共查询到20条相似文献,搜索用时 93 毫秒
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本文基于不同流速下变传质强度因子的Lee模型,对低热通量下上升管内流动沸腾进行了数值模拟。通过分析气相分布、局部气泡行为解释了沸腾换热特性和局部传热恶化。结果表明:低热通量下,不同流速的平均气体体积分数沿管长线性分布,沿径向呈双峰状分布,峰值在壁面附近;高流速时,近壁处气体体积分数的增长速率最大。换热性能受流速影响显著,流速越大,换热系数越大;三种流速下换热系数最小值对应的气体体积分数相同,气相分布不同是换热特性产生差异的直接原因。低中流速下,壁温局部升高位置与换热系数骤降位置是一致的,表明壁面附近局部气泡附着会造成壁温的局部升高,导致传热恶化。 相似文献
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Local heat transfer to a rotating disk in the presence of an imposed axial flow has been studied using thermochromic liquid crystals and the transient heating technique. Preliminary measurements were made for a smooth disk, for which the experimental data encompassed the laminar boundary layer, the transitional zone, and the beginning of the turbulent region. Measurements were then made for arrangements in which a circular trip wire installed concentrically on the disk was used to disturb the boundary layer. The main topic of the investigation concerned convective heat transfer to disks with concentric circular ribs of a rectangular cross section. Three roughness configurations have been investigated, and the results have been compared with data for a smooth disk. The ribs caused an early transition from laminar flow to turbulent flow. Otherwise the augmentation of heat transfer by the circular ribs was rather modest, except with high axial flows and low rotational speeds, when the velocities across the ribs would have been of a similar order of magnitude to the tangential velocities between the ribs. 相似文献
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In this presentation, the flow and heat transfer inside a microchannel with a triangular section, have been numerically simulated. In this three-dimensional simulation, the flow has been considered turbulent. In order to increase the heat transfer of the channel walls, the semi-truncated and semi-attached ribs have been placed inside the channel and the effect of forms and numbers of ribs has been studied. In this research, the base fluid is Water and the effect of volume fraction of Al2O3 nanoparticles on the amount of heat transfer and physics of flow have been investigated. The presented results are including of the distribution of Nusselt number in the channel, friction coefficient and Performance Evaluation Criterion of each different arrangement. The results indicate that, the ribs affect the physics of flow and their influence is absolutely related to Reynolds number of flow. Also, the investigation of the used semi-truncated and semi-attached ribs in Reynolds number indicates that, although heat transfer increases, but more pressure drop arises. Therefore, in this method, in order to improve the heat transfer from the walls of microchannel on the constant heat flux, using the pump is demanded. 相似文献
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基于计算流体动力学(CFD)方法,结合首个完整的模块系统对第一壁以及与其相连接的两个隔板结构进行了热工水力分析,包括压力分析、流速分析、流量分配分析、对流换热系数分析。给出了所有分析的计算结果。同时将数值模拟计算得到的对流换热系数与相关经验公式推导得到的结果进行了比较,基本一致。 相似文献
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基于计算流体动力学(CFD)方法,结合首个完整的模块系统对第一壁以及与其相连接的两个隔板结构进行了热工水力分析,包括压力分析、流速分析、流量分配分析、对流换热系数分析。给出了所有分析的计算结果。同时将数值模拟计算得到的对流换热系数与相关经验公式推导得到的结果进行了比较,基本一致。 相似文献
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A. Yu. Dyachenko Ya. I. Smul’sky V. I. Terekhov N. I. Yarygina 《Thermophysics and Aeromechanics》2015,22(6):677-688
In the present paper, we consider one of the most efficient and simple methods to additionally intensify the exchange processes and heat transfer in the separated flow behind a backward-facing step. The method uses small obstacles installed upstream the step; such obstacle act as turbulators smaller in size than the main obstacle. As the turbulators, solid mini ribs, comb ribbings, and wall-detached mini ribs were used. Intensification of the turbulent mixing process behind the main obstacle occurs due to the introduction of small-obstacle-induced 2D and 3D perturbations into the separated shear layer behind the step. Results of a detailed experimental study of the distributions of pressure and heat transfer for different heights of the small intensifier and its positions with respect to the step are reported. The influence of intensifier shape on the thermal and dynamic characteristics of the flow has been analyzed. The distributions of pressure and heat-transfer coefficients were used to evaluate the effectiveness of the various mini obstacles and the limits of their action on the drag and heat transfer. 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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扰流元诱发的二次流及其在强化传热中的应用 总被引:2,自引:0,他引:2
1前言通常所谓“茶杯效应”的二次流(即茶叶在搅拌的杯中聚集在杯中心)是一种常见的流动现象。在对流热传递过程中,常可激励传热的增强。在传热表面布置扰流结构是对流换热的无源强化技术经常采用的方式。传统的展向二维连续肋扰流元通过破坏边界层发展,减小粘性底层厚度,从而减小传热热阻。这种扰流结构所诱发的扰动是二维的,其传热强化的程度有限并且在助前、后缘附近出现回流区。流体的滞留明显消弱了回流区内的传热速率,甚至导致壁面出现局部“热点”。进一步研究发现将连续肋倾斜布置以引入展向二次流可使扰流元对流体产生三维… 相似文献
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In this paper, the effect of making swirling flow inside an annulus on the subcooled boiling heat transfer has been studied and discussed both experimentally and numerically. The Eulerian-Eulerian model and control volume technique have been used for numerical modeling of the problem. The experimental results show that the critical heat flux values are enhanced by making swirling flow. The experimental and numerical results also indicate that by making swirling flow inside the annulus, the subcooled boiling heat transfer coefficients are increased. Moreover, the experimental and numerical values of the boiling heat transfer coefficients show good agreement with each other. 相似文献