共查询到20条相似文献,搜索用时 187 毫秒
1.
2.
3.
以水蒸气为工质,实验研究了水平管内纯蒸汽冷凝的局部换热特性。实验选取换热管内径为25 mm、换热管进口压力为0.15~0.4 MPa、局部蒸汽的Re=5756~92289,分析了蒸汽压力及流速、壁面过冷度对冷凝传热系数的影响,并将采用现有关系式计算的冷凝传热系数与实验结果进行了对比。结果表明:冷凝传热系数随壁面过冷度的增大而减小,随压力的升高和流速的增大而增大;采用现有关系式计算的冷凝传热系数与实验值的偏差较大,关系式有待进一步改进;在实验范围内,由拟合换热关系式计算所得冷凝传热系数与实验结果的相对偏差在15%左右。 相似文献
4.
5.
在垂直环形窄缝流道中的沸腾传热特性研究 总被引:5,自引:0,他引:5
为了弄清在窄缝环形流道中气泡的形成、聚合和变形的特性 ,以及气泡在聚合变形之后对传热特性的影响 ,在常压下用蒸馏水对窄缝间隙为 0 75mm的垂直环形流道 ,进行了可视化的流动沸腾传热实验研究 ;实验段的有效加热长度为 90 0mm ,其加热方式为单面内侧加热 ,实验的流量变化范围为 1 667× 1 0 - 5m3/s至 5 833× 1 0 - 5m3/s。实验得到了在不同质量流密度和热流密度下窄缝流道中的沸腾传热系数随干度变化的分布。通过与常规流道中的沸腾传热系数的比较 ,得到了在窄缝环形流道中沸腾传热系数比常规流道中的沸腾传热系数约高 1 5 %的结论。另外通过用高速摄像机对可视化的垂直环形流道中的流型进行的拍摄研究 ,分清了存在在窄缝环形流道中的四种流型 相似文献
6.
《核动力工程》2016,(4):6-10
采用竖直窄缝通道内功率阶跃分布下的临界试验结果对非均匀加热临界预测模型进行验证。模型所预测临界触发位置、临界热流密度(CHF)及临界对应平均热流密度与试验结果的偏差均在合理范围内。采用该非均匀加热临界预测模型开展功率阶跃下CHF的数值计算,分析阶跃功率比、阶跃长度以及阶跃位置对沸腾临界的影响:随阶跃功率比的增大,CHF基本呈线性增大,但临界触发时的平均热流密度逐渐降低;阶跃长度的增大使得CHF逐渐减小,同时触发时的平均热流密度逐渐逼近均匀加热下的CHF值;随临界触发区域向流道上游迁移,临界触发位置将脱离功率阶跃区域的后端迁移至流道出口,此时的CHF值及临界触发时的平均热流密度值均趋近于均匀加热下的CHF值。 相似文献
7.
卧式螺旋管内流动沸腾传热研究 总被引:8,自引:0,他引:8
在较宽广的参数范围内对卧式螺旋管内水/水蒸汽两相流沸腾传热特性进行了详细的试验研究,螺旋管内径d=11mm,曲率直径比D/d为23.27。试验参数范围:压力0.5-3.0MPa:质量流速200-2500kg/m2·s;热负荷230-500kW/m2:出口干度0-0.86。得到了沸腾传热系数的实验关联式,并深入分析了局部传热与壁温特性,沿流动方向,管截面平均传热系数在螺旋管的上升段最大,而在下降段最小;沿管截面内表面圆周方向上,局部传热系数在外侧最大,在内侧最小,在顶部和底部处的值居中。得到了管截面局部传热系数的分布实验关联式。同一管截面外表面圆周方向上,外侧壁温最低而内侧最高。 相似文献
8.
9.
10.
三角形子通道超临界水热工水力特性数值分析 总被引:1,自引:1,他引:0
目前国际上对超临界水冷堆进行了大量的研究,但对其堆芯内超临界流体流动传热的认识还十分有限.本文采用CFX对超临界水冷堆典型三角形子通道内的流动传热特征进行了CFD研究,对比分析了包壳壁面等热流密度和燃料芯块等体积热流密度两种情况.计算结果表明,不锈钢包壳层的周向导热显著强化了燃料棒圆周上温度分布和传热系数的均匀性,但对二次流和湍流脉动的影响不大.间隙区的湍流脉动主要受几何参数P/D的影响,当P/D<1.3时,湍流交混系数在0.02~0.025之间,当P/D>1.3时,湍流交混系数较小,在温度拟临界点附近区域,存在交混系数的突变. 相似文献
11.
高温熔盐在熔盐堆和太阳能等能源领域有广泛的应用前景。为研究熔盐在强化换热管中的强化传热效果,本文基于三元硝酸盐KNO_3-NaNO_2-NaNO_3(摩尔分数比为53%-40%-7%)与导热油的对流传热实验装置,根据相似理论使用导热油代替熔盐,对翅片换热管湍流区的对流传热特性开展了测量,流体雷诺数(Re)变化范围10 000-60 000。通过威尔逊分离法获得翅片管中湍流区的对流传热系数(ho)和努赛尔数(Nu),基于实验数据与Dittus-Boelter公式,拟合翅片管湍流区的对流传热关联式,实验数据与拟合公式的误差在-7.1%-7.5%之间。与传统对流传热关联式Dittus-Boelter公式对比进行强化传热效果评估,结果表明,翅片管的强化传热效果为光滑管的2.32-3.63倍。 相似文献
12.
管内覆丝网强化对流换热及阻力特性的实验研究 总被引:1,自引:1,他引:0
通过实验对管内覆丝网管进行了强迫对流换热和阻力特性研究。结果表明:管内覆丝网使换热明显增强,阻力也相应增长。菱形丝网对角线距离与平行边距离之比对换热效果有决定作用,丝网厚度对换热的影响比较小,而丝网网格的大小对换热几乎没有影响,在相同的泵功率和几何条件下,换热系数最大增加21%。 相似文献
13.
14.
15.
采用STAR-CCM+软件对管束条件下含空气蒸汽冷凝开展了数值模拟研究。主要考察了3×3管束、管间距为2倍管径条件下不同传热管的局部场分布和流动传热特性。结果表明,在管束条件下,各传热管附近的空气层发生了重叠,形成了高空气浓度区。这一方面促进了气体的自然对流,提高了对流传热能力;另一方面增加了空气层厚度,抑制了冷凝传热。在管束结构的影响下,管束区域的浓度、温度和速度梯度均较单管有明显的差异,导致各传热管的局部传热系数沿轴向降低了50%以上,周向传热系数最大相差1.88倍。其中,轴向传热性能主要受浓度边界层发展的影响,周向传热性能主要受相邻传热管的影响。通过分析表面平均传热系数发现,各传热管较单管最大降低了9.06%。 相似文献
16.
17.
在自主研发的事故分析程序SCTRAN的基础上,开发并验证了二维导热模型和辐射换热模型,并将改进后的SCTRAN应用于加拿大压力管式超临界水堆在失水事故(LOCA)叠加丧失紧急堆芯冷却系统(LOECC)事故中的堆芯安全评估,并对燃料棒到慢化剂之间的传热效率以及关键的影响因素进行了评估。计算结果表明,在LOCA叠加LOECC工况下,燃料棒到燃料通道的辐射换热和燃料棒到蒸汽的自然对流换热能够有效导出反应堆的衰变余热,最高功率的燃料组件内、外圈燃料棒的最高包壳温度分别为1278℃和1192℃,均低于不锈钢包壳的熔化温度,因此整个事故过程中不会发生堆芯熔化。 相似文献
18.
A numerical solution for laminar flow heat transfer between a flowing gas and its containing rectangular duct has been obtained for many different boundary conditions which may arise in nuclear waste repository ventilation corridors. The problem has been solved for the cases of insulation on no walls, one wall, two walls, and three walls with various finite resistances on the remaining walls. Simplifications are made to decouple the convective heat transfer problem from the far field conduction problem, but peripheral conduction is retained. Results have been obtained for several duct aspect ratios in the thermal entrance and in the fully developed regions, including the constant temperature cases. When one wall is insulated and the other three are at constant temperature, the maximum temperature occurs in the fluid rather than on the insulated wall. This maximum moves toward the insulated wall with increasing axial distance. Nusselt numbers for the same constant flux on all four walls with peripheral conduction lie in a narrow band bounded by zero and infinite peripheral conduction cases. A dimensionless wall conduction group of four can be considered infinite for the purpose of estimating fully developed Nusselt numbers to within an accuracy of 3%. A decrease in wall and bulk temperatures by finite wall conduction has been demonstrated for the case of a black body radiation boundary condition. Nusselt numbers for the case of constant temperature on the top and bottom walls and constant heat flux on the side walls exhibited unexpected behavior. 相似文献
19.
The maximum heat flux which can be handled by water-cooled grid tubes is evaluated for different design and heat transfer constraints. The maximum allowable heat flux is usually found to be limited by the allowable thermal deformations of the grids for nonuniform heating around the circumference of the tube. Detailed results for a grid geometry specifically designed to give very small thermal deformations are presented. 相似文献
20.
Taisuke Yonomoto Yasuteru Sibamoto Akira Satou Yuria Okagaki 《Journal of Nuclear Science and Technology》2016,53(9):1342-1352
Our previous study investigated the rewetting behavior of dryout fuel surface during transients beyond anticipated operational occurrences for BWRs, which indicated the rewetting velocity was significantly affected by the precursory cooling defined as cooling immediately before rewetting. This study further investigated the previous experiments by conducting additional experimental and numerical heat conduction analyses to characterize the precursory cooling. For the characterization, the precursory cooling was first defined quantitatively based on evaluated heat transfer rates; the rewetting velocity was investigated as a function of the cladding temperature immediately before the onset of the precursory cooling. The results indicated that the propagation velocity appeared to be limited by the maximum heat transfer rate near the rewetting front. This limitation was consistent with results of the heat conduction analysis using heat transfer models for the precursory cooling expressed as a function of distance from the rewetting front, the maximum wetting temperature, and the heat transfer coefficients in the wetted region. This paper also discusses uncertainties in the evaluation of transient heat flux from the measured surface temperature, and technical issues requiring further investigation. 相似文献