Heat Transfer in Laminar Flow with Internal Heat Generation in Concentric Annulus

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.     

Heat Transfer to Steam-Water Annular Dispersed Flow in Vertical Annulus

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.     

在双面加热的窄缝环形流道中流动沸腾换热研究

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 )。     

Heat Transfer in Turbulent Flow with Internal Heat Generation in Concentric Annulus*,(I)

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.     

Heat Transfer in Turbulent Flow with Internal Heat Generation in Concentric Annulus, (II)

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.     

Heat Transfer in Laminar Flow of Bingham Plastic Fluid with Internal Heat Generation in Concentric Annulus

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.     

Measurement of Heat Transfer Coefficients for Axial Air Flow through Eccentric Annulus and Seven-Rod Cluster

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.     

双侧加热窄环隙流道强迫对流换热

本文用一回路水对竖直窄环隙流道进行了双侧加热强迫对流换热实验，将双侧加热和单侧加热时的换热特性进行了对比分析。结果表明，双侧加热使流道内侧的换热得到加强，而外侧换热却受到削弱，具有与单侧加热时相似的变化规律，综合因素影响使换热量基本保持不变。     

窄环隙内单相对流换热的实验研究

鉴于流体在小尺度流道内流动换热时所表现出的特殊性 ,对水在竖直环隙内受迫流动时的单相对流换热特性进行了实验研究 ,两组实验件的环隙宽度分别为 0 9mm和 2 4mm。实验结果表明 ,窄环隙可以对单相对流换热起到强化作用 ,但较 2 4mm环隙而言 ,0 9mm环隙不但不能进一步强化换热 ,反而削弱了环隙的强化换热作用     

窄环隙流道强迫对流换热实验研究

在一回路水分别从内侧和外侧加热二回路水的条件下，进行了竖直窄环隙流道强迫对流换热实验。结果表明，窄隙流道具有强化和抑制换热的双重作用，其换热特性与微槽道非常相似，而与普通流道显著不同．没有明显的层流区、过渡区和紊流区换热之分。     

Heat Transfer in Turbulent Separated Flow

An investigation was carried out with the object of determining the physical effects of separation and the associated reattachment and redevelopment, upon the heat transfer characteristics of turbulent flow in pipes and to compare the results of these flow conditions with the fully developed one-dimensional condition and with a recently developed numerical technique for the solution of recirculating flows.

Separation of the flow was induced in a 4 ft length of 2 in. internal diameter nicrome tube of wall thickness 0.001 in. by means of a sudden enlargement of diameter at the entry of the tube. The tube was electrically heated by the passage of a current along its length. The first 25 in. of the tube was metered by thermocouples which gave the wall temperatures and from these the local heat transfer rates and Reynolds numbers up to 5×10⁴ using air as the working fluid.     

环形通道内液态金属钠流动换热特性实验研究

对液态金属钠在环形通道内的单相流动换热特性进行了实验研究。结合实验数据,将液态金属钠单相流动分为层流区(Re≤2 000)、过渡区(2 000Re≤4 000)及湍流区(Re4 000),分别拟合得到不同流态下摩擦系数的计算关系式,并拟合得到液态金属钠环形通道内换热特性的相应关系式。结果表明:液态金属钠单相流动特性与常规流体(如水)类似,其层流区摩擦系数略大于水,湍流区与水的很接近。液态金属钠对流换热过程中,导热项占较大份额,同时Nu随Pe的增大而略有增大。     

稠密栅元内湍流流体的流动传热

本文对稠密栅元内的湍流流动和传热特性进行了分析。首先利用实验数据对计算结果进行了验证,然后分析了Re和P/D等参数对稠密栅元内的摩擦阻力系数和传热系数的影响。Re和P/D均会对稠密栅元内的流动传热特性产生显著影响,但传统的理论模型无法描述P/D对栅元内的摩擦阻力系数和传热系数的影响。P/D=1.03是一临界点,这种条件下的稠密栅元内的流动和传热是最安全的,也是最高效的。此时核反应堆的功率和系统的传热能力可同时达到最大。     

Heat Transfer Analysis of a Condensate Flow by VOF Method

One of the interesting subjects in reactor design is about the condensate flow. In this investigation, turbulent film condensation on a horizontal elliptical tube is investigated using volume of fluid (VOF) method. Heat transfer after the separation point is considered. The turbulence model incorporated in this investigation is the realizable k-epsilon model. The results for circular tube are compared to that of other investigations available in the literatures. It is observed that an amount of approximately 11% decrease in the overall Nusselt number will happen for the elliptical tube with respect to a circular tube of the same area and the same approach velocity.     

基于四方程模型的LBE环管湍流换热数值研究

为计算液态铅铋（LBE）在环管内不同加热环境下的湍流换热,基于开源计算流体力学程序OpenFOAM开发了四方程模型求解器4eqnFoam。将LBE在平板和圆管内的预测结果与直接数值模拟结果和实验结果进行对比,验证了求解器的有效性。基于该求解器,分别计算了LBE在外壁绝热内壁加热以及内外壁面等热流加热环管内不同雷诺数下的湍流换热量。结果表明：随着雷诺数的增加,两种加热条件下的无量纲温度脉动、雷诺热流、湍流热扩散作用增大,而平均湍流普朗特数减小;当雷诺数增加到一定程度时,平均湍流普朗特数变化不明显。基于4eqnFoam求解器,可为计算LBE热工水力现象提供更多参考。     

环形窄缝双面加热通道内欠热沸腾传热实验研究

在压力0.84～6.09 MPa、质量流速41.9～300.2 kg/(m2·s)、热流密度2.61～114.41 kw/m2范围内,以去离子水为工质,对间隙为1.5 mm环形窄通道实验段竖直向上流动的欠热沸腾传热特性进行了实验研究,得出了适用环形窄缝通道的欠热沸腾传热经验关系式。     

复合换热管过冷沸腾换热实验与关联式评价

以去离子水为实验介质,在单面受热流密度条件下,开展了聚变装置偏滤器的过冷流动沸腾强化换热特性实验研究,将内肋强化换热技术与内插扭带结构相结合,利用两者的协同强化传热效应,设计出一种复合换热管。实验参数为：质量流速,992～4 960 kg/(m2·s);压力,04～2 MPa;入口过冷度,8701～11921 ℃;热流密度,1～163 MW/m2。对4种强化换热管（光管、内插扭带管、内螺纹肋管和复合换热管）的管内过冷流动沸腾换热特性和综合性能评价指标（PEC）进行了对比实验。结果表明：与其他3种管道相比,复合换热管的对流换热系数和PEC最高,传热特性最好。研究了复合换热管的扭带扰动比、螺距、压力和质量流速对管内两相流动对流换热系数的影响规律,发现对流换热系数与螺距、质量流速呈正比,与扭带扰动比、压力呈反比。最后对比了4个现有的过冷流动沸腾换热经验公式,并在无量纲模型基础上,增加了扰动比和螺径比（t/Dh）进行修正,利用非线性拟合方法提出了适合复合换热管过冷流动沸腾的努塞尔数新公式。     

液态金属钠在圆管和环管内流动时放热问题的数值解

液态金属因导热系数很高,与普通流体相比,其传热规律独特。特别是由于湍流放热机理复杂,纯理论研究不能或难于给出精确解析解,但是借助数值计算法则可得到满意的结果。本文中广泛比较了影响 Nu 值的各种因素的关系式,验证了它们的适用性,而且用数值法研究了等热流边界条件下液态金属圆管和环管放热问题,所得结果与实验及他人理论计算结果符合得较好。     

竖直小通道内弹状流气弹长度的计算模型

针对小通道内弹状流建立了气弹长度计算模型,并结合实验研究,对模型进行验证。可视化实验以空气和水为工质,矩形通道截面尺寸为3.25 mm×43 mm,分气、液相Re范围分别为62~360和1255~3707。结果显示,模型的预测值与实验数据具有较好的一致性,平均绝对误差为26.8%。此外,将Mishima和Cheng等的实验数据与计算模型进行对比,实验段包括矩形通道（40 mm×1.07 mm,40 mm×2.45 mm）和圆形通道（D_e=4 mm）,平均绝对误差为34.9%,说明计算模型具有较好的适用性。