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基于已知的2087组水的过冷流动沸腾传热实验数据,通过努塞尔数(Nu)和格拉晓夫数(Gr)的关系探讨了不同流动方向和加热方式下浮升力对过冷流动沸腾传热性能的影响。对上壁面单边加热水平矩形管内过冷流动沸腾传热进行了实验研究。实验结果表明,向上的浮升力阻碍了气泡向流体中的扩散,使得传热恶化。在增加流速、增大压力和减小过冷度的条件下,Nu均随Gr增加,使过冷流动沸腾传热得到强化。 相似文献
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《工程热物理学报》2021,42(7):1784-1790
基于遗传算法构建了沸腾过程中加热固壁一维瞬态导热反问题计算方法,采用具有精确解的半无限瞬态导热问题构造了一个校核算例,验证了该算法具有较高的准确度和抗干扰能力,能够准确反演计算沸腾传热瞬态热流密度。基于该算法分析了 SOBER-SJ10地面和空间实验中沸腾传热特性,结果表明微重力环境中单相传热被严重抑制,热流密度远小于地面数值;不同重力条件下核态沸腾传热曲线落在同一位置,显示出低热流密度时核态沸腾传热具有某种重力无关特征;但微重力条件下核态沸腾曲线起始于远低于地面的热流密度,同时在远比地面小的热流密度值时达到临界热流状态,并转变为过渡沸腾模式。 相似文献
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对不同超声强度和辐射距离条件下过冷池沸腾换热特性进行了实验研究.超声波有效强化了沸腾起始段换热,对高热流密度沸腾传热也有一定的强化作用.超声辐射距离越近,强度越大,强化传热效果越好.对单相对流和沸腾起始区传热,超声波强化传热机理为空化作用;高热流密度沸腾时超声波对强化传热的主要机理是声流作用.得到了传热实验关联式. 相似文献
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Countercurrent flooding data have been obtained using air and water for vertical-to-downwardly inclined pipes containing elbows of varying angles. Experiments were performed with six different test sections, all having an inner diameter of 51 mm and a 1-m-tong vertical tube connected to an inclined or horizontal tube The flooding data for 112.5° and 135° elbow angles were almost identical and showed that these geometries required the largest gas flow rates for flooding among all the geometries tested. The flooding gas velocities for the 157.5° elbow were slightly less than those of the 112.5° and 135° elbows but greater than those of the vertical pipe without any elbow and vertical-to-horizontal pipes at low to moderate liquid flow rates In all vertical-to-inclined pipes, flooding was initiated in the inclined section at about 15 to 50 cm downstream of the elbow. Due to the countercurrent flow of gas, the liquid stream just downstream of the elbow became highly agitated and a frothy mixture was carried upstream by gas at flooding. At moderate to high liquid flow rates, the liquid was deflected off at the elbow to form a turbulent, jetlike stream that partially broke up into droplets, These droplets were, at the onset of flooding, entrained and carried over by the gas stream Comparison of the data with the slugging correlation at low liquid flow rates and with the liquid entrainment/carryover model at high liquid flow rates suggested that these mechanisms are likely responsible for flooding in vertical-to-inclined pipes. 相似文献
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本文应用近似解析方法对双组分混合液在竖直平壁上的膜态沸腾换热进行了理论分析,得到了其平均膜态换热系数的解析计算式,并通过三种典型的双组分混合液例证了传质过程对换热的影响。 相似文献
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The nucleate pool boiling heat transfer data on a smooth flat surface were measured for three binary mixtures of HC600a/HFC134a, HC600a/HC290, and HC600a/HFC23. Much effort was made to investigate the influence of the boiling range on the pool-boiling heat transfer performance. From the experimental results, the HC600a/HFC23 mixture with a wide boiling range showed lower heat transfer coefficients (HTCs) than the mixture with a narrow boiling range such as HC600a/HFC134a and HC600a/HC290 systems. The measured data were also compared with the results predicted by five well-known correlations. It can be found that the average deviation is less than 25% for mixtures with narrow boiling ranges, but a larger deviation for mixtures with wide boiling ranges. 相似文献
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A. R. Pati 《实验传热》2019,32(2):116-132
The significant reduction of Leidenfrost effect during the cooling of high carbon steel plate by different potential cooling methodologies does not assure their successful implementation in the fast quenching of high carbon steel plate due to the formation of oxide layer of comparatively low thermal conductivity on the quenching surface. Therefore, the role of oxide layer in case of different potential cooling methodologies needs to be addressed. In the present study, the effect of oxide layer on heat transfer rate in case of upward, downward, and both upward and downward facing spray with additives has been investigated by conducting and comparing the heat transfer cooling data of an AISI 1020 plate with the AISI 304 plate. The comparison clearly depicts that the formation of oxide layer during cooling significantly hinders the heat transfer rate in nucleate boiling regime; however, the reverse phenomenon is observed in transition boiling regime. Among all the coolants, the least effect of oxide layer on enhancement is obtained in case of NaCl (0.4 M)-added water spray due to the deposition of salt on the evaporating surface. The X-ray diffraction analysis and the thickness of the formed oxide layer clearly assert that the coolant depicting minimum oxidation characteristic is preferred.
Abbreviations: AISI: American iron and steel institute; OES: Optical emission spectrophotometer; CHF: Critical heat flux, MW/m2; IHF: Initial heat flux, MW/m2; TCHF: Temperature at which CHF is achieved, °C; Fps: Frames per second; XRD: X-Ray diffraction; k1: Thermal conductivity of steel plate, W/m °C; k2: Thermal conductivity of oxide layer, W/m °C; k3: Thermal conductivity of coolant, W/m °C; X: x-axis, mm; Y: y-axis, mm; Z: z-axis, mm 相似文献
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PTFE疏水修饰法消除多孔表面的沸腾迟滞现象 总被引:1,自引:0,他引:1
微纳多孔结构表面在提高沸腾传热性能的同时,通常也会伴随着沸腾迟滞现象出现.以底部树林状阵列结构、上部蜂窝状微纳双尺度多孔结构为基础的双层多孔表面在展示出良好性能的同时,也出现了沸腾迟滞现象。本文通过电泳沉积PTFE修饰的方法,降低多孔表面成核壁面过热度,从而基本消除双层多孔表面的沸腾迟滞效应。另外,修饰后的双层多孔表面的CHF和最大HTC与未修饰的双层多孔表面相比提高了20%和19%;和光滑铜表面相比,CHF提高了97%,HTC提高了400%,展现出优异的沸腾传热性能. 相似文献
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