双探针型海底热流计数据解算模型选取

选取适合于双探针型海底热流计数据解算的简化模型,是双探针型海底热流计结构优化的理论基础,对提高海底热流数据解算精度具有重要意义。本文基于脉冲式双探针海底工作的有限元数值模型,对双探针的脉冲加热时间、体生热率、热物性、长度及半径等因素在双探针脉冲法的3个线热源简化模型中所引起的模型误差作了详细的分析和讨论,并以模型误差最小为原则选取简化模型。结果表明:1)脉冲加热有限长线热源(PFLS:pulsed finite line source)模型是双探针脉冲法中较为实用的简化模型,它可消除加热时间和探针长度对介质热物性参数求解的影响;2)在PFLS模型下,探针热导率对待测介质热物性测量的影响可以忽略;而探针间距越大、半径越小及其体积比热容与待测介质越接近,则所求介质热物性的模型误差就越小;在保证温度传感器能有效记录到温度变化的前提下,探针脉冲功率的大小基本不影响介质热物性求解的模型误差。

Gardon型热流传感器隔热技术的优化

在无法向外散热的情况下,采用Gardon型热流传感器测量火焰强度的热流密度时,传感器对于热量的处理只能选择用储热体来吸收,故该类型的传感器有了工作时间的限制。为增加Gardon型热流传感器的工作时间,对其隔热技术加以改进,效果较为明显。

双探针型海底热流计的结构优化

本文在现有海底热流探针制作技术条件下,首先建立了脉冲式双探针海底测量单元的有限元数值模型,模拟获得多组参数F的温度-时间数据,作为"实测"数据,再用脉冲加热有限长线热源(PFLS)模型求解待测介质热导率及其相对误差上限(RE_(λ-UL)),并以RE_(λ-UL)最小为原则,对双探针热流计的结构进行优化.结果表明:(1)在不同探针脉冲强度(q)、温度测量误差(ΔT_m)和探针长度(L)组合下,都存在最佳探针间距(Best_r),使得RE_(λ-UL)降到最低;(2)随着q增大或ΔT_m减小,Best_r逐渐增大;(3)当q、ΔT_m及探针半径(a)都给定时,Best_r与探针长度(L)呈线性正相关;(4)当a=1.0 mm,且q、ΔT_m分别取为628.0～1100.0 J·m^(-1)、0.5～1.0 mK,若L在20.0～42.0 mm之间时,则Best_r在18.0～30.0 mm之间,此时介质热导率相对误差上限可控制在5.5%以内,同时测量温度可在6 min内达到最大值,即脉冲加热开始后,温度测量只需约7 min,便可满足介质热导率的求解,这比目前常用的Lister型热流计所需海底测量时间缩短8 min左右.

传导-对流型热流的计算模拟

本文对8个初始模型和7个组合模型中沿断层的水热对流、断层产状、山体地形和沉积盆地与基岩热导率反差等四个影响因素对传导型地表热流分布的影响进行了计算机模拟研究。模型设计和参数的选值以西藏中北部一些地热区实测的传导-对流型热流为主要参考依据,但不直接涉及对流组分的校正,而着眼于更广泛的单因子和多因素的模型研究。分析中采用无量纲参数:α=(K_1)/(K_2)(K_1和K_2分别为基岩和沉积盆地的热导率),β=(q_1)/(q_2)(q_1和q_2分别为地表热流的垂向分量和模型的底部热流)以及γ=L/H(L和H分别为离模型左侧边界的距离和山体的高度),以求更广的普适性。对模拟结果的分析表明,上述四项影响因素依其重要性可排序为对流强度—断层倾角—介质热导率反差—地形效应。

非稳态条件下温度梯度型热流计片误差分析

温度梯度型热流计由于其价格低廉、应用方便等特点在热工测试中被广泛的运用,然而在实际工程运用当中其精度往往得不到保证。建立了典型的热流计片测试的数学模型,在非稳态条件下对其误差进行分析研究。最后得出结论,热流计片本身的热工属性以及不同的边界条件对于热流计片的现场测试精度都有很重大的影响。

自制热电堆型热流计及测试误差分析

为使建筑能耗检测经济快捷,利用热电偶测温原理制作热电堆型热流计。该热电堆由0.2mm铜-康铜热电偶依次串联而成。运用热流计式导热仪对其进行标定。本文就制作热电堆型热流计中应注意的问题进行研究。在试验中利用自制的热电型热流计进行建筑围护结构现场温度及热流密度检测,在同一区域多点布置自制热电堆型热流计对围护结构主体进行现场检测,并分析测量误差及在实际现场测试中应该注意的问题。增加热电偶的对数,减小基板热阻,可以减小测量的相对误差,是提高灵敏度的有效方法。

Operation optimization of prefabricated light modular radiant heating system:Thermal resistance analysis and numerical study

The utilization of prefabricated light modular radiant heating system has demonstrated significant increases in heat transfer efficiency and energy conservation capabilities.Within prefabricated building construction,this new heating method presents an opportunity for the development of comprehensive facilities.The parameters for evaluating the effectiveness of such a system are the upper surface layer’s heat flux and temperature.In this paper,thermal resistance analysis calculation based on a simplified model for this unique radiant heating system analysis is presented with the heat transfer mechanism’s evaluation.The results obtained from thermal resistance analysis calculation and numerical simulation indicate that the thermal resistance analysis method is highly accurate with temperature discrepancies ranging from 0.44℃ to−0.44℃ and a heat flux discrepancy of less than 7.54%,which can meet the requirements of practical engineering applications,suggesting a foundation for the prefabricated radiant heating system.

差示扫描量热法及其在商品检验中的应用

差示扫描量热法(DSC)是一种较新型有效的热分析技术,由于技术上的进步和计算机的广泛使用,使得该技术得到了广泛的应用。扼要介绍了DSC的测试原理及其在进出口商品检验中的应用,并对其存在的问题进行了探讨。

Constitutive modeling of hot deformation behavior of X20Cr13 martensitic stainless steel with strain effect

Hot deformation behavior ofX20Cr13 martensitic stainless steel was investigated by conducting hot compression tests on Gleeble-1500D thermo-mechanical simulator at the temperature ranging from 1173 to 1423 K and the strain rate ranging from 0.001 to 10 s^-1. The material constants of a and n, activation energy Q and A were calculated as a function of strain by a fifth-order polynomial fit. Constitutive models incorporating deformation temperature, strain rate and strain were developed to model the hot deformation behavior of X20Cr13 martensitic stainless steel based on the Arrhenius equation. The predictable efficiency of the developed constitutive models of X20Cr13 martensitic stainless steel was analyzed by correlation coefficient and average absolute relative error which are 0.996 and 3.22%, respectively.

Analysis of hot-carrier degradation in N-LDMOS transistor with step gate oxide

In order to minimize the hot-carrier effect（HCE）and maintain on-state performance in the high voltage N-type lateral double diffused MOS（N-LDMOS）, an optimized device structure with step gate oxide is proposed. Compared with the conventional configuration, the electric field under the gate along the Si-SiO2 interface in the presented N-LDMOS can be greatly reduced, which favors reducing the hot-carrier degradation. The step gate oxide can be achieved by double gate oxide growth, which is commonly used in some smart power ICs. The differences in hot-carrier degradations between the novel structure and the conventional structure are investigated and analyzed by 2D technology computer-aided design（TCAD）numerical simulations, and the optimal length of the thick gate oxide part in the novel N-LDMOS device can also be acquired on the basis of maintaining the characteristic parameters of the conventional device. Finally, the practical degradation measurements of some characteristic parameters can also be carried out. It is found that the hot-carrier degradation of the novel N-LDMOS device can be improved greatly.

Unified Degradation Model in Low Gate Voltage Range During Hot-Carrier Stressing of p-MOS Transistors

Hot carrier effects of p MOSFETs with different oxide thicknesses are studied in low gate voltage range.All electrical parameters follow a power law relationship with stress time,but degradation slope is dependent on gate voltage.For the devices with thicker oxides,saturated drain current degradation has a close relationship with the product of gate current and electron fluence.For small dimensional devices,saturated drain current degradation has a close relationship with the electron fluence.This degradation model is valid for p MOSFETs with 0 25μm channel length and different gate oxide thicknesses.

A new mathematical model for predicting flow stress of X70HD under hot deformation

To realize numerical simulation of rolling and obtain the hot forming process parameters for X70 HD steel, the flow stress behaviors of X70 HD steel were investigated under different temperatures（820-1100 ℃ and strain rates（0.01-10 s-1） on a Gleeble-3500 thermo-simulation machine. A new flow stress model was established. The linear and exponential relationship methods were applied to the parameters with respect to temperature and deformation rates. The rise of curve ends under certain conditions was analyzed. The flow stress of X70 HD steel predicted by the proposed model agrees well with the experimental results. So, it greatly improves the precision of the metal thermoplastic processing through finite element method and practical application of engineering.

Effect of working parameters on performance characteristics of hydrostatic turntable by using FSI-thermal model

Effects of working parameters on performance characteristics of hydrostatic turntable are researched by applying the fluid-structure-thermal coupled model.Fluid-structure interaction(FSI)technique and computational fluid dynamics(CFD)method are both employed by this new model,and thermal effects are also considered.Hydrostatic turntable systems with a series of oil supply pressures,various oil recess depth and several surface roughness parameters are studied.Performance parameters,such as turntable displacement,system flow rate,temperature rise of lubrication,stiffness and damping coefficients,are derived from different working parameters(rotational speed of turntable and exerted external load)of the hydrostatic turntable.Numerical results obtained from this FSI-thermal model are presented and discussed,and theoretical predictions are in good agreement with the experimental data.Therefore,this developed model is a very useful tool for studying hydrostatic turntables.The calculation results show that in order to obtain better performance,a rational selection of the design parameters is essential.

Temperature Distribution in Ethylene Pyrolyzer

A good understanding of the detailed temperature distribution in the furnace plays an important role in the implementation of operation optimization and design improvement of ethylene pyrolyzer. Numerical simulation of the turbulent flow, combustion and heat transfer was carried out to investigate the temperature distribution in industrial furnace. Inhomogeneities of the flue-gas temperature distribution were observed in X, Y, and Z direction of the furnace from the simulated results. Along the height of the furnace, the average flue-gas temperature increased initially and decreased afterward, and reached its peak at the height of 5 m. The reactor tube skin temperature varied not only along the height of the furnace, but also around the circumference of the tube. The heat flux profiles from the furnace towards the reactor tubes followed the shape of the average flue-gas temperature profile. The heat flux of the inlet tubes was constantly higher than that of the outlet tubes at the same height in the furnace.

A Two-Layer Model for Superposed Electrified Maxwell Fluids in Presence of Heat Transfer

Based on a modified-Darcy-Maxwell model, two-dimensional, incompressible and heat transfer flow of two bounded layers, through electrified Maxwell fluids in porous media is performed. The driving force for the instability under an electric field, is an electrostatic force exerted on the free charges accumulated at the dividing interface. Normal mode analysis is considered to study the linear stability of the disturbances layers. The solutions of the linearized equations of motion with the boundary conditions lead to an implicit dispersion relation between the growth rate and wave number. These equations are parameterized by Weber number, Reynolds number, Marangoni number, dimensionless conductivities, and dimensionless electric potentials. The case of long waves interfaciaJ stability has been studied. The stability criteria are performed theoreticaily in which stability diagrams are obtained. In the limiting cases, some previously published results can be considered as particular cases of our results. It is found that the Reynolds number plays a destabilizing role in the stability criteria, while the damping influence is observed for the increasing of Marangoni number and Maxwell relaxation time.

Geometric Design of Anode-Supported Micro-Tubular Solid Oxide Fuel Cells by Multiphysics Simulations

High volumetric power density （VPD） is the basis for the commercial success of micro-tubular solid oxide fuel cells （mtSOFCs）. To find maximal VPD （MVPD） for anode-supported mtSOFC （as-mtSOFC）, the effects of geometric parameters on VPD are analyzed and the anode thickness, tan, and the cathode length, lea, are identified as the key design parameters. Thermo-fluid electrochemical models were built to examine the dependence of the electrical output on the cell parameters. The multiphysics model is validated by reproducing the experimental I-V curves with no adjustable parameters. The optimal lea and the corresponding MVPDs are then determined by the multiphysics model for 20 combinations of rin, the inner tube radius, and tan. And all these optimization are made at 1073.15 K. The results show that： （i） significant performance improvement may be achieved by geometry optimization, （ii） the seemingly high MVPD of 11 and 14 W/cm^3 can be easily realized for as-mtSOFC with single- and double-terminal anode current collection, respectively. Moreover, the variation of the area specific power density with/cac（2 mm, 40 mm） is determined for three representative （tin, tan） combinations. Besides, it is demonstrated that the current output of mtSOFC with proper geometric parameters is comparable to that of planar SOFC.

Recent Advances in Studies on Formation Mechanism of Subtropical Mode Water and Its Climate Features in North Pacific

Mode Water’, as a product of air-sea interaction, influences the thermal structure and circulation pattern in upper layer ocean and consequently affects the variations of climate. In this paper the recent research results about the subtropi-cal Mode Water in the North Pacific are overiewed. A detailed description of the three kinds of Mode Water in the subtropical North Pacific and some comparisons of their similarities and differences are introduced. Some science problems that need further exploration have been raised.

Flow stress prediction of Hastelloy C-276 alloy using modified Zerilli−Armstrong,Johnson−Cook and Arrhenius-type constitutive models

To better understand the hot deformation behaviors of Hastelloy C-276 alloy under elevated temperatures,hot tensile tests were carried out in the temperature range of 1223−1423 K and the strain rate range of 0.01−10 s^−1,respectively.Based on the modified Zerilli−Armstrong,modified Johnson-Cook,and strain-compensated Arrheniustype models,three constitutive equations were established to describe the high-temperature flow stress of this alloy.Meanwhile,the predictability of the obtained models was evaluated by the calculation of correlation coefficients(r)and absolute errors(Δ),where the values of r for the modified Zerilli−Armstrong,Johnson−Cook,and Arrhenius-type constitutive models were computed to be 0.935,0.968 and 0.984,and the values ofΔwere calculated to be 13.4%,10.5%and 6.7%,respectively.Moreover,the experimental and predicted flow stresses were compared in the strain range of 0.1−0.5,the results further indicated that the obtained modified Arrhenius-type model possessed better predictability on hot flow behavior of Hastelloy C-276.

Numerical method and model for calculating thermal storage time for an annular tube with phase change material

For calculating the thermal storage time for an annular tube with phase change material （PCM）, a novel method is proposed. The method is suitable for either low-temperature PCM or high-temperature PCM whose initial temperature is near the melting point. The deviation fit is smaller than 8% when the time is below 2x104 s. Comparison between the predictions and the reported experimental data of thermal storage time at same conditions is investigated and good agreements have been got. Based on this method, the performance of the thermal storage unit and the role of natural convection are also investigated. Results show a linear relation between the maximum amount of stored heat and thermal storage time, and their ratio increases with the height of the thermal storage unit. As the thickness of the cavity increases, natural convection plays an increasingly important role in promoting the melting behavior of paraffin. When the thickness of the cavity is small, natural convection restrains the melting behavior of paraffin.

Mathematical modelling and numerical optimization of particle heating process in copper flash furnace

A mathematical model of the particle heating process in the reaction shaft of flash smelting furnace was established and the calculation was performed.The results indicate that radiation plays a significant role in the heat transfer process within the first 0.6 m in the upper part of the reaction shaft,whilst the convection is dominant in the area below 0.6 m for the particle heating.In order to accelerate the particle ignition,it is necessary to enhance the convection,thus to speed up the particle heating.A high-speed preheated oxygen jet technology was then suggested to replace the nature gas combustion in the flash furnace,aiming to create a lateral disturbance in the gaseous phase around the particles,so as to achieve a slip velocity between the two phases and a high convective heat transfer coefficient.Numerical simulation was carried out for the cases with the high-speed oxygen jet and the normal nature gas burners.The results show that with the high-speed jet technology,particles are heated up more rapidly and ignited much earlier,especially within the area of the radial range of R=0.3−0.6 m.As a result,a more efficient smelting process can be achieved under the same operational condition.