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1.
During precision forging processes, the elastic and thermal deformations always take place simultaneously on the forging dies, which will affect the dimension accuracy of the final forging components. According to the classic Lamé formulas and thermoelastic mechanics theories, the thermoelastic deformation of a combined die was investigated. Directly related to geometric parameters, material properties, external stresses, and temperature distribution, the expressions of die deformation and contact normal stresses were derived. A three-layer combined die with three different temperature distributions was studied as a specific example. The thermoelastic deformations of each layer, as well as the contact normal stresses between them, were both calculated by the derived expressions and by finite element simulation. There was good agreement between the calculated values and simulated results, which demonstrated the effectiveness and accuracy of the theoretical derivation. Based on this, the total deformation on the inner surface of the combined die and the contact stress between contact layers under non-uniform temperature distribution that would influence the practical die initial design were discussed further. 相似文献
2.
Hsiu-Tao ChangChih-Kuang Lin Chien-Kuo LiuSzu-Han Wu 《Journal of power sources》2011,196(7):3583-3591
High-temperature mechanical properties of a silicate-based glass sealant (GC-9) for planar solid oxide fuel cell have been studied in sintered forms. Ring-on-ring biaxial flexural tests are carried out at room temperature to 800 °C for the sintered GC-9 glass. The results are also compared with those in cast bulk forms. From the force-displacement curves, the glass transition temperature (Tg) of the non-aged, sintered GC-9 glass is estimated to be between 700 °C and 750 °C, while that of the aged one is between 750 °C and 800 °C. Due to a crack healing effect of the residual glass at high temperature, the flexural strength of the sintered GC-9 glass at temperature of 650 °C to Tg point is greater than that at room temperature. At temperature above Tg, the flexural strength and stiffness are considerably reduced to a level lower than the room-temperature one. The sintered GC-9 glass with pores and crystalline phases has a flexural strength lower than the cast bulk one at temperature of 650 °C and below. Due to a greater extent of crystallization, the flexural strength and stiffness of the sintered GC-9 glass are greater than those of the cast bulk one at 700-800 °C. 相似文献
3.
The high-temperature mechanical properties of a newly developed silicate-based glass sealant, designated as GC-9, have been studied for use in planar solid oxide fuel cell (pSOFC). Four-point bending tests were conducted at room temperature, 550 °C, 600 °C, 650 °C, 700 °C and 750 °C to investigate the variation of flexural strength, elastic modulus, and stress relaxation with temperature for the given glass sealant. Weibull statistic analysis was applied to describe the fracture strength data. The results indicated that the flexural strength was increased with temperature when the testing temperature was below the glass transition temperature (Tg, 668 °C). This was presumably caused by a crack healing effect taking place at high temperatures for glasses. However, with a further increase of temperature to a level higher than Tg, significant stress relaxation was observed to cause extremely large deformation without breaking the specimen. When the controlled displacement rate was increased by an order of magnitude, the stress relaxation effect at 750 °C became less effective. However, the mechanical stiffness of the given glass was significantly reduced at a temperature higher than Tg. 相似文献
4.
The present work describes the development of a glass-ceramic in SiO2-BaO-ZnO-B2O3-Al2O3 system. The prepared glass samples were found to have good compatibility to act as a sealant in planar solid oxide fuel cell (SOFC) in terms of coefficient of thermal expansion (TEC) and glass transition temperature (Tg). The crystallization kinetics of present glass samples were investigated by various characterization techniques such as differential thermal analyzer (DTA), Dilatometery, X-Ray diffraction (XRD) and scanning electron microscopy (SEM). The crystallization behavior of the chosen glass samples was influenced by replacing B2O3 with Al2O3. With the addition of Al2O3 there is increase in glass transition temperature (Tg) and glass crystallization temperature (Tc). Also with the addition of Al2O3 crystallization phenomenon is hindered. XRD and SEM study was done at various temperatures for different time durations. The detail of the above discussed study is done in the present paper. 相似文献
5.
The glass transition temperature (Tg) of the Nafion 117 membrane was traced by DSC step by step during the preparation of the membrane electrode assembly (MEA). Wide-angle x-ray diffraction and frequency response analysis were used for the determination of the crystallinity and proton conductivity of the membrane. As-received Nafion 117 membrane showed two glass transition temperatures in the DSC thermogram. The first Tg, caused by the mobility of the main chain in the polymer matrix, was 125 °C; the second Tg, derived from the side chain due to the strong interaction between the sulfonic acid functional groups, was 195 °C. During the pretreatment of the membrane, the Tg of the Nafion 117 membrane drastically decreased because of the plasticizer effect of water. In the hot-pressing process, the Tg of the Nafion 117 membrane gradually increased due to the loss of water. When the Nafion 117 was completely dried, the Tg of the membrane finally reached 132 °C. Thermal heat treatment was then applied to the MEA to obtain high interfacial stability; however, the membrane developed a crystalline morphology that led to reduced water uptake and proton conductivity. Therefore, the thermal heat treatment of the MEA should be carefully controlled in the region of the glass transition temperature (120–140 °C) of the Nafion 117 membrane to ensure the high performance of the MEA. 相似文献
6.
Gorakshnath Takalkar 《国际能源研究杂志》2020,44(15):12269-12283
The combination of ionic liquid-refrigerant based [EMIM][DMP]-H2O as an alternative working pair for single effect vapor absorption cycles (VACs) is assessed and optimized by using energy and exergy based performances. Thermodynamics properties of binary mixture of [EMIM] [DMP]-H2O like Dühring's (P-T-x1) and h-T-X1 plots are computed from the activity coefficient based non-random two-liquid model (NRTL) model. Further modeling and simulation of VACs are accomplished in open source Scilab as mathematical programing software and used to ascertain the optimal generator temperature established on energetic and exergetic COP. Optimal results include an extensive range of temperatures like Te from 2.5 to 15°C and Ta and Tc from 30 to 45°C. Simulation of the single effect VAC with SHE by using [EMIM][DMP]-H2O mixture at Te = 10°C, Tg = 100°C, Ta = 30°C, and Tc = 40°C were evaluated and compared with the 5 working fluids. Simulation outcomes depicted greater COP of 0.82 for [EMIM][DMP]-H2O in comparison with NH3-H2O, EMISE-H2O, [EMIM][BF4]-H2O and nearly equal to LiBr-H2O (COP = 0.83). In addition, the effect of Tg on the COP, ECOP f , and composition are compared and optimized for the evaporation temperature range from 2.5 to 15°C, Ta/Tc from 30 to 45°C and cooling water (CW) flow in series and parallel. Additionally, the optimal Tg exhibited distinction based on energy and exergy analysis. Thus, it resulted in optimized performances of [EMIM] [DMP]-H2O that can be suitable to replace corrosive aqueous LiBr in VACs. 相似文献
7.
Józef Ignaczak 《热应力杂志》2013,36(9):779-793
In previous work a one-dimensional averaged theory of thermoelastic waves in a microperiodic layered infinite solid was proposed in which an eighth-order-in-time partial differential equation involving a high intrinsic mechanical frequency ΩM and a high intrinsic thermal frequency ΩT is a central equation. Also, the existence of two harmonic thermoelastic waves of a given frequency ω propagating in a positive direction normal to the layering was previously established when ΩM → ∞ and ΩT < ∞, or ΩM < ∞ and ΩT → ∞. The existence of two harmonic thermoelastic waves of a given frequency ω propagating in the positive direction normal to the layering is proved when ΩM < ∞ and ΩT < ∞. Also, a closed form of the associated velocities and attenuation coefficients is obtained. Numerical results illustrating propagation of the two waves in a particular microperiodic layered thermoelastic solid are included. 相似文献
8.
In this study, three dimensional computational predictions on the film cooling performance of single row and simple cylinder on the convex surface have been studied and compared with corresponding experimental data reported in the literature to validate the model. This computational prediction serves as the baseline for future studies of optimization in determining the film cooling effectiveness. Realizable κ–? turbulent model has been employed and energy equation has been solved. Grid independence study has been fulfilled using two kinds of meshing approach for the plenum and the cooling holes. Results of grid independence study showed that fine meshed plenum and cylinders of tetrahedral grids case have provide a good agreement with the related experimental data. Study of temperature ratio between the coolant and mainstream hot gas Tc/Tg has been performed using four values of temperature ratios that are 0.5, 0.6, 0.7, and 0.8. In all of these tests the mainstream duct of the models was generated with multigrid hexahedral mesh. Based on the heat-mass transfer analogy, results of this study showed good agreement of the film cooling effectiveness and temperature distribution in comparison to the related experimental data. The case in which combination of both plenum and cylinders in one volume with tetrahedral fine mesh generation and temperature ratio of Tc/Tg = 0.6 was found to be in good agreement with the experimental data among all of the other models. Computational prediction results have found an agreement with the experimental data, thus the approach is verified. 相似文献
9.
Sabine Bertho Ilse Haeldermans Ann Swinnen Wouter Moons Tom Martens Laurence Lutsen Dirk Vanderzande Jean Manca Alessia Senes Annalisa Bonfiglio 《Solar Energy Materials & Solar Cells》2007,91(5):385-389
A new approach is presented in order to improve the thermal stability of polymer: [6-6]-phenyl C61 butyric acid methyl ester (PCBM) bulk heterojunction solar cells. The central idea in this approach is the use of a polymer with high glass transition temperature (Tg), well above the normal operating temperatures of the devices. In this paper, a PPV-derivative with a Tg of 150 °C was used as an electron donor and the thermal stability of the obtained solar cells was compared with solar cells based on the reference material poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylene vinylene] (MDMO-PPV) with a Tg of 45 °C. The use of the material with higher glass transition temperature resulted in a significant improvement of the thermal stability of the photovoltaic parameters. Furthermore, a systematic transmission electron microscope (TEM) study demonstrates that the better thermal stability of performance coincides with a more stable active layer morphology. Both improvements are attributed to the reduced free movement of the electron donor material (PCBM) within the active layer of the solar cell. 相似文献
10.
Approximate method for computation of glass cover temperature and top heat-loss coefficient of solar collectors with single glazing 总被引:1,自引:0,他引:1
An improved equation form for computing the glass cover temperature of flat-plate solar collectors with single glazing is developed. A semi-analytical correlation for the factor f—the ratio of inner to outer heat-transfer coefficients—as a function of collector parameters and atmospheric variables is obtained by regression analysis. This relation readily provides the glass cover temperature (Tg). The results are compared with those obtained by numerical solution of heat balance equations. Computational errors in Tg and hence in the top heat loss coefficient (Ut) are reduced by a factor of five or more. With such low errors in computation of Tg and Ut, a numerical solution of heat balance equations is not required. The method is applicable over an extensive range of variables: the error in the computation of Ut is within 2% with the range of air gap spacing 8 mm to 90 mm and the range of ambient temperature 0°C to 45°C. In this extended range of variables the errors due to simplified method based on empirical relations for Ut are substantially higher. 相似文献
11.
Nanoscopic confinement of a cation coordinated polymer in the channels of organo-modified montmorillonite clay results in substantial improvement in conductivity, cation transport and stability properties required for energy storage/conversion devices. X-ray diffraction analysis confirms composite formation as evidenced by: (i) intercalation of PEO8-LiClO4 into the clay channels for clay loading ≥7.5 wt.% and (ii) partial intercalation/exfoliation for a lower clay loading (≤5 wt.%). Transmission electron microscopy analysis corroborates these findings as indicated by an enhancement in clay gallery width from 6 to 9 Å for 20 wt.% clay providing evidence for intercalation at higher clay loadings. Energy dispersive X-ray dot-mapping images confirm the homogeneous distribution of clay in nanocomposites. Thermal analysis indicates a strong dependence of thermodynamic parameters, e.g., glass transition (Tg), crystalline melting (Tm), melting enthalpy, glass transition width (ΔTg), and thermal relaxation strength (ΔCp), on clay concentration. These observations agree well with changes in electrical properties on nanocomposite formation. Substantial enhancement in ambient conductivity (∼208 times) occurs in a nanocomposite film (2 wt.% clay) relative to a clay-free film. The temperature dependence of conductivity obeys Arrhenius behaviour below Tm and the VTF (Vogel-Tamman-Fulcher) relationship above Tm. The ionic transport number (∼99.9%) confirms ionic charge transport with a cation contribution (tLi+)∼0.5 for 2 wt.% clay. It represents an increase by ∼65% in comparison with PEO8-LiClO4. Improvement in voltage and thermal stability is also observed with the nanocomposites. 相似文献
12.
A recent study of the design of solar distillation with solar radiation concentration was carried out by an independent device. Transformer oil was used as a fluid to transfer heat to the distilled basin. The design and operational variables are essential, such as distiller dimensions, concentration ratio, pressure, and temperature. A mathematical model was proposed to simulate the system for 2 July 2018 from 10 am to 4 pm in the climatic conditions of the city of Kirkuk, Iraq. Fuzzy logic (FL) was used to select the affected parameters: water temperature (Tw), water pressure (Pw), glass temperature (Tg), and vapor pressure (Pg) which have a separated membership function that control the linguistic variables. The results showed that the best performance of the distiller is at Tw = 100°C, Pg = 10 000 Pa, Tg = 20°C, and Pw = 20 000 Pa, and concentration ratio of 30. This study used FL to analyze solar distiller performance and identify optimum temperature, pressure, and concentration ratio on the productivity of solar distiller. 相似文献
13.
Generally in a vapour absorption refrigeration system (VARS) heat rejection temperatures at absorber (Ta) and condenser (Tc) are taken to be equal. However, different temperatures can exist when the cooling water flows in series through the two components. Under such situations, it is essential to know which of Ta and Tc has greater influence on the performance of the VARS. Here the influence of different Ta and Tc on the performance of a single-stage VARS working with HCFC22 as a refrigerant and three organic solvents, namely DMA, DMF and DEMTEG, as absorbents is studied. Results are obtained over a wide range of operating temperatures. To improve the performance of HCFC22-based VARS, results reveal that (i) the cooling water in parallel pipe connections should be used at low values of temperatures at evaporator, cooling water and heat source, and (ii) cooling water should first flow through condenser and then through the absorber when evaporator and heat source temperatures are high over the complete range of cooling water temperatures. COPth is more sensitive to Tc than to Ta. 相似文献
14.
We investigate the effect of heating or cooling from below at constant temperature and constant heat flux on the development of gravitactic bioconvection in vertical cylinders with stress free sidewalls. The governing equations are the continuity equation, the Navier–Stokes equations with the Boussinesq approximation, the diffusion equation for the motile micro-organisms and the energy equation. The control volume method is used to solve numerically the complete set of governing equations. The governing parameters are the thermal and bioconvection Rayleigh numbers, the bioconvection Peclet number, the Lewis number, the Schmidt number and the aspect ratio. We found that subcritical bifurcations of bioconvection became supercritical bifurcations when the thermal Rayleigh number RaT is different than zero. For RaT < 0, i.e. for cooling from below, we have opposing buoyancy forces, the convection is decreased and the critical thermo-bioconvection Rayleigh number is increased with respect to that of bioconvection. For RaT > 0, i.e. for heating from below, we have cooperating buoyancy forces, the convection is increased and the critical thermo-bioconvection Rayleigh number is decreased with respect to that of bioconvection. Heating and cooling from below at constant temperature and heat flux modify considerably the pattern formation of the gravitactic bioconvection. 相似文献
15.
Galliosilicate glasses were developed for sealing intermediate temperature planar solid oxide fuel cell (SOFC) stacks. Candidate sealing glasses were identified for use at operating temperatures of 750 °C and at 850 °C after assessing flow behavior, thermal expansion properties, and crystallization behavior. A series of non-alkali glasses was identified for use at 750 °C within a strontium boro-galliosilicate compositional region that exhibited glass transition temperatures (Tg) between 658 and 675 °C and coefficients of thermal expansion (CTE) between 8 and 9.4 × 10−6 K−1. Glass frits and powders flowed below 850 °C and did not crystallize dramatically after 500 h at 750 °C. Several glasses containing 5 mol% mixed alkali were identified in a strontium boro-galliosilicate compositional region for use at 850 °C. The glasses exhibited Tg between 615 and 620 °C with CTE from 7.8 to 9.7 × 10−6 K−1. Glass frits flowed well below 850 °C and retained remnant glass phase after partial crystallization at 850 °C. The galliosilicate glasses developed in this work enable viscous sealing of SOFC stacks. 相似文献
16.
Geometrical inaccuracy is often induced by heat generated during grinding. Furthermore, the transient thermal process is the main cause for the residual stresses on theground surface. The objective of this article is to investigate the three-dimensional transient temperature distribution of the workpiece using the finite difference method,and based on the acquired temperature and beam theory, the thermal moment and thermoelastic stress as calculated using Simpson's multiple numerical integral method. The energypartition is the key factor in accurately predicting the temperature distribution, on which the solution of the thermal moment and stress rely. As the heat conductivity of the workpiece decreases, the stress and moment increase near the wheel-workpiece contact zone and the peaks move closer to the contact position. A smaller thickness results in higher thermal stress and lower thermal moment. Enhancing cooling in grinding effectively reduces temperature and the induced stress. 相似文献
17.
A. Rockett K. Granath S. Asher M. M. Al Jassim F. Hasoon R. Matson B. Basol V. Kapur J. S. Britt T. Gillespie C. Marshall 《Solar Energy Materials & Solar Cells》1999,59(3):6819
Results of characterization of thin films of Mo deposited by DC magnetron sputtering on soda-lime glass (Mo/SLG) and CuInSe2 (CIS) on Mo/SLG are presented. The primary objective of the work was to clarify the factors determining the concentration of Na in commercial-grade CIS. Mo films were deposited by three laboratories manufacturing CIS thin film solar cells. Analysis was by secondary ion mass spectrometry, scanning electron microscopy and X-ray diffraction. Changes in Mo deposition parameters in general affected the Na level but there was no obvious link to any single Mo deposition parameter. Oxygen content directly affected the Na level. The Na behavior was not obviously connected to film preferred orientation. Selenization of the Mo layers was also examined. Elemental Se vapor was found to produce significantly less selenization than H2Se. The amount of selenization was also strongly dependent upon Mo deposition conditions, although a specific source of the change in reaction rate was not found. Na distributions in the CIS deposited on the Mo were not limited by the diffusivity of the Na. The Na concentration in the CIS was increased by annealing the Mo films both with and without intentionally added Na. The Na level in the CIS appears to be set more by the CIS deposition process than by the Na concentration in the Mo so long as the Mo contains sufficient Na to saturate the available sites in the CIS. 相似文献
18.
Events that induce or inhibit mixing layer development in a thermohaline system are simulated in laboratory experiments involving salt-stratified solutions heated from below, cooled from above and/or irradiated from above. A Mach-Zehnder interferometer is used to visualize mixing layer development and to infer salt concentration and mass density distributions in stable regions of the solution. In experiments involving cooling from above by means of an isothermal boundary, the development of a top mixing layer is strongly influenced by the cooling rate. While the formation of a secondary mixed layer is associated with large cooling rates ( 103 W/m2), no such layer is associated with lower rates (≈100 W/m2). Secondary mixed layer development is also observed to occur in experiments involving heating from below. Experiments involving irradiation of the solution reveal the strong effect which infrared radiation absorption in the upper layers can have on inhibiting the development of both top and bottom mixed layers. 相似文献
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20.
Adib Bazgir Ali Heydari Bahamin Bazooyar Milad Mohammadniakan Nader Nabhani 《亚洲传热研究》2020,49(1):533-564
This study provides analysis of a cooled Ranque–Hilsch vortex tube (RHVT) with various specifications. It shows how cooling influences energy conversion inside the RHVT and improves performance of the device in separation of hot gas from the cold stream within the fluid by presenting the temperature detachment (the temperature diminution of cold air (ΔTc = Ti ? Tc), isentropic efficiency (ηis), and coefficient of performance (COP) of divergent, convergent, and straight VTs. Two key parameters including hot tube length and number of nozzles for cooling and insulated cases are investigated to find out how the performance of the VT is affected by different geometry configurations under cooling conditions. These influences were researched for straight, convergent, and divergent VT separators under different flow characteristics. The optimum geometrical conditions for the cooling cases were identified. Results are indicative of positive influence of cooling for energy separation inside a VT. The quantities of ΔTc, ηis, and COP for the cooled RHVT are greater than uncooled RHVT for various types of VTs. Cooling the VTs leads to an increase of 12.5% in ΔTc, 14.4% in ηis, and 15.1% in COP when the base case was an uncooled VT. 相似文献