垂直横向冷气流动下圆柱气膜孔冷却和流动特性分析

透平动叶通常采用垂直横向内冷通道与气膜冷却结合的冷却结构,因此,需要考虑垂直横向冷气流动对气膜冷却流动和冷却特性的影响。以垂直横流进气条件下的简化平板气膜冷却为研究对象,采用流体计算动力学方法,对不同吹风比下常用圆柱形气膜孔的冷却和流动特性进行分析。相比于冷气腔进气条件,垂直横流进气条件下的面积平均效率在低吹风比下较小,而在中高吹风比下较大。随着吹风比的增大,孔下游冷却效率分布由单峰型转换为双峰型,孔出口近下游区域的冷却效率降低,而远下游区域的冷却效率提高,冷气射流流动和肾形涡对的非对称性随之减弱。

高位垂直进气旋转盘流动与换热的实验研究

本文用实验的方法对高位垂直进气转静系旋转盘附近冷气流动与换热特性进行了实验研究 ,得到了静盘表面压力、转盘表面温度、局部努赛尔特数的分布及平均努赛尔特数 ,并对结果进行了相应的分析。

微重力环境中空气流动与辐射热损失对火焰传播的影响

本文建立了包含辐射热损失的火焰沿热薄燃料表面传播的数学模型。燃毁点的密度作为待求参数出现在模型中。数值计算结果表明，在微重力环境中，火焰传播速度随空气流动速度的变化出现峰值。对比无辐射热损失模型和有辐射热损失模型的计算结果发现，辐射热损失是形成上述微重力燃烧特征的原因。在静止的微重力环境中或弱空气流动速度下，辐射热损失使燃毁点处有大量的残碳生成，但随着空气流动速度的增大，残碳生成量迅速减小。

垂直横流条件下扇形气膜孔的冷却和流动特性分析

目前国内外对于垂直横流条件下的平板气膜冷却研究较少,而在垂直横流条件下冷气流动的单侧偏向性对气膜孔的冷却和流动特性产生不可忽略的影响。建立扇形气模孔物理模型并采用算流体动力学的方法,分析在不同吹风比M为0.5、1.0、1.5和2.0时气膜孔的冷却和流动特性。随着吹风比的增大,垂直横流条件下的面积平均效率呈现先增大后减小的趋势,孔出口下游区域的冷却效率分布由近似对称的双峰型转换为单峰型,孔出口远下游区域的局部冷却效率和冷气覆盖程度均有提高,冷气射流形成的流场不对称性增强,冷气流动方向与低吹风比时相反,冷气横流在流场中逐渐占据主导地位。

Air interaction around outdoor air-cooled condensers

In order to increase cooling or heating efficiency,a porous computational fluid dynamics（CFD）model is employed to predict the thermo-fluid status and optimize the placement of outdoor units.A full scale model is established to validate the accuracy of CFD simulation in terms of velocity and temperature distributions.The comparison between the measurement and the simulation shows a good agreement.By evaluating the condensers＇ sucked air temperature with CFD for three units installed in a row,it is found that the minimum separation distance among neighboring units is 0.2 m;a vertical wall should be apart from the unit line by at least 0.8 m;and large different operating pressures among units do not impact the flow rate and the heat transfer of the other units meaningfully.

冰箱节电有技法

1、远离热源放置。冰箱应尽可能放在远离热源处，以通风背阴的地方为好。热食不要放进冰箱，一定要使食物在室温下晾凉后再放进冰箱；冷冻室内的食品用于净塑料袋小包包装，食物可以较快冷冻，既不易发干，又免湿气变成霜；食品不宜装得太满，与冰箱壁之间应留有空隙，以利于冷气流动。如遇停电，不要急于打开冰箱门。

冬季家电节电方法

1．电热毯。对有温度调节的电热毯，可在睡前5分钟开大档，当温度达到自身舒适时即开到小档。对无高、低温度调节开关的电热毯，睡前5分钟打开开关，睡时关闭，下半夜感到冷时再打玎8～10分钟。这样，一个冬天可以节省50～80度电。2．电冰箱。冰箱应尽呵能放置在远离热源处。热食不要放进冰箱，务必使食物在室温下晾凉后再放人冰箱；冷冻室内的食物最好用干净塑料袋小包包装，这样食物可以很快冷冻，既不易发十，义避免湿气变成霜；食物不宜装得太满，与冰箱壁之间应留有空隙，以利于冷气流动；冷冻的食物，在食用前最好有计划地将其转至冷藏室解冻。

电冰箱节电攻略

电冰箱周围的温度每升高5℃，其内部就要增加25％的电能消耗，因此，电冰箱应尽可能放置在远离热源处，以通风背阴的地方为好；电冰箱的开门时间要短；如遇停电，不要急于打开电冰箱门；热食不要放进电冰箱，一定要使食物在室温下晾凉后再放入电冰箱；冷冻室内的食品最好用干净保鲜袋进行包装，食物可以很快冷冻，既不易变干，又可避免湿气变成霜；食品不宜装得太满，与电冰箱壁之间应留有空隙，以利于冷气流动；冷冻的食品，在食用前最好有计划地把它转至冷藏室解冻；冷冻室如经常用-18℃代替-22℃，可节省30％的电能。

Numerical simulation of heat transfer and flow of cooling air in triangular wavy fin channels

Numerical computation models of air cooling heat transfer and flow behaviors in triangular wavy fin channels(TWFC) were established with structural parameters of fins considered.The air side properties of heat transfer coefficient and pressure drop are displayed with variable structural parameters of fins and inlet velocities of cooling air.Within the range of simulation,TWFC has the best comprehensive performance when inlet velocity vin=4-10 m/s.Compared with those of straight fins,the simulation results reveal that the triangular wavy fin channels are of higher heat transfer performances especially with the fin structural parameters of fin-height Fh=9.0 mm,fin-pitch Fp=2.5-3.0 mm,fin-wavelength λ=14.0-17.5 mm and fin-wave-amplitude A=1.0-1.2 mm.The correlations of both heat transfer factor and friction factor are presented,and the deviations from the experimental measurements are within 20%.

Cooling of Superheated Refrigerants Flowing inside Tubes Filled with Porous Media： Study of Heat Transfer and Pressure Drop, Carbon Dioxide Case Study

In this work an experimental study combined with an analytical investigation for cooling superheated Carbon Dioxide （CO2） gas were carried out. This work is intended to be part of the super critical Gustav Lorentzen refrigeration cycle of CO2. Experimental and analytical works concentrated on heat transfer and pressure drop for single phase flow during gas cooling inside tubes filled with porous media. Analytical empirical correlations were formulated for the coefficient of convectional heat transfer and for the pressure drop. A comparison between experimental results and that obtained by developed correlations were carried out, and a comparison between these results and literature published ones were carried out too. The results of this research showed that for cooling process the proposed correlations were proved to be acceptably accurate for pressure drop with difference from experimental results of 2%, while for convective heat transfer the difference from experimental results reached about 3%. More than 90% agreement with literature results was obtained. This work can enhance the calculations of heat flux and pressure drop of gases flow inside porous media filled tubes, and can help in the design procedure of heat exchangers and cooling processes.

Study on flow mode of combined converter for methanol synthesis from coal-based syngas

The mathematic model of combined converter with two different flow modes of gas-cooled reactor was established. The effects of gas flow mode in gas-cooled reactor on combined converter was investigated with the yield of methanol was 1 400 kt/a. The results show that if the flow mode of the cooling pipe gas and the catalytic bed gas change from countercurrent to concurrent, the catalytic bed temperature distribution does not fit the most optimum temperature curve of reversible exothermic reaction and the heat duty of heat changer in whole process increased seriously, which means that there is much more equipment investment and more operating cost. The gas flow mode of gas-cooled reactor affects the methanol yield slightly. There- fore, the countercurrent gas flow mode of gas-cooled reactor is more lucrative in the combined converter process.

Comparison between Conventional and Improved Gas Engine-Driven VRF under Same Climate Conditions

This paper reports the on-site performance evaluation of conventional and improved gas engine-driven VRF （variable refrigerant flow） units and （abbreviated as GHP） units. The study aims to elucidate two actual GHP units by using the probe insertion method. There is a tendency to decrease energy efficiency compared to a high loading factor. GHP operation was almost all part load operation. This on-site evaluation indicates a clear difference between conventional and improved GHP.

Effects of Clearance around Square Pillar in Rectangular Enclosure on Cooling Performance of Pulsating Airflow

This study focuses on a development of heat transfer enhancement techniques using pulsating flow for thermal equipment such as electronic equipment and heat exchangers. In this report, the heat transfer performance of the pulsating airflow around the heating pillar mounted in the rectangular enclosure was investigated experimentally while changing the size of the clearance between the enclosure wall and the pillar. The pillar simulates the components mounted in thermal equipment such as fins and electrical components. The rectangular enclosure simulates an enclosure of electronic equipment and heat exchangers. The shape of the cross section of the pillar was square having sides 30 mm. The dimension of the width of the enclosure was changed from 50 mm to 80 mm. It was found that the heat transfer performance of the pulsating airflow became higher than that of the steady flow regardless of the dimension of the clearance. The heat transfer enhancement around heating components by the pulsating flow can be available regardless of the clearance around the components.

An Experimental Investigation on the Confined and Elongated Bubbles in Subcooled Flow Boiling in a Single Microchannel

The characteristics of the confined bubble and elongated bubble in subcooled flow boiling in a single horizontal rectangular microchannel with hydraulic diameter Dh=1mm are studied experimentally. The channel with 1 ×1mm cross section is fabricated in a thin copper plate whose confinement number is Co=2.8 and the degassed deionized water is used as the working fluid. Visualization on the confined and elongated bubbles inside the microchannel is carded out by employing a high-speed CCD camera with a rnicrolens. The recorded images are carefully analyzed to illustrate the behaviors of the confinement and elongation processes of the bubble. The boiling number is used as an adjustable parameter to regulate the operating conditions which is eventually found to take a vital role in the bubble elongation process. Two formation patterns of the confined and elongated bubble are identified and the interactions between the neighboring confined and elongated bubbles are elucidated.

Experimental Investigation of Bubble Behaviors in Subcooled Flow Boiling

The experimental investigation on vapor bubble growth is performed for analyzing subcooled boiling in a vertical annular channel with inner heating surface and upward water flow under atmospheric pressure. Bulk liquid mass flux ranges from 79 kg/m2s to 316 kg/m2s, and subcooling is from 40 K to 60 K. The bubble behaviors from inception to collapse are captured by High-speed photography. The performance of bubble growth recorded by the high-speed photography is given in this paper. The bubble behaviors, effect of the bubble slippage on the heat transfer, and various forces acting on the bubble are discussed.

Flow Structure and Heat Exchange Analysis in Internal Cooling Channel of Gas Turbine Blade

This paper presents the study of the flow structure and heat transfer,and also their correlations on the four walls of a radial cooling passage model of a gas turbine blade.The investigations focus on heat transfer and aerodynamic measurements in the channel,which is an accurate representation of the configuration used in aeroengines.Correlations for the heat transfer coefficient and the pressure drop used in the design of radial 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 coiner fillet,ribs with fillet radii and special orientation.Therefore,this work provides detailed fluid flow and heat transfer data for a model of radial cooling geometry which possesses very realistic features.

Blow-by and tribological performance of piston ring pack during cold start and warm idle operations

To reduce the fuel consumption of internal combustion engines, more attention has been paid to the tribological performance of the piston ring pack during the cold start and idle operations. In this research, a numerical model considering the cylinder liner deformation and the piston ring conformability is developed to predict the blow-by, lubrication, friction and wear of the piston ring pack under different operating conditions. The gas flow rate, inter-ring gas pressures, minimum oil film thickness, frictional force and wear load during cold start are calculated and compared with those during warm idle operating conditions. The results show that cylinder liner deformation and piston ring conformability together obviously affect blow-by and other tribological performance. Meanwhile, it is found that friction loss is larger during cold start than during warm idle operating conditions. However, the wear process is more severe during warm idle operation than during cold start. From this research, the blow-by and tribological performance of the piston ring pack during cold start and warm idle operations are understood more deeply.