- 标题
- 摘要
- 关键词
- 实验方案
- 产品
过滤筛选
- 2019
- 2018
- Heat Trap
- outgassing
- lifetime
- Carbon nanotubes
- current stability
- cathode
- thermionic emission
- photovoltaic
- monocrystalline
- Heat mapping
- Nanomaterials and Technology
- Electrical Engineering and Automation
- University of British Columbia
- Univesitas Budi Luhur
- Institut Teknologi Sepuluh Nopember
-
High efficient nanostructured PbSe0.5Te0.5 exhibiting broad figure-of-merit plateau
摘要： To have a very good energy conversion efficiency, thermoelectric (TE) material should exhibit higher figure-of-merit (ZT) for broad range of temperatures. In that direction, n-type PbTe0.5Se0.5 material with enhanced and temperature insensitive figure-of-merit was developed through nanostructured approach. A temperature insensitive ZT of 0.7 was observed from 400 K to 600 K. The enhanced and stable ZT over a wide temperature range was ascribed to the presence of various types of nanostructures that facilitated scattering of mid and long wavelength phonons, keeping the thermal conductivity low in addition to scattering low energy charge carriers elevating the Seebeck coefficient (-380 m VK-1 at 600 K). Most thermoelectric n-type materials such as PbQ (Q = Te, Se) materials exhibits very low ZT at room temperature which hampers the overall conversation efficiency. However, the developed material exhibits highest ZT at room temperature among PbQ (Q = Te,Se) materials that enables this material to be used in wearable thermoelectric applications. In this study, newly introduced technique was adopted to calculate TE conversion efficiency, which addresses overestimations of conventional efficiency calculations. The developed material showed power generation efficiency higher than many state-of-the-art TE n-type materials in 300 K-600 K range making it a competitive material for waste heat recovery applications.
关键词： waste heat recovery,engineering figure-of-merit,sustainable energy,TE power generation efficiency,nanoprecipitates,lead selenides
更新于2025-09-19 17:15:36
-
Thermophysical Properties of Silicon-Carbide-Based Ceramic Composite Materials Obtained by Spark Plasma Sintering (SPS)
摘要： The factors influencing the thermal conductivity of SiC-based ceramic composite materials obtained by the spark plasma sintering technology with relative density 99% and B4C, AlN, Si3N4, Y2O3, Al2O3, and HfB2 as additives are examined. The thermophysical properties were determined in the temperature range 20 – 1300°C: specific heat, thermal diffusivity, and thermal conductivity of composites. The thermal diffusivity and specific heat were measured by the laser-spark method. The measurements of specific heat are supplemented by measurements performed with a DSC and adiabatic calorimeter. The thermal conductivity is calculated using data on the thermal diffusivity, specific heat, and density.
关键词： laser flash method,specific heat,adiabatic calorimeter,thermal conductivity,ceramic composite materials,thermal diffusivity,thermophysical properties,differential scanning calorimetry (DSC)
更新于2025-09-19 17:15:36
-
[ASME ASME 2018 International Mechanical Engineering Congress and Exposition - Pittsburgh, Pennsylvania, USA (Friday 9 November 2018)] Volume 8A: Heat Transfer and Thermal Engineering - Infrared Thermography to Measure Heat Transfer of a Heated Curved Thin Sheet
摘要： Heat transfer measurements on a heated curved thin sheet are performed by infrared thermography. The evolution of the temperature field is recorded to calculate the heat flux by using the two-dimensional unsteady heat balance equation. The thermal conduction term is estimated by the projection relationship between the curved surface of the thin sheet and the horizontal plane. Natural convection is neglected during the estimation of this heat flux. Unlike the traditional means of heat flux measurement, this method is non-intrusive and can measure the heat flux distribution within a curved space, allowing an easier evaluation of the errors due to radiation and tangential conduction. An electrical resistance foil with known power are applied as the heating source to compare the calculated heating power with the actual recorded power, the max relative error for different heating powers is about 10 %, which verified of the feasibility of the method. Considering possible applications, three different domestic gas cookers are used to heat three different curved thin pans, and then, in each case, the heat flux of the burners is analyzed. From the heat flux distribution of the three gas cookers, some heating characteristics such as heating power, maximum and average heating flux are investigated to help optimize the designs of the gas cookers, avoiding local over-heating and low uniformity of heat distribution.
关键词： Heat transfer measurements,infrared thermography,heating characteristics,gas cookers,curved thin-sheet
更新于2025-09-19 17:15:36
-
Measurement of photoionization cross-section of Li (2p, 3d) excited states using thermionic diode detector
摘要： Studies on photoionization cross-section measurement of lithium 2p and 3d excited states selectively populated by single and two photons are reported. The photoionization is carried out in a heat-pipe cum thermionic diode detector using nitrogen laser pumped pulsed dye laser. Rhodamine perchlorate (Rh-640) dye is used to generate the desired tunable laser output in the range of 635 to 675 nm. Both, the thermionic diode detector and dye laser are developed in-house. A negative space charge region formed around diode cathode filament is illuminated by dye laser exciting pulse followed by ionizing UV radiation from nitrogen laser. The effect of ionizing laser pulse energy and precise tuning of dye laser on photoionization signal, across 670.780 nm (2S1/2 → 2P1/2,3/2) single-photon transition and 639.145 nm (2S1/2 → 2D3/2,5/2) two-photon transition are studied. The results obtained are compared with model calculations of photoionization signal saturation curve. The ionization cross-section for both the states (2P1/2, 2D5/2) are determined as 15.40 ± 2.8 Mb and 8.04 ± 1.6 Mb, respectively and atomic number density N ～ 5.6 × 10^8 (cm^?3).
关键词： Dye laser,Photoionization cross-section,Thermionic diode,Heat-pipe,Lithium
更新于2025-09-19 17:15:36
-
Thermal driven natural convective flows inside the solar chimney flush-mounted with discrete heating sources: Reversal and cooperative flow dynamics
摘要： Fluid flow and heat transfer mechanism in a solar chimney induced by thermal buoyancy within a range of Ra numbers are reported by numerical and experimental investigations. The transport paths followed respectively by air and heat are visualized by streamlines and heatlines. Numerical results demonstrate that the reverse flow not only slows down the volume flow rate but also accelerates backflow presented in the solar chimney when Ra increases beyond a certain value, which makes the solar chimney lost its role of ventilation. In order to suppress the reverse flow and enhance ventilation performance, a solar chimney with multiple discrete sources flush attached the glazing wall is proposed. The effects of the sizes, positions, and numbers of those discrete heat sources on the system heat transfer rate and volume flow rate are discussed. After comparing with conventional solar chimney, the modified solar chimney with discrete heat source of height D0 = 1 and position S0 = 1 could perform better, not only preventing reverse flow but also enhancing the ventilation performance. The results obtained by the lab experimental measurements were agreed well with former numerical simulations. Temperature distributions along the heated wall for different heat input at ambient temperature illustrate the temperatures on the heated wall do not increase linearly and even drop near the top exit. This research could be significant for solar energy utilization and building energy conservation.
关键词： Discrete heat sources.,Solar energy,Reversal flow,Thermal driven natural convection
更新于2025-09-19 17:15:36
-
Influence of Heat Treatments on Microstructure and Mechanical Properties of Ti–26Nb Alloy Elaborated In Situ by Laser Additive Manufacturing with Ti and Nb Mixed Powder
摘要： In the present work, a Ti–26Nb alloy was elaborated in situ by laser additive manufacturing (LAM) with Ti and Nb mixed powders. The alloys were annealed at temperatures ranging from 650 °C to 925 °C, and the effects of the annealing temperature on the microstructure and mechanical properties were investigated. It has been found that the microstructure of the as-deposited alloy obtained in the present conditions is characterized by columnar prior β grains with a relatively strong <001> fiber texture in the build direction. The as-deposited alloy exhibits extremely high strength, and its ultimate tensile strength and yield strength are about 799 MPa and 768 MPa, respectively. The annealing temperature has significant effects on the microstructure and mechanical properties of the alloys. Annealing treatment can promote the dissolution of unmelted Nb particles and eliminate the micro-segregation of Nb at the elliptical-shaped grain boundaries, while increasing the grain size of the alloy. With an increase in annealing temperature, the strength of the alloy decreases but the ductility increases. The alloy annealed at 850 °C exhibits a balance of strength and ductility.
关键词： microstructure,Ti–Nb alloy,mechanical properties,in situ alloying,laser additive manufacturing,heat treatment
更新于2025-09-19 17:15:36
-
Theoretical studies on the structures, material properties, and IR spectra of polymorphs of 3,4-bis(1H-5-tetrazolyl)furoxan
摘要： Theoretical studies on the structures, densities, and heats of formation of conformational isomers of 3,4-bis(1H-5-tetrazolyl)furoxan (H2BTF) were performed based on density functional theory (DFT) calculations. Two stable planar conformational isomers, the face-to-back and the back-to-face conformers, and one stable slightly twisted conformer, the back-to-back conformer, were predicted for H2BTF at the M06-2X/6–311 + G(d,p) level of theory. The face-to-back conformer was calculated to be the most stable conformational isomer on the potential energy surface. No stable face-to-face conformer, whether planar or tilted, was identified in the calculations. The Vienna Ab Initio Simulation Package (VASP) was used in combination with molecular dynamics simulation to explore the stable crystal forms and the densities of the stable conformational isomers. Two of them exhibited high densities: the face-to-back conformer with P21 symmetry (2.01 g/cm3) and the back-to-back conformer with Pna21 symmetry (2.05 g/cm3). Their heats of formation were also predicted to be high when calculated at the same DFT level. The detonation pressures and velocities of these polymorphs, as calculated using the EXPLO5 program, are well above those of many advanced high energy density materials, pointing to the potential use of these conformers as novel explosives with good detonation performance. Also, IR spectra are shown to be able to distinguish these denser polymorphs of H2BTF. This study suggests that it could be worth investigating whether denser polymorphs of H2BTF can be grown.
关键词： 3,4-Bis(1H-5-tetrazolyl)furoxan,Detonation property,HEDM,Heat of formation,Density
更新于2025-09-19 17:15:36
-
Thermal properties of high purity zinc-tellurite glasses for fiber-optics
摘要： The thermal properties of the series glasses (TeO2)(0.86-x)(ZnO)x(La2O3)0.04(Na2O)0.1 were studied. The heat capacity and characteristics of transitions between aggregative states were determined by the method of differential scanning calorimetry (DSC) in the temperature range 320-950 K. The experimentally obtained values of thermal conductivity, density and coefficient of thermal expansion at room temperature are as follows: 1.14 ± 0.06 W/(m?K), 5.20 ± 0.02 g/cm3 and (54.6 ± 1.2)?10-6 K-1, respectively. The model-statistical processing of calorimetric data was used to determine the complete set of standard thermodynamic functions together with their approximation to the unexplored low-temperature region by means of parametric similarity. The approach allows predicting the functions for unexplored intermediate glasses compositions.
关键词： heat capacity,thermal conductivity,thermodynamic functions,coefficient of thermal expansion,density,Zinc-tellurite glasses
更新于2025-09-19 17:15:36
-
Study of infrared thermal application for detecting defects within tunnel lining
摘要： With the aging of tunnels, additional maintenance and assessment procedures are required to monitor their working conditions. The passive thermal infrared method, which is a nondestructive contact-free method, is used to find defects in a box-type and shield tunnels with concrete lining. In this study, this method is numerically applied to detect defects in an unhealthy concrete structure. The thermal field data measurements are reviewed and the governing heat transfer mechanisms for a defected concrete surface are presented. The heat transfer in the concrete segment, tunnel air, and the air inside the void due to the conduction, convection, and radiation mechanisms is explained. Further, the type of cavity, the temperature difference between the healthy and unhealthy concrete surfaces, the temperature difference between the tunnel air and concrete surfaces, and the influence of the void depth on the detection accuracy are investigated. The results show that the temperature difference between the concrete surface and the tunnel air is more than 0.35 °C, which is an ideal condition for detecting the voids with an approximate depth of 30 mm or less.
关键词： Hammering test,Heat transfer,Infrared thermography,Defected lining,RC tunnel lining
更新于2025-09-19 17:15:36
-
Assessment of the cost reduction potential of a novel loop-heat-pipe solar photovoltaic/thermal system by employing the distributed parameter model
摘要： A novel micro-channel loop-heat-pipe solar photovoltaic/thermal (LHP- PV/T) system is developed employing the co-axial tubular heat exchanger as the condenser and upper-end liquid header with tiny holes as the liquid feeder. The design facilitates an easier connection among the solar modules. It creates the improved condensation and separate evaporation effects within the LHP. A reduced evaporator area will thereby have a minor impact on the overall heat transfer performance, leading to significant potential for cost reduction. A distributed parameter model is established and validated by experimental data. The model is then applied to analyze the cost reduction potential of the LHP- PV/T via the optimization of geometrical and structural parameters. The impact of the area reduction on the LHP evaporator differs from that on the traditional integral heat pipe PV/T. The decrements in thermal and electrical efficiencies of the LHP- PV/T are 2.47% and 0.03% respectively when the width of heat pipes in the evaporator decreases from 26 to 10 mm. When the number of heat pipes decreases from 30 to 6, the decrements in thermal and electrical efficiencies are 4.63% and 0.12%, whilst the overall system cost drops by 28.58%, thus the cost-effectiveness of the system can be improved.
关键词： Co-axial tubular heat exchanger,Photovoltaic/thermal,Cost,Loop-heat-pipe,Micro-channel
更新于2025-09-19 17:13:59