Fluid flow and heat transfer characteristics of spiral coiled tube: Effects of Reynolds number and curvature ratio

Numerical analysis was performed to investigate flow and heat transfer characteristics in spiral coiled tube heat exchanger. Radius of curvature of the spiral coiled tube was gradually increased as total rotating angle reached 12π. As the varying radius of curvature became a dominant flow parameter, three-dimensional flow analysis was performed to this flow together with different Reynolds numbers while constant wall heat flux condition was set in thermal field. From the analysis, centrifugal force due to curvature effect is found to have significant role in behavior of pressure drop and heat transfer. The centrifugal force enhances pressure drop and heat transfer to have generally higher values in the spiral coiled tube than those in the straight tube. Even then, friction factor and Nusselt number are found to follow the proportionality with square root of the Dean number. Individual effect of flow parameters of Reynolds number and curvature ratio was investigated and effect of Reynolds number is found to be stronger than that of curvature effect.

Theoretical and Experimental Study on Ground Coupled Heat Pump with Vertical Spiral Coil

The numeric al simulation study on the temperature distribution of underground field for the ground coupled heat pump (GCHP) with vertical spira l coil was carried out by using finite element. The distribution and recovery of undergroun d field temperature under different operation ratio and the optimal operation ratio were simulated.The performance parameters, i.e. inlet and outlet temperature of the ground spiral coil in heating and cooling modes were tested, the heat extracted or emitted by the heat pump to the ground was calculated, and the coefficients of performance (COP) of GCHP at heat ing and cooling modes were analyzed.

Comparison of three formulations for eddy-current problems in a spiral coil electromagnetic acoustic transducer

Three differential equations based on different definitions of current density are compared. Formulation Ⅰ is based on an incomplete equation for total current density(TCD). Formulations Ⅱ and Ⅲ are based on incomplete and complete equations for source current density(SCD), respectively. Using the weak form of finite element method(FEM), three formulations were applied in a spiral coil electromagnetic acoustic transducer(EMAT) example to solve magnetic vector potential(MVP). The input impedances calculated by Formulation Ⅲ are in excellent agreement with the experimental measurements. Results show that the errors for Formulations Ⅰ& Ⅱ vary with coil diameter, coil spacing, lift-off distance and external excitation frequency, for the existence of eddy-current and skin & proximity effects. And the current distribution across the coil conductor also follows the same trend. It is better to choose Formulation I instead of Formulation Ⅲ to solve MVP when the coil diameter is less than twice the skin depth for Formulation Ⅰ is a low cost and high efficiency calculation method.

Finite Element Based Analysis of Magnetic Forces between Planar Spiral Coils

This paper elaborates on the magnetic forces between current carrying planar spiral coils. Direct and concentric rings methods are employed in order to calculate the magnetic force between these coils. The results obtained by two calculation methods show the efficiency of the replaced rings method in both simplicity and calculation time. Simula-tions using the Finite Element Method (FEM) are carried out to analyze the distribution of the magnetic flux density around the coils. Also, coils with precise size have been constructed and tested. The experimental results as well as the results obtained by FEM are used to validate the accuracy of the calculations.

水平多层spiral型地埋管数值模拟研究及换热特性分析

本文基于COMSOL软件建立了水平spiral型多层地埋管群传热三维数值模拟模型,并对其换热性能和温度场进行分析研究。结果表明:对比水平spiral多层并联管群来说,远离注入端的地埋管管内温度相对较低。地埋管群周围地层温度有所升高,远离注入端的地层温度变化相对较小。地埋管群的换热量随循环流体的流速增加而增加,但增幅降低。在进行换热器设计时,应合理控制循环水的流速。3层螺旋地埋管群的换热量略高,但层间干扰明显,建议选用2层并联螺旋管群。

PIV EXPERIMENTAL RESEARCH OF FLOW STRUCTURE IN RECTANGULAR CHANNEL WITH TRANSVERSELY PLACED SPIRAL COIL INSERT

The flow field in a rectangular channel with a transversely placed spiral coil insert is investigated by Particle Image Velocimetry （PIV） measurements in both transverse and longitudinal sections. The experimental results show that multi-longitudinal vortices are induced downstream of the spiral coil and are distributed as a symmetrical vortex array along the horizontal central line of the transverse section. Along the mainstream, due to the spiral motion of the longitudinal vortices, the velocity fluctuates in a manner of the damped sinusoidal curve and the velocity component in the wall normal direction is improved in the channel. Com- pared with the flow field in a smooth channel it is found that the movement of the longitudinal vortices can cause a continuous dis- turbance near the channel walls and thus enhances the fluid velocity in the near wall region, which consequently leads to the redu- ction of the velocity gradient and a more uniform velocity distribution. With the increase of the Reynolds number, the induced longitudinal vortices gain strength and become straighter and closer to the channel walls, thus the turbulence intensity is further enha- nced in this area.

INITIAL COMPARISON OF INTRACRANIAL ANEURYSM EMBOLIZATION WITH MECHANICAL DETACHABLE SPIRALS AND WITH GUGLIELMI DETACHABLE COILS

Objective.To compare the embolization effects of intracranial aneurysms with mechanical detachable spirals(MDS) and with Guglielmi detachable coils(GDC).Methods.One hundred and twenty cases with 125 intracranial aneurysms were embolized in Beijing Hospital from March 1995 to July 1999.Sixty-six aneursms in 64 cases were embolized with MDS,51 in 48 with GDC, and 8 in 8 with both MDS and GDC.Clinical data includng sex,age,subarachnoid hemorrhage(SAH),Hunt & Hess grading,diameter and neck width of aneurysms,number and length of coils used per aneurysm,occlusive radio,and complications were compared between MDS and groups.Results.MDS and GDC groups were comparable(t-test or X^2 -test ,all P value>0.10） in terms of age,sex,diameter of aneurysms[(8.46±3.42)mm vs.(7.38±3.45)mm],neck width[(3.49±1.50)mm vs.（3.26±1.52)mm],coils number [(4.65±3.01)vs.(4.24±2.65)] and their length[(460.2±398.5)mm vs.(422.9±387.1)mm] used per aneurysm,occlusive ratio in aneurysms embolized≥80%[(95.00±6.32%)vs.(94.19%±7.63%)],mortality and permanent complications(7.8% vs.4.25）。Couclusions,MDS and GDC are all materials for embolization of intracranial aneurysms.MDS is less expensive,but more difficult to control and of propensity to complications while GDC is more compliant ,easier to be used,safer,and have many alternative types for use as well as more extensive indications.

青贮机铁磁性金属异物智能检测报警系统

[目的/意义]青贮机作业时,田间遗落的铁丝等铁磁性金属异物如果混入其喂入系统,将会对青贮机的关键零部件和牲畜脏器造成严重损伤。为了确保青贮机在田间作业时能准确、高效地检测出金属异物,本研究开发了一套性能优良的金属探测系统。[方法]首先分析了青贮机金属检测原理,然后对平面螺旋线圈与圆柱线圈进行了仿真计算,选择平面螺旋线圈作为研究对象,通过使用非支配排序遗传算法(Nondominated Sorting Genetic Algorithm-Ⅱ,NSGA-Ⅱ)结合有限元仿真分析的方式,确定了线圈的线径、内径、外径、层数以及频率,并对弯曲线圈与未弯曲线圈以及阵列线圈进行了仿真计算。最后进行了系统集成,搭建了青贮机模拟试验台进行了模拟试验。[结果和讨论]仿真分析结果显示,平面螺旋线圈磁通密度模变化范围明显大于圆柱线圈,且其电感灵敏度、电阻灵敏度和被测物涡流损耗要明显高于圆柱线圈;另一方面,平面线圈弯曲后电感灵敏度、电阻灵敏度大幅度提高,有利于增强探测线圈的响应度。通过模拟台架试验,验证了该金属探测系统在探测距离小于70mm,对直径0.6 mm、长度20 mm铁丝报警率达到100%,且经过计算,系统响应时间为0.105 0 s,小于安全运输时间,系统可以在金属物到达切碎系统前及时停止。[结论]本研究设计出了一套青贮机金属异物探测系统,提出了一套金属探测线圈的优化方法,并开发了相应的金属探测软硬件系统,通过试验验证了金属探测系统的功能,为青贮机安全运行提供了有力技术支撑。

脐带螺旋指数与妊娠结局的相关性研究进展

脐带是母儿间气体交换、营养物质供应和代谢产物排出的唯一通道,脐带异常可直接影响妊娠结局,其中脐带螺旋异常占据重要位置,但目前尚无有效防治措施。脐带螺旋异常可导致胎儿缺氧,甚至危及患儿生命,在妊娠合并糖尿病、高血压等妊娠相关疾病中的发生率更高,且与不良围生结局相关。因此,通过产前超声观察脐带螺旋状态、监测胎儿宫内生长情况可进一步指导临床,改善不良妊娠结局。深入研究脐带螺旋指数与妊娠结局的相关性,可以为疾病的治疗提供新思路。

不同螺旋缠绕异形管换热器壳程性能数值研究

缠绕管的形状对螺旋缠绕管换热器的传热能力有重要影响,本文建立了具有不同截面形状的螺旋缠绕管换热器模型,数值研究了八种不同截面形状的缠绕管对螺旋缠绕管换热器壳程流动与传热性能的影响。相比于传统圆管,三叶管和水滴管对壳程流体造成的扰动较大,增强了螺旋缠绕管换热器的综合换热性能,而三叶管则具有最大换热能力。进一步分析了不同冲刷方式对螺旋三叶管换热器和螺旋水滴管换热器壳程性能的影响,结果表明:在相同的进口工况下,螺旋三叶管换热器壳程努塞尔数相比于传统圆管提高了11.8%~15.5%,阻力系数增大了41.9%~49.6%;螺旋水滴管换热器壳程努塞尔数相比于传统圆管提高了2.8%~4.3%,阻力系数增大了3.2%~6.8%;在雷诺数为2 603~5 206的工况条件下,管截面与流动方向夹角为0°的三叶管换热器综合换热性能最好,而管截面与流动方向呈逆流形式的水滴管换热器综合换热性能优于顺流形式。

不锈钢丝/尼龙螺旋线圈型人工肌肉的制备及其性能研究

将廉价的尼龙线和不锈钢丝混纺制备螺旋线圈型人工肌肉,探索尼龙线直径和不锈钢丝股数对人工肌肉的电热致动性能影响。结果表明:随着尼龙线直径的增加,不锈钢丝/尼龙人工肌肉的一个工作循环时间增长,在相同刺激时间下输出力和收缩率大幅提升,且输出力与尼龙线直径之间呈二次函数关系;随着不锈钢丝股数增加,人工肌肉的收缩率和输出力增大,3股不锈钢丝性能最优,50g恒定载荷下收缩率达17%,输出力达0.67N。可为聚合物基人工肌肉的制备及应用提供一定理论依据。

基于印刷螺旋线圈的自谐振无线能量传输系统

基于印刷螺旋线圈的自谐振无线能量传输系统,其PCB板的顶层和底层分布螺旋线圈,等效电路由电感、电阻和电容的RLC串联组成。自谐振无线能量传输线圈具有结构简单、无需额外补偿电路及便于和PCB电路集成等优点。理论推导了无线能量传输效率和线圈品质因数的关系,并参数化分析了螺旋线圈的圈数和线宽对线圈的电感、电阻和品质因数的影响。仿真实验表明,当发射线圈和接收线圈的传输距离在45 mm内,自谐振无线能量传输效率可达85%以上;当发射线圈和接收线圈的轴向距离设定为45 mm时,收发线圈的水平偏移量在30 mm内,自谐振无线能量传输效率可达80%以上。

空心挂面自动盘条装置设计与研究

针对空心挂面盘条工作自动化程度低、效率差和工人劳动强度大的现状,提出一种基于阿基米德螺线轨迹的自动盘条装置。利用PLC控制伺服电机实现盘条装置自动运行;利用Matlab软件研究笛卡尔坐标系下不同参数对阿基米德螺线轨迹的影响;利用Adams软件进行仿真计算,验证匀速阿基米德螺线的合理性;对盘条装置进行结构和电气控制系统设计,进行样机试验。结果表明,自动盘条装置盘条效果良好,以直径30 mm面条为例,最小盘条半径为30 mm,最大盘条半径为350 mm,最大盘条层数为7层,最大盘条速度达到21 m/min,可以替代人工进行面条盘放。研究为空心挂面盘条工作提供一种可行的解决方案。

双螺旋盘管内膨胀石墨对相变材料的传热强化机制与蓄放热性能

本工作提出了一种双螺旋盘管与膨胀石墨强化传热的相变蓄热器结构,通过建立双螺旋管相变蓄热器模型,模拟了双螺旋管的螺距、材料热物性对蓄放热性能的影响规律。探讨了限制空间下相变材料自然对流与材料导热增强在传热强化过程中的控制作用。结果表明,在加工螺距限制条件下,减小螺距及增加螺旋数可以提升蓄热器放热性能。膨胀石墨可以提升相变材料热导率,同时会导致材料黏度增大,因此添加膨胀石墨能增强蓄热器的导热换热,但抑制自然对流换热。通过对比分析发现,在限制空间下材料的导热增强带来的传热强化程度能够弥补由于材料自然对流不足导致的传热损失。因此,本工作揭示了相变蓄热器传热强化的控制步骤在于材料热导率强化。基于实验和仿真结合的方式,本工作设计了一款用于加热生活热水的蓄热器结构,验证了所设计的蓄热器在宽进口温度、进口流量等操作工况下具有优异的放热性能。该蓄热器与电加热器相结合,能够在电热功率小于2200 W的条件下实现热水加热功率超3500 W,突破了家用电热设备的功率限制。

基于平面螺旋发射线圈的胶囊机器人无线供能系统的设计与优化

针对传统环绕式发射线圈的尺寸过大及穿戴不便等问题,文章提出了一种使用平面螺旋线圈作为发射线圈的胶囊机器人无线供能系统,有效地减小了发射线圈的尺寸,同时避免了穿戴不便的问题,提高了胶囊机器人无线供能系统的适用性。论文给出了系统的等效电路模型,研究了系统传输效率与系统参数的关系;对接收端线圈匝数进行了优化,提高了系统的传输效率;通过阻抗变换将负载的等效阻抗优化为最优负载。最后对基于该方案的无线能量传输系统进行了实验验证。结果表明,样机系统在10 cm传输距离下的传输效率达到了8.8%,传输功率超过了1 W。

多发射线圈准全向无线充电研究

为了实现高效的无线充电能量传输,提出使用2个正交的平面螺旋线圈作为发射端,实现了全向充电,且使得产生的磁场在空间中的分布更加均匀。研究了该结构的磁场强度,并通过MATLAB仿真软件进行了分析。根据磁场模型的分析,比较了两正交平面螺旋线圈结构和两正交圆柱螺旋线圈结构的全向性。通过Maxwell仿真软件对两正交平面螺旋线圈进行了有限元分析。实验结果表明:正交平面螺旋发射线圈也可以产生效果不错的旋转磁场。当使用相同长度的线圈来绕制,且平面螺旋线圈外半径等于圆柱螺旋线圈的半径时,平面螺旋正交线圈产生的磁场分布更均匀,全向性更好。

螺旋微肋管腔体吸热器强化换热特性研究

吸热器作为碟式太阳能聚光集热系统的核心部件,其光热转换效率的提高具有重大意义。采用实验与fluent模拟相结合的方法,探究220 mm×160 mm圆柱腔体吸热器和螺旋微肋盘管组装模型的换热特性,研究表明,1 mm直径25 mm螺距的微肋丝结构涡流和二次流形成效果较为明显,综合换热效果较好。换热实验中,微肋丝能够加强流体的扰动,有效削减流体的径向温差;70 L/h入口流量的换热温升效果较为明显。光热转换实验中,吸热器热损与入口流量呈负相关,20 L/h之后达到最低;吸热器的光热转换效率与腔体工质温差的变化呈负相关,最高可以达到68%。

谐振式无线输电系统线圈参数优化

为优化同轴同心型无线电能传输系统的线圈尺寸,提高最大传输效率,文中基于等效电路理论建模,通过电感、互感表达式推导耦合系数、最大传输效率关于线圈尺寸参数的关系式,运用仿真分析线圈长度、线圈直径和传输距离对耦合系数的影响规律,进一步优化传输系统的最大传输效率,并通过多物理场仿真不同线圈尺寸的磁场分布特征。最后选定线圈尺寸进行实验测试,并与理论、仿真数据进行对比。结果表明,所提方法的最大传输效率的理论值、仿真值与实测值基本吻合。

考虑环境风时碟式太阳能热发电系统用腔式吸热器的热性能模拟

吸热器是碟式太阳能热发电系统中集热系统的关键部件,为了探究环境因素对吸热器热性能的影响,利用光线追踪和数值计算的方法,在考虑环境风的情况下,对腔式吸热器进行了不同工况时的热性能模拟,讨论分析了太阳高度角、环境风风向、风速及传热工质进口状态对腔式吸热器热性能的影响。结果表明:太阳高度角越小,腔式吸热器对流热损失越大;随着环境风风向角的增大,无论风速如何,腔式吸热器的热损失都呈现先减小后增大的趋势,当风向角为135°时的热损失最小,风向角小于45°时的热损失较大;任何风向下,腔式吸热器的热损失都随着环境风风速的增大而增大,且在0°和45°风向角下,腔式吸热器对于风速变化较为敏感;传热工质进口流量的增加会提升腔式吸热器的热性能,进口温度的提高则会降低腔式吸热器的热性能,且对其影响的规律呈线性。