Radiation-laminar free convection in a square duct with specular reflection by absorbing-emitting medium

The purpose of this work is to study the effects of specularly reflecting wall under the combined radiative and laminar free convective heat transfer in an infinite square duct. An absorbing and emitting gray medium is enclosed by the opaque and diffusely emitting walls. The walls may reflect diffusely or specularly. Boussinesq approximation is used for the buoyancy term. The radiative heat transfer is evaluated using the direct discrete ordinates method. The parameters under considerations are Rayleigh number, conduction to radiation parameter, optical thickness, wall emissivity and reflection mode. The differences caused by the reflection mode on the stream line, and temperature distribution and wall heat fluxes are studied. Some differences are observed for the categories mentioned above if the order of the conduction to radiation parameter is less than order of 10^-3 for the range of Rayleigh number studied. The differences at the side wall heat flux distributions are observed as long as the medium is optically thin. As the top wall emissivity decreases, the differences between these two modes are increased. As the optical thickness decreases at the fixed wall emissivity, the differences also increase. The difference of the streamlines or the temperature contours is not as distinct as the side wall heat flux distributions. The specular reflection may alter the fluid motion.     

模糊控制在半固态浆料制备装置中的应用

介绍了低转速输送管半固态浆料制备装置的原理和组成，采用模糊控制技术改进了该装置的温度控制系统，并详细介绍了该控制系统的总体设计及软硬件方案。试验证明，模糊控制技术的应用提高了该装置的温度控制效果，实现了良好稳定的铝金属半固态浆料微观组织控制作用。     

真空辅助灌浆工艺及其应用研究

真空辅助灌浆工艺是后张有粘结预应力混凝土结构施工中的一项新技术 ,采用该工艺施工有利于减小被灌水泥浆的泌水率和收缩率 ,增强孔道灌浆的密实度 ,从而达到提高预应力混凝土结构的安全度和耐久性的目的。本文主要介绍了真空辅助灌浆工艺的原理、设备、工艺流程、优点以及其在工程实践中的应用     

空调风管设计T方法基本理论及应用

介绍一种空调风管设计的新方法－T方法，它考虑了管路的安装成本及运行成本，能够得到唯一的优化计算结果，并通过传统的风管模拟方法可对实际的运行情况进行模拟分析。     

Experimental and CFD studies of fluid dynamic gauging in duct flows

Experimental and computational fluid dynamics (CFD) studies of the technique of fluid dynamic gauging (FDG) in duct flows have been performed. Experiments were performed using a stainless steel gauging nozzle located on the centreline of a Perspex duct of square cross section. The test fluid was water, flowing through the duct at 0.0077-0.74 m/s (Re_duct 116-11 100). The success of the experiments was confirmed by the results of Tuladhar et al. [2003. Dynamic gauging in duct flows. Canadian Journal of Chemical Engineering 81, 279-284].For the first time, CFD has been applied to simulate FDG in an imposed flow for steady, incompressible, laminar flows. Experimental data and simulation results agreed to within 6%, supporting the validity of both the experiments and the assumptions underpinning the simulation. CFD simulations predicted the stresses beneath the lip of the nozzle and confirmed the practical working range of the gauge (0.1<h/d_t<0.25). This is a major achievement, proving that CFD can be used to model this flow-FDG accurately, which is valuable for future work in this area, namely fouling in food, crude oil and cross-flow membrane systems.     

家用小型中央空调研究进展及应用展望

本文综述了国内外家用小型中央空调的基本类型、开发和研究现状，在此基础上指出热泵除霜、低温制热、压缩机变容等技术需要突破，行业现状需要规范，以此来推动家用小型中央空调在中国的应用和发展。     

Culturable and Total Fungi in Dust Accumulated in Air Ducts in Single-Family Houses

Abstract Fungal spore content in dust accumulated in air ducts was investigated in 24 mechanically ventilated single-family houses of which 15 had also a central air heating system. Dust was collected from the ducts simultaneously with cleaning of the ventilation systems. Besides spore concentrations and flora of culturable fungi, total fungal spore concentrations were determined in dust samples by the aqueous two-phase technique and spore counting with epifluorescence microscopy. Culturable spore concentrations in the dust varied from 10⁴ to 10⁷ CFU/g and total spore concentrations from 107 to 108 spores/g. Total spore concentrations in the duct dust were significantly higher in the air heated houses than in the other mechanically ventilated houses. The difference resulted mainly from a higher proportion of recirculation air and a higher age of the air heated houses. Cladosporium, Penicillium, Aspergillus and yeasts consisted of >90% of fungal flora in the dust. Although total spore concentrations were at the same level both in the exhaust and in the supply ducts in both types of house, culturable fungal spore concentrations were slightly higher in the exhaust ducts than in the supply ducts. The proportion of culturable spores was <5% of total spores in dust accumulated in the ducts.     

Effects of ridged walls on the heat transfer in a heated square duct

Turbulent flows in rectangular cooling ducts of rocket engine thrust chambers are characterized by secondary motions of Prandtl’s first and second kinds. These secondary currents play a prominent part in heat transfer between the thrust chamber and the cooling gas conveyed in the duct. Previous numerical and experimental works reveal that attaching ridges on the walls of the duct causes the formation of new secondary flows of Prandtl’s second kind. These new structures are likely to increase the heat transfer. The present study has investigated numerically, through large eddy simulations, the effect of different forms of ridges on heat transfer in straight square duct flows.     

The stability of flow in a channel or duct occupied by a porous medium

The hydrodynamic stability of flow of an incompressible fluid through a plane-parallel channel or circular duct filled with a saturated porous medium, modeled by the Brinkman equation, is discussed on the basis of an analogy with a magneto-hydrodynamic problem (Hartmann flow). Flow in a circular duct is found to be stable to small disturbances for all values of the Reynolds number, but for a plane-parallel channel the flow is unstable if the Reynolds number exceeds a critical value, dependent on a Darcy number.     

我国台湾地区共同管道规划建设法律制度研究

由于相关法律制度的缺乏,我国大陆地区的共同沟建设面临着很多问题,而台湾地区的法律制度体系完整、内容全面,值得借鉴。本文回顾了台湾地区共同管道的建设起因与概况、立法背景与立法过程的演变;详细阐述了有关工程设计制度、建设与管理经费制度、管理维护制度等核心内容,并简要提出了对大陆地区的启示。