Effect of mold and core preheating temperature on corrosion resistance of casting Al-12Si alloy U-shaped cooling channel

Temperature has an important impact on the corrosion resistance of mold with cooling channels prepared by casting method.The effect of preheating temperature of the mold and the carbon fiber core on the roughness and corrosion resistance of U-shaped cooling channels made of Al-12Si alloy was examined in depth.The experimental results suggest that as the preheating temperature increased from 273 K to 573 K,the roughness of the inner wall of the cooling channel reduced from 96.6μm to 77.0μm.When the preheating temperature continued to increase to 723 K,the roughness increased to 85.3μm.The wetting between the Al melt and the carbon fiber will reduce micro bubbles and waves on the channel wall as the preheating temperature rises,thereby reducing the roughness.However,with the further increase of preheating temperature,it will increase the solidification time of the Al melt.At this time,the carbon fiber and Al melt will take more time to react,which increases the roughness of the channel wall to a certain extent.The results of exfoliation corrosion show that the larger roughness will aggravate exfoliation corrosion.The prolongation of high temperature reaction time between the carbon fiber and the Al melt will lead to the segregation of Si,which is easy to cause intergranular corrosion.Therefore,reasonable preheating temperature has an important impact on the roughness and corrosion resistance of U-shaped cooling channels.

Experimental Investigation on Convective Heat Transfer Characteristics in Ribbed Channel

The heat transfer and pressure loss characteristics on a square channel with two opposite surfaces roughened by high blockage ratio ribs are measured by systematic experiments.Reynolds numbers studied in the channel range from 1 400 to 8 000.The ratios of rib height to hydraulic diameter (e/D) are 0.2and 0.33,respectively.The ratio of rib spacing to height (P/e) ranges from 5to 15.The rib orientations in the opposite surfaces are symmetrical and staggered arrangements.The results show that the heat transfer coefficients are increased with the increase of rib height and Reynolds number,though at the cost of higher pressure losses.When the rib spacing to height ratio is 10,it keeps the highest heat transfer coefficient in three kinds of rib spacing to height ratios 5,10 and 15.The heat transfer coefficient of symmetrical arrangement ribs is higher than that of the staggered arrangement ribs,but the pressure loss of the symmetrical arrangement ribs is larger than that of the staggered arrangement ribs.

Discussion on Standardization and Automatic Flow Measurement of U-shaped Channel Water

In human life,water resources are inseparable.In recent years,China’s population growth has accelerated,and the industrial level has been continuously improved,resulting in the rapid use and waste of water resources.The protection and rational distribution of water resources are the most pressing issue in China’s water resources.At present,the water measuring facilities of the U-shaped channel mainly include a straight wall measuring pool,a parabolic throat measuring pool,and a long throat measuring pool.In view of the problems in irrigation measurement,the empirical water measurement of basic open-channel and automatic flow measurement system in irrigation district is summarized to improve the accuracy,fairness,and rationality of water measurement,and promote irrigation district management to a higher level.

Experimental and Numerical Study on Heat Transfer Enhancement of a Rectangular Channel with Discontinuous Crossed Ribs and Grooves

Experimental and numerical investigations have been conducted to study turbulent flow of water and heat transfer characteristics in a rectangular channel with discontinuous crossed ribs and grooves.The tests investigated the overall heat transfer performance and friction factor in ribbed and ribbed-grooved channels with rib angle of 30°.The experimental results show that the overall thermo-hydraulic performance for ribbed-grooved channel is increased by 10%-13.6% when compared to ribbed channel.The investigation on the effects of different rib angles and rib pitches on heat transfer characteristics and friction factor in ribbed-grooved channel was carried out using Fluent with SST(shear-stress transport) k-ω turbulence model.The numerical results indicate that the case for rib angle of 45° shows the best overall thermo-hydraulic performance,about 18%-36% higher than the case for rib angle of 0°.In addition,the flow patterns and local heat transfer characteristics for ribbed and ribbed-grooved channels based on the numerical simulation were also analyzed to reveal the mechanism of heat transfer enhancement.

Numerical Study of Turbulent Periodic Flow and Heat Transfer in a Square Channel with Different Ribs

A numerical investigation has been carried out to examine turbulent flow and heat transfer characteristics in a three-dimensional ribbed square channels. Fluent 6.3 CFD code has been used. The governing equations are discretized by the second order upwind differencing scheme, decoupling with the SIMPLE (semi-implicit method for pressure linked equations) algorithm and are solved using a finite volume approach. The fluid flow and heat transfer characteristics are presented for the Reynolds numbers based on the channel hydraulic diameter ranging from 104 to 4 ′ 104. The effects of rib shape and orientation on heat transfer and pressure drop in the channel are investigated for six different rib configurations. Rib arrays of 45° inclined and 45° V-shaped are mounted in inline and staggered arrangements on the lower and upper walls of the channel. In addition, the performance of these ribs is also compared with the 90° transverse ribs.

PEMFC压差流道构型特征参数对电池性能的影响

针对质子交换膜燃料电池PEMFC(proton exchange membrane fuel cell)压差流道构型尺寸对电池电化学性能影响机理不明的问题,研究流道高度和脊背宽度对压差流道和直流道在氧气浓度、水浓度分布特征和电流密度、功率密度、压降等方面影响规律,并对两者进行了对比分析,结果表明流道高度对压差流道和直流道性能影响较小,压差流道在脊背宽度为1.25 mm和1.50 mm时具有明显优势;进一步研究压差流道变压区对流道性能的影响,结果表明变压区高度为0.05 mm和长度为1.50 mm时,压差流道峰值功率密度最高。综合考虑功率密度和压降的影响,选择压差流道高0.40 mm、宽1.25 mm、脊背宽1.25 mm、变压区长1.50 mm、高0.05 mm,此时压差流道峰值功率密度为0.3661 W/cm^(2),相较于直流道峰值功率密度提升6.3%。

带肋复合微通道换热器内流动传热性能研究

为探究微肋与二次通道复合结构对微通道换热器流动换热性能增强的影响机理,采用数值方法,研究了不同雷诺数下6种带肋复合微通道换热器内的压降、流场结构、摩擦系数、基底温度、相对努赛尔数和综合流动换热性能,并与矩形光滑微通道和无肋二次通道微通道的流动换热性能进行了对比。研究表明:在流动特性方面,引入二次通道结构对微通道内的压降损失和相对摩擦系数没有影响,但引入微肋结构会产生节流效应并诱发漩涡结构,导致微通道内的压降损失增大3~10倍;在传热特性方面,引入二次通道结构能够强化换热,在二次通道结构基础上增加微肋结构能进一步增强微通道换热器的传热性能;相比于矩形光滑微通道和无肋二次通道微通道,复合微通道换热器的基底温度最高下降13.52 K,相对努塞尔数最高增大35.36%;在综合性能方面,对于所研究的6种带肋复合微通道换热器,前三角肋复合微通道具有最优的流动传热综合性能,并具有高流速、低泵功率、低热阻等优点。

宽雷诺数下肋参数对U型内冷通道流动与换热特性影响的实验研究

为了研究肋高和通道高的比值(e/H)、肋间距与肋高的比值(P/e)以及肋角度(α)对U型带肋通道流动与换热特性的影响,采用铜板法结合热电偶测量壁面温度分布,对6个不同肋参数U型带肋通道的表面换热特性进行了实验研究。带肋通道截面为正方形,实验的Re为5.0×10^(3)~1.0×10^(5)。研究结果表明,随着e/H和Re的增大,带肋通道的对流换热系数逐渐增大,但相应的流动损失增幅明显,e/H从0.08增大到0.12时,通道的阻力系数增大了近一倍。对于e/H=0.08的通道,P/e分别为6、8、10时,P/e为8时的对流换热系数和阻力损失均高于其他两种情况。相较于90°正交肋,带角度的斜肋能够进一步增强带肋通道的对流换热,75°肋的强化效果略强于60°肋。在实验参数范围内,对于几种不同的带肋U型通道,对流换热系数为光滑通道的1.9~3.0倍,阻力系数为光滑通道的4~16倍。综合考虑换热与流阻,e/H=0.08、P/e=8、α=45°的通道性能最好。

RIB测井技术在昆北油田的应用

RIB测井技术有效包含了声幅密度测井的所有信息,如声幅、变密度等,能够识别窜槽和孔洞,能够准确反映第一界面水泥环全方位胶结情况。RIB测井技术不同于以往的其它水泥胶结评价方式,它能有效评价水泥胶结的周向固井质量,能测量井周八个扇区水泥胶结曲线、VDL变密度地层胶结波列、升幅衰减曲线。

菱湖大桥主跨钢拱肋快速安装施工方案设计

无锡菱湖大桥主桥为中承式三跨钢桁架系杆拱桥,跨越三级航道。为解决跨内河航道安装钢拱肋施工难度大、安全风险高、封航压力大等难题,采用支架、浮吊联合施工技术吊装大节段钢拱肋,并通过有限元仿真、现场监测进行验证。结果表明,支架、浮吊联合施工技术方案安全合理。吊装过程中,钢拱肋最小应力为-48MPa,第一阶稳定性系数最小为34.8,最大整体稳定应力比为0.3,支架立柱最小组合应力为-46.4MPa,最大偏位为7.92mm,结构受力和稳定性满足要求。

High-speed railway channel measurements and characterizations: a review

Wireless communication for high-speed railways （HSRs） that provides reliable and high data rate communi- cation between the train and trackside networks is a challenging task. It is estimated that the wireless communication traffic could be as high as 65 Mbps per high-speed train. The development of such HSR communications systems and standards requires, in turn, accurate models for the HSR propagation channel. This article provides an overview of ex- isting HSR channel measurement campaigns in recent years. Particularly, some important measurement and modeling results in various HSR scenarios, such as viaduct and U-shaped groove （USG）, are briefly described and analyzed. In addition, we review a novel channel sounding method, which can highly improve the measurement efficiency in HSR environment.

氧活化结合RIB测井技术在港西油田找窜的应用

油田开发进入后期由于多种原因的影响,管外窜槽时常发生,导致油井含水上升,影响油田开发。应用单一测井找窜技术,由于技术的局限性,符合率难以保证。港西油田应用氧活化结合RIB测井技术进行油井找窜效果显著,为找窜提供了新途径。

Heat Transfer and Friction Characteristics in Rectangular Channel using Different Coolants

Several industrial applications such as electronic devices,heat exchangers,gas turbine blades,etc.need cooling processes.The internal cooling technique is proper for some applications.In the present work,computational simulations were made using ANSYS CFX to predict the improvements of internal heat transfer in the rectangular ribbed channel using different coolants.Several coolants such as air,steam,air/mist and steam/mist were investigated.The shear stress transport model(SST)is selected by comparing the standard k-ωand Omega Reynolds Stress(ωRS)turbulence models with experimental results.The results indicate that the heat transfer coefficients are enhanced in the ribbed channel while injecting small amounts of mist.The heat transfer coefficients of air/mist,steam and steam/mist increase by 12.5%,49.5%and 107%over that of air,respectively.Furthermore,in comparison to air,the air/mist heat transfer coefficient enhances by about 1.05 to 1.14 times when the mist mass fraction increases from 2%to 8%,respectively.The steam/mist heat transfer coefficient increases by about 1.12 to 1.27 times higher than that of steam over the considered range of mist mass fraction.

Enhancement of laminar flow heat transfer with single/doubleinclined ribs for unilaterally-heated channel

To deal with the aerodynamic heating on the aircraft surface,a potential solution is to utilize liquid cooling via the channels in part of the fuselage.This is a typical problem of flow and heat transfer in channels with unilaterally-heated surfaces.The enhancement of heat transfer in the channel is significant due to the high heating flux.The optimal velocity and temperature fields are obtained first based on the field synergy optimization method.Four rib configurations are proposed to produce the longitudinal vortices suggested by the optimal velocity field.The flow and heat transfer characteristics of different rib configurations are obtained by numerical simulation.The numerical simulations show that the heat transfer enhancement of the rib configurations are quite different,but the pressure drop increases similarly in the laminar flow range of Re = 500–1500.The mechanism of heat transfer enhancement with the single/double-inclined ribs for the unilaterally-heated channel is analysed.The best enhancement of geometric parameter among the investigated parameters such as the angle,length,radius and the spacing of the ribs is obtained.

钢制流道泵站肋板局部加高对结构振动的影响

在泵站运行过程中,机组和泵房的振动是最为常见且需予以高度重视的问题。结合某钢制流道立式轴流泵站工程,运用有限元软件ADINA对该泵站的振动传递路径进行了仿真模拟。根据该机组金属结构的实际构造,将轴流泵、泵轴、机架等建入有限元模型中,建立泵站混凝土结构-钢制流道-流体的三维流固耦合有限元模型,分析了钢制流道关键测点的应力、变形和振动响应;针对局部振动剧烈问题,提出了加强该部位肋板厚度的解决思路,重点分析了肋板局部加高对结构静动力响应的影响。分析结果表明,采用局部肋板加高的措施可以有效地降低钢制流道的应力、变形和振动响应。

微圆柱阵微通道内沸腾换热及气泡运动特性研究

基于流体体积(VOF)模型对恒定热流密度下的微圆柱阵通道内的流动沸腾换热特性展开数值研究,并利用几何重构法捕捉气液两相界面迁移变化,研究了流道内流速的分布和微圆柱高度对气泡分布、沸腾换热性能及沸腾不稳定性的影响。结果表明:微圆柱的存在增加了气泡核化点密度;气泡运动增加了工质与加热壁面接触的可能性;微圆柱高度较低时,易发生气塞现象,加热面散热不均导致局部异常过热,换热性能下降;微圆柱阵通过阻碍气泡反向流动来降低沸腾不稳定性,但微圆柱高度过高会造成换热系统振荡,影响传热可靠性。

Effect of Guide Vane on Pressure Loss and Heat Transfer Characteristics of Supercritical CO_(2)in U-Shaped Channel

U-shaped channel is a common unit structure in heat exchanger.The pressure loss and heat transfer characteristics of U-shaped channel have important influence on the comprehensive performance of heat exchanger.In this paper,combined with the thermo-physical property of supercritical CO_(2)(SCO_(2)),the influence of the guide vanes on the pressure loss and heat transfer characteristics of SCO_(2)in U-shaped channel was studied numerically.The four different guide vanes included integral guide vane,two-stage symmetric guide vane,two-stage asymmetric guide vane and discrete guide vane.CO_(2)Real Gas Property file(RGP)was imported into ANSYS CFX commercial software for calculation,and the turbulence model was SST k-ω.At the same time,the influence of different inlet Reynolds numbers and heating conditions of channel wall were also studied.

涡轮叶片带肋通道换热性能数值和试验研究

采用数值模拟与试验测试相结合的方法,利用涡旋核心可视化技术对于带肋通道内部流动与换热机理进行研究。对于宽高比为1的45°斜置带肋直通道的原型结构(无切除结构)和另外6种优化结构,全部肋片在流动方向下游切除2个肋高(3.8 mm)的改良结构在综合换热性能上表现最优,相对于原型结构的带肋面平均Nu数、平均Nu数比和平均换热因子分别增长25.1%,24.8%,22.7%;经试验验证,带肋通道外壁面温度的试验值与数值模拟值误差在10%左右。

旋转条件下U形通道转弯段形状对流动和传热特性的影响

In this paper,the flow and heat transfer characteristics in U-shaped channel with three different turn shapes are studied.The rotation number ranges from 0~0.251,Reynolds number are 11500,23000,34500,respectively.The results show that the flow separation and reattachment in the turning section are the key factors affecting the local heat transfer and pressure loss of U-shaped channel.The square turn will generate corner vortices at the outside of the turning section,and the size of the inner separation vortex and reattachment vortex is larger than that of the other two turn shapes.The existence of vortex system will increase the mixing and enhance heat transfer,but increase the pressure loss,so its relative Nusselt number and pressure loss are the largest.There are corner vortices on the outside of the turning section of the channel with a inner circle turn and outer square turn,but the arc-shaped inner edge makes its separation delay and the separation vortex decrease,and the size of the reattachment vortex also decreases.The arc shaped outer edge of the channel with circle turn in both inner and outer further inhibits the generation of corner vortices,so its relative Nusselt number and pressure loss are the lowest.Rotation will cause the fluid to deflect under the influence of Coriolis force,strengthen the heat transfer on the trailing surface of radial outflow and the leading surface of radial internal flow,and generate secondary flow and separation vortex in the turning section,resulting in the change of vortex structure in the turning section.With the increase of rotation number,the Nusselt number of the three types of turning section structures increases.The thermal performance factor of the three channels increases with the increase of rotating speed,and the channel with a inner circle turn and outer square turn is the highest,which is 9.6%higher than the channel with circle turn in both inner and outer on average,and 17.8%higher than the channel with square turn in both inner and outer.

Very-large eddy simulation of the rotational effects on turbulent flow in a ribbed channel

For the simplified model of the internal cooling passage in the turbine blade of an aero-engine,the present study applies a newly developed turbulence modeling method,very-large eddy simulation(VLES),for analyzing rotational effects on the characteristics of complex turbulent flow.For comparison,not only are the delayed detached eddy simulation(DDES)method(recognized as one of the most popular hybrid Reynolds-averaged Navier-Stokes–large eddy simulation(RANS-LES)methods)and the LES method used with the same numerical setup,but also three RANS turbulence models,including the k-ωshear stress transport(SST),standard k-ε,and Reynolds stress models,are applied to analyze the flow structure in the ribbed channel(whether rotating or stationary).Complex turbulent flows in a square ribbed channel at high Reynolds number of 100000 in the stationary state and different rotational numbers(Ro)between 0.1 and 0.4 are simulated and analyzed in detail.The comparisons show that when compared with the experimental data the VLES method works best in both the stationary and rotating states.It can capture unsteady flow characteristics such as wall shear layer separation and the vortex structure resulting from the rib disturbance.The DDES method can only capture the larger-scale vortex structures,and its predictions of the time-averaged velocity differ considerably from experiments,especially in the stationary state.With a relatively coarse grid,satisfactory prediction cannot be achieved in either rotating or stationary state by the LES method with wall-adapting local eddy-viscosity(WALE)and dynamic Smagorinsky models.The three RANS models perform poorly in both the stationary and rotating states.The results demonstrate the advantages of the VLES method in analyzing the unsteady flow characteristics in the ribbed channel at high Reynolds numbers for both stationary and rotating conditions.On that basis,the study uses the VLES method to analyze the flow evolution under different rotational numbers,and the rotational effects on the fluid mechanisms are analyzed.