共查询到17条相似文献,搜索用时 125 毫秒
1.
本文严格按照实验程序,系统地研究了核沸腾传热受射流速度大小、液体流动方向、喷嘴直径和液体过冷度等因素的影响。实验结果表明:核沸腾传热曲线随过冷度增加而向左移动,与其它因素无关。池核沸腾和冲击核沸腾曲线可用同一关联式表达。对高速射流冲击驻点的核沸腾曲线及其过冷度进行了修正,使前者向左移动,而后者增加。 相似文献
2.
3.
本文对高温平板滞止区内三种过冷液体的圆形喷流冲击沸腾的临界热流密度进行了系统的稳态实验研究。考察了过冷度、流速、喷流直径等流动条件对喷流沸腾临界热流密度的影响。建立了预示液体临界热流密度的半经验型方程。 相似文献
4.
一、引言 受迫流动沸腾传热不仅受流动参数的影响,还受相际分布及流型变化等影响。Nelson等较新研究表明:与池沸腾相比,受迫流动沸腾不存在单一的沸腾曲线,过渡沸腾的变化规律尤其复杂,还会受过冷度的影响。涉及过渡沸腾的分析资料很少见诸报道,过冷液体流动过渡沸腾更少见。 相似文献
5.
目前还没有一种被广泛承认的理论能够解释高压过冷池沸腾换热,其机理尚不明确。为了揭示高压池内过冷核沸腾的物理传热机理,并获得气泡脱离频率与活化穴半径的函数关系,根据池内过冷核沸腾加热表面活化穴的分布,在统计方法的基础上,提出了高压池内过冷核沸腾的一个数学模型。从该模型中发现,池内过冷核沸腾热流密度是壁面过热度、液体过冷度、活化穴尺寸、流体的接触角以及流体物理特性的函数。对不同的过冷度,将模型预测的结果与实验数据进行了比较,两者吻合得极好,从而证明了数学模型的可靠性。该解析模型更深刻地揭示了过冷池沸腾换热的物理机理,且没有增加新的经验常数。 相似文献
6.
7.
过冷液体沿水平板受迫湍流时的膜沸腾传热 总被引:1,自引:0,他引:1
本文在前文分析的基础上,提出过冷液体沿水平板受迫湍流时膜沸腾传热的物理模型,建立起相应的数学模拟方法,对轸高流速和过冷度的平板湍流膜沸腾传热作了理论分析,并根据实验数据得到了可供实际工程应用的半经验传热计算式。 相似文献
8.
本文推导了包括饱和与高过冷两种极端情况的液体流动膜沸腾传热的统一半经验表达式,对过冷度的影响作了深入分析,根据特征参数Ja_2将过冷度影响按物理机制划分为三个区域,已为R11的实验数据所直接验证。 相似文献
9.
10.
11.
Results of experimental studies on dynamics of explosive boiling and third heat transfer crisis under the conditions of liquid subcooling are presented for the vertical arrangement of the heat-transfer surface. Acetone was used in experiments at the pressure in the working volume from 20 to 46 kPa and subcooling from 0 to 20 K. The studied processes were recorded. Data on the velocity of evaporation front propagation at liquid subcooling were obtained. These data are compared with the results of calculations according to the models available in the literature. The effect of liquid subcooling on the regions of regime parameters corresponding to explosive boiling and third heat transfer crisis is studied. 相似文献
12.
A. N. Pavlenko E. A. Tairov V. E. Zhukov A. A. Levin A. N. Tsoi 《Journal of Engineering Thermophysics》2011,20(4):380-406
The paper presents results on experimentally investigated dynamics of boiling development and formation of film boiling zones
under stepwise heat generation on a horizontally and vertically oriented cylindrical surface in a large volume of Freon-21.
Experimental data on the expectation time and boiling temperature, the propagation velocity and structure of evaporation and
boiling fronts for different heat flux density both in saturated liquid and in subcooling conditions are obtained. Results
of experiments on investigating the nucleation forms under development of nonstationary heat release crisis caused by heat
loading on the vertical heater immersed into the volume of liquid (water, ethanol) subcooled to saturation temperature are
presented. A calculation ratio for determining the expectation time to the beginning of intense vaporization in water is proposed
and compared with experimental data obtained on surfaces with different-size roughness. Peculiarities of evolution of evaporation
fronts from incipient bubbles are investigated in the experiments with ethanol. Data on the evaporation front velocity as
a function of wall overheating are obtained. The obtained experimental data on the propagation velocity of self-sustained
evaporation fronts are compared with the known calculated data. 相似文献
13.
14.
Pool boiling heat transfer and quench front propagation were investigated during quenching of cylindrical stainless steel rodlets in subcooled water. The degree of subcooling was varied from 0°C (saturated) to 40°C at an increment of 10°C at atmospheric pressure. The results showed that the increase of degree of subcooling accelerates quenching, with the total quenching time being shortened from 90 second (saturated) to 12 second (subcooled by 40°C). As revealed by the boiling curves that were obtained via solving an inverse heat conduction problem in cylindrical coordinates, boiling heat transfer is enhanced significantly for all boiling modes with raising the degree of subcooling. At the highest degree of subcooling of 40°C, the critical heat flux is improved by nearly 300% as compared to that in saturated water. In addition, the rewetting temperature (i.e., Leidenfrost point) was found to increase as a nearly linear function of the degree of subcooling. The quench front was observed to propagate upward from the bottom of the rodlet, which is accelerated noticeably with increasing the degree of subcooling. The average quench front velocity was shown to agree well with the predicted value of an existing theoretical model that was modified to take the influence of subcooling into consideration. 相似文献
15.
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
16.
17.
The effect of liquid subcooling below the saturation temperature on the third heat transfer crisis was studied experimentally
at pool boiling. Experimental data on the threshold values of superheating and heat fluxes, above which the evaporation front
and third heat transfer crisis for acetone at subcooling from 0.3 to 10 K are formed, were shown. Formation of evaporation
fronts is the necessary, but not sufficient condition for the third heat transfer crisis at subcooling. It was found that
formation of a stable vapor film after propagation of condensation fronts over the heater surface is possible at heat fluxes
considerably lower than the first critical one. 相似文献