high heat transfer coefficients and achieving high motor power within temperature limits. At the same time, the COP was lower when compared with other working fluids because of the high ambient temperature on the gas cooler side.
5
Kang, Yunxin, und Ling Xu. „First-order Bandgap Reference Source Design with High Power Supply Rejection Ratio“. Journal of Physics: Conference Series 2405, Nr. 1 (01.12.2022): 012003. http://dx.doi.org/10.1088/1742-6596/2405/1/012003.
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Abstract In this paper, a first-order bandgap reference source with a high power supply rejection ratio (PSRR) is designed. To obtain a low-temperature coefficient, a first-order bandgap temperature coefficient compensation method is used by adjusting the resistor resistance of the positive and negative temperature coefficients, and the gate-source voltage of the current mirror transistor is kept constant to increase the PSRR value in the low-frequency band. A self-start circuit is added to make the circuit start up quickly out of the simple bias point. The simulation results show that the bandgap reference voltage source has a constant 1.25V reference voltage with a temperature coefficient of 8.55ppm/°C in the temperature range of -40 to 125°C. The circuit is simulated using Cadence software. The circuit can be applied to OLED constant current source circuits and power management circuits.
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Hossain, Md Al Amin, Md Abdul Malek Soner, Md Abdus Salam, Md Fazlul Huq und Md Shamsul Huda Sohel. „Measurement of Feedback Reactivity Effects of the Baec Triga Reactor“. Journal of Bangladesh Academy of Sciences 42, Nr. 2 (30.12.2018): 183–90. http://dx.doi.org/10.3329/jbas.v42i2.40050.
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The aim of this study is to measure the feedback reactivity effects of the Bangladesh Atomic Energy Commission (BAEC) TRIGA Research Reactor (BTRR). Using digital instrumentation and control (I&C) system, feedback parameters such as reactivity coefficients of fuel, moderator and power effects are measured. At 300 kW reactor power, the obtained results for fuel temperature coefficient are 0.664 ꬿ/0c and 0.765 ꬿ/0c at C1 and D3 core positions respectively. The results for 100 kW to 400 kW reactor power show its increasing nature as the reactor power increases. The measured value of the moderator temperature coefficient is found to be 0.419 ꬿ/0c at 500 kW reactor power. The power coefficient of reactivity is measured for several power ranges from 50 kW to 2.5 MW and the average value is found to be 0.0757 ꬿ/kw. The measured values of the reactivity coefficients are found to be in a good agreement with the GA Safety Analysis Report (SAR) provided for BTRR.
Journal of Bangladesh Academy of Sciences, Vol. 42, No. 2, 183-190, 2018
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Prijić, Z., Z. Pavlović, S. Ristić und N. Stojadinović. „Zero-temperature-coefficient (ZTC) biasing of power VDMOS transistors“. Electronics Letters 29, Nr. 5 (1993): 435. http://dx.doi.org/10.1049/el:19930291.
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Imhoff, Eugene A., Karl D. Hobart, Francis J. Kub, M. G. Ancona, Rachael L. Myers-Ward, N. Y. Garces, Virginia D. Wheeler, Luke O. Nyakiti, Charles R. Eddy und D. Kurt Gaskill. „Positive Temperature Coefficient SiC PiN Diodes“. Materials Science Forum 717-720 (Mai 2012): 981–84. http://dx.doi.org/10.4028/www.scientific.net/msf.717-720.981.
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Integration of patterned ballast resistance into the anode of SiC PiNs is a solution to the dilemma of negative dVf /dT for such diodes. In fabricated 4H-SiC PiN diodes, we demonstrate a cross-over from negative to positive temperature coefficient for current densities as low as 80 A/cm2. Adjusting the percentage of the patterned anode area, the positive or neutral dVf /dT can be achieved over a wide current-density range without substantial penalty in the forward voltage drop. This characteristic is crucial for high-power SiC packages with ganged-parallel rectifier arrays.
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Lin, Jyun-Min, Ying-Chung Chen und Chi-Pi Lin. „Annealing Effect on the Thermoelectric Properties of Bi2Te3Thin Films Prepared by Thermal Evaporation Method“. Journal of Nanomaterials 2013 (2013): 1–6. http://dx.doi.org/10.1155/2013/201017.
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Bismuth telluride-based compounds are known to be the best thermoelectric materials within room temperature region, which exhibit potential applications in cooler or power generation. In this paper, thermal evaporation processes were adopted to fabricate the n-type Bi2Te3thin films on SiO2/Si substrates. The influence of thermal annealing on the microstructures and thermoelectric properties of Bi2Te3thin films was investigated in temperature range 100–250°C. The crystalline structures and morphologies were characterized by X-ray diffraction and field emission scanning electron microscope analyses. The Seebeck coefficients, electrical conductivity, and power factor were measured at room temperature. The experimental results showed that both the Seebeck coefficient and power factor were enhanced as the annealing temperature increased. When the annealing temperature increased to 250°C for 30 min, the Seebeck coefficient and power factor of n-type Bi2Te3-based thin films were found to be about −132.02 μV/K and 6.05 μW/cm·K2, respectively.
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Huang, Pei, Tong Shen, Zhenxing Liu, Renjun Dian, Wanlun Xu und Dan Wang. „Thermal characteristics analysis of medium frequency transformer under multiple working conditions“. Thermal Science, Nr. 00 (2023): 239. http://dx.doi.org/10.2298/tsci230807239h.
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Medium frequency transformer (MFT) plays an important role in high power AC-DC transformation in power grid, due to its high power density and high loss density, it brings difficulty to heat dissipation. Thermal reliability is crucial for transformer design, different from the previous work, the thermal characteristics of MFT under different working conditions are concerned and analyzed in this paper. The temperature field model of MFT is established, and the temperature field characteristics of MFT at rated load, no load, overload, fluctuating overload and short circuit conditions are simulated and analyzed, the results show that with the increase of load coefficient, the winding temperature increases obviously, the allowable load coefficient of MFT can be determined by calculating the transformer temperature at different load coefficients, which lays a foundation for thermal reliability and safe operation of MFT.
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Zhao, Xiaokun, Minghao Ni, Wencai Wang, Hongwei Wang und Jianing Wang. „Study on the Fire Characteristics of Dual Fire Sources and the Difference in Power Temperature of Different Fire Sources in Tunnel“. Fire 7, Nr. 8 (06.08.2024): 273. http://dx.doi.org/10.3390/fire7080273.
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To investigate the combustion characteristics of multiple fire sources in the tunnel caused by ‘jumping’ discontinuous fire spread, we utilized scaled model experiments, numerical simulation software, and theoretical research. Our study focused on analyzing the influence of different fire source powers on the temperature characteristics of double fire sources in the tunnel. We examined the temperature characteristics, critical wind speed, and change rule under various wind speeds, fire source spacing, and fire source powers. Additionally, we explored the temperature characteristics, critical wind speed, and change rule of different fire source powers under varying wind speed conditions. The mathematical model for roof temperature decay and the temperature decay coefficients of dual source fires were established through the analysis of scale-down model experiments and numerical simulations. In comparison to single-source fires, the temperature variations in the tunnel of dual source fires exhibit a more intricate pattern, with higher average temperature and temperature peak values. These values are influenced by factors such as fire source spacing and power. Numerical simulation software was utilized to investigate the impact of fire source spacing at 10 m, 15 m, and 20 m, as well as the effect of varying fire source power on the temperature distribution within a tunnel under consistent fire source position and growth coefficient. The study revealed that, with consistent double fire source position and ventilation conditions in the tunnel, the upstream fire source exhibited greater power than the downstream fire source, resulting in the lowest average and peak temperatures in the tunnel. This observation could potentially enhance escape and rescue operations within the tunnel. Similarly, the lowest average and peak temperatures in the tunnel were also identified, offering potential benefits for optimizing escape and rescue strategies in tunnel scenarios.
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Adedoja, Oluwaseye Samson, Damilola Elizabeth Babatunde und Olubayo Moses Babatunde. „HYBRID POWER SYSTEM FOR A FUEL STATION CONSIDERING TEMPERATURE COEFFICIENT“. International Journal of Energy Economics and Policy 10, Nr. 6 (10.10.2020): 476–82. http://dx.doi.org/10.32479/ijeep.9886.
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13
Chen, Pingwei, Tong Wang, Wensheng Ma, Zhongliang Xie und Guangbin Yu. „CFD-Predicted Rotordynamic Characteristics for High-Temperature Water Liquid Seal Considering Tooth Deformation“. Lubricants 10, Nr. 10 (28.09.2022): 240. http://dx.doi.org/10.3390/lubricants10100240.
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With the development of high-temperature centrifugal pump, the temperature of the medium in the pump must be higher than the normal water temperature. It is particularly important to study the rotordynamic characteristics of the seal at high temperature due to it being the core component of the rotor system. This paper takes the high temperature water liquid seal as a research object to study its rotordynamic characteristics based on the fluid-solid-thermal coupling, the deformation of seal teeth under thermal and dynamic loads was calculated. Based on the test rig, the leakage flow rate and drag power loss of water liquid seal at 20 °C, 50 °C, and 86 °C temperatures were tested and compared with the CFD (Computational Fluid Dynamics) calculation. Meanwhile, the DEFINE-CG-MOTION and DEFINE-PROFILE control macro were used to establish the rotor whirling equation, the frequency-independent rotordynamic coefficients (K, k, C, c) and frequency-dependent rotordynamic coefficients (Keff,Ceff) were evaluated by transient CFD method. This analysis was done at three different pressure drops (2.08, 4.12, and 8.25 bar) and three rotational speeds (2000, 4000, and 6000 r/min). The results show that with the increase of water temperature, both the leakage flow rate and drag power loss decrease, indicating the 86 °C water seal has a better sealing capacity. From the rotordynamic perspective, with the increase of water temperature, the direct stiffness coefficient decreases, and the effective stiffness coefficient Keff for 20 °C water seal possesses a better stiffness capability than the other two temperature seals. The effective damping coefficient Ceff for 20 °C water seal is larger than the other two temperature seals, which means it is more stable for the rotor system.
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PAEZ, B. A., H. MÉNDEZ und J. C. GIRALDO. „THERMOELECTRIC POWER COEFFICIENT IN A QUANTUM WELL“. Surface Review and Letters 09, Nr. 05n06 (Oktober 2002): 1765–68. http://dx.doi.org/10.1142/s0218625x02004372.
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Based on the solution of the quantum Boltzmann equation, in the linear transport approximation for an isotropic low-dimensional system, the thermoelectric power coefficient, Q, in a quantum well structure was determined. These calculations are based on variational methods, taking into account especial functions which include important parameters being varied at the time of evaluating the thermoelectric power, e.g. height and width barrier. Values of Q are carried out by using a computer code written in Mathematica, which allows one to depict them easily and in this way to compare different behaviors of Q against temperature according to the scattering mechanism (phonons).
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Feng, Wen Jiang, Chuan Yin Wang, Zhi Guo Zhang und Wei Zheng. „Physical Properties of High-Temperature Liquid Furnace Slags“. Applied Mechanics and Materials 319 (Mai 2013): 62–65. http://dx.doi.org/10.4028/www.scientific.net/amm.319.62.
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The room-temperature furnace slag from a pig iron plant was investigated and the corresponding chemical composition was obtained. The temperature dependences of viscosity coefficient, resistance, and heat transfer coefficient were measured in detail. With increasing temperatures, the value of viscosity coefficient and resistance is lowered, while that of heat transfer coefficient enlarged. The fit of temperature dependence of viscosity coefficient gives y0=1.9672, A=1.95×1019, t=31.8. Above 1000 oC, solid slags become melted and flown, with abrupt increase of heat transfer coefficient. Based on the designing of medium-frequency induction furnace, we can conclude as follows: (1) the liquid slags are conductive with a small conductance, which reveals that the medium-frequency induction furnace can be employed with a small power; (2) heat transfer coefficient gets enlarged with increasing temperature, which indicates that the higher the temperature is, the larger the heat loss gets.
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Hong, Chih-Chiang. „Determining the Advanced Frequency of Composited Functionally Graded Material Plates Using Third-Order Shear Deformation Theory and Nonlinear Varied Shear Coefficients“. Journal of Composites Science 8, Nr. 8 (16.08.2024): 325. http://dx.doi.org/10.3390/jcs8080325.
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The shear effect is usually considered in the numerical calculation of thick composited FGM plates. The characteristics that have the greatest effect on thickness are displacement type, shear correction coefficient, material property and temperature. For the advanced frequency study of thick composited functionally graded material (FGM) plates, it is interesting to consider the extra effects of the nonlinear coefficient c1 term of the third-order shear deformation theory (TSDT) of displacement on the calculation of varied shear correction coefficients. The values of nonlinear shear correction coefficients are usually functions of c1, the power-law exponent parameter and environment temperature. Numerical frequency computations are calculated using a simple homogeneous equation, and are investigated using TSDT and the nonlinear shear correction coefficient for thick composited FGM plates. Results for natural frequencies are found via the functions of length-to-thickness ratio, the power-law exponent parameter, c1 and environment temperature. This novel study in advanced frequency aims to determine the effects of the TSDT and nonlinear shear correction on thick FGM plates under free vibration.
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ZAITSEV, SERGEY, und VALENTIN ТIKHENKO. „DIAGNOSIS OF POWER OIL IN PUMPING UNITS COOLING SYSTEMS OF POWER PLANT EQUIPMENT“. Herald of Khmelnytskyi National University. Technical sciences 319, Nr. 2 (27.04.2023): 113–19. http://dx.doi.org/10.31891/2307-5732-2023-319-1-113-119.
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The article presents the results of improving the methods for diagnosing the energy oil “Tp-30” of the pumping unit of the NPP equipment coolant circulation system. When studying the physicochemical and thermophysical properties of this oil, it was found that: the indicators “acid number”, “water content”, “content of mechanical impurities”, “content of the additive “Ionol”, “flash point”, “kinematic viscosity” correspond to the established standards. When determining the concentration of the additive “Ionol” in the sample of this oil: the method of adding the additive “Ionol” is used; in the obtained calculation formula, the values of the distribution coefficient for the additive “Ionol” in the system “turbine oil – additive “Ionol” – liquid extractant” are not used, which simplifies the study of the content of this additive in turbine oil. The water content in mineral turbine oil, determined by gas chromatography and coulometric titration with K. Fischer’s reagent, exceeds the water content in this oil, determined by thermal extraction. When studying the effect of liquid extraction temperature on additives “Ionol” (when determining its content in a given oil), it was found by gas chromatography that: the dependence of the distribution coefficients Ki on temperature t in the temperature range 15–75 0С can be expressed by the equation lnKi = А/(t+273) – B ; It is recommended to extract the Ionol additive from this oil at a temperature of (20 ± 2) °С or at a temperature of (65 ± 10) °С. When studying the effect of the chemical nature of the extractant on the ability to extract the “Ionol” additive from this oil, it was found that: ethanol, isopropanol, acetonitrile can be used as extractants of the “Ionol” additive, and the mixture “acetonitrile – water” cannot be recommended as such extractant. The results obtained can be used to improve the method of diagnosing mineral turbine oil “Tp-30” of the pumping unit of the coolant circulation system of the equipment of the second circuit of NPP with a pressurized water power reactor.
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Choi, Han Na, Seung Hyun Jee, Jaehwan Ko, Dong Joo Kim und Sun Hee Kim. „Properties of Surface Heating Textile for Functional Warm Clothing Based on a Composite Heating Element with a Positive Temperature Coefficient“. Nanomaterials 11, Nr. 4 (01.04.2021): 904. http://dx.doi.org/10.3390/nano11040904.
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A high-stretch positive temperature coefficient (PTC) surface heating textile (PTC-SHT) was fabricated using a composite of PTC powder and multiwall carbon nanotubes (MWCNTs). The PTC-SHT (heating area = 100 × 100 mm2) was produced by screen-printing the PTC-MWCNT composite paste onto a high-stretch textile with embroidered electrodes. Overall, the temperature increased to 56.1 °C with a power consumption of 5 W over 7 min. Subsequently, the surface temperature of the PTC-SHT remained constant despite the continued decrease in power consumption. This indicated that heating was accompanied by an increase in resistance of the PTC-SHT, which is typical of this process—i.e., heating to a constant temperature under a constant voltage over an extended period of time. In addition, 4.63 W power was required to heat the PTC-SHT surface from an external temperature of 5 to 45 °C in 10 min, after which stable low-temperature heat generation behavior was observed at a constant temperature of 50 °C, which was maintained over 40 min. In contrast, negative temperature coefficient (NTC) behavior has been observed in an NTC-SHT consisting of only MWCNTs, where a slow heating rate in the initial stage of power application and a continuous increase in surface temperature and power consumption were noted. The PTC-SHT consumed less power for heat generation than the NTC-SHT and exhibited rapid heating behavior in the initial stage of power application. The heat generation characteristics of the PTC-SHT were maintained at 95% after 100,000 cycles of 20% stretch–contraction testing, and the heating temperature remained uniformly distributed within ± 2 °C across the entire heating element. These findings demonstrated that an SHT with PTC characteristics is highly suitable for functional warm clothing applications that require low power consumption, rapid heating, stable warmth, and high durability.
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Hong, Ye, Yimin Mo, Juncheng Lv und Jun Wang. „Tribological Properties of Polymer Friction Improvers Combined with MoDTC/ZDDP at Different Temperatures“. Lubricants 11, Nr. 5 (28.04.2023): 196. http://dx.doi.org/10.3390/lubricants11050196.
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To expand the applications of polymer friction modifiers in low viscosity oils suitable for hybrid power systems, the tribological properties of five kinds of oil samples at different temperatures were studied, which were compounded with polymer friction modifiers Perfad XG 2500, molybdenum dialkyl dithiocarbamate (MoDTC), zinc dialkyl dithiophosphate (ZDDP). When Perfad XG 2500 is used alone, it forms a brush-like surface film at low temperatures, which can provide lower initial friction. With the rise in temperature, its antifriction effect decreases significantly, which is related to the desorption behavior of physical film. When Perfad XG 2500 is combined with MoDTC, it has the best synergistic antifriction effect, and the average friction coefficient is reduced by a maximum of 20.83% (90 °C). Its friction coefficients decrease significantly with the increase in temperature due to the dissociation process of MoDTC catalyzed by high temperature. However, there are many furrows on the worn surfaces, and the sharp features of the profiles are obvious. When Perfad XG 2500 is combined with ZDDP, it has the best synergistic anti-wear effect, and the total wear depth is reduced by 49.6%. Its worn surface is smooth and defect-free, with minimal residual strain. The friction coefficients are hardly affected by temperature, and the average friction coefficient is reduced by a maximum of 14.4% (30 °C). When Perfad XG 2500, MoDTC and ZDDP are used together, the average friction coefficient is reduced by up to 15.2% (30 °C). Its friction coefficient increases slightly with the rise in temperature. The reason for its moderate tribological performance may be related to the superficial competition of various additives.
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Yamaguchi, Masahito, Jihyun Paek und Hiroshi Amano. „Thermoelectric Power Measurement of Catalyst-free Si-doped GaAs Nanowires“. MRS Proceedings 1439 (2012): 83–87. http://dx.doi.org/10.1557/opl.2012.1326.
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ABSTRACTSi-doped GaAs nanowires (NWs) were grown on (111)Si substrate by MBE-VLS method. The electrical characteristics of the GaAs NWs were measured. A joule heater was arranged near the tip of NW for making the gradient of substrate temperature. The obtained Seebeck coefficient of the GaAs NW increases linearly with a rise in temperature. The thermoelectric power of the Si doped GaAs NW was determined by the hole diffusion. It was estimated that the hole density in the Si-doped GaAs NW at room temperature was 5.9×1018 cm-3 from the slope of the temperature dependence of the Seebeck coefficient in the Si-doped GaAs NW. At room temperature, the Seebeck coefficient, thermoelectric power factor, and thermoelectric figure of merit (ZT) were 429 μV/K, 271μW/mK2, and 1.5×10-3, respectively.
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Shahhath, Ahmed A., Haroun A. K. Shahad und Alaa A. Mahdi. „Parametric Theoretical Study of Solar Assisted Cooling System Using Lithium Bromide-Water Pair“. IOP Conference Series: Earth and Environmental Science 877, Nr. 1 (01.11.2021): 012020. http://dx.doi.org/10.1088/1755-1315/877/1/012020.
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Abstract In this paper, the effect of parameters of solar absorption system such as evaporator, absorber, condenser, generator temperatures and the mass of the solution on the evaporator cooling load and the coefficient of performance has been explained theoretically. The results show that, increasing of evaporator and condenser temperatures increase the evaporator cooling load, performance coefficient and the Ratio of Circulation while increasing the temperature of condenser and absorber decreases the evaporator cooling load, performance coefficient and the Circulation Ratio. In addition, increasing the solution mass increases the refrigeration power while the performance coefficient and the Circulation Ratio was constant at increasing the solution mass. The reached maximum cooling load was (1.932 kW) at 15 kg solution mass and 100 °C generator temperature, the maximum COP was 0.774 at (10 °C) temperature of evaporator and the peak Circulation Ratio was 0.3066 at (30 °C) temperature of absorber and (100 °C) temperature of generator.
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Bowen, Zhang, Zhang Xiaoling, Xiong Wenwen, She Shuojie und Xie Xuesong. „The investigation of the zero temperature coefficient point of power MOSFET“. Journal of Semiconductors 37, Nr. 6 (Juni 2016): 064011. http://dx.doi.org/10.1088/1674-4926/37/6/064011.
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Hu, Zhi Cheng, Zhi Hua Ning und Le Nian He. „A Low Temperature Coefficient, High Voltage Detection Circuit Used in Power over Ethernet“. Advanced Materials Research 588-589 (November 2012): 839–42. http://dx.doi.org/10.4028/www.scientific.net/amr.588-589.839.
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A low temperature coefficient, high voltage detection circuit used in Power over Ethernet is proposed. This circuit realizes the detection comparison without utilizing an extra voltage reference circuit and comparator while the temperature coefficient of the threshold voltage is as low as that of a regular bandgap reference. The proposed detection circuit is implemented in CSMC 0.5μm 60V BCD process, Cadence Spectre simulation results show that the temperature coefficient of the threshold voltage is 66.5 ppm/°C over the temperature range of -40°C to 125°C, and the maximum variation of the threshold voltage is 2.7% under all corners.
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Balasubramanian, Andi, Venkatesan Jayaraman, Suresh Sivan und Mariappan Vairavan. „Experimental analysis of triple fluid vapour absorption refrigeration system driven by electrical energy and engine waste heat“. Thermal Science 23, Nr. 5 Part B (2019): 2995–3001. http://dx.doi.org/10.2298/tsci171129110a.
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In this study, performance analysis of absorption refrigeration cycle has been carried out under variable power sources namely electrical and thermal energy sources. The triple fluid vapour absorption system was used in this work. The temperatures at each point in the cycle such as generator, absorber, evaporator and condenser have been measured. The coefficient of performance of the system was calculated and then compared. The results showed that when the cycle driven by electricity, the coefficient of performance varied from 0.28-1.6 along the test time and the generator temperature changed from 66?C to 106?C. When thermal energy used to generate power, the coefficient of performance varied between 0.16 and 0.6 under the generator temperature of 98?C and 150?C. It was observed that the waste heat energy from engine exhaust can be used efficiently and can replace the conventional power source to drive the absorption refrigeration unit.
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Fu, Li, und Jing Feng Li. „Preparation and Thermoelectric Properties of LaCoO3 Ceramics“. Key Engineering Materials 434-435 (März 2010): 404–8. http://dx.doi.org/10.4028/www.scientific.net/kem.434-435.404.
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LaCoO3 ceramics were prepared by conventional solid state reaction and normal sintering at the temperatures ranging from 1373 to 1523 K. The sintered densities increased with increasing sintering temperature and exceeded 90 % of the theoretical values when sintered above 1473 K. The thermoelectric properties of the samples sintered at different temperatures were investigated from 323 to 673 K. The LaCoO3 samples showed a negative Seebeck coefficient, whose absolute values decreased dramatically with increasing temperature in the range of 323 to 460 K, then changed to a positive value and lightly decreased above 460 K. The electrical conductivity increased with increasing temperature, indicating a semiconducting behavior. The Seebeck coefficients showed little difference between the samples sintered at different temperatures, but the power factor of the sample sintered at a higher temperature was larger because of the higher electrical conductivity.
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Drizdal, Tomas, Gerard C. van Rhoon, Rene F. Verhaart, Ondrej Fiser und Margarethus M. Paulides. „A Guide for Water Bolus Temperature Selection for Semi-Deep Head and Neck Hyperthermia Treatments Using the HYPERcollar3D Applicator“. Cancers 13, Nr. 23 (05.12.2021): 6126. http://dx.doi.org/10.3390/cancers13236126.
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During hyperthermia cancer treatments, especially in semi-deep hyperthermia in the head and neck (H&N) region, the induced temperature pattern is the result of a complex interplay between energy delivery and tissue cooling. The purpose of this study was to establish a water bolus temperature guide for the HYPERcollar3D H&N applicator. First, we measured the HYPERcollar3D water bolus heat-transfer coefficient. Then, for 20 H&N patients and phase/amplitude settings of 93 treatments we predict the T50 for nine heat-transfer coefficients and ten water bolus temperatures ranging from 20–42.5 °C. Total power was always tuned to obtain a maximum of 44 °C in healthy tissue in all simulations. As a sensitivity study we used constant and temperature-dependent tissue cooling properties. We measured a mean heat-transfer coefficient of h = 292 W m−2K−1 for the HYPERcollar3D water bolus. The predicted T50 shows that temperature coverage is more sensitive to the water bolus temperature than to the heat-transfer coefficient. We propose changing the water bolus temperature from 30 °C to 35 °C which leads to a predicted T50 increase of +0.17/+0.55 °C (constant/temperature-dependent) for targets with a median depth < 20 mm from the skin surface. For deeper targets, maintaining a water bolus temperature at 30 °C is proposed.
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Zhang, Xiu Li, Zhong Wei Yin, Dan Jiang und Geng Yuan Gao. „Comparison of the Lubrication Performances of Water-Lubricated and Oil-Lubricated Plain Journal Bearings“. Applied Mechanics and Materials 711 (Dezember 2014): 27–30. http://dx.doi.org/10.4028/www.scientific.net/amm.711.27.
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Water-lubricated bearings have attracted increasing attention in recent years because of their environmental sustainability, simplified design, low cost, good cooling performance and low coefficient of friction. To show the characteristic of water lubrication more clearly, this paper quantitatively compares the lubrication performances of water-lubrication plain journal bearing and oil-lubricated plain journal bearing using CFD method. Bearing length, friction coefficients, power losses and temperature rises are obtained under the same working condition. Results show that water-lubricated bearing needs to be 3.4 times longer than oil-lubricated bearing, but its friction coefficient and power loss are only 11.7% of those of oil-lubricated bearing and its maximum temperature rise is less than 2 K, much lower than 96.76 K corresponding to oil lubrication.
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Feier, Ioan, Joseph Way und Rob Redfield. „Bicycle Disc Brake Thermal Performance: Combining Dynamometer Tests, Bicycle Experiments, and Modeling“. Proceedings 49, Nr. 1 (15.06.2020): 100. http://dx.doi.org/10.3390/proceedings2020049100.
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High-power bicycle disc braking can create excessive temperatures and boiling brake fluid, resulting in performance degradation and damage. The goal of this work is to understand brake friction performance and thermal behavior for bicycle disc brakes. A previously described disc braking dynamometer is used to assess brake pad performance of sintered metallic brake pads, organic brake pads, and ‘power’ organic pads in up to 400 W of braking power. The friction coefficient is found to be dependent on both temperature and normal force. Friction curve fits are provided for temperatures between 300 K and 550 K. Organic and ‘power’ organic pads are found to have similar behavior, and have higher friction coefficients compared to metallic pads. Further, brakes on an instrumented bicycle are tested in outdoor field trials during downhill descent. A MATLAB thermal model successfully predicts the downhill field brake disc temperatures when using the friction data curve fits.
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Filippou, Antria, Nikolas Evripidou, Andreas Georgiou, Anastasia Nikolaou und Christakis Damianou. „Estimation of the Proton Resonance Frequency Coefficient in Agar-based Phantoms“. Journal of Medical Physics 49, Nr. 2 (April 2024): 167–80. http://dx.doi.org/10.4103/jmp.jmp_146_23.
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Aim: Agar-based phantoms are popular in high intensity focused ultrasound (HIFU) studies, with magnetic resonance imaging (MRI) preferred for guidance since it provides temperature monitoring by proton resonance frequency (PRF) shift magnetic resonance (MR) thermometry. MR thermometry monitoring depends on several factors, thus, herein, the PRF coefficient of agar phantoms was estimated. Materials and Methods: Seven phantoms were developed with varied agar (2, 4, or 6% w/v) or constant agar (6% w/v) and varied silica concentrations (2, 4, 6, or 8% w/v) to assess the effect of the concentration on the PRF coefficient. Each phantom was sonicated using varied acoustical power for a 30 s duration in both a laboratory setting and inside a 3T MRI scanner. PRF coefficients were estimated through linear trends between phase shift acquired using gradient sequences and thermocouple-based temperatures changes. Results: Linear regression (R 2 = 0.9707–0.9991) demonstrated a proportional dependency of phase shift with temperature change, resulting in PRF coefficients between −0.00336 ± 0.00029 and −0.00934 ± 0.00050 ppm/°C for the various phantom recipes. Weak negative linear correlations of the PRF coefficient were observed with increased agar. With silica concentrations, the negative linear correlation was strong. For all phantoms, calibrated PRF coefficients resulted in 1.01–3.01-fold higher temperature changes compared to the values calculated using a literature PRF coefficient. Conclusions: Phantoms developed with a 6% w/v agar concentration and doped with 0%–8% w/v silica best resemble tissue PRF coefficients and should be preferred in HIFU studies. The estimated PRF coefficients can result in enhanced MR thermometry monitoring and evaluation of HIFU protocols.
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Chamkha, Ali J. „Compressible Dusty-Gas Boundary-Layer Flow Over a Flat Surface“. Journal of Fluids Engineering 118, Nr. 1 (01.03.1996): 179–85. http://dx.doi.org/10.1115/1.2817498.
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Equations governing compressible boundary-layer laminar flow of a two-phase particulate suspension are developed based on a continuum representation of both phases. These equations include such effects as particle-phase viscous stresses, variable position-dependent particle slip coefficient, and general power-law viscosity-temperature and thermal conductivity-temperature relations. The dimensionless form of the equations are applied to the problem of flow over a semi-infinite flat surface. An appropriate transformation is employed to allow proper comparison with previously published results for special cases of this problem. The full coupled system of equations is solved numerically via an implicit finite-difference method. Graphical results for the density, and temperature profiles as well as the displacement thicknesses, skin-friction coefficients, and the wall heat transfer coefficient for both the fluid and particle phases are presented and discussed in detail. In addition, a parametric study is performed to illustrate the influence of the particle to fluid viscosity ratio and the viscosity-temperature power exponent on the flow properties.
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Jun, Dongsuk, Soojung Kim, Wonchul Choi, Junsoo Kim, Taehyoung Zyung und Moongyu Jang. „Silicide/Silicon Hetero-Junction Structure for Thermoelectric Applications“. Journal of Nanoscience and Nanotechnology 15, Nr. 10 (01.10.2015): 7472–75. http://dx.doi.org/10.1166/jnn.2015.11148.
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We fabricated silicide/silicon hetero-junction structured thermoelectric device by CMOS process for the reduction of thermal conductivity with the scatterings of phonons at silicide/silicon interfaces. Electrical conductivities, Seebeck coefficients, power factors, and temperature differences are evaluated using the steady state analysis method. Platinum silicide/silicon multilayered structure showed an enhanced Seebeck coefficient and power factor characteristics, which was considered for p-leg element. Also, erbium silicide/silicon structure showed an enhanced Seebeck coefficient, which was considered for an n-leg element. Silicide/silicon multilayered structure is promising for thermoelectric applications by reducing thermal conductivity with an enhanced Seebeck coefficient. However, because of the high thermal conductivity of the silicon packing during thermal gradient is not a problem any temperature difference. Therefore, requires more testing and analysis in order to overcome this problem. Thermoelectric generators are devices that based on the Seebeck effect, convert temperature differences into electrical energy. Although thermoelectric phenomena have been used for heating and cooling applications quite extensively, it is only in recent years that interest has increased in energy generation.
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Kazansky, Yury, und Yanis Slekenichs. „Power coefficient of reactivity: definition, interconnection with other coefficients of reactivity, evaluation of results of transients in power nuclear reactors“. Nuclear Energy and Technology 4, Nr. 2 (26.11.2018): 111–18. http://dx.doi.org/10.3897/nucet.4.30663.
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It is assumed by the authors of the present paper that with growing contribution of nuclear power in the production of electricity, nuclear power plants will be used to a higher degree in a manoeuvrable mode of operation rather than in the base-load mode. In other words, change of power from the nominal level to that of coverage of auxiliary loads will be becoming quite common and not so rare event as scheduled reactor shutdowns for fuel reloading or preventive works. There exist well-known problems in the use of nuclear reactors in the manoeuvrable operation mode, which include the task shared by all types of nuclear reactors. It is advisable to have a unified indicator weakly power-dependent and fairly easy to measure, which would make it possible to formulate the judgement about the nature of the transient processes within the entire power range and to assess the reactivity required for changing the power level by the preset value. Power reactivity coefficient (PRC) can be used as such indicator. Analysis was made of existing definitions and understanding of PRC in relevant references. It turned out that there is no generally accepted definition of the PRC. Based on the performed study, the following definition was suggested: the PRC is the ratio of the low reactivity introduced into the reactor to the power increment at the end of the transient process. It is assumed here that variation of reactivity is dependent on the energy released in nuclear fission but is not related to the changes of reactivity induced by feedback signals in the automatic reactor power control system. Analysis of the relationship between the PRC and temperature coefficients and technological parameters associated with the steady-state control program was performed taking the above suggested definition into account. PRC calculations were performed using the simplest model of VVER-1000 type power reactor. It was found that PRC is weakly power-dependent. The purpose of the present study is to investigate dependence of PRC on the temperature reactivity effects and on the technological parameters associated with the steady-state control program of the power unit, using the example of VVER-1000. Effects of PRC on the static and dynamic power reactor operation modes are analyzed.
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Bunganaen, Wenseslaus. „Simulasi Termodinamika Pengaruh Temperatur Subcooling di Kondensor Terhadap Kinerja Cold Storage“. LONTAR Jurnal Teknik Mesin Undana 9, Nr. 02 (18.12.2022): 40–46. http://dx.doi.org/10.35508/ljtmu.v9i02.9365.
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The subcooling temperature in the condenser can affect the overall performance of the refrigeration system. One of the refrigeration systems that plays an important role in the cold chain of fishery products is cold storage. This paper discusses thermodynamic study of the effect of condenser subcooling temperatures on the performance of cold storage that operates based on a vapor compression refrigeration cycle based on the CoolPack software. The subcooling temperatures varied was 5 – 10 Kelvin and the system performance parameters analyzed were refrigerant mass flow rate, heat rejected in the condenser, compressor power and coefficient of performance. The results of this study indicate that as the subcooling temperature increases, the refrigerant mass flow rate decreases so that the compressor power and the rate of heat release in the condenser also decrease. Thus, the performance coefficient of cold storage will increase as the subcooling temperature increases.
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Unyanin, Alexander N., und Pavel R. Finageev. „Research of the Influence of Cutting Conditions on the Temperature Field during Turning“. Key Engineering Materials 910 (15.02.2022): 271–77. http://dx.doi.org/10.4028/p-l205d1.
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Numerical simulation of the temperature field and parameters of the turning process of workpieces made of 45 and 12Kh18N10T steels is performed. The front angle of the cutter, as well as the coefficients of chip friction on the front surface of the tool μ1, the flank surface on the workpiece μ2, and the coefficient of friction on the yield stress μ were selected as variable parameters. The degree of influence of the variable parameters on the tangential component of the cutting force, the friction force on the front and flank surfaces of the cutting tool, the power of heat sources, contact temperatures and the average temperature of the workpiece is estimated.
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Liu, Junchao, und Xiaocha Wang. „Design of a High PSRR Low-pressure Bandgap Reference Source with Curvature Compensation“. Journal of Physics: Conference Series 2625, Nr. 1 (01.10.2023): 012078. http://dx.doi.org/10.1088/1742-6596/2625/1/012078.
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Abstract Based on the NUVOTON 0.35 μm BCD process, a low voltage bandgap reference with an input voltage of 5 V and output voltage of 0.6 V is designed in this paper. The traditional low-voltage bandgap reference output voltage has a large temperature coefficient and poor ability to suppress power supply fluctuations. In this paper, a circuit with high order compensation is proposed to reduce the temperature coefficient of the circuit, and a pre-regulated circuit is used to increase the power supply rejection ratio. The simulation results are at -30 °C∼130 °C. The output voltage of reference voltage is 947.5 μV, the temperature coefficient is 9.58 ppm/°C, and the power suppression ratio is -104.62 dB, which meets the design requirements of the power management chip.
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SUHA H. IBRAHEEM,. „Effect of Laser annealing on structural and thermoelectric properties of SnSe thin films“. journal of the college of basic education 28, Nr. 115 (25.06.2022): 1–9. http://dx.doi.org/10.35950/cbej.v28i115.5828.
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This study adopted the flash evaporation technique to prepare SnSe thin films onto glass substrates kept at room temperature. The effect of CO2 laser annealing on the structural properties and thermoelectric characterizations of SnSe films was investigated in power annealing (10 W) at (10,15,20 Min). Morphologies and structures of the crystalline were determined using an atomic force microscope and X-ray diffraction. Power factor, electrical conductivity, and the Seebeck coefficients were determined. The results demonstrated that the power factor and the Seebeck coefficient were enhanced as the annealing time increased. When the annealing time reaches twenty minutes at 500K, the power factor and Seebeck coefficient of SnSe thin films were found to be about 6.33 μW/cm.K2 and 650 μV/K., respectively.
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Жуков, В. П., und Е. В. Чулков. „Электронная зонная структура и термоэлектрические характеристики SrTiO-=SUB=-3-=/SUB=-, BaTiO-=SUB=-3-=/SUB=- и CaTiO-=SUB=-3-=/SUB=-: ab initio подход“. Физика твердого тела 64, Nr. 12 (2022): 1891. http://dx.doi.org/10.21883/ftt.2022.12.53638.383.
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The calculations of Seebeck’s coefficient, conductivity and power functions for the electron-doped SrTiO_3, BaTiO_3 and CaTiO_3 compounds have been performed depending on temperature and current carrier concentration by employing ab initio method based on the electron density functional theory, on the Frohlich’s approach for the electron-phonon interaction and on the theory of Boltzmann–Onsager for the thermoelectric properties. The calculated Seebeck’s coefficient and conductivity correspond to experimental data. It is shown that for SrTiO_3 and BaTiO_3 the dependencies of power functions on the carrier concentration have maxima in the range of (200–250) × 10^{19} cm^{–3} at any temperature, while for CaTiO_3 the maxima are typical only at temperatures below 500 K. The temperature dependencies of the power function also confirm that such carrier concentration range is favorable for achieving high values of the SrTiO_3 figure of merit, while the maximally possible carrier concentration is necessary for optimal CaTiO_3 figure of merit.
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Zhukov V. P. und Chulkov E. V. „Electronic band structure and thermoelectric properties of SrTiO-=SUB=-3-=/SUB=-, BaTiO-=SUB=-3-=/SUB=- and CaTiO-=SUB=-3-=/SUB=-: ab initio approach“. Physics of the Solid State 64, Nr. 12 (2022): 1855. http://dx.doi.org/10.21883/pss.2022.12.54377.383.
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The calculations of Seebeck's coefficient, conductivity and power functions for the electron-doped SrTiO3, BaTiO3 and CaTiO3 compounds have been performed depending on temperature and current carrier concentration by employing ab initio method based on the electron density functional theory, on the Frohlich's approach for the electron-phonon interaction and on the theory of Boltzmann--Onsager for the thermoelectric properties. The calculated Seebeck's coefficient and conductivity correspond to experimental data. It is shown that for SrTiO3 and BaTiO3 the dependencies of power functions on the carrier concentration have maxima in the range of (200-250)·1019 cm-3 at any temperature, while for CaTiO3 the maxima are typical only at temperatures below 500 K. The temperature dependencies of the power function also confirm that such carrier concentration range is favorable for achieving high values of the SrTiO3 figure of merit, while the maximally possible carrier concentration is necessary for optimal CaTiO3 figure of merit. Keywords: Ca, Sr, Ba titanates, PAW method, electronic structure, thermoelectric properties.
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Van Der Veen, C. J., und K. C. Jezek. „Seasonal variations in brightness temperature for central Antarctica“. Annals of Glaciology 17 (1993): 300–306. http://dx.doi.org/10.3189/s0260305500013008.
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The radiative-transfer model developed by Zwally (1977) is modified and coupled to a one-dimensional time-dependent temperature model, to calculate the seasonal variation in brightness temperature. By comparing this with observed records, the radiative properties of firn can be determined. By retaining scattering as a source term in the radiative transfer function, agreement between model-derived scattering and absorption coefficients and those calculated from the Mie/Rayleigh scattering theory can be obtained. The horizontal brightness temperature is not linked to the vertical one through a constant power reflection coefficient.
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Van Der Veen, C. J., und K. C. Jezek. „Seasonal variations in brightness temperature for central Antarctica“. Annals of Glaciology 17 (1993): 300–306. http://dx.doi.org/10.1017/s0260305500013008.
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The radiative-transfer model developed by Zwally (1977) is modified and coupled to a one-dimensional time-dependent temperature model, to calculate the seasonal variation in brightness temperature. By comparing this with observed records, the radiative properties of firn can be determined. By retaining scattering as a source term in the radiative transfer function, agreement between model-derived scattering and absorption coefficients and those calculated from the Mie/Rayleigh scattering theory can be obtained. The horizontal brightness temperature is not linked to the vertical one through a constant power reflection coefficient.
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Cui, Yun Xian, Yang An, Jia Hui Zhao und Xiao Xing Sheng. „Research on Seebeck Coefficient of Thin-Film Thermocouple on Temperature-Testing Cutter“. Applied Mechanics and Materials 757 (April 2015): 139–46. http://dx.doi.org/10.4028/www.scientific.net/amm.757.139.
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Performance of current temperature sensor is not satisfactory on monitoring transient temperature of cutting edge. A temperature-testing cutter is presented in this paper and analysis of Seebeck coefficient on thin film thermocouple is proposed with experiments. Thin film thermocouple is embedded into the cutting edge using magnetron sputtering technology. According to the fact that electrical conductivity can be replaced by the multiplication of electron mean free path λ and effective Fermi surface area A, a universal formula of thermoelectric power is given based on the diffuse thermoelectric power equation put forward by Mott and Jones. Using the expression of electron mean free path in gas model λ, the relationship of thermoelectric power between thin film and bulk material can be deduced. Result shows that the main influential factor of Seebeck coefficient is film thermal junction thickness. In addition, the Seebeck coefficient of different junction size and film thickness were tested by LabVIEW automatic calibration system. The experimental data indicates that Seebeck coefficient is determined by thermal junction thickness, and the sensor is found to be linear from room temperature up to 600°C while the Seebeck coefficient of thin film thermocouple becomes closer to standard thermocouple as the film thickness increments. However, junction size does not have a major influence on the Seebeck coefficient which is agreed by both theoretical analysis and test.
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Du, Chao, Yangyang Zhang, Jiangmin Lin, Guotao Fan, Can Zhou und Yan Yu. „Flexible Positive Temperature Coefficient Composites (PVAc/EVA/GP-CNF) with Room Temperature Curie Point“. Polymers 16, Nr. 14 (16.07.2024): 2028. http://dx.doi.org/10.3390/polym16142028.
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Polymeric positive temperature coefficient (PTC) materials with low switching temperature points are crucial for numerous electronic devices, which typically function within the room temperature range (0–40 °C). Ideal polymeric PTC materials for flexible electronic thermal control should possess a room-temperature switching temperature, low room-temperature resistivity, exceptional mechanical flexibility, and adaptive thermal control properties. In this study, a novel PTC material with a room-temperature switching temperature and superb mechanical properties has been designed. A blend of a semi-crystalline polymer EVA with a low melting temperature (Tm) and an amorphous polymer (PVAc) with a low glass transition temperature (Tg) was prepared. Low-cost graphite was chosen as the conductive filler, while CNF was incorporated as a hybrid filler to enhance the material’s heating stability. PVAc0.4/EVA0.6/GP-3wt.% CNF exhibited the lowest room temperature resistivity, and its PTC strength (1.1) was comparable to that without CNF addition, with a Curie temperature of 29.4 °C. Room temperature Joule heating tests revealed that PVAc0.4/EVA0.6/GP-3wt.% CNF achieved an equilibrium temperature of approximately 42 °C at 25 V, with a heating power of 3.04 W and a power density of 3.04 W/cm2. The Young’s modulus of PVAc0.4/EVA0.6/GP-3wt.% CNF was 9.24 MPa, and the toughness value was 1.68 MJ/m3, indicating that the elasticity and toughness of the composites were enhanced after mixing the fillers, and the mechanical properties of the composites were improved by blending graphite with CNF.
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Sun, Sheng-Wei, und Xian-Fang Li. „Exact solution of a nonlinear fin problem of temperature-dependent thermal conductivity and heat transfer coefficient“. Canadian Journal of Physics 98, Nr. 7 (Juli 2020): 700–712. http://dx.doi.org/10.1139/cjp-2019-0435.
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This paper studies a class of nonlinear problems of convective longitudinal fins with temperature-dependent thermal conductivity and heat transfer coefficient. For thermal conductivity and heat transfer coefficient dominated by power-law nonlinearity, the exact temperature distribution is obtained analytically in an implicit form. In particular, the explicit expressions of the fin temperature distribution are derived explicitly for some special cases. An analytical expression for fin efficiency is given as a function of a thermogeometric parameter. The influences of the nonlinearity and the thermogeometric parameter on the temperature and thermal performance are analyzed. The temperature distribution and the fin efficiency exhibit completely different behaviors when the power-law exponent of the heat transfer coefficient is more or less than negative unity.
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Kostić, Ljiljana. „Monitoring of the temperature reactivity coefficient at the PWR nuclear power plant“. Annals of Nuclear Energy 24, Nr. 1 (Januar 1997): 55–64. http://dx.doi.org/10.1016/0306-4549(96)00025-4.
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Lee, Min Chin, Ming Chia Hsie und Chi Jing Hu. „Implementation of Low Bandgap Reference Voltage Circuit for Power Management Applications“. Advanced Materials Research 562-564 (August 2012): 1517–21. http://dx.doi.org/10.4028/www.scientific.net/amr.562-564.1517.
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This paper proposes a low bandgap reference voltage circuit with low temperature coefficient and independent of suply voltage for applications to power management IC. This proposed circuit is design and implemented using the TSMC 0.35μm CMOS 2P4M process. Based on simulated and measured results , the chip size is 20.6000.680mm with power dissipation about 3.3mW, and the operation temperature range form 0Cto 100C with temperature coefficient about 9.29/ppmC. The chip suply voltage can from 2.9V to 3.3V with PSRR about 44.2 dB, and its output reference voltage can stable at 0.65V.
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Ren, Ming Yuan, und En Ming Zhao. „A Bandgap Reference with Temperature Coefficient of 13.2 ppm/°C“. Advanced Materials Research 981 (Juli 2014): 66–69. http://dx.doi.org/10.4028/www.scientific.net/amr.981.66.
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This paper presents a design and analysis method of a bandgap reference circuit. The Bandgap design is realized through the 0.18um CMOS process. Simulation results show that the bandgap circuit outputs 1.239V in the typical operation condition. The variance rate of output voltage is 0.016mV/°C? with the operating temperature varying from-60°C? to 160°C?. And it is 3.27mV/V with the power supply changes from 1.8V to 3.3V.
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Wang, Yanzhong, Wentao Niu, Song Wei und Guanhua Song. „Convective heat transfer under different jet impingement conditions – optimum design to spray parameters“. Industrial Lubrication and Tribology 68, Nr. 2 (14.03.2016): 242–49. http://dx.doi.org/10.1108/ilt-07-2015-0100.
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Purpose – This paper aims to improve the cooling performance of the impinging jet to the machining and power transmissions, and provides more parameters to the design of the cooling system. Design/methodology/approach – A multiphase flow model with heat transfer terms is established to calculate the convective heat transfer coefficient. The computational fluid dynamics method is used to simulate the jet flow. The convective heat transfer coefficients with different spray parameters are calculated and their variations are obtained. Temperatures are tested to reflect the cooling performance (convective heat transfer coefficients) with different spray parameters. Findings – The results show that the higher convective heat transfer coefficient can be obtained with the same flow rate by decreasing nozzle diameter while increasing either the number of nozzles or the oil supply pressure. The spray distance was found to have little influence on convective heat transfer; however, the more the spray is directed parallel to the surface, the higher the convective heat transfer coefficient. The computational results coincide well with the experimental results. Originality/value – The research presented here leads to a design reference guideline that could be used in machining and power transmissions to reduce the temperature, thus improving their quality and efficiency, and preventing failure at high speeds and/or under heavy loads.
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ZHU, ZHANGMING, WEI WEI, LIANXI LIU und YINTANG YANG. „A HIGH PRECISION CMOS VOLTAGE REFERENCE WITHOUT RESISTORS“. Journal of Circuits, Systems and Computers 21, Nr. 03 (Mai 2012): 1250019. http://dx.doi.org/10.1142/s0218126612500193.
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With the application of the voltage divider to the traditional bandgap reference without resistors, a high precision CMOS voltage reference without resistors has been proposed. The temperature coefficient has improved because the divider introduces the temperature compensation. The output reference voltage is 410.39 mV at the room temperature. The temperature coefficient of the voltage reference is 3.02 ppm/°C in the range from -20°C to 120°C. Moreover, the power supply rejection ratio of the voltage reference is -52.6 dB and the power consumption is 5.61 μW.
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Ndlovu, Partner L., und Raseelo J. Moitsheki. „Analytical Solutions for Steady Heat Transfer in Longitudinal Fins with Temperature-Dependent Properties“. Mathematical Problems in Engineering 2013 (2013): 1–14. http://dx.doi.org/10.1155/2013/273052.
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Explicit analytical expressions for the temperature profile, fin efficiency, and heat flux in a longitudinal fin are derived. Here, thermal conductivity and heat transfer coefficient depend on the temperature. The differential transform method (DTM) is employed to construct the analytical (series) solutions. Thermal conductivity is considered to be given by the power law in one case and by the linear function of temperature in the other, whereas heat transfer coefficient is only given by the power law. The analytical solutions constructed by the DTM agree very well with the exact solutions even when both the thermal conductivity and the heat transfer coefficient are given by the power law. The analytical solutions are obtained for the problems which cannot be solved exactly. The effects of some physical parameters such as the thermogeometric fin parameter and thermal conductivity gradient on temperature distribution are illustrated and explained.
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GAO, SHANG, SHUYUN WANG, JIE LIAN, PING LI und XIAO WANG. „EFFECTS OF TEMPERATURE AND SPUTTERING POWER ON THE MORPHOLOGY AND OPTICAL CONSTANTS OF THIN TANTALUM FILMS“. Surface Review and Letters 19, Nr. 04 (26.07.2012): 1250039. http://dx.doi.org/10.1142/s0218625x12500394.
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A set of thin tantalum films was prepared by direct current (DC) magnetron sputtering using different substrate temperatures and sputtering power. In order to identify the optimal condition for hillock free thin tantalum (Ta) film deposition, AFM was employed to measure surface morphology of the Ta films and to research the effect of substrate temperatures and sputtering power on the films surface. The relationship between optical constants and film stress of thin Ta films was also investigated. The comparison of AFM results showed that thin Ta films deposited at 500 K with a sputtering power of 56 W produced a hillock free surface as well as minimum surface roughness. All films were also measured by spectroscopic ellipsometry (SE) to characterize their optical properties. Refractive index and extinction coefficient of thin Ta films obtained from SE results by using a 5-layer model increased simultaneously, when sputtering power increased and the substrate temperature remain unchanged. However when the power was a constant, the thin Ta film sputtered at 500 K had a lower refractive index and extinction coefficient than other samples sputtered with other substrate temperatures from 300 to 700 K.