共查询到20条相似文献,搜索用时 758 毫秒
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G. El Hitti M. Nemer K. El Khoury D. Clodic 《Numerical Heat Transfer, Part B: Fundamentals》2013,63(2):110-125
Great efforts have been made to date toward modeling nongray radiative heat transfer accurately. In this article, a new version of the plating algorithm, designated the re-plating algorithm, for total exchange areas (TEAs) calculation from direct exchange areas (DEAs) for nongray radiative problems is presented. The re-plating algorithm calculates TEAs for a given band number b from those of band number b ? 1 by performing successive re-plating procedures. The effectiveness of the new algorithm is demonstrated for thermal modeling of an aluminum brazing furnace and a glass treatment furnace. CPU requirements for TEA calculation were reduced significantly. 相似文献
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D.P. Sekulic P.K. Galenko L. Walker 《International Journal of Heat and Mass Transfer》2005,48(12):2385-2396
The computational heat and mass transfer modeling approach presented in this paper emphasizes the influence of undercoolings on dendrite structure formations of the alpha phase crystals inherent to advanced phases of an aluminum brazing netshape manufacturing sequence. In the first segment of this work, the empirical evidence involving the outcome of the solidification process and its kinetics was presented. In this paper, simulation of the alpha phase crystal pattern formation is corroborated with empirical findings obtained by utilizing an AA4343/AA3003 brazing sheet exposed to controlled atmosphere brazing (CAB) in ultra-high purity nitrogen. 相似文献
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Eric B. Ratts 《传热工程》2013,34(5):55-64
Transient three-dimensional heat transfer between a traversing, structured, and rectangular object and an enclosure is studied. This study investigates the heat transfer process that occurs in brazing an aluminum heat exchanger in a controlled-atmosphere furnace. A model's development is discussed with prescribed enclosure temperature boundary conditions. The program determines the radiant heat exchange between gray diffuse surfaces, and solves the three-dimensional conduction equation for a solid with a radiant heat flux boundary condition using an implicit finite-difference method. The structured object's conduction and radiant thermal properties are described by effective values. It was shown that radiative thermal properties of the traversing object and the enclosure's temperature have a strong impact on the object's temperature history. The effective thermal emissivity was found to influence the object's rate of temperature change. The enclosure's temperatures influenced the object's equilibrium temperature. Also, it was shown that the object's position and rotation can alter its temperature distribution, but not as strong as the effect of boundary conditions and thermal properties. In addition to numerical methods, experiments were performed to further understand the process. 相似文献
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Abdel Raouf Mayyas Dilip Ramani Arunachala M. Kannan Keng Hsu Ahmad Mayyas Tony Schwenn 《International Journal of Hydrogen Energy》2014
The 3D Thermal modeling utilizes a Finite Differencing heat alteration method augmented with empirical boundary conditions is employed to develop 3D thermal model for the integration of thermoelectric modules with proton exchange membrane fuel cell stack. Hardware-in-Loop was designed under pre-defined drive cycle to obtain fuel cell performance parameters along with anode and cathode gas flow-rates and surface temperatures. The fuel cell model is used to conjugate the experimental boundary conditions with the Finite Differencing code, which implemented heat generation across the stack to depict the chemical composition process. The structural and temporal temperature contours obtained from this model are in compliance with the actual recordings obtained from the infrared detector and thermocouples. The model is harmonized with thermo-electric modules with a modeling strategy, which enables optimize better temporal profile across the stack. This study presents the improvement of a 3D thermal model for proton exchange membrane fuel cell stack along with the interfaced thermo-electric module. The model provided a virtual environment using a model-based design approach to assist the design engineers to manipulate the design correction earlier in the process and eliminate the need for costly and time consuming prototypes. 相似文献
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Processes in non-energy systems have not been as frequent a subject of sustainability studies based on Thermodynamics as have processes in energy systems. This paper offers insight into thermodynamic thinking devoted to selection of a sustainability energy-related metric based on entropy balancing of a non-energy system. An underlying objective in this sustainability oriented study is product quality involving thermal processing during manufacturing vs. resource utilization (say, energy). The product quality for the considered family of materials processing for manufacturing is postulated as inherently controlled by the imposed temperature non-uniformity margins. These temperature non-uniformities can be converted into a thermodynamic metric which can be related to either destruction of exergy of the available resource or, on a more fundamental level of process quality, to entropy generation inherent to the considered manufacturing system. Hence, a manufacturing system can be considered as if it were an energy system, although in the later case the system objective would be quite different. In a non-energy process, a metric may indicate the level of perfection of the process (not necessarily energy efficiency) and may be related to the sustainability footprint or, as advocated in this paper, it may be related to product quality. Controlled atmosphere brazing (CAB) of aluminum, a state-of-the-art manufacturing process involving mass production of compact heat exchangers for automotive, aerospace and process industries, has been used as an example. 相似文献
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Dehong XIA Gang ZHANG Liang GUO Department of Thermal Engineering University of Science Technology Beijing Beijing China Professor 《热科学学报(英文版)》2006,15(3):269-273
The thermal process of L.M.Pidgeon's reduction art,widely used in magnesium production,is numericallysimulated.It is shown that the thermal efficiency will be highly enhanced with the increase of heat-exchange areaor the intensification of heat exchange between flame and the outer surface of the reduction jars.An innovationhas been made by fuel-shifting(from coal to Coal-Water Mixture),up-draft reduction furnace configuration,multi-layer jars installation and waste heat recovery.A bench scale furnace has been constructed and put intooperation to identify the simulation and new design. 相似文献
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分析了铝合金NOCOLOK钎焊和真空钎焊的原理、设备及目前存在的问题,介绍一种新型半连续保护气氛铝钎焊炉的结构、原理和应用,建立了氮气置换净化和真空净化的等效关系。通过对比重型板翅式换热器在两种炉型中的生产效果,证明较真空钎焊炉,此种新炉型可以获得更好的焊接质量,生产效率大幅提高,而生产成本仅是真空炉的1/2。 相似文献
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《International Journal of Heat and Mass Transfer》2007,50(19-20):3740-3748
A mathematical heat transfer model for the prediction of heat flux on the slab surface and temperature distribution in the slab has been developed by considering the thermal radiation in the furnace chamber and transient heat conduction governing equations in the slab, respectively. The furnace is modeled as radiating medium with spatially varying temperature and constant absorption coefficient. The steel slabs are moved on the next fixed beam by the walking beam after being heated up through the non-firing, charging, preheating, heating, and soaking zones in the furnace. Radiative heat flux calculated from the radiative heat exchange within the furnace modeled using the FVM by considering the effect of furnace wall, slab, and combustion gases is introduced as the boundary condition of the transient conduction equation of the slab. Heat transfer characteristics and temperature behavior of the slab is investigated by changing such parameters as absorption coefficient and emissivity of the slab. Comparison with the experimental work show that the present heat transfer model works well for the prediction of thermal behavior of the slab in the reheating furnace. 相似文献
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根据炉内热平衡和物料平衡原理,建立了石灰炉内反应与传热过程数学物理模型以及石灰燃烧分解率的在线监测模型;运行计算机模拟研究了各操作参数对石灰石燃烧过程的影响,提出了改善技术经济指标的措施;采用VB进行数据通讯和实时监测编程,实现了石灰炉运行的集中监测,有利于石灰炉高效稳定运行,达到增产降耗的目标。 相似文献
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蒸汽发生系统(steam generation system,SGS)是塔式太阳能热发电站的重要组成部分。采用仿真模拟软件Thermoflex对塔式太阳能热发电站的熔盐SGS进行了建模,并基于实际工程数据验证了所搭建模型的准确性。以此为基础,仿真研究了熔盐SGS的换热工质参数(给水温度、主蒸汽温度、主蒸汽压力)对熔盐SGS性能的影响,其中,水侧温度和压力的变化对熔盐侧参数(熔盐流量、熔盐SGS出口的熔盐温度)和换热设备的换热功率均存在较大影响。研究得到的不同换热工质参数对熔盐SGS性能和整个塔式太阳能热发电站的影响规律可为熔盐SGS的设计提供理论依据。 相似文献
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A simple model for optical and thermal properties of two-component biological tissues is proposed as applied to studies of thermal fields under external illumination. The model comprises a small number of varying input parameters to enable one to find all the optical characteristics required to compute light fields in tissue and to state the thermal source function. Thermal parameters of tissues determining heat transfer in a two-component medium are calculated with accounting for heat exchange conditions between the components and at the interface with various external media. A set of heat conduction equations is stated for the two-component medium simulating biological tissues. Its analytical solution is derived. Spatial distributions of the fluence rate and temperature over the tissue depth are investigated at varying time moments after the irradiation by a short light pulse. Localized absorption of light by blood vessels and its effect on optical parameters of the medium, more intense heating of blood as compared with its surrounding (basic) tissue and heat exchange between the blood and tissue, as well as heat transfer at the interface with different environments are taken into account. The solutions are derived via characteristic times of thermal processes to enable one to easy and vividly evaluate the features in tissue heating as well as the effects of optical and thermal parameters on temperature distributions of the components. The calculations are illustrated by examples. 相似文献
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D.P. Sekulic P.K. Galenko L. Walker 《International Journal of Heat and Mass Transfer》2005,48(12):2372-2384
This work provides empirical evidence needed for an in depth phenomenological study of dendrite growth phenomena during brazing of aluminum alloys in form of composite brazing sheets. The main objective of this study was (1) a collection of experimental evidence associated with heat and mass transfer modeling of the Al + Si solid solution dendrite macro morphology evolution inherent to joint formation during brazing, and (2) the dendrite growth kinetics analysis. The isothermal dwell and the quench that follow the clad molten aluminum binary alloy surface-tension-driven flow into the joint at the peak brazing temperature upon melting lead to the solidification of the metal micro layer and joint formation. Before, during and after the isothermal dwell a significant reduction of Si content in the melt is found. So, a subsequent dissolution may affect the interface zone between the molten clad and substrate. α-phase dendrite assemblies imbedded in an irregular eutectic in the joint zone are the main morphological features of the solidification microstructures. The major characteristic of the phenomenon is a sensitivity of the dendrite pattern selection and dendrite population on brazing process parameters, in particular on the temperature during the dwell. 相似文献
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Chin-Ru Su Cha’o-Kuang Chen Wei-Long Liu Hsin-Yi Lai 《International Journal of Heat and Mass Transfer》2009,52(15-16):3595-3605
In this work the inner surface geometry of a cylindrical furnace wall is estimated using inverse process method combined with grey prediction model. In estimating process a virtual area extended from the inner surface of furnace wall is used for analysis. The heat conduction equation and the boundary condition are first discretized by finite difference method to form a linear matrix equation; the inverse model is then optimized by linear least-squares error method and the temperatures of virtual boundary are obtained from a few of measured temperatures in furnace wall using the linear inverse model; and finally the temperature distribution of system is got by direct process and the inner surface geometry of furnace wall can be estimated accordingly. The result shows that using inverse process combined with grey prediction model the geometry can be exactly estimated from relatively small number of measured temperatures. Moreover, the effects of measurement error, location, and number of measured points on the estimation for inner surface geometry of furnace wall are discussed in detail. 相似文献
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J. Brillo H. Behnken A. Drevermann Y. Plevachuk E. Pagounis V. Sklyarchuk L. Sturz 《International Journal of Heat and Mass Transfer》2011,54(19-20):4167-4174
Ni–Mn–Ga magnetic shape memory alloys (MSMA) are well-known smart materials for actuation applications, due to their large magnetic field-induced shape change of up to 10%. The production of larger amounts of single-crystalline material from these alloys with reproducible and homogeneous properties is demanding and calls for optimization of the corresponding crystal growth process. In order to support this optimization, sensitive process parameters are varied in simulations and their effects are studied.Here, we report on thermal field simulations in a Bridgman–Stockbarger furnace. The lab furnace is equipped with liquid metal cooling (LMC) to achieve high and homogeneous thermal gradients at the crystallization front during crystal growth of cylindrical Ni–Mn–Ga-rods. The calibration of the thermal simulation model requires (i) the knowledge/measurement of the relevant thermophysical properties of the Ni–Mn–Ga alloy as functions of temperature and (ii) thermal data from a reference benchmark experiment in the lab furnace using the same alloy.The calibrated simulation model is used for the simulation of a specific virtual Bridgman-experiment and for the determination of the temperature distributions. Moreover, the influence of the type of liquid metal coolant on the simulation results is investigated. 相似文献
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真空隔热油管传热性能研究 总被引:1,自引:0,他引:1
真空隔热油管是稠油注蒸汽开采的主要设施之一,其隔热性能直接影响热采效果,因此,分析隔热油管隔热层内部的传热过程,研究隔热层各种结构参数对隔热油管隔热性能的影响,对改善隔热油管隔热性能有重要的指导作用。本文在测试隔热油管视导热系数的实验模型基础上,建立了隔热层传热的物理及数学模型,计算得到不同结构参数下隔热油管的视导热系数;研究了玻璃丝布孔隙比、隔热层层数、支撑材料导热系数以及铝箔发射率对隔热油管隔热性能的影响,研究表明:隔热层层数宜选为4~6层之间;选用的铝箔发射率应在0.01~0.05之间;在缠绕玻璃丝布工艺中,尽量不要让玻璃丝布对角线方向受力,以确保较大的孔隙比;在隔热油管加工过程中,应尽量使玻璃丝布和铝箔保持干燥。 相似文献
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对于测量条件恶劣,不能用常规传感器实现的温度测量,如高温强腐蚀性介质、高温熔体、真空、渗碳条件下,必须开发特种专用传感器。阐述了钨铼热电偶等特种温度传感器的特点、性能及应用,着重探讨了当前测温领域热点问题:渗碳炉、铝液、铜液等高温熔体连续测温;真空钎焊炉、真空粉末冶金烧结炉等的温度测量以及现场温度校准。实践证明,新开发的特种温度传感器,不仅与国际接轨,替代进口产品,而且还可以打入国际市场。 相似文献