旋转效应下射流冲击速度对换热的影响

采用数值计算方法模拟磨削工件表面的射流冲击对流换热过程,对不同射流冲击速度,考虑旋转盘诱导的气旋卷吸和射流冲击的耦合作用下,研究分析加热壁面的对流换热效果。在转盘诱导的气旋流动影响下,冲击射流向转盘和加热表面之间区域的侵入能力受到抑制,而射流速度的提高能够加强射流冲击的穿透力;在旋转盘诱导的气旋运动和卷吸作用下,空气射流冲击能有效改善磨削弧区的对流换热,且随着射流速度的增加,其强化对流换热的效果更显著。     

单孔蒸汽射流冲击平板换热的数值研究

对充分发展的过热蒸汽湍流射流冲击平板的流动和换热进行了数值研究,分析了射流温度和射流雷诺数对蒸汽射流冲击换热的影响,并与空气射流冲击换热进行了比较。通过AKN k-ε、V2F和SST k-ω三种湍流模型计算结果的对比可知,SSTk-ω模型模拟冲击射流流动和换热的效果最好。研究表明:在相同条件下蒸汽的冲击换热能力强于空气;射流温度的变化对空气的冲击换热基本没有影响,但是对蒸汽有较大影响;射流雷诺数越大,则蒸汽冲击射流的换热越强。     

脉冲流冲击冷却换热的液晶显示实验研究

采用热色液晶定量测温技术对稳态及脉冲式空气-氮气圆形浸没射流冲击冷却换热进行了实验研究.脉冲射流的实验结果表明,对于喷嘴直径D=3 mm的情形,无论脉冲频率高低,均无强化换热效果;对于D=I0 mm的情形,在较高Re数时出现个别工况的驻点换热强化.脉冲射流表现出换热系数沿径向分布趋于均匀的特点.     

冲击射流结构中应用粗糙表面的实验研究

在单侧开口的冲击射流冷却结构中,逐步增加的横流将影响冲击板上的对流换热效率,本文提出了压窝板和肋片板两种粗糙冲击板构型,增加横流的扰动以减少对冲击流的影响并且增大横流与壁面的对流换热。实验采用瞬态热敏液晶测量方法,可以得到大尺度壁面的二维对流换热系数分布,可以较为系统地分析压窝及肋片周围的局部换热系数分布。通过实验研究,发现压窝板可以显著增大平均换热系数,而肋片板降低了平均换热系数。     

强化换热通道中扰流元场协同优化研究

对一种场协同式周期性强化换热通道进行了数值模拟研究,考察了折流翅片不同角度、不同间距对通道换热特性的影响。计算结果表明,翅片倾角增大或间距缩小均有利于换热强化。强化效果随Re数的增大而愈加显著。     

多孔涂层横向抽吸效应强化膜状凝结换热的研究

研究多孔涂层界面抽吸效应对强化膜状凝结换热的影响。考察了多孔涂层的特性参数对凝液膜厚度和换热系数的影响。与Nusselt理论预示值对照表明,多孔涂层界面抽吸效应是强化膜状凝结换热的重要因素。     

纵向涡强化换热的M-Z干涉流动显示技术

本文采用M-Z干涉测量的方法,研究了半三角形翼片纵向涡发生器强化换热方案对矩形通道内气体流动换热的影响,获得了安装纵向涡发生器前后对流换热温度场的M-Z干涉图像.通过对实验获得的干涉图像进行分析处理,表明安装纵向涡发生器后,通道内入口段流动的热边界层明显变薄,反映了纵向涡对流动换热的强化作用,验证了将M-Z干涉测量方法应用于纵向涡强化换热研究的可行性.     

电场极性对池沸腾换热影响的实验研究

利用EHD技术对工质R123进行了非均匀高压电场下电场极性对池沸腾换热影响的实验研究.结果表明,无论加正、负电压,强化系数均随热流密度的增加而下降,最终达到稳定值;高热流密度下,正电压有较弱的强化效果,负电压对沸腾换热具有削弱作用;正电压下的强化换热效果优于负电压下的强化换热效果.     

流体低速绕流振动圆柱对流换热数值研究

运用Fluent的动态网格技术,对空气低速绕流振动圆柱的对流换热进行了研究,分析了流动和振动参数对换热的影响。数值计算表明,在本文计算范围内,壁面振动可使换热强化,最大可强化9倍,换热的强化随振幅和频率的增大而增大。场协同分析表明,圆柱振动强化换热的原因在于速度场和温度梯度场之间的协同程度得到了改善。     

狭缝射流冲击泡沫金属强化换热的数值模拟

为了分析泡沫金属在狭缝射流冲击泡沫金属强化换热的作用,在计算流体力学(CFD)的基础上,采用数值模拟的方法,对影响换热的一系列因素做了详细的研究。在模型中泡沫金属材质为纯铜,尺寸是定值,通过改变喷嘴内空气速度v、泡沫金属孔隙率φ、喷嘴宽度W与泡沫金属的高度H的比值、喷嘴到泡沫金属上表面的高度C与泡沫金属的高度H的比值,来分析各个因素对热表面换热系数、泡沫金属内温度分布和流线分布等因变量的影响。     

旋转射流冲击换热液晶显示实验研究

采用热色液晶测温技术对以二氧化碳为工质的稳态射流冲击换热和管内插入扭转带方式的旋转射流冲击换热进行了实验研究。与普通射流相比,旋转射流导致驻点附近区域的换热趋于均匀化。其换热系数在大于某一半径之后高于普通射流,但在驻点附近相对较低。旋转射流对换热的此种影响随雷诺数的增大而减弱。     

INVESTIGATION INTO METHODS OF ENHANCING HEAT TRANSFER UNDER IMPINGING AIR JETS

Impinging air jets are widely used in industry, for heating, cooling, drying, etc., because of the high heat transfer rates which are developed in the impingement region. In this study, two methods of enhancing jet heat transfer have been investigated, namely, by using turbulence promoters to artificially raise the turbulence level, and by using a loudspeaker to excite the jet acoustically. In both these cases, the increases in heat transfer from enhancement were found to be modest. Some experimental hot-wire anemometry data obtained for free and impinging air jet flows are presented here. The existence of a relationship between turbulence intensity and heat transfer mechanism is also discussed.     

微射流阵列冲击恒热流壁面换热数值模拟

微射流冲击作为一种高热流冷却技术,在大功率激光器、微电子芯片等微型高热流器件冷却方面有广阔应用前景.本文对微射流阵列冲击恒热流表面的换热情况进行数值模拟,详细分析了微射流阵列的换热特点,对比了射流孔顺排和叉排方式的冷却性能,得出射流入口雷诺数、射流孔间距、射流高度等因素对冷却特性的影响规律.     

高效微射流阵列冷却热沉传热特性

微射流阵列冷却热沉是利用射流冲击在驻点区能产生很薄的边界层来提高换热效率,本次研究设计的热沉是5层结构的模块式铜微射流阵列冷却热沉,以去离子水为工质对传热特性进行了实验研究.结果表明,采用微射流阵列冷却不仅能通过增加驻点数目来强化换热,而且能有效地降低换热表面的温差.热沉的热阻会随着泵功的增加而降低;随着泵功的不断提高,热阻变化趋于平缓.     

Heat transfer and flow characteristics of turbulent slot jet impingement on plane and ribbed surfaces

A computational study is carried out to assess the suitability of various RANS based turbulence models for slot jet impingement on flat and ribbed surfaces with various values of Reynolds number and jet to plate spacing. The com-puted results are compared with the reported experimental data. It was observed that none of the turbulence models considered predicted the heat transfer data accurately. However, some models predicted the experimental data with good trends, e.g., secondary peak and several spikes in Nusselt number for ribbed surface, with a precise computation of the stagnation point Nusselt number. Further, the effects of slot width, rib pitch and jet to ribbed surface spacing were investigated for jet impingement on a ribbed surface. It was observed that the local Nusselt number increased with slot width and rib to plate spacing. It was also observed that increasing Reynolds number had a positive effect on the local heat transfer. With increasing rib pitch the local Nusselt number increased near the stagnation zone but de-creased downstream. The observed flow pattern was different for jet impingement on a ribbed surface than that on a flat surface.     

Experimental Design and Methodology for Estimation of Local Heat Transfer Coefficient in Jet Impingement Using Transient Inverse Heat Conduction Problem

Abstract

This article aims to employ a two-dimensional inverse heat conduction technique in designing an experiment for accurately estimating the local convective heat transfer coefficient in slot jet impingement, given temperature measurements at some interior locations in the target plate. The method uses a sequential procedure together with the Beck function specification approach. Solution accuracy and experimental errors are examined using simulated temperature data. It is concluded that a good estimation of the space variable heat transfer coefficient can be made from the knowledge of the transient temperature recordings. The technique is used in a series of numerical experiments to provide the optimum experimental design for a slot jet impingement heat transfer investigation.     

旋转状态半受限冲射流流动和换热特性研究

利用数值模拟的方法,通过改变冲击雷诺数Rej(20000-35000)、旋转数Ro(0-0．0117)等参数,分析旋转条件下半受限单孔冲击射流的流动和换热特性,讨论了旋转对冲击射流的流场结构和换热特性的影响．研究结果表明:冲击射流在离心力和哥氏力的共同作用下发生弯曲,造成冲击靶面上的冲击斑随着旋转数Ro的增加而不断偏移,显著影响了冲击的冷却效果．冲击靶面的平均Nu数随着冲击雷诺数Rej的增加而增加;当旋转数Ro增加时,冲击靶面的平均Nu数先增加,后减小,然后再增加．计算结果和试验结论基本一致．     

Heat Transfer and Emission Characteristics of Impinging Rich Methane and Ethylene Jet Flames

Flame impingement heat transfer has widespread industrial and domestic applications and attaining high heat flux as well as low emission of pollutants is the important prerequisite for all such applications. In this article, the heat transfer and emission characteristics of a laminar flame jet impinging on a flat target plate have been investigated experimentally. The effect of reactant jet Reynolds number, equivalence ratio and burner to plate separation distance on the average heat flux, and emissions of CO and NO_x are studied using methane and ethylene fuels. Results indicate that the heat flux is maximized under certain operating conditions of jet Re, equivalence ratio, and separation distance between the burner and the target. Fuel type is found to have an effect on the heat transfer rate because of the varying luminosity of the flame with different fuels. Operating regimes that produce lower emission of pollutants are also identified. Findings of this article have direct industrial relevance to flame impingement heat transfer applications that have small target plate-to-burner port diameter ratios.     

两种喷嘴喷射性能的试验研究

为比较自激振荡脉冲喷嘴和连续射流喷嘴的喷射性能,利用自行搭建的喷嘴性能测试装置对两种喷嘴的喷射性能进行了试验研究,实测了不同压力下两种喷嘴的时均喷液量,分析了不同口径的连续射流喷嘴和自激脉冲喷嘴的喷射特性,主要探讨了连续射流喷嘴、自激喷头下喷嘴直径对喷嘴喷液性能的影响,并进行了两种射流打击油泥样本的对比试验．试验结果表明,时均喷液特性相似的连续射流和脉冲射流在冲击油泥样本时,相同时间下脉冲射流的冲击破坏范围要大于连续射流,根据试验中油泥的屈服破坏过程,确定了射流有效打击力的临界值,建立射流清洗油泥时有效射程的经验估算式．     

阵列射流冲击冷却局部对流换热特性的数值计算与试验验证

本文运用数值计算的方法对具有初始横流的阵列射流在不同的排列方式、冲击间距和横流/射流质量流量比下 的流动换热进行了三维数值研究,并采用热色液晶测试技术对阵列射流冲击的冷却表面温度分布进行了试验研究。获得了 每一股射流的冲击冷却局部对流换热系数分布的特征,研究结果表明本文的计算结果与实验特征是基本吻合的。