共查询到20条相似文献,搜索用时 15 毫秒
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《Journal of Nuclear Science and Technology》2013,50(11):468-475
This paper deals with an analysis of heat transfer by slug flow in an annulus with different heat fluxes at the two wall surfaces. The local Nusselt numbers at each wall surface are calculated upon analyzing the radial distribution of the fluid temperature. The local Nusselt number varies with the ratios of the radii as well as of the wall heat fluxes. The heat transfer in a circular tube and between two parallel plates are also discussed. As a special case, the present results agree very well with Dwyer's obtained for the heat transfer between two wall surfaces. 相似文献
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《Journal of Nuclear Science and Technology》2013,50(7):411-418
An experiment on the direct heat transfer process between supersonic steam and subcooled water jet was performed, using a steam-water condensing-injector. Photographic observation provided information on the state of flow, and establishment of a critical separate steam-water flow was confirmed. The temperature and pressure distributions along the flow were measured and the effective coefficients of condensing heat transfer were evaluated from the observed data, based on a model embodying an idealized interface between vapor and liquid. In the vicinity of the water nozzle exit, where the vapor-liquid interface was distinct, the heat transfer coefficients obtained were 14–28 (cal/°C.cm2.sec), and some correlation was observed among Nusselt, Reynolds and Jakob numbers, upon adopting the velocity and the physical properties of the steam phase. The relations Nu=6.0.Re 0.9(Pr=1.04–1.10), and Re=1.8×108.Ja 3.0, i.e., Nu=1.6×108.Ja 2.7 were derived as a rough estimation. No clear correlation could be discerned in the corresponding data obtained from observation points further downstream, where a distinct steam-water interface no longer existed. In conclusion, it is proposed that, in deriving the correlations between Nu and Re or Ja, the physical properties of the vapor and the vapor-liquid relative velocity should be adopted, on account of the strong dependence of condensing heat transfer on steam velocity and water subcooling. 相似文献
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《Journal of Nuclear Science and Technology》2013,50(11):479-485
This paper deals with an analysis of heat transfer in laminar flow with uniform internal heat generation in a concentric annulus with uniform but different heat fluxes at the two wall surfaces. The Nusselt numbers at each wall surface are calculated upon analyzing the radial distribution of the fluid temperature. It is shown that the Nusselt numbers are affected by the ratios of the radii as well as of the wall heat fluxes, and also by the internal heat generation. As a special case, the analytical results of heat transfer in the absence of internal heat generation are compared with Dwyer's and Lundberg, et al.'s theories. 相似文献
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《Journal of Nuclear Science and Technology》2013,50(12):965-984
A heat transfer experiment was performed on steam-water two-phase flow in an annular flow path with a uniformly heated rod under the conditions of the mass flow rates from 0.2xlO6 to l.Ox 106 kg/m2-h, inlet qualities from 0.5 to 1.0, heat fluxes below 4.7x 105 W/m2 and pressure of 31 bar. Dryout of the heater rod surface was observed resulting in the sharp rise of the heater rod surface temperature. Measured heat transfer coefficients were compared with the several empirical and semi-empirical correlations with the emphasis on the applicability of the correlations to the present test conditions being important in the analysis of the thermal hydraulic behavior during a LOCA of a nuclear reactor. The measured heat transfer coefficient in the pre-dryout region is lower than the existing correlations. The cooling of the heat transfer surface by the liquid phase in the post-dryout region is significant, which is neglected in the existing correlations. The heat transfer coefficients calculated for the post-dryout region by the Groeneveld correlation show good agreement with the presently measured results within the accuracy of 0~27%. 相似文献
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垂直上升圆环形通道内超临界压力水的传热特性 总被引:1,自引:0,他引:1
在压力P=23~28 MPa、质量流速G=350~1000 kg/(m2.s)、外壁面热流密度q=200~1000 kW/m2的试验参数范围内,对垂直上升圆环形通道内超临界压力水的传热特性进行试验研究。分析q、P、G、螺旋绕丝对传热特性的影响,比较有、无绕丝结构时出现的两种传热恶化。试验结果表明:提高G或降低q都可以强化超临界水的传热;在不同的传热类型下,P对传热特性有不同的影响;螺旋绕丝具有很好的局部强化传热作用,并且可以推迟在高热流密度、低质量流速下发生的传热恶化。 相似文献
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在窄缝流道内发生沸腾换热现象时,由于沸腾产生的汽泡受窄缝流道的限制,受压变形而消除了汽泡表面张力对传热的影响。因此对此现象进行基础性理论研究具有很重要的意义。本文在常压下用蒸馏水对窄缝间隙为 0.75mm的垂直环形流道,进行了流动沸腾传热实验研究。实验段的有效加热长度为 900mm,其加热方式为内外侧双面加热,实验的流量变化范围在 1.67× 10- 5~ 5.83× 10- 5m3/s。通过实验得到了在不同质量流速和热流密度下双面加热的窄缝流道中内外侧沸腾换热系数随干度变化的分布和特点。研究结果表明,由于在窄缝流道中存在着大量的运动聚合受压变形汽泡,因此使内外侧沸腾换热系数都很高 (可达 105W· m- 2· K- 1以上 )。 相似文献
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《Journal of Nuclear Science and Technology》2013,50(9):476-484
This paper deals with the problem of heat transfer in fully developed turbulent flow with uniform internal heat generation in a concentric annulus under conditions of uniform but different heat fluxes at the two wall surfaces. The Nusselt numbers at each wall surface are calculated by analyzing the radial distribution of the fluid temperature. We further derive approximate equations, which are found to represent very well the analytical results. The Nusselt numbers vary with the ratios of the radii of annular space as well as of the wall heat fluxes, as also with internal that generation. These predictions agree well with available experimental data for various fluids. 相似文献
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《Journal of Nuclear Science and Technology》2013,50(1):26-33
The previous paper(1) dealt with the problem of fully developed heat transfer in a turbulent flow with uniform internal heat generation in a concentric annulus under conditions of uniform but different heat fluxes at the two wall surfaces. This sequel presents analyses of the heat transfer problem in the thermal entrance region. First, a graphical representation is given of the variations of Nusselt number at each wall surface with distance along the passage. Second, these fundamental solutions for uniform internal heat generation and uniform wall heat fluxes are applied to the case of arbitrary variations of internal heat generation and wall heat flux along the axial direction. 相似文献
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《Journal of Nuclear Science and Technology》2013,50(2):82-91
This paper deals with an analysis of flow characteristics and heat transfer of a Bingham plastic fluid in laminar flow through concentric annuli. The friction factor obtained for a given Hedström number in fully established flow varies with the radius ratios of the annular space and of the bounds of the plug region. The Nusselt numbers at the two wall surfaces in both fully developed and thermal entrance regions are calculated under the conditions of uniform internal heat generation and uniform but mutually differing heat fluxes at the two wall surfaces. Analytical results show that the Nusselt numbers become negative or infinite under certain thermal conditions at the walls. 相似文献
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采用高雷诺数(Re)k-ε模型与壁面函数法对液态金属钠在环管中湍流流动传热特性进行计算,并与实验结果进行比较,结果表明计算值与实验结果符合较好。应用该方法研究湍流程度、加热条件、几何条件等因素对液态金属钠在环管中湍流传热特性的影响。研究表明,湍流程度对传热的影响主要集中在流道前半段,后半段分子扩散对传热的影响逐渐凸现出来,使不同湍流程度下传热特性的区别逐渐缩小;初始温度与加热热流密度对传热特性无明显影响;环管间隙增大,湍流传热效果增强,同等间隙时管径变化对传热特性无明显影响。 相似文献
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以去离子水为工质的高温流体 ,由下向上流过电加热内、外管壁间的环形狭缝 ,对同心竖直环形狭缝进行了干涸后换热试验研究。试验结果表明 :环形缝隙中的干涸后换热 ,与普通环形通道中的换热有着明显不同。试验中发现在相同热流密度下内管换热能力大于外管。应用Groeneveld公式 ,拟给出适合试验数据的换热公式。在试验的基础上 ,对内外管中较大的热流密度 ,与内外管热流密度的平均值的比值建立变量 ,并应用多元线性回归方法 ,建立了适合工程实际应用的环形狭缝通道干涸后传热计算经验关联式。 相似文献
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《Journal of Nuclear Science and Technology》2013,50(4):207-214
The heat transfer characteristics of non-concentric annuli with various eccentricities and also of a seven-rod cluster were experimentally determined by means of mass transfer technique. A coating of naphthalene was applied to the surface of the test rod and changes in its thickness measured. The mass transfer coefficients have been represented in terms of Colburn's j-factor, with which both the average and local values were analyzed. The measured average heat transfer j-factors were found to be in part equal to those for smooth round ducts, but the circumferential variations of the local factors for the eccentric annulus did not agree with the theoretical prediction proposed by Dwyer & Yu. The existence of secondary flow in the seven-rod cluster is also discussed. 相似文献