Equivalent thermal resistance minimization for a circular disc heat sink with reverting microchannels based on constructal theory and entransy theory

Thermal designs for microchannel heat sinks with laminar flow are conducted numerically by combining constructal theory and entransy theory. Three types of 3-D circular disc heat sink models, i.e. without collection microchannels, with center collection microchannels, and with edge collection microchannels, are established respectively. Compared with the entransy equivalent thermal resistances of circular disc heat sink without collection microchannels and circular disc heat sink with edge collection microchannels, that of circular disc heat sink with center collection microchannels is the minimum, so the overall heat transfer performance of circular disc heat sink with center collection microchannels has obvious advantages. Furthermore, the effects of microchannel branch number on maximum thermal resistance and entransy equivalent thermal resistance of circular disc heat sink with center collection microchannels are investigated under different mass flow rates and heat fluxes. With the mass flow rate increasing, both the maximum thermal resistances and the entransy equivalent thermal resistances of heat sinks with respective fixed microchannel branch number all gradually decrease. With the heat flux increasing, the maximum thermal resistances and the entransy equivalent thermal resistances of heat sinks with respective fixed microchannel branch number remain almost unchanged. With the same mass flow rate and heat flux, the larger the microchannel branch number, the smaller the maximum thermal resistance. While the optimal microchannel branch number corresponding to minimum entransy equivalent thermal resistance is 6.     

Thermal performance analysis of non-uniform height rectangular fin based on constructal theory and entransy theory

A model of non-uniform height rectangular fin, in which the variation of base’s thickness and width are taken into account, is established in this paper. The dimensionless maximum thermal resistance (DMTR) and the dimensionless equivalent thermal resistance (DETR) defined based on the entransy dissipation rate (EDR) are taken as performance evaluation indexes. According to constructal theory, the variations of the two indexes with the geometric parameters of the fin are analyzed by using a finite-volume computational fluid dynamics code, the effects of the fin-material fraction on the two indexes are analyzed. It is found that the two indexes decrease monotonically as the ratio between the front height and the back height of the fin increases subjected to the non-uniform height rectangular fin. When the model is reduced to the uniform height fin, the two indexes increase first and then decrease with increase in the ratio between the height of the fin and the fin space. The fin-material fraction has no effect on the change rule of the two indexes with the ratio between the height of the fin and the fin space. The sensitivity of the DETR to the geometric parameters of the fin is higher than that of the DMTR to the geometric parameters. The results obtained herein can provide some theoretical support for the thermal design of rectangular fins.     

潜热蒸发冷却控制的膜状冷却塔特性研究

基于膜状冷却热、质传递机理,建立水膜薄层的速度分布, 热、质传递方程和潜热蒸发冷却控制的数学模型.结合特定时间段内气候条件、冷水机组负荷和运行工况,通过测算制冷系数、冷却水和空气参数,进行质量和热量衡算.分析空气返混现象及冷却塔并联运行对塔性能的影响,采用湿度计分析法分析潜热蒸发为主的热、质传递过程,由冷却塔蒸发冷却效率和效能的计算结果表明,它们系同一表征冷却塔性能的参数.     

高烈度区1000MW空冷机组结构体系研究与设计实践

直接空冷技术在我国近年来得到了广泛的应用和发展.目前我国正在建造世界上首台1000MW直接空冷机组,结构地处高烈度区.该工程采用了钢筋混凝土管柱+钢桁架+钢斜撑的新型结构体系,为保证结构安全,进行了计算分析和振动台模型试验.试验研究表明,该结构体系相对传统结构体系更适合高烈度区,能够保证小震不坏和大震不倒的设防要求,可供同类工程参考.     

间接空冷散热器空冷塔流动和传热的数值研究

依托实际工程项目,利用计算传热学(NHT)软件FLUENT,对自然通风状态下,某600 MW机组表面式间接空冷散热器空冷塔的流动和换热性能进行了数值模拟、分析和研究.确定了考核工况基准下,不同环境风速对空冷塔通风量和间接空冷散热器散热量的影响.模拟结果显示,随着环境风速的增加,空冷塔通风量和间接空冷散热器散热量减小.它为间接空冷系统的优化设计提供理论依据.     

Thermal design of a novel heat sink cooled by natural convection with phase transition in the series loop

In this paper, a novel heat sink, cooled by natural convection, with phase transition in the circulation loop was designed, and the heat sink was applied on averaging temperature and cooling the electronic equipment. The working fluid in the heat sink was driven by the capillary pump. Numerical simulations were performed, to study the heat transfer performance of two systems with various heating power, filling ratios and refrigerants. The influences of above elements on temperature uniformity of two systems were also studied and the thermal performances of two systems were compared. The volume of fluid (VOF) model was utilized to simulate fluid motion in ANSYS FLUENT. The simulation results indicate that the temperature differences of the system comprising two substrates (system 1) are very small under suitable filling ratio conditions, and the thermal performance of system 1 is preferable to the system comprising one substrate (system 2) at the same volume. Besides, the simulation results also show that the system using R245fa possesses excellent temperature uniformity for the same filling ratio and heating power. Finally, the experiments were investigated and the experimental results proved the correctness of the theoretical model.     

Generalized constructal optimization for the secondary cooling process of slab continuous casting based on entransy theory

Based on constructal theory and entransy theory,a generalized constructal optimization of a solidification heat transfer process of slab continuous casting for a specified total water flow rate in the secondary cooling zone was carried out.A complex function was taken as the optimization objective to perform the casting.The complex function was composed of the functions of the entransy dissipation and surface temperature gradient of the slab.The optimal water distribution at the sections of the secondary cooling zone were obtained.The effects of the total water flow rate in the secondary cooling zone,casting speed,superheat and water distribution on the generalized constructal optimizations of the secondary cooling process were analyzed.The results show that on comparing the optimization results obtained based on the optimal water distributions of the 8 sections in the secondary cooling zone with those based on the initial ones,the complex function and the functions of the entransy dissipation and surface temperature gradient after optimization decreased by 43.25%,5.90%and 80.60%,respectively.The quality and energy storage of the slab had obviously improved in this case.The complex function,composed of the functions of the entransy dissipation and surface temperature gradient of the slab,was a compromise between the internal and surface temperature gradients of the slab.Essentially,it is also the compromise between energy storage and quality of the slab.The"generalized constructal optimization"based on the minimum complex function can provide an optimal alternative scheme from the point of view of improving energy storage and quality for the parameter design and dynamic operation of the solidification heat transfer process of slab continuous casting.     

Numerical simulation of heat transfer and flow of cooling air in triangular wavy fin channels

Numerical computation models of air cooling heat transfer and flow behaviors in triangular wavy fin channels（TWFC） were established with structural parameters of fins considered.The air side properties of heat transfer coefficient and pressure drop are displayed with variable structural parameters of fins and inlet velocities of cooling air.Within the range of simulation,TWFC has the best comprehensive performance when inlet velocity vin=4-10 m/s.Compared with those of straight fins,the simulation results reveal that the triangular wavy fin channels are of higher heat transfer performances especially with the fin structural parameters of fin-height Fh=9.0 mm,fin-pitch Fp=2.5-3.0 mm,fin-wavelength λ=14.0-17.5 mm and fin-wave-amplitude A=1.0-1.2 mm.The correlations of both heat transfer factor and friction factor are presented,and the deviations from the experimental measurements are within 20%.     

Retrofit design of composite cooling structure of a turbine blade by fluid networks and conjugate heat transfer methods

This article discusses the development of the numerical methods of gas flow coupled with heat transfer, and introduces the fluid net-works method for rapid prediction of the performance of the composite cooling structures in turbine blade. The reliability of these methods is verified by comparing experimental data. For a HPT rotor blade, a rapid prediction on the internal cooling structures is first made by using the fluid network analysis, then an assessment of aerodynamic and heat transfer characteristics is conducted. Based on the network analysis results, three ways to improve the design of the cooling structures are tested, i.e., adjusting the cooling gas flow mass ratios for different inner cooling cavities, reducing the flow resistances of the channel turning structures, and improving the local internal cooling structure geometries with high temperature distribution. Through the verification of full three-dimensional gas/solid/coolant conjugate heat transfer calculation, we conclude that the modified design can make the overall temperature distribution more even by significantly reducing the highest temperature of the blade surface, and reasonably matching the parameters of different coolant inlets. The results show that the proposed calculation methods can remarkably reduce the design cycle of complex turbine blade cooling structure.     

含内热源堆积球床对流换热特性的实验研究

为了研究含内热源球床通道内的换热特性,采用直径为8 mm表面氧化碳钢球堆积形成球床,并采用电磁感应加热方式对球床进行整体加热.研究了球床通道内部的功率分布情况和换热系数随热流密度、工质Re的变化规律;并且根据实验数据拟合得到了球床通道内换热系数的无量纲准则关联式,拟合结果与实验结果的偏差在7％以内,符合良好.     

Visualization study on atomization characteristics and heat transfer performance of R1336mzz flash spray cooling

Visualization experiments are carried out to investigate the atomization characteristics of R1336mzz flash spray cooling. The influences of superheat, spray distance, and nozzle orifice diameter on spray cooling performance are analyzed experimentally. As the superheat increases, finer droplets and thinner liquid film are observed; this is helpful to improve the two-phase heat transfer efficiency. Enlarging atomization angle under high superheat is also observed for flash spray cooling, and it benefits for reducing the spray distance. It can be found that when the inlet superheat is 19.8°C and the spray distance is 6 mm, the critical heat flux (CHF) reaches 251 W/cm² and the maximum heat transfer coefficient (HTC) reaches 37.4 kW/(m² °C), which are 55% and 11.6% higher than those when the inlet subcooling is 6.9°C and the spray distance is 12 mm, respectively. Using flash spray reduces the spray distance, which benefits for designing compact spray cooling device. In addition, the nozzle orifice diameter has great influence on the cooling performance of flash spray, and the choice of the nozzle depends on the superheat. This study provides a physical insight into the heat transfer enhancement in flash spray cooling.

     

宽带曲折线圆极化器的分析与设计

通过分析单层曲折线极化栅板结构,得到N层曲折线极化器等效电路。根据级联网络的传输矩阵,推导曲折线圆极化器对入射电场两极化分量的传输系数和反射系数的表达式,进而得到入射波通过多层曲折线圆极化器后的轴比。建立曲折线周期结构单元仿真模型,分析单元参数对传输系数幅度和相位差的影响,从而设计一种宽带多层曲折线圆极化器。实验结果表明,该圆极化器在2.5~6.2GHz频带内轴比小于3dB,带宽可达到1.5倍频程。     

衣领结构设计的优化研究

从衣领的结构设计出发,阐述了服装中最重要的部位衣领与人体的关系,衣领中翻领与领座的关系,翻折线与领下口线的关系,通过各种优化设计方法改变领翻折线与领下口线的长度,从而使衣领更加符合人体,穿着更美观。     

具有非均相化学反应的耦合传热传质熵产率方程

从质量、能量和熵平衡的基本原理出发,导出了具有非均相化学反应的耦合传热传质系统熵产率方程,得到了各种条件下熵产率方程的简化形式,为对具有非均相化学反应的耦合传热传质系统进行性能分析与改进提供了一种有力的工具。     

MapBasic应用软件设计技术研究

MapInfo是公认的最好的桌面地理信息系统平台之一。MapBasic是MapInfo理想的二次开发工具。然而 ,由于MapBasic编程环境的限制 ,单一的MapBasic程序不适合构建大型应用系统。本文基于对MapInfo运行环境以及MapBasic语言特点的分析 ,从面向对象的观点提出了一种新的适于构建大型系统的MapBasic软件结构 ,即先按空间对象的大类分别构造MapBasicApplication ,再用一个控制程序依次加载各个Application ,并通过共享地图窗口实现不同Application间的信息交换 ,通过共享系统事件实现各个Application的同步。用MapBasic开发MapInfo应用系统 ,能够最大限度地发挥MapInfo空间数据处理功能。相信本文的讨论有助于MapBasic用户开发出高质量的应用型地理信息系统     

不同射流方式对钢板换热的影响研究

气雾冷却具有冷却范围大、冷却均匀等特点,对铸坯的最终质量也起到了关键性的作用.本文以实验室条件为基础,采用求解二维导热反问题计算方法,研究了竖直对称射流和倾斜非对称射流冷却过程下钢板由1200℃冷却至100℃过程中的表面热流密度及表面温度的变化过程,对实际生产过程中连铸二次冷却的冷却工艺起到了一定的理论支持.     

基于正交设计的凹坑蜂窝板强化传热性能研究

采用CFD软件对蜂窝板在不同板片间距、凹坑直径、凹坑深度、凹坑横向间距下进行了数值模拟研究．结果表明,在一定范围内,随着Re的增大,努塞尔数Nu和阻力增大因子．f／fo成指数倍增大,范宁摩擦系数f、传热增强因子Nu／Nu。和综合传热性能增强因子η成指数倍减小;流道高度日对其各性能基本无影响;Nu／Nu。和．f／fo随着凹坑间距P的增大而减小,随着凹坑投影直径d的增大而增大,随着凹坑深度Hd。的增大而先增大后减小;η随着P和d的增大而稍微增大,随着巩的增大而减小．通过正交设计综合考虑各结构参数的影响,拟合得到凹坑蜂窝板结构的传热性能与阻力综合准则性能关系式．     

圆孔型铜冷却壁冷面及热面热态特性研究

在自行研制的热态试验炉上对圆孔型铜冷却壁进行了热模拟试验.在保证试验平台运行良好的情况下,研究了铜冷却壁热面及冷面不同部位的温度分布,并从传热学角度作了分析.本研究可为进一步优化铜冷却壁的结构提供参考.     

宽板坯连铸二冷区喷嘴冷却特性研究

根据宽板坯连铸实际工况条件,测定不同冷却条件下喷嘴的冷却特性曲线,分析不同喷嘴布置与连铸实际需要条件的关系。结果表明,喷嘴水流密度峰值随着冷却水量的增加而变大,水流覆盖区域变宽;当喷嘴冷却水量过大时,水流密度分布均匀性不好;气体压力对喷嘴水流密度分布影响不大;双喷嘴喷淋水重叠区的叠加效应随着左边喷嘴冷却水量的递减呈明显的下降趋势,随两喷嘴间距的变大而逐渐减弱;喷嘴间距为450mm时,铸坯表面喷淋水流密度分布更为合理。