管肋式辐射器排热特性的数值分析与优化设计

为得到按单面辐射方式布置的管肋式空间辐射器的排热特性，建立了相应的数学模型．采用数值模拟方法分析了管内流体温度、肋片几何尺寸和等效热沉温度对辐射器排热特性的影响，得到了不同参数值下辐射器单位面积排热量以及特定参数范围内的辐射器肋片最佳宽度和肋片效率．数值模拟结果对辐射器的工程结构设计以及空间站热管理方案的优化分析具有一定的参考价值．     

湿工况下平直翅片对流传热传质数值研究

建立了湿空气流经平直翅片通道并伴有凝结现象发生的三维对流传热传质的数值模型,在空气进口雷诺数Re为190～3770,进口相对湿度φ_(in)为50%～90%的范围内,对干湿两种工况,平直翅片通道内的换热流动进行了对比研究。结果表明:湿工况换热系数为干工况换热系数的2.8～3.1倍,干工况翅片效率比湿工况翅片效率高35.8%～41.9%。当翅片为部分湿工况时,翅片效率随进口相对湿度的增大而增大,换热系数随进口相对湿度的增大而减小;当翅片为全湿工况后,进口相对湿度对翅片效率和换热系数的影响微弱。     

不同翅片单元外颗粒流换热特性的数值研究

由于成本低,运行稳定,重力驱动移动床在高温固体散料余热回收领域应用潜力较大。然而,相关强化传热技术目前仍待完善。本文基于离散单元法,对颗粒流外掠翅片单元的流动换热特性进行了数值研究。研究表明:通过翅片增加换热面,可以显著提高传热量,但不同翅片单元外颗粒流传热特性不同。颗粒流与不同表面的换热,由颗粒更新、颗粒接触、颗粒竞争掺混以及表面面积共同决定。总体来说,在迎流区,倾斜平表面能扩大面积并确保颗粒更新,更有利于换热增强。而对于背流区,竞争掺混与颗粒接触的影响更大,采用圆弧表面更有优势。     

椭圆管矩形翅片间空气流动的扰流特征

针对椭圆管矩形翅片间的空气流动特性,将应用于直接空冷电站椭圆管矩形翅片的几何中心相对于椭圆管的几何中心偏置.针对不同偏心距离x,以及不同入口风速u,得到空气侧对流换热系数h和压差P随u的变化规律.模拟结果表明翅片的偏置会对着空气侧的流动与换热产生不同影响:翅片向前偏置,低速尾流区对翅片表面换热的影响减小,空气侧总的表面...     

换热器表面结霜状态下翅片效率公式的理论分析及改进

１引言制冷设备中换热器是重要的部件，在进行换热器设计或对实际系统中换热性能进行计算时，采用的翅片效率的准确与否将会关系到整个系统的工作状况。对于换热器表面处于干或湿工况时，文献中的翅片效率公式形式较统一，但对结霜情况下的研究相对没有一致的结论［１］。Ｓａｎｄｅｒｓ［１］、Ｂａｒｒｏｗ［２］和Ｋｏｎｄｅｐｕｄｉ［３］都曾提及霜工况下换热器翅片效率公式，此外还有包含析湿系数的翅片效率形式。由于所采用的结霜翅片效率表达式不同，最终得到的翅片效率及翅片温度分布也难免存在差别。因而，从众多公式中选择相对准…     

A note on a symmetry analysis and exact solutions of a nonlinear fin equation

A similarity analysis of a nonlinear fin equation has been carried out by M. Pakdemirli and A.Z. Sahin [Similarity analysis of a nonlinear fin equation, Appl. Math. Lett. (2005) (in press)]. Here, we consider a further group theoretic analysis that leads to an alternative set of exact solutions or reduced equations with an emphasis on travelling wave solutions, steady state type solutions and solutions not appearing elsewhere.     

Heating characteristics of blunt swept fin-induced shock wave turbulent boundary layer interaction

An experimental study was conducted on shock wave turbulent boundary layer interactions caused by a blunt swept fin-plate configuration at Mach numbers of 5.0, 7.8, 9.9 for a Reynolds number range of (1.0∼4.7)×10⁷/m. Detailed heat transfer and pressure distributions were measured at fin deflection angles of up to 30° for a sweepback angle of 67.6°. Surface oil flow patterns and liquid crystal thermograms as well as schlieren pictures of fin shock shape were taken. The study shows that the flow was separated at deflection of 10° and secondary separation were detected at deflection of ϑ≥20°. The heat transfer and pressure distributions on flat plate showed an extensive plateau region followed by a distinct dip and local peak close to the fin foot. Measurements of the plateau pressure and heat transfer were in good agreement with existing prediction methods, but pressure and heating peak measurements atM≥6 were significantly lower than predicted by the simple prediction techniques at lower Mach numbers. The project supported by China Academy of Launch Vehicle Technology     

Asymptotics of Neumann harmonics when a cavity is close to the exterior boundary of the domain

We construct the asymptotics (as ε→0) of solutions to the Neumann problem for the Laplace equation and of the corresponding Dirichlet integral. The problem concerns a three-dimensional domain having two connected components of the boundary at the distance ε>0. To cite this article: G. Cardone et al., C. R. Mecanique 335 (2007).     

Unsteady flow and heat transfer adjacent to the sidewall wall of a differentially heated cavity with a conducting and an adiabatic fin

The unsteady natural convection flow adjacent to the finned sidewall of a differentially heated cavity is numerically investigated through comparisons between the cases with a conducting fin and an adiabatic fin. The results show that the flow and temperature structures in the transition to a periodic flow induced by a conducting fin are considerably different from those by an adiabatic fin. Based on the present numerical results, the temporal development and spatial structures of the flow adjacent to the finned sidewall are described, and instabilities are characterized. It is found that the conducting fin improves the transient convective flows in the cavity and enhances heat transfer across the cavity (by up to 52% in comparison with the case without a fin).