非均匀截面自激振荡流热管内热传输特性实验研究

针对两种不同截面结构的回路型自激振荡流热管,其中,一种内径为3 mm的均匀截面;另一种是在此均匀截面的基础上,将其加热段和绝热段断面加工成垂直交错布置的椭圆形非均匀截面。运用实验研究的方法,在热管壁面不同部位分别布置了温度测点,在不同功率的激光加热条件下,通过对热管壁温监测数据的采集和分析,研究了这种非均匀截面回路型自激振荡流热管内部的热传输性能,并与均匀截面自激振荡流热管进行了对比分析。结果表明:非均匀截面自激振荡流热管内的脉动机制以及热传输特性与均匀截面有很大不同,在中、高负荷条件下,非均匀截面结构热管可以明显起到强化传热效果,与均匀截面结构热管相比,热传输功率提高了13.6%。     

等截面直肋温度分布与传热分析

在固体表面与流体的对流换热的设备中,例如各种换热设备中,常在换热表面上增添一些肋,以增大换热表面,达到减少换热热阻的目的。对各种肋片的温度场和传热性能的分析常归结为扩展表面问题,其中等截面直肋是最简单的例子。如肋片的宽度足够大,其内部温度分布是二维的。但肋片足够薄,导热系数足够大,肋片厚度方向的温差也可忽略不记,这样即简化为一维问题。那什么时候能简化,其一维与二维模型有什么差别,又与哪些因素有关呢?将分别按一维与二维模型计算肋片传热量与温度分布,并得出其进行一维简化所造成的误差。     

耦合模型预测槽式太阳能系统性能

以槽式太阳能系统管式集热器的二维热学和三维光学耦合模型为研究对象,提出快速的数值算法。模型考虑温度对材料热性能的影响,计算两种集热器在太阳辐照下的性能,并与实验数据及其他二维传热模型的计算结果进行比较,结果表明,工作温度达到250℃以上时,模型预测的热损平均相对误差对于真空和空气两种工况分别为4.66%和2.61%。     

竖直U型埋管地下换热器的传热模型

以钻孔壁为界,将所研究的传热区域划分为土壤部分和钻孔内两部分.对于钻孔外土壤部分的传热过程,采用线热源理论建立非稳态模型进行分析讨论;在钻孔内,对一维模型和二维模型进行了对比,从而得出增强地下换热器换热的措施.     

具有波纹板陶瓷型砖两段转子的再生式换热器的温度场计算与转子动态传热方程

本文介绍了一种再生式换热器的传热传质数学模型和温度场的计算方法。这种换热器具有两段以不同材料做传热元件的转子。模型考虑了以下几点因素:第一段转子的传热元件内部存在一维导热;第二段转子的传热元件内部存在二维导热;在第二段转子的受热面上可能发生结露与露蒸发。     

航空发动机模糊滑模控制方法的比较研究

研究了航空发动机的模糊滑模控制方法,使航空发动机在较广的运行条件下满足控制需求。采用一维间接模糊滑模控制、二维直接模糊滑模控制这两种方法设计模糊滑模控制器,并通过仿真对比,分析了两种设计方法在航空发动机线性模型和用LPV建模法建立的非线性模型上的控制效果。仿真结果表明,二维模糊滑模控制方法具有响应快,对外界干扰不敏感,系统鲁棒性强且非线性跟踪效果好的优点,其控制效果优于一维模糊滑模控制方法。     

矩形和圆形槽道脉动热管传热性能的实验研究

为了探讨不同截面形状的脉动热管在复杂工况下的传热性能,本文设计了矩形和圆形两种截面形状的脉动热管,采用对比实验的方法探究不同截面形状的脉动热管在水平、竖直工况下,不同功率对其传热性能的影响。实验结果表明:水平工况下矩形脉动热管表面温度和最大温差均低于圆形管;随着功率负荷增加,两种脉动热管表面温度及最大温差均增大,在高功率区,圆形管最大温差明显高于矩形管;竖直工况相比于水平工况,脉动热管表面温度及最大温差均降低。因此,矩形脉动热管相比于圆形脉动热管更适合在电子芯片散热领域中应用。     

回转式空气预热器的传热特性方程

本文介绍了一种再生式换热器的传热传质数学模型和温度场的计算方法。这种换热器具有两段以不同材料做传热元件的转子。模型考虑了以下几点因素:第一段转子的传热元件内部存在一维导热;第二段转子的传热元件内部存在二维导热;在第二段转子的受热面上可能发生结露与蒸发。本文还以火电站用的波纹板-陶瓷砖两段转子的空气予热器为对象,在计算温度场的基础上提出了这种换热器的转子动态传热方程。     

大容量超超临界锅炉水冷壁壁温特性研究

采用区域法建立二维小区计算模型,分别得到不同计算条件下烟气侧、工质侧以及二者耦合传热下模型截面上壁温分布规律,并与实测数据进行比较。结果表明:3种计算条件下耦合迭代模型计算的平均误差分别为2.66%、2.11%和2.38%,均远小于炉内辐射传热模型和管内换热模型的计算平均误差,表明耦合传热计算模型具有较好的准确性和适用性。     

溃堤洪水数值模拟在变电站设计洪水中的应用

基于Abbott六点中心隐式差分格式的河道一维非恒定水流模型和平底宽顶堰堰流公式计算堤防渍口流量过程,构建了根据非结构网格的有限体积法离散的二维水动力模型,并模拟了堤国内洪水过程,计算了变电站站址处溃堤设计水位,采用水量平衡法验证了二维水动力模型的计算结果.实例结果表明,水动力模型可为堤国内变电站的设计提供可靠的技术支持,供借鉴.     

Factors Influencing the Temperature Distribution of 200 W Light Emitting Diode Module Used in the Spotlight

The junction temperature of LED (light emitting diode) has a significant impact on its performance and lifetime. In this paper, a simplified model based on the finite element analysis is developed to simulate the temperature distribution of the 200 W LED module using software ANSYS. The model contains LED package, the heat pipe radiator, as well as TIM (thermal interface material) between the LED package and radiator. The temperature distribution of the simulation agrees with that of the experimental measurement. Thickness of TIM affects the heat dissipation significantly, the chips temperature and the maximum temperature difference of chips increases sharply with TIM thickness increasing. Substituting aluminum fins with copper fins cannot improve the heat dissipation performance of heat pipe radiator, and the air velocity of heat pipe radiator plays a key role in the heat dissipation. Thermal conductivity of package submount directly affects the chip temperature and the uniformity of temperature distribution of package submount.     

热泵-废热回收在空间站热管理中的应用

从系统角度出发，对热泵排热系统与尿液处理系统、空气再生系统间的相关性进行了分析，提出了一种较为合理的热管理集成模式。在此基础上，对该热泵－－废热回收集成模式用于空间站CO2去除系统和废水再生系统给整个空间站质量和功耗所带来的影响进行了理论分析。结果表明：热泵－－废热回收集成模式不仅可强化空间辐射器的排热能力，而且还具有回收废热、降低系统质量和功耗的作用，表明其在未来航天热管理技术中具有应用潜力。     

Heat Transfer Performance of Heat Pipe Radiator with SiO2/Water Nanofluids

The effect of nanofluids on thermal performance of the miniature heat pipe radiator which was assembled by two heat pipes containing 0.6 vol.% SiO₂/water nanofluids and 30 pieces of rectangular aluminum fins was investigated experimentally and theoretically. The wall temperatures of the miniature heat pipe and fin surface temperatures were measured. Results showed that the utilization of SiO₂/water nanofluids as a working fluid in the heat pipe enhanced the heat performance by reducing wall temperature differences. Compared with Deionized water (DI water), the thermal resistance of the miniature heat pipe with SiO₂/water nanofluids decreased by about 23% to 40%. Furthermore, the theoretical calculation on a basis of one dimension found that the fin heat dissipation in the miniature heat pipe radiator charged SiO₂/water nanofluids was about 1.17 times of that of the DI water radiator.     

Experimental validation of an analytical model for predicting the thermal and hydrodynamic capabilities of flat micro heat pipes

An analytical model by Lefèvre and Lallemand [F. Lefèvre, M. Lallemand, Coupled thermal and hydrodynamic models of flat micro heat pipes for the cooling of multiple electronic components, Int. J. Heat Mass Transfer 49 (2006) 1375–1383] that couples a 2D hydrodynamic model for both the liquid and the vapor phases inside a flat micro heat pipe (FMHP) and a 3D thermal model of heat conduction inside the FMHP wall has been modified. It consists of superposing two independent solutions in order to take into account the impact of evaporation or condensation on the equivalent thermal conductivity of the capillary structure. The temperature, pressure and velocity fields can be determined using Fourier solutions. The model has been experimentally validated based on literature data from a grooved FMHP. Two new correlations for the equivalent thermal conductivities during evaporation and condensation inside rectangular micro-grooves have been proposed based on a numerical database. The influence of the saturation temperature and geometry on the maximum heat flux transferred by the system is presented.     

Optimization of a space radiator with energy storage

A simple model for heat transfer from a space radiator with latent heat thermal energy storage has been developed. For a given heat storage and dissipation capability, analytical results have been obtained for the optimum geometry of a radiator panel/fin based on a minimum mass criterion. Numerical results for a typical configuration show that mass reductions of 20–25% or more can be achieved for pulsed heating loads of durations of the order of 1 h or less. At the same time, the radiator sizes can be reduced by a factor of 4 or more. The results also suggest that the benefits of energy storage will be higher for operating conditions with lower heat dissipation rates.     

Inverse heat conduction estimation of inner wall temperature fluctuations under turbulent penetration

Turbulent penetration can occur when hot and cold fluids mix in a horizontal T-junction pipe at nuclear plants. Caused by the unstable turbulent penetration, temperature fluctuations with large amplitude and high frequency can lead to time-varying wall thermal stress and even thermal fatigue on the inner wall. Numerous cases, however, exist where inner wall temperatures cannot be measured and only outer wall temperature measurements are feasible. Therefore, it is one of the popular research areas in nuclear science and engineering to estimate temperature fluctuations on the inner wall from measurements of outer wall temperatures without damaging the structure of the pipe. In this study, both the one-dimensional(1D) and the two-dimensional(2D) inverse heat conduction problem(IHCP) were solved to estimate the temperature fluctuations on the inner wall. First, numerical models of both the 1D and the 2D direct heat conduction problem(DHCP) were structured in MATLAB, based on the finite difference method with an implicit scheme. Second, both the 1D IHCP and the 2D IHCP were solved by the steepest descent method(SDM), and the DHCP results of temperatures on the outer wall were used to estimate the temperature fluctuations on the inner wall. Third, we compared the temperature fluctuations on the inner wall estimated by the 1D IHCP with those estimated by the 2D IHCP in four cases:(1) when the maximum disturbance of temperature of fluid inside the pipe was 3℃,(2) when the maximum disturbance of temperature of fluid inside the pipe was 30℃,(3) when the maximum disturbance of temperature of fluid inside the pipe was 160℃, and(4) when the fluid temperatures inside the pipe were random from 50℃ to 210℃.     

Study on heat transfer characteristics of reservoir embedded loop heat pipe (Influence of condenser cooling method on heat transfer characteristics)

As heat generation in satellites increases, securing sufficient radiator panel area is an important problem. Deployable radiators, whose radiator panels are deployed post‐launch in space to increase the effective radiator panel area of the satellite, is becoming an important thermal control technology. A reservoir embedded loop heat pipe (RELHP) is applied to the deployable radiator for a thermal transport device. This paper presents the heat transport dynamic characteristics of a RELHP using a radiant cooling condenser and liquid forced convection cooling condenser by an experimental study. It was found that heat leak into the liquid line, flexible line, and reservoir increases the length of the sub‐cooling region in the condenser. In the case of the radiant cooling condenser, the sub‐cooling region length is shorter than that of a liquid forced convection cooling condenser. Furthermore, vapor temperature is mainly decided by the radiation capacity of the radiator panel, because liquid temperature returned into the evaporator rises with an increase in radiator panel temperature. In addition, time length from start‐up until steady state is greater than the liquid forced convection cooling condenser case, because the radiator panel has a large heat capacity. © 2008 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20229     

PERFORMANCE OF A HEAT PIPE THERMOSYPHON RADIATOR

A heat pipe thermosyphon radiator for use in domestic and industrial heating applications is presented. A test cell for the radiator is described and various experimental tests have been performed to determine the feasibility and performance of a heat pipe thermosyphon radiator. The thermosyphon radiator has been tested with freon 11, acetone, methanol and water as working fluids, and was compared with a conventional radiator. Best performance was obtained using methanol and acetone, and compares well with the conventional radiator. In addition, with these working fluids the thermosyphon radiator, by design, has desirable isothermal surfaces. The worst performance was with water, where local hot and cold spots formed on the radiator surface and the performance was poor. A natural convection/radiation model is presented for the thermosyphon radiator, and good agreement between measured and calculated heat transfer is obtained. The model reveals that typically 60% of the heat is transferred by natural convection and the remaining 40% by radiation. Advantages and further development of the thermosyphon radiator are discussed. © 1997 by John Wiley & Sons, Ltd.     

Comprehensive optimization of a heat pipe radiator assembly filled with ammonia or acetone

Optimal mass characteristics for a heat pipe radiator assembly for space application are investigated. The assembly consists of the heat pipe itself, an evaporator saddle and a radiator. The internal HP geometry and the dimensions of the saddle and radiator panel are the variables to be optimized. Operational and structural constraints are considered and the assembly is optimized for different operational modes in 0g and 1g gravity conditions. A new global search metaheuristic, called generalized extremal optimization, was used as the optimization tool. The results show that under certain combinations of input parameters the assembly with acetone HP can be more weight effective than the one with ammonia, in spite of the liquid transport factor criterion indicates an opposite trend.     

基于一维/三维耦合仿真的工程机械冷却系统优化设计

本文针对一款设计中的工程机械冷却系统,建立了一维数值模型与三维CFD模型。通过一维/三维耦合计算,研究在散热器模块串联安置并留有间隙的情况下,部分空气绕过前排散热器流动对工程机械冷却系统换热性能造成的影响。将CFD计算结果的风速数据嵌入标准的一维数值模型,对一维仿真计算进行修正。修正后,前排低温油散热器尺寸需要增加约11.3%,经实验验证满足要求。一维/三维耦合仿真使冷却系统热管理仿真计算的精度得到提高,使一维仿真结果更加接近实际情况。