多晶硅真空定向凝固系统的结构特性优化研究

采用非稳态集中参数法分别计算了沿轴向和径向增加装料量对多晶硅定向凝固过程中加热时间的影响,并通过数值模拟对比分析了多晶硅定向凝固过程中晶体生长时的温度场、熔体流动、固-液界面形状和应力大小及分布等情况。并对装料沿径向增加以提高单炉生产率的方案提出了添加硅料表面上加热器的优化措施,不仅可以显著缩短加热时间,还能减小硅料的径向温度梯度,调节固-液界面形状。这将为大型化多晶硅真空定向凝固设备的优化设计与开发利用提供理论基础。     

WZ003041有发展前途的轧钢连续加热炉符合能量与资源保护的热工制度——《иэвегияВУ3 черная метапдгургня》

讨论的第1个问题是加热最终参数。首先，认为加热终了时的温度可降低50～200℃。此举可以减少金属氧化烧损的热损失(可减少50％)，降低炉膛温度，减少砌体向外的热损失，降低燃料消耗，减少Nox排放，并可提高炉子生产率。其次，应采取料坯在炉外(炉子与轧机之间)实现料坯温度均匀化的措施，以允许把在炉内的加热不均匀性提高50～150℃。此举可缩小甚至在某些条件可取消均热段或均热期(它们通常占总加热时间的30％)，     

感应加热在锻造工业中的应用

在从500到4000赫之间的通常的频率范围内,旋转变频器现时已大部分为闸流管静止变频器所取代。有的静止变频器的功率已达3400KW,频率是500赫。在锻造业中所采用的主要有以下的几种加热类型:块料加热设备;棒料加热设备以及棒料局部加热设备。现时块料加热设备类型的区分主要是在传送系统方面,推送式传送装置及步进式传送装置。局部加热     

直接启动盐浴炉

由于盐浴炉具有加热速度快,工件不易氧化、脱碳,炉温均匀及可局部加热等优点,故在热处理过程中,盐浴炉还是主要的加热设备,至今还广泛地使用着。     

炉体旋转式锻造炉的开发

为解决炉底旋转式锻造炉电动机同步不良和谋求烧嘴均匀加热,日本东京瓦斯公司开发了炉体旋转式锻造炉。该炉的主要特点是运行中整个炉体旋转;烧嘴仅一台设在加热室顶部的中心部,火焰呈扁平状,可对工件实施均匀加热,燃烧排气可由炉侧壁各装出料口排出;装出料口即为燃烧排气口,故工件装入过     

室式锻造炉加热粗圆柱体料坯最终断面加热不均匀性的计算——《ЗHергеTика，изBеcTия BYз》

料坯加热终了时其断面温度的不均匀性对生产有很大影响。对加热不均匀性的计算实质是断面温度场的计算。写出了断面温度场的微分方程式，并给出边界条件，得出了分析解。对直径为0．1m和0．2m的钢坯分别进行了加热计算。根据计算结果，认为可以进一步缩短加热时间，仍能满足加热均匀性的要求。这便为降低单位燃料消耗提供了可能性。图4     

非均匀受热管管壁温度场的数值计算

针对非均匀受热管管壁周向壁温和热负荷等热特性参数分布不均性,将外壁温度与外壁散热热负荷作为边界条件,建立非均匀受热管的温度场计算二维模拟数学模型,基于径向节点推进思想,采用有限容积法建立离散方程,编制求解流体换热和管壁导热耦合决定的非均匀受热管二维温度场导热反问题数值计算程序。利用程序计算了Φ32mm×3mm和Φ24mm×4mm半周加热垂直上升光管对超临界水的传热特性,计算结果都可以很好地反映非均匀加热管管壁温的分布规律,同时计算收敛性良好。计算结果表明:超临界压力下,半周加热垂直上升光管壁温及壁面热负荷周向分布不均,高热负荷侧温度高,而低热负荷侧温度低。在拟临界区,出现传热强化,管内传热系数的增大会减小热量沿管壁周向的均流作用。     

不同加热方式下大尺寸物料的传热特性

以秸秆料包为原料,采用微波加热和电加热2种方法对其进行了加热试验,测得了料包内部的温度分布,并进行了对比研究.结果表明:微波加热迅速,均匀性好,但物料特性和加热过程中的化学反应对温度分布有重要影响;电加热时,料包内部温度沿导热方向单调递减,由于导热热阻的存在,使得沿导热方向分布的各层物料进入热解阶段的时间间隔逐渐增大,热平衡时各层物料间存在明显的温度梯度.在功率可对比的情况下,微波加热比电加热速度更快、效率更高.     

Numerical simulation of mixed convective heat transfer of a molten salt in a square tube with a thermally conductive wall

熔盐因具有传热能力强、工作温度高、使用温度广、系统压力低、经济适用等优点,成为太阳能热发电系统蓄热工质的理想选择。熔盐在实际应用中会因加热过程的非均匀性产生存在于固体表面和流体间的温差,造成流体工质中的密度梯度,因此出现重力导致的浮升力效应,其叠加到主流流动方向上即形成混合对流。管壁导热会对熔盐混合对流传热过程产生一定的影响。本文对熔盐在水平方管内非均匀加热条件下的单面加热的混合对流过程进行了数值模拟研究,在考虑壁厚的情况下研究了方管单面加热熔盐混合对流传热特性,分析了无量纲参数间的变化关系,并将结果与流型判定图和经典关联式进行对比。结果表明,非均匀加热时,浮升力效应会造成随流动距离增加主流核心区域的形状发生改变,且更加靠近加热壁面。Nu数随Re数、Ri数的增大而增大,局部Nu_x数随流动距离的深入先减小后增大。与忽略管壁导热数值模拟结果相比,主流核心区形状更加均匀,局部Nu_x更高且回升位置更加提前,流动特性和传热特性基本保持一致。     

电炉熔炼铝合金废料的改进(俄)

目前,铝合金残料均在火焰炉或感应炉里熔炼,由于感应炉熔炼时热量产生在被加热料的内部,能充分利用热量,且金属的搅拌剧烈,加热速度快。当金属的外表面被加热后,通过传热使内表面也被加热。因此,感应炉是熔炼铝合金废料的理想设备。     

火焰加热炉与加热缺陷

本文简要介绍了法国工业炉的状况及加热缺陷研究的最新成果。通过模型实验和模拟计算掌握了炉内的流场，这样就可通过一些简单、易行，但有效的措施改善钢坯的出炉热状态。     

Integrated performance of liquid-based solar heating systems

A closed form model for the integrated performance of liquid-based solar heating systems is presented. The model is general enough to be used for most liquid-based systems. It can be used for systems with either flat plate or concentrating collectors and the load is not restricted to space heating applications. Three new system parameter are introduced by this model. These are the system heat storage factor, the solar distribution factor and the load distribution factor. These three factors respectively account for the reduction in system performancev which results from finite storage, non-uniform solar flux and non-uniform load. These factors are discussed in detail and closed form mathematical expressions, from which numerical values can be calculated, as persented.     

Pulsed electromagnetic heating of microparticles

The application of pulsed heating by a laser beam to determine the thermal properties of microparticles is explored. Two problems are analyzed : (i) spatially uniform heating of the surface of an absorbing microsphere, and (ii) non-uniform surface heating based on Mie theory computations of the electromagnetic energy source. A parametric study shows that the spatially uniform heating model is sufficient when the thermal conductivity of the microparticle is sufficiently large or the Biot number is sufficiently low, but a more rigorous model is needed to predict the temperature distribution with the microsphere for lower thermal conductivity materials. The resulting analytical solutions are compared with previously published experiments involving infrared heating of single spherocarb particles and are shown to be in good agreement with time-dependent surface temperature measurements.     

Is space heating in offices really necessary?

New office buildings in Sweden are thoroughly insulated due to the Swedish building code. This code, however, does not consider the type of activity occurring in the building. This means that the heating equipment is designed as if no activity at all is going on. In modern offices there is a lot of equipment installed which uses electricity. This electricity is converted into heat which can be utilized for heating the premises, mostly in a direct way but also by the use of exhaust-air heat-pumps or heat exchangers. This paper deals with a modern office building plus office hotel complex located in Linköping, Sweden, about 200 km south of Stockholm. The tenants deal with the design of hard- and software for computers. The lighting and computers in the building use electricity which converts into heat. In this paper, it is shown that this electricity is all that is needed during normal conditions, i.e. when people work in the building. The building is also equipped with a district-heating system, which is designed as if no activity goes on in the building, so subsequently the heating equipment is larger than it need be. In this special case, it might have been better to install an electric heating device for hot-water heating and very cold winter conditions, instead of using district heating. This is so even if district heat is about half the unit price compared with that due to the dissipation of electricity. At present, when district heating is used, no measures for saving heat can be profitable due to the low district-heating price. The fact is that the tenants complain of too much heat instead of too little: the prevailing indoor temperature was about 24° C in January 1990 even though 20° C would have been sufficient. There is subsequently a need for a properly working regulation system. The one currently in use is designed to a modern standard, but is not able to maintain temperatures at a modest level.     

Analysis of microwave heating for cylindrical shaped objects

Microwave heating is very popular in food industries as well as in home and office to warm up foodstuffs quickly. However, this technique provides non-uniform heating within the system. The potential existence of standing wave due to the transmission and reflection from interfaces is responsible for this non-uniform heating. Therefore, it is important to study the coupling between electromagnetic wave propagation and energy transfer in the system to predict the temperature distribution within the foodstuff. In this paper, a closed-form analytic solution is presented to predict the temperature distribution within a cylindrical shaped foodstuff under microwave heating by solving an unsteady energy equation. A simplified Maxwell’s equation is solved for electric field distribution within the body. The heat generation by microwave is calculated from the electric field distribution within the body using Poynting theorem. The effects of cylinder radius, heat transfer coefficient and incident frequency are studied for different length of the cylindrical foodstuff. It is found that the temperature within the body is very sensitive to cylinder length and time. The results indicate that uniform and effective heating depend on the proper integration of geometric parameters and dielectric properties of the object as well as the frequency of the incident electromagnetic wave. This rigorous analytic investigation will provide significant insight to understand and overcome the challenge of non-uniformity in temperature distribution in microwave heating.     

Numerical study on mixed convection in a lid-driven cavity with non-uniform heating on both sidewalls

A numerical study has been performed on mixed convection in a lid-driven cavity. The vertical sidewalls of the cavity are maintained with sinusoidal temperature distribution. A finite volume method is used to solve numerically the non-dimensional governing equations. Results are analyzed over a range of the Richardson numbers, amplitude ratios and phase deviations. The results show that heat transfer rate is increased on increasing amplitude ratio. It is observed that average Nusselt numbers are increased first and then decreased when increasing the phase deviation from 0 to π. The non-uniform heating on both walls provides higher heat transfer rate than non-uniform heating of one wall.     

经皮经脾碘油门静脉造影——肝内占位性病变的平片和 CT 观察

碘油门静脉造影以往多采用剖腹门脉置管来实现。笔者对18例肝内占位性病变患者采用经皮穿刺脾静脉灌注碘油的方法,完成门静脉造影,造影全部成功。术后没有发生脾破裂,脾出血及明显肝功能损害;18例肝肿瘤(直径1～18 cm)平片和 CT 扫描,瘤内及瘤周没有发现碘油沉积。笔者推测这是瘤内、瘤周的门脉分支高压或存在离肝血流的结果;本法有3例3 cm 以下的小结节灶检测数比常规 CT多,提示本法的敏感性可能与动门脉 CT 相似,从平片和 CT 观察瘤内及瘤周并没有象肝动脉灌注碘油那样有碘油充盈,而是呈充盈缺损,相反,正常肝组织分布碘油,这使得笔者对门脉置管化疗栓塞治疗肝癌的作用产生疑虑。     

Application of nanofluids in heating buildings and reducing pollution

This paper presents nanofluid convective heat transfer and viscosity measurements, and evaluates how they perform heating buildings in cold regions. Nanofluids contain suspended metallic nanoparticles, which increases the thermal conductivity of the base fluid by a substantial amount. The heat transfer coefficient of nanofluids increases with volume concentration. To determine how nanofluid heat transfer characteristics enhance as volume concentration is increased; experiments were performed on copper oxide, aluminum oxide and silicon dioxide nanofluids, each in an ethylene glycol and water mixture. Calculations were performed for conventional finned-tube heat exchangers used in buildings in cold regions. The analysis shows that using nanofluids in heat exchangers could reduce volumetric and mass flow rates, and result in an overall pumping power savings. Nanofluids necessitate smaller heating systems, which are capable of delivering the same amount of thermal energy as larger heating systems using base fluids, but are less expensive; this lowers the initial equipment cost excluding nanofluid cost. This will also reduce environmental pollutants because smaller heating units use less power, and the heat transfer unit has less liquid and material waste to discard at the end of its life cycle.     

Experimental study on microchannel heat sinks considering mass flow distribution with non-uniform heat flux conditions

This study investigates cooling performance of microchannel heat sinks under various heat flux conditions for different geometry of the channels and headers. Thermal load is applied to the microchannel heat sinks by nine separate heaters in order to provide uniform or non-uniform heat flux. Straight or diverging channels have been made with rectangular or trapezoidal headers, so four kinds of microchannel heat sinks have been fabricated by the microfabrication processes, such as deep reactive ion etch (DRIE), anodic bonding techniques, and so on. The temperatures of the heaters have been measured under the uniform and non-uniform heat flux conditions, including local heating at hotspots. Moreover, the maximum temperatures for different microchannel heat sink under various heating conditions have been obtained as well as the pressure drops.     

Capillary pumping systems for solar heating application

Capillary pumping two-phase loops have been continuously investigated for electronic cooling systems, satellite thermal control and other space applications. Most tests were performed in capillary evaporators using plastic or metallic porous wick as capillary structure and anhydrous ammonia as the working fluid. In this work, capillary pumping system assisting flat solar collectors is proposed as an alternative to residential and commercial water heating systems, using fine circumferential grooves as capillary structure and acetone as the working fluid. The experimental results are obtained for a small-scale solar heating system, using one capillary pump attached to a flat copper plate of 46 cm in length and 6 cm in width. The capillary pump consists of a 19 mm OD and 500 mm long aluminium tube, with fine internal circumferential groves as the capillary structure. The working fluid is pumped from a condenser designed to delivery heat to the water storage. Heat inputs up to 14 W (507 W/m²) were estimated for heating purpose. The system presented reliable start-ups and good performance in continuous operation. The measurements were found to be in good agreement with theoretical results for the temperature field and solar power absorbed by the system.