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。     

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     

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。     

窄环隙流道内自然对流沸腾换热实验研究

以水为工质 ,在常压下对竖直和倾斜环隙流道进行了自然对流沸腾换热实验研究 ,给出并讨论了间隙大小、热负荷、倾角和表面张力对换热性能的影响 ,可视化观察加深了对窄小空间沸腾现象的认识。在实验的基础上 ,提出了一个新的、可以较方便使用的传热计算关联式。     

窄环隙内强迫流动阻力特性的实验研究

鉴于流体在小尺度流道内流动时所表现出的特殊性,对水在竖直环隙内受迫流动状况下单相对流换热时的流动阻力特性进行了实验研究。实验结果表明,雷诺数在900-1100时流态便开始向紊流转变,摩擦阻力压降的大小与加热方式和换热温差的关系很小,而主要取决于质量流速和环隙宽度比值的大小。     

窄环隙流道冷却传热特性实验与仿真研究

用实验与仿真的方法对6个不同尺寸的环隙流道进行了单相冷却传热研究.实验表明:窄环隙流道内强迫对流换热与常规流道不同,紊流区明显提前,尺寸为0.94 mm的流道只有紊流区;窄环隙流道对换热起强化、抑制的双重作用.仿真与实验结果符合较好,仿真表明芯管内径变化对窄环隙流道换热有一定影响.     

竖直环隙流道内沸腾换热启动时的动态特性

对常压下竖直环隙流道内沸腾换热启动阶段壁温的瞬态变化特性和流动不稳定性进行了实验研究。结果表明环隙流道壁温变化经历跃升回落、各截面平均温度基本不变和快速和快速升三个阶段,存在强烈的流动不稳定性和壁温波动,并伴随着局部干湿交替现象。产生流动不稳定性的主要原因是流道中间歇生成长聚合汽泡,引起介质的突然加速、停滞或倒流。影响壁温波动的主要因素有环隙宽度、加热热流密度、初始水温、进出口附近大容积液体的过冷     

扁管单相对流换热实验研究

本文以单相水为介质,对结构尺寸不同的3种扁管的换热与阻力特性进行了实验研究。并根据工程实际的需要,选用适当的方法对扁管在实验范围内的强化换热效率指标进行评价,确定了扁管的最佳工作区域。结果表明,扁管的管内换热系数明显高于光圆管的,换热系数最高可达光圆管的2.62倍,在换热面积和泵功率相同情况下,扁管最佳工作区域的换热量最高可达光圆管的2.2倍。     

单头螺纹槽管管内紊流对流换热

以水为工质，进行了适合于船舶换热器使用的螺纹槽管管内紊流对流换热和阻力特性的实验研究，同时还讨论了旋流对换热的影响以及影响旋流强度和强化换热效果的因素，分析了变物性对螺纹槽管阻力特性的影响。     

单头螺旋槽管管内紊流对流换热

以水为工质，进行了适合船舶换热器使用的螺纹槽管管内紊流对流换热和阻力特性的实验研究，同时还讨论了旋流对换热的影响以及影响旋流强度和强化换热效果的因素，分析了变物性对螺旋纹槽管阻力特性的影响。     

Experimental study on convective boiling heat transfer in narrow-gap annulus tubes

Since convective boiling or highly subcooled single-phase forced convection in micro-channels is an effective cooling mechanism with a wide range of applications, more experimental and theoretical studies are required to explain and verify the forced convection heat transfer phenomenon in narrow channels. In this experimental study, we model the convective boiling behavior of water with low latent heat substance Freon 113 (R-113), with the purpose of saving power consumption and visualizing experiments. Both heat transfer and pressure drop characteristics were measured in subcooled and saturated concentric narrow gap forced convection boiling. Data were obtained to qualitatively identify the effects of gap size, pressure, flow rate and wall superheat on boiling regimes and the transition between various regimes. Some significant differences from unconfined forced convection boiling were found, and also, the flow patterns in narrow vertical annulus tubes have been studied quantitatively.     

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。     

Natural convection heat transfer from horizontal rod bundles in liquid sodium. Part 2: Correlations for horizontal rod bundles based on theoretical results

Natural convection heat transfer from horizontal rod bundles in N_xm × N_ym arrays (N_xm, N_ym = 5–9) in liquid sodium was numerically analyzed for three types of the bundle geometry (in-line rows, staggered rows I and II). The unsteady laminar two-dimensional basic equations for natural convection heat transfer caused by a step heat flux were numerically solved until the solution reaches a steady state. The PHOENICS code was used for the calculation considering the temperature dependence of thermophysical properties concerned. The surface heat fluxes for each cylinder were equally given for a modified Rayleigh number, R_f, ranging from 0.0637 to 63.1 (q = 1×10⁴ to 7×10⁶ W/m²). S_x/D and S_y/D for the rod bundle, which are the ratios of the distance between center axes on the abscissa and the ordinate to the rod diameter, respectively, were ranged from 1.6 to 2.5 on each bundle geometry. The spatial distribution of Nusselt numbers, Nu, on horizontal rods of a bundle was clarified. The average value of Nusselt number, Nu_av, for three types of bundle geometry with various values of S_x/D and S_y/D were calculated to examine the effect of the array size, S/D and R_f on heat transfer. The bundle geometry for the higher Nu_av value under the condition of S_x/D×S_y/D = 4 was examined by changing the ratio of S_x/S_y. A correlation for Nu_av for the three types of bundle geometry above mentioned including the effects of S_x/D and S_y/D was developed. The correlation can describe the theoretical values of Nu_av for the three types of bundle geometry in N_xm × N_ym arrays (N_xm, N_ym = 5–9) for S_x/D and S_y/D ranging from 1.6 to 2.5 within 10% difference.     

Natural convection heat transfer from horizontal rod bundles in liquid sodium. Part 1: Correlations for two parallel horizontal cylinders based on experimental and theoretical results

Natural convection heat transfer coefficients on two parallel horizontal test cylinders in liquid sodium were obtained experimentally and theoretically for various setting angles, γ, between vertical direction and the plane including both of these cylinders’ axes, over the range of 0°–90°. Both test cylinders are 7.6 mm in diameter and 50 mm in heated length with the ratio of the distance between each cylinder axis to the cylinder diameter, S/D, of 2. Theoretical equations for laminar natural convection heat transfer from the two horizontal cylinders were numerically solved for the same conditions as the experimental ones. The average Nusselt numbers Nu on the cylinders obtained experimentally were compared with the corresponding theoretical values on the Nu versus modified Rayleigh number R_f [= Gr*Pr²/(4?+?9Pr^1/2?+ 10Pr)] graph. The experimental values of Nu for the upper cylinder are about 20% lower than those for the lower cylinder at γ = 0° for the range of R_f tested here. The value of Nu for the upper cylinder becomes higher and approaches that for the lower cylinder with the increase in γ over the range of 0°–90°: the values for each cylinder agree with each other at γ = 90°. The values of Nu for the lower cylinder at each γ are almost in agreement with those for a single cylinder. The theoretical values of Nu on two cylinders except those for R_f < 4 at γ = 0° are in agreement with the experimental data at each γ with the deviations less than 15%. Correlations for two cylinders were obtained as functions of S/D and γ based on the theoretical solutions. A combined correlation for multi-cylinders in a vertical array based on the correlations for two cylinders was developed. The values by the correlation agree with the theoretical solution for the multi-cylinders for R_f ranging from 4.7 to 63 within 10% difference.     

Single-phase convective heat transfer enhancement by spacer grids in a rod bundle

The spacer grids within a fuel assembly of a nuclear reactor core disrupt and re-establish the momentum and thermal boundary layers so that they enhance the local heat transfer within and downstream of the spacer grids. An experimental study in a 6×6 rod bundle has been performed to investigate the effects of spacer grids on the single-phase convective heat transfer enhancement. The experimental data showed that the Reynolds number has a significant impact on the heat transfer enhancement only when the Reynolds numbers are lower than about 10,000. The conventional correlations showed poor predictions of the heat transfer enhancement by spacer grids at low Reynolds numbers; in particular, the maximum heat transfer rate at the top end of the spacer grids was significantly overestimated. Furthermore, the conventional correlations did not properly account for the effects of the Reynolds numbers on the heat transfer enhancement. Therefore, more systematic experiments should be performed using various spacer grids with large blockage ratios at low Reynolds numbers, considering an early phase of the reflood conditions.     

斜微肋扁管单相对流换热实验研究

以单相水为介质,对肋高或结构尺寸不同的4种斜微肋扁管的换热与阻力特性进行了实验研究,并根据工程实际需要,选用适当的方法对斜微肋扁管在实验范围内的强化换热效率指标进行评价,确定了斜微肋扁管的最佳工作区域。结果表明：斜微肋扁管的管内换热系数明显高于光管,换热系数最高可达光管的5.9倍,在换热面积和泵功率相同的情况下,斜微肋扁管最佳工作区域的平均换热量均可达光管的3倍以上。     

Experimental research on heat transfer to liquid sodium and its incipient boiling wall superheat in an annulus

Liquid sodium is mainly used as a cooling fluid in the liquid metal fast breeder reactor （LMFBR）, whose heat transfer, whether convective heat transfer or boiling heat transfer, is different from that of water. So it is important for both normal and accidental operations of LMFBR to perform experimental research on heat transfer to liquid sodium and its boiling heat transfer. This study deals with heat transfer with high temperature （300-700℃） and low Pe number （20-70） and heat transfer with low temperature （250-270℃） and high Pe number （125-860）, and its incipient boiling wall superheat in an annulus. Research on heat transfer involves theoretical research and experiments on heat transfer to liquid sodium. It also focuses on the theoretical analysis and experimental research on its incipient boiling wall superheat at positive pressure in an annulus. Semiempirical correlations were obtained and they were well coincident with the experimental data.