冲击射流中圆柱尾流的流动特性与分析

本研究通过在冲击射流中设置圆柱棒作可视化观察,分析强化传热机构的流动特性;利用统计分析,探导圆柱棒直径及圆柱间距等对强化传热的影响。     

圆形液体浸没射流冲击驻点传热的数值模拟

对圆形液体浸没层流射流的流场结构和冲击驻点的单相传热进行了数值模拟．考虑的因素为喷嘴直径、喷嘴至冲击板距离、射流速度和加热面尺寸等．计算结果表明：冲击板上涡的位置随Ｒｅ的增加而远离对称轴．对于充分发展的管形喷嘴而言,驻点换热随射流出口Ｒｅ的增加和喷嘴直径的减小而增强;在５＜Ｚ／ｄ＜９内出现峰值,与加热面尺寸无关．     

淹没前混合磨料射流的数值分析

利用CFD方法对淹没条件下前混合磨料射流流场进行了数值模拟,研究了喷嘴内外液固两相流的速度规律.仿真结果表明:磨料水射流在淹没条件下的耗散较大,磨料粒子速度最大值出现在一定喷距处;对于圆柱、圆锥、锥直型3种不同形式喷嘴,以锥直型喷嘴效果更优;仿真结果与实验结果基本一致.     

射流搅拌发酵罐中循环液量气含率和气泡直径的研究

本文测定了射流搅拌发酵罐中自由射流气泡区的气含率、气泡直径和液体循环量。研究了混合器、喷嘴尺寸、气速、清液层高度、液体粘度、表面张力对自由射流气泡区的液体循环量、气含率、气泡直径的影响。由理论分析及实验数据获得了液体循环量、气含率、气泡直径的的关联式。模型关联式与实验值吻合良好。     

基于FLUENT的人工淹没射流喷嘴流场仿真

根据Fluent流体仿真软件和人工淹没射流喷嘴内流场的特点,基于流体力学基本理论,对人工淹没射流喷嘴进行了仿真研究。通过数值模拟计算,得到了人工淹没射流喷嘴的压力分布云图和速度分布矢量图和静压力分布图等。模拟结果表明,在人工淹没射流喷嘴的圆柱段存在速度最大值,射流在圆柱段出口处与周围的水产生了强烈的剪切作用,出现了流速不均匀和脉动现象,再加上圆柱段出口端明显的负压区,这些都为空化作用的产生提供了有利条件。     

脉冲射流喷嘴机理及水力特性研究

在对新型射流机理探讨的基础上，研究了脉冲射流喷嘴的机理和水力能量关系．得出了计算式．结果表明．脉冲喷嘴的瞬时高频射流所获能量是低频射流的２．５５８倍，是连续射流的１．４３８倍．还得出了脉冲射流喷嘴的水马力和冲击力的计算式．为脉冲射流喷嘴的应用及进一步研究，提供了理论依据．     

高压气蚀水射流切割装置的试验研究

提出了一种能较好地诱发气蚀的高压水射流切割装置－射流砂式切割装置,在非淹没条件下对该装置与普通单喷嘴装置进行了对比试验。试验结果表明,在相同的工作条件下,射流泵式切割装置比普通单喷嘴切割装置能耗低,切割深度大,根据试验结果,提出了射流泵式切割装置的最佳工作参数。     

高压气蚀水射流切割装置的试验研究

提出了一种能较好地诱发气蚀的高压水射流切割装置———射流泵式切割装置．在非淹没条件下对该装置与普通单喷嘴装置进行了对比试验．试验结果表明,在相同的工作条件下,射流泵式切割装置比普通单喷嘴切割装置能耗低、切割深度大．根据试验结果,提出了射流泵式切割装置的最佳工作参数     

结构参数对自激式脉冲射流装置性能的影响

运用自行研制的脉冲射流试验装置,就自激式脉冲射流装置的上下喷嘴直径、腔长和腔径等结构参数对其性能的影响进行了试验,分析了上喷嘴直径一定时,其他结构参数对射流打击力的影响.研究表明,在一定工作压力下,不同下喷嘴直径下的射流打击力随腔长的变化和不同腔径下的射流打击力随下喷嘴直径的变化不同;在不同工作压力下,某一下喷嘴直径下...     

淹没条件下星形喷嘴射流流动特点的模拟研究

为了优化钻头水功率配置,提高井眼净化效果,对新近引入石油工程中的星形喷嘴射流进行了模拟研究,建立了喷嘴射流流场的流动控制方程,采用有限体积法对其进行离散,结合Realizable k-ε模型对方程组进行求解,并将计算结果与圆形喷嘴射流的结果进行了对比.对比结果发现,淹没条件下喷嘴出口截面形状对射流的影响主要体现在射流的起始段,起始段内星形喷嘴射流流场较圆形喷嘴射流的要复杂.当喷距大于4倍喷嘴当量直径时,星形喷嘴最大、最小截面上轴向速度和湍动能的衰减趋势同圆形喷嘴的衰减趋势一致,两个截面上射流速度剖面满足自相似性.     

气雾射流动态传热实验研究

设计搭建了气雾射流动态传热实验装置,建立了二维非稳态导热反问题模型,研究了表面温度和表面热流密度的时间分布.结果表明在冷却过程中缸体穿越喷射区与淌水区历经了几个不同的换热阶段,温度曲线出现了明显的周期性的特点,成功的模拟了连铸二冷气雾冷却周期性换热的特征.     

Experimental investigations on separation control and flow structure around a circular cylinder with synthetic jet

Circular cylinder separation control and flow structure influenced by the synthetic jet have been experimentally investigated in a water channel. The synthetic jet issues from a slot and ejects toward upstream from the front stagnation point of the cylinder. It has been found that, similar to the traditional synthetic jet which is positioned near the separation point or inside the separation region, the present synthetic jet arrangement constitutes an efficient way to control flow separation of the circular cylinder, but with a different control mechanism. The present synthetic jet leads to an upstream displacement of the front stagnation point and the formation of a vortex pair near both sides of the exit orifice. When Re _u based on the synthetic jet average exit orifice velocity is about lower than 43, a closed envelope forms in front of the windward side of the cylinder during the blowing cycle of synthetic jet, which acts as an apparent modification for the cylinder configuration. When Re _u is high enough, an open envelope forms upstream of the cylinder, and the flow around the cylinder becomes much energetic. Thus, regardless of Re _u, the present synthetic jet can improve separation for flow around a circular cylinder. With regard to the leeward side, as Re _u increases, the flow separation region behind the cylinder gradually disappears. The flow over cylinder may be fully attached when the open envelope forms upstream of the cylinder and Re _u is greater than 344. Then, the flow past the cylinder will converge near the back stagnation point of the cylinder, where a new vortex pair shedding periodically is generated due to the high shear layer. Recommended by Prof. DONG ZengNan, Member of Editorial Committee of Science in China, Series E: Technological Sciences Supported by the National Natural Science Foundation of China (Grant No. 10425207)     

二元两相射流冲击传热研究

研究了用氮气和水同时喷射时的传热规律,在热负荷小于10~5(W/m~2)时,出现了所谓“负温差传热”的特殊现象,在高负荷下,有很高的传热系数,存q=2.8×10~8(W/m~2)时,壁温只有58℃,本实验研究了喷射间距和氮气、水流速对换热的影响,发现在一定条件下都有一个最佳值,同时还测定了横向局部换热系数。     

单束圆形射流冲击在小尺寸加热面上的局部换热特性

实验研究了液体射流垂直冲击在加热竖直小壁面上的局部换热特性,在Re_d=4.04×10~3～1.37×10~4范围内,驻点换热可以用方程 Nu_d=1.29P_r~m·Re_d~(0.5)表示,对于湍流,势流核心长度L/d与速度无关,L/d=5,建议势流核心外驻点Nu与Z/d的关系用 Nu_d/Nu_(max)=[(L/d)/(Z/d)]~(0.5)表示,势流核心区内换热系数的径向分布用以下方程表示: 驻点区:Nu_d/Nu_(max)=(r/d)~(-0.5)tanh~(0.5)(0.88r/d) 壁面射流区:Nu_d/Nu_(max)=0.348Re_(d,u_0)~(n-0.5)·(r/d)~(-1.25)实验比较了自由射流与浸没射流的换热效果,发现驻点及径向分布结果相同,喷距的影响有差别。     

Experimental investigation on heat transfer characteristics of microcapsule phase change material suspension in array jet impingement

A closed-loop experimental system is established to investigate the heat transfer characteristics of microcapsule phase change material (MEPCM) suspension in an array jet impingement. Eicosane with a melting peak at 40.8°C is used as the capsule core of the MEPCM particle. Five kinds of array-hole nozzles with the same hole cross-sectional area are employed to analyze the influence of critical parameters, including the nozzle hole number, hole spacing, impinging distance, and jet temperature. It shows that a 5% suspension may improve the heat transfer coefficient of the array jet by up to 23.5% compared with water. The heat transfer of an array jet is obviously stronger than that of a single jet, but too much hole number is not conducive because of the entrainment interference between adjacent jets. A larger hole spacing or smaller impinging distance may weaken the cross-flow accumulation on the impinged surface, thus enhancing the heat transfer capability. The heat transfer coefficient of the array jet presents a secondary peak value at the end of the jet-core region. The latent heat absorption of the capsule core results in superior heat transfer of the suspension compared to that of water only in a specific range of jet temperatures, the optimum of which is approximately 10°C lower relative to the peak melting temperature. In addition, the melt completion time of a single MEPCM particle and the critical flow rate of the suspension are predicted theoretically.

     

突片激励射流冲击冷却的实验研究

对突片激励射流冲击冷却特性进行实验研究,分析突片形成的流向涡对冲击换热特性的影响,总结了双排射流孔的传热规律. 实验结果表明,在双排突片射流冲击冷却中,突片具有改善冲击换热特性的作用,射流孔的排列方式以及两排孔之间流向孔间距的变化对冲击靶面的温度分布具有较大的影响,叉排孔的有效冷却范围更大,冷却效果更好.     

Fluid mechanics of ventilation system generated by buoyancy and momentum sources and experiments research

This paper presents fluid mechanics of ventilation system formed by the momentum source and the buoyancy source,which investigates inter-action between the plume and the non-isothermal air jet since buoyancy source is produced by the plume and momentum source is generated by the air jet,respectively. The interaction is discussed by a mathematical model,an idealized situation of the plume rising from a point heat source of buoyancy alone-in particular the initial momentum flux at the source is zero. Furthermore,the paper discusses the effects of the parameters such as strength of source,air-flow volume and air-flow velocity used in the mathematical-physical model. Considering the effect of the plume generated by the indoor heat source,one expression of trajectory of the non-isothermal air jet produced by jet diffuser is deduced. And field-experiment has also been carried out to illustrate the effect on flowing-action of the air jet and validate the theoretical work. It can be concluded that the heat sources do have effect on the flowing-action of the air jet,and the effect mainly depends on the interaction produced by the plume and the air jet. The results show that the thermal buoyant effect of plumes on the air jet should be taken into account if the indoor heat sources are large enough. Numerical simulation is conducted and coincides with the experimental results as well.     

Fundamental studies on enhancing heat transfer in contact zone during high efficiency grinding

On the basis of research on the thermal effect in grinding contact zone during high efficiency grinding, an idea of enhancing heat transfer in contact zone using high pressure water jet impinging is advanced. Fundamental heat transfer experiments on enhancing heat transfer with high pressure water jet impinging were completed. The maximum speed of jet impinging reaches 110m/s. The experimental results of transient and steady-state experiment prove that the critical heat flux and the heat-transfer coefficient of water jet impinging are 70 and 30 times those of the pool boiling, respectively. Furthermore, a new grinding fluid supply system was employed to enhance heat transfer in grinding zone by high-pressure water jet impingement during creep feed grinding. The experimental results show that high-pressure water jet impinging has remarkable cooling effect. The temperature of the workpiece surface can be steadily kept below 100℃, while the workpiece is badly burnt with conventional coolant supply. The stu     

Numerical simulation of circular jet impinging on hot steel plate

Flow structure and heat transfer characteristics of an axisymmetric circular jet impinging on a hot 1Crl8Ni9Ti medium plate have been simulated numerically using computational fluid dynamic (CFD) code. The relation between flow field of jet impingement and its heat transfer capability is analyzed, and the phenomenon that heat transfer at stagnation point is smaller than that of points directly around is discussed. The simulation result provides boundary conditions for thermal analysis of medium plate quenching.