圆形自由表面水射流冲击换热特性

对圆形自由表面水射流冲击换热特性进行了系统的实验研究,总结了喷距、射流出口速度以及相变等因素对换热的影响,并对其形成机理进行了分析,得到了驻点传热系数以及局部传热系数径向分布的关联式.     

变压器油圆形浸没射流冲击换热特性

对变压器油圆形浸没射流冲击换热特性进行了系统的实验研究,分析了恢复效应、喷距、射流Re、喷嘴尺寸等因素对换热的影响.对极小尺寸射流冲击换热情况下的一些特殊现象进行了描述,并对其形成机理进行了分析.     

强润湿性液体在圆形断面喷嘴浸没射流冲击下沸腾的热滞后

系统地研究了液体在圆形断面喷嘴浸没射流作用下沸腾热滞后与射流冲击速度大小、液体流动方向、液体过冷度和喷嘴直径等因素的影响 .结果表明 :沸腾起始过热度随液体过冷度增加而减小 ,与其他因素无关 ,而温度过头值则随射流速度和液体过冷度减小而增加 .从强润湿性液体沸腾机理的角度对起始沸腾点的影响给出了相应的解释 .最后总结出了几种减小或消除沸腾热滞后的方法     

圆形自由射流冲击曲面的换热特性

采用直接表面温度测量的方法对水喷射高温曲面的传热过程进行实验研究.通过实验得到了驻点区及附壁射流区的对流传热系数的分布情况,并且系统地研究了射流出口速度、喷嘴至加热面的间距等参数对对流传热系数的影响.结果表明,圆形射流冲击曲面的局部传热系数沿传热面随X/D的增大而逐渐减小,驻点处的传热系数最大并且随射流速度的增大而增大,但是当射流速度增大到一定值时,驻点的对流传热系数的增大比较缓慢.在射流速度较低的情况下,喷距对局部传热系数的影响较为显著.     

提高水射流喷嘴清洗效率的理论分析

主要从高压水射流基本参数出发,分析高压水射流清洗机喷嘴效率提高途径．以便使我国生产使用的数千台清洗机发挥出更高的效率,让广大清洗机用户获得更大的经济效率。     

流线型平面喷嘴结构设计

液动式射流冲击器因其独特的优点使其在石油、科学勘探等钻井中具有广泛的应用前景.其核心部件射流元件平面喷嘴结构好坏直接影响液流能量的利用率,因此在设计射流元件时,有必要设计出高效结构的喷嘴,以减少能量损失.本次试验中设计有"Y"型、流线型喷嘴,且在室内进行了试验.试验结果表明:流线型喷嘴的流量系数比目前大量采用的"Y"型进口喷嘴流量系数大得多.建议在以后设计射流元件时采用流线型进口喷嘴,以期提高过流能力,从而提高冲击器的性能.     

高压水射流喷嘴效率解析

在高压水射流清洗机械中,整机重量约有2 000～3 000kg,可是它的主要工作机构喷嘴的直径和长度只有2～3cm,其重量也就100～200g.但是高压水射流却完全是从这里产生的,因此喷嘴的效率分析就显得非常重要.     

高压水射流清洗用喷嘴及喷头

在高压水射流清洗设备中!射流喷嘴及喷头是关键部件,主要对喷嘴及喷头的种类、形状及用途进行了简要的介绍。     

液体阵列射流冲击冷板工质与传热结构研究进展

液体阵列射流冲击冷却是解决高热流密度散热问题的最有效技术之一,能够有效地对目标表面进行散热,具有散热能力高、能效比高和噪声低的优点,在散热方面具有巨大优势。本文简述了国内外对阵列射流冲击的研究进展,从换热工质和射流冲击冷板的换热结构两个方面,指出了其对液体阵列射流冲击换热特性的影响,并介绍了倾斜射流和旋流射流两种新型阵列射流方式。综合分析了常用的液体换热工质和纳米流体换热工质在射流冲击过程中强化换热的原理,介绍了喷嘴孔型、喷嘴的排列方式和冲击表面结构三种阵列射流结构。分析表明,不同孔型的喷嘴会影响流体的射流速度和湍流特性,不同的喷嘴排列方式会对射流流体的相互作用和有效冲击面积产生影响,不同的冲击表面会影响射流工质的循环混合,这些都将对射流冷板的换热特性产生很大影响。指出了解影响液体阵列射流冲击效果的主要因素,是改善和提高射流换热性能的根本方法。     

适应系统要求的射流喷嘴的研究

根据系统理论模型建立了射流泵系统装置并采用了理论分析和统计分析的方法论述了射流泵内部结构和系统装置的关系。实验结果分析表明,射流泵的结构参数和系统效率存在最优化关系,同时系统条件对射流泵的内部流场流动有着重要的影响,指出射流泵只有适应系统工艺条件才是射流泵充分发挥效率的关键。     

Nanofluid impingement jet heat transfer

Experimental investigation to study the heat transfer between a vertical round alumina-water nanofluid jet and a horizontal circular round surface is carried out. Different jet flow rates, jet nozzle diameters, various circular disk diameters and three nanoparticles concentrations (0, 6.6 and 10%, respectively) are used. The experimental results indicate that using nanofluid as a heat transfer carrier can enhance the heat transfer process. For the same Reynolds number, the experimental data show an increase in the Nusselt numbers as the nanoparticle concentration increases. Size of heating disk diameters shows reverse effect on heat transfer. It is also found that presenting the data in terms of Reynolds number at impingement jet diameter can take into account on both effects of jet heights and nozzle diameter. Presenting the data in terms of Peclet numbers, at fixed impingement nozzle diameter, makes the data less sensitive to the percentage change of the nanoparticle concentrations. Finally, general heat transfer correlation is obtained verses Peclet numbers using nanoparticle concentrations and the nozzle diameter ratio as parameters.     

磁场对熔盐射流冲击传热的影响

以永磁铁构建定磁场,进行外加磁场作用下熔盐射流冲击传热的实验研究,并得到Nusselt数Nu驻点关联式和径向分布。结果表明,在驻点区范围内,Nusselt数较无磁场作用时增大,传热得到比较明显的增强,而在壁面射流区,这种强化传热效果逐渐减弱。此外,当Reynolds数Re一定时,熔盐Nusselt数随着磁场强度的增加而增大,且驻点处强化传热效果最为显著。在Reynolds数Re=6400与磁场强度B=2800 Gs条件下,熔盐驻点Nusselt数Nu₀提高约6％,可见磁场作用对熔盐射流冲击传热具有一定的强化效果。     

Influence of magnetic field on jet impingement heat transfer with molten salt

Experimental study of jet impingement heat transfer with molten salt under the influence of external constant magnetic field was generated by permanent magnets. Both stagnation correlation and radial distribution of Nusselt number under magnetic field were obtained. The results showed that the Nusselt number with magnetic field became higher than that without magnetic field at stagnation region and jet impingement heat transfer was comparatively enhanced, while in wall jet region, the enhancement of heat transfer was gradually weakened. In addition, when the Reynolds number was constant, the Nusselt number of molten salt increased with increasing of the intensity of magnetic field, and the most enhanced heat transfer existed at the stagnation point. Under the conditions of Reynolds number Re=6400 and the intensity of magnetic field B=2800 Gs, the stagnation Nusselt number of molten salt was about 6 % higher than that without magnetic field. It can be seen that the magnetic field may promote the jet impingement heat transfer of molten salt.     

超亲水表面上滞止区水喷流沸腾的临界热通量

引言二氧化钛(TiO2)作为一种光催化剂,由于其独特的特性近年来引起了人们的重视.研究者发现,TiO2有着极其特殊的超亲水特性[1].当具有TiO2涂层的表面受到紫外线的辐射时,水在其表面的接触角会一直减小,最后接近于0°.对于水沸腾这类有气液相变现象的传热过程来说,这一特性有着重要的应用价值.利用超亲水传热表面,相变传热过程可以被大大强化.高温壁面上液体喷流和钢铁工业中应用十分广泛的一种高效方法.有关滞止区内喷流沸腾的研究,以往主要集中在对沸腾区域内非稳态换热特性的研究上,而对滞止区内喷流沸腾的稳态实验研究则很少[2～4].最…     

Ag纳米流体浸没射流冲击换热特性

采用超声膜扩散法一步制备出水基Ag纳米流体作为实验工质,并对不同质量分数的Ag纳米流体在受限浸没阵列射流冲击针肋热沉中的流动和换热特性进行了实验研究.结果表明:采用超声膜扩散法制备的Ag纳米颗粒粒径分布均匀,平均粒径只有4.8 nm;表面活性剂对纳米流体的黏度影响较大;相同射流速度下,与基液(水+表面活性剂)相比,Ag...     

空化水射流喷嘴设计与模拟分析

结合相关资料设计一款空化喷嘴,并运用有限元分析软件,对空化喷嘴进行流体分析,最终通过试验检测空化喷嘴和普通喷嘴之间清洗能力的不同。     

CFD study of turbulent jet impingement on curved surface

The heat transfer and flow characteristics of air jet impingement on a curved surface are investigated with computational fluid dynamics(CFD)approach.The first applied model is a one-equation SGS model for large eddy simulation(LES)and the second one is the SST-SAS hybrid RANS-LES.These models are utilized to study the flow physics in impinging process on a curved surface for different jet-to-surface(h/B)distances at two Reynolds numbers namely,2960 and 4740 based on the jet exit velocity(U_e)and the hydraulic diameter(2B).The predictions are compared with the experimental data in the literature and also the results from RANS k-εmodel.Comparisons show that both models can produce relatively good results.However,one-equation model(OEM)produced more accurate results especially at impingement region at lower jet-to-surface distances.In terms of heat transfer,the OEM also predicted better at different jet-to-surface spacings.It is also observed that both models show similar performance at higher h/B ratios.     

Ceiling heat transfer during fire plume and fire impingement

The impingement of turbulent fires and fire plumes on a horizontal ceiling was considered. Free flame heights, impinging flame lengths along the ceiling and ceiling heat fluxes were measured for both unconfined and confined ceilings. The study was limited to the initial stage of ceiling heating by fire under conditions where convection dominates the flow. Fire sources were simulated by burning liquid methanol, ethanol, 1-propanol or n-pentane from the top surface of a cylindrical wick. Test variables include fire heat release rate of 50–7890 W, ceiling diameters of 610 and 660 mm, ceiling heights of 58–940 mm, wick diameters of 10–107 mm and curtain wall lengths (for confined ceilings) as large as the ceiling height. Simplified models were employed to suggest expressions for data correlation. Flame lengths increased up to 40% when the ceiling was confined. Ceiling heat fluxes were relatively independent of position in the stagnation region (radius along ceiling <20% of the ceiling height). Heat fluxes in the stagnation region for plumes were 25–40% of those measured for impinging jets at comparable conditions. In the ceiling jet region, at larger distances from the point of impingement, the heat flux decreased with increasing radius, in agreement with other studies. Confinement tended to increase ceiling heat fluxes in both regions. Ceiling heat fluxes for impinging flames and plumes were approximately the same, for flame lengths along the ceiling up to 25% of the ceiling height; however, stagnation point heat fluxes decreased for longer flame lengths.