Investigation on Temperature Field Calibration and Analysis of Wind Tunnel

For wind tunnels,it is essential to conduct temperature and flow field calibration on their test section,which is an important indicator for evaluating the quality of wind tunnel flow fields.In the paper,a truss composed of temperature sensors was used to calibrate the temperature field of a completed wind tunnel section.By adjusting the distance between the temperature measurement truss and the nozzle,as well as the wind speed,the temperature field distribution data at different positions could be obtained.Analyze these data to identify important factors that affect the distribution of temperature field.Simultaneously,the temperature field of the wind tunnel was simulated accordingly.The purpose is to further analyze the fluid heat transfer between air and wind tunnel walls through numerical simulation.Through the above analysis methods,the quality of the temperature field in the wind tunnel has been further verified,providing reference for future wind tunnel tests of relevant models.

Experimental Studies of the Enhanced Heat Transfer from a Heating Vertical Flat Plate by Ionic Wind

The effects of the ionic wind on the heat transfer rate from a heated vertical flat plate are described. The ionic wind is induced by three different types of discharge, corona discharge, dielectric barrier discharge （DBD） and dc glow discharge. The heat transfer coefficients for the heated copperplate under free convection conditions with and without an ionic wind are obtained by measuring the temperature and the heating power of the copper plate. It has been proved that the convective heat transfer coefficients increase by several times with the help of the ionic wind. With the ionic wind induced by a uniform dc glow discharge, the heat transfer coefficient of the heated copper plate is highly enhanced compared with those induced by a corona discharge or DBD. With the use of DBD, the breakdown voltage is increased significantly, which is helpful in avoiding a breakdown when heat transfer is enhanced by the ionic wind. In addition, it makes the application of the ionic wind much safer.

Thermal Conductivity and Heat Transfer Coefficient of Concrete

A very simple model for predicting thermal conductivity based on its definiensis was presented. The thermal conductivity obtained using the model provided a good coincidence to the investigations performed by other authors. The heat transfer coefficient was determined by inverse analysis using the temperature measurements. From experimental results, it is noted that heat transfer coefficient increases with the increase of wind velocity and relative humidity, a prediction equation on heat transfer coefficient about wind velocity and relative humidity is given.

Influence of Wind Speed on Heat Flow through Polypropylene Insulating Material

The heat transfer properties of polypropylene insulation at different ambient temperature against wind were analysed. A theoretical model of the combined conductive, convective and radiative heat flow through fibrous insulating material was presented. Detail study was carried out by using the finite element method. The theoretical results are in accordance to the experimental results which were accomplished in an artificial climate chamber.

Earth’s Atmosphere Prevailing Surface Winds Based on Effectiveness of Mbane Biouele Formula Derived in 2009

Any system designed to simulate the earth's atmosphere general circulation, must necessarily be based on the spatial-or temporal average conditions. Irregularities in the profiles of air motions that we observe on daily weather maps often make lose any real meaning to the general circulation. As complicated and inconsistent that is the daily traffic of air particles, it is interesting to define a general circulation characteristic of the average air transportation around the globe. Indeed, this transport responds to a need to transfer heat from the equator (heat source) to the poles (cold sources). Mbane Biouele formula (2009), derived from Clausius-Clapeyron relation (1832), now allows faithful and unique representation of the tricellular general circulation: Hence, the possibility of access to the earth’s atmosphere prevailing surface winds in summer as well as winter.

基于能量流向的变压器饼式绕组散热分析及试验研究

变压器热点温度作为运行经济性、安全性的关键指标,是设备在线监测及状态评估中的重点。该文对变压器内部散热进行研究,着眼于饼式绕组及其油道结构,基于能量流向建立绕组温度变化的物理模型。基于这一模型,在一台内置分布式传感光纤的110kV三相ONAN变压器上开展试验研究,使用分布式光纤测温(distributed temperature sensing,DTS)技术对运行状况下的绕组整体温度分布进行实时监测,分析绕组在ONAN冷却方式下的散热状况。在变压器启动初期,绕组各处散热量较低,温升速率较快。约2 h后,各饼散热量基本与损耗相一致,散热率可达98%以上,因此将这一阶段称为准稳态。准稳态阶段,绕组整体散热率基本一致。负载变化前期不同位置散热量的差异是温度梯度形成的主要原因。基于DTS手段及散热器进出口处油温,提出绕组每饼平均对流换热系数的计算方法,基于无量纲数建立绕组内外表面局部对流换热系数的计算方法,对不同位置、负载率下两种对流换热系数的变化规律进行分析获得了绕组运行过程中对流换热系数分布规律及变化趋势。

Numerical Study of Convective and Radiation Heat Transfer Characteristics in an Upward-Facing Cylindrical Cavity under Back-Side Windy Condition

Under the back-side windy condition,the convection and radiation heat transfer characteristics in an iso-flux upward-facing cylindrical cavity were studied by three-dimensional numerical simulation.The impacts of cavity tilt angle,wind incident angle and wind speed on convection and radiation heat transfer Nusselt number Nuc and Nur were analyzed,and the possible explanations for their impacts were presented.Results show that due to the disturbance of wind,the influence of cavity tilt angle becomes more complicated and is related to wind incident angle and wind speed.The variation of Nuc or Nur with wind incident angle is different for different cavity tilt angles.Despite of the changes of cavity tilt angle or wind incident angle,the Nuc increases with the wind speed while the Nur presents a declination with the increasing of wind speed.Hence,compared with cavity tilt angle and wind incident angle,wind speed may be the dominant factor affecting or controlling the convective and radiation heat transfer of cavity.

超高速风洞温敏漆膜基结构传热特性分析

磷光热图技术是实现超高速风洞流场下飞行器模型表面热环境测量的关键技术之一,但目前仍缺乏温敏漆(TSP)膜基结构传热特性及膜基材料适用性的系统研究。本文开展了不同材料厚度的TSP膜基结构在不同流场工况下内部传热特性的数值仿真分析。针对超高速脉冲式和暂冲式风洞,分别研究了流场作用时间、表面热流密度和TSP层厚变化对不同材料体系膜基结构内部热扩散深度及表面温升的影响规律。结果表明:TSP膜基结构内部热扩散深度主要与模型材料热扩散率和流场作用时间有关,受热流密度和TSP层厚的影响较小;表面温升主要随热流密度和TSP层厚变化,且均呈正相关趋势。研究成果可为磷光热图在风洞试验应用中定制化设计膜基结构材料和厚度提供理论支撑。

风速与风向对人体热交换影响的CFD仿真模拟

为了提升灾害环境中人体热损伤评估精度并保障应急救援人员的生命安全,首先将暖体假人进行三维激光扫描得到数值假人,并按照人体生理构造将其划分为20个区块,通过ICEM软件建立气候室,设置0°~180°的风向;然后通过FLUENT软件计算得到0.2~5.0 m/s风速时的人体显热换热量和辐射换热量,在此基础上求得对流换热量;最后将模拟结果与文献中数据进行对比验证,并分析不同风速与风向对人体热交换的影响。结果表明:提出的计算流体动力学(CFD)仿真模拟方法可有效模拟人体不同部位的换热量;风速的增加会促进人体与环境之间的热交换,当风速从0.2 m/s增加到5.0 m/s时,人体整体对流换热量从56 W/m^(2)增加到360 W/m^(2);人体表面局部部位之间对流换热量有明显的差异,其中四肢部位与环境之间的热交换受风速影响更为明显;风向对人体整体对流换热几乎没有影响,但躯干部位对流换热量受风向的影响较大;在非对称风向(45°、90°、135°)下,人体对流换热量呈现非对称式分布。本研究可为人员安全评估、极端环境下人体热反应建模、防护装备研发等提供基础数据。

电力机车走行风相变散热器风洞试验研究

文章基于电力机车走行风相变散热器的结构模型,建立了其等效热阻网络,分析其传热特性,推导了风速影响下散热量的修正系数关系式;通过风洞试验,研究了散热器在不同风速、不同水流量下散热量和热阻的变化特性,以及散热器在不同风速下的热启动性能及阻力特性。结果表明:散热器散热量随风速及水流量的增大而不断增大,而散热器热阻则刚好相反;散热器静态启动时间和散热启动时间均小于4 min;单个散热器产生阻力仅为机车牵引力的0.17‰,对整车阻力影响很小。

风对砂土非饱和带水汽热运移规律影响研究

针对目前以非饱和带土体水汽热运移对类似铁路、公路工程以及污染物运移影响根本认识不足的问题,基于室内砂土土柱试验,开展了在一定热辐射条件下,考虑风速(0、0.56、1.44 m/s)对砂土非饱和带水汽热运移规律影响研究。结果表明:温度控制系统和风速控制系统工作以后,风速的增大一方面降低了土表的温度梯度,并减缓着水分的流失,另一方面加快土表水分的流失作用,2种机制共同影响着土体的含水率变化。蒸发速率受到温度梯度的影响,随着温度梯度以及基质势作用下气态水向上运移速率趋于稳定,土体的瞬时蒸发量在40 h之后也趋于稳定。总结的经验可供今后类似项目借鉴。

不同截面柱体绕流及换热特性的数值研究

为了研究不同截面柱体绕流及换热特性,使用Fluent软件数值模拟了圆柱、方柱、三棱柱三种柱体绕流和换热问题,得到了不同截面柱体的绕流及换热规律。结果表明:方柱和三棱柱的平均阻力系数相近,且均大于圆柱平均阻力系数;方柱的升力系数幅值最大,其次为圆柱,三棱柱最小。方柱和三棱柱的漩涡脱落频率相近,且均小于圆柱的漩涡脱落频率。增大雷诺数可以提高柱体表面换热系数,三种柱体表面换热能力为:三棱柱>方柱>圆柱。

TWO DIMENSIONAL SUPERSONIC SHOCK TUNNEL AND ITS APPLICATION

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电机端部绕组表面对流换热系数的研究

电机端部绕组的温升求解是电机温度场计算过程中的难点所在。针对端部绕组周围的流场域不规则,难以用热路法或有限元法精确计算其表面换热系数的难题,提出了一种基于简易风洞实验装置的对流换热系数测量方法,搭建了实验平台对不同绝缘等级、不同成型工艺的绕组线圈的表面对流换热系数进行了测量,并分析了对流换热系数在不同影响因素下的变化规律。结果表明,不同绝缘等级的绕组端部表面对流换热系数相差不大,相比于成型线圈,散开线圈端部表面的对流换热系数更大。通过实验实现了对端部绕组表面对流换热系数的准确测量,为后续电机温度场的准确计算奠定了基础。

变工况下地铁屏蔽门风压特性实测研究

针对屏蔽门风压问题,通过改变车站公共区机械送排风系统、轨行区上下排热系统和活塞风井通风系统得到8种组合工况,对列车正常运行下屏蔽门风压进行测试。结果表明:在车站公共区机械送排风系统变工况下,不同位置屏蔽门同一时刻承受的风压极值最大相差近50%,不能作为调控屏蔽门风压的有效手段;轨行区上下排热系统变工况下,开启上排热能降低中部屏蔽门的最大正压值,但对两侧屏蔽门的效果并不好,因此轨行区上排热系统不能作为调控屏蔽门风压的有效手段;双活塞风井连通风阀变工况下,开启连通风阀能有效降低屏蔽门风压值,正压峰值最大能降低88.3%,负压峰值最大能降低50%。

涂装车间低浓度废气余热回收实施改造案例分析

涂装车间废气主要有两种,一种是烘干废气,一种是喷漆室、点补室、输调漆间等低浓度废气;烘干废气属于高浓度废气,通常焚烧处理通过多级换热给烘干室提供能量,换热的废气经过多级换热之后直接排放;低浓度废气通常采用KPR+RTO处理,废气处理之后通过一次新风换热之后通过涂装车间烟囱高空排放。

500kV避雷器受潮情况下温升计算及影响因素分析

针对避雷器温升计算过程对流换热系数依靠经验确定的问题,提出了对流换热系数计算方法,研究了避雷器内部温度场分布,分析了污秽、风速、日照三种因素对不同受潮程度、不同受潮位置下避雷器温升的影响。结果表明,不同影响因素下,避雷器表面对流换热系数取值范围分别为5-31、27-35、19-34 W/(m^(2)·℃);污秽位置会影响MOA表面温升分布,且受潮程度越大,对温升影响越显著;随着风速的增加,阀片上的温度下降较小,表面的温度下降较大;日照对受潮时的避雷器温升影响明显增大,但较于污秽和风速影响偏小。

Simulation of steel beam under ceiling jet based on a wind–fire–structure coupling model

For localized fires, it is necessary to consider the thermal and mechanical responses of building elements subject to uneven heating under the influence of wind. In this paper, the thermomechanical phenomena experienced by a ceiling jet and I-beam in a structural fire were simulated. Instead of applying the concept of adiabatic surface temperature (AST) to achieve fluid–structure coupling, this paper proposes a new computational fluid dynamics–finite element method numerical simulation that combines wind, fire, thermal, and structural analyses. First, to analyze the velocity and temperature distributions, the results of the numerical model and experiment were compared in windless conditions, showing good agreement. Vortices were found in the local area formed by the upper and lower flanges of the I-beam and the web, generating a local high-temperature zone and enhancing the heat transfer of convection. In an incoming-flow scenario, the flame was blown askew significantly;the wall temperature was bimodally distributed in the axial direction. The first temperature peak was mainly caused by radiative heat transfer, while the second resulted from convective heat transfer. In terms of mechanical response, the yield strength degradation in the highest-temperature region in windless conditions was found to be significant, thus explaining the stress distribution of steel beams in the fire field. The mechanical response of the overall elements considering the incoming flows was essentially elastic.

环境风影响下换流变压器空冷系统换热性能研究

针对北方地区某高压直流输电换流站,建立了换流变压器空冷系统以及周围建筑物的计算流体动力学仿真模型,研究了不同环境风向和风速影响下空冷系统换热性能的变化规律。研究结果表明:由于周围建筑物的影响,空冷系统的换热性能在不同的环境风向下均有所衰减。当风向为W、风速为6m/s时,环境风流动方向与风机进气方向相反,极1和极2换流变空冷系统的换热能力衰减最为严重,分别下降了38%与40%。在高风速占比最多的NW28°风向下,环境风速逐渐升高时换热器上方的涡旋随着风向移动,迎风侧换热器出口高温气流回流至其他换热器入口;处于迎风侧的变压器2F换热器换热量最低,沿着环境风的运动方向不同位置换热器换热量呈现先升高后降低的趋势。研究结果为深入理解环境风影响下空冷系统换热性能的变化规律提供了理论依据,也为设计适应真实场景的变压器空冷系统提供了技术支撑。

不同构型电晕放电离子风强化传热的数值模拟研究

为了探索不同构型下离子风的传热性能,针对3种不同结构的离子风装置进行数值模拟,分析电压、电极高度与散热片宽度对平均风速、换热系数以及功率的影响规律。计算结果表明,电压的增大可以提升离子风的强化传热效果,但是消耗的功率也会逐渐增大,其中线-板型功率增大的幅度最大;电极高度越小,离子风的强化传热效果越好;当散热片的宽度比较小,散热需求比较低时,由于直接接地型电极的功率较小,所以其更加适用。研究结果对不同情况下的离子风结构选型提供了参考。