磨削弧区采用径向射流冲击强化换热的试验研究

在分析缓进给磨削烧伤机理的基础上,提出了高压射流冲击强化磨削弧区换热的创新构想,研制了带径向射流的ＣＢＮ 开槽砂轮试验装置,并通过缓进给断续磨削时采用径向射流冲击弧区的磨削试验研究其换热效果。结果表明,射流冲击强化换热技术可有效提高弧区换热效率,在解决难加工材料磨削烧伤方面具有广阔的应用前景。     

带射流收缩通道内部换热特性数值模拟

采用数值模拟的方法对简化后的燃气涡轮发动机进气道支板内部换热特性进行三维数值模拟,具体通过对带射流收缩型通道内部的流场结构和换热分布进行研究来揭示其内部换热机理,并与采用热色液晶全面表面瞬态测量技术测得的换热实验结果进行对比,从而验证计算方法的可行性.研究结果表明:射流在通道内呈现对涡结构流动,矩形出气缝的位置对通道内部流动和换热特性影响较大,换热计算结果与实验测量结果基本吻合,所用的数值模拟方法较为真实的预测了带射流收缩型通道内部的换热特性.     

非稳态冲击射流强化传热试验研究

利用一个特殊的质量流量控制装置产生波形和频率可调的周期性变化非稳态射流,进行非稳态射流冲击换热性能的试验研究。研究采用正弦、三角形和矩形三种典型的周期性波形,频率变化范围为1.25～40Hz,其传热性能用传热强化系数(定义为相同流量下非稳态和稳态射流冲击时的努塞尔数之比)来描述。研究表明,在频率较低时非稳态的射流冲击换热效果反而没有稳定射流冲击时好,但当频率超过一阈值时,其强化传热的优势逐渐明显。传热强化的效果还与射流信号的变化规律有关,有阶跃变化的矩形射流强化传热最为有效,在频率为40Hz时传热强化效果可达30%以上,但对于信号变化缓和的正弦波和三角形波而言,即使在较高的频率下,它们对传热的强化作用也是非常有限的。     

周期性冲击射流流动对传热特性的影响分析

采用经过实验验证的数值模型研究了周期性射流冲击下的流场对传热强化的影响。根据不同波形（正弦波、三角形波和矩形波）规律变化的射流对平板的冲击会产生不同的传热特性,研究得到了滞止点处的温度、传热系数和湍流强度随时间变化的规律。研究结果表明：当正弦波射流、三角形波射流的信号处于上升阶段时,湍流强度在稍有延迟后会产生一个瞬时的增强,可对强化传热起到促进作用,但在它们随后的波形变化中湍流强度仅有缓慢的升降,矩形波射流在信号发生阶跃变化时,会产生湍流强度的脉冲增强,尤其是在信号跃降时产生的瞬时脉冲增强比信号跃升时产生的脉冲增强更大,可有效强化传热;远离滞止点的流场的周期性波动仍然存在,但幅值大大减小,矩形波射流的平均速度大于其他波形射流的速度。     

射流对天然气管道冲击的数值模拟

本文分析了管线在充压操作时,气体高速射流冲出时对管壁的冲击作用。文中采用分析以及数值模拟了管道充压时气流的跨音速流动过程。分析方法结合气体动力学和自由射流模型,计算射流的冲击作用。数值模拟利用高精度格式离散欧拉方程仿真模拟了管线在冲压操作时的气体参数变化过程。研究表明：由于管线中射流前后管径相差很大,高速气流会减弱到管壁可承受的范围。     

带孔扰流片核废液浓缩器强化换热数值研究

为提高核废液浓缩器的换热性能,并研究带孔扰流片螺旋板式换热器在核废液浓缩中的应用。文章采用周期流模型进行数值模拟,分析了不同带孔扰流片结构参数对换热器流动阻力和换热性能的影响。结果表明：增加扰流片长度或减小间距会增强流道内的传热性能,带孔扰流片强化传热综合性能受扰流片长度变化的影响较小,扰流片间距对综合性能影响大;大孔结构会减小压降和换热系数,但综合换热性能更高。在片长60 mm、间距为100 mm、开孔直径13 mm的条件下,Re值为33 238时综合性能评价系数达最大值E=0.89,Re大于49 858时未开孔扰流片的综合性能更好。     

强化单相对流换热的基本机制

对强化对流换热的强化机制研究的进展做了回顾与综述,包括:①将场协同原理从抛物形流动推广到椭圆形流动.②通过数值模拟与试验的手段,对场协同原理进行了多方面的验证,特别是设计了专门的试验台,验证了当流速与流体的温度梯度方向垂直时流体流动对该方向的热量传递没有贡献.③用数值分析实例论证了场协同原理能将现有文献中三种关于强化传热的解释统一起来,从而是一种最基本的强化传热的机制.④应用场协同原理开发了两种高效强化传热结构,它们与基本结构相比,具有传热强化的倍率高于阻力增加的比的特点.最后提出了场协同原理需要进一步研究的内容.     

微尺度受限冲击冷却通道换热特性研究

为了更进一步研究真实发动机尺寸下冲击通道的流动与换热情况,针对冲击孔与气膜孔组合形式的受限冲击通道,在保证与真实发动机工况相等的克努森数,通过实验研究与数值模拟研究,进一步解释了不同结构微小冲击通道的整体换热情况,结果表明,在相同的雷诺数下,冲击射流孔径越小,冲击靶面驻点区域内换热越强,冲击平均对流换热系数越大。孔间距越小,冲击靶面平均对流换热系数越大,并且随着射流冲击距的增大,换热减弱。     

三维方管层流冲击射流流动与传热的数值研究

通过求解三维稳态不可压缩N-S方程和能量方程,对半封闭层流方管冲击射流的流动与传热特性进行了数值研究。根据计算结果分析了射流中四个偏心速度峰值形成的原因,在层流范围内考察了射流雷诺数和冲击高度对流场结构和传热性能的影响。计算结果表明,冲击射流的传热特性受流场结构的控制,冲击面附近水平断面上四个偏心速度峰值的形成,导致在相应断面上形成温度分布的四个偏心最小值,以及在冲击面上形成局部Nu数的四个偏心峰值。     

气体压力对气流冲击平板换热特性的影响研究

对气流冲击平板不同工况换热特性进行数值模拟,分析随着压力降低舱内设备换热特性的变化规律,并与经验公式进行对比研究。随着压力的降低,平板发热面换热系数降低,但降低的幅度会随着与来流方向的不同而不同。研究结果对密闭舱内设备的通风系统设计提供一定的理论依据。     

涡轮工作叶片内冷通道换热特性数值模拟

采用非结构化网格和SST紊流模型,求解三维N-S方程,对带90°肋和气膜孔的矩形通道在入口雷诺数60000,罗斯贝数0.11,气膜孔总出流比为0.22时的三维流场进行了数值模拟。分析了通道旋转和静止时各个面的换热变化规律。结果表明,通道静止时,不但布置了粗糙肋的上、下壁面换热得到了增强,光滑的侧壁换热同样获得了增强;通道旋转时流场更加复杂,旋转所产生的二次流动使各个壁面的换热进一步增强。     

不同湍流模型对叶片表面换热系数结果的影响

为了比较湍流模型对涡轮叶片外换热计算结果的影响,采用的三种湍流模型对NASA-C3X导向叶片进行了表面换热计算并与实验数据进行了对比,结果表明:边界层流态的转变对换热的影响很显著,缺乏对湍动能发展的控制是影响换热计算结果主要原因;标准的k-ε模型换热计算效果较差,Reynolds Stress模型体现了边界层流动状态的转变对换热影响;研究在不同计算域采用不同湍流模型的计算技术,是一种较好的可行的方案.     

Turbulent flow and heat transfer characteristics of a two-dimensional oblique plate impinging jet

Turbulent flow and heat transfer characteristics of a two-dimensional oblique plate impinging jet (OPIJ) were experimentally investigated. The local heat transfer coefficients were measured using thermochromic liquid crystals. The jet mean velocity and turbulent intensity profiles were also measured along the plate. The jet Reynolds number (Re, based on the nozzle width) ranged from 10, 000 to 35,000, the nozzle-to-plate distance (H/B) from 2 to 16, and the oblique angle (α) from 60 to 90 degree. It has been found that the stagnation point shifted toward the minor flow region as the oblique angle decreased and the position of the stagnation point nearly coincided with that of the maximum turbulent intensity. It has also been observed that the local Nusselt numbers in the minor flow region were larger than those in the major flow region for the same distance along the plate mainly due to the higher levels in turbulent intensity caused by more active mixing of the jet flow.     

翅片热板散热器的传热数值模拟研究

采用有限元法,应用ANSYS软件的热分析功能对翅片热板散热器的传热性能进行了数值模拟,并计算出该散热器表面的瞬态温度变化曲线,与实验测试结果吻合得较好.最后的研究结果表明:所研制的新型功率电子元器件翅片热板散热器散热性能良好,具有良好的启动性能和等温性能.     

The effect of ambient air condition on heat transfer of hot steel plate cooled by an impinging water jet

It has been observed that the cooling capacity of an impinging water jet is affected by the seasonal conditions in large-scale steel manufacturing processes. To confirm this phenomenon, cooling experiments utilizing a hot steel plate cooled by a laminar jet were conducted for two initial ambient air temperatures (10°C and 40°C) in a closed chamber, performing an inverse heat conduction method for quantitative comparison. This study reveals that the cooling capacity at an air temperature of 10°C is lower than the heat extracted at 40°C. The amount of total extracted heat at 10°C is 15% less than at 40°C. These results indicate the quantity of water vapor, absorbed until saturation, affects the mechanism of boiling heat transfer.     

Numerical simulation of fluid flow and heat transfer in a plasma spray gun

A computational fluid dynamics (CFD) simulation for analyzing fluid flow patterns in a plasma spray gun is presented in this study. It is coupled with a heat transfer simulation of the plasma spray gun. Based on CFD and heat transfer theory, the numerical model of the nozzle in the plasma spray gun is developed, and the coupled simulation of the flow fluid and heat transfer is carried out with the semi-implicit method for pressure-linked equations (SIMPLE) method. Local turbulence, which will lead to appearance of a static-water region, is found at the front corner of the cooling channel in the nozzle. The locations insufficiently cooled are found in the wall near the heat source and in the gasket in the rear of the nozzle. Then, cooling processes with different parameters of cooling water are analyzed. The optimal velocity and direction of cooling water, which efficiently cool the nozzle and improve the service life of the plasma jet, are obtained .     

Heat/mass transfer measurement on concave surface in rotating jet impingement

The objective of this paper is to investigate the heat/mass transfer characteristics on a concave surface for rotating impinging jets. The jet with Reynolds number of 5,000 is applied to the concave surface and the flat surface, respectively. The rotating experiments have been carried out at the rotating speed of 560RPM which is corresponding to Ro number of 0.075. The two jet orientation (front and trailing orientation) are considered. Detailed heat/mass transfer coefficients on the target plate were measured using a naphthalene sublimation method. The result indicates that the rotation leads to change in local heat/mass transfer distributions and the slight increase in the Sh level. The front orientation induces asymmetric Sh distributions, whereas the trailing orientation shows the shifted heat/mass transfer feature due to rotation-induced flow behavior. The crossflow effect on heat/mass transfer is also observed as the streamwise direction increases. Compared to flat surface, the heat/mass transfer on the concave surface is enhanced with increasing the spanwise direction due to the curvature effect, providing the higher averaged Sh value. It is proved that the difference of surface geometry affects somewhat the local and averaged heat/mass transfer regardless of rotation condition. This paper was presented at the 9^th Asian International Conference on Fluid Machinery (AICFM9), Jeju, Korea, October 16–19, 2007.     

Ion slip effect on the flow due to a rotating disk with heat transfer

The steady hydromagnetic flow due to a rotating disk is studied with heat transfer considering the ion slip. The governing equations are solved numerically using finite differences. The results show that the inclusion of the ion slip has important effects on the velocity distribution as well as the heat transfer.     

螺旋角度不同的螺旋折流板换热器壳程传热性能研究

对螺旋角度分别为25°、30°和40°的螺旋折流板换热器壳程传热性能进行了试验与研究,同时对螺旋角度为25° 30°和40°的螺旋折流板换热器与传统的弓形折流板换热器壳程传热性能进行了比较.实验结果表明,螺旋角为40°的螺旋折流板换热器的传热效率最高,螺旋折流板换热器的壳程传热效率都比传统的弓形折流板换热器壳程传热效率高.