High-Resolution Heat Transfer Coefficients Measurement for Jet Impingement Using Thermochromic Liquid Crystals

A high-resolution testing technique named liquid crystal thermography is used for the experimental study on jet array impingement to map out the distribution of heat transfer coefficients on the cooling surface. Effects of the impingement distance, the impinging hole arrangement and the initial crossflow on heat transfer characteristics are investigated. The thermal images show truly the features of local heat transfer for each jet impingement cooling. The applications of thermochromic liquid crystal are successful in the qualitative and quantitative measurement for heat transfer coefficients distribution.

Experiment on Effect of Tip Clearance Leakage Flow on Heat Transfer of Turbine Outer Ring

The cascade model was tested using transient liquid crystal temperature measurement technology.The effects of main flow Reynolds number,blowing ratio and tip clearance height on the convective heat transfer coefficient of the turbine outer ring were studied.Two feature lines were marked on the turbine outer ring corresponding to the position of the blade.The conclusions are as follows:The tip clearance leakage flow has a great influence on the convective heat transfer coefficient of the turbine outer ring.When the clearance height and the blowing ratio are kept constant,gradually increasing the main flow Reynolds number will result in an increase in the convective heat transfer coefficient of the turbine outer ring.When the clearance height and the main flow Reynolds number are kept constant and the blowing ratio is gradually increased,the convective heat transfer coefficient of the turbine outer ring is almost constant.The heat transfer coefficient of the turbine outer ring surface is little affected by the blowing ratio;The clearance height has great influence on the heat transfer characteristics of the turbine outer ring.Under the typical working condition in this paper,when the tip clearance height ratio is 1.6%,the convective heat transfer coefficient of the outer surface of the turbine is the highest.

Modelling of heat transfer for progressive freeze concentration process by spiral finned crystallizer

This study presents a novel design for a spiral finned crystallizer which is the primary element of progressive freeze concentration(PFC) system, which simplifies the setup of the conventional system. After the crystallizer has been designed, the research experiments have been conducted and evaluated through a thorough analysis of its performance by developing a mathematical model that can be used to predict the productivity of ice crystal at a range of coolant temperature. The model is developed based on the basic heat transfer equation, and by considering the solution's and the coolant's convective heat transfer coefficient(h) under the forced flow condition.The model's accuracy is verified by making comparison between the ice crystal mass' experimental value and the values predicted by the model. Consequently, the study found that the model helps in enhancing the PFC system.

Measurements of heat transfer and pressure in a trailing edge cavity of a turbine blade

An experimental investigation is conducted to obtain the heat transfer and pressure drop data for an integral trailing edge cavity test section that simulates a novel turbine blade＇s internal cooling passage with bleed holes. Local heat transfer is measured on both the suction and pressure sides by a transient liquid crystal technique, while pressures at six positions are recorded by pressure calibrators. Moreover, flow characteristic and its effect on heat transfer are analyzed for conditions with or without bleed flow. The experimental results show that, in the cases with bleed flow, local heat transfer on the pressure side exceeds that on the suction side in the first and second channels. In the cases without bleed flow, in the first and third channels, local heat transfer on the suction side weakens whilst it increases significantly on the pressure side. For the second channel, non-bleed condition leads to a more balanced heat transfer distribution between the upstream and downstream channel. Besides, after the bleed holes are blocked, heat transfer in the first bend region on the suction side declines sharply, while the opposite phenomenon occurs for the second bend region on the pressure side. In both bleed and non-bleed cases, the total pressure of six measurement positions decreases continuously along the channel at the same Reynolds number and it promotes for higher Reynolds number. Among all the measurement points, under the same flow rate condition, the highest speed occurs at Position 5, which also shows the maximum difference between the total and static pressures. When the bleed holes are blocked, the total pressure at each measurement position appears to increase.

液晶瞬态技术测量带侧向流扰流柱通道端壁换热

采用热色液晶瞬态测量技术测量带侧向流扰流柱通道端壁全表面换热系数的分布，研究了侧流比及雷诺数对换热的影响，其中，侧流比为0．25～1．0，雷诺数为3×10^4～9×10^4。结果表明：（1）侧流比对扰流柱通道的流动形态及端壁换热有重要影响；（2）存在一个临界侧流比，在临界侧流比以下，流动形态沿主流方向呈错排流状态；在临界侧流比以上，流动形态沿侧流方向呈错排流状态；在临界侧流比附近，流动为顺排流动状态，方向在主流和侧流方向之间；（3）侧流比较小或较大时，扰流柱通道端壁换热较强；在临界侧流比附近，换热相对较弱。

轴向磁场对硅单晶Czochralski生长过程的影响

利用有限元方法对炉内的传递过程进行了全局数值模拟,假定熔体和气相中的流动都为准稳态轴对称层流,熔体为不可压缩流体,Cz炉外壁温度维持恒定,模拟磁场强度范围为(0-0.3)T,研究了用Czochralski(Cz)法生长单晶硅轴向磁场对熔体流动和氧传输过程的影响.结果表明:轴向磁场可有效地抑制熔体内的流动,但增大加热器功率和结晶界面处晶体内的轴向温度梯度;对于常规Cz炉,轴向磁场可增大结晶界面平均氧浓度,而对于具有气体导板的Cz炉,则会减小结晶界面平均氧浓度.

流量比对气膜冷却叶片表面换热系数的影响

为深入了解某型涡轮叶栅进口导叶叶片的换热规律,采用瞬态液晶技术测量了无气膜孔叶片和带气膜孔叶片在不同流量比下的表面换热系数,通过对比分析,研究了气膜出流和流量比变化对叶片表面换热的影响.实验中叶栅通道来流雷诺数为108 000,叶片气膜出流与叶栅通道来流的质量流量比为0、3.46%、4.61%、5.77%、6.93%、8.08%、9.23%.实验测量获得了无气膜叶片中截面的压力分布曲线,以及各流量比下叶片表面的换热系数分布云图及其平均值线图.研究结果表明:叶片吸力面存在气流流动分离;气膜出流使得分离点位置提前,并且缩短了分离再附着的过渡区域;气膜出流使叶片前缘、压力面和吸力面气膜孔区域的换热系数大幅升高,但对吸力面分离点后区域的换热影响不大;在实验工况范围内,气膜出流流量比越大,换热系数越高.

高超音速后掠激波与边界层干扰流场特性

应用表面油流和液晶温度显示，表面热流率的压力测量四种测试技术，在Ｍａ∞＝７．８、单位长度雷诺数Ｒｅ∞＝３．５×１０＾７／ｍ条件下，研究了３０°迎角尖前缘翼面诱导激波和湍流边界层干扰流场特性，结果表明，表面流动是准锥型；在强相互作用下，流动发生了二次分离和再附，导致表面油流线的流向角、温度、热流率和压力分布均出现明显的凹坑。

循环水流速对换热器壁面CaCO_3水垢晶体的影响

模拟火电厂循环冷却水系统的运行工况,采用强制对流换热方式,在不同的水流速度下,分别对换热管壁面析出的CaCO_3附着垢及游离于水中的脱除垢进行多晶X射线衍射分析.结果表明,水垢中方解石和文石的晶粒尺寸均随水流速度的增加而增大,其中附着垢中方解石和文石的晶粒尺寸变化较大,脱除垢中方解石和文石的晶粒尺寸变化较小;水流速度的增大会影响方解石和文石的晶面间距,附着垢中方解石和文石的最强衍射峰的晶面间距d_(104)和d_(111)均比脱除垢中的有所减小.从循环冷却水流速、剪切力变化和成垢离子有序稳定密堆积方面,对实验现象进行了解释.

降膜结晶过程的数值模拟

本文采用数值方法对在工业上有着广泛应用前景的降膜结晶分离过程进行了模拟，提出了一套描述降膜结晶过程的降膜流动、传热、传质及结晶相变相互耦合的以控制容积为基础的有限差分的湍流数值计算模型和算法。本模型的计算结果与以前简化模型的计算结果相比，更符合实验值．

液晶热像测量精度分析及其在湍流传热研究中的应用

通过开展液晶热像校准实验研究,分析了各测量参数对液晶热像测量精度的影响,得到了提高测量精度的有效方法,并对液晶热像技术应用于湍流传热研究进行了分析和讨论.实验结果表明,采用液晶图像滤波技术、控制液晶涂层厚度(>20μm)、减小光源照射角度以及提高液晶涂层的喷涂质量都有利于提高液晶热像的测量精度.最后,介绍了稳态和瞬态液晶热像技术在航空发动机透平叶片湍流对流冷却中的应用.

蒸发结晶中三相流沸腾传热的研究

提出了蒸发结晶体系为汽-液-固三相流沸腾传热体系,建立了沸腾传热模型,并用工业生产数据进行验证,结果表明计算值和实验实测值吻合较好。用此理论指导。可提高产品质量,为三相流应用于烧碱蒸发结晶工业生产提供了理论和模型。

海水-冰晶两相流非等温流动及传热

船舶在冰区航行时,存在冰晶颗粒混合海水流入船舶冷却系统现象。基于颗粒动力学理论,建立适用于海水-冰晶两相流的欧拉-欧拉双流体模型,耦合相间传热传质模型对海水-冰晶两相流在水平直管内流动及传热特性数值模拟。研究表明,冰晶颗粒流动过程中,在管道上部位置R为8 mm^10 mm处冰晶体积分数达到最大值,且随着速度增加而增大;当入口含冰率(IPF)为4%时,冰晶速度的最大值出现在管道中心轴线上方。当入口速度为1.0m/s^3.0m/s,含冰率4%~30%时,局部传热系数随入口速度及含冰率增大而增加。

管内冰浆在振动工况下的流动及传热特性

针对船舶在北极航道航行时管道内流体流动受到船舶机械振动的影响,本文采用计算流体力学(CFD)中的欧拉-欧拉模型、壁面函数模型,并通过UFD加载相间传质模型对水平管道中的冰晶进行数值模拟。研究振幅、频率、入口含冰率和速度对冰晶流动和传热特性的影响。结果显示:在振动工况下在流速改变时其压降增长趋势为二次函数增长趋势。振动频率及振幅增强管内扰动促进温度及相间传质率的升高。振动和振动频率的提高使最大体积的冰晶颗粒浓度减少,并且在40 Hz与50 Hz时出现冰晶在两侧聚集趋势。

降膜蒸发器旋液流态化在线自动清洗能力研究

针对降膜蒸发器管内结垢问题,提出旋液流态化技术实现自动清洗。由结晶速率等效原理,将饱和溶液在加热面结晶问题等效为在冷却面结晶问题。以0.4m/s平均流速饱和硫酸钠溶液为例进行试验研究。结果表明:近壁面溶液在忽略管壁及污垢热阻的绝对过饱和度Δcsur为4.20%时,与空管连续运行0.5h总传热系数下降80%相比,管内加钢丝螺旋的总传热系数保持不变。Δcsur=5.60%时,钢丝螺旋达到最大清洗速率,超过此值总传热系数下降。Δcsur=6.46%时,加入体积分数1%的粒子,总传热系数未降反升,同未结垢时相比提高6%。降膜蒸发器旋液流态化既能在线自动清洗又可起到对流强化传热效果。其结构简单,便于工业推广。

航空发动机涡轮叶片尾缘楔形通道交错肋冷却实验

为研究涡轮叶片尾缘部分楔形通道交错肋流动传热性能,对其进行实验研究.实验应用瞬态液晶测试技术,对比研究了交错肋上、下主表面的局部传热特性,同时用压力扫描阀测得不同雷诺数下的通道压力损失.研究结果表明:尾缘段转折流动配置下,楔形通道交错肋上、下主表面传热差异显著,下主表面平均努塞尔数比上主表面平均高30%以上,尾缘楔形通道内交错肋结构主表面平均换热系数高出针肋结构约46%;交错肋上、下通道之间的交界面处存在强烈的质量交换作用,上、下主表面间断性的高换热区与上、下通道交界面呈现对应关系;随入口雷诺数的增加,通道压降快速增大.楔形通道交错肋压降是针肋的5~7倍,但其换热面积高出针肋107.4%,仍比针肋冷却增加约66%的综合换热性能.

Numerical Simulation of an Airfoil Electrothermal-Deicing-System in the Framework of a Coupled Moving-Boundary Method

A numerical method for the analysis of the electrothermal deicing system for an airfoil is developed taking into account mass and heat exchange at the moving boundary that separates the water film created due to droplet impingement and the ice accretion region.The method relies on a Eulerian approach(used to capture droplet dynamics)and an unsteady heat transfer model(specifically conceived for a multilayer electrothermal problem on the basis of the enthalpy theory and a phase-change correction approach).Through application of the continuous boundary condition for temperature and heat flux at the coupled movingboundary,several simulations of ice accretion,melting and shedding,runback water flow and refreezing phenomena during the electrothermal deicing process are conducted.Finally,the results are verified via comparison with experimental data.A rich set of data concerning the dynamic evolution of the distribution of surface temperature,water film height and ice shape is presented and critically discussed.

振荡流结晶过程传热效应的模拟分析

通过振荡流调控传热特性以获得结晶器中分布特征良好的局部过饱和度,是有效优化冷却结晶过程的新设想。对具有光滑周期收缩孔(SPC)的振荡流结晶器,进行了三维非稳态数值模拟。考察了振荡流产生的时变流场结构,应用涡量表征涡旋强度,并得到剪切应变率分布,表明涡旋促进了流场混合,增强了剪切成核的调控能力。分析了振荡参数对结晶器传热特性的影响,结果表明振荡流导致了努塞尔数Nu随时间呈周期性变化,并且其周期特征与强度受振荡雷诺数Reo和斯特劳哈尔数St控制。因此,可以通过调节振荡参数达到对过饱和度的调控,这为结晶过程分析提供了依据。

LHPG生长YAG晶体的掺杂Nd^(3+)和Cr^(3+)浓度研究

以人工方式生长高质量的晶体宝石,是现今材料发展的趋势之一。由于宝石的质量还须考虑到宝石内掺杂的离子浓度高低与分布,因此探讨掺杂物浓度也是宝石晶体研究的重要课题。以低浓度钕与铬离子掺杂于钇铝石榴石(YAG)为实验材料,配合二维数值模拟分析,试图探讨激光加热基座法对晶体生长所造成的浓度变化与相关物理机制,期望能优化以LHPG或类似浮动熔区方法生长晶体的工艺流程,为提升晶体质量作出贡献。