考虑热流通道效应的沥青路面温度数据的处理方法研究

以温度场实测数据为基础,提出了温度实测数据的处理及拟合方法。路面实测温度沿深度呈散点分布,但在短时间间隔内路面沿深度的升温曲线近似为线性分布。根据导热理论推断温度沿深度的二次导数为深度的一次函数,可以近似用三次曲线拟合路面温度的深度分布;用最小二乘拟合路面温度的深度曲线,发现路面内部存在热流通道,温度高的部位热流大,温度低的位置热流小。最后推荐采用加权最小二乘法拟合路面温度分布。

一种接触热阻的预测方法

采用当量热流通道的概念对接触热阻的预测进行简化分析，即对表面情况建立相应的表面模型后，确定出当量热流通道上的各个参数，整个接触面上的接触热阻即可视为有多个当量热流通道形成的接触热阻并联而成，从而可以预测出两个物体间的接触热阻。

用接触分热阻讨论接触热阻问题

为预测接触热阻 ,引入了接触分热阻概念 ,把接触热阻视为两个接触物体之间接触分热阻的串联 .通过建立单热流通道上接触分热阻的截锥体模型及热流通道上的温度分布方程 ,研究了接触热阻中的三维传热现象 .对该模型进行数值求解后得到截锥体接触模型上的温度分布情况 ,继而通过大量的数值计算 ,拟合出了一个求解单热流通道上接触分热阻的计算式 .研究结果表明 ,在较大的范围内该式的计算值同数值解法的结果较为吻合 ,如果以这样单热流通道作为接触面上的当量单热流通道 。

正确使用硅脂

一般的散热片底部均会有一层薄薄的硅脂,它的作用是减少或克服散热器底与处理器表面接触不充分而产生的接触热阻,填充空气缝隙,增大热源与散热片的接触面积,减小热流距离,增加热流通道,增大热传导量,因此您不可将其刮掉。安装时,不需再加导热硅脂,硅脂不能太多,因为越多,厚度越厚。

Numerical analysis on forced convection enhancement in an annulus using porous ribs and nanoparticle addition to base fluid

Miniaturization of electronic equipment has forced researchers to devise more effective methods for dissipating the generated heat in these devices.In this study,two methods,including porous media inserting and adding nanoparticles to the base fluid,are used to improve heat transfer in an annulus heated on both walls.To study porous media insert,porous ribs are used on the outer and inner walls independently.The results show that when porous ribs are placed on the outer wall,although the heat transfer enhances,the pressure drop increment is so considerable that performance number (the ratio of heat transfer enhancement pressure increment,PN) is less than unity for all porous rib heights and porous media permeabilities that are studied.On the other hand,the PN of cases where porous ribs were placed on the inner wall depends on the Darcy number (Da).For example,for ribs with Da=0.1 and Da=0.0001,the maximum performance number,PN=4,occurs at the porous ribs height to hydraulic diameter ratios H/Dh=1 and H/Dh=0.25.Under these conditions,heat transfer is enhanced by two orders of magnitude.It is found that adding 5% nanoparticles to the base fluid in the two aforementioned cases improves the Nusselt number and PN by 10%–40%.

Research of Temperature Tracer Method to Detect Tubular Leakage Passage in Earth-Dam

The location, intensity and scope of concentrated leakage must be determined in order to repair earth-Dam scoured by the leakage. In this paper, firstly, heat tracer theory and distribution laws of temperature in soil body with leakage are discussed. Then temperature tracer model is established according to stable heat conduction theory. In such model, the concentrated seepage passage is simplified into a circular pipe as a boundary condition. The location, scope and flow-velocity of the concentrated leakage are estimated via ichnography of the lowest temperature based on temperature data from detecting wells by quantitative computation and qualitative analysis. In case study, the distribution characteristic of temperature (including temperature data of water in reservoir, drainage pipes and tail pond) can be interpreted by this model. A modified model is also set up, applied for detected data at different cross-sections of the leakage passage, in which the temperature data are rectified according to distances from data locations to calculating section. Finally, the model is solved by numerical iterative method, and the possible error of this theoretical model is discussed. The permeability coefficient in leakage area is identical with that of normal soil in magnitude after anti-seepage repairing accomplished, which indicates this model is effective.

Heat transfer of copper/water nanofluid flow through converging-diverging channel

The main objective of this work is to investigate analytically the steady nanofluid flow and heat transfer characteristics between nonparallel plane walls. Using appropriate transformations for the velocity and temperature, the basic nonlinear partial differential equations are reduced to the ordinary differential equations. Then, these equations have been solved analytically and numerically for some values of the governing parameters, Reynolds number, Re, channel half angle, α, Prandtl number, Pr, and Eckert number, Ec, using Adomian decomposition method and the Runge-Kutta method with mathematic package. Analytical and numerical results are searched for the skin friction coefficient, Nusselt number and the velocity and temperature profiles. It is found on one hand that the Nusselt number increases as Eckert number or channel half-angle increases, but it decreases as Reynolds number increases. On the other hand, it is also found that the presence of Cu nanoparticles in a water base fluid enhances heat transfer between nonparallel plane walls and in consequence the Nusselt number increases with the increase of nanoparticles volume fraction. Finally, an excellent agreement between analytical results and those obtained by numerical Runge-Kutta method is highly noticed.

Temperature distribution of the incompletely mixed fluid flowing in the tubes and the unmixed fluid crossing over the tubes

A new model is established to describe heat exchanging of the incompletely mixed fluid flowing in the tubes and the unmixed fluid crossing out of the tubes in the heat-exchangers especially in air cooler. In the model, a new method of analyzing volume is proposed to develop the temperature distribution equations of the two fluids --tw（x） and ta（X,,7＂）. With tw（x） and ta （x, ,7）, the curves of the temperature distribution of the two fluids can be obtained. Also tw（x） and ta（x,n） can be used to calculate parameters of structure of an air cooler and to improve performances of it.

Convective mass transfer enhancement in a membrane channel by delta winglets and their comparison with rectangular winglets

Numerical calculations were conducted to simulate the flow and mass transfer in narrow membrane channels equipped with delta winglets, which are often used as longitudinal vortex generators to enhance heat transfer in heat exchanger applications. The channel consists of an impermeable solid wall and a membrane. The delta winglets are attached to the solid wall surface to enhance the mass transfer near the membrane surface and suppress the concentration polarization. The winglet performance was evaluated in terms of concentration polarization factor versus consumed pumping power. Calculations were implemented for NaCl solution flow in a membrane channel having a height of 2.0 mm for Reynolds numbers ranging from 400 to 1000. The delta wing- lets were optimized under equal pumping power condition, and the results of optimization suggest winglet height of 5/6 of the channel height, aspect ratio of 2.0, attack angle of 30% and a winglet interval equal to the channel height The optimal delta winglets were compared with the optimal rectangular winglets we found previously, and it is shown that the rectangular winglets yield a somewhat better performance than the delta winglets. @ 2015 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.

Effective Channel Length Degradation under Hot-Carrier Stressing

This article describes the effective channel length degradation under hot carrier stressing. The extraction is based on the IDs-Vcs characteristics by maximum transconductance （maximum slope of IDs ＆ VGS） in the linear region. The transconductance characteristics are determine for the several devices of difference drawn channel length. The effective channel length of submicron LDD （Lightly Doped Drain） NMOSFETs （Metal Oxide Semiconductor Field Effect Transistor） under hot carrier stressing was measured at the stress time varying from zero to 10,000 seconds. It is shown that the effective channel length was increased with time. This is caused by charges trapping in the oxide during stress. The increased of effective channel length （△Leff） is seem to be increased sharply as the gate channel length is decrease.

Study on dryout point and heat transfer in subcooled flow boiling through vertical narrow annular channels

The purpose of this study is to conduct the dryout point and heat transfer correlation for subcooled boiling flow in narrow annuli. First, the dryout point of subcooled flow boiling of water was measured in narrow annular channels under the working condition of pressure ranging from 0.1 to 0.3 MPa and low mass flow rate from 6 to 60 kgm^-2 s^-1. Experimental test channels were annular and heated bilaterally with the channel gap of lmm and 1.5mm, and heated length of 1500mm.The location of the dryout was observed and measured by experiment with investigating the various system parameter effects on dryout point, and the results show that the location of dryout point is basically stable and repeating and the heat transfer coefficient increased with heat flux, mass flux and pressure, however, decreases with the gap size. Next, new correlations of CHF and critical vapor quality for narrow annular channels was proposed and calculation results shown a good agreement with the experimental data.

预报纤维增强复合材料有效热导率的随机微结构胞元模型

发展了能预报复合材料有效性质的随机微结构胞元模型以预测单向纤维增强复合材料横向热导率。研究了能反映宏观有效性质的模型最小化问题,探讨了微结构影响宏观有效热传导性能的机制。结果表明:通过对模型指定周期边界条件并且以多个合适的小规模模型计算的平均值取代大模型计算,可大大改进收敛性并提高计算效率,从10×10个到30×30个子胞的模型,所得有效热导率计算结果的最大相对变化量仅为0.6%。不同纤维排列引起热流穿过热阻大的基体的路径长度改变,造成有效热导率不同;纤维热导率远大于基体热导率时,纤维随机分布造成纤维偏聚,部分纤维接触形成'热流通道',使得有效热导率增大,揭示了某一体积分数下有效热导率急剧增加是由'热流通道'贯通引起。与实验结果的比较说明了微结构随机性研究的必要性和本文工作的实用价值。

Heat transfer and flow characteristics in a channel with one corrugated wall

The present study numerically investigates the characteristics of three-dimensional turbulent flow and heat transfer in the channel with one corrugated wall heated with constant temperature by means of large eddy simulation.The corrugated wall is sinusoidal in the streamwise and spanwise directions.The Reynolds number in terms of bulk velocity and channel half-height is fixed at 2800 and the wave amplitude to wavelength ratio is varied in the rangeα/λ=0.01,0.02,0.04 in the streamwise direction andα/λ=0.01,0.02,0.04 in the spanwise direction.The results show that flow separation bubbles appear and near-wall streamwise vortices are generated with larger population in the upslope region of the bottom wall as wave amplitude increases.Compared with flat wall,the corrugated geometry increases the pressure coefficient and decreases the friction coefficient on the corrugated wall,and consequently increases the total drag coefficient owing to the increase of pressure coefficient,as expected,the heat transfer is higher.The waves in the spanwise direction converge the vortices into the trough along the streamwise direction and push them away from the bottom wall.Finally,thermal performance factor is defined and the effects of wave amplitude on the thermal performance are scrutinized.

Influence of Internal Channel Geometry of Gas Turbine Blade on Flow Structure and Heat Transfer

This paper presents the study of the influence of channel geometry on the flow structure and heat transfer, and also their correlations on all the walls of a radial cooling passage model of a gas turbine blade. The investigations focus on the heat transfer and aerodynamic measurements in the channel, which is an accurate representation of the configuration used in aeroengines. Correlations foi： the heat transfer coefficient and the pressure drop used in the design of internal cooling passages are often developed from simplified models. It is important to note that real engine passages do not have perfect rectangular cross sections, but include a comer fillets, ribs with fillet radii and a special orientation. Therefore, this work provides detailed fluid flow and heat transfer data for a model of radial cooling geometry which has very realistic features.

Analysis of 2D Flow and Heat Transfer Modeling in Fracture of Porous Media

Heat and mass transfer between porous media and fluid is a complex coupling process, which is widely used in various fields of engineering applications, especially for natural and artificial fractures in oil and gas extraction. In this study, a new method is proposed to deal with the flow and heat transfer problem of steady flow in a fracture. The fluid flow in a fracture was described using the same method as Mohais, who considered a fracture as a channel with porous wall, and the perturbation method was used to solve the mathematical model. Unlike previous studies, the shear jump boundary condition proposed by Ochoa-Tapia and Whitaker was used at the interface between the fluid and porous media. The main methods were perturbation analysis and the application of shear jump boundary conditions. The influence of permeability, channel width, shear jump degree and effective dynamic viscosity on the flow and heat transfer in the channel was studied by analysing the analytical solution. The distribution of axial velocity in the channel with the change of the typical parameters and the sensitivity of the heat transfer was obtained.

The Investigation on Flow Boiling Heat Transfer of R134a in Micro-channels

The present study reports an experimental evaluation of heat transfer characteristic of R134a flow boiling in mi- cro-channel heat sink. The heat sink is composed of 30 parallel rectangular micro-channels with cross-sectional dimensions of 500μm width and depth, as well as total length 30ram. Experiments were conducted with heat flux up to 80.212 W/cm2, mass velocity ranging from 373.33 to 1244.44 kg/m2s, vapor quality ranging from 0.06 to 0.9. The wall temperature of heat sink heated could be controlled at around 50℃. Heat transfer coefficient could be up to 180 kW/mZK. Two dominating flow patterns were observed by analyzing boiling curves. The heat trans- fer characteristics of nucleate boiling and convective boiling were presented in the study. Revised correlations of R134a flow boiling in micro-channel heat sink were carded out with the consideration of nucleate boiling and convective boiling mechanisms.

The Effect of Heating Direction on Flow Boiling Heat Transfer of R134a in Microchannels

This paper presents effects of heating directions on heat transfer performance of R134 a flow boiling in micro-channel heat sink. The heat sink has 30 parallel rectangular channels with cross-sectional dimensions of 500mm width 500mm depth and 30 mm length. The experimental operation condition ranges of the heat flux and the mass flux were 13.48 to 82.25 W/cm^2 and 373.3 to 1244.4 kg/m^2 s respectively. The vapor quality ranged from 0.07 to 0.93. The heat transfer coefficients of top heating and bottom heating both were up to 25 k W/m^2 K. Two dominate transfer mechanisms of nucleate boiling and convection boiling were observed according to boiling curves. The experimental results indicated that the heat transfer coefficient of bottom heating was 13.9% higher than top heating in low heat flux, while in high heat flux, the heat transfer coefficient of bottom heating was 9.9%.higher than the top heating, because bubbles were harder to divorce the heating wall. And a modified correlation was provided to predict heat transfer of top heating.

Flow Patterns and Thermal Drag in a One-Dimen-sional Inviscid Channel with Heating or Cooling

In this paper investigations on the flow patterns and the thermal drag phenomenon in one -dimensional inviscid channel flow with heating or cooling are described and discussed:expressions of flow rate ratio and thermal drag coefficient for different flow patterns and its physical mechanism are presented.

Laminar Periodic Flow and Heat Transfer in a Rectangular Channel with Tri-angular Wavy Baffles

This paper presents a numerical analysis of laminar periodic flow and heat transfer in a rectangular constant temperature-surfaced channel with triangular wavy baffles (TWBs).The TWBs were mounted on the opposite walls of the rectangular channel with inline arrangements.The TWBs are placed on the upper and lower walls with attack angle 45?.The numerical is performed with three dif-ferent baffle height ratios (BR=b/H=0.05 0.3) at constant pitch ratio (PR) of 1.0 for the range 100 ≤ Re ≤ 1000.The computational results are shown in the topology of flow and heat transfer.It is found that the heat transfer in the channel with the TWB is more effective than that without baffle.The in-crease in the blockage ratio,BR leads to a considerable increase in the Nusselt number and friction factor.The results indicate that at low BR,a fluid flow is significantly disturbed resulting in inefficient heat transfer.As BR increases,both heat transfer rate in terms of Nusselt number and pressure drop in terms of friction factor increase.Over the range examined,the maximum Nu/Nu0 of 7.3 and f/f0 of 126 are both found with the use of the baffles with BR=0.30 at Re=1000.In addition,the flow structure and temperature field in the channel with TWBs are also reported.