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):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(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(11):590-595
This paper deals with heat transfer in a fluid, with uniformly distributed internal heat source, flowing upwards through a vertical tube. Measurements were made of the temperature distribution in both laminar and turbulent flow, and both with and without heat transfer at wall. Heat generation within the fluid was brought about by passing an electrical current through the working fluid, which was an aqueous solution of sodium chloride. The experimental results were compared with analytical calculations. Free convection, which occurs and is superimposed on the movement by forced convection, flattens the fluid temperature distribution in laminar flow through thermally insulated vertical tube. In turbulent flow with heat transfer to wall, the temperature distribution near the wall is affected considerably by the outgoing heat flux. 相似文献
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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):400-405
The heat transfer coefficient and slow burnout heat flux were measured for a stream-water annular dispersed upward flow under pressures up to 3.5 ata in an electrically heated vertical annular channel. An empirical equation was derived for the heat transfer coefficient as function of mass flow rate, steam quality and heat flux. The dominant mechanism of heat transfer to the annular dispersed two-phase flow is forced convection of liquid film on the heater surface even in the region of low steam quality (down to about 0.03). The observed slow burnout heat flux was near the point of intersection of the lines representing liquid film forced convective heat transfer and nucleate boiling heat transfer on the q vs. δT sat diagram. A dryout mechanism is proposed in which increasingly violent evaporation comes to impede the rewetting of the dry patches generated on the heater surface, which thus spread to cover the whole surface. A maximum value is observed in the slow burnout heat flux plotted against exit steam quality. This can be explained as the effect of heat removal by droplet exchange between liquid film and steam flow. 相似文献
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《Journal of Nuclear Science and Technology》2013,50(7):354-359
This paper deals with an analysis of the characteristics of fully developed turbulent Newtonian flow in a concentric annulus. The time-averaged velocity distribution, mixing length, eddy diffusivity and friction factor are calculated on the bases of Reichardt's expression for the eddy diffusivity of momentum and of Nikuradse's expression for the mixing length in a circular tube. These predictions agree well with available experimental data. 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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In this work, a magnetic fluid dynamics (MHD) model is used to simulate the electromagnetic field, heat transfer and fluid flow in a DC non-transferred arc plasma torch under laminar and turbulent conditions. The electric current density, temperature and velocity distributions in the torch are obtained through the coupled iterative calculation about the electromagnetic equations described in a magnetic vector potential format and the modified fluid dynamics equations. The fluid-solid coupled calculation method is applied to guarantee the continuity of the electric current and heat transfer at the interface between the electrodes and fluid. The predicted location of the anodic arc root attachment and the arc voltage of the torch are consistent with corresponding experimental results. Through a specific analysis of the influence of mass flow rates and electric current on the torch outlet parameters, the total thermal efficiency, thermal loss of each part, and the laws of the variation of outlet parameters with the variation of mass flow rates and electric current was obtained. It is found that operation under a laminar condition with a limited area of the anode could increase the total thermal efficiency of the torch. 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
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AP1000依托项目的热态功能试验中包括了非能动余热排出热交换器(PRHR HX)性能试验,在试验过程中会伴随着内置换料水箱(IRWST)内水的升温。本文针对PRHR HX性能试验中的自然循环工况,对IRWST升温过程进行PRHR HX自然循环下流动传热分析。通过分析获得了在PRHR HX自然循环试验工况下IRWST内各个监测点流体温度随时间的变化过程,及各个典型瞬态时刻下IRWST内典型流体截面的流场分布和温度场分布情况,同时将分析计算所获得的监测点温度值与现场实测值进行了对比验证,结果吻合较好,为热态调试提供了重要的技术支持。 相似文献