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针对聚变堆固态包层的产氚载体中锂陶瓷颗粒组成的氚增殖球床,建立了基于离散元-计算流体力学(DEM-CFD)方法的球床传热分析模型,进行了离散元(DEM)几何模型有效性验证、网格敏感性分析和计算流体力学(CFD)传热模型有效性验证.用该模型模拟计算了粒径分布球床、不同粒径的一元球床、二元球床的有效热导率,研究了相同填充率... 相似文献
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Abstract The effect of streamwise jet-to-jet spacing on local heat transfer distribution due to an in-line rectangular array of confined multiple circular air jets impinging on a surface parallel to the jet plate are experimentally studied. The length-to-diameter ratio of nozzles of the jet plate is 1.0. The flow, after impingement, is constrained to exit in two opposite directions from the confined passage formed between the jet plate and target plate. Mean jet Reynolds numbers based on the nozzle exit diameter (d) covered are 3,000, 5,000, 7,500, and 10,000; jet-to-plate distances studied are d, 2d, and 3d. Streamwise jet-to-jet distances of 3d, 4d, and 5d, and a constant spanwise pitch of 4d, are considered. The jet plates have ten spanwise rows in the streamwise direction and six jets in each spanwise row. The flat heat transfer surface is made of thin stainless-steel metal foil. Local temperature distribution on a target plate is measured using a thermal infrared camera. Wall static pressures in the streamwise direction are measured midway between the spanwise jets to estimate cross-flow velocities and individual jet velocities. The streamwise distribution of the jet flow and the cross flow is found to be least influenced by the streamwise pitch variation for the range of parameters considered during the present study. Heat transfer characteristics are explained partially on the basis of flow distribution. The cooling performance, based on the strip-averaged Nusselt number per unit mass flow rate of coolant per unit area of cooled surface, indicates deterioration for lower streamwise pitch and higher jet-to-plate distance. 相似文献
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Abstract The mechanisms of nucleate boiling on the outside of a horizontal tube differ fundamentally from those on a flat plate. In this experimental work the variation of heat transfer coefficient around the periphery of a tube is measured with the aim of clarifying these mechanisms. A specially designed tube is used in which local variations are not masked by conduction through the metal surface. The tube diameter is 27 mm, and the working fluid is R113 under saturated conditions at 1 atm. When there is no imposed velocity the peripheral variations are typically 10–20% with the maximum heat transfer coefficient at the base of the tube. At very low velocity of upward flow ( ? 0.1 m/s) there is a marked change in the variation, with the maximum coefficient occurring at a point about 70° from the base. At higher velocities there is a slight increase in angle to the maximum point with maximum peripheral variations in heat transfer coefficient of around 25%. The variations are explained in terms of nucleate boiling at the base and top and flow boiling at the sides. The thin layer of two-phase bubbly flow at the sides leads to the predominance of heat transfer caused by sliding bubbles aver other mechanisms in this region. The complex mix of mechanisms involved in boiling on tubes implies an inherent limit to the accuracy of predictive correlations. 相似文献
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A rotating flexible annular thin disk subjected to the temperature increment of the shaft clamping the disk was modeled in this paper. At disk top and bottom surfaces and free outer edge, the heat convection boundaries were assumed. Disk transverse deflection was considered as a function of both disk radial and circumferential coordinates, and temperature distribution was solved along disk thickness and radial directions simultaneously. As a result, the shaft temperature increment causes thermo-elastic instability of some disk modes. Effects of the shaft temperature increment, ratio of disk convective heat transfer coefficient to thermal conductivity, disk thickness, nodal circle and diameter numbers of disk mode on the natural frequencies, thermo-elastic instability and critical angular speed of the disk were discussed. 相似文献
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In this article, an experimental investigation is performed to measure the boiling heat transfer coefficient of water flow in a microchannel with a hydraulic diameter of 500 μm. Experimental tests are conducted with heat fluxes ranging from 100 to 400 kW/m2, vapor quality from 0 to 0.2, and mass fluxes of 200, 400, and 600 kg/m2s. Also, this study has modified the liquid Froude number to present a flow pattern transition toward an annular flow. Experimental results show that the flow boiling heat transfer coefficient is not dependent on mass flux and vapor quality but on heat flux to a certain degree. The measured heat transfer coefficient is compared with a few available correlations proposed for macroscales, and it is found that previous correlations have overestimated the flow boiling heat transfer coefficient for the test conditions considered in this work. This article proposes a new correlation model regarding the boiling heat transfer coefficient in mini- and microchannels using boiling number, Reynolds number, and modified Froude number. 相似文献
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通过离散元法初步模拟了微球在重力作用下的堆积行为,并分析了氚增殖区Li4SiO4球床的局部堆积结构.研究结果表明,摩擦系数和恢复系数对球床最终堆积结构有很大的影响.当摩擦系数较小时,摩擦系数对球床堆积结构的影响起主要作用;当摩擦系数较大时,恢复系数对球床堆积结构的影响起主要作用.球形颗粒从靠近壁面处的规则分布逐渐过渡到内部区域的均匀随机分布.球床局部堆积因子表现出了明显的壁面效应,其分布随着微球到壁面距离的增加而呈现出振幅逐渐减小的振荡趋势.所得到的球床堆积结构信息可用于研究球床传热特性和提氚气体流动特性的随机堆积球床模型的建立. 相似文献
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本文对垂直上升光管中环状流流动沸腾的理论模型进行了分析,以液膜紊流的动量方程和能量方程为基础,推导了环状流的数学模型,通过求解动量方程和能量方程,获得了流动沸腾换热系数的预测模型,并对该预测模型进行了数值求解,将预测的换热系数同实验值作了比较。 相似文献
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通过计算流体力学(CFD)数值模拟方法,对氚增殖剂球床内部的氦气流动特性进行了初步研究。分析了球床流通长度和流通截面对提氚气体压降的影响,获得了不同入口流速下规则堆积球床和随机堆积球床的压降和阻力系数。 相似文献
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An analytical solution was derived from a two-dimensional heat conduction model with non-uniform boundary conditions for a
side-pumped, side-cooled cylindrical laser rod. The convective heat transfer coefficient and the spatially varying fluid temperature
were determined from the theoretical solutions or experimental correlations of convective heat transfer in an annular passage
with prescribed heat fluxes. The first term of the analytical solution coincides with the result of the one-dimensional model.
The other terms indicate that the axial temperature-rise in a laser rod has positive correlations with the axial coolant temperature-rise,
the radial Biot number and the length-to-radius ratio of the laser rod. Subsequently, a conjugate numerical simulation that
couples up the fluid convection and the solid conduction was performed. Compared with the analytical solution, the conjugate
numerical simulation better exhibits the entrance effects of flow and heat transfer; therefore, it may provide more accurate
solution in specific cases.
PACS 44.10.+i; 44.90.+c 相似文献
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In this work, the heat transfer characteristics of supercritical pressure CO2 in vertical heating tube with 10 mm inner diameter under high mass flux were investigated by using an SST k-ω turbulent model. The influences of inlet temperature, heat flux, mass flux, buoyancy and flow acceleration on the heat transfer of supercritical pressure CO2 were discussed. Our results show that the buoyancy and flow acceleration effect based on single phase fluid assumption fail to explain the current simulation results. Here, supercritical pseudo-boiling theory is introduced to deal with heat transfer of scCO2. scCO2 is treated to have a heterogeneous structure consisting of vapor-like fluid and liquid-like fluid. A physical model of scCO2 heat transfer in vertical heating tube was established containing a gas-like layer near the wall and a liquid-like fluid layer. Detailed distribution of thermophysical properties and turbulence in radial direction show that scCO2 heat transfer is greatly affected by the thickness of gas-like film, thermal properties of gas-like film and turbulent kinetic energy in the near-wall region. Buoyancy parameters Bu < 10−5, Bu* < 5.6 × 10−7 and flow acceleration parameter Kv < 3 × 10−6 in this paper, which indicate that buoyancy effect and flow acceleration effect has no influence on heat transfer of scCO2 under high mass fluxes. This work successfully explains the heat transfer mechanism of supercritical fluid under high mass flux. 相似文献
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In the present study, the turbulent heat transfer and fiction in a square duct roughened by continuous and truncated ribs on one wall has been investigated experimentally. The ribs are oriented transversely to the main stream in a periodic arrangement. For both cases, the rib height-to-hydraulic diameter ratio is 0.15, the rib pitch-to-height ratio is fixed at 12, and the Reynolds number varies from 8,000–20,000. Liquid crystal thermography is applied to demonstrate detailed distribution of heat transfer coefficient between a pair of ribs. The results show that the horseshoe vortices produced by truncated ribs are quite different from the flow structures altered by continuous ribs. It is noted that continuous ribs give higher heat transfer augmentation and pressure drop than truncated ribs. Moreover, the truncated ribs cannot be employed to eliminate hot spots which occur in the corresponding continuous types. 相似文献
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基于 CFD 软件平台,针对中国 HCCB-TBM 氚增殖区球床热工水力学特性开展 3 维数值模拟研究。 依据 ITER 实际运行工况给出吹氚氦气和结构冷却剂氦气在硅酸锂球床内的流动与传热特性,获取球床内详细的 速度分布、温度分布和压力降。计算结果表明:圆球的排列方式影响球床内氦气流场和球床的最高温度;ITER 运行工况下 HCCB-TBM 增殖区硅酸锂小球及其壁面的最高温度不会超过设计温度。研究结果为增殖区热工水力 学方案的设计验证和下一步开展实验提供参考。 相似文献
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������ ���̵�ʤ ���뿪�� ���˺��� 《核聚变与等离子体物理》2014,34(3):200-206
Based on the CFD software platform FLUENT, three-dimensional numerical simulation was carried out for thermal hydraulics characteristics of the breeder zone pebble bed for China helium cooled ceramic breeder-test blanket module (HCCB-TBM). According the actual operating conditions of ITER, such as the nuclear heat distributions in the breeder zone and structure wall, the inlet velocities and temperatures of purge gas helium and coolant helium, the flow field and heat transfer characteristics of the purge gas helium carrying the tritium flowing over the lithium silicate pebble bed were obtained, and the temperature distribution and pressure drop were presented as well. The calculation results show that the permutation mode of the lithium silicate spheres in the pebble bed have an influence on the flow field and the maximum temperature of the pebble-bed. The maximum temperature of the pebble-bed and the structure wall does not exceed the designed temperature under the ITER operating conditions. The results will be benefit for the design verification of the breeder zone thermal hydraulics scheme and improving the following experiments of the purge gas. 相似文献
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Heat transfer enhancement in the annular fins with uniform profile is investigated in the present study. Conventional fin materials are replaced with the functionally graded materials in order to increase the rate of heat transfer and corresponding fin efficiency. Here, the fin material properties, such as conductivity, are assumed to be graded along the annular fin radius, R, as a linear function. The governing equation of the annular fin is computed with an approximate analytical method using the mean value theorem. It is revealed that the in-homogeneity index, β, of the fin material plays an important role on the thermal characteristics of the annular fins. Alternatively, heat dissipation between the fin surface and surrounding fluid in the annular fins increases with increasing the inhomogeneity indices, β. Finally, it is stated that application of the functionally graded material in the annular fins enhances the fin efficiency in comparison to the annular fins with homogeneous material. It is hoped that the results obtained from this study arouse interest among thermal designers and heat exchanger industries. 相似文献