结合产水与发电的太阳能烟囱系统特性分析

针对一种可从空气中得到淡水同时还可发电的太阳能烟囱系统,建立了热湿空气在烟囱中沿程冷却析出凝结水并发电的一维可压缩流动与传热数学模型,分析了这种结合发电与产水功能的工程结构的输出性能。结果表明:烟囱高度对凝结水量的影响较大,在一定条件下提高烟囱高度可以获得更多的水;安装在烟囱底部的风力透平功率与水力透平功率之间存在着某种相互制约的关系;随风力透平压降因子的增加,系统总功率先增大后减小,在临界点取得最大值;但当烟囱高度较高时,水力透平的功率不容忽视,系统总功率取得最大值时的风力透平压降因子临界点会减小,表明此时水力透平转换出的电能也较大。

The effect of noise barriers on viaducts on pollutant dispersion in complex street canyons

The noise reduction effect of noise barriers has been extensively studied,but the effect on pollutant dispersion remains unclear.A computational fluid dynamics(CFD)simulation is conducted to investigate the effects of different heights,lengths,and types of noise barriers and different wind speeds on pollutant dispersion in street canyons with viaducts.The field synergy theory of the convective mass transfer process is used for quantitative analysis of pollutant dispersion in street canyons.The results show that as the height and length of the noise barrier increase,the pollutant dispersion capacity decreases.As the wind speed increases,the rate of decrease in the average CO concentration declines.The effect of the wind speed on the synergistic improvement of the speed and concentration gradient vectors differs for different types of noise barriers.The performance follows the order:fully-closed noise barrier>left noise barrier>right noise barrier>semi-closed noise barrier.The different noise barrier types significantly impact the flow field and pollutant dispersion and reduce the CO concentration to varying degrees,except for the fully-closed type.The average CO concentration in the pedestrian breathing zone is reduced by a maximum of 55.85%on the leeward side and by 53%on the windward side,indicating that an appropriate noise barrier on the viaduct reduces noise pollution and improves the air quality in street canyons,especially in the pedestrian breathing zone.

Field synergy analysis of pollutant dispersion in street canyons and its optimization by adding wind catchers

The microenvironment,which involves pollutant dispersion of the urban street canyon,is critical to the health of pedestrians and residents.The objectives of this work are twofold:(i)to effectively assess the pollutant dispersion process based on a theory and(ii)to adopt an appropriate stratigy,i.e.,wind catcher,to alleviate the pollution in the street canyons.Pollutant dispersion in street canyons is essentially a convective mass transfer process.Because the convective heat transfer process and the mass transfer process are physically similar and the applicability of field synergy theory to turbulence has been verified in the literature,we apply the field synergy theory to the study of pollutant dispersion in street canyons.In this paper,a computational fluid dynamics(CFD)simulation is conducted to investigate the effects of wind catcher,wind speed and the geometry of the street canyons on pollutant dispersion.According to the field synergy theory,Sherwood number and field synergy number are used to quantitatively evaluate the wind catcher and wind speed on the diffusion of pollutants in asymmetric street canyons.The results show that adding wind catchers can significantly improve the air quality of the step-down street canyon and reduce the average pollutant concentrations in the street canyon by 75%.Higher wind speed enhances diffusion of pollutants differently in different geometric street canyons.