摘要
造成室内空气质量不好的原因很多,其中之一是通风管道内部的颗粒沉积,它对送风质量具有直接、重要的影响。空调系统通风管道尘粒的沉积会降低空调系统的性能并影响室内空气品质。掌握含尘气流的流动、沉降规律及在各式结构通风管道中的尘粒沉积规律,可以全面地了解通风管道中的粒子行为,对提高通风空调工程送风效果的可预见性、改善室内空气质量和建筑综合症有理论指导作用。
本文首先回顾了以往的研究成果,介绍了颗粒物在风管中的运动和沉降原理,分析了空调系统管道内气流运动的规律;并分析了颗粒沉降的几种方式及一些影响因素。然后建立了颗粒物沉降速度的数学模型,选取了具体的模型并进行计算,通过比较分析颗粒沉降速度的数据,对通风管道影响尘粒沉积的诸因素,如尘粒粒径、送风风速和管壁粗糙度等进行了探讨研究发现:(i)在风速不变的情况下,随颗粒粒径的增加,沉降速率总体趋势上是相应增加的;但在亚微米级粒径颗粒的附近,因为在近壁面处受布朗扩散力作用和重力沉降作用的变化,沉降速度存在一个极小值;(ii)对于粒径大于1μm的粒子,尘粒的沉降速度与风速呈线性递增的关系,但对于粒径小于1μm的尘粒沉降而言,在风速达到5m/s以前,其沉降速度增大的比较快,当风速达到5m/s后,沉降速度又趋于平缓;(iii)壁面粗糙度越大,沉降速度越大;反之越小。
最后通过实地采样对西安市室外粉尘的质量浓度和粒度变化规律进行了分析,以西安市某商厦内的中央空调运行情况为例,预测了中央空调风系统中风管的清洗周期。
There are many reasons for the low indoor air quality,one of which is the sedimentation of dust in ventilating pipes of air-conditioning system.It can lower the performance of air-conditioning system and indoor air quality.The mastery of the law of flow and sedimentation of dusty air flow and the sedimentation law of dust particles in ventilating ducts of different structure can help comprehensively understand the behavior of the particles in ventilating duct which can be a guidance in theory but also in practice for implementing the mechanism of sediment process of particles in ventilating duct,predicting the effect of air supply of ventilating system, improving indoor air quality and preventing the sick building syndrome.
This paper first reviewed the previous research findings,introduced the movement and sedimentation mechanism of particles in air duct,analyzed the movement law of air flow in air duct of air-conditioning system and demonstrated the classification and the main influencing factors of particle sedimentation.The mathematical model of the sedimentation velocity of particles was established.By analyzing and comparing the calculated particle sedimentation data,the factors related to dusty particles sedimentation such as dusty particle diameter,air supply velocity and the roughness concentration of the wall of duct were analyzed.(i) The sedimentation velocity increased as the particle diameter increased.Owing to the Brown diffusive force near the wall of duct,it also increased as the sub micron grade particle diameter decreased.(ii) For particles of which the particle diameter was greater than 1μm,the sedimentation velocity of dusty particles nearly increased linearly with air flow velocity in the logarithmic coordinate system.For particles of which the particle diameter was relatively small,the sedimentation velocity of dusty particles increased fast when air flow velocity was below 5m/s,but increased gently when air flow velocity reached 5m/s.(iii) The sedimentation velocity of dusty particles increased as the roughness concentration of the wall of duct increased,and decreased as the roughness concentration of the wall of duct decreased.
At the end of this paper,the distribution of outdoor dusty particles of Xi'an city was analyzed.The cleaning interval of air ducts of the central air-conditioning system of a commercial building in Xi'an city was predicted.
引文
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