Fin formation model during pre-roll ploughing of copper 3D outside fin tube

The mechanism of pre roll ploughing for 3D fins on the outside surface of copper tube was studied systematically, and especially the process and conditions of 3D fin formation were analyzed. The right mathematical model was also established. Based on the volume of fin ploughed out is equal to the volume of the metal extruded up by the extruding face of the tool, the relations between fin height, pre roll ploughing feed and pre roll ploughing depth have been achieved. With the increase of pre roll ploughing depth which must be equal to groove depth, the fin height gradually becomes larger. There are different critical feeds with the various depths of pre roll ploughing. The pre roll ploughing feed is the critical one, the height of fin is largest. And when the feed is above the critical one, the fin height will reduce with the increase of feed. The theoretical analysis basically accords with experimental results.

A CFD Based Investigation of the Unsteady Hydrodynamic Coefficients of 3-D Fins in Viscous Flow

The motion of the fins and control surfaces of underwater vehicles in a fluid is an interesting and challenging research subject.Typically the effect of fin oscillations on the fluid flow around such a body is highly unsteady, generating vortices and requiring detailed analysis of fluid-structure interactions.An understanding of the complexities of such flows is of interest to engineers developing vehicles capable of high dynamic performance in their propulsion and maneuvering.In the present study, a CFD based RANS simulation of a 3-D fin body moving in a viscous fluid was developed.It investigated hydrodynamic performance by evaluating the hydrodynamic coefficients (lift, drag and moment) at two different oscillating frequencies.A parametric analysis of the factors that affect the hydrodynamic performance of the fin body was done, along with a comparison of results from experiments.The results of the simulation were found in close agreement with experimental results and this validated the simulation as an effective tool for evaluation of the unsteady hydrodynamic coefficients of 3-D fins.This work can be further be used for analysis of the stability and maneuverability of fin actuated underwater vehicles.

R134a在水平三维微肋管内的沸腾换热

实验研究了Ｒ１３４ａ 在水平三维微肋管内的沸腾换热。实验段有效长度３ ．０ ｍ ，内径１２ｍｍ ，工质质量流率１００ ～２７７ ｋｇ／（ｍ２·ｓ） ，热负荷１０ ～２０ ｋＷ／ｍ２ ，饱和压力０．５４ ～０ ．６５ ＭＰａ．实验考察了质量流率，质量干度和饱和压力对换热系数的影响。这种三维内微肋管的换热特性同时与Ｗａｔｔｅｌｅｔ 关系式的预测值进行了比较，得到的换热强化因子在１ ．５ ～２ ．１ 之间。

Transient air-water flow patterns in the vent tube in hydropower tailrace system simulated by 1-D-3-D coupling method

The vent tube is commonly used for the water hammer protection in the hydropower tailrace system. In transient processes, with air entering and exiting the vent tube, one sees complex hydraulic phenomena, which threaten the station＇s safe operation. It is necessary to investigate the transient mechanisms in the tailrace system with vent tube. In this paper, a 3-D, two-phase numerical model of a vent tube on the connection of the tailrace tunnel and the diversion tunnel, is developed based on the FLUENT with the volume of fluid（VOF） algorithm to investigate the transient air-water flow patterns and the complex hydraulic phenomena in the vent tube of the tailrace system. A 1-D and 3-D unidirectional adjacent coupling（1-D-3-D-UAC） approach with a linear interpolation method is adopted to adjust the timesteps between the 1-D model and the 3-D model on the tunnel inlet and outlet boundaries through the user defined function（UDF）, to transmit the data from the 1-D model to the 3-D model. The model is verified by comparing the results obtained by using the 1-D model alone and from the experiments in literature. The transient flow processes under the full load rejection consist of four stages： the water level dropping stage, the air entering stage, the air pocket collapsing stage, and the air exiting stage. Detailed hydraulic phenomena in the air pocket collapsing process are also discussed.

Fin performance of 3-D aerator devices with backward lateral deflectors

In the present work,a 3-D aerator device with backward lateral deflectors,called BLD-3-D aerator device,is developed,and the lateral cavity and fin performance of the BLD-3-D aerator device are experimentally investigated.The findings show that,the relative lateral cavity length with backward lateral deflectors is shorter than that with current lateral deflectors under the same approach flow conditions,and on the basis of the results of the relative cavity length ratio between the lateral and bottom aerators the BLD-3-D aerator device is of remarkable performance for the water fin control thanks to the decrease of the relative lateral cavity length.

水平三维肋管外含不凝性气体的水蒸汽凝结换热的实验研究

对水平光管和三维肋管管外具有不同空气含量的水蒸汽凝结换热性能进行了实验研究。获得了不凝性气体含量和壁面过冷度对光管和三维肋管凝结换热性能的影响规律。实验结果表明：在相同的工况条件下，水平三维肋管的凝结换热系数是光管的1．7～2．9倍；不凝性气体含量越高，凝结换热系数越低；壁面过冷度越大，凝结换热系数越大。最后，获得了水平三维肋管管外凝结换热实验关系式。

水蒸汽在水平三维微肋管内的凝结换热及阻力特性

本文以水蒸汽为工质对水平三维微肋管内凝结换热及阻力特性进行了实验研究．与光管和二维管相比，在相同条件下，实验中效果最好的T3管全长平均凝结换热系数分别提高了113％～410％和20％～65％，同时，与二维管相比流动阻力增加较小，最大值不超过6．3％．比较另两种管型（T1，T2管）也证明三维管以较小的流阻增加为代价换取了明显的强化效果．

翅片管式冷凝器的稳态三维分布参数模型与实验验证

建立了翅片管式冷凝器的稳态三维分布参数模型,用数值计算结果分析了边界条件对冷凝器运行的影响,并用实验验证了模型的准确性。本文所建模型为翅片管式冷凝器的设计和性能优化提供了依据。

三维内肋管内流态的划分及过渡流判据的实验研究

This paper performs experiment on heat transfer and pressure drop in different 3-D internally finned tubes, investigates the transition from critical zone to transition zone. Four expressions about the Reynolds criterion for transition, the largest Fanning friction factor, the Nusselt number and Fanning friction factor have been obtained respectively.

NUMERICAL STUDIES ON LOCOMOTION PERFROMANCE OF FISH-LIKE TAIL FINS

Flapping plates of typical fishlike tail shapes are simulated to investigate their locomotion performance using the multi-block Lattice Boltzmann Method （LBM） and Immersed Boundary （IB） method. Numerical results show that fishlike forked configurations have better locomotion performance compared with unforked plates. Based on our results, the caudal fin in carangi- form mode has greater thrust, and the lunate tail fin in thtmniform mode has higher efficiency. These findings are qualitatively con- sistent with biological observations of fish swimming. Analysis of wake topology shows that the wake of the forked plate consists of a chain of alternating reverse horseshoe-like vortical structures. These structures induce a backward jet and generate a positive thrust. Moreover, this backward jet has a more favorable direction compared with that behind an unforked plate.

低温烟气条件下三维肋管积灰腐蚀特性的实验研究

本文开展了三维肋管在低温含尘含酸烟气条件下的积灰腐蚀特性实验,对不同工况下三维肋管腐蚀积灰形貌、酸沉积率及积灰量的变化规律进行了研究,揭示了三维肋管低温含尘烟气条件下的腐蚀机理,获得了积灰腐蚀规律。发现在冷却水进口温度和硫酸体积分数变化时,三维肋管迎风面主要发生析氢腐蚀,背风面主要发生吸氧腐蚀;降低冷却水进口温度,肋管表面酸沉积率先增大后减小,积灰量逐渐增大;增大酸体积分数,肋管表面酸沉积率上升,积灰量逐渐增加。

油浸式自冷变压器用三维肋管散热器换热特性研究

为研究三维肋管散热器的自然对流换热特性,分析不同温升下三维肋管散热器的强化换热性能,搭建了模拟油浸式自冷变压器工作过程的实验平台,在不同功率下分别测试了片间距为45 mm的片式散热器、排间距为45和55 mm的三维肋管散热器的进口温升,拟合得到散热器的温升-功率曲线,计算出3个散热器在相同温升下的散热量。研究表明:相比于片式散热器,三维肋管散热器在温升较小时没有显现出明显的强化换热性能,但随着温升的增加三维肋管的散热性能逐渐优于片式散热器,当温升达到50 K时45和55 mm排间距的三维肋管散热器的单位体积散热量分别增加了14%和11%。

竖直三维内肋管管内变压器油自然对流换热特性

利用田口法对具有不同肋结构参数的竖直三维内肋管管内变压器油自然对流换热特性进行了实验研究,获得了肋高、肋宽、轴向间距和周向间距等肋结构参数对管内自然对流换热性能的影响规律,提出了肋结构参数最佳组合。结果表明:变压器顶层油温从40变化至100℃,肋高和肋宽对换热性能的影响占比基本不变,周向间距的影响占比逐渐减小,轴向间距的影响占比逐渐增大;相比光管,三维内肋管的自然对流强化换热性能随顶层油温的增大而增加,变压器油自然对流Nu最大约为光管的1.75倍。拟合了竖直三维内肋管管内变压器油自然对流换热计算关联式,其与实验数据的最大偏差为±16%。